Vibration monitoring is one of crucial functions of structural health monitoring (SHM) systems. Traditional structural vibration monitoring usually relies on specialized sensors, data transmission and acquisition equipment, which are expensive and may not be easily available in urgently needed situations like post-disaster structural evaluation. Therefore, developing an affordable and efficient structural vibration monitoring technique becomes an important topic in SHM research. In this paper, the authors developed an android system APP that can easily convert multiple android smartphones into a wireless structural vibration monitoring system. To make the designed system reliable and easy to use, the server/client architecture is adopted. One smartphone is designated as the serve of the system to remotely control all other smartphones, which function as sensors to measure structural vibration. An efficient method is proposed herein to establish the smartphone-based structural vibration monitoring network, allowing the server smartphone to quickly and easily connect multiple sensor smartphones to form the wireless network for structural vibration monitoring. Additionally, a synchronization method is also proposed to synchronize different smartphones for simultaneously measuring structural vibration. To verify the time synchronization accuracy of the developed system, an experiment is designed and conducted. Moreover, a new analysis method of the time synchronization accuracy is also proposed, which verifies that the designed smartphone-based monitoring can achieve the millisecond-level time synchronization accuracy. Finally, a shaking table experiment is conducted on a three-story bench-scale structural model, the results of which demonstrate that the designed smartphone-based wireless structural vibration monitoring system can quite accurately identify the modal parameters of the tested structure. With gradual degradation of many important civil structures , the safety of these structures becomes a public concern, particularly after these structures are subjected to extreme loads . Structural health monitoring (SHM) systems are an effective measure to detect structural damage in time and ensure the safe operation of these engineering structures ,2,3. StrIn recent years, smartphone technology has advanced very rapidly. Nowadays, smartphones are not only equipped with powerful data acquisition, processing, storage and transmission capabilities but also integrated with a variety of high-performance vibration sensors , which makes it possible to utilize smartphones to carry out the SHM tasks, like structural vibration monitoring.Compared with the traditional dedicated SHM system, using smartphones for structural vibration monitoring has many attractive advantages: (1) smartphones are very popular and easily available; thus, it is possible to quickly deploy a large number of smartphones as vibration sensors on the structure at relatively low cost, which may be very useful in emergent case, like post-disaster structural evaluation, to quickly access structural integrity condition; (2) smartphones are integrated with a lot of telecommunication technology , which provides many flexible ways to build a smartphone-based wireless structural health monitoring network, allowing the smartphones to easily communicate and transmit the monitoring data one other; (3) smartphones also have powerful computing and data storing capacity, which can be used to analyze the monitored structural responses and evaluate structural health status directly on the smartphones, achieving the efficient distributed SHM.Due to the above attracting features of using smartphones to carry out SHM tasks, many researchers have conducted different research on smartphone-based SHM applications. Kong etc.  verifiedDespite a lot of smartphone-based SHM research have been carried out, there are still many challenges for smartphone-based SHM. First, the smartphone-integrated vibration sensor is not of scientific instrument standard and the sensors in different smartphone may have large different accuracy, which greatly affect the quality of the measured data. Second, since smartphones are not initially designed as sensors, they cannot collect signals from integrated sensors according to a strict time schedule as regular sensors do, which poses a difficulty for data analysis. Third, the sampling rate of the smartphone sensors may not be higher enough to measure the vibration of a very stiff structure, which limits the application ranges of the smartphone-based SHM.Moreover, extensive research of using smartphones for SHM have been conducted, but most of them focus on the utilization of single smartphone. Although there are a few studies ,12,13 thIn this paper, an android system-based APP, developed by the authors, is presented, which can easily convert multiple android smartphones into a wireless structural vibration monitoring system, measuring structural vibration with high accuracy of time synchronization. The developed smartphone-based system provides a new and easy way to quickly deploy a wireless structural vibration monitoring network on the structure, which is of great value for the applications like post-disaster structural evaluation.The organization of the paper is listed as follows. First, the system architecture of the smartphone-based system is introduced in detail, which can efficiently organize multiple smartphones to form a wireless sensor monitoring network. Second, a time synchronizing method is developed for the smartphone-based system, which can synchronize the time clocks of the smartphones with high accuracy for simultaneously structural vibration monitoring. Then, an experiment is designed and conducted to verify the time synchronization accuracy of the designed smartphone-based monitoring system; and a new upsampling-based analysis method is also proposed to improve the resolution of time synchronization accuracy analysis. Finally, shake table tests are conducted on a three-story small-scale structural model to check the performance of the developed smartphone-based monitoring system for structural modal parameter identification, demonstrating that the system can quite accurately identify the structural natural frequencies and mode shapes.To convert multiple smartphones into a wireless sensor network for structural vibration monitoring, an android system-based APP was developed by the authors. The APP adopts the server/client architecture and consists of two parts, namely iSHM-Server (iSHM-S) and iSHM-Client (iSHM-C). One smartphone installing the iSHM-S, called server smartphone, serves as the server of the wireless monitoring network. The other smartphones installing the iSHM-C, called sensor smartphones, work as sensor nodes of the wireless network to measure structural vibrations. The users can utilize the server smartphone to remotely control all sensor smartphones to conduct all kinds of operations for structural vibration monitoring . The system architecture of the smartphone-based structural vibration system is shown To facilitate the maintenance and future development of the APP, all functions of the APP are modular in design, as shown in To build a smartphone-based wireless monitoring system, the first step is to select the wireless communication technology that the system is used to connect different sensor nodes. Generally, smartphones integrate several wireless communication technologies, including WIFI, 4G, Bluetooth, near field communication (NFC). In order for the server and sensor smartphones to communicate each other, creating a reliable network connection between them is a critical step, which requires that the IP addresses of the server and sensor smartphones must be known by the other. However, since the smartphone is not initially designed as a wireless sensor node, its IP address is not fixed and generally unknown in advance. Although the IP address of server smartphone can be manually input into all sensor smartphones, it requires a lot of human intervention, making the designed system difficult to use.To solve the above difficulty as well as make the network connection convenient and secure, the Android AP network was adopted herein. When the iSHM-S is started, it will use the Android AP network to create a local WIFI network (hotspot), through which the other sensor smartphones can connect. The Android AP network will automatically assign the IP addresses to the connected sensor smartphones, which are saved in the system cache file of Android system on the server smartphone. The iSHM-S will read the system cache file to obtain the sensor smartphones’ IP addresses. Then, the iSHM-S utilizes the Android API Socket to initiate a dedicated network connection with each sensor smartphone via TCP/IP protocol, through which the server smartphone can remotely control all sensor smartphones to conduct the operations of time synchronization, structural vibration measuring, measurement data storage and management, etc. The above procedure is very efficient to setup a smartphone-based structural vibration monitoring network. It only takes about 20 s to set up one sensor smartphone, greatly facilitating the quick deployment of a large number of sensor smartphones on the structure.The full operation procedure of the iSHM-S and iSHM-C is illustrated in To make the designed smartphone-based monitoring system easy to use, the APP’s graphic user interfaces (GUI) is designed to be concise and easily understandable. For a structural vibration measurement system, time synchronization among different sensors is of great importance, because asynchronized structural measurements may lead to large errors of structural modal parameter estimation ,15,16. IThere are many time synchronization algorithms for wireless sensor network . In thisTo obtain the local time difference Since the client will immediately reply to the ping command from the server, the time delay between the client’s receiving and replying the ping command is ignored herein. Combining Equations (1) and (2), the local time difference n times for each time synchronization operation, and the mean value of all n estimated time differences However, due to the uncertainties in the wireless communication as well as the operation status of the server and client, the estimated time differences n results will reduce to n can lead to a more accurate time synchronization result. After considering the trade-off between the synchronization accuracy and the synchronization operation time, the average time n is selected as 30 in the APP design; consequently, the time synchronization accuracy can reach around one millisecond. It is noted that the above time synchronization analysis is conducted based on a very idealistic assumption, which may not be true in real situation. Thus, an experiment will be performed in the next section to verify the effectiveness of the proposed time synchronization method for the developed smartphone-based structural vibration monitoring system.The reason that the above averaging operation can reduce the uncertainty of time synchronization is explained as follows. It is assumed herein that all the estimated time differences are statistically independent and identically distributed, which follow a normal probability distribution In To evaluate the time synchronization accuracy, the local time clocks of both server and sensor smartphones are needed. However, since smartphones are not initially designed as wireless sensors, it is very difficult to simultaneously have a direct access to multiple smartphones’ local time clocks from the outside. Therefore, an experiment is designed to indirectly assess the time synchronization accuracy, which is explained as follows.Since smartphones are not initially designed for structural vibration monitoring, the developed smartphone-based system can only rely on Android system built-in function “onSensorChanged” to access the vibration sensor’s data in the smartphone. However, such approach cannot guarantee that the smartphones collect the vibration data at a pre-defined fixed time interval. Because the three smartphones measure the same structural response, if the phones are accurately time-synchronized, the three recorded structural responses should be well overlap in time domain. n times, then the time interval of the structural responses can be reduced to 20/n milliseconds; and the resolution of the time synchronization analysis is also improved to 20/n milliseconds. Note that an antialiasing FIR lowpass filter of order 20*n is utilized in the above upsampling procedure. Due to the hardware limitation, the smallest time interval of the measured responses that the smartphones in this test can reachis only 0.02 s , and no structural responses are recorded between two adjacent discrete time steps. Since, in the proposed time synchronization accuracy analysis method, the smallest of the time shift τ is one sample, the resolution of the analysis is limited by the time interval of the measured responses . To improve the resolution of the time synchronization analysis, the following method is adopted. Noting that the structural free-decay responses in the test only contain the vibration of low frequencies, the structural responses between the two discrete time steps can be obtained by upsampling the measured responses via polyphase antialiasing filter  without Moreover, it needs pointing out that the above upsampling operation does have some limitations. Because the upsampled responses can only match the underlining continuous responses given that the sampling time instances and the magnitudes of the sampled response are perfectly accurate, which is not true in practice. The resolution of the sampling time instance in the smartphone is limited to 1 millisecond, and the measured response is not accurate either due to the sensor’s imperfection. Both of them determine that the proposed upsampling method cannot accurately reconstruct the underlining continuous structural response. With a higher upsampling rate, more artificially generated response data points will be added to the original response, which may induce higher uncertainty of the calculated index To cope with the above problem, an adaptive upsampling strategy is adopted herein. A series of upsampling operations with upsampling rate from small to large are conducted and the time synchronization errors in every upsampled response are calculated based on the smallest value of the index n = 2, 4, 10, 20) are used in this study. Using the proposed method, the upsampled structural responses and the corresponding time synchronization indices among the three tested sensor smartphones are re-calculated. Four upsampling rates , the opposite value of cross correlation coefficient function With the addition constraint, the adaptive upsampling procedure, proposed in Structural modal parameter identification is one of most important applications for structural vibration monitoring. In order to evaluate the performance of the developed smartphone-based system for structural modal parameter identification, shake table tests are conducted on a 3-story bench-scale shear structural model, as shown in The structure was shaken at the bottom. The structural accelerations of all floors are measured by the smartphones and the wired accelerometers simultaneously. C is the power spectrum of the structural excitation; superscript H denotes the complex conjugatetranspose operation; k-th mode; overhead bar denotes complex conjugate operation. Combining Equations (6) and (7), the power spectrum matrix kth residue of matrix To identify the structural natural frequencies and mode shapes, the frequency domain decomposition (FDD) method is adopted ,20 hereik-th structural natural frequency Since the structural damping ratios are small for general civil structures, mated by .(10)Gyyk-th mode shape of the structure can be approximated by the 1st singular value vector of the singular value decomposition.Then, the singular value decomposition of matrix Totally, five tests are conducted in this study. In each test, 10 min structural responses are measured by the smartphones and the wired sensors. The sampling rates for the smartphone sensors and wired sensors are 50 and 200 Hz, respectively. The power spectra of all structural responses are calculated via the Welch method . To reduAfter the structural natural frequencies are identified, the power spectrum matrices of structural responses at the structural natural frequencies are extracted. The singular value decomposition operation is conducted for the power spectrum matrices to estimate the structural mode shapes. To quantitively evaluate the accuracy of the identified mode shapes, the mode assurance criterion (MAC) value of the estimated mode shapes by the smartphones and by the wired accelerometers are computed. As demonstrated in Equation (11), the MAC value reflects the linear similarity of two mode shape vectors, which takes the value between zero and one. The MAC value being very close to one indicates that the two mode shapes are almost same.This interesting phenomenon may be explained as follows. Although the sensors integrated in the smartphones are not accurately calibrated as the professional wired sensors, all the smartphones used in the tests belong to the same model  and it is very likely that these vibration sensors are very similar. Therefore, the peak magnitudes of the spectrum responses measured by all the smartphones can be considered to be amplified or reduced by a similar factor. According to the nature of the FDD method, if the power spectrum matrix To further test the ability of the developed smartphone-based vibration monitoring system, two damage scenarios were simulated by removing some diagonal springs of the test structure. In the first scenario, the four springs of the 3rd story were removed. In the second scenario, the four springs of 2nd story were removed. The damage condition is proximately equal to reducing the corresponding stiffness by about 20%. It is worth of mentioning that although the experimental results in this paper demonstrated that the developed system can achieve quite accurate structural modal identification results, it does not provide any implication of the identification accuracy of future experiments using different smartphones, as the developed software is based on the android system. Theoretically, it can be used on any android smartphone. However, the structural identification accuracy highly depends on the accuracy of measured structural responses, which relies on quality of the integrated vibration sensors in the tested smartphone. Different smartphones may have different integrated vibration sensors which have different measurement accuracy. Therefore, in order to have accurate structural identification results using the developed software in this paper, the first crucial step is to select the smartphones that integrate high quality vibration sensor, which is out of control of the developed software.In this study, an android-smartphone based structural vibration system was developed, which can easily convert multiple android smartphones into a wireless sensor network to measure structural vibration. The server/client architecture is adopted for the designed system. One smartphone is selected as the server to remotely control all other smartphones that serves as sensors to measure structural accelerations. A new method is proposed to quickly set up the network communication between the server and sensor smartphones, which facilitates fast deployment of a lot of smartphones as sensors on the structure. Furthermore, to ensure sensor smartphones simultaneously measuring structural responses, a time synchronization method is proposed for the smartphone-based structural vibration monitoring system, which is verified by the experiment to be able to achieve the time synchronization accuracy of millisecond level between sensor smartphones. Finally, a shaking table experiment is conducted, which demonstrates that the designed smartphone-based wireless structural vibration monitoring system can quite accurately identify the modal parameters of the tested structure.Although the preliminary study in this paper has demonstrated promising potentials for the developed smartphone-based structural vibration monitoring system, more comprehensive tests are still needed to further test the performance of the developed system in more complex working environments. Because the performance of the time synchronization and the structural modal parameter identification of the developed system is affected by many parameters, including the specifications of the smartphone sensors, the electro-magnetic working environment of the system, etc., all of these have not been extensively tested in this paper, which will be an important research direction in future.


Significance: Shear wave optical coherence elastography is an emerging technique for characterizing tissue biomechanics that relies on the generation of elastic waves to obtain the mechanical contrast. Various techniques, such as contact, acoustic, and pneumatic methods, have been used to induce elastic waves. However, the lack of higher-frequency components within the elastic wave restricts their use in thin samples. The methods also require moving parts and/or tubing, which therefore limits the extent to which they can be miniaturized.Aim: To overcome these limitations, we propose an all-optical approach using photothermal excitation. Depending on the absorption coefficient of the sample and the laser pulse energy, elastic waves are generated either through a thermoelastic or an ablative process. Our study aimed to experimentally determine the boundary between the thermoelastic and the ablative regimes for safe all-optical elastography applications.Approach: Tissue-mimicking graphite-doped phantoms and chicken liver samples were used to investigate the boundary between thermoelastic and ablative regimes. A pulsed laser at 532 nm was used to induce elastic waves in the samples. Laser-induced elastic waves were detected using a line field low coherence holography instrument. The shape of the elastic wave amplitude was analyzed and used to determine the transition point between thermoelastic and ablative regimes.Results: The transition from the thermoelastic to the ablative regime is accompanied by the nonlinear increase in surface wave amplitude as well as the transformation of the wave shape. Correlation between the absorption coefficient and the transition point energy was experimentally determined using graphite-doped phantoms and applied to biological samples ex vivo.Conclusions: Our study described a methodology for determining the boundary region between thermoelastic and ablative regimes of elastic wave generation. These can be used for the development of a safe method for completely noncontact, all-optical microscale assessment of tissue biomechanics using laser-induced elastic waves. Different techniques have been used to enhance the absorption of pulsed laser energy by the sample, such as the injection of nanoparticles,–,Depending on the pulsed laser fluence and the absorption coefficient of the sample, the mechanism for generating elastic waves can be classified into two regimes: thermoelastic and ablative.2Tissue-mimicking phantoms were made of 1% (w/w) agarChicken liver from a local supermarket was used as an example of a biological sample with strong endogenous absorption at 532 nm. To avoid dehydration of the liver tissue, phosphate-buffered saline was regularly applied.In these experiments, a Q-switched, frequency-doubled Nd:YAG laser at 532 nm  was used to induce elastic waves in the samples. Energy per pulse was adjusted from 0.29 to 12.27 mJ by changing the flashlamp intensity. The laser beam was focused on the sample surface with an incidence angle of Laser-induced elastic waves were detected using a line field low coherence holography (LF-LCH) instrument, fully described in Refs. A 30-kHz swept-source OCT imaging system with the central wavelength of 1310 nm and 3The complete spatiotemporal maps of elastic waves propagating in a 1% graphite phantom in (a) thermoelastic and (b) ablative regimes are shown in Representative temporal displacement profiles of the elastic wave in 1% graphite phantom as a function of excitation energy were taken from the full spatiotemporal maps and are shown in –Spatiotemporal profiles of the elastic wave were used to calculate its amplitude and group velocity.The dependence of the surface wave amplitude (SWA) on laser energy was quantitatively investigated by gradually increasing the laser beam energy from 0.29 to 12.27 mJ. SWAs were averaged over three trials at each energy and on three samples of each graphite concentration. Laser pulse impact location was changed after each shot by translating the sample to ensure a fresh surface was hit with each shot. A microscope image demonstrating the impact points of the pulsed laser on the sample surface (1% graphite doping) is shown in As the laser pulse energy is reduced, the diameter of the ablated zone decreases and eventually, at low pulse energy, no visual damage spot is observed under the microscope. However, due to the high displacement sensitivity of the LF-LCH system, elastic wave propagation is observed even at the lower energy levels despite the lack of a visible impact spot.The evolution of the surface displacement as a function of laser pulse energy was used to determine the boundary between the thermoelastic and ablative regimes. Wave amplitude was calculated as the root mean square of the maximum displacements on the phantom surface caused by the laser excitation. The root mean square is calculated over the distance of 0.1 mm from the start of the imaging region . For the proof-of-concept, the same experiments were performed with real tissue (chicken liver). Due to the curvature and roughness of the chicken liver sample, a smaller field of view with finer pixel resolution was selected for precise measurements. Additionally, as the attenuation of the elastic wave in chicken liver is high compared to agar phantoms, offset distance between the pulsed laser and the line focus was reduced from The measured surface wave group velocity in the chicken liver is Temporal displacement profiles of the elastic wave in the chicken liver were extracted from the spatiotemporal maps and are shown in As a further analysis, the SWA versus laser pulse energy in the chicken liver is compared with two graphite phantoms of absorption coefficients 1.87 and One set of results shows the transition point from thermoelastic to the ablative regime, just as in the agar phantom control experiments; while the other set demonstrates no transition point energy. This result appears to demonstrate that the absorption coefficient of the chicken liver is not homogeneous across the sample surface. Comparing with the results from graphite phantoms, it appears that some locations on the liver sample exhibit an absorption coefficient of nearly en face OCT image of the liver surface, taken at the central wavelength of 1310 nm, cannot clearly show heterogeneity in the absorption coefficient. In contrast, full-color microscopic images clearly indicate that some regions on the chicken liver are darker than others due to the strong absorption of visible light by blood. These color images qualitatively represent the heterogeneous absorption of the chicken liver sample.As hemoglobin is considered the primary chromophore in the liver tissue, then it may be expected to see the absorption coefficient as high as An optical attenuation measurement at 1310 nm for each A-line in the OCT image4,,,In this study, we demonstrated that the transition from the thermoelastic to the ablative regime is accompanied by the nonlinear increase in SWA as well as the transformation of the wave shape. Such results are in agreement with the results of measurements of laser-generated acoustic waves. In the low irradiance regime, before ablation takes place, the amplitude of the laser-generated acoustic wave shows a linear increase with pulse energy.–Theoretical modeling for laser-generated ultrasound in metals has demonstrated that the resulting force on the sample surface is a combination of a time-varying normal force and the forces generated by thermal expansion.Although the amplitude of the elastic waves depends on the distance between the excitation and measurement locations, we assume the estimated transition point of the wave shape is independent of this distance. Indeed, the displacement amplitude on the sample is less than a micron. Therefore, it can be considered that the deformation is in the linear elastic region, and the dependence of the amplitude on the laser energy is defined only by the absorption coefficient of the sample. However, the shape of the elastic wave presented in ,in vivo application.All-optical OCE has advantages of measuring tissue biomechanical properties using a single shot excitation by a laser. However, there is a valid concern about the damage of tissue at the excitation area. Since the phenomenon is basically the sudden thermal expansion of the localized tissue by absorbing the laser irradiation, the temperature at the excitation position rises sharply. Due to the laser-induced heating of the tissue, a change in microstructure in collagenous tissue has been reported.5in vivo.This study described a methodology for determining the boundary region between thermoelastic and ablative regimes of elastic wave generation. These can be used for the development of a safe method for completely noncontact, all-optical microscale assessment of tissue biomechanics using laser-induced elastic waves. With the proper selection of laser wavelengths to match the optical absorption of the target tissue, it may be possible to perform laser-induced elastography without optical damage. These results open up the potential for nondestructive all-optical OCE measurements


Crystallisation is a crucial step in many industrial processes. Many sensors are being investigated for monitoring such processes to enhance the efficiency of them. Ultrasound techniques have been used for particle sizing characterization of liquid suspensions, in crystallisation process. An ultrasound tomography system with an array of ultrasound sensors can provide spatial information inside the process when compared to single-measurement systems. In this study, the batch crystallisation experiments have been conducted in a lab-scale reactor in calcium carbonate crystallisation. Real-time ultrasound tomographic imaging is done via a contactless ultrasound tomography sensor array. The effect of the injection rate and the stirring speed was considered as two control parameters in these crystallisation functions. Transmission mode ultrasound tomography comprises 32 piezoelectric transducers with central frequency of 40 kHz has been used. The process-based experimental investigation shows the capability of the proposed ultrasound tomography system for crystallisation process monitoring. Information on process dynamics, as well as process malfunction, can be obtained via the ultrasound tomography system. There is a great need for on-line monitoring in many industrial operations ,2,3,4. TUltrasound computed tomography (USCT) has been gaining interest in both medical and industrial applications. Non-destructive testing (NDT) is a field in which ultrasonic solutions are widely used ,9,10. USIn this study, we examine the batch crystallisation procedure. Basic industrial crystallisation set-ups consist of the batch, semi-batch and continuous crystallisers . Batch cUltrasonic measurement techniques have been proven efficient to characterise slurry mixtures during crystallisation processes ,31,32. SThis work investigates the functionality of ultrasound tomography in industrial crystallisation. Two sections with experimental processes are presented. The first section consists of experimental processes using fine sugar particles and water/sugar suspensions focusing on the ultrasonic imaging in liquid slurry mixture of sucrose/water particles. The second section focuses on reactive crystallisation experiments, such as calcium carbonate crystallisation. The aim of this research is to examine the USCT capabilities in providing useful information on the distribution of phases within flowing mixtures by distinguishing between different suspension particle concentrations or even between differences in compounds’ structural phase.The proposed USCT system consists of a ring of piezoelectric transducers array, a sensing electronics setup, and a computer system for image reconstruction. These sensors are mounted to the outer surface of the tank using an ultrasonic coupling gel and a belt, keeping the system in place. c is the speed of sound. This, together with the source position and the initial take-off angle, fully specifies the ray. In the case of a uniform sound speed model that only depends on the depth, one can use a convenient parameterisation for the rays which is based on the ray-approximation approach.T gives the time of flight of the pulse. Assuming that the ray-path is intensive to a small slowness perturbation, the perturbation in travel-time is given by the path integral of the slowness perturbation along the ray.A travel-time transmission tomography method was developed and applied to this work. The tomographic system measures the time-of-flight of transmitted pulses. TOF values are calculated by measuring the arrival time of the first transmitted pulse of the captured waveform. The most used approximation for USCT is the ray-based method. It is fundamental for most tomographic schemes. The main advantage is the computational efficiency, since the wave propagation is described using a finite number of rays instead of solving the continuous wave equation. The ray trajectories are calculated by solving the following vector equation and accounting for very high emission frequencies .(1)dds(A is the modelling operator which describes the sensitivity distribution and Since travel-time perturbations given by Equation (3) are insensitive to slowness perturbations anywhere off the geometric ray-path, the sensitivity kernel is identically zero everywhere in space except along the ray-path where it is constant. The implication for ray-based travel-time tomography is that travel-time perturbations should be back-projected purely along the ray-path. A tomographic approach consists of many of these rays, whose amount depends on the angle of the emission beam. All these equations of rays form a system of linear equations, the so-called forward problem. The measurement data formed from subtraction between reference and inclusion data for sound speed led to the reconstructed image of travel-time delays. For a generalised tomographic problem, the above Equation (3) can be expressed as:Fréchet sensitivity kernels are based on the first Fresnel zone . Fresnelx. The delay time is given in Equation (5).The first Fresnel zone is that part of the refracting medium through which energy is transmitted from the source to the receiver within less than a quarter of a period of the ray arrival. In this approach, a weighting function based on the travel-time delay dictates that more sensitivity is attributed to pixels nearer the axis of the Fresnel volume, which is the infinite frequency ray path. To find the first Fresnel zone, we calculate the delay time, s) to x and from x to the receiver (r) and x is always within the first Fresnel zone if the corresponding travel-time satisfies the following equation, in which T defines the emitted wave’s period:Here The following function defines the sensitivity of a Fréchet kernel based on the first Fresnel zone:x)S, x (scattered wave) and K the normalisation factor. The sensitivity formula has been developed on the Fresnel zones method [In this case s method ,38. SIPPs method . In thiss method .The internal time delays are reconstructed by using pulse Total variation regularisation (TV) ,41,42 haThis is solved by the split Bregman-based TV algorithm . After aM is the 256 receiving data coming from the tomographic device and N is the number of captured frames.To analyse the experiments related to crystalline particle imaging and crystallisation we use some quantitative information from data and the image. We calculate the average values of TOF delays, namely of the subtraction of background from full data, for every recorded frame.This section presents experiments for USCT on the combination of fluid and solid particles. Specifically, its main purpose is to analyse the TOF responses in inhomogeneous two-phase media. In the first two experiments fine sugar particles were used as the adding substance to the liquid medium, without any stirring being applied. In the third experiment a water/sugar suspension was injected, while stirring has been applied using a magnetic stirrer. In all three experiments, a temporal resolution of 10 fps was applied (without accounting for reconstruction time for fps). An acrylic circular tank of 20 cm diameter, filled with tap water, and a ring of 16 ultrasonic transducers were used in all experimental set-ups of this section.In the first experiment, fine sugar particles were thrown in the medium, at a steady, continuous pace. This experiment aimed at ascertaining the efficiency of the USCT device in real-time measurements and in a continuous change of the injection point. Sugar particles were fed into the medium (contaminated water) as shown in The reconstructions agree with the injection’s shifting position. The intermittent injection drove a continuous change of particles’ concentration over time, being at a high then lower and then higher level, again. This change of the particles’ concentration within the field of view translated into higher then lower and then higher again delays of TOF signals. After 4:30 min from the start of the process, the injection point passed through position A again, which drove of sugars in the region to higher concentration. Therefore, one can notice a significant increase of TOF delays in the last reconstructed frames. Moreover, the injection stayed a bit longer between position A and C and, subsequently, as the experiment approached the end, bigger TOF delays could be noticed.In this experiment, a sucrose/water suspension of 75% kg/mL was used as a tracer. Automatic injection by using an electronic pump was applied. The feed rate speed was 35 mL/min. During the process, which lasted for 7 min, mixing occurred. Stirring speed was at 40 rpm. This rate was assumed to be moderate as no swirl effect  was depiExperimental photos and schematics are displayed to clearly present the experimental set-up. In this section, lab-scale batch crystallisation experiments were conducted. The experimental apparatuses were designed to be aligned to industrial framework. The current study focuses on stirred crystallisation tanks . CalciumThe first step of the experimental procedure was the preparation of the reagent. Three hundred grams of sodium hydroxide was dissolved in a vessel filled with 1 L of demineralised water. A carbon dioxide dosing tube and pH meter probe were used to control the pH of the sodium hydroxide. The sodium hydroxide solution was gassed with carbon dioxide to reach and maintain a pH of about 11, resulting to an 1 M However, when the injection point moved, the crystallisation in the region stopped and subsequently already created crystalline suspensions whether start dissolving or start the sedimentation process. Therefore, one can notice this decay of TOF delays values after the moving of the injection in the reconstructed frames.Reconstructions provide clear depictions of the localised forming suspensions in almost all the cases, as a gradual increase of TOF values over time. In the first case of 9 mL/min, no localised suspension was noticed due to the nature of the low injection rate. Comparing all the cases, the results show a quantitative relation between the travel-time imaging and the concentrations of the forming suspensions, since the increase of the injection rate turns the suspensions more concentrated. A common scale is used for the presentation of results to point out this fact. Contours were applied to clearly distinguish the higher concentrated regions of the tank. The tomographic system proves accuracy by monitoring efficiently almost all the experimental cases and providing a quantitative scale of TOF values related to the concentration of crystalline particle in the forming suspensions.Four experiments with stirring calcium carbonate crystallisation were conducted aligned to industrial standards. Four different reagent injection rates of 9, 18, 27 and 36 mL/min were applied. The injection point was the same in every case. Two litres of calcium chloride solution used as reagent in all the processes. Experiments lasted different amounts of time related to the rate of injection. Recording took place from the beginning until the end of the injection process and an averaging method over 100 frames was applied.The stirring process created significant changes in the forming suspensions and the aim of these tests was to inspect and analyse the system’s responses in stirred tanks and crystallisers. A good combination of the mixing factor and the tank’s kinetics led to a uniform distribution of crystalline suspensions across the whole medium. This fact significantly affected the crystal yield. The optimal agitation is the minimum stirring rate needed to keep all crystal particles suspended from the bottom. Therefore, the size distribution and concentration of particles vary within an agitated suspension according to the dynamical state of the medium . StirrinA quantitative relationship between the TOF delays and the localised forming suspensions can be noticed in non-stirring cases. The quantitative relationship is an ascending trend of the maximum TOF values while the injection rate increases, as shown in Examining the stirring experiments, one can realise the importance of the different combinations of stirring and injection rates. In the 9 and 18 mL/min cases, a dissolution of the forming suspensions can be noticed after a point, which caused slightly decreased TOF values. On the other hand, this could not be seen in the two higher injection stirring cases , since 100 rpm was not enough to dissolve formations of such a high injection rate. Subsequently, an efficient combination of stirring and injection should assure a homogenous formation so that the localised suspensions, or even the direct dissolution of them are not occurring.These results display a promising potential of travel-time ultrasound tomography not only for monitoring the process by detecting and reconstructing regions with higher crystalline particle concentration but also for quantifying different formations of crystalline suspensions by utilising the scale of the travel-time delays.This paper presents a travel-time ultrasound tomography for monitoring batch crystallisation processes. The system was first demonstrated in monitoring processes consisting of crystalline suspensions in a nonstationary setting. This followed the monitoring of the calcium carbonate crystallisation reaction. The study examined the combination of injection and stirring factor to the process through the results of the ultrasound tomography system.The travel-time ultrasound tomographic system provided satisfactory responses in almost all the cases. This has been shown based on a gradual increase of TOF differences due to the gradual crystalline suspension formation over time. The device also shows a good response to distinguishing between different material phases, such as liquid solutions and crystalline liquid suspensions. Experimental results in A calcium carbonate crystallisation reaction aligned with industrial standards is shown in For low-feed rates, there is a more uniform image showing that the process of crystallisation occurred without any localised issues. With higher rate of injection, the USCT device showed the localised changes in TOF images, which could lead to localised crystallisation. This demonstrated the application of a proposed tomographic device for quality assurance in batch crystallisation process. The process of dynamic information could be extracted both from measured USCT data and images providing key insight on process efficiency and process safety.Reaction progress by the mean TOF delays values.Homogeneity of the medium during injection process by the reconstructions.Unwanted by-product formation by the reconstructions.This study presented a feasibility investigation of ultrasound tomography’s functionality in batch crystallisers. Results are promising for the on-line monitoring and the characterisation of the forming of the suspensions by sound propagation principles. Injection rate and stirring speeds were used as control parameters. The aim was to identify the capabilities of travel-time USCT in the gradually increasing suspension concentration. Results from the experiments were satisfying, showing good potential in distinguishing between phases of different concentrations of particles in suspension. Important conclusions of this study are the determination of:Even though such a device cannot measure the particle’s size directly, it seems that it could be of great aid in crystallisation processes. It can be used as monitoring of homogeneity or detecting malfunctions and faults. It could work as a quality assurance figure to protect from process malfunctions that could lead to a nonuniform crystal yield. By on-line monitoring, unexpectedly higher formed suspensions can be detected, and, with that, one can control the stirring and injection factors, which are significant adjustable parameters of the process.On-going research will focus on investigating the effect of a full-waveform ultrasound tomography instrument, utilising attenuation, and back-scattering information. Moreover, higher excitation frequencies will be tested to investigate the penetration depth of the ultrasounds in the process, as it is a crucial adjustment for wave propagation and interaction with particles and slurries.


Since production and trade are increasingly organized within global value chains (GVCs), assessing who effectively pays the cost of protection is not straightforward and since productive processes are internationally fragmented, quantifying the effects of trade policy requires an enhanced analytical framework that takes international input–output linkages into account to assess the implications trade costs have on competitiveness at national and sector levels. This paper defines a new synthetic measure of trade protection based on the value added in trade, capturing the effects that the tariff structure has on exporting firms that rely on imported intermediate inputs. The index, defined in a general equilibrium framework, provides a theoretically sound protection measurement in the context of GVCs. We assess trade protection by computing protection indexes at the bilateral level on both gross imports and imports to exports using the Global Trade Analysis Project computable general equilibrium model. These indexes are used to investigate the relationship between the European Union tariffs and integration of the Italian GVCs. In the case of Italy, imports to exports are overall less protected than gross imports with significant differences at the sector level. Despite the low levels of nominal protection, industrial sectors play a central role in explaining our results. EU tariffs mostly affect Italian exporting firms in the case of chemical products, wearing apparel and leather products.The online version of this article (10.1007/s40888-020-00202-8) contains supplementary material, which is available to authorized users. The long European stagnation following the 2008–2009 global crisis has fuelled renewed debate about the importance of a strong industrial base to sustain and strengthen recovery and foster competitiveness. The debate is going to be even more important in the coming months due to the economic consequences of the COVID-19 epidemic. The design of appropriate trade policy measures to achieve this goal requires a full understanding of the characteristics of the current manufacturing production paradigm in terms of organization of international supply chains and production networks and clear identification of the main linkages between countries and sectors.About one half of global exchanges is related to global value chains (GVCs). The associated increase in trade in intermediates  magnifies trade costs that are incurred several times along the chain Yi . Since tThe focus of this article is on the challenges posed by the increased complexity of international trade patterns on trade policy analysis. We extend the set of trade restrictiveness indexes proposed initially by Anderson and Neary  to assesOur framework builds on global input–output accounting and trade in value added (VA). In multi-country production chains, fragments of value added  from different locations are combined to form final goods. Therefore, the empirical assessment of trade policy must acknowledge which country is the source of the value that is embedded in trade. This information can be used to determine who is effectively paying the cost of protection. For instance, firms that require a large share of intermediate imports to export pay higher tax rates in terms of value added  and how it is used by the importing country. The resulting restrictiveness index is equivalent to the actual trade policies in terms of the impact on the foreign value added embedded in a country's exports.The empirical analysis is performed using a modified version of the Global Trade Analysis Project (GTAP) model, GTAP-VA /World Trade Organization (WTO) schedule at the end of the Uruguay Round. Applied rates are generally identical to the WTO bindings and the EU has bound 100% of tariff lines.Agricultural tariffs stand out from industrial tariffs for several reasons: significantly higher rates, about three-fold; a higher percentage of non-ad valorem rates; and several tariff lines for the implementation of TRQs. On average, bound tariffs on agricultural products remain higher (14.1%) than on non-agricultural products (4.3%) and vary considerably from one agricultural product to another with a standard deviation of 23.7 compared to 4.4 for non-agricultural products. About 25% of tariff lines were duty free in 2014: the sectors with the highest percentages of duty-free lines are for cotton, wood and paper, minerals and metals, and other agricultural products WTO .The EU maintains preferential tariffs for imports from certain countries under its reciprocal or preferential agreements. The EU is the largest trading partner for many low- and middle-income countries, and trade preferences make up one of the central policies aimed at improving integration between the EU and these countries. The EU was the first high income importer to introduce preferential policies. Since the 1971 Generalised System of Preferences (GSP), the tide of preferential schemes has continued to rise, significantly widening the number of countries and products covered. Imports of agricultural products from many countries can enter the EU at zero or reduced tariffs under the EU's everything-but-arms initiative, its GSP and GSP + schemes, and its network of trade agreements.There are two main methodological challenges in the evaluation of any type of trade policy: measurement and aggregation  model incorporating the deconstruction of the gross trade flows to reallocate the value added generated in the production of goods and services back to the countries in which that income is generated , we applied a uniform value of 0.425.As for the production side, separable, constant returns-to-scale technologies are assumed. A common approach in CGE literature is to model the production side through a sequence of nested constant elasticity of substitution (CES) functions that aims to re-produce the substitution possibilities across the full set of inputs. The firms' conditional demand for components of value added depends on the relative prices of factors of production whereas composite value added and intermediates are used in fixed proportions (a fixed coefficient function of the Leontief type). In the intermediate input side, imported intermediates are assumed to be separable from domestically produced intermediate inputs. However, in the standard GTAP framework, the elasticity of intermediate input substitution is usually set to 0, i.e. no substitution is allowed in the production intermediates mix which becomes a limit for our analysis. Following Antimiani and Cernat , we intrThe import demand is modelled following the Armington aggregation structure, with an exogenous differentiation scheme given by the geographical origin of nationally homogeneous products. That is, under Armington trade, the output of each sector is assumed to be a region-specific variety. Consumer and intermediate goods are a CES composite of domestic and trade partner varieties. This specification explains the cross-hauling of similar products and makes it possible to track bilateral trade flows.The GTAP model is based on a complete IO accounting framework which takes into account all sources and uses of each economic good and all inputs into production. However, it requires some manipulations to perform GVC analysis.First, in the standard GTAP model, the sourcing of imports occurs at the border, providing information on total purchases of intermediate inputs by firms (domestic and imported), and total purchases of final goods by households, government and for investment (domestic and imported), but not attributing bilateral trade to the consuming agent . This amounts to applying a proportionality assumption which is not realistic. To overcome this limitation of existing models, we consider a richer input–output structure across countries and sectors that we can match with the actual structure reported in input–output tables. We link the import demand for each specific agent to the sourcing country/sector by applying broad economic categories (BEC)-informed shares to bilateral trade , as the product-generic tariff levied on imports from region r into region s.Second, value added multipliers are obtained from the cost structure of firms. They combine the sectoral VA shares in each country with the direct and indirect intermediate usage in the productive process. The multipliers are applied to trade which allows the entire value structure underlying gross trade to be retrieved, thus disentangling each country's contribution, in terms of income, in the production of traded goods. This enables us to define the benchmark for the value-added trade restrictiveness index within the GTAP framework. Finally, to compute the uniform tariffs, we define a new variable, We consider trade in intermediate goods and allocate the value added therein contained according to its geographical origin. This enables us to distinguish different portions of value in a country's imports according to the importer's usage of foreign goods Fig. . Specifi2In what follows, we specify theory-consistent indexes of trade restrictiveness on both gross and VA bases. First, we provide a decomposition of gross imports based on an input–output framework.s and r denote countries and i and j sectors. Define s' value added originated in sector i of goods produced by country r sector j. The multiplier matrix provides a breakdown of the flows of value added across country/sector of production since diagonal  sub-blocks represent domestic (foreign) value added in domestic production. Than define Let The first term in Eq.  gives thThe last component can be characterized as GVC-related trade since it includes goods and services crossing more than one border, thus involving at least two production stages located in different countries before the final product reaches the destination market ,,3), supeIn this study, data are taken from version 10 of the GTAP Data Base for a baseline of consistent data on consumption, production and trade Specifically, we start with UN COMTRADE import data at the six-digit level of the Harmonized Commodity and Coding System (HS) and apply the first concordance between HS and the BEC Rev.5. Each economic category is completely decomposable by end use. Accordingly, the mapping between BEC and the System of National Accounts (SNA) end-use dimension makes it possible to identify three different end use classes, namely, intermediate consumption, gross fixed capital formation and final consumption. Finally, the HS-GTAP concordance is applied to map each HS line to a GTAP commodity which gives the BEC-informed shares. A similar procedure is applied by Aguiar et al. , Liapis ad valorem equivalents of applied border protection worldwide. However, one caveat is that it does not include information about tariff exemptions granted in export processing zones and through inward and outward processing trade regimes. These regimes introduce a differential tariff treatment of imports depending on the sectors and the firms to which they are destined since imported goods that enter into the production of exports are not subject to import duties. They are particularly relevant in the case of China trade flows (Yu and Tian Protection data in the GTAP Data Base are sourced from the Market Access Maps (MAcMap).We aggregate the GTAP Data Base in 12 countries and regions, identified in terms of their relevance as Italy's suppliers of goods and services imports in 2014, the benchmark of the dataset. Together, the extra-EU countries considered in our aggregation account for more than 50% of extra-EU Italy's imports. In the discussion of our findings, we do not present results for Russia (because of the extreme concentration of the extractive sector) or for Switzerland and Turkey (due to the extremely low level of tariffs they face in the EU). The sectoral aggregation consists of 30 sectors and keeps all manufacturing sectors disaggregated. Details on the aggregation are reported in Table Figure EU tariffs are more relevant for the agricultural and food sectors. For these sectors, tariffs can be higher than 50%, as for sugar. On the contrary, manufacturing sectors tariffs are more homogeneous and show lower peaks given that the highest rates never reach 12%.In this section, we review Italian imports and firms' international linkages, with some descriptive statistics on sectoral backward integration and patterns of imports both on a gross and a value-added basis with selected trade partners.Figure Overall, Italy appears to be significantly integrated into international production networks as a buyer of intermediates used in its exports, showing an aggregate backward integration index value in 2014 of 33.1% (18.4% for extra-EU imports). These figures are slightly lower than the German ones  and broadly in line with the other EU countries. It is worth recalling that getting embedded in global value chains is a powerful determinant of export growth. It has a positive effect on the domestic value added  even if it implies that a growing share of gross exports represents the value added that has been produced in foreign countries  and non-ferrous metals (more than 50%). Chemicals, an important exporting sector for Italy, embeds about 45% of foreign value added in its exports, mainly sourced regionally from other EU economies. The other EU countries are significant providers and in most cases, they provide more than 50% of total foreign inputs. Among the extra-EU providers, the role of China is apparent but overall, these figures confirm the importance of regional value chains in the development of GVCs . At the bottom of each panel, we report the ratio between total intermediate and imports.Next, we focus on Italy's import structure from the most important exporters: US, Japan, China, India and Brazil. In Fig. On average, around 38% of Italy's imports from the five countries considered represents intermediate inputs used by Italian firms to produce their exports, a share that is slightly higher than the overall average  trade flows, the evaluation of the impact of trade policies requires standard (gross) trade statistics to be complemented with trade metrics on a value-added base in order to take into account the backward linkages. Accordingly, we assess the impact the EU trade policy has on Italian imports not only in terms of total flows through the MTRI, but also in terms of intermediates used by firms to exports through the FVATRI. This is done on a bilateral basis for the leading exporters. To quantify the protection granted by the EU tariffs to the Italian economy, we keep constant extra-regional imports  in both gross and VA terms. Uniform tariff equivalents are then obtained by setting bilateral tariffs to zero and replacing them with the uniform one that keeps constant imports either in gross value or in value added. The trade flows considered only include goods since services are not subject to any tariffs.8Table The average MTRI value is equal to 4.2% and there are large differences across exporters. Such differences are not surprising given the discrepancies between the trade-weighted averages presented in Fig. The FVATRI values are always lower than the MTRI ones, and the smaller range of variation could be expected given that the value of intermediate goods cannot exceed the gross value. The average FVATRI (2%) is less than half of the MTRI, but the difference between the two indexes varies a great deal across exporters: the tax on intermediate goods is close to overall protection in the case of China, US and Japan whereas it represents a small percentage in the case of Brazil. It is worth noting the change in the exporter ranking where China is the country facing on average the highest protection on the exported value added (3.2%).To explain what drives these results, we compute the weight of each sector on the indexes level. Figure The vertical axes of the diagrams display the weight each sector has on the FVATRI expressed as a percentage of the total of the index. On the horizontal axes, sectoral weights are displayed for the MTRI. Then, the sectors above the bisector are those whose tariffs are more relevant in the production of Italian exports. Similarly, the sectors which are more relevant for the protection in gross terms are below the bisector.The importance of sectors is different when considering gross or VA imports. Although industrial sectors overall face low levels of nominal protection in the EU markets Fig. , they shGiven that these sectors play quite a different role in bilateral export flows, this sheds some light on the bilateral protection scores previously mentioned. For instance, Meat plays a prominent role in Brazilian exports whereas Wearing apparel and Leather products are quite significant in Chinese exports.9In this section, we show that the same trade policy, namely the Common External Tariff of the EU, leads to different outcomes according to the structural features of the economy it is applied to. To this end, we compute the protection indexes for the largest EU economy, i.e. Germany. Comparing Italy with Germany seems a reasonable choice given their levels of integration in global and regional value chains. We have already mentioned that backward participation indexes are similar for both countries and they also get similar shares of FVA from EU partners: 46% for Germany, 44% for Italy.On the other hand, Italy and Germany present different trade specialization patterns  to domestic produces in Germany and Italy. However, German and Italian firms are affected very differently by the EU tariffs as far as the cost of foreign inputs is concerned. Accordingly, we can expect the Italian and German governments to have different priorities in terms of trade negotiation both in terms of countries and sectors to be targeted.Although the quantification of the impact of trade policy on prices, economic activity and welfare have always been at the core of trade policy analysis, the complexity of today’s trade relations raises new unprecedented challenges. In particular, the rise of GVCs requires the adoption of enhanced analytical frameworks that take the international input–output linkages into account. Since exports rely on imported inputs, the evaluation of trade policies requires the use of new trade metrics based on the value-added components to assess the implications of trade costs on competitiveness at national and sector levels. In this paper, we define a new protection index framework and show how it can be operationalized for quantitative trade policy analysis.We then apply the proposed index to the quantitative analysis of the EU tariffs affecting Italian imports. The index is computed through an applied general equilibrium model of the global economy with trade in both final and intermediate products. By mapping bilateral supply chain linkages and value-added flows, the model provides a rich framework that captures countries’ heterogeneity in terms of the composition of their trade flows as well as in terms of their involvement in GVCs.The main caveat is that the model is based on comparative statistics and a few crucial assumptions, for instance, in terms of employment levels or international labour mobility. Consequently, the model’s results do not include dynamic effects such as the effects on productivity and growth, unemployment and migration. On the other hand, the simulation model allows the impact of trade policies to be explored through the reorganizations of the GVCs and shows that some tariffs impacts differ across countries depending on the sectoral composition of their economies and the relative importance of different foreign markets. Properly accounting for observed GVC linkages makes a substantial difference to the quantification of the general equilibrium effects of protectionist trade policies. In this respect, the FVATRI represents a useful addition to the tools available for policy analysis since it takes into account how cross-border multi-stage production affects the transmission of trade policy to national welfare.This study provides an assessment of the protectionist impact of EU tariffs, with a focus on Italy. The main policy implication of our analysis is that bilateral nominal tariffs and trade flows alone do not provide an accurate picture of the impact of protectionist measures through backward and forward linkages.beggar thyself’ content of protectionism. By exploiting the methodology for value-added accounting of trade flows, we find that the EU tariffs impose a burden of up to around 3.2% in the case of Italian imports from China. The figure is not trivial considering that it is an average and taking tariff rates variability into account.The value of the index for foreign value added in the exports component is indicative of the harm inflicted to domestic producers using foreign intermediate inputs to produce their exports. This shows the ‘Indeed, manufacturing sectors imports play a significant role in explaining the protection of imports for exports, notwithstanding the low levels of nominal EU tariffs. In particular, we find that EU tariffs mostly affect Italian exporters sourcing inputs of chemical products, wearing apparel and leather from abroad.We also document a significant difference in the impact of the EU tariffs on Italy and Germany. Since the nominal tariffs are (by definition) the same, this highlights how the same policy has a different impact according to the country in which it is implemented. The German market is more protected, but Italian firms pay a higher cost for the foreign inputs they need to export.Finally, our results shed some light on the implications of the most recent trade policy moves of the EU Commission. Italian consumers and firms are going to benefit more than German ones from the latest bilateral agreements with Japan and (possibly) Brazil. On the other hand, German consumers and firms are already more negatively affected when they import from the US and the situation could deteriorate if there are escalating transatlantic trade wars.Supplementary file1 (DOCX 28 kb)Below is the link to the electronic supplementary material.


The goal of this study was to translate the Beliefs about Medicines Questionnaire—Specific (BMQ-Specific) for cholesterol-lowering drugs, into the Hungarian, Slovak, Czech and Polish languages and test their reliability with statistical methods. For this purpose, Cronbach’s alpha, confirmatory and exploratory factor analyses were conducted. The analyses included 235 Czech, 205 Hungarian, 200 Polish, and 200 Slovak respondents, all of whom were taking cholesterol-lowering drugs. The translations from English into the target languages were always done by two independent translators. As part of the validation process these translations were pilot tested and after the necessary alterations, they were translated back into English by a third translator. After the approval by the creator of the questionnaire, nationwide surveys were conducted in all four countries. The results of the confirmatory factor analysis were exceptionally good for the Czech and Slovak translations, while the Polish and Hungarian translations marginally crossed the predetermined thresholds. With the exception of a single Polish question, the results of the exploratory factor analysis were deemed acceptable. The translated versions of BMQ-Specific are reliable and valid tools to assess patients’ beliefs about medication, especially medication adherence among patients taking cholesterol-lowering medication. A comparison between the four countries with this questionnaire is now possible. The health status of the population of Central and Eastern European countries is worse than the health status of the populations of high-income member states within the European Union. Although epidemiological data strongly suggest that cardiovascular mortality is higher in Central and Eastern European countries , only onIn a systematic review it was found that several factors may contribute to inadequate statin therapy. One factor is that doctors do not prescribe statin or use statin treatment with a lower intensity than the dose specified in the guidelines because they are afraid of the harmful side effects of the drug. Another influencing factor may be the fear of patients related to statin therapy because information from communication channels often suggests that a number of serious adverse side effects may occur when taking this kind of medication. Therefore, some patients stop taking statins after a while or do not follow the dose prescribed by their doctor, resulting in worse adherence. According to a survey conducted in the United States, 62% of patients stopped taking statins because they thought statins had side effects, and one-third of these patients stopped taking the drug without even consulting their doctor .In patients without established cardiovascular disease (CVD) but with cardiovascular risk factors, statin use was associated with significantly improved survival rate and large reductions in the risk of major cardiovascular events . It was One such reliable questionnaire used in international research studies is the Beliefs about Medicines Questionnaire (BMQ) . This inStudies have demonstrated that there is a relationship between BMQ scores and adherence behavior regarding medicine for various chronic diseases , includiTherefore, the primary aim of this study was to conduct a cultural adaptation and validation of the BMQ-Specific and test the reliability of the translation via statistical methods. These translations then can be applied in studies examining patients’ beliefs about cholesterol-lowering medicines in Hungary, Slovakia, the Czech Republic and Poland.It is worth noting that validated translations already exist for the BMQ-Specific in both the Czech and Polish languages. The Czech version tested general drug use of patients with either diabetes, hypertension or rheumatic disease , and wasNeither patients nor the public were involved in the design, conduct, reporting or dissemination plans of our research. In all four countries the data gathering method was identical. An online questionnaire was sent out to the citizens by private polling companies. These citizens were part of an online market research panel that is used by the companies to conduct surveys at an international level . The panp. and Český Národní Panel Ltd. and were fully anonymous to all of the authors of the study. Written informed consent for the study was obtained from all respondents prior to the study by SZLEM Service L. p. and Český Národní Panel Ltd. The study was approved by the Scientific Research and Ethics Committee of the Medical Research Council in Hungary (ETT TUKEB 55704–5/2017/EKU) and by the Ethics Committee of the Czech University Hospital Hradec Kralove in Czechia (Ref. number: 201802 S15 P). For the Slovak ethical approval, the Ethics Committee of the Ministry of Health and the Ethics Committee of the University of Kosice were contacted. Both committees stated that non-interventional studies and market research studies do not require ethics approval. Regarding the Polish ethical approval, the Bioethics Committee of the Ministry of Health was contacted, which also stated that non-interventional studies and market research studies do not require ethics approval.Ethics approval: All respondents of this study were approached via online market research panels by the companies SZLEM Service L. A common process was used to translate and adapt the BMQ-Specific across the four languages. The original English version  was tranThe four translations were treated independently from one another in all statistical analyses. Besides the general descriptive statistics, Cronbach’s alpha was calculated to investigate the internal reliability of both the Necessity and Concerns scales. The internal reliability was deemed acceptable if the alpha value was equal to or above 0.70 . Chi-squThe patients’ demographic characteristics are presented in In The confirmatory factor analysis  revealedThe results of the exploratory factor analysis of the BMQ-Specific are reported in Validation of a questionnaire and testing its reliability are complex and comprise multiple methods . As indiThe original BMQ study by Horne et al.  suggesteConsidering the confirmatory factor analysis, a similar French study revealed CFI as 0.89 and RMSEA as 0.08 . FurtherFinally, in our study, with the exception of a single Polish question the factor loadings were all above the acceptable threshold. However, for the sake of uniformity, the aforementioned question was not altered.The translation and testing of the BMQ-Specific for cholesterol-lowering drugs was done in four languages simultaneously. International standards were used by testing their reliability with various statistical methods. While the Slovak and Czech translations met the suggested thresholds for the confirmatory factor statistics, the Hungarian and Polish translations marginally crossed the predetermined thresholds. The factor loading of a single Polish question was below the acceptable threshold.Based on the results of our statistical analyses the Hungarian, Slovak, Czech and Polish versions of BMQ-Specific are all reliable, and based on the four pilot tests, these are also valid tools to assess patients’ beliefs about medication adherence in relation to cholesterol-lowering medication. A comparison between the four countries is now possible.


Prolonging the network lifetime is one of the fundamental requirements in wireless sensor networks (WSNs). Sensor node clustering is a very popular energy conservation strategy in WSNs, allowing to achieve energy efficiency, low latency, and scalability. According to this strategy, sensor nodes are grouped into several clusters, and one sensor node in each cluster is assigned to be a cluster head (CH). The responsibility of each CH is to aggregate data from the other sensor nodes within its cluster and send these data to the sink. However, the distribution of sensor nodes in the sensing region is often non-uniform, which may lead to an unbalanced number of sensor nodes between clusters and thus unbalanced energy consumption between CHs. This, in turn, may result in a reduced network lifetime. Furthermore, a different number of clusters lead to a different quality of service of a WSN system. To address the problems of unbalanced number of sensor nodes between clusters and selecting an optimal number of clusters, this study proposes an energy-balanced cluster-routing protocol (EBCRP) based on particle swarm optimization (PSO) with five mutation operators for WSNs. The five mutation operators are specially proposed to improve the performance of PSO in optimizing sensor node clustering. A rotation CH selection scheme based on the highest residual energy is used to dynamically select a CH for each cluster in each round. Simulation results show that the proposed EBCRP method performs well in balancing energy consumption and prolonging the network lifetime. Wireless sensor networks (WSNs) compose a large number of sensor nodes, which are scattered in the sensing region, and one or more sink nodes . GeneralProlonging the network lifetime is one of the fundamental requirements in WSNs. The lifetime of a network is mainly affected by energy consumption by sensor nodes. A significant amount of the energy consumed by sensor nodes is used for data transmission ,6,7. HowSensor node clustering is one of the effective strategies for prolonging the network lifetime ,10,11,12However, the clustering of sensor nodes still faces many challenges. Generally, sensor nodes are randomly scattered in the sensing region. Grid-based clustering or assigning sensor nodes to their corresponding nearest randomly selected CH may cause an imbalance in the number of sensor nodes between clusters, resulting in different energy consumption by CHs. A CH within a cluster containing a large number of sensor nodes would consume a lot of energy and be exhausted quickly. Furthermore, the number of clusters affects the performance of WSNs. On the one hand, a small number of clusters would increase the energy consumption of each CH when gathering data from sensor nodes within its cluster and sensor nodes far away from the CH when sending data to the CH. On the other hand, a large number of clusters would increase the traffic burden in the network. Therefore, a crucial task for increasing the network lifetime is to adaptively determine the number of clusters and group sensor nodes into clusters evenly according to their distribution. This is important to improve the performance of WSN such as the network lifetime.Recently, computational intelligence has been widely used in WSNs to provide solutions for some problems such as nodes deployment, task allocation, path planning, and movement control ,25,26. CAn energy-balanced cluster-routing protocol for WSNs is proposed to balance the energy consumption of sensor nodes and prolong the network lifetime.An adaptive sensor node clustering scheme based on PSO is proposed to determine the number of clusters and group sensor nodes into clusters evenly.Five mutation operators are specially proposed to improve the performance of PSO in optimizing the clustering of sensor nodes.This study proposes an energy-balanced cluster-routing protocol (EBCRP) using PSO with five mutation operators for WSN that groups sensor nodes into clusters evenly. In the step of EBCRP, the number of clusters and their centroids is optimized c, in whiThe rest of the paper is organized as follows. Many clustering methods have been proposed for WSNs, and the effectiveness of sensor nodes clustering for prolonging the network lifetime has been verified. In this section, existing methods for clustering sensor nodes are reviewed from two aspects, namely, non-computational intelligence and computational intelligence.Many methods for sensor node clustering based on non-computational intelligence have been proposed. These methods group sensor nodes into several clusters and select a CH for each cluster. The CH can gather data from other sensor nodes within the same cluster and send the aggregated data to the sink. This effectively saves energy and prolongs the network lifetime.For clustering of sensor nodes based on non-computational intelligence, LEACH is a very popular clustering routing protocol for WSNs proposed by Heinzelman et al. . In LEACClustering sensor nodes based on computational intelligence is another active research trend ,37,38,39The existing sensor node clustering methods based on computational intelligence have proved the effectiveness of computational intelligence technologies in providing effective solutions for WSNs. However, sensor nodes are usually randomly scattered in the sensing region. Most existing sensor node clustering methods do not balance the number of sensor nodes between clusters, which causes unbalanced energy consumption. In addition, in different applications, the distribution and number of sensor nodes are different, it is critical to automatically determine the number of clusters according to the number and distribution of sensor nodes. Furthermore, existing technologies of computational intelligence still have some shortcomings. For some optimization methods of computational intelligence, it is easy to converge into the local optimum when dealing with high-dimensional and complex problems. Additionally, in order to cope with different WSN problems, technologies of computational intelligence should be improved accordingly. To prolong the network lifetime and make WSN systems effective data collection , the senTherefore, this work proposes an energy-balanced cluster-routing protocol using PSO with five mutation operators for WSN, which can automatically determine the number of clusters and balance the number of sensor nodes between clusters. In addition, five mutation operators are specially proposed to improve the performance of PSO in optimizing sensor node clustering by increasing the search diversity. The energy-balanced cluster-routing protocol can effectively balance the energy consumption of sensor nodes and thus prolonging the network lifetime.N static sensor nodes and one sink node. The sink is placed in the center of the sensing region R, and sensor nodes are randomly scattered over R to monitor the environment. Sensor nodes can be grouped into several clusters, with one sensor node being appointed as the CH to aggregate data from the remaining cluster members within the same cluster. The set of sensor nodes is defined as k is the number of clusters. Each CH creates a time division multiple access (TDMA) communication message for its cluster members, which is used to inform cluster members to send data to the corresponding CH according to the schedule. The data collection, processing, and communication functions of sensor nodes are determined by the architecture of the nodes . The power module can provide energy to the above mentioned functional modules. Most of the available energy is consumed during data transmission. Unreasonable data transmission can lead to high and unbalanced energy consumption of sensor nodes, thereby reducing the lifetime of the network. The energy consumption model and network lifetime are described in the following subsections based on the following assumptions.d between the sender and the receiver. If d is smaller than a threshold L-bit packet is The energy consumed by sensor nodes is mainly used for data transmission. In this study, sensor nodes can be divided into two types: cluster members and CHs. Both of them can obtain data from the sensing region. Cluster members send the acquired data to their CH instead of directly to the sink. Each CH can aggregate data from its cluster members and send these data to the sink. The energy of cluster members is mainly used for sending data; the energy consumption of CHs includes both sending and receiving data. To calculate energy consumption, the channel model is employed based on the Euclidean distance Equation :(1)ET=L×It can be noticed from Equations  and 2)  2) that In this study, the lifetime of the network is considered to start from its initialization until it cannot work effectively. Generally, some existing studies define the network lifetime as a period from network initialization until the energy of at least one sensor node is depleted, that is, one sensor node fails ,41,42. TBalancing the energy consumption of sensor nodes can extend the network lifetime of both small and large WSNs systems, because the energy consumption of sensor nodes become similar in this case. This can avoid the phenomenon where some sensor nodes consume energy faster while other sensors have a lot of residual energy, which is helpful to prolong the lifetime of WSNs.R with randomly deployed sensor nodes, the sensor nodes are first grouped into clusters evenly using PSO with five mutation operators. In this step, the numbers of clusters and their centroids are optimized, in which some sensor nodes are selected as the centroids of clusters and other sensor nodes are assigned to their respective nearest centroid. Additionally, the sensor node clustering scheme is optimized according to the following two objectives: minimizing the average distances between sensor nodes and their centroids, and maximizing the balance index of the number of sensor nodes between clusters. To increase the diversity of search, five mutation operators are proposed for optimizing the sensor node clustering scheme. Finally, the data collection task is performed based on the clustering results. In each round, the sensor node with the highest residual energy in each cluster is selected as a CH. Each CH is responsible for aggregating data from its cluster members and sending these data to the sink. The residual energy of all sensor nodes is also updated in each round until the end of the network lifetime.Based on the sensing region M particles to search for the best solution, with each particle representing a potential solution. Particles have two attributes: velocity v and position x. The solution (position) of the i-th particle can be expressed as D is the dimension of particles. The velocity of the i-th particle, w to the traditional PSO to change the convergence speed of the optimization algorithm, which is called standard PSO [i-th particle are updated by Equations ,,M particIn EBCRP, PSO is used to optimize the number of clusters and centroid of each cluster. N denotes the number of sensor nodes. In this structure of particles, the first dimension represents the number of clusters k, while the i-th  of each particle in each generation.During the optimization process, for each particle (solution), Each particle corresponds to a sensor node clustering solution in each generation. These solutions are expected to be searched towards the desired target . Therefore, the fitness of the clustering solutions need to be evaluated.i-th cluster. The value of N is a positive integer, Equation maxfimaxfi(5)BEquation .(7)maxfk  sensor nodes with the highest probability are selected as cluster centroids of clusters. This means that it is necessary to not only simply optimize the value of each dimension of particles, but also adjust the position (dimension) of the value corresponding to the highest k probabilities. In addition, the clustering solution is significantly affected by the first dimension of particles representing the number of clusters. To increase the search diversity, the following five mutation operators are proposed for optimizing the sensor node clustering scheme.Reversing probability operator: it is used to reverse a part of the probabilities of sensor nodes. The detail process is shown in Algorithm 1.Decreasing probability operator: it is used to decrease the probability of some sensor nodes becoming cluster centroids. The detail process is shown in Algorithm 2.Increasing probability operator: it is used to increase the probability of some sensor nodes becoming the cluster centroids. The detail process is shown in Algorithm 3.Swapping probability operator: it is used to swap the probabilities of two sensor nodes in a particle. The detail process is shown in Algorithm 4.Transforming number operator: it is used to transform the number of clusters in the first dimension of particles. The detail process is shown in Algorithm 5.In the sensor node clustering optimization process, Algorithm 1: Reversing probability operatorAlgorithm 2: Decreasing probability operatorAlgorithm 3: Increasing probability operatorAlgorithm 4: Swapping probability operatorAlgorithm 5: Transforming number operatorx, velocity v, and fitness) are first initialized for all particles. The best experience of particles chi=N is varied from 50 to 200. Some parameters of the WSN system are listed in This section presents several simulations performed using MATALAB to evaluate the effectiveness and performance of the proposed EBCRP method. The effectiveness of EBCRP is first validated in terms of the clustering performance and balanced energy consumption of sensor nodes. Further, simulations are also performed to compare EBCRP with some existing methods, namely, LEACH , SEP 2929, and IIn EBCRP, an adaptive sensor node clustering scheme based on PSO is proposed to determine the number of clusters and group sensor nodes into clusters evenly. Additionally, five mutation operators are specially proposed to improve the performance of PSO in optimizing sensor node clustering. This subsection examines the effectiveness of the proposed EBCRP method.The effectiveness of PSO and five mutation operators in EBCRP are verified. PSO with five mutation operators (PSO-FMO) and without five mutation operators (SPSO) are compared. The same parameters are used for both PSO-FMO and SPSO. The population size is set to 50. Acceleration constants R. However, the allocation of cluster centroids by SPSO is not reasonable. For example, the clusters highlighted by circles have extremely asymmetrical centroids, which results in an increased distance between sensor nodes and their centroids and thus a deceased fitness It can be noticed from the figure that while both PSO-FMO and SPSO group the sensor nodes scattered into clusters in the sensing region To reduce the statistical error, both methods are run 30 times under the same conditions. It can be noticed from the figure that PSO-FMO achieves a higher average fitness for different numbers of sensor nodes compared to SPSO. SPSO converges quickly and falls into a local optima. In contrast, PSO-FMO continuously searches the best solution and avoids falling into local optima. This is because the five mutation operators continuously provide the diversity of particles for the entire swarm, which helps particles find a better solution. Hence, the mean convergence curves also verify the effectiveness of PSO-FMO in EBCRP.To verify the effectiveness of PSO-FMO in balancing the number of sensor nodes between clusters, To verify the effectiveness of EBCRP method in balancing the energy consumption of sensor nodes, the residual energy of sensor nodes during the network lifetime is analyzed. While the residual energies of sensor nodes fluctuate up and down, it still demonstrates balance within a small energy range. In sensor node clusters, some sensor nodes are dynamically selected as CHs, while others are selected as cluster members. The rates of energy consumption of CHs and cluster members are different. Therefore, there are some sensor nodes with a higher energy consumption. Furthermore, all sensor nodes cannot consume energy completely synchronously. Small range fluctuations of the residual energy of sensor nodes prove the effectiveness of EBCRP in balancing the energy consumption of sensor nodes.To validate the performance of the proposed EBCRP method, it was compared to other methods, namely, LEACH , SEP 2929, and ITo fully compare the performance of each method, simulations were performed for four different numbers of sensor nodes: 50, 100, 150 and 200. For LEACH and SEP, 5% of sensor nodes were selected as CHs. For the IICMH and EBCRP methods, 5% of sensor nodes are set as the expected number of clusters and a maximum number of clusters, respectively.The first row displays the number of dead sensor nodes from 0 to 300 rounds, while the second row shows the round corresponding to the first dead sensor node for each method. It can be noticed from the figure that the number of dead sensor nodes in LEACH and SEP increases slowly. It is obvious that some sensor nodes consume energy too fast, while others consume energy slowly due to the unbalanced energy consumption of sensor nodes in LEACH and SEP. In contrast, IICMH considers the balance of the number of sensor nodes between clusters when clustering sensor nodes, which helps balance the energy consumption of sensor nodes. Therefore, there is a period of a sharp increase in the number of dead sensor nodes. Nevertheless, IICMH still does not deal with the energy balance of sensor nodes well as some sensor nodes ran out of energy prematurely. EBCRP only shows a period of a sharp rise in the number of dead sensor nodes, whereas there is no problem of sensor nodes consuming energy prematurely. This is because EBCRP balances the energy consumption of sensor nodes well by balancing the number of sensor nodes between clusters and employing the rotation CH selection scheme based on the highest residual energy. It can be noticed that the first dead sensor node appears in a later round for EBCRP compared to the other methods, which also indicates that the energy balance of sensor nodes in EBCRP is better. Overall, EBCRP presents a good performance in balancing the energy consumption of sensor nodes.i-th sensor node. To further verify the balance of energy consumption between sensor nodes in EBCRP, the energy consumption balance index (ECBI) is calculated based on the fairness index as shown in Equation .(9)ECBIIn addition, From The network lifetime of EBCRP is also compared with other methods. EBCRP achieves the longest lifetime compared to LEACH, SEP, and IICMH. There are two main factors that prolong the network lifetime of EBCRP. First, EBCRP employs an adaptive sensor node clustering scheme to determine the number of clusters and group sensor nodes into clusters evenly. This helps to balance the energy consumption between clusters. Second, EBCRP adopts a rotation CH selection scheme based on the highest residual energy to dynamically select CHs for each cluster. This approach can balance the energy consumption of sensor nodes within each cluster. Balancing the energy consumption between clusters and within clusters in EBCRP prevents some sensor nodes from consuming energy prematurely, thereby prolonging the lifetime of the WSN. However, LEACH and SEP randomly select some sensor nodes as CHs, while other sensor nodes are assigned to their respective nearest CHs, which cannot balance the number of sensor nodes between clusters and energy consumption of sensor nodes. At the same time, a certain proportion of sensor nodes in SEP are equipped with more energy, and CHs selection in SEP takes into account the residual energy of sensor nodes. Thus, the network lifetime of SEP is higher than that of LEACH, but it is still lower than the proposed EBCRP method. Although the IICMH also considers the balance of the number of sensor nodes between clusters, the CH of each cluster is reselected after the energy of the previous CH is lower than a threshold. This makes the energy of sensor nodes selected as CHs for the first time to quickly depleted. In addition, sensor nodes close to the sink in each cluster are preferentially selected as CHs in IICMH, which increases the energy consumption of some sensor nodes  when they send data to their CHs. Thus, the network lifetime of IICMH is lower compared to the other methods. Overall, the proposed EBCRP method performs better in prolonging the network lifetime by performing balanced clustering and employing the rotation CH selection scheme based on the highest residual energy.This study proposes an energy balanced cluster-routing protocol based on particle swarm optimization with five mutation operators for wireless sensor networks to balance energy consumption of sensor nodes and prolong the network lifetime. An adaptive sensor node clustering scheme based on the PSO is proposed to determine the number of clusters and group sensor nodes into clusters evenly, which is helpful to balance the energy consumption between sensor nodes. To increase the search diversity, five mutation operators are specially proposed in EBCRP to improve the performance of PSO in optimizing sensor node clustering. In addition, a rotation CH selection scheme based on the highest residual energy is used in EBCRP to dynamically select a CH for each cluster. In each round, the sensor node with the highest residual energy in each cluster is selected as a CH responsible for aggregating data from the remaining sensor nodes within each cluster and sending these data to the sink. This can balance the energy consumption of sensor nodes within each cluster. Comprehensive simulations are performed to investigate the effectiveness of the proposed EBCRP method and compare it to some other methods. The simulation results demonstrate that the proposed EBCRP method can effectively balance the number of sensor nodes between clusters and energy consumption of sensor nodes, thereby prolonging the network lifetime.Some limitations still exist in the EBCRP method and become important research work in the future. The PSO-based sensor node clustering scheme is greatly affected by the performance of the PSO. For the multimodal, high-dimensional, complex, and nonlinear optimization problems in WSNs, the PSO is easy to prematurely converges to local optima. To find an optimal or near-optimal solutions, PSO and other optimization algorithms could be studied in the future to further improve the performance of EBCRP. In addition, the EBCRP selects CH for each cluster in each round, which reduces the stability of the network system. A more efficient CH selection mechanism could be further studied, e.g, each cluster selects multiple CHs to cooperate with each other to aggregate the data from other sensor nodes within their cluster. When the energy of the current CHs is lower than a threshold, the new CHs are reselected. Another important future work is about the application of the EBCRP to complex WSNs problems with large sensing region, some relay nodes can be selected to assist the communication between CHs.