Collecting 3D point cloud data of buildings is important for many applications such as urban mapping, renovation, preservation, and energy simulation. However, laser-scanned point clouds are often difficult to analyze, visualize, and interpret due to incompletely scanned building facades caused by numerous sources of defects such as noise, occlusions, and moving objects. Several point cloud scene completion algorithms have been proposed in the literature, but they have been mostly applied to individual objects or small-scale indoor environments and not on large-scale scans of building facades. This paper introduces a method of performing point cloud scene completion of building facades using orthographic projection and generative adversarial inpainting methods. The point cloud is first converted into the 2D structured representation of depth and color images using an orthographic projection approach. Then, a data-driven 2D inpainting approach is used to predict the complete version of the scene, given the incomplete scene in the image domain. The 2D inpainting process is fully automated and uses a customized generative-adversarial network based on Pix2Pix that is trainable end-to-end. The inpainted 2D image is finally converted back into a 3D point cloud using depth remapping. The proposed method is compared against several baseline methods, including geometric methods such as Poisson reconstruction and hole-filling, as well as learning-based methods such as the point completion network (PCN) and TopNet. Performance evaluation is carried out based on the task of reconstructing real-world building facades from partial laser-scanned point clouds. Experimental results using the performance metrics of voxel precision, voxel recall, position error, and color error showed that the proposed method has the best performance overall. Point cloud data of buildings can be used for making 3D models for civil engineering applications . These aHaving an automatic point cloud scene completion method has several benefits, including improving data quality and reducing manual labor for data acquisition. Furthermore, point cloud completion has many application scenarios including reducing errors in registration , improviThis research proposes a point cloud scene completion method for building facades using orthographic projection and generative adversarial inpainting methods. Since a scan of a building facade lies on a mostly two-dimensional surface, it is beneficial to convert the 3D unstructured data into a 2D structured representation that can encode neighborhood information. Thus, the raw 3D point cloud is first converted into a depth image and a color image using an orthographic projection. Next, a 2D inpainting method is applied to predict the location and color information of missing pixels in the converted image. The inpainting method consists of a deep neural network that is trained on a database with pairs of incomplete and complete images. Finally, the inpainted 2D image is converted back into a 3D point cloud by remapping the previously stored depth information. The output point cloud is evaluated by comparing it to the ground truth point cloud in a dataset of laser scans of building facades. The rest of the paper is organized in the following order: literature review, methodology, results, discussion, and conclusion.Existing geometry-based scene completion methods include mesh-based methods  and poinOther geometry-based methods include As-is-BIM (Building Information Modeling) , which iScene completion has also been widely explored in the 2D domain in the form of image inpainting. Image inpainting can be defined as the task of filling in missing or marked pixels in an image to create a contextually relevant result. It is widely used for completing holes or restoring damaged and occluded regions. Classical approaches to image inpainting focus on propagating information from neighboring pixels to the masked regions by using techniques like isophote feature propagation ,24,25 anThe use of convolutional neural networks (CNN) and deep learning for image inpainting brought seminal progress to image inpainting. Ren et al.  used a tOne major limitation of these existing image inpainting methods is that manual annotation of a mask over the missing regions is required. Several later studies thus focus on eliminating the manual masking process. One study proposed a semiautomatic inpainting model that allows a user to specify some of the preselected candidates of potentially damaged regions . Other aRecent advances in deep learning have created opportunities for the approaches to automated shape generation and scene completion that are more data-driven as opposed to purely geometry-based. Earlier works focus on single object shape completion ,50,51,52Other point cloud completion methods that use point-based neural networks for scene completion include point completion network (PCN), TopNet, and FoldingNet ,54,55. TIn view of these limitations, this research proposes a novel projection and inpainting method for the case of point cloud scene completion of building facades. In contrast to many works in the literature, which only consider 2D images or small 3D objects, this research will consider large, complex 3D scenes. The proposed method can work directly with point cloud data, is able to reconstruct color information, and can also work for curved surfaces. In addition, the generative adversarial inpainting network is data-driven and trainable end-to-end, which makes the method highly automated and can be implemented without significant manual annotation or tuning.The proposed method for scene completion consists of first preprocessing the 3D point cloud, converting the 3D point cloud into 2D representations, then using data-driven methods to predict the geometry and color of missing regions in the scene, and finally converting the 2D representation back into a 3D point cloud. This section describes how the raw point cloud data was preprocessed into a standardized format that could be used for scene completion. For each building facade, the laser scans from different scan positions were manually registered so that they lay in the same coordinate system. The scans were also rotated so that the building point cloud was aligned with the X–Y axes. In addition, the scans were downsampled using a voxel grid filter. Voxel grid downsampling had the added effect of equalizing resolution throughout the entire point cloud since the resulting points were evenly spaced according to the voxel grid. The input and ground truth point clouds for the purposes of evaluating scene completion were generated according to the following rule: (i) the input point cloud is obtained from an individual partial scan of a building facade, which is incomplete, and (ii) the ground truth point cloud is obtained from the combination of all scans of the same building facade, which is usually more complete. Note that the combinations of all scans may still be an imperfect representation of the scene but they were considered as the ground truth because it had the most available information.The point cloud data was also further processed to generate training data for the learning-based scene completion method that will be described in 2 by trial and error to balance image quality while saving computation time. The RGB values for each point in the point cloud were projected to the corresponding space in the scaled plane. Equations (1) and (2) below show the calculation of image coordinates based on the projection from point cloud coordinates. Whereas, the depth information  of the points were projected in a similar manner and stored separately  based on Pix2Pix . Pix2PixThe dataset used to train the network consists of pairs of an input image, which represents the incomplete scene, with a target image, which represents the ground truth (more complete scene). By analyzing patterns in the training data, the generator can learn how to fill in incomplete regions in the input image. The discriminator then used the generator output and tried to differentiate between the artificial image that was generated and the real target image. This conditioned the generator to also output more visually realistic images.The framework for training the generator and discriminator networks is shown in To train and evaluate our model on our dataset, we used the method of leave-one-out cross validation. This is a form of K-fold cross validation where K was equal to N (the number of samples in the dataset). This means that every time the network was trained, the test data was obtained from one scene, whereas the training data was obtained from all the remaining N-1 scenes. In the case of the dataset used in this paper, we used one scene for testing and the remaining ten scenes for training. This allows the training process to maximize the amount of training data available while maintaining the separation between training data and test data. The image inpainting output, whether using semiautomated or fully automated inpainting, was in a 2D image form and needs to be converted back to a 3D point cloud to obtain the desired result. For this, we used the depth information of the original point cloud that was previously stored when performing the orthographic projection in To predict the depth of the newly filled pixels, we used the nearest neighbors method to find the nearest pixel in the original depth image and set the missing depth to that of the nearest pixel. In the general case, it is true that depth remapping can have errors when the depth of the obstructed area is different from the depth of the neighboring areas. However, in our case of building facades, the scene did not have arbitrary depth but was well structured with many repeating patterns. For example, when considering a flat planar section of a wall, it is usually the case that a small section of the wall and not the entire wall is occluded; thus, we could reconstruct the depth of the occluded part of the wall using the depth of the non-occluded part of the wall. For depth remapping, we used a k-d tree  data structure, implemented in the Fast Library for Approximate Nearest Neighbors (FLANN) library , to speeThe point cloud data used in this research was taken from laser scans of different buildings on the Georgia Tech campus. An average of 3–5 scans was taken for each building facade. There were 11 building facades in total that were used for testing. As shown in This section will present four baseline algorithms for point cloud scene completion that will be used for comparison against the proposed method, namely (i) Poisson reconstruction , (ii) hoPoisson reconstruction works by creating a filled mesh over existing point cloud data. The input data was a set of points, each containing its coordinates in a 3D volume, its RGB values, and its inward-facing normals, whereas the target output was a triangulated approximation to the surface. Initially, based on the fact that the normal field of the object can be interpreted as the gradient of the solid’s indicator function, the surface integral can be constructed. Next, the indicator function was reconstructed from this gradient field by formulating it as a Poisson problem. This led to a reconstructed watertight, triangulated approximation to the surface by approximating the indicator function of the model and extracting the isosurface. Finally, points were sampled from the resulting mesh to obtain the surface approximation represented in the point cloud. This method exported the normals and color information of the original mesh, through interpolating the information in each triangulated surface, to obtain the final point cloud. The implementation used in this study was from the CloudCompare software , which iThe hole filling process works as follows: given a set of input points containing coordinates in 3D space, and their RGB values, the output is the original set of points with additional synthetic points that cover the holes. The points were first normalized by shifting the points to the origin in one axis. Next, the neighboring points were connected to form triangles in the 3D scene. Larger triangles were identified by computing the circumradius and area. These larger triangles were then converted to polygons, which represent the holes in the input scene. A size threshold was used to differentiate between holes that were caused by occlusions and holes that were naturally present in the scene. To achieve this, a minimum size cutoff was used to prevent the hole filling step from completely filling in windows and other openings that were naturally present in the scene. Note that this cutoff procedure led to the side effect that some holes caused by occlusions were filled whereas others were not. Once the locations of the holes were identified, we could generate the X,Y,Z coordinates of the synthetic points that were to be added to the scene. These points were evenly distributed within the extent of each hole. Once the synthetic points were generated, the points outside of the bounding shape were clipped. Whereas, the points inside of the bounding shape were preserved and assigned an RGB color value based on the average RGB value of the input data. The implementation used in this study was from an open-source algorithm for hole detection and filling .Since most buildings consist of flat planes, plane fitting is a reasonable method to use for scene completion. Several works in the literature also take advantage of local planarity to reconstruct 3D point clouds ,13,15. TGiven the converted 2D building images, we could apply a semiautomated method for image inpainting. The input image was annotated with a user-defined mask over the incomplete regions and processed using a neural network with partial convolutions . Unlike The performance of each point cloud scene completion algorithm was evaluated using laser-scanned point clouds of building facades acquired at the Georgia Tech campus , which usually has the critical issue of occlusions and missing data. There are other alternatives to address the problem of occlusions such as using advanced laser scanners with multistation measurements, increasing the number of scan locations, or using advanced scan planning and optimization techniques. These scanning methods could still have missing data when taking multiple scans due to inaccessibility or occlusions that are too close to or in close contact with the target object . The main advantage of applying an automated scene completion algorithm is the ability to save manual labor and manual operation in laser scanning at the cost of having some uncertainty in the reconstructed point cloud. In any case, the authors expect that the idea of automated scene completion is still applicable to fix imperfections in the acquired data.In this study, the point cloud preprocessing steps such as registration, segmentation, filtering, and extraction of individual facades from the original scene were carried out manually for simplicity and convenience. In an actual application, these steps can potentially be automated using established point cloud processing algorithms. For example, the point cloud scans can be automatically registered by feature point matching . In addiThe objective of this research was to improve point cloud quality for 3D reconstruction, to improve visualization of point cloud scenes, to reduce scanning time for acquiring a complete point cloud scene, and to fix defective point cloud scans. To achieve this, we propose a method of performing point cloud scene completion of building facades using orthographic projection and generative adversarial inpainting. The proposed method was compared against several baseline methods on the task of reconstructing building facades in a dataset of laser-scanned point clouds. Through a comparison of several performance metrics based on both geometry and color, the proposed method is shown to achieve the best performance overall. In summary, the contributions of this research were as follows: (i) we proposed a framework necessary for 3D reconstruction of full building facades from incomplete scans using orthographic projection and 2D inpainting methods, (ii) we identified strengths and weaknesses of different scene completion methods through qualitative analyses, and (iii) we demonstrated the feasibility of scene completion for different scenarios including whole buildings and curved facades. For future work, the authors plan to further automate the scene completion pipeline by implementing an automatic segmentation algorithm for building facades before applying an orthographic projection and inpainting. The authors will also work on developing new methods for inpainting point clouds directly in 3D without having to perform orthographic projection. In addition, the authors will work on combining deep neural networks with other geometric methods  to improve the scene completion results.


Photonic true time delay beam steering on the transmitter side of terahertz time-domain spectroscopy (THz TDS) systems requires many wideband variable optical delay elements and an array of coherently driven emitters operating over a huge bandwidth. We propose driving the THz TDS system with a monolithic mode-locked laser diode (MLLD). This allows us to use integrated optical ring resonators (ORRs) whose periodic group delay spectra are aligned with the spectrum of the MLLD as variable optical delay elements. We show by simulation that a tuning range equal to one round-trip time of the MLLD is sufficient for beam steering to any elevation angle and that the loss introduced by the ORR is less than 0.1 dB. We find that the free spectral ranges (FSRs) of the ORR and the MLLD need to be matched to 0.01% so that the pulse is not significantly broadened by third-order dispersion. Furthermore, the MLLD needs to be frequency-stabilized to about 100 MHz to prevent significant phase errors in the terahertz signal. We compare different element distributions for the array and show that a distribution according to a Golomb ruler offers both reasonable directivity and no grating lobes from 50 GHz to 1 THz. N coherently driven spatially distributed emitters instead of a single emitter. This way, both the directivity and—through spatial power combining—the total radiated power can be increased, yielding a possible increase of the equivalent isotropically radiated power by Wideband terahertz systems, operating in the frequency range between the microwave and far-infrared region of the electromagnetic spectrum, have the potential to combine the best of two worlds. On the one hand, they offer hundreds of GHz of spectral bandwidth and sub-mm spatial resolution. On the other hand, they have the capability to see through dielectric materials that are opaque to infrared and visible light. These properties make them attractive for a variety of applications, including material identification ,2, matersteering ,14,15,16steering . In a mosteering . HoweverIn this paper, we propose a concept that exploits the periodicity of the ORRs’ group delay response to circumvent their bandwidth limitation. We choose the optical perimeter of the ORRs so that their free spectral range (FSR) is identical to the FSR of the mode-locked laser that drives the THz TDS system. This way the laser modes can be aligned with the resonant frequencies of the ORR. Consequently, the ORR introduces identical delays to all laser modes. To keep the ORRs small enough to be realized in an integrated optical circuit, the FSR needs to be on the order of several tens of GHz. This condition is fulfilled by using a monolithic mode-locked laser diode (MLLD) in an approach we call ultra-high repetition rate terahertz time-domain spectroscopy (UHRR THz TDS). This approach has first been demonstrated by Merghem et al.  and systThe paper is structured as follows. In quasi-true time delay approach the direction of the main beam is frequency-independent. Furthermore, we consider the design for wideband operation of a linear array and compare different element distributions for the frequency range from 50 GHz to 1 THz.In ORRs play an important role in integrated photonic circuits as components with multiple functionalities. They have been used as optical switches , filtersOne of the means for adjusting the coupling coefficient is using a Mach–Zehnder modulator as shown in In To obtain the group delay response and the transmission spectrum of the ring resonator, we calculate its transfer function. As shown in L is the perimeter of the ring, We assume that the couplers are reflection-free and lossless and the length of two couplers together with the arms in between can be neglected compared to the perimeter of the ring. Furthermore, the frequency dependence of the phase shifts etail in bc1,3bc1,L of the ring is determined asThe perimeter ion loss . Its proAttenuation constant Effective refractive index Group index With the information of the effective refractive index In For simplicity, the characteristics of the ring resonator shown above are calculated by Equation  in whichFor a thermo-optic phase shifter, the change of phase The frequency-dependent phase response of the thermo-optic phase shift is thenk-th mode of the MLLD, respectively, and N is the number of significant laser modes. In the following, we consider a laser with 40 significant modes and a rectangular spectrum, i.e., Taking into account this frequency-dependent phase response of the phase shifters in Equation , the dellated as ,28(12)pWith The crucial requirement of the proposed concept for introducing identical delays to all laser modes is perfect alignment between the modes of the MLLD and the resonances of the ORR. However, the FSRs of the ORR and the MLLD may be slightly different due to the fabrication inaccuracy. In this section, we investigate the effect on the resulting terahertz pulse for different FSR mismatches.For illustrative purposes, a case where the FSRs of the ORR and the MLLD are severely mismatched  is depicted in With increasing group delay the bandwidth of the ORR decreases. As a consequence, the laser chirp due to the FSR mismatch becomes more severe. To consider the worst-case scenario, we thus investigate an ORR with a group delay around 30 ps. To quantify the nonlinear chirp and the effect on the terahertz pulse, we show the third order dispersion The instabilities of the injection current and the temperature control of the MLLD can lead to fluctuations of its center frequency and FSR. Consequently, the laser modes drift around the resonances of the ORR. Under stable mode-locked conditions, the FSR of the MLLD changes less than 1 MHz, whereas the fluctuation of the center frequency can be tens of MHz. Therefore, we consider the FSR of the MLLD to be constant. In order to perform photonic beam steering on the transmitter side of a wideband UHRR THz TDS system, both the photonic beam steering network and the antenna array need to operate across a large bandwidth. While the ODUs need to introduce the same delay across the entire optical spectrum, the antenna array needs to be designed and operated in a way that the main beam direction is independent of frequency. At the same time, the radiation pattern needs to exhibit high directivity and no grating lobes across the entire range of emitted terahertz frequencies. The first challenge has been addressed in N-element array of antennas arranged along the z-axis, as depicted in N branches and the signal in each branch is delayed by the delay We consider a linear array of identical antenna-integrated photodiodes that are fed through a photonic beam steering network. For an The delayed signals are fed into antenna-integrated photodiodes to generate the terahertz photocurrents n-th element has the phase leadN elements, the array factor results [If  results (15)g(θ,Because the emitted terahertz pulse repeats itself once every quasi-true time delay beam steering. As has been shown in We call this concept photonic N, the length of the array L, the spatial distribution of the elements along the length of the array, the amplitude distribution, and the element pattern of the antennas. A good array design aims to fulfill the following criteria across the usable frequency range.The design of a linear array allows as main design parameters the number of elements The directivity of the main lobe should be as high as possible.Side-lobes should be suppressed as much as possible and grating lobes should not occur.The beam should be steerable across the entire elevation range N as a constraint and allow the length of the array as well as the distribution of the elements to be arbitrarily chosen. Furthermore, as transmit power is at a premium at terahertz frequencies, it is advisable to choose directivity over sidelobe level and thus use a uniform amplitude distribution, i.e., equal amplitudes for all elements of the array. For reasons of simplicity, we consider isotropic antennas. This leaves the element distribution and the length of the array as the design parameters. For our analysis we choose a 10-element array, so that each photodiode receives sufficient optical power from the MLLD, which has an output power of roughly 100 mW. We propose the following three element distributions as depicted in Dense uniform distribution with Sparse uniform distribution with Nonuniform distribution according to a 10-mark Golomb ruler with Although the usable frequency range, e.g., The two uniform distributions represent two extreme cases. In the case of the dense distribution, the array is optimized for the highest occurring frequency, whereas in the case of the sparse distribution, the array is optimized for the lowest occurring frequency. The former case will lead to low directivity and a wide beamwidth at lower frequencies, whereas the latter case will lead to the appearance of grating lobes for y arrays ,31,32. Ty arrays . We expeCalculated frequency-dependent radiation patterns for all three distributions are depicted in  spacing a, radiat spacing b exhibitThe array with an element distribution according to the Golomb ruler c is wellFor a quantitative comparison, the direction-dependent directivity and beamwidth are numerically evaluated at several discrete frequencies as shown in The directivity in the case of the Golomb ruler is significantly higher at low frequencies than that of a dense uniform array and reaches its maximum of 10 dBi at 1 THz. The beamwidth is close to that of the sparse uniform array around broadside. However, the beam widens more significantly towards the end-fire directions. The Golomb ruler is an excellent choice for applications that require a reasonable angular selectivity across the entire frequency range.In this work, we have proposed a solution for beam steering on the transmitter side of wideband UHRR THz TDS systems. Our quasi-true time delay beam steering concept is based on integrated ORRs as ODUs in a photonic network driving a linear array of antenna-integrated photodiodes. The amplitude and phase information of the UHRR THz TDS system can be recovered by calibration against a reference measurement. The intrinsic bandwidth limitation of the ORRs is overcome by aligning their resonances with the modes of the MLLD that drives the UHRR THz TDS system. We have studied the feasibility of the ORR-based ODUs analytically and numerically. Our analysis shows that the intrinsic dispersion of the integrated optical phase shifters leads to a small chirp of the optical spectrum. This chirp causes the delay of the generated terahertz signal to differ from the group delay of the optical signal in a well-defined way. We have paid particular attention to the effects of a potential mismatch between the FSRs of the MLLD and the ORR. Numerical analysis shows that they need to match to within 0.01% so as not to severely affect the generated terahertz pulse and that the laser needs to be stabilized within 100 MHz for the phase stability to be better than 1


The work assumed the possibility of the introduction natural fibers as a hybrid reinforcement of bio-polyethylene composites. Coconut fibers, basalt fibers and wood flour were used in different combination as a hybrid merger. Mechanical tests were conducted. An increase in the mechanical properties was shown as an effect of the introduction of the fibers info the polymeric matrix. A synergic influence of hybrid reinforcement was also presented. Experimental results were compared with modeling parameters. The hydrothermal and accelerated thermal ageing effects on the mechanical behavior of composites were presented. Scanning electron microscope images were observed in order to analyze structure of examined composites. The rapidly growing production volume of polymer materials, caused by the increase in the scope of their applications and the use of polymer materials reinforced with particles or fibers, is associated with a significant increase in the amount of plastic waste. This provides an increasing burden on the natural environment with non-degradable materials, as well as indirectly the extraction and processing of fossil materials intended for the manufacture of plastics. Therefore, scientists as well as producers are increasingly focusing on the production of new, environmentally friendly, polymeric usable materials. These materials can be made from fossil sources as well as from renewable sources. Polymers obtained from both these sources can be completely biodegradable or resistant to this. The amount of new and ecological polymer materials that appear on the market is definitely smaller than the classic non-biodegradable polymers such as polyethylene (PE), polypropylene (PP), poly (vinyl chloride) (PVC), poly  (PET) or polystyrene (PS). Despite this, the global production of bioplastics, i.e., plastics produced from renewable and/or biodegradable raw materials, is important, and its growth dynamics is greater than in the case of classic polymers . BiopolyPE is most commonly used plastic. PE is an essential technical polymer produced from fossil raw materials. The simplicity of its production and chemical resistance make it popular in the chemical industry . PolyethThe requirement for natural fibres has been growing in recent years. Firstly, the natural fibers are fully biodegradable, they are derived from regenerative resources, and their acquisition does not affect the climate effect. Moreover, natural fibers possess good mechanical and bio-chemical properties. The bio-chemical composition ensures that natural fibers are non–toxic and non-carcinogenic, unlike synthetic fibers, for which such properties have been noted. The best known vegetable fibers are: oil palm, wood, rice straw, bamboo, sisal, ramie, hemp, doum fruit, marc, pineapple leaf, mesta, wheat straw, cotton, flax, date palm, rice husk, curare, coconut, jovar, kenaf, rape waste, rose, banana, abaca, agave, maize and jute ,7. KucieReinforcement with two or more fibers to a single matrix results in the advancement of hybrid composites with a wide variety of material properties. In the last few years, hybrid composites have been created in which more than one type, form or size of the reinforcement was introduced. Those composites have been tested in order to ensure the synergy properties of selected fillers and matrix. They provide a number of features that cannot be achieved with one type of reinforcement.Hybridization can overcome the defects of one component by inclusion another type of fibers. The condition for the hybrid effect to occur is that the two fibers will be different due to their mechanical behavior and the interfaces between the matrix. The most useful would be to combine only two types of fiber. For example, connection of two types of short biological or cellulosic fibers with different shapes has some advantages compared to only one type of introduced fibers. Hybrid reinforcement with good fiber selection is likely to provide attractive properties and meet the present need for plastic matrix composites ,10,11,12In past years, many studies on hybridization of artificial and vegetable lignocellulose fibers have been conducted. However, plant-fibre hybrid composites are less researched and the most frequently published reports are limited to hybrid composites containing one type of vegetable fibre and one type of artificial fibre. Examples of such reinforcements may be the use of carbon fiber in combination with flax fiber or carbon fiber with sisal fiber provided by Khanam et al. and Fiore et al. Glass fiber was also used in combination with natural fibers like banana or bamboo on a polypropylene basis in the work of Venkatasubramanian, and basalt fiber with flax, hemp or glass fiber combination were investigated by Petrucc. All presented works pointed to a great effect of hybrid reinforcement in polymer matrix composites ,24,25,26The main gain of this work is to explore the possibility of using hybrid reinforcement made of natural fibers. This is the second part of the research conducted on the fibers of coconut, wood flour and basalt fiber introduced into the bio-polyethylene matrix. The first stage of the research involved examining the influence of natural fibers on the mechanical properties of bio-PE composites. The tests showed a positive effect of strengthening the fibers already at 6% content by weight, hence this work presents the hybridization effect of the introduced fibers. Basalt fiber ;Coconut shell fibers ;Wood flour ;Coupling agent Scona TPPP 9112 FA was used .This work presents investigations on hybrid composites based on bio-polyethylene . The standard dumbbell and dogbone samples were made at Cracow University of Technology using KM 40–125 Winner Krauss Maffei . As a reinforcement, natural fibers were used and include:Manufactured materials for the experiment are described in −1 resolution as an average of 64 scans. The spectrum in the 4000–400 cm−1 range was recorded.Physicomechanical tests were performed to investigate strength behavior of hybrid composites based on bio-polyethylene with natural fiber. The density was calculated by the hydrostatic method using scales RADWAG WAS 22W . Mechanical tests include: static tensile test (PN-EN ISO 527-1:20100), the three-point flexural test (PN-EN ISO 178:2011) which were carried out with a MTS Criterion Model 43 universal testing machine , using the MTS axial extensometer. The test speed was set to 10 mm/min. A Charpy impact test (PN-EN ISO 179-1:2010) was verified on the unnotched specimens using a Zwick HIT 5.5P . The values were estimated from an average of at least of 5 specimens. After the mechanical test, micrographic images were taken using a scanning electron microscope (SEM) JEOL JSN5510LV . The surface chemistry of the neat polymer and composites containing natural fibers was characterized using a Fourier transform infrared (FTIR) spectrometer Thermo Scientific Nicolet iS5 FTIR spectrometer  equipped with iD7 ATR accessory . Spectra were acquired at 4 cmW0 is the initial weight of the sample, Wn is the weight of the saturated sample, and %W is the percentage increase in weight.A water absorption calculation was carried out in accordance with ASTM D570-98. Samples were weighed periodically to saturation level using an electronic balance (RADWAG WAS 22W). At first, samples were conditioned at a temperature of 23 ± 2 °C and a humidity equal to 50 ± 5% for 24 h. The hydrothermal ageing process was undertaken in distilled water at 23 ± 2 °C. Samples were removed from the water at the following frequency: 1, 7, 14, 21 and 30 days. Before weight measurement the samples were dried by the tissue. Water absorption was calculated using the following equation:Physicomechanical investigations were verified after water and thermal ageing processes. Accelerated ageing tests were proceeding according to the EN ISO 2440 in autoclave  parameters of the test include: temperature of 120 °C, humidity of 100%, and pressure of 0.3 MPa. The aging process lasted 144 h. To calculate the elastic modulus of hybrid composites the Voigt approximation, Reiss approximation, Hashin–Shtrikman bounds, and Halpin–Tsai model were compared with the experimental data.Strengthening and filling polymeric construction materials involve the addition of a second component to the matrix material. This effect occurs when the considered mechanical strength and rigidity of the composite increase related to the pure material, while other properties may remain unchanged or even deteriorate. Fiber reinforcement depends on the geometry of the filler, and in the case of fibers the length to diameter ratio , fiber adhesion to the matrix and other interactions such as incubation of crystalline nuclei, interatomic interactions or the ability to form chemical connections. The highest modulus value is obtained with unidirectional oriented fibers with a developed surface. Considering production of composites by means of the injection moulding process, the flow process of the material in the injection mold is quite complex, and the fiber orientation inside the sample is random, and oriented at the surface . Considerable differences in the properties obtained from the static tensile and flexural test result from the material loading method. In the case of the static tensile test, it is assumed that the applied stress is in accordance with the direction of the fibers. Analyzing the test results, a minor increase in strength can be explained by the fact that only a small portion of fibers with such a limited amount is oriented in the direction of force.Hybridization of basalt with natural fibers significantly improved mechanical properties compared with the introduction of only cellulose fibers. From the natural fibers wood flour in combination with basalt fibers had significantly higher results than basalt fibers /coconut fibers. Particularly noticeable effect was for the Young’s modulus. A twofold increment of fiber in hybrid mixtures increased reinforcement efficiency by 25–40% in most cases for the wood-basalt system, but least for the wood-coconut, which suggests a reduced adhesion of the coconut additive to the polymer material than the bond between wood flour and polyethylene, which can additionally be associated with diameter and length, and fiber surface development. The combination of wood flour and coconut fibers provided the least effect on strength properties as well as dynamic impact properties .Adhesion depends on the forces at the fibre/matrix contact. Adhesion strengths are physical forces derived from the chemical constitution of the polymer matrix and filler. They can also be chemical interactions based on similarities in functional groups. The properties of the composite rely on the action of macromolecules in thin layers on the filler surface. Chain elasticity of macromolecules and changes in macromolecular conformation influence the size of adhesion, as they significantly determine the degree of contact spots between macromolecular chains and fillers .The values of modulus of elasticity changed proportionally with an increase in the fibers’ contribution and were lower in a flexural test compared to the tensile modulus. The reason for such a difference is the orientation of the reinforcement in the material. In injection moulding, the fibers in the material are positioned along the material stream in the mould. During stretching, due to the characteristic arrangement of the fibers, the forces are in line with the direction of the fibre and the load is transferred from the matrix to the fibers correctly. Flexural forces, there are shear forces perpendicular to the fiber axis in the specimen, which leads to separation of the reinforcement from the matrix and introduces additional stresses .−1 wavelength range. −1 corresponds to the vibrations of the -CH groups Polymer spectra were typical of PE with characteristic strong absorption peaks at 2912.95 cm−1 derived from the stretching vibrations of the C–H and 1470, 46 cm −1 functional groups derived from the vibrations of the bending C–H functional groups. The presence of filler in the composite was mainly manifested by a drop in absorbance in the range 400–1500 cm−1 and 2600–3100. A comparison of the FTIR spectra of the raw polymer and polymer composites showed that there were no shifts at the position of the absorption peaks, and suggested that the potential interaction of the fiber with the polymer matrix was elatively low. FTIR analysis was performed with a FTIR Thermo Scientific Nicolet iS5 spectrometer equipped with an iD7 ATR  accessory . The tests were carried out in the 400–4000 cmConstruction materials are used in various environments, including changing temperatures, humidity and mechanical loads. Since the softening process in semicrystalline plastics starts smoothly in amorphous areas and then the crystalline areas melt. The establishment of thermal boundaries of application is a very hard condition during designing structural elements.The static flexural test was carried out at 3 different temperatures in the range of extreme working temperatures to show the influence of temperature on changes of strength abilities. Results are presented in Analyzing the flexural modulus, higher parameters are obtained when the reinforcement is in the form of particles, and works by blocking the movements of polymer segments. The neat matrix also provides increased rigidity. At low temperatures, the particles are not very mobile and cannot respond to vibrations and remain rigid. It is said that Brown micromovements have been frozen, which means that no changes of macromolecule segments is possible, especially around C–C bonds, and that the looping of these molecules act as crosslinking points. At higher temperatures, sections of the macromolecules become more mobile and can easily respond to loads, loops still persist, but may react in some cases by slipping and the macromolecules slip relative to each other, reducing strength and stiffness, but also causing an increase in deformability .The materials were also subjected to a water absorption test. This study is particularly important for biopolymers that are used in applications as structural materials under thermally or mechanically loaded conditions. Water molecules penetrate deeply into the material mass and settle mainly in less-packed amorphous areas due to the formation of hydrogen bridges. The lower the crystalline phase, the greater the moisture absorption capacity. Polyethylene, in principle, is a material that does not absorb water, however the introduction of fibers or particles, especially cellulosic, causes water absorption inside the material, because the fibers act as water-carrying capillaries, and in addition, natural particles and fibers strongly absorb water by swelling and introduce stresses inside the material.Highly important changes in the case of plastics and composites on their matrix are changes caused by ageing processes, because they largely define the suitability of the material to work in a given environment, and the lifetime of such a material. Aging of polymers is the decomposition of polymers under the influence of the sum of physical and chemical factors that affect them during usage and storage. In linear polymeric materials, as a result of degradation, the chain of macromolecules is shortened and consequently the molar mass decreases. In the polymers with a more complex chain structure, apart from the processes of breakage of the main polymer chain, there are also side group fracture reactions. As a result of physical factors such as temperature or moisture, a destructive change in the chemical and physical structure of the polymers occurs, resulting in changes in properties . An important issue related to creating a new material is the ability to predict its properties at every stage of design. In the case of materials subjected to mechanical loads, key parameters are the magnitude of Young’s modulus and ultimate tensile strength. When considering composite materials, it should be kept in mind that their mechanical properties at the macro scale are the result of a certain combination of properties of each component . The VoiCurrently, both the Voigt (V) model and the Reuss (R) model are rarely used to estimate the properties of the composite, but rather constitute certain boundaries of the space in which the estimated parameters are located. This half-space is filled with numerous micromechanical models that have been derived from the continuum mechanics ,37,38,39Another model that is widely used to homogenize the elastic parameters of the composite is the Halpin-Tsai model . This isThe parameter When calculating the volume fraction of individual components in the composite, the following formula was used:In each case, the H–T model describes the elastic properties sought for well. The trend associated with the increasing non-volume share of reinforcing phases is correct; however, only in the case of hybrid composites based on polyethylene with wood flour and basalt fibres(PE–W–B) there is a small estimation error quantitatively.The case of composite reinforced with fibers of coconut and wood flour is worth noting and thinking about. In this case, for a smaller volume fraction, the obtained Young’s modulus value exceeded the theoretical value of the Voigt model, which is generally accepted as the upper limit of the searched space of averaged values. This result could be related to the fact that in some cases the Poisson effect can lead to estimations which are beyond the Voigt approximation . The disThe presented studies on the natural fibers used as a filler in a hybrid reinforced bio-polyethylene composite showed higher rigidity and strength properties. The best results were obtained for basalt fiber-reinforced material and pointed to an increase in strength by about 30% and more than a twofold increase in stiffness. However, the purpose of this work was to assess the suitability of natural fibers in a hybrid combination to obtain lightweight structural composites. Hybridization of cellulose fibers with basalt fibers significantly improved the properties compared to the introduction of cellulose fibers alone. From natural fibers, wood flour in this combination had much better results than coconut fibers, an increase in strength by 50% and stiffness by about 65% compared to the basalt–coconut combination. The effect was particularly visible in the case of Young’s modulus. Research after accelerated thermal and water aging showed the scale of changes occurred in composite materials based on a polyethylene matrix. Accelerated aging caused a decrease in strength properties compared to materials not subject to this process. The research is interesting because it shows the potential for using renewable sources to produce lightweight composite materials with good strength properties. There has been little research on the subject of hybrid composites based on bio-polyethylene. This work allowed us to assess the use of natural fibers in experimental research and the usefulness of mathematical models to predict gain effects. Further research by researchers will focus on a deeper understanding of the effects of material aging to minimize the impact of the external environment on the properties of these materials.


The integration of medical signal processing capabilities and advanced sensors into Internet of Things (IoT) devices plays a key role in providing comfort and convenience to human lives. As the number of patients is increasing gradually, providing healthcare facilities to each patient, particularly to the patients located in remote regions, not only has become challenging but also results in several issues, such as: (i) increase in workload on paramedics, (ii) wastage of time, and (iii) accommodation of patients. Therefore, the design of smart healthcare systems has become an important area of research to overcome these above-mentioned issues. Several healthcare applications have been designed using wireless sensor networks (WSNs), cloud computing, and fog computing. Most of the e-healthcare applications are designed using the cloud computing paradigm. Cloud-based architecture introduces high latency while processing huge amounts of data, thus restricting the large-scale implementation of latency-sensitive e-healthcare applications. Fog computing architecture offers processing and storage resources near to the edge of the network, thus, designing e-healthcare applications using the fog computing paradigm is of interest to meet the low latency requirement of such applications. Patients that are minors or are in intensive care units (ICUs) are unable to self-report their pain conditions. The remote healthcare monitoring applications deploy IoT devices with bio-sensors capable of sensing surface electromyogram (sEMG) and electrocardiogram (ECG) signals to monitor the pain condition of such patients. In this article, fog computing architecture is proposed for deploying a remote pain monitoring system. The key motivation for adopting the fog paradigm in our proposed approach is to reduce latency and network consumption. To validate the effectiveness of the proposed approach in minimizing delay and network utilization, simulations were carried out in iFogSim and the results were compared with the cloud-based systems. The results of the simulations carried out in this research indicate that a reduction in both latency and network consumption can be achieved by adopting the proposed approach for implementing a remote pain monitoring system. There are to be about 237.1 million wearable body devices available on the market by 2020 with an estimated reach of market share related to the healthcare industry of USD 117 billion by 2020 ,5. TherePain is an important parameter to detect the discomfort and illness of a patient. The results of a survey conducted through different groups of patients endorse the necessity and effectiveness of remote pain monitoring . Three mHigh latency and network usage are the key factors limiting the large-scale implementation of cloud-based remote pain monitoring systems. In , a remotAn efficient fog-based remote pain monitoring system is proposed, consisting of a three-tier structure. Fog nodes reside in the middle tier, implementing the fog computing concept. Fog devices process the biopotential signals and transmit the pain information to the web servers via gateway devices.The parameters under consideration are execution cost, latency, and network consumption. The proposed architecture reduces these factors, making the proposed system most suitable for health-related applications. Moreover, it ensures real-time monitoring of patients and rapid medical assistance provisioning by minimizing the time spent from pain detection to display in the web application. The proposed architecture not only reduces time but also reduces the data to be transmitted to the cloud by discarding the unwanted data at the fog nodes.Simulations are performed on different scales for appraising the proposed fog-based remote pain monitoring architecture. The results of the comparison performed between cloud architecture and proposed architecture validate the superiority of the proposed architecture in terms of execution cost, delay, and network consumption.The key contributions of this research work are summarized as follows:The rest of this paper is organized as follows. Cloud computing has emerged as the most feasible solution for the development of IoT and big data applications by providing resourceful cloud servers for storage and processing. High latency, extra network utilization, energy efficiency, and QoS are challenges arising due to rapid growth in data traffic . These pDelay in cloud-centric healthcare applications increases when deployed on a large scale , thus faFog computing has a distributed architecture to reduce the load on the cloud. Fog computing distributes the cloud resources throughout the network by introducing fog devices with limited resources between cloud and edge devices ,22. All Different researchers have proposed fog-based architectures in creating different applications that are more effective, secure, and cost-efficient. A multi-level fog-based architecture was proposed by Chen et al.  which enDesigning applications in the fog computing paradigm reduces frequent data transmissions between cloud and edge devices, assuring low latency and minimum network utilization. Research performed in ,29,30 coFog nodes are geographically distributed throughout the network with locally available enough computing power to provide services to a variety of heterogeneous devices . In thisThe proposed remote pain monitoring system makes real-time information about the pain conditions of patients available in the web portal using digital signal processing techniques and fog computing architecture. To ensure immediate medical relief to patients, the pain-related information has to be processed to make it available for remote monitoring purposes on a real-time basis. Therefore, it is desirable to achieve minimum latency and network usage. Fog computing can effectively resolve these issues by providing data processing and storage capacity near to the end devices and consequently reducing the load on the cloud .In our proposed architecture, fog nodes are located to process biopotential signals of patients in hospitals to gather their pain-related information. A web application is linked with the system to present the pain-related information for remote monitoring. The platform used for the evaluation of the proposed architecture is iFogSim. Fog computing-based and cloud computing-based models for remote pain monitoring system are created and compared on different scales. The result of these simulations confirms that the proposed remote pain monitoring architecture is more effective than cloud-based architecture in terms of network load and latency.We briefly define the state-of-the-art healthcare monitoring systems pertinent to the cloud- and fog-based architectures in the following section.In , the autMobile cloud computing is used by the authors in  to proviRahmani et al.  explaineThe authors described data secrecy and the improper use of advanced information and communication technologies to be among the major reasons behind the unacceptability of cloud-based healthcare applications by patients in developing countries. In , a sociaiFogSim is a toolkit to simulate IoT applications in cloud and fog computing architectures. Several researchers have used iFogSim to evaluate their research work. In , the autThe proposed three-layer architecture is illustrated in The first layer of the proposed architecture consists of wearable sensors that include two modules for sensing and transmitting the detected biopotential signals. To satisfy the data acquisition requirements of the EMG and ECG signals of patients, sensors are designed with passive electrodes with a battery power supply. For the transmission of data to fog nodes, the Wi-Fi module is integrated with the sensor nodes. Sensors have to continuously provide signals for pain monitoring so low power consumption is seriously considered while designing the sensor nodes to prolong battery life. The sensors deployed in our proposed system for the collection of biopotential signals have a sampling rate of 1000 samples per second, satisfying the Nyquist criteria. The sensors detect the EMG and ECG signals and transmit the sensed data to the fog nodes where they are further processed as defined in .This layer exists between the sensor and the cloud layer. The fog layer consists of fog nodes to collect biopotential signals from sensors to perform further processing for the identification of pain. Among most of the prominent features of fog computing, interoperability is a significant one. Interoperability deals with a diverse variety of IoT devices, as shown in The third layer in our proposed architecture is the cloud layer which comprises the cloud server. The main purpose of the cloud is to provide extra storage capacity. The storage module is embedded in the cloud server, which is used for storing and updating pain-related data for record-keeping. Fog nodes are connected to the cloud via a proxy server. Fog nodes periodically submit the biopotential signal data to the cloud server after consuming these data for remote pain detection. In our proposed model, the cloud server is bypassed when computational resources available at fog nodes fulfill the processing requirements of incoming biopotential data, thus reducing the additional delay.The proposed fog-based remote pain monitoring system consists of biopotential sensors, Wi-Fi modules, fog nodes, a web application, and a cloud server. The sensor node continuously detects the EMG and ECG signals of the patients in hospitals using electrodes. To detect pain using the facial action coding system , differeCloud computing has enough resources to store and process the data. However, repeated communication between sensors and the cloud produces excessive delays with high network consumption. Therefore, employing cloud computing architecture for this type of application is not desirable. Introducing a fog computing layer in between the sensor and cloud layer reduces the latency, as fog nodes provide extra capacity to process the biopotential signals close to the edge of the network. The transmission of detected pain information directly from fog nodes to the web server reduces latency and network consumption. The architecture proposed in this paper avoids the cloud server while transmitting detected pain information from fog nodes to the web application, thus offering reduced network consumption and low latency. Signal processing tasks for achieving pain information are performed at the fog nodes. Our proposed fog computing-based architectures for single and multiple hospitals are presented in In At the start, all the sensors are initialized for the acquisition of EMG and ECG signals of patients. After the signal acquisition phase, biopotential signals are transferred to fog nodes, where the pattern recognition of facial expressions is achieved using root mean square (RMS) feature extraction and visualization techniques. Later, the signal is segmented and dimension reduction is performed ,56. ProcIn our simulations, different scenarios are evaluated, comprising a different number of biopotential sensors to detect sEMG and ECG signals of the patients. These captured biopotential signals are frequently transmitted to the fog nodes. Further processing is performed by the fog nodes to detect pain status and they transmit the pain information to the web application and cloud for remote monitoring and record updates, respectively. The connection of fog node(s) with the web application and the cloud server is established via a proxy server. For simulating and evaluating our scenarios in terms of latency, execution cost, and network consumption, we used the iFogSim toolkit.Variables of hospitals and sensors are created in the simulations. In our scenarios, there are four hospitals and one fog node is assigned to each hospital. Initially, four sensors are attached to each fog node to capture the biopotential signals of the patients. Fog nodes are connected with the cloud and web application through a proxy server. We created sensors in the simulation environment according to the policies of . ScenariAlgorithm 1 Fog-based remote pain monitoring system with first come first served (FCFS) scheduling.The topology created in iFogSim to evaluate fog computing-based architecture is defined in Algorithm 1 and depicted in To evaluate the performance on a large scale, the number of sensors per fog device is increased in each scenario and the task of pain detection is performed for a growing number of patients using the resources of each fog node. An increase in the number of sensors attached to a fog node eventually increases the processing load on that particular fog node, causing a rise in the latency and network consumption of that specific fog node. The benefit of fog-based processing is a decrease in the computational burden on the cloud. On the contrary, connecting the sensors and web server directly to the cloud results in a longer delay and excessive network utilization.In our scenarios, there are Equation (2) is used to calculate the total time consumed (itecture .(2)Tft=At any time Fog devices receive and process the data sensed by the edge devices by using the locally available resources. The data which require more computational and storage resources than those available at the fog nodes are transferred to the cloud. This fog-based orchestration minimizes the load on the cloud, thus reducing the cost of execution. The execution of application modules at the cloud increases the total execution cost. Equations (6) and (7) are derived from  to calcuFog architecture provides processing resources near to the edge of the network. Fog devices collect and process the biopotential data coming from the sensors. The data demanding higher storage and processing resources than available at the fog node are transferred to the cloud. The execution cost at cloud includes the cost required for the execution of application modules in the cloud ,58,59. FLatency is an obligatory aspect to be reduced when implementing in real-time environments that demand high efficiency. The key advantage of fog architecture is that it tends to repetitively minimize access to the cloud by executing the required task at the fog nodes by using locally available resources to provide rapid response to the edge nodes, reducing latency.As one fog node is allocated to each hospital, sufficient processing capacity is available to process the signals of patients for detecting pain and make it available for remote monitoring in the web application within less time. We simulated all the scenarios in iFogSim to compute the results. To evaluate the fog-based system, there are four fog devices to which sensors are attached. Initially, in the first scenario, there are four sensors attached to each fog node to monitor patients. In each succeeding scenario, there is an increase of one sensor per fog device. With an increase in the number of sensors, the data to be processed at the fog devices also increase. Modules at the fog nodes have to process the data of an increasing number of sensors using locally available limited resources. Therefore, an increase in the data to be processed by the modules results in increased execution delays offered by modules. An increase in processing load on each fog device at the same instant results in an abrupt rise in the latency of the system, as depicted in Only cloud resources are available to process the inquiries in the case of cloud-based implementation. An increase in the number of patients to be monitored results in increased traffic towards the cloud server, thus causing increased network usage. In the case of geographically dispersed servers, a single fog node is assigned to a hospital to monitor patients of only that specific hospital. As a result, the use of the network in this situation decreases, thus providing improved throughput for the remaining traffic.The outcomes of the simulations verified that for implementing a remote pain monitoring system, our proposed architecture, which is depicted in When using the fog-based architecture for remote pain monitoring, information about the pain of patients of a certain hospital can be extracted promptly and will also reduce the delay in the provision of medical assistance to the patients. The findings also enable us to understand the importance of fog computing architecture in IoT applications, where a rapid response is extremely desired. In conclusion, low latency and efficient network utilization make fog-based architecture more viable for real-time health applications.We have presented improvement in the results by adopting a fog computing approach in different applications. To the best of our knowledge, no application using fog computing architecture for remote pain monitoring has been proposed before. To validate the effectiveness of the proposed architecture, the results are compared with the cloud-based systems that use sEMG or ECG signals for pain detection and healthcare service ,40,60. EVarious simulations are performed to compare the proposed fog-based approach with the cloud-based implementation of remote pain monitoring applications. Network consumption calculated for each scenario is shown in In , a remotCloud computing architecture provides resources in a centralized manner. Latency is a major concern in the deployment of remote health monitoring applications. Fog computing introduces a new layer comprising fog nodes near to the edge of the system. Resources available at fog nodes are limited but are sufficient for the pre-processing of the biopotential data coming from the edge of the network. Therefore, to meet the QoS requirements of e-healthcare applications, especially in terms of real-time response, the results of simulations performed in this research confirm fog computing-based deployment to be a more suitable option than the cloud. In To ensure the provision of medical facilities to each patient, the healthcare industry is moving towards remote health monitoring applications. Several cloud computing-based remote healthcare applications are available on the market. The key factor limiting the large-scale implementation of such applications is latency. Fog computing architecture provides an additional layer of resources near to the edge of the network. For this purpose, we proposed a fog computing-based remote pain monitoring system that collects and processes sEMG signals of patients to detect pain. In the proposed model, pain-related information is available for remote access through a web application within a minimum time, thus enabling timely medical facilitation to the patients. The result of the simulations carried out on different scales reveals that the proposed fog-based approach not only reduces latency but also minimizes the network consumption and execution cost as compared to the cloud.The proposed approach limits the use of a single fog device for a hospital. An increase in the number of patients requires more processing resources than assigned to a fog node. Therefore, load balancing will be required to maintain the efficiency of the system. Hence, our future work includes the investigation of load balancing issues in fog computing and presenting an effective solution to resolve them. Moreover, our proposed system is just limited to pain monitoring and, in future, we are enthusiastic to design and implement a real-time fog computing-based remote healthcare system capable of monitoring multiple biostatistics related to the overall health of a patient.


High) and 80 bpm (Low), which in this experiment, led to faster and slower gait speeds, respectively. The results indicate that subjects altered the use of the balance mechanisms at different cadences. The lateral ankle mechanism was used more in the Low condition, while the foot placement mechanism was used more in the High condition. There was no difference in the use of the push-off mechanism between cadence conditions. These results suggest that neural control of balance is altered when gait characteristics, such as cadence change, suggesting a flexible balance response that is sensitive to the constraints of the gait cycle. We speculate that the use of the balance mechanisms may be a factor resulting in well-known characteristics of gait in populations with compromised balance control, such as slower gait speed in older adults or higher cadence in people with Parkinson's disease.We have previously identified three balance mechanisms that young healthy adults use to maintain balance while walking. The three mechanisms are: (1) The lateral ankle mechanism, an active modulation of ankle inversion/eversion in stance; (2) The foot placement mechanism, an active shift of the swing foot placement; and (3) The push-off mechanism, an active modulation of the ankle plantarflexion angle during double stance. Here we seek to determine whether there are changes in neural control of balance when walking at different cadences and speeds. Twenty-one healthy young adults walked on a self-paced treadmill while immersed in a 3D virtual reality cave, and periodically received balance perturbations  eliciting a perceived fall to the side. Subjects were instructed to match two cadences specified by a metronome, 110 bpm ( There is an ongoing debate about whether or not walking slower is more stable  and the center of pressure (CoP). The behavior of the CoM behavior, can be explained by the relationship between CoP and CoM, as in Equation (1) Winter, .p is the CoP, x the CoM position and ẍ the CoM acceleration. The CoM acceleration is proportional to the distance between the CoP and CoM. Where ω = g/l, l is the distance from the CoM to the ankle joint center and g the acceleration from gravity. This relationship holds true for both the anterior-posterior direction and the medial-lateral direction.where Applying Equation (1), a threat to balance would be an undesired movement of the CoM relative to the CoP. To correct this undesired movement, a motor action has to be taken to accelerate the CoM in the opposite direction or, rather, to decelerate the CoM, thus stopping the movement. To prevent a fall, the CoM should not be able to accelerate to the point of no return in any particular direction. So the CoP must be moved to accelerate the CoM in the opposite direction of its current travel Hof, .In a previous study with young healthy adults, we have identified three different mechanisms of balance control in response to perceived falls . Importantly, these mechanisms have a temporal order. The earliest response to a balance disturbance  is the lateral ankle mechanism, followed by a change in foot placement and push-off  volunteered for the study. Subjects provided informed verbal and written consent to participate. Subjects did not have a history of neurological disorders or surgical procedures involving legs, spine or head. The experiment was approved by the University of Delaware Institutional Review Board #1125078-7. We used a statistical power analysis based on pilot data from another experiment  to keep the middle of the posterior superior iliac spine (MPSIS) markers on the mid-line of the treadmill. The same speed command was sent to each belt of the treadmill. The virtual environment consisted of a tiled marble floor with floating cubes randomly distributed in a volume 0–10 m above the floor, 2–17 m to each side from the midline, and infinitely into the distance, forming a 4 m wide corridor for the subjects to walk through see , implemeLow) or 110 bpm (High), which alternated on every 2 min trial. Subjects were asked to match their cadence to the metronome. After a 2-min trial there was a 15 s washout period of no metronome, followed by a 30 s adaptation period for the new metronome frequency before introducing the balance perturbations. Breaks were offered after every five 2-min trials.The subjects performed 20 2-min trials. A metronome generated by custom Labview software played throughout the trials at a frequency of 80 bpm , passed between Axelgaard PALS 3.2 cm round electrodes  placed on the mastoid processes for 1,000 ms, inducing a feeling of falling to the side, as observed in other experiments  positions based on a geometric model with 15 segments  and 38 degrees of freedom (DoF) in OpenSim  or 110 bpm metronome trials (High cadence). Here we combine the conditions that are anatomically similar , and statistically supported to be symmetric . For the model corrected foot placement, we fitted a linear regression model relating the foot placement changes for each subject to the changes of lateral position and velocity of the CoM at midstance using the control data  the foot placement is defined as the Δ swing leg heel position relative to the trigger leg heel position at swing leg heel strike. (ii) the model correct foot placement is defined as the measured foot placement value and the foot placement value predicted based on the position and velocity of the CoM at mid-stance using the linear model (see above). (iii) the Δ trigger leg knee internal/external rotation angle. (iv) the Δ swing leg hip internal/external rotation angle. (v) the Δ swing leg hip abduction/adduction angle.To test our hypothesis about the lateral ankle mechanism, we analyzed the following four variables related to the stance leg lateral ankle activation: (vi) the Δ CoP-CoM distance integrated over the time between the triggering heel strike and the first post-stimulus swing leg heel strike. (vii) the Δ stance leg ankle eversion/inversion angle integrated over the time between the triggering heel strike and the first post-stimulus swing leg heel strike. (viii) the Δ peroneus longus EMG of the stance leg integrated over the time between the triggering heel strike and the first post-stimulus swing leg heel strike. (ix) the Δ tibialis anterior EMG of the stance leg integrated over the time between the triggering heel strike and the first post-stimulus swing leg heel strike.To test our hypothesis about the push-off mechanism, we analyzed the following two variables related to the stance leg ankle push-off: (x) the Δ plantarflexion angle integrated over the second post-stimulus double stance phase. (xi) the Δ medial gastrocnemius EMG of the stance leg integrated over the first post-stimulus swing phase.To test the our hypothesis about the overall balance response, we used (xii) the maximum shift of the CoM following the stimulus onset.High/Low) to test the difference in response to the balance perturbation in the two conditions. As random effects, we used individual intercepts for subjects. To analyze whether the differences between stimulus and control steps represented by the outcome variables were statistically significant, we calculated the least squares means and estimated the 95% confidence intervals for the intercept of each outcome variable at each level of the significant factor, using a Kenward-Roger approximation  electromyography readings. The ankle inverted to a larger degree in Low, indicating that the larger shift of the CoP in the Low condition is a result of the use of the lateral ankle mechanism. The increased inversion, along with the prolonged single stance period allows the CoP and CoM to separate for a longer period of time. The combination of decreased peroneus longus muscle activity and increased activity of the tibialis anterior muscle in the Low condition compared to the High condition, yields an increased inversion angle , but at some point the CNS responds to the self-inflated fall due to the response to the perceived fall. It is difficult to uncover when precisely the CNS determines the initial response to the balance perturbation is erroneous, but we speculate that the total balance response to the perturbation is similar between cadence conditions due to the similar overall deviation of the CoM in Our current results show that higher cadence results in faster gait speed, at least for healthy young adults walking on a self-paced treadmill. The relationship between gait speed and cadence is non-trivial, making it problematic to unpack the effects of cadence vs. gait speed. The convergence to a faster gait speed when adopting a higher cadence may be related to metabolic efficiency, but this is an avenue far removed from the focus of the current work. To our knowledge this relationship has not been explored.Our current experimental methods may lead to limitations in the presentation of the push-off mechanism. We refer to the change in ankle plantarflexion in response to the balance perturbation as push-off, because to date this is the best term to describe what we believe the change in ankle plantarflexion does. Due to the experimental design, we do not have reliable ground reaction forces and moments. Providing balance perturbations, in addition to instructions to “walk normally,” leads to many situations where one foot is on two force plates, or during double stance, two feet are on one force plate. These situations make it difficult to determine the ground reaction forces and moments associated with the change in ankle plantarflexion angle.Low condition. Therefore, the stimulus for the Low condition was triggered on average ~175 ms prior to heel strike, and the stimulus for the High condition was triggered ~110 ms prior to heel strike, coincidentally corresponding to ~20% of the time between heel strikes for each condition. The earlier trigger in the Low condition may partially explain the earlier response time in the CoP-CoM . Increasing the vertical threshold created a longer period of time from threshold crossing to actual heel strike for the  CoP-CoM  and corr CoP-CoM , but notLow condition, the lateral ankle mechanism plays the primary role in the overall balance response, while the foot placement mechanism is not observed. When cadence is decreased (Low), single stance is longer, providing more opportunity to modulate the CoP through ankle roll, and diminishing the need for a change in foot placement to maintain upright posture. In the High condition, with shorter single stance duration, the lateral ankle mechanism is less effective and the balance response shifts to reliance on the foot placement mechanism. These findings suggest lateral stability is not dependent on cadence or gait speed, but the method of obtaining stability is altered with cadence, providing evidence of a flexible neural control scheme that adapts to changing constraints while walking. Moreover, such findings provide insight into adoption of preferred gait parameters, particularly in populations who have drastically altered gait speed or cadence, such as older adults or people with Parkinson's disease.We investigated whether individuals altered the control of balance if they were asked to step at different frequencies while walking on a self-paced treadmill as they periodically received a vestibularly-induced sensation of a fall to the side. The current findings support the idea that balance mechanisms are coordinated to produce an overall balance response. In the All datasets generated for this study are included in the manuscript/supplementary files.The studies involving human participants were reviewed and approved by University of Delaware IRB. The patients/participants provided their written informed consent to participate in this study.TF, HR, DG, and JJ designed the experiment. TF, HR, and DG performed the experiment. TF, HR, DG, JC, JH, and JJ analyzed the data. TF, HR, DG, JC, JH, and JJ wrote the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Voluntary contribution games are a classic social dilemma in which the individually dominant strategies result in a poor performance of the population. However, the negative zero-contribution predictions from these types of social dilemma situations give way to more positive (near-)efficient ones when assortativity, instead of random mixing, governs the matching process in the population. Under assortative matching, agents contribute more than what would otherwise be strategically rational in order to be matched with others doing likewise. An open question has been the robustness of such predictions when heterogeneity in budgets amongst individuals is allowed. Here, we show analytically that the consequences of permitting heterogeneity depend crucially on the exact nature of the underlying public-good provision efficacy, but generally are rather devastating. Using computational methods, we quantify the loss resulting from heterogeneity vis-a-vis the homogeneous case as a function of (i) the public-good provision efficacy and (ii) the population inequality.The online version of this article (10.1007/s10614-017-9774-5) contains supplementary material, which is available to authorized users. On the other hand, we allow heterogeneity in players’ budgets, expressing the ion Perc . Our worion Perc , who conMethodologically, we blend analytical and computational approaches. Our results summarize as follows. We show analytically that the consequences of permitting heterogeneity in terms of provision of the public good depend crucially on the exact nature of the underlying public-good provision efficacy, but generally are devastating. Indeed, all near-efficient Nash equilibria that exist under homogeneity fall apart when heterogeneity is allowed. Instead, we are either back at the negative all-contribute-nothing equilibrium or new, previously impossible, complex mixed-strategy Nash equilibria emerge. In the latter case, the expected level of resulting public-good provision depends crucially on (i) the public-good provision efficacy and (ii) the population inequality. These mixed equilibria are virtually impossible to characterize and to evaluate analytically for general cases. We therefore use computational methods and quantify the loss resulting from heterogeneity vis-a-vis the homogeneous case as a function of parameters regarding (i) and (ii). Thus, our analysis provides novel insights regarding the possible consequences in terms of making wrong predictions when assuming a homogeneous population, which in many real-world cases may be unrealistic.The rest of this paper is structured as follows. Next, we set up the model including details about our computational algorithm. Section N players are assigned an initial endowment i, and play the following game, of which all aspects are common knowledge:Actions Each player makes a simultaneous and committed unilateral decision regarding how much of his endowment to contribute. We will indicate with i. We indicate with i.Matching Players are ranked by their effective contributions Outcome Payoffs Q : i belongs.The mpcr Q represents the benefits of cooperation among members of the same group. When efficiencyThe parameter entclass1pt{minima1.Initialization: We assign the initial endowments to each player sampling them from a truncated Gaussian distribution with mean 2.Setting initial strategies: The initial strategy 3.Dynamics of play: Each player updates his strategy in the following way:p he keeps playing the strategy played the round before.With probability With probability The agent checks what would his rank and consequent payoff be for each of the possible strategies4.Group matching: Based on the contribution of each player, groups are formed as described above and payoffs are then materialized.5.Update and repeat: The endowment of each player is then reset to his initial one and the algorithm repeats from step 3. After T rounds the algorithm stops and the population average of the strategies is computed. The procedure is repeated EN times and the ensemble average of the population average is obtained.We simulate the above model in the following way: The above game exhibits different Nash equilibria depending on the value of As already shown in Gunnthorsdottir et al. , in the A key property of the game, necessary for the nearly efficient equilibria to exist, is that ties in the ranking placement are broken at random. In all these equilibria, in fact, there exists a mixed group where fully contributive players are grouped with defectors, i.e. players contributing the within group Nash Equilibrium. In order for this to be a NE, the fully contributive players must have a sufficiently high probability to be grouped only with other full contributors so that they would not benefit (in expectation) by decreasing their contribution and be placed with certainty in the defectors group.If each player is endowed with a different initial wealth, however, things change drastically. The heterogeneity of the players implies that there cannot be an equilibrium where more than one player contributes the same positive percentage of his endowment: Since players are ranked based on their effective contributions Furthermore, for sublinear payoffs  equilibria in the case of heterogeneous players and the equilibria reached in the homogeneous case. In particular, we are interested in how much efficiency (see footnote 2) is lost due to the heterogeneity of players. Indeed, even though non contribution by all is a Nash Equilibrium, the quasi Pareto optimal equilibrium is payoff dominantIn Fig. We observe, as predicted, that for superlinear payoffs the only possible equilibrium is non contribution by all and thus that the loss of efficiency is total. For intermediate sublinear payoff the system achieves different efficiency level, from quite low ones to levels closer to the homogeneous case. The quantitative value of efficiency that the mixed equilibrium achieves depends on the value of the mpcr and the width of the distribution of initial wealth as well as from other parameters. For values of the exponent of the public good provision lower than Interestingly, one can observe that the efficiency loss doesn’t seem to change much for different widths of the endowment distribution .For the width of the distribution equal to 0 we observe, as expected, the Nash Equilibria in case of homogeneous endowments.For different values of the marginal per capita rate of return we observe from the simulations  that the higher the mpcr, the wider is the area with partial efficiency losses in the picture and the smaller is the gain in efficiency around Hence we can conclude that for a wide range of payoffs, the more realistic assumption of heterogeneous players leads to a disruptive loss in efficiency when compared to the homogeneous case. For a very limited range of In summary, mechanisms based on assortative matching promise large efficiency gains when the interaction is such that it is safe to assume that the population consists only of equals. In the presence of heterogeneity, however, whether and how much assortative matching is likely to gain the population (relative to random matching) depends crucially on the provision efficacy of the public good and on the precise degree of heterogeneity. This implies that guarantees of more equal playing fields in these environments may be as important as implementation of assortative matching.Supplementary material 1 (pdf 232 KB)Supplementary material 2 (pdf 231 KB)Supplementary material 3 (pdf 118 KB)Below is the link to the electronic supplementary material.


The present study analyses the psychometric properties of the irrational procrastination scale IPS; , 2010 in Defined as the inclination “to voluntarily delay an intended course of action despite expecting to be worse off for the delay” , p. 66, The rise in recognition of the prevalence and negative consequences of procrastination has inspired growing efforts to validate and refine instruments for this construct see . ExpliciNotably, previous studies on the construct validity and other psychometric properties of the IPS were mainly conducted in the lens of Classical Test Theory (CTT). A major weakness of CTT-based approaches to examining the dimensionality of scales is that these methods presume the existence of linear relationships between the variables and factors – a condition that numerous measures (including the IPS) could not satisfy . Also, bTherefore, the purpose of the present study is to examine the psychometric properties of the IPS within the framework of Rasch modeling. Specifically, reliability, content validity, structural validity, substantive validity, and gender-based DIF of the scale are evaluated. To our knowledge, there have been no attempts at applying Rasch analysis for the IPS.N = 382 college students who participated in the study through SONA system for research credit rewards at a large public university in the Southern United States. After providing their written informed consent, participants completed a standard demographic survey in addition to the nine-item IPS (SD = 0.75). The sample is slightly predominated by female students . Self-reported ethnic information suggested that the sample was ethnically diverse . In terms of college major, the majority of the sample was in Psychology (62.8%). All participants were included in the final analysis sample (N = 382).The sample is comprised of item IPS , 2010. TGiven the polytomous item format of the IPS , the Rating Scale Model RSM;  was adopPnik represents the probability that person n would be observed in category k of item ni represents the probability that person n would be in category k−1 of item ni, B represents the latent ability level  of person n, Di represents the difficulty of item i , and Fk represents the probability of being observed in category k relative to category k−1. This step calibration parameter Fk is thus a rating scale threshold defined as the location associated with the equal probability of observing the two adjacent categories k−1 and k.where Therefore, the RSM allows non-linear raw rating-scale data to be converted into calibrated item and person measures on a common, linear interval-level scale  of the nine items on the scale range from 0.58 to 0.74, indicating the absence of non-modeled dependence among the items and potentially a common underlying construct of all items (SE) in As presented in ll items . In accoll items , the revll items . MoreoveThe content validity of the IPS was primarily evaluated by the items’ mean square fit statistics (infit and outfit). Infit and outfit indices express the correspondence between observed and expected model parameters; appropriate fit values could indicate that the expected parameters represent the observed responses adequately. As shown in To examine the internal structure  of the IPS directly, a principal component analysis (PCA) of the standardized residuals was performed with controlling for the primary dimension in the Rasch model to determine the possibility of local dependency or a redundant secondary dimension not intended for the scale . As suggBn) and the step calibration parameter (Fk) increased monotonically throughout the five response categories . Additionally, both the infit and outfit mean square fit indices of the response categories are less than the cut-off point of 2.00, suggesting that no unexpected response was observed. In all, these results demonstrated the adequacy and efficiency of the response scale for the IPS and that the five categories in the response scale functioned properly as initially expected the scale developer . As depicted in 1. DIF in Rasch modeling is established when participants with equal levels of the latent trait responded differentially to an item  an item . The DIFProvided the methodological pitfalls in previous IPS validation studies that relied on CTT, in the present study we chose to resort to IRT using Rasch analysis in an attempt to gather complementing evidence for the psychometric properties of the IPS. Overall, the results confirmed the measurement robustness of the IPS within the Rasch modeling framework. Specifically, the results indicated good score reliability, content validity, and substantive validity of the IPS. Regarding the dimensionality, consistent with Although this study focused on the application of Rasch analysis, it is worth noting that because Rasch models assume unidimensionality, they are not suitable for examining factorial structures of scales that include multiple constructs. Factor-analytic approaches, however, can accommodate multidimensional latent variables with ease, which allows for the investigation and comparison of competing single- or multi-factor models [see Two study limitations are worth noting, particularly with regard to the sample characteristics. First, an obvious drawback pertains to the fact that the results were obtained from a college student population, and thus further research is warranted in order to try to replicate these findings in the general population. Past research e.g.,  has founTo summarize, Rasch analysis was conducted to examine the psychometric properties of the IPS in the present study. Using the RSM , we founThe raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.The studies involving human participants were reviewed and approved by the University of Houston IRB. The patients/participants provided their written informed consent to participate in this study.Both authors contributed to the conceptualization, data collection, data analysis, and manuscript preparation.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Possible mechanisms of particle attraction providing formation of the field aligned microparticle strings in complex plasmas at elevated gas pressures are theoretically investigated in the light of the Plasmakristall-4 (PK-4) experiment on board the International Space Station. The particle interaction energy is addressed by two different approaches: (i) using the dynamically screened wake potential for small Mach numbers derived by Kompaneets et al., in 2016, and (ii) introducing effect of polarization of the trapped ion cloud by discharge electric fields. Is is found that both approaches yield the particle interaction energy which is independent of the operational discharge mode. In the parameter space of the performed experiments, the first approach can provide onset of the particle attraction and string formation only at gas pressures higher than 40–45 Pa, whilst the mechanism based on the trapped ion effect yields attraction in the experimentally important pressure range 20–40 Pa and may reconcile theory and observations. For some years, numerous experiments have pointed out electrorheological properties of complex plasmas showing that small micrometer-sized grains introduced into the discharge plasma can form string structures aligned with external electric fields. Such a particle alignment has been observed in the sheath of radio-frequency (rf) discharges ,2,3, strThe PK-4 instrument  polarity switching causes time variations of the induced dipole moment We now consider the energy of interaction between two particles Now, only the charge-quadrupole interactions can provide the mutual particle attraction. In ssure in pn>45 PaContrary to the dynamically shielded potential used in the previous section, another approach is based on the effect of trapped ions and polarization of the associated ion cloud by external electric fields. The standard charging models ignore plasma ions that are trapped in the Debye sphere surrounding a negatively charged grain. In collisional plasmas, however, a large negative charge carried by grains neutrals ,21. Therneutrals . First, Analytical modeling of the density and distribution function of the trapped ions by Lampe et al., in 2003, revealed the dominating role of the trapped ions in the particle shielding. It was found that, in the limit the ions ,18. The 40–50 Pa .U is defined as a product of the dynamical potential and the particle charge, now, it additionally involves the dipole-dipole and higher moment interactions.A grain with a trapped ion cloud is similar to the classical atom in the sense that electrons bound in an atom cancel the charge of the nucleus within. Embedded even in weak external electric fields such a system reveals charge separation and appearance of nonzero dipole and higher moments describing a spatial distribution of the bound charges. Therefore, contrary to the first approach, where the particle interaction energy For complex plasmas, the main difficulties lie in estimating the multipole moments associated with the trapped ions. Recently, an iterative multipole expansion techniques has been applied for the particle potential in collisional complex plasmas that takes into account the trapped ion effect and slow ion flows ,23. It t in Ref. ). In theFor estimations of a dipole moment associated with the trapped ions  of Ref. , where weference  for detaIt turns out that variations of the PK-4 discharge parameters with gas pressure provide the slow decreasing function otential : p=QλDd The energy of a grain “coated” by trapped ion cloud and immersed in a potential  is givenIt should be stressed that, although mathematically the potential energy  and consNote the olved in . The chaviz.Similar to the first approach, calculating the pair interaction energy of two “coated” particles in the dc field rules out the charge-dipole terms, and the pair interaction energy is given by the same expression as the time averaged pair interaction energy in the polarity switching mode, At this stage, it is interesting to further compare the interaction energy  to that ), while  reveals e  and (6) is reduced with dc power and gas pressure).Argon is more favorable for the string formation than neon (the dipole moment shows a stronger reduction with pressure in neon, than in argon; see The particle longitudinal attraction in the dc and ac operational mode is found to be the same, but, in the PK-4 experiments, the string formation is observed more easily in the ac mode. One can assume that a short drift time of the particles in the dc field withing the camera field of view (To explore possible mechanisms of the microparticle attraction in collisional complex plasmas and hence shed a light on the string formation and transition to the string fluid state observed experimentally at very ion low Mach numbers, we theoretically analyzed the pair interaction energy addressing two approaches. The first one applies the theoretical model for the particle wake potential in collisional flowing plasmas , and anoWe conclude, therefore, that the approach invoked the trapped ion effect can reconcile qualitatively the theory and PK-4 observations. Since the string formation is quite generic in complex plasmas, the results presented here might also be applicable to other experiments performed in similar conditions. However, note that the used plasma parameters relate to the particle-free discharge plasmas and, thus, are not fully constrained by measurements yet. This means that a little stretching or new interpretation of particle attraction is possible.