Although the angular distribution of noise gratings in holographic photopolymer is understood to arise from Bragg matching, the details of scatter strength and dynamics are not fully understood. This confounds development of materials and recording techniques that minimize haze. Here, the kinetics are studied using a multi-physics numerical approach coupling diffraction of light from the dynamic material including scatter centers, reactions of chemical species initiated by this light, diffusion and swelling of these constituents, and the formation of the refractive index from the resulting composition. The approach is validated in the case of two-beam transmission holography by comparison to traditional harmonic series and rigorous coupled-mode approaches. Two beam holography in the presence of scatter is then used to study haze development. This reveals that haze due to weak noise gratings grows significantly above initial scatter only in reaction-limited materials, consistent with proposed Bragg-matched amplification mechanisms. Amplified haze is found to be proportional to initial scatter, quantifying the impact of clean sample fabrication. Conversely, haze is found to grow super-linearly with sample thickness, illustrating the significant challenge for applications requiring low haze in large thickness. Most applications of holographic photopolymers require high diffraction efficiency but also low scatter. Examples include data storage, where scatter contributes to the bit error rate, and augmented reality where scatter contributes to haze that detracts from visibility. Unfortunately, it is commonly observed in material development that these two quantities are coupled. That is, high dynamic range materials capable of recording high diffraction efficiency also typically develop large scatter. It is thus a significant challenge to develop materials formulations and processing methods resulting in a high signal to noise ratio (SNR).Previous theoretical studies of scatter development in holographic photopolymers have identified noise gratings seeded by initial scatter centers as the source of recorded haze ,2. The cxz plane.The observed scatter patterns can be explained by the Ewald sphere analysis shown in While this analysis and the previous studies explain the angular distribution of recorded scatter patterns, they do little to guide materials and process development that would maximize SNR. The amplitude of the noise gratings is expected to be strongly dependent on the statics of the scatter centers, the dynamics of the recording process, Bragg selectivity of the noise gratings, and recording parameters such as period and intensity. These are difficult to study experimentally since it is challenging to know or precisely control the details of the initial weak scattering. Additionally, experimentally exploring the parameter space of materials formulations and processing conditions is costly when it is not clear what variables should be probed and in what ranges they would be expected to impact the SNR.The goal of this paper is to therefore to establish a numerical approach to study these questions. Because the observed Bragg-matched noise gratings have structure in both transverse dimensions and the amplification process depends on growth in both depth and time, such a study requires a simulation in three spatial dimensions and time. Conversely, numerical studies of predominantly local effects such as phase segregation in holographic polymers have typically been restricted to a slice through the hologram in the plane of the grating wave vector and time .For generality, we will simulate a specific model material broadly similar to widely available commercial formulations . The goaTo study the how coherent light illuminating a scattering, photosensitive medium drives the development of both signal and noise, we implement a multi-physics code suite. The technique models the holographic recording process by iterating four primary calculations as a function of exposure time. These are (1) the Fourier beam-propagation (FBPM) method used to calculate optical propagation and diffraction within the 3D index structure, (2) a discrete time-stepping solution of the first-order photochemical rate equations, (3) diffusion of mobile species via a fast-Fourier transform (FFT) solution of Fick’s law and (4) update of the material index via an a priori model for two-component holographic photopolymers. We describe each step in more detail below.The substrates and recording material are assumed to contain photo-insensitive scattering centers that initiate noise gratings. These may be scratches in the substrate, dust, or incompletely mixed components of the formulation, for example. These scatter centers can be described either by shape  or via their angular scatter distribution . In the latter case, the microscopic shape of the scatter center sampled on the computational grid is found by inverse Fourier transforming the specified angular scatter distribution. Identical copies of these shapes are randomly distributed throughout the 3D recording medium and/or substrates with a specified number density. Given the shape and number density, the cross-section of the scatter centers is adjusted to create a specified initial haze. For each time step of the exposure, two coherent Gaussian writing beams, symmetrically tilted relative to the surface normal, are propagated through the depth of the material using the non-paraxial FBPM method. The x and y spatial dimensions are at least Nyquist sampled relative to the optical wavelength in the material in order to capture scattering angles over the full forward hemisphere. The writing beam angle is chosen to yield a transmission hologram with period, D and terminate via a unimolecular reaction with rate constant This intensity then drives a sequence of chemical reactions, calculated through time-stepping the first order chemical rate equations. The first reaction in the sequence is the photolysis of an initiator (assumed to be present in sufficient excess that it does not significantly deplete) by the optical intensity to generate primary radicals with rate constant polymers . To our The termination rate constant aterials . This exaterials . Here weThese radicals then drive the propagation reaction with rate constant The concentration of polymer  studied . The goaD, is independent of space and time, that transfer function is Mobile monomer must diffuse to implement the first term in Equation (4). The three-dimensional distribution of monomer is Fourier transformed via the FFT and multiplied by the transfer function of Fick’s second law in homogenous space, then inverse transformed. Assuming that diffusivity, The index of the photopolymer is then calculated from these chemical distributions. The local volume fraction of polymer is first found from the fractional conversion and the known polymerization shrinkage. The volume fraction of the rubbery solid matrix is found assuming perfect mixing and incompressibility as one minus the monomer and polymer volume fractions. Finally, the index of the three-component mixture is calculated by the Lorentz–Lorenz equation:An important aspect of this calculation is that index change and shrinkage upon polymerization result in finite index contrast immediately upon polymerization. Subsequent diffusion amplifies this response. Since the development of haze is hypothesized to be self-reinforced noise gratings that form during exposure, the time dynamics of the index formation process are critical.Finally, the efficiency of the hologram is found by illuminating the material index. This index is taken to be the sum of the static (scattering) and dynamic (holographic photopolymer) index distributions. A Bragg matched reference beam incident on the surface z = 0 is propagated through the volume with FBPM. The diffracted intensity is integrated at the exit face in an angular range centered on the object beam. The readout reference beam at 405 or 660 nm is assumed to be sufficiently weak and/or outside the initiator absorption spectrum that it does not modify the index distribution. Next, a normally incident beam is used to measure the haze. Haze is calculated, per ASTM standard D1003, as the fraction of the power scattered by the sample out of a normally incident probe for all angles  greater than Finally, after the exposure is complete, monomer is allowed to diffuse, becoming spatially uniform. This step simulates dark development time and assumes no limits to monomer transport due to finite solubility in high conversion regions. The uniform monomer is then fully converted to polymer, simulating a perfectly incoherent and spatially uniform flood cure. Quantitative conversion is assumed, that is no monomer remains. A Bragg selectivity curve is then calculated by measuring the diffraction efficiency as a function of reference beam angle.To ensure the appropriateness and proper implementation of this combination of methods, it is critical that the code suite be validated. There are limited theoretical methods for predicting scatter development in these materials and the problem is inherently statistical. Thus, we instead validate the technique using a fully theoretical model of two-beam Bragg holography. A comparison to theory is chosen rather than experiment to enable direct comparison with no fitting to find parameters that are not always easily accessible experimentally, e.g., diffusion and reaction rates.Combining Equations (2) and (4) results in a single rate equation governing this simplified system. Restricting the analysis to one dimension in the plane of incidence gives:th order . The resThese equations describe how the sinusoidal radical distribution of finite visibility given by Equation (10) is a sufficiently simple set of coupled first-order differential equations that it can be solved in closed form with the help of a symbolic mathematics package. With the monomer distribution With the monomer and polymer distributions known in space and time, the volume fraction of the matrix, e method . The resThe reason for developing this fully theoretical expression for holographic efficiency is that it can be compared to the numerical code suite which ideally implements the same physics but in a completely numerical, discrete manner. Specifically, in the limit of no scattering, the code suite will reproduce the intensity pattern, chemical reactions, distribution of species and refractive index to predict Bragg diffraction efficiency via the numerical techniques described previously. A comparison of the numerical to the theoretical solutions thus serves to validate the implementation and numerical approximations of the code suite.First, we use both the theory and numerical system to compare the evolution of the index grating itself. A 10 µm thick film of 20 wt% bisphenol A diacrylate in polyurethane matrix is exposed to two 405 nm Gaussian beams tilted to produce an unslanted 1 µm period transmission hologram. Radical diffusion is taken to be negligible e radius of the electric field [To further validate that the code correctly implements volume diffraction of off the numerically calculated index structure, a Bragg detuning curve found from both methods is compared. In the theoretical case, the calculated first harmonic of the refractive index is used in the beta value method  to prediic field . Figure The validated code is now applied to investigate how noise and signal develop in a holographic photopolymer containing scatter centers. The holographic photopolymer uses bisphenol A diacrylate (BPADA) as a writing monomer in a polyurethane matrix initiated with 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) at 405 nm. At 633 nm, the refractive indices of the monomer, polymer and matrix are 1.545, 1.5789, and 1.476 respectively. Dispersion of the indices is not included in this study. The shrinkage of the monomer in matrix upon full polymerization is found via the slanted grating technique  to be σ=e2 intensity diameter of 200 µm. The readout beam used for nondestructive measurement of diffraction efficiency and haze is at 660 nm with a 40 µm 1/e2 intensity diameter, tilted at the appropriate Bragg matched angle or normally incident, respectively. Initial haze is generated by Rayleigh scatter centers with number density The writing beams are tilted, except where stated, to produce a grating period of one µm and have a 1/Typical growth dynamics are shown in Haze growth via amplification of Bragg-matched noise gratings is further supported by recording in diffusion and reaction-limited materials as shown in The top and bottom plots of The significant dependence of total haze upon the diffusion to reaction rate ratio shown in Since haze is seeded by scattering, an obvious strategy for reduction of haze is to reduce the initial scatter, e.g., via resin filtering and clean-room processing. Given that recorded haze is an amplified growth process, it is possible that reductions in initial haze could have super-linear impact on final haze. Finally, we consider the dependence of recorded haze on sample thickness. It is commonly observed experimentally that haze grows rapidly with sample thickness and this is confirmed in The results show that the development of both intended holographic signal and unwanted noise gratings in holographic photopolymer can be studied by numerically solving the coupled physics of optical diffraction, reaction, diffusion and index formation. The technique is demonstrated to accurately reproduce a closed-form solution to the two-beam recording condition including the shape and amplitude of the index grating as well as the Bragg selectivity curve. Numerical studies of signal and haze development reveal the dynamics of haze formation as a function of experimental parameters. Integrated haze is found to depend linearly on initial scatter strength and super-linearly on sample thickness. Haze growth is shown to be largely suppressed for diffusion-limited recording. This condition can be achieved via a number of experimental routes including high intensity, short exposures. The required intensity to record in the diffusion-limited regime can be found from the unitless parameter fined in , which i


The cell wall is a complex and integral part of the plant cell. As a structural element it sustains the shape of the cell and mediates contact among internal and external factors. We have been aware of its involvement in both abiotic (like drought or frost) and biotic stresses (like bacteria or fungi) for some time. In contrast to bacterial and fungal pathogens, viruses are not mechanical destructors of host cell walls, but relatively little is known about remodeling of the plant cell wall in response to viral biotic stress. New research results indicate that the cell wall represents a crucial active component during the plant’s response to different viral infections. Apparently, cell wall genes and proteins play key roles during interaction, having a direct influence on the rebuilding of the cell wall architecture. The plant cell wall is involved in both susceptibility as well as resistance reactions. In this review we summarize important progress made in research on plant virus impact on cell wall remodeling. Analyses of essential defensive wall associated proteins in susceptible and resistant responses demonstrate that the components of cell wall metabolism can affect the spread of the virus as well as activate the apoplast- and symplast-based defense mechanisms, thus contributing to the complex network of the plant immune system. Although the cell wall reorganization during the plant-virus interaction remains a challenging task, the use of novel tools and methods to investigate its composition and structure will greatly contribute to our knowledge in the field. Moreover, they were associated with paramural bodies within the plasmodesmata in the affected portions of cell wall and with virus cytoplasmic inclusions. These changes correlated with alterations in the quantity and distribution of PR-2 and with the catalytic subunits of cellulose synthase (CesA4). Accumulation of PR-2 was noticeably elevated in the susceptible potato. Compared to mock-inoculated plants, the level of CesA4 was decreased in hosts that were susceptible to PVYNTN. This infection also changed the distribution of both proteins inside the cells of compatible plant hosts. In the infected susceptible potato, PR-2 was more frequently accumulated in the cell wall and vacuoles compared to the healthy plants. Moreover, in susceptible plants, CesA4 was deposited in the cell wall, plasma membrane, and endoplasmic reticulum. This suggests that both the decrease in CesA4 and increase in PR-2 determined the susceptibility of potato , expansin 10 (EXP10), and xyloglucan transferase 6 (XTH6), varied based on the areas in which the samples were harvested. The authors also noticed a reduction in mRNA transcript accumulation after infection by turnip mosaic virus (TuMV). In addition, they found that the genes PME3, XTH6, and EXP10 were activated against TuMV after 10 days of inoculation. Moreover, NTN  and damage-associated molecular patterns (DAMPs), respectively—is the key function of innate immunity in plants . Damage The PAMP and DAMP response pathways associated with the cell wall were not precisely recognized for plant viral infections. In fact, numerous results indicate that the cell wall is actively modified during a plant resistance response against viral pathogens. Years of plant-virus co-evolution did not only lead to susceptibility but also lead to resistance. Generally, resistance, or high resistance (associated with hypersensitive reaction), results from well-developed and effective defense mechanisms induced to prevent or limit the damage caused by infection by a viral pathogen . Plant rNTN  gene leads to resistance against TuMV. StEXT4 gene is often gradually activated and StEXPA3 is repressed during HR against PVYNTN. They demonstrated that the levels of StEXPAs in cell walls decreased, while the content of HRGPs dynamically increased in the reinforced cell walls; the HRGP extensins accumulated mainly in apoplast, but they were also observed to be deposited in the symplast in the case of resistant plants. Thus, we conclude that changes in the intracellular distribution of HRGPs and StEXPAs are differentially controlled based on the type of PVYNTN-potato interactions. These observations confirm that apoplast as well as symplast is involved in defense response mechanisms.Moreover, the HR reaction of potato to PVYll walls ,b, 2020.a to PDV . Along tPlant cell wall performs a number of important functions in the cell. So far, the structural properties and composition of the cell wall as well as its involvement in the interaction of plants with bacterial and fungal pathogens have been well described. However, modifications occurring in the cell wall during viral infection remain poorly understood. This review presents recent interesting insights into the role the cell wall plays in compatible (susceptible) and incompatible (resistance) reactions. Significant progress has been made in identifying the important components of the cell wall. Results have shown that changes observed in the intracellular dissemination and accumulation of β-1,3 glucanase, components of hemicellulosic cell wall matrix, and cell wall structural and modifying proteins such as expansins, HRGPs, and extensins might be differentially controlled, based on the type of plant-virus interactions, leading to cell wall loosening or the appearance of a reinforced cell wall. This confirms that apoplast as well as symplast is activated as a mechanism of the defense response.Fusarium graminearum (Verticillium dahliae) as presented by This research topic is promising and provides a better understanding of the multilevel complex network of plant responses to viruses. Further analysis of the functions of specific plant cell components is necessary to establish the regulatory pathways involved in communication between the plant and viral pathogen. This can be possible with the use of tools such as atomic force microscopy (AFM). AFM images can show, at the nanometer scale, the heterogeneity of the cell wall as well as the spatial distribution of both soft and rigid polymers of the cell wall matrix . AFM canminearum . MutantsEK and KO-K conceived the project, analyzed data, and participated in writing the manuscript. JB analyzed data and helped with critical comments of the manuscript. All authors contributed to the article and approved the submitted version.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.


WiFi backscatter communication has emerged as a promising enabler of ultralow-power connectivity for Internet of things, wireless sensor network and smart energy. In this paper, we propose a multi-filter design for effective decoding of WiFi backscattered signals. Backscattered signals are relatively weak compared to carrier WiFi signals and therefore require algorithms that filter out original WiFi signals without affecting the backscattered signals. Two multi-filter designs for WiFi backscatter decoding are presented: the summation and delimiter approaches. Both implementations employ the use of additional filters with different window sizes to efficiently cut off undesired noise/interference, thus enhancing frame detection and decoding performance, and can be coupled with a wide range of decoding algorithms. The designs are particularly productive in the frequency-shift WiFi backscatter communication. We demonstrate via prototyping and testbed experiments that the proposed design enhances the performance of various decoding algorithms in real environments. From unmanned aerial vehicles (UAVs) to smart homes, smart factories, smartphones and many more, Internet of things (IoT) brings together data, processes, people and things all networked to produce an immense infrastructure of information system. Technological advances in IoT open a wide range of applications that call for hundreds of billions of sensors communicating. One critical challenge towards the vision of IoT is to build devices that can be easily deployed and run autonomously for a lengthy duration ,2. BacksBackscatter communication is simply reflecting and modulating an incident radio frequency (RF) signal. A backscatter tag switches between reflection and absorption states by impedance tuning. Over the past years, two types of backscatter communication exist: monostatic backscatter and bistatic backscatter. Typical applications of monostatic backscatter communication are point-to-point communication in the RFID tag where the transmitter and receiver are the reader communicating with a tag. Only two devices are involved in conventional RFID leading to a limitation in distance (range), data rate, modulation scheme, point-to-point networking and a dedicated energy source. Ambient backscatter ,4, a bisIEEE 802.11 popularly known as WiFi is more or less built into almost all modern-day electronic gadgets from PCs, laptops, smartphones to gaming devices and even running shoes. Abundance creates a solid platform for WiFi backscatter communication. WiFi backscatter is a type of ambient backscatter that utilizes only WiFi signals as its carrier signal. This plausible concept leverages the possibility to reuse existing WiFi infrastructure to provide connectivity relying on ambient WiFi as its excitation signal. As a result of its attractive features, WiFi backscatter has seen developments and prototyping lately from the industry and academia ,13,14.A critical observation on the trend of WiFi backscatter reveals a paramount issue which is the severe fluctuation of WiFi signals due to the nature of orthogonal frequency-division multiplexing (OFDM). Such fluctuation remains not only in backscattered signals but equally in carrier WiFi signals known as self-interference, making decoding a challenging task. Since WiFi signals have a much shorter symbol duration  than backscatter signals, the fluctuation can be smoothed out to some degree by a low-pass filter. Therefore, low-pass filtering of received signals is essential prior to decoding in WiFi backscatter communication. However, designing a filter dedicated to WiFi backscatter has been unexplored in the literature.Frequency-shifted backscatter (FS-backscatter)  can alsoIn this paper, we proposed a multi-filter design for decoding in WiFi backscatter communication with frequency shift, which can be combined with a wide range of existing decoding algorithms for performance enhancement. We propose two multi-filter schemes—summation and delimiter—and a hybrid of the two with engaging the use of more filters. The placement of filters and evaluation of signal processing account for the difference in the design methodology. The utilization of multiple filters in our proposal allows us to repeatedly remove unwanted signals with different filter parameters and efficiently identify packets. As a result, it becomes easy for the determination of a threshold relevant for decoding. The proposed schemes accommodate for changes in amplitude fluctuation as well as the needless effort to preview the raw signals severally before setting the threshold.We demonstrate via our prototype implementation and testbed experiments in office and hallway scenarios that the proposed designs outperform the conventional single-filter decoding in various conditions. The margin of BER decrease reveals a huge performance difference between the single filter design to the tune of 34% and 44% enhancement for our multi-filter summation and delimiter schemes, respectively, under a good channel condition. On the other hand, i.e., in worse channel conditions, the maximum BER improvement shows approximately 98.5% and 97% for summation and delimiter multi-filter designs, respectively, attained over the single filter design.Experimental observations that reveal the high sensitivity of signal shape to the configuration of a preprocessing filter.Design of multi-filter schemes for effective noise isolation for reliable decoding in WiFi backscatter communication with frequency shift implementation.Prototyping and a testbed experiment performed to verify the validity of the proposed multi-filter designs in real-world environments.In summary, the contributions of this work are as follows:The remainder of this paper is sectioned as follows: The research community has published a rich body of papers on backscatter communication ,23,24,25BackFi  proposedThe novel approach of FS-backscatter is from the article . The basThe authors in  design aThe communication system model presented for this paper is illustrated in The tag system in the model dictates the actual operation of the backscatter communication, thus reflection, modulation and frequency shifting. Notice the inclusion/addition of an oscillator shown in In this section, we take a look at two major points that serve to initiate the essence of this paper. We first observe from the experiment the impact of threshold to eliminate unwanted signal fluctuations and finally the effect of moving average filter in regards to the length.The application of a filter in digital signal processing targets both the separation of combined signals and signal restorations distorted in some way. In this instance, the filter is employed as a low-pass filter implemented with moving average. However, after the separation, certain unwanted signal fluctuations or interference signals are propagated through to the output. The ability to remove such fluctuation or interference significantly affects the frame identification leading to the deletion of such signals. A threshold elevated above those signals will do the work but determining the accurate value is difficult especially in frequency-shift where the actual signals are close to the noise floor.Traditionally, a trial-and-error approach is adopted to find the appropriate threshold value. The above-mentioned appropriate threshold value, even though it comes with many challenges, works when the suitable value is determined. However, determining the correct threshold can be time-consuming and unstable when that fixed threshold moves through a fluctuating signal. From experimental observation, it can be seen that, a very small change in threshold causes the performance of the system to behave differently. N is the length of the average or number of points.The moving average filter has widely been used because of its simplicity, efficiency in noise reduction and a good step response in the time domain ,27,28. BN. N increases, there is more smoothing action, i.e., noise reduction evident from the amplitude. However, the sharpness of the edge becomes more blunt. It is worthy to note that both features of smoothing and sharp edge have technical benefits that can combine to achieve enhanced performance. It is shown in the figure that N affects how these features appear in the filtered signal. In summary, we seek to explore the merits of each side to improve the BER of frequency-shift backscatter decoding by exploiting multiple filters with different N values. It is also noted that N also affects the level of an appropriate threshold for bit decoding. This is because as shown in N values result in various amplitudes of the filtered signal. A critical observation can be witnessed when the multiplying factor of the window length is five causing over-smoothing.The key parameter of interest to us in the equation is the value of How many filters are needed?N is optimal?What length of filter How is the threshold determined for efficient operation?To address the above observations, the following questions are primarily considered:In this section, we propose multi-filter designs as low-pass filters for efficient fluctuation/interference suppression before decoding. Convolution operation easily computes moving average filtering ,28. As sN, i.e., Filter 1, produces an output coded with a significantly good amount of information although separation from the noise floor is difficult. The introduction of multiple filters with the length of m is an integer greater than one, results in loss of coded information due to smoothing but with relatively elevated signal from the noise floor. A pivotal examination from The summation approach depicted in N, but use the other filters to uniquely identify the frames. The margins or edges of the filter with length The structural design of the delimiter approach shown in The hybrid design is a straightforward approach derived from the combination of the summation and delimiter designs. While the core rationale behind the summation approach is to elevate the received signal by means of aggregating signals from different filters, the delimiter aims to keep signal quality and yet efficiently recognize frames. Both schemes have their strengths and weaknesses as will be seen in P is the number of sample points, c is the scaling factor. The scaling factor c is set to ensure that none of actual signal samples are removed by lowering the threshold.A key element in the proposed filter design is the threshold finder for frame detection. The development and design of the multi-level filters are to stabilize the received signals for easy elimination of undesired signals. We propose the use of a mean-based approach in determining the threshold instead of a constant value which produces practically unrealistic outcomes. The equation for the threshold finder is as follows:N, m and c cannot be underestimated as they alter the operation design massively. From experimental observation, the optimal value for the filter length N equals half the symbol length where symbol length = sample rate/tag rate. The delimiter design is less affected by the choice of m provided the choice is multiple of 4. The optimal constants for m from c for the threshold finder upon several tests were evaluated at 0.5 as illustrated in Selecting optimal configurations for This section is categorized into four areas: configuration and setup, filter significance, indoor experimental analysis and hallway experimental analysis. Components, parameters and settings are explained in the first part whereas the essence or need of filter and for that matter, multi-level design is considered in the second part. Detailed analysis of the setup for good and bad circumstances are further investigated.The proposed multi-filter designs were implemented in MATLAB after raw signals are captured from the hardware peripherals. The physical components of the testbed are shown in Before we move into the deep analysis of the proposed multi-filter design in comparison with the classical approach, it is imperative to validate the reason why the low-pass filter is important in the decoding process. The low-pass filter is purposefully meant to filter out signal fluctuations and provide smoothing for effective decoding. The smoothing effect in addition to noise removal improves frame identification and for that matter boosts the overall system performance. Basically, there are two reasons why filter(s) are required for data extraction: (1) adequate identification (detection) of frames and (2) efficient decoding in terms of BER performance. It is of particular interest to note that there is no significant difference as the number of filters increases from two upwards even so in both figures. In The experiment inside the office room was characterized as a good channel environment due to the fact that (1) the transmission gain of the transmitter USRP is relatively higher, (2) the tag-to-transmitter distance is close and fixed and (3) there is less network traffic. The transmitter was positioned 50 cm away from the tag system while the receiver was placed at 0.5, 1.0, 1.5, 2.0 and 3.0 m away from the tag in the opposite direction. Tag data rates of 200 kbps and lower achieve BER of zeros for proposed designs. The conventional method considers the best threshold for each distance by means of trial and error. Selecting a constant threshold for the traditional approach will fail as the distance increases. Bear in mind that in the plot, the conventional method could not identify 1000 frames for all cases as the others could. It can be observed from Next, the experiment was carried on in the hallway of a building with relatively bad channel conditions such as lower transmission gain, varying tag-to-transmitter and tag-to-receiver distance and long distance of about 6 m between receiver and transmitter. The transmitter and receiver are fixed as shown in Mean-based decoding: The arithmetic mean of the samples of a detected frame is used as the threshold to decide if a signal is deemed zero or one. In this context, since the reference signal is an FM0, the mean-based threshold is fixed to 0.5.Sliding-based decoding: A specific window size of a given buffer or array of signal samples is defined and the mean of window is used as the threshold for decoding.Pattern-based decoding [decoding : The sloThe BER was evaluated in combination with three different decoding algorithms to ascertain and prove the wide applicability and validity of our proposed schemes:In general from The cumulative distribution function (CDF) graphs for the multi-filter designs and the classical method are seen in Lastly, two cases of obstacles in the hallway scenario are considered. Let TT be the instance where there is an obstacle between the transmitter and the tag and let TR be the scenario where an obstacle is placed between the tag and the receiver. The obstacle employed is a corrugated box made from 4 mm-thick corrugated cardboards; the overall dimension of the box is approximately 30 × 20 × 4 inches. The obstacle is erected to directly cover the full angle of line-of-sight. While power consumption and processing costs remain intact in the tag, those of the receiver will increase due to increased complexity. For detailed analysis, the proposed multi-filter designs are implemented in an FPGA using Vivado Design Suite release 2020.1 from Xilinx . This apIn this paper, we explored the significance of preprocessing filter for WiFi backscatter communication leading to a conventional single filter design, to be inefficient in noise removal and frame detection which causes significant degradation in performance. In an attempt to resolve this issue, we proposed multi-filter designs for WiFi backscatter communication with frequency-shift implementation. The proposed filters, i.e., the summation and delimiter designs, allow captured signals at the receiver to be separable by means of multi-level filtering and then input to a decoding algorithm. Our proposed designs from experimental results indicate a significant enhancement in throughput performance over the conventional approach. The BER performance of both multi-filter designs achieved better outcomes in various communication environments. Employing the proposed schemes with various decoding algorithms demonstrated a stable consistency of superior performance.


A comprehensive understanding of the behaviour of the heterogenous layers within the paint stratigraphies in historical paintings is crucial to evaluate their long term stability. We aim to refine nanoindentation as a new tool to investigate the mechanical behaviour of historical oil paints, by adapting the probes and the protocol already used in biomechanical research on soft tissues. The depth-controlled indentation profile performed with a spherical probe provides an evaluation of the non-linear viscoelastic behaviour of the individual layers in paint at local scale. The technique is non-destructive and guarantees the integrity of the surface after indentation. The mapping of elasticity demonstrates the properties’ heterogeneity of the composite material within the paint layers, as well as between the individual layers and their interfaces. A further understanding of the stress distribution within the different layers (support-ground-paint-varnish) is essential to evaluate crack initiation and propagation and to develop preventive conservation as well as paint consolidation methods5.Natural aging, external mechanical impacts, and variations in relative humidity and temperature, as well as inherent chemical processes between pigments and binding media, can induce internal stresses in paint stratigraphies, which can lead to cracking and delamination1. Furthermore, they can only be used to extract an overview on the macroscopic scale behaviour, giving no insight on how the heterogeneous properties of the various layers at the local scale may contribute to the overall mechanics. Methodologies investigating the local mechanical properties on small samples like cross-sections from paintings are, therefore, of major interest.Classical mechanical investigation methods, such as tensile, bending or biaxial measurements, usually require large samples, and provide limited information on the viscosity or rheological behaviour of the paint filmet al.4 and Freeman et al.6. Salvant et al.4 used this method to investigate the hardness and reduced modulus of reconstructions as well as cross-sections of paintings6. presented results from nanoindentation used on reconstruction samples embedded in polyester resin. In these two studies, however, the samples were indented by means of a diamond Berkovitch tip - a method that is known to have severe limitations9 and, importantly, to induce mechanical plastic deformations that destroy the sample4.One methodology applied to evaluate the mechanical properties of paintings is nanoindentation, as proposed by Salvant 22. This new nanoindenter relies on a millimeter size cantilever, equipped with a microsphere glued at its free hanging end. The sphere is brought to contact with the sample, while the bending of the cantilever spring is monitored with an optical fiber based interferometer. Observing the deflection of the cantilever spring when the sphere is in contact with the sample, one can then assess the mechanical properties of the sample. The instrument allows one to gather maps of the local viscoelastic properties of materials with (sub)micron resolution without causing any damage to the indented point.Over the last couple of years, some of us have introduced a new indentation instrument that, in the field of life sciences, is nowadays recognized as a bridging tool between classical mechanical investigation methods and nanoindentation15.The optomechanical device proposed to carry out these specific measurements also guarantees more accurate measurements. The depth-controlled indentation profile allows more precise analysis and accurate dynamic mechanical analysis (DMA) at constant indentation depth, providing better estimation of both elastic and viscous moduli of the materialth-century painting, and was meant to illustrate the mapping capability of the instrument. From the results reported, one can conclude that our nanoindentation instrument truly represents a unique tool for cultural heritage studies.The aim of this paper is to demonstrate that this very same instrument can be used to successfully map the mechanical properties of painting samples. To achieve this goal, we present here two sets of measurements. The first set was performed on laboratory reconstructions, where we could test whether the instrument can perform well-controlled, reproducible analyses to assess the (non-linear) viscoelastic properties of the samples. The second set was carried out on a cross-section of a sample from a 1723. It is thus expected that an instrument that has been designed to work on biological tissues may need significant adjustments before it can be used on paintings. To address this issue, we have conducted a series of experiments on mock-ups that mimic a stratigraphy typically found in Netherlandish 17th-century paintings, limiting it to the ground layers build-up. It should be noted that this is mainly intended as an historically informed mock-up of just the ground layers, which however is sufficient for our test.Oil based paints are much stiffer than biological tissuesTo set up the samples, we prepared a stretched canvas with a size layer of rabbit skin glue in water. This was followed by a layer consisting of chalk  and a red earth pigment (iron oxide), mixed with raw linseed oil, resulting in a reddish brown ground layer. Then, a second grey ground layer made up of lead white, chalk and small amounts of yellow ochre, umber and ivory black in raw linseed oil, was applied. This ground layer system mimics an often found build-up of a double ground comprising a red layer followed by a grey layer Fig. . Each lath-century painting by Jan Baptiste Weenix, the Portrait of Silvester van Tongeren, , from the Rijksmuseum collection  to expose a cross-section of the paint stratigraphy and provide a smooth and flat surface , we carried out depth-controlled dynamic indentation measurements (DMA) to evaluate the frequency-dependent storage μm.At both the indentation depths ncy Fig. . The freTo validate our method, we repeated the measurements indenting the sample from the side as well Fig. . The resHaving access to the sample from the side, we further measured the viscoelastic properties of the red ground layer and of the sized canvas. At und Fig. , and \do24 (see Methods section). This method is relatively fast and provides the instantaneous elastic modulus. Figure To map the mechanical properties of the 23, seems to confirm the substantial impact of natural aging on the elastic behaviour of historical paintings. Pigments-oils systems’ evolution over centuries implies a stiffening of all the layers.It is further evident that the elastic moduli measured on this sample are much larger than those measured on the mock-ups. This result, which has been already observed by othersFinally, it is important to stress that our indentation protocol does not induce any damage to the sample. Figure 27.The nanoindentation protocol developed in this study allows the evaluation of the mechanical behaviour of laboratory paint reconstructions and historical oil paintings. The protocol defined for each type of sample guarantees a constant indentation depth and indentation speed along the measurements, and allows dynamic analysis of the mechanical properties of the laboratory reconstructions. This methodology provides better stability during the analyses and thus more accurate results than those obtained with piezo-control atomic force microscopy experiments. The indentation depths proposed in the protocols maintain the deformation fields within the boundaries necessary to apply for the theories consideredDepth-controlled indentation profile quantifies the properties of the paint reconstruction stratigraphy. The laboratory reconstructions, comprising a lead white containing layer and a layer with earth pigments applied on a sized canvas, mimick a traditional The adapted methodology supports the study of the overall structure of the paint or the reconstruction. Thanks to the investigation on the surface layer, the underneath layers and the sized canvas, this protocol enables a broader evaluation of the behaviour of each individual layer, especially under environmental variations, and provides data on the mismatch in the elastic behaviour, which can lead to cracks and delamination of the painting.It should also be noted that the results are obtained under a specific protocol, that combines specific approach speed, indentation depth and frequency sweep. Because of the highly non-linear behaviour of the material, a comparison of the values measured with other settings has to be handled carefully. It is important to recognize that this is not a limitation of the instrument, but is due to the intrinsic nature of the sample. Actually, the measurements reported above demonstrate that the instrument is capable of detecting non-linear behaviours that are often neglected in the literature.Portrait of Silvester van Tongeren by Jan Baptiste Weenix (Rijksmuseum). The elasticity mapping at 0.15 To demonstrate the feasibility of the measurement on historical paintings, we adapted a specific depth-controlled indentation protocol to map the cross-section of a sample from the We believe that this study represents a significant step forward in the field of cultural heritage research, as it paves the way for more accurate, non-destructive laboratory analyses of the viscoelastic properties of historical paintings. In the longer term, it may be even possible to mount the instrument on a robotic arm to allow in situ investigations.28 (see Fig. Nanoindentation is a local contact method used to quantify the mechanical behaviour of a material. Using a tip with a known geometry, one can apply a deformation while controlling the load or the penetration depth within the sample. In the instrument presented here, the load is brought via a borosilicate sphere glued to the hanging end of a cantilever spring, whose deflection is monitored by means of an optical fiber Fabry-Pérot interferometer, as already amply documented in the literaturesee Fig. . A camerTo adjust the indentation protocol to the much higher stiffness of the indented samples, we modified the geometry of the cantilever spring to obtain a much higher spring constant 29. The sphere used as non-destructive tip on these cultural heritage objects were respectively 35 The stiffness of each probe was measured applying the calibration methodology described inrs Figs. .To characterize the material’s behaviour, we could resort to either a static indentation protocol or to a dynamic analysis. For the latter, after a loading at controlled depth and speed, and a relaxation period, small oscillations are applied along a frequency sweep. If present, the phase lag between the load and the deformation illustrates the amount of energy dissipated. Such dynamic analysis highlights the viscoelastic behaviour and provides the storage Indentation measurements were performed in a room under controlled conditions at fixed temperature T = 20 °C and fixed relative humidity RH = 50%. To investigate the mechanical behaviour of paintings cross-sections and reconstructions through the most adequate protocol, different indentation profiles were tested.The evaluation of the viscoelastic properties of the mock-ups was performed via a depth-controlled dynamic analysis. After touching the surface at an approach speed of The oscillations at an A = 0.05 These dynamic analyses were first performed on the outmost surface of the reconstruction, the grey layer Fig. , and repth-century paintings23, the oscillations required for dynamic analysis on the cross-section surface were not achievable. We adapted our protocol to harvest a depth-controlled static indentation profile, and evaluate the properties through the Hertz model24.As expected because of the high stiffness of the 17In this protocol, a 2 seconds loading up to


One of the materials that is used widely for wind turbine blade manufacturing are fiber-reinforced composites. Although glass fiber reinforcement is the most used in wind turbine blades, the use of carbon fiber allows larger blades to be manufactured due to their better mechanical characteristics. Some turbine manufacturers are using carbon fiber in the most critical parts of the blade design. The larger rotors are exposed to complex loading conditions in service. One of the most relevant structures on a wind turbine blade is the spar cap. It is usually manufactured by means of unidirectional laminates, and one of its major failures is the delamination. The determination of material features that influence delamination initiation and advance by appropriate testing is a fundamental topic for the study of composite delamination. The fracture behavior is studied across coupons of carbon fiber reinforcement epoxy laminates. Fifteen different test conditions have been analyzed. Fracture surfaces for different mode ratios have been explored using optical microscope and scanning electron microscope. Experimental results shown in the paper for critical fracture parameters agree with the theoretically expected values. Therefore, this experimental procedure is suitable for wind turbine blade material characterizing at the initial coupon-scale research level. Wind energy generation is a fundamental issue within energy production in order to reduce fossil fuel necessity. In the last years, the number and size of the wind energy farms have increased. For instance, in the European Union (EU), wind based production is expected to be over 200 GW and become the largest renewable source of energy . The devOptimum features of materials suitable for wind turbines are: high stiffness, low weight and their ability to withstand fatigue damage. Composite materials are usually designed to have these properties. The characteristics of the composite material of blades often establish the performance and lifetime of the wind turbine. Rotor blades are often made from different subcomponents of fiber-reinforced composites linked together . Blades Regarding the manufacturing process, using prepregs instead of resin infusion has the advantage of giving better composite material properties and, again, the disadvantage of the higher cost. However, it is a technological step for the mass reduction of the blades when manufacturing bigger blades, as is shown in Delamination between layers is one of the principal causes of many problems of structures made by composite material, among others, wind turbine blades . SeparatDelamination in a skin-stiffener intersection was investigated by Mandell et al.  for the The development of new composite blades should involve an interaction between materials, the manufacturing process and structural design.Regarding materials’ development, some key issues include improvement of material properties or better understanding of material behavior. Experimental tests can be carried out on different scales to determine relevant material properties and to assess the numerical models used to simulate loading effects. In In order to provide a better description of the materials’ properties, better material models and testing methods are needed .Ic obtained from a DCB test, they determined the modification factor that should be applied to the stresses of the matrix layer. The way to predict delamination in the adjacent lamina is to analyze whether a tensile or shear failure occurs in the secondary layer, that is to say, the matrix-rich layer: if there is a failure, then delamination will occur. Giannis et al. The specimens were cut by means of a diamond disc saw. The nominal dimensions of the specimens were 3 mm thickness, 15 mm width and 250 mm length, respectively. Tests were performed on an MTS-Insight 100 electromechanical testing machine , see fE is the flexural modulus and LT’G is the out of plane shear modulus. The velocity of the load application point is not always the same. It has been calculated in order to get a constant displacement rate of 0.01 min−1, which was the one proposed in the standard ISO 14125 [−1 could be obtained.Before starting fracture tests, it is necessary to determine the elastic moduli of each sample. They were determined based on a procedure proposed by Mujika . These fSO 14125 . The velSO 14125 . ExpressEvery specimen had to be prepared propagating the artificial initial crack around 5 mm. This crack propagation was performed in Mode-II in the ENF test configuration in order to avoid the effect of the resin-rich area.IG and IIG. These parameters are the roller position, the roller radius and the initial crack length. Based on this fact, ai-Rj-ck is the nomenclature that has been followed in this work being ai the initial crack length; Rj the radius of the roller; and ck the position of the roller. Once these three parameters were defined, the roller is collocated in the proper position and the specimen was collocated in the rig, as is shown in Provided that the specimen geometry and the material are defined previously, three parameters can be modified in the ENFR test configuration in order to get different contribution of As it is shown in In order to get the fracture parameters, data reduction procedure is explained in the flow chart of specC is the experimental compliance of the specimen, sistC is the system compliance including the stiffness of the load application chain and expδ the displacement measured by the test machine. The system compliance has been calculated in a previous test, and the value obtained was sistC = 1/24,000 mm/N.As shown in a that fulfils that theoretical compliance given in Equation (2) is equal to the experimental compliance of the specimen given in Equation (10). Thereupon, the crack length is determined at each point of the test where load and displacement are measured, without any optical device [The determination of the crack length is performed by means of an iterative process using MATLAB software (R2020b), seeking for the value of l device .a, the value of the load measured in the test machine and the rest of the already known parameters in Equation (4), the ERR corresponding to each mode of fracture, IG and IIG, are obtained at every point of the crack propagation where load and displacement have been measured. The next step is to verify that the linear criterion of Equation (6) is met in order to obtain the critical values of the energy release rates, and hence the equivalent energy release rate presented in Equation (8).Following the flow diagram shown in IG and IIG, or the mode-mixity, is called the mode ratio in this study is taken as II/GG, where G is the total energy release rate and in this case was G = IG + IIG.The relation between b = 15 mm, span 2L = 120 mm and thickness 2h = 3 mm. The initial mode ratio analyzed in this work is between 65% and 75% approximately, with a number of different testing conditions. All of the test conditions are summarized in The nominal dimensions of the test are width ICG, IICG and eqcG. Fracture toughness for Mode-I and Mode-II, that is, the values of ICG and IICG are obtained after fitting the results of all the test to the linear failure criterion of Equation (6). The mean value and the standard deviation obtained are:As it is shown in 2, gives the quality of the linear regression [ICG and IICG mentioned above. The black dots are all the experimental data of the fifteen test conditions presented in These values agree with the ones obtained in pure mode tests ,51 publigression  and the ICG = 273 (±32) J/m2 and IICG= 1177 (±179) J/m2 in Equation (8), the critical value of the theoretical equivalent energy release rate was eqcG = 567 (J/m2).Substituting the values of eqG must be assessed. According to the mixed-mode fracture crack propagation condition from Equation (7), if the experimental value of the equivalent ERR tends to a constant value during crack propagation, that value can be considered the critical value of eqG, thus, it can be considered a material property, i.e., the mixed-mode fracture toughness. In eqG for all tests are depicted. The line in blue represents the theoretical value of eqcG = 567 (J/m2).Since the linear criterion is suitable for representing the mixed-mode fracture of the material of this work on the ENFR test configuration, eqG present a plateau. Furthermore, the mean value of all the data from a crack advance of Δa = 0.5 mm was 568 ± 19 J/m2. The relative error between that mean value and the theoretical value of eqcG was less than 1%. Consequently, the equivalent energy release rate approach can be considered suitable to represent the fracture criterion for the material studied, and the critical value can be considered a material property.As it can be seen in Besides, microstructural observation of the fracture surfaces was carried out by optical microscopy. The surface morphology was examined at the nanoscale using an scanning electron microscopy. Prior to examination, all the samples were cleaned with ethanol to eliminate impurities such as dust. Then in order to improve the conductivity by the electrons absorbed during the SEM observation, a thin layer of gold was applied to the fracture surfaces. Four different fracture types have been examined. In In In Micrographs of the same row are taken at the same magnification. Micrographs of the same column correspond to the same type of surface.As it can be seen in eqcG with one simple mixed-mode test configuration, provided that the linear criterion is fulfilled. The fracture surfaces have been explored using optical microscopy and scanning electron microscopy finding different features depending on the fracture mode mixity. Therefore, at the coupon testing level and with the aim of characterizing unidirectional composite laminates of wind turbine, this procedure can be considered as an alternative.Wind turbine blades are usually manufactured from fiber-reinforced composites. The trustworthy determination of composites improves the efficiency of wind turbines. Fracture damage in composite materials may drastically reduce the component performance. A mixed-mode test configuration, the End Notched Flexure test with Roller (ENFR), was applied for fracture mechanics characterization of composites. The equivalent energy release rate was assessed during crack propagation. The experimental data obtained agreed with the theoretical value, being the method valid for characterizing mixed-mode fracture. The analyzed delamination test can be used for obtaining the value of


Healthy brain function is marked by neuronal network dynamics at or near the critical phase, which separates regimes of instability and stasis. A failure to remain at this critical point can lead to neurological disorders such as epilepsy, which is associated with pathological synchronization of neuronal oscillations. Using full Hodgkin-Huxley (HH) simulations on a Small-World Network, we are able to generate synthetic electroencephalogram (EEG) signals with intervals corresponding to seizure  or non-seizure  states that can occur based on the hyperexcitability of the artificial neurons and the strength and topology of the synaptic connections between them. These interictal simulations can be further classified into scale-free critical phases and disjoint subcritical exponential phases. By changing the HH parameters, we can model seizures due to a variety of causes, including traumatic brain injury (TBI), congenital channelopathies, and idiopathic etiologies, as well as the effects of anticonvulsant drugs. The results of this work may be used to help identify parameters from actual patient EEG or electrocorticographic (ECoG) data associated with ictogenesis, as well as generating simulated data for training machine-learning seizure prediction algorithms. The human brain must remain sensitive to new stimuli and coordinate spatially distant information processing modules to function optimally in a continuously changing environment. To accomplish this, the brain needs to dynamically operate at or near a critical state  diseases  or non-seizure  states that can occur based on the hyperexcitability of the artificial neurons and the strength and topology of the synaptic connections between them. By generating this synthetic data, we aim to train machine learning (ML) algorithms for predicting seizures in patients with epilepsy. Due to the difficulty in acquiring high-quality patient data, and the relative rarity of seizures events compared with interictal intervals, the ability to generate synthetic data may alleviate an important bottleneck in seizure prediction methods   1.0 and 2.0 mathematical models. THINKER version 1.0 simulations were instantiated in + activation, K+ activation, and Na+ inactivation, respectively. The term Iinject represents incoming synaptic stimuli from connected neurons, and C is the membrane capacitance , critical , and supercritical . The model biophysical parameter whose variation determines in which state the system exists is One of the traditional criticisms of ML, including deep learning neural networks (DLNNs), has been that the trained systems appear to be “black boxes” for which it is not easy to understand how they are making decisions. The recent development of topological data analysis (TDA)  to seizure  states. These simulations help provide a better understanding of the ways network topology, synaptic strength, and neuron excitability influence both healthy brain function and pathological states such as epilepsy. A primary biomarker of the seizure state is a spike in either the power spectral density of an averaged signal like patient ECoG measurements, or the histogram of the number of simultaneously firing neurons in the highly spatially resolved simulation data. In addition, during the healthy intervals marked by activity at or near the critical point, the simulations reproduce power-law behavior seen in patient data. This project also makes more visible the distinct brain phases observed in actual patients. The next steps are obtaining ECoG recordings from patients with temporal lobe epilepsy who underwent presurgical evaluation for temporal lobectomy. This will allow us to refine and validate the insights from the models, especially important given the scarcity of actual patient ECoG data. The synthetic data generated by the model can also be used to train future machine-learning algorithms to assess the real-time risk of seizure onset.The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.LN created and performed the simulations and wrote portions of the manuscript. GC conceived the project and wrote portions of the manuscript. RW worked on the neuroscience aspects and wrote portions of the manuscript. FM and VC worked on the mathematical theory. AP worked on the physiological aspects and edited the manuscript. JL cowrote the introduction and edited the manuscript. All authors contributed to the article and approved the submitted version.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.


Studies involving turbulent flow have been carried out in many parts of the cardiovascular system, and it has been widely reported that turbulence related to stenosis (narrowing) of arteries creates audible sounds, which may be analyzed to yield information about the nature and severity of the blockage. Results so far indicate that the high frequency content of the sounds generally increases with the degree of stenosis. In this paper, we designed and built an MEMs microphone array and a signal acquisition board to improve the detection of coronary occlusions using an approach based on the recording and analysis of isolated diastolic heart sounds associated with turbulent blood flow in occluded coronary arteries. The nonlinear dynamic analysis method based on approximate entropy has been proposed for the analysis of diastolic heart sounds from patients with single coronary occlusions, before and after stent placement procedures. The nonlinear dynamic analysis (approximate entropy) measures of the diastolic heart sounds recorded from eight patients with single coronary occlusions and two normal subjects were estimated. In addition, a spectral analysis based on the fast Fourier transform was used to estimate the energy content of the recorded signals. Results suggest the presence of high nonlinear (approximate entropy) values of diastolic heart sounds associated with coronary artery disease ( The goal of this research is to detect coronary occlusions using a noninvasive, passive, quick and inexpensive approach that could eventually be implemented as part of the standard medical exam. To improve the quality of the heart sound recordings associated with coronary occlusions, a novel MEMs microphone array platform was designed and used to record diastolic heart sounds from patients with coronary occlusions undergoing a coronary stent placement procedure. Results suggest the presence of more high frequency energy above 150Hz and high complexity values in diastolic heart sound signals of patients with coronary occlusions and significant decrease of these values after stent placement. I.An estimated seven million Americans suffer from coronary artery disease (CAD), which causes more than half a million deaths annually and may cost more than $100 billion each year. For this reason, early detection of CAD is one of the most important research areas. Direct assessment of the coronary occlusion is usually done with cardiac catheterization and coronary angiography, followed by treatment using percutaneous coronary intervention (PCI) In many cases, a stent was placed in the artery to keep the vessel open after angioplasty Soon after the introduction of bare metal stents, drug eluting stents were approved by the FDA to reduce the occurrence of restenosis in the artery and decrease the risk of sub-acute thrombosis and latent sub-acute thrombosis, which can occur up to one year after the procedure Non-invasive and lower risk modalities with varying degrees of accuracy and precision that have been proposed for diagnosis and risk stratification of CAD, such as coronary CT angiography, nuclear imaging and cardiac MRI, are still costly and associated with some risk. A.Initial studies showed that coronary arterial stenosis might give rise to diastolic murmurs In one of our previous studies, we investigated the effect of femoral artery stenosis on the turbulent sound generation mechanisms. We simulated an occluded artery by using a Teflon bead, which, after insertion into the femoral artery of a dog, created a reasonable simulation of sound generation in human coronary arteries In addition to the in vitro testing, Wang et al. In another previous study, we investigated the diagnostic capability of the acoustic approach in detecting CAD, and recorded heart sounds of 23 angioplasty patients before and after angioplastic surgery. Results from this angioplasty study showed that pre- and post-angioplasty records were correctly distinguished in 21 out of 23 cases Ye et al used the combination of wavelet transform and neural network methods to analyze the heart sounds recorded from 30 normal subjects and 30 subjects with coronary artery occlusions In addition to the previous angioplasty and normal CAD studies, we recently introduced the nonlinear dynamic analysis method based on the approximate entropy and fractal estimators for the analysis of diastolic heart sounds associated with coronary occlusion In our previous studies, we used one sensor (accelerometer) or the commercially available e- stethoscope to detect the acoustical signals associated coronary occlusions. In this study, we designed an auscultation system based on a compact, ultra-low noise MEMS microphone array to improve the signal-to-noise ratio (SNR) and reduce electromagnetic interference (EMI). Microphone designs based on MEMS technology have become increasingly popular in the past two decades, with various applications in aerospace and military industry, as well as speech recognition II.A.Subjects were recruited from a set of patients undergoing angioplasty surgery at the DeBakey VA Medical Center hospital. The DeBakey VA Hospital R&D Committee and Baylor College of Medicine IRB approved the study. Study staff members who had completed the human subject protection educational requirements in compliance with all Federal regulations conducted informed consent negotiations. Prospective subjects were interviewed to determine preliminary eligibility. Informed consent was obtained and subjects were enrolled in the study prior to any clinical testing, laboratory testing or intervention. Subjects were given a copy of the IRB approved consent form during the initial interview, and study staff explained to the subjects, in detail, the nature of the informed consent process, study purpose and procedures, time commitments, risks, potential benefits, treatment alternatives, rights as research participants, study staff contact information, confidentiality procedures, and arrangements for medical care provided in case of injury during the study. Subjects were given adequate time to consider their decision and encouraged to ask questions, both during the initial interview and throughout the study. Subjects were provided with a signed copy of the completed consent form.Eight patients with coronary artery disease, as determined by coronary angiography, were screened for the study.B.Patients were screened and tested at the Michael E. DeBakey Houston VA Hospital in collaboration with the Winter Center for Cardiology Research of the Baylor College of Medicine. The inclusion criteria for study patients were as follows: Body mass index (BMI) less than 30, single lesion CAD, and patient consent for the procedure.Patients were not enrolled in the study if they had one or more of the following exclusion criteria: heart valve disease, multi-vessel CAD and implanted pacemaker or defibrillator. We enrolled patients with a low BMI in order to minimize the amount of fatty tissue between the heart and the electronic stethoscope. The fatty tissue could muffle and attenuate the sounds in the recording. We excluded patients with valve disease, as this can disrupt the duration and magnitude of the S1 and S2 heart sounds. Leaky valves could also allow for regurgitation, which would cause high frequency noise in the diastolic window and interfere with our analysis of coronary artery sounds. Similarly, implanted pacemakers and defibrillators create noise, which would be difficult to eliminate from recordings.C.We built a compact MEMS microphone array to improve the signal-to-noise ratio (SNR) and reduce electromagnetic interference (EMI). This new system consisted of several modules, including the front-end sensor board (microphone array), the signal-processing unit for digital data acquisition and transfer, along with the interface to microphone array and the USB module for connection to a PC. There are several critical technical features in building the new system, including the design and integration of the front-end microphone array with high SNR, the multi-channel data acquisition and transfer and the design of the signal-processing unit and system integration.We have designed different configurations for the microphone array using digital microphones, such as several microphones placed in a line, circle, or rectangle. The digital microphone offers high SNR, flat frequency response and digital output with low power consumption and affordability. Our preliminary studies and lab tests showed that even two microphones improve the recording system performance, compared to that of a single microphone. The signal-processing unit handles data acquisition and transfer. The digital signal coming out of the microphone is received and rearranged by the signal-processing unit, then transferred to a PC through the USB (A Field Programmable Gate Array (FPGA) is used for the signal-processing unit design because of its programmability for multi-channel signal processing.Digital data is transferred to a PC through the USB. The interface to the USB module is designed inside the FPGA. For portable consideration, a wireless module is under design using Wi-Fi for wireless data transfer. Our next version of the system will also integrate the wireless module. D.After finalizing our system, consisting of the microphone array unit and the signal-processing unit, we used the The array was placed at fourth intercostal space, 6–8 cm to the right of the midline of the sternum , top andE.Raw 4-channel recordings were subsequently beamformed into a single signal using conventional time-delay beamforming, which is essentially a spatial filtering technique Briefly, considering an array of o and SNRi are the signal-to-noise ratios at the output and input of the beamformer. SNRi was estimated as:i the 4-channel powers are averaged into a single value. SNRo is computed in a similar manner, using instead the beamformed signal to estimate the signal and noise powers, respectively.SNR enhancement performance was evaluated by means of a gain measure computed as:F.Having the second heart sound as a time reference, the diastolic heart sounds associated with coronary occlusions were preprocessed and 128 msec long segments located 100 msec after the second heart sound (S2) were isolated from the beamformed signal. The first (S1) and the second (S2) heart sound signals are clearly identified, as well as the diastolic and systolic segments. The recorded segments selected for analysis avoid the trailing edge of the second heart sound and the expected leading edge of the succeeding first heart sound, and coincide with the maximum coronary blood flow All recordings were sampled at a rate of 4 kHz. Each isolated diastolic segment was initially normalized with respect to its mean energy value in order to account for sound attenuation effects due to physical differences between patients, such as chest mass and size. Isolated segments were then bandpass filtered between 65 and 500 Hz in order to reduce noise and because the amount of power above 500 Hz was negligible. The bandpass filter used was a Butterworth filter of order 5. Subsequently, segments were analyzed using the approximate entropy method and FFT-based spectral analysis.G.The approximate entropy (ApEn) is a nonlinear measure quantifying the regularity of a time-series. ApEn is particularly efficient in the case of short data segments and is less sensitive to noise and outliers than other regularity statistics m, remain close in the next incremental comparisons. A higher likelihood for these segments of remaining close within the threshold produces smaller ApEn values, indicating a higher level of regularity for the signal.It characterizes a time series signal into a non-negative number, with higher ApEn values corresponding to more random signals, which generally reflect more complex generating systems. Basically, ApEn measures the logarithmic likelihood that runs of temporal patterns that are close within a certain threshold, In order to estimate approximate entropy values segments For any given The approximate entropy, ApEn from pre-stent to post-stent, there was also an increase in the low frequency energy (below 150Hz) in seven of the eight patients (except patient #2).This increase in low frequency is most likely attributed to the improvement in heart function after stent placement. When blood flow is restored to the coronary artery, oxygen is again brought to the ischemic area of the heart. The heart muscle can then contribute to the contraction of the heart during the cardiac cycle, increasing the ejection fraction of the blood and therefore increasing the pressure on the valves when closing. The closing sounds may then become stronger, adding low frequency noise to the heart sound recording. All power ratio values were averaged across patients to give an average pre-stent ratio and an average post-stent ratio value , showed considerable promise, further improvements are needed for a reliable mass-screening procedure for the detection of coronary occlusions.In this study, we used spectral analysis and a nonlinear dynamic analysis method to quantify and characterize the turbulent sounds associated with single coronary occlusions.Overall, our results furthermore confirm the previous findings de novo stenotic coronary lesions.This study has encouraged use to further develop and scale our platform for future longitudinal studies monitoring single or multiple in-stent restenosis as a low-cost and reliable surrogate for current imaging diagnostics preceding percutaneous coronary intervention. Our acoustical approach could be a low-cost noninvasive method to assess restenosis and/or development of We plan to increase the patient enrollment in the next study. This study enrolled eight patients who underwent stent placement procedures with single occlusions, which is adequate for a preliminary efficacy study, despite the small sample size. For more robust results, future studies will include more patients, thus strengthening the statistics. Our first challenge was to find patients with only single coronary artery occlusions, as most patients with established coronary disease in our screening pool had multivessel disease. The second challenge was to have patients without any other cardiac disease. These two criteria limited the enrollment in our study.For each subject, we would like to collect more recordings to increase the sample size for each subject; instead of simply 10 cardiac cycles for analysis, we could use 20 or 30 cycles. Additionally, we want to improve the recording quality, possibly by reducing the noise in the recording room. This would require patient isolation in a room with little to no electromagnetic interference.Furthermore, implementation of a multichannel recording system would not only provide more data about the acoustic signature, it might also be used for ascertaining the location of the lesion. The beamforming technique can be successfully used to estimate the direction of arrival, as well as to localize the source of the heart sound (stenosis) when it is not known Finally, we plan to automate the recording analysis for clinical use. Instead of visually inspecting the signal and choosing the best sections by hand, we would create a program to perform these functions and calibrate it in another clinical study. Once the CAD acoustic signature – the power ratio – threshold has been optimized, the system could easily be implemented in a clinical setting, providing a simple, inexpensive and accurate screening tool for CAD.


Point cloud registration is a key problem in computer vision applications and involves finding a rigid transform from a point cloud into another such that they align together. The iterative closest point (ICP) method is a simple and effective solution that converges to a local optimum. However, despite the fact that point cloud registration or alignment is addressed in learning-based methods, such as PointNetLK, they do not offer good generalizability for point clouds. In this stud, we proposed a learning-based approach that addressed existing problems, such as finding local optima for ICP and achieving minimum generalizability. The proposed model consisted of three main parts: an encoding network, an auxiliary module that weighed the contribution of each input point cloud, and feature alignment to achieve the final transform. The proposed architecture offered greater generalization among the categories. Experiments were performed on ModelNet40 with different configurations and the results indicated that the proposed approach significantly outperformed the state-of-the-art point cloud alignment methods. Point clouds are collections of points in 3D space  that repPoint cloud registration or alignment is a fundamental process for numerous applications including robotics , autonomThe iterative closest point (ICP)  has beenIn this work, we introduce a new framework designed to solve a class of registration problems. Like ICP, this method was designed iteratively, finding a misalignment estimate. The Alignment Weight Estimation Network (Awe-Net) is a new component for our framework that includes a weight score and orientation estimator to identify the contribution of each point cloud to the final misalignment estimation using the weight scores. Furthermore, it assisted the optimization using only the 1D orientation angle. This framework provided greater generalizability and faster convergence for the correct transform estimate. This approach mainly consisted of two components: one extracted global features and the other assisted in network optimization. Compared to classical approaches based on handcrafted features to understand 3D data, the proposed approach aims to learn the global 3D features, with the model trained to estimate the transform between the target point cloud and source point cloud. The proposed model was trained to understand the point cloud based on prior knowledge of the shape formed by the point cloud and was able to output the desired registration transform. This was achieved by robustness to noise and also by producing an estimate correct transform between the source point cloud and the required target template. Therefore, a different learning paradigm is created that consisted of extracting point cloud global features, aligning the features with the Lucas–Kanade (LK) algorithm , weighin(1)A new learning paradigm was proposed for point cloud alignment, which weighed the contribution of each of the point clouds by extract global features. (2)An Awe-Net module was proposed to obtain the estimate transform using the aligned global features. Not only does the Awe-Net output the weight scores but also the orientation of the input point cloud.(3)The proposed model offered higher generalizability to shapes unseen during training by obtaining accurate global features.(4)The proposed network was fully able to boost the benchmark for point alignment, exhibiting the least estimation errors among other methods. It demonstrated the ability to learn the features between the target and source point cloud by using the features produced by Awe-Net.The main contributions can be summarized as follows.The rest of the paper is organized as follows: Related works are discussed in Current registration methods can be classified into two groups: those dealing with coarse registration and those dealing with fine registration. Coarse registration methods do not consider any prior assumptions of the point cloud pose. However, fine registration or alignment algorithms assume that the input clouds are partially aligned. Hence, they use an initial proximity between the points to tweak the alignment between the two different coordinate systems.There exists a variety of methods for local point cloud alignment, and high-end solutions are now available for applications such as SLAM , which rThere are works in literature that estimated interest points to assist with registration, i.e., scale invariant curvature descriptors , orienteRecently, deep learning has achieved remarkable progress on point cloud registration. PointNet  is the rIn this paper, we proposed a new learning approach that consisted of PointNet to extract global features and the LK algorithm was proposed in PointNetLK to align the features. Generally, this approach relies on extracted global features and the proposed Awe-Net module outputs to weigh the contribution of each point cloud to the final estimate transform during the alignment process. Our network consisted of global-features-extracting-network where we referred to PointNet and we used the LK algorithm for the point cloud alignment. As these are existing works and limited to global feature extracting, we proposed Awe-Net module outputs to weigh the contribution of each point cloud to the final estimate transform. Generally, this approach relies on extracted global features and the proposed Awe-Net module outputs to weigh the contribution of each point cloud to the final estimate transform during the alignment process. Thus, one contribution was a new Awe-Net component, which included a weight score and orientation estimator to identify the contribution of each point cloud to the final misalignment estimation using the weight scores. Predicting the orientation and the point cloud weights implicitly to the final output of the network allowed the network to converge in less iterations.Global features extraction was required since we dealt with the global point cloud alignment. However, due to a lack of inherent structure of the point cloud, deep learning architectures could not directly handle the point cloud. To address this representation of the point cloud, the PointNet network was utilized as an encoding function.G such that Aoki et al.  proposedmulation .(2)ϕPS=The Jacobian is denoted as where Equation (3) becomes:The Awe-Net architecture module was proposed to obtain the estimate transform using the procedure described in the feature’s extraction and alignment procedure. This module was the MLP-based network that learned important weights to evaluate the contribution of each input, which regularized A block diagram of the architecture is presented as in We only predicted a 1D rotation angle This section introduces our proposed architecture. A diagram of the architecture is presented in itecture  followedIn φS and the template φT should both be equal, which means that for each iteration, the orientation φS tends to converge to φT.Meanwhile, the orientations of the source The network was presented through an iterative scheme. In addition, introducing the iterations empirically allowed the use of lesser hidden layers in Awe-Net. Using the proposed loss function, the model could achieve comparable results with less parameters, since the iterations guarantee continuous update of the parameters of the model instead of one-shot model which will require more distinctive features. The model was not pretrained on the classification that helped distinguish among categories, requiring more iterations to converge.The algorithm consisted of a looping computation of the optimized twist parameters (6).After performing n iterations, the overall transformation between the original source and template point clouds was obtained by combining all transforms in each iteration:The convergence criteria were also usedThe objective of the loss function is to minimize the distance between the corresponding points in the source and template point cloud as well as the error between ce (EMD)  was usedce (EMD)  or the Lce (EMD) . The L1 In this section, we introduce the dataset of 3D models used for training and testing. ModelNet  is one oThe models in the original ModelNet40 are not aligned and have widely different scales. Therefore, when processing the data for neural networks, all models require to be scaled to fit a unit sphere. The categories in the dataset are not equally populated. For instance, there are over 700 airplane models and only over 100 wardrobe models. ModelNet40 contains files in the off format. Therefore, preprocessing is required to generate the point clouds from the meshes and sub-sample them to feed the neural network.In this paper, various training combinations were performed using the training data and the test data. The results were then compared to those of PointNetLK as the baseline and with the ICP algorithm. The networks were trained in three different scenarios: (1) Training and testing on fully visible data, (2) training and testing on partially visible data, and (3) training and testing with additive noise. For the proposed method and other PointNetLK-based approaches, a maximum of 20 iterations were allowed when performing tests, while the maximum iterations for ICP were 100. Experiment 1: In the first experiment, the proposed model and PointNetLK were trained on 20,175 different data in ModelNet40, then tested on the test set for the same 20 categories. There was no noise in the source data during training and testing.The standard version of PointNet for classification was trained first using ModelNet40. Therefore, the feature extractor Experiment 2: To test the generalizability of the proposed model, we repeated experiment 1, yet the training in this experiment was done on the other 20 categories of ModelNet40. The test was performed on 20 categories in ModelNet40, which were in the same categories as Experiment 1. The proposed model was able to generalize much more precisely than PointNetLK and ICP for alignment on object categories that were not seen in the training. Our method in Experiment 1 and Experiment 2 produced better results compared to others. Mean rotational error at the left graph shows that our proposed model obtained less errors compared to the existing state-of-the-art methods, such as ICP, PointNetLK, and PointNetLK-LUT. Mean translational error at the right graph also exhibits the comparison results with ICP, PointNetLK, and PointNetLK-LUT, obtaining less error. Moreover, when we applied Awe-Net to PointNetLK, the errors were greatly reduced.In both experiments, all approaches produced lower errors from angle 0 to 50 degrees, but the errors rose rapidly afterward. However, our approach remained the lowest one. Our model trained only 10 iterations, yet it was sufficient due to its consistent results in every angle of the range from 0 to 90 degrees.In a real-world scenario, the template used is commonly a 3D model and the sources are taken from the scanner. To reproduce the same environment in the real world, sampling visible points is typically based on simulating a 3D sensor that has a horizontal and vertical field-of-view and a minimum and maximum depth. The sampling is done on the ModelNet40 dataset following the same process conducted in the PointNetLK. The faces of the template are sampled and placed into a unit box The test on the ModelNet40 was conducted using random translation between 0, 0.3. The area under the curve (AUC) was used as the metric to evaluate the performance of the registration algorithms. Plots showing the success ratio versus success criteria on rotation error (in degrees) were generated for ICP, PointNetLK, PointNetLK-AweNet, and the proposed model. This section presented experiments conducted with additive Gaussian noise. The template point cloud was randomly sampled from faces and the source point cloud was equal to the template with additive Gaussian noise at a certain standard deviation. The first 1000 points were selected during the sampling process. The authors of PointNetLK hypothesized that the choice of the symmetric operator was critical to the performance with additive noise. PointNet used a max pool operator yield to output the global feature vector. In case of noisy data, the choice was subject to variations among the different random noise samples. Therefore, PointNetLK used average pooling when learning global features rather than the max pool operator, assuming that it would be better suited to learn global features. However, the proposed model was trained using the same symmetric operator, which meant that the max-pooling operator was used during training. The shortcoming of approaches based on hand-crafted features ,36 (learWe proposed a novel learning approach to solve the point cloud alignment problem with highly accurate registration, based on an effective auxiliary Awe-Net module that assisted with the overall network in converging to the correct estimate and learning in order to apply the contribution of each input point clouds. The proposed network was implemented in an iterative manner to obtain highly accurate transform estimates comparable to other global registration methods. The advantage of our framework was that it provided a good approach for different scenarios where prior knowledge existed of the shape formed by the point cloud and where noise was present. The Awe-Net showed its robustness to noise and initial random misalignment. It provided higher generalizability to shapes unseen during training and was fully able to boost the benchmark for point alignment. Experimental results showed the robustness of the proposed framework to noisy real-world data, partial overlap data, and fully visible data. Despite the success of this approach, there is still room for improvement since the network can only be implemented iteratively. We aim to adopt a single-shot design as well as handling occluded point clouds.