Search

Parity-time (PT) symmetry has enabled the demonstration of fascinating wave phenomena in non-Hermitian systems characterized by precisely balanced gain and loss. Until now, the exploration and observation of PT symmetry in scattering settings have largely been limited to propagating waves. Here, we demonstrate a versatile coupled-resonator acoustic waveguide (CRAW) system that enables the observation of PT-symmetric scattering responses for evanescent waves within a bandgap. By examining the generalized scattering matrix in the evanescent wave regime, we observe hallmark PT-symmetric phenomena—including phase transitions at an exceptional point, anisotropic transmission resonances, and laser-absorber modes—in systems that do not require balanced distributions of gain and loss. Owing to the peculiar energy transfer features of evanescent waves, our results not only demonstrate a distinct pathway for observing PT symmetry, but also enable strategies for exotic energy tunneling mechanisms, paving fresh directions for wave engineering grounded in non-Hermitian physics. Non-Hermitian physics and parity-time (PT) symmetry are of broad interest in classical wave systems. This work demonstrates evanescent wave manipulation and scattering control based on PT symmetry in a versatile coupled-resonator acoustic waveguide (CRAW) system, which not only extends the framework of non-Hermitian physics but also offers strategies for near-field manipulation and control. [ABSTRACT FROM AUTHOR]

Linear discriminant analysis (LDA) is a well-known supervised method that can perform dimensionality reduction and feature extraction effectively. However, traditional LDA-based methods need to be turned into the trace ratio form to compute the closed-form solution, in which the within-class scatter matrix should be nonsingular. In this article, we design a new model named generalized robust linear discriminant analysis (GRLDA) method to tackle this disadvantage and improve the robustness. GRLDA uses L 2 , 1 -norm on both loss functions to reduce the influence of outliers and on regularization term to obtain joint sparsity simultaneously. The intrinsic graph and the penalty graph are constructed to characterize the intraclass similarity and interclass separability, respectively. A novel optimization method is proposed to solve the proposed model, in which a quadratic problem on the Stiefel manifold is involved to avoid the inverse computation on a singular matrix. We also analyze the computational complexity rigorously. Finally, the experimental results on face, object, and medical images exhibit the superiority of GRLDA. [ABSTRACT FROM AUTHOR]

String theory on AdS3 × S3 × T4 geometries supported by a combination of NS-NS and R-R charges is believed to be integrable. We elucidate the kinematics and analytic structure of worldsheet excitations in mixed charge and pure NS-NS backgrounds, when expressed in momentum, Zhukovsky variables and the rapidity u which appears in the quantum spectral curve. We discuss the relations between fundamental and bound state excitations and the role of fusion in constraining and determining the S matrices of these theories. We propose a scalar dressing factor consistent with a novel u-plane periodicity and comment on its close relation to the XXZ model at roots of unity. We solve the odd part of crossing and show that our solution is consistent with fusion and reduces in the relativistic limit to dressing phases previously found in the literature. [ABSTRACT FROM AUTHOR]

Non-Hermitian optics has revealed a series of counterintuitive phenomena with profound implications for sensing, lasing, and light manipulation. While the non-Hermiticity of Hamiltonians has been intensively investigated, recent advancements in the non-Hermitian scattering matrix have given birth to a lot of unique phenomena, such as simultaneous lasing and anti-lasing, reflectionless scattering modes (RSMs), and coherent chaos control. Despite these developments, the investigation has predominantly focused on static and symmetric configurations, leaving the dynamic properties of non-Hermitian scattering in detuned systems, which is essential for applications in sensing and beyond, largely unexplored. Here, we extend the stationary behaviors associated with the RSMs to resonant detuned systems. Contrary to the common belief of exceptional point (EP) sensors as being susceptible to parametric disturbances, we induce an RSM EP in a one-dimensional optical cavity and demonstrate its robustness in displacement sensing against laser frequency drifts up to 10 MHz. Our findings not only contribute to the broader understanding of non-Hermitian scattering phenomena but also pave the way for the next generation of non-Hermitian sensors. [ABSTRACT FROM AUTHOR]

As more and more numerical and analytical solutions to the linear neutron transport equation become available, verification of the numerical results becomes increasingly important. This presentation concerns the development of another benchmark for the linear neutron transport equation in a benchmark series, each employing a different method of solution. In 1D, there are numerous ways of analytically solving the monoenergetic transport equation, such as the Wiener–Hopf method, based on the analyticity of the solution, the method of singular eigenfunctions, inversion of the Laplace and Fourier transform solutions, and analytical discrete ordinates in the limit, which is arguably one of the most straightforward, to name a few. Another potential method is the PN (Legendre polynomial order N) method, where one expands the solution in terms of full-range orthogonal Legendre polynomials, and with orthogonality and series truncation, the moments form an open set of first-order ODEs. Because of the half-range boundary conditions for incoming particles, however, full-range Legendre expansions are inaccurate near material discontinuities. For this reason, a double PN (DPN) expansion in half-range Legendre polynomials is more appropriate, where one separately expands incoming and exiting flux distributions to preserve the discontinuity at material interfaces. Here, we propose and demonstrate a new method of solution for the DPN equations for an isotropically scattering medium. In comparison to a well-established fully analytical response matrix/discrete ordinate solution (RM/DOM) benchmark using an entirely different method of solution for a non-absorbing 1 mfp thick slab with both isotropic and beam sources, the DPN algorithm achieves nearly 8- and 7-place precision, respectively. [ABSTRACT FROM AUTHOR]

Density fluctuation potential induced by a screening of the photohole scatters the photoelectron and generally causes its emission delay from the scattering matrix in the photoemission spectroscopy, where the photoemission delay usually quantifies the extrinsic loss of the photoelectron depending on the atomic orbital. Without the potential scattering, however, the photoemission from the coherent two-state mixture created by the laser driving is found to undergo the unexpected photoemission delay, which originates from the mixed photoemission matrix. Using the Haldane model, we analytically calculate such coherent mixing induced photoemission delay in an angle-resolved mode, which is found to reveal the local Berry curvature structure as long as the coherent mixing is sustained. This finding is confirmed through the streaking computation for the photoemission delay by solving the time-dependent Schrödinger equation and suggests that the photoemission delay be a new spectroscopic diagnosis of the material topology of two-dimensional semiconductors. [ABSTRACT FROM AUTHOR]

We apply subspace migration (SM) for fast identification of a small object in microwave imaging. Most research in this area is performed under the assumption that the diagonal elements of the scattering matrix can be easily measured if the transmitter and the receiver are in the same location. Unfortunately, it is very difficult to measure such elements in most real-world microwave imaging. To address this issue, several studies have been conducted with the unknown diagonal elements set to zero. In this paper, we generalize the imaging problem by using SM to set the diagonal elements of the scattering matrix to a constant. To demonstrate the applicability of SM and its dependence on the constant, we show that the imaging function of SM can be represented by an infinite series of Bessel functions of integer order, antenna number and arrangement, and the applied constant. This result allows us to discover additional properties, such as the unique determination of the object. We also demonstrated simulation results using synthetic data to back up the theoretical result. [ABSTRACT FROM AUTHOR]

Manipulating orthogonally polarized waves independently in a single metasurface is pivotal. However, independently controlling the phase shifts of orthogonally polarized waves is difficult, especially in the same frequency bands. Here, we propose a receiver-phase shift-transmitter transmitarray with independent control of arbitrary polarization states in the same frequency bands, in which transmission rates reach more than 90% in the frequency bands 4.2~4.9 GHz and 5.3~5.5 GHz. By introducing a phase-regulation structure to each element, phases covering 360 ° for different polarized incident waves can be independently controlled by different geometric parameters, and two-bit coding phases can be obtained. The design principle based on the two-port network's scattering matrix has been analyzed. To verify the independent tuning abilities of the proposed transmitarray for different polarization incidences in the same frequency bands, a multifunctional receive-phase shift-radiation coding transmitarray (RPRCT), which is composed of 16 × 16 elements, with functions of anomalous refraction (for example, orbital angular momentum wave) and focusing transmission for different polarized incident waves was simulated and measured. The measured results agree reasonably well with the simulated ones. Our findings provide a simple method for obtaining a multifunctional metasurface with orthogonal polarization in the same frequency bands, which greatly improves the capacity and spectral efficiency of communication channels. [ABSTRACT FROM AUTHOR]

New SPICE-compatible circuit models of a multiport are presented here that are suitable for the frequency-domain and time-domain analyses of hybrid systems containing linear distributed elements and possibly non-linear lumped elements. Distributed elements models are based on scattering parameters with potentially complex reference impedances, which are not necessarily equal for all ports. Both exact and approximated (lumped) models are proposed. The scattering parameters are directly taken as the model element values in the former case. In the latter case, the model element values are equal to the real and imaginary parts of the poles and residues of the rational approximation. The models comprise a multiport (with an admittance matrix numerically equal to the modeled scattering matrix or approximating it) equipped with a pair of coupled impedances at each port. A few examples validate the proposed approach and prove its efficiency in terms of matrix size and analysis time compared to some selected commercial counterparts. [ABSTRACT FROM AUTHOR]

Speckle reduction is a key preprocessing approach for the applications of Synthetic Aperture Radar (SAR) data. For many interpretation tasks, high-quality SAR images with a rich texture and structure information are useful. Therefore, a satisfactory SAR image filter should retain this information well after processing. Some quantitative assessment indicators have been presented to evaluate the edge-preservation capability of single-polarization SAR filters, among which the non-clean-reference-based (i.e., blind) ones are attractive. However, most of these indicators are derived based only on the basic fact that the speckle is a kind of multiplicative noise, and they do not take into account the detailed statistical distribution traits of SAR data, making the assessment not robust enough. Moreover, to our knowledge, there are no specific blind assessment indicators for fully Polarimetric SAR (PolSAR) filters up to now. In this paper, a blind assessment indicator based on an SAR Ratio Gradient Operator (RGO) and Confidence Interval Estimation (CIE) is proposed. The RGO is employed to quantify the edge gradient between two neighboring image patches in both the speckled and filtered data. A decision is then made as to whether the ratio gradient value in the filtered image is close to that in the unobserved clean image by considering the statistical traits of speckle and a CIE method. The proposed indicator is also extended to assess the PolSAR filters by transforming the polarimetric scattering matrix into a scalar which follows a Gamma distribution. Experiments on the simulated SAR dataset and three real-world SAR images acquired by ALOS-PALSAR, AirSAR, and TerraSAR-X validate the robustness and reliability of the proposed indicator. [ABSTRACT FROM AUTHOR]

The problem of the real-time microwave imaging of small, moving objects from a scattering matrix without diagonal elements, whose elements are measured scattering parameters, is considered herein. An imaging algorithm based on a Kirchhoff migration operated at single frequency is designed, and its mathematical structure is investigated by establishing a relationship with an infinite series of Bessel functions of integer order and antenna configuration. This is based on the application of the Born approximation to the scattering parameters of small objects. The structure explains the reason for the detection of moving objects via a designed imaging function and supplies some of its properties. To demonstrate the strengths and weaknesses of the proposed algorithm, various simulations with realdata are conducted. [ABSTRACT FROM AUTHOR]

In this paper we consider time-harmonic acoustic wave propagation in a half-plane filled by inhomogeneous periodic medium. If the refractive index depends on the horizontal coordinate only, we define upward and downward radiating modes by solving a one-dimensional Sturm-Liouville eigenvalue problem with a complex-valued periodic coefficient. The upward and downward radiation conditions are introduced based on a generalized Rayleigh series. Using the variational method, we then prove uniqueness and existence for the scattering of an incoming wave mode by a grating located between an upper and lower half plane with such inhomogeneous periodic media. The solution operator of the quasiperiodic boundary value problem yields a well-defined scattering operator, the numerical approximation of which is nothing else but the S-matrix in scattering matrix algorithms like Rigorous Coupled Wave Analysis (RCWA) or Fourier Modal Method (FMM). [ABSTRACT FROM AUTHOR]

Measuring the orientation, mass and body length of migratory insects through entomological radar is crucial for early warnings of migratory pests. The fully polarized entomological radar is an efficient device for observing migratory insects by calculating insect parameters through the scattering matrix obtained from the target. However, the measured target scattering matrix will be affected by system polarization measurement errors, leading to errors in insect parameter calculation, while the related analysis is currently relatively limited. Therefore, the scattering matrix measurement process is modeled, followed by an analysis of the effects of different errors on orientation, mass and body length estimation. The influence of polarization measurement errors on insect scattering characteristics is also analyzed. The results present that for fixed polarization measurement errors, the measurement errors of insect orientation, mass and body length will vary with insect orientation in specific patterns, and the distribution of measured insect parameters will be drastically distorted compared to the true parameter distribution. In addition, polarization measurement errors could seriously disrupt the reciprocity and bilateral symmetry of the measured insect scattering matrix. These analyses and conclusions provide a good basis for eliminating the effects of polarization measurement errors and improving the accuracy of insect parameter measurement. [ABSTRACT FROM AUTHOR]

The propagation characteristics of sub-terahertz (sub-THz) waves through the sharp-coned plasma sheath are investigated, revealing a frequency selection phenomenon. Two significant electron density gradients within the sharp-coned plasma sheath, which result in high reflection coefficients, are identified. These strong reflective interfaces divide the plasma into distinct regions, and the frequency selection mechanism is analyzed using the improved scattering matrix method. This research finds that the combination of these reflective interfaces and the intervening plasma forms a "resonator structure," leading to the observed frequency selection. A quantitative relationship between plasma parameters and the frequency selection phenomenon is analyzed. The results indicate that the reflection coefficients of the reflective interfaces increase, making the frequency selection more pronounced, when the thickness of the interfaces decreases or the peak electron density increases. In addition, a lower collision frequency leads to reduced absorption effects and a more pronounced frequency selection. The phenomenon suggests that enhancing transmissivity at lower frequencies may be feasible, providing a theoretical insight into the application of sub-THz waves in mitigating communication blackouts. [ABSTRACT FROM AUTHOR]

Most domain adaptive methods enhance the classification performance of target domain via overcoming the distribution difference between source and target domains while ignoring the nature of classifier, i.e., the data being correctly classified by classifier is due to the high separability of data. Therefore, inspired by this, we propose a simple yet effective domain adaptive method in accordance with the property of classifier, namely cross-domain Fisher discrimination criterion (CFDC). CDFC is intended to upgrade the inter-class discrimination and intra-class compactness of samples for the scenario where the target domain has few labeled samples. Specifically, we reconstruct the intra- and inter- class scatter matrices of Fisher's criterion from a geometrically intuitive perspective, enabling it to extract highly discriminative features from cross-domain samples. The reconstructed between-class scatter matrix aims to maximize the class separation of target samples, while the redefined within-class scatter matrix seeks to have samples from different domains densely clustered around the class center of target samples. Six widely used image datasets are involved to verify the effectiveness and efficiency of CFDC. Experimental results demonstrate that the performance of CFDC is significantly superior to similar methods and conventional unsupervised domain adaptation methods, comparable to non-deep semi-supervised domain adaptation methods, but with a significantly lower time consumption. Even compared with state-of-the-art deep semi-supervised domain adaptation methods, CFDC exhibits performance advantages on certain datasets. [ABSTRACT FROM AUTHOR]

We study the two-particle form-factors for the relativistic limit of the integrable S-matrix of the mixed-flux AdS3 × S3 × T4 string theory. The S-matrix theory was formally constructed in two distinct ways by two different teams. We focus on the massive theory built up by Frolov, Polvara and Sfondrini, and derive expressions for the minimal solutions to the axioms, in both integral and manifestly meromorphic form, and then proceed to apply the off-shell Bethe ansatz method of Babujian et al. We obtain the integral formulas for the two-particle complete form-factors and check the axioms at this particle number. [ABSTRACT FROM AUTHOR]

This document is a correction notice for a paper titled "The Asymmetric Dynamical Casimir Effect" published in the journal Physics. The correction addresses an error in the calculation of the DCE spectrum from time-dependent perturbations. The matching conditions computed in the original paper were solved incorrectly, and it appears that these conditions cannot be generally solved by any known method. The correction provides revised content for Section 2.4 and adds a paragraph to the end of Section 2.3. It also corrects erroneous inclusions in equations and modifies the discussion of fluctuations in Section 6. Appendix A is added to highlight the difficulties in calculating the time-dependent perturbations. The author contributions have been corrected to include Patrick M. Brown and Jacob A. Matulevich as authors. [Extracted from the article]

We study the two-particle form-factors for the relativistic limit of the integrable S-matrix of the mixed-flux AdS3 × S3 × T4 string theory. The S-matrix theory was formally constructed in two distinct ways by two different teams. We focus on the massive theory built up by Frolov, Polvara and Sfondrini, and derive expressions for the minimal solutions to the axioms, in both integral and manifestly meromorphic form, and then proceed to apply the off-shell Bethe ansatz method of Babujian et al. We obtain the integral formulas for the two-particle complete form-factors and check the axioms at this particle number. [ABSTRACT FROM AUTHOR]

Reconfigurable photonic filters represent cutting-edge technology that enhances the capabilities of space payloads. These advanced devices harness the unique properties of light to deliver superior performance in signal processing, filtering, and frequency selection. They offer broad filtering capabilities, allowing for the selection of specific frequency ranges while significantly reducing Size, Weight, and Power (SWaP). In scenarios where satellite communication channels are crowded with various signals sharing the same bandwidth, reconfigurable photonic filters enable efficient spectrum management and interference mitigation, ensuring reliable signal transmission. Furthermore, reconfigurable photonic filters demonstrate their ability to adapt to the dynamic space environment, withstanding extreme temperatures, radiation exposure, and mechanical stress while maintaining stable and reliable performance. Leveraging the inherent speed of light, these filters enable high-speed signal processing operations, paving the way to various space payload applications, such as agile frequency channelization. This capability allows for the simultaneous processing and analysis of different frequency bands. In this theoretical study, we introduce a fully reconfigurable filter comprising two decoupled ring resonators, each with the same radius. Each resonator can be independently thermally tuned to achieve reconfigurability in both central frequency and bandwidth. The precise reconfiguration of both central frequency and bandwidth is achieved by using the thermo-optic effect along the whole ring resonator path. A stopband rejection of 45 dB, with a reconfigurable bandwidth and central frequency of 20 MHz and 180 MHz, respectively, has been numerically achieved, with a maximum electrical power of 11.50 mW and a reconfiguration time of 9.20 µs, by using the scattering matrix approach, where the elements have been calculated through Finite Element Method-based and Beam Propagation Method-based simulations. This performance makes the proposed device suitable as key building block of RF optical filters, useful in the next-generation telecommunication payload domain. [ABSTRACT FROM AUTHOR]

We present the experimental study of the distributions of the reflection amplitudes ri = |Sii| of the two-port scattering matrix Ŝ for networks with unitary and symplectic symmetries for the intermediate absorption strength parameter γ. The experimental results confirm the theoretical predictions obtained within the framework of the Gaussian unitary and symplectic ensembles of the random matrix theory. [ABSTRACT FROM AUTHOR]

We analytically derive the updates of a transmission-line network’s interaction matrix and scattering matrix as a consequence of a fault (an interrupted transmission line). We find that the fault alters not only the direct coupling between the two nodes that were previously connected by the faulty cable, but that the fault also alters these nodes’ self-interactions in a non-trivial manner. Given the network’s topology, it is then possible to remotely localize the fault on the faulty cable based on measurements of the faulty network’s scattering coefficient(s). Our analytical expressions make it possible to efficiently calculate the expected scattering matrix for different fault locations (orders of magnitude faster than a brute-force evaluation). We report a simple demonstration for which we assume to know the network’s topology as well as which cable is faulty; we identify the location of the fault on the faulty cable by comparing the broadband scattering coefficient(s) swept across candidate fault locations to the one(s) measured on the faulty network. [ABSTRACT FROM AUTHOR]

Local Fisher discriminant analysis (LFDA) has been widely applied to dimensionality reduction and fault classification fields. However, it often suffers from small sample size (SSS) problem and incorporates all process variables without emphasizing the key faulty ones, thus leading to degraded fault diagnosis performance and poor model interpretability. To this end, this paper develops the sparse variables selection based exponential local Fisher discriminant analysis (SELFDA) model, which can overcome the two limitations of basic LFDA concurrently. First, the responsible faulty variables are identified automatically through the least absolute shrinkage and selection operator, and the current optimization problem are subsequently recast as an iterative convex optimization problem and solved by the minimization-maximization method. After that, the matrix exponential strategy is implemented on LFDA, it can essentially overcome the SSS problem by ensuring that the within-class scatter matrix is always full-rank, thus more practical in real industrial practices, and the margin between different categories is enlarged due to the distance diffusion mapping, which is benefit for the enhancement of classification accuracy. Finally, the Tennessee Eastman process and a real-world diesel working process are employed to validate the proposed SELFDA method, experimental results prove that the SELFDA framework is more excellent than the other approaches. [ABSTRACT FROM AUTHOR]

Environmental conditions, including temperature, humidity, and light, can impact the quality of drugs. Microwave-based approaches offer a fast and cost-effective way to detect quality variations, providing an alternative to traditional techniques in the pharmaceutical and cosmetic industries. This article proposes the use of a microwave sensor for monitoring the quality of pharmaceutical drugs at distinct temperature levels. A small planar sensor based on three hexagonal split ring resonators (TH-SRR) is fabricated. The design is manufactured on an FR-4 dielectric substrate. The sensor is tested on a 1000 mg paracetamol tablet, at temperatures ranging from 40 to 80 ∘ C. The Variation in the permittivity that characterizes product degradation is translated into a shift in the frequency of the scattering matrix elements. To validate the microwave approach, drug quality is examined with the laser-induced breakdown spectroscopy (LIBS) technique, an optical emission laser used for both qualitative and quantitative investigations of elements contained in a sample. The existing elements are classified using the National Institute of Standards and Technology (NIST) database and categorized according to their spectral line wavelengths. The experiments show the presence of optimal wavelength values for carbon (C), hydrogen (H), nitrogen (N), and oxygen (O) at 247.92 nm, 656.49 nm, 244.23 nm, and 777.48 nm, respectively. The microwave experimental results show a shift frequency of approximately 1 MHz on average when the tablet is heated at 80 ∘ C for 15 min. Meanwhile, the LIBS measurement shows a remarkable shift in terms of intensity of approximately 8884 and 812 for carbon and hydrogen, respectively. Understanding how paracetamol dries under high temperatures and improving the process settings of the microwave sensor are investigated and assessed in this work. [ABSTRACT FROM AUTHOR]

It is well known that the scattering matrix plays an important role in quantum optics. This matrix converts the incoming characteristics of scattered radiation into output characteristics. Currently, only special cases of such a scattering matrix are known, which are determined by a specific problem. In this work, a general form of the scattering matrix is obtained, which can be applied to a wide range of problems. It is shown that previously well-known and widely used scattering matrices can be obtained from the resulting scattering matrix. The results obtained can be used to describe new quantum states, the scattering matrices of which have not yet been studied. [ABSTRACT FROM AUTHOR]

Remote control of the state of the atmosphere is an urgent problem nowadays. The problem of remote monitoring of the optical parameters of the atmosphere is solved using a matrix polarization lidar (MPL). The scattering matrix obtained from polarization measurements contains complete information on the scattering parameters in the atmosphere. The purpose of the present research is the derivation of the theory and description of methods for solving problems of practical implementation of the multiwave MPL (MMPL). The problem is considered within the framework of the concept of the unified methodological approach to polarization studies. The MMPL operation principle is based on simultaneous use for sensing of the first, second, and third harmonics of radiation of a widespread Nd:YAG laser. The basis for achieving this purpose is provided by new methods of optical selection of the polarization components of radiation received in the experiment, methods of conducting polarization studies, and new solutions in experimental data processing methods. It has been shown that this challenge can be solved within the framework of simple solutions. Thus, the proposed MMPL is structurally simple and compact and can be implemented in mobile polarization lidar systems. [ABSTRACT FROM AUTHOR]

Human activity recognition (HAR) is one of the key applications of health monitoring that requires continuous use of wearable devices to track daily activities. The most efficient supervised machine learning (ML)-based approaches for predicting human activity are based on a continuous stream of sensor data. Sensor data analysis for human activity recognition using conventional algorithms and deep learning (DL) models shows promising results, but evaluating their ambiguity in decision-making is still challenging. In order to solve these issues, the paper proposes a novel Wasserstein gradient flow legonet WGF-LN-based human activity recognition system. At first, the input data is pre-processed. From the pre-processed data, the features are extracted using Haar Wavelet mother- Symlet wavelet coefficient scattering feature extraction (HS-WSFE). After that, the interest features are selected from the extracted features using (Binomial Distribution integrated-Golden Eagle Optimization) BD-GEO. The important features are then post-processed using the scatter plot matrix method. Obtained post-processing features are finally given into the WGF-LN for classifying human activities. From these experiments, the results can be obtained and showed the efficacy of the proposed model. [ABSTRACT FROM AUTHOR]

The primitive Wigner-Seitz cell and corresponding first Brillouin zone (FBZ) are typically used in calculations of lattice vibrational and transport properties as they contain the smallest number of degrees of freedom and thus have the cheapest computational cost. However, in complex materials, the FBZ can take on irregular shapes where lattice symmetries are not apparent. Thus, conventional cells (with more atoms and regular shapes) are often used to describe materials, though dynamical and transport calculations are more expensive. Here we discuss an efficient anharmonic lattice dynamic method that maps conventional cell dynamics to primitive cell dynamics based on translational symmetries. Such symmetries have not been utilized in typical lattice dynamical calculations. This leads to phase interference conditions that act like conserved quantum numbers and a conservation rule for phonon scattering that is hidden in conventional dynamics which significantly reduces the computational cost. We demonstrate this method for phonon transport in a variety of materials with inputs from first-principles calculations and attribute its efficiency to reduced scattering phase space and fewer summations in scattering matrix element calculations. [ABSTRACT FROM AUTHOR]

Our main result is the analysis of singularities of the integrands of integrals representing the matrix elements of the scattering matrix and the inclusive scattering matrix in perturbation theory. These results are proven for any quantum field theory in any dimension. [ABSTRACT FROM AUTHOR]

Background: microwave imaging (MWI) has emerged as a promising modality for breast cancer screening, offering cost-effective, rapid, safe and comfortable exams. However, the practical application of MWI for tumor detection and localization is hampered by its inherent low resolution and low detection capability. Methods: this study aims to generate an accurate tumor probability map directly from the scattering matrix. This direct conversion makes the probability map independent of specific image formation techniques and thus potentially complementary to any image formation technique. An approach based on a convolutional neural network (CNN) is used to convert the scattering matrix into a tumor probability map. The proposed deep learning model is trained using a large realistic numerical dataset of two-dimensional (2D) breast slices. The performance of the model is assessed through visual inspection and quantitative measures to assess the predictive quality at various levels of detail. Results: the results demonstrate a remarkably high accuracy (0.9995) in classifying profiles as healthy or diseased, and exhibit the model's ability to accurately locate the core of a single tumor (within 0.9 cm for most cases). Conclusion: overall, this research demonstrates that an approach based on neural networks (NN) for direct conversion from scattering matrices to tumor probability maps holds promise in advancing state-of-the-art tumor detection algorithms in the MWI domain. [ABSTRACT FROM AUTHOR]

The intriguing properties of polaritons resulting from strong and ultrastrong light–matter coupling have been extensively investigated. However, most research has focused on spectroscopic characteristics of polaritons, such as their eigenfrequencies and Rabi splitting. Here, we study the decay rates of a plasmon–microcavity system in the strong and ultrastrong coupling regimes experimentally and numerically. We use a classical scattering matrix approach, approximating our plasmonic system with an effective Lorentz model, to obtain the decay rates through the imaginary part of the complex quasinormal mode eigenfrequencies. Our classical model automatically includes all the interaction terms necessary to account for ultrastrong coupling without dealing with the rotating-wave approximation and the diamagnetic term. We find an asymmetry in polaritonic decay rates, which deviate from the expected average of the uncoupled system's decay rates at zero detuning. Although this phenomenon has been previously observed in exciton–polaritons and attributed to their disorder, we observe it even in our homogeneous system. As the coupling strength of the plasmon–microcavity system increases, the asymmetry also increases and can become so significant that the lower (upper) polariton decay rate reduction (increase) goes beyond the uncoupled decay rates, γ− < γ0,c < γ+. Furthermore, our findings demonstrate that polaritonic linewidth asymmetry is a generic phenomenon that persists even in the case of bulk polaritons. [ABSTRACT FROM AUTHOR]

This paper presents a stabilized scheme that solves the wave propagation problem in a general bianisotropic, stratified medium. The method utilizes the concept of propagators, i.e., the wave propagation operators that map the total tangential electric and magnetic fields from one plane in the slab to another. The scheme transforms the propagator approach into a scattering matrix form, where a spectral decomposition of the propagator enables separation of the exponentially growing and decaying terms in order to obtain a well-conditioned formulation. Multilayer structures can be handled in a stable manner using the dissipative property of the Redheffer star product for cascading scattering matrices. The reflection and transmission dyadics for a general bianisotropic medium with an isotropic half space on both sides of the slab are presented in a coordinate-independent dyadic notation, as well as the reflection dyadic for a bianisotropic slab with perfect electric conductor backing (PEC). Several numerical examples that illustrate the performance of the stabilized algorithm are presented. [ABSTRACT FROM AUTHOR]

Within this study, we explored the augmented security measures for the electronics of unmanned aerial vehicles (UAVs) within an RF environment. UAVs are commonly utilised across various sectors, and their use as auxiliary platforms for cellular networks, as parallel networks working in tandem with ground-based base stations, holds considerable promise. In this context, ensuring the uninterrupted operation of UAVs is a paramount objective. However, the considerable external electromagnetic interference emitted by existing base stations may jeopardise the functionality of UAV electronics. This could potentially lead to an unintended flight path and a sudden cessation of communication with the operator. To mitigate the detrimental impact of the RF field, we advocate covering the UAV casing with reduced graphene oxide (RGO). The efficacy of RGO's shielding effectiveness (SE) was investigated over a frequency spectrum from 100 MHz to 10 GHz. Our scrutiny of this property was centred around the measurement of scattering matrix coefficients of the unadulterated material—without additives of any kind. Our findings show that this material is a favourable candidate for UAV absorbers due to its low reflection coefficient coupled with its high absorption capacity. The studied absorber ensures an SE value of 25 dB and 30 dB for a 3 mm layer at frequencies of 3.6 GHz (pertaining to the 5G system) and 5.8 GHz (pertaining to LTE), respectively. [ABSTRACT FROM AUTHOR]

Simultaneously polarimetric radar (SPR) realizes the rapid measurement of a target's polarimetric scattering matrix by transmitting orthogonal radar waveforms of good ambiguity function (AF) properties and receiving their echoes via two orthogonal polarimetric channels at the same time, e.g., horizontal (H) and vertical (V) channels (antennas) sharing the same phase center. The orthogonality of the transmitted waveforms can be realized using low-correlated phase-coded sequences in the H and V channels. However, the Doppler tolerances of the waveforms composed by such coded sequences are usually quite low, and it is hard to meet the requirement of accurate measurement regarding moving targets. In this paper, a joint design approach for unimodular orthogonal complementary sequences along with the optimal receiving filter is proposed based on the majorization–minimization (MM) method via alternate iteration for obtaining simultaneously polarimetric waveforms (SPWs) of good orthogonality and of the desired AF. During design, the objective function used for minimizing the sum of the complementary integration sidelobe level (CISL) and the complementary integration isolation level (CIIL) is constructed under the mismatch constraint of signal-to-noise ratio (SNR) loss. Different SPW examples are given to show the superior performance of our design in comparison with other designs. Finally, practical experiments implemented with different SPWs are conducted to show our advantages more realistically. [ABSTRACT FROM AUTHOR]

In this paper, the power handling of a slot loop frequency selective surface based on approximate analytical method is proposed. The physical nature of the slot array periodic moment method is derived in detail. It is found that the left and right sides of periodic scatter matrix respectively represent the total tangential magnetic field acting on the left and the right magnetic dipole arrays and moving in the direction of the reference array. According to the principle of equivalence, a slot array can be modeled by an array of magnetic currents on each side of the perfect electronic conductor. As a result, the total tangential magnetic field is zero in the sense of physical concept. Furthermore, a simple sinusoidal function is then used to approximate the magnetic current distribution along the slot loop which is similar to that of dipole antenna. By studying the corresponding zero points and extreme point of the magnetic current for the slot loop frequency selective surface element, the transmission coefficients and maximum electronic field are calculated. Examples of rectangle and triangle slot ring frequency selective surface have verified the efficiency and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

This is a non-standard exposition of the main notions of quantum mechanics and quantum field theory, including recent results. It is based on the algebraic approach in which the starting point is a star-algebra and on the geometric approach in which the starting point is a convex set of states. Standard formulas for quantum probabilities are derived from decoherence. This derivation allows us to go beyond quantum theory in the geometric approach. Particles are defined as elementary excitations of the ground state (and quasiparticles as elementary excitations of any translation invariant state). The conventional scattering matrix does not work for quasiparticles (or even for particles if the theory does not have particle interpretation). The analysis of scattering in these cases is based on the notion of an inclusive scattering matrix, which is closely related to inclusive cross-sections. It is proven that the conventional scattering matrix can be expressed in terms of Green functions (LSZ formula) and the inclusive scattering matrix can be expressed in terms of generalized Green functions that appear in the Keldysh formalism of non-equilibrium statistical physics. The derivation of the expression of the evolution operator and other physical quantities in terms of functional integrals is based on the notion of the symbol of an operator; these arguments can be applied in the geometric approach as well. In particular, this result can be used to provide a simple derivation of the diagram technique for generalized Green functions. The notion of an inclusive scattering matrix makes sense in the geometric approach, although it seems that a definition of the conventional scattering matrix cannot be provided in this situation. The geometric approach is used to show that quantum mechanics and its generalizations can be considered as classical theories where our devices are able to measure only a part of the observables. [ABSTRACT FROM AUTHOR]

Many theoretical models of iron-based superconductors (IBSC) have been proposed, but the superconducting transition temperature (Tc) calculations based on these models are usually missing. We have chosen two models of iron-based superconductors from the literature and computed the Tc values accordingly; recently two models have been announced which suggest that the superconducting electron concentration involved in the pairing mechanism of iron-based superconductors may have been underestimated and that the antiferromagnetism and the induced xy potential may even have a dramatic amplification effect on electron–phonon coupling. We use bulk FeSe, LiFeAs and NaFeAs data to calculate the Tc based on these models and test if the combined model can predict the superconducting transition temperature (Tc) of the nanostructured FeSe monolayer well. To substantiate the recently announced xy potential in the literature, we create a two-channel model to separately superimpose the dynamics of the electron in the upper and lower tetrahedral plane. The results of our two-channel model support the literature data. While scientists are still searching for a universal DFT functional that can describe the pairing mechanism of all iron-based superconductors, we base our model on the ARPES data to propose an empirical combination of a DFT functional for revising the electron–phonon scattering matrix in the superconducting state, which ensures that all electrons involved in iron-based superconductivity are included in the computation. Our computational model takes into account this amplifying effect of antiferromagnetism and the correction of the electron–phonon scattering matrix, together with the abnormal soft out-of-plane lattice vibration of the layered structure. This allows us to calculate theoretical Tc values of LiFeAs, NaFeAs and FeSe as a function of pressure that correspond reasonably well to the experimental values. More importantly, by taking into account the interfacial effect between an FeSe monolayer and its SrTiO3 substrate as an additional gain factor, our calculated Tc value is up to 91 K and provides evidence that the strong Tc enhancement recently observed in such monolayers with Tc reaching 100 K may be contributed from the electrons within the ARPES range. [ABSTRACT FROM AUTHOR]

Early intervention for depression could provide a means to reducing the disease burden, but there is a lack of objective diagnostic methods. This study investigated automatic depression classification on a speech dataset of 85 healthy controls (51 females and 34 males) and 85 depressed patients (53 females and 32 males). Considering that there are obvious differences in the performance of different types of speech features, we propose a radius-incorporated localized multiple kernel learning (trLMKL) algorithm for detecting depression in speech to make the best use of speech features. To improve the classification accuracy, we combine the information of both the margin and the radius of the MEB to learn the gating model parameters in our algorithm. Furthermore, we do not directly incorporate the radius of the MEB, but incorporate the trace of the total scattering matrix of training data. This method can avoid the time cost of calculating the radius at each iteration and decrease the computational complexity. Comprehensive experiments were carried out on our depressed speech dataset and 10 UCI datasets. Our algorithm achieved better classification performance overall than SimpleMKL and LMKL, and it was efficient at detecting depression, indicating its potential for use as a diagnostic method for depression. [ABSTRACT FROM AUTHOR]

We provide an asymptotic completeness criterion and a representation formula for the scattering matrix of the scattering couple. AB; A/, where both A and AB are self-adjoint operator and AB formally corresponds to adding to A two terms, one regular and the other singular. In particular, our abstract results apply to the couple. B; /, where  is the free selfadjoint Laplacian in L2.R3/and B is a self-adjoint operator in a class of Laplacians with both a regular perturbation, given by a short-range potential, and a singular one describing boundary conditions (like Dirichlet, Neumann and semi-transparent ı and ı0 ones) at the boundary of an open, bounded Lipschitz domain. The results hinge upon a limiting absorption principle for AB and a Kre˘ın-like formula for the resolvent difference. 􀀀AB C z/􀀀1 􀀀. 􀀀A C z/􀀀1 which puts on an equal footing the regular (here, in the case of the Laplacian, a Kato-Rellich potential suffices) and the singular perturbations. [ABSTRACT FROM AUTHOR]

We present a novel broadband permittivity characterization method for liquids measured in a semi-open vertically oriented test cell with an uncalibrated vector network analyzer. For this goal, we utilize three scattering matrices measured at different levels of liquid in the cell. With mathematical operations, we remove the effects of systematic measurement errors caused by both the vector network analyzer and a meniscus shaping the top of the liquid samples in such a type of test cell. To the best authors' knowledge, this is the first of such a calibration-independent method dealing with meniscus. We verify its validity by comparing our results with the data available in the literature and with the outcomes of our previously published calibration-dependent meniscus removal method (MR) for propan-2-ol (IPA), a 50% aqueous solution of IPA and distilled water. The new method yields results comparable with the MR method, at least for IPA and the IPA solution, revealing, however some problems when testing high-loss water samples. Nevertheless, it allows one to cut down on expenditures in the system calibration engaging skilled labor and expensive standards. [ABSTRACT FROM AUTHOR]

Numerous acoustic features have been proposed as useful measures to characterize natural soundscapes, which can be employed to examine the impact of land transformation on the audible properties of a location. The extensive collection of available features demands an examination to identify the most informative and discriminative ones for a given problem. In this study, we conduct an empirical investigation into the selection of acoustic features for discriminating between highly and moderately transformed versions of four Colombian soundscapes: moorlands, coffee plantations, dry tropical forests, and pastures. We employ classical supervised feature selection techniques along with exploratory tools such as correlation matrices and scatter plots. Our results indicate that a few acoustic features are sufficient to differentiate between the classes. Specifically, those features that estimate acoustic complexity via intrinsic variability of sound intensities or biodiversity through species richness or abundance in specific frequency bands are the most discriminative ones. These Findings suggest that the selection of acoustic features can assist in analyzing and distinguishing between different soundscapes. [ABSTRACT FROM AUTHOR]

The scattering matrix is the mathematical representation of the scattering characteristics of any scatterer. Nevertheless, except for scatterers with high symmetry like spheres or cylinders, the scattering matrix does not have any analytical forms and thus can only be calculated numerically, which requires heavy computation. Here, we have developed a well-trained deep neural network (DNN) that can calculate the scattering matrix of scatterers without symmetry at a speed thousands of times faster than that of finite element solvers. Interestingly, the scattering matrix obtained from the DNN inherently satisfies the fundamental physical principles, including energy conservation, time reversal and reciprocity. Moreover, inverse design based on the DNN is made possible by applying the gradient descent algorithm. Finally, we demonstrate an application of the DNN, which is to design scatterers with desired scattering properties under special conditions. Our work proposes a convenient solution of deep learning for scattering problems. [ABSTRACT FROM AUTHOR]

During the process of the airborne synthetic aperture radar (SAR) system platform in space, platform attitude deflection is inevitable. However, large attitude deflection angles are unacceptable for polarimetric calibration using point targets, especially the dihedral, which is very sensitive to the pointing angle of the radar. To mitigate the impact of attitude angles on calibration accuracy, attitude compensation of the corner reflector is necessary during the calibration process. The conventional approach to attitude compensation typically maps the three-dimensional attitude angle information to the one-dimensional polarimetric orientation angle (POA) information. However, the reduction of dimension inevitably results in information loss, leading to errors that affect calibration performance when the attitude angle is large. In order to ensure the accuracy of point target calibration, this paper proposes a novel point target compensation method based on the reflection theory of electromagnetic waves. This method is based on three-dimensional attitude angle information and has higher reliability than the POA method. Finally, this paper calculates the distance between the scattering matrices obtained after compensation based on the proposed method and the POA method to obtain the difference in the performance of the two methods. Through a simulation, this paper finds that when the attitude angle is small, the results of the two schemes are approximately the same, but as the attitude angle increases, the error between the two gradually increases. This suggests that the proposed method has greater advantages in the case of attitude deflection. Furthermore, the proposed method does not require additional information supplementation compared with the equivalent POA method, making it highly practical. [ABSTRACT FROM AUTHOR]

The Wigner–Smith (WS) time delay matrix relates a lossless system's scattering matrix to its frequency derivative. First proposed in the realm of quantum mechanics to characterize time delays experienced by particles during a collision, this article extends the use of WS time delay techniques to acoustic scattering problems governed by the Helmholtz equation. Expression for the entries of the WS time delay matrix involving renormalized volume integrals of energy densities are derived, and shown to hold true, independent of the scatterer's geometry, boundary condition (sound-soft or sound-hard), and excitation. Numerical examples show that the eigenmodes of the WS time delay matrix describe distinct scattering phenomena characterized by well-defined time delays. [ABSTRACT FROM AUTHOR]

We study the interactions of systems of two and three nondegenerate mesons composed of pions and kaons at maximal isospin using lattice QCD, specifically π+K+, π+π+K+ and K+K+π+. Utilizing the stochastic LapH method, we determine the spectrum of these systems on two CLS Nf = 2 + 1 ensembles with pion masses of 200 MeV and 340 MeV, and include many levels in different momentum frames. We constrain the K matrices describing two- and three-particle interactions by fitting the spectrum to the results predicted by the finite-volume formalism, including up to p waves. This requires also results for the π+π+ and K+K+ spectrum, which have been obtained previously on the same configurations. We explore different fitting strategies, comparing fits to energy shifts with fits to energies boosted to the rest frame, and also comparing simultaneous global fits to all relevant two- and three-particle channels to those where we first fit two-particle channels and then add in the three-particle information. We provide the first determination of the three-particle K matrix in π+π+K+ and K+K+π+ systems, finding statistically significant nonzero results in most cases. We include s and p waves in the K matrix for π+K+ scattering, finding evidence for an attractive p-wave scattering length. We compare our results to Chiral Perturbation Theory, including an investigation of the impact of discretization errors, for which we provide the leading order predictions obtained using Wilson Chiral Perturbation Theory. [ABSTRACT FROM AUTHOR]

The main objective of this work is to isolate Effective Field Theory scattering amplitudes in the space of non-perturbative two-to-two amplitudes, using the S-matrix Bootstrap. We do so by introducing the notion of Effective Field Theory cutoff in the S-matrix Bootstrap approach. We introduce a number of novel numerical techniques and improvements both for the primal and the linearized dual approach. We perform a detailed comparison of the full unitarity bounds with those obtained using positivity and linearized unitarity. Moreover, we discuss the notion of Spin-Zero and UV dominance along the boundary of the allowed amplitude space by introducing suitable observables. Finally, we show that this construction also leads to novel bounds on operators of dimension less than or equal to six. [ABSTRACT FROM AUTHOR]