Generalized optical theorem for an arbitrary incident field

© 2019 Acoustical Society of America. A formalism of optical theorem extended for an arbitrarily shaped wave field is presented. The formalism concerns only time-harmonic scattering in free space. The theorem relates the extinction cross section to the imaginary part of the total scattering amplitude at the forward direction of the individual plane wave components multiplied by the corresponding plane wave amplitude in the angular spectrum of the incident wave. A differential extinction cross section is defined from the theorem. An alternative formalism relating the total cross section to plane wave scattering is also presented. Physical interpretation is provided and applications are discussed

Oscillation-free method for semilinear diffusion equations under noisy initial conditions

Noise in initial conditions from measurement errors can create unwanted oscillations which propagate in numerical solutions. We present a technique of prohibiting such oscillation errors when solving initial-boundary-value problems of semilinear diffusion equations. Symmetric Strang splitting is applied to the equation for solving the linear diffusion and nonlinear remainder separately. An oscillation-free scheme is developed for overcoming any oscillatory behavior when numerically solving the linear diffusion portion. To demonstrate the ills of stable oscillations, we compare our method using a weighted implicit Euler scheme to the Crank-Nicolson method. The oscillation-free feature and stability of our method are analyzed through a local linearization. The accuracy of our oscillation-free method is proved and its usefulness is further verified through solving a Fisher-type equation where oscillation-free solutions are successfully produced in spite of random errors in the initial conditions.Comment: 19 pages, 9 figure

Metascreen-Based Acoustic Passive Phased Array

Conventional phased arrays require a large number of sources in forming a complex wave front, resulting in complexity and a high cost to operate the individual sources. We present a passive phased array using an acoustic metascreen that transmits sound energy from a single source and steers the transmitted wave front to form the desired fields. The metascreen is composed of elements that have a discrete resolution along the screen at an order smaller than the wavelength, allowing for fine wave-front shaping beyond the paraxial approximation. The performance is verified in experiment by forming a self-bending beam. Our metascreen-based passive array with its simplicity and capability has applications in places where conventional active arrays are complex and have limitations.Acoustical Society of AmericaNational Basic Research Program of China (973 Program) 2010CB327803 2012CB921504National Natural Science Foundation of China 11174138 11174139 11222442 81127901 11274168Physic

Acoustic orbital angular momentum Hall effect and realization using a metasurface

Vortex beams with a twisted wavefront possess both intrinsic and extrinsic orbital angular momenta. Their coupling (viz. orbital-orbital coupling) leads to an orbital angular momentum Hall effect previously found in light, providing applications in light manipulation. Here an analogous orbital Hall effect in acoustics is reported via modeling vortex beam propagation in an inhomogeneous medium. A shift of the beam center perpendicular to the inhomogeneous direction is numerically observed to follow a path predicted by ray theory in the weak inhomogeneity approximation where the coupling and conservation of total angular momenta are identified. Experimental observation of the acoustic phenomenon with the aid of a gradient metasurface or a stratified fluid is proposed

Asymptotic posterior normality of the generalized extreme value distribution

The univariate generalized extreme value (GEV) distribution is the most commonly used tool for analysing the properties of rare events. The ever greater utilization of Bayesian methods for extreme value analysis warrants detailed theoretical investigation, which has thus far been underdeveloped. Even the most basic asymptotic results are difficult to obtain because the GEV fails to satisfy standard regularity conditions. Here, we prove that the posterior distribution of the GEV parameter vector, given an independent and identically distributed sequence of observations, converges to a normal distribution centred at the true parameter. The proof necessitates analysing integrals of the GEV likelihood function over the entire parameter space, which requires considerable care because the support of the GEV density depends on the parameters in complicated ways

Computer Forensics Model Based on Evidence Ring and Evidence Chain

AbstractIn recent years, with the development of technology, judicial practice involving electronic crime is frequent. To combat this crime, computer forensics bears the irreplaceable role. This is a combination science of law and computer, but there is a “mismatch” phenomenon exists on the research on computer forensics currently, most of them only study the technical aspects of computer or electronic evidence related to legal issues, the two studies combined less. To solve this problem, in this paper, evidence of the general attributes: objectivity, relevance, legitimacy as a criterion to build a computer forensics model based on ring and chain of evidence. In this model, forensic evidence of links forms a ring, in accordance with the forensic to form chain of evidence. In order to ensure the objectivity, legitimacy of evidence, in building a chain of evidence and evidence ring as well as a supervisory chain in supervision, the final forms a electronic evidence forensics system

SESS: A Self-Supervised and Syntax-Based Method for Sentiment Classification

PACLIC 23 / City University of Hong Kong / 3-5 December 200

Flexible and efficient spatial extremes emulation via variational autoencoders

Many real-world processes have complex tail dependence structures that cannot be characterized using classical Gaussian processes. More flexible spatial extremes models exhibit appealing extremal dependence properties but are often exceedingly prohibitive to fit and simulate from in high dimensions. In this paper, we develop a new spatial extremes model that has flexible and non-stationary dependence properties, and we integrate it in the encoding-decoding structure of a variational autoencoder (XVAE), whose parameters are estimated via variational Bayes combined with deep learning. The XVAE can be used as a spatio-temporal emulator that characterizes the distribution of potential mechanistic model output states and produces outputs that have the same statistical properties as the inputs, especially in the tail. As an aside, our approach also provides a novel way of making fast inference with complex extreme-value processes. Through extensive simulation studies, we show that our XVAE is substantially more time-efficient than traditional Bayesian inference while also outperforming many spatial extremes models with a stationary dependence structure. To further demonstrate the computational power of the XVAE, we analyze a high-resolution satellite-derived dataset of sea surface temperature in the Red Sea, which includes 30 years of daily measurements at 16703 grid cells. We find that the extremal dependence strength is weaker in the interior of Red Sea and it has decreased slightly over time.Comment: 30 pages, 8 figure

Inhibitory effect of chitosan oligosaccharide on human hepatoma cells in vitro

Background: Chitosan oligosaccharide, the degradation products of chitin, was reported to have a wide range of physiological functions and biological activities. In this study, we explored the inhibitory effect of Chitosan oligosaccharide on human hepatoma cellsMaterials and Methods: MTT assay was applied to detect cell viability of the human hepatoma cells treated with Chitosan oligosaccharide. Flow cytometric analysis was used to investigate the apoptosis of the human hepatoma cells treated with Chitosan oligosaccharide. We employed western blot to investigate the underlying mechanisms involved in the apoptosis.Results: Our data indicated that chitosan oligosaccharide dose-dependently inhibited the growth of hepatoma cells and induced apoptosis. On the molecular level, chitosan oligosaccharide decreased Bcl-2 and increased Caspase-3 expression which may be related to the apoptosis of hepatoma cells.Conclusion: Our results provide an experimental basis for the clinical development of Chitosan oligosaccharide as a novel anti-hepatoma drug.Keywords: Chitosan oligochitosan, Hepatoma cells, Apoptosis, Bcl-2, Caspase-