Miracle-dz/UniFAR-FTUs huggingface dataset:
Focusing of Acoustic Waves through Acoustic Materials with Subwavelength Structures

Focusing of Acoustic Waves through Acoustic Materials with Subwavelength Structures Bingmu Xiao In this thesis, wave propagation through acoustic materials with subwavelength slits structures is studied. Guided by the findings, acoustic wave focusing is achieved with a specific material design. By using a parameter retrieving method, an effective medium theory for a slab with periodic subwavelength cut-through slits is successfully derived. The theory is based on eigenfunction solutions to the acoustic wave equation. Numerical simulations are implemented by the finite-difference time-domain (FDTD) method for the twodimensional acoustic wave equation. The theory provides the effective impedance and refractive index functions for the equivalent medium, which can reproduce the transmission and reflection spectral responses of the original structure. I analytically and numerically investigate both the validity and limitations of the theory, and the influences of material and geometry on the effective spectral responses are studied. Results show that large contrasts in impedance and density are conditions that validate the effective medium theory, and this approximation displays a better accuracy for a thick slab with narrow slits in it. Based on the effective medium theory developed, a design of a flat slab with a “snake shaped” subwavelength structure is proposed as a means of achieving acoustic 5 focusing. The property of focusing is demonstrated by FDTD simulations. Good agreement is observed between the proposed structure and the equivalent lens predicted by the theory, which leads to robust broadband focusing by a thin flat slab.
Novel dual-frequency and broad-band designs of slot-loaded equilateral triangular microstrip antennas

By loading properly arranged slots in an equilateral-triangular microstrip patch, novel dual-frequency and broad-band operations of a single-feed triangular microstrip antenna are presented. For dual-frequency operation, the proposed design is achieved by loading two pairs of narrow slots in the triangular patch, one embedded close to the side edges of the patch and the other inserted at the bottom edge of the patch. The obtained two operating frequencies are of same polarization planes and by varying the positions and lengths of the inserted slots at the bottom edge of the patch, a tunable frequency ratio of the two frequencies ranging from about 1.16 to 2.06 is obtained. Furthermore, it is found that by protruding a narrow slot out of the embedded slots close to the side edges, broad-band operation of the triangular microstrip antenna near its fundamental resonant mode can be achieved. Results show that the antenna bandwidth of the proposed broad-band design can be greater than 2.6 times that of a conventional triangular microstrip antenna. Details of the proposed dual-frequency and broad-band designs are described and typical experimental results are presented and discussed.
Spatial evolutionary game theory: Hawks and Doves revisited

We consider a spatial generalization of evolutionary game theory in which strategies are distributed over a spatial array of sites. We assume that the strategy corresponding to a given site has local interactions with the strategies sitting on neighbouring sites, and that the strategies change if neighbouring strategies are doing better. After briefly setting the stage with a formal definition of spatial evolutionary game theory, we consider the spatial extension of the Hawk—Dove game, and we show that the results are qualitatively different from those obtained from classical evolutionary game theory. For example, the proportion of Hawks in the population is in general lower in the spatial game than in the classical one. We also consider spatial generalizations of the extensions of the Hawk—Dove game obtained by including strategies such as Retaliator and Bully. Here, too, the results from the spatial game are very different from the classical results. In particular, with space Retaliator is a much more successful strategy than one would expect from classical considerations. This suggests that, in general, spatial structure may facilitate the evolution of strategies such as Retaliator, which do not necessarily prosper classically, and which are reminiscent of the ‘nice’, ‘provokable’ and ‘forgiving’ strategies which seem to play a central role in the evolution of cooperation. The results indicate that including spatial structure in evolutionary game theory is a fruitful extension.
A Control Problem Arising in the Sequential Design of Experiments

The Pele problem. Starting from an initial point x not in his playing field, a football player is to dribble onto the field. Due to irregularities in the surface on which the player is dribbling, and perhaps also to small inconsistencies in his kick, the movement of the ball has a “random” component; moreover, a kick with the left foot tends to have a somewhat different effect than a kick with the right foot. The player’s objective is to move the ball onto the playing field with as few kicks as possible.
Diffractive transducers for angle-independent velocity measurements

Usual Doppler (or equivalent) methods produce a value proportional to the product of flow velocity and the cosine of the angle between the flow and insonating beam. By using a diffractive transducer, multiple insonating beams can be obtained from one transducer, permitting multiple measurements, at known increments of angle, to be made. In effect, the conventional single equation in the two unknowns of velocity and angle, is, by using a diffractive transducer, replaced by two (or more) equations in the two unknowns, that can be solved for the velocity and angle. The theory and experimental verification of operation of diffractive transducers is presented. Diffractive transducers may enable simple and inexpensive hemodynamic monitoring
Unobtrusive Human Fall Detection System Using mmWave Radar and Data Driven Methods

As the population ages, health issues like injurious falls demand more attention. One solution is to use wearable devices to detect falls. Nevertheless, most of these devices raise obtrusiveness, and older people generally resist or might forget to wear them. The millimeter-wave (mmWave) radar technology was used in this study to unobtrusively detect human falls. Data were collected from healthy young volunteers with the radar mounted on the side wall (trial 1) or overhead (trial 2) of an experimental room. A set of features were manually extracted from the data point clouds; then, multilayer perceptron (MLP), random forest (RF), <inline-formula> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula>-nearest neighbor (KNN), and support vector machine (SVM) classifiers were applied on the features. Additionally, we devised a convolutional neural network (CNN)-based deep learning model for the underlying fall detection problem that receives a 3-D representation of the point cloud data, known as occupancy grid, as the input. The optimal installation position of the radar sensor was unknown. Therefore, the sensor was mounted on side wall and on the ceiling of the room to allow the performance comparison between these sensor placements. RF classifier achieved the best results in trial 2 (an accuracy of 92.2%, a recall of 0.881, a precision of 0.805, and an <inline-formula> <tex-math notation="LaTeX">${F}1$ </tex-math></inline-formula>-score of 0.841), and the proposed CNN model achieved slightly better results comparing to the RF method in trial 2 (an accuracy of 92.3%, a recall of 0.891, a precision of 0.801, and an <inline-formula> <tex-math notation="LaTeX">${F}1$ </tex-math></inline-formula>-score of 0.844). These results suggest that the development of an unobtrusive monitoring system for fall detection using mmWave radar is feasible.
Iterative Methods for Linear and Nonlinear Equations

Preface How to Get the Software Part I. Linear Equations. 1. Basic Concepts and Stationary Iterative Methods 2. Conjugate Gradient Iteration 3. GMRES Iteration Part II. Nonlinear Equations. 4. Basic Concepts and Fixed Point Iteration 5. Newton's Method 6. Inexact Newton Methods 7. Broyden's Method 8. Global Convergence Bibliography Index.
Spatiotemporal dynamics of photoexcited quasiparticles in two-dimensional crystals studied by ultrafast laser techniques

Layered materials in which atomic sheets are stacked together by weak van der Waals forces can be used to fabricate two-dimensional systems. They represent a diverse and rich, but largely unexplored, source of materials. Atomically-thin structures derived from these materials possess a number of interesting electrical, optical, and mechanical properties, and are attractive for new nanodevices. For their applications in semiconductor industry, it is necessary to understand the dynamics of photoexcited quasiparticles that occur on ultrafast time scales of less than one nanosecond. In this dissertation, I discuss ultrafast optical experimental techniques and results from various two-dimensional materials, which provide information about electronic dynamics. First, a second harmonic generation technique that can be used to find the crystalline orientation, thickness uniformity, layer stacking, and single-crystal domain size is discussed, with results presented on exfoliated and chemical vapor deposition MoS2 samples. Second, a third harmonic generation technique is discussed, which can be used to explore nonlinear optical properties of materials, and results are presented on graphene and few-layer graphite films. Third, a spatially resolved femtosecond pumpprobe is described, which can be used to study hot carrier and photoexcited phonon dynamics and results are presented on Bi2Se3 sample. Then, exciton dynamics in MoS2 and MoSe2 are explored by using transient absorption microscopy with a high spatiotemporal resolution. Finally, a polarization-resolved femtosecond transient absorption spectroscopy that can be used to study valley and spin dynamics is discussed, with results presented on monolayer, few-layer, and bulk MoSe2 samples.
Probabilistic Seismic Hazard Analysis without the Ergodic Assumption

INTRODUCTION An ergodic process is a random process in which the distribution of a random variable in space is the same as the distribution of that same random variable at a single point when sampled as a function of time. An ergodic assumption is commonly made in probabilistic seismic hazard analysis (PSHA). A regression analysis is used to obtain a mean curve to predict ground motion as a function of magnitude and distance (and sometimes other parameters). The standard deviation of this ground-motion regression is determined mainly by the misfit between observations and the corresponding predicted ground motions at multiple stations for a small number of well recorded earthquakes. Thus, the standard deviation of the ground-motion regression is dominantly related to the statistics of the spatial variability of the ground motions. An ergodic assumption is made when PSHA treats that spatial uncertainty of ground motions as an uncertainty over time.
Using dynamical embedding to isolate seizure components in the ictal EEG

A system for isolating seizure components in the epileptic electroencephalogram (EEG) is presented. The method of independent component analysis (ICA) is implemented to decompose multichannel recordings of scalp EEG known to contain epileptic seizures into their underlying independent components (ICs). The ICs are treated as a convenient expansion basis and in order to identify the relevant seizure components amongst the ICs, a series of dynamical embedding matrices are first constructed along each IC. By observing the change in structure of the singular spectra obtained by performing a singular value decomposition on each consecutive dynamical embedding matrix, it is possible to track changes in the underlying complexity of each IC with time. The change in complexity is linked to the change in entropy that can be calculated from each consecutive singular spectrum. The change in complexity, coupled with the topographical distribution of each IC, allows seizure-related components extracted by the ICA process to be subjectively identified. The method has been applied to four seizure EEG segments, and in each case probable seizure components were identified subjectively. As a proof-of-principle study, the method indicates that ICA coupled with dynamical embedding may be useful as a tool in pre-processing seizure EEG segments.
A Model of a Multi-Site Fishery with Variable Price: from Over-Exploitation to Sustainable Fisheries

We present a mathematical model of a fishery on several sites with a variable price. The model takes into account the evolution during the time of the resource, fishes and boats movements between the different sites, fishing effort and price that varies with respect to supply and demand. We suppose that boats and fishes movements as well as prices variations occur at a fast time scale. We use methods of aggregation of variables in order to reduce the number of variables and we derive a reduced model governing two global variables, respectively the biomass of the resource and the fishing effort of the whole fishery. We look for the existence of equilibria of the aggregated model. We show that the aggregated model can have 1, 2 or 3 non trivial equilibria. We show that a variation of the total number of sites can induce a switch from over-exploitation to sustainable fisheries.
The simulation of turbulent particle‐laden channel flow by the Lattice Boltzmann method

We perform direct numerical simulation of three‐dimensional turbulent flows in a rectangular channel, with a lattice Boltzmann method, efficiently implemented on heavily parallel general purpose graphical processor units. After validating the method for a single fluid, for standard boundary layer problems, we study changes in mean and turbulent properties of particle‐laden flows, as a function of particle size and concentration. The problem of physical interest for this application is the effect of water droplets on the turbulent properties of a high‐speed air flow, near a solid surface. To do so, we use a Lagrangian tracking approach for a large number of rigid spherical point particles, whose motion is forced by drag forces caused by the fluid flow; particle effects on the latter are in turn represented by distributed volume forces in the lattice Boltzmann method. Results suggest that, while mean flow properties are only slightly affected, unless a very large concentration of particles is used, the turbulent vortices present near the boundary are significantly damped and broken down by the turbulent motion of the heavy particles, and both turbulent Reynolds stresses and the production of turbulent kinetic energy are decreased because of the particle effects. We also find that the streamwise component of turbulent velocity fluctuations is increased, while the spanwise and wall‐normal components are decreased, as compared with the single fluid channel case. Additionally, the streamwise velocity of the carrier (air) phase is slightly reduced in the logarithmic boundary layer near the solid walls. Copyright © 2015 John Wiley & Sons, Ltd.
Optimal biorthogonal transform for colored noise suppression with subband Wiener filtering

It is well-known that the Karhunen-Loeve transform (KLT) is optimal for white noise suppression. Akkarakaran and Vaidyanathan (see IEEE Trans. Signal Processing, vol.49, no.1, p.100-114, 2001) showed that for the case of colored noise, if both the noise and signal have a common KLT, then the KLT is optimal for subband noise suppression. We derive the optimal transform (not restricting to the class of unitary transforms) for the noise suppression problem when the signal and noise have arbitrary spectrum.
Are stellar flares energized by the missing energy in starspots

We suggest that the energy released in stellar flares is provided by a steady accumulation of a fraction of the missing energy in starspots. The mechanism by which the missing energy might be converted to flare-compatible form is not discussed here. However, the principal result of the paper, equation (9), is independent of the (speculative) details of the conversion and storage mechanisms. (AIP)
Etching‐back of uniaxially strained silicon on insulator investigated by spectroscopic ellipsometry

Spectroscopic Ellipsometry was employed to study the etching process of uniaxially strained Si (sSi) layers obtained by direct wafer bonding of Si wafers in a mechanically bent state followed by thinning one of the Si wafers, the donor wafer, by the smart‐cut process, keeping the other, the handle wafer intact. The smart‐cut process requires a high dose hydrogen implantation into the donor wafer prior to bonding. As a result of the implantation conditions a ∼600 nm uniaxially sSi layer could be transferred onto the handle wafer. In order to thin down and smooth the surface damage of the transferred layer induced by the implantation and splitting process, the samples were dipped in a solution of tetra‐methyl ammonium hydroxide (TMAH). The thicknesses of the transferred sSi layers determined from ellipsometry were in good agreement with those obtained from Transmission Electron Microscopy (TEM), while the roughness values were matching those obtained from Atomic Force Microscopy (AFM). The etching rate has also been determined. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensitivity limitation of a SQUID gravity gradiometer due to elastic interaction between sensing currents and test masses

Differential displacement due to a gravitational force gradient, acting on two superconducting test masses which are elastically suspended from the instrument frame, is sensed by a superconducting quantum interference device (SQUID) coupled to the masses by a current flowing in the sensing circuits. An elastic interaction between the sensing currents and the currents mirrored on the superconducting surfaces of the test masses can stiffen the movement of the masses, reducing the sensitivity of the instrument. However, this interaction is not principally limiting, and the SQUID can be built so that stiffening does not occur.
Prevalence of Campylobacter spp. in broilers in North Lebanon

Background and Aim: Great attention has been given recently to the prevalence of different Campylobacter spp. in poultry since the latter are considered the major contributing reservoir of human campylobacteriosis. In Lebanon, the occurrence of campylobacteriosis in humans is high. The aim of our first-of-its-kind study in the country was to estimate the prevalence of Campylobacter spp. in broilers from a convenient sample of farms in North Lebanon. Materials and Methods: One hundred twenty-five fecal samples were collected from 25 broiler farms, which were selected, examined, and classified according to their biosecurity level and rearing system. All samples were subjected to qualitative microbiological culture testing and polymerase chain reaction (PCR) assays to detect Campylobacter spp. Results: Despite the reported use of antibiotics, cell culture and PCR were positive for 44% and 88%, respectively. This implies that this bacterium is resistant to antibiotics used on the farms. Furthermore, Campylobacter infection rate was higher in open (92%) than in closed (85%) system farms. All farms with poor biosecurity measures, and 82% of farms with good biosecurity measures had Campylobacter infections, and the difference was significant (p < 0.05). Conclusion: Our results show that campylobacteriosis was found prevalent among broilers in North Lebanon, making them potential carriers of Campylobacter spp. Future studies should include antibiotic susceptibility testing to check the susceptibility pattern of isolates.
Dynamical intersecting brane solutions of supergravity

We present dynamical intersecting brane solutions in higher‐dimensional gravitational theory coupled to dilaton and several forms. Assuming the forms of metric, form fields, and dilaton field, we can give the dynamical intersecting brane solutions. The dynamical solutions can be always obtained by replacing the constant modulus h0 in the warp factor for supersymmetric solutions by a linear function h0(t) of the time coordinates t.
A Distributed Coordination Control for Islanded Hybrid AC/DC Microgrid

Poor power sharing of hybrid ac/dc microgrid leads to the inefficient operation of distributed generators (DGs). Besides, the lack of inertia caused by droop and phase-locked loop-based current control brings negative effects to the system. In this article, we propose a distributed normalized power coordination (NPC) embedded with virtual synchronous generator for hybrid microgrid. The proposed NPC controller can achieve cross inertia support, accurate global power sharing, and frequency/voltage recovery among dispatchable DGs simultaneously. Furthermore, to suppress frequency and power oscillation, the index of inertia deviation is proposed to guide the inertia placement of hybrid MG based on Participation Factor analysis. Finally, the proposed strategy is validated by the simulation and hardware-in-loop tests compared to the conventional methods.
DETECTION OF PERIODICITIES BY HIGHER‐ORDER CROSSINGS

The axis-crossing counts in a time series and in its successive differences are called higher-order crossings (HOC). Under the Gaussian assumption the sequence of expected HOC is monotone increasing and admits a spectral representation which establishes a clear connection between HOC and the spectrum. In particular the normalized number of axis-crossings (first HOC) tends to admit values at or near a dominant frequency, while the sequence of normalized HOC converges to the highest frequency in the spectrum. When the series is first lowpass filtered, the resulting normalized HOC tend to ‘visit’ true discrete frequencies on their way to the highest frequency. If the successive differences are replaced by successive summation, the resulting modified normalized HOC converge monotonically to the lowest frequency in the spectrum.
Scale selection in low-order spectral models of two-dimensional thermal convection

The non-linear dynamics of two-dimensional thermal convection is investigated with the help of two low-order spectral models. The first model is the three-coefficient Lorenz model, in which the aspect ratio has not been used in scaling the variables. This means that the aspect ratio is a free parameter in addition to the Rayleigh number and the Prandtl number. The stability and the energetics of steady-state convection as a function of the three free parameters are investigated. The second model is a ten-coefficient model which describes the evolution and non-linear interaction of two horizontal scales of motion (with vertical wave number equal to one). It is found that the circulation mostly chooses a steady-state equivalent to the steady-state convective solution of the Lorenz model, i.e., a roll with a definite aspect ratio, even when one or more of the seven other coefficients would grow according to linear theory. It is also found that in most cases, the larger scale is favoured over the smaller scale, as the Rayleigh number is increased, especially at low Prandtl number. This agrees qualitatively with laboratory experiments. The paper is, however, principally meant as a contribution to the physical and mathematical insight into, as well as an illustration of, the non-linear dynamics of two-dimensional thermal convection. DOI: 10.1111/j.1600-0870.1984. tb00262.x