Narrow Results

This research focuses on studying the influence of the Hall current on the propagation and reflection of elastic waves in a non-local isotropic rotating solid. The dispersion relation is derived to determine the speed of propagation, revealing the presence of three coupled quasi-waves within the solid: coupled qP-wave, qT-wave and qSV-wave. The rotational motion and the Hall current introduce anisotropic characteristics to the medium, leading to the emergence of quasi-type waves. The rotation disrupts the isotropic nature of the solid, transforming it into an anisotropic medium. Consequently, the purely longitudinal and transverse waves are converted into quasi-longitudinal and quasi-transverse waves. The speed of the propagating waves is dependent on specific elastic parameters. By employing free boundary conditions, the mathematical calculation and graphical representation of wave amplitude ratios are determined. The influence of rotational frequency, non-locality, fractional order and Hall current parameters on the computed results is investigated. The conservation of energy validates the accuracy of the obtained results. Furthermore, it is observed that the previously reported results in the literature can be obtained as a special case when rotation and the Hall current are absent.

The propagation and reflection of thermo-elastic waves through diffusive nonlocal isotropic medium had been studied in this paper. The Green–Lindsay model of thermo-elasticity is incorporated in the context of Temperature Rate Dependent Theory. Using Helmholtz vector decomposition rule, the system of governing equations has been transformed to their respective components. The dispersion relation in frequency indicates the existence of three coupled waves and one independent wave propagating through the medium. The coupled waves are affected by non-locality, temperature field and diffusivity in the medium; anyhow, un-coupled shear vertical wave is only affected by the non-local parameter. The reflection of $P$-wave is also studied at the free boundary of the solid and their corresponding amplitude ratios are computed using set of suitable boundary conditions. The obtained results are further discussed graphically for significant physical parameters of interest. The results in the literature are obtained as a special case after ignoring the diffusivity in the solid.

We demonstrate a large area time domain terahertz (THz) imaging system capable of scanning 1 meter square area in less than 20-100 minutes for several security applications. The detection of concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); and flammables in luggage, packages and personnel has been demonstrated. Transmission mode images of luggage containing threat items are discussed. Reflection mode images of luggage and personnel are discussed. Time domain THz images can be analyzed for 3 dimensional and volumetric information. Time domain THz images have advantages over coherent narrow band imaging methods, with freedom from interference artifacts and with greater ability to discard irrelevant or intervening reflections through time discrimination.

Accurate iris segmentation is presented in this paper, which is composed of two parts, reflection detection and eyelash detection. Eyelashes are classified into two categories, separable and multiple. An edge detector is applied to detect separable eyelashes, and intensity variances are used to recognize multiple eyelashes. Reflection is also divided into two types, strong and weak. A threshold and statistical model is proposed to recognize the strong and weak reflection, respectively. We have developed an iris recognition approach for testing the effectiveness of the proposed segmentation method. The results show that the proposed method can reduce recognition error for the iris recognition approach.

Learning from examples has a number of distinct algebraic forms, depending on what is to be learned from the available information. One of these forms is , where the input-output tuple (x, y) is the available information, and G represents the process determining the mapping from x to y. Various models, y = f(x), of G can be constructed using the information from the (x, y) tuples. In general, and for real-world problems, it is not reasonable to expect the exact representation of G to be found (i.e. a formula that is correct for all possible (x, y)). The modeling procedure involves finding a satisfactory set of basis functions, their combination, a coding for (x, y) and then to adjust all free parameters in an approximation process, to construct a final model. The approximation process can bring the accuracy of the model to a certain level, after which it becomes increasingly expensive to improve further. Further improvement may be gained through constructing a number of agents {α}, each of which develops its own model f_α. These may then be combined in a second modeling phase to synthesize a team model. If each agent has the ability for internal reflection the combination in a team framework becomes more profitable. We describe reflection and the generation of a confidence function: the agent's estimate of the correctness of each of its predictions. The presence of reflective information is shown to increase significantly the performance of a team.

Recently, the notion of having programming languages and computational systems that allow their programs to reason about themselves and reflect on their computations has attracted the attention of many researchers. These systems, called "Reflective Systems", promise many advantages over conventional systems. For example, dynamic program stepping, execution tracing, and code analysis and modification at run time are few of the reflective operations that can be easily implemented in reflective systems.

Reflectivity of programming languages allows the language users to extend the language to support other programming paradigms. Reflective systems can also play an important role in programming solutions for non-conventional domains. Artificial intelligence applications, particularly learning systems, benefit from the reflectivity of a programming language. A learning system must be able to modify itself at run time to incorporate its learned behaviors.

The goal of this article is to define reflection and its components, introduce the appropriate terminology, and present briefly some reflective applications in object-oriented systems.

The aim of this study is the formation of porous silicon (PS) and the heat treatment effect on the optical properties of the PS layer. An optimized HF:HNO₃ chemical solution is used at ambient temperature on the n + p silicon surface. Scanning electron microscopy (SEM) pictures show the form of the nanopores. We studied the effect of the heating on the morphology and the reflection of the PS layer. A chemical analysis of the surface is also carried out. The measurements show that the pore shape and the oxygen content on the surface are changing with temperature. Specular reflection spectra under variable incidence angles are measured on each treated surface. Curves of weighted reflection R_w are drawn to illustrate the evolution with temperature. The modification of oxygen content of the porous surface is correlated with the sheet resistance of the emitter. Results show the lower the oxygen percent the lower the resistivity. The layout of R_w according to the temperature of annealing indicates that the shape of the curve is the same for the angles of incidences 20°, 30°, 40°, and 50°. At a low temperature R_w is minimal indicating the presence of an oxide coating on the porous layer an indication of optical adaptation between the air and the substrate of silicon.

In this paper, the transmission and reflection of acoustic waves into and from an underground tunnel are investigated by producing an impact load on the ground and measuring the acoustic pressure levels at different time intervals. For this purpose, a sound detector is placed on the ground and then from an arbitrary location on the surface, acoustic waves are transmitted into the ground from an acoustic source. The pressure levels of acoustic waves transmitted into the tunnel space and reflected back to the ground surface are measured, and the effects of several parameters on the attenuation of acoustic pressure levels of transmitted and reflected sound waves are evaluated. Moreover, the effects of parameters such as soil type, concrete type and thickness, buried depth of the underground structure and also the effect of acoustic absorbers on the transmission, propagation and reflection of acoustic waves into and from the tunnel are investigated. The results obtained indicate that the two parameters of soil type and buried depth have the greatest effect on the transmission of acoustic waves, whereas all the parameters considered are important with regard to the reflection of acoustic waves. In addition, it was observed that the use of acoustic absorbers in tunnel structures has a significant effect on the attenuation of transmitted and reflected acoustic waves.

A method is presented that enables the determination of transient absorption in Langmuir films made from a monolayer of spiropyran on water. This is achievable even though the optical pathlength of such a monolayer is < 10^-9 m. The approach is to monitor reflectivity changes close to the Brewster angle, where the background of reflected light is minimized. This is the key to the sensitivity of the method. Relatively speaking the small changes in reflectivity due to changes in both real and imaginary parts of the refractive index are easier to observe with the intrinsically low backgrounds at the Brewster angle. Notably using Fresnel equations we can show that the real and imaginary parts of the refractive index can be independently assessed for ultrathin films and monolayers using the approach presented.

Recent designs of dielectric-metamaterial composites have some advantages in improving the coupling effect of light in the visible region. The refractive index of the designed metal mesh or fishnet metamaterial structure consists of metals such as Ag, Cu and Al with MgF₂ dielectric material as the substrate which is calculated theoretically using Bruggeman equation. It has been established recently that the dielectric-metamaterial reflector coating (DMMRC) produces outstanding results. It drastically increases the internal reflection and enhances absorption in the visible region. DMMRC is designed by two slabs with exclusive thickness and contrary refractive indices. One is dielectric material and the other is negative refractive index material (NIM). This theoretical model can be treated as a photonic crystal and hence novel light trapping mechanism can be revealed. The transmission spectrum is analyzed using the transverse matrix method (TMM). This system may also be analyzed for various incident angles and for various substrates which are used to improve the efficiency of the solar cell.

This article briefly reflects some of my interactions with Dr. Britton Chance (BC), from a perspective of his graduate student.

The purpose of this research work is to study the diffraction of surface gravity waves propagating through rectangular porous medium in three dimensions. The considered porous structure consists of dense arrays of surface piercing vertical cylinders. Experiments for different regular wave conditions have been carried out, especially for three-wave frequencies. The experimental data of wave refraction–diffraction and reflection have been compared to computed results from potential linear theory solved with an integral matching method. Comparison with a previous 2D study about wave propagation through porous medium in a 10 m long wave flume is also discussed in order to highlight the refraction–diffraction effect due to the porous structure.

In the recent years, various geo-synthetic components find an extensive application in civil and coastal engineering practice. Commonly, geo-synthetics have a wide application for secondary or tertiary purposes, such as filtration, separation, barrier, reinforcement, whereas, they can be potentially exploited for various other applications in the coastal engineering practice. A sustainable seawall cross-section comprising different geo-synthetic products was proposed to be erected along the Pallana Beach ($19^{\circ }17^{\prime }55.19^{\prime \prime }$ N and $76^{\circ }23^{\prime }18.55^{\prime \prime }$ E), located in Alleppey district of Kerala along the south-west Indian coastline. Since the subsoil at the location is poorly graded, it was decided to replace the conventional materials like rock boulders and concrete armour units with geo-synthetic products. A comprehensive physical model study was conducted to assess the hydrodynamic performance (i.e. reflection, run-up, and pressure distribution) of the geo-synthetic seawall cross-section for a wide range of random wave characteristics and two water depth conditions. The relative overtopping rates for the seawall at varying water levels are computed conservatively from the guidelines prescribed by the EurOtop Manual and XGB Overtopping model.

This chapter has two objectives: (1) to present the micro-mechanics model of Piezoelectric Fiber-Reinforced Composites (PFRCs) and illustrate some of its advantages and (2) to analytically study the impacts of normal/shear initial stresses and rotation on energies carried by different reflected/transmitted waves at the interface of two dissimilar PFRCs. Numerical studies are performed on PFRCs comprised of PZT-5A-epoxy combination and CdSe-epoxy combination, which are modeled employing Strength of Materials (SM) technique with Rule of Mixtures (RM). Some electro-mechanical advantages of PFRC over monolithic piezoelectric materials are demonstrated. Due to incidence of a quasi-longitudinal (qP) wave, three reflected/transmitted waves, viz. quasi-longitudinal (qP), quasi-transverse (qSV), and electro-acoustic (EA) waves are generated in the PFRCs. The propagation directions of all reflected/transmitted waves are graphically demonstrated. The closed-form expressions of amplitude ratios of all reflected/transmitted waves are derived utilizing appropriate electro-mechanical boundary conditions. As the amplitude ratios cannot be used exclusively to validate the numerical results, the expressions of energy ratios of all reflected/transmitted waves and interaction energy are derived, which exhibit the influence of existing parameters, and the law of conservation of energy is established. This work presents a novel effort to develop a connection between deriving the PFRC’s micro-mechanical model and analyzing the wave reflection/transmission phenomenon in it.

We demonstrate a large area time domain terahertz (THz) imaging system capable of scanning 1 meter square area in less than 20-100 minutes for several security applications. The detection of concealed explosives; metallic and non-metallic weapons (such as ceramic, plastic or composite guns and knives); and flammables in luggage, packages and personnel has been demonstrated. Transmission mode images of luggage containing threat items are discussed. Reflection mode images of luggage and personnel are discussed. Time domain THz images can be analyzed for 3 dimensional and volumetric information. Time domain THz images have advantages over coherent narrow band imaging methods, with freedom from interference artifacts and with greater ability to discard irrelevant or intervening reflections through time discrimination.

The method of estimating Head-Related Impulse Responses (HRIRs) from impulse responses involving the reflection and/or noise was investigated. This method is based on the Auto Regressive (AR) model of HRIR. The AR coefficients are estimated using the conventional Linear Prediction (LP) algorithm. The data used for estimation are the part of the response which is regarded as the direct component of the impulse response from the sound source to the ear, i.e., the part of the HRIR. A computer simulation in which the method is applied to the estimation of the HRIRs of the Head-and-Torso Simulator (HATS) showed the following: (1) SDR was improved in some directions examined when the order of AR coefficients is half of the cutout points. Otherwise the improvement of SDR was not observed. Although the reason for such occasional improvement remains unclear, the improvement demonstrates that the proposed method can better estimate the part of the HRIRs lost by reflection and/or noise; (2) The number of samples used for the computation of AR coefficients greatly affects the estimation accuracy. Ideally, the whole waveform of the HRIR is useful for estimation of the AR coefficients, which shows that the proposed method brings about accurate estimation in an ideal situation.