Inhomogeneity Factor Research Articles

Role of tilted congruence and f(R) gravity on regular compact objects

The purpose of this paper is to check the impact of observer and Palatini $f(R)$ terms in the formulations of inhomogeneity factors of spherical relativistic systems. We consider Lema\^{i}tre-Tolman-Bondi dynamical model as a compact object and studied its evolution with both tilted and non-tilted observers. We performed our analysis for particular cases of fluid distribution in tilted frame and found some energy density irregularity variables. We found that these variables are drastically different from those observed by non-tilted observer. The conformal flat dust and perfect matter contents are homogeneous as long as they impregnate vacuum core. However, this restriction is relaxed, when the complexity in the fluid description is increased. The radial fluid velocity due to tilted congruences and Palatini $f(R)$ curvature terms tend to produce hindrances in the appearance of energy-density inhomogeneities in the initially regular spherical stellar populations.

Robust seed detection for coronary arteries segmentation using thresholded Frangi response

Automatic detection of initial seed points has become an essential step towards delineating coronary arteries in coronary computed tomography angiography (CCTA) images due to image inhomogeneity and other factors. Most coronary segmentation algorithms require user interaction for seed point selection, which may lead to erroneous segmentation. In this study, we present an improved technique of seed detection for coronary segmentation using a thresholded Frangi response. Before computing region of interest (ROI), the proposed method first computes the Frangi response of the complete CCTA volume, followed by thresholding with respect to quantile and median values, and then the ROI selection procedure is applied. Further, this procedure is joined with a feature that is built according to the resemblance among consecutive orthogonal cross-sections. The proposed method was evaluated on nine clinical datasets, and the proposed framework automatically detected coronary seeds accurately and can be used for an accurate delineation of coronary arteries. The obtained results were compared qualitatively and quantitatively by a radiologist, and the proposed method outperformed the previous method with an improvement of 45.9%.

Dosimetric Accuracy Using the New Mathematical Tools for Inhomogeneous Denser Medium

It is possible to obtain a quality assurance (QA) of the dosimetry within a short time by using the new mathematical tools for a water phantom where dose measurements were made at two points only for a few square field sizes of the linear accelerator beam. The human body is not homogeneous. Water phantom makes it possible to create inhomogeneous phantoms by introducing blocks within it at suitable position to simulate body organs that may affect the dosage significantly. Two low cost inhomogeneous phantoms were developed using cork sheets and acrylic blocks to simulate the effects of normal lungs and cancerous lungs respectively using finite geometry and layer geometry. Monte Carlo Simulation was performed for each of these phantoms and detailed vertical and horizontal dose measurements were carried out. Percentage Depth Dose (PDD) measurements performed for the two point formalisms fixed at 100 cm Source to Surface Distance for both the homogeneous and inhomogeneous mediums and were compared with the doses generated by a Treatment Planning System. The quality of the methodology has ascertained firstly for a homogeneous medium. The formulated formalism of Tissue phantom ratio (TPR) was employed for inhomogeneous media particularly for finite and layer geometry using scattering factors obtained initially from detailed depth dose measurements. TPR conversion factors from homogeneous to inhomogeneous geometry were determined. The scattering factor was determined as a ratio of the depth dose in inhomogeneous medium and homogeneous medium. The quality factors of TPR values of homogeneous to inhomogeneous TPR conversion factor were also calculated. For all cases, the present results gave values which agreed very well to either actually measured values or with values calculated using TPS and these were also less than the international standard of deviation of 5%. The low cost inhomogeneous phantoms through modifications of the water phantom deliver better information on QA consuming less time than before and offering better QA than a detector array. The present work will have an impact on the quality assurance of dosimetry and safety of radiotherapy.

Brittle Fracture Modeling for Steel Structures operated in the Extreme

The Extreme here is an environment that contains conditions that are hard to survive even for steel structures due to extreme temperature, corrosion, inappropriate service and repair. So not only the mechanical properties and behavior of steel structures are important for structural integrity but also the phase transition processes, inhomogeneity and uncertainty factors. These problems are observed and discussed in the paper consisting of three main theoretical parts: the multiscale modeling approach for structural damage accumulation, the theory of low-temperature brittle-ductile transition for bcc steels, and uncertainty factors estimation concept. The applications describe the locomotive tire lifetime estimation at low temperature conditions, weld inhomogeneity calculation and bridge service life prediction. The modeling approach based on Kachanov-Rabotnov structural damage accumulation theory and stochastic crack growth modeling. Bayesian probability approach has been used for uncertainty factor estimation. The experimental research included the internal friction study of bcc steel, the mechanical tension and impact toughness testing for probes prepared from used in climatic condition of Central Yakutia locomotive tire steel, the low-cycling testing for welded steel probes, and microhardness estimation. The inhomogeneity of probes used for stress and strain state modeling. The microstructural study reveals the small cracks in heat affected zone so the size and distance between such defects used for stochastic modeling visualization of crack propagation and crack velocity estimation. The concept of service life estimation for welded steel bearing for bridges has been presented.

Effect of Rigid Boundary on the Propagation of Torsional Surface Waves in Heterogeneous Earth Media

The present paper has been framed to study the influence of rigid boundary on the propagation of torsional surface waves in an inhomogeneous crustal layer over an inhomogeneous half space. In the layer the rigidity and density vary linearly along the depth whereas the inhomogeneous half space exhibits inhomogeneity of exponential type. The dispersion equation is derived in a closed form. For a homogeneous layer over a homogeneous half space the dispersion equation turns into the dispersion equation of the propagation of Love type wave under rigid boundary. The effects of inhomogeneity factor on the phase velocity are depicted by means of graphs.

Filtration Properties of Nanofiber/Microfiber Mixed Filter and Prediction of its Performance

ABSTRACTThere is an increasing demand of air filters with a high collection performance, i.e., high collection efficiency and low pressure drop, for the application to indoor air cleaning. Air filters consisting of nanofibers have attracted great interests since they may have a low pressure drop because of slip flow effect and high collection efficiency due to interception. Although various nanofiber filters are available on the market, their collection performance is not as high as expected by the conventional filtration theory because non-uniform packing of fibers plays a significant role. In the present work, the collection performance of nanofiber (780 nm) and microfiber (11.2 µm) mixed filters with various mixing fractions was studied in order to maximize the quality factor of filter, qF, as a function of mixing fraction of nanofibers. The collection performance of mixed fiber filters was predicted by using theoretical equations reported by Bao et al. (1998) for bimodal distribution of fibers. As a result, it was found that the mixed fiber filters had a uniform fiber packing compared to laminated filters and that the collection efficiency was well predicted by introducing the inhomogeneity factor calculated for the filter consisting of two distinct fiber sizes. Furthermore, we found that the mixed fiber filter with the nanofiber mixing fraction of 5% in mass had the highest quality factor.

Effect of the Dielectric Inhomogenity Factor's Range on the Electrical Tree Evolution Solid Dielectrics

The main contribution of the presented paper is to investigate the influence of the Dielectric Inhomogeneity Factor on the electrical tree evolution in solid dielectrics using cellular automata. We have a sample of the XLPE which is located between needle-to-plane electrodes under DC voltage. The electrical tree emanates from the end of the needle in which the electric stress attains a dielectric strength of the material. At every time step, Laplace's equation is solved to calculate the potential distribution which changes according to electrical tree development. Dynamic simulations clearly demonstrate the influence of the range of the Dielectric Inhomogeneity Factor on the electrical tree growth. Simulation results confirm the published technical literature.

Die Profile Optimization of Rectangular Cross Section Extrusion in Plane Strain Condition Using Upper Bound Analysis Method and Simulated Annealing Algorithm

Extrusion die profile has a significant role on material flow characteristics, product microstructure, die life, and required load. Nowadays, economic requirements and effort to improve and homogenize metallurgical product properties have compelled the researchers to modify the conventional constant angle extrusion dies by employing streamlined die profiles. In the present research work, an optimum plane strain extrusion profile has been presented through implementation of upper bound analysis and Bezier curve in a simulated annealing (SA) algorithm to minimize the process force and its redundant work. The effect of material properties, friction conditions, reduction of area, and cross-sectional ratio on the optimum die profile is considered. The results of finite-element simulation proved that utilizing the optimum curved die instead of the constant angle die is superior regarding the decrease of the maximum required force, 10.5%, and the product inhomogeneity factor (IF), 50%. In addition, based on stress analysis of die/work piece interfaces, it is expected that the die life of optimal curved dies be longer than that of the optimum constant angle dies. Also, it has been demonstrated that the material work hardening characteristics does not have remarkable effect on the optimum curved die profile.

Dynamics of tilted cylindrical geometry

In this paper, we study the dynamics of tilted cylindrical model with imperfect matter distribution. We formulate the field equations and develop relations between tilted and non-tilted variables. We evaluate kinematical as well as dynamical quantities and discuss the inhomogeneity factor. We also obtain the Raychaudhuri equation to study evolution of expansion scalar. The solutions of field equations are also investigated for static cylinder under isotropy and conformally flat condition. Finally, we analyze some thermoinertial aspects of the system.

The Effect of Homogenous and Inhomogeneous Broadening and Gain Compression Factor on Dynamical Characteristics and Modulation of Tunneling Injection InGaAs/GaAs Quantum Dot Lasers

The Effect of Homogenous and Inhomogeneous Broadening and Gain Compression Factor on Dynamical Characteristics and Modulation of Tunneling Injection InGaAs/GaAs Quantum Dot Lasers

Causes of irregular energy density inf(R,T)gravity

We investigate irregularity factors for a self-gravitating spherical star evolving in the presence of imperfect fluid. We explore the gravitational field equations and the dynamical equations with the systematic construction in $f(R,T)$ gravity, where $T$ is the trace of the energy-momentum tensor. Furthermore, we analyze two well-known differential equations (which occupy principal importance in the exploration of causes of energy density inhomogeneities) with the help of the Weyl tensor and the conservation laws. The irregularity factors for a spherical star are examined for particular cases of dust, isotropic and anisotropic fluids in dissipative and non-dissipative regimes in the framework of $f(R,T)$ gravity. It is found that as the complexity in the matter with the anisotropic stresses increases, the inhomogeneity factor has more correspondences to one of the structure scalars.

Effect of irregularity on torsional surface waves in an initially stressed anisotropic porous layer sandwiched between homogeneous and non-homogeneous half-space

The present paper is concerned with the propagation of torsional surface waves in an initially stressed anisotropic porous layer sandwiched between homogeneous and non-homogeneous half-space. We assume the quadratic inhomogeneity in rigidity and density in the lower half-space and irregularity is taken in the form of rectangle at the interface separating the layer from the lower half-space. The dispersion equation for torsional waves has been obtained in a closed form. Velocity equation is also obtained in the absence of irregularity. The study reveals that the presence of irregularity, initial stress, porosity, inhomogeneity and anisotropy factor in the dispersion equation approves the significant effect of these parameters in the propagation of torsional waves in porous medium. It has also been observed that for a uniform media, the velocity equation reduces to the classical result of Love wave.

Influence of electric charge and modified gravity on density irregularities

This work aims to identify some inhomogeneity factors for plane symmetric topology with anisotropic and dissipative fluid under the effects of both electromagnetic field as well as Palatini $f(R)$ gravity. We construct the modified field equations, kinematical quantities and mass function to continue our analysis. We have explored the dynamical quantities, conservation equations and modified Ellis equations with the help of a viable $f(R)$ model. Some particular cases are discussed with and without dissipation to investigate the corresponding inhomogeneity factors. For non-radiating scenario, we examine such factors with dust, isotropic and anisotropic matter in the presence of charge. For dissipative fluid, we investigate the inhomogeneity factor with charged dust cloud. We conclude that electromagnetic field increases the inhomogeneity in matter while the extra curvature terms make the system more homogeneous with the evolution of time.

Cloaking the magnons

We propose two approaches to cloak the spin waves (magnons) by investigating magnetization dynamics. One approach is based on a spatially inhomogeneous anisotropic magnetic moment tensor. The other mechanism is using a spatially inhomogeneous anisotropic gyromagnetic factor tensor and an inhomogeneous external magnetic field. For both approaches, the damping tensor is also inhomogeneous and anisotropic. The magnetic characteristic functions of the magnetic materials have been theoretically derived for both mechanisms. A non-magnetic core, which prevents magnons from entering and consequently distorts the spin wave propagation, can be cloaked by a structured magnetic shell to redirect the spin wave around the core using the above design mechanisms. We discuss the feasibility of the proposed mechanisms in an ensemble of quantum dot molecules and magnetic semiconductors. The proposed approaches shed light on transformation magnonics, and can be utilized for future spin-wave lenses, concentrators, low back-scattering waveguides, and ultimately quantum computing.

Propagation of Torsional Surface Wave in Anisotropic Layer Between Two Half-Spaces

The present paper studies the possibility of propagation of torsional surface waves in an inhomogeneous anisotropic layer lying between two half-space. Upper half-space is considered as homogeneous as well as lower half-space is heterogeneous. Both the half-spaces are assumed to be under compressive initial stress. The study reveals that under the assumed conditions, a torsional surface wave propagates in the medium. The dispersion relation of torsional surface wave has been obtained in the presence of heterogeneity, initial stress and anisotropic, and it is observed that the inhomogeneity factor due to quadratic and hyperbolic variations in rigidity, density and initial stress of the medium decreases the phase velocity as it increases. The result also shows that the initial stresses have a pronounced influence on the propagation of torsional surface waves. In the absence of anisotropy, Initial stress, inhomogeneity and rigidity of the upper half-space, then the dispersion relation coincide with the classical dispersion relation of Love wave.

Verification of slip flow in nanofiber filter media through pressure drop measurement at low-pressure conditions

Abstract Slip flow phenomena are of great concern in aerosol filtration because of their ability to develop low-pressure drops and high collection efficiency air filters by using nanofibers. However, it is a difficult task to verify the slip flow effect on the reduction in pressure drop because the inhomogeneity in fiber packing also results in a decrease in pressure drop. In the present work, we propose pressure drop measurements at low pressures to verify the slip flow effect by distinguishing the effects of filter inhomogeneity. We found that the experimental dimensionless drag at low-pressure conditions, which was obtained with correction by the inhomogeneity factor measured at atmospheric pressure, followed the theoretical prediction that includes the slip flow correction (Kirsch and Stechkina, 1978) for both conventional PTFE and newly developed fluororesin nanofiber filter media. Because the dimensionless drags of both nanofiber filters decreased inversely proportional to the Knudsen number, we concluded that these nanofiber filters have low-pressure drops because of slip flow effects.

Interaction between diffusion and stresses in composition-gradient electrodes

Composition-gradient electrode material is one of the most promising materials in lithium-ion battery resulting from its inhomogeneous mechanical and electrochemical properties. The present work studies the interaction between stresses and diffusion in spherical composition-gradient electrodes. The large deformation theory is adopted to establish the mechanical equations, and the stress-induced diffusion is adopted to establish the diffusion equations. Compared with the interaction effects on lithium-ion distributions and stress distributions in homogeneous electrodes, the results in composition-gradient electrodes may show differences. Three inhomogeneous factors are investigated here—diffusion coefficient, elastic modulus and partial molar volume. When elastic modulus and diffusion coefficient are inhomogeneous, the interaction effects increase the magnitudes of radial stresses initially and then reduce the magnitudes of radial stresses, whose variations are same as the hoop stresses at the electrode center. On the other hand, the interaction effects can reduce the magnitudes of hoop stresses at electrode surface throughout the process of charge. However, when partial molar volume is inhomogeneous, the interaction effects show totally different influences on lithium-ion concentration distributions and stress distributions compared with those in homogeneous electrodes. The interaction effects play a positive role for the decreasing form of partial molar volume Ω(R), while the opposite conclusion hold for the increasing form of partial molar volume Ω(R). The results can guide the design of composition-gradient electrode materials.

Torsional surface waves in an inhomogeneous layer over a gravitating anisotropic porous half-space

The present work aims to deal with the propagation of torsional surface wave in an inhomogeneous layer over a gravitating anisotropic porous half space. The inhomogeneous layer exhibits the inhomogeneity of quadratic type. In order to show the effect of gravity the equation for the velocity of torsional wave has been obtained. It is also observed that for a layer over a homogeneous half space without gravity, the torsional surface wave does not propagate. An attempt is also made to assess the possible propagation of torsional surface waves in that medium in the absence of the upper layer. The effects of inhomogeneity factors and porosity on the phase velocity are depicted by means of graphs.

Free vibration analysis of homogeneous and FGM skew plates resting on variable Winkler-Pasternak elastic foundation

In this research study, free vibration of homogeneous and functionally graded skew plates resting on Winkler-Pasternak elastic foundation is investigated. The elastic foundation is assumed to be a combination of Winkler and Pasternak elastic support with linearly or parabolically variable stiffness coefficients along the directions. Plate skewness is obtained by using a transformation from Cartesian coordinate to oblique coordinate system. The energy of the functionally graded skew plate and the elastic foundation is derived, and the natural frequency of the plate is calculated by the Rayleigh-Ritz method. The results are compared with available results in the literature, showing an excellent agreement. Furthermore, a parametric study is carried out to thoroughly investigate the effects of different boundary conditions, skew angles, inhomogeneity factors, and variable elastic foundation stiffness on the free vibration of skew plates.

Rheological model of Love wave propagation in viscoelastic layered media under gravity

Purpose – The purpose of this paper is to deal with the propagation of Love waves in inhomogeneous viscoelastic layer overlying a gravitational half-space. It has been observed velocity of Love waves depends on viscosity, gravity, inhomogeneity and initial stress of the layer. Design/methodology/approach – The dispersion relation for the Love wave in closed form is obtained with Whitaker’s function. Findings – The effect of various non-dimensional inhomogeneity factors, gravity factor and internal friction on the non-dimensional Love wave velocity has been shown graphically. The authors observed that the dispersion curve of Love wave increases as the inhomogeneity factor increases. It is seen that increment in gravity, inhomogeneity and internal friction decreases the damping phase velocity of Love waves but it is more prominent in case of internal friction. Originality/value – Surface plot of Love wave reveals that the velocity ratio increases with the increase of non-dimensional phase velocity and non-dimensional wave number. The above results may attract seismologists and geologists.