Effect Of Non-homogeneity Research Articles

On the Addams family of discrete frailty distributions for modeling multivariate case I interval-censored data.

Random effect models for time-to-event data, also known as frailty models, provide a conceptually appealing way of quantifying association between survival times and of representing heterogeneities resulting from factors which may be difficult or impossible to measure. In the literature, the random effect is usually assumed to have a continuous distribution. However, in some areas of application, discrete frailty distributions may be more appropriate. The present paper is about the implementation and interpretation of the Addams family of discrete frailty distributions. We propose methods of estimation for this family of densities in the context of shared frailty models for the hazard rates for case I interval-censored data. Our optimization framework allows for stratification of random effect distributions by covariates. We highlight interpretational advantages of the Addams family of discrete frailty distributions and theK-point distribution as compared to other frailty distributions. A unique feature of the Addams family and the K-point distribution is that the support of the frailty distribution depends on its parameters. This feature is best exploited by imposing a model on the distributional parameters, resulting in a model with non-homogeneous covariate effects that can be analyzed using standard measures such as the hazard ratio. Our methods are illustrated with applications to multivariate case I interval-censored infection data.

Non-homogeneity effect on the vibration of the rectangular visco-elastic plate subjected to the linear temperature effect with quadratic thickness variation in both directions

The present work investigates the effect of non-homogeneity on the vibration of a rectangular visco-elastic plate. The plate is subjected to linear temperature variation in the x-direction with quadratic thickness variation in both directions. The quadratic variation has been considered in the material density of the plate only along the x-axis, and it is assumed that non-homogeneity transpires because of this variation. The governing differential equation is solved using the Rayleigh-Ritz technique. All four edges of the plate should be clamped to drive the frequency equation. Deflection and time period have been evaluated for several combinations of values of the thermal constant, constant of nonhomogeneity, taper constants, and length-to-width ratio (aspect ratio) for the first two vibrationmodes of the clamped plate. The results presented are compared with those found in the literature.

Positive solutions for a nonhomogeneous nonlocal logistic equation

In this paper, we deal with the nonhomogeneous nonlocal dispersal equation∫ΩJ(x−y)u(y)dy−u(x)+λu(x)−a(x)up(x)+Mf(x)=0,x∈Ω¯, where Ω is a bounded and smooth domain, p>1 and the parameters M,λ>0. The kernel function J(x) is nonnegative and symmetric, and the coefficients a,f∈C(Ω¯) are assumed to be nonnegative. We are interested in the existence, uniqueness and asymptotic profiles of positive solutions. It is shown that the structure of positive solutions makes a fundamental change due to the nonhomogeneous effect. Moreover, we study the sharp profiles of positive solutions when there is a spatial degeneracy of a(x). The result exhibits that the blow-up profiles are determined by the degeneracy of a(x).

Investigation of heat and mass transfer performance in Casson fluid flow over nonlinear stretching sheet: Impact of novel similarity transformations

This article primarily aims to utilize novel similarity transformations that were created to overcome a limitation found in previous research. These similarity methods have proven to be effective in finding solutions to systems of partial differential equations. The study analyzed mass and heat transfer in a Casson fluid near a boundary on a stretchy, permeable surface, considering radiative heat transmission and non-homogeneous thermal effects. It focused on two heating methods: prescribed surface temperature (PST) and prescribed surface heat flux (PHF). Prior research involving stretchable surfaces has mostly used non-dimensional similarity metrics related to one variable that is not dependent on others (e.g., only or), which resulted in certain errors. To tackle this issue, we have introduced a novel set of similarity transformations that encompass all the independent variables in the equations. that are being studied (that is, x and y ). This novel strategy seeks to significantly improve the accuracy of our results. The equations that dictate the behavior were transformed into nonlinear ordinary differential equations by employing specific similarity transformations. The Runge–Kutta-Fehlberg approach proved to be highly efficient in computing solutions, yielding fourth- and fifth-order approximations. The solutions were found to rely on various physical parameters, including the Casson fluid factor, Prandtl and Schmidt numbers, heat source and sink components, radiation parameters, and suction and injection factors. These parameters elucidate the behavior of velocity, concentration, and temperature profiles. When the Casson parameter increases by 212.5%, the temperature increases by 0.5270% for the PST case and by 1.4050% for the PHF case under suction conditions, and similarly, rises by 1.3238% for the PST case and by 5.7224% for the PHF case under blowing conditions.

Investigating the Influence of Non-Uniform Characteristics of Layered Foundation on Ground Vibration Using an Efficient 2.5D Random Finite Element Method

High-speed train operation may cause vibration near track facilities and propagate far through the ground, affecting people’s lives, work, and normal use of precision instruments in an urban environment. An efficient numerical method is proposed to calculate the non-uniform ground vibration under a moving high-speed railway load. The theory of stochastic variables is used to describe the soil spatial variability of the non-uniform layered elastic ground, and the coupled 2.5D random finite element method (FEM) is proposed to reduce the computational cost without losing accuracy. Vibration propagation and attenuation of the non-uniform layered ground are investigated and the effect of train speed and soil non-homogeneity are analyzed. Results show that (1) at cross speed and high speed, the homogeneity coefficient of the layered ground has the most important influence on the ground vibration amplitude; (2) the upward acceleration is much larger than the downward acceleration at most speeds, and at cross speed and high speed, the acceleration amplitude decreases with the increase in the homogeneity coefficient; (3) as train speed increases from 60 m/s to 130 m/s, the influencing range of the homogeneity coefficient increases to 10 m from 2 m; and (4) the phenomenon of an in increase in local rebound can be observed in the velocity and acceleration attenuation curve at cross speed when the ground soil has a weaker homogeneity.

Effect of Non-Homogeneity and Initial Stress on Torsional Surface Wave Propagation in Initially Stressed Poroelastic Medium Bounded by a Heterogeneous Layer and Half-Space

Effect of Non-Homogeneity and Initial Stress on Torsional Surface Wave Propagation in Initially Stressed Poroelastic Medium Bounded by a Heterogeneous Layer and Half-Space

Examining the relationship between brain activation and proxies of disease severity using quantile regression in individuals at risk of Alzheimer's disease

Previous studies have reported a pattern of hyperactivation in the pre-dementia phase of Alzheimer's disease (AD), followed by hypoactivation in later stages of the disease. This pattern was modeled as an inverse U-shape function between activation and markers of disease severity. In this study, we used quantile regression to model the association between task-related brain activation in AD signature regions and three markers of disease severity (hippocampal volume, cortical thickness, and associative memory). This approach offers distinct advantages over standard regression models as it analyzes the relationship between brain activation and disease severity across various levels of brain activation. Participants were 54 older adults with subjective cognitive decline+ (SCD+) or mild cognitive impairment (MCI) from the CIMA-Q cohort. The analysis revealed an inverse U-shape quadratic function depicting the relationship between disease severity markers and the activation of the left superior parietal region, while a linear relationship was observed for activation of the hippocampal and temporal regions. Quantile differences were observed for temporal and parietal activation, with more pronounced effects observed in the higher quantiles of activation. When comparing quantiles, we found that higher quantile of activation featured a greater number of individuals with SCD+ compared to mild cognitive impairment (MCI). Results are globally consistent with the presence of an inverse-U shape function of activation in relation to disease severity. They study also underscores the utility of employing quantile regression modeling as the modeling approach revealed the presence of non-homogeneous effects across various quantiles.

Embedding Fiber Bragg Grating Sensors in Carbon Composite Structures for Accurate Strain Measurement

Fiber Bragg Grating (FBG) sensors written by femtosecond laser pulses in polyamide-coated low bending loss optical fibers are succesfully embedded in carbon composite structures, following laminating and light resin moulding processes which optimize the size of each ply to address aesthetic, drapability and structural requirements of the final components. The sensors are interrogated by a tunable laser operating at around 1.55 μm and their response to temperature and strain variations is characterized in a thermally controlled chamber and by bending tests using suspended calibrated loads and a laser scanning system. Experimental results are in good agreement with simulations, confirming that the embedding process effectively overcomes potential issues related to FBG spectral distortion, birefringence and losses. In particular the effects of the composite material non homogeneity and FBG birefringence are investigated to evaluate their impact on the monitoring capabilities. A bi-material mechanical beam model is proposed to characterize the orthotropic laminates, pointing out better accuracy in estimating the applied load with respect to the classical homogeneous beam model. A comparative analysis, performed on different instrumented carbon composite samples and supported by theory, points out the repeatability of the FBG sensors embedding process and the effectiveness of the technology for real time accurate strain measurement. Based on such measurements damages and/or changes in local stiffness can be effectively detected, allowing for structural health monitoring of composite structures for applications in specific industrial fields like automotive and aerospace.

Partial suppression of acetaminophen dust explosion by synergistic multiphase inhibitors

Drug powder explosions pose a potential threat to the process safety of pharmaceutical companies in the processing and storage of products. To explore a reasonable and efficient technology to prevent and mitigate the explosion of combustible drug dust, an experimental system of vertical combustion pipeline equipped with a partial suppression device was built, and the performance of N2 and CO2 loaded with hydrophobic SiO2 encapsulated SiO2 gel (HSESG) respectively to synergistically suppress the explosion of acetaminophen powder was investigated. The results demonstrated that N2/HSESG and CO2/HSESG were effective in reducing the flame average velocity (Vavg), maximum velocity (Vmax), velocity to the top of the pipe (Vtop), and maximum flame temperature (Tmax). N2 loaded with 60 wt% HSESG reduced the Vmax, Vavg, and Vtop of the explosion flame by 68.1%, 66.7%, and 81.3%, respectively, and Tmax by 58.7%. Acetaminophen dust explosion could be completely suppressed by CO2/40 wt% HSESG with 83.7%, 73.0%, and 85.7% decrease in Vmax, Vavg, and Vtop values, respectively, and 80.7% decline in Tmax. The results of thermal decomposition tests and residues characterization indicated that the partial suppression of N2/HSESG and CO2/HSESG was mainly accomplished through the synergistic interaction among thermodynamic, kinetic, and non-homogeneous chemical effects. Subsequently, the reason for the more pronounced suppression effect under the impact of CO2/HSESG was further explained.

Tensor response quantile regression with neuroimaging data.

Collecting neuroimaging data in the form of tensors (i.e. multidimensional arrays) has become more common in mental health studies, driven by an increasing interest in studying the associations between neuroimaging phenotypes and clinical disease manifestation. Motivated by a neuroimaging study of post-traumatic stress disorder (PTSD) from the Grady Trauma Project, we study a tensor response quantile regression framework, which enables novel analyses that confer a detailed view of the potentially heterogeneous association between a neuroimaging phenotype and relevant clinical predictors. We adopt a sensible low-rank structure to represent the association of interest, and propose a simple two-step estimation procedure which is easy to implement with existing software. We provide rigorous theoretical justifications for the intuitive two-step procedure. Simulation studies demonstrate good performance of the proposed method with realistic sample sizes in neuroimaging studies. We conduct the proposed tensor response quantile regression analysis of the motivating PTSD study to investigate the association between fMRI resting-state functional connectivity and PTSD symptom severity. Our results uncover non-homogeneous effects of PTSD symptoms on brain functional connectivity, which cannot be captured by existing tensor responsemethods.

Syntheses of novel topical hemostatic agents based on pectin biopolymer aiming hemorrhage control: Thromboelastographic studies and non-homogeneous swelling effect

Topical hemostatic agents based on pectin biopolymer were synthesized and characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy (SEM), Phase Contrast Microscopy, Infrared spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC) and Solid State 13C MAS NMR. The pectin biofilms were crosslinked with CaCl2 using different concentrations of Ca2+ solutions ( 4.5 ×10-2 M, 2.7 ×102 M, 4.5 ×102 M). 13C MAS NMR and FT-IR data revealed that crosslinking with Ca2+ was successfully achieved, in line with the formation of egg-box type structures. The anti-hemorragic effect caused by the interaction of the red blood cells with the pectin biofilm interface was showed in details by phase contrast microscopy. The images showed that higher Ca2+ concentration (0.45 ×102 M) positively favor the coagulation cascade by facilitating the migration and an orderly stacking of the red blood cells into the pectin biofilm scaffold. The hemostatic action of the prepared pectin biofilms were analyzed by Thromboelastography (TEG). The results indicated that the hemostatic action of the biofilms is as effective as that of the hybrid materials reported in the literature, indicating that these pectin biofilms have potential to become safe topic hemostat. It was also observed a non-homogeneous swelling effect caused by the interaction between the pectin biofilms interface and blood cells which induced a rapid bending and a bucking instability that swollen the pectin network.

Power fluctuation and wake characteristics of tidal stream turbine subjected to wave and current interaction

Turbulence and waves interactions are present in tidal streams ensuing the poorly comprehended unsteady state. To clarify several aspects of the wave influence on the flow and turbine power output, the 1:60 scale rotor experiments (Froude similarity) are carried out: current only and with parallel waves. Compared to steady predictions, the mean power in current and with waves against a range of rotor speeds are analogous. The power spectrum under wave conditions is almost a superposition of current and additional components, including wave frequency, rotation frequency, and their mixing frequency. The waves distort significantly the operating flow, by augmenting the turbulent intensity, wake rotation, anisotropy, and Reynold stresses, both in large proportion with the wave energy flux. The mean wake recovery was analogous, with deficits following symmetrical distributions of diminishing height longitudinally. Strikingly, the turbulence in the undisturbed flow resembles mostly near the pancake shape. This transitions towards the cigar-shaped in both most of the stream tube due to the turbine obstruction, and of the channel with the wave introduction. Further studies are required to validate these findings on non-isotropy and non-homogeneous effects in other wave conditions, such as a range of frequencies, heights and incident directions.

Vertical Bearing Capacity of Foundations with Large Embedment Depth in Normally Consolidated Clay

Foundation bearing capacity has been well studied in homogeneous soil under a condition of embedment depth within five times the foundation effective characteristic length. However, the penetration depth of deep-sea anchoring foundations can be far more than five times the effective characteristic length. This study aims to investigate the vertical bearing capacity of the strip, circular, and conical foundations within a large embedment depth range in normally consolidated clay. Parametric studies were conducted to analyze the effect of soil nonhomogeneity and foundation–soil interface roughness with the aid of the finite-element method combined with a developed subroutine. Results show that no critical value was found for the vertical bearing capacity even at a large embedment depth. The embedment depth also influences the relationship between the soil nonhomogeneity and the foundation bearing capacity factor, Nc. Friction coefficient has a great influence on Nc of the conical foundation. Comprehensive formulas for calculating Nc of the three common foundations are proposed based on parametric studies. The simple formulas will provide a reference for geotechnical engineers.

Improved asynchronous stabilization method for nonhomogeneous Markovian jump fuzzy systems with incomplete transition rates

This paper proposes an improved asynchronous stabilization method for nonhomogeneous Markovian jump fuzzy systems (MJFSs) with incomplete transition rates via a nonparallel distributed compensation (non-PDC) control scheme. To cover a more realistic situation in the continuous-time MJFS domain, this paper focuses on addressing the following issues differently from previous studies: 1) emergence of a nonhomogeneous Markov process and asynchronous control mode, 2) separation of the Lyapunov matrix from the control gain within stabilization conditions, and 3) relaxation of stabilization conditions subject to multiple time-varying parameters. Specifically, the effects of nonhomogeneity and asynchronism are simultaneously reflected in the stabilization conditions, and separation and relaxation techniques are additionally developed as needed. Finally, the advantages of our method are illustrated through two examples: the first is provided to show the effectiveness of the proposed separation technique, and the second is provided to show that the relaxed stabilization conditions are less conservative than previous results.

Response of rigid circular plate in a functionally graded transversely isotropic, half-space under horizontal steady-state excitation

In this paper, a theoretical formulation for lateral translation and impedance function of a rigid foundation in a transversely isotropic functionally graded (TIFG) half-space is presented. Accordingly, the medium is considered linear elastic and the elastic constants of materials vary exponentially along the depth for considering the effect of elastic non-homogeneities. The relax treatment of mixed boundary value problem is formulated by integrating the transformed kernels of Green’s functions over the foundation area with unknown surface traction function, which can be reduced into a Fredholm integral equation. The results represent the impact and treatment of frequency and material anisotropy through the medium. In addition, static and dynamic distribution of tangential shear stress over the foundation for surface and embedded disk extracted and the cutoff frequency is found out explicitly. The proposed solution gives exact concurrence with accessible literature.

Numerical investigation on the temperature effect in nanometric cutting of polycrystalline silicon

In nanometric cutting, the deformation mechanism is significantly affected by the cutting temperature. In this paper, molecular dynamics simulation was conducted to investigate the cutting mechanism of polycrystalline silicon with increasing temperature. The surface generation, plastic deformation, and phase transition mechanism were discussed with consideration of the effect of grain boundaries and non-homogeneity of crystal orientation in workpiece. The results indicate that the surface generation and subsurface damage mechanism of polycrystalline silicon is greatly influenced by the cutting temperature. Squeeze of amorphous atoms into grain boundaries is observed at room temperature while sliding of grains becomes more apparent when the cutting temperature is increased. Besides, intra-granular and inter-granular fracture can be detected near the triple junction, leading to voids and cracks on the machined surface. Furthermore, the plastic deformation is promoted with increasing cutting temperature, and the deformation depth for polycrystalline silicon is larger than that for single-crystal silicon. Moreover, the amorphization of crystal phase in workpiece involves intra-granular and inter-granular mode. When the cutting temperature is increased, the inter-granular amorphization can be effectively promoted. In addition, the recrystallization is observed when cutting polycrystalline silicon at high temperature while the crystal purity of the machined surface is less than that in single-crystal silicon.

Torsion vibration of foundation in a functionally graded transversely isotropic, linearly elastic half-space

The compliance function of a torsion excitation plays an important role in the response of dynamic excitation and is widely used in applied mechanics, foundation vibration and soil-structure interaction (SSI) problems. In this paper, an analytical and efficient method is presented to calculate the SSI coefficients of compliance function due to torsional oscillation of a rigid foundation in a transversely isotropic functionally graded (TIFG) half-space. Accordingly, the medium is considered linear elastic and the properties vary along the depth in exponential form to model the effect of elastic non-homogeneities. The problem is formulated by integrating the transformed components of traction acting on the foundation region which can be changed into a Fredholm integral equation. The results represent the impact of input frequency and material anisotropy on the SSI coefficients and shear stress variation. In addition, the distribution of angular shear stress over the foundation and the cut-off frequency is found explicitly. Also, the derived cut-off frequency of the present study characterizes whether wave propagation occurs in medium or not.

Nonhomogeneous volume conduction effects affecting needle electromyography: an analytical and simulation study

Objective. Needle electromyography (EMG) is used to study the electrical behavior of myofiber properties in patients with neuromuscular disorders. However, due to the complexity of electrical potential spatial propagation in nonhomogeneous diseased muscle, a comprehensive understanding of volume conduction effects remains elusive. Here, we develop a framework to study the conduction effect of extracellular abnormalities and electrode positioning on extracellular local field potential (LFP) recordings. Methods. The framework describes the macroscopic conduction of electrical potential in an isotropic, nonhomogeneous (i.e. two tissue) model. Numerical and finite element model simulations are provided to study the conduction effect in prototypical monopolar EMG measurements. Results. LFPs recorded are influenced in amplitude, phase and duration by the electrode position in regards to the vicinity of tissue with different electrical properties. Conclusion. The framework reveals the influence of multiple mechanisms affecting LFPs including changes in the distance between the source–electrode and tissue electrical properties. Clinical significance. Our modeled predictions may lead to new ways for interpreting volume conduction effects on recorded EMG activity, for example in neuromuscular diseases that cause structural and compositional changes in muscle tissue. These change will manifest itself by changing the electric properties of the conductor media and will impact recorded potentials in the area of affected tissue.

Bearing capacity of conical footings on clays considering combined effects of anisotropy and non-homogeneity

ABSTRACT A spudcan is one of the foundation systems widely used to support the load transferred from a jack-up platform for most offshore drilling operations. The spudcan is an axisymmetric footing with a conical shape. The study on the stability effects of anisotropic and non-homogeneous clays on the bearing capacity of this kind of footings is yet to be found in the current literature. This paper presents novel plastic solutions of the bearing capacity factor for conical footings on clays with linearly increasing anisotropic shear strength. The finite element limit analysis is employed to perform the bearing capacity solutions based on three dimensionless parameters including the cone apex angle, the strength gradient ratio, and the ratio between the undrained shear strength ratio obtained from the triaxial compression test and triaxial extension test. The proposed equations in this study provide a reliable solution to improve the current design standard for conical footings in anisotropic and non-homogeneous clays.

Asynchronous [formula omitted] observer-based control synthesis of nonhomogeneous Markovian jump systems with generalized incomplete transition rates

This paper deals with the problem of asynchronous H∞ observer-based control for continuous-time nonhomogeneous Markovian jump systems with generalized incomplete transition rates. Different from other existing papers, the effects of both nonhomogeneity and asynchronism on observer-based control design are discussed in detail to address more realistic phenomena. Furthermore, to decouple the Lyapunov matrix from the control gain while improving the control performance, this paper proposes a state extension method as an alternative to the conventional separation method. Not only that, to derive a set of LMI-based stabilization conditions, this paper presents a less conservative relaxation technique that reduces its computational burden. Finally, two illustrative examples are provided to show the validity of the proposed method.