Search

The role of strain in material properties is well-established, serving as a tool for altering atomic positions and defect formation, adjusting electronic structures and lattice vibrations, and influencing phase transitions, physical characteristics, and chemical properties. In this study, we conducted theoretical calculations of the binding energy and photoionization cross section (PCS) within a spherical core/shell quantum dot (CSQD) for the different transitions between the ground state of a donor impurity and the four low-lying conduction band states. During our study, we employed the finite element method to determine the energy levels and wave functions of the system within the effective mass approximation. Subsequently, we investigated the changes in PCS and binding energy while varying shell width under the influence of an applied electric field, considering both cases with and without the effect of strain. The strain effect was incorporated based on Hooke's law, and we developed specific expressions and utilized the continuum linear elasticity mechanical model for a single spherically symmetric shell. The results demonstrate that the strain correction enhances the binding energy of the four low-lying energy levels, leading to a shift of the PCS peaks toward higher energies. Conversely, the application of an external electric field has varying effects depending on the specific transition being considered. We compared our theoretical results with available experimental data and found them to be in good agreement. The pronounced blue-shift and substantial enhancement in magnitude of PCS spectra concerning shell width, electric field, and strain make CSQDs highly promising candidates for applications in adjustable nano-optoelectronic devices. [ABSTRACT FROM AUTHOR]

The Schrödinger equation, which describes the behaviour of an electron with a single dopant inside the system, has been constructed. It is composed of three InAs cubic quantum dots (CQDs) immersed in GaAs material under the influence of an electric field applied along the x-growth direction. The equation has been solved by the finite element method within effective mass approximation. Our investigation shows that in the absence of the electric field, the binding energy (BE) reaches its maximum value when the impurity is at the centre of the system, with two smaller peaks at the other quantum dots (QDs) and a minimum at the centre of the barriers. The BE changes considerably with the electric field, especially for large dots and barriers. Both the BE and the photoionization cross-section (PCS) can be tuned by adjusting the system's dimensions and the electric field. An increase in the dot width, barrier width along the x-axis, or the electric field results in a redshift of photoionization when the impurity is at the centre of the system. The amplitude of the PCS also changes significantly, becoming more pronounced as the dot width or electric field increases and exhibiting non-monotonic behaviour in the case of the barrier width. [ABSTRACT FROM AUTHOR]

This study employs the finite element method based on the effective-mass approximation (EMA) to numerically investigate the behavior of impurities in multilayer cylindrical quantum dots (MLCQDs). We consider the applied hydrostatic pressure (P) in our numerical analysis. The study presents numerical results for macroscopic parameters that follow the electronic properties, the binding energy (Eb), and diamagnetic susceptibility (χdia) of the ground state (1 s) and some excited states (1p and 2 s) of the impurity in the MLCQDs. The Eb and the χdia for the three states are calculated as a function of the radius R , impurity position z 0 and the hydrostatic pressure. The numerical results show that the binding energies of impurities decrease with the radius for all levels. The E b 1 s and E b 1 p have three maximum values that typify the number of the quantum dot layer materials contained in our system. Moreover, the diamagnetic susceptibility for the three levels is strongly affected by the hydrostatic pressure, impurity location, and radius. [ABSTRACT FROM AUTHOR]

This work presented a study of nonlinear optical rectification (NOR) in a double quantum dot (DQD) made of GaAs / Ga 1 - η Al η As under the influence of pressure (P) and temperature (T) in the presence of shallow donor impurities. Both the approximations of the parabolic band and effective mass, as well as the variational technique, were used as tools to calculate the electronic and optical properties of the donor impurity. The result revealed a redshift in the peak of the nonlinear optical rectification as the width of the DQD increases due to the reduction of the energy difference. The amplitude of the resonant peak of nonlinear optical rectification was tuned by changing the barrier width, depending on the location of the impurity. The findings also showed that the maximum value of NOR shifted to higher energies as the pressure increased. The temperature change caused a blueshift in the maximum peak of NOR for both impurity positions as well as a decrease in their amplitude. Under external perturbations P and T, the NOR varied more significantly for impurities located at the border of the DQD compared to those at the center position of the dot. This was due to the higher confinement effect induced by the external factors in this position. [ABSTRACT FROM AUTHOR]

In the present paper, we look at how the applied electric field (EF) and structure sizes affect the shallow donor impurity binding energy ( E b ), polarizability ( P α ) and photoionization cross section (PCS) of multilayer spherical quantum dots (MSQDs). The structure's wave functions and eigenvalues are calculated using the finite-element method (FEM) and in the framework of the effective mass approximation. The obtained numerical results show that the system sizes (core radius and well width) and the external EF have a considerable influence on the E b of shallow donor impurity, polarizability as well as on the dependence of the PCS on the incident photon energy. [ABSTRACT FROM AUTHOR]

Mixed convection is commonly used in electronic cooling processes and nuclear reactor technology. As a result, this study aims to demonstrate the mathematical formulation of fluid flow, heat and mass transfer under the controlling physical parameters such as mixed convection, buoyancy ratio, suction, magnetic field, and rotation angle of the sheet. The variation in the wall shrinking velocity, temperature and concentration is expressed as an exponential function. Since controlling equations are partial differential equations, similarity transformations convert these partial differential equations to ordinary differential equations. Finally, these ordinary differential equations are considered as a non-linear and non-dimensional boundary value problem. The final solution of these ordinary differential equations is obtained numerically by applying the Matlab bvp4c programme. Stability analysis which determines the most stable numerical solution between duel solutions is also made using the Matlab bvp4c programme. Comparing the obtained computational results to previously published data shows a good agreement. All numerical results are graphically illustrated and explained, including the velocity, temperature and concentration profiles, skin friction coefficient, local Nusselt number, and local Sherwood number. [ABSTRACT FROM AUTHOR]

Linear stability analysis is performed to study the effects of nonuniform basic temperature gradients on the onset of Rayleigh- Bénard-Marangoni electroconvection in a dielectric Eringen's micropolar fluid by using the Galerkin technique. In the case of Rayleigh-Bénard-Marangoni convection, the eigenvalues are obtained for an upper free/adiabatic and lower rigid/isothermal boundaries. The influence of various parameters has been analysed. Three nonuniform basic temperature profiles are considered and their comparative influence on onset of convection is discussed. Different values of feedback control and electric number are added up to examine whether their presence will enhance or delay the onset of electroconvection. [ABSTRACT FROM AUTHOR]

Metal matrix composites (MMCs) have become attractive in a variety of applications due to its advantage of having intermediate properties between metal and ceramic. This paper presents the investigation of the effect of sintering duration on mechanical properties of Al/SiC composites. In the present work, SiC particle reinforced Al matrix composites were produced via powder metallurgical processing. Pure aluminium powder with a particle size of 63 µm and silicon carbide powder with a particle size of 37µm were used. The range of sintering duration was 1, 2, 3, 4, 5 and 6 h at a fixed temperature of 590 °C. The compressive, hardness and impact tests were performed on the sintered samples to characterize the mechanical properties. It was found that as the sintering duration increased from 1 to 6 hours, the mechanical properties of the samples were enhanced. Furthermore, microscopic observations showed that the porosity level decreased as the sintering duration was increased. [ABSTRACT FROM AUTHOR]

This paper presents the investigation of the effect of sintering temperature on mechanical properties of Al/SiC composites. The composites were produced via conventional powder metallurgy processing. The particle size of Al and SiC powders are 63 µm and 37 µm respectively. The sintering temperatures exerted on the samples were 550, 570, 590, 610, 630 and 650°C at a fixed time of 1 h. The compressive, hardness and impact tests were performed on the sintered samples to characterize their mechanical properties. It was found that as the sintering temperature increase, the mechanical properties of the samples were also increased at earlier temperature and show a decrease trend thereafter. Similarly, this trend was also observed in the density test. Furthermore, microscopic observations showed that the porosity level decrease as the sintering temperature increase excluding at the temperature of 650°C. [ABSTRACT FROM AUTHOR]

Objective: During the acute and post acute period following a mild traumatic brain injury (mTBI) multiple cognitive processes are negatively affected. Prior studies have reported numerous cognitive domains affected during the acute and post-acute period. Studies have demonstrated cognitive recovery, with subjective and objective assessments, that within days to weeks these cognitive abilities are recovered. This study examines the recovery of neurocognitive functions longitudinally. Method: In this study, we compared 12 adults entering an emergency department that met the criteria for a mTBI to a healthy control group of 13 adults. The neuropsychological evaluation for the mTBI group was performed within 10 days of the injury and 4 months following the injury. Results: The results demonstrate the mTBI group has significant deficits in processing speed, attention and concentration, as well as verbal and visual memory compared to the control group at baseline. The mTBI group showed cognitive recovery in most cognitive areas at the four month follow-up. Processing speed and visual memory were still significantly below the performance of the control group at the 4-month post-assessment. Conclusion(s): The results support prior studies that processing speed and memory may be the most sensitive cognitive domains affected by a mTBI. Furthermore, this study reveals individuals that experience a mTBI may still experience impairment in these cognitive domains 4-months post injury. [ABSTRACT FROM AUTHOR]