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In this research, we conducted a numerical analysis on the photoionization cross section (PCS) of a shallow donor impurity confined in a diluted magnetic semiconductor (DMS) C d 1 − x w M n x w T e / C d 1 − x b M n x b T e double quantum well (DQW). The effective-mass approximation was employed, and the Schrödinger equation describing the electron motion was solved using the variational method. This study focuses on calculating the binding energy (E b) by taking into account the effect of spin polaronic shift. Moreover, we calculated the photoionization cross-section (PCS) considering different polarized light directions, varying well widths (L w) , barrier thickness (L b) , and different hydrostatic pressure (P) values as well as the incorporation of the effect of the non-parabolicity (NP) conduction band and polaronic mass (PM). The results reveal that the overall shape of the PCS depends strongly on the light polarization axis. Additionally, the threshold energy exhibits a blueshift with increasing barrier thickness and hydrostatic pressure, and a redshift with increasing the well width. [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]

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]

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]

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]

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]

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]

The features of electron-impurity polarizability in a quantum nanostructure are investigated from the knowledge of allowed electron states coupled to a shallow-donor impurity. The influence of geometry on the carrier confinement and the presence of external probes such as electric fields are explicitly considered. For the sake of illustration, the example of CdS/ZnSe-based prolate ellipsoidal core/shell quantum dot (PECSQD) configuration is chosen. This problem allows to consider a finite confinement potential model, employing both the finite element method and the effective mass approximation. Within this framework, impurity-related energies and associated polarizability for the lowest states were determined as functions of the shell thickness, core dimensions, impurity position, and applied electric field strength - while keeping the shell dimensions fixed. Electron-impurity energies are largely affected by electric field values. Under thinner shell conditions, polarizability shows variations with field strength that include "anomalous" negative values for certain states. Then, the increase in shell thickness causes a significant increment in the polarizabilities, regardless impurity position. • Electronic properties in prolate ellipsoidal core/shell quantum dots. • Effects of a shallow donor impurity. • Influence of externally applied electric field. • Calculation of electron-impurity polarizability for different allowed states. • Appearance of negative values of polarizability for certain excited states. [ABSTRACT FROM AUTHOR]

This study systematically explored the binding energy and the photoionization cross-section (PCS) of a hydrogenic shallow donor impurity within a GaAs double quantum box structure incorporated into a Ga (1 − x) Al x As matrix under the influence of an external intense magnetic field. The computations are performed using the effective-mass approximation (EMA) and the finite element method (FEM), taking into account a finite potential across all surfaces of the nanosystem. The results emphasize the significant role of the magnetic field, primarily in enhancing the donor binding energy within the double quantum box system. We demonstrate that increasing the magnetic field results in an augmentation of binding energy across various aluminum concentrations. The PCS of a shallow donor impurity undergoes a blue shift when shifted from the barrier center to the box center, attributed to the increased binding energy. When the double quantum box is subjected to a magnetic field effect, the amplitude peaks of PCS show an elevation coupled with a blue shift. By setting magnetic field values at 0 T, 35 T, or 70 T and varying aluminum concentrations, we observe a shift in the PCS towards higher energy levels along with an increase in peak amplitude. We also study the PCS of the donor impurity as a function of photon energy, mainly examining the effects of box width and barrier width modifications in the double quantum box. [ABSTRACT FROM AUTHOR]

This work presents a theoretical analysis of a CdTe/CdS core/shell quantum dots embedded in a dielectric oxide matrix under the influence of hydrogenic impurity and the applied electric field intensity. The eigenstates and their corresponding eigenfunctions are computed by solving the Schrodinger equation using the finite element method within the effective mass approximation. The first-order linear and third-order nonlinear optical absorption coefficients as well as the refractive index changes are computed based on the compact density matrix approach. The obtained result shows that the first-order linear and third-order nonlinear optical properties are more pronounced with the electric field, surrounding oxide matrix and the donor impurity effects. However, the first-order linear and third-order nonlinear optical absorption coefficients and refractive index changes can experience a red or blue shift under the influence of electric field, oxide matrix and hydrogenic impurity. In addition, under all conditions, the height peaks of these optical properties can be raised (fall). Our findings demonstrate the critical importance of considering the roles of electric field, the presence of donor impurity, and the capped dielectric oxide matrix in the design and fabrication of core–shell-based optoelectronic devices. • The presence of the emergent TiO 2 oxide matrix (OM) significantly improves the peak values of the optical properties compared to other OM or isolated quantum dots. • The application of an external electric field affects the absorption coefficient differently depending on the nature of the transition. • The presence of a hydrogen-confined impurity causes a blue-shift of the peak absorption coefficient. [ABSTRACT FROM AUTHOR]

This study delves into the optical characteristics of multilayered spherical quantum dots (MLSQDs). By employing the finite element method, we systematically explore the impact of varying layer dimensions, the A l -concentration, and the intersubband relaxation time on the linear, third nonlinear, and total optical absorption coefficients and refractive index changes within this nanostructure. Our findings reveal intriguing correlations between the sizes of individual layers and the resultant optical responses. Notably, subtle adjustments in layer dimensions manifest profound changes in both linear and third-order nonlinear absorption coefficients. Furthermore, the investigation of relaxation time elucidates the key role it plays in changing optical properties, illustrating how relaxation time influences the optical behavior of MLSQDs. This study provides a comprehensive understanding of the impact of layer sizes, relaxation time, and A l concentration on the optical properties of MLSQDs. These findings offer valuable guidance for engineering customized optical functionalities in nanophotonic technologies. • The OAC peaks shift red with increased core radius, then blue shifts at larger sizes. • The OACs and RICs generally follow the trends observed in the transition energy. • Higher relaxation times lead to stronger and sharper absorption peaks. • A l -concentration is another dimension to the control and tuning of QD properties.. [ABSTRACT FROM AUTHOR]

GaAs/GaAlAs quantum dots can be doped with various impurities to modify their optoelectronic properties. Common impurities used for doping include: Hydrogenic impurity (HI), Silicon (Si), Selenium (Se), Germanium (Ge), and Sulfur (S) are common n-type dopant in GaAs-based materials. This work has investigated the effects of temperature and pressure on the refractive index changes (RICs) and optical absorption coefficients (OACs) in the multi-layer quantum disk, accounting for central cell correction. We have used the finite element method to calculate the eigenvalues and their corresponding wave-functions. These values are utilized in the computation of the OACs and RICs. Our outcomes can be summarized as follows: (i) The applied pressure induces a red-shift of the OACs peaks, and their magnitude is reduced. Similarly, temperature causes a blue-shift of the OACs peaks, and their magnitude is enhanced. (ii) The presence and type of impurity lead to significant changes in both OACs and RICs. • The pressure induces a red-shift of the OACs peaks, and their magnitude is reduced. • Temperature causes a blue-shift of the OACs peaks, and their magnitude is enhanced. • The presence and type of impurity lead to significant changes in both OACs and RICs. • Different impurity atoms significantly impact the opto-electronic properties of MLQD. [ABSTRACT FROM AUTHOR]

Utilizing the FEniCS Project and Python programming, we conduct a comprehensive characterization and analysis of the n -type doped layer in double quantum wells made of GaAs and featuring AlGaAs barriers through self-consistent Schrödinger–Poisson simulations. The main findings reveal that the dimensions of the system and the doping layer significantly influence the electronic properties, energy levels, Fermi energy, wave functions, and electron density. Upon doping the intermediate barrier, electrons exhibit notable migration from the doping region to the quantum well zones, particularly pronounced for thin barriers. Conversely, for large barriers, the emergence of a new well, akin to a real quantum well, imposes constraints on the movement of charge carriers. The electron density varies in accordance with the impurity density, which assumes significant importance as the quantum well and barrier width are reduced. The Fermi energy level, which play a crucial role in semiconductors, rises with a decrease in quantum well width or an increase in doped layer width and n-type doping density, remaining almost unaffected by variations in barrier width. [Display omitted] [ABSTRACT FROM AUTHOR]

We have looked numerically at variations of the nonlinear optical rectification (NOR) for an impurity donor localized in a wurtzite In x 0 Ga 1 − x 0 N / GaN multilayer cylindrical quantum dots (MLCQDs), which is under the effect of hydrostatic pressure and temperature. Using the effective mass approximation, the compact density matrix formalism, we have solved the Schrödinger equation by the finite element method (FEniCS Project). Firstly, we consider the impact of altering the polarization direction of the incident electromagnetic radiation. Specifically, we explore two distinct scenarios: axial, along the growth axis of the structure, and circular, across the cross-section of the cylinder. From our investigation, we found that the nonlinear optical rectification is determined by two main parameters: the transition energy, which is mainly related to quantum confinement, and the geometrical factor that depends on the distribution of the electron wave functions. The NOR experiences a blueshift with an increase in hydrostatic pressure or indium composition, and a redshift with an increase in temperature or quantum dot radius, where the impurity is located in the center of the upper QD. Furthermore, the results show that the amplitude and resonance peak position of NOR are significantly influenced by varying the impurity's position and the barrier width. • The NOR undergoes a blueshift with an increase in hydrostatic pressure when the impurity is located at the center of the upper quantum dot. • The NOR experiences a redshift with an increment in temperature or quantum dot radius, where the impurity is located at the center of the upper quantum dot. • The amplitude and resonance peak position of NOR are significantly influenced by varying the impurity's position and the barrier width. • A distinct correlation between the magnitude of the NOR resonance peak and the polarization direction. • Our theoretical investigation aims to advance nonlinear optics and enhance optoelectronic devices, such as far-infrared nano-lasers and photodetectors. [ABSTRACT FROM AUTHOR]