The First Principles Investigations of the Thermoelectric Properties of GaN with p- and n-Type Doping

We investigate the thermoelectric properties of GaN with p-and n-type doping by the first principles calculation and the semi-classical Boltzmann theory. We find that the power factors (S2σof p-type GaN (-3500 W/mK2) is about twice that of the n-type (-1750 W/mK2), which indicates the thermoelectric properties of p-type GaN would be better. Thermal conductivity of GaN crystal decreases rapidly as the temperature increases, but it is still too large for thermoelectric applications. The figure of merit (ZT) estimated at 1500 K is 0.134 for p-type GaN crystal and 0.062 for the n-type.     

Effect of Cascading Amplification Stages on the Performance of Serial Hybrid Fiber Amplifier

Abstract

This study demonstrates simulation and experimental validation of a wideband serial hybrid Raman/erbium-doped fiber amplifier. Two configurations are adopted; in type A, a Raman amplifier is the first stage, and in type B, an erbium-doped fiber amplifier is the first stage. At low input signal power, the average gain level is 20 dB with a flat gain bandwidth of 40 nm for both configurations. The noise figure in type B is dominated by the erbium-doped fiber amplifier and produces lower values and flatter spectra than in type A. The gain of the proposed hybrid amplifiers is affected more by the second amplification stage.     

Quantum Monte Carlo study of the CO interaction with a dimer model surface for Cr(110)

The chemisorption of CO on a Cr (110) surface is investigated using the quantum Monte Carlo method in the diffusion Monte Carlo (DMC) variant and a model Cr₂CO cluster. The present results are consistent with the earlier ab initio HF study with this model that showed the tilted/near-parallel orientation as energetically favoured over the perpendicular arrangement. The DMC energy difference between the two orientations is larger (1.9 eV) than that computed in the previous study. The distribution and reorganization of electrons during CO adsorption on the model surface are analysed using the topological electron localization function method that yields electron populations, charge transfer and clear insight on the chemical bonding that occurs with CO adsorption and dissociation on the model surface.     

Absolute line wavenumbers in the near infrared: 12C2H2 and 12C16O2

40 absolute line wavenumbers in the 3v ₃ band of ¹²C¹⁶O₂ between 6927 cm^?1 and 6989 cm^?1 and 626 absolute line wavenumbers in the near infrared absorption spectrum of ¹²C₂H₂ between 7060 cm^?1 and 9900 cm^?1 have been measured using high resolution Fourier transform spectroscopy. The calibration of the CO₂ line wavenumbers relied on heterodyne frequencies available in the v ₁ + v ₃ band of ¹²C₂H₂ near 6556 cm^?1. The absolute uncertainty of the calibrated CO₂ line wavenumbers is estimated to 0.000 08 cm^?1. The acetylene spectra were calibrated using heterodyne frequencies available in the 2—0 band of ¹²C¹⁶O and the line wavenumbers obtained in the 3v ₃ band of ¹²C¹⁶O₂. The absolute uncertainty of the calibrated acetylene line wavenumbers is estimated to range from 0.0003 cm^?1 to 0.006 cm^?1 for strong to very weak isolated lines. Comparison with absolute line wavenumbers obtained independently at JPL in the 3v ₃ band of ¹²C₂H₂ near 9649 cm^?1, calibrated using absolute wavenumbers available in the 2—0 and 3—0 (near 6350 cm^?1) bands of ¹²C¹⁶O, shows very good agreement. Also, the vibration—rotation constants for the observed upper vibrational states of ¹²C₂H₂ were determined, but without accounting for the perturbations affecting these states.     

Integrated 3D-QSAR,molecular docking,and molecular dynamics simulation studies on 1,2,3-triazole based derivatives for designing new acetylcholinesterase inhibitors

Alzheimer’s disease (AD) is a multifactorial and polygenic disease. It is the most prevalent reason for dementia in the aging population. A dataset of twenty-six 1,2,3-triazole-based derivatives previously synthetized and evaluated for acetylcholinesterase inhibitory activity were subjected to the three-dimensional quantitative structure-activity relationship (3D-QSAR) study. Good predictability was achieved for comparative molecular field analysis (CoMFA) (Q² = 0.604, R² = 0.863, r_ext² = 0.701) and comparative molecular similarity indices analysis (CoMSIA) (Q² = 0.606, R² = 0.854, r_ext² = 0.647). The molecular features characteristics provided by the 3D-QSAR contour plots were quite useful for designing and improving the activity of acetylcholinesterase of this class. Based on these findings, a new series of 1,2,3-triazole based derivatives were designed, among which compound A1 with the highest predictive activity was subjected to detailed molecular docking and compared to the most active compound. The selected compounds were further subjected to 20 ns molecular dynamics (MD) simulations to study the comparative conformation dynamics of the protein after ligand binding, revealing promising results for the designed molecule. Therefore, this study could provide worthy guidance for further experimental analysis of highly effective acetylcholinesterase inhibitors.     

Structural and magnetic characterisation of the perovskite oxides La0.7Ca0.3−x Na x MnO3

X-ray powder diffraction (XRD) and magnetic measurements were performed in order to investigate the effect of Na⁺ ion substitution for Ca²⁺ ions on the crystallographic structure, the character of magnetic ordering, and the effect of transition temperature in La_0.7Ca_0.3−x Na _x MnO₃ manganites series (0 ⩽ × ⩽ 0.2). All samples crystallise in an orthorhombic structure with the Pnma space group. We have found a strong dependence of structural and magnetic properties on the cation-size disorder parameter σ ². The temperature dependence of magnetization of all samples obeys the Bloch T ^3/2 law. The values of the spin wave constant at low temperature B increase with the increase of x and the Curie temperature decreases. It is concluded that the substitution of Ca by Na⁺ ions causes a decrease in total exchange integral Aof the samples.      

Magnetic properties of a ferrimagnetic core/shell nanocube Ising model: A Monte Carlo simulation study

Monte Carlo simulation has been used to study the magnetic properties and hysteresis loops of a single nanocube, consisting of a ferromagnetic core of spin- surrounded by a ferromagnetic shell of spin-1 with antiferromagnetic interface coupling. We find a number of characteristic phenomena. In particular, the effects of the shell coupling and the interface coupling on both the compensation temperature and the magnetization profiles are investigated. The effects of the interface coupling on the hysteresis loops are also examined.     

Monte Carlo study of the spin-1 Blume–Capel Ising film

Using Monte Carlo simulations with the Metropolis algorithm, we have studied the influence of crystal-field interaction on the critical behavior of magnetic spin-1 Ising film on a cubic lattice structure. The phase diagrams in the (_kBTc/J,R=_Js/J)$(k_{\mathrm{B}}{T}_{\mathrm{c}}/J,R=J_{\mathrm{s}}/J)$ plane are obtained for different values of the crystal-field interaction. We found that the special point _Rsp(_Rc)$R_{\mathrm{sp}}(R_{\mathrm{c}})$, at which the critical temperature is independent of the film thickness N, is independent of the crystal-field interaction and that the system may exhibit a tricritical behavior.     

QCD PERTURBATION THEORY AND NUCLEI (1) THE ENERGY SHIFTS OF HADRENS AND HADRONS MASS DIFFERENCE MASS DIFFERENCE

QCD perturbation theory for confined quarks and gluons (inhadrons) is discussed.Based on the equivalent potential for the quark-gluon interaction derived, the energyshifts of hadrons and hadron mass difference in MIT bag (cavity) model and correcpond-ing approximation of the w. f. with Gassian form are calculated.