Realistic semiconductor heterostructures design using inverse scattering

We discuss the construction of optimized electronic filters using inverse scattering methods. We study a wide range of densities and temperatures, room temperature included. Discretization methods of the potential (including the self-consistent potential of the conduction electrons) are worked out that retain all its properties.     

Accelerating scientific computations with mixed precision algorithms

On modern architectures, the performance of 32-bit operations is often at least twice as fast as the performance of 64-bit operations. By using a combination of 32-bit and 64-bit floating point arithmetic, the performance of many dense and sparse linear algebra algorithms can be significantly enhanced while maintaining the 64-bit accuracy of the resulting solution. The approach presented here can apply not only to conventional processors but also to other technologies such as Field Programmable Gate Arrays (FPGA), Graphical Processing Units (GPU), and the STI Cell BE processor. Results on modern processor architectures and the STI Cell BE are presented.

Program summary

Program title: ITER-REFCatalogue identifier: AECO_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECO_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 7211No. of bytes in distributed program, including test data, etc.: 41 862Distribution format: tar.gzProgramming language: FORTRAN 77Computer: desktop, serverOperating system: Unix/LinuxRAM: 512 MbytesClassification: 4.8External routines: BLAS (optional)Nature of problem: On modern architectures, the performance of 32-bit operations is often at least twice as fast as the performance of 64-bit operations. By using a combination of 32-bit and 64-bit floating point arithmetic, the performance of many dense and sparse linear algebra algorithms can be significantly enhanced while maintaining the 64-bit accuracy of the resulting solution.Solution method: Mixed precision algorithms stem from the observation that, in many cases, a single precision solution of a problem can be refined to the point where double precision accuracy is achieved. A common approach to the solution of linear systems, either dense or sparse, is to perform the LU factorization of the coefficient matrix using Gaussian elimination. First, the coefficient matrix A is factored into the product of a lower triangular matrix L and an upper triangular matrix U. Partial row pivoting is in general used to improve numerical stability resulting in a factorization PA=LU, where P is a permutation matrix. The solution for the system is achieved by first solving Ly=Pb (forward substitution) and then solving Ux=y (backward substitution). Due to round-off errors, the computed solution, x, carries a numerical error magnified by the condition number of the coefficient matrix A. In order to improve the computed solution, an iterative process can be applied, which produces a correction to the computed solution at each iteration, which then yields the method that is commonly known as the iterative refinement algorithm. Provided that the system is not too ill-conditioned, the algorithm produces a solution correct to the working precision.Running time: seconds/minutes     

两种工作电源的设计与实现

给出了直流稳压电源和逆变电源的设计方案。直流稳压电源具有两路±1 5 V,两路±1 2 V,两路±5 V和一路1.25～37V连续可调七路输出,每路输出电流最大可达1.5A;逆变电源输出功率可达250VA。经测试,这两种电源输出精确,稳定性好,是一种理想的实验室或家用电源。     

遗传算法在直流传感器磁屏蔽体优化设计中的应用

应用遗传算法对直流传感器的磁屏蔽体进行优化设计,对遗传算法的适应度线性尺度变换作了改进.文中选取直流传感器的磁屏蔽效能为目标函数,给出了一个具体设计实例.优化后磁屏蔽效能增大了534,表明在磁屏蔽体优化设计中采用改进的遗传算法取得了良好效果.     

Symmetry in electron diffractions from helical structures

In this work, we elucidate the regular rule of the symmetry in electron diffraction patterns from helical structures. It is affected by the value of the dominating Bessel function orders for the layer lines and relative orientation of the samples with respect to the electron beam. For Single-Walled Carbon nanotubes (SWCNTs), we use analytic analysis and computer simulations to demonstrate that the 2mm symmetry of the electron diffraction may break down not only from an achiral SWCNT, but also from a chiral SWCNT. Also, the simulation work for B-DNA is presented to corroborate the theoretical analysis.     

Digital memory look-up based implementation of sliding mode control for dc–dc converters

Switched power electronic converters involve different control actions for different system events. A local control strategy may be developed which reacts only to some local information available to each component without any communication between the different system components located far away in real time. The purpose of this paper is to present a low cost memory based control strategy in a dc–dc boost converter. The control employed in this work is based on a sliding-mode hysteretic control strategy where the sliding manifold is derived a priori and stored as a look-up table in digital memory hardware. The proposed control implementation strategy is low cost and offers a robust dynamic response that is used to mitigate many disturbances in the system.     

Study of thiol capped CdSe quantum dots using SeO2 precursor for selenium source

CdSe quantum dots in aqueous medium using thioglycollic acid as capping agent have been synthesized. The reaction was carried out in an open atmosphere at pH of 12 and refluxed at 100 °C for 8 h. Selenium dioxide which is less expensive and less toxic has been used as a precursor for selenium source by replacing Se powder and sodium selenite. For characterization QD solutions was taken at different time intervals ranging from 15 min to 6 h. UV–Vis spectroscopy shows that there is a strong blue shift in the prepared quantum dots due to quantum confinement effect. Band gap calculated at different time intervals lies between 2.34 and 2.73 eV which is more than the bulk band gap 1.74 eV and with the increase in size of the QDs, bandgap also decreases. Photoluminescence study was carried out at excitation wavelength of 350 nm and results shows that with increase in time the peak position shift toward higher wavelength. FTIR spectroscopy shows peaks of thioglycollic acid. SEM micrographs of the prepared quantum dots show zero dimensional spherical particles in nm range. For electrical conductivity dc conductivity measurement has been done which shows that with increase of temperature conductivity increases, it confirms the semiconducting nature of the quantum dot. Conduction mechanism found to be mainly due to localized states.     

新型模板法制备ZnO纳米结构薄膜及其光学性能研究

通过电化学阳极氧化-化学溶蚀技术制备了一种由无数纳米凸点和凹点所构成的新型铝基纳米点阵模板.采用直流反应磁控溅射法在这种新型模板上沉积得到氧化锌纳米结构薄膜.在室温下观察了氧化锌纳米结构薄膜的形貌,测定材料的晶体结构和光致发光(PL)性能,并讨论了不同溅射时间下制备的氧化锌纳米阵列结构以及其对氧化锌PL谱的性能影响.结果表明,采用直流反应磁控溅射-铝基纳米点阵模板可以制备ZnO纳米结构薄膜;PL谱表明溅射时间为10 min得到的氧化锌薄膜在396.5 nm和506.4 nm处分别出现紫外发射峰和蓝绿色荧光发射峰;随着溅射时间延长,氧化锌薄膜PL谱伴有红移现象且强度逐渐增强.这可能是由于改善了晶粒结构导致不能观测到ZnO薄膜的深能级发射峰所致.     

Processing effects on in-flight particle state and functional coating properties of plasma-sprayed manganese zinc ferrite

Magnetic properties of manganese zinc ferrite (MZF) coatings deposited by atmospheric dc plasma spraying largely depend on zinc and oxygen loss during particle flight. The temperature and velocity of in-flight MZF particles were widely varied by changing plasma spray conditions to examine these chemistry changes and resultant magnetic properties. Zn loss increases with increased particle temperature or decreased particle velocity. Meanwhile, wüstite (FeO) formation, related to the oxygen loss, is more complicated, partly because oxygen, which is lost during flight in the high-temperature zone of the plasma jet, can be recovered at longer spray distances. As a result, the saturation magnetization of MZF coatings decreases and the coercivity increases with increased particle temperature or decreased particle velocity.     

Structural, elastic and thermophysical properties of divalent metal oxides with NaCl structure

In the present paper, we have investigated the high-pressure structural phase transition of divalent metal oxides using the three-body potential modified by incorporating the covalency effects. Phase transition pressures are associated with a sudden collapse in volume. The phase transition pressures and associated volume collapses obtained from present potential model show a generally better agreement with available experimental data than others. The elastic constants and their pressure derivatives are also reported. It is found that the present model has a promise to predict the phase transition pressure and, the elastic constants and their pressure derivatives of other chalcogenides as well. Moreover the thermophysical properties have also been obtained successfully.