Cathodoluminescence and Raman research of V-shape inverted pyramid in HVPE grown GaN film

Thick GaN films with high quality have been grown on (0001) sapphire substrate in a home-made vertical HVPE reactor. Micron-size hexagonal pits with inverted pyramid shape appear on the film surface, which have six triangular {10-11} facets. These {10-11} facets show strong luminescence emission and are characteristic of doped n-type materials. Broad red emission is suppressed in {10-11} facets and is only found at the flat region out of the pit, which is related with the decreasing defects on {10-11} facets. Low CL emission intensity is observed at the apex of V-shape pits due to the enhanced nonradiative recombination. Raman spectra show that there are higher carrier concentration and low strain in the pit in comparison to the flat region out of the pit. The strain relaxation may be the main mechanism of the V-shape pits formation on the GaN film surface.     

Ff现场总线技术在丁二烯生产装置中的应用

现场总线技术是当今自动化领域发展最快的技术之一,现场总线控制系统正推动工业自动化控制向一个全新的领域发展。由于扬子石化公司丁二烯生产装置采用的是传统的DCS系统,随着生产和管理的需要,它已不能适应工厂工业控制系统的数字化、网络化、智能化的发展要求,因而提出了一种基于基金会现场总线的控制系统,主要介绍了该系统在丁二烯生产装置中的应用,以及工厂管控网的建立。该系统的成功应用使得工厂管理层和生产层的有效结合得以实现,从而组成了网络集成式全分布控制系统。     

New travelling wave solutions to modified CH and DP equations

A new procedure for finding exact travelling wave solutions to the modified Camassa-Holm and Degasperis-Procesi equations is proposed. It turns out that many new solutions are obtained. Furthermore, these solutions are in general forms, and many known solutions to these two equations are only special cases of them.     

SPICE: Simulation Package for Including Flavor in Collider Events

We describe SPICE: Simulation Package for Including Flavor in Collider Events. SPICE takes as input two ingredients: a standard flavor-conserving supersymmetric spectrum and a set of flavor-violating slepton mass parameters, both of which are specified at some high “mediation” scale. SPICE then combines these two ingredients to form a flavor-violating model, determines the resulting low-energy spectrum and branching ratios, and outputs HERWIG and SUSY Les Houches files, which may be used to generate collider events. The flavor-conserving model may be any of the standard supersymmetric models, including minimal supergravity, minimal gauge-mediated supersymmetry breaking, and anomaly-mediated supersymmetry breaking supplemented by a universal scalar mass. The flavor-violating contributions may be specified in a number of ways, from specifying charges of fields under horizontal symmetries to completely specifying all flavor-violating parameters. SPICE is fully documented and publicly available, and is intended to be a user-friendly aid in the study of flavor at the Large Hadron Collider and other future colliders.

Program summary

Program title: SPICECatalogue identifier: AEFL_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFL_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.: 8153No. of bytes in distributed program, including test data, etc.: 67 291Distribution format: tar.gzProgramming language: C++Computer: Personal computerOperating system: Tested on Scientific Linux 4.xClassification: 11.1External routines: SOFTSUSY [1,2] and SUSYHIT [3]Nature of problem: Simulation programs are required to compare theoretical models in particle physics with present and future data at particle colliders. SPICE determines the masses and decay branching ratios of supersymmetric particles in theories with lepton flavor violation. The inputs are the parameters of any of several standard flavor-conserving supersymmetric models, supplemented by flavor-violating parameters determined, for example, by horizontal flavor symmetries. The output are files that may be used for detailed simulation of supersymmetric events at particle colliders.Solution method: Simpson's rule integrator, basic algebraic computation.Additional comments: SPICE interfaces with SOFTSUSY and SUSYHIT to produce the low energy sparticle spectrum. Flavor mixing for sleptons and sneutrinos is fully implemented; flavor mixing for squarks is not included.Running time: <1 minute. Running time is dominated by calculating the possible and relevant three-body flavor-violating decays of sleptons, which is usually 10-15 seconds per slepton.References:

[1]

B.C. Allanach, Comput. Phys. Commun. 143 (2002) 305, arXiv:hep-ph/0104145.

[2]

B.C. Allanach, M.A. Bernhardt, arXiv:0903.1805 [hep-ph].

[3]

A. Djouadi, M.M. Muhlleitner, M. Spira, Acta Phys. Pol. B 38 (2007) 635, arXiv:hep-ph/0609292.

     

An events based algorithm for distributing concurrent tasks on multi-core architectures

In this paper, a programming model is presented which enables scalable parallel performance on multi-core shared memory architectures. The model has been developed for application to a wide range of numerical simulation problems. Such problems involve time stepping or iteration algorithms where synchronization of multiple threads of execution is required. It is shown that traditional approaches to parallelism including message passing and scatter-gather can be improved upon in terms of speed-up and memory management. Using spatial decomposition to create orthogonal computational tasks, a new task management algorithm called H-Dispatch is developed. This algorithm makes efficient use of memory resources by limiting the need for garbage collection and takes optimal advantage of multiple cores by employing a “hungry” pull strategy. The technique is demonstrated on a simple finite difference solver and results are compared to traditional MPI and scatter-gather approaches. The H-Dispatch approach achieves near linear speed-up with results for efficiency of 85% on a 24-core machine. It is noted that the H-Dispatch algorithm is quite general and can be applied to a wide class of computational tasks on heterogeneous architectures involving multi-core and GPGPU hardware.     

Technologies of parallel database systems for hierarchical multiprocessor environments

For the multiprocessor systems of the hierarchical-architecture relational databases, a new approach to data layout and load balancing was proposed. Described was a database multiprocessor model enabling simulation and examination of arbitrary multiprocessor hierarchical configurations in the context of the on-line transaction processing applications. An important subclass of the symmetrical multiprocessor hierarchies was considered, and a new data layout strategy based on the method of partial mirroring was proposed for them. The disk space used to replicate the data was evaluated analytically. For the symmetrical hierarchies having certain regularity, theorems estimating the laboriousness of replica formation were proved. An efficient method of load balancing on the basis of the partial mirroring technique was proposed. The methods described are oriented to the clusters and Grid-systems.     

Energy dissipation and frequency shift of a damped dynamic force microscopy

The closed-form solution of the transient response of damped dynamic force microscopy subjected to the nonlinear interatomic force is derived. The frequency shift and the decay rate of a V-typed probe can be determined easily and precisely by the proposed method. If the taper ratio is zero, a uniform cantilever is obtained. Moreover, the transient response of a non-uniform cantilever can be determined also in the same way. The complex Young's modulus is used to describe the viscoelastic material property. In the modulus, the loss factor is introduced. The relation between the Q-factor and the loss factor is discussed. Moreover, the relation between the energy dissipation and the frequency shift is revealed. Finally, the effects of several parameters on the Q-factor, the frequency shift and the decay rate are investigated. The proposed method can be easily applied to investigate the tapping mode of AFM.     

Estimating the latent time of fault detection in finite automaton tested in real time

The notions of potential and real latent times of fault detection in finite automata were introduced. The potential latent time is the minimal theoretical time of automaton fault detection, the real time is defined as the time of fault manifestation at a certain point. A method for determination of the statistical characteristics of both times for the automaton tested in the course of its real operation was proposed. It is based on selection of the trajectories of the Markov chain describing behavior of the operable and faulty automata. Additionally, a method for determination of the upper bound of the mean latent time in the case of limited information about the automaton characteristics was proposed.     

The evaluation of mechanical stresses developed in underlying silicon substrates due to electroless nickel under bump metallization using synchrotron X-ray topography

The switch-over to the use of flip-chip Si integrated circuit bonding techniques has been driven by a need to develop higher power and lower voltage devices, capable of carrying larger currents with greater reliability. With the increased use of solder bump interconnections, an understanding of the behaviour of commonly used electroless nickel under bump metallization (UBM) layers is becoming ever more crucial. The aim of this paper is to evaluate the usefulness of white beam synchrotron X-ray topography (WBSXRT) for non-destructive evaluation of the induced mechanical stresses on Si substrates for different Ni(P) based UBM sizes and thicknesses. It is shown that WBSXRT is a powerful tool for non-destructively mapping strain and/or defect distributions within the underlying silicon substrate. Using this technique, it was also found that the crystalline misorientation induced in the underlying silicon is increased for larger UBM diameters. Stress magnitudes in the Si substrate directly under the UBM can reach values as high as 260 MPa.     

Characterization of strained silicon on relaxed SiGe layer made by H ion implantation and annealing in ultra-high vacuum ambient

Twenty-nanometer-thick Si cap layer/74-nm-thick Si_0.72Ge_0.28 epilayer/Si heterostructural sample was implanted by 25 keV H⁺ ion to a dose of 1 × 10¹⁶ cm⁻² and subsequently annealed in ultra-high vacuum ambient at the temperature of 800 °C for 30 min. Rutherford backscattering/ion channeling (RBS/C), Raman spectra, high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were used to characterize the structural characteristic of Si/SiGe/Si heterostructure. Investigations by RBS/C demonstrate that the Si_0.72Ge_0.28 layer show good crystal quality (21.1% of channel minimum yield). The relaxation degree of partially relaxed Si_0.72Ge_0.28 layer was around 74%, which was obtained by HRXRD. The computation process of the relaxation degree of strain in SiGe layer according to HRXRD rocking curve was also thoroughly introduced. Raman analysis revealed that stress, σ and strain, ε in the thin strained-Si layer were around 1.2 Gpa and 0.52%, respectively. In addition, the small surface roughness in the formed strained-Si/relaxed Si_0.72Ge_0.28 layer/Si heterostructural sample was observed via AFM image.