Spectral properties of a double-quantum-dot structure: A causal Green's function approach

Spectral properties of a double quantum dot (QD) structure are studied by a causal Green's function (GF) approach. The double QD system is modeled by an Anderson-type Hamiltonian in which both the intra- and interdot Coulomb interactions are taken into account. The GF's are derived by an equation-of-motion method and the real-space renormalization-group technique. The numerical results show that the average occupation number of electrons in the QD exhibits staircase features and the local density of states depends appreciably on the electron occupation of the dot.

Cancer classification based on direction-basis-function neural networks

Automatic molecular classification of cancer based on DNA microarray has many advantages over conventional classification based on morphological appearance of the tumor. Using artificial neural networks is a general approach for automatic classification. In this paper, Direction-Basis-Function neuron and Priority-Ordered algorithm are applied to neural networks. And the leukemia gene expression dataset is used as an example to testify the classifier. The result of our method is compared to that of SVM. It shows that our method makes a better performance than SVM.

A two-step backoff scheme for improving the performance of the IEEE 802.11 distributed coordination function

This paper describes the binary exponential backoff mechanism of 802.11 distributed coordination function (DCF), and introduces some methods of modifying the backoff scheme. Then a novel backoff scheme, called Two-step Backoff scheme, is presented and illustrated. The simulation process in OPNET environment has been described also. At last, the analysis and simulation results show that the Two-step backoff scheme can enhance the performance of the IEEE 802.11 DCF.

The structure and function of neurons with variable nonlinear transfer function

One novel neuron with variable nonlinear transfer function is firstly proposed, It could also be called as subsection transfer function neuron. With different transfer function components, by virtue of multi-thresholded, the variable transfer function neuron switch on among different nonlinear excitated state. And the comparison of output's transfer characteristics between it and single-thresholded neuron will be illustrated, with some practical application experiments on Bi-level logic operation, at last the simple comparison with conventional BP, RBF, and even DBF NN is taken to expect the development foreground on the variable neuron.. The novel nonlinear transfer function neuron could implement the random nonlinear mapping relationship between input layer and output layer, which could make variable transfer function neuron have one much wider applications on lots of reseach realm such as function approximation pattern recognition data compress and so on.

On detection wavelength and electron-hole wave function overlap of type II InAs/In-x Ga1-x Sb superlattice infrared photodetector

In this paper, the detection wavelength and the electron-hole wave function overlap of InAs/IrxGa1-xSb type II superlattice photodetectors are numerically calculated by using the envelope function and the transfer matrix methods. The band offset is dealt with by employing the model solid theory, which already takes into account the lattice mismatch between InAs and InxGa1-xSb layers. Firstly, the detection wavelength and the wave function overlap are investigated in dependence on the InAs and InxGa1-xSb layer thicknesses, the In mole fraction, and the periodic number. The results indicate that the detection wavelength increases with increasing In mole fraction, InAs and InxGa1-xSb layer thicknesses, respectively. When increasing the periodic number, the detection wavelength first increases distinctly for small periodic numbers then increases very slightly for large period numbers. Secondly, the wave function overlap diminishes with increasing InAs and InxGa1-xSb layer thicknesses, while it enhances with increasing In mole fraction. The dependence of the wave function overlap on the periodic number shows the same trend as that of the detection wavelength on the periodic number. Moreover, for a constant detection wavelength, the wave function overlap becomes greater when the thickness ratio of the InAs over InxGa1-xSb is larger.

Formal specification and refinement of a safe train control function

Motivated by the design and development challenges of the BART case study, an approach for developing and analyzing a formal model for reactive systems is presented. The approach makes use of a domain specific language for specifying control algorithms able to satisfy competing properties such as safety and optimality. The domain language, called SPC, offers several key abstractions such as the state, the profile, and the constraint to facilitate problem specification. Using a high-level program transformation system such as HATS being developed at the University of Nebraska at Omaha, specifications in this modelling language can be transformed to ML code. The resulting executable specification can be further refined by applying generic transformations to the abstractions provided by the domain language. Problem dependent transformations utilizing the domain specific knowledge and properties may also be applied. The result is a significantly more efficient implementation which can be used for simulation and gaining deeper insight into design decisions and various control policies. The correctness of transformations can be established using a rewrite-rule based induction theorem prover Rewrite Rule Laboratory developed at the University of New Mexico.

密码Hash函数相关问题研究

密码Hash函数是信息安全密码学的一个重要研究内容，是一类广泛应用的密码算法，用于把任意长度的字符串压缩成特定长度的字符串，同时需要在各种应用环境下满足一定的安全要求如抗碰撞，抗原象等。Hash函数广泛应用于数字签名、可证明安全、密码算法的构造以及重要的安全协议中。对Hash函数进行研究、分析Hash函数的安全性、构造安全高效的Hash算法有着重要意义。 本文研究了Hash函数的安全性质、设计结构以及常用分析方法，研究了Hash函数扩散层部件的设计，并且对MAME压缩函数算法进行了分析，取得了如下研究结果： (1) 研究了密码Hash函数的安全性质、设计结构、设计原理和常用分析方法，归纳总结了51个SHA-3候选算法的设计特点、设计原理和实现效率，研究了最新的分析进展，总结了新的攻击方法如REBOUND攻击等。NIST仿照AES的征集过程的SHA-3竞赛，目标是选出新的Hash函数标准SHA-3。进入第一轮的候选算法有51个，经过筛选选出其中的14个作为当前第二轮的候选算法。这些新Hash算法是由世界各国密码学家精心设计，是Hash函数领域最新设计思想的集体展示，当中涌现出很多新的设计结构和设计方法，同时激励密码学家发展新的分析方法。 (2) 设计并实现了了有限域上的扩散层构造算法以及扩散层分支数测试的算法，并针对多元域上的扩散层矩阵，本文使用编码理论，利用GRS码和柯西矩阵等设计了多元域扩散层矩阵的构造算法；使用有限域上的高斯消元法和线性码的性质设计了多元域扩散层矩阵的分支数的检测；设计了高效的二元域扩散层矩阵分支数测试算法。 (3) 针对MAME压缩函数算法进行差分分析，MAME算法是SHA-3候选算法Lesamnta的前身，于CHES 2007上提出的面向硬件有效实现的Hash算法。本文利用差分攻击对MAME算法进行分析，首先针对MAME的结构性质利用对通用Feistel结构的攻击方法构造了22轮差分攻击，碰撞攻击的复杂度为2^97，（第二）原象攻击的复杂度为2^197；对23轮的差分攻击需要的预计算是2^64张表，每张表的大小为2^64；对24轮的差分攻击需要的预计算是2^128张表，每张表的大小为2^64。针对24轮差分攻击很大的内存复杂度，我们利用了算法的细节特性，改进了差分攻击，新的差分不需要预计算的辅助内存，（第二）原象的复杂度为2^224。

function definition language fdl and its implementation

A Function Definition Language (FDL) is presented. Though designed for describing specifications, FDL is also a general-purpose functional programming language. It uses context-free language as data type, supports pattern matching definition of functions, offers several function definition forms, and is executable. It is shown that FDL has strong expressiveness, is easy to use and describes algorithms concisely and naturally. An interpreter of FDL is introduced. Experiments and discussion are included.