Humanoid walking pattern generation based on model predictive control approximated with basis functions

This paper proposes a real-time walking pattern generator (WPG) based on model predictive control (MPC). Since reducing the calculation time is a crucial problem in real-time WPG, we consider introducing basis functions to reduce the number of control input. The control inputs in the MPC are described by a series of basis functions. Compared with the standard discrete-time MPC formulation, the approach with basis functions requires fewer optimization variables at the cost of decreasing precision. In order to find an appropriate trade-off, two basis functions named Laguerre functions and Haar functions, are tested in this paper. MPC with Laguerre functions decreases more computational load while MPC with Haar functions offers a more accurate solution. The approach is not restricted to Laguerre functions or Haar functions, users can select their own basis functions for different applications and preferences.     

Linear cryptanalysis and block cipher design in East Germany in the 1970s

Linear cryptanalysis (LC) is an important codebreaking method that became popular in the 1990s and has roots in the earlier research of Shamir in the 1980s. In this article we show evidence that linear cryptanalysis is even older. According to documents from the former East Germany cipher authority ZCO, the systematic study of linear characteristics for nonlinear Boolean functions was routinely performed in the 1970s. At the same time East German cryptologists produced an excessively complex set of requirements known as KT1, which requirements were in particular satisfied by known historical used in the 1980s. An interesting line of inquiry, then, is to see if KT1 keys offer some level of protection against linear cryptanalysis. In this article we demonstrate that, strangely, this is not really the case. This is demonstrated by constructing specific counterexamples of pathologically weak keys that satisfy all the requirements of KT1. However, because we use T-310 in a stream cipher mode that uses only a tiny part of the internal state for actual encryption, it remains unclear whether this type of weak key could lead to key recovery attacks on T-310.     

Problems and solutions from the fourth International Students’ Olympiad in Cryptography (NSUCRYPTO)

Mathematical problems and their solutions from the fourth International Students’ Olympiad in cryptography (NSUCRYPTO-2017) are presented. We consider problems related to attacks on ciphers and hash functions, cryptographic Boolean functions, linear branch numbers, addition chains, and error correction codes, among others. We discuss several open problems involving the algebraic structures of cryptographic functions, useful proof-of-work algorithms, the Boolean hidden shift problem, and quantum computing.     

The impact of the dependence structure in risk management: a focus on credit-risk

The aim of the paper is to discuss the important role of the dependence structure in risk management. Therefore, we focus on credit-risk and propose an innovative model to value the credit risk of a portfolio. This new approach (HYC for short) is based on a hierarchical hybrid copula and involves a clusterization of the portfolio in several risk's classes. The HYC model is classified as hybrid because the computation of the loss cdf depends on the class's cardinality: for large groups one is justified to apply a limiting approach, while for small ones one applies a procedure preserving the granularity of the group itself. In order to appreciate the impact of the dependence structure in credit-risk evaluation, a VaR analysis based on the HYC loss function is here compared to the CreditMetrics approach in an in-sample exercise and to the empirical VaR in an out-of sample exercise aimed to test the forecasting effectiveness of the model. This comparison allows us to appreciate over/under-valuation of the capital detained from the financial institution. Moreover, the impact of an enlargement of the dependence structure is discussed with respect to the systemic/contagious effects in the context of a portfolio optimisation with constraint on a sub-portfolio's risk.     

街道环境V2V通信信道建模与容量分析

针对街道3D散射环境下的车载通信信道,考虑到道路两边高楼、树木等散射体,且收发两端处于移动状态,采用多天线技术,建立椭圆柱散射模型。运用几何分析法,推导了时间自相关函数（ACF）、空间互相关函数（CCF）,比较视距（LOS）和非视距（NLOS）情况下ACF和CCF的差异,验证仿真方法的可行性;研究了信道容量在不同天线阵列和散射环境下的区别,突出了3D模型更加精确。测量结果与理论分析的一致性表明该3D模型的可用性,拓宽了车载通信系统的研究。     

基于麦克风阵列的GCC时延估计算法分析

准确的时延估计（Time Delay Estimation,TDE）是基于到达时间差（Time Difference of Arrival,TDOA）的声源定位技术的前提.在众多时延估计算法中,广义互相关（Generalized Cross Correlation,GCC）算法因其较低的运算复杂度和易于实现的特点得到了广泛的应用.针对不同的噪声情况,GCC时延估计算法利用不同的加权函数来抑制噪声干扰.本文在介绍麦克风阵列模型和GCC时延估计算法的基础上,针对GCC算法的弊端提出了一种改进算法,并在多种信噪比条件下,对部分加权函数的GCC时延估计算法进行了MATLAB仿真,通过比较其时延估计性能和声源定位精度,分析了这些加权函数各自的优劣性.     

A Game Changer: Functional Nano/Micromaterials for Smart Rechargeable Batteries

The imperative to electrify the transport sector in the past few decades has put millions of electric vehicles on the road worldwide with an extended mile range from critical technological breakthroughs in developing the rechargeable energy storage systems, which also covers electronic devices and smart grid applications. However, the available energy density of prevailing systems in the market (i.e., batteries) is reaching its boundaries due to the limited choice of electrochemical reactions that necessarily depend on the thermodynamics and kinetics of the components (e.g., cathode, anode, electrolyte, separator, and current collectors). Reaching the high energy density of batteries exploits new redox chemistry such as sensitive metal anodes, insulating and highly dissolving sulfur cathodes, etc., thus requiring novel designs of various multiscale functional materials to address the corresponding issues. Here, the recent achievements on the designs of smart functional materials for emerging problems in the whole range of systems are discussed: i) interfacial control/kinetic regulation of Li–S battery; ii) self‐healing‐driven structural stability in the electrode and electrolyte; iii) ion‐sieving functional membranes for selective scavenging capability; and iv) functional materials to ensure battery safety.     

融合显式反馈与隐式反馈的协同过滤推荐算法

显式反馈与隐式反馈相结合,可以有效提升推荐性能.但是现有的融合显式反馈与隐式反馈的推荐系统存在未能发挥隐式反馈数据缺失值反映用户隐藏偏好的能力,或者未能保留显式反馈数据反映用户偏好程度的能力的局限性.为了解决这个问题,提出了一种融合显式反馈与隐式反馈的协同过滤推荐算法.该算法分为两个阶段:第1阶段利用加权低秩近似处理隐式反馈数据,训练出隐式用户/物品向量;第2阶段引入了基线评估,同时将隐式用户/物品向量作为补充,通过显隐式用户/物品向量结合,训练得出用户对物品的预测偏好程度.该算法与多个典型算法在标准数据集上进行了实验比较,其可行性和有效性得到验证.     

融合隐含信任度和项目关联度的矩阵分解推荐算法

随着社交网络的发展,融合社交信息的推荐系统在一定程度上解决了协同过滤推荐系统的冷启动和数据稀疏等问题,但是在信任数据稀疏情况下,仍会造成推荐精度降低等问题。为此,提出了一种融合隐含信任度和项目关联度的矩阵分解推荐算法。首先,利用矩阵分解模型将信任数据进行分解,得到用户的潜在被信任矩阵,在此基础上引入用户的影响力,从而提出了基于隐含信任度的推荐模型;然后,为了更好的利用项目间的关联信息,反映项目间的有向性,提出了基于项目关联度的推荐模型;最后,综合两种推荐模型并构建了一种推荐算法TCRMF。实验结果表明,所提算法在评分数据和信任数据稀疏的情况下仍然可以有效地提高推荐算法的精度,具有良好的应用前景。     

On a method for solving a local boundary problem for a nonlinear stationary system with perturbations in the class of piecewise constant controls

The wide class of nonlinear stationary systems of ordinary differential equations taking into account restrictions on control and external perturbation is considered. An algorithm for constructing a discrete control function that guarantees the transfer of the systems from the initial state to the origin and an arbitrary neighborhood of the origin is proposed. A constructive sufficient condition of the Kalman type, in which the specified translation is possible, is obtained. The problem of robot‐manipulator control is considered and its numerical simulation is carried out.