A Unifying Framework and Comparison of Algorithms for Non-negative Matrix Factorisation

Non-negative matrix factorisation (NMF) is an increasingly popular unsupervised learning method. However, parameter estimation in the NMF model is a difficult high-dimensional optimisation problem. We consider algorithms of the alternating least squares type. Solutions to the least squares problem fall in two categories. The first category is iterative algorithms, which include algorithms such as the majorise–minimise (MM) algorithm, coordinate descent, gradient descent and the Févotte-Cemgil expectation–maximisation (FC-EM) algorithm. We introduce a new family of iterative updates based on a generalisation of the FC-EM algorithm. The coordinate descent, gradient descent and FC-EM algorithms are special cases of this new EM family of iterative procedures. Curiously, we show that the MM algorithm is never a member of our general EM algorithm. The second category is based on cone projection. We describe and prove a cone projection algorithm tailored to the non-negative least square problem. We compare the algorithms on a test case and on the problem of identifying mutational signatures in human cancer. We generally find that cone projection is an attractive choice. Furthermore, in the cancer application, we find that a mix-and-match strategy performs better than running each algorithm in isolation.     

Digital Signatures

Abstract

The growing use of the Internet for business makes digital signatures a crucial issue. This article discusses three methods used in digital signatures: symmetric encryption, asymmetric encryption and signature dynamics. In addition, the need for consistent laws governing digital signatures in all of the United States, and indeed in the world, is discussed.     

Customer Efficient Electronic Cash Protocols

The technology of electronic cash makes it possible to transmit digital money over communication networks during electronic transactions. Owing to the untraceability and unforgeability properties, electronic cash can protect the privacy of customers and guarantee security of payments in the transactions. This paper introduces a customer-efficient electronic cash protocol where each customer only needs to store 1 coin for w dollars and transmit 1 coin for a w-dollar payment. Compared with traditional electronic cash protocols, the proposed method greatly reduces not only the storage required for the customers, but the communication traffic in the payments as well. Furthermore, the computation cost of each customer in the payment stage is greatly reduced by more than 99% as compared with other storage efficient electronic cash protocols. The proposed protocol is quite suitable for situations where storage and computation capabilities are limited, such as smart-card or mobile environments. In addition, both the problem of money laundering and the unlimited-growth problem of the bank's database, which records all spent coins for double-spending checking, are also considered in the proposed protocol. Especially, our basic idea is independent of the underlying cryptographic primitives such that it can be implemented by any public-key encryption, symmetric encryption, digital signature, and partially blind signature scheme.     

利用频谱排序和筛选的突变噪声快速估计

针对最小值控制递归平均(Minima Controlled Recursive Averaging,MCRA)算法不能快速跟踪突变噪声的问题，提出了一种基于频谱排序和筛选的突变噪声快速估计方法。该方法在MCRA算法的基础上对带噪语音的功率谱进行排序，筛选出不含语音信号的频点来估计噪声的平均功率谱；当检测到噪声突变时，对当前的平滑参数和状态变量进行校正。仿真结果表明，该方法可以将突变噪声的跟踪时间缩短90%以上；用于语音降噪处理时，音质可以提升约0.4分。该方法具有一定的工程应用价值。     

Fair e-lottery system proposal based on anonymous signatures

The games in which large amount of money is involved are always called into question about the existence of the possibility to manipulate the game for an immediate benefit. Lottery system is not an exception in this regard; moreover, it is a subject of rumours that the game is not as fair as it is pretended to be. After studying the advantages and drawbacks of conventional lottery systems, the authors are proposing an e-lottery system based on anonymous signatures. Even though the proposal is using electronic signatures, which imply complex calculus and the possession of digital certificates for each player, the proposed system compensates these drawbacks by increasing trust and confidence of both the players and the lottery organizer. This will lead to more players participating in the lottery, which translates to more revenue for the lottery and larger prizes for the players.     

电子病案突破双轨制管理的措施探讨

文章主要探讨我国电子病案的发展现状,促进我国电子病案突破双轨制管理,探讨双轨制管理模式所存在的问题与发展瓶颈问题,寻求对策,真正的实现电子病案的信息化。     

企业网络组织异变的内在机理

由于网络组织运行主体的松散性、运行边界曲弹性以及主体间交易关系的交错性,企业网络常被视为动态的网络组织,因而异变是网络组织的一个重要特征。在主体、资源与任务三重异变基因的作用下,企业网络组织异变往往呈现出渐变与激变两种路径,即保持网络架构稳定的问隔式均衡与突破网络架构的裂变式均衡。这种差异化的均衡异变会对网络组织产生重要影响,进而影响到网络组织的治理效应。