解密成本为常数的具有追踪性的密文策略属性加密方案

该文针对单调访问结构提出了一个解密成本为常数的具有追踪性的密文策略属性加密(CP-ABE)方案,该方案基于合数阶双线性群实现了标准模型下的适应安全性。在所有已知的追踪性CP-ABE方案中,都使用线性秘密共享方案(LSSS)来表示单调访问结构,并用LSSS矩阵加密明文数据。因此,其加密成本都随着LSSS矩阵的大小成线性增长,同时解密成本则随着满足要求的属性数量成线性增长。而在该文提出的追踪性CP-ABE方案中,使用最小授权子集集合来表示单调访问结构,并用该子集集合加密明文数据。因此,其加密成本随着最小授权子集的集合大小成线性增长,对于某些单调访问结构,该文方案具有更短的密文长度和更小的加密成本。最重要的是,该文方案进行解密时,只需要3个双线性对操作和2个指数操作,解密成本为常数,实现了更快更高效的数据解密。最后基于合数阶双线性群下的3个静态假设对方案进行了安全性证明,并进行了性能分析与实验验证。     

基于LSSS共享矩阵无授权策略的属性密码解密效率提高方案

在基于LSSS(Linear Secret-Sharing Schemes)共享矩阵的属性密码方案中,为了获得相对较高的解密效率,需要剔除授权集合中冗余参与方在解密时的计算.为达到这一目的,现有方案都需要使用授权策略进行最小参与方搜寻,而在一些应用场合下,授权策略的出现是不安全的.如果不使用授权策略,现有的解密优化方案便无法运行.本文提出一种LSSS共享矩阵下,无授权策略的属性密码解密效率提高方案.理论分析和实验表明,它可以在无授权策略情况下,找到最小参与方集合,从而提高了解密效率.     

Multiplicative Linear Secret Sharing Schemes Based on Connectivity of Graphs

The multiplicative property is important for a linear secret sharing scheme (LSSS) to be used in constructing a multiparty computation (MPC) protocol. In general, an LSSS has to expand its share size to obtain the multiplicative property. In this paper, with respect to an MPC problem based on connectivity of graphs we devise an ideal multiplicative LSSS, that is, the LSSS is of the multiplicative property without expanding its share size. Moreover, it provides a new class of access structures that have ideal multiplicative LSSSs.     

Programmed Wrapping and Assembly of Droplets with Mesoscale Polymers

Nature is remarkably adept at using interfaces to build structures, encapsulate reagents, and regulate biological processes. Inspired by nature, flexible polymer‐based ribbons, termed “mesoscale polymers” (MSPs), are described to modulate interfacial interactions with liquid droplets. This produces unprecedented hybrid assemblies in the forms of flagellum‐like structures and MSP‐wrapped droplets. Successful preparation of these hybrid structures hinges on interfacial interactions and tailored MSP compositions, such as MSPs with domains possessing distinctly different affinity for fluid–fluid interfaces as well as mechanical properties. In situ measurements of MSP–droplet interactions confirm that MSPs possess a negligible bending stiffness, allowing interfacial energy to drive mesoscale assembly. By exploiting these interfacial driving forces, mesoscale polymers are demonstrated as a powerful platform that underpins the preparation of sophisticated hybrid structures in fluids.     

Model selection in electromagnetic source analysis with an application to VEFs

In electromagnetic source analysis, it is necessary to determine how many sources are required to describe the electroencephalogram or magnetoencephalogram adequately. Model selection procedures (MSPs) or goodness of fit procedures give an estimate of the required number of sources. Existing and new MSPs are evaluated in different source and noise settings: two sources which are close or distant and noise which is uncorrelated or correlated. The commonly used MSP residual variance is seen to be ineffective, that is it often selects too many sources. Alternatives like the adjusted Hotelling's test, Bayes information criterion and the Wald test on source amplitudes are seen to be effective. The adjusted Hotelling's test is recommended if a conservative approach is taken and MSPs such as Bayes information criterion or the Wald test on source amplitudes are recommended if a more liberal approach is desirable. The MSPs are applied to empirical data (visual evoked fields).     

Truthful double auction of spectrum trading for femtocell service provision

The femtocell has been considered as a promising technology to improve indoor mobile network coverage co‐working with macrocell networks. However, lack of licensed spectrum limits the development of the femtocell service provision. A feasible solution is that a femtocell service provider (FSP) leases spectrum from the existing licensed spectrum holder, the macrocell service provider (MSP). Existing research focuses on the interaction between a single FSP and MSP. In this paper, we investigate a spectrum trading framework for multiple FSPs and MSPs. Under such a scenario, both FSPs and MSPs have to compete with their peers in the trading. To balance the revenue and the cost from the spectrum trading, an analysis is made on how to determine the acceptable spectrum trading prices and volumes for both MSPs and FSPs. To guarantee the fairness of the transaction, we introduce a truthful double auction mechanism for the spectrum trading between FSPs and MSPs, which compels them to report their bids or asks honestly according to their valuations. In particular, the truthfulness and other properties of the spectrum double auction have been proved. Finally, the numerical results illustrate how the acceptable spectrum trading prices and volumes are determined and also how the spectrum double auction mechanism works. Copyright © 2016 John Wiley & Sons, Ltd.     

Unprecedented Dual Alignment Mode and Freedericksz Transition in Planar Nematic Liquid Crystal Cells Doped with Gold Nanoclusters

We demonstrate that alkylthiol‐capped gold nanoclusters doped into nematic liquid crystals (N‐LCs) with positive dielectric anisotropy give rise to an unprecedented dual alignment mode and electro‐optical response, which has a potential impact on current liquid crystal (LC) display technologies and N‐LC optical‐biosensor design. By fine‐tuning experimental conditions (temperature, electric field, and alignment), N‐LCs doped with gold nanoclusters can be aligned and electrically reoriented either like N‐LCs with a positive dielectric anisotropy in a planar cell or, alternatively, as N‐LCs with a negative dielectric anisotropy in a homeotropic cell, both at lower threshold voltages than the pure N‐LC.     

Inside Front Cover: Unprecedented Dual Alignment Mode and Freedericksz Transition in Planar Nematic Liquid Crystal Cells Doped with Gold Nanoclusters (Adv. Funct. Mater. 2/2008)

On p. 212, Torsten Hegmann and co‐workers describe nematic liquid crystals (N‐LCs) confined in planar liquid crystal cells after doping with small quantities of gold nanoclusters. These give rise to a dual alignment mode and electro‐optic response (Freedericksz transition). By fine‐tuning of experimental conditions, N‐LCs doped with gold nanoclusters can be electrically reoriented and aligned either like N‐LCs with a positive dielectric anisotropy (used in twisted nematic displays) in a planar cell or alternatively as N‐LCs with a negative dielectric anisotropy (used in large LCD TVs based on the vertical alignment mode). We demonstrate that alkylthiol‐capped gold nanoclusters doped into nematic liquid crystals (N‐LCs) with positive dielectric anisotropy give rise to an unprecedented dual alignment mode and electro‐optical response, which has a potential impact on current liquid crystal (LC) display technologies and N‐LC optical‐biosensor design. By fine‐tuning experimental conditions (temperature, electric field, and alignment), N‐LCs doped with gold nanoclusters can be aligned and electrically reoriented either like N‐LCs with a positive dielectric anisotropy in a planar cell or, alternatively, as N‐LCs with a negative dielectric anisotropy in a homeotropic cell, both at lower threshold voltages than the pure N‐LC.     

A lower bound on the undetected error probability and strictlyoptimal codes

Error detection is a simple technique used in various communication and memory systems to enhance reliability. We study the probability that a q-ary (linear or nonlinear) block code of length n and size M fails to detect an error. A lower bound on this undetected error probability is derived in terms of q, n, and M. The new bound improves upon other bounds mentioned in the literature, even those that hold only for linear codes. Block codes whose undetected error probability equals the new lower bound are investigated. We call these codes strictly optimal codes and give a combinatorial characterization of them. We also present necessary and sufficient conditions for their existence. In particular, we find all values of n and M for which strictly optimal binary codes exist, and determine the structure of all of them. For example, we construct strictly optimal binary-coded decimal codes of length four and five, and we show that these are the only possible lengths of such codes     

Securing light clients in blockchain with DLCP

In blockchain, full nodes (FNs) are peers that store and verify entire chains of transactions. In contrast, light clients (LCs) are those with limited resources, and for this reason, they request only block headers from FNs for transaction verification—using protocols like Simple Payment Verification (SPV). In an approach to prevent FN tampering on transaction verification (byzantine fault), LCs request block headers from multiple FNs and compare received responses. One problem with this approach is that an LC must connect to each FN and perform the same cryptographic operations with each one repeatedly, which leads to client‐side complexity and slower response. We propose an alternate approach to tackle this issue, in which LCs can encrypt a request for block headers only once, and send that request to a predetermined set of FNs to access, process, and reply back in a single response. Our approach, called Distributed Lightweight Client Protocol (DLCP), enables LCs to verify with little effort if FNs have agreed on a response. From an experimental evaluation, we observed that DLCP provided lower latency and reduced computing and communication overhead in comparison with the existing conventional approach.     

Magnetic and Transparent Composites by Linking Liquid Crystals to Ferrite Nanoparticles through Covalent Networks

The fabrication of transparent, flexible, and optically homogeneous magnetic composites containing ferrite (Fe₃O₄) nanoparticles, liquid crystals (LCs), and siloxane backbones is reported. The transparent magnets are achieved by covalently bonding LCs to the siloxane backbones and then linking them to dopamine‐functionalized ferrite nanocrystals. They exhibit simultaneous high transparency and strong magnetic properties. A remarkable feature of these films is that the surface morphology of the LC‐attached ferrite films can be tuned by an external magnetic field, demonstrating a striped surface in the direction of the field. We show that the LC‐attached film can act as an alignment layer to orient LCs, enabling the development of LC alignment surfaces on the basis of these nanomagnet–LC polymer composites.     

香蕉形液晶中非标准的电流体效应

本文重点介绍了香蕉形液晶中的电流体效应。由于具有独特的V形分子结构,香蕉形液晶的电输运参数与传统的棒状液晶非常不同,从而引发了非标准的电流体效应。通过改变外加电场频率、幅度、极性以及温度详细研究了这种新的流体动力学行为,为将来物理模型的建立提供了良好的实验基础。     

快速解密的自适应安全KP-ABE方案

已有的自适应安全ABE(attribute-based encryption)方案的解密开销随着解密时用到的属性数量呈线性增长。针对该问题,提出了一种快速解密的自适应安全key-policy ABE(FKP-ABE)方案,在合数阶群上构造,支持任意可以表达为线性秘密分享体制(LSSS, linear secret sharing schemes)的单调访问策略,将解密开销降为常数级,并在标准模型下证明该方案是自适应安全的。     

Optical orthogonal codes with large crosscorrelation and their performance bound for asynchronous optical CDMA systems

Optical orthogonal codes (OOCs) are commonly used as signature codes for optical code-division multiple-access (OCDMA) communication systems. Many OOCs have been proposed and investigated. Asynchronous OCDMA systems using conventional OOCs have a very limited number of subscribers and few simultaneous users. Recently, we reported a new code family with large code size by relaxing the crosscorrelation constraint to 2. In this paper, by further loosening the crosscorrelation constraint, we adopt the random greedy algorithm to construct a code family which has larger code size and more simultaneous users. We also derive an upper bound of the number of simultaneous users for a given code length, code weight, and bit error rate. The study shows that it is possible to have codes approaching this bound.     

Towards Efficient Dispersion of Carbon Nanotubes in Thermotropic Liquid Crystals

Motivated by numerous recent reports indicating attractive properties of composite materials of carbon nanotubes (CNTs) and liquid crystals (LCs) and a lack of research aimed at optimizing such composites, the process of dispersing CNTs in thermotropic LCs is systematically studied. LC hosts can perform comparably or even better than the best known organic solvents for CNTs such as N‐methyl pyrrolidone (NMP), provided that the dispersion process and choice of LC material are optimized. The chemical structure of the molecules in the LC is very important; variations in core as well as in terminal alkyl chain influence the result. Several observations moreover indicate that the anisotropic nematic phase, aligning the nanotubes in the matrix, per se stabilizes the dispersion compared to a host that is isotropic and thus yields random tube orientation. The chemical and physical phenomena governing the preparation of the dispersion and its stability are identified, taking into account enthalpic, entropic, as well as kinetic factors. This allows a guideline on how to best design and prepare CNT–LC composites to be sketched, following which tailored development of new LCs may take the advanced functional material that CNT–LC composites comprise to the stage of commercial application.     

Shift-full-rank matrices and applications in space-time trellis codes for relay networks with asynchronous cooperative diversity

To achieve full cooperative diversity in a relay network, most of the existing space-time coding schemes require the synchronization between terminals. A family of space-time trellis codes that achieve full cooperative diversity order without the assumption of synchronization has been recently proposed. The family is based on the stack construction by Hammons and El Gamal and its generalizations by Lu and Kumar. It has been shown that the construction of such a family is equivalent to the construction of binary matrices that have full row rank no matter how their rows are shifted, where a row corresponds to a terminal (or transmit antenna) and its length corresponds to the memory size of the trellis code on that terminal. We call such matrices as shift-full-rank (SFR) matrices. A family of SFR matrices has been also constructed, but the memory sizes of the corresponding space-time trellis codes (the number of columns of SFR matrices) grow exponentially in terms of the number of terminals (the number of rows of SFR matrices), which may cause a high decoding complexity when the number of terminals is not small. In this paper, we systematically study and construct SFR matrices of any sizes for any number of terminals. Furthermore, we construct shortest (square) SFR (SSFR) matrices that correspond to space-time trellis codes with the smallest memory sizes and asynchronous full cooperative diversity. We also present some simulation results to illustrate the performances of the space-time trellis codes associated with SFR matrices in asynchronous cooperative communications.     

两种典型的MIMO系统信道容量分析与仿真

为了研究多输入多输出系统的信息论基础,从信息理论的角度给出其理论依据,本文通过从信息论角度对使用多个发射、多个接收天线的MIMO系统的信道容量进行的理论推导,得到了MIMO系统在输入信号向量为循环对称复高斯输入信号向量且平均分配发射功率条件下,可以达到比传统单发单收无线通信系统高的多的信道容量的结论,得到了信道容量公式,并据此分析研究了全1和单位传输矩阵所对应的两种典型的MIMO系统的信道容量,给出了一种更容易理解的信道容量的虚拟等效实现结构,以便理解其取得高信道容量的原因及条件;同时我们也给出了验证MIMO系统高信道容量的计算机仿真结果.     

Liquid Crystal Enabled Early Stage Detection of Beta Amyloid Formation on Lipid Monolayers

Liquid crystals (LCs) can serve as sensitive reporters of interfacial events, and this property has been used for sensing of synthetic or biological toxins. Here it is demonstrated that LCs can distinguish distinct molecular motifs and exhibit a specific response to beta‐sheet structures. That property is used to detect the formation of highly toxic protofibrils involved in neurodegenerative diseases, where it is crucial to develop methods that probe the early‐stage aggregation of amyloidogenic peptides in the vicinity of biological membranes. In the proposed method, the amyloid fibrils formed at the lipid–decorated LC interface can change the orientation of LCs and form elongated and branched structures that are amplified by the mesogenic medium; however, nonamyloidogenic peptides form ellipsoidal domains of tilted LCs. Moreover, a theoretical and computational analysis is used to reveal the underlying structure of the LC, thereby providing a detailed molecular‐level view of the interactions and mechanisms responsible for such motifs. The corresponding signatures can be detected at nanomolar concentrations of peptide by polarized light microscopy and much earlier than the ones that can be identified by fluorescence‐based techniques. As such, it offers the potential for early diagnoses of neurodegenerative diseases and for facile testing of inhibitors of amyloid formation.     

Universal variable-to-fixed length source codes

A universal variable-to-fixed length algorithm for binary memoryless sources which converges to the entropy of the source at the optimal rate is known. We study the problem of universal variable-to-fixed length coding for the class of Markov sources with finite alphabets. We give an upper bound on the performance of the code for large dictionary sizes and show that the code is optimal in the sense that no codes exist that have better asymptotic performance. The optimal redundancy is shown to be H log log M/log M where H is the entropy rate of the source and M is the code size. This result is analogous to Rissanen's (1984) result for fixed-to-variable length codes. We investigate the performance of a variable-to-fixed coding method which does not need to store the dictionaries, either at the coder or the decoder. We also consider the performance of both these source codes on individual sequences. For individual sequences we bound the performance in terms of the best code length achievable by a class of coders. All the codes that we consider are prefix-free and complete