科技辞典:Flexible Display-可挠式显示器

可挠式显示器是利用塑料当作基板的平面显示器,相较于目前的平面显示器所使用之玻璃基材,塑料具有更轻薄、耐冲击、可挠曲及可连续制程(降低成本)的优点,被视为是下一世代平面显示器的理想基板材料。     

A new worm propagation threat in BitTorrent: modeling and analysis

Peer-to-peer (P2P) networking technology has gained popularity as an efficient mechanism for users to obtain free services without the need for centralized servers. Protecting these networks from intruders and attackers is a real challenge. One of the constant threats on P2P networks is the propagation of active worms. Recent events show that active worms can spread automatically and flood the Internet in a very short period of time. Therefore, P2P systems can be a potential vehicle for active worms to achieve fast worm propagation in the Internet. Nowadays, BitTorrent is becoming more and more popular, mainly due its fair load distribution mechanism. Unfortunately, BitTorrent is particularly vulnerable to topology aware active worms. In this paper we analyze the impact of a new worm propagation threat on BitTorrent. We identify the BitTorrent vulnerabilities it exploits, the characteristics that accelerate and decelerate its propagation, and develop a mathematical model of their propagation. We also provide numerical analysis results. This will help the design of efficient detection and containment systems.     

Complex Adaptive ICA Employing the Conjugate Gradient Technique for Signal Separation in Time-Varying Flat Fading Channels

The conjugate gradient method is a prominent technique for solving systems of linear equations and unconstrained optimization problems, including adaptive filtering. Since it is an iterative method, it can be particularly applied to solve sparse systems which are too large to be handled by direct methods. The main advantage of the conjugate gradient method is that it employs orthogonal search directions with optimal steps along each direction to arrive at the solution. As a result, it has a much faster convergence speed than the steepest descent method, which often takes steps in the same direction as earlier steps. Furthermore, it has lower computational complexity than Newton’s iteration approach. This unique tradeoff between convergence speed and computational complexity gives the conjugate gradient method desirable properties for application in numerous mathematical optimization problems. In this paper, the conjugate gradient principle is applied to complex adaptive independent component analysis (ICA) for maximization of the kurtosis function, to achieve separation of complex-valued signals. The proposed technique is called the complex block conjugate independent component analysis (CBC-ICA) algorithm. The CBC-ICA derives independent conjugate gradient search directions for the real and imaginary components of the complex coefficients of the adaptive system employed for signal separation. In addition, along each conjugate direction an optimal update is generated separately for the real and imaginary components using the Taylor series approximation. Simulation results confirm that in dynamic flat fading channel conditions, the CBC-ICA demonstrates excellent convergence speed and accuracy, even for large processing block sizes.     

On Expected Probabilistic Polynomial-Time Adversaries: A Suggestion for Restricted Definitions and Their Benefits

This paper concerns the possibility of developing a coherent theory of security when feasibility is associated with expected probabilistic polynomial-time (expected PPT). The source of difficulty is that the known definitions of expected PPT strategies (i.e., expected PPT interactive machines) do not support natural results of the type presented below. To overcome this difficulty, we suggest new definitions of expected PPT strategies, which are more restrictive than the known definitions (but nevertheless extend the notion of expected PPT noninteractive algorithms). We advocate the conceptual adequacy of these definitions and point out their technical advantages. Specifically, identifying a natural subclass of black-box simulators, called normal, we prove the following two results:

Learning a Parallelepiped: Cryptanalysis of GGH and NTRU Signatures

Lattice-based signature schemes following the Goldreich–Goldwasser–Halevi (GGH) design have the unusual property that each signature leaks information on the signer’s secret key, but this does not necessarily imply that such schemes are insecure. At Eurocrypt ’03, Szydlo proposed a potential attack by showing that the leakage reduces the key-recovery problem to that of distinguishing integral quadratic forms. He proposed a heuristic method to solve the latter problem, but it was unclear whether his method could attack real-life parameters of GGH and NTRUSign. Here, we propose an alternative method to attack signature schemes à la GGH by studying the following learning problem: given many random points uniformly distributed over an unknown n-dimensional parallelepiped, recover the parallelepiped or an approximation thereof. We transform this problem into a multivariate optimization problem that can provably be solved by a gradient descent. Our approach is very effective in practice: we present the first successful key-recovery experiments on NTRUSign-251 without perturbation, as proposed in half of the parameter choices in NTRU standards under consideration by IEEE P1363.1. Experimentally, 400 signatures are sufficient to recover the NTRUSign-251 secret key, thanks to symmetries in NTRU lattices. We are also able to recover the secret key in the signature analogue of all the GGH encryption challenges. P.Q. Nguyen part of this work is supported by the Commission of the European Communities through the IST program under contract IST-2002-507932 ECRYPT and by the French government through the X-Crypt RNRT project. O. Regev supported by the Binational Science Foundation, by the Israel Science Foundation, by the European Commission under the Integrated Project QAP funded by the IST directorate as Contract Number 015848, and by a European Research Council (ERC) Starting Grant.     

Design-to-testing: a low-power, 1.25 GHz,single-bit single-loop continuous-time $$\Delta \Sigma$$ modulator with 15 MHz bandwidth and 60 dB dynamic range

Continuous-time Delta-Sigma (CT-\(\Delta \Sigma\)) analog-to-digital converters have been extensively investigated for their use in wireless receivers to achieve conversion bandwidths >15 MHz and higher resolution of 10–14 bits. This paper presents the complete design-to-testing tutorial of a state-of-the-art high-speed single-bit CT-\(\Delta \Sigma\) architecture and its circuit design details in 0.13 μm CMOS technology node sampling at 1.25 GS/s. The designed modulator achieves higher dynamic range of 60 dB in a wide conversion bandwidth of 15 MHz and consumes only 3.5 mW. The proposed modulator achieves a Figure of Merit of 154 fJ/level.     

Information system security compliance to FISMA standard: a quantitative measure

To ensure that safeguards are implemented to protect against a majority of known threats, industry leaders are requiring information processing systems to comply with security standards. The National Institute of Standards and Technology Federal Information Risk Management Framework (RMF) and the associated suite of guidance documents describe the minimum security requirements (controls) for non-national-security federal information systems mandated by the Federal Information Security Management Act (FISMA), enacted into law on December 17, 2002, as Title III of the E-Government Act of 2002. The subjective compliance assessment approach described in the RMF guidance, though thorough and repeatable, lacks the clarity of a standard quantitative metric to describe for an information system the level of compliance with the FISMA-required standard. Given subjective RMF assessment data, this article suggests the use of Pathfinder networks to generate a quantitative metric suitable to measure, manage, and track the status of information system compliance with FISMA.     

Resource planning and incentive engineering for a congested wireless access point: an integrated multiple time scale control mechanism

Wireless networks are playing an increasingly important role for global communications. Many resource allocation mechanisms have been proposed to efficiently utilize the limited radio resources in wireless networks to support a large number of mobile users with a diversity of applications. Among them, pricing frameworks that provide incentives to users to maximize their individual utility while optimizing allocation of network resources have attracted a lot of attention recently. Nevertheless, most of these pricing schemes require dynamic charging rates and may be too complex for wide acceptance by users, as most users would prefer relatively simple charging schemes. Moreover, use of a pricing framework to facilitate resource planning and future expansion at the service provider’s side has not yet been widely considered. In this paper, we propose Integrated Multiple Time Scale Control (IMTSC), a novel incentive engineering mechanism to facilitate resource allocation and network planning. Over different time scales, IMTSC combines the functions of network capacity planning, admission control for resource allocation, and tracking of users’ instantaneous traffic demands. The proposed mechanism is applied for access control at a congested access point in a wireless network. By decomposing the original problem into distributed optimization problems that are solved locally by the service provider through adjusting charging rate and remotely by individual users by appropriately changing her service requests, we show that maximization of user’s utility and increase of network efficiency can be simultaneously achieved. Results from extensive simulations demonstrate the effectiveness of the proposed IMTSC mechanism.     

The Structure of Complex Thin-Film Systems from Ellipsometric Simulation: A PbI2–Cu Photoresist

It is shown that the structure of complex thin-film systems can be studied ellipsometrically. In the ellipsometric method used in this work, the distribution of the rf permittivity (z) across the depth is simulated within models of uniform layers and linearly nonuniform layers. Difficulties associated with finding the ellipsometric parameters for a reflecting system with nonuniformly distributed (z) are considered. It was demonstrated that vacuum deposition of PbI₂–Cu thin-film inorganic photoresist causes the transition layer to form at the Cu/PbI₂ interface due to copper penetrating into the interface region of PbI₂. The parameters of this layer correlate with the PbI₂ film porosity.     

Advanced Engineering for Cathode in Lithium–Oxygen Batteries: Flexible 3D Hierarchical Porous Architecture Design and Its Functional Modification

Modern technology constantly requires smaller, more efficient lithium–oxygen batteries (LOBs). To meet this need, a chemical vapor deposition (CVD) method is used to create an innovative cathode design with both a hierarchical porous nanostructure and a 3D flexible macroscopical morphology. This method employs architectural optimization to further improve cathodic ORR and OER performance via heteroatom doping, surface-sprouted carbon nanofibers (CNFs) grafting, and boundary exposing. The cathode consists of a 3D hierarchical porous graphene foam (PGF), along with RuO₂ nanoparticles impregnated and nitrogen doped CNFs (RuO₂@NCNFs), where the PGF serves as a structural support and cathodic current collector, and the RuO₂@NCNFs work as a superior bi-functional catalyst. The cathode delivers an outstanding discharge capacity of 8440 mAh g_cathode⁻¹ while maintaining a recharge plateau at ≈4.0 V, and can cycle for over 700 rounds without obvious degeneration under a fixed capacity. Notably, this free-standing cathode can be directly used in LOBs without the need for additional substrates or current collectors. Therefore, the current densities and capacities herein are calculated based on the total weight of the cathodes. These results demonstrate the RuO₂@NCNFs-PGF cathode's remarkable potential for LOB applications, and this rational cathodic structure may be extended to other highly efficient catalyst applications.     

Fractional Lambda Switching for Flexible Bandwidth Provisioning in WDM Networks: Principles and Performance<Superscript>†</Superscript>

A new approach is introduced in this paper to make possible a flexible utilization of WDM networks using current technology. It is shown that the bandwidth made available end-to-end by a single wavelength can be simply broken up into smaller pieces, or fraction of lambda, by relying on a worldwide common time reference system, such as GPS, previously deployed for different applications. The common time reference system is used to synchronize switches and to facilitate pipeline forwarding of data units. Pipeline forwarding is a known optimal method widely used in manufacturing and computing. It is shown how this new approach, called Time Driven Switching, behaves in terms of call blocking when the basic parameters of the scheme are varied.Work carried out at Politecnico di Milano, Italy. A preliminary version of this paper has been presented at GLOBECOM 2003, San Francisco, USA.     

Conductive Anodic Filament Formation Part II: Electrochemical Reactions Leading to CAF

Conductive anodic filament (CAF) formation has been studied for a number of years, but the mechanism of its formation has not previously been defined. In 2002, Ready identified CAF as atacamite, Cu₂(OH)₃Cl. Electrochemical studies have shown that both CuCl and CuCl ₂ ^? participate in the formation of Cu₂(OH)₃Cl, with the predominating species being CuCl. This paper proposes a mechanism for CAF formation based on x-ray photoelectron spectroscopy. The data show that CuCl is the precursor to the formation of Cu₂(OH)₃Cl in the presence of oxygen and water. Earlier, Meeker and Lu Valle had proposed that CAF failure is best represented by two competing reactions: the formation of a copper chloride corrosion compound (now identified as Cu₂(OH)₃Cl) and the formation of innocuous trapped chlorine compounds. Since no evidence of any trapped chloride compounds has been found, we propose that the formation of CAF is best represented by a single nonreversible reaction.     

Multi-Hop Wireless Backhaul Networks above 10 GHz: Connectivity and Critical Density Evaluation

Microwave links are the obvious mobile backhauling solution for many mobile operators. Multi-hops are likely to be necessary in order to ensure connectivity for mobile backhaul solutions. The subject of the present paper is the evaluation of the connectivity of wireless multi-hop backhaul networks assuming high frequency transmissions among the relays. A novel analytical physical propagation and engineering model is presented for the calculation of the connectivity of wireless multi-hop networks that appropriate for operating frequencies above 10 GHz. Assuming equal power transmissions from every node and a random spatial node distribution following the homogeneous Poisson process, we calculate the node isolation probability. Furthermore, we calculate the minimum required node density in order to keep the backhaul network almost connected. The sensitivity of the isolation probability and of the minimum node density on frequency of operation, transmission power and climatic conditions is also investigated. Some useful conclusions are drawn.     

Authenticated Encryption: Relations among Notions and Analysis of the Generic Composition Paradigm

An authenticated encryption scheme is a symmetric encryption scheme whose goal is to provide both privacy and integrity. We consider two possible notions of authenticity for such schemes, namely integrity of plaintexts and integrity of ciphertexts, and relate them, when coupled with IND-CPA (indistinguishability under chosen-plaintext attack), to the standard notions of privacy IND-CCA and NM-CPA (indistinguishability under chosen-ciphertext attack and nonmalleability under chosen-plaintext attack) by presenting implications and separations between all notions considered. We then analyze the security of authenticated encryption schemes designed by “generic composition,” meaning making black-box use of a given symmetric encryption scheme and a given MAC. Three composition methods are considered, namely Encrypt-and-MAC, MAC-then-encrypt, and Encrypt-then-MAC. For each of these and for each notion of security, we indicate whether or not the resulting scheme meets the notion in question assuming that the given symmetric encryption scheme is secure against chosen-plaintext attack and the given MAC is unforgeable under chosen-message attack. We provide proofs for the cases where the answer is “yes” and counter-examples for the cases where the answer is “no.” M. Bellare’s work was supported in part by a 1996 Packard Foundation Fellowship in Science and Engineering, NSF CAREER Award CCR-9624439, NSF grants CNS-0524765 and CNS-0627779, and a gift from Intel Corporation. C. Namprempre’s work was supported in part by grants of the first author and the Thailand Research Fund.     

Taming Single Input Chaotic Systems by Fractional Differentiator-Based Controller: Theoretical and Experimental Study

A simple fractional differentiator-based controller is proposed to suppress chaos in a 3D single input chaotic system by stabilizing some of the fixed points. The tuning procedure for the proposed controller is based on the stability concepts in the incommensurate fractional order systems. To show the efficiency of the controller, some numerical simulations are given. Also, to evaluate the practical capability of the proposed controller, we experimentally apply it to control chaos in a chaotic circuit. Moreover, some mathematical analyses are presented to show the applicability of the proposed controller, when its structure is not exactly implementable.     

Indoor Radio Propagation and Interference in 2.4 GHz Wireless Sensor Networks: Measurements and Analysis

In wireless sensor networks (WSNs), the performance and lifetime are significantly affected by the indoor propagation and the interference from other technologies using the 2.4 GHz band. Next to an overview of the propagation and coexistence issues in the literature, we present a model for analysing these effects in WSNs. We also present our measurements results on the indoor propagation, the interference of the microwave oven (MWO) and their impact on the performance of the WSN. The propagation measurements reveal significant influence of the multipath: changing a node position with a few centimetres or changing the communication channel can lead up to 30 dB difference in the received power. The power leakage of MWO has been observed around $-$ 20 dBm at 1 m distances to the oven. This leads to extra retries of the 802.15.4 messages which matches our simulation results: the packet success ratio at first try decreases to 30–40 %, which increases the average active time of the sensor, closely located to the MWO. We observe that the ON–OFF pattern of the MWO could be exploited by WSNs to improve the performance.     

Weighted H ∞ Filtering of Switched Systems with Time-Varying Delay: Average Dwell Time Approach

This paper is concerned with the H _∞ filtering problem for a continuous-time linear switched system with time-varying delay in its state. To reduce the overdesign of the quadratic framework, this paper proposes a parameter-dependent filter design procedure, which is much less conservative than the quadratic approach. By using an average dwell time approach and the piecewise Lyapunov function technique, a sufficient condition is first proposed to guarantee the exponential stability with a weighted H _∞ performance for the filtering error system with the decay estimate explicitly given. Then, the corresponding solvability condition for a desired filter is established, and the filter design is cast into a convex optimization problem which can be efficiently handled by using standard numerical software. All the conditions obtained in this paper are delay dependent. Finally, a numerical example is given to illustrate the effectiveness of the proposed theory.     

Room-Temperature Quantum Cascade Laser: ZnO/Zn1−x Mg x O Versus GaN/Al x Ga1−x N

A ZnO/Zn_1?x Mg _x O-based quantum cascade laser (QCL) is proposed as a candidate for generation of THz radiation at room temperature. The structural and material properties, field dependence of the THz lasing frequency, and generated power are reported for a resonant phonon ZnO/Zn_0.95Mg_0.05O QCL emitting at 5.27 THz. The theoretical results are compared with those from GaN/Al _x Ga_1?x N QCLs of similar geometry. Higher calculated optical output powers [ $ {P}_{\rm{ZnMgO}} $  = 2.89 mW (nonpolar) at 5.27 THz and 2.75 mW (polar) at 4.93 THz] are obtained with the ZnO/Zn_0.95Mg_0.05O structure as compared with GaN/Al_0.05Ga_0.95N QCLs [ $ {P}_{\rm{AlGaN}} $  = 2.37 mW (nonpolar) at 4.67 THz and 2.29 mW (polar) at 4.52 THz]. Furthermore, a higher wall-plug efficiency (WPE) is obtained for ZnO/ZnMgO QCLs [24.61% (nonpolar) and 23.12% (polar)] when compared with GaN/AlGaN structures [14.11% (nonpolar) and 13.87% (polar)]. These results show that ZnO/ZnMgO material is optimally suited for THz QCLs.