Complex optical index of single wall carbon nanotube films from the near-infrared to the terahertz spectral range

We retrieve the complex optical index of single-walled carbon nanotube (CNT) films in the 0.6-800 μm spectral range. Results are obtained from a complete set of optical measurements, reflection and transmission, of free-standing CNT films using time domain spectroscopy in the terahertz (THz) and Fourier transform infrared (IR) spectroscopy in the visible-IR. Based on a Drude-Lorentz model, our results reveal a global metallic behavior of the films in the IR, and confirm their high optical index in the THz range.     

A Fair, Secure and Trustworthy Peer-to-Peer Based Cycle-Sharing System

The increased popularity of Grid systems and cycle sharing across organizations requires scalable systems that provide facilities to locate resources, to be fair in the use of those resources, to allow resource providers to host untrusted applications safely, and to allow resource consumers to monitor the progress and correctness of jobs executing on remote machines. This paper presents such a framework that locates computational resources with a peer-to-peer network, assures fair resource usage with a distributed credit accounting system, provides resource contributors a safe environment, for example Java Virtual Machine (JVM), to host untrusted applications, and provides the resource consumers a monitoring system, GridCop, to track the progress and correctness of remotely executing jobs. We present the details of the credit accounting subsystem and the GridCop remote job monitoring subsystem. GridCop and the distributed credit accounting system together enable incremental payments so that the risk for both resource providers and resource consumers is bounded.*This work was supported by NSF CAREER award grant ACI-0238379 and NSF grants CCR-0313026 and CCR-0313033.     

基于DSC的全数字控制高频开关电源整体解决方案

数字控制由于高集成度带来的低成本、设计沿继性、控制灵活等优点而应用逐渐广泛，本文利用Freescale半导体公司新型号数字信号控制器(DSC)－MC56F8323的高性能特性，提供了基于DSC数字控制的高频开关电源的完整解决方案，给出了全数字控制的软开关数字功率因数校正和全数字控制的带同步整流的软开关移相全桥直直变换器两个子系统的详细设计，最后用一台500W实验样机验证了基于数字控制的完整开关电源系统的优良系统性能。     

Achieving developability of a polygonal surface by minimum deformation: a study of global and local optimization approaches

Surface developability is required in a variety of applications in product design, such as clothing, ship hulls, automobile parts, etc. However, most current geometric modeling systems using polygonal surfaces ignore this important intrinsic geometric property. This paper investigates the problem of how to minimally deform a polygonal surface to attain developability, or the so-called developability-by-deformation problem. In our study, this problem is first formulated as a global constrained optimization problem and a penalty-function-based numerical solution is proposed for solving this global optimization problem. Next, as an alternative to the global optimization approach, which usually requires lengthy computing time, we present an iterative solution based on a local optimization criterion that achieves near real-time computing speed.     

Algebraic grid generation on trimmed parametric surface using non‐self‐overlapping planar Coons patch

Using a Coons patch mapping to generate a structured grid in the parametric region of a trimmed surface can avoid the singularity of elliptic PDE methods when only C¹ continuous boundary is given; the error of converting generic parametric C¹ boundary curves into a specified representation form is also avoided. However, overlap may happen on some portions of the algebraically generated grid when a linear or naïve cubic blending function is used in the mapping; this severely limits its usage in most of engineering and scientific applications where a grid system of non‐self‐overlapping is strictly required. To solve the problem, non‐trivial blending functions in a Coons patch mapping should be determined adaptively by the given boundary so that self‐overlapping can be averted. We address the adaptive determination problem by a functional optimization method. The governing equation of the optimization is derived by adding a virtual dimension in the parametric space of the given trimmed surface. Both one‐ and two‐parameter blending functions are studied. To resolve the difficulty of guessing good initial blending functions for the conjugate gradient method used, a progressive optimization algorithm is then proposed which has been shown to be very effective in a variety of practical examples. Also, an extension is added to the objective function to control the element shape. Finally, experiment results are shown to illustrate the usefulness and effectiveness of the presented method. Copyright © 2004 John Wiley & Sons, Ltd.     

Enhancing Electrocatalytic Water Splitting by Strain Engineering

Electrochemical water splitting driven by sustainable energy such as solar, wind, and tide is attracting ever‐increasing attention for sustainable production of clean hydrogen fuel from water. Leveraging these advances requires efficient and earth‐abundant electrocatalysts to accelerate the kinetically sluggish hydrogen and oxygen evolution reactions (HER and OER). A large number of advanced water‐splitting electrocatalysts have been developed through recent understanding of the electrochemical nature and engineering approaches. Specifically, strain engineering offers a novel route to promote the electrocatalytic HER/OER performances for efficient water splitting. Herein, the recent theoretical and experimental progress on applying strain to enhance heterogeneous electrocatalysts for both HER and OER are reviewed and future opportunities are discussed. A brief introduction of the fundamentals of water‐splitting reactions, and the rationalization for utilizing mechanical strain to tune an electrocatalyst is given, followed by a discussion of the recent advances on strain‐promoted HER and OER, with special emphasis given to combined theoretical and experimental approaches for determining the optimal straining effect for water electrolysis, along with experimental approaches for creating and characterizing strain in nanocatalysts, particularly emerging 2D nanomaterials. Finally, a vision for a future sustainable hydrogen fuel community based on strain‐promoted water electrolysis is proposed.     

DNA Nanotweezers and Graphene Transistor Enable Label‐Free Genotyping

Electronic DNA‐biosensor with a single nucleotide resolution capability is highly desirable for personalized medicine. However, existing DNA‐biosensors, especially single nucleotide polymorphism (SNP) detection systems, have poor sensitivity and specificity and lack real‐time wireless data transmission. DNA‐tweezers with graphene field effect transistor (FET) are used for SNP detection and data are transmitted wirelessly for analysis. Picomolar sensitivity of quantitative SNP detection is achieved by observing changes in Dirac point shift and resistance change. The use of DNA‐tweezers probe with high‐quality graphene FET significantly improves analytical characteristics of SNP detection by enhancing the sensitivity more than 1000‐fold in comparison to previous work. The electrical signal resulting from resistance changes triggered by DNA strand‐displacement and related changes in the DNA geometry is recorded and transmitted remotely to personal electronics. Practical implementation of this enabling technology will provide cheaper, faster, and portable point‐of‐care molecular health status monitoring and diagnostic devices.