Optical behaviour of photoimageable cholesteric liquid crystal cells with various novel chiral compounds

In theory, both polarity and steric hindrance are basic factors which affect molecular interactions. To investigate the optical properties and steric structures of chiral compounds having different chiral moieties which affect the wavelength of light reflection in liquid crystal (LC) cells, a series of novel chiral compounds and azobenzene derivatives were synthesized. The liquid crystalline phases of the compounds were identified using small angle X-ray diffraction, differential scanning calorimetry and polarizing optical microscopy. Cholesteric LC cells with various synthesized chiral dopants which selectively reflect visible light were first prepared, the photochemical switching behaviour of colours was then investigated, with special reference to the change in transmittance in cholesteric LC cells containing an azobenzene derivative as a photoisomerizable guest molecule. Reversible isomerization of azobenzene molecules occurred in the cholesteric systems, resulting in a depression of T_ChI and a shift of the selectively reflected wavelength. We discuss the photochemically driven change in the helical pitch of the cholesteric LCs with respect to structural effects involving the chiral moieties. Molecular interactions caused by the added dopants, reliability and stability of the photoisomerization, and UV irradiation effects on the cholesteric LC cells were also investigated. A real image was recorded through a mask on a cholesteric LC cell fabricated in this investigation.     

A time-based energy-efficient analog-to-digital converter

Dual-slope converters use time to perform analog-to-digital conversion but require 2/sup N+1/ clock cycles to achieve N bits of precision. We describe a novel current-mode algorithm that also uses time to perform analog-to-digital conversion but requires 5N clock cycles to achieve N bits of precision via a successive subranging technique. The algorithm requires one asynchronous comparator, two capacitors, one current source, and a state machine. Amplification of two is achieved without the use of an explicit amplifier by simply doing things twice in time. The use of alternating voltage-to-time and time-to-voltage conversions provides natural error cancellation of comparator offset and delay, 1/f noise, and switching charge-injection. The use of few components and an efficient mechanism for amplification and error cancellation allow for energy-efficient operation: in a 0.35-/spl mu/m implementation, we were able to achieve 12 bit of DNL limited precision or 11 bit of thermal noise-limited precision at a sampling frequency of 31.25 kHz with 75 /spl mu/W of total analog and digital power consumption. These numbers yield a thermal noise-limited energy efficiency of 1.17 pJ per quantization level, making it one of the most energy-efficient converters to date in the 10-12 bit precision range.     

Bio-Plasmonics: Nano/micro Structure of Surface Plasmon Resonance Devices for Biomedicine

We have reported a novel design of surface plasmon resonance (SPR) device, which uses alternating dielectric layers to enhance the SPR signal quality and modulate its resonant position. Admittance loci method of thin film design has been used in the design of such a device. The use of biomolecular thin film, such as DNAs or Porteins, in this design can result in resonant condition of wavelength changes as well. Bio-plasmonics is proposed for the research and development of novel devices, which use biomolecules as a part of the plasmon oscillation system to actively interact with nano/micro structure.     

A complete boundary integral formulation for compressible Navier–Stokes equations

A complete boundary integral formulation for compressible Navier–Stokes equations with time discretization by operator splitting is developed using the fundamental solutions of the Helmholtz operator equation with different order. The numerical results for wall pressure and wall skin friction of two‐dimensional compressible laminar viscous flow around airfoils are in good agreement with field numerical methods. Copyright © 2004 John Wiley & Sons, Ltd.     

Coordinating Agents in Shop Floor Environments From a Dynamic Systems Perspective

In this paper, we address agent coordination from a dynamic systems perspective and propose a dynamic coordination model, which is inspired by biological metabolic systems. A new coordination mechanism through dynamic local adjustment (CDLA) is presented, and coordination is achieved when every agent utilizes explicitly the global system dynamics and performs iteratively a dynamic local adjustment procedure. The CDLA mechanism is investigated in an example multiagent shop floor system. The results show that the example manufacturing process is well-coordinated and the coordination approach is practically applicable and effective     

无线局域网技术及应用

无线局域网技术是目前发展迅速的技术，相对于有线局域网有许多优点。随着无线网络产品性能的提高和价格的不断下降，无线局域网技术有着广泛的应用前景。据此对无线局域网的基本概念、特点及其技术作了简单的介绍，提出了无线局域网面向应用的几种解决方案，并对发展前景作了预测。     

Multicasting in a class of multicast-capable WDM networks

Multicast is the ability to transmit information from a single source node to multiple destination nodes. Multicast can be supported more efficiently in optical domain by utilizing the inherent light-splitting capacity of optical switches than by copying data in electronic domain. In this paper, we study multicast communication in a class of multicast-capable WDM networks (i.e., the networks that have light splitting switches) with regular topologies under some commonly used routing algorithms. Upper and lower bounds on the minimum number of wavelengths required are determined for a network to be rearrangeable for arbitrary multicast assignments, and compared with those WDM networks without light splitting switches. Our results indicate that in most of the networks we study, the number of wavelengths required can be significantly reduced by utilizing light splitting switches     

Adaptive alignment packaging for 2-D arrays of free-spaceoptical-interconnected optoelectronic systems

An adaptive alignment scheme for packaging two-dimensional (2D) arrays of optoelectronic systems interconnected by free-space optics is presented. A method of using three quadrant detectors to detect alignment errors in six degrees of freedom is described. However, the complexity of this system increases due to the interactions among the detected error signals. A novel control algorithm is presented to eliminate the interaction and simplify the design of the closed-loop feedback control. A computer simulation compares different algorithms and shows the effectiveness of the proposed algorithm. An experimental closed-loop feedback system demonstrated the principle of the error detection and correction of the proposed system with initial errors in multiple degrees of freedom     

Sensitivity of depolarized lidar signals to cloud and aerosol particle properties

Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer.     

《无线电频率划分规定》学习心得

主要介绍学习新的《无线电频率划分规定》的目的，《无线电频率划分规定》的特点，作了哪些重要修改和划分表的主要内容及如何贯彻执行《无线电频率划分规定》。