MEMS助力推动下一代无线通信

未来的无线通信系统将具备各种新功能并高度微型化。而且,3代和4代多模/多波段无线终端设备将为新业务、互联网与Mcommerce(移动电子商务)数据、以及静态/视频图象提供网络连接。此外,终端设备也应具备更多新功能来吸引更多终端用户。微电子 机械(microelectromechanical,MEM)元件与系统可提高创新性3代产品的集成化水平,并可调整器件的特性和工作方式,因此可降低3代 图 产品的尺寸和成本。它们还将为 　　　无线系统带来新的体系结构和功耗管理特征。此外,MEMS还将推动新功能、传感器、执行器在无线终端设备上的集成。用户接口需要采用新的技术解决方案。微机械传感器和麦克风已经有元件形式的产品,它们可以被看作是更复杂、包括若干集成化传感器元件的智能系统的一个组成部分。对移动终端来说,娱乐和游戏功能是新功能开发的重要推动力,传感器和执行器也是如此。微反射镜和微透镜为照相机和显示器的实现带来了新的可能,如投影显示。因此MEMS将极大地促进未来无线系统的发展。本文将对 MEMS 在无线通信发展 中的应用进行探讨,首先讨论微系统 化、多功能器件在紧凑系统中的集成、...     

Data offloading and task allocation for cloudlet-assisted ad hoc mobile clouds

Nowadays, although the data processing capabilities of the modern mobile devices are developed in a fast speed, the resources are still limited in terms of processing capacity and battery lifetime. Some applications, in particular the computationally intensive ones, such as multimedia and gaming, often require more computational resources than a mobile device can afford. One way to address such a problem is that the mobile device can offload those tasks to the centralized cloud with data centers, the nearby cloudlet or ad hoc mobile cloud. In this paper, we propose a data offloading and task allocation scheme for a cloudlet-assisted ad hoc mobile cloud in which the master device (MD) who has computational tasks can access resources from nearby slave devices (SDs) or the cloudlet, instead of the centralized cloud, to share the workload, in order to reduce the energy consumption and computational cost. A two-stage Stackelberg game is then formulated where the SDs determine the amount of data execution units that they are willing to provide, while the MD who has the data and tasks to offload sets the price strategies for different SDs accordingly. By using the backward induction method, the Stackelberg equilibrium is derived. Extensive simulations are conducted to demonstrate the effectiveness of the proposed scheme.     

Handover and Uplink Power Control Performance in the 3.84 Mcps TDD mode of UTRA Network

In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out.     

Molecular Weight Characterization and Gelling Properties of Acid-Modified Maize Starches

The reduction in the molecular weight distribution during acid hydrolysis of ordinary and waxy maize starch occured in two stages: first amylopectin degraded to intermediate high molecular weight polysac-charides, secondly, these were further hydrolyzed. The amylose moiety of ordinary and high-amylose starch was not affected very much by the hydrolysis conditions used (0.1–1 M HCI, 40°C, 0.3–4 h), but the gelling properties of starch weakened. The amylopectin degradation products, probably branched dextrins, were shown to hinder the gel formation of amylose in the starch pastes.     

Friction and a Tribochemical Reaction between Ice and Hexagonal Boron Nitride: A Theoretical Study

Friction between ice-Ih and hexagonal boron nitride (h-BN) has been determined by periodic ab initio calculations. Surfaces of ice-Ih and h-BN were brought into sliding contact, and the interaction energies were calculated as a function of interplanar distance and lateral displacement of the surfaces. The friction between the surfaces was calculated from the interaction energies, producing a friction coefficient of 0.140. Friction is further influenced at high loads by a tribochemical reaction between ice-Ih and h-BN.     

Chlorate Formation in Chlorine Dioxide Delignification—An Analysis via Elementary Kinetic Modeling

Abstract

Elementary kinetic modeling was used to study the mechanism of chlorate formation in chlorine dioxide delignification. Reaction conditions reflecting typical industrial processes (T = 50°C, pH 1.5–4) were examined. Fe mediated Cl(III) decomposition and a reaction between hypochlorous acid and chlorous acid (or their equilibrium counterparts) were found to be the major reaction routes responsible for chlorate formation at pH < 3. The latter route accounts for chlorate formation at pH ≥ 3. The rate of chlorous acid (HClO₂) self-decomposition was too slow either to compete against the other routes (pH < 3) or to yield notable amounts of chlorate within the given time frame (pH ≥ 3). The results suggest that chlorate formation could be suppressed, without adverse effects on chlorine dioxide regeneration, by aiming for end pH 3–3.5, ensuring a moderate chloride ion concentration and by favoring concentrated solutions/suspensions.     

A Model for Chlorine Dioxide Delignification of Chemical Pulp

Abstract

A phenomenon based model for chlorine dioxide delignification of chemical pulp is introduced. The pulp suspension environment is modeled using the concept of two liquid phases, one inside and the other external to the fiber wall. Physico-chemical processes taking place during delignification are implemented with thermodynamic, mass transfer and reaction kinetic models. A broad library of chemical reactions is introduced. Inclusion of each reaction is justified. The model response is tested against experimental laboratory delignification results (o-delignified birch pulp). The experimental data consists of kappa number, hexenuronic acid, inorganic oxy-chlorine compound, and organochlorine (AOX, OX) measurements at several time points during five delignification experiments. The model predictions are mainly in good agreement with the experimental results. The predictions regarding hypochlorous acid driven processes (HexA removal, organochlorine formation, chlorite and chlorate concentration) are somewhat incoherent, indicating that knowledge regarding the intermediately formed hypochlorous acid is presently insufficient.     

Organochlorine Formation in Tertiary Amine Catalyzed Pulp Bleaching

An oxygen delignified eucalyptus kraft pulp was bleached by applying a catalytic amount of a tertiary amine, 1,4-diazabicyclo[2,2,2]octane, and hypochlorous acid at varying pH, temperature, and time. The bleaching filtrate was analyzed for chloroform and AOX and the pulp for residual lignin, hexenuronic acid, and OX. In comparison with chlorine dioxide bleaching, the novel catalytic bleaching (pH < 6) generated only traces of chloroform and low contents of AOX and OX. Separate catalytic oxidations of authentic hexenuronic acid showed that it was a major precursor of chloroform. The results demonstrate a practical way to reduce organochlorine formation in pulp bleaching and provide new understanding on the reaction pathways that yield chloroform.     

Hippocampal theta-band activity and trace eyeblink conditioning in rabbits.

The authors examined the relationship between hippocampal theta activity and trace eyeblink conditioning. Hippocampal electrophysiological local field potentials were recorded before, during, and after conditioning or explicitly unpaired training sessions in adult male New Zealand White rabbits. As expected, a high relative power of theta activity (theta ratio) in the hippocampus predicted faster acquisition of the conditioned response during trace conditioning but, contrary to previous results obtained using the delay paradigm, only in the initial stage of learning. The presentation of the conditioned stimulus overall elicited an increase in the hippocampal theta ratio. The theta ratio decreased in the unpaired group as a function of training, remained high throughout conditioning in the fast learners, and rapidly increased in the slow learners initially showing a low theta ratio. Our results indicate a reciprocal connection between the hippocampal oscillatory activity and associative learning. The hippocampal theta ratio seems to reflect changes and differences in the subjects’ alertness and responsiveness to external stimuli, which affect the rate of learning and are, in turn, affected by both conditioning and unpaired training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exit pupil expander with a large field of view based on diffractive optics

Abstract— The field of view is an important parameter of a near‐to‐eye display. To achieve an immersive viewing experience, the field of view should be as high as possible. Presently, in most of the commercially available devices the field of view is between 15° and 30°. In this paper, a large‐field‐of‐view exit pupil expander that is based on diffractive optics was demonstrated. Usually these types of diffractive expanders cannot have a field of view much more than 25°. Here, an exit pupil expander with an extended field of view, based on two stacked plates, was demonstrated. The expander is designed for green light and it achieves a field of view of more than 40°.