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871.
生物洁净室的污染控制 总被引:1,自引:0,他引:1
生物洁净室的目的是控制细菌污染。通过对细菌特性、来源及污染途径的分析,确定了全方位、全过程控制的基本思想,即污染源控制,污染传播过程控制和交叉污染控制,通过分析微粒的运动特性,提出了空气途径污染的主要手段是气流流动控制和表面污染控制,最后分析了交叉污染的形成原因及其防治措施。 相似文献
872.
Vahedi Tafreshi H. Piseri P. Barborini E. Benedek G. Milani P. 《Journal of nanoparticle research》2002,4(6):511-524
We describe a simulation of the nanoparticle trajectories in a pulsed cluster beam source. Clusters, formed by condensation of atomic vapor in a helium bath, and considered here as rigid spheres having a diameter of 1.5nm, were tracked during their travel inside the source cavity, an aerodynamic lens, and a cylindrical nozzle. Steady state supersonic laminar flow of helium is considered in an axi-symmetric geometry aiming to simulate, within some limitations, the conditions under which cluster formation takes place in a pulsed microplasma cluster source. In spite of the unsteady nature of the pulsed source, the time scale characterizing particle motion in the flow field is significantly smaller than the characteristic time constant for the evolution of gas pressure in the source. For this reason, a steady simulation can shed some light on the understanding of processes governing nanoparticle motion in a pulsed vaporization source. The extent to which the Brownian diffusion can affect the particle extraction from the source is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the source internal walls. However, it does not hinder the aerodynamic focalization produced by the lens even in nano-size cluster regime. This result is qualitatively confirmed by experiment. 相似文献
873.
H. C. Leligou Ch. Linardakis K. Kanonakis J. D. Angelopoulos Th. Orphanoudakis 《International Journal of Communication Systems》2006,19(5):603-617
The steadily rising demand for multimedia and data services, the falling cost and omnipresence of Ethernet and the maturity of passive optical networks (PON) technology, promise to radically change the landscape in the local loop. The heart of a gigabit PON system (recently standardized by FSAN/ITU) is the medium access controller (MAC), which arbitrates access to the upstream link among users with fluctuating traffic demands and effects the multiplexing and concentration policy. At the same time, it has to safeguard the service quality and enforce the parameters agreed in the service level agreements (SLAs) between the users and the service provider. In this paper, a MAC protocol designed to serve any mix of services according to their quality of service (QoS) needs, employing four priority levels along with a high number of logically separate data queues is presented. The architecture and implementation in hardware of a MAC algorithm capable of allocating bandwidth down to a resolution of a byte with QoS differentiation is the focus of this paper. It employs the bandwidth arbitration tools of the FSAN/ITU G.984.3 standard and maps SLA parameters to GPON service parameters to create an efficient, fair and flexible residential access system. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
874.
875.
LIAO Ning YAN Dan QUAN Zi-yi MEN Ai-dongMultimedia Center Beijing University of Posts Telecommunications Beijing China 《中国邮电高校学报(英文版)》2006,13(3):87-92
1 Introduction With the ubiquitous use of Internet and the deployment of next generation of networks, video communications are increa- singly becoming the major services in demand. Unlike data transmission, video communication is essentially time-sensitiv… 相似文献
876.
One of the challenges that must be overcome to realize the practical benefits of ad hoc networks is quality of service (QoS).
However, the IEEE 802.11 standard, which undeniably is the most widespread wireless technology of choice for WLANs and ad
hoc networks, does not address this issue. In order to support applications with QoS requirements, the upcoming IEEE 802.11e
standard enhances the original IEEE 802.11 MAC protocol by introducing a new coordination function which has both contention-based
and contention-free medium access methods. In this paper, we consider the contention-based medium access method, the EDCA,
and propose an extension to it such that it can be used to provide QoS guarantees in WLANs operating in ad hoc mode. Our solution
is fully distributed, uses admission control to regulate the usage of resources and gives stations with high-priority traffic
streams an opportunity to reserve time for collision-free access to the medium. 相似文献
877.
Giuseppe Ferri Vincenzo Stornelli 《Analog Integrated Circuits and Signal Processing》2006,47(3):293-301
In this work we present an integrated interface for wide range resistive gas sensors able to heat the sensor resistance through
a constant power heater block at 0°C–350°C operating temperatures. The proposed temperature control system is formed by a
sensor heater (which fixes the sensor temperature at about 200°C), a R/f (or R/T) converter, which converts the resistive value into a period (or frequency), and can be able to reveal about 6 decades variation
(from 10 KΩ up to 10 GΩ), and a digital subsystem that control the whole systems loop. This interface allows high sensibility
and precision and performs good stability in temperature and power supply drift and low power characteristics so it can be
used also in portable applications. Test measurements, performed on the fabricated chip, have shown an excellent agreement
between theoretical expectations and simulation results.
Giuseppe Ferri is an associate professor in Electronics at the Department of Electrical Engineering of L’ Aquila University, Ital. In 1993
he has been a visiting researcher at SGS-Thomson Milano, working in bipolar low-voltage op-amp design. In 1994-95 he has been visiting researcher at KU Leuven working in low-voltage CMOS design in the group of Prof. Sansen. His research activity is actually centred on the analog
design of integrated circuits for portable applications (e.g., sensors and biomedicals) and circuit theory. He is co-author
of a book entitled “Low Voltage, Low Power CMOS Current Conveyors”, Kluwer ed. (2003) and four text-books in Italian on Analogue Microelectronics (2005, 2006). Moreover, he is author and
co-author of 74 papers on international and Italian journals and 123 talks at national and international conferences.
Vincenzo Stornelli was born in Avezzano (AQ), Italy, on May 31, 1980. He received the Electronics Engineering degree (cum laude) in July 2004.
In October 2004 he joined the Department of Electronic Engineering, University of L’Aquila, where he is actually involved
with problems concerning project and design of integrated circuits for RF and sensor applications, CAD modelling, characterization,
and design analysis of active microwave components, circuits, and subsystems. He regularly teaches courses of the European
Computer patent and has regular collaborations with national corporations such as Thales Italia 相似文献
878.
We propose and analyze call admission control algorithms integrated with pricing for revenue optimization with QoS guarantees to serve multiple service classes in mobile wireless networks. Traditional admission control algorithms make acceptance decisions for new and handoff calls to satisfy certain QoS constraints such as the dropping probability of handoff calls and the blocking probability of new calls being lower than a pre-specified threshold. We analyze a class of partitioning and
threshold-based admission control algorithms that make acceptance/rejection decisions not only to satisfy QoS requirements but also to optimize the revenue of the system by taking prices and arrival/departure information of service calls into account. We show that for a “charge-by-time” pricing scheme, there exist optimal resource allocation settings under which the partitioning and threshold-based admission control algorithms would produce the maximum revenue obtainable by the system without sacrificing QoS requirements. Further, we develop a new hybrid admission control algorithm which outperforms both partitioning and threshold-based admission control algorithms over a wide range of input parameters characterizing the operating environment and service workload conditions. Methods for utilizing of the analysis results for realtime admission control for revenue optimization with QoS guarantees are described with numerical data given to demonstrate the applicability. 相似文献
879.
基于网络相变理论对网络异常流量的本质进行了研究,提出了基于Hurst参数反馈的动态拥塞缓解机制,理论分析和仿真结果验证了该方法的可行性和相对于传统方法的优越性,为异常流量的检测、控制研究做出了有益的探索。 相似文献
880.