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Collision Probability (collision + probability)

Distribution by Scientific Domains
Life Sciences40%
Engineering40%

Selected Abstracts

Theoretical performance evaluation of EDCA in IEEE 802.11e wireless LANs

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2010
Fei PengArticle first published online: 25 SEP 200
While the original IEEE 802.11 distributed coordinated function (DCF) has been widely analysed by both theoretical and simulation studies, the performance of the new IEEE 802.11e enhanced distributed channel access (EDCA) has not yet been investigated extensively. In this paper, we extend an analytical model to capture the operations of the arbitrary inter-frame space, contention window differentiation and transmission opportunity in EDCA for the evaluation of throughput performance and collision probability of different service classes. The performance analyses are validated by simulation results. Our analysis provides insightful results for evaluating the impact of different priority parameters on the performance of EDCA service differentiation. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Achieving performance enhancement in IEEE 802.11 WLANs by using the DIDD backoff mechanism

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2007
P. Chatzimisios
Abstract Wireless local area networks (WLANs) based on the IEEE 802.11 standards have been widely implemented mainly because of their easy deployment and low cost. The IEEE 802.11 collision avoidance procedures utilize the binary exponential backoff (BEB) scheme that reduces the collision probability by doubling the contention window after a packet collision. In this paper, we propose an easy-to-implement and effective contention window-resetting scheme, called double increment double decrement (DIDD), in order to enhance the performance of IEEE 802.11 WLANs. DIDD is simple, fully compatible with IEEE 802.11 and does not require any estimation of the number of contending wireless stations. We develop an alternative mathematical analysis for the proposed DIDD scheme that is based on elementary conditional probability arguments rather than bi-dimensional Markov chains that have been extensively utilized in the literature. We carry out a detailed performance study and we identify the improvement of DIDD comparing to the legacy BEB for both basic access and request-to-send/clear-to-send (RTS/CTS) medium access mechanisms. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Nonisothermal cure kinetics of DGEBA with novel aromatic diamine

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007
M. Ghaemy
Abstract The effect of the molar ratio of diglycidyl ether of a bisphenol-A based epoxy (DGEBA) and synthesized 4-phenyl-2,6-bis(4-aminophenyl)pyridine (PAP) as curing agent during nonisothermal cure reaction by the Kissinger, Ozawa, and isoconversional equations was studied. The cure mechanism was studied by FTIR analysis. Kinetic analysis of the curing reaction of DGEBA at two different concentrations (42 and 32 phr) of the curing agent was studied by using DSC analysis. With an increasing PAP content, the pre-exponential factor increased by increasing collision probability between epoxide and primary or secondary amine groups in noncataltyic or catalytic modes. The activation energy also increased because of the increasing content of crosslink density. The activation energies obtained from three equations were in good agreement. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3076,3083, 2007. [source]

Spatial arrangement and macrodomain organization of bacterial chromosomes

MOLECULAR MICROBIOLOGY, Issue 1 2005
Frédéric Boccard
Summary Recent developments in fluorescence microscopy have shown that bacterial chromosomes have a defined spatial arrangement that preserves the linear order of genes on the genetic map. These approaches also revealed that large portions of the chromosome in Escherichia coli or Bacillus subtilis are concentrated in the same cellular space, suggesting an organization as large regions defined as macrodomains. In E. coli, two macrodomains of 1 Mb containing the replication origin (Ori) and the replication terminus (Ter) have been shown to relocalize at specific steps of the cell cycle. A genetic analysis of the collision probability between distant DNA sites in E. coli has confirmed the presence of macrodomains by revealing the existence of large regions that do not collide with each other. Two macrodomains defined by the genetic approach coincide with the Ori and Ter macrodomains, and two new macrodomains flanking the Ter macrodomain have been identified. Altogether, these results indicate that the E. coli chromosome has a ring organization with four structured and two less-structured regions. Implications for chromosome dynamics during the cell cycle and future prospects for the characterization and understanding of macrodomain organization are discussed. [source]

The influence of homogenisation conditions on biomass-adsorbent interactions during ion-exchange expanded bed adsorption

BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2006
Jürgen J. Hubbuch
Expanded bed adsorption (EBA) is an integrative step in downstream processing allowing the direct capture of target proteins from cell-containing feedstocks. Extensive co-adsorption of biomass, however, may hamper the application of this technique. The latter is especially observed at anion exchange processes as cells or cell debris are negatively charged under common anion exchange conditions. The restrictions observed under these conditions are, however, directly related to processing steps prior to fluidised bed application. In this study, it could be shown that the effective surface charge of cell debris obtained during homogenisation is closely related to the debris size and thus to the homogenisation method and conditions. The amount and thus effect of cells binding to the adsorbent could be significantly decreased when optimising the homogenisation step not only towards optimal product release but towards a reduction of debris size and charge. The lower size and charge of the debris results not only in a reduced retention probability but also, in a lower collision probability between debris and adsorbent. The applicability was shown in an example where the homogenisation conditions of E. coli were optimised towards EBA applications. In a previous report (Reichert et al., 2001) studying the suitability of EBA for the capture of formate dehydrogenate from E. coli homogenate the pseudo affinity resin Streamline Red was identified as the only suitable adsorbent. The new approach, however, led to a system where anion exchange as capture step became possible, however, to the cost of binding capacity. © 2006 Wiley Periodicals, Inc. [source]