A Comprehensive Performance Analysis of Random Early Detection Mechanism

One of the most promising active queue management schemes being proposed for deployment in the Internet is the Random Early Detection (RED) scheme. However, research results on RED performance are highly mixed, especially in the field of tuning its parameters. In this paper, a comprehensive performance analysis of RED is presented. We revisit some features in RED and study them in greater detail. We point out that RED, in general, does not possess proportional loss between flows as claimed and widely adopted in previous research. We suggest the generalization of the PASTA property and give a proof for TCP flows. We also evaluate the performance of the Exponential Weighted Moving Average (EWMA) algorithm in RED. We find that EWMA in RED is an unbiased estimator of the average queue-length, regardless of the weighting value w _q . We also point out the theoretical and practical limits of EWMA in RED. Finally, we propose the use of fuzzy EWMA to RED (fuzzy RED) to alleviate the inflexibility of RED tuning. We use simulations to evaluate the performance of fuzzy RED and compare it with other versions of RED. Our simulations show that, in the case of a high workload and a high level of variation, fuzzy RED, by tracking system variation in an on-line manner, improves RED performance in a number of important router-based metrics like packet loss rate, average queueing delay, link utilization, and global power.     

Student acceptance of unique meals

Students (N = 167) from the 4th, 8th, and 11th grades sorted meals, listed on individual cards, according to whether they would or would not eat them. Students were told to either consider eating the meals at home or at school. Forty-two different meals were selected from a pool of unique meals created by students in a previous study. The meals differed in head component, the presence or absence of vegetables, and the number of different foodstuffs. On average, approximately half of the meals were deemed acceptable, but older students accepted more meals than younger ones, boys accepted more meals than girls, and meals to be consumed at home were accepted more than those to be consumed at school. In addition, students tended to accept meals comprised of a small number of foodstuffs that did not contain vegetables. The also chose more meat-based meals over those containing fish or soup. These results suggest that students have rather unique food preferences that do not correspond well with nutritional standards. In order to address this problem we recommended that students be given more good choices in the school cafeteria through the introduction of a two-meal system and salad bars.     

The Effect of Ozone Gas-Liquid Contacting Conditions in a Static Mixer on Microorganism Reduction

The effect of gas-liquid contacting conditions in a static mixer on ozone transfer efficiency and reduction of Bacillus subtilis spores was studied in an experimental ozone contactor. An empirical mathematical model was developed that related the transfer efficiency in the experimental system to the superficial liquid velocity in the mixer, the gas-liquid flow rate ratio and the height of the down-stream bubble column. Spore reduction was determined primarily by the dissolved ozone concentration-time (C_avgt_m) product in the reactive flow segment and was independent of the gas-liquid contacting conditions in the static mixer. In an integrated ozone contacting system, the static mixer should be designed to maximize ozone mass transfer while the reactive flow segment should be designed for efficient microorganism reduction.     

The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91

The influence of NaCl and CO₂ on the atmospheric corrosion of magnesium alloy AZ91 is studied in the laboratory. Samples were exposed under carefully controlled air and flow conditions; the relative humidity was 95%, the temperature was 22.0°C and the concentration of CO₂ was < 1 ppm or 350 ppm. Different amounts of sodium chloride (0–70 μg/cm²) were added before exposure. The corrosion products were analyzed by gravimetry, ion chromatography, X‐ray diffraction and scanning electron microscopy. Mass gain and metal loss results are reported. The combination of high humidity and NaCl is very corrosive towards AZ91. However, the NaCl‐induced corrosion is inhibited by ambient concentrations of CO₂. Exposure in the absence of CO₂ gives rise to heavy pitting, with brucite, Mg(OH)₂, being the dominant corrosion product. In the presence of CO₂ a layer of hydrated magnesium hydroxy carbonate, Mg₅(CO₃)₄(OH)₂ · 5 H₂O forms. A tentative corrosion mechanism is presented that explains the behavior in the two environments.     

北电网络安全路由技术

北电网络提供的Contivity解决方案不仅可以使用户建立各种类型的VPN，而且还可以把这些VPN集成到未来的融合话音和数据的网络中。该方案已实现了安全路由选择；可通过多种技术支持鉴权功能，从而实现安全接入；允许用户使用其各自的安全性配置文件设置；其设计中没有“后门”，重点介绍了Contivity 2700网关的主要特征及其优势。     

Tagging of η mesons using the pd → 3Heη reaction near threshold

A zero-degree spectrometer for tagging η mesons on the CELSIUS/WASA facility is described, and its characteristics are presented. Tagging of η mesons is performed by detecting ³He ions produced by reaction pd → ³Heη close to the production threshold. The low background level (<2%) is in good agreement with the data obtained earlier on the SATURNE accelerator.