选择高集成度DSP的关键因素

在系统级上,工程师习惯于在三个“P”即:性能(Performance),功率(Power)消耗和价格(Price)之间权衡利弊。在DSP高度集成的今天,有关外围器件的第四个“P”可能影响和此前三个“P”相关的决定,而且它增加了一套新的设计考虑因素。要选择合适的DSP,设计人员必须选择具备最能满足整个系统要求、最佳外围器件组合的SoC(System-on-Chip)。另外,由于现在可以把模拟和射频电路象数字逻辑电路一样集成在同一个芯片上,则选择片上外围器件的范围比以前更广泛。本文列举了部分关键问题,讨论了可能对工程师在系统设计方面有影响的因素。 系统需求 系统设计的第一项任务就是分析整个系统的需求,这关系到其他所有决定。应用是否支持音频、视频或射频方面的工作?功率是多少?使用哪个标准?需要其他什么功能?是否支持某种电源非常宝贵的移动器件?这些基本的需求经常决定着哪个外围器件满足系统需求。 举例来说,电信基础设施系统需要各种各样用于便携式媒体或者无线手持终端的外围器件。尽管电信系统和其他应用领域存在交集,但电信基础设施设计师主要关注高信道密度和 单通道低成本时的吞吐量。单通道功 率也是电信基础设施的一...     

Performance of the timed token scheme in MAP

Two new analytic approximations are given for the mean delay in the timed token bus network specified in MAP (manufacturing automation protocol). Each station on the network has two kinds of timer for controlling the maximum amount of time for data transfer before giving up the token. High-priority stations would set large values in the token holding timer (THT) and transmit until the timer expires. Low-priority stations compare the elapsed time since the last token arrival (measured cycle time) to the token rotation timer (TRT) setting, and transmit only for the time left in the timer. The first approximation, based on Fuhrmann's bound for the limited-k service discipline, is for the symmetric case where all the stations have the same traffic load and the identical THT or TRT settings. The approximation has been compared to simulation results, and found to be quite accurate for a representation factory network, with THT or TRT set at two and five times the average total walk time. The second approximation is for the asymmetric case where there is one saturated low-priority (limited-TRT) station, and the rest of the stations in the network have high priority with limited-THT service. These two formulas will be useful in the planning and operation of MAP networks by providing guidance in the choice of timer settings for meeting different priority service requirements     

Predictor@Home: A "Protein Structure Prediction Supercomputer' Based on Global Computing

Predicting the structure of a protein from its amino acid sequence is a complex process, the understanding of which could be used to gain new insight into the nature of protein functions or provide targets for structure-based design of drugs to treat new and existing diseases. While protein structures can be accurately modeled using computational methods based on all-atom physics-based force fields including implicit solvation, these methods require extensive sampling of native-like protein conformations for successful prediction and, consequently, they are often limited by inadequate computing power. To address this problem, we developed Predictor@Home, a "structure prediction supercomputer” powered by the Berkeley Open Infrastructure for Network Computing (BOINC) framework and based on the global computing paradigm (i.e., volunteered computing resources interconnected to the Internet and owned by the public). In this paper, we describe the protocol we employed for protein structure prediction and its integration into a global computing architecture based on public resources. We show how Predictor@Home significantly improved our ability to predict protein structures by increasing our sampling capacity by one to two orders of magnitude.     

Remediation of RDX-Contaminated Water Using Alkaline Hydrolysis

The objective of this study was to assess the effectiveness of alkaline hydrolysis as an alternative ex situ technology for remediating groundwater contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Treatment in both batch reactor and continuous stirred tank reactor (CSTR) was investigated. RDX reactivity was strongly dependent on the reaction pH investigated (11–13). The batch system achieved pseudo-first-order RDX reaction rates in the range of (0.8–27.7)×10?3?min?1, corresponding to half-life periods of 17.9?to?0.5?h, respectively. In the CSTR system operated at the initial RDX concentration of 4.5×10?3?mM, 99% RDX removal was achieved with the hydraulic retention time of 2?days and the reaction pH of 11.9. Formate and nitrite were produced as the major hydrolysates in the CSTR system, indicating a simultaneous reaction mechanism involving RDX ring cleavage and elimination of the ring nitrogen. The net OH? demand used only for RDX removal in the CSTR was found to be 1.5, 390, and 130?M OH?/M RDXremoved at pH values of 11.9, 11.5, and 11.0, respectively. A conceptual cost analysis indicated that the expense of alkaline treatment may be comparable to the expense of granular activated carbon treatment for long treatment periods (30?years or more), due to the potentially lower annual operational cost of alkali treatment.     

Residential fuelwood consumption in the Southeastern U.S.

A telephone survey of households in 13 states in the southeastern U.S. determined residential fuelwood acquisition and use for heating during the 1991 heating season. Although wood burning accounted for only 10% of the total household heat requirement of the region, it accounted for 51% of the total heat requirements of wood-burning households. One-quarter (25%) of the households burned wood, consuming almost 9 million standard cords. Three-quarters (77%) of wood-burning households reported that wood burning contributed to household heating requirements. Wood as a source of home heating was particularly important to low income households, both rural and urban. Wood is the sole source of home heating for 17% of the wood-burning households in the region.     

Evaluation of passive samplers for assessment of community exposure to toxic air contaminants and related pollutants

The precision, accuracy, and sampling rates of Radiello and Ogawa passive samplers were evaluated in the laboratory using a flow-through chamber and under field conditions prior to their use in the 2007 Harbor Community Monitoring Study (HCMS), a saturation monitoring campaign in the communities adjacent to the Ports of Los Angeles and Long Beach. Passive methods included Radiello samplers for volatile organic compounds (benzene, toluene, ethylbenzene, xylenes, 1,3-butadiene), aldehydes (formaldehyde, acetaldehyde, acrolein) and hydrogen sulfide, and Ogawa samplers for nitrogen oxides and sulfur dioxide. Additional experiments were conducted to study the robustness of the passive sampling methods under variable ambient wind speed, sampling duration, and storage time before analysis. Our experimentally determined sampling rates were in agreement with the rates published by Radiello and Ogawa with the following exceptions: we observed a diffusion rate of 22.4 ± 0.1 mL/min for benzene and 37.4 ± 1.5 mL/min for ethylbenzene compared to the Radiello published values of 27.8 and 25.7 mL/min, respectively. With few exceptions, the passive monitoring methods measured one-week average ambient concentrations of selected pollutants with sensitivity and precision comparable to conventional monitoring methods averaged over the same period. Radiello Carbograph 4 VOC sampler is not suitable for the collection of 1,3-butadiene due to backdiffusion. Results for the Radiello aldehyde sampler were inconclusive due to lack of reliable reference methods for all carbonyl compounds of interest.     

Implementation of targeted interventions to control Escherichia coli O157:H7 in a commercial abattoir

The objective of this study was to define locations on the carcass with highest contamination of E. coli O157 throughout the harvest process and implement targeted interventions to reduce or eliminate contamination. To establish a pathogen baseline, samples were collected at the foreshank, hindshank, inside round, neck and midline area and evaluated for E. coli O157:H7 presence. Environmental samples were also collected in the harvest area and the fabrication area of the facility. E. coli O157:H7 prevalence was highest on the foreshank, hindshank and inside rounds in the baseline study and steam vacuums/cones were implemented as an intervention in these specific areas on the harvest floor. At pre-evisceration, foreshank prevalence of E. coli O157:H7 was significantly (P<0.05) reduced from 21.7% to 3.1% after the application of steam interventions. At the final rail, foreshank prevalence in the baseline study was 4.2% while no E. coli O157:H7 was detected post-intervention implementation. E. coli O157:H7 on hindshanks and inside rounds was significantly reduced after intervention implementation from 24.2 to 11.5% and 37.5 to 16.7%, respectively at the final rail. Pathogen contamination of environmental samples collected in fabrication declined from 6.7% to 0.7% after slaughter interventions were implemented. Data indicate the identifying areas of contamination on the carcass and implementing interventions can significantly reduce E. coli O157 on the carcasses and in the fabrication environment.     

爬升作业要谨慎

安全完成塔式起重机的升高作业,有赖于精心的策划、良好的通讯和精良的技术和团队合作。爬升作业中如果发生事故,通常会伴随有人员伤亡、拖延建设工期、面临渎职指控、丧失信誉和造成重大经济损失等严重后果。