离心式冷水机组的制冷剂选择

描述冷水机组特别是大型机组最常用的替代制冷剂。总结了蒙特利尔议定书所制定的制冷剂淘汰时间表。对冷水机组(压缩式与吸收式)目前所使用的制冷剂进行探讨,包括大气寿命、ODP与GWP。概述了离心式冷水机组的最低能效标准。对主要的制冷剂进行科学评估。介绍了除R-123以外的其他替代制冷剂。研究表明,R-123作为目前离心式冷水机组应用最广泛的制冷剂,其ODP与GWP较低,且大气寿命短,放射率低,效率高。对中国而言R-123至少在未来的几十年内仍具有非常显著的环境和经济优势。     

The 802.11n MIMO-OFDM Standard for Wireless LAN and Beyond

An overview is given of the new IEEE 802.11n standard. This is the first wireless LAN standard based on MIMO-OFDM, a technique pioneered by Airgo Networks to give a significant performance increase in both range and rate relative to conventional wireless LAN. Performance results show that net user throughputs over 100 Mbps are achievable, which is about four times larger than the maximum achievable throughput using IEEE 802.11a/g. For the same throughput, MIMO-OFDM achieves a range that is about 3 times larger than non-MIMO systems. This significant improvement in range-rate performance makes MIMO-OFDM the ideal solution not only for wireless LAN, but also for home entertainment networks and 4G networks. Richard van Nee received the M.Sc. degree in Electrical Engineering from Twente University in Enschede, the Netherlands, in 1990. In May 1995, he received the PhD degree from Delft University of Technology. From 1995 to 2000, he worked for Lucent Technologies Bell Labs on wireless LAN transmission techniques. He was one of the original proposers of the CCK and OFDM modulation techniques which were adopted by the IEEE 802.11b and IEEE802.11a wireless LAN standards. In 2001, he cofounded Airgo Networks that developed the first MIMO-OFDM modem for wireless LAN and which techniques form the basis of the IEEE 802.11n standard. Together with Ramjee Prasad, he wrote a book on OFDM, entitled ‘OFDM for Mobile Multimedia Communications.’ In 2002 he received the Dutch Veder award for his contributions to standardization of wireless communications.     

Bioreduction of Hexavalent Chromium in Flow-Through Quartz Sand Columns

Hexavalent chromium (Cr(VI)) contamination of soil and groundwater is a major environmental concern for some industrial sites and most of the U.S. Department of Energy sites. Cr(VI) is toxic and fairly mobile in groundwater. Bioreduction of Cr(VI) to less toxic and less mobile Cr(III) is considered to be a feasible option. Among the Cr(VI) reducing bacteria, Shewanella oneidensis MR-1 (MR-1) has been shown to be effective in metal reduction under anaerobic conditions. Data on bioreduction of Cr(VI) by MR-1 in a flow-through soil column that better approximates the subsurface condition are not available. The objective of this research project was to study the bioreduction of Cr(VI) by MR-1 in a continuous-flow quartz sand column system. MR-1 was found to be very effective in reducing Cr(VI) to Cr(III) for concentrations ranging from 0.055 mM (2.85?mg/L) to 0.006 mM (0.31?mg/L). The amount of Cr(VI) reduced prior to its breakthrough was found to be inversely proportional to its concentration in the feed due to increased inhibition of microbial activity and a residual reduction of 20–45% of Cr(VI) was observed even after its breakthrough.     

Characteristics for Leveraging Value Management Processes on Capital Facility Projects

A more competitive business environment requires that a variety of value management process (VMP) options be continuously introduced into the construction industry. Project stakeholders and managers are highly concerned about value maximization through implementation of one or more beneficial VMP options. The objective of this study is to identify the most leveraging project characteristic factors (PCFs) in need of VMP implementation. Furthermore, the levels of importance of each PCF in association with the optional VMPs are quantified to effectively assess the applicability of VMP implementation using the fuzzy-based analytic hierarchy process method. Four real-case validation tests provide robust research findings. The proposed project assessment tool is useful in evaluating individual projects in terms of whether the subject project is leveraged or has much to be improved by implementing the optional VMPs. The results of this study can facilitate a rigorous evaluation of a project and eventually help the decision-making process in selecting the most beneficial VMP options to maximize the optimum project value.     

Intact attentional control of working memory encoding in schizophrenia.

This study reports evidence that individuals with schizophrenia (SC) demonstrate intact attentional selection for visual working memory (WM) storage. A group of 62 participants with SC and 55 control participants without SC were studied in a series of 5 experiments that examined the ability to use top-down and bottom-up cues to guide WM encoding, as well as the ability to spontaneously select a subset of representations for storage. Participants with SC exhibited a consistent and robust ability to use selective attention in the control of WM in all 5 experiments, demonstrating a remarkable island of preserved functioning given the broad spectrum of impairments of attention and WM that have been widely reported in those with SC. These findings indicate that attention is not globally impaired in SC and make it possible to delineate more precisely the nature of the specific impairment of attention in this disorder. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deficits on the continuous performance test within the schizophrenia spectrum and the mediating effects of family history of schizophrenia.

Individuals with schizophrenia spectrum personality disorders (SSPD) and schizophrenia show similar cognitive impairments. The authors examined the contributions of SSPD symptoms and familial risk for schizophrenia to impairments on the Continuous Performance Test-Identical Pairs Version. Participants included 103 schizophrenia patients, 66 first-degree relatives (29 SSPD), and 103 community controls (26 SSPD) screened for family history of psychosis. Patients and SSPD relatives performed significantly worse than non-SSPD relatives and SSPD and non-SSPD community controls. No differences in performance were observed among non-SSPD relatives and SSPD and non-SSPD community controls. Results suggest a continuum in which risk for schizophrenia-related cognitive impairments is highest among patients and SSPD relatives, intermediate among non-SSPD relatives, and lowest among SSPD and non-SSPD community controls. Results suggest that SSPD in the absence of a family history of psychosis may be a phenocopy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Model simplification for switched hybrid systems

This paper is concerned with the problem of model reduction for switched system, which is an important class of hybrid systems frequently encountered in practical situations. Two sharply different approaches are proposed to solve this problem. The first approach casts the model reduction into a convex optimization problem, which is the first attempt to solve the model reduction problem by using linearization procedure. The second one, based on the cone complementarity linearization idea, casts the model reduction problem into a sequential minimization problem subject to linear matrix inequality constraints. Both approaches have their own advantages and disadvantages concerning conservatism and computational complexity. A numerical example illustrates the effectiveness of the proposed theories.     

Multi-objective model-based control for an automotive catalyst

A model-based feedforward/feedback air fuel ratio controller that optimizes the oxygen storage capacity of the three-way catalyst in automotive emission control systems is presented. This work incorporates a simplified dynamic catalyst model that describes the physical behavior of oxygen chemisorption and reversible deactivation in the catalyst system. A novel aspect of this work is the use of the oxygen storage capability of the catalyst not only to minimize vehicle emissions but also to optimize engine performance and fuel economy during transient engine demand. The feedback/feedforward controller is a nonlinear model predictive controller that incorporates catalyst, engine air fuel ratio controller, and fuel system models to determine the optimal air fuel ratio target trajectory. Feedback is provided by a nonlinear moving horizon estimation strategy for the determination of the oxygen storage level of the catalyst based on air fuel ratio sensors.     

Automation of Chemical Reaction Kinetics and Product Distribution Studies in Pharmaceutical Development

An automated instrument was designed and constructed to facilitate the performance of pharmaceutical degradation studies. A brief theoretical background on degradation kinetics is given to rationalize the design of the instrument and representative data are provided to illustrate its successful application. This system was found to be capable of conducting multiple simultaneous isothermal and nonisothermal kinetic studies with user-defined temperature profiles, sampling periods, and data logging.