Effect of electrolyte on electrochemical characteristics of MmNi3.55Co0.72Al0.3Mn0.43 alloy electrode for hydrogen storage

A series of experiments have been performed to investigate the effects of three electrolytes of different compositions (EO, EA and EM) on the electrochemical characteristics of MmNi_3.55Co_0.72Al_0.3Mn_0.43 hydrogen storage alloy electrode. Electrolytes EA and EM were obtained by adding appropriate amounts of Al₂(SO₄)₃ and MnSO₄ to the original electrolyte EO (6 M KOH + 1 wt% LiOH), respectively. Electrode activation, maximum capacity, cycle life, self-discharge and high-rate discharge characteristics have been studied. It was found that a maximum capacity of about 260 mA h/g has been obtained for the alloy electrodes in all these electrolytes after 5–7 cycles of charging/discharging. The alloy electrodes have a good durability in electrolytes EA and EM, especially after 175 cycles. Using the capacity retention as an indication of self-discharge resistance, almost identical degree of capacity retention (82% after 4 days and 45% after 16 days) has been observed at 298 K, regardless of the electrolytes used. When tested at higher temperature, however, a higher capacity retention (46% after 3 days) at 333 K has been observed for electrodes in electrolyte EA, and about 32% for electrodes in both electrolytes EO and EM. As to high-rate discharge behavior of the results of high-rate discharge tests indicated that about 50% of discharge efficiencies were obtained in the three electrolytes at 333 K by continuous-model high-rate discharge method, at a discharge rate of 7C, and 22% in 298 K. The alloy electrode in electrolyte EM has the best durability, in which about 50% of discharge efficiency at DC = 9C was obtained by step-model high-rate discharge method at 333 K, which was even higher than that at 298 K.     

Application of ICME to Engineer Fatigue-Resistant Ni-Base Superalloys Microstructures

Critical rotating components used in the hot section of gas turbine engines are subject to cyclic loading conditions during operation, and the life of these structures is governed by their ability to resist fatigue. Since it is well known that microstructural parameters, such as grain size, can significantly influence the fatigue behavior of the material, the conventional processes involved with the manufacture of these structures are carefully controlled in an effort to engineer the resulting microstructure. For a commercial Ni-base superalloy, RR1000, the development of process models and deformation mechanism maps has enabled not only control of the resultant grain size but also the ability to tailor and manipulate the resulting grain boundary character distribution. The increased level of microstructural control was coupled with a physics-based fatigue model to form an integrated computational materials engineering framework that was used to guide the design of damage-tolerant microstructures. Simulations from a 3D crystal plasticity finite element model were used to identify microstructural features associated with strain localization during cyclic loading and to guide the design of polycrystalline microstructures optimized for fatigue resistance. Conventionally processed and grain boundary engineered forgings of a commercial Ni-based superalloy, RR1000, were produced to validate the design methodology. For nominally equivalent grain sizes, high-resolution strain maps generated via digital image correlation confirmed that the high density of twin boundaries in the grain boundary engineered material were desirable microstructural features as they contribute to limiting the overall length of persistent slip bands that often serve as precursors for the nucleation of fatigue cracks.     

On the Handover Performance of a Tri‐threshold Bandwidth Reservation CAC Scheme

A dynamic tri‐threshold call admission control scheme has been developed. This scheme supports voice, data, and multimedia services and it complies with the universal mobile telecommunications system. The performance of the proposed scheme is evaluated under varying handover rates. The QoS performance–including channel utilization, call dropping probability, and blocking probability–is investigated. The performance of the developed scheme is found to be encouraging.     

A comparison of avian communities and habitat characteristics in floodplain forests associated with valley plugs and unchannelized streams

Channelization of streams associated with floodplain forested wetlands has occurred extensively throughout the world and specifically in the southeastern United States. Channelization of fluvial systems alters the hydrologic and sedimentation processes that sustain these systems. In western Tennessee, channelization and past land‐use practices have caused drastic geomorphic and hydrologic changes, resulting in altered habitat conditions that may affect avian communities. The objective of this study was to determine if there were differences in avian communities utilizing floodplain forests along unchannelized streams compared to channelized streams with valley plugs, areas where sediment has completely filled the channel. During point count surveys, 58 bird species were observed at unchannelized sites and 60 species were observed at valley plug sites. Species associated with baldcypress‐tupelo (Taxodium‐Nyssa) swamps (e.g. Great Egret (Ardea albus) and Black‐crowned Night Heron (Nycticorax nycticorax)) and mature hardwood forests with open midstories (e.g. Eastern Wood‐Pewee (Contopus virens), Yellow‐throated Vireo (Vireo flavifrons), Cerulean Warbler (Dendroica cerulea) and Scarlet Tanager (Piranga olivacea)) were either only found at unchannelized sites or were more abundant at unchannelized sites. Conversely, species associated with open and early successional habitats (e.g. Tree Swallow (Tachycineta bicolor), Northern Mockingbird (Mimus polyglottos) and Blue Grosbeak (Passerina caerulea)) were either only found at valley plug sites or were more abundant at valley plug sites. Results of habitat modelling suggest that the habitat characteristics of floodplain forests at unchannelized sites are more suitable for Neotropical migrant bird species of conservation concern in the region than at valley plug sites. This study, in combination with previous research, demonstrates the ecological impacts of valley plugs span across abiotic and biotic processes and tropic levels. Copyright © 2010 John Wiley & Sons, Ltd.     

2008年奔瑞数据通信业务增长22％

2008年的布线行业内，从整个行业的发展上讲，发生的哪些事情让您印象深刻？2008年影响电缆业并至今让人记忆犹新的是十月和十一月份的全球性金融危机。在我们地区的很多公司都采取了一种保守态度，并且已经停止或者取消了他们在2008年十月份以后的扩张计划。因此，和去年同期相比，2008年下半年的工程相对较少。     

A congestion control framework for available bit rate service in ATM networks

Fair packet discarding (FPD) is a mechanism which provides incentives to users to co‐operate in congestion control, so that ATM networks can operate more efficiently. In this paper, we propose a simple congestion control framework consisting of a combination of FPD and ATM Forum's explicit‐rate flow control scheme. We show by simulations that this frame‐work achieves all objectives of congestion control: (1) control congestion, (2) achieve high user‐perceived throughput, (3) maintain fairness and (4) provide protection from misbehaving users. In addition, we equip this framework with two enhancements to improve efficiency, and reduce end‐to‐end delay. Copyright © 2002 John Wiley & Sons, Ltd.     

A refined model for performance analysis of output-buffered Banyan networks

In this paper, a new analytical model for performance analysis of output-buffered Banyan networks is proposed. In this model, we consider not only the number of packets stored in a buffer, but also the state of the buffer's Head of Line (HOL) packet (“new” or “blocked”). Simulations are used to verify the model's accuracy. The analytical results show that the maximum throughput decreases when the switch size increases, and that the throughput increases as the buffer size increases. When the buffer size is large enough, say 10, the maximum throughput is close to saturation. The maximum normalized delay increases almost linearly with the increase in buffer size. This revised version was published online in June 2006 with corrections to the Cover Date.     

Performance analysis and optimization of best‐effort service in IEEE 802.16 networks

The IEEE 802.16‐based WiMAX technology has great potential for the fourth‐generation mobile networks. Some of its service classes use the contention‐based broadcast polling mechanism to request resources. In this paper, we investigate the performance experienced by these services when the network is unsaturated. In particular, we model each subscriber station as an M/G/1 queue where the service time is determined by the parameters of the network configuration and the binary exponential backoff contention resolution algorithm. We develop a fixed‐point analysis to derive analytical expressions for network throughput and packet access delay. The accuracy of the analytical model is validated by comparing it with simulation over a wide range of operating conditions. The implications of various different parameter configurations on the performance are investigated using the analytical model. Moreover, we show that the model can be degenerated to the saturated condition. The utility of both the unsaturated and saturated models is further demonstrated by finding the optimal set of parameter values that maximize the network throughput. Copyright © 2011 John Wiley & Sons, Ltd.