The recovery current density of hard superconductors

In order to quantify stability in superconductors, the power supplied as external heat to drive the superconductor normal was measured. At constant current and temperature, it was found that the conductor could not be driven normal below a certain critical field, and likewise at constant field there was a threshold critical current I_t. The threshold current density J_t was found to correspond to the critical current density for the recovery of superconductivity after a disturbance, J_r.     

Oxidative coupling of methane over doped Li/MgO catalysts

A series of zirconia doped Li/MgO catalysts with a fixed amount of zirconia and varying concentrations of lithium was used for the oxidative coupling of methane. It was found that an increase in lithium concentration resulted in a decrease in initial activity, while the selectivity was not affected. The life-time of Zr doped Li/MgO catalysts with a fixed concentration of ZrO₂ is a function of the lithium concentration. Previous results have shown that Li₂Mg₃ZrO₆ is active and selective but it is now shown to be instable under reaction conditions.     

Performance and design evaluation of the RAID-II storage server

RAID-II is a high-bandwidth, network-attached storage server designed and implemented at the University of California at Berkeley. In this paper, we measure the performance of RAID-II and evaluate various architectural decisions made during the design process. We first measure the end-to-end performance of the system to be approximately 20 MB/s for both disk array reads and writes. We then perform a bottleneck analysis by examining the performance of each individual subsystem and conclude that the disk subsystem limits performance. By adding a custom interconnect board with a high-speed memory and bus system and parity engine, we are able to achieve a performance speedup of 8 to 15 over a comparative system using only off-the-shelf hardware.     

Influence of preparation method on the performance of vanadia-niobia catalysts for the oxidative dehydrogenation of propane

The influence of various preparation methods on the performance of V-Nb-0 catalysts has been investigated. It was found that the activity and selectivity of a vanadium site depend on the nature of the neighbouring atoms. Vanadium neighbours provide activity, while niobium neighbours provide selectivity. Careful preparation of these catalysts ensures a homogeneous distribution and good mixing of the vanadium and niobium. It was also found that the vanadium becomes mobile upon reduction and this results in better distribution of vanadium in used catalysts.     

Mechanistic Aspects of Catalytic Steam Reforming of Biomass-related Oxygenates

Catalytic steam reforming of acetic acid, as a model oxygenate derived from biomass, was studied over supported Pt catalysts. It is suggested that both Pt and the support are involved in the activation of acetic acid and water, respectively. This manifests in different intrinsic activity for Pt when anchored on different supports. Accordingly, the reforming proceeds most likely at the boundary between the Pt and the support and the number of Pt sites that are in the close proximity of the support determine hydrogen formation rates.     

The effect of addition of a third component on the behaviour of the lithium doped magnesium catalysts for the oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane was studied with the use of promoted Li/MgO catalysts at temperatures of 600–650°C. The addition of known promoters, cobalt and tin, gave a slight Increase In activity but a strong decrease in selectivity to ethylene under the conditions used. The addition of sodium improved the selectivity to ethylene and suppressed the formation of carbon monoxide. Using a feed of 12 vol% ethane and 6 vol% oxygen, the U/Na/MgO catalyst with 3.2wt% sodium showed a selectivity of 86 % to ethylene at 38 % conversion of ethane; the Li/MgO catalyst showed a selectivity of 80 % at similar conversions Thermal Investigations of the Li/Na/MgO catalyst showed that an eutectic melt of LINaCO₃ is formed at 490°C; the existence of this molten phase is probably the cause of the Increased selectivity.     

The role of graphite morphology and matrix structure on low frequency thermal cycling of cast irons

Low frequency thermal cycling tests were carried out on four types of cast iron (viz., austempered ductile iron, pearlitic ductile iron, compacted/vermicular graphite iron and grey cast iron) at predetermined ranges of thermal cycling temperatures. The specimens were unconstrained. Results show that austempered ductile iron has the highest thermal cycling resistance, followed by pearlitic ductile iron and compacted graphite iron, while grey cast iron exhibits the lowest resistance. Microstructural analysis of test specimens subjected to thermal cycling indicates that matrix decomposition and grain growth are responsible for the reduction in hardness while graphite oxidation, de-cohesion and grain boundary separation are responsible for the reduction in the modulus of elasticity upon thermal cycling.     

Self-management in chaotic wireless deployments

Over the past few years, wireless networking technologies have made vast forays into our daily lives. Today, one can find 802.11 hardware and other personal wireless technology employed at homes, shopping malls, coffee shops and airports. Present-day wireless network deployments bear two important properties: they are unplanned, with most access points (APs) deployed by users in a spontaneous manner, resulting in highly variable AP densities; and they are unmanaged, since manually configuring and managing a wireless network is very complicated. We refer to such wireless deployments as being chaotic. In this paper, we present a study of the impact of interference in chaotic 802.11 deployments on end-client performance. First, using large-scale measurement data from several cities, we show that it is not uncommon to have tens of APs deployed in close proximity of each other. Moreover, most APs are not configured to minimize interference with their neighbors. We then perform trace-driven simulations to show that the performance of end-clients could suffer significantly in chaotic deployments. We argue that end-client experience could be significantly improved by making chaotic wireless networks self-managing. We design and evaluate automated power control and rate adaptation algorithms to minimize interference among neighboring APs, while ensuring robust end-client performance. This work was supported by the Army Research Office under grant number DAAD19-02-1-0389, and by the NSF under grant numbers ANI-0092678, CCR-0205266, and CNS-0434824, as well as by IBM and Intel. Aditya Akella obtained his Ph.D. in Computer Science from Carnegie Mellon University in September 2005. He obtained a B.Tech in Computer Science and Engineering from IIT Madras in May 2000. Currently, Dr. Akella is a post-doctoral associate at Stanford University. He will join the Computer Sciences faculty at the University of Wisconsin-Madison in Fall 2006. Dr. Akella's research interests include Internet Routing, Network Protocol Design, Internet Security, and Wireless Networking. His web page is at . Glenn Judd, is a Computer Science Ph.D. candidate at Carnegie Mellon University. His research interests include wireless networking and pervasive computing. He has an M.S. and B.S. in Computer Science from Brigham Young University. Srinivasan Seshan is currently an Associate Professor and holds the Finmeccanica chair at Carnegie Mellon University’s Computer Science Department. Dr. Seshan received his Ph.D. in 1995 from the Computer Science Department at University of California, Berkeley. From 1995 to 2000, Dr. Seshan was a research staff member at IBM’s T.J. Watson Research Center. Dr. Seshan’s primary interests are in the broad areas of network protocols and distributed network applications. In the past, he has worked on topics such as transport/routing protocols for wireless networks, fast protocol stack implementations, RAID system design, performance prediction for Internet transfers, Web server benchmarking, new approaches to congestion control, firewall design and improvements to the TCP protocol. His current work explores new approaches in overlay networking, sensor networking, online multiplayer games and wide-area Internet routing. His web page is at . Peter Steenkiste is a Professor of Computer Science and of Electrical and Computer Engineering at Carnegie Mellon University. His research interests include networking, distributed systems, and pervasive computing. He received an M.S. and Ph.D. in Electrical Engineering from Stanford University and an Engineering degree from the University of Gent, Belgium. You can learn more about his research from his home page .