Suppression of low-energy Andreev states by a supercurrent in YBa_2Cu_3O_7-delta

We report a coherence-length scale phenomenon related to how the high-Tc order parameter (OP) evolves under a directly-applied supercurrent. Scanning tunneling spectroscopy was performed on current-carrying YBa_2Cu_3O_7-delta thin-film strips at 4.2K. At current levels well below the theoretical depairing limit, the low-energy Andreev states are suppressed by the supercurrent, while the gap-like structures remain unchanged. We rule out the likelihood of various extrinsic effects, and propose instead a model based on phase fluctuations in the d-wave BTK formalism to explain the suppression. Our results suggest that a supercurrent could weaken the local phase coherence while preserving the pairing amplitude. Other possible scenarios which may cause the observed phenomenon are also discussed.Comment: 6 pages, 4 figures, to appear in Physical Review

Glassy dynamics in mono-, di-, and tri-propylene glycol: From the alpha- to the fast beta-relaxation

We present a thorough characterization of the glassy dynamics of three propylene glycols (mono-, di- and trimer) by broadband dielectric spectroscopy. By covering a frequency range of more than 15 decades, we have access to the entire variety of dynamic processes typical for glassy dynamics. These results add three more molecular glass formers to the sparse list of materials for which real broadband spectra, including the region of the fast beta-process, are available. Some first analyses of the various observed dynamic processes are provided

DURABILITY OF RUNNING SHOES WITH EVA AND PU MIDSOLE

Running shoes may play an important role in preventing injuries by absorbing external shock due to ground impact (Cook et al., 1990; Verdejo and Mills, 2004). Shoe age maybe an important factor in running injuries. One prospective study showed that running injury was associated with shoe age (Taunton et al., 2003). In recent years, different types of foam materials have been developed for running shoe midsoles. Two common types of foam materials, Ethylene Vinyl Acetate (EVA) and Polyurethane (PU), are now widely used in running shoe midsoles. The purpose of the present study was to examine the durability of running shoes with common types of EVA and PU midsole materials

A Hybrid Mechanics of Materials Course Part 1: Evolution of the Course to Improve Student Performance and Retention

A hybrid Mechanics of Materials course consisting of recorded lecture videos and face-to-face class meetings was developed. Initial offerings of the hybrid course resulted in a drop in average student performance by – 0.18 grade points as well as a reduction in the student pass rate of 3%. Over time, average student performance in the course improved; however, the student pass rate remained relatively constant. A number of ad hoc internal studies by the hybrid course instructors were conducted to attempt to determine the factors contributing to the reduction in the student pass rate. A test over prerequisite Statics and Calculus material was developed and incorporated into the course in order to gauge incoming student capability and knowledge. Results of this pre-test provided a baseline measure so that the effect of various changes to the hybrid course could be objectively measured independent of differences in student capability. Internal studies suggested that a lack of student engagement as manifested by poor attendance in face-to-face class attendance contributed to poor performance and reduced student retention. The hybrid course policy was changed by incorporating a one letter grade penalty for students who did not have good attendance. This resulted in an improvement in average performance by 0.18 grade points and an increase in student retention by 12.5% compared to the optional-attendance hybrid course

A Framework for Adaptive Routing in Multicomputer Networks

Message-passing concurrent computers, also known as multicomputers, such as the Caltech Cosmic Cube [47] and its commercial descendents, consist of many computing nodes that interact with each other by sending and receiving messages over communication channels between the nodes. The communication networks of the second-generation machines, such as the Symult Series 2010 and the Intel iPSC2 [2], employ an oblivious wormhole-routing technique that guarantees deadlock freedom. The network performance of this highly evolved oblivious technique has reached a limit of being capable of delivering, under random traffic, a stable maximum sustained throughput of ~~45 to 50% of the limit set by the network bisection bandwidth, while maintaining acceptable network latency. This thesis examines the possibility of performing adaptive routing as an approach to further improving upon the performance and reliability of these networks. In an adaptive multipath routing scheme, message trajectories are no longer deterministic, but are continuously perturbed by local message loading. Message packets will tend to follow their shortest-distance routes to destinations in normal traffic loading, but can be detoured to longer but less-loaded routes as local congestion occurs. A simple adaptive cut-through packet-switching framework is described, and a number of fundamental issues concerning the theoretical feasibility of the adaptive approach are studied. Freedom of communication deadlock is achieved by following a coherent channel protocol and by applying voluntary misrouting as needed. Packet deliveries are assured by resolving channel-access conflicts according to a priority assignment. Fairness of network access is assured either by sending round-trip packets or by having each node follow a local injection-synchronization protocol. The performance behavior of the proposed adaptive cut-through framework is studied with stochastic modeling and analysis, as well as through extensive simulation experiments for the 2D and 3D rectilinear networks. Theoretical bounds on various average network-performance metrics are derived for these rectilinear networks. These bounds provide a standard frame of reference for interpreting the performance results. In addition to the potential gain in network performance, the adaptive approach offers the potential for exploiting the inherent path redundancy found in richly connected networks in order to perform fault-tolerant routing. Two convexity-related notions are introduced to characterize the conditions under which our adaptive routing formulation is adequate to provide fault-tolerant routing, with minimal change in routing hardware, The effectiveness of these notions is studied through extensive simulations, The 2D octagonal-mesh network is suggested; this displays excellent fault-tolerant potential under the adaptive routing framework. Both performance and reliability behaviors of the octagonal mesh are studied in detail. A number of implementation issues are examined. Encoding schemes for packet headers that admit simple incremental updates while providing all necessary routing information in the first flit of a relatively narrow flit width are developed. A pipelined control structure that allows a packet to cut through an intermediate node with a minimum delay of two cycles is described. A distributed clocking scheme is developed that eliminates the problem of global clock-signal distribution. Under this clocking scheme, the adaptive routers can be tessellated to form a network of arbitrary size

The General Interconnect Problem of Integrated Circuits

This thesis is concerned with the interconnection problem of custom integrated circuits. It may be broadly defined as the transformation of circuit description represented by the notion of modules together with the circuit connectivity requirements, into wiring patterns which implement the required connectivities. Conventional approaches to its solution are presented. Issues such as partition to placement and routing and various layout optimization tradeoffs are discussed. A detail hierarchical routing model with timing considerations that extends naturally to multiple conducting layer environment is presented. Several of the implications of this extension are also discussed. The rest of this thesis deals with an experiment with the stepping approach to routing as an alternative to the conventional cellular approach empahasing simplicity rather than optimization. Algorithms for routing signals and power developed for the stepping router are presented. An implementation of this approach by the author together with some test examples and their results are also described, This thesis concludes with a few suggestions for further research work in this area which the author considers very important from the experience gained during the work on this thesis