Mass Transport in Shallow Turbulent Wake Flow by Planar Concentration Analysis Technique

A planar concentration analysis (PCA) system is used for observing the transport and mixing of a tracer mass in a shallow turbulent free-surface wake flow of a large cylindrical obstacle. The nonintrusive, fieldwise PCA measuring technique is applied to evaluate depth-averaged mass concentrations by making use of light attenuation due to absorption and scattering processes related to a dissolved tracer mass. The scalar fields are decomposed into a low-frequency quasiperiodic part, the coherent flow, and a randomly fluctuating part. From accompanying near-surface velocity measurements, large-scale coherent structures are identified and related to the coherent mass fields. This allows one to assess the role of the large-scale vortices for advection and diffusion in shallow wake flows. The time–mean wake flow displays a self-similar spanwise distribution both for mass and velocity. The longitudinal development of shallow wakes initially shows the growth of unbounded wakes; in the wake far field an attenuated behavior applies.     

Effects of Particle Crushing in Stress Drop-Relaxation Experiments on Crushed Coral Sand

Stress relaxation and stress drop-relaxation tests have been performed to complement a test series performed to study strain rate, creep, and stress drop-creep effects on crushed coral sand. Drained experiments with constant effective confining pressure of 200 kPa were performed in which triaxial specimens of crushed coral sand were loaded to initial stress differences of 500, 700, and 900 kPa, followed by stress drops of 0, 100, 200, 300, and 400 kPa at which points the axial strains were kept constant while the axial stress relaxation and the volumetric strains were observed. The stress drops produced delays in initiation of stress relaxation that were proportional with the magnitudes of the stress drops. The experiments show that sands do not exhibit classic viscous effects, and their behavior is indicated as “nonisotach,” while the typical viscous behavior of clay is termed “isotach.” Thus, there are significant differences in the time-dependent behavior patterns of sands and clay. A mechanistic picture of time effects in sands is proposed.     

Rotary actuators with multipole ring magnets

Rotary actuators are electromagnetic devices developing mechanical torque with limited rotary motion. Because of their simplicity and low cost they are finding more and more applications, especially in the automotive field. This paper describes a novel homopolar rotary actuator with a ring-type radially magnetized multipolar permanent magnet featuring a high force density “transverse flux” configuration which performs a spring action by developing electromagnetic torques with limited angular movement. Because of the magnetically complicated and nonsymmetrical rotary actuator configuration, the analysis of this actuator is based on 3-D finite element software. The analysis, which is well supported by test results, shows that symmetrical magnetic forces in both directions of rotation were achieved with a stable equilibrium position, satisfying all design requirements to enhance the basic hydraulic power steering system of passenger vehicles     

An in vitro assay to evaluate competitive exclusion products for poultry

An in vitro assay was developed to measure the ability of competitive exclusion (CE) bacteria to protect Caco-2 and CRL-2117 epithelial cells from invasion by Salmonella Typhimurium. The proposed assay is needed to expedite the development of defined-flora CE products. The average significantly protective concentration of the commercial poultry-specific CE product Preempt was 4.05 log CFU/6.41 log human Caco-2 cells and 3.71 log CFU/6.89 log CFU chicken CRL-2117 cells, Enterococcus faecalis isolated from Preempt protected CRL-2117 cells, Escherichia coli isolates protected Caco-2 cells, Lactococcus lactis and Bacteroides distasonis isolates protected both cell lines, and three species of Lactobacillus isolates failed to protect either cell line. A defined mixture of 29 strains of bacteria similar to the constituents of Preempt protected both cell lines from Salmonella invasion at a concentration of 7.83 log CFU. The constituents of the defined CE culture were separated into mixtures of obligate (8.42 log CFU) and facultative (8.49 log CFU) anaerobes, which both protected the cell lines, suggesting that both types of bacteria were equally protective. Although not a substitute for in vivo testing, the in vitro CE assay is a rapid technique for the evaluation of bacterial mixtures for potential CE products.     

The Impact of Short-Sale Constraints on Asset Allocation Strategies via the Backward Markov Chain Approximation Method

This paper considers an asset allocation strategy over a finite period under investment uncertainty and short-sale constraints as a continuous-time stochastic control problem. Investment uncertainty is characterised by a stochastic interest rate and inflation risk. If there are no short-sale constraints, the optimal asset allocation strategy can be obtained analytically. We consider several kinds of short-sale constraints and employ the backward Markov chain approximation method to explore the impact of short-sale constraints on asset allocation decisions. Our results show that the short-sale constraints do indeed have a significant impact on these decisions.     

The Multifactor Nature of the Volatility of Futures Markets

This paper estimates a model of interest rate dynamics containing multi-factor Wiener and single-factor Poisson jump volatility components. Data from the highly liquid but short term futures markets are used. The difficult numerical problem of estimating such multi-factor models is resolved by using a genetic algorithm to carry out the optimization procedure. It is established that the multi-factor Wiener volatility components are adequate to model the interest rate dynamics without the need to incorporate Poisson jump components, the existence of which would create difficulties in the practical use of interest rate models. Jel Classification No: C51, C61, E43     

The UCSC Kestrel parallel processor

The architectural landscape of high-performance computing stretches from superscalar uniprocessor to explicitly parallel systems, to dedicated hardware implementations of algorithms. Single-purpose hardware can achieve the highest performance and uniprocessors can be the most programmable. Between these extremes, programmable and reconfigurable architectures provide a wide range of choice in flexibility, programmability, computational density, and performance. The UCSC Kestrel parallel processor strives to attain single-purpose performance while maintaining user programmability. Kestrel is a single-instruction stream, multiple-data stream (SIMD) parallel processor with a 512-element linear array of 8-bit processing elements. The system design focuses on efficient high-throughput DNA and protein sequence analysis, but its programmability enables high performance on computational chemistry, image processing, machine learning, and other applications. The Kestrel system has had unexpected longevity in its utility due to a careful design and analysis process. Experience with the system leads to the conclusion that programmable SIMD architectures can excel in both programmability and performance. This work presents the architecture, implementation, applications, and observations of the Kestrel project at the University of California at Santa Cruz.     

Optimizing Grid-Based Workflow Execution

Large-scale applications can be expressed as a set of tasks with data dependencies between them, also known as application workflows. Due to the scale and data processing requirements of these applications, they require Grid computing and storage resources. So far, the focus has been on developing easy to use interfaces for composing these workflows and finding an optimal mapping of tasks in the workflow to the Grid resources in order to minimize the completion time of the application. After this mapping is done, a workflow execution engine is required to run the workflow over the mapped resources. In this paper, we show that the performance of the workflow execution engine in executing the workflow can also be a critical factor in determining the workflow completion time. Using Condor as the workflow execution engine, we examine the various factors that affect the completion time of a fine granularity astronomy workflow. We show that changing the system parameters that influence these factors and restructuring the workflow can drastically reduce the completion time of this class of workflows. We also examine the effect on the optimizations developed for the astronomy application on a coarser granularity biology application. We were able to reduce the completion time of the Montage and the Tomography application workflows by 90% and 50%, respectively.