Simple stability criteria for systems with time-varying delays

This paper considers the problem of checking stability of linear feedback systems with time-varying but bounded delays. Simple but powerful criteria of stability are presented for both continuous-time and discrete-time systems. Using these criteria, stability can be checked in a closed loop Bode plot. This makes it easy to design the system for robustness.     

SACST: smart anthropomorphic contact surface technology

In this article, we present the ongoing research work of smart anthropomorphic contact surface technology (SACST) and applications in robotics and human-augmented systems. Integrating MEMS technology with contact theory and intelligent-control techniques, SACST can alter the behavior of contact surfaces based on robotics theories. To make SACST products more reliable and efficient, certain critical components are indispensable. For example, MEMS valves should be able to work under more resistant force and with less power consumption; the contact sensor should have higher and flexible resolution; and the actuation mechanism of the bladders should become more integrated, more flexible, and easier to control. Next-generation SACST technology will also integrate intelligent operation systems and control with actuators and sensors.     

Aggregate Profit-Based Caching Replacement Algorithms for Streaming Media Transcoding Proxy Systems

This work derives a generalized video object profit function from the extended weighted transcoding graph to calculate the individual cache profit of certain versions of a video object, and the aggregate profit from caching multiple versions of the same video object. This proposed function takes into account the popularity of certain versions of an object, the transcoding delay among versions, and the average duration of access of each version. Based on the profit function, cache-replacement algorithms are proposed to reduce the startup delay and network traffic by efficiently caching video objects with the most profits. Two kinds of simulations were conducted to evaluate the performance of the proposed algorithms. These simulations exploit partial viewing traces and complete viewing traces, separately. The results demonstrate that the proposed algorithms outperform the competing algorithms by 15%-39% in delay saving ratio and 5%-10% in byte-hit ratio     

A new line integral convolution algorithm for visualizingtime-varying flow fields

New challenges on vector field visualization emerge as time dependent numerical simulations become ubiquitous in the field of computational fluid dynamics (CFD). To visualize data generated from these simulations, traditional techniques, such as displaying particle traces, can only reveal flow phenomena in preselected local regions and thus, are unable to track the evolution of global flow features over time. The paper presents an algorithm, called UFLIC (Unsteady Flow LIC), to visualize vector data in unsteady flow fields. Our algorithm extends a texture synthesis technique, called Line Integral Convolution (LIC), by devising a new convolution algorithm that uses a time-accurate value scattering scheme to model the texture advection. In addition, our algorithm maintains the coherence of the flow animation by successively updating the convolution results over time. Furthermore, we propose a parallel UFLIC algorithm that can achieve high load balancing for multiprocessor computers with shared memory architecture. We demonstrate the effectiveness of our new algorithm by presenting image snapshots from several CFD case studies     

New Concepts in Interior Lighting Design

In the past several decades, most lighting designers have been using the "lumen method" to design an illumination system for interior spaces. This design approach would at its best produce a mediocre lighting environment and most likely waste considerable energy. As people become more energy conscious and better understood in human visual performance, many new concepts, and tools for interior lighting design will be generated. Among them are 1) new method of determining lighting levels required for the task, 2) the equivalent sphere illumination (ESI), 3) visual comfort probability (VCP) 4) new control devices, 5) daylighting, and 6) improved luminaries. Sophisticated lighting design techniques to embody these new concepts and tools must be developed in order to achieve optimal effectiveness in the system performance and attendant energy savings by the system. Discussed here are these new concepts and lighting design techniques which help to promote their applications.     

The Development of a Distributed Surface Machining System

1 Introduction Owing to the drastically continuous performance enhancement on the information technology such as com-puter ,communication,and network technology,the resources sharing and in-ti me information integration fornetwork-based automationin manufacturing industry has become an extremely i mportant focus . Furthermore ,withthe growing trend of the transnational enterprise number towards globalization, promotion of the globalcompetitiveness has also been increasingly paid more attention…     

Effect of Cu additives on Sn whisker formation of Sn(Cu) finishes

Sn whisker formation on Sn(Cu) finishes has been studied. (1) With respect to the thickness effect, we found that Sn whisker density for pure Sn and Sn0.7Cu finishes has a linear relationship with the finish thickness. The safety thickness for Sn and Sn0.7Cu finishes is about 10 μm and 20 μm, respectively. (2) With respect to the alloying effect, we found that Sn whisker formation could be retarded by increasing Cu content in the Sn(Cu) finishes. We conclude that the Cu additives could reduce the two major driving forces of the Sn whisker formation, i.e., metal underlayer dissolution and thermal stress. The Cu additives self-formed a Cu-Sn compound barrier layer, which effectively prevents the reaction and dissolution with the metal underlayer. On the other hand, the Cu additives precipitated out as Cu-Sn compound in the Sn(Cu) finish layer, which is believed to be the reason for smaller values of the coefficient of thermal expansion (CTE) for Sn(Cu) alloys. The smaller CTE values results in a lower thermal stress level in the Sn(Cu) finishes.     

In-situ observation of material migration in flip-chip solder joints under current stressing

This investigation studies how electron flow distribution and the vacancy concentration gradient affect the diffusion of solder atoms in a flip-chip solder joint under current stress. The migration of materials was traced by monitoring the positions of 21 Pb grains of the eutectic PbSn solder joint. Experimental results indicate that the displacements of the Pb grains were not uniform along the electron flow direction. Additionally, certain Pb grains exhibited lateral displacements. The nonuniform material migration is attributable to the combined effect of electromigration and the vacancy concentration gradient, which was caused by electromigration. By measuring the displacements of the Pb grains, we estimated that the DZ* value of Sn in eutectic SnPb solder was 5×10⁻¹⁰ cm²/s.     

Validity of an Arterial System Model: A Quantitative Evaluation

The purpose of this investigation was to validate an arterial system model in a quantitative fashion. The model is based on a finite difference solution to the Navier?Stokes equations and retains certain nonlinear features of the system. Rather than apply standard error measures that test waveform correlation, the validation method used relies on the quantification of differences between the model and animals over a wide range of parametric changes. A series of functions was used to define the difference between the dependent variables of the model and corresponding hemodynamic variables of the animals. These functions were displayed as a family of three-dimensional difference surfaces which related the function value to parametric changes of the independent variables. Experimental data from three dogs were compared with model predictions. Regions of validity for the independent variables were then assessed by examining the difference surfaces.     

Positron trapping at phase interfaces and dislocations in pearlitic eutectoid steel

Positron annihilation studies of isothermally annealed eutectoid steel revealed that positrons prefer to trap and annihilate at discrete dislocations rather than phase interfaces. PO-WE KAO, formerly with the Department of Materials Science and Engineering, University of Utah, Salt Lake City, UT.