Stochastic models for degradation-based reliability

This paper presents a degradation-based procedure for estimating the full and residual lifetime distribution of a single-unit system subject to Markovian deterioration. The hybrid approach unites real degradation measures with analytical, stochastic failure models to numerically compute the distributions and their moments. Two distinct models are shown to perform well when compared with simulated data. Moreover, results obtained from the second model are compared with empirically generated lifetimes of 2024-T3 aluminum alloy specimens. The numerical experiments indicate that the proposed techniques are useful for remaining lifetime prognosis in both cases.     

Port Placement Planning in Robot-Assisted Coronary Artery Bypass

Properly selected port sites for robot-assisted coronary artery bypass graft (CABG) improve the efficiency and quality of these procedures. In clinical practice, surgeons select port locations using external anatomic landmarks to estimate a patient's internal anatomy. This paper proposes an automated approach to port selection based on a preoperative image of the patient, thus avoiding the need to estimate internal anatomy. Using this image as input, port sites are chosen from a grid of surgeon-approved options by defining a performance measure for each possible port triad. This measure seeks to minimize the weighted squared deviation of the instrument and endoscope angles from their optimal orientations at each internal surgical site. This performance measure proves insensitive to perturbations in both its weighting factors and moderate intraoperative displacements of the patient's internal anatomy. A validation study of this port site selection was performed. cardiac algorithm also Six surgeons dissected model vessels using the port triad selected by this algorithm with performance compared to dissection using a surgeon-selected port triad and a port triad template described by Tabaie et al., 1999. With the algorithm-selected ports, dissection speed increased by up to 43% (p = 0.046) with less overall vessel trauma. Thus, this algorithmic approach to port site selection has important clinical implications for robot-assisted CABG which warrant further investigation.     

Laser-induced fluorescence spectroscopy of dark- and light-adapted bean (Phaseolus vulgaris L.) and wheat (Triticum aestivum L.) plants grown under three irradiance levels and subjected to fluctuating lighting conditions

Fluorescence spectral characteristics associated with growth under different irradiance levels, and during rapidly changing lighting conditions, were measured on healthy bean (Phaseolus vulgaris L.) and wheat (Triticum aestivum L.) plants using a laser-induced fluorescence spectroscopy (LIFS) system. The LIFS system was designed as a prototype of a handheld field remote sensing system and used a tripled Nd:YAG laser to produce ultraviolet (UV) excitation photons at 355 nm. Dark-adapted canopies of the bean and wheat plants grown under 150, 300, or 450 μmol m⁻² s⁻¹ of photosynthetically active radiation (PAR) exhibited LIFS spectra with higher relative fluorescence intensities than emissions from light-adapted plants at all three light levels. Blue/red and blue/far-red leaf fluorescence ratios for both bean and wheat plants increased dramatically as PAR increased, but red/far-red ratios decreased as PAR increased. Light-adapted plants grown under the three light levels were then subjected to several rapidly changing lighting conditions. Plants were exposed sequentially to 150, 300, and 650 μmol m⁻² s⁻¹ PAR from metal halide lamps, followed by a fourth light treatment of 650 μmol m⁻² s⁻¹ PAR from a mixture of metal halide and tungsten-halogen lamps. The tungsten-halogen lamps added significant amounts of near-infrared (NIR) irradiation to the background light environment provided by the metal halide lamps. Results indicated that both bean and wheat canopies generally exhibited stable blue, green, red, and far-red fluorescence emissions when plants were exposed to 150, 300, and 650 μmol m⁻² s⁻¹ PAR from the metal halide lamps. In contrast, when bean and wheat plants were exposed to the NIR-enriched light supplied by the tungsten-halogen lamps, blue and green fluorescence remained stable, but red and far-red fluorescence increased dramatically immediately after exposure to the NIR photons. However, the increased levels of red and far-red fluorescence observed after exposure to NIR light decreased quickly (within 55 s) and returned to “baseline” levels observed at the start of the rapidly changing light experiments. Results indicate that handheld LIFS instruments can be used for remote sensing of plant canopies under a diversity of lighting conditions including full darkness, dawn and dusk lighting environments, and under rapidly changing light environments similar to those encountered on partly cloudy days.     

Querying websites using compact skeletons

Several commercial applications, such as online comparison shopping and process automation, require integrating information that is scattered across multiple websites or XML documents. Much research has been devoted to this problem, resulting in several research prototypes and commercial implementations. Such systems rely on wrappers that provide relational or other structured interfaces to websites. Traditionally, wrappers have been constructed by hand on a per-website basis, constraining the scalability of the system. We introduce a website structure inference mechanism called compact skeletons that is a step in the direction of automated wrapper generation. Compact skeletons provide a transformation from websites or other hierarchical data, such as XML documents, to relational tables. We study several classes of compact skeletons and provide polynomial-time algorithms and heuristics for automated construction of compact skeletons from websites. Experimental results show that our heuristics work well in practice. We also argue that compact skeletons are a natural extension of commercially deployed techniques for wrapper construction.     

Typing correspondence assertions for communication protocols

Woo and Lam propose correspondence assertions for specifying authenticity properties of security protocols. Prior work on checking correspondence assertions depends on model-checking and is limited to finite-state systems. We propose a dependent type and effect system for checking correspondence assertions. Since it is based on type-checking, our method is not limited to finite-state systems. This paper presents our system in the simple and general setting of the π-calculus. We show how to type-check correctness properties of example communication protocols based on secure channels. In a related paper, we extend our system to the more complex and specific setting of checking cryptographic protocols based on encrypted messages sent over insecure channels.     

Coping with Uncertainty in Map Learning

In many applications in mobile robotics, it is important for a robot to explore its environment in order to construct a representation of space useful for guiding movement. We refer to such a representation as a map, and the process of constructing a map from a set of measurements as map learning. In this paper, we develop a framework for describing map-learning problems in which the measurements taken by the robot are subject to known errors. We investigate approaches to learning maps under such conditions based on Valiant's probably approximately correct learning model. We focus on the problem of coping with accumulated error in combining local measurements to make global inferences. In one approach, the effects of accumulated error are eliminated by the use of local sensing methods that never mislead but occasionally fail to produce an answer. In another approach, the effects of accumulated error are reduced to acceptable levels by repeated exploration of the area to be learned. We also suggest some insights into why certain existing techniques for map learning perform as well as they do. The learning problems explored in this paper are quite different from most of the classification and boolean-function learning problems appearing in the literature. The methods described, while specific to map learning, suggest directions to take in tackling other learning problems.     

A heuristic technique for multi‐agent planning

The subject of multi‐agent planning has been of continuing concern in Distributed Artificial Intelligence (DAI). In this paper, we suggest an approach to multi‐agent planning that contains heuristic elements. Our method makes use of subgoals, and derived sub‐plans, to construct a global plan. Agents solve their individual sub‐plans, which are then merged into a global plan. The suggested approach reduces overall planning time and derives a plan that approximates the optimal global plan that would have been derived by a central planner, given those original subgoals. We explore three different scenarios. The first involves a group of agents with a common goal. The second considers how agents can interleave planning and execution when planning towards a common, though dynamic, goal. The third examines the case where agents, each with their own goal, can plan together to reach a state in consensus for the group. Finally, we consider how these approaches can be adapted to handle rational, manipulative agents. This revised version was published online in June 2006 with corrections to the Cover Date.     

基于割集分析与回路分析的撕裂方程的直接生成方法

基于割集分析与回路分析的撕裂方程直接生成方法，是一咱能避免撕裂方程生成过程中大量阵运算的一种方法，具有计算简单、便于编制计算程序的特点。     

Motivation of Engineering Students to Participate in Teaching Evaluations

This study employs expectancy theory to evaluate some key factors that motivate students to participate in the teaching evaluation process. The results show that engineering students generally consider the improvement of teaching to be the most important outcome of teaching evaluations, followed by the improvement of course content and format. Making the results of evaluations available for students' decisions on course and instructor selection ranked third, while the least important use was influencing a professor's tenure, promotion, and salary raise. Students' motivation to participate in teaching evaluations is also impacted significantly by their expectation that they will be able to provide meaningful feedback.     

Conditioned Activity and Instrumental Reinforcement Following Long-Term Oral Consumption of Cocaine by Rats.

Food-reinforced conditioned activity and instrumental responding were measured in rats after 50 weeks of continuous access to a cocaine-saccharin solution in their home cages. The elevation of conditioned activity produced by acute access to the cocaine-saccharin solution in the home cage during testing was abolished by long-term preexposure to the cocaine solution, an effect that was reversed by systemic administration of cocaine immediately prior to testing. By contrast, chronic cocaine preexposure enhanced instrumental responding for both cocaine-sucrose and pure sucrose solutions. These results support the idea that long-term cocaine exposure enhances subsequent reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)