A quantitative methodology for reactor vessel pressurized thermal shock decision making

The recent operating experience of the Pressurized Water Reactor (PWR) Industry has focused increasing attention on the issue of reactor vessel pressurized thermal shock (PTS). Previous reactor vessel integrity concerns have led to changes in vessel and plant system design and to operating procedures, and increased attention to the PTS issue is causing consideration of further modifications. Events such as excess feedwater, loss of normal feedwater, and steam generator tube rupture have led to significant primary system cooldowns. Each of these cooldown transients occurred concurrently with a relatively high primary system pressure. Consideration of these and other postulated cooldown events has drawn attention to the impact of operator action and control system effects on reactor vessel PTS.A methodology, which couples event sequence analysis with probabilistic fracture mechanics analyses, was developed to identify those events that are of primary concern for reactor vessel integrity. Operating experience is utilized to aid in defining the appropriate event sequences and event frequencies of occurrence for the evaluation.Once the specific event sequences of concern are identified, detailed thermal-hydraulic and structural evaluations can be performed to determine the conditions required to minimize the extension of postulated flaws or enhance flaw arrest in the reactor vessel. This paper addresses key aspects of the thermal-hydraulic and fracture mechanics analyses of the reactor vessel. The effects of incomplete mixing of safety injection flow in the primary cold leg and vessel downcomer and the application of warm prestressing are emphasized. The results of these analyses are being used to define further modifications in vessel and plant system design and to operating procedures.Previous design considerations that have evolved as a result of reactor vessel integrity evaluations are mentioned. These include the development of realistic design analysis tools and selection of plant system modifications. Modifications that are being developed or are under consideration are also mentioned. These include vessel fluence reductions, additional modifications to operating procedures, increased use of probabilistic event sequence and fracture mechanics analysis methods, enhanced material fracture toughness, and reductions in the severity or frequency of occurrence of dominant reactor vessel PTS transients.     

Effects of ion beam hydrogenation on silicon solar cell structures

A Kaufman ion source was used to hydrogenate polycrystalline silicon structures at energies from 250 to 5000 eV. This results in improvements in photovoltaic properties and in shorter hydrogenation times than have been reported by other groups using arc or plasma discharges. Single-crystal silicon samples exposed to similar hydrogenation conditions were evaluated using scanning electron microscopy, IR spectroscopy, reflectometry and ellipsometry. The thickness and other characteristics of this modified surface region vary as a function of the ion energy and the dose rate. The properties of this surface region may influence the choice of subsequent antireflective coatings that are used to provide optimum performance of these devices.     

Simultaneous registration and activation detection for fMRI

Registration using the least-squares cost function is sensitive to the intensity fluctuations caused by the blood oxygen level dependent (BOLD) signal in functional MRI (fMRI) experiments, resulting in stimulus-correlated motion errors. These errors are severe enough to cause false-positive clusters in the activation maps of datasets acquired from 3T scanners. This paper presents a new approach to resolving the coupling between registration and activation. Instead of treating the two problems as individual steps in a sequence, they are combined into a single least-squares problem and are solved simultaneously. Robustness tests on a variety of simulated three-dimensional EPI datasets show that the stimulus-correlated motion errors are removed, resulting in a substantial decrease in false-positive and false-negative activation rates. The new method is also shown to decorrelate the motion estimates from the stimulus by testing it on different in vivo fMRI datasets acquired from two different 3T scanners.     

The internship supply-demand imbalance: The APPIC perspective.

The internship has long been considered the capstone experience in the sequence of doctoral education in professional psychology. Since at least 1999, the number of available internship positions in the United States and Canada has been outstripped by the number of students seeking these positions. The resulting imbalance between supply and demand for internship positions has grown substantially since 2002 and now should be considered to have reached crisis proportions. Although no complete solution to this imbalance is imminently feasible, a comprehensive approach to addressing the crisis requires that both the supply of internships and the growth in demand be addressed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

MVA Processing of Speech Features

In this paper, we investigate a technique consisting of mean subtraction, variance normalization and time sequence filtering. Unlike other techniques, it applies auto-regression moving-average (ARMA) filtering directly in the cepstral domain. We call this technique mean subtraction, variance normalization, and ARMA filtering (MVA) post-processing, and speech features with MVA post-processing are called MVA features. Overall, compared to raw features without post-processing, MVA features achieve an error rate reduction of 45% on matched tasks and 65% on mismatched tasks on the Aurora 2.0 noisy speech database, and an average 57% error reduction on the Aurora 3.0 database. These improvements are comparable to the results of much more complicated techniques even though MVA is relatively simple and requires practically no additional computational cost. In this paper, in addition to describing MVA processing, we also present a novel analysis of the distortion of mel-frequency cepstral coefficients and the log energy in the presence of different types of noise. The effectiveness of MVA is extensively investigated with respect to several variations: the configurations used to extract and the type of raw features, the domains where MVA is applied, the filters that are used, the ARMA filter orders, and the causality of the normalization process. Specifically, it is argued and demonstrated that MVA works better when applied to the zeroth-order cepstral coefficient than to log energy, that MVA works better in the cepstral domain, that an ARMA filter is better than either a designed finite impulse response filter or a data-driven filter, and that a five-tap ARMA filter is sufficient to achieve good performance in a variety of settings. We also investigate and evaluate a multi-domain MVA generalization     

Effect of synthesis condition and annealing on the sensitivity and stability of gas sensors made of Zn-doped <Emphasis Type=Italic>γ</Emphasis>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> particles

Gas sensors made of flame-synthesized Zn-doped γ-Fe₂O₃ nanoparticles were found to have high sensitivity and high aging resistance. Zinc-doped γ-Fe₂O₃ nanoparticles and microparticles were synthesized by flame spray pyrolysis (FSP). Gas sensors were fabricated with as-synthesized particles, and with particles that had been annealed. The sensors’ response to acetone vapor and H₂ was measured as fabricated, and measured again after the sensors were aged for three days. The sensors made from as-synthesized particles showed a gas sensing sensitivity 20 times higher than the literature value. However, sensors made of microparticles lost their sensing ability after three days of aging; sensors made of nanoparticles retained their gas sensing capability after aging. Sensors made of annealed particles did not have significant gas sensing capabilities. Analysis using the William and Hall method showed that the microstrains decreased significantly in both H₂/O₂ and H₂/Air flame synthesized particles after annealing. The results showed that sensors made of flame-synthesized particles have much higher sensitivity than sensors made of particles previously reported. Especially, sensors made of flame-synthesized nanoparticles are resistant towards aging. This aging resistance may be attributed to the particles’ ability to retain their microstrains.     

Interactive Simulation of Rigid Body Dynamics in Computer Graphics

Interactive rigid body simulation is an important part of many modern computer tools, which no authoring tool nor game engine can do without. Such high‐performance computer tools open up new possibilities for changing how designers, engineers, modelers and animators work with their design problems. This paper is a self contained state‐of‐the‐art report on the physics, the models, the numerical methods and the algorithms used in interactive rigid body simulation all of which have evolved and matured over the past 20 years. Furthermore, the paper communicates the mathematical and theoretical details in a pedagogical manner. This paper is not only a stake in the sand on what has been done, it also seeks to give the reader deeper insights to help guide their future research.     

Oxygen reduction activity of Pt and Pt-Mn-Co electrocatalysts sputtered on nano-structured thin film support

We report on extensive measurements of oxygen reduction activity of Pt and Pt-Co-Mn electrocatalysts using the rotating ring-disk electrode (RRDE) method. The electrocatalysts were prepared by sputtering from Pt or Pt, Co and Mn targets onto 3M's nano-structured thin film support (NSTF) structures. The area specific activity of Pt/NSTF, measured in 0.1 M HClO₄ and at room temperature, is similar to that of bulk Pt. The area specific measurements show a 20 mV reduction in the Pt-Co-Mn/NSTF overpotential compared to Pt/NSTF. The corresponding kinetic gain in the area specific activity of the ternary alloy is about a factor of two. This ORR enhancement factor observed in the ternary Pt-Co-Mn/NSTF by RRDE measurements is similar to the results obtained in 50 cm² H₂/air fuel cells.