High-performance thermionic converter Quarterly progress report, 13 Aug. - 13 Nov. 1965

Fabrication and testing of cesium loaded thermionic converter test vehicl

High-performance thermionic converter Quarterly progress report, 13 Nov. 1965 - 13 Feb. 1966

Stability and optimization parameters of cesium vapor thermionic converters studied in high performance long life equipment fabrication projec

Permutation sampling in Path Integral Monte Carlo

A simple algorithm is described to sample permutations of identical particles in Path Integral Monte Carlo (PIMC) simulations of continuum many-body systems. The sampling strategy illustrated here is fairly general, and can be easily incorporated in any PIMC implementation based on the staging algorithm. Although it is similar in spirit to an existing prescription, it differs from it in some key aspects. It allows one to sample permutations efficiently, even if long paths (e.g., hundreds, or thousands of slices) are needed. We illustrate its effectiveness by presenting results of a PIMC calculation of thermodynamic properties of superfluid Helium-four, in which a very simple approximation for the high-temperature density matrix was utilized

Fatigue damage growth mechanisms in continuous fiber reinforced titanium matrix composites

The role of fiber/matrix interface strength, residual thermal stresses, and fiber and matrix properties on fatigue damage accumulation in continuous fiber metal matrix composites (MMC) is discussed. Results from titanium matrix silicon carbide fiber composites is the primary topic of discussion. Results were obtained from both notched and unnotched specimens at room and elevated temperatures. The stress in the 0 deg fibers was identified as the controlling factor in fatigue life. Fatigue of the notched specimens indicated that cracks can grow in the matrix materials without breaking fibers

Analytic Framework for Students' Use of Mathematics in Upper-Division Physics

Many students in upper-division physics courses struggle with the mathematically sophisticated tools and techniques that are required for advanced physics content. We have developed an analytical framework to assist instructors and researchers in characterizing students' difficulties with specific mathematical tools when solving the long and complex problems that are characteristic of upper-division. In this paper, we present this framework, including its motivation and development. We also describe an application of the framework to investigations of student difficulties with direct integration in electricity and magnetism (i.e., Coulomb's Law) and approximation methods in classical mechanics (i.e., Taylor series). These investigations provide examples of the types of difficulties encountered by advanced physics students, as well as the utility of the framework for both researchers and instructors.Comment: 17 pages, 4 figures, 3 tables, in Phys. Rev. - PE

Development of quantum perspectives in modern physics

Introductory undergraduate courses in classical physics stress a perspective that can be characterized as realist; from this perspective, all physical properties of a classical system can be simultaneously specified and thus determined at all future times. Such a perspective can be problematic for introductory quantum physics students, who must develop new perspectives in order to properly interpret what it means to have knowledge of quantum systems. We document this evolution in student thinking in part through pre- and post-instruction evaluations using the Colorado Learning Attitudes about Science Survey. We further characterize variations in student epistemic and ontological commitments by examining responses to two essay questions, coupled with responses to supplemental quantum attitude statements. We find that, after instruction in modern physics, many students are still exhibiting a realist perspective in contexts where a quantum-mechanical perspective is needed. We further find that this effect can be significantly influenced by instruction, where we observe variations for courses with differing learning goals. We also note that students generally do not employ either a realist or a quantum perspective in a consistent manner.Comment: 18 pages, plus references; 3 figures; 9 tables. PACS: 01.40.Fk, 03.65._

Lower Mississippian Chert Development, Southern Midcontinent Region

The Lower Mississippian Boone Formation is a chert-bearing, fossiliferous limestone typically 100-115m. thick forming the Springfield Plateau across the tri-state region of northwestern Arkansas, southwestern Missouri, and northeastern Oklahoma. The Boone represents the maximum flooding, highstand, and regressive intervals of a single, third order transgressive-regressive carbonate cycle bounded by regional unconformities. Two types of chert occur in this formation, and provide the basis for subdivision of the Boone into informal lower and upper members in northern Arkansas. The lower Boone represents early Osagean maximum flooding conditions and consists of calcisiltites with interbedded dark, nodular chert. This chert exhibits compaction phenomena and shrinkage fractures, indicating a penecontemporaneous origin from reorganization of silica immediately below the sediment water interface prior to lithification of the carbonate sediments (Manger et al. 1988a). The upper Boone represents late Osagean highstand and regression and consists primarily of carbonate grainstones and packstones (Shelby 1986). This interval contains white, later diagenetic chert, interpreted as a groundwater phenomenon in which silica has replaced lithified carbonate along its bedding planes, replicating the fabric of the limestone (Manger and Shelby 2000). This later diagenetic chert replacement favors the finer grained intervals and replicates the fabric of the limestone being replaced. Previous studies have shown that the penecontemporaneous chert typically comprises 40-50% of the lower Boone interval, while the later diagenetic chert contribution to the upper Boone ranges from 30-95% (Liner 1979). Understanding chert development is unsettled, and has been the subject of debate, primarily involving the source of the silica producing the chert, and the mode of formation of the chert-bearing intervals. Geochemical analyses suggest a volcanic rather than biogenic source for the silica in the Boone Formation

Practical risk assessment of the relaxation of LOM protection settings in NIE networks' distribution system

This paper presents methodology, experience and practical outcomes of the risk assessment-based revision of Loss-OfMains (LOM) protection settings in NIE Networks’ distribution system. An investigative project has been undertaken by the authors to revise the current LOM practice as recommended by the G59/1/NI regulation, and to propose the settings which would meet the all-Ireland transmission system stability criteria. It is also important to ensure that any increased personal risk is realistically quantified and satisfies the Health and Safety requirements. Both aspects (i.e. LOM protection stability and sensitivity) are covered in the paper. The results and observations included in the paper aim to provide the means and supporting evidence for achieving best compromise in the revision of LOM protection settings

Performance Evaluation of Judgmental Directional Exchange Rate Predictions

Cataloged from PDF version of article.A procedure is proposed for examining different aspects of performance for judgemental directional probability predictions of exchange rate movements. In particular, a range of new predictive performance measures is identified to highlight specific expressions of strengths and weaknesses in judgemental directional forecasts. Proposed performance qualifiers extend the existing accuracy measures, enabling detailed comparisons of probability forecasts with ex-post empirical probabilities that are derived from changes in the logarithms of the series. This provides a multi-faceted evaluation that is straightforward for practitioners to implement, while affording the flexibility of being used in situations where the time intervals between the predictions have variable lengths. The proposed procedure is illustrated via an application to a set of directional probability exchange rate forecasts for the US Dollar/Swiss Franc from 23/7/96 to 7/12/99 and the findings are discussed. D 2005 International Institute of Forecasters. Published by Elsevier B.V. All rights reserved