5,410 research outputs found
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
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
Correlating Student Beliefs With Student Learning Using The Colorado Learning Attitudes about Science Survey
A number of instruments have been designed to probe the variety of attitudes, beliefs, expectations, and epistemological frames taught in our introductory physics courses. Using a newly developed instrument -- the Colorado Learning Attitudes about Science Survey (CLASS)[1] -- we examine the relationship between students' beliefs about physics and other educational outcomes, such as conceptual learning and student retention. We report results from surveys of over 750 students in a variety of courses, including several courses modified to promote favorable beliefs about physics. We find positive correlations between particular student beliefs and conceptual learning gains, and between student retention and favorable beliefs in select categories. We also note the influence of teaching practices on student beliefs
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._
Introduction of CAA into a mathematics course for technology students to address a change in curriculum requirements
The mathematical requirements for engineering, science and technology students has been debated for many years and concern has been expressed about the mathematical preparedness of students entering higher education. This paper considers a mathematics course that has been specifically designed to address some of these issues for technology education students. It briefly chronicles the changes that have taken place over its lifetime and evaluates the introduction of Computer Assisted Assessment (CAA) into a course already being delivered using Computer Aided Learning (CAL).
Benefits of CAA can be categorised into four main areas.
1. Educational â achieved by setting short, topic related, assessments, each of which has to be passed, thereby increasing curriculum coverage.
2. Students â by allowing them to complete assessments at their own pace removing the stress of the final examination.
3. Financial â increased income to the institution, by broadening access to the course. Improved retention rate due to self-paced learning.
4. Time â staff no longer required to set and mark exams.
Most students preferred this method of assessment to traditional exams, because it increased confidence and reduced stress levels. Self-paced working, however, resulted in a minority of students not completing the tests by the deadline
Lowering of the Kinetic Energy in Interacting Quantum Systems
Interactions never lower the ground state kinetic energy of a quantum system.
However, at nonzero temperature, where the system occupies a thermal
distribution of states, interactions can reduce the kinetic energy below the
noninteracting value. This can be demonstrated from a first order weak coupling
expansion. Simulations (both variational and restricted path integral Monte
Carlo) of the electron gas model and dense hydrogen confirm this and show that
in contrast to the ground state case, at nonzero temperature the population of
low momentum states can be increased relative to the free Fermi distribution.
This effect is not seen in simulations of liquid He-3.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett., June, 200
Variational Density Matrix Method for Warm Condensed Matter and Application to Dense Hydrogen
A new variational principle for optimizing thermal density matrices is
introduced. As a first application, the variational many body density matrix is
written as a determinant of one body density matrices, which are approximated
by Gaussians with the mean, width and amplitude as variational parameters. The
method is illustrated for the particle in an external field problem, the
hydrogen molecule and dense hydrogen where the molecular, the dissociated and
the plasma regime are described. Structural and thermodynamic properties
(energy, equation of state and shock Hugoniot) are presented.Comment: 26 pages, 13 figures. submitted to Phys. Rev. E, October 199
Clinical surveillance of thrombotic microangiopathies in Scotland, 2003-2005
The prevalence, incidence and outcomes of haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopaenic purpura (TTP) are not well established in adults or children from prospective studies. We sought to identify both outcomes and current management strategies using prospective, national surveillance of HUS and TTP, from 2003 to 2005 inclusive. We also investigated the links between these disorders and factors implicated in the aetiology of HUS and TTP including infections, chemotherapy, and immunosuppression. Most cases of HUS were caused by verocytotoxin-producing Escherichia coli (VTEC), of which serotype O157 predominated, although other serotypes were identified. The list of predisposing factors for TTP was more varied although use of immunosuppressive agents and severe sepsis, were the most frequent precipitants. The study demonstrates that while differentiating between HUS and TTP is sometimes difficult, in most cases the two syndromes have quite different predisposing factors and clinical parameters, enabling clinical and epidemiological profiling for these disorders
The XMM-Newton EPIC X-ray Light Curve Analysis of WR 6
We obtained four pointings of over 100 ks each of the well-studied Wolf-Rayet
star WR 6 with the XMM-Newton satellite. With a first paper emphasizing the
results of spectral analysis, this follow-up highlights the X-ray variability
clearly detected in all four pointings. However, phased light curves fail to
confirm obvious cyclic behavior on the well-established 3.766 d period widely
found at longer wavelengths. The data are of such quality that we were able to
conduct a search for "event clustering" in the arrival times of X-ray photons.
However, we fail to detect any such clustering. One possibility is that X-rays
are generated in a stationary shock structure. In this context we favor a
co-rotating interaction region (CIR) and present a phenomenological model for
X-rays from a CIR structure. We show that a CIR has the potential to account
simultaneously for the X-ray variability and constraints provided by the
spectral analysis. Ultimately, the viability of the CIR model will require both
intermittent long-term X-ray monitoring of WR 6 and better physical models of
CIR X-ray production at large radii in stellar winds.Comment: to appear in Ap
Playing on the boundaries: a childhood across cultural and geographical lines
This is not a conventional paper. It is a personal narrative. It is subjective not only to its author but to the child-self of the author. It is not a detached academic look at a personal history. In fact it could be described more as âarchaeologicalâ than historical; an examination of what appears to be a random collection of fragments of a personal history, found in memory and artefacts of a childhood. The telling of the story is an attempt to understand the development and trajectory of an individual identity across geographical, cultural, and religious boundaries. It is not the whole story, but it gives the writer and the reader a few selected pieces of the full picture
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