4,079 research outputs found
Combining gravity with the forces of the standard model on a cosmological scale
We prove the existence of a spectral resolution of the Wheeler-DeWitt
equation when the underlying spacetime is a Friedman universe with flat spatial
slices and where the matter fields are comprised of the strong interaction,
with \SU(3) replaced by a general \SU(n), , and the electro-weak
interaction. The wave functions are maps from to a subspace of the
antisymmetric Fock space, and one noteworthy result is that, whenever the
electro-weak interaction is involved, the image of an eigenfunction is in
general not one dimensional, i.e., in general it makes no sense specifying a
fermion and looking for an eigenfunction the range of which is contained in the
one dimensional vector space spanned by the fermion.Comment: 53 pages, v6: some typos correcte
Expansion of pinched hypersurfaces of the Euclidean and hyperbolic space by high powers of curvature
We prove convergence results for expanding curvature flows in the Euclidean
and hyperbolic space. The flow speeds have the form , where and
is a positive, strictly monotone and 1-homogeneous curvature function. In
particular this class includes the mean curvature . We prove that a
certain initial pinching condition is preserved and the properly rescaled
hypersurfaces converge smoothly to the unit sphere. We show that an example due
to Andrews-McCoy-Zheng can be used to construct strictly convex initial
hypersurfaces, for which the inverse mean curvature flow to the power
loses convexity, justifying the necessity to impose a certain pinching
condition on the initial hypersurface.Comment: 18 pages. We included an example for the loss of convexity and
pinching. In the third version we dropped the concavity assumption on F.
Comments are welcom
An Analysis of the Influence of Age and Ionizing Radiation on Cognitive Performance
This thesis was designed to study whether age has a significant effect on cognitive test results among persons exposed to ionizing radiation. The data for this investigation came from the fourth year of a 1995-98 longitudinal study of subjects exposed to radiation from the 1986 Chernobyl, Ukraine, nuclear power plant accident. Accuracy and efficiency scores from four cognitive tests taken by 84 Ukrainian volunteers were divided into two age groups and three radiation dosage groups for analysis. The results of this study found that decrements in human performance on tasks involving spatial processing increase with age in persons who have been exposed to ionizing radiation, but only in efficiency scores. However, no significant age/radiation dose interaction was evident from the ANOVA tests
The impact of a parent-child pre-kindergarten program on the parent involvement perceptions, attitudes and practices of primary teachers in the Omaha public schools.
THE IMPACT OF A PARENT-CHILD PRE-KINDERGARTEN PROGRAM ON THE PARENT INVOLVEMENT PERCEPTIONS, AITITUDES AND PRACTICES OF PRIMARY TEACHERS IN THE OMAHA PUBLIC SCHOOLS This study is a causal-comparative examination of the impact of a pre-kindergarten program with a mandatory parent involvement component on primary teachers\u27 perceptions, practices and attitudes toward parent involvement in a public school district located in a metropolitan area. A 56 question survey, based upon one from the publication Hopkins Survey of Schools and Family Connections, Questionnaires for Teachers, Parents and Students, was sent to 285 primary teachers of kindergarten, first, second and third grades. The survey was self-reporting with guaranteed anonymity. Independent variables included the presence of a pre-kindergarten program and the grade level taught. Dependent variables included perceptions, practices and attitudes towards parent involvement. Both one-way and two-way analyses of variance were run to examine the variables. The results of the survey indicated that the presence of a Parent-Child Pre-Kindergarten currently has no impact on primary teachers\u27 perceptions, attitudes and practices of parent involvement in the Omaha Public School District. Differences were found by grade level taught in the practices teachers use to involve parents. Kindergarten teachers showed a higher use of parent involvement practices than first, second or third grade teachers. No difference was seen in the grade level taught in either perceptions or attitudes. Over all, the survey indicated that primary teachers perceived parent involvement as an important part of the school curriculum. However, teachers showed more unity than diversity in their perceptions, attitudes and practices of parent involvement regardless of the presence of a Parent-Child Pre-Kindergarten program within a school building
Quantum cosmological Friedman models with a massive Yang-Mills field
We prove the existence of a spectral resolution of the Wheeler-DeWitt
equation when the matter field is provided by a massive Yang-Mills field. The
resolution is achieved by first solving the free eigenvalue problem for the
gravitational field and then the constrained eigenvalue problem for the
Yang-Mills field. In the latter case the mass of the Yang-Mills field assumes
the role of the eigenvalue.Comment: 16 pages, v3: typos corrected, final version, to appear in CQ
Tribology of Skin: Review and Analysis of Experimental Results for the Friction Coefficient of Human Skin
In this review, we discuss the current knowledge on the tribology of human skin and present an analysis of the available experimental results for skin friction coefficients. Starting with an overview on the factors influencing the friction behaviour of skin, we discuss the up-to-date existing experimental data and compare the results for different anatomical skin areas and friction measurement techniques. For this purpose, we also estimated and analysed skin contact pressures applied during the various friction measurements. The detailed analyses show that substantial variations are a characteristic feature of friction coefficients measured for skin and that differences in skin hydration are the main cause thereof, followed by the influences of surface and material properties of the contacting materials. When the friction coefficients of skin are plotted as a function of the contact pressure, the majority of the literature data scatter over a wide range that can be explained by the adhesion friction model. The case of dry skin is reflected by relatively low and pressure-independent friction coefficients (greater than 0.2 and typically around 0.5), comparable to the dry friction of solids with rough surfaces. In contrast, the case of moist or wet skin is characterised by significantly higher (typically >1) friction coefficients that increase strongly with decreasing contact pressure and are essentially determined by the mechanical shear properties of wet skin. In several studies, effects of skin deformation mechanisms contributing to the total friction are evident from friction coefficients increasing with contact pressure. However, the corresponding friction coefficients still lie within the range delimited by the adhesion friction model. Further research effort towards the analysis of the microscopic contact area and mechanical properties of the upper skin layers is needed to improve our so far limited understanding of the complex tribological behaviour of human ski
Intrinsic time gravity and the Lichnerowicz-York equation
We investigate the effect on the Hamiltonian structure of general relativity
of choosing an intrinsic time to fix the time slicing. 3-covariance with
momentum constraint is maintained, but the Hamiltonian constraint is replaced
by a dynamical equation for the trace of the momentum. This reveals a very
simple structure with a local reduced Hamiltonian. The theory is easily
generalised; in particular, the square of the Cotton-York tensor density can be
added as an extra part of the potential while at the same time maintaining the
classic 2 + 2 degrees of freedom. Initial data construction is simple in the
extended theory; we get a generalised Lichnerowicz-York equation with nice
existence and uniqueness properties. Adding standard matter fields is quite
straightforward.Comment: 4 page
Enabling EASEY deployment of containerized applications for future HPC systems
The upcoming exascale era will push the changes in computing architecture
from classical CPU-based systems in hybrid GPU-heavy systems with much higher
levels of complexity. While such clusters are expected to improve the
performance of certain optimized HPC applications, it will also increase the
difficulties for those users who have yet to adapt their codes or are starting
from scratch with new programming paradigms. Since there are still no
comprehensive automatic assistance mechanisms to enhance application
performance on such systems, we are proposing a support framework for future
HPC architectures, called EASEY (Enable exASclae for EverYone). The solution
builds on a layered software architecture, which offers different mechanisms on
each layer for different tasks of tuning. This enables users to adjust the
parameters on each of the layers, thereby enhancing specific characteristics of
their codes. We introduce the framework with a Charliecloud-based solution,
showcasing the LULESH benchmark on the upper layers of our framework. Our
approach can automatically deploy optimized container computations with
negligible overhead and at the same time reduce the time a scientist needs to
spent on manual job submission configurations.Comment: International Conference on Computational Science ICCS2020, 13 page
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