558 research outputs found
Summary of electric vehicle dc motor-controller tests
The differences in the performance of dc motors are evaluated when operating with chopper type controllers, and when operating on direct current. The interactions between the motor and the controller which cause these differences are investigated. Motor-controlled tests provided some of the data the quantified motor efficiency variations for both ripple free and chopper modes of operation
A Note on The Influence of Soil Parent Material on Northern Red OAK Specific Gravity
Soil parent material was found to affect the specific gravity of northern red oak wood (Quercus rubra L.). The unextracted specific gravity of wood grown on limestone soils was 0.597 and that of wood grown on sandstone soils was 0.581. Site quality within a soil type had no significant effect. The relationship was independent of both rate of growth and latewood percentage
Quantum Pair Creation of Soliton Domain Walls
A large body of experimental evidence suggests that the decay of the false
vacuum, accompanied by quantum pair creation of soliton domain walls, can occur
in a variety of condensed matter systems. Examples include nucleation of charge
soliton pairs in density waves [eg. J. H. Miller, Jr. et al., Phys. Rev. Lett.
84, 1555 (2000)] and flux soliton pairs in long Josephon junctions. Recently,
Dias and Lemos [J. Math. Phys. 42, 3292 (2001)] have argued that the mass
of the soliton should be interpreted as a line density and a surface density,
respectively, for (2+1)-D and (3+1)-D systems in the expression for the pair
production rate. As the transverse dimensions are increased and the total mass
(energy) becomes large, thermal activation becomes suppressed, so quantum
processes can dominate even at relatively high temperatures. This paper will
discuss both experimental evidence and theoretical arguments for the existence
of high-temperature collective quantum phenomena
T violation and the unidirectionality of time
An increasing number of experiments at the Belle, BNL, CERN, DA{\Phi}NE and
SLAC accelerators are confirming the violation of time reversal invariance (T).
The violation signifies a fundamental asymmetry between the past and future and
calls for a major shift in the way we think about time. Here we show that
processes which violate T symmetry induce destructive interference between
different paths that the universe can take through time. The interference
eliminates all paths except for two that represent continuously forwards and
continuously backwards time evolution. Evidence from the accelerator
experiments indicates which path the universe is effectively following. This
work may provide fresh insight into the long-standing problem of modeling the
dynamics of T violation processes. It suggests that T violation has previously
unknown, large-scale physical effects and that these effects underlie the
origin of the unidirectionality of time. It may have implications for the
Wheeler-DeWitt equation of canonical quantum gravity. Finally it provides a
view of the quantum nature of time itself.Comment: 24 pages, 5 figures. Final version accepted for publishing in
Foundations of Physics. The final publication is available at
http://www.springerlink.com/content/y3h4174jw2w78322
Quantum Tunneling Effect in Oscillating Friedmann Cosmology
It is shown that the tunneling effect in quantum cosmology is possible not
only at the very beginning or the very end of the evolution, but also at the
moment of maximum expansion of the universe. A positive curvature expanding
Friedmann universe changes its state of evolution spontaneously and completely,
{\it without} any changes in the matter content, avoiding recollapse, and
falling into oscillations between the nonzero values of the scale factor. On
the other hand, an oscillating nonsingular universe can tunnel spontaneously to
a recollapsing regime. The probability of such kind of tunneling is given
explicitly. It is inversely related to the amount of nonrelativistic matter
(dust), and grows from a certain fixed value to unity if the negative
cosmological constant approaches zero.Comment: 18 pages Latex + 2 figures available by fax upon reques
Do UK universities communicate their brands effectively through their websites?
This paper attempts to explore the effectiveness of UK universities’ websites. The area of branding in higher education has received increasing academic investigation, but little work has researched how universities demonstrate their brand promises through their websites. The quest to differentiate through branding can be challenging in the university context, however. It is argued that those institutions that have a strong distinctive image will be in a better position to face a changing future. Employing a multistage methodology, the web pages of twenty UK universities were investigated by using a combination of content and multivariable analysis. Results indicated ‘traditional values’ such as teaching and research were often well communicated in terms of online brand but ‘emotional values’ like social responsibility and the universities’ environments were less consistently communicated, despite their increased topicality. It is therefore suggested that emotional values may offer a basis for possible future online differentiation
Spontaneous Creation of Inflationary Universes and the Cosmic Landscape
We study some gravitational instanton solutions that offer a natural
realization of the spontaneous creation of inflationary universes in the brane
world context in string theory. Decoherence due to couplings of higher
(perturbative) modes of the metric as well as matter fields modifies the
Hartle-Hawking wavefunction for de Sitter space. Generalizing this new
wavefunction to be used in string theory, we propose a principle in string
theory that hopefully will lead us to the particular vacuum we live in, thus
avoiding the anthropic principle. As an illustration of this idea, we give a
phenomenological analysis of the probability of quantum tunneling to various
stringy vacua. We find that the preferred tunneling is to an inflationary
universe (like our early universe), not to a universe with a very small
cosmological constant (i.e., like today's universe) and not to a 10-dimensional
uncompactified de Sitter universe. Such preferred solutions are interesting as
they offer a cosmological mechanism for the stabilization of extra dimensions
during the inflationary epoch.Comment: 52 pages, 7 figures, 1 table. Added discussion on supercritical
string vacua, added reference
Gametófitos de Pleurosorus papaverifolius (Kunze) Fée (Aspleniaceae) y Cheilanthes glauca (Cav.) Mett. (Pteridaceae), dos helechos rupícolas sudamericanos
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