1,068 research outputs found
Quintessential Phenomena in Higher Dimensional Space Time
The higher dimensional cosmology provides a natural setting to treat, at a
classical level, the cosmological effects of vacuum energy. Here we discuss two
situations where starting with an ordinary matter field without any equation of
state we end up with a Chaplygin type of gas apparently as a consequence of
extra dimensions. In the second case we study the quintessential phenomena in
higher dimensional spacetime with the help of a Chaplygin type of matter field.
The first case suffers from the disqualification that no dimensional reduction
occurs, which is, however, rectified in the second case. Both the models show
the sought after feature of occurrence of \emph{flip} in the rate of expansion.
It is observed that with the increase of dimensions the occurrence of
\emph{flip} is delayed for both the models, more in line with current
observational demands. Interestingly we see that depending on some initial
conditions our model admits QCDM, CDM and also Phantom like evolution
within a unified framework. Our solutions are general in nature in the sense
that when the extra dimensions are switched off the known 4D model is
recovered.Comment: 17 Pages, 7 figure
Embeddings in Spacetimes Sourced by Scalar Fields
The extension of the Campbell-Magaard embedding theorem to general relativity
with minimally-coupled scalar fields is formulated and proven. The result is
applied to the case of a self-interacting scalar field for which new embeddings
are found, and to Brans-Dicke theory. The relationship between Campbell-Magaard
theorem and the general relativity, Cauchy and initial value problems is
outlined.Comment: RevTEX (11 pages)/ To appear in the Journal of Mathematical Physic
The Structure of the Big Bang from Higher-Dimensional Embeddings
We give relations for the embedding of spatially-flat
Friedmann-Robertson-Walker cosmological models of Einstein's theory in flat
manifolds of the type used in Kaluza-Klein theory. We present embedding
diagrams that depict different 4D universes as hypersurfaces in a higher
dimensional flat manifold. The morphology of the hypersurfaces is found to
depend on the equation of state of the matter. The hypersurfaces possess a
line-like curvature singularity infinitesimally close to the
3-surface, where is the time expired since the big bang. The family of
timelike comoving geodesics on any given hypersurface is found to have a
caustic on the singular line, which we conclude is the 5D position of the
point-like big bang.Comment: 11 pages, 5 figures, revtex4, accepted in Class. Quant. Gra
Low Background Signal Readout Electronics for the MAJORANA DEMONSTRATOR
The MAJORANA DEMONSTRATOR is a planned 40 kg array of Germanium detectors
intended to demonstrate the feasibility of constructing a tonne-scale
experiment that will seek neutrinoless double beta decay () in
. Such an experiment would require backgrounds of less than 1
count/tonne-year in the 4 keV region of interest around the 2039 keV Q-value of
the decay. Designing low-noise electronics, which must be placed
in close proximity to the detectors, presents a challenge to reaching this
background target. This paper will discuss the MAJORANA collaboration's
solutions to some of these challenges
Search for Pauli Exclusion Principle Violating Atomic Transitions and Electron Decay with a P-type Point Contact Germanium Detector
A search for Pauli-exclusion-principle-violating K-alpha electron transitions
was performed using 89.5 kg-d of data collected with a p-type point contact
high-purity germanium detector operated at the Kimballton Underground Research
Facility. A lower limit on the transition lifetime of 5.8x10^30 seconds at 90%
C.L. was set by looking for a peak at 10.6 keV resulting from the x-ray and
Auger electrons present following the transition. A similar analysis was done
to look for the decay of atomic K-shell electrons into neutrinos, resulting in
a lower limit of 6.8x10^30 seconds at 90 C.L. It is estimated that the MAJORANA
DEMONSTRATOR, a 44 kg array of p-type point contact detectors that will search
for the neutrinoless double-beta decay of 76-Ge, could improve upon these
exclusion limits by an order of magnitude after three years of operation
Economic Feasibility of Passive Strate gies for Energy Efficient Envelopes of Mass-Built Housing in Hot -Dry Climate
The authors thank the Autonomous University of Baja California and the Master and Doctorate program in Architecture, Urbanism and Design (MyDAUD) for the support provided to carry out this study, the National Council of Science and Technology (CONACyT) for the scholarship provided for the completion of master’s degree studies, as well as the RUBA construction company.The building and construction industry represents 36% of the world’s final energy use and 39% of carbon emissions, while the residential sector is responsible for 22% of total energy consumption and 17% of carbon emissions. Therefore, energy consumption reduction measures are required by this sector, without affecting the living conditions of its occupants. In Baja California, Mexico, the more commonly used construction systems in mass-built housing are concrete block walls and cast in place insulated reinforced concrete roof deck. These systems negatively affect comfort conditions, especially in hot summer periods, and therefore increase energy consumption, particularly in areas with an hot-dry climate, such as Mexicali, Baja California. The objective of this article is to determine the cost-benefit of two passive design strategies applied in the housing envelope, which are thermal insulation and ventilated facade. A commercial model of mass-built housing was taken as a benchmark case. Building energy simulations were carried out with the Design Builder® program, whereby the performance of the house was evaluated without passive design strategies (benchmark case) and with applied strategies, that is, variations in thickness and position of the materials that make up the layers of the walls and roof. Additionally, the net present value (NPV) criterion was used to obtain the costs and benefits of the design strategies. The results show the differences in cooling demand, indoor operative temperature, and the total costs, in Mexican pesos, of the application of the strategies; the results show that there are significant energy savings, which contribute to reducing carbon emissions to the environment and provide economic savings for the user
- …