1,977,672 research outputs found
Source of CP Violation for the Baryon Asymmetry of the Universe
We give a description of why the existence of a fourth generation is likely
to provide enough CP violation for baryogenesis, and trace how this observation
came about. We survey the current experimental and theoretical pursuits and
outline a research agenda, touching upon unitarity violation and very heavy
chiral quarks, and comment on how the electroweak phase transition picture
might be altered.Comment: Invited talk presented at 2nd International Workshop on Dark Matter,
Dark Energy and Matter-antimatter Asymmetry, Hsinchu, Taiwan, November 5-6,
201
The Superscattering Matrix for Two Dimensional Black Holes
A consistent Euclidean semi classical calculation is given for the
superscattering operator in the RST model for states with a constant flux
of energy. The operator is CPT invariant. There is no loss of quantum
coherence when the energy flux is less than a critical rate and complete loss
when the energy flux is critical.Comment: 12 pages (R/94/4
On the discrepancies in the low energy neutron-deuteron breakup
In view of recent neutron-deuteron (nd) breakup data for neutron-neutron (nn)
and neutron-proton (np) quasi-free-scattering (QFS) arrangements and the large
discrepancy found between theoretical predictions and measured nn QFS cross
sections, we analyze the sensitivity of the QFS cross sections to different
partial wave components of the nucleon-nucleon (NN) interaction. We found that
the QFS cross section is strongly dominated by the 1S0 and 3S1-3D1
contributions. Because the standard three-nucleon force (3NF) only weakly
influence the QFS region, we conjecture, that it must be the nn 1S0 force
component which is responsible for the discrepancy in the nn QFS peak. A
stronger 1S0 nn force is required to bring theory and data into agreement. Such
an increased strength of the nn interaction will, however, not help to explain
the nd breakup symmetric-space-star (SST) discrepancy. Further experimental
cross-checkings are required.Comment: 17 pages, 10 figure
Investigation of Micro Porosity Sintered wick in Vapor Chamber for Fan Less Design
Micro Porosity Sintered wick is made from metal injection molding processes,
which provides a wick density with micro scale. It can keep more than 53 %
working fluid inside the wick structure, and presents good pumping ability on
working fluid transmission by fine infiltrated effect. Capillary pumping
ability is the important factor in heat pipe design, and those general
applications on wick structure are manufactured with groove type or screen
type. Gravity affects capillary of these two types more than a sintered wick
structure does, and mass heat transfer through vaporized working fluid
determines the thermal performance of a vapor chamber. First of all, high
density of porous wick supports high transmission ability of working fluid. The
wick porosity is sintered in micro scale, which limits the bubble size while
working fluid vaporizing on vapor section. Maximum heat transfer capacity
increases dramatically as thermal resistance of wick decreases. This study on
permeability design of wick structure is 0.5 - 0.7, especially permeability (R)
= 0.5 can have the best performance, and its heat conductivity is 20 times to a
heat pipe with diameter (Phi) = 10mm. Test data of this vapor chamber shows
thermal performance increases over 33 %.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Unified models of the cosmological dark sector
We model the cosmological substratum by a viscous fluid that is supposed to
provide a unified description of the dark sector and pressureless baryonic
matter. In the homogeneous and isotropic background the \textit{total} energy
density of this mixture behaves as a generalized Chaplygin gas. The
perturbations of this energy density are intrinsically non-adiabatic and source
relative entropy perturbations. The resulting baryonic matter power spectrum is
shown to be compatible with the 2dFGRS and SDSS (DR7) data. A joint statistical
analysis, using also Hubble-function and supernovae Ia data, shows that,
different from other studies, there exists a maximum in the probability
distribution for a negative present value of the
deceleration parameter. Moreover, different from other approaches, the unified
model presented here favors a matter content that is of the order of the
baryonic matter abundance suggested by big-bang nucleosynthesis.Comment: 4 pages, 1 figure, submitted to the Proceedings of the Spanish
Relativity Meeting - ERE 2010, Granada, September 6 - September 10, 201
van Vleck determinants: geodesic focussing and defocussing in Lorentzian spacetimes
The van Vleck determinant is an ubiquitous object, arising in many physically
interesting situations such as: (1) WKB approximations to quantum time
evolution operators and Green functions. (2) Adiabatic approximations to heat
kernels. (3) One loop approximations to functional integrals. (4) The theory of
caustics in geometrical optics and ultrasonics. (5) The focussing and
defocussing of geodesic flows in Riemannian manifolds. While all of these
topics are interrelated, the present paper is particularly concerned with the
last case and presents extensive theoretical developments that aid in the
computation of the van Vleck determinant associated with geodesic flows in
Lorentzian spacetimes. {\sl A fortiori} these developments have important
implications for the entire array of topics indicated. PACS: 04.20.-q,
04.20.Cv, 04.60.+n. To appear in Physical Review D47 (1993) 15 March.Comment: plain LaTeX, 18 page
Two-stage coaxial gas compressor
Compressor raises pressure of gases from low ambient supply during space experiments by a system of low weight, size, and power input. Dc rotary-torque motor and ball-screw drive shaft activate first and second stage of compressor, utilizing inertia forces to operate check valves
- …