9,799 research outputs found
Active optical clock based on four-level quantum system
Active optical clock, a new conception of atomic clock, has been proposed
recently. In this report, we propose a scheme of active optical clock based on
four-level quantum system. The final accuracy and stability of two-level
quantum system are limited by second-order Doppler shift of thermal atomic
beam. To three-level quantum system, they are mainly limited by light shift of
pumping laser field. These limitations can be avoided effectively by applying
the scheme proposed here. Rubidium atom four-level quantum system, as a typical
example, is discussed in this paper. The population inversion between
and states can be built up at a time scale of s.
With the mechanism of active optical clock, in which the cavity mode linewidth
is much wider than that of the laser gain profile, it can output a laser with
quantum-limited linewidth narrower than 1 Hz in theory. An experimental
configuration is designed to realize this active optical clock.Comment: 5 page
Low-momentum Pion Enhancement Induced by Chiral Symmetry Restoration
The thermal and nonthermal pion production by sigma decay and its relation
with chiral symmetry restoration in a hot and dense matter are investigated.
The nonthermal decay into pions of sigma mesons which are popularly produced in
chiral symmetric phase leads to a low-momentum pion enhancement as a possible
signature of chiral phase transition at finite temperature and density.Comment: 3 pages, 2 figure
Patterns Formation in Drying Drops of Blood
The drying of a drop of human blood exhibits coupled physical mechanisms,
such as Marangoni flow, evaporation and wettability. The final stage of a whole
blood drop evaporation reveals regular patterns with a good reproducibility for
a healthy person. Other experiments on anaemic and hyperlipidemic people were
performed, and different patterns were revealed. The flow motion inside the
blood drop is observed and analyzed with the use of a digital camera: the
influence of the red blood cells (RBCs) motion is revealed at the drop
periphery as well as its consequences on the final stage of drying. The
mechanisms which lead to the final pattern of the dried blood drops are
presented and explained on the basis of fluid mechanics in conjunction with the
principles of haematology. The blood drop evaporation process is evidenced to
be driven only by Marangoni flow. The same axisymetric pattern formation is
observed, and can be forecast for different blood drop diameters. The
evaporation mass flux can be predicted with a good agreement, assuming only the
knowledge of the colloids mass concentration.Comment: 1 page + conference APS 2011 (1 movie for the gallery + 1 movie for
ArXiv
Thermal and Nonthermal Pion Enhancements with Chiral Symmetry Restoration
The pion production by sigma decay and its relation with chiral symmetry
restoration in a hot and dense matter are investigated in the framework of the
Nambu-Jona-Lasinio model. The decay rate for the process sigma -> 2pion to the
lowest order in a 1/N_c expansion is calculated as a function of temperature T
and chemical potential mu. The thermal and nonthermal enhancements of pions
generated by the decay before and after the freeze-out present only in the
crossover region of the chiral symmetry transition. The strongest nonthermal
enhancement is located in the vicinity of the endpoint of the first-order
transition.Comment: Latex2e, 12 pages, 8 Postscript figures, submitted to Phys. Rev.
An Analytic Solution of Hydrodynamic Equations with Source Terms in Heavy Ion Collisions
The energy and baryon densities in heavy ion collisions are estimated by
analytically solving a 1+1 dimensional hydrodynamical model with source terms.
Particularly, a competition between the energy and baryon sources and the
expansion of the system is discussed in detail.Comment: LaTeX2e, 7 pages, 4 postscript figures, submitted to Int. J. Mod.
Phys.
Liquid Crystal-Solid Interface Structure at the Antiferroelectric-Ferroelectric Phase Transition
Total Internal Reflection (TIR) is used to probe the molecular organization
at the surface of a tilted chiral smectic liquid crystal at temperatures in the
vicinity of the bulk antiferroelectric-ferroelectric phase transition. Data are
interpreted using an exact analytical solution of a real model for
ferroelectric order at the surface. In the mixture T3, ferroelectric surface
order is expelled with the bulk ferroelectric-antiferroelectric transition. The
conditions for ferroelectric order at the surface of an antiferroelectric bulk
are presented
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