80,454 research outputs found
Dispelling the Anthropic Principle from the Dimensionality Arguments
It is shown that in d=11 supergravity, under a very reasonable ansatz, the
nearly flat spacetime in which we are living must be 4-dimensional without
appealing to the Anthropic Principle. Can we dispel the Anthropic Principle
completely from cosmology?Comment: 7 pages, Essa
A fracture mechanics-based method for prediction of cracking of circular and elliptical concrete rings under restrained shrinkage
A new experimental method, utilizing elliptical ring specimens, is developed for assessing the likelihood of cracking and cracking age of concrete subject to restrained shrinkage. To investigate the mechanism of this new ring test, a fracture mechanics-based numerical approach is proposed to predict crack initiation in restrained concrete rings by using the R-curve method. It has been found that numerical results accord well with experimental results in terms of cracking ages for both circular and elliptical concrete rings, indicating that the proposed fracture mechanics-based numerical approach is reliable for analyzing cracking in concrete ring specimens subject to restrained condition.UK Engineering and Physical Sciences Research Council under the grant of EP/I031952/1, and the National Natural Science Foundation of China under the grant of NSFC 51121005/5110902
Intense terahertz laser fields on a two-dimensional electron gas with Rashba spin-orbit coupling
The spin-dependent density of states and the density of spin polarization of
an InAs-based two-dimensional electron gas with the Rashba spin-orbit coupling
under an intense terahertz laser field are investigated by utilizing the
Floquet states to solve the time-dependent Schr\"odinger equation.
It is found that both densities are strongly affected by the terahertz laser
field. Especially a terahertz magnetic moment perpendicular to the external
terahertz laser field in the electron gas is induced. This effect can be used
to convert terahertz electric signals into terahertz magnetic ones efficiently.Comment: 3 pages, 3 figures, a typo in Fig. 3(b) is correcte
Hawking Radiation of Dirac Particles in an Arbitrarily Accelerating Kinnersley Black Hole
Quantum thermal effect of Dirac particles in an arbitrarily accelerating
Kinnersley black hole is investigated by using the method of generalized
tortoise coordinate transformation. Both the location and the temperature of
the event horizon depend on the advanced time and the angles. The Hawking
thermal radiation spectrum of Dirac particles contains a new term which
represents the interaction between particles with spin and black holes with
acceleration. This spin-acceleration coupling effect is absent from the thermal
radiation spectrum of scalar particles.Comment: Revtex, 12pt, 16 pages, no figure, to appear in Gen. Rel. Grav. 34
(2002) N0.
Level sequence and splitting identification of closely-spaced energy levels by angle-resolved analysis of the fluorescence light
The angular distribution and linear polarization of the fluorescence light
following the resonant photoexcitation is investigated within the framework of
the density matrix and second-order perturbation theory. Emphasis has been
placed on "signatures" for determining the level sequence and splitting of
intermediate (partially) overlapping resonances, if analyzed as a function of
the photon energy of the incident light. Detailed computations within the
multiconfiguration Dirac-Fock method have been performed especially for the
photoexcitation and subsequent fluorescence emission of atomic sodium. A
remarkably strong dependence of the angular distribution and linear
polarization of the fluorescence emission is found upon the level
sequence and splitting of the intermediate overlapping resonances owing to their finite lifetime
(linewidth). We therefore suggest that accurate measurements of the angular
distribution and linear polarization might help identify the sequence and small
splittings of closely-spaced energy levels, even if they can not be
spectroscopically resolved.Comment: 9 pages, 7 figure
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