149,373 research outputs found
Decay Modes of the Hoyle State in
Recent experimental results give an upper limit less than 0.043\% (95\% C.L.)
to the direct decay of the Hoyle state into 3 respect to the sequential
decay into {Be}+. We performed one and two-dimensional tunneling
calculations to estimate such a ratio and found it to be more than one order of
magnitude smaller than experiment depending on the range of the nuclear force.
This is within high statistics experimental capabilities. Our results can also
be tested by measuring the decay modes of high excitation energy states of
C where the ratio of direct to sequential decay might reach 10\% at
(C)=10.3 MeV. The link between a Bose Einstein Condensate (BEC) and
the direct decay of the Hoyle state is also addressed. We discuss a
hypothetical `Efimov state' at (C)=7.458 MeV, which would mainly
{\it sequentially} decay with 3 of {\it equal energies}: a
counterintuitive result of tunneling. Such a state, if it would exist, is at
least 8 orders of magnitude less probable than the Hoyle's, thus below the
sensitivity of recent and past experiments.Comment: 6 pages, 2 figures, accepted by Phys. Lett.
A Study of Anyon Statistics by Breit Hamiltonian Formalism
We study the anyon statistics of a dimensional Maxwell-Chern-Simons
(MCS) gauge theory by using a systemmetic metheod, the Breit Hamiltonian
formalism.Comment: 25 pages, LATE
G\"{o}del-type universes in f(R) gravity
The gravity theories provide an alternative way to explain the current
cosmic acceleration without a dark energy matter component. If gravity is
governed by a theory a number of issues should be reexamined in this
framework, including the violation of causality problem on nonlocal scale. We
examine the question as to whether the gravity theories permit
space-times in which the causality is violated. We show that the field
equations of these gravity theories do not exclude solutions with
breakdown of causality for a physically well-motivated perfect-fluid matter
content. We demonstrate that every perfect-fluid G\"{o}del-type solution of a
generic gravity satisfying the condition is necessarily
isometric to the G\"odel geometry, and therefore presents violation of
causality. This result extends a theorem on G\"{o}del-type models, which has
been established in the context of general relativity. We also derive an
expression for the critical radius (beyond which the causality is
violated) for an arbitrary theory, making apparent that the violation of
causality depends on both the gravity theory and the matter content. As
an illustration, we concretely take a recent gravity theory that is free
from singularities of the Ricci scalar and is cosmologically viable, and show
that this theory accommodates noncausal as well as causal G\"odel-type
solutions.Comment: 7 pages, V3: Version to appear in Phys. Rev. D (2009), typos
corrected, the generality of our main results is emphasized. The illustrative
character of a particular theory is also made explici
Transition Temperature of a Uniform Imperfect Bose Gas
We calculate the transition temperature of a uniform dilute Bose gas with
repulsive interactions, using a known virial expansion of the equation of
state. We find that the transition temperature is higher than that of an ideal
gas, with a fractional increase K_0(na^3)^{1/6}, where n is the density and a
is the S-wave scattering length, and K_0 is a constant given in the paper. This
disagrees with all existing results, analytical or numerical. It agrees exactly
in magnitude with a result due to Toyoda, but has the opposite sign.Comment: Email correspondence to [email protected] ; 2 pages using REVTe
Quantum dynamics of a qubit coupled with structured bath
The dynamics of an unbiased spin-boson model with Lorentzian spectral density
is investigated theoretically in terms of the perturbation theory based on a
unitary transformation. The non-equilibrium correlation function and
susceptibility are calculated for both the
off-resonance case and the on-resonance case
. The approach is checked by the Shiba's relation and the
sum rule. Besides, the coherent-incoherent transition point can be
determined, which has not been demonstrated for the structured bath by previous
authors up to our knowledge.Comment: 25 pages, 11 figure
Universality and itinerant ferromagnetism in rotating strongly interacting Fermi gases
We analytically determine the properties of three interacting fermions in a
harmonic trap subject to an external rotation. Thermodynamic quantities such as
the entropy and energy are calculated from the third order quantum virial
expansion. By parameterizing the solutions in the rotating frame we find that
the energy and entropy are universal for all rotations in the strongly
interacting regime. Additionally, we find that rotation suppresses the onset of
itinerant ferromagnetism in strongly interacting repulsive three-body systems.Comment: 5 pages with 3 figure
Packet narrowing and quantum entanglement in photoionization and photodissociation
The narrowing of electron and ion wave packets in the process of
photoionization is investigated, with the electron-ion recoil fully taken into
account. Packet localization of this type is directly related to entanglement
in the joint quantum state of electron and ion, and to Einstein-Podolsky-Rosen
localization. Experimental observation of such packet-narrowing effects is
suggested via coincidence registration by two detectors, with a fixed position
of one and varying position of the other. A similar effect, typically with an
enhanced degree of entanglement, is shown to occur in the case of
photodissociation of molecules
In vitro Culture of Several Rice Cultivars
Tissue culture methods have been established to regenerate certain rice (Oryza sativa L) cultivars, but regeneration of the rice cultivars widely grown in Arkansas has not been reported. This study has established an in vitroculture for the rice cultivars \u27Nortai\u27, \u27Starbonnet\u27, \u27Mars\u27, Tebonnet\u27, \u27Newbonnet\u27, and \u27Lemont\u27. Callus was induced in the dark at either 20 or 28 C from dehusked seeds cultured on Murashige and Skoog (MS) medium (Murashige and Skoog, 1962) containing 40 g L^-1 sucrose, 10 g L^1 agar, 0.5, 1.0, or 2.0 mg L^-1 1 2,4-dichlorophenoxyacetic acid (2,4-D) and adjusted to pH 5.7. After four weeks the calli were weighed, transferred onto MS medium containing no 2,4-D, and maintained in a 1 2-h photoperiod (65 uE m^-2 s^-1) at 25 ± 2 C to induce plant regeneration. Callus production was best when cultured on a medium containing 1.0 mg L^-1 2,4-D and incubated at 28 C. Plant regeneration was observed two to four weeks later. The percentage of calli regenerating platlets varied with the cultivar and the callus induction treatment. Callus induction at 20 C on a medium with a 2,4-D level less than 2.0 mg L^-1 enhanced the regenerability of most cultivars. Regenerates were transplanted to soil and grow normally to maturity. This system can be helpful in improving rice cultivars with tissue culture techniques such as somaclonal variant selection and somatic hybridization
- âŠ