1,438 research outputs found
Relative biological effectiveness of fast neutrons compared with X-rays: Prenatal mortality in the mouse
The effects of fission neutrons and of X-rays on the mouse zygote are discussed. Seven-week-old virgin mice were allowed a 12-hour mating opportunity beginning at 7:00 P.M. Between 1:30 and 4:00 P.M., except where indicated otherwise, the females which had mated (vaginal plug) during the night were either irradiated or sham-irradiated. At the time of irradiation the zygotes were in a pronuclear stage. Sixteen days later the mice were killed and the uteri dissected. The number of dead embryos, live embryos, and gross anomalies were determined. Dead embryos were classified as to stage of development
In-medium Yang-Mills equations: a derivation and canonical quantization
The equations for Yang-Mills field in a medium are derived in a linear
approximation with respect to the gauge coupling parameter and the external
field. The obtained equations closely resemble the macroscopic Maxwell
equations. A canonical quantization is performed for a family of Fermi-like
gauges in the case of constant and diagonal (in the group indices) tensors of
electric permittivity and magnetic permeability. The physical subspace is
defined and the gauge field propagator is evaluated for a particular choice of
the gauge. The propagator is applied for evaluation of the cross-section of
ellastic quark scattering in the Born approximation. Possible applications to
Cherenkov-type gluon radiation are commented briefly.Comment: 27 pages, references added, version extended with emphasis on
non-Abelian gauge group impact on medium characteristics. To appear in J.
Phys.
Modification of radiation pressure due to cooperative scattering of light
Cooperative spontaneous emission of a single photon from a cloud of N atoms
modifies substantially the radiation pressure exerted by a far-detuned laser
beam exciting the atoms. On one hand, the force induced by photon absorption
depends on the collective decay rate of the excited atomic state. On the other
hand, directional spontaneous emission counteracts the recoil induced by the
absorption. We derive an analytical expression for the radiation pressure in
steady-state. For a smooth extended atomic distribution we show that the
radiation pressure depends on the atom number via cooperative scattering and
that, for certain atom numbers, it can be suppressed or enhanced.Comment: 8 pages, 2 Figure
Microwave emission from a crystal of molecular magnets -- The role of a resonant cavity
We discuss the effects caused by a resonant cavity around a sample of a
magnetic molecular crystal (such as Mn-Ac), when a time dependent
external magnetic field is applied parallel to the easy axis of the crystal. We
show that the back action of the cavity field on the sample significantly
increases the possibility of microwave emission. This radiation process can be
supperradiance or a maser-like effect, depending on the strength of the
dephasing. Our model provides further insight to the theoretical understanding
of the bursts of electromagnetic radiation observed in recent experiments
accompanying the resonant quantum tunneling of magnetization. The experimental
findings up to now can all be explained as being a maser effect rather than
superradiance. The results of our theory scale similarly to the experimental
findings, i.e., with increasing sweep rate of the external magnetic field, the
emission peaks are shifted towards higher field values.Comment: 12 pages, 6 figures. To appear in Phys. Rev.
Mean field and corrections for the Euclidean Minimum Matching problem
Consider the length of the minimum matching of N points in
d-dimensional Euclidean space. Using numerical simulations and the finite size
scaling law , we obtain
precise estimates of for . We then consider
the approximation where distance correlations are neglected. This model is
solvable and gives at an excellent ``random link'' approximation to
. Incorporation of three-link correlations further improves
the accuracy, leading to a relative error of 0.4% at d=2 and 3. Finally, the
large d behavior of this expansion in link correlations is discussed.Comment: source and one figure. Submitted to PR
Dynamical evolution of boson stars in Brans-Dicke theory
We study the dynamics of a self-gravitating scalar field solitonic object
(boson star) in the Jordan-Brans-Dicke (BD) theory of gravity. We show
dynamical processes of this system such as (i) black hole formation of
perturbed equilibrium configuration on an unstable branch; (ii) migration of
perturbed equilibrium configuration from the unstable branch to stable branch;
(iii) transition from excited state to a ground state. We find that the
dynamical behavior of boson stars in BD theory is quite similar to that in
general relativity (GR), with comparable scalar wave emission. We also
demonstrate the formation of a stable boson star from a Gaussian scalar field
packet with flat gravitational scalar field initial data. This suggests that
boson stars can be formed in the BD theory in much the same way as in GR.Comment: 13 pages by RevTeX, epsf.sty, 16 figures, comments added, refs
updated, to appear in Phys. Rev.
Non-perturbative Landau gauge and infrared critical exponents in QCD
We discuss Faddeev-Popov quantization at the non-perturbative level and show
that Gribov's prescription of cutting off the functional integral at the Gribov
horizon does not change the Schwinger-Dyson equations, but rather resolves an
ambiguity in the solution of these equations. We note that Gribov's
prescription is not exact, and we therefore turn to the method of stochastic
quantization in its time-independent formulation, and recall the proof that it
is correct at the non-perturbative level. The non-perturbative Landau gauge is
derived as a limiting case, and it is found that it yields the Faddeev-Popov
method in Landau gauge with a cut-off at the Gribov horizon, plus a novel term
that corrects for over-counting of Gribov copies inside the Gribov horizon.
Non-perturbative but truncated coupled Schwinger-Dyson equations for the gluon
and ghost propagators and in Landau gauge are solved
asymptotically in the infrared region. The infrared critical exponents or
anomalous dimensions, defined by and are obtained in space-time dimensions . Two
possible solutions are obtained with the values, in dimensions, , or .Comment: 26 pages. Modified 2.25.02 to update references and to clarify
Introduction and Conclusio
Origin of Pure Spin Superradiance
The question addressed in this paper is: What originates pure spin
superradiance in a polarized spin system placed inside a resonator? The term
"pure" means that no initial coherence is imposed on spins, and its appearance
manifests a purely self-organized collective effect. The consideration is based
on a microscopic model with dipole spin interactions. An accurate solution of
evolution equations is given. The results show that the resonator Nyquist noise
does not play, contrary to the common belief, any role in starting spin
superradiance, but the emergence of the latter is initiated by local spin
fluctuations. The decisive role of nonsecular dipole interactions is stressed.Comment: 1 file, 13 pages, RevTe
Immigration Federalism: A Reappraisal
This Article identifies how the current spate of state and local regulation is changing the way elected officials, scholars, courts, and the public think about the constitutional dimensions of immigration law and governmental responsibility for immigration enforcement. Reinvigorating the theoretical possibilities left open by the Supreme Court in its 1875 Chy Lung v. Freeman decision, state and local offi- cials characterize their laws as unavoidable responses to the policy problems they face when they are squeezed between the challenges of unauthorized migration and the federal government’s failure to fix a broken system. In the October 2012 term, in Arizona v. United States, the Court addressed, but did not settle, the difficult empirical, theoretical, and constitutional questions necessitated by these enactments and their attendant justifications. Our empirical investigation, however, discovered that most state and local immigration laws are not organic policy responses to pressing demographic challenges. Instead, such laws are the product of a more nuanced and politicized process in which demographic concerns are neither neces- sary nor sufficient factors and in which federal inactivity and subfederal activity are related phenomena, fomented by the same actors. This Article focuses on the con- stitutional and theoretical implications of these processes: It presents an evidence- based theory of state and local policy proliferation; it cautions legal scholars to rethink functionalist accounts for the rise of such laws; and it advises courts to reassess their use of traditional federalism frameworks to evaluate these sub federal enactments
Pion Breather States in QCD
We describe a class of pionic breather solutions (PBS) which appear in the
chiral lagrangian description of low-energy QCD. These configurations are
long-lived, with lifetimes greater than fm/c, and could arise as
remnants of disoriented chiral condensate (DCC) formation at RHIC. We show that
the chiral lagrangian equations of motion for a uniformly isospin-polarized
domain reduce to those of the sine-gordon model. Consequently, our solutions
are directly related to the breather solutions of sine-gordon theory in 3+1
dimensions. We investigate the possibility of PBS formation from multiple
domains of DCC, and show that the probability of formation is non-negligible.Comment: 9 pages, 4 figure
- …