19,347 research outputs found
The generalized Fenyes-Nelson model for free scalar field theory
The generalized Fenyes--Nelson model of quantum mechanics is applied to the
free scalar field. The resulting Markov field is equivalent to the Euclidean
Markov field with the times scaled by a common factor which depends on the
diffusion parameter. This result is consistent between Guerra's earlier work on
stochastic quantization of scalar fields. It suggests a deep connection between
Euclidean field theory and the stochastic interpretation of quantum mechanics.
The question of Lorentz covariance is also discussed.Comment: 6 page
Sulfur and Methionine Supplementation With Urea for Feedlot Cattle
Efficiency of urea utilization may be affected by several factors. Among these are level and source of energy, level and source of protein and amount of urea in the total diet and in the supplement. Other essential nutrients in the diet should be properly balanced. There has been a tendency in recent years to use higher levels of urea than was earlier recommended. Under some conditions, urea has been satisfactory as the only supplemental protein to diets for cattle. However, consideration should be given to likely problems of palatability and potential toxicity as well as to efficiency of urea utilization
Damping of bulk excitations over an elongated BEC - the role of radial modes
We report the measurement of Beliaev damping of bulk excitations in cigar
shaped Bose Einstein condensates of atomic vapor. By using post selection,
excitation line shapes of the total population are compared with those of the
undamped excitations. We find that the damping depends on the initial
excitation energy of the decaying quasi particle, as well as on the excitation
momentum. We model the condensate as an infinite cylinder and calculate the
damping rates of the different radial modes. The derived damping rates are in
good agreement with the experimentally measured ones. The damping rates
strongly depend on the destructive interference between pathways for damping,
due to the quantum many-body nature of both excitation and damping products.Comment: 5 pages, 4 figure
Stringent limitations on reductive perturbation studies of nonplanar acoustic solitons in plasmas
More than fifty years ago, the Korteweg-de Vries equation was shown to describe not only solitary surface waves on shallow water, but also nonlinear ion-acoustic waves. Because of the algorithmic ease of using reductive perturbation theory, intensive research followed on a wide range of wave types. Soon, the formalism was extended to nonplanar modes by introducing a stretching designed to accommodate spherically and cylindrically symmetric ion-acoustic waves. Over the last two decades many authors followed this approach, but almost all have ignored the severe restrictions in parameter space imposed by the Ansatz. In addition, for other steps in the formalism, the justification is often not spelled out, leading to effects that are physically undesirable or ambiguous. Hence, there is a need to critically assess this approach to nonplanar modes and to use it with the utmost care, respecting the restrictions on its validity. Only inward propagation may be meaningfully studied and respect for weak nonlinearities of at most 1/10 implies that one cannot get closer to the axis or centre of symmetry than about 30 Debye lengths. Thus, one is in a regime where the modes are quasi-planar and not particularly interesting. Most papers disregard these constraints and hence reach questionable conclusions
Vector meson spectral function and dilepton rate in an effective mean field model
We have studied the vector meson spectral function (VMSF) in a hot and dense
medium within an effective QCD model namely the Nambu-Jona-Lasinio (NJL) and
its Polyakov Loop extended version (PNJL) with and without the effect of
isoscalar vector interaction (IVI). The effect of the IVI has been taken into
account using the ring approximation. We obtained the dilepton production rate
(DPR) using the VMSF and observed that at moderate temperature it is enhanced
in the PNJL model as compared to the NJL and Born rate due to the suppression
of color degrees of freedom.Comment: 5 pages, 7 figures, conference proceedings of the XXI DAE-BRNS HEP
Symposium, IIT Guwahati, December 2014; to appear in 'Springer Proceedings in
Physics Series
Characterization study of polycrystalline tin oxide surfaces before and after reduction in CO
Polycrystalline tin oxide surfaces have been examined before and after reduction in 40 Torr of CO at 100 and 175 C using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS) and electron stimulated desorption (ESD). The changes in the surface composition and chemical states of the surface species generally are subtle for the reductive conditions used. However, significant changes do occur with regard to the amounts and the chemical forms of the hydrogen-containing species remaining after both the 100 and 175 C reductions
Events, processes, and the time of a killing
The paper proposes a novel solution to the problem of the time of a killing (ToK), which persistently besets theories of act-individuation. The solution proposed claims to expose a crucial wrong-headed assumption in the debate, according to which ToK is essentially a problem of locating some event that corresponds to the killing. The alternative proposal put forward here turns on recognizing a separate category of dynamic occurents, viz. processes. The paper does not aim to mount a comprehensive defense of process ontology, relying instead on extant defenses. The primary aim is rather to put process ontology to work in diagnosing the current state of play over ToK, and indeed in solving it
Collisional decay of a strongly driven Bose-Einstein condensate
We study the collisional decay of a strongly driven Bose-Einstein condensate
oscillating between two momentum modes. The resulting products of the decay are
found to strongly deviate from the usual s-wave halo. Using a stochastically
seeded classical field method we simulate the collisional manifold. These
results are also explained by a model of colliding Bloch states.Comment: 4 pages, 4 figure
Closed-form expressions for correlated density matrices: application to dispersive interactions and example of (He)2
Empirically correlated density matrices of N-electron systems are
investigated. Exact closed-form expressions are derived for the one- and
two-electron reduced density matrices from a general pairwise correlated wave
function. Approximate expressions are proposed which reflect dispersive
interactions between closed-shell centro-symmetric subsystems. Said expressions
clearly illustrate the consequences of second-order correlation effects on the
reduced density matrices. Application is made to a simple example: the (He)2
system. Reduced density matrices are explicitly calculated, correct to second
order in correlation, and compared with approximations of independent electrons
and independent electron pairs. The models proposed allow for variational
calculations of interaction energies and equilibrium distance as well as a
clear interpretation of dispersive effects on electron distributions. Both
exchange and second order correlation effects are shown to play a critical role
on the quality of the results.Comment: 22 page
Experiments on wave turbulence : the evolution and growth of second sound acoustic turbulence in superfluid 4He confirm self-similarity.
We report our experiments on the formation of second sound acoustic turbulence in superfluid 4He. The initial growth in spectral amplitude follows power laws that steepen rapidly with increasing harmonic number n, corresponding to a propagating front in frequency space. The lower growth exponents agree well with analytic predictions and numerical modeling. The observed increase in the formation delay with n validates the concept of selfsimilarity in the growth of wave turbulence
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