428 research outputs found
Coherent control of enrichment and conversion of molecular spin isomers
A theoretical model of nuclear spin conversion in molecules controlled by an
external electromagnetic radiation resonant to rotational transition has been
developed. It has been shown that one can produce an enrichment of spin isomers
and influence their conversion rates in two ways, through coherences and
through level population change induced by radiation. Influence of conversion
is ranged from significant speed up to almost complete inhibition of the
process by proper choice of frequency and intensity of the external field.Comment: REVTEX, 13 pages + 6 eps figure
Comment on Neutron-Proton Spin-Correlation Parameter A_{ZZ} at 68 Mev
We present two arguments indicating that the large value for the
mixing parameter at 50 MeV, which the Basel group extracted from their recent
measurement, may be incorrect. First, there are nucleon-nucleon (NN)
potentials which predict the at 50 MeV substantially below the
Basel value and reproduce the Basel data accurately. Second, the large
value for at 50 MeV proposed by the Basel group can only be
explained by a model for the NN interaction which is very unrealistic (no
-meson and essentially a point-like vertex) and overpredicts the
in the energy range where it is well determined (150--500 MeV) by
a factor of two.Comment: 6 pages text (LaTex) and 2 figures (paper, will be faxed upon
request), UI-NTH-930
Self-Referential Noise and the Synthesis of Three-Dimensional Space
Generalising results from Godel and Chaitin in mathematics suggests that
self-referential systems contain intrinsic randomness. We argue that this is
relevant to modelling the universe and show how three-dimensional space may
arise from a non-geometric order-disorder model driven by self-referential
noise.Comment: Figure labels correcte
Probing potential priming: Defining, quantifying, and testing the causal priming effect using the potential outcomes framework
Having previously seen an item helps uncover the item another time, given a perceptual or cognitive cue. Oftentimes, however, it may be difficult to quantify or test the existence and size of a perceptual or cognitive effect, in general, and a priming effect, in particular. This is because to examine the existence of and quantify the effect, one needs to compare two outcomes: the outcome had one previously seen the item vs. the outcome had one not seen the item. But only one of the two outcomes is observable. Here, we argue that the potential outcomes framework is useful to define, quantify, and test the causal priming effect. To demonstrate its efficacy, we apply the framework to study the priming effect using data from a between-subjects study involving English word identification. In addition, we show that what has been used intuitively by experimentalists to assess the priming effect in the past has a sound mathematical foundation. Finally, we examine the links between the proposed method in studying priming and the multinomial processing tree (MPT) model, and how to extend the method to study experimental paradigms involving exclusion and inclusion instructional conditions
Lambda-proton correlations in relativistic heavy ion collisions
The prospect of using lambda-proton correlations to extract source sizes in
relativistic heavy ion collisions is investigated. It is found that the strong
interaction induces a large peak in the correlation function that provides more
sensitive source size measurements than two-proton correlations under some
circumstances. The prospect of using lambda-proton correlations to measure the
time lag between lambda and proton emissions is also studied.Comment: 4 pages, 3 figure, revtex style. Two short paragraphs are added at
referees' recommendations. Phys. Rev. Lett. in pres
Strange vector currents and the OZI-rule
We investigate the role of correlated exchange in the extraction of
matrix elements of the strange vector current in the proton. We show that a
realistic isoscalar spectral function including this effect leads to sizeably
reduced strange vector form factors based on the dispersion--theoretical
analysis of the nucleons' electromagnetic form factors.Comment: 8 pp, plain LaTeX, uses epsf, 3 figure
A nonlinear approach to NN interactions using self-interacting meson fields
Motivated by the success of models based on chiral symmetry in NN
interactions we investigate self-interacting scalar, pseudoscalar and vector
meson fields and their impact for NN forces. We parametrize the corresponding
nonlinear field equations and get analytic wavelike solutions. A probability
amplitude for the propagation of particle states is calculated and applied in
the framework of a boson-exchange NN potential. Using a proper normalization of
the meson fields makes all self-scattering amplitudes finite. The same
normalization is able to substitute for the phenomenological form factors used
in conventional boson exchange potentials and thus yields an phenomenological
understanding of this part of the NN interaction. We find an empirical scaling
law which relates the meson self-interaction couplings to the pion mass and
self-interaction coupling constant. Our model yields np phase shifts comparable
to the Bonn B potential results and deuteron properties, in excellent agreement
with experimental data.Comment: Reviewed version, 25 pages REVTeX, more info at
http://i04ktha.desy.d
Flatte-like distributions and the a_0(980)/f_0(980) mesons
We explore the features of Flatte-like parametrizations. In particular, we
demonstrate that the large variation in the absolute values of the coupling
constants to the pi-eta (or pi-pi) and KKbar channels for the a_0(980) and
f_0(980) mesons that one can find in the literature can be explained by a
specific scaling behaviour of the Flatte amplitude for energies near the KKbar
threshold. We argue that the ratio of the coupling constants can be much better
determined from a fit to experimental data.Comment: 12 pages, 12 figure
Hall-Effect Sign Anomaly and Small-Polaronic Conduction in (La_{1-x}Gd_x)_{0.67}Ca_{0.33}MnO_3
The Hall coefficient of Gd-doped La_{2/3}Ca_{1/3}MnO_3 exhibits Arrhenius
behavior over a temperature range from 2T_c to 4T_c, with an activation energy
very close to 2/3 that of the electrical conductivity. Although both the doping
level and thermoelectric coefficient indicate hole-like conduction, the Hall
coefficient is electron-like. This unusual result provides strong evidence in
favor of small-polaronic conduction in the paramagnetic regime of the
manganites.Comment: 11 pages, 4 figures, uses revtex.st
The Lambda-Lambda Interaction and ^{6}_{Lambda Lambda}He
An OBE potential model for the ^{1}S_0 S = -2 interaction is analyzed with
emphasis on the role of coupling between the Lambda Lambda, N Xi, and Sigma
Sigma channels. Singlet scalar exchange, an approximation to two-pion exchange,
is significant in all channels; surprisingly, the one-pion exchange component
is almost negligible. The size of the channel coupling as a function of the
overall strength of the OBE model potential is examined. Implications of the
analysis for the binding energy of ^{6}_{Lambda Lambda}He are considered; the
new experimental datum may suggest a consistency between the extracted Lambda
Lambda matrix element and the relation implied by SU(3) among OBE baryon-baryon
interactions. \\Comment: 4 pages brief report to Physical Review
- …