2,140 research outputs found
A note on the time evolution of the fission decay width under the influence of dissipation
The claim put forward in a recent paper by B. Jurado, K.-H. Schmidt and J.
Benlliure that the transient effect of nuclear fission may be described simply
as a relaxation process in the upright oscillator around the potential minimum
is refuted. Some critical remarks on the relevance of this effect in general
are added.Comment: 6 pages, LaTex, no figures; final, shorter version, to appear in PL
Mean first passage time for fission potentials having structure
A schematic model of over-damped motion is presented which permits one to
calculate the mean first passage time for nuclear fission. Its asymptotic value
may exceed considerably the lifetime suggested by Kramers rate formula, which
applies only to very special, favorable potentials and temperatures. The
additional time obtained in the more general case is seen to allow for a
considerable increment in the emission of light particles.Comment: 7 pages, LaTex, 7 postscript figures; Keywords: Decay rate, mean
first passage tim
Angular correlation of electrons and positrons in internal pair conversion
The angular distribution of electrons and positrons emitted in internal pair conversion is calculated. Coulomb-distorted waves are used as electron wave functions. Nuclear transitions of various multipolarities L>0 and of magnetic (ML) and of electric (EL) type are considered as well as E0 conversion. Analytical expressions for the angular correlation are derived, which are evaluated numerically assuming a finite extension of the nucleus and, for the EL and ML conversion, also in the point-nucleus approximation. The calculated angular correlations are compared with results obtained within the Born approximation and, for the E0 case, with experimental data
Managing a portal of digital web resources by content syndication
As users become more accustomed to continuous Internet access, they will have less patience with the offering of disparate resources. A new generation of portals is being designed that aids users in navigating resource space and in processing the data they retrieved. Such portals offer added value by means of content syndication: the effort to have multiple, federated? resources co-operate in order to profit optimally from their synergy. A portal that offers these advantages, however, can only be of lasting value if it is sustainable. We sketch a way to set up and run an organisation that can manage a content syndication portal in a sustainable way.\ud
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On the nature of nuclear dissipation, as a hallmark for collective dynamics at finite excitation
We study slow collective motion of isoscalar type at finite excitation. The
collective variable is parameterized as a shape degree of freedom and the mean
field is approximated by a deformed shell model potential. We concentrate on
situations of slow motion, as guaranteed, for instance, by the presence of a
strong friction force, which allows us to apply linear response theory. The
prediction for nuclear dissipation of some models of internal motion are
contrasted. They encompass such opposing cases as that of pure independent
particle motion and the one of "collisional dominance". For the former the wall
formula appears as the macroscopic limit, which is here simulated through
Strutinsky smoothing procedures. It is argued that this limit hardly applies to
the actual nuclear situation. The reason is found in large collisional damping
present for nucleonic dynamics at finite temperature . The level structure
of the mean field as well as the -dependence of collisional damping
determine the -dependence of friction. Two contributions are isolated, one
coming from real transitions, the other being associated to what for infinite
matter is called the "heat pole". The importance of the latter depends strongly
on the level spectrum of internal motion, and thus is very different for
"adiabatic" and "diabatic" situations, both belonging to different degrees of
"ergodicity".Comment: 50 pages plus 10 figures, uuencoded postscript file
Relativistic Shock Acceleration: A Hartree-Fock Approach
We examine the problem of particle acceleration at a relativistic shocks
assuming pitch-angle scattering and using a Hartree-Fock method to approximate
the associated eigenfunctions. This leads to a simple transcendental equation
determining the power-law index, , given the up and downstream velocities.
We compare our results with accurate numerical solutions obtained using the
eigenfunction method. In addition to the power-law index this method yields the
angular and spatial distributions upstream of the shock.Comment: 4 pages, 2 figures, proceedings of the "4th Heidelberg International
Symposium on High Energy Gamma-Ray Astronomy" July 7-11, 2008, Heidelberg,
German
Statistical fluctuations for the fission process on its decent from saddle to scission
We reconsider the importance of statistical fluctuations for fission dynamics
beyond the saddle in the light of recent evaluations of transport coefficients
for average motion. The size of these fluctuations are estimated by means of
the Kramers-Ingold solution for the inverted oscillator, which allows for an
inclusion of quantum effects.Comment: 12 pages, Latex, 5 Postscript figures; submitted to PRC e-mail:
[email protected] www home page:
http://www.physik.tu-muenchen.de/tumphy/e/T36/hofmann.htm
Mean first passage time for nuclear fission and the emission of light particles
The concept of a mean first passage time is used to study the time lapse over
which a fissioning system may emit light particles. The influence of the
"transient" and "saddle to scission times" on this emission are critically
examined. It is argued that within the limits of Kramers' picture of fission no
enhancement over that given by his rate formula need to be considered.Comment: 4 pages, RevTex, 4 postscript figures; with correction of misprints;
appeared in Phys. Rev. Lett.90.13270
Children's emotion understanding: A meta-analysis of training studies.
BACKGROUND: In the course of development, children show increased insight and understanding of emotions-both of their own emotions and those of others. However, little is known about the efficacy of training programs aimed at improving children's understanding of emotion. OBJECTIVES: To conduct an effect size analysis of trainings aimed at three aspects of emotion understanding: external aspects (i.e., the recognition of emotional expressions, understanding external causes of emotion, understanding the influence of reminders on present emotions); mental aspects (i.e., understanding desire-based emotions, understanding belief-based emotions, understanding hidden emotions); and reflective aspects (i.e., understanding the regulation of an emotion, understanding mixed emotions, understanding moral emotions). DATA SOURCES: A literature search was conducted using PubMed, PsycInfo, the Cochrane Library, and manual searches. REVIEW METHODS: The search identified 19 studies or experiments including a total of 749 children with an average age of 86 months (S.D.=30.71) from seven different countries. RESULTS: Emotion understanding training procedures are effective for improving external (Hedge's g = 0.62), mental (Hedge's g = 0.31), and reflective (Hedge's g = 0.64) aspects of emotion understanding. These effect sizes were robust and generally unrelated to the number and lengths of training sessions, length of the training period, year of publication, and sample type. However, training setting and social setting moderated the effect of emotion understanding training on the understanding of external aspects of emotion. For the length of training session and social setting, we observed significant moderator effects of training on reflective aspects of emotion. CONCLUSION: Emotion understanding training may be a promising tool for both preventive intervention and the psychotherapeutic process. However, more well-controlled studies are needed.R34 MH086668 - NIMH NIH HHS; R01 AT007257 - NCCIH NIH HHS; R21 MH101567 - NIMH NIH HHS; R34 MH099311 - NIMH NIH HHS; R21 MH102646 - NIMH NIH HHS; K23 MH100259 - NIMH NIH HHS; R01 MH099021 - NIMH NIH HH
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