800 research outputs found
The 14C(n,g) cross section between 10 keV and 1 MeV
The neutron capture cross section of 14C is of relevance for several
nucleosynthesis scenarios such as inhomogeneous Big Bang models, neutron
induced CNO cycles, and neutrino driven wind models for the r process. The
14C(n,g) reaction is also important for the validation of the Coulomb
dissociation method, where the (n,g) cross section can be indirectly obtained
via the time-reversed process. So far, the example of 14C is the only case with
neutrons where both, direct measurement and indirect Coulomb dissociation, have
been applied. Unfortunately, the interpretation is obscured by discrepancies
between several experiments and theory. Therefore, we report on new direct
measurements of the 14C(n,g) reaction with neutron energies ranging from 20 to
800 keV
Impaired Competence for Pretense in Children with Autism: Exploring Potential Cognitive Predictors.
Lack of pretense in children with autism has been explained by a number of theoretical explanations, including impaired mentalising, impaired response inhibition, and weak central coherence. This study aimed to empirically test each of these theories. Children with autism (n=60) were significantly impaired relative to controls (n=65) when interpreting pretense, thereby supporting a competence deficit hypothesis. They also showed impaired mentalising and response inhibition, but superior local processing indicating weak central coherence. Regression analyses revealed that mentalising significantly and independently predicted pretense. The results are interpreted as supporting the impaired mentalising theory and evidence against competing theories invoking impaired response inhibition or a local processing bias. The results of this study have important implications for treatment and intervention
Modeling bursts and heavy tails in human dynamics
Current models of human dynamics, used from risk assessment to
communications, assume that human actions are randomly distributed in time and
thus well approximated by Poisson processes. We provide direct evidence that
for five human activity patterns the timing of individual human actions follow
non-Poisson statistics, characterized by bursts of rapidly occurring events
separated by long periods of inactivity. We show that the bursty nature of
human behavior is a consequence of a decision based queuing process: when
individuals execute tasks based on some perceived priority, the timing of the
tasks will be heavy tailed, most tasks being rapidly executed, while a few
experiencing very long waiting times. We discuss two queueing models that
capture human activity. The first model assumes that there are no limitations
on the number of tasks an individual can hadle at any time, predicting that the
waiting time of the individual tasks follow a heavy tailed distribution with
exponent alpha=3/2. The second model imposes limitations on the queue length,
resulting in alpha=1. We provide empirical evidence supporting the relevance of
these two models to human activity patterns. Finally, we discuss possible
extension of the proposed queueing models and outline some future challenges in
exploring the statistical mechanisms of human dynamics.Comment: RevTex, 19 pages, 8 figure
Hole dynamics in noble metals
We present a detailed analysis of hole dynamics in noble metals (Cu and Au),
by means of first-principles many-body calculations. While holes in a
free-electron gas are known to live shorter than electrons with the same
excitation energy, our results indicate that d-holes in noble metals exhibit
longer inelastic lifetimes than excited sp-electrons, in agreement with
experiment. The density of states available for d-hole decay is larger than
that for the decay of excited electrons; however, the small overlap between d-
and sp-states below the Fermi level increases the d-hole lifetime. The impact
of d-hole dynamics on electron-hole correlation effects, which are of relevance
in the analysis of time-resolved two-photon photoemission experiments, is also
addressed.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let
Randomized clinical trial of therapeutic music video intervention for resilience outcomes in adolescents/young adults undergoing hematopoietic stem cell transplant: a report from the Children's Oncology Group
BACKGROUND:
To reduce the risk of adjustment problems associated with hematopoietic stem cell transplant (HSCT) for adolescents/young adults (AYAs), we examined efficacy of a therapeutic music video (TMV) intervention delivered during the acute phase of HSCT to: 1) increase protective factors of spiritual perspective, social integration, family environment, courageous coping, and hope-derived meaning; 2) decrease risk factors of illness-related distress and defensive coping; and 3) increase outcomes of self-transcendence and resilience.
METHODS:
This was a multisite randomized, controlled trial (COG-ANUR0631) conducted at 8 Children's Oncology Group sites involving 113 AYAs aged 11-24 years undergoing myeloablative HSCT. Participants, randomized to the TMV or low-dose control (audiobooks) group, completed 6 sessions over 3 weeks with a board-certified music therapist. Variables were based on Haase's Resilience in Illness Model (RIM). Participants completed measures related to latent variables of illness-related distress, social integration, spiritual perspective, family environment, coping, hope-derived meaning, and resilience at baseline (T1), postintervention (T2), and 100 days posttransplant (T3).
RESULTS:
At T2, the TMV group reported significantly better courageous coping (Effect Size [ES], 0.505; P = .030). At T3, the TMV group reported significantly better social integration (ES, 0.543; P = .028) and family environment (ES, 0.663; P = .008), as well as moderate nonsignificant effect sizes for spiritual perspective (ES, 0.450; P = .071) and self-transcendence (ES, 0.424; P = .088).
CONCLUSIONS:
The TMV intervention improves positive health outcomes of courageous coping, social integration, and family environment during a high-risk cancer treatment. We recommend the TMV be examined in a broader population of AYAs with high-risk cancers
New measurement of neutron capture resonances of 209Bi
The neutron capture cross section of Bi209 has been measured at the CERN n
TOF facility by employing the pulse-height-weighting technique. Improvements
over previous measurements are mainly because of an optimized detection system,
which led to a practically negligible neutron sensitivity. Additional
experimental sources of systematic error, such as the electronic threshold in
the detectors, summing of gamma-rays, internal electron conversion, and the
isomeric state in bismuth, have been taken into account. Gamma-ray absorption
effects inside the sample have been corrected by employing a nonpolynomial
weighting function. Because Bi209 is the last stable isotope in the reaction
path of the stellar s-process, the Maxwellian averaged capture cross section is
important for the recycling of the reaction flow by alpha-decays. In the
relevant stellar range of thermal energies between kT=5 and 8 keV our new
capture rate is about 16% higher than the presently accepted value used for
nucleosynthesis calculations. At this low temperature an important part of the
heavy Pb-Bi isotopes are supposed to be synthesized by the s-process in the He
shells of low mass, thermally pulsing asymptotic giant branch stars. With the
improved set of cross sections we obtain an s-process fraction of 19(3)% of the
solar bismuth abundance, resulting in an r-process residual of 81(3)%. The
present (n,gamma) cross-section measurement is also of relevance for the design
of accelerator driven systems based on a liquid metal Pb/Bi spallation target.Comment: 10 pages, 5figures, recently published in Phys. Rev.
Recommended from our members
Measurement of Neutron Total Cross Sections in Support of the APT Program
The authors have completed a new set of total cross section measurements of 37 samples spanning the periodic table. The authors employed the same technique as in a previous measurement, with refinements intended to allow measurements on separated isotopes, and with improved systematic error control. The goal of the new measurement was 1% statistical accuracy in 1% energy bins with systematic errors less than 1%. This was achieved for all but the smallest samples, for which the statistical accuracy was as large as 2% in 1% bins
- …