2,737 research outputs found
Enhanced radiative strength in the quasi-continuum of 117Sn
Radiative strength functions of 117Sn has been measured below the neutron
separation energy using the (3He,3He'gamma) reactions. An increase in the slope
of the strength functions around E_gamma= 4.5 MeV indicates the onset of a
resonance-like structure, giving a significant enhancement of the radiative
strength function compared to standard models in the energy region 4.5 <=
E_gamma <= 8.0 MeV. For the first time, the functional form of this
resonance-like structure has been measured in an odd tin nucleus below neutron
threshold in the quasi-continuum region.Comment: 4 pages, 3 figure
Standard energy metabolism of a desert harvester ant, Pogonomyrmex rugosus: Effects of temperature, body mass, group size, and humidity
Radial Color Gradients in K+A Galaxies in Distant Clusters of Galaxies
Galaxies in rich clusters with z 0.3 are observed to have a higher
fraction of photometrically blue galaxies than their nearby counterparts. This
raises the important question of what environmental effects can cause the
termination of star formation between z 0.3 and the present. The star
formation may be truncated due to ram-pressure stripping, or the gas in the
disk may be depleted by an episode of star formation caused by some external
perturbation. To help resolve this issue, surface photometry was carried out
for a total of 70 early-type galaxies in the cluster Cl1358+62, at z
0.33, using two-color images from the Hubble Archive. The galaxies were divided
into two categories based on spectroscopic criteria: 24 are type K+A (e.g.,
strong Balmer lines, with no visible emission lines), while the remaining 46
are in the control sample with normal spectra. Radial color profiles were
produced to see if the K+A galaxies show bluer nuclei in relation to their
surrounding disks. Specifically, a linear gradient was fit to the radial color
profile of each galaxy. We find that the K+A galaxies on average tend to have
slightly bluer gradients towards the center than the normals. A
Kolmogorov-Smirnov two-sample test has been applied to the two sets of color
gradients. The result of the test indicates that there is only a 2%
probability that the K+A and normal samples are drawn from the same parent
distribution. There is a possible complication from a trend in the apparent
magnitude vs. color gradient relation, but overall our results favor the
centralized star formation scenario as an important process in the evolution of
galaxies in dense clusters.Comment: 16 pages, 12 figures, accepted for publication in A
Evolution of level density step structures from 56,57-Fe to 96,97-Mo
Level densities have been extracted from primary gamma spectra for 56,57-Fe
and 96,97-Mo nuclei using (3-He,alpha gamma) and (3-He,3-He') reactions on
57-Fe and 97-Mo targets. The level density curves reveal step structures above
the pairing gap due to the breaking of nucleon Cooper pairs. The location of
the step structures in energy and their shapes arise from the interplay between
single-particle energies and seniority-conserving and seniority-non-conserving
interactions.Comment: 9 pages, including 5 figure
Fragmentation and systematics of the Pygmy Dipole Resonance in the stable N=82 isotones
The low-lying electric dipole (E1) strength in the semi-magic nucleus 136Xe
has been measured which finalizes the systematic survey to investigate the
so-called pygmy dipole resonance (PDR) in all stable even N=82 isotones with
the method of nuclear resonance fluorescence using real photons in the entrance
channel. In all cases, a fragmented resonance-like structure of E1 strength is
observed in the energy region 5 MeV to 8 MeV. An analysis of the fragmentation
of the strength reveals that the degree of fragmentation decreases towards the
proton-deficient isotones while the total integrated strength increases
indicating a dependence of the total strength on the neutron-to-proton ratio.
The experimental results are compared to microscopic calculations within the
quasi-particle phonon model (QPM). The calculation includes complex
configurations of up to three phonons and is able to reproduce also the
fragmentation of the E1 strength which allows to draw conclusions on the
damping of the PDR. Calculations and experimental data are in good agreement in
the degree of fragmentation and also in the integrated strength if the
sensitivity limit of the experiments is taken into account
Narrow Optical and Spin Linewidths in Rare-earth Doped Micro- and Nano-structures
This invited presentation was given at the 47th conference on the Physics of Quantum Electronics, which took place in Snowbird, USA from January 8 to 13, 2017. It gives an overview of the current developments on rare earth doped nanoparticles and transparent ceramics spectroscopy at Chimie ParisTech
Photoactivation experiment on 197Au and its implications for the dipole strength in heavy nuclei
The 197Au(gamma,n) reaction is used as an activation standard for
photodisintegration studies on astrophysically relevant nuclei. At the
bremsstrahlung facility of the superconducting electron accelerator ELBE
(Electron Linear accelerator of high Brilliance and low Emittance) of
Forschungszentrum Dresden-Rossendorf, photoactivation measurements on 197Au
have been performed with bremsstrahlung endpoint energies from 8.0 to 15.5 MeV.
The measured activation yield is compared with previous experiments as well as
with calculations using Hauser-Feshbach statistical models. It is shown that
the experimental data are best described by a two-Lorentzian parametrization
with taking the axial deformation of 197Au into account. The experimental
197Au(gamma,n) reaction yield measured at ELBE via the photoactivation method
is found to be consistent with previous experimental data using photon
scattering or neutron detection methods.Comment: 9 page
Di-neutron correlation and soft dipole excitation in medium mass neutron-rich nuclei near drip-line
The neutron pairing correlation and the soft dipole excitation in medium-mass
nuclei near drip-line are investigated from a viewpoint of the di-neutron
correlation. Numerical analyses by means of the coordinate-space HFB and the
continuum QRPA methods are performed for even-even O, Ca
and Ni. A clear signature of the di-neutron correlation is found in
the HFB ground state; two neutrons are correlated at short relative distances
\lesim 2 fm with large probability . The soft dipole excitation is
influenced strongly by the neutron pairing correlation, and it accompanies a
large transition density for pair motion of neutrons. This behavior originates
from a coherent superposition of two-quasiparticle configurations consisting of continuum states with high orbital angular momenta
reaching an order of . It raises a picture that the soft dipole
excitation under the influence of neutron pairing is characterized by motion of
di-neutron in the nuclear exterior against the remaining subsystem.
Sensitivity to the density dependence of effective pair force is discussed.Comment: 35 pages, 22 figure
Hummingbirds Budget Energy Flexibly in Response to Changing Resources
A key component of individual fitness is the ability to manage energy stores in response to variable resource availability, but because directly measuring energy budgets is difficult, daily energy management is rarely measured. Hummingbirds\u27 energy management is relatively simple to model compared to other endotherms because they have high mass‐specific metabolic rates and store little fat. We determined which aspects of the hummingbird daily energy budget (i.e. thermoregulation, daytime activity costs, night‐time costs) change at the individual level in response to environmental variation. We found that daily energy expenditure varied threefold in two populations of broad‐billed hummingbirds (Cynanthus latirostris). Our model indicated the energy budget was distributed in the following proportions: daytime activity, 59% (range 22%–84%); thermoregulation, 23% (11%–32%); basal metabolism, 7% (3%–16%); and night‐time energy, 17% (6%–37%). Activity costs were higher at the hotter, homogeneous site and during the early‐wet season at both sites. Increased daily energy expenditure was related to decreased nectar availability and not significantly related to temperature or bird mass. With climate change, the indirect energetic costs of shifting resources could have greater impacts on endotherm energy budgets than direct costs such as thermoregulation. Increased foraging and activity costs could decrease the energy available to birds for somatic repair and reproduction, potentially causing differential fitness across seasons and sites
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