3,828 research outputs found
Measurement of the 187Re({\alpha},n)190Ir reaction cross section at sub-Coulomb energies using the Cologne Clover Counting Setup
Uncertainties in adopted models of particle+nucleus optical-model potentials
directly influence the accuracy in the theoretical predictions of reaction
rates as they are needed for reaction-network calculations in, for instance,
{\gamma}-process nucleosynthesis. The improvement of the {\alpha}+nucleus
optical-model potential is hampered by the lack of experimental data at
astrophysically relevant energies especially for heavier nuclei. Measuring the
Re187({\alpha},n)Ir190 reaction cross section at sub-Coulomb energies extends
the scarce experimental data available in this mass region and helps
understanding the energy dependence of the imaginary part of the
{\alpha}+nucleus optical-model potential at low energies. Applying the
activation method, after the irradiation of natural rhenium targets with
{\alpha}-particle energies of 12.4 to 14.1 MeV, the reaction yield and thus the
reaction cross section were determined via {\gamma}-ray spectroscopy by using
the Cologne Clover Counting Setup and the method of {\gamma}{\gamma}
coincidences. Cross-section values at five energies close to the
astrophysically relevant energy region were measured. Statistical model
calculations revealed discrepancies between the experimental values and
predictions based on widely used {\alpha}+nucleus optical-model potentials.
However, an excellent reproduction of the measured cross-section values could
be achieved from calculations based on the so-called Sauerwein-Rauscher
{\alpha}+nucleus optical-model potential. The results obtained indicate that
the energy dependence of the imaginary part of the {\alpha}+nucleus
optical-model potential can be described by an exponential decrease. Successful
reproductions of measured cross sections at low energies for {\alpha}-induced
reactions in the mass range 141{\leq}A{\leq}187 confirm the global character of
the Sauerwein-Rauscher potential
A variable neurodegenerative phenotype with polymerase gamma mutation
mtDNA replication and repair, causes mitochondrial diseases including autosomal dominant
progressive external ophthalmoplegia (PEO),1 childhood hepato-encephalopathy (Alpers–
Huttenlocher syndrome), adult-onset spinocerebellar ataxia, and sensory nerve degeneration with
dysarthria and ophthalmoparesis (SANDO)
Isospin properties of electric dipole excitations in 48Ca
Two different experimental approaches were combined to study the electric
dipole strength in the doubly-magic nucleus 48Ca below the neutron threshold.
Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and
nearly mono-energetic linearly polarized photons with energies between 6.6 and
9.51 MeV provided strength distribution and parities, and an
(\alpha,\alpha'\gamma) experiment at E_{\alpha}=136 MeV gave cross sections for
an isoscalar probe. The unexpected difference observed in the dipole response
is compared to calculations using the first-order random-phase approximation
and points to an energy-dependent isospin character. A strong isoscalar state
at 7.6 MeV was identified for the first time supporting a recent theoretical
prediction.Comment: 6 pages, 5 figures, as accepted in Phys. Lett.
Possible experimental signature of octupole correlations in the 0 states of the actinides
= 0 states have been investigated in the actinide nucleus
Pu up to an excitation energy of 3 MeV with a high-resolution (p,t)
experiment at = 24 MeV. To test the recently proposed = 0
double-octupole structure, the phenomenological approach of the
spdf-interacting boson model has been chosen. In addition, the total 0
strength distribution and the strength fragmentation have been compared
to the model predictions as well as to the previously studied (p,t) reactions
in the actinides. The results suggest that the structure of the 0 states
in the actinides might be more complex than the usually discussed pairing
isomers. Instead, the octupole degree of freedom might contribute
significantly. The signature of two close-lying 0 states below the
2-quasiparticle energy is presented as a possible manifestation of strong
octupole correlations in the structure of the 0 states in the actinides.Comment: 6 pages, 5 figures, published in Phys. Rev. C 88, 041303(R) (2013
The Legal Needs of Farmers: An Analysis of the Family Farm Legal Needs Survey
The Legal Needs of Farmer
The decay of quadrupole-octupole states in Ca and Ce
Background: Two-phonon excitations originating from the coupling of two
collective one-phonon states are of great interest in nuclear structure
physics. One possibility to generate low-lying excitations is the coupling
of quadrupole and octupole phonons.
Purpose: In this work, the -decay behavior of candidates for the
state in the doubly-magic nucleus Ca and in
the heavier and semi-magic nucleus Ce is investigated.
Methods: experiments have been carried out at the
High Intensity -ray Source (HIS) facility in combination with
the high-efficiency -ray spectroscopy setup consisting of
HPGe and LaBr detectors. The setup enables the acquisition of
- coincidence data and, hence, the detection of direct decay
paths.
Results: In addition to the known ground-state decays, for Ca the
decay into the state was observed, while for Ce the direct
decays into the and the state were detected. The experimentally
deduced transition strengths and excitation energies are compared to
theoretical calculations in the framework of EDF theory plus QPM approach and
systematically analyzed for isotones. In addition, negative parities for
two states in Ca were deduced simultaneously.
Conclusions: The experimental findings together with the theoretical
calculations support the two-phonon character of the excitation in the
light-to-medium-mass nucleus Ca as well as in the stable even-even
nuclei.Comment: 11 pages, 6 figures, as accepted in Phys. Rev.
Complex microwave conductivity of Na-DNA powders
We report the complex microwave conductivity, , of
Na-DNA powders, which was measured from 80 K to 300 K by using a microwave
cavity perturbation technique. We found that the magnitude of near
room temperature was much larger than the contribution of the surrounding water
molecules, and that the decrease of with decreasing temperature was
sufficiently stronger than that of the conduction of counterions. These results
clearly suggest that the electrical conduction of Na-DNA is intrinsically
semiconductive.Comment: 16 pages, 7 figure
White matter hyperintensities are an independent predictor of cognitive decline 3 years following first-ever stroke-results from the PROSCIS-B study
Background: White matter hyperintensities (WMH) are the result of cerebral small vessel disease and may increase the risk of cognitive impairment (CI), recurrent stroke, and depression. We aimed to explore the association between selected cerebrovascular risk factors (CVRF) and WMH load as well as the effect of increased WMH burden on recurrent vascular events, CI, and depression in first-ever ischemic stroke patients.Methods: 431 from the PROSpective Cohort with Incident Stroke (PROSCIS) were included; Age-Related White Matter Changes (ARWMC) score was used to assess WMH burden on FLAIR. The presence of CVRF (defined via blood pressure, body-mass-index, and serological markers of kidney dysfunction, diabetes mellitus, and hyperlipoproteinemia) was categorized into normal, borderline, and pathological profiles based on commonly used clinical definitions. The primary outcomes included recurrent vascular events (combined endpoint of recurrent stroke, myocardial infarction and/or death), CI 3 years post-stroke, and depression 1-year post-stroke.Results: There was no clear association between CVRF profiles and WMH burden. High WMH lesion load (ARWMC score ≥ 10) was found to be associated with CI (adjusted OR 1.05 [95% CI 1.00-1.11]; p Conclusion: Higher WMH burden was associated with a significant decline in cognition 3 years post-stroke in this cohort of first-ever stroke patients
Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction
The spatial charge arrangement of a typical quasi-two-dimensional organic
conductor alpha-(BEDT-TTF)2I3 is revealed by single crystal structure analysis
using synchrotron radiation. The results show that the horizontal stripe type
structure, which was suggested by mean field theory, is established. We also
find the charge disproportion above the metal-insulator transition temperature
and a significant change in transfer integrals caused by the phase transition.
Our result elucidates the insulating phase of this material as a 2k_F charge
density localization.Comment: 8 pages, 5 figures, 1 tabl
Increased accuracy of ligand sensing by receptor internalization
Many types of cells can sense external ligand concentrations with
cell-surface receptors at extremely high accuracy. Interestingly, ligand-bound
receptors are often internalized, a process also known as receptor-mediated
endocytosis. While internalization is involved in a vast number of important
functions for the life of a cell, it was recently also suggested to increase
the accuracy of sensing ligand as the overcounting of the same ligand molecules
is reduced. Here we show, by extending simple ligand-receptor models to
out-of-equilibrium thermodynamics, that internalization increases the accuracy
with which cells can measure ligand concentrations in the external environment.
Comparison with experimental rates of real receptors demonstrates that our
model has indeed biological significance.Comment: 9 pages, 4 figures, accepted for publication in Physical Review
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