2,509 research outputs found
The equation of state of neutron star matter and the symmetry energy
We present an overview of microscopical calculations of the Equation of State
(EOS) of neutron matter performed using Quantum Monte Carlo techniques. We
focus to the role of the model of the three-neutron force in the high-density
part of the EOS up to a few times the saturation density. We also discuss the
interplay between the symmetry energy and the neutron star mass-radius
relation.
The combination of theoretical models of the EOS with recent neutron stars
observations permits us to constrain the value of the symmetry energy and its
slope. We show that astrophysical observations are starting to provide
important insights into the properties of neutron star matter.Comment: 7 pages, 3 figure, talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Analytical formula for the Uehling potential
The closed analytical expression for the Uehling potential is derived. The
Uehling potential describes the lowest-order correction on vacuum polarisation
in atomic and muon-atomic systems. We also derive the analytical formula for
the interaction potential between two electrically charged point particles
which includes correction to the vacuum polarisation, but has correct
asymptotic behaviour at larger . Our three-term analytical formula for the
Uehling potential opens a new avenue in the study of the vacuum polarisation in
light atomic systems.Comment: arXiv admin note: substantial text overlap with arXiv:1103.204
Increased dietary zinc oxide changes the bacterial core and enterobacterial composition in the ileum of piglets
This study was conducted to investigate the effects of increased dietary ZnO
on the bacterial core and enterobacterial composition in the small intestine
of piglets that were fed diets containing a total of 124 or 3,042 mg of Zn per
kilogram of diet, respectively. Zinc was supplemented to the basal diet as
ZnO. Bacterial 16S rRNA genes of ileal DNA extracts were PCR-amplified with 2
bar-coded primer sets and sequenced by 454 pyrosequencing. The bacterial core
species were calculated from the relative abundances of reads present in 5 of
6 samples per group and at a minimum of 5 sequences per sample. The reference
database SILVA was used to assign sequence reads at an alignment minimum of
200 bases and 100% identity. Lactic acid bacteria dominated the bacterial
core, but showed diverse responses to dietary ZnO. Of the dominant
Lactobacillus spp., Lactobacillus reuteri was reduced due to increased dietary
ZnO (44.7 vs. 17.9%; P=0.042), but L. amylovorus was not influenced. However,
the changes of relative abundances of other lactic acid bacteria were more
noteworthy; Weissella cibaria (10.7 vs. 23.0%; P=0.006), W. confusa (10.0 vs.
22.4%; P=0.037), Leuconostoc citreum (6.5 vs. 14.8%; P=0.009), Streptococcus
equinus (0.14 vs. 1.0%; P=0.044), and S. lutetiensis (0.01 vs. 0.11%; P=0.016)
increased in relative abundance. Nonlactic acid bacteria that were influenced
by increased dietary ZnO included the strict anaerobic species, Sarcina
ventriculi, which showed a strong numerical decrease in relative abundance
(14.6 vs. 5.1%). Species of the Enterobacteriaceae increased their relative
abundance, as well as species diversity, in the high dietary ZnO experimental
group. Bacterial diversity indices were increased due to increased dietary ZnO
(P < 0.05), which was traced back to the increase of sequences from
subdominant species. Increased dietary ZnO led to an increase of less
prominent species and, thus, had a major impact on the bacterial composition
and diversity in piglets. This effect may help to stabilize the intestinal
microbiota in the sensitive postweaning period
Intrinsic channel closing in strong-field single ionization of H2
The ionization of H2 in intense laser pulses is studied by numerical
integration of the time-dependent Schr\"odinger equation for a
single-active-electron model including the vibrational motion. The electron
kinetic-energy spectra in high-order above-threshold ionization are strongly
dependent on the vibrational quantum number of the created H2+ ion. For certain
vibrational states, the electron yield in the mid-plateau region is strongly
enhanced. The effect is attributed to channel closings, which were previously
observed in atoms by varying the laser intensity.Comment: 11 pages, LaTeX; changed conten
The structure of the QED-Vacuum and Electron-Positron Pair Production in Super-Intense, pulsed Laser Fields
We discuss electron-positron pair-production by super-intense, short laser
pulses off the physical vacuum state locally deformed by (stripped) nuclei with
large nuclear charges. Consequences of non-perturbative vacuum polarisation
resulting from such a deformation are shortly broached. Production
probabilities per pulse are calculated.Comment: 10 pages, 1 figure, submitted to Journal of Physics
Recent Developments in the Nuclear Many-Body Problem
The study of quantum chromodynamics (QCD) over the past quarter century has
had relatively little impact on the traditional approach to the low-energy
nuclear many-body problem. Recent developments are changing this situation. New
experimental capabilities and theoretical approaches are opening windows into
the richness of many-body phenomena in QCD. A common theme is the use of
effective field theory (EFT) methods, which exploit the separation of scales in
physical systems. At low energies, effective field theory can explain how
existing phenomenology emerges from QCD and how to refine it systematically.
More generally, the application of EFT methods to many-body problems promises
insight into the analytic structure of observables, the identification of new
expansion parameters, and a consistent organization of many-body corrections,
with reliable error estimates.Comment: 15 pages, 10 figures, plenary talk at the 11th Conference on Recent
Progress in Many-Body Theories (MB 11), Manchester, England, 9-13 Jul 200
Impact of ^(16)O(γ,α)^(12)C measurements on the ^(12)C(α,γ)^(16)O astrophysical reaction rate
The ^(12)C(α,γ)^(16)O reaction, an important component of stellar helium burning, plays a key role in nuclear astrophysics. It has direct impact on the evolution and final state of massive stars, while also influencing the elemental abundances resulting from nucleosynthesis in such stars. Providing a reliable estimate for the energy dependence of this reaction at stellar helium burning temperatures has been a major goal for the field. In this work, we study the role of potential new measurements of the inverse reaction, ^(16)O(γ,α)^(12)C, in reducing the overall uncertainty. A multilevel R-matrix analysis is used to make extrapolations of the astrophysical S factor for this reaction to the stellar energy of 300 keV. The statistical precision of the S-factor extrapolation is determined by performing multiple fits to existing E1and E2 ground-state capture data, including the impact of possible future measurements of the ^(16)O(γ,α)^(12)C reaction. In particular, we consider a proposed Jefferson Laboratory (JLab) experiment that will make use of a high-intensity low-energy bremsstrahlung beam that impinges on an oxygen-rich single-fluid bubble chamber in order to measure the total cross section for the inverse reaction. The importance of low-energy data as well as high-precision data is investigated
- …