47,992 research outputs found
The Giant Monopole Resonance in Pb isotopes
The extraction of the nuclear incompressibility from the isoscalar giant
monopole resonance (GMR) measurements is analysed. Both pairing and mutually
enhanced magicity (MEM) effects play a role in the shift of the GMR energy
between the doubly closed shell Pb nucleus and other Pb isotopes.
Pairing effects are microscopically predicted whereas the MEM effect is
phenomenologically evaluated. Accurate measurements of the GMR in open-shell Pb
isotopes are called for.Comment: 4 page
Microscopic HFB+QRPA predictions of dipole strength for astrophysics applications
Large-scale QRPA calculations of the E1 strength are performed on top of HFB
calculations in order to derive the radiative neutron capture cross sections
for the whole nuclear chart. The spreading width of the GDR is taken into
account by analogy with the second-RPA (SRPA) method. The accuracy of HFB+QRPA
model based on various Skyrme forces with different pairing prescription and
parameterization is analyzed. It is shown that the present model allows to
constrain the effective nucleon-nucleon interaction with the GDR data and to
provide quantitative predictions of dipole strengths.Comment: 21 pages, 9 figure
Continuous Spin Representations from Group Contraction
We consider how the continuous spin representation (CSR) of the Poincare
group in four dimensions can be generated by dimensional reduction. The
analysis uses the front-form little group in five dimensions, which must yield
the Euclidean group E(2), the little group of the CSR. We consider two cases,
one is the single spin massless representation of the Poincare group in five
dimensions, the other is the infinite component Majorana equation, which
describes an infinite tower of massive states in five dimensions. In the first
case, the double singular limit j,R go to infinity, with j/R fixed, where R is
the Kaluza-Klein radius of the fifth dimension, and j is the spin of the
particle in five dimensions, yields the CSR in four dimensions. It amounts to
the Inonu-Wigner contraction, with the inverse K-K radius as contraction
parameter. In the second case, the CSR appears only by taking a triple singular
limit, where an internal coordinate of the Majorana theory goes to infinity,
while leaving its ratio to the KK radius fixed.Comment: 22 pages; some typos correcte
Experimental verification of an Oseen flow slender body theory
Consider uniform flow past four slender bodies with elliptical cross-section of
constant ellipticity along the length of 0, 0.125, 0.25 and 0.375, respectively, for each
body. Here, ellipticity is defined as the ratio of the semiminor axis of the ellipse to
the semimajor axis. The bodies have a pointed nose which gradually increases in
cross-section with a radius of curvature 419mm to a mid-section which then remains
constant up to a blunt end section with semimajor axis diameter 160 mm, the total
length of all bodies being 800 mm. The bodies are side-mounted within a low-speed
wind tunnel with an operational wind speed of the order 30ms−1. The side force (or
lift) is measured within an angle of attack range of −3◦ to 3◦ such that the body is
rotated about the major axis of the ellipse cross-section. The lift slope is determined
for each body, and how it varies with ellipticity. It is found that this variance follows
a straight line which steadily increases with increasing ellipticity. It is shown that
this result is predicted by a recently developed Oseen flow slender body theory, and
cannot be predicted by either inviscid flow slender body theory or viscous crossflow
theories based upon the Allen and Perkins method
Temperature and finite-size effects in collective modes of superfluid Fermi gases
We study the effects of superfluidity on the monopole and quadrupole
collective excitations of a dilute ultra-cold Fermi gas with an attractive
interatomic interaction. The system is treated fully microscopically within the
Bogoliubov-de Gennes and quasiparticle random-phase approximation methods. The
dependence on the temperature and on the trap frequency is analyzed and
systematic comparisons with the corresponding hydrodynamic predictions are
presented in order to study the limits of validity of the semiclassical
approach.Comment: 9 pages, 4 figure
- …