980 research outputs found
Kinetic-theory description of isoscalar dipole modes
A semiclassical model, based on a solution of the Vlasov equation for finite
systems with moving-surface, is employed to study the isoscalar dipole modes in
nuclei. It is shown that, by taking into account the surface degree of freedom,
it is possible to obtain an exact treatment of the centre of mass motion. It is
also shown that a method often used to subtract the spurious strength in RPA
calculations does not always give the correct result. An alternative analytical
formula for the intrinsic strength function is derived in a simple
confined-Fermi-gas model. In this model the intrinsic isoscalar dipole strength
displays essentially a two-resonance structure, hence there are two relevant
modes. The interaction between nucleons couples these two modes and changes the
compressibility of the system. The evolution of the strength profile is then
studied as a function of the compressibility of the nuclear fluid. Comparison
with available data favours values of the incompressibility parameter of
nuclear matter smaller than those suggested by the analysis of the monopole
``breathing'' mode.Comment: 17 pages, 4 figures, revised version to be published in Nucl. Phys.
Unified semiclassical approach to isoscalar collective modes in heavy nuclei
A semiclassical model based on the solution of the Vlasov equation for finite
systems with a sharp moving surface has been used to study the isoscalar
quadrupole and octupole collective modes in heavy spherical nuclei. Within this
model, a unified description of both low-energy surface modes and higher-energy
giant resonances has been achieved by introducing a coupling between surface
vibrations and the motion of single nucleons. Analytical expressions for the
collective response functions of different multipolarity can be derived by
using a separable approximation for the residual interaction between nucleons.
The response functions obtained in this way give a good qualitative description
of the quadrupole and octupole response in heavy nuclei. Although shell effects
are not explicitly included in the theory, our semiclassical response functions
are very similar to the quantum ones. This happens because of the well known
close relation between classical trajectories and shell structure. The role
played by particular nucleon trajectories and their connection with various
features of the nuclear response is displayed most clearly in the present
approach, we discuss in some detail the damping of low-energy octupole
vibrations and give an explicit expression showing that only nucleons moving on
triangular orbits can contribute to this damping.Comment: 9 pages, 2 figures, Talk presented at the 8th International Spring
Seminar on Nuclear Physics on Key Topics in Nuclear Structure, Paestum,
Italy, May 23-27, 200
Instabilities in a Mean-field dynamics of Asymmetric Nuclear Matter
We discuss the features of instabilities in asymmetric nuclear matter, in
particular the relation between the nature of fluctuations, the types of
instabilities and the properties of the interaction. We show a chemical
instability appears as an instability against isoscalar-like fluctuations. Then
starting from phenomenological hadronic field theory (QHD), including exchange
terms, we discuss the symmetry energy and the relation to the dynamical
response inside the spinodal region.Comment: 8 pages, 5 Postscript figures, talk at Cortona 2000 Conference, Oct.
17 - Oct. 20, Italy, World Scientific (in press
Revisiting the Expanded Use of Hyperbaric Oxygen Therapy for Treatment of Resistant Migraines
There are currently 13 indications approved by the U.S. Food and Drug Administration for use of hyperbaric oxygen therapy. The European Consensus Conference on Hyperbaric Medicine has 28 indications approved for its use. However, neither includes the use of hyperbaric oxygen therapy for neurological conditions such as migraines with aura. Recent research has made the attempt to fully understand the use of hyperbaric therapy in treatment of neurological conditions, but results have so far been inconclusive. We report a 23-year-old female with an 11-year history of migraines with aura who has received inadequate pharmacological treatment for her migraines since she began having them. Migraines have led her to significant loss of function. The patient underwent treatment at 1.5 absolute atmospheres in a hyperbaric chamber Monday through Friday for 1 hour each day for a total of 40 sessions but reported missing a few sessions over the 8-week period. No more than 1 session during a given week was missed and the patient received no other treatments for her migraines throughout this time period. By her 2
Rapid onset of bronchodilation with formoterol/beclomethasone Modulite and formoterol/budesonide Turbuhaler as compared to formoterol alone in patients with COPD
In the present study, we examined whether there is a difference in the onset of bronchodilatation between formoterol/beclomethasone 12/200 μg Modulite and formoterol/budesonide 9/320 μg Turbuhaler in patients with COPD. We enrolled 28 patients with stable COPD. Both formoterol/beclomethasone and formoterol/budesonide elicited a larger mean FEV1–AUC0−15min than formoterol alone, whereas there was no significant difference between their FEV1–AUC0−15min. Also the change in FEV1 15 min after inhalation of formoterol/beclomethasone combination or formoterol/budesonide combination was greater than that induced by formoterol alone. This study confirms the rapid effect of the inhaled corticosteroid component when combined with formoterol and indicates that the onset of bronchodilation of formoterol/beclomethasone Modulite and formoterol/budesonide Turbuhaler are similar and greater than formoterol alone in patients with COPD
Kinetic-theory approach to low-energy collective modes in nuclei
Two different solutions of the linearized Vlasov equation for finite systems,
characterized by fixed and moving-surface boundary conditions, are discussed in
a unified perspective. A condition determining the eigenfrequencies of
collective nuclear oscillations, that can be obtained from the moving-surface
solution, is studied for isoscalar vibrations of lowest multipolarity. Analytic
expressions for the friction and mass parameters related to the low-enegy
surface excitations are derived and their value is compared to values given by
other models. Both similarities and differences are found with respect to the
other approaches, however the close agreement obtained in many cases with one
of the other models suggests that, in spite of some important differences, the
two approaches are substantially equivalent. The formalism based on the Vlasov
equation is more transparent since it leads to analytical expressions that can
be a basis for further improvement of the model.Comment: 16 pages, 1 EPS figure, to be published in Nucl. Phys.
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