719 research outputs found
Extraction of level density and gamma strength function from primary gamma spectra
We present a new iterative procedure to extract the level density and the
gamma strength function from primary gamma spectra for energies close up to the
neutron binding energy. The procedure is tested on simulated spectra and on
data from the Yb-173(He-3,alpha)Yb-172 reaction.Comment: 23 pages including 1 table and 7 figure
Heat capacity and pairing transition in nuclei
A simple model based on the canonical-ensemble theory is outlined for hot
nuclei. The properties of the model are discussed with respect to the Fermi gas
model and the breaking of Cooper pairs. The model describes well the
experimental level density of deformed nuclei in various mass regions. The
origin of the so-called S-shape of the heat capacity curve Cv(T) is discussed.Comment: 6 pages + 8 figure
Level densities and -strength functions in Sm
The level densities and -strength functions of the weakly deformed
Sm and Sm nuclei have been extracted. The temperature versus
excitation energy curve, derived within the framework of the micro canonical
ensemble, shows structures, which we associate with the break up of Cooper
pairs. The nuclear heat capacity is deduced within the framework of both the
micro canonical and the canonical ensemble. We observe negative heat capacity
in the micro canonical ensemble whereas the canonical heat capacity exhibits an
S-shape as function of temperature, both signals of a phase transition. The
structures in the -strength functions are discussed in terms of the
pygmy resonance and the scissors mode built on exited states. The samarium
results are compared with data for the well deformed Dy,
Er and Yb isotopes and with data from
(n,)-experiments and giant dipole resonance studies.Comment: 12 figure
Level density and gamma strength function in 162-Dy from inelastic 3-He scattering
Complementary measurements have been performed for the level density and
gamma strength function in 162-Dy using inelastic 3-He scattering. Comparing
these results to previous measurements using the 163-Dy(3-He,alpha) reaction,
reveals that the measured quantities above 1.5 MeV do not depend significantly
on the nuclear reaction chosen.Comment: 15 pages, including 7 figure
Critical temperature for quenching of pair correlations
The level density at low spin in the 161,162-Dy and 171,172-Yb nuclei has
been extracted from primary gamma rays. The nuclear heat capacity is deduced
within the framework of the canonical ensemble. The heat capacity exhibits an
S-formed shape as a function of temperature, which is interpreted as a
fingerprint of the phase transition from a strongly correlated to an
uncorrelated phase. The critical temperature for the quenching of pair
correlations is found at Tc=0.50(4) MeV.Comment: 8 pages including 4 figures, different method to extract Tc,
different figures, text partly rewritte
Thermal and electromagnetic properties of 166-Er and 167-Er
The primary gamma-ray spectra of 166-Er and 167-Er are deduced from the
(3-He,alpha gamma) and (3-He,3-He' gamma) reaction, respectively, enabling a
simultaneous extraction of the level density and the gamma-ray strength
function. Entropy, temperature and heat capacity are deduced from the level
density within the micro-canonical and the canonical ensemble, displaying
signals of a phase-like transition from the pair-correlated ground state to an
uncorrelated state at Tc=0.5 MeV. The gamma-ray strength function displays a
bump around E-gamma=3 MeV, interpreted as the pygmy resonance.Comment: 21 pages including 2 tables and 11 figure
Adaptation to the Edge of Chaos in the Self-Adjusting Logistic Map
Self-adjusting, or adaptive systems have gathered much recent interest. We
present a model for self-adjusting systems which treats the control parameters
of the system as slowly varying, rather than constant. The dynamics of these
parameters is governed by a low-pass filtered feedback from the dynamical
variables of the system. We apply this model to the logistic map and examine
the behavior of the control parameter. We find that the parameter leaves the
chaotic regime. We observe a high probability of finding the parameter at the
boundary between periodicity and chaos. We therefore find that this system
exhibits adaptation to the edge of chaos.Comment: 3 figure
Effect of Omega-3 Fatty Acids on Lipoprotein Profile and Particle Size in Hispanic Women
The effect of increased Ω3 fatty acids on lipoprotein sub-fractions has not been well studied in Hispanic women, a group with a high prevalence of dyslipidemia and metabolic syndrome. The purpose of this randomized, placebo-controlled trial was to examine the effect of a 90-day (90D) combined EPA+DHA supplementation on lipoprotein profiles of Hispanic women. Twenty-seven non-diabetic women were randomly assigned to the Ω3 group (n=17, 1.9 g/day EPA+DHA) or the placebo group (n=10, 2 g/day oleic acid). At baseline (0D) and 90D a fasting blood sample was drawn for determination of lipoprotein profile and lipoprotein particle sub-fractions. For the Ω3 group, total cholesterol increased 6.5%, triglycerides were reduced 14.8%, LDL concentration increased 5.6%, and total LDL particle size concentration increased 8.2% (P \u3c 0.05). Large LDL particle size concentration increased 16% from 0D to 90D, this change was not significant (P = 0.051). At 90D, total cholesterol, LDLs, and LDL particle concentration were higher in the Ω3 group compared to placebo (P \u3c 0.05). Omega-3 supplementation resulted in reduced plasma TGs and an increase in large LDL particle size concentration, yet had no effect on HDL particle size or concentration. Further research is necessary to examine the effects of increased Ω3 fatty acid intake in Hispanic women on dyslipidemia and related co-morbidities
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