93 research outputs found
Impact of level densities and -strength functions on -process simulations
Studies attempting to quantify the sensitivity of the -process abundances
to nuclear input have to cope with the fact that the theoretical models they
rely on, rarely come with confidence intervals. This problem has been dealt
with by either estimating these intervals and propagating them statistically to
the final abundances using reaction networks within simplified astrophysical
models, or by running more realistic astrophysical simulations using different
nuclear-physics models consistently for all the involved nuclei. Both of these
approaches have their strengths and weaknesses. In this work, we use the
reaction network code SkyNet to run -process calculations for five
trajectories using 49 different neutron-capture rate models. Our results shed
light on the importance of taking into account shell effects and pairing
correlations in the network calculations.Comment: 11 pages, 7 figure
Comprehensive test of nuclear level density models
For the last two decades, experimental information on nuclear level densities
for about 60 different nuclei has been obtained on the basis of the Oslo
method. While each of these measurements has been typically compared to one or
a few level density models, a global study including all the measurements has
been missing. The present study provides a systematic comparison between Oslo
data and six global level density models for 42 nuclei for which -wave
resonance spacings are also available. We apply a coherent normalization
procedure to the Oslo data for each of the six different models, all being
treated on the same footing.
Our quantitative analysis shows that the constant-temperature model presents
the best global description of the Oslo data, closely followed by the
mean-field plus combinatorial model and Hartree-Fock plus statistical model.
Their accuracies are quite similar, so that it remains difficult to clearly
favour one of these models. When considering energies above the threshold where
the experimental level scheme is complete, all the six models are shown to lead
to rather similar accuracies with respect to Oslo data.
The recently proposed shape method can, in principle, improve the situation
since it provides an absolute estimate of the excitation-energy dependence of
the measured level densities. We show for the specific case of Cd that
the shape method could exclude the Hartree-Fock plus statistical model. Such an
analysis remains to be performed for the bulk of data for which the shape
method can be applied to the Oslo measurements before drawing conclusions on
the general quality of a given nuclear level density model.Comment: 11 pages, 7 figures, published in PR
Pygmy resonance and low-energy enhancement in the -ray strength functions of Pd~isotopes
An unexpected enhancement in the -ray strength function, as compared
to the low energy tail of the Giant Dipole Resonance (GDR), has been observed
for Sc, Ti, V, Fe and Mo isotopes for MeV. This enhancement was
not observed in subsequent analyses on Sn isotopes, but a Pygmy Dipole
Resonance (PDR) centered at MeV was however detected. The
-ray strength functions measured for Cd isotopes exhibit both features
over the range of isotopes, with the low-energy enhancement decreasing- and PDR
strength increasing as a function of neutron number. This suggests a
transitional region for the onset of low-energy enhancement, and also that the
PDR strength depends on the number of neutrons. The -ray strength
functions of Pd have been measured in order to further explore the
proposed transitional region. Experimental data were obtained at the Oslo
Cyclotron Laboratory by using the charged particle reactions (He,
He) and (He, ) on Pd
target foils. Particle coincidence measurements provided information
on initial excitation energies and the corresponding -ray spectra,
which were used to extract the level densities and -ray strength
functions according to the Oslo method. The -ray strength functions
indicate a sudden increase in magnitude for MeV, which is
interpreted as a PDR centered at MeV. An enhanced
-ray strength at low energies is also observed for Pd, which is
the lightest isotope measured in this work. Further, the results correspond and
agree very well with the observations from the Cd isotopes, and support the
suggested transitional region for the onset of low-energy enhancement with
decreasing mass number. The neutron number dependency of the PDR strength is
also evident
La(, ) cross sections constrained with statistical decay properties of La nuclei
The nuclear level densities and -ray strength functions of
La were measured using the La(He, ),
La(He, He) and La(d, p) reactions. The
particle- coincidences were recorded with the silicon particle
telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these
experimental results, the low-energy enhancement in the A140 region is
discussed. The La( cross sections were calculated
at - and -process temperatures using the experimentally measured nuclear
level densities and -ray strength functions. Good agreement is found
between La( calculated cross sections and previous
measurements
Experimentally constrained rates and implications for the process
The -ray strength function and the nuclear level density of
Ho have been extracted using the Oslo method from a
Ho experiment carried out at the Oslo
Cyclotron Laboratory. The level density displays a shape that is compatible
with %can be approximated with the constant temperature model in the
quasicontinuum, while the strength function shows structures indicating the
presence of both a scissors and a pygmy dipole resonance. Using our present
results as well as data from a previous
Ho experiment, the
and MACS uncertainties
have been constrained. The possible influence of the low-lying, long-lived
6~keV isomer Ho in the process is investigated in the context of a
2~, [Fe/H]=-0.5 AGB star. We show that the newly obtained
MACS affects the final Ho abundance, while
the MACS only impacts the enrichment of
Er to a limited degree due to the relatively rapid decay of
the thermalized Ho at typical -process temperatures.Comment: 11 pages, submitted to Physical Reviews
Study of oblate nuclear shapes and shape coexistence in neutron-deficient rare earth isotopes
Narcissism and the strategic pursuit of short-term mating : universal links across 11 world regions of the International Sexuality Description Project-2.
Previous studies have documented links between sub-clinical narcissism and the active pursuit of short-term mating strategies (e.g., unrestricted sociosexuality, marital infidelity, mate poaching). Nearly all of these investigations have relied solely on samples from Western cultures. In the current study, responses from a cross-cultural survey of 30,470 people across 53 nations spanning 11 world regions (North America, Central/South America, Northern Europe, Western Europe, Eastern Europe, Southern Europe, Middle East, Africa, Oceania, Southeast Asia, and East Asia) were used to evaluate whether narcissism (as measured by the Narcissistic Personality Inventory; NPI) was universally associated with short-term mating. Results revealed narcissism scores (including two broad factors and seven traditional facets as measured by the NPI) were functionally equivalent across cultures, reliably associating with key sexual outcomes (e.g., more active pursuit of short-term mating, intimate partner violence, and sexual aggression) and sex-related personality traits (e.g., higher extraversion and openness to experience). Whereas some features of personality (e.g., subjective well-being) were universally associated with socially adaptive facets of Narcissism (e.g., self-sufficiency), most indicators of short-term mating (e.g., unrestricted sociosexuality and marital infidelity) were universally associated with the socially maladaptive facets of narcissism (e.g., exploitativeness). Discussion addresses limitations of these cross-culturally universal findings and presents suggestions for future research into revealing the precise psychological features of narcissism that facilitate the strategic pursuit of short-term mating
Narcisismo y búsqueda estratégica del emparejamiento a corto plazo a través de las culturas: Enlaces omnipresentes a través de 11 regiones mundiales del Proyecto de la descripción de la sexualidad internacional 2
Previous studies have documented links between sub-clinical narcissism and the active pursuit of short-term mating strategies (e.g., unrestricted sociosexuality, marital infidelity, mate poaching). Nearly all of these investigations have relied solely on samples from Western cultures. In the current study, responses from a cross-cultural survey of 30,470 people across 53 nations spanning 11 world regions (North America, Central/South America, Northern Europe, Western Europe, Eastern Europe, Southern Europe, Middle East, Africa, Oceania, Southeast Asia, and East Asia) were used to evaluate whether narcissism (as measured by the Narcissistic Personality Inventory; NPI) was universally associated with short-term mating. Results revealed narcissism scores (including two broad factors and seven traditional facets as measured by the NPI) were functionally equivalent across cultures, reliably associating with key sexual outcomes (e.g., more active pursuit of short-term mating, intimate partner violence, and sexual aggression) and sex-related personality traits (e.g., higher extraversion and openness to experience). Whereas some features of personality (e.g., subjective well-being) were universally associated with socially adaptive facets of Narcissism (e.g., self-sufficiency), most indicators of short-term mating (e.g., unrestricted sociosexuality and marital infidelity) were universally associated with the socially maladaptive facets of narcissism (e.g., exploitativeness). Discussion addresses limitations of these cross-culturally universal findings and presents suggestions for future research into revealing the precise psychological features of narcissism that facilitate the strategic pursuit of short-term mating.Estudios previos, en primer lugar a través de las muestras de culturas occidentales, han documentado asociaciones sistemáticas del narcisismo subclínico con múltiples indicadores de estrategias del emparejamiento a corto plazo (p. ej. sociosexualidad ilimitada, infidelidad, caza de pareja). En este estudio se han usado respuestas de la encuesta transcultural de 30.470 personas de 53 naciones de 11 regiones mundiales (América del Norte, América del Sur/América Central, Europa del Norte, Europa del Oeste, Europa del Este, Europa del Sur, Oriente Próximo, África, Asia del Sur/Sudoeste de Asia, Asia del Este y Oceanía) para evaluar si el narcisismo (medido por el Inventario de Personalidad Narcisista; NPI) se asocia panuniversalmente con los indicadores del emparejamiento a corto plazo, tanto en la dirección, como en la intensidad. Los resultados sugieren que el narcisismo (incluidos muchos aspectos suyos medidos por el NPI) tiene las mismas asociaciones básicas con los rasgos de personalidad relacionados con el sexo (p. ej. extraversión alta) y con los resultados sexuales claves (p. ej. búsqueda más activa de las estrategias del emparejamiento a corto plazo) a través de las 11 mayores regiones mundiales del PDSI 2. La discusión se enfoca en las implicaciones y limitaciones del estudio actual
Statistical properties in the quasi-continuum of atomic nuclei
Almost a century after the discovery of the atomic nucleus, all of its secrets are still not revealed. This dissertation presents experimental observations on statistical properties of medium-mass nuclei at high temperatures. This has long been the main research field of the nuclear physics group at the Oslo Cyclotron Laboratory, where the experiments were performed.
In the experiments, the nuclei were excited to high-energy quantum levels and the decay from these levels was studied by means of statistical methods. By impinging small helium particles on metallic vanadium and scandium foils, the temperature of these nuclei were increased up to about ten billion degrees Celsius. When the nucleus cools down, it emits small particles and light. These were measured with nanosecond precision.
The most surprising observation is that the nucleus emits -rays with much lower energies than previously thought. The results are especially interesting from an astrophysical point of view, as the nuclear structure close to the particle separation energies influences strongly the nucleosynthesis processes that take place in extreme stellar environments such as supernovae.
* In 2006 I changed my last name from 'Sunde' to 'Larsen'
Low-energy enhancement of M1 strength
Magnetic dipole strength functions have been deduced from averages of a large number of M1 transition strengths calculated within the shell model for the nuclides 90Zr, 94Mo, 95Mo, and 96Mo. An enhancement of M1 strength toward low transition energy has been found for all nuclides considered. Large M1 strengths appear for transitions between close- lying states with configurations including proton as well as neutron high-j orbits that re-couple their spins and add up their magnetic moments coherently. The M1 strength function deduced from the calculated M1 transition strengths is compatible with the low-energy enhancement found in (3He,3He') and (d,p) experiments. The present work presents an explanation of the experimental findings
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