503 research outputs found
Connecting the X(5)-, X(5)-, and X(3) models to the shape/phase transition region of the interacting boson model
The parameter independent (up to overall scale factors) predictions of the
X(5)-, X(5)-, and X(3) models, which are variants of the X(5)
critical point symmetry developed within the framework of the geometric
collective model, are compared to two-parameter calculations in the framework
of the interacting boson approximation (IBA) model. The results show that these
geometric models coincide with IBA parameters consistent with the phase/shape
transition region of the IBA for boson numbers of physical interest (close to
10). Nuclei within the rare-earth region and select Os and Pt isotopes are
identified as good examples of X(3), X(5)-, and X(5)-
behavior
Systematics of 2+ states in semi-magic nuclei
We propose a simple systematics of low lying 2+ energy levels and
electromagnetic transitions in semi-magic isotopic chains Z=28,50,82 and
isotonic chains N=28,50,82,126. To this purpose we use a two-level pairing plus
quadrupole Hamiltonian, within the spherical Quasiparticle Random Phase
Approximation (QRPA). We derive a simple relation connecting the 2+ energy with
the pairing gap and quadrupole-quadupole (QQ) interaction strength. It turns
out that the systematics of energy levels and B(E2) values predicted by this
simple model is fulfilled with a reasonable accuracy by all available
experimental data. Both systematics suggest that not only active nucleons but
also those filling closed shells play an important role
Transition from the Seniority to the Anharmonic Vibrator Regime in Nuclei
A recent analysis of experimental energy systematics suggests that all
collective nuclei fall into one of three classes -- seniority, anharmonic
vibrational, or rotational -- with sharp phase transitions between them. We
investigate the transition from the seniority to the anharmonic vibrator regime
within a shell model framework involving a single large j-orbit. The
calculations qualitatively reproduce the observed transitional behavior, both
for U(5) like and O(6) like nuclei. They also confirm the preeminent role
played by the neutron-proton interaction in producing the phase transition.Comment: 9 pages with 2 tables, submitted to Physical Review C, November 199
Band structure from random interactions
The anharmonic vibrator and rotor regions in nuclei are investigated in the
framework of the interacting boson model using an ensemble of random one- and
two-body interactions. We find a predominance of L(P)=0(+) ground states, as
well as strong evidence for the occurrence of both vibrational and rotational
band structures. This remarkable result suggests that such band structures
represent a far more general (robust) property of the collective model space
than is generally thought.Comment: 5 pages, 4 figures, Phys. Rev. Lett., in pres
Rapidity of change in population age structures: A local approach based on multiway factor analysis
In the light of complex adaptive system thinking, population age structures in Europe have increasingly reflected the interplay between 'fast' and 'slow' socioeconomic dynamics driven by natural population growth and migration. Assuming the importance of demographic dynamics shaping regional growth in recent times, a diachronic analysis of local-scale population age structures was developed for 156 districts of Greece between 1971 and 2011. By using appropriate indicators, the analysis was aimed at demonstrating how 'fast' and 'slow' transitions contribute to socioeconomic change in both urban and rural areas. Acomprehensive analysis of change in population age structures between 1971 and 2011 allows identification of latent spatial structures as a result of population re-distribution from urban cores to broader rural regions. Following residential mobility, the empirical results of this study indicate (i) a late phase of urbanization (1971-1981) with population densification and settlement compactness, (i) a rapid suburbanization (1981-1991) consolidating distinctive demographic structures in urban and rural areas, (ii) a mild counter-urbanization (1991-2001) with moderate aging of suburban populations and (iii) a latent re-urbanization (2001-2011) reducing the suburban-urban divide in population age structures. Residential mobility contributed to a more balanced age structure during suburbanization and an increased demographic divide in the subsequent urban waves. A refined analysis of long-term population dynamics in metropolitan regions reflects spatial outcomes and latent aspects of demographic transitions shedding light on the debate over the future development of urban and rural societies in advanced economies
Long-term urbanization dynamics and the evolution of green/blue areas in eastern europe: Insights from Romania
Urbanization is a dynamic process performed at the expense of natural and/or semi-natural areas, with direct impacts on the ecosystem services provided to human society. The increasing population density in urban areas and the associated demand for housing and public services have led to progressive changes in the structure, architecture, and design of urban areas. The present study analyzes long-term urban development in Western Romania, focusing on green/blue areas’ strategies in Timisoara over centuries. The empirical results of a literature review carried out with a historical perspective have delineated the time periods that favored “urban green development” (1716–1918 and 1918–1940) and those restricting their development (1940–2000), as well as the factors that influenced long-term urbanization dynamics and the evolution of green/blue areas. These factors can be generalized to other socioeconomic contexts in Eastern Europe. Characteristic issues of this geographical area impacting the evolution of urban green/blue areas include (i) common historical aspects (e.g., the influence of geo-political and strategic dimensions, the dominations of former great empires such as the Turkish empire and the communist period) and (ii) population migration after 1990
Land degradation and mitigation policies in the mediterranean region. A brief commentary
Land degradation is more evident where conditions of environmental vulnerability already exist because of arid climate and unsustainable forms of land exploitation. Consequently, semi-arid and dry areas have been identified as vulnerable land, requiring attention from both science and policy perspectives. In some regions, such as the Mediterranean region, land degradation is particularly intense, although there are no extreme ecological conditions. In these contexts, a wide range of formal and informal responses is necessary to face particularly complex and spatially differentiated territorial processes. However, the fit of responses has been demonstrated to be different over time and space according to the underlying socioeconomic context and the specific ecological conditions. The present commentary discusses this sort of \u201centropy\u201d in the policy response to land degradation in Southern Europe, outlining the intrinsic complexity of human\u2013nature dynamics at the base of such processes. Reflecting the need of differentiated regional strategies and more specific national measures to combat desertification, three policy frameworks (agro-environmental, economic, social) with an indirect impact on fighting land degradation have been considered, delineating the importance of policy assemblages. Finally, the importance of policy impact assessment methodologies was highlighted, focusing on the possible responses reinforcing a continental strategy against land degradation. By evidencing the role of participatory planning, developmental policies indirectly addressing land degradation reveal to be an important vector of more specific measures abating desertification risk, creating, in turn, a favorable context for direct interventions of mitigation or adaptation to climate change
Possible experimental signature of octupole correlations in the 0 states of the actinides
= 0 states have been investigated in the actinide nucleus
Pu up to an excitation energy of 3 MeV with a high-resolution (p,t)
experiment at = 24 MeV. To test the recently proposed = 0
double-octupole structure, the phenomenological approach of the
spdf-interacting boson model has been chosen. In addition, the total 0
strength distribution and the strength fragmentation have been compared
to the model predictions as well as to the previously studied (p,t) reactions
in the actinides. The results suggest that the structure of the 0 states
in the actinides might be more complex than the usually discussed pairing
isomers. Instead, the octupole degree of freedom might contribute
significantly. The signature of two close-lying 0 states below the
2-quasiparticle energy is presented as a possible manifestation of strong
octupole correlations in the structure of the 0 states in the actinides.Comment: 6 pages, 5 figures, published in Phys. Rev. C 88, 041303(R) (2013
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