2,761 research outputs found
GTI-space : the space of generalized topological indices
A new extension of the generalized topological indices (GTI) approach is carried out torepresent 'simple' and 'composite' topological indices (TIs) in an unified way. Thisapproach defines a GTI-space from which both simple and composite TIs represent particular subspaces. Accordingly, simple TIs such as Wiener, Balaban, Zagreb, Harary and Randićconnectivity indices are expressed by means of the same GTI representation introduced for composite TIs such as hyper-Wiener, molecular topological index (MTI), Gutman index andreverse MTI. Using GTI-space approach we easily identify mathematical relations between some composite and simple indices, such as the relationship between hyper-Wiener and Wiener index and the relation between MTI and first Zagreb index. The relation of the GTI space with the sub-structural cluster expansion of property/activity is also analysed and some routes for the applications of this approach to QSPR/QSAR are also given
'Samen voor ons eigen' : de geschiedenis van een Nederlandse volksbuurt : de Haagse Schilderswijk 1920-1985
In dit proefschrift gaat de auteur op zoek naar de historische realiteit achter de beeldvorming. Op basis van onder meer tientallen interviews laat hij zien dat de wijk al v__r de jaren tachtig verre van homogeen was. Het was een dynamisch stadsdeel met een continu veranderende bevolking. Wel ontwikkelden de blijvers een eigen subcultuur en kwamen ze in de loop van de tijd steeds meer met de rug naar de samenleving te staan. Door zijn historische aanpak veranderd dit proefschrift onze kijk op het fenomeen van de achterstandswijkCities, Migration and Global Interdependenc
Diabatic and Adiabatic Collective Motion in a Model Pairing System
Large amplitude collective motion is investigated for a model pairing
Hamiltonian containing an avoided level crossing. A classical theory of
collective motion for the adiabatic limit is applied utilising either a
time-dependent mean-field theory or a direct parametrisation of the
time-dependent Schr\"odinger equation. A modified local harmonic equation is
formulated to take account of the Nambu-Goldstone mode. It turns out that in
some cases the system selects a diabatic path. Requantizing the collective
Hamiltonian, a reasonable agreement with an exact calculation for the low-lying
levels are obtained for both weak and strong pairing force. This improves on
results of the conventional Born-Oppenheimer approximation.Comment: 23 pages, 7 ps figures. Latex, uses revtex and graphic
Boson-fermion mappings for odd systems from supercoherent states
We extend the formalism whereby boson mappings can be derived from
generalized coherent states to boson-fermion mappings for systems with an odd
number of fermions. This is accomplished by constructing supercoherent states
in terms of both complex and Grassmann variables. In addition to a known
mapping for the full so(2+1) algebra, we also uncover some other formal
mappings, together with mappings relevant to collective subspaces.Comment: 40 pages, REVTE
Theories for multiple resonances
Two microscopic theories for multiple resonances in nuclei are compared,
n-particle-hole RPA and quantized Time-Dependent Hartree-Fock (TDHF). The
Lipkin-Meshkov-Glick model is used as test case. We find that quantized TDHF is
superior in many respects, except for very small systems.Comment: 14 Pages, 3 figures available upon request
Quantized bulk scalar fields in the Randall-Sundrum brane-model
We examine the lowest order quantum corrections to the effective action
arising from a quantized real scalar field in the Randall-Sundrum background
spacetime. The leading term is the familiar vacuum, or Casimir, energy density.
The next term represents an induced gravity term that can renormalize the
4-dimensional Newtonian gravitational constant. The calculations are performed
for an arbitrary spacetime dimension. Two inequivalent boundary conditions,
corresponding to twisted and untwisted field configurations, are considered. A
careful discussion of the regularization and renormalization of the effective
action is given, with the relevant counterterms found. It is shown that the
requirement of self-consistency of the Randall-Sundrum solution is not simply a
matter of minimizing the Casimir energy density. The massless, conformally
coupled scalar field results are obtained as a special limiting case of our
results. We clarify a number of differences with previous work.Comment: 31 pages, 1 figur
Competition for Light and Nutrients in Layered Communities of Aquatic Plants
Dominance of free-floating plants poses a threat to biodiversity in many freshwater ecosystems. Here we propose a theoretical framework to understand this dominance, by modeling the competition for light and nutrients in a layered community of floating and submerged plants. The model shows that at high supply of light and nutrients, floating plants always dominate due to their primacy for light, even when submerged plants have lower minimal resource requirements. The model also shows that floating-plant dominance cannot be an alternative stable state in light-limited environments but only in nutrient-limited environments, depending on the plants’ resource consumption traits. Compared to unlayered communities, the asymmetry in competition for light—coincident with symmetry in competition for nutrients—leads to fundamentally different results: competition outcomes can no longer be predicted from species traits such as minimal resource requirements ( rule) and resource consumption. Also, the same two species can, depending on the environment, coexist or be alternative stable states. When applied to two common plant species in temperate regions, both the model and field data suggest that floating-plant dominance is unlikely to be an alternative stable state
Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRuRhO
The solid-solution SrRuRhO () is a
variable-electron-configuration system forming in the nearly-cubic-perovskite
basis, ranging from the ferromagnetic 4 to the enhanced paramagnetic
4. Polycrystalline single-phase samples were obtained over the whole
composition range by a high-pressure-heating technique, followed by
measurements of magnetic susceptibility, magnetization, specific heat,
thermopower, and electrical resistivity. The ferromagnetic order in long range
is gradually suppressed by the Rh substitution and vanishes at .
The electronic term of specific-heat shows unusual behavior near the critical
Rh concentration; the feature does not match even qualitatively with what was
reported for the related perovskites (Sr,Ca)RuO. Furthermore, another
anomaly in the specific heat was observed at .Comment: Accepted for publication in PR
Electrodynamics of quasi-two-dimensional BEDT-TTF charge transfer salts
We consider the millimeter-wave electrodynamics specific to
quasi-two-dimensional conductors and superconductors based on the organic donor
molecule BEDT-TTF. Using realistic physical parameters, we examine the current
polarizations that result for different oscillating (GHz) electric and magnetic
field polarizations. We show that, in general, it is possible to discriminate
between effects (dissipation and dispersion) due to in-plane and interlayer ac
currents. However, we also show that it is not possible to selectively probe
any single component of the in-plane conductivity tensor, and that excitation
of interlayer currents is strongly influenced by the sample geometry and the
electromagnetic field polarization.Comment: 5 pages including 3 figures Minor correction to figure
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