21,473 research outputs found
W-graph ideals
We introduce a concept of a W-graph ideal in a Coxeter group. The main goal
of this paper is to describe how to construct a W-graph from a given W-graph
ideal. The principal application of this idea is in type A, where it provides
an algorithm for the construction of W-graphs for Specht modules.Comment: 25 page
The effects of foundation size on the seismic performance of buildings considering the soil-foundation-structure interaction
Copyright © 2016 Techno-Press, Ltd. Shallow footings are one of the most common types of foundations used to support mid-rise buildings in high risk seismic zones. Recent findings have revealed that the dynamic interaction between the soil, foundation, and the superstructure can influence the seismic response of the building during earthquakes. Accordingly, the properties of a foundation can alter the dynamic characteristics (natural frequency and damping) of the soil-foundation-structure system. In this paper the influence that shallow foundations have on the seismic response of a mid-rise moment resisting building is investigated. For this purpose, a fifteen storey moment resisting frame sitting on shallow footings with different sizes was simulated numerically using ABAQUS software. By adopting a direct calculation method, the numerical model can perform a fully nonlinear time history dynamic analysis to realistically simulate the dynamic behaviour of soil, foundation, and structure under seismic excitations. This three-dimensional numerical model accounts for the nonlinear behaviour of the soil medium and structural elements. Infinite boundary conditions were assigned to the numerical model to simulate free field boundaries, and appropriate contact elements capable of modelling sliding and separation between the foundation and soil elements are also considered. The influence of foundation size on the natural frequency of the system and structural response spectrum was also studied. The numerical results for cases of soil-foundation-structure systems with different sized foundations and fixed base conditions (excluding soil-foundation-structure interaction) in terms of lateral deformations, inter-storey drifts, rocking, and shear force distribution of the structure were then compared. Due to natural period lengthening, there was a significant reduction in the base shears when the size of the foundation was reduced. It was concluded that the size of a shallow foundation influences the dynamic characteristics and the seismic response of the building due to interaction between the soil, foundation, and structure, and therefore design engineer should carefully consider these parameters in order to ensure a safe and cost effective seismic design
The Gamow-Teller States in Relativistic Nuclear Models
The Gamow-Teller(GT) states are investigated in relativistic models. The
Landau-Migdal(LM) parameter is introduced in the Lagrangian as a contact term
with the pseudo-vector coupling. In the relativistic model the total GT
strength in the nucleon space is quenched by about 12% in nuclear matter and by
about 6% in finite nuclei, compared with the one of the Ikeda-Fujii-Fujita sum
rule. The quenched amount is taken by nucleon-antinucleon excitations in the
time-like region. Because of the quenching, the relativistic model requires a
larger value of the LM parameter than non-relativistic models in describing the
excitation energy of the GT state. The Pauli blocking terms are not important
for the description of the GT states.Comment: REVTeX4, no figure
Nuclear halo structure and pseudo-spin symmetry
Nuclear halo structure and restoration of relativistic symmetry are studied
within the framework of the relativistic Hartree-Fock-Bogoliubov (RHFB) theory.
Giant halos as well as ordinary ones are found in Cerium isotopes close to the
neutron drip line. Bridged by T=0 {channel}, the restoration of pseudo-spin
symmetry (PSS) plays an essential role in stabilizing the neutron halo
structures. The Fock terms, especially the -tensor couplings, not only
play significant role in the PSS restoration but also present substantial
contributions to the T=0 {channel}, from which is well demonstrated the
necessity of Fock terms.Comment: 5pages, 4figures, 1tabl
Nuclear response functions in homogeneous matter with finite range effective interactions
The question of nuclear response functions in a homogeneous medium is
examined. A general method for calculating response functions in the random
phase approximation (RPA) with exchange is presented. The method is applicable
for finite-range nuclear interactions. Examples are shown in the case of
symmetric nuclear matter described by a Gogny interaction. It is found that the
convergence of the results with respect to the multipole truncation is quite
fast. Various approximation schemes such as the Landau approximation, or the
Landau approximation for the exchange terms only, are discussed in comparison
with the exact results.Comment: 9 pages, 9 figure
Pairing effects on the collectivity of quadrupole states around 32Mg
The first 2+ states in N=20 isotones including neutron-rich nuclei 32Mg and
30Ne are studied by the Hartree-Fock-Bogoliubov plus quasiparticle random phase
approximation method based on the Green's function approach. The residual
interaction between the quasiparticles is consistently derived from the
hamiltonian density of Skyrme interactions with explicit velocity dependence.
The B(E2) transition probabilities and the excitation energies of the first 2+
states are well described within a single framework. We conclude that pairing
effects account largely for the anomalously large B(E2) value and the very low
excitation energy in 32Mg.Comment: 14 pages, 9 figure
Resonant continuum in the Hartree-Fock+BCS approximation
A method for incorporating the effect of the resonant continuum into
Hartree-Fock+BCS equations is proposed. The method is applied for the case of
a neutron-rich nucleus calculated with a Skyrme-type force plus a zero-range
pairing interaction and the results are compared with
Hartree-Fock-Bogoliubov calculations. It is shown that the widths of resonant
states have an important effect on the pairing properties of nuclei close to
the drip line.Comment: 9 pages, 2 figures, comparison with HFB adde
Relativistic Hartree-Fock-Bogoliubov theory with Density Dependent Meson-Nucleon Couplings
Relativistic Hartree-Fock-Bogoliubov (RHFB) theory with density-dependent
meson-nucleon couplings is presented. The integro-differential RHFB equations
are solved by expanding the different components of the quasi-particle spinors
in the complete set of eigen-solutions of the Dirac equations with Woods-Saxon
potentials. Using the finite-range Gogny force D1S as an effective interaction
in the pairing channel, systematic RHFB calculations are performed for Sn
isotopes and N=82 isotones. It is demonstrated that an appropriate description
of both mean field and pairing effects can be obtained within RHFB theory with
finite range Gogny pairing forces. Better systematics are also found in the
regions from the stable to the neutron-rich side with the inclusion of Fock
terms, especially in the presence of -tensor couplings.Comment: 11 pages, 2 tables and 4 figure
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