5,977 research outputs found
Effective Field Theory for the Quantum Electrodynamics of a Graphene Wire
We study the low-energy quantum electrodynamics of electrons and holes, in a
thin graphene wire. We develop an effective field theory (EFT) based on an
expansion in p/p_T, where p_T is the typical momentum of electrons and holes in
the transverse direction, while p are the momenta in the longitudinal
direction. We show that, to the lowest-order in (p/p_T), our EFT theory is
formally equivalent to the exactly solvable Schwinger model. By exploiting such
an analogy, we find that the ground state of the quantum wire contains a
condensate of electron-hole pairs. The excitation spectrum is saturated by
electron-hole collective bound-states, and we calculate the dispersion law of
such modes. We also compute the DC conductivity per unit length at zero
chemical potential and find g_s =e^2/h, where g_s=4 is the degeneracy factor.Comment: 7 pages, 2 figures. Definitive version, accepted for publication on
Phys. Rev.
Engineering Seismology Aspects of the M-6.5, Southern Italy Earthquake of Nov. 23, 1980: A Preliminary Review
The paper provides an overview of salient engineering seismology features of the earthquake, which was one of the major seismic catastrophes occurring in Italy in this century. After a short description of the characteristics of the earthquake source and of the historical seismicity of the region, preliminary strong-motion and intensity data are presented. Aspects of geotechnical engineering interest include some large landslides in inhabited areas, and notable cases of correlation between severity of damage and local soil conditions and topography
Instantons, diquarks and non-leptonic weak decays of hyperons
This work is devoted to the study of the non-perturbative contributions in
non-leptonic hyperon decays. We show that the instanton-induced 't Hooft
interaction can naturally explain the Delta I=1/2 rule, by generating
quark-diquark clustering inside octet baryons. We compute P-wave and S-wave
amplitudes in the Instanton Liquid Model (ILM), and find good agreement with
experiment. We propose a model-independent procedure to test on the lattice if
the leading quark-quark attraction in the 0^+ anti-triplet channel responsible
for diquark structures in hadrons is originated by the interaction generated by
quasi-classical fields or it is predominantly due to other perturbative and/or
confining forces.Comment: Final version to appear on PR
Seismic Amplification in the Presence of Geological and Topographic Irregularities
Following some introductory remarks on the key aspects of seismic site effects evaluation and on new data of special interest from recent earthquakes, the first part of the paper discusses and compares the performance of numerical 2D and 1D models, as well as of simple exact solutions, in problems of local soil response and of topographic amplification. The second part is devoted to the illustration of a very promising computational tool, i.e. the Fourier (or pseudo spectral) method, for time-domain analyses of seismic wave propagation in heterogeneous elastic media
Garigliano nuclear power plant: seismic evaluation of the turbine building
The Italian Garigliano Nuclear Power Plant (NPP) started its energy production in 1963. At present it is in the decommissioning stage. In order to get a proper management of the radioactive waste that will be produced during the dismantling operations it has been considered convenient to convert the turbine building of the plant into a temporary waste repository. This decision posed a remarkable seismic safety assessment issue. As a matter of fact, the challenge was to extend, in satisfactory safety conditions, the use of an important facility that has reached the end of its designed lifetime and to have this extended use approved by nuclear safety agencies. In this context many tasks have been accomplished, of which the most important are:
(a) a new appraisal of site seismic hazard;
(b) the execution of many investigations and testing on the
construction materials;
(c) the set up of a detailed 3D finite element model including the explicit representation of foundation piles and soil;
(d) consideration of soil structure kinematic and dynamic nteraction effects.
This paper describes the adopted seismic safety assessment criteria which are based on a performance objectives design approach. While performance based design is the approach currently recommended by European Regulations to manage seismic risk and it is fully incorporated in the Italian code for conventional buildings, bridges and plants, NPP are not explicitly considered. Therefore it was necessary to delineate a consistent interpretation of prescribed rules in order to properly select the maximum and operating design earthquakes on one side and corresponding acceptable limit states on the other side. The paper further provides an outline of the numerical analyses carried out, of the main results obtained and of the principal retrofitting actions that will be realized
Instantons, Chiral Dynamics and Hadronic Resonances
We use the Interacting Instanton Liquid Model (IILM) as a tool to study the
role played by the chiral interactions in the lowest-lying vector and axial
vector meson resonances. We find that narrow a1 and rho meson resonances can be
generated by instanton-induced chiral forces, even in the absence of
confinement. In the IILM, these hadrons are found to have masses only about 30%
larger than the experimental value and small width <10-50 MeV. This result
suggests that chiral interactions are very important in these systems and
provide most of their mass. We explore the decaying patterns of the rho meson,
in the absence of confinement. We argue that, in our model where only chiral
forces are switched on, this meson decays dissociating into its quark
anti-quark constituents
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