19,129 research outputs found
From Disordered Crystal to Glass: Exact Theory
We calculate thermodynamic properties of a disordered model insulator,
starting from the ideal simple-cubic lattice () and increasing the
disorder parameter to . As in earlier Einstein- and Debye-
approximations, there is a phase transition at . For the
low-T heat-capacity whereas for , . The van
Hove singularities disappear at {\em any finite }. For we discover
novel {\em fixed points} in the self-energy and spectral density of this model
glass.Comment: Submitted to Phys. Rev. Lett., 8 pages, 4 figure
The role of slip transfer at grain boundaries in the propagation of microstructurally short fatigue cracks in Ni-based superalloys
Crack initiation and propagation under high-cycle fatigue conditions have
been investigated for a polycrystalline Ni-based superalloy by in-situ
synchrotron assisted diffraction and phase contrast tomography. The cracks
nucleated along the longest coherent twin boundaries pre-existing on the
specimen surface, that were well oriented for slip and that presented a large
elastic incompatibility across them. Moreover, the propagation of
microstructurally short cracks was found to be determined by the easy slip
transfer paths across the pre-existing grain boundaries. This information can
only be obtained by characterization techniques like the ones presented here
that provide the full set of 3D microstructural information
Length-dependent oscillations of the conductance through atomic chains: The importance of electronic correlations
We calculate the conductance of atomic chains as a function of their length.
Using the Density Matrix Renormalization Group algorithm for a many-body model
which takes into account electron-electron interactions and the shape of the
contacts between the chain and the leads, we show that length-dependent
oscillations of the conductance whose period depends on the electron density in
the chain can result from electron-electron scattering alone. The amplitude of
these oscillations can increase with the length of the chain, in contrast to
the result from approaches which neglect the interactions.Comment: 7 pages, 4 figure
Strange and charm mesons at FAIR
We study the properties of strange and charm mesons in hot and dense matter
within a self-consistent coupled-channel approach for the experimental
conditions of density and temperature expected for the CBM experiment at
FAIR/GSI. The in-medium solution at finite temperature accounts for Pauli
blocking effects, mean-field binding of all the baryons involved, and meson
self-energies. We analyze the behaviour in this hot and dense environment of
dynamically-generated baryonic resonances together with the evolution with
density and temperature of the strange and open-charm meson spectral functions.
We test the spectral functions for strange mesons using energy-weighted sum
rules and finally discuss the implications of the properties of charm mesons on
the D_{s0}(2317) and the predicted X(3700) scalar resonances.Comment: 12 pages, 9 figures, invited talk at XXXI Mazurian Lakes Conference
on Physics: Nuclear Physics and the Road to FAIR, August 30-September 6,
2009, Piaski, Polan
Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field
We use neutron diffraction to probe the magnetization components of a crystal
of Mn12 single-molecule magnets. Each of these molecules behaves, at low
temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the
crystallographic c axis. Application of a magnetic field perpendicular to c
induces quantum tunneling between opposite spin orientations, enabling the
spins to attain thermal equilibrium. Below approximately 0.9 K, intermolecular
interactions turn this equilibrium state into a ferromagnetically ordered
phase. However, long range ferromagnetic correlations nearly disappear for
fields larger 5.5 T, possibly suggesting the existence of a quantum critical
point.Comment: 4 pages, 4 figure
Charmed hadrons in nuclear medium
We study the properties of charmed hadrons in dense matter within a
coupled-channel approach which accounts for Pauli blocking effects and meson
self-energies in a self-consistent manner. We analyze the behaviour in this
dense environment of dynamically-generated baryonic resonances as well as the
open-charm meson spectral functions. We discuss the implications of the
in-medium properties of open-charm mesons on the and the
predicted X(3700) scalar resonances.Comment: 4 pages, 5 figures, invited parallel talk in the 5th International
Conference on Quarks and Nuclear Physics (QNP09), Beijing, September 21-26,
200
The \rho\rho interaction in the hidden gauge formalism and the f_0(1370) and f_2(1270) resonances
We have studied the interaction of vectors mesons within the hidden gauge
formalism and applied it to the particular case of the interaction.
We find a strong attraction in the isospin, spin channels I,S=0,0 and 0,2,
which is enough to bind the system. We also find that the
attraction in the I,S=0,2 channel is much stronger than in the 0,0 case. The
states develop a width when the mass distribution is considered, and
particularly when the decay channel is turned on. Using a
regularization scheme with cut offs of natural size, we obtain results in fair
agreement with the mass and the width of the and meson
states, providing a natural explanation of why the tensor state is more bound
than the scalar and offering a new picture for these states, which would be
dynamically generated from the interaction or, in simpler words,
molecular states.Comment: Version accepted for publicatio
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