527 research outputs found
Large magnetocaloric effect in the frustrated antiferromagnet EuIrP
We present a theoretical analysis of the magnetocaloric effect in the
frustrated antiferromagnet \Eu. Monte Carlo simulations indicate a large
magnetic entropy change J kgK
at K for a moderate change in the external magnetic field Tesla. The highest value of seems to be associated with the
presence of a multicritical point in the magnetic field versus temperature
phase diagram (at Tesla and K) but it persists with
similar large values for a broad range of temperatures . Single
crystal \Eu~magnetization vs magnetic field experiments allowed us to obtain
the magnetocaloric effect for K. The results are consistent with the
theoretical analysis and show a large magnetocaloric effect for K.
Finally, we present a phenomenological Landau functional analysis that provides
a simplified description of the phase diagram and of the magnetocaloric effect.
Although the magnetic frustration in this system leads to a rich phase diagram,
we found no clear indication that it plays a significant role enhancing the
magneticaloric effect, other than by reducing the transition temperatures and
fields.Comment: 10 pages, 10 figure
Rapid increase of resistance to erythromycin and clindamycin in Streptococcus pyogenes in Italy, 1993-1995. The Italian Surveillance Group for Antimicrobial Resistance.
A survey of antibiotic resistance in Streptococcus pyogenes in Italy showed a sharp increase in erythromycin resistance. In 1993, the incidence of erythromycin-resistant strains was on average 5.1%, with marked variations by geographic area. Two years later, the incidence of these strains had registered a 1.5- to roughly 20-fold increase, with a mean value of 25.9%, exceeding 40% in three centers out of 13 and 30% in another four. For all the strains studied, normal levels of susceptibility to penicillin were reported
Enhanced Kondo Effect in an Electron System Dynamically Coupled with Local Optical Phonon
We discuss Kondo behavior of a conduction electron system coupled with local
optical phonon by analyzing the Anderson-Holstein model with the use of a
numerical renormalization group (NRG) method. There appear three typical
regions due to the balance between Coulomb interaction and
phonon-mediated attraction . For , we
observe the standard Kondo effect concerning spin degree of freedom. Since the
Coulomb interaction is effectively reduced as , the
Kondo temperature is increased when is increased. On
the other hand, for , there occurs the Kondo effect
concerning charge degree of freedom, since vacant and double occupied states
play roles of pseudo-spins. Note that in this case, is decreased
with the increase of . Namely, should be maximized for
. Then, we analyze in detail the Kondo behavior
at , which is found to be explained by the polaron
Anderson model with reduced hybridization of polaron and residual repulsive
interaction among polarons. By comparing the NRG results of the polaron
Anderson model with those of the original Anderson-Holstein model, we clarify
the Kondo behavior in the competing region of .Comment: 8 pages, 8 figure
Lattice specific heat for the RMIn (R = Gd, La, Y, M = Co, Rh) compounds: non-magnetic contribution subtraction
We analyze theoretically a common experimental process used to obtain the
magnetic contribution to the specific heat of a given magnetic material. In the
procedure, the specific heat of a non-magnetic analog is measured and used to
subtract the non-magnetic contributions, which are generally dominated by the
lattice degrees of freedom in a wide range of temperatures. We calculate the
lattice contribution to the specific heat for the magnetic compounds GdMIn
(M = Co, Rh) and for the non-magnetic YMIn and LaMIn (M = Co, Rh),
using density functional theory based methods. We find that the best
non-magnetic analog for the subtraction depends on the magnetic material and on
the range of temperatures. While the phonon specific heat contribution of
YRhIn is an excellent approximation to the one of GdCoIn in the full
temperature range, for GdRhIn we find a better agreement with LaCoIn,
in both cases, as a result of an optimum compensation effect between masses and
volumes. We present measurements of the specific heat of the compounds
GdMIn (M = Co, Rh) up to room temperature where it surpasses the value
expected from the Dulong-Petit law. We obtain a good agreement between theory
and experiment when we include anharmonic effects in the calculations
Effective electron-electron and electron-phonon interactions in the Hubbard-Holstein model
We investigate the interplay between the electron-electron and the
electron-phonon interaction in the Hubbard-Holstein model. We implement the
flow-equation method to investigate within this model the effect of correlation
on the electron-phonon effective coupling and, conversely, the effect of
phonons in the effective electron-electron interaction. Using this technique we
obtain analytical momentum-dependent expressions for the effective couplings
and we study their behavior for different physical regimes. In agreement with
other works on this subject, we find that the electron-electron attraction
mediated by phonons in the presence of Hubbard repulsion is peaked at low
transferred momenta. The role of the characteristic energies involved is also
analyzed.Comment: 23 pages, 5 figure
Carbapenem-resistant Pseudomonas aeruginosa with acquired bla(vim) metallo-beta-lactamase determinants, Italy.
6nonenoneROSSOLINI G.M.; RICCIO M.L.; CORNAGLIA G.; PAGANI L.; LAGATOLLA C.; SELAN L. AND FONTANA R.Rossolini, G. M.; Riccio, M. L.; Cornaglia, G.; Pagani, L.; Lagatolla, Cristina; Selan, L. AND FONTANA R
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