15,949 research outputs found
Magnetocaloric effect in integrable spin-s chains
We study the magnetocaloric effect for the integrable antiferromagnetic
high-spin chain. We present an exact computation of the Gr\"uneisen parameter,
which is closely related to the magnetocaloric effect, for the quantum spin-s
chain on the thermodynamical limit by means of Bethe ansatz techniques and the
quantum transfer matrix approach. We have also calculated the entropy S and the
isentropes in the (H,T) plane. We have been able to identify the quantum
critical points H_c^{(s)}=2/(s+1/2) looking at the isentropes and/or the
characteristic behaviour of the Gr\"uneisen parameter.Comment: 6 pages, 3 figure
Are the anti-charmed and bottomed pentaquarks molecular heptaquarks?
I study the charmed resonance D*p (3100) very recently
discovered by the H1 collaboration at Hera. An anticharmed resonance was
already predicted, in a recent publication mostly dedicated to the S=1
resonance Theta+(1540). To confirm these recent predictions, I apply the same
standard quark model with a quark-antiquark annihilation constrained by chiral
symmetry. I find that repulsion excludes the D*p (3100) as a
s-wave pentaquark. I explore the D*p (3100) as a heptaquark, equivalent to a
N-pi-D* linear molecule, with positive parity and total isospin I=0. I find
that the N-D repulsion is cancelled by the attraction existing in the N-pi and
pi-D channels. In our framework this state is harder to bind than the Theta+
described by a k-pi-N borromean bound-state, a lower binding energy is expected
in agreement with the H1 observation. Multiquark molecules N-pi-D, N-pi-B* and
N-pi-B are also predicted.Comment: 5 pages, 2 figures, RevTe
Ensaio de Proficiência Interlaboratorial para Contagem de Células Somáticas em Leite.
bitstream/item/31512/1/comunicado-225.pd
Amostras Piloto no Controle da Qualidade dos Resultados da Composição Centesimal de Leite.
bitstream/item/31510/1/comunicado-223.pd
Approaching the Asymptotic Regime of Rapidly Rotating Convection: Boundary Layers vs Interior Dynamics
Rapidly rotating Rayleigh-B\'enard convection is studied by combining results
from direct numerical simulations (DNS), laboratory experiments and asymptotic
modeling. The asymptotic theory is shown to provide a good description of the
bulk dynamics at low, but finite Rossby number. However, large deviations from
the asymptotically predicted heat transfer scaling are found, with laboratory
experiments and DNS consistently yielding much larger Nusselt numbers than
expected. These deviations are traced down to dynamically active Ekman boundary
layers, which are shown to play an integral part in controlling heat transfer
even for Ekman numbers as small as . By adding an analytical
parameterization of the Ekman transport to simulations using stress-free
boundary conditions, we demonstrate that the heat transfer jumps from values
broadly compatible with the asymptotic theory to states of strongly increased
heat transfer, in good quantitative agreement with no-slip DNS and compatible
with the experimental data. Finally, similarly to non-rotating convection, we
find no single scaling behavior, but instead that multiple well-defined
dynamical regimes exist in rapidly-rotating convection systems.Comment: Submitted to Physical Review Letters on 17 July 201
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