27,027 research outputs found
Ground-states of spin-1 bosons in asymmetric double-wells
In this work we investigate the different states of a system of spin-1 bosons
in two potential wells connected by tunneling, with spin-dependent interaction.
The model utilizes the well-known Bose-Hubbard Hamiltonian, adding a local
interaction term that depends on the modulus of the total spin in a well,
favoring a high- or low-spin state for different signs of the coupling
constant. We employ the concept of fidelity to detect critical values of
parameters for which the ground state undergoes significant changes. The nature
of the states is investigated through evaluation of average occupation numbers
in the wells and of spin correlations. A more detailed analysis is done for a
two-particle system, but a discussion of the three-particle case and some
results for larger numbers are also presented.Comment: 7 pages, 10 figure
Absence of Gluonic Components in Axial and Tensor Mesons
A quarkonium-gluonium mixing scheme previously developed to describe the
characteristic of the pseudoscalar mesons is applied to axial and tensor
mesons. The parameters of the model are determined by fitting the eigenvalues
of a mass matrix. The corresponding eigenvectors give the proportion of light
quarks, strange quarks and glueball in each meson. However the predictions of
the model for branching ratios and electromagnetic decays are incompatible with
the experimental results. These results suggest the absence of gluonic
components in the states of axial and tensor isosinglet mesons analyzed here.Comment: 12 page
Understanding thio-effects in simple phosphoryl systems : role of solvent effects and nucleophile charge.
Recent experimental work (J. Org. Chem., 2012, 77, 5829) demonstrated pronounced differences in measured thio-effects for the hydrolysis of (thio)phosphodichloridates by water and hydroxide nucleophiles. In the present work, we have performed detailed quantum chemical calculations of these reactions, with the aim of rationalizing the molecular bases for this discrimination. The calculations highlight the interplay between nucleophile charge and transition state solvation in SN2(P) mechanisms as the basis of these differences, rather than a change in mechanism
Berry phases and zero-modes in toroidal topological insulator
An effective Hamiltonian describing the surface states of a toroidal
topological insulator is obtained, and it is shown to support both bound-states
and charged zero-modes. Actually, the spin connection induced by the toroidal
curvature can be viewed as an position-dependent effective vector potential,
which ultimately yields the zero-modes whose wave-functions harmonically
oscillate around the toroidal surface. In addition, two distinct Berry phases
are predicted to take place by the virtue of the toroidal topology.Comment: New version, accepted for publication in EPJB, 6 pages, 1 figur
Ground-state configurations in ferromagnetic nanotori
Magnetization ground states are studied in toroidal nanomagnets. The
energetics associated to the ferromagnetic, vortex and onion-like
configurations are explicitly computed. The analysis reveals that the vortex
appears to be the most prominent of such states, minimizing total energy in
every torus with internal radius (for Permalloy). For
the vortex remains the most favorable pattern whenever
( is the torus external radius and is
the exchange length), being substituted by the ferromagnetic state whenever
.Comment: 16 pages, 9 figures, 3 apendices, Revtex forma
Thermal evolution of hybrid stars within the framework of a nonlocal Nambu--Jona-Lasinio model
We study the thermal evolution of neutron stars containing deconfined quark
matter in their core. Such objects are generally referred to as quark-hybrid
stars. The confined hadronic matter in their core is described in the framework
of non-linear relativistic nuclear field theory. For the quark phase we use a
non-local extension of the SU(3) Nambu Jona-Lasinio model with vector
interactions. The Gibbs condition is used to model phase equilibrium between
confined hadronic matter and deconfined quark matter. Our study indicates that
high-mass neutron stars may contain between 35 and 40 % deconfined quark-hybrid
matter in their cores. Neutron stars with canonical masses of around would not contain deconfined quark matter. The central proton
fractions of the stars are found to be high, enabling them to cool rapidly.
Very good agreement with the temperature evolution established for the neutron
star in Cassiopeia A (Cas A) is obtained for one of our models (based on the
popular NL3 nuclear parametrization), if the protons in the core of our stellar
models are strongly paired, the repulsion among the quarks is mildly repulsive,
and the mass of Cas A has a canonical value of .Comment: 10 pages, 7 figure
Supergiant Barocaloric Effects in Acetoxy Silicone Rubber over a Wide Temperature Range: Great Potential for Solid-state Cooling
Solid-state cooling based on caloric effects is considered a viable
alternative to replace the conventional vapor-compression refrigeration
systems. Regarding barocaloric materials, recent results show that elastomers
are promising candidates for cooling applications around room-temperature. In
the present paper, we report supergiant barocaloric effects observed in acetoxy
silicone rubber - a very popular, low-cost and environmentally friendly
elastomer. Huge values of adiabatic temperature change and reversible
isothermal entropy change were obtained upon moderate applied pressures and
relatively low strains. These huge barocaloric changes are associated both to
the polymer chains rearrangements induced by confined compression and to the
first-order structural transition. The results are comparable to the best
barocaloric materials reported so far, opening encouraging prospects for the
application of elastomers in near future solid-state cooling devices.Comment: 19 pages, 7 figures, 2 table
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