2,607 research outputs found
Solitons in tunnel-coupled repulsive and attractive condensates
We study solitons in the condensate trapped in a double-well potential with
far-separated wells, when the s-wave scattering length has different signs in
the two parts of the condensate. By employing the coupled-mode approximation it
is shown that there are unusual stable bright solitons in the condensate, with
the larger share of atoms being gathered in the repulsive part. Such unusual
solitons derive their stability from the quantum tunneling and correspond to
the strong coupling between the parts of the condensate. The ground state of
the system, however, corresponds to weak coupling between the condensate parts,
with the larger share of atoms being gathered in the attractive part of the
condensate.Comment: LaTex, 23 pages, 6 figures; revised version; to appear in Physical
Review
Comment on ``Validity of Feynman's prescription of disregarding the Pauli principle in intermediate states''
In a recent paper Coutinho, Nogami and Tomio [Phys. Rev. A 59, 2624 (1999);
quant-ph/9812073] presented an example in which, they claim, Feynman's
prescription of disregarding the Pauli principle in intermediate states of
perturbation theory fails. We show that, contrary to their claim, Feynman's
prescription is consistent with the exact solution of their example.Comment: 1 pag
Lythraceae.
MARHOLD, K.; FELINER, G. N. (Ed.). IOPB Column
A new broken U(1)-symmetry in extreme type-II superconductors
A phase transition within the molten phase of the Abrikosov vortex system
without disorder in extreme type-II superconductors is found via large-scale
Monte-Carlo simulations. It involves breaking a U(1)-symmetry, and has a
zero-field counterpart, unlike vortex lattice melting. Its hallmark is the loss
of number-conservation of connected vortex paths threading the entire system
{\it in any direction}, driving the vortex line tension to zero. This tension
plays the role of a generalized ``stiffness'' of the vortex liquid, and serves
as a probe of the loss of order at the transition, where a weak specific heat
anomaly is found.Comment: 5 pages, 3 figure
Plasmon polaritons in photonic superlattices containing a left-handed material
We analyze one-dimensional photonic superlattices which alternate layers of
air and a left-handed material. We assume Drude-type dispersive responses for
the dielectric permittivity and magnetic permeability of the left-handed
material. Maxwell's equations and the transfer-matrix technique are used to
derive the dispersion relation for the propagation of obliquely incident
optical fields. The photonic dispersion indicates that the growth-direction
component of the electric (or magnetic) field leads to the propagation of
electric (or magnetic) plasmon polaritons, for either TE or TM configurations.
Furthermore, we show that if the plasma frequency is chosen within the photonic
zeroth-order bandgap, the coupling of light with plasmons
weakens considerably. As light propagation is forbidden in that particular
frequency region, the plasmon-polariton mode reduces to a pure plasmon mode.Comment: 4 pages, 4 figure
COMPARATIVE ANALYSIS OF THE EFFICIENCY OF THERMAL SYSTEMS BUILT WITH REFLECTIVE INSULATORS WITH AND WITHOUT VACUUM
The use of reflective surfaces functioning as thermal insulators has grown significantly over the years. Reflective thermal insulators are materials that have several characteristics such as low emissivity, low absorptivity and high reflectivity in the infrared spectrum. The use of these materials has grown very much lately, since they contain several important radioactive properties that minimize the heat loss of thermal systems and cooling systems that are used to block the heat on the roof of buildings. A system made of three surfaces of 430 stainless steel mirror was built to analyze the influence of reflective surfaces as a way to reduce the heat loss and thereby conserve the energy of a thermal system. The system was analyzed both with and without the presence of vacuum, and then compared with a system that contained glass wool between the stainless steel mirror walls, since this insulator is considered resistive and also broadly used around the world in thermal systems. The reflectivity and emissivity of the surfaces used were also measured in this experiment. A type K thermocouple was fixed on the wall of the system to obtain the temperature of the stainless steel mirror surfaces and to analyze the thermal behavior of each configuration used. The results showed an efficiency of 13% when the reflective surfaces were used to minimize the heat loss of the thermal system. However, the system with vacuum had the best outcome, a 60% efficiency. Both of these were compared to the system made of glass wool as a thermal insulator
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