2,454 research outputs found
Diffeomorphisms, Noether Charges and Canonical Formalism in 2D Dilaton Gravity
We carry out a parallel study of the covariant phase space and the
conservation laws of local symmetries in two-dimensional dilaton gravity. Our
analysis is based on the fact that the Lagrangian can be brought to a form that
vanishes on-shell giving rise to a well-defined covariant potential for the
symplectic current. We explicitly compute the symplectic structure and its
potential and show that the requirement to be finite and independent of the
Cauchy surface restricts the asymptotic symmetries.Comment: 14 pages, latex with psfig macro, one figur
Universal relations in the finite-size correction terms of two-dimensional Ising models
Quite recently, Izmailian and Hu [Phys. Rev. Lett. 86, 5160 (2001)] studied
the finite-size correction terms for the free energy per spin and the inverse
correlation length of the critical two-dimensional Ising model. They obtained
the universal amplitude ratio for the coefficients of two series. In this study
we give a simple derivation of this universal relation; we do not use an
explicit form of series expansion. Moreover, we show that the Izmailian and
Hu's relation is reduced to a simple and exact relation between the free energy
and the correlation length. This equation holds at any temperature and has the
same form as the finite-size scaling.Comment: 4 pages, RevTeX, to appear in Phys. Rev. E, Rapid Communication
Off-pump HeartMate II Exchange in a Patient with Severe Lower Extremity Peripheral Artery Disease: A Case Report
Thrombosis of left ventricular assist device (LVAD) pumps is a serious complication that often requires exchange of the device. A 66-year-old man with severe peripheral vascular disease presented with pump thrombosis of the HeartMate II (HMII) LVAD 1.5 years after implantation. The HMII was exchanged to another HMII through a subcostal incision and without the use of cardiopulmonary bypass. For safety, the patient was prepared for cardiopulmonary bypass by exposing the right subclavian artery and insertion of a 5 FR cannula in the left common femoral vein. The pump was exchanged through a subcostal incision made over the LVAD pump pocket perpendicular to the costal margin. After deairing the pump and graft, LVAD support was resumed, postoperative course was uneventful, and the patient was discharged from the hospital four days later. Re-thrombosis, stroke, and right heart failure are frequent complications after LVAD exchange. Exchange through a subcostal incision with cardiopulmonary bypass backup appears to be safe
Black Hole Formation by Sine-Gordon Solitons in Two-dimensional Dilaton Gravity
The CGHS model of two-dimensional dilaton gravity coupled to a sine-Gordon
matter field is considered. The theory is exactly solvable classically, and the
solutions of a kink and two-kink type solitons are studied in connection with
black hole formation.Comment: 11 pages, no figures, revte
Boson gas in a periodic array of tubes
We report the thermodynamic properties of an ideal boson gas confined in an
infinite periodic array of channels modeled by two, mutually perpendicular,
Kronig-Penney delta-potentials. The particle's motion is hindered in the x-y
directions, allowing tunneling of particles through the walls, while no
confinement along the z direction is considered. It is shown that there exists
a finite Bose- Einstein condensation (BEC) critical temperature Tc that
decreases monotonically from the 3D ideal boson gas (IBG) value as the
strength of confinement is increased while keeping the channel's cross
section, constant. In contrast, Tc is a non-monotonic function of
the cross-section area for fixed . In addition to the BEC cusp, the
specific heat exhibits a set of maxima and minima. The minimum located at the
highest temperature is a clear signal of the confinement effect which occurs
when the boson wavelength is twice the cross-section side size. This
confinement is amplified when the wall strength is increased until a
dimensional crossover from 3D to 1D is produced. Some of these features in the
specific heat obtained from this simple model can be related, qualitatively, to
at least two different experimental situations: He adsorbed within the
interstitial channels of a bundle of carbon nanotubes and
superconductor-multistrand-wires NbSn.Comment: 9 pages, 10 figures, submitte
Scaling and finte-size-scaling in the two dimensional random-coupling Ising ferromagnet
It is shown by Monte Carlo method that the finite size scaling (FSS) holds in
the two dimensional random-coupled Ising ferromagnet. It is also demonstrated
that the form of universal FSS function constructed via novel FSS scheme
depends on the strength of the random coupling for strongly disordered cases.
Monte Carlo measurements of thermodynamic (infinite volume limit) data of the
correlation length () up to along with measurements of
the fourth order cumulant ratio (Binder's ratio) at criticality are reported
and analyzed in view of two competing scenarios. It is demonstrated that the
data are almost exclusively consistent with the scenario of weak universality.Comment: 9 pages, 4figuer
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