226 research outputs found
Local production of tumor necrosis factor encoded by recombinant vaccinia virus is effective in controlling viral replication in vivo.
Nernst and Seebeck Coefficients of the Cuprate SuperconductorYBaCuO: A Study of Fermi Surface Reconstruction
The Seebeck and Nernst coefficients and of the cuprate
superconductor YBaCuO (YBCO) were measured in a single crystal with
doping in magnetic fields up to H = 28 T. Down to T=9 K,
becomes independent of field by T, showing that superconducting
fluctuations have become negligible. In this field-induced normal state,
and are both large and negative in the limit, with the
magnitude and sign of consistent with the small electron-like Fermi
surface pocket detected previously by quantum oscillations and the Hall effect.
The change of sign in at K is remarkably similar to that
observed in LaBaCuO, LaNdSrCuO and
LaEuSrCuO, where it is clearly associated with the onset
of stripe order. We propose that a similar density-wave mechanism causes the
Fermi surface reconstruction in YBCO.Comment: Final version accepted for publication in Phys. Rev. Lett. New title,
shorter abstract, minor revision of text and added reference
Scale-invariant magnetoresistance in a cuprate superconductor
The anomalous metallic state in high-temperature superconducting cuprates is
masked by the onset of superconductivity near a quantum critical point. Use of
high magnetic fields to suppress superconductivity has enabled a detailed study
of the ground state in these systems. Yet, the direct effect of strong magnetic
fields on the metallic behavior at low temperatures is poorly understood,
especially near critical doping, . Here we report a high-field
magnetoresistance study of thin films of \LSCO cuprates in close vicinity to
critical doping, . We find that the metallic state
exposed by suppressing superconductivity is characterized by a
magnetoresistance that is linear in magnetic field up to the highest measured
fields of T. The slope of the linear-in-field resistivity is
temperature-independent at very high fields. It mirrors the magnitude and
doping evolution of the linear-in-temperature resistivity that has been
ascribed to Planckian dissipation near a quantum critical point. This
establishes true scale-invariant conductivity as the signature of the strange
metal state in the high-temperature superconducting cuprates.Comment: 10 pages, 3 figure
Fermi Surface of the Electron-doped Cuprate Superconductor Nd_{2-x}Ce_xCuO_{4} Probed by High-Field Magnetotransport
We report on the study of the Fermi surface of the electron-doped cuprate
superconductor NdCeCuO by measuring the interlayer
magnetoresistance as a function of the strength and orientation of the applied
magnetic field. We performed experiments in both steady and pulsed magnetic
fields on high-quality single crystals with Ce concentrations of to
0.17. In the overdoped regime of we found both semiclassical
angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas
(SdH) oscillations. The combined AMRO and SdH data clearly show that the
appearance of fast SdH oscillations in strongly overdoped samples is caused by
magnetic breakdown. This observation provides clear evidence for a
reconstructed multiply-connected Fermi surface up to the very end of the
overdoped regime at . The strength of the superlattice potential
responsible for the reconstructed Fermi surface is found to decrease with
increasing doping level and likely vanishes at the same carrier concentration
as superconductivity, suggesting a close relation between translational
symmetry breaking and superconducting pairing. A detailed analysis of the
high-resolution SdH data allowed us to determine the effective cyclotron mass
and Dingle temperature, as well as to estimate the magnetic breakdown field in
the overdoped regime.Comment: 23 pages, 8 figure
On the Geometry and Entropy of Non-Hamiltonian Phase Space
We analyze the equilibrium statistical mechanics of canonical, non-canonical
and non-Hamiltonian equations of motion by throwing light into the peculiar
geometric structure of phase space. Some fundamental issues regarding time
translation and phase space measure are clarified. In particular, we emphasize
that a phase space measure should be defined by means of the Jacobian of the
transformation between different types of coordinates since such a determinant
is different from zero in the non-canonical case even if the phase space
compressibility is null. Instead, the Jacobian determinant associated with
phase space flows is unity whenever non-canonical coordinates lead to a
vanishing compressibility, so that its use in order to define a measure may not
be always correct. To better illustrate this point, we derive a mathematical
condition for defining non-Hamiltonian phase space flows with zero
compressibility. The Jacobian determinant associated with time evolution in
phase space is altogether useful for analyzing time translation invariance. The
proper definition of a phase space measure is particularly important when
defining the entropy functional in the canonical, non-canonical, and
non-Hamiltonian cases. We show how the use of relative entropies can circumvent
some subtle problems that are encountered when dealing with continuous
probability distributions and phase space measures. Finally, a maximum
(relative) entropy principle is formulated for non-canonical and
non-Hamiltonian phase space flows.Comment: revised introductio
Path Integral for Quantum Operations
In this paper we consider a phase space path integral for general
time-dependent quantum operations, not necessarily unitary. We obtain the path
integral for a completely positive quantum operation satisfied Lindblad
equation (quantum Markovian master equation). We consider the path integral for
quantum operation with a simple infinitesimal generator.Comment: 24 pages, LaTe
Microscopic Foundation of Nonextensive Statistics
Combination of the Liouville equation with the q-averaged energy leads to a microscopic framework for nonextensive q-thermodynamics. The
resulting von Neumann equation is nonlinear: . In spite
of its nonlinearity the dynamics is consistent with linear quantum mechanics of
pure states. The free energy is a stability function for the
dynamics. This implies that q-equilibrium states are dynamically stable. The
(microscopic) evolution of is reversible for any q, but for
the corresponding macroscopic dynamics is irreversible.Comment: revte
Thermodynamic Description of the Relaxation of Two-Dimensional Euler Turbulence Using Tsallis Statistics
Euler turbulence has been experimentally observed to relax to a
metaequilibrium state that does not maximize the Boltzmann entropy, but rather
seems to minimize enstrophy. We show that a recent generalization of
thermodynamics and statistics due to Tsallis is capable of explaining this
phenomenon in a natural way. The maximization of the generalized entropy
for this system leads to precisely the same profiles predicted by the
Restricted Minimum Enstrophy theory of Huang and Driscoll. This makes possible
the construction of a comprehensive thermodynamic description of Euler
turbulence.Comment: 15 pages, RevTe
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