22,877 research outputs found
Two New Pahlavi Inscriptions from Fars Province, Iran
First edition of two previously unknown Middle Persian inscriptions from the region of Fars in Iran
The nonequilibrium Ehrenfest gas: a chaotic model with flat obstacles?
It is known that the non-equilibrium version of the Lorentz gas (a billiard
with dispersing obstacles, electric field and Gaussian thermostat) is
hyperbolic if the field is small. Differently the hyperbolicity of the
non-equilibrium Ehrenfest gas constitutes an open problem, since its obstacles
are rhombi and the techniques so far developed rely on the dispersing nature of
the obstacles. We have developed analytical and numerical investigations which
support the idea that this model of transport of matter has both chaotic
(positive Lyapunov exponent) and non-chaotic steady states with a quite
peculiar sensitive dependence on the field and on the geometry, not observed
before. The associated transport behaviour is correspondingly highly irregular,
with features whose understanding is of both theoretical and technological
interest
Semiclassical limit for the nonlinear Klein Gordon equation in bounded domains
We are interested to the existence of standing waves for the nonlinear Klein
Gordon equation {\epsilon}^2{\box}{\psi} + W'({\psi}) = 0 in a bounded domain
D. The main result of this paper is that, under suitable growth condition on W,
for {\epsilon} sufficiently small, we have at least cat(D) standing wavesfor
the equation ({\dag}), while cat(D) is the Ljusternik-Schnirelmann category
The canonical Naimark extension for the Pauli quantum roulette wheel
We address measurement schemes where certain observables are chosen at random
within a set of non-degenerate isospectral observables and then measured on
repeated preparations of a physical system. Each observable has a given
probability to be measured, and the statistics of this generalized measurement
is described by a positive operator-valued measure (POVM). This kind of schemes
are referred to as quantum roulettes since each observable is chosen at random,
e.g. according to the fluctuating value of an external parameter. Here we focus
on quantum roulettes for qubits involving the measurements of Pauli matrices
and we explicitly evaluate their canonical Naimark extensions, i.e. their
implementation as indirect measurements involving an interaction scheme with a
probe system. We thus provide a concrete model to realize the roulette without
destroying the signal state, which can be measured again after the measurement,
or can be transmitted. Finally, we apply our results to the description of
Stern-Gerlach-like experiments on a two-level system.Comment: 8 pages, 2 figures, published on PRA with a different title (the
arXiv one was too sexy
On conformally recurrent manifolds of dimension greater than 4
Conformally recurrent pseudo-Riemannian manifolds of dimension n>4 are
investigated. The Weyl tensor is represented as a Kulkarni-Nomizu product. If
the square of the Weyl tensor is nonzero, a covariantly constant symmetric
tensor is constructed, that is quadratic in the Weyl tensor. Then, by Grycak's
theorem, the explicit expression of the traceless part of the Ricci tensor is
obtained, up to a scalar function. The Ricci tensor has at most two distinct
eigenvalues, and the recurrence vector is an eigenvector. Lorentzian
conformally recurrent manifolds are then considered. If the square of the Weyl
tensor is nonzero, the manifold is decomposable. A null recurrence vector makes
the Weyl tensor of algebraic type IId or higher in the Bel - Debever - Ortaggio
classification, while a time-like recurrence vector makes the Weyl tensor
purely electric.Comment: Title changed and typos corrected. 14 page
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