326 research outputs found
Quantum coherence generated by interference-induced state selectiveness
The relations between quantum coherence and quantum interference are
discussed. A general method for generation of quantum coherence through
interference-induced state selection is introduced and then applied to `simple'
atomic systems under two-photon transitions, with applications in quantum
optics and laser cooling.Comment: 17 pages, 7 figures, to be published in Journal of Modern Optics'
special issue on quantum interferenc
Holographic renormalization as a canonical transformation
The gauge/string dualities have drawn attention to a class of variational
problems on a boundary at infinity, which are not well defined unless a certain
boundary term is added to the classical action. In the context of supergravity
in asymptotically AdS spaces these problems are systematically addressed by the
method of holographic renormalization. We argue that this class of a priori ill
defined variational problems extends far beyond the realm of holographic
dualities. As we show, exactly the same issues arise in gravity in non
asymptotically AdS spaces, in point particles with certain unbounded from below
potentials, and even fundamental strings in flat or AdS backgrounds. We show
that the variational problem in all such cases can be made well defined by the
following procedure, which is intrinsic to the system in question and does not
rely on the existence of a holographically dual theory: (i) The first step is
the construction of the space of the most general asymptotic solutions of the
classical equations of motion that inherits a well defined symplectic form from
that on phase space. The requirement of a well defined symplectic form is
essential and often leads to a necessary repackaging of the degrees of freedom.
(ii) Once the space of asymptotic solutions has been constructed in terms of
the correct degrees of freedom, then there exists a boundary term that is
obtained as a certain solution of the Hamilton-Jacobi equation which
simultaneously makes the variational problem well defined and preserves the
symplectic form. This procedure is identical to holographic renormalization in
the case of asymptotically AdS gravity, but it is applicable to any Hamiltonian
system.Comment: 37 pages; v2 minor corrections in section 2, 2 references and a
footnote on Palatini gravity added. Version to appear in JHE
Enhanced ERbeta immunoexpression and apoptosis in the germ cells of cimetidine-treated rats
<p>Abstract</p> <p>Background</p> <p>Cimetidine, refereed as antiandrogenic drug, causes hormonal changes in male patients such as increased testosterone and FSH levels. In the rat testis, structural alterations in the seminiferous tubules have been related to germ cell loss and Sertoli cell death by apoptosis. Regarding the important role of Sertoli cells in the conversion of testosterone into estrogen, via aromatase, the immunoexpression of estrogen receptors-beta (ERbeta) was evaluated in the germ cells of untreated and treated rats with cimetidine. A relationship between ERbeta immunoreactivity and apoptosis was also investigated in the germ cells of damaged tubules.</p> <p>Methods</p> <p>Immunohistochemistry for detection of ERbeta and TUNEL method were performed in testicular sections of adult male rats treated with 50 mg/Kg of cimetidine (CmG) or saline solution (CG) for 52 days.</p> <p>Results</p> <p>In CG, a cytoplasmic immunoexpression for ERbeta was observed in spermatogonia, primary spermatocytes and spermatids. An evident ERbeta immunoreactivity was always observed in the flagellum and residual bodies of late spermatids. In CmG, the cytoplasm or cytoplasm and nuclei of germ cells of the damaged tubules by cimetidine showed enhanced ERbeta immunostaining. TUNEL-labeling was usually observed in the same germ cell types exhibiting enhanced ERbeta immunoreactivity.</p> <p>Conclusion</p> <p>The presence of ERbeta immunolabeling in the flagellum and residual bodies of spermatids reinforces the role of estrogen in spermiogenesis. The overexpression of ERbeta in the germ cells of CmG could be related to a possible interference of cimetidine on tubular androgenization and/or on the intratubular aromatase due to Sertoli cell damage. The parallelism between ERbeta overexpression and apoptosis indicates a participation of ERbeta on germ cell death.</p
A new equation for the mid-plane potential of power law discs. II. Exact solutions and approximate formulae
The first-order ordinary differential equation (ODE) that describes the
mid-plane gravitational potential in flat finite size discs in which the
surface density is a power-law function of the radius R with exponent s (Hur\'e
& Hersant 2007) is solved exactly in terms of infinite series. The formal
solution of the ODE is derived and then converted into a series representation
by expanding the elliptic integral of the first kind over its modulus before
analytical integration. Inside the disc, the gravitational potential consists
of three terms: a power law of radius R with index 1+s, and two infinite series
of the variables R and 1/R. The convergence of the series can be accelerated,
enabling the construction of reliable approximations. At the lowest-order, the
potential inside large astrophysical discs (s ~ -1.5 +/- 1) is described by a
very simple formula whose accuracy (a few percent typically) is easily
increased by considering successive orders through a recurrence. A basic
algorithm is given. Applications concern all theoretical models and numerical
simulations where the influence of disc gravity must be checked and/or reliably
taken into account.Comment: Accepted for publication in A&A, 13 pages, 8 figure
The Generalized Star Product and the Factorization of Scattering Matrices on Graphs
In this article we continue our analysis of Schr\"odinger operators on
arbitrary graphs given as certain Laplace operators. In the present paper we
give the proof of the composition rule for the scattering matrices. This
composition rule gives the scattering matrix of a graph as a generalized star
product of the scattering matrices corresponding to its subgraphs. We perform a
detailed analysis of the generalized star product for arbitrary unitary
matrices. The relation to the theory of transfer matrices is also discussed
Green functions for generalized point interactions in 1D: A scattering approach
Recently, general point interactions in one dimension has been used to model
a large number of different phenomena in quantum mechanics. Such potentials,
however, requires some sort of regularization to lead to meaningful results.
The usual ways to do so rely on technicalities which may hide important
physical aspects of the problem. In this work we present a new method to
calculate the exact Green functions for general point interactions in 1D. Our
approach differs from previous ones because it is based only on physical
quantities, namely, the scattering coefficients, and , to construct .
Renormalization or particular mathematical prescriptions are not invoked. The
simple formulation of the method makes it easy to extend to more general
contexts, such as for lattices of general point interactions; on a line; on
a half-line; under periodic boundary conditions; and confined in a box.Comment: Revtex, 9 pages, 3 EPS figures. To be published in PR
Quantum Cosmology of Generalized Two--Dimensional Dilaton Gravity Models
The quantum cosmology of two-dimensional dilaton-gravity models is
investigated. A class of models is mapped onto the constrained
oscillator-ghost-oscillator model. A number of exact and approximate solutions
to the corresponding Wheeler-DeWitt equation are presented. A wider class of
minisuperspace models that can be solved in this fashion is identified.
Supersymmetric extensions to the induced gravity theory and the bosonic string
theory are then considered and closed-form solutions to the associated quantum
constraints are derived. The possibility of applying the third-quantization
procedure to two-dimensional dilaton-gravity is briefly discussed.Comment: 28 pages, late
Effect of acute copper sulfate exposure on olfactory responses to amino acids and pheromones in goldfish (Carassius auratus)
Exposure of olfactory epithelium to environmentally relevant concentrations of copper disrupts olfaction in fish. To examine
the dynamics of recovery at both functional and morphological levels after acute copper exposure, unilateral exposure of goldfish olfactory epithelia to 100 μM CuSO4 (10 min) was followed by electro-olfactogram (EOG) recording and scanning electron microscopy. Sensitivity to amino acids (L-arginine
and L-serine), generally considered food-related odorants, recovered most rapidly (three days), followed by that to
catecholamines(3-O-methoxytyramine),bileacids(taurolithocholic acid) and the steroid pheromone, 17,20 -dihydroxy-4-pregnen-
3-one 20-sulfate, which took 28 days to reach full recovery. Sensitivity to the postovulatory pheromone prostaglandin F2R had
not fully recovered even at 28 days. These changes in sensitivity were correlated with changes in the recovery of ciliated and microvillous receptor cell types. Microvillous cells appeared largely unaffected by CuSO4 treatment. Cilia in
ciliated receptor neurones, however, appeared damaged one day post-treatment and were virtually absent after three days but
had begun to recover after 14 days. Together, these results support the hypothesis that microvillous receptor neurones detect amino acids whereas ciliated receptor neurones were not functional and are responsible for detection of social stimuli (bile acidsandpheromones).Furthermore, differences in sensitivity to copper may be due to different transduction pathways in
the different cell types
Kirchhoff's Rule for Quantum Wires
In this article we formulate and discuss one particle quantum scattering
theory on an arbitrary finite graph with open ends and where we define the
Hamiltonian to be (minus) the Laplace operator with general boundary conditions
at the vertices. This results in a scattering theory with channels. The
corresponding on-shell S-matrix formed by the reflection and transmission
amplitudes for incoming plane waves of energy is explicitly given in
terms of the boundary conditions and the lengths of the internal lines. It is
shown to be unitary, which may be viewed as the quantum version of Kirchhoff's
law. We exhibit covariance and symmetry properties. It is symmetric if the
boundary conditions are real. Also there is a duality transformation on the set
of boundary conditions and the lengths of the internal lines such that the low
energy behaviour of one theory gives the high energy behaviour of the
transformed theory. Finally we provide a composition rule by which the on-shell
S-matrix of a graph is factorizable in terms of the S-matrices of its
subgraphs. All proofs only use known facts from the theory of self-adjoint
extensions, standard linear algebra, complex function theory and elementary
arguments from the theory of Hermitean symplectic forms.Comment: 40 page
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