31,153 research outputs found
Science with the World Space Observatory - Ultraviolet
The World Space Observatory-Ultraviolet (WSO-UV) will provide access to the
UV range during the next decade. The instrumentation on board will allow to
carry out high resolution imaging, high sensitivity imaging, high resolution
(R~55000) spectroscopy and low resolution (R~2500) long slit spectroscopy. In
this contribution, we briefly outline some of the key science issues that
WSO-UV will address during its lifetime. Among them, of special interest are:
the study of galaxy formation and the intergalactic medium; the astronomical
engines; the Milky Way formation and evol ution, and the formation of the Solar
System and the atmospheres of extrasolar p lanets.Comment: Just one text file (aigomezdecastro.tex). To be published in the
proceeding of the conference: "New Quest in Stellar Astrophysics II: UV
properties of evolved stellar populations" held in Puerto Vallarta - Mexico,
in april 200
Noncommutative associative superproduct for general supersymplectic forms
We define a noncommutative and nonanticommutative associative product for
general supersymplectic forms, allowing the explicit treatment of
non(anti)commutative field theories from general nonconstant string backgrounds
like a graviphoton field. We propose a generalization of deformation
quantization a la Fedosov to superspace, which considers noncommutativity in
the tangent bundle instead of base space, by defining the Weyl super product of
elements of Weyl super algebra bundles. Super Poincare symmetry is not broken
and chirality seems not to be compromised in our formulation. We show that, for
a particular case, the projection of the Weyl super product to the base space
gives rise the Moyal product for non(anti)commutative theories.Comment: 22 pages, revtex4. References added. Comments added. Includes
additional theorem proof
Ambipolar Filamentation of Turbulent Magnetic Fields : A numerical simulation
We present the results of a 2-D, two fluid (ions and neutrals) simulation of
the ambipolar filamentation process, in which a magnetized, weakly ionized
plasma is stirred by turbulence in the ambipolar frequency range. The higher
turbulent velocity of the neutrals in the most ionized regions gives rise to a
non-linear force driving them out of these regions, so that the initial
ionization inhomogeneities are strongly amplified. This effect, the ambipolar
filamentation, causes the ions and the magnetic flux to condense and separate
from the neutrals, resulting in a filamentary structure.Comment: 8 pages, 6 figures, accepted for publication in A&
Unstable particles versus resonances in impurity systems, conductance in quantum wires
We compute the DC conductance for a homogeneous sine-Gordon model and an
impurity system of Luttinger liquid type by means of the thermodynamic Bethe
ansatz and standard potential scattering theory. We demonstrate that unstable
particles and resonances in impurity systems lead to a sharp increase of the
conductance as a function of the temperature, which is characterized by the
Breit-Wigner formula.Comment: 5 pages Latex, 1 figure replaced, version to appear in J. Phys.
Coulomb blockade in graphene nanoribbons
We propose that recent transport experiments revealing the existence of an
energy gap in graphene nanoribbons may be understood in terms of Coulomb
blockade. Electron interactions play a decisive role at the quantum dots which
form due to the presence of necks arising from the roughness of the graphene
edge. With the average transmission as the only fitting parameter, our theory
shows good agreement with the experimental data.Comment: 4 pages, 2 figure
QFT results for neutrino oscillations and New Physics
The CP asymmetry in neutrino oscillations, assuming new physics at production
and/or detection processes, is analyzed. We compute this CP asymmetry using the
standard quantum field theory within a general new physics scenario that may
generate new sources of CP and flavor violation. Well known results for the CP
asymmetry are reproduced in the case of V -A operators, and additional
contributions from new physics operators are derived. We apply this formalism
to SUSY extensions of the Standard Model where the contributions from new
operators could produce a CP asymmetry observable in the next generation of
neutrino experiments.Comment: 6 pages, 3 figures, version to be published in Phys.Rev.
HREM studies of intergrowths in Sr2[Srn-1TinO3n+1] Ruddlesden-Popper phases synthesized by mechanochemical activation
A mechanochemical activation route has been applied in order to obtain the <i>n</i>=1–4 and ∞ members of the Sr<sub>2</sub>[Sr<sub>n</sub><sub>−1</sub>Ti<sub>n</sub>O<sub>3n+1</sub>] Ruddlesden–
Popper series from different (<i>n</i>+1)SrO:nTiO<sub>2</sub> mixtures. The mechanosynthesis of SrTiO<sub>3</sub> and Sr<sub>2</sub>TiO<sub>4</sub> was observed during the milling process
from the initial stoichiometric mixture, but in the cases of the <i>n</i>=2–4 members, a subsequent thermal treatment was needed. The synthesis
protocol of Sr<sub>3</sub>Ti<sub>2</sub>O<sub>7</sub> has been greatly improved and this compound can be isolated as a single, crystalline phase after annealing at 800°C. In the
case of Sr<sub>4</sub>Ti<sub>3</sub>O<sub>10</sub> and Sr<sub>5</sub>Ti<sub>4</sub>O<sub>13</sub>, the formation temperature was also decreased, but members with <i>n</i>=3 and 4 could not be isolated. Detailed
investigations using electron microscopy methods (TEM, HREM and SAED) were carried out in the samples corresponding to <i>n</i>=2–4. Although
a single ordered Sr<sub>3</sub>Ti<sub>2</sub>O<sub>7</sub> structure is dominant in the sample corresponding to <i>n</i>=2, a few intergrowths of other Ruddlesden–Popper phases were
observed. In the cases of <i>n</i>=3 and 4, the intergrowths of Ruddlesden–Popper phases are more frequent than in the <i>n</i>=2 composition and are
randomly distributed in the sample. The more frequent occurrence of such stacking faults, with increasing <i>n</i> value, leads to a somewhat disordered
layer stacking sequence
The evolution with temperature of magnetic polaron state in an antiferromagnetic chain with impurities
The thermal behavior of a one-dimensional antiferromagnetic chain doped by
donor impurities was analyzed. The ground state of such a chain corresponds to
the formation of a set of ferromagnetically correlated regions localized near
impurities (bound magnetic polarons). At finite temperatures, the magnetic
structure of the chain was calculated simultaneously with the wave function of
a conduction electron bound by an impurity. The calculations were performed
using an approximate variational method and a Monte Carlo simulation. Both
these methods give similar results. The analysis of the temperature dependence
of correlation functions for neighboring local spins demonstrated that the
ferromagnetic correlations inside a magnetic polaron remain significant even
above the N\'eel temperature implying rather high stability of the
magnetic polaron state. In the case when the electron-impurity coupling energy
is not too high (for lower that the electron hopping integral ), the
magnetic polaron could be depinned from impurity retaining its magnetic
structure. Such a depinning occurs at temperatures of the order of . At
even higher temperatures () magnetic polarons disappear and the chain
becomes completely disordered.Comment: 17 pages, 5 figures, RevTe
The SEALS Yardsticks for Ontology Management
This paper describes the rst SEALS evaluation campaign
over ontology engineering tools (i.e., the SEALS Yardsticks for Ontology Management). It presents the dierent evaluation scenarios dened to evaluate the conformance, interoperability and scalability of these tools, and the test data used in these scenarios
- …