14,011 research outputs found
The mixed black hole partition function for the STU model
We evaluate the mixed partition function for dyonic BPS black holes using the
recently proposed degeneracy formula for the STU model. The result factorizes
into the OSV mixed partition function times a proportionality factor. The
latter is in agreement with the measure factor that was recently conjectured
for a class of N=2 black holes that contains the STU model.Comment: 14 page
Anisotropic superconducting properties of aligned MgB2 crystallites
Samples of aligned MgB2 crystallites have been prepared, allowing for the
first time the direct identification of an upper critical field anisotropy
Hc2^{ab}/Hc2^{c}= xi_{ab}/xi_{c} ~ 1.73; with xi_{o,ab} ~ 70 A, xi_{o,c} ~ 40
A, and a mass anisotropy ratio m_{ab}/m_{c} ~ 0.3. A ferromagnetic background
signal was identified, possibly related to the raw materials purity.Comment: 4 pages, 4 figures; Revised version to appear in Phys. Rev. Let
Localization properties of a tight-binding electronic model on the Apollonian network
An investigation on the properties of electronic states of a tight-binding
Hamiltonian on the Apollonian network is presented. This structure, which is
defined based on the Apollonian packing problem, has been explored both as a
complex network, and as a substrate, on the top of which physical models can
defined. The Schrodinger equation of the model, which includes only nearest
neighbor interactions, is written in a matrix formulation. In the uniform case,
the resulting Hamiltonian is proportional to the adjacency matrix of the
Apollonian network. The characterization of the electronic eigenstates is based
on the properties of the spectrum, which is characterized by a very large
degeneracy. The rotation symmetry of the network and large number of
equivalent sites are reflected in all eigenstates, which are classified
according to their parity. Extended and localized states are identified by
evaluating the participation rate. Results for other two non-uniform models on
the Apollonian network are also presented. In one case, interaction is
considered to be dependent of the node degree, while in the other one, random
on-site energies are considered.Comment: 7pages, 7 figure
Extreme vortex pinning in the non-centrosymmetric superconductor CePtSi
We report on the vortex dynamics of a single crystal of the
non-centrosymmetric heavy-fermion superconductor CePtSi. Decays of the
remnant magnetization display a clean logarithmic time dependence with rates
that follow the temperature dependence expected from the Kim-Anderson theory.
The creep rates are lower than observed in any other centrosymmetric
superconductor and are not caused by high critical currents. On the contrary,
the critical current in CePtSi is considerably lower than in other
superconductors with strong vortex pinning indicating that an alternative
impediment on the flux line motion might be at work in this superconductor.Comment: 4 pages, 5 figure
Plataforma portátil de pesagem para bovinos: apresentação e funcionamento.
Características da Plataforma; Larguras ajustáveis da base e abas; Disposição e uso no brete; Medida do maior componente; Apoios no solo; Produto divisível ao meio; Sistema de regulagem de abertura das abas; Engenharia; Segurança e conforto animal.bitstream/item/31972/1/DT-104online.pd
Protective action of oxalic acid in relation to ascorbic acid against its oxidation by the ascorbic acid oxidase
O artigo não apresenta resumo.1. Oxalic acid has a definite protective action on ascorbic acid in its oxidation by ascorbic acid oxidase, an enzyme whose active group contains copper; this action is best revealed at pH 4.5. 2. Oxalic acid exerts also its protective action on ascorbic acid oxidation by copper; the comparison between the oxidative effect of copper oxalate and that of copper sulphate shows that the latter is much more intense. 3. The protective action of thiourea exerts itself in the oxidation by copper though less intensively than that of oxalic acid but it does not reveal itself in the oxidation by ascorbic acid oxidase. 4. The protective action of oxalic acid in the oxidation of ascorbic acid by the ascorbic acid oxidase suggests a new field of investigation in the branch of knowledge of those substances, not identified up to the present, which, in natural substrata, protect the ascorbic acid against such an oxidation
The pros and cons of using SDL for creation of distributed services
In a competitive market for the creation of complex distributed services, time to market, development cost, maintenance and flexibility are key issues. Optimizing the development process is very much a matter of optimizing the technologies used during service creation. This paper reports on the experience gained in the Service Creation projects SCREEN and TOSCA on use of the language SDL for efficient service creation
On walls of marginal stability in N=2 string theories
We study the properties of walls of marginal stability for BPS decays in a
class of N=2 theories. These theories arise in N=2 string compactifications
obtained as freely acting orbifolds of N=4 theories, such theories include the
STU model and the FHSV model. The cross sections of these walls for a generic
decay in the axion-dilaton plane reduce to lines or circles. From the
continuity properties of walls of marginal stability we show that central
charges of BPS states do not vanish in the interior of the moduli space. Given
a charge vector of a BPS state corresponding to a large black hole in these
theories, we show that all walls of marginal stability intersect at the same
point in the lower half of the axion-dilaton plane. We isolate a class of
decays whose walls of marginal stability always lie in a region bounded by
walls formed by decays to small black holes. This enables us to isolate a
region in moduli space for which no decays occur within this class. We then
study entropy enigma decays for such models and show that for generic values of
the moduli, that is when moduli are of order one compared to the charges,
entropy enigma decays do not occur in these models.Comment: 40 pages, 2 figure
Effective action for the field equations of charged black holes
In this article, we consistently reduce the equations of motion for the
bosonic N = 2 supergravity action, using a multi-centered black hole ansatz for
the metric. This reduction is done in a general, non-supersymmetric setup, in
which we extend concepts of BPS black hole technology. First of all we obtain a
more general form of the black hole potential, as part of an effective action
for both the scalars and the vectors in the supergravity theory. Furthermore,
we show that there are extra constraints specifying the solution, which we
calculate explicitly. In the literature, these constraints have already been
studied in the one-center case. We also show that the effective action we
obtain for non-static metrics, can be linked to the "entropy function" for the
spherically symmetric case, as defined by Sen and Cardoso et al.Comment: 18 pages, (v2: small corrections, version to be published in CQG
Least Dependent Component Analysis Based on Mutual Information
We propose to use precise estimators of mutual information (MI) to find least
dependent components in a linearly mixed signal. On the one hand this seems to
lead to better blind source separation than with any other presently available
algorithm. On the other hand it has the advantage, compared to other
implementations of `independent' component analysis (ICA) some of which are
based on crude approximations for MI, that the numerical values of the MI can
be used for:
(i) estimating residual dependencies between the output components;
(ii) estimating the reliability of the output, by comparing the pairwise MIs
with those of re-mixed components;
(iii) clustering the output according to the residual interdependencies.
For the MI estimator we use a recently proposed k-nearest neighbor based
algorithm. For time sequences we combine this with delay embedding, in order to
take into account non-trivial time correlations. After several tests with
artificial data, we apply the resulting MILCA (Mutual Information based Least
dependent Component Analysis) algorithm to a real-world dataset, the ECG of a
pregnant woman.
The software implementation of the MILCA algorithm is freely available at
http://www.fz-juelich.de/nic/cs/softwareComment: 18 pages, 20 figures, Phys. Rev. E (in press
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