246 research outputs found
Properties of low-lying states in some high-nuclearity Mn, Fe and V clusters: Exact studies of Heisenberg models
Using an efficient numerical scheme that exploits spatial symmetries and spin
parity, we have obtained the exact low-lying eigenstates of exchange
Hamiltonians for the high nuclearity spin clusters, Mn_{12}, Fe_8 and V_{15}.
The largest calculation involves the Mn_{12} cluster which spans a Fock space
of a hundred million. Our results show that the earlier estimates of the
exchange constants need to be revised for the Mn_{12} cluster to explain the
level ordering of low-lying eigenstates. In the case of the Fe_8 cluster,
correct level ordering can be obtained which is consistent with the exchange
constants for the already known clusters with butterfly structure. In the
V_{15} cluster, we obtain an effective Hamiltonian that reproduces exactly, the
eight low-lying eigenvalues of the full Hamiltonian.Comment: Revtex, 12 pages, 16 eps figures; this is the final published versio
An optimal gap theorem
By solving the Cauchy problem for the Hodge-Laplace heat equation for
-closed, positive -forms, we prove an optimal gap theorem for
K\"ahler manifolds with nonnegative bisectional curvature which asserts that
the manifold is flat if the average of the scalar curvature over balls of
radius centered at any fixed point is a function of .
Furthermore via a relative monotonicity estimate we obtain a stronger
statement, namely a `positive mass' type result, asserting that if is
not flat, then for any
Gravitational-wave astronomy: the high-frequency window
This contribution is divided in two parts. The first part provides a
text-book level introduction to gravitational radiation. The key concepts
required for a discussion of gravitational-wave physics are introduced. In
particular, the quadrupole formula is applied to the anticipated
``bread-and-butter'' source for detectors like LIGO, GEO600, EGO and TAMA300:
inspiralling compact binaries. The second part provides a brief review of high
frequency gravitational waves. In the frequency range above (say) 100Hz,
gravitational collapse, rotational instabilities and oscillations of the
remnant compact objects are potentially important sources of gravitational
waves. Significant and unique information concerning the various stages of
collapse, the evolution of protoneutron stars and the details of the
supranuclear equation of state of such objects can be drawn from careful study
of the gravitational-wave signal. As the amount of exciting physics one may be
able to study via the detections of gravitational waves from these sources is
truly inspiring, there is strong motivation for the development of future
generations of ground based detectors sensitive in the range from hundreds of
Hz to several kHz.Comment: 21 pages, 5 figures, Lectures presented at the 2nd Aegean Summer
School on the Early Universe, Syros, Greece, September 200
Neutron charge form factor at large
The neutron charge form factor is determined from an analysis of
the deuteron quadrupole form factor data. Recent calculations, based
on a variety of different model interactions and currents, indicate that the
contributions associated with the uncertain two-body operators of shorter range
are relatively small for , even at large momentum transfer . Hence,
can be extracted from at large without undue
systematic uncertainties from theory.Comment: 8 pages, 3 figure
Young and Intermediate-age Distance Indicators
Distance measurements beyond geometrical and semi-geometrical methods, rely
mainly on standard candles. As the name suggests, these objects have known
luminosities by virtue of their intrinsic proprieties and play a major role in
our understanding of modern cosmology. The main caveats associated with
standard candles are their absolute calibration, contamination of the sample
from other sources and systematic uncertainties. The absolute calibration
mainly depends on their chemical composition and age. To understand the impact
of these effects on the distance scale, it is essential to develop methods
based on different sample of standard candles. Here we review the fundamental
properties of young and intermediate-age distance indicators such as Cepheids,
Mira variables and Red Clump stars and the recent developments in their
application as distance indicators.Comment: Review article, 63 pages (28 figures), Accepted for publication in
Space Science Reviews (Chapter 3 of a special collection resulting from the
May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space
Age
On the EPR-type Entanglement in the Experiments of Scully et Al. I. The Micromaser Case and Delayed-choice Quantum Erasure
Delayed-choice erasure is investigated in two-photon two-slit experiments
that are generalizations of the micromaser experiment of Scully et al. [Scully,
M. O. et al. Nature 351, 111-116 (1991)]. Applying quantum mechanics to the
localization detector, it is shown that erasure with delayed choice in the
sense of Scully, has an analogous structure as simple erasure. The description
goes beyond probabilities. The EPR-type disentanglement, consisting in two
mutually incompatible distant measurements, is used as a general framework in
both parts of this study. Two simple coherence cases are shown to emerge
naturally, and they are precisely the two experiments of Scully et al. The
treatment seems to require the relative-reality-of-unitarily-evolving-state
(RRUES) approach. Besides insight in the exoeriments, this study has also the
goal of insight in quantum mechanics. The question is if it can be more than
just a "book-keeping device" for calculating probabilities as Scully et al.
modestly and cautiously claim.Comment: Latex2e, no figures, this manuscript is the first part of a study in
two part
Partitioning variability in animal behavioral videos using semi-supervised variational autoencoders
Action Contro
Diversidade genética de populações naturais de pariparoba [Pothomorphe umbellata (L.) Miq.] por RAPD
Empirically-grounded development of legal ontologies: a socio-legal perspective
This paper shows the multiple relationships between empirical data and semantic content in the legal field. One of the well-known problems of ontology construction is the "knowledge acquisition bottleneck problem" pointed out by Edward Feigenbaum and others, many years ago. In the next generation of Semantic Web developments this problem has not been completely solved. It is our con-tention that an accurate description of the legal environment, and well-grounded previous sociological studies may help to face it in a more satisfactory way. This means adopting a user-centered approach for legal ontologies, in what we will call an "iterative and integrated pragmatic circle" involving legal theorists, socio-legal researchers, professional people (lawyers, magistrates, prosecutors…) and com-puter scientists. We put the example of how the ontology of IURISERVICE was built up
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