4,593 research outputs found
High resolution probe of coherence in low-energy charge exchange collisions with oriented targets
The trapping lasers of a magneto-optical trap (MOT) are used to bring Rb
atoms into well defined oriented states. Coupled to recoil-ion momentum
spectroscopy (RIMS), this yields a unique MOTRIMS setup which is able to probe
scattering dynamics, including their coherence features, with unprecedented
resolution. This technique is applied to the low-energy charge exchange
processes Na+Rb() Na()+Rb. The
measurements reveal detailed features of the collisional interaction which are
employed to improve the theoretical description. All of this enables to gauge
the reliability of intuitive pictures predicting the most likely capture
transitions
Extensive population synthesis of isolated neutron stars with field decay
We perform population synthesis studies of different types of neutron stars
taking into account the magnetic field decay. For the first time, we confront
our results with observations using {\it simultaneously} the Log N -- Log S
distribution for nearby isolated neutron stars, the Log N -- Log L distribution
for magnetars, and the distribution of radio pulsars in the --
diagram. We find that our theoretical model is consistent with all sets of data
if the initial magnetic field distribution function follows a log-normal law
with and . The
typical scenario includes about 10% of neutron stars born as magnetars,
significant magnetic field decay during the first million years of a NS life.
Evolutionary links between different subclasses may exist, although robust
conclusions are not yet possible.
We apply the obtained field distribution and the model of decay to study
long-term evolution of neuton stars till the stage of accretion from the
interstellar medium. It is shown that though the subsonic propeller stage can
be relatively long, initially highly magnetized neutron stars ( G) reach the accretion regime within the Galactic lifetime if their
kick velocities are not too large. The fact that in previous studies made 10
years ago, such objects were not considered results in a slight increase of the
Accretor fraction in comparison with earlier conclusions. Most of the neutron
stars similar to the Magnificent seven are expected to become accreting from
the interstellar medium after few billion years of their evolution. They are
the main predecestors of accreting isolated neutron stars.Comment: 4 pages, conference "Astrophysics of Neutron Stars - 2010" in honor
of M. Ali Alpar, Izmir, Turke
Learning to Reconstruct People in Clothing from a Single RGB Camera
We present a learning-based model to infer the personalized 3D shape of people from a few frames (1-8) of a monocular video in which the person is moving, in less than 10 seconds with a reconstruction accuracy of 5mm. Our model learns to predict the parameters of a statistical body model and instance displacements that add clothing and hair to the shape. The model achieves fast and accurate predictions based on two key design choices. First, by predicting shape in a canonical T-pose space, the network learns to encode the images of the person into pose-invariant latent codes, where the information is fused. Second, based on the observation that feed-forward predictions are fast but do not always align with the input images, we predict using both, bottom-up and top-down streams (one per view) allowing information to flow in both directions. Learning relies only on synthetic 3D data. Once learned, the model can take a variable number of frames as input, and is able to reconstruct shapes even from a single image with an accuracy of 6mm. Results on 3 different datasets demonstrate the efficacy and accuracy of our approach
Reparameterization invariants for anisotropic Bianchi I cosmology with a massless scalar source
Intrinsic time-dependent invariants are constructed for classical, flat,
homogeneous, anisotropic cosmology with a massless scalar material source.
Invariance under the time reparameterization-induced canonical symmetry group
is displayed explicitly.Comment: 28 pages, to appear in General Relativity and Gravitation.
Substantial revisions: added foundational overview section 2, chose new
intrinsic time variable, worked with dimensionless variables, added appendix
with comparison and criticism of other approache
Near-threshold high-order harmonic spectroscopy with aligned molecules
We study high-order harmonic generation in aligned molecules close to the
ionization threshold. Two distinct contributions to the harmonic signal are
observed, which show very different responses to molecular alignment and
ellipticity of the driving field. We perform a classical electron trajectory
analysis, taking into account the significant influence of the Coulomb
potential on the strong-field-driven electron dynamics. The two contributions
are related to primary ionization and excitation processes, offering a deeper
understanding of the origin of high harmonics near the ionization threshold.
This work shows that high harmonic spectroscopy can be extended to the
near-threshold spectral range, which is in general spectroscopically rich.Comment: 4 pages, 4 figure
Switching the Conductance of a Molecular Junction using a Proton Transfer Reaction
A novel mechanism for switching a molecular junction based on a proton
transfer reaction triggered by an external electrostatic field is proposed. As
a specific example to demonstrate the feasibility of the mechanism, the
tautomers [2,5-(4-hydroxypyridine)] and {2,5-[4(1H)-pyridone]} are considered.
Employing a combination of first-principles electronic structure calculations
and Landauer transport theory, we show that both tautomers exhibit very
different conductance properties and realize the "on" and "off" states of a
molecular switch. Moreover, we provide a proof of principle that both forms can
be reversibly converted into each other using an external electrostatic field.Comment: 14 pages, 5 figure
AnĂ lisi de les causes accidentals de mortalitat de rapinyaires a Mallorca des del 2004 al 2016
[cat] Al present treball sâavaluen les entrades de rapinyaires al COFIB (Consorci per a la RecuperaciĂł de la Fauna de les Illes Balears) en el perĂode 2004/2016. Les dades recopilades de tots els rapinyaires ferits o morts durant aquest perĂode en dona una mostra significativa amb lâafectaciĂł de 4.603 individus. AixĂ, sâanalitzen les set principals causes dâentrada: atropellaments; electrocucions/impactes amb esteses elĂšctriques; tirotejats; enverinats; trampejats; molĂšsties als nius i confiscats (rapinyaires que es tenien en captivitat de manera il·legal). De cada una dâaquestes causes dâentrada sâanalitzen les espĂšcies que han estat mĂ©s afectades, els municipis on se nâhan trobat mĂ©s i si el fenomen va a lâalça o a la baixa al llarg del temps. Es pretĂ©n determinar els principals factors que delimiten el correcte desenvolupament dâaquestes espĂšcies dâaus.[eng] The present work evaluates the entries of raptors to the COFIB (Consortium for the Recovery of the Fauna of the Balearic Islands) in the period 2004/2016. The data collected from all the injured or killed raptors during this period gives a significant sample with the involvement of 4603 individuals. Thus, the seven main causes of entry are analyzed: runoffs; electrocutions / impacts with electrical extensions; shot; poisoned; trampled; annoyances to the nests and confiscated (birds of prey that were captivated illegally). Each of these causes of entry analyzes the most affected species, the municipalities where they have been found most and if the phenomenon is rising or falling over time. It is intended to determine the main factors that delimit the correct development of these bird species
Generally covariant theories: the Noether obstruction for realizing certain space-time diffeomorphisms in phase space
Relying on known results of the Noether theory of symmetries extended to
constrained systems, it is shown that there exists an obstruction that prevents
certain tangent-space diffeomorphisms to be projectable to phase-space, for
generally covariant theories. This main result throws new light on the old fact
that the algebra of gauge generators in the phase space of General Relativity,
or other generally covariant theories, only closes as a soft algebra and not a
a Lie algebra.
The deep relationship between these two issues is clarified. In particular,
we see that the second one may be understood as a side effect of the procedure
to solve the first. It is explicitly shown how the adoption of specific
metric-dependent diffeomorphisms, as a way to achieve projectability, causes
the algebra of gauge generators (constraints) in phase space not to be a Lie
algebra --with structure constants-- but a soft algebra --with structure {\it
functions}.Comment: 22 pages, version to be published in Classical & Quantum Gravit
- âŠ