21,700 research outputs found
Tracing the magnetic field morphology of the Lupus I molecular cloud
Deep R-band CCD linear polarimetry collected for fields with lines-of-sight
toward the Lupus I molecular cloud is used to investigate the properties of the
magnetic field within this molecular cloud. The observed sample contains about
7000 stars, almost 2000 of them with polarization signal-to-noise ratio larger
than 5. These data cover almost the entire main molecular cloud and also sample
two diffuse infrared patches in the neighborhood of Lupus I. The large scale
pattern of the plane-of-sky projection of the magnetic field is perpendicular
to the main axis of Lupus I, but parallel to the two diffuse infrared patches.
A detailed analysis of our polarization data combined with the Herschel/SPIRE
350 um dust emission map shows that the principal filament of Lupus I is
constituted by three main clumps acted by magnetic fields having different
large-scale structure properties. These differences may be the reason for the
observed distribution of pre- and protostellar objects along the molecular
cloud and its apparent evolutive stage. On the other hand, assuming that the
magnetic field is composed by a large-scale and a turbulent components, we find
that the latter is rather similar in all three clumps. The estimated
plane-of-sky component of the large-scale magnetic field ranges from about 70
uG to 200 uG in these clumps. The intensity increases towards the Galactic
plane. The mass-to-magnetic flux ratio is much smaller than unity, implying
that Lupus I is magnetically supported on large scales.Comment: 10 pages, 9 figures. Accepted for publication in Ap
Local Interstellar Medium Kinematics towards the Southern Coalsack and Chamaeleon-Musca dark clouds
The results of a spectroscopic programme aiming to investigate the kinematics
of the local interstellar medium components towards the Southern Coalsack and
Chamaeleon-Musca dark clouds are presented. The analysis is based upon
high-resolution (R ~ 60,000) spectra of the insterstellar NaI D absorption
lines towards 63 B-type stars (d < 500 pc) selected to cover these clouds and
the connecting area defined by the Galactic coordinates: 308 > l > 294 and -22
< b < 5. The radial velocities, column densities, velocity dispersions, colour
excess and photometric distances to the stars are used to understand the
kinematics and distribution of the interstellar cloud components. The analysis
indicates that the interstellar gas is distributed in two extended sheet-like
structures permeating the whole area, one at d < 60 pc and another around
120-150 pc from the Sun. The dust and gas feature around 120-150 pc seem to be
part of an extended large scale feature of similar kinematic properties,
supposedly identified with the interaction zone of the Local and Loop I
bubbles.Comment: 19 pages, accepted for MNRA
Switchable coupling for superconducting qubits using double resonance in the presence of crosstalk
Several methods have been proposed recently to achieve switchable coupling
between superconducting qubits. We discuss some of the main considerations
regarding the feasibility of implementing one of those proposals: the
double-resonance method. We analyze mainly issues related to the achievable
effective coupling strength and the effects of crosstalk on this coupling
approach. We also find a new, crosstalk-assisted coupling channel that can be
an attractive alternative when implementing the double-resonance coupling
proposal.Comment: 4 pages, 3 figure
Optical Properties of Graphene Nanoflakes: Shape Matters
In recent years there has been significant debate on whether the edge type of
graphene nanoflakes (GNF) or graphene quantum dots (GQD) are relevant for their
electronic structure, thermal stability and optical properties. Using computer
simulations, we have proven that there is a fundamental difference in the
calculated absorption spectra between samples of the same shape, similar size
but different edge type, namely, armchair or zigzag edges. These can be
explained by the presence of electronic structures near the Fermi level which
are localized on the edges. These features are also evident from the dependence
of band gap on the GNF size, which shows three very distinct trends for
different shapes and edge geometries.Comment: 8 pages, 9 figures. Submitted to The Journal of Chemical Physic
2000 CKM-Triangle Analysis A Critical Review with Updated Experimental Inputs and Theoretical Parameters
Within the Standard Model, a review of the current determination of the sides
and angles of the CKM unitarity triangle is presented, using experimental
constraints from the measurements of |\epsilon_K|, |V_{ub}/V_{cb}|, \Delta m_d
and from the limit on \Delta m_s, available in September 2000. Results from the
experimental search for {B}^0_s-\bar{B}^0_s oscillations are introduced in the
present analysis using the likelihood. Special attention is devoted to the
determination of the theoretical uncertainties. The purpose of the analysis is
to infer regions where the parameters of interest lie with given probabilities.
The BaBar "95 %, C.L. scanning" method is also commented.Comment: 44 pages (revised version
Majorana fermions in pinned vortices
Exploiting the peculiar properties of proximity-induced superconductivity on
the surface of a topological insulator, we propose a device which allows the
creation of a Majorana fermion inside the core of a pinned Abrikosov vortex.
The relevant Bogolyubov-de Gennes equations are studied analytically. We
demonstrate that in this system the zero-energy Majorana fermion state is
separated by a large energy gap, of the order of the zero-temperature
superconducting gap , from a band of single-particle non-topological
excitations. In other words, the Majorana fermion remains robust against
thermal fluctuations, as long as the temperature remains substantially lower
than the critical superconducting temperature. Experimentally, the Majorana
state may be detected by measuring the tunneling differential conductance at
the center of the Abrikosov vortex. In such an experiment, the Majorana state
manifests itself as a zero-bias anomaly separated by a gap, of the order of
, from the contributions of the nontopological excitations.Comment: 9 pages, 2 eps figures, new references are added, several typos are
correcte
Dispersal of larval and juvenile seabream: Implications for Mediterranean marine protected areas
In the marine context, information about dispersal is essential for the design of networks of marine protected areas (MPAs). Generally, most of the dispersal of demersal fishes is thought to be driven by the transport of eggs and larvae in currents, with the potential contribution of dispersal in later life stages relatively minimal.Using otolith chemistry analyses, we estimate dispersal patterns across a spatial scale of approximately 180. km at both propagule (i.e. eggs and larvae) and juvenile (i.e. between settlement and recruitment) stages of a Mediterranean coastal fishery species, the two-banded seabream Diplodus vulgaris. We detected three major natal sources of propagules replenishing local populations in the entire study area, suggesting that propagule dispersal distance extends to at least 90. km. For the juvenile stage, we detected dispersal of up to 165. km. Our work highlights the surprising and significant role of dispersal during the juvenile life stages as an important mechanism connecting populations. Such new insights are crucial for creating effective management strategies (e.g. MPAs and MPA networks) and to gain support from policymakers and stakeholders, highlighting that MPA benefits can extend well beyond MPA borders, and not only via dispersal of eggs and larvae, but also through movement by juveniles
An SU(5)Z_{13} Grand Unification Model
We propose an SU(5) grand unified model with an invisible axion and the
unification of the three coupling constants which is in agreement with the
values, at , of , , and . A discrete,
anomalous, symmetry implies that the Peccei-Quinn symmetry is an
automatic symmetry of the classical Lagrangian protecting, at the same time,
the invisible axion against possible semi-classical gravity effects. Although
the unification scale is of the order of the Peccei-Quinn scale the proton is
stabilized by the fact that in this model the standard model fields form the
SU(5) multiplets completed by new exotic fields and, also, because it is
protected by the symmetry.Comment: 14 pages, more typos correcte
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