591 research outputs found
ArqueologÃa en Catamarca : El Valle de Santa MarÃa de Yocavil : arqueoastronomÃa en un poblado precolombino de Yocavil : la frontera del sol en Rincón Chico
Fil: Reynoso, Alejandra D. Universidad de Buenos Aires. Facultad de FilosofÃa y Letras. Museo Etnográfico; Argentina.Mil años atrás, aproximadamente, se construyó en Rincón Chico una señal para no olvidar\nnunca la llegada de los dÃas más largos. Un lugar para mirar el sol poniente durante el\nsolsticio de verano. Un lugar y también una frontera. El observatorio solar del poblado\nprecolombino de Rincón Chico pone en juego tres construcciones desde ya únicas en\nrelación con todas las demás, muy numerosas por cierto, que conforman el antiguo\nasentamiento
On hadronic beam models for quasars and microquasars
Most of the hadronic jet models for quasars (QSOs) and microquasars (MQs)
found in literature represent beams of particles (e.g. protons). These
particles interact with the matter in the stellar wind of the companion star in
the system or with crossing clouds, generating gamma-rays via proton-proton
processes. Our aim is to derive the particle distribution in the jet as seen by
the observer, so that proper computation of the -ray and neutrino
yields can be done. We use relativistic invariants to obtain the transformed
expressions in the case of a power-law and power-law with a cutoff particle
distribution in the beam. We compare with previous expressions used earlier in
the literature. We show that formerly used expressions for the particle
distributions in the beam as seen by the observer are in error, differences
being strongly dependent on the viewing angle. For example, for
( is the Lorentz factor of the blob) and angles larger than , the earlier-used calculation entails an over-prediction (order of
magnitude or more) of the proton spectra for , whereas it always
over-predicts (two orders of magnitude) the proton spectrum at lower energies,
disregarding the viewing angle. All the results for photon and neutrino fluxes
in hadronic models in beams that have made use of the earlier calculation are
affected. Given that correct gamma-ray fluxes will be in almost any case
significantly diminished in comparison with published results, and that the
time of observations in Cherenkov facilities grows with the square of the
flux-reduction factor in a statistically limited result, the possibility of
observing hadronic beams is undermined.Comment: Accepted for publication in A&A Letter
Spin-orbit induced chirality of Andreev states in Josephson junctions
We study Josephson junctions (JJs) in which the region between the two
superconductors is a multichannel system with Rashba spin-orbit coupling (SOC)
where a barrier or a quantum point contact (QPC) is present. These systems
might present unconventional Josephson effects such as Josephson currents for
zero phase difference or critical currents that \textit{depend on} the current
direction. Here, we discuss how the spin polarizing properties of the system in
the normal state affect the spin characteristic of the Andreev bound states
inside the junction. This results in a strong correlation between the spin of
the Andreev states and the direction in which they transport Cooper pairs.
While the current-phase relation for the JJ at zero magnetic field is
qualitatively unchanged by SOC, in the presence of a weak magnetic field a
strongly anisotropic behavior and the mentioned anomalous Josephson effects
follow. We show that the situation is not restricted to barriers based on
constrictions such as QPCs and should generically arise if in the normal system
the direction of the carrier's spin is linked to its direction of motion.Comment: 19 pages, 9 figures. To appear in PR
Anomalous Josephson Current in Junctions with Spin-Polarizing Quantum Point Contacts
We consider a ballistic Josephson junction with a quantum point contact in a
two-dimensional electron gas with Rashba spin-orbit coupling. The point contact
acts as a spin filter when embedded in a circuit with normal electrodes. We
show that with an in-plane external magnetic field an anomalous supercurrent
appears even for zero phase difference between the superconducting electrodes.
In addition, the external field induces large critical current asymmetries
between the two flow directions, leading to supercurrent rectifying effects.Comment: 4 pages, 4 figures, to appear in PR
A molecular shell with star formation toward the supernova remnant G349.7+0.2
A field of ~38'x38' around the supernova remnant (SNR) G349.7+0.2 has been
surveyed in the CO J=1-0 transition with the 12 Meter Telescope of the NRAO,
using the On-The-Fly technique. The resolution of the observations is 54". We
have found that this remnant is interacting with a small CO cloud which, in
turn, is part of a much larger molecular complex, which we call the ``Large CO
Shell''. The Large CO Shell has a diameter of about 100 pc, an H_2 mass of
930,000 solar masses, and a density of 35 cm-3. We investigate the origin of
this structure and suggest that an old supernova explosion ocurred about 4
million years ago, as a suitable hypothesis. Analyzing the interaction between
G349.7+0.2 and the Large CO Shell, it is possible to determine that the shock
front currently driven into the molecular gas is a non-dissociative shock
(C-type), in agreement with the presence of OH 1720 MHz masers. The positional
and kinematical coincidence among one of the CO clouds that constitute the
Large CO Shell, an IRAS point-like source and an ultracompact H II region,
indicate the presence of a recently formed star. We suggest that the formation
of this star was triggered during the expansion of the Large CO Shell, and
suggest the possibility that the same expansion also created the progenitor
star of G349.7+0.2. The Large CO Shell would then be one of the few
observational examples of supernova-induced star formation.Comment: accepted in Astronomical Journal, corrected typo in the abstract (in
first line, 38' instead of 38"
Sea anemone model has a single Toll-like receptor that can function in pathogen detection, NF-κB signal transduction, and development
In organisms from insects to vertebrates, Toll-like receptors (TLRs) are primary pathogen detectors that activate downstream pathways, specifically those that direct expression of innate immune effector genes. TLRs also have roles in development in many species. The sea anemone Nematostella vectensis is a useful cnidarian model to study the origins of TLR signaling because its genome encodes a single TLR and homologs of many downstream signaling components, including the NF-κB pathway. We have characterized the single N. vectensis TLR (Nv-TLR) and demonstrated that it can activate canonical NF-κB signaling in human cells. Furthermore, we show that the intracellular Toll/IL-1 receptor (TIR) domain of Nv-TLR can interact with the human TLR adapter proteins MAL and MYD88. We demonstrate that the coral pathogen Vibrio coralliilyticus causes a rapidly lethal disease in N. vectensis and that heat-inactivated V. coralliilyticus and bacterial flagellin can activate a reconstituted Nv-TLR–to–NF-κB pathway in human cells. By immunostaining of anemones, we show that Nv-TLR is expressed in a subset of cnidocytes and that many of these Nv-TLR–expressing cells also express Nv-NF-κB. Additionally, the nematosome, which is a Nematostella-specific multicellular structure, expresses Nv-TLR and many innate immune pathway homologs and can engulf V. coralliilyticus. Morpholino knockdown indicates that Nv-TLR also has an essential role during early embryonic development. Our characterization of this primitive TLR and identification of a bacterial pathogen for N. vectensis reveal ancient TLR functions and provide a model for studying the molecular basis of cnidarian disease and immunity.IOS-1354935 - National Science Foundation (NSF); GRFP - National Science Foundation (NSF); GRFP - National Science Foundation (NSF); 1262934 - National Science Foundation (NSF); 2014-BSP - Arnold and Mabel Beckman Foundatio
The antenna DSA 3 and its potential use for Radio Astronomy
The European Space Agency (ESA) will inaugurate its third Deep Space Antenna
(DSA 3) by the end of 2012. DSA 3 will be located in Argentina near the city of
Malarg"ue in the Mendoza province. While the instrument will be primarily
dedicated to communications with interplanetary missions, the characteristics
of its antenna and receivers will also enable standalone leading scientific
contributions, with a high scientific-technological return. We outline here
scientific proposals for a radio astronomical use of DSA 3.Comment: 4 pages, submitted as Proceedings for the BAA
Imaging transverse electron focusing in semiconducting heterostructures with spin-orbit coupling
Transverse electron focusing in two-dimensional electron gases (2DEGs) with
strong spin-orbit coupling is revisited. The transverse focusing is related to
the transmission between two contacts at the edge of a 2DEG when a
perpendicular magnetic field is applied. Scanning probe microscopy imaging
techniques can be used to study the electron flow in these systems. Using
numerical techniques we simulate the images that could be obtained in such
experiments. We show that hybrid edge states can be imaged and that the
outgoing flux can be polarized if the microscope tip probe is placed in
specific positions.Comment: Contribution to the Book/Proceedings of the PITP Les Houches School
on "Quantum Magnetism" held on June, 2006. Final forma
Detection of spin polarized currents in quantum point contacts via transverse electron focusing
It has been predicted recently that an electron beam can be polarized when it
flows adiabatically through a quantum point contact in a system with spin-orbit
interaction. Here, we show that a simple transverse electron focusing setup can
be used to detect such polarized current. It uses the amplitude's asymmetry of
the spin-split transverse electron focusing peak to extract information about
the electron's spin polarization. On the other hand, and depending on the
quantum point contact geometry, including this one-body effect can be important
when using the focusing setup to study many-body effects in quantum point
contacts.Comment: 5 pages, 5 figure
Atomic gravimeter robust to environmental effects
Atomic accelerometers and gravimeters are usually based on freely-falling
atoms in atomic fountains, which not only limits their size, but also their
robustness to environmental factors such as tilts, magnetic fields or
vibrations. Such limitations have precluded their broad adoption in the field,
for geophysics, geology, and inertial navigation. More recently, atom
interferometers based on holding atoms in an optical lattice have been
developed. Such gravimeters also suppress the influence of vibrations in the
frequency range of ~1 Hz and above by several orders of magnitude relative to
conventional atomic gravimeters. Here, we show that such interferometers are
robust to tilts of more than 8 mrad with respect to the vertical and can
suppress the effect of even strong environmental magnetic fields and field
gradients by using atoms in the F=3,4 hyperfine ground states as
co-magnetometers, potentially eliminating the need for shielding. We
demonstrate gravimeter sensitivity of () in a compact geometry where atoms only travel over mm
of space.Comment: 9 pages, 4 figure
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