1,081 research outputs found
A VLA Study of Newly-Discovered Southern Latitude Non-Thermal Filaments in the Galactic Center: Radio Continuum Total-intensity and Spectral Index Properties
The non-thermal filament (NTF) radio structures clustered within a few
hundred parsecs of the Galactic Center (GC) are apparently unique to this
region of the Galaxy. Recent radio images of the GC using MeerKAT at 1 GHz have
revealed a multitude of faint, previously unknown NTF bundles (NTFBs), some of
which are comprised of as many as 10 or more individual filaments. In this work
we present Very Large Array (VLA) observations at C- and X-bands (4 - 12 GHz)
at arcsecond-scale resolutions of three of these newly-discovered NTFBs, all
located at southern Galactic latitudes. These observations allow us to compare
their total-intensity properties with those of the larger NTF population. We
find that these targets generally possess properties similar to what is
observed in the larger NTF population. However, the larger NTF population
generally has steeper spectral index values than what we observe for our chosen
targets. The results presented here based on the total-intensity properties of
these structures indicate that the NTFs are likely all formed from Cosmic Rays
(CRs). These CRs are either generated by a nearby compact source and then
diffuse along the NTF lengths or are generated by extended, magnetized
structures whose magnetic field undergoes reconnection with the NTF magnetic
field.Comment: 18 pages, 13 figures, 2 tables. Submitted to ApJ for peer-revie
Three-dimensional view of ultrafast dynamics in photoexcited bacteriorhodopsin in the multiphoton regime and biological relevance
How does chemistry scale in complexity to unerringly direct biological functions? Nass Kovacs et al. have shown that bacteriorhodopsin undergoes structural changes tantalizingly similar to the expected pathway even under excessive excitation. Is the protein structure so highly evolved that it directs all deposited energy into the designed function
A rat model of post-traumatic stress disorder reproduces the hippocampal deficits seen in the human syndrome
Despite recent progress, the causes and pathophysiology of post-traumatic stress disorder (PTSD) remain poorly understood, partly because of ethical limitations inherent to human studies. One approach to circumvent this obstacle is to study PTSD in a valid animal model of the human syndrome. In one such model, extreme and long-lasting behavioral manifestations of anxiety develop in a subset of Lewis rats after exposure to an intense predatory threat that mimics the type of life-and-death situation known to precipitate PTSD in humans. This study aimed to assess whether the hippocampus-associated deficits observed in the human syndrome are reproduced in this rodent model. Prior to predatory threat, different groups of rats were each tested on one of three object recognition memory tasks that varied in the types of contextual clues (i.e., that require the hippocampus or not) the rats could use to identify novel items. After task completion, the rats were subjected to predatory threat and, one week later, tested on the elevated plus maze (EPM). Based on their exploratory behavior in the plus maze, rats were then classified as resilient or PTSD-like and their performance on the pre-threat object recognition tasks compared. The performance of PTSD-like rats was inferior to that of resilient rats but only when subjects relied on an allocentric frame of reference to identify novel items, a process thought to be critically dependent on the hippocampus. Therefore, these results suggest that even prior to trauma PTSD-like rats show a deficit in hippocampal-dependent functions, as reported in twin studies of human PTSD
Long-range electronic reconstruction to a -dominated Fermi surface below the LaAlO/SrTiO interface
Low dimensionality, broken symmetry and easily-modulated carrier
concentrations provoke novel electronic phase emergence at oxide interfaces.
However, the spatial extent of such reconstructions - i.e. the interfacial
"depth" - remains unclear. Examining LaAlO/SrTiO heterostructures at
previously unexplored carrier densities cm,
we observe a Shubnikov-de Haas effect for small in-plane fields, characteristic
of an anisotropic 3D Fermi surface with preferential orbital
occupancy extending over at least 100~nm perpendicular to the interface.
Quantum oscillations from the 3D Fermi surface of bulk doped SrTiO emerge
simultaneously at higher . We distinguish three areas in doped
perovskite heterostructures: narrow ( nm) 2D interfaces housing
superconductivity and/or other emergent phases, electronically isotropic
regions far ( nm) from the interface and new intermediate zones where
interfacial proximity renormalises the electronic structure relative to the
bulk.Comment: Supplementary material available at Scientific Reports websit
Adaptive Identification of SIS Models
Effective containment of spreading processes such as epidemics requires
accurate knowledge of several key parameters that govern their dynamics. In
this work, we first show that the problem of identifying the underlying
parameters of epidemiological spreading processes is often ill-conditioned and
lacks the persistence of excitation required for the convergence of adaptive
learning schemes. To tackle this challenge, we leverage a relaxed property
called initial excitation combined with a recursive least squares algorithm to
design an online adaptive identifier to learn the parameters of the
susceptible-infected-susceptible (SIS) epidemic model from the knowledge of its
states. We prove that the iterates generated by the proposed algorithm minimize
an auxiliary weighted least squares cost function. We illustrate the
convergence of the error of the estimated epidemic parameters via several
numerical case studies and compare it with results obtained using conventional
approaches
Multi-band Superconductivity in the Chevrel Phases SnMo6S8 and PbMo6S8
Sub-Kelvin scanning tunnelling spectroscopy in the Chevrel Phases SnMo6S8 and
PbMo6S8 reveals two distinct superconducting gaps with Delta_1 = 3 meV, Delta_2
~ 1.0 meV and Delta_1 = 3.1 meV, Delta_2 ~ 1.4 meV respectively. The gap
distribution is strongly anisotropic, with Delta_2 predominantly seen when
scanning across unit-cell steps on the (001) sample surface. The spectra are
well-fitted by an anisotropic two-band BCS s-wave gap function. Our
spectroscopic data are confirmed by electronic heat capacity measurements which
also provide evidence for a twin-gap scenario.Comment: 5 pages, 4 figure
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