643 research outputs found
Spectroscopy of bulk and few-layer superconducting NbSe with van der Waals tunnel junctions
Tunnel junctions, a well-established platform for high-resolution
spectroscopy of superconductors, require defect-free insulating barriers with
clean engagement to metals on both sides. Extending the range of materials
accessible to tunnel junction fabrication, beyond the limited selection which
allows high-quality oxide formation, requires the development of alternative
fabrication techniques. Here we show that van-der-Waals (vdW) tunnel barriers,
fabricated by stacking layered semiconductors on top of the transition metal
dichalcogenide (TMD) superconductor NbSe, sustain a stable, low noise
tunneling current, and exhibit strong suppression of sub-gap tunneling. We
utilize the technique to measure the spectra of bulk (20 nm) and ultrathin (3-
and 4-layer) devices at 70 mK. The spectra exhibit two distinct energy gaps,
the larger of which decreases monotonously with thickness and , in
agreement with BCS theory. The spectra are analyzed using a two-band model
modified to account for depairing. We show that in the bulk, the smaller gap
exhibits strong depairing in an in-plane magnetic field, consistent with a high
Fermi velocity. In the few-layer devices, depairing of the large gap is
negligible, consistent with out-of-plane spin-locking due to Ising spin-orbit
coupling. Our results demonstrate the utility of vdW tunnel junctions in
mapping the intricate spectral evolution of TMD superconductors over a range of
magnetic fields.Comment: This submission contains the first part of arxiv:1703.07677 with the
addition of spectra taken on this devices. The second part of 1703.07677 will
be published separatel
An efficient CDMA decoder for correlated information sources
We consider the detection of correlated information sources in the ubiquitous
Code-Division Multiple-Access (CDMA) scheme. We propose a message-passing based
scheme for detecting correlated sources directly, with no need for source
coding. The detection is done simultaneously over a block of transmitted binary
symbols (word). Simulation results are provided demonstrating a substantial
improvement in bit-error-rate in comparison with the unmodified detector and
the alternative of source compression. The robustness of the error-performance
improvement is shown under practical model settings, including wrong estimation
of the generating Markov transition matrix and finite-length spreading codes.Comment: 11 page
High and Low Dimensions in The Black Hole Negative Mode
The negative mode of the Schwarzschild black hole is central to Euclidean
quantum gravity around hot flat space and for the Gregory-Laflamme black string
instability. We analyze the eigenvalue as a function of space-time dimension by
constructing two perturbative expansions: one for large d and the other for
small d-3, and determining as many coefficients as we are able to compute
analytically. Joining the two expansions we obtain an interpolating rational
function accurate to better than 2% through the whole range of dimensions
including d=4.Comment: 17 pages, 4 figures. v2: added reference. v3: published versio
Constraining evaporation rates based on large-scale sea surface transects of salinity or isotopic compositions
Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(2), (2019): 1322-1330, doi:10.1029/2018JC014106.A Lagrangian model is constructed for a surface column of initial height h(0) that propagates at an average speed u and is subject to excess (i.e., net) evaporation of q m/year. It is shown that these parameters combine to form an evaporation length, L = uh(0)/q, which provides an estimate for the distance the column must travel before evaporating completely. While these changes in the surface water level due to evaporation are compensated by entrainment of water into the overall column, the changes in either near‐surface salinity or isotopic compositions are retained and can be measured. Observations of surface salinity and isotopic compositions of δ18O and δD along 1,000‐ to 3,500‐km long transects are used to estimate values of L in the Red Sea, Mediterranean Sea, Indian Ocean, and Gulf Stream. The variations of salinity, δ18O and δD in all four basins are linear. As anticipated, the estimated value of L is smallest in the slowly moving and arid Red Sea and is greatest in the fast‐moving Gulf Stream.The salinity and δ18O data collected aboard the Indian Ocean cruise described in Srivastava et al. (2007) can be accessed at this website (https://www.nodc.noaa.gov). The salinity, δ18O and δD data collected during the Red Sea cruise of the Interuniversity Institute for Marine Sciences, Eilat, described in Steiner et al. (2014) and can be accessed in the supporting information section of doi: 10.1073/pnas.1414323111. H. B. acknowledges the support provided by the Eshkol Foundation of the Israel Ministry of Science.2019-07-2
Minocycline rescues decrease in neurogenesis, increase in microglia cytokines and deficits in sensorimotor gating in an animal model of schizophrenia
Adult neurogenesis in the hippocampus is impaired in schizophrenic patients and in an animal model of schizophrenia. Amongst a plethora of regulators, the immune system has been shown repeatedly to strongly modulate neurogenesis under physiological and pathological conditions. It is well accepted, that schizophrenic patients have an aberrant peripheral immune status, which is also reflected in the animal model. The microglia as the intrinsic immune competent cells of the brain have recently come into focus as possible therapeutic targets in schizophrenia. We here used a maternal immune stimulation rodent model of schizophrenia in which polyinosinic-polycytidilic acid (Poly I:C) was injected into pregnant rats to mimic an anti-viral immune response. We identified microglia IL-1{beta} and TNF-{alpha} increase constituting the factors correlating best with decreases in net-neurogenesis and impairment in pre-pulse inhibition of a startle response in the Poly I:C model. Treatment with the antibiotic minocycline (3mg/kg/day) normalized microglial cytokine production in the hippocampus and rescued neurogenesis and behavior. We could also show that enhanced microglial TNF-{alpha} and IL-1{beta} production in the hippocampus was accompanied by a decrease in the pro-proliferative TNFR2 receptor expression on neuronal progenitor cells, which could be attenuated by minocycline. These findings strongly support the idea to use anti-inflammatory drugs to target microglia activation as an adjunctive therapy in schizophrenic patients
Paradoxical augmented relapse in alcohol-dependent rats during deep-brain stimulation in the nucleus accumbens
Case reports indicate that deep-brain stimulation in the nucleus accumbens may
be beneficial to alcohol-dependent patients. The lack of clinical trials and
our limited knowledge of deep-brain stimulation call for translational
experiments to validate these reports. To mimic the human situation, we used a
chronic-continuous brain-stimulation paradigm targeting the nucleus accumbens
and other brain sites in alcohol-dependent rats. To determine the network
effects of deep-brain stimulation in alcohol-dependent rats, we combined
electrical stimulation of the nucleus accumbens with functional magnetic
resonance imaging (fMRI), and studied neurotransmitter levels in nucleus
accumbens-stimulated versus sham-stimulated rats. Surprisingly, we report here
that electrical stimulation of the nucleus accumbens led to augmented relapse
behavior in alcohol-dependent rats. Our associated fMRI data revealed some
activated areas, including the medial prefrontal cortex and caudate putamen.
However, when we applied stimulation to these areas, relapse behavior was not
affected, confirming that the nucleus accumbens is critical for generating
this paradoxical effect. Neurochemical analysis of the major activated brain
sites of the network revealed that the effect of stimulation may depend on
accumbal dopamine levels. This was supported by the finding that brain-
stimulation-treated rats exhibited augmented alcohol-induced dopamine release
compared with sham-stimulated animals. Our data suggest that deep-brain
stimulation in the nucleus accumbens enhances alcohol-liking probably via
augmented dopamine release and can thereby promote relapse
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