3,149 research outputs found
Anxious to see you: Neuroendocrine mechanisms of social vigilance and anxiety during adolescence.
Social vigilance is a behavioral strategy commonly used in adverse or changing social environments. In animals, a combination of avoidance and vigilance allows an individual to evade potentially dangerous confrontations while monitoring the social environment to identify favorable changes. However, prolonged use of this behavioral strategy in humans is associated with increased risk of anxiety disorders, a major burden for human health. Elucidating the mechanisms of social vigilance in animals could provide important clues for new treatment strategies for social anxiety. Importantly, during adolescence the prevalence of social anxiety increases significantly. We hypothesize that many of the actions typically characterized as anxiety behaviors begin to emerge during this time as strategies for navigating more complex social structures. Here, we consider how the social environment and the pubertal transition shape neural circuits that modulate social vigilance, focusing on the bed nucleus of the stria terminalis and prefrontal cortex. The emergence of gonadal hormone secretion during adolescence has important effects on the function and structure of these circuits, and may play a role in the emergence of a notable sex difference in anxiety rates across adolescence. However, the significance of these changes in the context of anxiety is still uncertain, as not enough studies are sufficiently powered to evaluate sex as a biological variable. We conclude that greater integration between human and animal models will aid the development of more effective strategies for treating social anxiety
Effects of chemical releases by the STS-3 Orbiter on the ionosphere
The Plasma Diagnostics Package, flown aboard STS-3 as part of the first Shuttle payload (OSS-1), recorded the effects of various chemical releases from the Orbiter. Changes in the plasma environment was observed during flash evaporator system releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electrostatic noise was enhanced and plasma density irregularities were observed to increase by 3 to 30 times with a spectrum which rose steeply and peaked below 6 Hz. In the case of water dumps, background electrostatic noise was enhanced at frequencies below about 3 kHz and suppressed at frequencies above 2 kHz. Thruster activity also stimulated electrostatic noise with a spectrum which peaked at approximately 0.5 kHz. In addition, ions with energies up to 1 keV were seen during some thruster events
Quantum limit of the triplet proximity effect in half-metal - superconductor junctions
We apply the scattering matrix approach to the triplet proximity effect in
superconductor-half metal structures. We find that for junctions that do not
mix different orbital modes, the zero bias Andreev conductance vanishes, while
the zero bias Josephson current is nonzero. We illustrate this finding on a
ballistic half-metal--superconductor (HS) and superconductor -- half-metal --
superconductor (SHS) junction with translation invariance along the interfaces,
and on HS and SHS systems where transport through the half-metallic region
takes place through a single conducting channel. Our calculations for these
physically single mode setups -- single mode point contacts and chaotic quantum
dots with single mode contacts -- illustrate the main strength of the
scattering matrix approach: it allows for studying systems in the quantum
mechanical limit, which is inaccessible for quasiclassical Green's function
methods, the main theoretical tool in previous works on the triplet proximity
effect.Comment: 12 pages, 10 figures; v2: references added, typos correcte
Magnetic Coupling Between Non-Magnetic Ions: Eu3+ in EuN and EuP
We consider the electronic structure of, and magnetic exchange (spin)
interactions between, nominally nonmagnetic Eu^3+ ions (4f^6, S=3, L=3, J=0)
within the context of the rocksalt structure compounds EuN and EuP. Both
compounds are ionic [Eu^3+; N^3- and P^3-] semimetals similar to isovalent GdN.
Treating the spin polarization within the 4f shell, and then averaging
consistent with the J=0 configuration, we estimate semimetallic band overlaps
(Eu 5d with pnictide 2p or 3p) of ~0.1 eV (EuN) and ~1.0 eV (EuP) that increase
(become more metallic) with pressure. The calculated bulk modulus is 130 (86)
GPa for EuN (EuP). Exchange (spin-spin) coupling calculated from correlated
band theory is small and ferromagnetic in sign for EuN, increasing in magnitude
with pressure. Conversely, the exchange coupling is antiferromagnetic in sign
for EuP and is larger in magnitude, but decreases with compression. Study of a
two-site model with S_1*S_2 coupling within the J=0,1 spaces of each ion
illustrates the dependence of the magnetic correlation functions on the model
parameters, and indicates that the spin coupling is sufficient to alter the Van
Vleck susceptibility. We outline a scenario of a spin-correlation transition in
a lattice of S=3, L=3, J=0 nonmagnetic ions
The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks II. Extended Simulations with Varied Cooling Rates
In order to investigate mass transport and planet formation by gravitational
instabilities (GIs), we have extended our 3-D hydrodynamic simulations of
protoplanetary disks from a previous paper. Our goal is to determine the
asymptotic behavior of GIs and how it is affected by different constant cooling
times. Initially, Rdisk = 40 AU, Mdisk = 0.07 Mo, M* = 0.5 Mo, and Qmin = 1.8.
Sustained cooling, with tcool = 2 orps (outer rotation periods, 1 orp ~ 250
yrs), drives the disk to instability in ~ 4 orps. This calculation is followed
for 23.5 orps. After 12 orps, the disk settles into a quasi-steady state with
sustained nonlinear instabilities, an average Q = 1.44 over the outer disk, a
well-defined power-law Sigma(r), and a roughly steady Mdot ~ 5(-7) Mo/yr. The
transport is driven by global low-order spiral modes. We restart the
calculation at 11.2 orps with tcool = 1 and 1/4 orp. The latter case is also
run at high azimuthal resolution. We find that shorter cooling times lead to
increased Mdots, denser and thinner spiral structures, and more violent dynamic
behavior. The asymptotic total internal energy and the azimuthally averaged
Q(r) are insensitive to tcool. Fragmentation occurs only in the high-resolution
tcool = 1/4 orp case; however, none of the fragments survive for even a quarter
of an orbit. Ring-like density enhancements appear and grow near the boundary
between GI active and inactive regions. We discuss the possible implications of
these rings for gas giant planet formation.Comment: Due to document size restrictions, the complete manuscript could not
be posted on astroph. Please go to http://westworld.astro.indiana.edu to
download the full document including figure
Magnetism, Spin-Orbit Coupling, and Superconducting Pairing in UGe
A consistent picture on the mean-field level of the magnetic properties and
electronic structure of the superconducting itinerant ferromagnet UGe is
shown to require inclusion of correlation effects beyond the local density
approximation (LDA). The "LDA+U" approach reproduces both the magnitude of the
observed moment, composed of strongly opposing spin and orbital parts, and the
magnetocrystalline anisotropy. The largest Fermi surface sheet is comprised
primarily of spin majority states with orbital projection =0,
suggesting a much simpler picture of the pairing than is possible for general
strong spin-orbit coupled materials. This occurrence, and the
quasi-two-dimensional geometry of the Fermi surface, support the likelihood of
magnetically mediated p-wave triplet pairing.Comment: accepted for publication in Phys. Rev. Lett; URL for better quality
image of Fig.3 (2MB) at http://yammer.ucdavis.edu/public/UGe2/fig3.ep
Dispersive Gap Mode of Phonons in Anisotropic Superconductors
We estimate the effect of the superconducting gap anisotropy in the
dispersive gap mode of phonons, which is observed by the neutron scattering on
borocarbide superconductors. We numerically analyze the phonon spectrum
considering the electron-phonon coupling, and examine contributions coming from
the gap suppression and the sign change of the pairing function on the Fermi
surface. When the sign of the pairing function is changed by the nesting
translation, the gap mode does not appear. We also discuss the suppression of
the phonon softening of the Kohn anomaly due to the onset of superconductivity.
We demonstrate that observation of the gap dispersive mode is useful for
sorting out the underlying superconducting pairing function.Comment: 7 pages, 12 figures, to be published in J. Phys. Soc. Jp
The Superconductivity, Intragrain Penetration Depth and Meissner Effect of RuSr2(Gd,Ce)2Cu2O10+delta
The hole concentration (p)(delta), the transition temperature Tc, the
intragrain penetration depth lambda, and the Meissner effect were measured for
annealed RuSr2(Gd,Ce)2Cu2O10+delta samples. The intragrain superconducting
transition temperature Tc} varied from 17 to 40 K while the p changed by only
0.03 holes/CuO2. The intragrain superfluid-density 1/lambda^2 and the
diamagnetic drop of the field-cooled magnetization across Tc (the Meissner
effect), however, increased more than 10 times. All of these findings are in
disagreement with both the Tc vs. p and the Tc vs. 1/lambda^2 correlations
proposed for homogeneous cuprates, but are in line with a possible
phase-separation and the granularity associated with it.Comment: 7 pages, 6 figures, accepted for publication in Phys. Rev. B (May 2,
2002
Phenomenological Theory of Superconductivity and Magnetism in HoDyNiBC
The coexistence of the superconductivity and magnetism in the
HoDyNiBC is studied by using Ginzburg-Landau theory. This
alloy shows the coexistence and complex interplay of superconducting and
magnetic order. We propose a phenomenological model which includes two magnetic
and two superconducting order parameters accounting for the multi-band
structure of this material. We describe phenomenologically the magnetic
fluctuations and order and demonstrate that they lead to anomalous behavior of
the upper critical field. The doping dependence of in
HoDyNiBC showing a reentrance behavior are analyzed
yielding a very good agreement with experimental data.Comment: 4 pages, 3 figures, REVTeX, submitted to PR
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