896 research outputs found
Extended Red Emission and the evolution of carbonaceaous nanograins in NGC 7023
Extended Red Emission (ERE) was recently attributed to the photo-luminescence
of either doubly ionized Polycyclic Aromatic Hydrocarbons (PAH), or
charged PAH dimers. We analysed the visible and mid-infrared (mid-IR) dust
emission in the North-West and South photo-dissociation regions of the
reflection nebula NGC 7023.Using a blind signal separation method, we extracted
the map of ERE from images obtained with the Hubble Space Telescope, and at the
Canada France Hawaii Telescope. We compared the extracted ERE image to the
distribution maps of the mid-IR emission of Very Small Grains (VSGs), neutral
and ionized PAHs (PAH and PAH) obtained with the Spitzer Space
Telescope and the Infrared Space Observatory. ERE is dominant in transition
regions where VSGs are being photo-evaporated to form free PAH molecules, and
is not observed in regions dominated by PAH. Its carrier makes a minor
contribution to the mid-IR emission spectrum. These results suggest that the
ERE carrier is a transition species formed during the destruction of VSGs.
Singly ionized PAH dimers appear as good candidates but PAH molecules
seem to be excluded.Comment: Accepted for publication in A&
Three-dimensional flow instability in a lid-driven isosceles triangular cavity
Linear three-dimensional modal instability of steady laminar two-dimensional states developing in a lid-driven cavity of isosceles triangular cross-section is investigated theoretically and experimentally for the case in which the equal sides form a rectangular corner. An asymmetric steady two-dimensional motion is driven by the steady motion of one of the equal sides. If the side moves away from the rectangular corner, a stationary three-dimensional instability is found. If the motion is directed towards the corner, the instability is oscillatory. The respective critical Reynolds numbers are identified both theoretically and experimentally. The neutral curves pertinent to the two configurations and the properties of the respective leading eigenmodes are documented and analogies to instabilities in rectangular lid-driven cavities are discussed
Resistance noise scaling in a 2D system in GaAs
The 1/f resistance noise of a two-dimensional (2D) hole system in a high
mobility GaAs quantum well has been measured on both sides of the 2D
metal-insulator transition (MIT) at zero magnetic field (B=0), and deep in the
insulating regime. The two measurement methods used are described: I or V
fixed, and measurement of resp. V or I fluctuations. The normalized noise
magnitude SR/R^2 increases strongly when the hole density is decreased, and its
temperature (T) dependence goes from a slight increase with T at the largest
densities, to a strong decrease at low density. We find that the noise
magnitude scales with the resistance, SR /R^2 ~ R^2.4. Such a scaling is
expected for a second order phase transition or a percolation transition. The
possible presence of such a transition is investigated by studying the
dependence of the conductivity as a function of the density. This dependence is
consistent with a critical behavior close to a critical density p* lower than
the usual MIT critical density pc.Comment: 13 pages, 8 figures, Proceedings of SPIE: Fluctuations and noise in
materials, D. Popovic, M.B. Weissman, Z.A. Racz Eds., Vol. 5469, pp. 101-113,
Mspalomas, Spain, 200
Ultra-short pulses in linear and nonlinear media
We consider the evolution of ultra-short optical pulses in linear and
nonlinear media. For the linear case, we first show that the initial-boundary
value problem for Maxwell's equations in which a pulse is injected into a
quiescent medium at the left endpoint can be approximated by a linear wave
equation which can then be further reduced to the linear short-pulse equation.
A rigorous proof is given that the solution of the short pulse equation stays
close to the solutions of the original wave equation over the time scales
expected from the multiple scales derivation of the short pulse equation. For
the nonlinear case we compare the predictions of the traditional nonlinear
Schr\"odinger equation (NLSE) approximation which those of the short pulse
equation (SPE). We show that both equations can be derived from Maxwell's
equations using the renormalization group method, thus bringing out the
contrasting scales. The numerical comparison of both equations to Maxwell's
equations shows clearly that as the pulse length shortens, the NLSE
approximation becomes steadily less accurate while the short pulse equation
provides a better and better approximation
Adaptive mesh refinement with spectral accuracy for magnetohydrodynamics in two space dimensions
We examine the effect of accuracy of high-order spectral element methods,
with or without adaptive mesh refinement (AMR), in the context of a classical
configuration of magnetic reconnection in two space dimensions, the so-called
Orszag-Tang vortex made up of a magnetic X-point centered on a stagnation point
of the velocity. A recently developed spectral-element adaptive refinement
incompressible magnetohydrodynamic (MHD) code is applied to simulate this
problem. The MHD solver is explicit, and uses the Elsasser formulation on
high-order elements. It automatically takes advantage of the adaptive grid
mechanics that have been described elsewhere in the fluid context [Rosenberg,
Fournier, Fischer, Pouquet, J. Comp. Phys. 215, 59-80 (2006)]; the code allows
both statically refined and dynamically refined grids. Tests of the algorithm
using analytic solutions are described, and comparisons of the Orszag-Tang
solutions with pseudo-spectral computations are performed. We demonstrate for
moderate Reynolds numbers that the algorithms using both static and refined
grids reproduce the pseudo--spectral solutions quite well. We show that
low-order truncation--even with a comparable number of global degrees of
freedom--fails to correctly model some strong (sup--norm) quantities in this
problem, even though it satisfies adequately the weak (integrated) balance
diagnostics.Comment: 19 pages, 10 figures, 1 table. Submitted to New Journal of Physic
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TEAMwork: Testing Emotional Attunement and Mutuality During Parent-Adolescent fMRI.
The parent-child relationship and family context influence the development of emotion regulation (ER) brain circuitry and related skills in children and adolescents. Although both parents' and children's ER neurocircuitry simultaneously affect how they interact with one another, neuroimaging studies of parent-child relationships typically include only one member of the dyad in brain imaging procedures. The current study examined brain activation related to parenting and ER in parent-adolescent dyads during concurrent fMRI scanning with a novel task - the Testing Emotional Attunement and Mutuality (TEAM) task. The TEAM task includes feedback trials indicating the other dyad member made an error, resulting in a monetary loss for both participants. Results indicate that positive parenting practices as reported by the adolescent were positively correlated with parents' hemodynamic activation of the ventromedial prefrontal cortex, a region related to empathy, during these error trials. Additionally, during feedback conditions both parents and adolescents exhibited fMRI activation in ER-related regions, including the dorsolateral prefrontal cortex, anterior insula, fusiform gyrus, thalamus, caudate, precuneus, and superior parietal lobule. Adolescents had higher left amygdala activation than parents during the feedback condition. These findings demonstrate the utility of dyadic fMRI scanning for investigating relational processes, particularly in the parent-child relationship
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Always on my mind: Cross-brain associations of mental health symptoms during simultaneous parent-child scanning.
How parents manifest symptoms of anxiety or depression may affect how children learn to modulate their own distress, thereby influencing the children's risk for developing an anxiety or mood disorder. Conversely, children's mental health symptoms may impact parents' experiences of negative emotions. Therefore, mental health symptoms can have bidirectional effects in parent-child relationships, particularly during moments of distress or frustration (e.g., when a parent or child makes a costly mistake). The present study used simultaneous functional magnetic resonance imaging (fMRI) of parent-adolescent dyads to examine how brain activity when responding to each other's costly errors (i.e., dyadic error processing) may be associated with symptoms of anxiety and depression. While undergoing simultaneous fMRI scans, healthy dyads completed a task involving feigned errors that indicated their family member made a costly mistake. Inter-brain, random-effects multivariate modeling revealed that parents who exhibited decreased medial prefrontal cortex and posterior cingulate cortex activation when viewing their child's costly error response had children with more symptoms of depression and anxiety. Adolescents with increased anterior insula activation when viewing a costly error made by their parent had more anxious parents. These results reveal cross-brain associations between mental health symptomatology and brain activity during parent-child dyadic error processing
Prevalence and family-related factors associated with suicidal ideation, suicide attempts, and self-injury in children aged 9 to 10 years
Importance: Although suicide is a leading cause of death for children in the United States, and the rate of suicide in childhood has steadily increased, little is known about suicidal ideation and behaviors in children.
Objective: To assess the overall prevalence of suicidal ideation, suicide attempts, and nonsuicidal self-injury, as well as family-related factors associated with suicidality and self-injury among preadolescent children.
Design, Setting, and Participants: Cross-sectional study using retrospective analysis of the baseline sample from the Adolescent Brain Cognitive Development (ABCD) study. This multicenter investigation used an epidemiologically informed school-based recruitment strategy, with consideration of the demographic composition of the 21 ABCD sites and the United States as a whole. The sample included children aged 9 to 10 years and their caregivers.
Main Outcomes and Measures: Lifetime suicidal ideation, suicide attempts, and nonsuicidal self-injury as reported by children and their caregivers in a computerized version of the Kiddie Schedule for Affective Disorders and Schizophrenia.
Results: A total of 11 814 children aged 9 to 10 years (47.8% girls; 52.0% white) and their caregivers were included. After poststratification sociodemographic weighting, the approximate prevalence rates were 6.4% (95% CI, 5.7%-7.3%) for lifetime history of passive suicidal ideation; 4.4% (95% CI, 3.9%-5.0%) for nonspecific active suicidal ideation; 2.4% (95% CI, 2.1%-2.7%) for active ideation with method, intent, or plan; 1.3% (95% CI, 1.0%-1.6%) for suicide attempts; and 9.1% (95% CI, 8.1-10.3) for nonsuicidal self-injury. After covarying by sex, family history, internalizing and externalizing problems, and relevant psychosocial variables, high family conflict was significantly associated with suicidal ideation (odds ratio [OR], 1.12; 95% CI, 1.07-1.16) and nonsuicidal self-injury (OR, 1.09; 95% CI, 1.05-1.14), and low parental monitoring was significantly associated with ideation (OR, 0.97; 95% CI, 0.95-0.98), attempts (OR, 0.91; 95% CI, 0.86-0.97), and nonsuicidal self-injury (OR, 0.95; 95% CI, 0.93-0.98); these findings were consistent after internal replication. Most of children\u27s reports of suicidality and self-injury were either unknown or not reported by their caregivers.
Conclusions and Relevance: This study demonstrates the association of family factors, including high family conflict and low parental monitoring, with suicidality and self-injury in children. Future research and ongoing prevention and intervention efforts may benefit from the examination of family factors
Compositionality, stochasticity and cooperativity in dynamic models of gene regulation
We present an approach for constructing dynamic models for the simulation of
gene regulatory networks from simple computational elements. Each element is
called a ``gene gate'' and defines an input/output-relationship corresponding
to the binding and production of transcription factors. The proposed reaction
kinetics of the gene gates can be mapped onto stochastic processes and the
standard ode-description. While the ode-approach requires fixing the system's
topology before its correct implementation, expressing them in stochastic
pi-calculus leads to a fully compositional scheme: network elements become
autonomous and only the input/output relationships fix their wiring. The
modularity of our approach allows to pass easily from a basic first-level
description to refined models which capture more details of the biological
system. As an illustrative application we present the stochastic repressilator,
an artificial cellular clock, which oscillates readily without any cooperative
effects.Comment: 15 pages, 8 figures. Accepted by the HFSP journal (13/09/07
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