28 research outputs found
Resolved Magnetic Field Mapping of a Molecular Cloud Using GPIPS
We present the first resolved map of plane-of-sky magnetic field strength for
a quiescent molecular cloud. GRSMC 45.60+0.30 subtends 40 x 10 pc at a distance
of 1.88 kpc, masses 16,000 M_sun, and exhibits no star formation. Near-infrared
background starlight polarizations were obtained for the Galactic Plane
Infrared Polarization Survey using the 1.8 m Perkins telescope and the Mimir
instrument. The cloud area of 0.78 deg2 contains 2684 significant starlight
polarizations for Two Micron All Sky Survey matched stars brighter than 12.5
mag in the H band. Polarizations are generally aligned with the cloud's major
axis, showing an average position angle dispersion of 15 \pm 2{\deg} and
polarization of 1.8 \pm 0.6%. The polarizations were combined with Galactic
Ring Survey 13CO spectroscopy and the Chandrasekhar-Fermi method to estimate
plane-of-sky magnetic field strengths, with an angular resolution of 100
arcsec. The average plane-of-sky magnetic field strength across the cloud is
5.40 \pm 0.04 {\mu}G. The magnetic field strength map exhibits seven
enhancements or "magnetic cores." These cores show an average magnetic field
strength of 8.3 \pm 0.9 {\mu}G, radius of 1.2 \pm 0.2 pc, intercore spacing of
5.7 \pm 0.9 pc, and exclusively subcritical mass-to-flux ratios, implying their
magnetic fields continue to suppress star formation. The magnetic field
strength shows a power-law dependence on gas volume density, with slope 0.75
\pm 0.02 for n_{H_2} >=10 cm-3. This power-law index is identical to those in
studies at higher densities, but disagrees with predictions for the densities
probed here.Comment: 11 pages, 15 figures, published in ApJ (2012, 755, 130
The Two States of Star Forming Clouds
We examine the effects of self-gravity and magnetic fields on supersonic
turbulence in isothermal molecular clouds with high resolution simulations and
adaptive mesh refinement. These simulations use large root grids (512^3) to
capture turbulence and four levels of refinement to capture high density, for
an effective resolution of 8,196^3. Three Mach 9 simulations are performed, two
super-Alfv\'enic and one trans-Alfv\'enic. We find that gravity splits the
clouds into two populations, one low density turbulent state and one high
density collapsing state. The low density state exhibits properties similar to
non-self-gravitating in this regime, and we examine the effects of varied
magnetic field strength on statistical properties: the density probability
distribution function is approximately lognormal; velocity power spectral
slopes decrease with field strength; alignment between velocity and magnetic
field increases with field; the magnetic field probability distribution can be
fit to a stretched exponential. The high density state is characterized by
self-similar spheres; the density PDF is a power-law; collapse rate decreases
with increasing mean field; density power spectra have positive slopes,
P({\rho},k) \propto k; thermal-to-magnetic pressure ratios are unity for all
simulations; dynamic-to-magnetic pressure ratios are larger than unity for all
simulations; magnetic field distribution is a power-law. The high Alfv\'en Mach
numbers in collapsing regions explain recent observations of magnetic influence
decreasing with density. We also find that the high density state is found in
filaments formed by converging flows, consistent with recent Herschel
observations. Possible modifications to existing star formation theories are
explored.Comment: 19 pages, 20 figure
A Chandra Observation of the Obscured Star-Forming Complex W40
The young stellar cluster illuminating the W40 H II region, one of the
nearest massive star forming regions, has been observed with the ACIS detector
on board the Chandra X-ray Observatory. Due to its high obscuration, this is a
poorly-studied stellar cluster with only a handful of bright stars visible in
the optical band, including three OB stars identified as primary excitation
sources. We detect 225 X-ray sources, of which 85% are confidently identified
as young stellar members of the region. Two potential distances of the cluster,
260 pc and 600 pc, are used in the paper. Supposing the X-ray luminosity
function to be universal, it supports a 600 pc distance as a lower limit for
W40 and a total population of at least 600 stars down to 0.1 Mo under the
assumption of a coeval population with a uniform obscuration. In fact, there is
strong spatial variation in Ks-band-excess disk fraction and non-uniform
obscuration due to a dust lane that is identified in absorption in optical,
infrared and X-ray. The dust lane is likely part of a ring of material which
includes the molecular core within W40. In contrast to the likely ongoing star
formation in the dust lane, the molecular core is inactive. The star cluster
has a spherical morphology, an isothermal sphere density profile, and mass
segregation down to 1.5 Mo. However, other cluster properties, including a
\leq{1} Myr age estimate and ongoing star formation, indicate that the cluster
is not dynamically relaxed. X-ray diffuse emission and a powerful flare from a
young stellar object are also reported.Comment: Accepted for publication in The Astrophysical Journal. 60 pages, 16
figure
Postsynaptic nigrostriatal dopamine receptors and their role in movement regulation
The article presents the hypothesis that nigrostriatal dopamine may regulate movement by modulation of tone and contraction in skeletal muscles through a concentration-dependent influence on the postsynaptic D1 and D2 receptors on the follow manner: nigrostriatal axons innervate both receptor types within the striatal locus somatotopically responsible for motor control in agonist/antagonist muscle pair around a given joint. D1 receptors interact with lower and D2 receptors with higher dopamine concentrations. Synaptic dopamine concentration increases immediately before movement starts. We hypothesize that increasing dopamine concentrations stimulate first the D1 receptors and reduce muscle tone in the antagonist muscle and than stimulate D2 receptors and induce contraction in the agonist muscle. The preceded muscle tone reduction in the antagonist muscle eases the efficient contraction of the agonist. Our hypothesis is applicable for an explanation of physiological movement regulation, different forms of movement pathology and therapeutic drug effects. Further, this hypothesis provides a theoretical basis for experimental investigation of dopaminergic motor control and development of new strategies for treatment of movement disorders
Anatomy of a decision: Striato-orbitofrontal interactions in reinforcement learning, decision making, and reversal.
NGF effects on developing forebrain cholinergic neurons are regionally specific
Nerve growth factor (NGF) has been shown to have an effect on neurons in the central nervous system (CNS). A number of observations suggest that NGF acts as a trophic factor for cholinergic neurons of the basal forebrain and the caudate-putamen. We sought to further characterize the CNS actions of NGF by examining its effect on choline acetyltransferase (ChAT) activity in the cell bodies and fibers of developing neurons of the septum and caudate-putamen. ChAT activity was increased after even a single NGF injection. Interestingly, the magnitude of the effect of multiple NGF injections suggested that repeated treatments may augment NGF actions on these neurons. The time-course of the response to NGF was followed after a single injection on postnatal day (PD) 2. NGF treatment produced long-lasting increases in ChAT activity in septum, hippocampus and caudate-putamen. The response in cell body regions (septum, caudate-putamen) was characterized by an initial lag period of approximately 24 hr, a rapid rise to maximum values, a plateau phase and a return to baseline. The response in hippocampus was delayed by 48 hr relative to that in septum, indicating that NGF actions on ChAT were first registered in septal cell bodies. Finally, developmental events were shown to have a regionally specific influence on the response of neurons to NGF. For though the septal response to a single NGF injection was undiminished well into the third postnatal week, little or no response was detected in caudate-putamen at that time. In highlighting the potency and regional specificity of NGF effects, these observations provide additional, support for the hypothesis that NGF is a trophic factor for CNS cholinergic neurons.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45403/1/11064_2004_Article_BF00970927.pd