19 research outputs found
Segregated neural explants exhibit co-oriented, asymmetric, neurite outgrowth
Explants of embryonic chick sympathetic and sensory ganglia were found to exhibit asymmetric radial outgrowth of neurites under standard culture conditions with or without exogenous Nerve Growth Factor [NGF]. Opposing sides of an explant exhibited: a) differences in neurite length and, b) differences in neurite morphology. Strikingly, this asymmetry exhibited co-orientation among segregated, neighboring explants. The underlying mechanism(s) of the asymmetry and its co-orientation are not known but appear to depend on cell clustering because dissociated sympathetic neurons do not exhibit co-orientation whereas re-aggregated clusters of cells do. This emergent behavior may be similar to the community effect described in other cell types. If a similar phenomenon exists in the embryo, or in maturity, it may contribute to the establishment of proper orientation of neurite outgrowth during development and/or injury-induced neuronal plasticity
Does External Pressure Explain Recent Results for Molecular Clouds?
The recent paper by Heyer et al (2009) indicates that observations of size,
linewidth and column density of interstellar clouds do not agree with simple
virial equilibrium (VE) as a balance between gravitational and kinetic energies
in the sense that the clouds either have too much kinetic energy or too little
mass to be bound. This may be explained by violation of VE as suggested by
Dobbs et al 2011, by observational underestimation of the masses as suggested
by Heyer et al 2009, or by an external pressure acting as an additional
confining force as suggested earlier by Heyer et al 2004. The data of Heyer et
al. 2009 cannot be explained with a single value for the external pressure, but
if different clouds in the sample have different external pressures in the
range of Pe/k = E4 to E7 cm-3 K, then most of the clouds could be in pressure
virial equilibrium (PVE). In this paper we discuss two consequences of the
external pressure. First, we show that the observational data are consistent
with the hypothesis (Chie\'ze 1987) that most clouds are at a critical mass for
dynamical stability determined solely by the pressure. Above this mass a cloud
is unstable to gravitational collapse or fragmentation. Second, we show that
the external pressure modifies the well-known size-linewidth relationship first
proposed by Larson (1981) so that the proportionality is no longer constant but
depends on the external pressure.Comment: Accepted for publication in MNRA
The Far-Infrared--Radio Correlation at High Redshifts: Physical Considerations and Prospects for the Square Kilometer Array
(Abridged) I present a predictive analysis for the behavior of the FIR--radio
correlation as a function of redshift in light of the deep radio continuum
surveys which may become possible using the SKA. To keep a fixed ratio between
the FIR and predominantly non-thermal radio continuum emission of a normal
star-forming galaxy requires a nearly constant ratio between galaxy magnetic
field and radiation field energy densities. While the additional term of IC
losses off of the cosmic microwave background (CMB) is negligible in the local
Universe, the rapid increase in the strength of the CMB energy density (i.e.
suggests that evolution in the FIR-radio correlation should
occur with infrared (IR; 8-1000 \micron)/radio ratios increasing with
redshift. At present, observations do not show such a trend with redshift;
radio-quiet QSOs appear to lie on the local FIR-radio correlation
while a sample of and SMGs exhibit ratios that are a
factor of 2.5 {\it below} the canonical value. I also derive a 5
point-source sensitivity goal of 20 nJy (i.e. nJy) requiring that the SKA specified be m K; achieving this sensitivity should enable the detection
of galaxies forming stars at a rate of \ga25 M_{\sun} {\rm yr}^{-1}, at all
redshifts if present. By taking advantage of the fact that the non-thermal
component of a galaxy's radio continuum emission will be quickly suppressed by
IC losses off of the CMB, leaving only the thermal (free-free) component, I
argue that deep radio continuum surveys at frequencies \ga10 GHz may prove to
be the best probe for characterizing the high- star formation history of the
Universe unbiased by dust.Comment: 16 pages, 8 figures, accepted for publication in Ap
Potential Hazard to Human Health from Exposure to Fragments of Lead Bullets and Shot in the Tissues of Game Animals
Peer reviewedPublisher PD
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
The James Webb Space Telescope
The James Webb Space Telescope (JWST) is a large (6.6m), cold (50K),
infrared-optimized space observatory that will be launched early in the next
decade. The observatory will have four instruments: a near-infrared camera, a
near-infrared multi-object spectrograph, and a tunable filter imager will cover
the wavelength range, 0.6 to 5.0 microns, while the mid-infrared instrument
will do both imaging and spectroscopy from 5.0 to 29 microns. The JWST science
goals are divided into four themes. The End of the Dark Ages: First Light and
Reionization theme seeks to identify the first luminous sources to form and to
determine the ionization history of the early universe. The Assembly of
Galaxies theme seeks to determine how galaxies and the dark matter, gas, stars,
metals, morphological structures, and active nuclei within them evolved from
the epoch of reionization to the present day. The Birth of Stars and
Protoplanetary Systems theme seeks to unravel the birth and early evolution of
stars, from infall on to dust-enshrouded protostars to the genesis of planetary
systems. The Planetary Systems and the Origins of Life theme seeks to determine
the physical and chemical properties of planetary systems including our own,
and investigate the potential for the origins of life in those systems. To
enable these observations, JWST consists of a telescope, an instrument package,
a spacecraft and a sunshield. The telescope consists of 18 beryllium segments,
some of which are deployed. The segments will be brought into optical alignment
on-orbit through a process of periodic wavefront sensing and control. The JWST
operations plan is based on that used for previous space observatories, and the
majority of JWST observing time will be allocated to the international
astronomical community through annual peer-reviewed proposal opportunities.Comment: 96 pages, including 48 figures and 15 tables, accepted by Space
Science Review
HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1
We report new polarimetric and photometric maps of the massive star-forming region OMC-1 using the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy. We present continuum polarimetric and photometric measurements of this region at 53, 89, 154, and 214 μm at angular resolutions of 5'', 8'', 14'', and 19'' for the four bands, respectively. The photometric maps enable the computation of improved spectral energy distributions for the region. We find that at the longer wavelengths, the inferred magnetic field configuration matches the "hourglass" configuration seen in previous studies, indicating magnetically regulated star formation. The field morphology differs at the shorter wavelengths. The magnetic field inferred at these wavelengths traces the bipolar structure of the explosive Becklin–Neugebauer/Kleinman–Low outflow emerging from OMC-1 behind the Orion Nebula. Using statistical methods to estimate the field strength in the region, we find that the explosion dominates the magnetic field near the center of the feature. Farther out, the magnetic field is close to energetic equilibrium with the ejecta and may be providing confinement to the explosion. The correlation between polarization fraction and the local polarization angle dispersion indicates that the depolarization as a function of unpolarized intensity is a result of intrinsic field geometry as opposed to decreases in grain alignment efficiency in denser regions
Eye tracking – The overlooked method to measure cognition in neurodegeneration?
Eye tracking (ET) studies are becoming increasingly popular due to rapid methodological and technological advances as well as the development of cost efficient and portable eye trackers. Although historically ET has been mostly employed in psychophysics or developmental cognition studies, there is also promising scope to use ET for movement disorders and measuring cognitive processes in neurodegeneration. Particularly, ET can be a powerful tool for cognitive and neuropsychological assessments of patients with pathologies affecting motor and verbal abilities, as tasks can be adapted without requiring motor (except eye movements) or verbal responses. In this review, we will examine the existing evidence of ET methods in neurodegenerative conditions and its potential clinical impact for cognitive assessment. We highlight that current evidence for ET is mostly focused on diagnostics of cognitive impairments in neurodegenerative disorders, where it is debatable whether it has any more sensitivity or specificity than existing cognitive assessments. By contrast, there is currently a lack of ET studies in more advanced disease stages, when patients’ motor and verbal functions can be significantly affected, and standard cognitive assessments are challenging or often not possible. We conclude that ET is a promising method not only for cognitive diagnostics but more importantly, for potential cognitive disease tracking in progressive neurodegenerative conditions
SKA studies of in-situ synchrotron radiation from molecular clouds
Observations of the properties of dense molecular clouds are critical in understanding the process of star-formation. One of the most important, but least understood, is the role of the magnetic fields. We discuss the possibility of using high-resolution, high-sensitivity radio observations with the SKA to measure for the first time the in-situ synchrotron radiation from these molecular clouds. If the cosmic-ray (CR) particles penetrate clouds as expected, then we can measure the B-field strength directly using radio data. So far, this signature has never been detected from the collapsing clouds themselves and would be a unique probe of the magnetic field. Dense cores are typically ∼0:05 pc in size, corresponding to ∼arcsec at ∼kpc distances, and flux density estimates are ∼mJy at 1 GHz. The SKA should be able to readily detect directly, for the first time, along lines-of-sight that are not contaminated by thermal emission or complex foreground/background synchrotron emission. Polarised synchrotron may also be detectable providing additional information about the regular/turbulent fields