2,868 research outputs found
Multi-epoch Sub-arcsecond [Fe II] Spectroimaging of the DG Tau Outflows with NIFS. II. On the Nature of the Bipolar Outflow Asymmetry
The origin of bipolar outflow asymmetry in young stellar objects (YSOs)
remains poorly understood. It may be due to an intrinsically asymmetric outflow
launch mechanism, or it may be caused by the effects of the ambient medium
surrounding the YSO. Answering this question is an important step in
understanding outflow launching. We have investigated the bipolar outflows
driven by the T Tauri star DG Tauri on scales of hundreds of AU, using the
Near-infrared Integral Field Spectrograph (NIFS) on Gemini North. The
approaching outflow consists of a well-collimated jet, nested within a
lower-velocity disc wind. The receding outflow is composed of a
single-component bubble-like structure. We analyse the kinemat- ics of the
receding outflow using kinetic models, and determine that it is a
quasi-stationary bubble with an expanding internal velocity field. We propose
that this bubble forms because the receding counterjet from DG Tau is
obstructed by a clumpy ambient medium above the circumstellar disc surface,
based on similarities between this structure and those found in the modeling of
active galactic nuclei outflows. We find evidence of interaction between the
obscured counterjet and clumpy ambient material, which we attribute to the
large molecular envelope around the DG Tau system. An analytical model of a
momentum-driven bubble is shown to be consistent with our interpretation. We
conclude that the bipolar outflow from DG Tau is intrinsically symmetric, and
the observed asymmetries are due to environmental effects. This mechanism can
potentially be used to explain the observed bipolar asymmetries in other YSO
outflows.Comment: 16 pages, 10 figures, accepted for publication in MNRA
Turbulent mixing layers in supersonic protostellar outflows, with application to DG Tauri
Turbulent entrainment processes may play an important role in the outflows
from young stellar objects at all stages of their evolution. In particular,
lateral entrainment of ambient material by high-velocity, well-collimated
protostellar jets may be the cause of the multiple emission-line velocity
components observed in the microjet-scale outflows driven by classical T Tauri
stars. Intermediate-velocity outflow components may be emitted by a turbulent,
shock- excited mixing layer along the boundaries of the jet. We present a
formalism for describing such a mixing layer based on Reynolds decomposition of
quantities measuring fundamental properties of the gas. In this model, the
molecular wind from large disc radii provides a continual supply of material
for entrainment. We calculate the total stress profile in the mixing layer,
which allows us to estimate the dissipation of turbulent energy, and hence the
luminosity of the layer. We utilize MAPPINGS IV shock models to determine the
fraction of total emission that occurs in [Fe II] 1.644 {\mu}m line emission in
order to facilitate comparison to previous observations of the young stellar
object DG Tauri. Our model accurately estimates the luminosity and changes in
mass outflow rate of the intermediate-velocity component of the DG Tau
approaching outflow. Therefore, we propose that this component represents a
turbulent mixing layer surrounding the well-collimated jet in this object.
Finally, we compare and contrast our model to previous work in the field.Comment: 18 pages, 13 figures, accepted for publication in MNRA
Problematic Internet use, mental health and impulse control in an online survey of adults
Background and aims:
Internet use has become a popular entertainment source and has become highly integrated into daily life. However, some people display problematic or addictive usage of the Internet. The present study attempts to fill current knowledge gaps regarding at-risk/problematic Internet use (ARPIU) and its relation to various health and functioning measures.
Methods:
Online survey data from 755 adults in the United States were analyzed using chi-square and ANOVAs.
Results:
The ARPIU group did not differ from the non-ARPIU group with respect to substance use. Individuals with ARPIU were, however, more likely to report at-risk/problematic engagement in video-game playing and gambling. Compared to the non-ARPIU group, the ARPIU group reported poorer self-control and higher levels of impulsivity and depression.
Conclusions:
ARPIU appears associated with other risk behaviors, particularly those that might be performed on the Internet. Future studies should examine the extent to which the Internet may promote engagement in these risk behaviors and the extent to which preventative interventions targeting better self-control or negative mood states might help a range of non-substance-related addictive behaviors
Engineering soil organic matter quality: Biodiesel Co-Product (BCP) stimulates exudation of nitrogenous microbial biopolymers
Biodiesel Co-Product (BCP) is a complex organic material formed during the transesterification of lipids. We investigated the effect of BCP on the extracellular microbial matrix or ‘extracellular polymeric substance’ (EPS) in soil which is suspected to be a highly influential fraction of soil organic matter (SOM). It was hypothesised that more N would be transferred to EPS in soil given BCP compared to soil given glycerol. An arable soil was amended with BCP produced from either 1) waste vegetable oils or 2) pure oilseed rape oil, and compared with soil amended with 99% pure glycerol; all were provided with 15N labelled KNO3. We compared transfer of microbially assimilated 15N into the extracellular amino acid pool, and measured concomitant production of exopolysaccharide. Following incubation, the 15N enrichment of total hydrolysable amino acids (THAAs) indicated that intracellular anabolic products had incorporated the labelled N primarily as glutamine and glutamate. A greater proportion of the amino acids in EPS were found to contain 15N than those in the THAA pool, indicating that the increase in EPS was comprised of bioproducts synthesised de novo. Moreover, BCP had increased the EPS production efficiency of the soil microbial community (μg EPS per unit ATP) up to approximately double that of glycerol, and caused transfer of 21% more 15N from soil solution into EPS-amino acids. Given the suspected value of EPS in agricultural soils, the use of BCP to stimulate exudation is an interesting tool to consider in the theme of delivering sustainable intensification
AEGIS: Chandra Observation of DEEP2 Galaxy Groups and Clusters
We present a 200 ksec Chandra observation of seven spectroscopically
selected, high redshift (0.75 < z < 1.03) galaxy groups and clusters discovered
by the DEEP2 Galaxy Redshift Survey in the Extended Groth Strip (EGS). X-ray
emission at the locations of these systems is consistent with background. The
3-sigma upper limits on the bolometric X-ray luminosities (L_X) of these
systems put a strong constraint on the relation between L_X and the velocity
dispersion of member galaxies sigma_gal at z~1; the DEEP2 systems have lower
luminosity than would be predicted by the local relation. Our result is
consistent with recent findings that at high redshift, optically selected
clusters tend to be X-ray underluminous. A comparison with mock catalogs
indicates that it is unlikely that this effect is entirely caused by a
measurement bias between sigma_gal and the dark matter velocity dispersion.
Physically, the DEEP2 systems may still be in the process of forming and hence
not fully virialized, or they may be deficient in hot gas compared to local
systems. We find only one possibly extended source in this Chandra field, which
happens to lie outside the DEEP2 coverage.Comment: 5 pages, 3 figures. Accepted for publication in AEGIS ApJ Letters
special editio
Interrelation of Superconducting and Antiferromagnetic Gaps in High-Tc Compounds: a Test Case for a Microscopic Theory
Recent angle resolved photoemission (ARPES) data, which found evidence for a
d-wave-like modulation of the antiferromagnetic gap, suggest an intimate
interrelation between the antiferromagnetic insulator and the superconductor
with its d-wave gap. This poses a new challenge to microscopic descriptions,
which should account for this correlation between, at first sight, very
different states of matter. Here, we propose a microscopic mechanism which
provides a definite correlation between these two different gap structures: it
is shown that a projected SO(5) theory, which aims at unifying
antiferromagnetism and d-wave superconductivity via a common symmetry principle
while explicitly taking the Mott-Hubbard gap into account, correctly describes
the observed gap characteristics. Specifically, it accounts for both the
dispersion and the order of magnitude difference between the antiferromagnetic
gap modulation and the superconducting gap.Comment: 8 pages, 5 figure
Changes in Hepatic Blood Flow and Liver Function during Closed Abdominal Hyperthermic Intraperitoneal Chemotherapy following Cytoreduction Surgery
Background. The increase in intra-abdominal pressure (IAP) during closed abdominal hyperthermic intraperitoneal chemotherapy (HIPEC) leads to major haemodynamic changes and potential organ dysfunction. We investigated these effects on hepatic blood flow (HBF) and liver function in patients undergoing HIPEC following cytoreductive surgery and fluid management guided by dynamic preload indices. Methods. In this prospective observational clinical study including 15 consecutive patients, we evaluated HBF by transesophageal echocardiography and liver function by determination of the indocyanine green plasma disappearance rate (ICG-PDR). Friedman’s two-way analysis of variance by ranks and Wilcoxon signed-rank test were performed for statistical analysis. Results. During HIPEC, HBF was markedly reduced, resulting in the loss of any pulsatile Doppler flow signal in all but one patient. The ICG-PDR, expressed as median (interquartile 25–75), decreased from 23 (20–30) %/min to 18 (12.5–19) %/min (p<0.001). Despite a generous crystalloid infusion rate (27 (22–35) ml/kg/h), cardiac index decreased during the increased IAP period, inferior vena cava diameter decreased, stroke volume variation and pulse pressure variation increased, lung compliance dropped, and there was an augmentation in plateau pressure. All changes were significant (p<0.001) and reversed to baseline values post HIPEC. Conclusion. Despite optimizing intravenous fluids during closed abdominal HIPEC, we observed a marked decrease in HBF and liver function. Both effects were transient and limited to the period of HIPEC but could influence the choice between closed or open abdominal cavity procedure for HIPEC and should be considered in similar clinical situations of increased IAP
Stripes in Doped Antiferromagnets: Single-Particle Spectral Weight
Recent photoemission (ARPES) experiments on cuprate superconductors provide
important guidelines for a theory of electronic excitations in the stripe
phase. Using a cluster perturbation theory, where short-distance effects are
accounted for by exact cluster diagonalization and long-distance effects by
perturbation (in the hopping), we calculate the single-particle Green's
function for a striped t-J model. The data obtained quantitatively reproduce
salient (ARPES-) features and may serve to rule out "bond-centered" in favor of
"site-centered" stripes.Comment: final version as appeared in PRL; (c) 2000 The American Physical
Society; 4 pages, 4 figure
Atomistic Mechanism of Force Generation, Translocation, and Coordination in a Viral Genome Packaging Motor [preprint]
Double-stranded DNA viruses package their genomes into pre-assembled protein capsids using virally-encoded ATPase ring motors. While several structures of isolated monomers (subunits) from these motors have been determined, they provide little insight into how subunits within a functional ring coordinate their activities to efficiently generate force and translocate DNA. Here we describe the first atomic-resolution structure of a functional ring form of a viral DNA packaging motor and characterize its atomic-level dynamics via long timescale molecular dynamics simulations. Crystal structures of the pentameric ATPase ring from bacteriophage asccφ28 show that each subunit consists of a canonical N-terminal ASCE ATPase domain connected to a ‘vestigial’ nuclease domain by a small lid subdomain. The lid subdomain closes over the ATPase active site and engages in extensive interactions with a neighboring subunit such that several important catalytic residues are positioned to function in trans. The pore of the ring is lined with several positively charged residues that can interact with DNA. Simulations of the ATPase ring in various nucleotide-bound states provide information about how the motor coordinates sequential nucleotide binding, hydrolysis, and exchange around the ring. Simulations also predict that the ring adopts a helical structure to track DNA, consistent with recent cryo-EM reconstruction of the φ29 packaging ATPase. Based on these results, an atomistic model of viral DNA packaging is proposed wherein DNA translocation is powered by stepwise helical-to-planar ring transitions that are tightly coordinated by ATP binding, hydrolysis, and release
A Resolved Ring of Debris Dust around the Solar Analog HD 107146
We present resolved images of the dust continuum emission from the debris disk around the young (80-200 Myr) solar-type star HD 107146 with CARMA at λ = 1.3 mm and the CSO at λ = 350 μ. Both images show that the dust emission extends over an approximately 10" diameter region. The high-resolution (3") CARMA image further reveals that the dust is distributed in a partial ring with significant decrease in a flux inward of 97 AU. Two prominent emission peaks appear within the ring separated by ~140° in the position angle. The morphology of the dust emission is suggestive of dust captured into a mean motion resonance, which would imply the presence of a planet at an orbital radius of ~45-75 AU
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