1,297 research outputs found
Tidal Disruption of Protoclusters in Giant Molecular Clouds
We study the collapse of protoclusters within a giant molecular cloud (GMC)
to determine the conditions under which collapse is significantly disrupted.
Motivated by observations of star forming regions which exhibit flattened cloud
structures, this study considers collapsing protoclusters with disk geometries.
The collapse of a 10^3 Msun protocluster initially a distance of 2-10 pc from a
10^3 - 10^6 Msun point mass is numerically calculated. Simulations with zero
initial relative velocity between the two are completed as well as simulations
with relative velocities consistent with those observed in GMCs. The results
allow us to define the conditions under which it is safe to assume protocluster
collapse proceeds as if in isolation. For instance, we find the collapse of a
10^3 Msun protocluster will be significantly disrupted if it is within 2-4 pc
of a 10^4 Msun point mass. Thus, the collapse of a 10^3 Msun protocluster can
be considered to proceed as if in isolation if it is more than ~ 4 pc away from
a 10^4 Msun compact object. In addition, in no portion of the sampled parameter
space does the gravitational interaction between the protocluster disk and the
massive particle significantly disperse the disk into the background GMC. We
discuss the distribution of clusters of young stellar objects within the
Perseus and Mon R2 star forming regions, which are consistent with the results
of our simulations and the limitations of our results in gas dominated regions
such as the Orion cloud.Comment: 12 pages, 6 figures, Accepted for publication in Ap
Molecular Line Profile Fitting with Analytic Radiative Transfer Models
We present a study of analytic models of starless cores whose line profiles
have ``infall asymmetry,'' or blue-skewed shapes indicative of contracting
motions. We compare the ability of two types of analytical radiative transfer
models to reproduce the line profiles and infall speeds of centrally condensed
starless cores whose infall speeds are spatially constant and range between 0
and 0.2 km s-1. The model line profiles of HCO+ (J=1-0) and HCO+ (J=3-2) are
produced by a self-consistent Monte Carlo radiative transfer code. The analytic
models assume that the excitation temperature in the front of the cloud is
either constant (``two-layer'' model) or increases inward as a linear function
of optical depth (``hill'' model). Each analytic model is matched to the line
profile by rapid least-squares fitting.
The blue-asymmetric line profiles with two peaks, or with a blue shifted peak
and a red shifted shoulder, can be well fit by the ``HILL5'' model (a five
parameter version of the hill model), with an RMS error of 0.02 km s-1. A peak
signal to noise ratio of at least 30 in the molecular line observations is
required for performing these analytic radiative transfer fits to the line
profiles.Comment: 48 pages, 20 figures, accepted for publication in Ap
A simple, automated device for the precise addition of liquids
Metering liquid reagents into reaction mixtures in a controlled and
reproducible manner has often been a problem in synthetic
chemistry. Carrying out the real simultaneous addition of two or
more liquid reagents (concurrent additions) is even more inconvenient.
Difficulties increase when addition volumes become small,
when addition times become long, or when the reagents are corrosive
or air-sensitive. We have constructed and tested an inexpensive,
automated device for the slow, precise delivery of liquid reagents
into laboratory-scale reaction mixtures. Controlled by a standard
personal computer, this slow adder can accommodate liquid
volumes from hundreds of microlitres to litres and addition times
from minutes to days. Its glass and Teflon construction makes it
useful for nearly all reagents. By using multiple slow adders, true
concurrent addition of several liquids can be easily achieved
Validation of EPIC for Two Watersheds in Southwest Iowa
The Erosion Productivity Impact Calculator (EPIC) model is validated using long-term data collected for two southwest Iowa watersheds that have been cropped in continuous corn under two different tillage systems. The annual hydrologic balance was calibrated during 1988-94 by adjusting the runoff curve numbers and residue effects on soil evaporation. Model validation was performed for 1976-87 using both summary statistics and parametric and nonparametric statistical tests. Overall, results show that EPIC was able to replicate the long-term relative differences between the two tillage systems
Comparative genetic and physiological characterisation of Pectinatus species reveals shared tolerance to beer-associated stressors but halotolerance specific to pickle-associated strains
This work was supported by Heineken Supply Chain B.V. PL, SD & HJF receive support from the Scottish Government Rural and Environment Sciences and Analytical Services (RESAS). We would like to express thanks to Nicola Smith for her help formatting Fig. 1, Dr Paul Sheridan for bioinformatics-based advice and help with troubleshooting scripts, Dr Kenneth Forbes for his advice on core and pan genome analysis, Sandro Cocuzza for providing the hop extract and Marine Freyereisen for supplying Lactobacillus brevis MB521.Peer reviewedPostprin
Resistivity of a Metal between the Boltzmann Transport Regime and the Anderson Transition
We study the transport properties of a finite three dimensional disordered
conductor, for both weak and strong scattering on impurities, employing the
real-space Green function technique and related Landauer-type formula. The
dirty metal is described by a nearest neighbor tight-binding Hamiltonian with a
single s-orbital per site and random on-site potential (Anderson model). We
compute exactly the zero-temperature conductance of a finite size sample placed
between two semi-infinite disorder-free leads. The resistivity is found from
the coefficient of linear scaling of the disorder averaged resistance with
sample length. This ``quantum'' resistivity is compared to the semiclassical
Boltzmann expression computed in both Born approximation and multiple
scattering approximation.Comment: 5 pages, 3 embedded EPS figure
Oral Treatment with CuII(atsm) Increases Mutant SOD1 In Vivo but Protects Motor Neurons and Improves the Phenotype of a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis
Mutations in the metallo-protein Cu/Zn-superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS) in humans and an expression level-dependent phenotype in transgenic rodents. We show that oral treatment with the therapeutic agent diacetyl-bis(4-methylthiosemicarbazonato)copperII [CuII(atsm)] increased the concentration of mutant SOD1 (SOD1G37R) in ALS model mice, but paradoxically improved locomotor function and survival of the mice. To determine why the mice with increased levels of mutant SOD1 had an improved phenotype, we analyzed tissues by mass spectrometry. These analyses revealed most SOD1 in the spinal cord tissue of the SOD1G37R mice was Cu deficient. Treating with CuII(atsm) decreased the pool of Cu-deficient SOD1 and increased the pool of fully metallated (holo) SOD1. Tracking isotopically enriched 65CuII(atsm) confirmed the increase in holo-SOD1 involved transfer of Cu from CuII(atsm) to SOD1, suggesting the improved locomotor function and survival of the CuII(atsm)-treated SOD1G37R mice involved, at least in part, the ability of the compound to improve the Cu content of the mutant SOD1. This was supported by improved survival of SOD1G37R mice that expressed the human gene for the Cu uptake protein CTR1. Improving the metal content of mutant SOD1 in vivo with CuII(atsm) did not decrease levels of misfolded SOD1. These outcomes indicate the metal content of SOD1 may be a greater determinant of the toxicity of the protein in mutant SOD1-associated forms of ALS than the mutations themselves. Improving the metal content of SOD1 therefore represents a valid therapeutic strategy for treating ALS caused by SOD1
BMQ
BMQ: Boston Medical Quarterly was published from 1950-1966 by the Boston University School of Medicine and the Massachusetts Memorial Hospitals
Bostonia: The Boston University Alumni Magazine. Volume 12
Founded in 1900, Bostonia magazine is Boston University’s main alumni publication
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