699 research outputs found
Fragmentation And Evolution Of Molecular Clouds. III. The Effect Of Dust And Gas Energetics
Dust and gas energetics are incorporated into a cluster-scale simulation of star formation in order to study the effect of heating and cooling on the star formation process. We build on our previous work by calculating separately the dust and gas temperatures. The dust temperature is set by radiative equilibrium between heating by embedded stars and radiation from dust. The gas temperature is determined using an energy-rate balance algorithm which includes molecular cooling, dust-gas collisional energy transfer, and cosmic-ray ionization. The fragmentation proceeds roughly similarly to simulations in which the gas temperature is set to the dust temperature, but there are differences. The structure of regions around sink particles has properties similar to those of Class 0 objects, but the infall speeds and mass accretion rates are, on average, higher than those seen for regions forming only low-mass stars. The gas and dust temperature have complex distributions not well modeled by approximations that ignore the detailed thermal physics. There is no simple relationship between density and kinetic temperature. In particular, high-density regions have a large range of temperatures, determined by their location relative to heating sources. The total luminosity underestimates the star formation rate at these early stages, before ionizing sources are included, by an order of magnitude. As predicted in our previous work, a larger number of intermediate-mass objects form when improved thermal physics is included, but the resulting initial mass function (IMF) still has too few low-mass stars. However, if we consider recent evidence on core-to-star efficiencies, the match to the IMF is improved.NASA NAG5-10826, NAG5-13271Canada Research Chair programNSERCNSF AST-0607793, AST-1109116NASA GSRP Fellowship ProgramAstronom
Analytical techniques for single-cell metabolomics: state of the art and trends
Single-cell metabolomics is an emerging field that addresses fundamental biological questions and allows one to observe metabolic phenomena in heterogeneous populations of single cells. In this review, we assess the suitability of different detection techniques and present considerations on sample preparation for single-cell metabolomics. Although targeted analysis of single cells can readily be conducted using fluorescent probes and optical instruments (microscopes, fluorescence detectors), a comprehensive metabolomic approach requires a powerful label-free method, such as mass spectrometry (MS). Mass-spectrometric techniques applied to study small molecules in single cells include electrospray MS, matrix-assisted laser desorption/ionization MS, and secondary ion MS. Sample preparation is an important aspect to be taken into account during further development of methods for single-cell metabolomic
Magnetic Switching of Phase-Slip Dissipation in NbSe2 Nanobelts
The stability of the superconducting dissipationless and resistive states in
single-crystalline NbSe2 nanobelts is characterized by transport measurements
in an external magnetic field (H). Current-driven electrical measurements show
voltage steps, indicating the nucleation of phase-slip structures. Well below
the critical temperature, the position of the voltage steps exhibits a sharp,
periodic dependence as a function of H. This phenomenon is discussed in the
context of two possible mechanisms: the interference of the order parameter and
the periodic rearrangement of the vortex lattice within the nanobelt.Comment: 4 figure
Fragmentation and Evolution of Molecular Clouds. II: The Effect of Dust Heating
We investigate the effect of heating by luminosity sources in a simulation of
clustered star formation. Our heating method involves a simplified continuum
radiative transfer method that calculates the dust temperature. The gas
temperature is set by the dust temperature. We present the results of four
simulations, two simulations assume an isothermal equation of state and the two
other simulations include dust heating. We investigate two mass regimes, i.e.,
84 Msun and 671 Msun, using these two different energetics algorithms. The mass
functions for the isothermal simulations and simulations which include dust
heating are drastically different. In the isothermal simulation, we do not form
any objects with masses above 1 Msun. However, the simulation with dust
heating, while missing some of the low-mass objects, forms high-mass objects
(~20 Msun) which have a distribution similar to the Salpeter IMF. The envelope
density profiles around the stars formed in our simulation match observed
values around isolated, low-mass star-forming cores. We find the accretion
rates to be highly variable and, on average, increasing with final stellar
mass. By including radiative feedback from stars in a cluster-scale simulation,
we have determined that it is a very important effect which drastically affects
the mass function and yields important insights into the formation of massive
stars.Comment: 19 pages, 28 figures. See
http://www.astro.phy.ulaval.ca/staff/hugo/dust/ms_dust.big.pdf for high
resolution version of documen
Interfacing Microfluidics and Laser Desorption/Ionization Mass Spectrometry by Continuous Deposition for Application in Single Cell Analysis
We present a simple method for continuous deposition of effluent originating from a microfluidic device on a flat metal surface for subsequent analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The sample is delivered using a microscale fused silica
capillary and passed onto the surface of a stainless steel plate coated with a layer of a standard matrix. The key parameters optimized in order to obtain high quality and reproducible sample traces are: i) sampleflow rate, ii) speed of the XY-stage movement, and iii) distance of the capillary
tip from the plate. Tapering the capillary end as well as surface functionalization to induce hydrophobicity were shown to further enhance the deposition process. The described continuous deposition method is compared with a previously published mass spectrometric method utilizing a piezoelectric
microdispenser for microspotting onto the MALDI plates which enabled detection of primary metabolites at the singlecell level. Research is underway to adapt the continuous deposition as an interface for single cell metabolite detection and enhancement of quantitative abilities of the MALDI
methodology. We envisage that the presented continuous deposition method may also be suitable for sensitive detection of analytes using other surface analysis tools
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2-LED-μspectrophotometer for rapid on-site detection of pathogens using noble-metal nanoparticle-based colorimetric assays
Novel point-of-care compatible methods such as colorimetric assays have become increasingly important in the field of early pathogen detection. A simple and hand-held prototype device for carrying out DNA-amplification assay based on plasmonic nanoparticles in the colorimetric detection is presented. The low-cost device with two channels (sample and reference) consists of two spectrally different light emitting diodes (LEDs) for detection of the plasmon shift. The color change of the gold-nanoparticle-DNA conjugates caused by a salt-induced aggregation test is examined in particular. A specific and sensitive detection of the waterborne human pathogen Legionella pneumophila is demonstrated. This colorimetric assay, with a simple assay design and simple readout device requirements, can be monitored in real-time on-site. © 2020 by the authors
A Parameter Study of the Dust and Gas Temperature in a Field of Young Stars
We model the thermal effect of young stars on their surrounding environment
in order to understand clustered star formation. We take radiative heating of
dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling
into account. Using Dusty, a spherical continuum radiative transfer code, we
model the dust temperature distribution around young stellar objects with
various luminosities and surrounding gas and dust density distributions. We
have created a grid of dust temperature models, based on our modeling with
Dusty, which we can use to calculate the dust temperature in a field of stars
with various parameters. We then determine the gas temperature assuming energy
balance. Our models can be used to make large-scale simulations of clustered
star formation more realistic.Comment: 29 pages, 19 figures. Submitted to Ap
A Parameter Study Of The Dust And Gas Temperature In A Field Of Young Stars
We model the thermal effect of young stars on their surrounding environment in order to understand clustered star formation. We take radiative heating of dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling into account. Using DUSTY, a spherical continuum radiative transfer code, we model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. We have created a grid of dust temperature models, based on our modeling with DUSTY, which we can use to calculate the dust temperature in a field of stars with various parameters. We then determine the gas temperature assuming energy balance. Our models can be used to make large-scale simulations of clustered star formation more realistic.NSF AST-0307250, AST-0607793Research Corporation (SDD)Astronom
Examination of carbon partitioning into austenite during tempering of bainite
The redistribution of carbon after tempering of a novel nanocrystalline bainitic steel consisting of a mixture of supersaturated
ferrite and retained austenite has been analyzed by atom probe tomography. No direct evidence supporting the additional carbon
enrichment of austenite beyond that initially achieved during the bainite heat treatment was obtained during subsequent tempering
of this high carbon, high silicon steel.The authors gratefully acknowledge the support
of the Research Fund for Coal and Steel and the
Spanish Ministry of Science and Innovation for funding
this research under the contracts RFSR-CT-2008-00022
and MAT2007 – 63873, respectively. Research at the
Oak Ridge National Laboratory SHaRE User Facility
was sponsored by the Scientific User Facilities Division,
Office of Basic Energy Sciences, U.S. Department of Energy.
A.J. Clarke gratefully acknowledges support from
Los Alamos National Security, LLC, operator of the
Los Alamos National Laboratory under contract number
DE-AC52-06NA25396 with the U.S. Department of Energy and the Advanced Steel Processing and Products
Research Center, a National Science Foundation
Industry/University Cooperative Research Center at
the Colorado School of Mines and the Inter-American
Materials Collaboration ProgramPeer reviewe
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