8,775 research outputs found
Influence of organic films on the evaporation and condensation of water in aerosol
Uncertainties in quantifying the kinetics of evaporation and condensation of water from atmospheric aerosol are a significant contributor to the uncertainty in predicting cloud droplet number and the indirect effect of aerosols on climate. The influence of aerosol particle surface composition, particularly the impact of surface active organic films, on the condensation and evaporation coefficients remains ambiguous. Here, we report measurements of the influence of organic films on the evaporation and condensation of water from aerosol particles. Significant reductions in the evaporation coefficient are shown to result when condensed films are formed by monolayers of long-chain alcohols [C(n)H((2n+1))OH], with the value decreasing from 2.4 × 10(−3) to 1.7 × 10(−5) as n increases from 12 to 17. Temperature-dependent measurements confirm that a condensed film of long-range order must be formed to suppress the evaporation coefficient below 0.05. The condensation of water on a droplet coated in a condensed film is shown to be fast, with strong coherence of the long-chain alcohol molecules leading to islanding as the water droplet grows, opening up broad areas of uncoated surface on which water can condense rapidly. We conclude that multicomponent composition of organic films on the surface of atmospheric aerosol particles is likely to preclude the formation of condensed films and that the kinetics of water condensation during the activation of aerosol to form cloud droplets is likely to remain rapid
Dynamics of particle size on inhalation of environmental aerosol and impact on deposition fraction
Inhalation of elevated
levels of particulate air pollution has
been shown to elicit the onset of adverse health effects in humans,
where the magnitude of the response is a product of where in the lung
the particulate dose is delivered. At any point in time during inhalation
the depositional flux of the aerosol is a function of the radius of
the droplet, thus a detailed understanding of the rate and magnitude
of the mass flux of water to the droplet during inhalation is crucial.
In this study, we assess the impact of aerosol hygroscopicity on deposited
dose through the inclusion of a detailed treatment of the mass flux
of water to account for the dynamics of particle size in a modified
version of the standard International Commission on Radiological Protection
(ICRP) whole lung deposition model. The ability to account for the
role of the relative humidity (RH) of the aerosol prior to, and during,
inhalation on the deposition pattern is explored, and found to have
a significant effect on the deposition pattern. The model is verified
by comparison to previously published measurements, and used to demonstrate
that ambient RH affects where in the lung indoor particulate air pollution
is delivered
A Survey for Low-Surface-Brightness Galaxies Around M31. I. The Newly Discovered Dwarf Andromeda V
We present images and a color-magnitude diagram for And V, a new dwarf
spheroidal companion to M31 that was found using a digital filtering technique
applied to 1550 square degrees of the second Palomar Sky Survey. And V resolves
into stars easily in follow-up 4-m V- and I-band images, from which we deduce a
distance of 810 +/- 45 kpc using the tip of the red giant branch method. Within
the uncertainties, this distance is identical to the Population II distances
for M31 and, combined with a projected separation of 112 kpc, provides strong
support for a physical association between the two galaxies. There is no
emission from And V detected in H alpha, 1.4 GHz radio continuum, or IRAS
bandpasses, and there is no young population seen in the color-magnitude
diagram that might suggest that And V is an irregular. Thus, the classification
as a new dwarf spheroidal member of the Local Group seems secure. With an
extinction-corrected central surface brightness of 25.2 V mag per square
arcsec, a mean metal abundance of [Fe/H] approximately -1.5, and no evidence
for upper AGB stars, And V resembles And I & III.Comment: Accepted for publication in The Astronomical Journal, November 1998
issue; 4 embedded PostScript figures, 4 JPEG figures; see
http://aloe.tuc.noao.edu/jacoby/dwarfs.html for a complete full-resolution
PostScript versio
Stellar Collisions and the Interior Structure of Blue Stragglers
Collisions of main sequence stars occur frequently in dense star clusters. In
open and globular clusters, these collisions produce merger remnants that may
be observed as blue stragglers. Detailed theoretical models of this process
require lengthy hydrodynamic computations in three dimensions. However, a less
computationally expensive approach, which we present here, is to approximate
the merger process (including shock heating, hydrodynamic mixing, mass
ejection, and angular momentum transfer) with simple algorithms based on
conservation laws and a basic qualitative understanding of the hydrodynamics.
These algorithms have been fine tuned through comparisons with the results of
our previous hydrodynamic simulations. We find that the thermodynamic and
chemical composition profiles of our simple models agree very well with those
from recent SPH (smoothed particle hydrodynamics) calculations of stellar
collisions, and the subsequent stellar evolution of our simple models also
matches closely that of the more accurate hydrodynamic models. Our algorithms
have been implemented in an easy to use software package, which we are making
publicly available (see http://vassun.vassar.edu/~lombardi/mmas/). This
software could be used in combination with realistic dynamical simulations of
star clusters that must take into account stellar collisions.Comment: This revised version has 37 pages, 13 figures, 4 tables; submitted to
ApJ; for associated software package, see
http://vassun.vassar.edu/~lombardi/mmas/ This revised version presents
additional comparisons with SPH results and slightly improved merger recipe
Primary accumulation in the Soviet transition
The Soviet background to the idea of primary socialist accumulation is presented. The mobilisation of labour power and of products into public sector investment from outside are shown to have been the two original forms of the concept. In Soviet primary accumulation the mobilisation of labour power was apparently more decisive than the mobilisation of products. The primary accumulation process had both intended and unintended results. Intended results included bringing most of the economy into the public sector, and industrialisation of the economy as a whole. Unintended results included substantial economic losses, and the proliferation of coercive institutions damaging to attainment of the ultimate goal - the building of a communist society
Dynamics of aerosol size during inhalation : Hygroscopic growth of commercial nebulizer formulations
We thank the Elizabeth Blackwell Institute (EBI) for financial support through the EBI Early Career Research Fellowship awarded to AEH, and the EPSRC for financial support through a Leadership Fellowship awarded to JPR (grant reference EP/G007713/1). This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are creditedThe size of aerosol particles prior to, and during, inhalation influences the site of deposition within the lung. As such, a detailed understanding of the hygroscopic growth of an aerosol during inhalation is necessary to accurately model the deposited dose. In the first part of this study, it is demonstrated that the aerosol produced by a nebulizer, depending on the airflows rates, may experience a (predictable) wide range of relative humidity prior to inhalation and undergo dramatic changes in both size and solute concentration. A series of sensitive single aerosol analysis techniques are then used to make measurements of the relative humidity dependent thermodynamic equilibrium properties of aerosol generated from four common nebulizer formulations. Measurements are also reported of the kinetics of mass transport during the evaporation or condensation of water from the aerosol. Combined, these measurements allow accurate prediction of the temporal response of the aerosol size prior to and during inhalation. Specifically, we compare aerosol composed of pure saline (150 mM sodium chloride solution in ultrapure water) with two commercially available nebulizer products containing relatively low compound doses: Breath, consisting of a simple salbutamol sulfate solution (5 mg/2.5 mL; 1.7 mM) in saline, and Flixotide Nebules, consisting of a more complex stabilized fluticasone propionate suspension (0.25 mg/mL; 0.5 mM in saline. A mimic of the commercial product Tobi (60 mg/mL tobramycin and 2.25 mg/mL NaC1, pH 5.5-6.5) is also studied, which was prepared in house. In all cases, the presence of the pharmaceutical was shown to have a profound effect on the magnitude, and in some cases the rate, of the mass flux of water to and from the aerosol as compared to saline. These findings provide physical chemical evidence supporting observations from human inhalation studies, and suggest that using the growth dynamics of a pure saline aerosol in a lung inhalation model to represent nebulizer formulations may not be representative of the actual behavior of the aerosolized drug solutions. (C) 2014 Published by Elsevier B.V.Peer reviewe
A rebellious son? Hugo Odeberg and the interpretation of John 5.18
A solution to the difficult question of how to interpret John 5.18 appeared to have been provided with the publication of Hugo Odeberg\u27s monumental work, The Fourth Gospel, published in 1929. Odeberg cited a rabbinic expression which characterized a rebellious son as one who \u27makes himself equal with his father, and thus suggested that \u27the Jews\u27 are here making a similar accusation: they regard Jesus as rebelling against the divine authority. Subsequent scholarship for a long time cited Odeberg as a definitive demonstration of the background and meaning of John 5.18, and thus of the entire passage
WFPC2 Images of the Central Regions of Early-Type Galaxies - I. The Data
We present high resolution R-band images of the central regions of 67
early-type galaxies obtained with the Wide Field and Planetary Camera 2 (WFPC2)
aboard the Hubble Space Telescope (HST). Our sample strikingly confirms the
complex morphologies of the central regions of early-type galaxies. In
particular, we detect dust in 43 percent of all galaxies, and evidence for
embedded stellar disks in a remarkably large fraction of 51 percent. In 14 of
those galaxies the disk-like structures are misaligned with the main galaxy,
suggesting that they correspond to stellar bars in S0 galaxies. We analyze the
luminosity profiles of the galaxies in our sample, and classify galaxies
according to their central cusp slope. To a large extent we confirm the clear
dichotomy found in previous HST surveys: bright, boxy ellipticals with shallow
inner cusps (`core' galaxies) on one hand and faint, disky ellipticals with
steep central cusps (`power-law' galaxies) on the other hand. The advantages
and shortcomings of classification schemes utilizing the extrapolated central
cusp slope are discussed, and it is shown that this cusp slope might be an
inadequate representation for galaxies whose luminosity profile slope changes
smoothly with radius rather than resembling a broken power-law. In fact, we
find evidence for an `intermediate' class of galaxies, that cannot
unambiguously be classified as either core or power-law galaxies, and which
have central cusp slopes and absolute magnitudes intermediate between those of
core and power-law galaxies.Comment: 44 pages, 7 Postscript figures. Accepted for publication in the
Astronomical Journal. The associated Appendix with figures of luminosity
profiles, contour plots and isophotal parameters for all galaxies is
available at http://www.astro.washington.edu/rest/centralpro
Dynamical Friction in dE Globular Cluster Systems
The dynamical friction timescale for globular clusters to sink to the center
of a dwarf elliptical galaxy (dE) is significantly less than a Hubble time if
the halos have King-model or isothermal profiles and the globular clusters
formed with the same radial density profile as the underlying stellar
population. We examine the summed radial distribution of the entire globular
cluster systems and the bright globular cluster candidates in 51 Virgo and
Fornax Cluster dEs for evidence of dynamical friction processes. We find that
the summed distribution of the entire globular cluster population closely
follows the exponential profile of the underlying stellar population. However,
there is a deficit of bright clusters within the central regions of dEs
(excluding the nuclei), perhaps due to the orbital decay of these massive
clusters into the dE cores. We also predict the magnitude of each dE's nucleus
assuming the nuclei form via dynamical friction. The observed trend of
decreasing nuclear luminosity with decreasing dE luminosity is much stronger
than predicted if the nuclei formed via simple dynamical friction processes. We
find that the bright dE nuclei could have been formed from the merger of
orbitally decayed massive clusters, but the faint nuclei are several magnitudes
fainter than expected. These faint nuclei are found primarily in M_V > -14 dEs
which have high globular cluster specific frequencies and extended globular
cluster systems. In these galaxies, supernovae-driven winds, high central dark
matter densities, extended dark matter halos, the formation of new star
clusters, or tidal interactions may act to prevent dynamical friction from
collapsing the entire globular cluster population into a single bright nucleus.Comment: 15 pages, 2 tables, 7 figures; to appear in the Astrophysical
Journal, April 20, 200
Tetraquarks in a chiral constituent quark model
We analyze the possibility of heavy-light tetraquark bound states by means of
a chiral constituent quark model. The study is done in a variational approach.
Special attention is paid to the contribution given by the different terms of
the interacting potential and also to the role played by the different color
channels. We find a stable state for both and
configurations. Possible decay modes of these structures are
analyzed.Comment: 13 pages, no figures. Accepted for publication in European Journal of
Physics
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