563 research outputs found
Transport coefficients of multi-particle collision algorithms with velocity-dependent collision rules
Detailed calculations of the transport coefficients of a recently introduced
particle-based model for fluid dynamics with a non-ideal equation of state are
presented. Excluded volume interactions are modeled by means of biased
stochastic multiparticle collisions which depend on the local velocities and
densities. Momentum and energy are exactly conserved locally. A general scheme
to derive transport coefficients for such biased, velocity dependent collision
rules is developed. Analytic expressions for the self-diffusion coefficient and
the shear viscosity are obtained, and very good agreement is found with
numerical results at small and large mean free paths. The viscosity turns out
to be proportional to the square root of temperature, as in a real gas. In
addition, the theoretical framework is applied to a two-component version of
the model, and expressions for the viscosity and the difference in diffusion of
the two species are given.Comment: 31 pages, 8 figures, accepted by J. Phys. Cond. Matte
Simulation of fluid-solid coexistence in finite volumes: A method to study the properties of wall-attached crystalline nuclei
The Asakura-Oosawa model for colloid-polymer mixtures is studied by Monte
Carlo simulations at densities inside the two-phase coexistence region of fluid
and solid. Choosing a geometry where the system is confined between two flat
walls, and a wall-colloid potential that leads to incomplete wetting of the
crystal at the wall, conditions can be created where a single nanoscopic
wall-attached crystalline cluster coexists with fluid in the remainder of the
simulation box. Following related ideas that have been useful to study
heterogeneous nucleation of liquid droplets at the vapor-liquid coexistence, we
estimate the contact angles from observations of the crystalline clusters in
thermal equilibrium. We find fair agreement with a prediction based on Young's
equation, using estimates of interface and wall tension from the study of flat
surfaces. It is shown that the pressure versus density curve of the finite
system exhibits a loop, but the pressure maximum signifies the "droplet
evaporation-condensation" transition and thus has nothing in common with a van
der Waals-like loop. Preparing systems where the packing fraction is deep
inside the two-phase coexistence region, the system spontaneously forms a "slab
state", with two wall-attached crystalline domains separated by (flat)
interfaces from liquid in full equilibrium with the crystal in between;
analysis of such states allows a precise estimation of the bulk equilibrium
properties at phase coexistence
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Infrared Spectral Energy Distributions of Seyfert Galaxies: Spitzer Space Telescope Observations of the 12 micron Sample of Active Galaxies
The mid-far-infrared spectral energy distributions (SEDs) of 83 active
galaxies, mostly Seyfert galaxies, selected from the extended 12 micron sample
are presented. The data were collected using all three instruments, IRAC, IRS,
and MIPS, aboard the Spitzer Space Telescope. The IRS data were obtained in
spectral mapping mode, and the photometric data from IRAC and IRS were
extracted from matched, 20 arcsec diameter circular apertures. The MIPS data
were obtained in SED mode, providing very low resolution spectroscopy (R ~ 20)
between ~ 55 and 90 microns in a larger, 20 by 30 arcsec synthetic aperture. We
further present the data from a spectral decomposition of the SEDs, including
equivalent widths and fluxes of key emission lines; silicate 10 and 18 micron
emission and absorption strengths; IRAC magnitudes; and mid-far infrared
spectral indices. Finally, we examine the SEDs averaged within optical
classifications of activity. We find that the infrared SEDs of Seyfert 1s and
Seyfert 2s with hidden broad line regions (HBLR, as revealed by
spectropolarimetry or other technique) are qualitatively similar, except that
Seyfert 1s show silicate emission and HBLR Seyfert 2s show silicate absorption.
The infrared SEDs of other classes with the 12 micron sample, including Seyfert
1.8-1.9, non-HBLR Seyfert 2 (not yet shown to hide a type 1 nucleus), LINER and
HII galaxies, appear to be dominated by star-formation, as evidenced by blue
IRAC colors, strong PAH emission, and strong far-infrared continuum emission,
measured relative to mid-infrared continuum emission.Comment: 78 pages, 13 figure
A Super-Oxidized Radical Cationic Icosahedral Boron Cluster
While the icosahedral closo-[BââHââ]ÂČâ» cluster does not display reversible electrochemical behavior, perfunctionalization of this species via substitution of all 12 BâH vertices with alkoxy or benzyloxy (OR) substituents engenders reversible redox chemistry, providing access to clusters in the dianionic, monoanionic, and neutral forms. Here, we evaluated the electrochemical behavior of the electron-rich Bââ(O-3-methylbutyl)ââ (1) cluster and discovered that a new reversible redox event that gives rise to a fourth electronic state is accessible through one-electron oxidation of the neutral species. Chemical oxidation of 1 with [N(2,4-BrâCâHâ)â]·âș afforded the isolable [1]·âș cluster, which is the first example of an open-shell cationic Bââ cluster in which the unpaired electron is proposed to be delocalized throughout the boron cluster core. The oxidation of 1 is also chemically reversible, where treatment of [1]·âș with ferrocene resulted in its reduction back to 1. The identity of [1]·âș is supported by EPR, UVâvis, multinuclear NMR (ÂčH, ÂčÂčB), and X-ray photoelectron spectroscopic characterization
A Super-Oxidized Radical Cationic Icosahedral Boron Cluster
While the icosahedral closo-[BââHââ]ÂČâ» cluster does not display reversible electrochemical behavior, perfunctionalization of this species via substitution of all 12 BâH vertices with alkoxy or benzyloxy (OR) substituents engenders reversible redox chemistry, providing access to clusters in the dianionic, monoanionic, and neutral forms. Here, we evaluated the electrochemical behavior of the electron-rich Bââ(O-3-methylbutyl)ââ (1) cluster and discovered that a new reversible redox event that gives rise to a fourth electronic state is accessible through one-electron oxidation of the neutral species. Chemical oxidation of 1 with [N(2,4-BrâCâHâ)â]·âș afforded the isolable [1]·âș cluster, which is the first example of an open-shell cationic Bââ cluster in which the unpaired electron is proposed to be delocalized throughout the boron cluster core. The oxidation of 1 is also chemically reversible, where treatment of [1]·âș with ferrocene resulted in its reduction back to 1. The identity of [1]·âș is supported by EPR, UVâvis, multinuclear NMR (ÂčH, ÂčÂčB), and X-ray photoelectron spectroscopic characterization
The Chandra ACIS Survey of M33 (ChASeM33): The final source catalog
This study presents the final source catalog of the Chandra ACIS Survey of
M33 (ChASeM33). With a total exposure time of 1.4 Ms, ChASeM33 covers ~70% of
the D25 isophote (R\approx4kpc) of M33 and provides the deepest, most complete,
and detailed look at a spiral galaxy in X-rays. The source catalog includes 662
sources, reaches a limiting unabsorbed luminosity of ~2.4x10^(34) erg/s in the
0.35-8.0keV energy band, and contains source positions, source net counts,
fluxes and significances in several energy bands, and information on source
variability. The analysis challenges posed by ChASeM33 and the techniques
adopted to address these challenges are discussed. To constrain the nature of
the detected X-ray source, hardness ratios were constructed and spectra were
fit for 254 sources, followup MMT spectra of 116 sources were acquired, and
cross-correlations with previous X-ray catalogs and other multi-wavelength data
were generated. Based on this effort, 183 of the 662 ChASeM33 sources could be
identified. Finally, the luminosity function for the detected point sources as
well as the one for the X-ray binaries in M33 is presented. The luminosity
functions in the soft band (0.5-2.0 keV) and the hard band (2.0-8.0 keV) have a
limiting luminosity at the 90% completeness limit of 4.0x10^(34) erg/s and
1.6x10^(35) erg/s (for D=817kpc), respectively, which is significantly lower
than what was reported by previous X-ray binary population studies in galaxies
more distant than M33. The resulting distribution is consistent with a dominant
population of high mass X-ray binaries as would be expected for M33.Comment: 186 pages, 11 figures, 10 tables. Accepted for publication in the
ApJS. For a high resolution version of the paper, see
http://hea-www.harvard.edu/vlp_m33_public
Nuclear Morphometry using a Deep Learning-based Algorithm has Prognostic Relevance for Canine Cutaneous Mast Cell Tumors
Variation in nuclear size and shape is an important criterion of malignancy
for many tumor types; however, categorical estimates by pathologists have poor
reproducibility. Measurements of nuclear characteristics (morphometry) can
improve reproducibility, but manual methods are time consuming. In this study,
we evaluated fully automated morphometry using a deep learning-based algorithm
in 96 canine cutaneous mast cell tumors with information on patient survival.
Algorithmic morphometry was compared with karyomegaly estimates by 11
pathologists, manual nuclear morphometry of 12 cells by 9 pathologists, and the
mitotic count as a benchmark. The prognostic value of automated morphometry was
high with an area under the ROC curve regarding the tumor-specific survival of
0.943 (95% CI: 0.889 - 0.996) for the standard deviation (SD) of nuclear area,
which was higher than manual morphometry of all pathologists combined (0.868,
95% CI: 0.737 - 0.991) and the mitotic count (0.885, 95% CI: 0.765 - 1.00). At
the proposed thresholds, the hazard ratio for algorithmic morphometry (SD of
nuclear area ) was 18.3 (95% CI: 5.0 - 67.1), for manual
morphometry (SD of nuclear area ) 9.0 (95% CI: 6.0 - 13.4),
for karyomegaly estimates 7.6 (95% CI: 5.7 - 10.1), and for the mitotic count
30.5 (95% CI: 7.8 - 118.0). Inter-rater reproducibility for karyomegaly
estimates was fair ( = 0.226) with highly variable
sensitivity/specificity values for the individual pathologists. Reproducibility
for manual morphometry (SD of nuclear area) was good (ICC = 0.654). This study
supports the use of algorithmic morphometry as a prognostic test to overcome
the limitations of estimates and manual measurements
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