927 research outputs found
Effect of molecular models on viscosity and thermal conductivity calculations
The effect of molecular models on viscosity and thermal conductivity calculations is investigated. The Direct Simulation Monte Carlo (DSMC) method for rarefied gas flows is used to simulateCouette and Fourier flows as a means of obtaining the transport coefficients. Experimentalmeasurements for argon (Ar) provide a baseline for comparison over a wide temperature range of 100–1,500 K. The variable hard sphere (VHS), variable soft sphere (VSS), and Lennard-Jones (L-J) molecular models have been implemented into a parallel version of Bird’s one-dimensional DSMC code, DSMC1, and the model parameters have been recalibrated to the current experimental data set. While the VHS and VSS models only consider the short-range, repulsive forces, the L-J model also includes constributions from the long-range, dispersion forces. Theoretical results for viscosity and thermal conductivity indicate the L-J model is more accurate than the VSS model; with maximum errors of 1.4% and 3.0% in the range 300–1,500 K for L-J and VSS models, respectively. The range of validity of the VSS model is extended to 1,650 K through appropriate choices for the model parameters
Secondary Scoliosis from a Retroperitoneal Ganglioneuroma in a 9-year-old Female: Case Report
Ganglioneuromas are rare benign tumors that tend to be asymptomatic until large enough to compress adjacent structures. These tumors are often found during childhood during evaluations for other pathologies. Retroperitoneal ganglioneuromas may be a secondary cause of scoliosis. Here, we present a case of a child who was found to have a retroperitoneal ganglioneuroma during an evaluation for scoliosis.
Old and Young X-ray Point Source Populations in Nearby Galaxies
We analyzed 1441 Chandra X-ray point sources in 32 nearby galaxies. The total
point-source X-ray luminosity L_XP is well correlated with B, K, and FIR+UV
luminosities of spiral host galaxies, and with the B and K luminosities for
ellipticals. This suggests an intimate connection between L_XP and both the old
and young stellar populations, for which K and FIR+UV luminosities are proxies
for the galaxy mass M and star-formation rate SFR. We derive proportionality
constants 1.3E29 erg/s/Msol and 0.7E39 erg/s/(Msol/yr), which can be used to
estimate the old and young components from M and SFR, respectively. The
cumulative X-ray luminosity functions for the point sources have quite
different slopes for the spirals (gamma ~= 0.5-0.8) and ellipticals (gamma ~=
1.4), implying *the most luminous point sources dominate L_XP* for the spirals.
Most of the point sources have X-ray colors that are consistent with either
LMXBs or Ultraluminous X-ray sources (ULXs a.k.a. IXOs) and we rule out
classical HMXBs (e.g. neutron-star X-ray pulsars) as contributing much to L_XP.
Thus, for spirals, the ULXs dominate L_XP. We estimate that >~20% of all ULXs
found in spirals originate from the older (pop II) stellar populations,
indicating that many of the ULXs that have been found in spiral galaxies are in
fact pop II ULXs, like those in elliptical galaxies. The linear dependence of
L_XP on the SFR argues for either a steepening in the X-ray luminosity function
of the young (pop I) X-ray source population at L_X >~10^(38.5-39) erg/s, or a
decreasing efficiency for producing all types of young X-ray point sources as
the galaxy SFR increases.Comment: 33 pages AASTEX, ApJ accepted. Please download full version with
figures from http://www.pha.jhu.edu/~colbert/chps_accepted.p
Courseware Considered Harmful
The study of DNS is an important quandary. After years of key research into local-area networks, we prove the simulation of IPv7. In order to accomplish this goal, we demonstrate that though the much-touted semantic algorithm for the understanding of thin clients by Zheng and Martin is optimal, the famous game-theoretic algorithm for the refinement of the transistor by J. M. Davis et al. [11] is maximally efficient
The Nature and Frequency of the Gas Outbursts in Comet 67P/Churyumov-Gerasimenko observed by the Alice Far-ultraviolet Spectrograph on Rosetta
Alice is a far-ultraviolet imaging spectrograph onboard Rosetta that, amongst
multiple objectives, is designed to observe emissions from various atomic and
molecular species from within the coma of comet 67P/Churyumov-Gerasimenko. The
initial observations, made following orbit insertion in August 2014, showed
emissions of atomic hydrogen and oxygen spatially localized close to the
nucleus and attributed to photoelectron impact dissociation of H2O vapor.
Weaker emissions from atomic carbon were subsequently detected and also
attributed to electron impact dissociation, of CO2, the relative H I and C I
line intensities reflecting the variation of CO2 to H2O column abundance along
the line-of-sight through the coma. Beginning in mid-April 2015, Alice
sporadically observed a number of outbursts above the sunward limb
characterized by sudden increases in the atomic emissions, particularly the
semi-forbidden O I 1356 multiplet, over a period of 10-30 minutes, without a
corresponding enhancement in long wavelength solar reflected light
characteristic of dust production. A large increase in the brightness ratio O I
1356/O I 1304 suggests O2 as the principal source of the additional gas. These
outbursts do not correlate with any of the visible images of outbursts taken
with either OSIRIS or the navigation camera. Beginning in June 2015 the nature
of the Alice spectrum changed considerably with CO Fourth Positive band
emission observed continuously, varying with pointing but otherwise fairly
constant in time. However, CO does not appear to be a major driver of any of
the observed outbursts.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journal Letter
3D printed fluidics with embedded analytic functionality for automated reaction optimisation
Additive manufacturing or ‘3D printing’ is being developed as a novel manufacturing process for the production of bespoke micro- and milliscale fluidic devices. When coupled with online monitoring and optimisation software, this offers an advanced, customised method for performing automated chemical synthesis. This paper reports the use of two additive manufacturing processes, stereolithography and selective laser melting, to create multifunctional fluidic devices with embedded reaction monitoring capability. The selectively laser melted parts are the first published examples of multifunctional 3D printed metal fluidic devices. These devices allow high temperature and pressure chemistry to be performed in solvent systems destructive to the majority of devices manufactured via stereolithography, polymer jetting and fused deposition modelling processes previously utilised for this application. These devices were integrated with commercially available flow chemistry, chromatographic and spectroscopic analysis equipment, allowing automated online and inline optimisation of the reaction medium. This set-up allowed the optimisation of two reactions, a ketone functional group interconversion and a fused polycyclic heterocycle formation, via spectroscopic and chromatographic analysis
Photometry of Kuiper belt object (486958) Arrokoth from New Horizons LORRI
On January 1st 2019, the New Horizons spacecraft flew by the classical Kuiper belt object (486958) Arrokoth (provisionally designated 2014 MU69), possibly the most primitive object ever explored by a spacecraft. The I/F of Arrokoth is analyzed and fit with a photometric function that is a linear combination of the Lommel-Seeliger (lunar) and Lambert photometric functions. Arrokoth has a geometric albedo of p_v = 0.21_(−0.04)^(+0.05) at a wavelength of 550 nm and ≈0.24 at 610 nm. Arrokoth's geometric albedo is greater than the median but consistent with a distribution of cold classical Kuiper belt objects whose geometric albedos were determined by fitting a thermal model to radiometric observations. Thus, Arrokoth's geometric albedo adds to the orbital and spectral evidence that it is a cold classical Kuiper belt object. Maps of the normal reflectance and hemispherical albedo of Arrokoth are presented. The normal reflectance of Arrokoth's surface varies with location, ranging from ≈0.10–0.40 at 610 nm with an approximately Gaussian distribution. Both Arrokoth's extrema dark and extrema bright surfaces are correlated to topographic depressions. Arrokoth has a bilobate shape and the two lobes have similar normal reflectance distributions: both are approximately Gaussian, peak at ≈0.25 at 610 nm, and range from ≈0.10–0.40, which is consistent with co-formation and co-evolution of the two lobes. The hemispherical albedo of Arrokoth varies substantially with both incidence angle and location, the average hemispherical albedo at 610 nm is 0.063 ± 0.015. The Bond albedo of Arrokoth at 610 nm is 0.062 ± 0.015
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