50,325 research outputs found
Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe
The Standard Model of particle physics assumes that the so-called fundamental
constants are universal and unchanging. Absorption lines arising in molecular
clouds along quasar sightlines offer a precise test for variations in the
proton-to-electron mass ratio, mu, over cosmological time and distance scales.
The inversion transitions of ammonia are particularly sensitive to mu compared
to molecular rotational transitions. Comparing the available ammonia spectra
observed towards the quasar B0218+357 with new, high-quality rotational
spectra, we present the first detailed measurement of mu with this technique,
limiting relative deviations from the laboratory value to |dmu/mu| <
1.8x10^{-6} (95% confidence level) at approximately half the Universe's current
age - the strongest astrophysical constraint to date. Higher-quality ammonia
observations will reduce both the statistical and systematic uncertainties in
these measurements.Comment: Science, 20th June 2008. 22 pages, 5 figures (12 EPS files), 2
tables, including Supporting Online Material; v2: Corrected reference for
laboratory mu-variation bound
PANIC: A Near-infrared Camera for the Magellan Telescopes
PANIC (Persson's Auxiliary Nasmyth Infrared Camera) is a near-infrared camera
designed to operate at any one of the f/11 folded ports of the 6.5m Magellan
telescopes at Las Campanas Observatory, Chile. The instrument is built around a
simple, all-refractive design that reimages the Magellan focal plane to a plate
scale of 0.125'' pixel^{-1} onto a Rockwell 1024x1024 HgCdTe detector. The
design goals for PANIC included excellent image quality to sample the superb
seeing measured with the Magellan telescopes, high throughput, a relatively
short construction time, and low cost. PANIC has now been in regular operation
for over one year and has proved to be highly reliable and produce excellent
images. The best recorded image quality has been ~0.2'' FWHM.Comment: 8 pages, 5 figures. To appear in "Astronomical Telescopes and
Instrumentation," Proc SPIE (Glasgow), June 2004. Version with higher
resolution figures is available at
http://cfa-www.harvard.edu/~pmartini/professional/publications/panic.pd
Aerosol hygroscopicity in the marine atmosphere: a closure study using high-time-resolution, multiple-RH DASH-SP and size-resolved C-ToF-AMS data
We have conducted the first airborne hygroscopic growth closure study to utilize data from an Aerodyne compact Time-of-Flight Aerosol Mass Spectrometer (C-ToF-AMS) coupled with size-resolved, multiple-RH, high-time-resolution hygroscopic growth factor (GF) measurements from the differential aerosol sizing and hygroscopicity spectrometer probe (DASH-SP). These data were collected off the coast of Central California during seven of the 16 flights carried out during the MASE-II field campaign in July 2007. Two of the seven flights were conducted in airmasses characterized by continental origin. These flights exhibited elevated organic volume fractions (VF_(organic)=0.56±0.19, as opposed to 0.39±0.20 for all other flights), corresponding to significantly suppressed GFs at high RH (1.61±0.14 at 92% RH, as compared with 1.91±0.07 for all other flights), more moderate GF suppression at intermediate RH (1.53±0.10 at 85%, compared with 1.58±0.08 for all other flights), and no measurable GF suppression at low RH (1.31±0.06 at 74%, compared with 1.31±0.07 for all other flights). Organic loadings were slightly elevated in above-cloud aerosols, as compared with below-cloud aerosols, and corresponded to a similar trend of significantly suppressed GF at high RH, but more moderate impacts at lower values of RH. A hygroscopic closure based on a volume-weighted mixing rule provided good agreement with DASH-SP measurements (R^2=0.78). Minimization of root mean square error between observations and predictions indicated mission-averaged organic GFs of 1.22, 1.45, and 1.48 at 74, 85, and 92% RH, respectively. These values agree with previously reported values for water-soluble organics such as dicarboxylic and multifunctional acids, and correspond to a highly oxidized, presumably water-soluble, organic fraction (mission-averaged O:C=0.92±0.33). Finally, a backward stepwise linear regression revealed that, other than RH, the most important predictor for GF is VF_(organic), indicating that a simple emperical model relating GF, RH, and the relative abundance of organic material can provide accurate predictions (R^2=0.77) of hygroscopic growth for the California coast
Review of meteoroid-bumper interaction studies at McGill University
Experimental investigation of meteoroid-bumper impact, debris cloud expansion, and second surface pressure loadin
Barium release system
A chemical system is described for releasing a good yield of free barium neutral atoms and barium ions in the upper atmosphere and interplanetary space for the study of the geophysical properties of the medium. The barium is released in the vapor phase so that it can be ionized by solar radiation and also be excited to emit resonance radiation in the visible range. The ionized luminous cloud of barium becomes a visible indication of magnetic and electrical characteristics in space and allows determination of these properties over relatively large areas at a given time
Phase stability and the arsenic vacancy defect in In<sub>x</sub>Ga<sub>1-x</sub>As
The introduction of defects, such as vacancies, into InxGa1-xAs can have a dramatic impact on the physical and electronic properties of the material. Here we employ ab initio simulations of quasirandom supercells to investigate the structure of InxGa1-xAs and then examine the energy and volume changes associated with the introduction of an arsenic vacancy defect. We predict that both defect energies and volumes for intermediate compositions of InxGa1-xAs differ significantly from what would be expected by assuming a simple linear interpolation of the end member defect energies/volumes
Rocket having barium release system to create ion clouds in the upper atmosphere
A chemical system for releasing a good yield of free barium atoms and barium ions to create ion clouds in the upper atmosphere and interplanetary space for the study of the geophysical properties of the medium is presented
Prison as Seen by Convict Criminologists
Most criminologists tend to base their view of prison on ideological assumptions gathered from secondary sources, with at best limited entry to the prison world. They nearly always get it wrong, as they systematically exclude the perspectives and real life experiences of their human subjects. These academic researchers have contributed to poor public policy that promotes the violent repression of prisoners in the USA and other countries. In response, Convict Criminologists are ex‐convicts working as criminology and criminal justice professors, along with “non‐con” associates, that insist that as a means for societies to develop humane, effective, and cost efficient prisons, we must develop ways to incorporate the voice of prisoners in our theorizing about, policy recommendations for, and management of the prison
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