987 research outputs found
Laboratory measurements of forward and backward scattering of laser beams in water droplet clouds
Many aspects of the forward and backward scattering in dense water droplet clouds were studied using a laboratory scattering facility. This system is configured in a lidar geometry to facilitate comparison of the laboratory results to current lidar oriented theory and measurements. The backscatter measurements are supported with simultaneous measurements of the optical density, mass concentration, and droplet size distribution of the clouds. Measurements of the extinction and backscatter coefficients at several important laser wavelength have provided data on the relationship between these quantities for laboratory clouds at .633, 1.06, and 10.6 microns. The polarization characteristics of the backscatter of 1.06 microns were studied using several different types of clouds. More recently, the laboratory facility was modified to allow range-resolved backscatter measurements at 1.06 microns. Clouds made up of 3 layers, each with its own density, can be constructed. This allows the study of the effect of cloud inhomogeneity on the forward and backscatter
The potential of low-intensity and online interventions for depression in low- and middle-income countries
The World Health Organization (WHO) reports that low- and middle-income countries (LMICs) are confronted with a serious âmental health gapâ, indicating an enormous disparity between the number of individuals in need of mental health care and the availability of professionals to provide such care (WHO in 2010). Traditional forms of mental health services (i.e. face-to-face, individualised assessments and interventions) are therefore not feasible. We propose three strategies for addressing this mental health gap: delivery of evidence-based, low-intensity interventions by non-specialists, the use of transdiagnostic treatment protocols, and strategic deployment of technology to facilitate access and uptake. We urge researchers from all over the world to conduct feasibility studies and randomised controlled studies on the effect of low-intensity interventions and technology supported (e.g. online) interventions in LMICs, preferably using an active control condition as comparison, to ensure we disseminate effective treatments in LMICs
Mapping Low-Density Intergalactic Gas: a Third Helium Lyman-alpha Forest
We present a new HST/STIS spectrum of the z=3.18 quasar PKS 1935-692 and
summarize the spectral features shortwards of 304A in the rest frame likely to
be caused by foreground HeII Lyman-alpha absorption. In accord with previous
results on two other quasars at similar redshifts, we demonstrate a correlation
with the HI Lyman-alpha forest absorption, and show that much of the helium
absorption is caused by a comparable quantity of more diffuse gas with
Omega~0.01, that is not detected in HI. The helium ionization zone around the
quasar is detected as well as a void seen in both HI and HeII. The properties
of the absorption are in broad agreement with those of the other quasars and
with models of the protogalactic gas distribution and ionization at this
redshift.Comment: 17 pages including 5 figures. As accepted for publication in The
Astronomical Journal (minor revisions
Spectroscopic Analysis of H I Absorption Line Systems in 40 HIRES Quasars
We list and analyze H I absorption lines at redshifts 2 < z < 4 with column
density (12 < log(N_HI) < 19) in 40 high-resolutional (FWHM = 8.0 km/s) quasar
spectra obtained with the Keck+HIRES. We de-blend and fit all H I lines within
1,000 km/s of 86 strong H I lines whose column densities are log(N_HI/[cm^-2])
> 15. Unlike most prior studies, we use not only Lya but also all visible
higher Lyman series lines to improve the fitting accuracy. This reveals
components near to higher column density systems that can not be seen in Lya.
We list the Voigt profile fits to the 1339 H I components that we found. We
examined physical properties of H I lines after separating them into several
sub-samples according to their velocity separation from the quasars, their
redshift, column density and the S/N ratio of the spectrum. We found two
interesting trends for lines with 12 < log(N_HI) < 15 which are within 200-1000
km/s of systems with log(N_HI) > 15. First, their column density distribution
becomes steeper, meaning relatively fewer high column density lines, at z <
2.9. Second, their column density distribution also becomes steeper and their
line width becomes broader by about 2-3 km/s when they are within 5,000 km/s of
their quasar.Comment: 32 pages, 14 figures, accepted for publication in the Astronomical
Journal. A complete version with all tables and figures is available at
http://www.astro.psu.edu/users/misawa/pub/Paper/40hires.ps.g
A Uniform Analysis of the Ly-alpha forest at z = 0 - 5: I. The sample and distribution of clouds at z > 1.7
We present moderate resolution data for 39 QSOs at z 2 obtained at
the Multiple Mirror Telescope. These data are combined with spectra of
comparable resolution of 60 QSOs with redshifts greater than 1.7 found in the
literature to investigate the distribution of Ly-alpha forest lines in redshift
and equivalent width. We find a value for , the parameter describing
the number distribution of Ly-alpha forest lines in redshift, of
for lines stronger than a rest equivalent width of 0.32 , in good
agreement with some previous studies. The Kolmogorov-Smirnov test was applied
to the data and it is found that this single power law is a good fit over the
relevant redshift ranges. Simulations of the Lyman alpha forest were performed
to determine the completeness of the line lists and to test how well the
analysis the underlying line statistics, given this level of completeness.Comment: minor corrections to text, 37 Latex pages, 11 encapsulated Postscript
figures, uses emulateapj.sty, To appear in the Sept. 2000 ApJS, line lists
and spectra available at http://qso.as.arizona.edu/~jscott/Spectra/index.htm
Modelling long-term impacts of fertilization and liming on soil acidification at Rothamsted experimental station
Liming is widely used to reduce the impacts of soil acidification and optimize soil pH for agricultural production. Whether models can simulate the effect of liming on soil pH, and base saturation (BS), and thereby guide lime application, is still largely unknown. Long-term experimental data from a grassland (Park Grass, 1965â2012)and arable land (Sawyers Field, 1962â1972) at Rothamsted Research, UK, were thus used to assess the ability of the VSD+ model to simulate the effects of long-term fertilization and liming on soil acidification. The VSD+model was capable of simulating observed soil pHand BS changes over time in the long-termliming experiments, except for a treatment in which sulphur (S) was added. NormalizedMean Absolute Errors (NMAE) and Normalized Root Mean Square Errors (NRMSE) of simulated and observed pH values, averaged over the observation periods varied between 0.02 and 0.08 (NMAE) and 0.01â0.05 (NRMSE). The acidity budget results for Park Grass suggest that nitrogen (N) transformations contributed most to acidity production, causing predominantly aluminium (Al) exchange in the topsoil (0â23 cm) followed by base cation (BC) release, but in the treatment with S addition, BC uptake had a nearly similar effect on acidity production.However, in Sawyers Field, the acidity budget suggested that BC uptakewas the dominant cause of soil acidification,while the impacts of N transformations were limited. Liming was found to sufficiently replenish BC and decrease Al exchange in the topsoil layer. Overall, the VSD+ model can adequately reconstruct the impacts of fertilizer and liming applications on acid neutralizing processes and related soil pH and BC changes at the soil exchange complex
A High Deuterium Abundance at z=0.7
Of the light elements, the primordial abundance of deuterium, (D/H)_p,
provides the most sensitive diagnostic for the cosmological mass density
parameter Omega_B. Recent high redshift (D/H) measurements are highly
discrepant, although this may reflect observational uncertainties. The larger
(D/H) values, which imply a low Omega_B and require the Universe to be
dominated by non-baryonic matter (dynamical studies indicate a higher total
density parameter), cause problems for galactic chemical evolution models since
they have difficulty in reproducing the large decline down to the lower
present-day (D/H). Conversely, low (D/H) values imply an Omega_B greater than
derived from ^7Li and ^4He abundance measurements, and may require a deuterium
abundance evolution that is too low to easily explain. Here we report the first
measurement at intermediate redshift, where the observational difficulties are
smaller, of a gas cloud with ideal characteristics for this experiment. Our
analysis of the z = 0.7010 absorber toward 1718+4807 indicates (D/H) = 2.0 +/-
0.5 x 10^{-4} which is in the high range. This and other independent
observations suggests there may be a cosmological inhomogeneity in (D/H)_p of
at least a factor of ten.Comment: 6 pages, 1 figur
The UVES Spectral Quasar Absorption Database (SQUAD) Data Release 1: The first 10 million seconds
We present the first data release (DR1) of the UVES Spectral Quasar
Absorption Database (SQUAD), comprising 467 fully reduced, continuum-fitted
high-resolution quasar spectra from the Ultraviolet and Visual Echelle
Spectrograph (UVES) on the European Southern Observatory's Very Large
Telescope. The quasars have redshifts -5, and a total exposure time of 10
million seconds provides continuum-to-noise ratios of 4-342 (median 20) per
2.5-km/s pixel at 5500 \AA. The SQUAD spectra are fully reproducible from the
raw, archival UVES exposures with open-source software, including our
UVES_popler tool for combining multiple extracted echelle exposures which we
document here. All processing steps are completely transparent and can be
improved upon or modified for specific applications. A primary goal of SQUAD is
to enable statistical studies of large quasar and absorber samples, and we
provide tools and basic information to assist three broad scientific uses:
studies of damped Lyman- systems (DLAs), absorption-line surveys and
time-variable absorption lines. For example, we provide a catalogue of 155 DLAs
whose Lyman- lines are covered by the DR1 spectra, 18 of which are
reported for the first time. The HI column densities of these new DLAs are
measured from the DR1 spectra. DR1 is publicly available and includes all
reduced data and information to reproduce the final spectra.Comment: 21 pages, 18 figures. Accepted by MNRAS. All final quasar spectra,
reduced contributing exposures, and supplementary material available via
https://github.com/MTMurphy77/UVES_SQUAD_DR
Deuteronomy and Numbers
Four light isotopes - D, ^3He, ^4He and ^7Li - were produced by nuclear
reactions a few seconds after the big bang. New measurements of ^3He in the ISM
by Gloeckler and Geiss and of deuterium in high redshift hydrogen clouds by
Tytler and his collaborators provide further confirmation of big-bang
nucleosynthesis and new insight about the density of ordinary matter (baryons).Comment: 6 pages LaTeX with 1 eps Figur
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