62 research outputs found
Discovery of Interstellar Hydrogen Fluoride
We report the first detection of interstellar hydrogen fluoride. Using the
Long Wavelength Spectrometer (LWS) of the Infrared Space Observatory (ISO), we
have detected the 121.6973 micron J = 2 - 1 line of HF in absorption toward the
far-infrared continuum source Sagittarius B2. The detection is statistically
significant at the 13 sigma level. On the basis of our model for the excitation
of HF in Sgr B2, the observed line equivalent width of 1.0 nm implies a
hydrogen fluoride abundance of 3E-10 relative to H2. If the elemental abundance
of fluorine in Sgr B2 is the same as that in the solar system, then HF accounts
for ~ 2% of the total number of fluorine nuclei. We expect hydrogen fluoride to
be the dominant reservoir of gas-phase fluorine in Sgr B2, because it is formed
rapidly in exothermic reactions of atomic fluorine with either water or
molecular hydrogen; thus the measured HF abundance suggests a substantial
depletion of fluorine onto dust grains. Similar conclusions regarding depletion
have previously been reached for the case of chlorine in dense interstellar
clouds. We also find evidence at a lower level of statistical significance (~ 5
sigma) for an emission feature at the expected position of the 4(3,2)-4(2,3)
121.7219 micron line of water. The emission line equivalent width of 0.5 nm for
the water feature is consistent with the water abundance of 5E-6 relative to H2
that has been inferred previously from observations of the hot core of Sgr B2.Comment: 11 pages (AASTeX using aaspp4.sty) plus 2 figures; to appear in ApJ
Letter
Detection of water at z = 0.685 towards B0218+357
We report the detection of the H_2O molecule in absorption at a redshift z =
0.68466 in front of the gravitationally lensed quasar B0218+357. We detect the
fundamental transition of ortho-water at 556.93 GHz (redshifted to 330.59 GHz).
The line is highly optically thick and relatively wide (15 km/s FWHM), with a
profile that is similar to that of the previously detected CO(2--1) and
HCO^+(2--1) optically thick absorption lines toward this quasar. From the
measured level of the continuum at 330.59 GHz, which corresponds to the level
expected from the power-law spectrum already
observed at lower frequencies, we deduce that the filling factor of the H_2O
absorption is large. It was already known from the high optical thickness of
the CO, ^{13}CO and C^{18}O lines that the molecular clouds entirely cover one
of the two lensed images of the quasar (all its continuum is absorbed); our
present results indicate that the H_2O clouds are covering a comparable
surface. The H_2O molecules are therefore not confined to small cores with a
tiny filling factor, but are extended over parsec scales. The H_2O line has a
very large optical depth, and only isotopic lines could give us the water
abundance. We have also searched for the 183 GHz line in absorption, obtaining
only an upper limit; this yields constraints on the excitation temperature.Comment: 4 pages, 3 figures, accepted in ApJ Letter
Probing the Early Stages of Low-Mass Star Formation in LDN 1689N: Dust and Water in IRAS 16293-2422A, B, and E
We present deep images of dust continuum emission at 450, 800, and 850 micron
of the dark cloud LDN 1689N which harbors the low-mass young stellar objects
(YSOs) IRAS 16293-2422A and B (I16293A and I16293B) and the cold prestellar
object I16293E. Toward the positions of I16293A and E we also obtained spectra
of CO-isotopomers and deep submillimeter observations of chemically related
molecules with high critical densities. To I16293A we report the detection of
the HDO 1_01 - 0_00 and H2O 1_10 - 1_01 ground-state transitions as broad
self-reversed emission profiles with narrow absorption, and a tentative
detection of H2D+ 1_10 - 1_11. To I16293E we detect weak emission of
subthermally excited HDO 1_01 - 0_00. Based on this set of submillimeter
continuum and line data we model the envelopes around I16293A and E. The
density and velocity structure of I16293A is fit by an inside-out collapse
model, yielding a sound speed of a=0.7 km/s, an age of t=(0.6--2.5)e4 yr, and a
mass of 6.1 Msun. The density in the envelope of I16293E is fit by a radial
power law with index -1.0+/-0.2, a mass of 4.4 Msun, and a constant temperature
of 16K. These respective models are used to study the chemistry of the
envelopes of these pre- and protostellar objects.
The [HDO]/[H2O] abundance ratio in the warm inner envelope of I16293A of a
few times 1e-4 is comparable to that measured in comets. This supports the idea
that the [HDO]/[H2O] ratio is determined in the cold prestellar core phase and
conserved throughout the formation process of low-mass stars and planets.Comment: 61 pages, 17 figures. Accepted for publication in ApJ. To get Fig.
13: send email to [email protected]
Search for Interstellar Water in the Translucent Molecular Cloud toward HD 154368
We report an upper limit of 9 x 10^{12} cm-2 on the column density of water
in the translucent cloud along the line of sight toward HD 154368. This result
is based upon a search for the C-X band of water near 1240 \AA carried out
using the Goddard High Resolution Spectrograph of the Hubble Space Telescope.
Our observational limit on the water abundance together with detailed chemical
models of translucent clouds and previous measurements of OH along the line of
sight constrain the branching ratio in the dissociative recombination of H_3O+
to form water. We find at the level that no more than 30% of
dissociative recombinations of H_3O+ can lead to H_2O. The observed spectrum
also yielded high-resolution observations of the Mg II doublet at 1239.9 \AA
and 1240.4 \AA, allowing the velocity structure of the dominant ionization
state of magnesium to be studied along the line of sight. The Mg II spectrum is
consistent with GHRS observations at lower spectral resolution that were
obtained previously but allow an additional velocity component to be
identified.Comment: Accepted by ApJ, uses aasp
Herschel observations of deuterated water towards Sgr B2(M)
Observations of HDO are an important complement for studies of water, because
they give strong constraints on the formation processes -- grain surfaces
versus energetic process in the gas phase, e.g. in shocks. The HIFI
observations of multiple transitions of HDO in Sgr~B2(M) presented here allow
the determination of the HDO abundance throughout the envelope, which has not
been possible before with ground-based observations only. The abundance
structure has been modeled with the spherical Monte Carlo radiative transfer
code RATRAN, which also takes radiative pumping by continuum emission from dust
into account. The modeling reveals that the abundance of HDO rises steeply with
temperature from a low abundance () in the outer envelope
at temperatures below 100~K through a medium abundance () in
the inner envelope/outer core, at temperatures between 100 and 200~K, and
finally a high abundance () at temperatures above 200~K in
the hot core.Comment: A&A HIFI special issue, accepte
The Post-Shock Chemical Lifetimes of Outflow Tracers and a Possible New Mechanism to Produce Water Ice Mantles
We have used a coupled time-dependent chemical and dynamical model to
investigate the lifetime of the chemical legacy left in the wake of C-type
shocks. We concentrate this study on the chemistry of H2O and O2, two molecules
which are predicted to have abundances that are significantly affected in
shock-heated gas. Two models are presented: (1) a three-stage model of
pre-shock, shocked, and post-shock gas; and (2) a Monte-Carlo cloud simulation
where we explore the effects of stochastic shock activity on molecular gas over
a cloud lifetime. In agreement with previous studies, we find that shock
velocities in excess of 10 km s^-1 are required to convert all of the oxygen
not locked in CO into H2O before the gas has an opportunity to cool. For pure
gas-phase models the lifetime of the high water abundances, or ``H2O legacy'',
in the post-shock gas is 4 - 7 x 10^5 years. Through the Monte Carlo cloud
simulation we demonstrate that the time-average abundance of H2O is a sensitive
function of the frequency of shocks. Thus we predict that the abundance of H2O
and other known outflow tracers can be used to trace the history of shock
activity in molecular gas. For gas-grain models we find that the abundance of
water-ice on grain surfaces can be quite large and is comparable to that
observed in molecular clouds. This offers a possible alternative method to
create water mantles without resorting to grain surface chemistry: gas heating
and chemical modification due to a C-type shock and subsequent depletion of the
gas-phase species onto grain mantles.Comment: 31 pages (including 16 figures), using aas2pp4.sty. To be published
in ApJ, June 1 1998 issu
Isotonic Glycerol and Sodium Hyaluronate Containing Artificial Tear Decreases Conjunctivochalasis after One and Three Months: A Self-Controlled, Unmasked Study.
Dry eye complaints are ranked as the most frequent symptoms of patients visiting ophthalmologists. Conjunctivochalasis is a common dry eye disorder, which can cause an unstable tear film and ocular discomfort. The severe conjunctivochalasis characterized by high LId-Parallel COnjunctival Folds (LIPCOF) degree usually requires surgical intervention, where a conservative therapy would be highly desirable. Here we examined the efficacy of a preservative-free, inorganic salt-free unit-dose artificial tear, called Conheal containing isotonic glycerol and 0.015% sodium hyaluronate in a prospective, unmasked, self-controlled study involving 20 patients. The regular use of the glycerol/hyaluronate artificial tear in three months caused a significant improvement in the recorded parameters. Conjunctivochalasis decreased from a mean LIPCOF degree of 2.9 ± 0.4 on both eyes to 1.4 ± 0.6 on the right (median decrease of -2 points, 95% CI from -2.0 to -1.0), and to 1.4 ± 0.7 on the left eye (median decrease of -1 points, 95% CI from -2.0 to -1.0) (p<0.001 for both sides). The tear film breakup time (TFBUT) lengthened from 4.8 ± 1.9 seconds on both eyes to 5.9 ± 2.3 seconds (mean increase of 1.1 seconds, 95% CI from 0.2 to 2.0) and 5.7 ± 1.8 seconds (mean increase of 0.9 seconds, 95% CI from 0.3 to 1.5) on the right and left eyes, respectively (p(right eyes) = 0.020, p(left eyes) = 0.004). The corneal lissamine staining (Oxford Scheme grade) was reduced from 1.3 ± 0.6 on the right and 1.4 ± 0.6 on the left eye significantly (p<0.001) to 0.3 ± 0.4 and 0.2 ± 0.4 on the right and the left eyes. The Ocular Surface Disease Index (OSDI) questionnaire score indicating the subjective complaints of the patients also decreased from a mean value of 36.2 ± 25.3 to 15.6 ± 16.7 (p<0.001). In this study, the artificial tear, Conheal decreased the grade of the conjunctivochalasis significantly after one month of regular use already, from the LIPCOF degree 3, considered as indication of conjunctival surgery, to a LIPCOF degree 2 or lower requiring a conservative therapy. Our results raise the possibility that vision-related quality of life can be significantly improved by conservative therapies even in severe conjunctivochalasis
Rapid detection of pandemic influenza in the presence of seasonal influenza
Background: Key to the control of pandemic influenza are surveillance systems that raise alarms rapidly and sensitively. In addition, they must minimise false alarms during a normal influenza season. We develop a method that uses historical syndromic influenza data from the existing surveillance system 'SERVIS' (Scottish Enhanced Respiratory Virus Infection Surveillance) for influenza-like illness (ILI) in Scotland. Methods: We develop an algorithm based on the weekly case ratio (WCR) of reported ILI cases to generate an alarm for pandemic influenza. From the seasonal influenza data from 13 Scottish health boards, we estimate the joint probability distribution of the country-level WCR and the number of health boards showing synchronous increases in reported influenza cases over the previous week. Pandemic cases are sampled with various case reporting rates from simulated pandemic influenza infections and overlaid with seasonal SERVIS data from 2001 to 2007. Using this combined time series we test our method for speed of detection, sensitivity and specificity. Also, the 2008-09 SERVIS ILI cases are used for testing detection performances of the three methods with a real pandemic data. Results: We compare our method, based on our simulation study, to the moving-average Cumulative Sums (Mov-Avg Cusum) and ILI rate threshold methods and find it to be more sensitive and rapid. For 1% case reporting and detection specificity of 95%, our method is 100% sensitive and has median detection time (MDT) of 4 weeks while the Mov-Avg Cusum and ILI rate threshold methods are, respectively, 97% and 100% sensitive with MDT of 5 weeks. At 99% specificity, our method remains 100% sensitive with MDT of 5 weeks. Although the threshold method maintains its sensitivity of 100% with MDT of 5 weeks, sensitivity of Mov-Avg Cusum declines to 92% with increased MDT of 6 weeks. For a two-fold decrease in the case reporting rate (0.5%) and 99% specificity, the WCR and threshold methods, respectively, have MDT of 5 and 6 weeks with both having sensitivity close to 100% while the Mov-Avg Cusum method can only manage sensitivity of 77% with MDT of 6 weeks. However, the WCR and Mov-Avg Cusum methods outperform the ILI threshold method by 1 week in retrospective detection of the 2009 pandemic in Scotland. Conclusions: While computationally and statistically simple to implement, the WCR algorithm is capable of raising alarms, rapidly and sensitively, for influenza pandemics against a background of seasonal influenza. Although the algorithm was developed using the SERVIS data, it has the capacity to be used at other geographic scales and for different disease systems where buying some early extra time is critical
The line-of-sight distribution of water in the SgrB2 complex
We report the detection, with the Caltech Submillimeter Observatory, of the
894-GHz HDO(111-000) transition, observed in absorption against the background
continuum emission of the SgrB2 cores M and N. Radiative transfer modeling of
this feature, together with the published data set of mm and submm HDO and
H2O-18 transitions, suggests that ground-state absorption features from
deuterated and non-deuterated water trace different gas components along the
line of sight. In particular, while the HDO line seems to be produced by the
large column densities of gas located in the SgrB2 warm envelope, the H2O-18
ground-state transition detected by SWAS and KAO at 548 GHz (Neufeld et al.
2000; Zmuidzinas et al. 1995a) is instead a product of the hot, diffuse, thin
gas layer lying in the foreground of the SgrB2 complex.Comment: Accepted by A&
Formal System Processing of Juveniles: Effects on Delinquency
Justice practitioners have tremendous discretion on how to handle juvenile
offenders. Police officers, district attorneys, juvenile court intake officers, juvenile
and family court judges, and other officials can decide whether the juvenile should
be âofficially processedâ by the juvenile justice system, diverted from the system to a
program, counseling or some other services, or to do nothing at all (release the
juvenile altogether). An important policy question is which strategy leads to the best
outcomes for juveniles. This is an important question in the United States, but many
other nations are concerned with the decision to formally process or divert juvenile
offenders. There have been a number of randomized experiments in the juvenile
courts that have examined the impact of juvenile system processing that should be
gathered together in a systematic fashion to provide rigorous evidence about the
impact of this decision on subsequent offending by juveniles. Our objective is to answer the question: Does juvenile system processing reduce
subsequent delinquency? Based on the evidence presented in this report, juvenile system processing appears
to not have a crime control effect, and across all measures appears to increase
delinquency. This was true across measures of prevalence, incidence, severity, and
self-report. Given the additional financial costs associated with system processing
(especially when compared to doing nothing) and the lack of evidence for any public
safety benefit, jurisdictions should review their policies regarding the handling of
juveniles
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