1,284 research outputs found
Modeling chemistry in and above snow at Summit, Greenland – Part 2: Impact of snowpack chemistry on the oxidation capacity of the boundary layer
The chemical composition of the boundary layer in snow covered regions is impacted by chemistry in the snowpack via uptake, processing, and emission of atmospheric trace gases. We use the coupled one-dimensional (1-D) snow chemistry and atmospheric boundary layer model MISTRA-SNOW to study the impact of snowpack chemistry on the oxidation capacity of the boundary layer. The model includes gas phase photochemistry and chemical reactions both in the interstitial air and the atmosphere. While it is acknowledged that the chemistry occurring at ice surfaces may consist of a true quasi-liquid layer and/or a concentrated brine layer, lack of additional knowledge requires that this chemistry be modeled as primarily aqueous chemistry occurring in a liquid-like layer (LLL) on snow grains. The model has been recently compared with BrO and NO data taken on 10 June–13 June 2008 as part of the Greenland Summit Halogen-HOx experiment (GSHOX). In the present study, we use the same focus period to investigate the influence of snowpack derived chemistry on OH and HOx + RO2 in the boundary layer. We compare model results with chemical ionization mass spectrometry (CIMS) measurements of the hydroxyl radical (OH) and of the hydroperoxyl radical (HO2) plus the sum of all organic peroxy radicals (RO2) taken at Summit during summer 2008. Using sensitivity runs we show that snowpack influenced nitrogen cycling and bromine chemistry both increase the oxidation capacity of the boundary layer and that together they increase the midday OH concentrations. Bromine chemistry increases the OH concentration by 10–18 % (10 % at noon LT), while snow sourced NOx increases OH concentrations by 20–50 % (27 % at noon LT). We show for the first time, using a coupled one dimensional snowpack-boundary layer model, that air-snow interactions impact the oxidation capacity of the boundary layer and that it is not possible to match measured OH levels without snowpack NOx and halogen emissions. Model predicted HONO compared with mistchamber measurements suggests there may be an unknown HONO source at Summit. Other model predicted HOx precursors, H2O2 and HCHO, compare well with measurements taken in summer 2000, which had lower levels than other years. Over 3 days, snow sourced NOx contributes an additional 2 ppb to boundary layer ozone production, while snow sourced bromine has the opposite effect and contributes 1 ppb to boundary layer ozone loss
Gas-phase CO depletion and N2H+ abundances in starless cores
Seven isolated, nearby low-mass starless molecular cloud cores have been
observed as part of the Herschel key program Earliest Phases of Star formation
(EPoS). By applying a ray-tracing technique to the obtained continuum emission
and complementary (sub)mm emission maps, we derive the physical structure
(density, dust temperature) of these cloud cores. We present observations of
the 12CO, 13CO, and C18O (2-1) and N2H+ (1-0) transitions towards the same
cores. Based on the density and temperature profiles, we apply time-dependent
chemical and line-radiative transfer modeling and compare the modeled to the
observed molecular emission profiles. CO is frozen onto the grains in the
center of all cores in our sample. The level of CO depletion increases with
hydrogen density and ranges from 46% up to more than 95% in the core centers in
the core centers in the three cores with the highest hydrogen density. The
average hydrogen density at which 50% of CO is frozen onto the grains is
1.1+-0.4 10^5 cm^-3. At about this density, the cores typically have the
highest relative abundance of N2H+. The cores with higher central densities
show depletion of N2H+ at levels of 13% to 55%. The chemical ages for the
individual species are on average 2+-1 10^5 yr for 13CO, 6+-3 10^4 yr for C18O,
and 9+-2 10^4 yr for N2H+. Chemical modeling indirectly suggests that the gas
and dust temperatures decouple in the envelopes and that the dust grains are
not yet significantly coagulated. We observationally confirm chemical models of
CO-freezeout and nitrogen chemistry. We find clear correlations between the
hydrogen density and CO depletion and the emergence of N2H+. The chemical ages
indicate a core lifetime of less than 1 Myr.Comment: 24 pages, 25 figures, Accepted for publication in Astronomy and
Astrophysic
Using Molecules to Measure Nuclear Spin-Dependent Parity Violation
Nuclear spin-dependent parity violation arises from weak interactions between
electrons and nucleons, and from nuclear anapole moments. We outline a method
to measure such effects, using a Stark-interference technique to determine the
mixing between opposite-parity rotational/hyperfine levels of ground-state
molecules. The technique is applicable to nuclei over a wide range of atomic
number, in diatomic species that are theoretically tractable for
interpretation. This should provide data on anapole moments of many nuclei, and
on previously unmeasured neutral weak couplings
Search for the electric dipole moment of the electron with thorium monoxide
The electric dipole moment of the electron (eEDM) is a signature of
CP-violating physics beyond the Standard Model. We describe an ongoing
experiment to measure or set improved limits to the eEDM, using a cold beam of
thorium monoxide (ThO) molecules. The metastable state in ThO
has important advantages for such an experiment. We argue that the statistical
uncertainty of an eEDM measurement could be improved by as much as 3 orders of
magnitude compared to the current experimental limit, in a first-generation
apparatus using a cold ThO beam. We describe our measurements of the state
lifetime and the production of ThO molecules in a beam, which provide crucial
data for the eEDM sensitivity estimate. ThO also has ideal properties for the
rejection of a number of known systematic errors; these properties and their
implications are described.Comment: v2: Equation (11) correcte
Excellent agreement between genetic and hydrogen breath tests for lactase deficiency and the role of extended symptom assessment
Clinical manifestations of lactase (LCT) deficiency include intestinal and extra-intestinal symptoms. Lactose hydrogen breath test (H2-BT) is considered the gold standard to evaluate LCT deficiency (LD). Recently, the single-nucleotide polymorphism C/T−13910 has been associated with LD. The objectives of the present study were to evaluate the agreement between genetic testing of LCT C/T−13910 and lactose H2-BT, and the diagnostic value of extended symptom assessment. Of the 201 patients included in the study, 194 (139 females; mean age 38, range 17-79 years, and 55 males, mean age 38, range 18-68 years) patients with clinical suspicion of LD underwent a 3-4h H2-BT and genetic testing for LCT C/T−13910. Patients rated five intestinal and four extra-intestinal symptoms during the H2-BT and then at home for the following 48h. Declaring H2-BT as the gold standard, the CC−13910 genotype had a sensitivity of 97% and a specificity of 95% with a κ of 0·9 in diagnosing LCT deficiency. Patients with LD had more intense intestinal symptoms 4h following the lactose challenge included in the H2-BT. We found no difference in the intensity of extra-intestinal symptoms between patients with and without LD. Symptom assessment yielded differences for intestinal symptoms abdominal pain, bloating, borborygmi and diarrhoea between 120min and 4h after oral lactose challenge. Extra-intestinal symptoms (dizziness, headache and myalgia) and extension of symptom assessment up to 48h did not consistently show different results. In conclusion, genetic testing has an excellent agreement with the standard lactose H2-BT, and it may replace breath testing for the diagnosis of LD. Extended symptom scores and assessment of extra-intestinal symptoms have limited diagnostic value in the evaluation of L
ESAF: Full Simulation of Space-Based Extensive Air Showers Detectors
Future detection of Extensive Air Showers (EAS) produced by Ultra High Energy
Cosmic Particles (UHECP) by means of space based fluorescence telescopes will
open a new window on the universe and allow cosmic ray and neutrino astronomy
at a level that is virtually impossible for ground based detectors. In this
paper we summarize the results obtained in the context of the EUSO project by
means of a detailed Monte Carlo simulation of all the physical processes
involved in the fluorescence technique, from the Extensive Air Shower
development to the instrument response. Particular emphasis is given to
modeling the light propagation in the atmosphere and the effect of clouds. Main
results on energy threshold and resolution, direction resolution and Xmax
determination are reported. Results are based on EUSO telescope design, but are
also extended to larger and more sensitive detectors.Comment: 38 pages, 48 figures Corrected typos. Changed content. Added figure
Looking into the hearts of Bok globules: MM and submm continuum images of isolated star-forming cores
We present the results of a comprehensive infrared, submillimetre, and
millimetre continuum emission study of isolated low-mass star-forming cores in
32 Bok globules, with the aim to investigate the process of star formation in
these regions. The submillimetre and millimetre dust continuum emission maps
together with the spectral energy distributions are used to model and derive
the physical properties of the star-forming cores, such as luminosities, sizes,
masses, densities, etc. Comparisons with ground-based near-infrared and
space-based mid and far-infrared images from Spitzer are used to reveal the
stellar content of the Bok globules, association of embedded young stellar
objects with the submm dust cores, and the evolutionary stages of the
individual sources. Submm dust continuum emission was detected in 26 out of the
32 globule cores observed. For 18 globules with detected (sub)mm cores we
derive evolutionary stages and physical parameters of the embedded sources. We
identify nine starless cores, most of which are presumably prestellar, nine
Class 0 protostars, and twelve Class I YSOs. Specific source properties like
bolometric temperature, core size, and central densities are discussed as
function of evolutionary stage. We find that at least two thirds (16 out of 24)
of the star-forming globules studied here show evidence of forming multiple
stars on scales between 1,000 and 50,000 AU. However, we also find that most of
these small prototstar and star groups are comprised of sources with different
evolutionary stages, suggesting a picture of slow and sequential star formation
in isolated globulesComment: 60 pages, 28 figures, accepted by The Astrophysical Journal
Supplement Serie
Ecological study of aquatic midges and some related insects with special reference to feeding habits
Die Schweiz ist ein reiches Land. Sie verfügt über viele Millionäre. Der große Reichtum konzentriert sich auf wenige Familien und Personen. In der Schweiz leben aber auch eine halbe Million der Bevölkerung (7,5 Mio.) in Haushalten von Erwerbstätigen, die weniger als das Existenzminimum verdienen. Über 200‘000 Personen sind auf Sozialhilfe angewiesen. Bei den Vermögen und den verfügbaren Einkommen hat sich in den letzten Jahren die Kluft zwischen den obersten und untersten zehn Prozent verschärft. Die Zunahme der sozialen Ungleichheit erhöht die soziale Brisanz, was mehr zu ergründen ist. Die soziale Differenzierung dokumentiert Prozesse der Globalisierung. Sie reproduziert und spezifiziert alte soziale Ungleichheiten. Wichtig ist, dass die Soziale Arbeit das thematisiert und weiter theoretisiert
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