2,805 research outputs found
Objectives of permanent lunar bases
Permanent manned lunar surface and orbiting base
Defining Success: The Politics of Evaluation in Alcohol and Drug Abuse Treatment Programs
Alcohol and drug abuse treatment programs must respond to several important stakeholders or beneficiaries of services who have an investment in how success is defined. Utilizing data from recent statewide studies of treatment outcomes of alcohol and drug abuse services, this paper concludes that a strict adherence to an abstinence-only model of success, rigidly adopted by many in the treatment industry is counterproductive. Multiple measures of success are essential to fully understand and assess a changing model of intervention in the chemical dependency field
Experimental study of the role of physicochemical surface processing on the IN ability of mineral dust particles
During the measurement campaign FROST 2 (FReezing Of duST 2), the Leipzig Aerosol Cloud Interaction Simulator (LACIS) was used to investigate the influence of various surface modifications on the ice nucleating ability of Arizona Test Dust (ATD) particles in the immersion freezing mode. The dust particles were exposed to sulfuric acid vapor, to water vapor with and without the addition of ammonia gas, and heat using a thermodenuder operating at 250 °C. Size selected, quasi monodisperse particles with a mobility diameter of 300 nm were fed into LACIS and droplets grew on these particles such that each droplet contained a single particle. Temperature dependent frozen fractions of these droplets were determined in a temperature range between −40 °C ≤T≤−28 °C. The pure ATD particles nucleated ice over a broad temperature range with their freezing behavior being separated into two freezing branches characterized through different slopes in the frozen fraction vs. temperature curves. Coating the ATD particles with sulfuric acid resulted in the particles' IN potential significantly decreasing in the first freezing branch (T>−35 °C) and a slight increase in the second branch (T≤−35 °C). The addition of water vapor after the sulfuric acid coating caused the disappearance of the first freezing branch and a strong reduction of the IN ability in the second freezing branch. The presence of ammonia gas during water vapor exposure had a negligible effect on the particles' IN ability compared to the effect of water vapor. Heating in the thermodenuder led to a decreased IN ability of the sulfuric acid coated particles for both branches but the additional heat did not or only slightly change the IN ability of the pure ATD and the water vapor exposed sulfuric acid coated particles. In other words, the combination of both sulfuric acid and water vapor being present is a main cause for the ice active surface features of the ATD particles being destroyed. A possible explanation could be the chemical transformation of ice active metal silicates to metal sulfates. The strongly enhanced reaction between sulfuric acid and dust in the presence of water vapor and the resulting significant reductions in IN potential are of importance for atmospheric ice cloud formation. Our findings suggest that the IN concentration can decrease by up to one order of magnitude for the conditions investigated
Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation
During the FROST-2 (FReezing Of duST) measurement campaign conducted at the
Leipzig Aerosol Cloud Interaction Simulator (LACIS), we investigated changes
in the ice nucleation properties of 300 nm Arizona Test Dust mineral
particles following thermochemical processing by varying amounts and
combinations of exposure to sulphuric acid vapour, ammonia gas, water
vapour, and heat. The processed particles' heterogeneous ice nucleation
properties were determined in both the water subsaturated and supersaturated
humidity regimes at −30 °C and −25 °C using Colorado State
University's continuous flow diffusion chamber. The amount of sulphuric acid
coating material was estimated by an aerosol mass spectrometer and from
CCN-derived hygroscopicity measurements. The condensation of sulphuric acid
decreased the dust particles' ice nucleation ability in proportion to the
amount of sulphuric acid added. Heating the coated particles in a
thermodenuder at 250 °C – intended to evaporate the sulphuric acid
coating – reduced their freezing ability even further. We attribute this
behaviour to accelerated acid digestion of ice active surface sites by heat.
Exposing sulphuric acid coated dust to ammonia gas produced particles with
similarly poor freezing potential; however a portion of their ice nucleation
ability could be restored after heating in the thermodenuder. In no case did
any combination of thermochemical treatments increase the ice nucleation
ability of the coated mineral dust particles compared to unprocessed dust.
These first measurements of the effect of identical chemical processing of
dust particles on their ice nucleation ability under both water subsaturated
and mixed-phase supersaturated cloud conditions revealed that ice nucleation
was more sensitive to all coating treatments in the water subsaturated
regime. The results clearly indicate irreversible impairment of ice
nucleation activity in both regimes after condensation of concentrated
sulphuric acid. This implies that the sulphuric acid coating caused
permanent chemical and/or physical modification of the ice active surface
sites; the possible dissolution of the coating during droplet activation did
not restore all immersion/condensation-freezing ability
Physiological modeling of isoprene dynamics in exhaled breath
Human breath contains a myriad of endogenous volatile organic compounds
(VOCs) which are reflective of ongoing metabolic or physiological processes.
While research into the diagnostic potential and general medical relevance of
these trace gases is conducted on a considerable scale, little focus has been
given so far to a sound analysis of the quantitative relationships between
breath levels and the underlying systemic concentrations. This paper is devoted
to a thorough modeling study of the end-tidal breath dynamics associated with
isoprene, which serves as a paradigmatic example for the class of low-soluble,
blood-borne VOCs.
Real-time measurements of exhaled breath under an ergometer challenge reveal
characteristic changes of isoprene output in response to variations in
ventilation and perfusion. Here, a valid compartmental description of these
profiles is developed. By comparison with experimental data it is inferred that
the major part of breath isoprene variability during exercise conditions can be
attributed to an increased fractional perfusion of potential storage and
production sites, leading to higher levels of mixed venous blood concentrations
at the onset of physical activity. In this context, various lines of supportive
evidence for an extrahepatic tissue source of isoprene are presented.
Our model is a first step towards new guidelines for the breath gas analysis
of isoprene and is expected to aid further investigations regarding the
exhalation, storage, transport and biotransformation processes associated with
this important compound.Comment: 14 page
The immersion mode ice nucleation behavior of mineral dusts: A comparison of different pure and surface modified dusts
In this study we present results from immersion freezing experiments with size-segregated mineral dust particles. Besides two already existing data sets for Arizona Test Dust (ATD), and Fluka kaolinite, we show two new data sets for illite-NX, which consists mainly of illite, a clay mineral, and feldspar, a common crustal material. The experiments were carried out with the Leipzig Aerosol Cloud Interaction Simulator. After comparing the different dust samples, it became obvious that the freezing ability was positively correlated with the K-feldspar content. Furthermore, a comparison of the composition of the ATD, illite-NX, and feldspar samples suggests that within the K-feldspars, microcline is more ice nucleation active than orthoclase. A coating with sulfuric acid leads to a decrease in the ice nucleation ability of all mineral dusts, with the effect being more pronounced for the feldspar sample. Key Points The freezing ability of mineral dusts correlated with the K-feldspar contentAmong feldspars, microcline shows a better ice nucleation ability than orthoclaseAfter coating, all investigated dusts feature a similar ice nucleation abilit
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Surface modification of mineral dust particles by sulphuric acid processing: Implications for ice nucleation abilities
The ability of coated mineral dust particles to act as ice nuclei (IN) was investigated at LACIS (Leipzig Aerosol Cloud Interaction Simulator) during the FROST1- and FROST2-campaigns (Freezing of dust). Sulphuric acid was condensed on the particles which afterwards were optionally humidified, treated with ammonia vapour and/or heat. By means of aerosol mass spectrometry we found evidence that processing of mineral dust particles with sulphuric acid leads to surface modifications of the particles. These surface modifications are most likely responsible for the observed reduction of the IN activation of the particles. The observed particle mass spectra suggest that different treatments lead to different chemical reactions on the particle surface. Possible chemical reaction pathways and products are suggested and the implications on the IN efficiency of the treated dust particles are discussed
Opinion: Tropical cirrus – from micro-scale processes to climate-scale impacts
Tropical cirrus clouds, i.e., any type of ice cloud with tops above 400 hPa, play a critical role in the climate system and are a major source of uncertainty in our understanding of global warming. Tropical cirrus clouds involve processes spanning a wide range of spatial and temporal scales, from ice microphysics on cloud scales to mesoscale convective organization and planetary wave dynamics. This complexity makes tropical cirrus clouds notoriously difficult to model and has left many important questions stubbornly unanswered. At the same time, their multi-scale nature makes them well-positioned to benefit from the rise of global, high-resolution simulations of Earth's atmosphere and a growing abundance of remotely sensed and in situ observations. Rapid progress on our understanding of tropical cirrus requires coordinated efforts to take advantage of these modern computational and observational abilities.
In this opinion paper, we review recent progress in cirrus studies, highlight important unanswered questions, and discuss promising paths forward. Significant progress has been made in understanding the life cycle of convectively generated “anvil” cirrus and the response of their macrophysical properties to large-scale controls. On the other hand, much work remains to be done to fully understand how small-scale anvil processes and the climatological anvil radiative effect will respond to global warming. Thin, in situ formed cirrus clouds are now known to be closely tied to the thermal structure and humidity of the tropical tropopause layer, but microphysical uncertainties prevent a full understanding of this link, as well as the precise amount of water vapor entering the stratosphere. Model representation of ice-nucleating particles, water vapor supersaturation, and ice depositional growth continue to pose great challenges to cirrus modeling. We believe that major advances in the understanding of tropical cirrus can be made through a combination of cross-tool synthesis and cross-scale studies conducted by cross-disciplinary research teams.</p
Localized precipitation and runoff on Mars
We use the Mars Regional Atmospheric Modeling System (MRAMS) to simulate lake
storms on Mars, finding that intense localized precipitation will occur for
lake size >=10^3 km^2. Mars has a low-density atmosphere, so deep convection
can be triggered by small amounts of latent heat release. In our reference
simulation, the buoyant plume lifts vapor above condensation level, forming a
20km-high optically-thick cloud. Ice grains grow to 200 microns radius and fall
near (or in) the lake at mean rates up to 1.5 mm/hr water equivalent (maximum
rates up to 6 mm/hr water equivalent). Because atmospheric temperatures outside
the surface layer are always well below 273K, supersaturation and condensation
begin at low altitudes above lakes on Mars. In contrast to Earth lake-effect
storms, lake storms on Mars involve continuous precipitation, and their
vertical velocities and plume heights exceed those of tropical thunderstorms on
Earth. Convection does not reach above the planetary boundary layer for lakes
O(10^2) mbar. Instead, vapor is
advected downwind with little cloud formation. Precipitation occurs as snow,
and the daytime radiative forcing at the land surface due to plume vapor and
storm clouds is too small to melt snow directly (<+10 W/m^2). However, if
orbital conditions are favorable, then the snow may be seasonally unstable to
melting and produce runoff to form channels. We calculate the probability of
melting by running thermal models over all possible orbital conditions and
weighting their outcomes by probabilities given by Laskar et al., 2004. We
determine that for an equatorial vapor source, sunlight 15% fainter than at
present, and snowpack with albedo 0.28 (0.35), melting may occur with 4%(0.1%)
probability. This rises to 56%(12%) if the ancient greenhouse effect was
modestly (6K) greater than today.Comment: Submitted to JGR Planet
Magnetothermal properties of molecule-based materials
We critically review recent results obtained by studying the low-temperature
specific heat of some of the most popular molecular magnets. Perspectives of
this field are discussed as well.Comment: 12 pages text + 14 pages figures, Submitted as "feature article" to
Journal of Materials Chemistr
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