483 research outputs found
A novel model to predict the physical state of atmospheric H2SO4/NH3/H2O aerosol particles
No full textColberg CA, Luo BP, Wernli H, Koop T, Peter T. A novel model to predict the physical state of atmospheric H2SO4/NH3/H2O aerosol particles. ATMOSPHERIC CHEMISTRY AND PHYSICS. 2003;3(4):909-924.The physical state of the tropospheric aerosol is largely unknown despite its importance for cloud formation and for the aerosol's radiative properties. Here we use detailed microphysical laboratory measurements to perform a systematic global modelling study of the physical state of the H2SO4/NH3/H2O aerosol, which constitutes an important class of aerosols in the free troposphere. The Aerosol Physical State Model (APSM) developed here is based on Lagrangian trajectories computed from ECMWF (European Centre for Medium Range Weather Forecasts) analyses, taking full account of the deliquescence/efflorescence hysteresis. As input APSM requires three data sets: (i) deliquescence and efflorescence relative humidities from laboratory measurements, (ii) ammonia-to-sulfate ratios (ASR) calculated by a global circulation model, and (iii) relative humidities determined from the ECMWF analyses. APSM results indicate that globally averaged a significant fraction (17-57%) of the ammoniated sulfate aerosol particles contain solids with the ratio of solid-containing to purely liquid particles increasing with altitude (between 2 and 10 km). In our calculations the most abundant solid is letovicite, (NH4)(3)H(SO4)(2), while there is only little ammonium sulfate, (NH4)(2)SO4. Since ammonium bisulfate, NH4HSO4, does not nucleate homogeneously, it can only form via heterogeneous crystallization. As the ammonia-to-sulfate ratios of the atmospheric H2SO4/NH3/H2O aerosol usually do not correspond to the stoichiometries of known crystalline substances, all solids are expected to occur in mixed-phase aerosol particles. This work highlights the potential importance of letovicite, whose role as cloud condensation nucleus (CCN) and as scatterer of solar radiation remains to be scrutinized
On the importance of high-redshift intergalactic voids
No full textWe investigate the properties of 1D flux 'voids' (connected regions in the flux distribution above the mean-flux level) by comparing hydrodynamical simulations of large cosmological volumes with a set of observed high-resolution spectra at z ∼ 2. After addressing the effects of box size and resolution, we study how the void distribution changes when the most significant cosmological and astrophysical parameters are varied. We find that the void distribution in the flux is in excellent agreement with predictions of the standard Λcold dark matter (ΛCDM) cosmology, which also fits other flux statistics remarkably well. We then model the relation between flux voids and the corresponding 1D gas-density field along the line of sight and make a preliminary attempt to connect the 1D properties of the gas-density field to the 3D dark matter distribution at the same redshift. This provides a framework that allows statistical interpretations of the void population at high redshift using observed quasar spectra, and eventually it will enable linking the void properties of the high-redshift universe with those at lower redshifts, which are better known
Supercooling of single H2SO4/H2O aerosols to 158 K: No evidence for the occurrence of the octrahydrate
No full textKrieger UK, Colberg CA, Weers U, Koop T, Peter T. Supercooling of single H2SO4/H2O aerosols to 158 K: No evidence for the occurrence of the octrahydrate. GEOPHYSICAL RESEARCH LETTERS. 2000;27(14):2097-2100.Polar stratospheric clouds (PSCs) are important for the chemical activation of chlorine compounds and subsequent ozone depletion. However, how solid PSCs form is still subject to controversial discussion. Recently, the octahydrate of sulfuric acid (H2SO4. 8H(2)O) has been proposed as a solid phase for PSC particles. In our experiment single H2SO4/H2O aerosols levitated in an electrodynamic balance are cooled to 158 K along the ice-liquid equilibrium line. This coexistence curve has been measured for the first time in the temperature interval between 200 K and 158 K. Three independent methods are used for measuring the H2SO4 concentration of the aerosol. No phase transition is observed over a time period of 24 hours and longer at these or higher temperatures. There is no indication for the occurrence of the octahydrate in our experiments. Since the product of experimental volume and suspension time is equal to that of stratospheric droplets over an entire winter, the homogeneous formation of the octahydrate at quasi-thermodynamic equilibrium can be practically excluded
Dissertatio Politico Juridica, De Majestate Laesa
No full textGreifswald, Univ., Jur. Diss., 1703Qvam ... Præside Dn. Henn. Christoph. Gerdesio, J. U. L. & Profess. Ordinario, ... in Auditorio Majori ad Diem VII. Junii, Anno M D CCIII. horis consuetis Modesto Eruditorum Examini & publicæ ventilationi submittit Martinus Bernhardi, Colberg. Pom. Author & RespondensAutopsie nach Ex. der ULB Sachsen-AnhaltVorlageform des Erscheinungsvermerks: Gryphiswaldiæ, Typis Danielis Benjaminis Starckii, Reg. Academ. Typogr
Relationships between plant communities and soil carbon in the prairie ecozone of Saskatchewan
No full textAccumulation of CO2 in the atmosphere has triggered research on topics related to causes, effects, and solutions to potential problems associated with global warming. The present research was conducted to determine if grassland plant communities can be managed to promote sequestration of carbon in the soil, potentially mitigating the effects of increasing atmospheric CO2. The effects of shrub invasion or heavy livestock grazing on peak standing crop of phytomass, root mass and soil organic carbon content were therefore studied. These studies were complimented by a study of the decomposition rates of leaves and roots of snowberry and grasses. The effects of snowberry encroachment on peak standing crop of aboveground phytomass, and soil organic carbon content (SOC) were also studied. Total aboveground phytomass in the snowberry community was more than triple that of the ecotone and was 6-times greater than that of the grassland community. Similarly, the mass of large roots was greatest in the snowberry community (1.2 kg m-2, SE= 0.19), intermediate in the ecotone (0.5 kg m-2, SE= 0.08), and least in the grassland (0.1 kg m-2, SE= 0.04). Conversely, the mass of fine and medium roots was not different (P>0.05) among the three communities, averaging 0.7 kg m-2 in all communities (SE= 0.03, 0.07, 0.49 in snowberry, ecotone and grassland, respectively). Greater aboveground phytomass did not correspond with greater SOC in the snowberry community. Soil organic carbon in the upper 50 cm averaged 8.3 (SE= 0.7), 7.9 (SE= 1.0), and 7.9 (SE= 0.7) kg m-2 in snowberry, ecotone, and grassland communities, respectively. Peak standing crop of aboveground phytomass averaged 157 g m-2 (SE= 27) and 488 g m-2 (SE= 48) in grazed and ungrazed grassland, respectively. Conversely, grazing had no affect on root mass. The mass of fine roots averaged 0.9 kg m-2 (SE= 0.04) and 0.8 kg m-2 (SE= 0.06) in grazed and ungrazed grassland, respectively, while that of medium roots averaged 0.6 kg m-2 (SE= 0.07) in both grazing treatments. Total SOC in the upper 50 cm of soil was not affected (P>0.05) by livestock grazing, averaging 5.5 kg m-2 (SE= 0.7) in grazed and 6.8 kg m-2 (SE= 0.9) in ungrazed grassland. Livestock grazing also had no effect (P>0.05) on SOC at the 0-3, 3-10, 10-20, 20-30, and 30-40 cm depths. The SOC in fine- and coarse-textured soils averaged 7.6 kg m-2 (SE= 0.8) and 5.1 kg m-2 (SE=0.7), respectively. Differences existed between decomposition of roots and leaves for graminoids and snowberry. On a monthly basis decomposition was 0.6 to 0.8 % greater in leaves than roots. The decomposition of roots and leaves ranged from 2.2 to 5.0 % month-1. Decay rate constants for leaves ranged from 0.45 yr-1 (SE= 0.03) to 0.71 yr-1 (SE= 0.02) while those of roots ranged from 0.34 yr-1 (SE= 0.03) to 0.47 yr-1 (SE= 0.04). The decomposition of roots and leaves did not correspond with macroclimatic or regional climate data nor with initial C:N content of the plant material. In summary, invasion of snowberry into grassland does not appear to conflict with goals related to maintenance of SOC in Mixed Prairie. Current grazing management regimes also appear to be consistent with goals related to maintenance of existing SOC. Soil texture had a greater effect on SOC than management of the plant community. Decomposition of leaves and roots appeared to be controlled by many interacting factors such as plant organ type, collection year, study year (climate) and physical and/or chemical characteristics of the site
684 TITRATION OF INTRANASAL FENTANYL SPRAY (INFS) FOR BREAKTHROUGH PAIN IN CANCER PATIENTS: EVIDENCE FOR DOSE PROPORTIONALITY VS BACKGROUND ANALGESIA
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