Influence of the ice growth rate on the incorporation of gaseous HCl

International audienceIce crystals were grown in the laboratory at -15°C, at different growth rates and in the presence of a partial pressure of HCl of 1.63×10-3 Pa, to test whether the ice growth rate influences the amount of HCl taken up, XHCl, as predicted by the ice growth mechanism of Domine and Thibert (1996). The plot of HCl concentration in ice as a function of growth rate has the aspect predicted by that mechanism: XHCl decreases with increasing growth rate, from a value that depends on thermodynamic equilibrium to a value that depends only on kinetic factors. The height of the growth steps of the ice crystals is determined to be about 1.5 nm from these experiments. We discuss that the application of these laboratory experiments to cloud ice crystals and to snow metamorphism is not quantitatively possible at this stage, because the physical variables that determine crystal growth in nature, and in particular the step height, are not known. Qualitative applications are attempted for HCl and HNO3 incorporation in cloud ice and snowpack crystals

Impact of water vapor diffusion and latent heat on the effective thermal conductivity of snow

Heat transport in snowpacks is understood to occur through the two processes of heat conduction and latent heat transport carried by water vapor, which are generally treated as decoupled from one another. This paper investigates the coupling between both these processes in snow, with an emphasis on the impacts of the kinetics of the sublimation and deposition of water vapor onto ice. In the case when kinetics is fast, latent heat exchanges at ice surfaces modify their temperature and therefore the thermal gradient within ice crystals and the heat conduction through the entire microstructure. Furthermore, in this case, the effective thermal conductivity of snow can be expressed by a purely conductive term complemented by a term directly proportional to the effective diffusion coefficient of water vapor in snow, which illustrates the inextricable coupling between heat conduction and water vapor transport. Numerical simulations on measured three-dimensional snow microstructures reveal that the effective thermal conductivity of snow can be significantly larger, by up to about 50 % for low-density snow, than if water vapor transport is neglected. A comparison of our numerical simulations with literature data suggests that the fast kinetics hypothesis could be a reasonable assumption for modeling heat and mass transport in snow. Lastly, we demonstrate that under the fast kinetics hypothesis the effective diffusion coefficient of water vapor is related to the effective thermal conductivity by a simple linear relationship. Under such a condition, the effective diffusion coefficient of water vapor is expected to lie in the narrow 100 % to about 80 % range of the value of the diffusion coefficient of water vapor in air for most seasonal snows. This may greatly facilitate the parameterization of water vapor diffusion of snow in models.</p

Three examples where the specific surface area of snow increased over time

Snow on the ground impacts climate through its high albedo and affects atmospheric composition through its ability to adsorb chemical compounds. The quantification of these effects requires the knowledge of the specific surface area (SSA) of snow and its rate of change. All relevant studies indicate that snow SSA decreases over time. Here, we report for the first time three cases where the SSA of snow increased over time. These are (1) the transformation of a melt-freeze crust into depth hoar, producing an increase in SSA from 3.4 to 8.8m2 kg−1. (2) The mobilization of surface snow by wind, which reduced the size of snow crystals by sublimation and fragmented them. This formed a surface snow layer with a SSA of 61m2 kg−1 from layers whose SSAs were originally 42 and 50m2 kg−1. (3) The sieving of blowing snow by a snow layer, which allowed the smallest crystals to penetrate into open spaces in the snow, leading to an SSA increase from 32 to 61m2 kg−1. We discuss that other mechanisms for SSA increase are possible. Overall, SSA increases are probably not rare. They lead to enhanced uptake of chemical compounds and to increases in snow albedo, and their inclusion in relevant chemical and climate models deserves consideration

Influence of the ice growth rate on the incorporation of gaseous HCl

Ice crystals were grown in the laboratory at &minus;15&deg;C, at different growth rates and in the presence of a partial pressure of HCl of 1.63&times;10-3 Pa, to test whether the ice growth rate influences the amount of HCl taken up, XHCl, as predicted by the ice growth mechanism of Domine and Thibert (1996). The plot of HCl concentration in ice as a function of growth rate has the aspect predicted by that mechanism: XHCl decreases with increasing growth rate, from a value that depends on thermodynamic equilibrium to a value that depends only on kinetic factors. The height of the growth steps of the ice crystals is determined to be about 150 nm from these experiments. We discuss that the application of these laboratory experiments to cloud ice crystals and to snow metamorphism is not quantitatively possible at this stage, because the physical variables that determine crystal growth in nature, and in particular the step height, are not known. Qualitative applications are attempted for HCl and HNO3 incorporation in cloud ice and snowpack crystals

New Shortwave Infrared Albedo Measurements for Snow Specific Surface Area Retrieval

Snow grain-size characterization, its vertical and temporal evolution is a key parameter for the improvement and validation of snow and radiative transfer models (optical and microwave) as well as for remote-sensing retrieval methods. We describe two optical methods, one active and one passive shortwave infrared, for field determination of the specific surface area (SSA) of snow grains. We present a new shortwave infrared (SWIR) camera approach. This new method is compared with a SWIR laser- based system measuring snow albedo with an integrating sphere (InfraRed Integrating Sphere (IRIS)). Good accuracy (10%) and reproducibility in SSA measurements are obtained using the IRIS system on snow samples having densities greater than 200 kg m-3, validated against X-ray microtomography measurements. The SWIRcam approach shows improved sensitivity to snow SSA when compared to a near-infrared camera, giving a better contrast of the snow stratigraphy in a snow pit

USO DO DUBLIN CORE NA DESCRIÇÃO DE OBRAS RARAS NA WEB: \ud A COLEÇÃO DA BIBLIOTECA BRASILIANA DIGITAL

Acessível ao público desde junho de 2009, a Biblioteca Brasiliana Digital, da Universidade de \ud São Paulo tem por objetivo facultar para a pesquisa, a maior Brasiliana custodiada por uma \ud universidade. Sua intenção é disponibilizar virtualmente parte do acervo da Universidade \ud oferecendo-se como um instrumento útil e funcional para a pesquisa e o estudo dos temas e \ud cultura brasileiros, além de oferecer um modelo tecnológico de gestão que possa ser difundido \ud a outras coleções, acervos e instituições. Este trabalho apresenta os resultado da implantação \ud de um esquema de metadados baseado no formato Dublin Core, para a descrição de obras \ud raras e especiais na web. Especificamente, apresenta os procedimentos e processos de \ud descrição de conteúdos das diversas tipologias documentais (livros, periódicos, gravuras etc.) \ud e formatos digitais (pdf, jpeg entre outros). \ud Palavras-Chave: Bibliotecas digitais; Metadados; Dublin Core.Available for the public access since June 2009, the University of Sao Paulo Brasiliana \ud Digital Library, aims to provide to the research the largest Brasiliana guarded by an \ud University. The purpose is make available online part of the University Collection, as an \ud useful and functional instrument to the research and study of Brazilian themes and culture, \ud and also offer a technological management model able to be disseminated to other collections \ud and institutions. This work shows the results of the implantation of a metadata schema based \ud on Dublin Core format, for the description of rare and special works on the \ud web. Specifically, it shows the content description procedures and processes of several \ud documents typologies (books, journals, images etc) and digital formats (pdf, jpeg and others). \ud Keywords: Digital Libraries, Metadata, Dublin Core

CoSyR: a novel beam dynamics code for the modeling of synchrotron radiation effects

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamic code is developed based on a Lagrangian method for the calculation of the particles' radiation near-fields using wavefront/wavelet meshes via the Green's function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in the simulation at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed.Comment: 17 pages, 14 figure

Surprisingly small HONO emissions from snow surfaces at Browning Pass, Antarctica

Measured Fluxes of nitrous acid at Browning Pass, Antarctica were very low, despite conditions that are generally understood as favorable for HONO emissions, including: acidic snow surfaces, an abundance of NO₃^- anions in the snow surface, and abundant UV light for NO₃^- photolysis. Photochemical modeling suggests noon time HONO fluxes of 5&ndash;10 nmol m^-2 h^-1; the measured fluxes, however, were close to zero throughout the campaign. The location and state of NO₃^- in snow is crucial to its reactivity. The analysis of soluble mineral ions in snow reveals that the NO₃^- ion is probably present in aged snows as NaNO₃. This is peculiar to our study site, and we suggest that this may affect the photochemical reactivity of NO₃^-, by preventing the release of products, or providing a reactive medium for newly formed HONO. In fresh snow, the NO₃^- ion is probably present as dissolved or adsorbed HNO₃ and yet, no HONO emissions were observed. We speculate that HONO formation from NO₃^- photolysis may involve electron transfer reactions of NO₂ from photosensitized organics and that fresh snows at our site had insufficient concentrations of adequate organic compounds to favor this reaction

973MO KEYNOTE-189 5-year update: First-line pembrolizumab (pembro) + pemetrexed (pem) and platinum vs placebo (pbo) + pem and platinum for metastatic nonsquamous NSCLC

Background: Pembro + pem-platinum significantly improved survival vs pbo + pem-platinum in patients (pts) with previously untreated, metastatic nonsquamous NSCLC without sensitizing EGFR/ALK alterations, regardless of PD-L1 TPS, in the phase III KEYNOTE-189 study (NCT02578680). We report updated results with ∼5 y of follow-up. Methods: Pts were randomized 2:1 to receive pembro 200 mg or pbo Q3W for up to 35 cycles (2y). All pts also received pem and investigator’s choice of carboplatin/cisplatin for 4 cycles, followed by maintenance pem until PD/unacceptable toxicity. Crossover from the pbo + pem-platinum group to pembro monotherapy was permitted after PD. Primary endpoints were OS and PFS. Results: Among 616 pts randomized (pembro + pem-platinum, n = 410; pbo + pem-platinum, n = 206), median time from randomization to data cutoff (Mar 8, 2022) was 64.6 (range, 60.1–72.4) mo. 116/202 (57.4%) treated pts crossed over from pbo + pem-platinum to anti–PD-(L)1 therapy during/outside the study. Median (95% CI) OS was 22.0 (19.5‒24.5) mo vs 10.6 (8.7‒13.6) mo with pembro + pem-platinum vs pbo + pem-platinum (HR, 0.60; 95% CI, 0.50‒0.72) and 5-y OS rates were 19.4% vs 11.3%, respectively. Median (95% CI) PFS was 9.0 (8.1‒10.4) mo vs 4.9 (4.7‒5.5) mo (HR, 0.50; 95% CI, 0.42‒0.60). Additional efficacy results are in the table. Among pts with ≥1 dose of assigned treatment, grade 3‒5 AEs occurred in 295/405 (72.8%) vs 136/202 (67.3%) of pts. Among 57 pts who completed 35 cycles of pembro, ORR was 86.0% (CR, n = 8; PR, n = 41); 3-y OS rate after completion of 35 cycles of pembro was 71.9%. Conclusions: First-line pembro + pem-platinum continued to show OS and PFS benefits with manageable toxicity vs pbo + pem-platinum, irrespective of PD-L1 expression. Pts who completed 35 cycles of pembro experienced durable responses. These data further support pembro + pem-platinum as a standard of care for metastatic nonsquamous NSCLC without sensitizing EGFR/ALK alterations