79 research outputs found
Nitrate Photochemistry and Interrelated Chemical Phenomena in Ice
No full textThe detailed photochemistry of nitrate ions trapped within polycrystalline ice has been investigated. Using a variety of experimental techniques, the photolysis of NO3- within ice is shown to produce NO, HONO, NO2- and NO2 as stable and metastable products. The gaseous products are released to the overlying gas phase. Implications of these results for chemical transformations in polar regions are discussed.
The isotopic composition of nitrate in polar ice cores exhibits mass-independent fractionation (?????~ 25 ‰). However, in this study it is shown that nitrate photolysis is a mass-dependent process and that nitrate can be a conservative tracer for past atmospheric conditions.
Photolysis of NO3- produces nitrite ion within ice and the rate of photolysis increases with increasing temperature. A linear Arrhenius temperature dependence for the measured quantum yield, , was found both above and below the normal melting point of water ice. These results indicate that nitrate photochemistry occurs primarily in the quasi-liquid layer (QLL), which is a disordered layer of ice that has chemical properties closer to water than solid crystalline ice.
The photochemical production of gas-phase NO and NO2 from ice-phase nitrate was determined in real-time using laser-induced fluorescence, two-photon laser-induced fluorescence, and chemiluminescence. These results showed that NO and NO2, which was produced at lower temperatures is released in much larger quantities at ?7 ± 2 oC from subsurface regions of the QLL or at the ice/vapor interface. These results highlight the importance of the QLL and sub-eutectic sub-surface solutions at grain boundaries in polycrystalline ice. In addition, it was shown that the total amount of NO2 that is photodesorbed scales nonlinearly with [NO3?]o or the heating rate. Evidence for extensive chemical and photochemical losses of NO2 before release into the gas-phase is presented. In the case of NO, photo-induced desportion occured at ~ ?20 oC, which suggests a preferential retention of NO2 over NO in the nanoporous water channels of the QLL domains.
The impact of the specific nature of the chemical solutes in water on the nominal pH of the QLL was explored using the temperature dependence of 19F-NMR chemical shifts of 3-fluorobenzoic acid. The 19F-NMR measurements during the freezing of NaCl, NaNO2 and KNO3 solutions indicated that the QLL domains within the polycrystalline ice were shifted to higher pH values, while the freezing of NH4OH or Na2SO4 solutions produced QLL domains that showed a drop in pH (i.e., protons were released from the ice-phase to the QLL). These results help explain the release of HONO which is formed by protonation of NO2- within the QLL domains and are relevant to the observed release of nitrous acid to the atmospheric boundary layer in the Arctic and Antarctic.</p
Educação física escolar e literatura: uma possibilidade de ensinar e aprender boxe no ensino médio
No full textThe following research aimed to understand how cultural artifacts - specifically literature - relate to the didactic and pedagogical issues of teaching and learning physical education in school and having as methodological aspect the strategy of content analysis, taking into account the information present in the text. and the respective contexts in which they were included, having as object of study the work "Knockout - Five Boxing Stories" by the American author Jack London. It was found, cut, and analyzed some excerpts of the work in which body boxing practice appeared, having its foundations and concepts detailed and that through these would be possible to teach and learn this sport in the classroom, as well as its cultural influences in relation to women. in sport, how the female gender was treated in relation to this theme and how it has advanced over time in Brazil, as well as the relations of immigrants in sport and how this dynamic is present today and reverberate in other sports, such as France and its nineteen immigrant athletes attending the 2018 World Cup title held in Russia. After applying lessons with reflections on the tale, practical experimentation of the sport and playing the combat that occurred in the book, as well as student testimonials about the experience of using a narrative literature in Physical Education, we could conclude that it is possible to use this tool for teaching certain content, and the attribution of meaning in the practice occurs through the development and relationship in teaching practice.CNPqA seguinte pesquisa objetivou compreender como os artefatos culturais - em específico a literatura - se relaciona com as questões didáticas e pedagógicas do ensinar e aprender educação física na escola e tendo como aspecto metodológico a estratégia da análise de conteúdo, se atendo às informações presentes no texto e aos respectivos contextos nos quais estavam incluídas, tendo como objeto de estudo a obra “Nocaute - Cinco histórias de boxe” do autor estadunidense Jack London. Foram encontrados, recortados, e analisados alguns trechos da obra em que a prática corporal boxe aparecia, tendo seus fundamentos e conceitos detalhados e que através destes seria possível ensinar e aprender esse esporte em sala de aula, bem como suas influências culturais em relação a mulher no esporte, como o sexo feminino era tratado em relação a essa temática e como avançou no decorrer dos tempos no Brasil, assim como também as relações de imigrantes no esporte e como essa dinâmica se apresenta nos dias atuais e reverberam em outros esportes, como o caso da França e seus dezenove atletas imigrantes presentes no título da Copa do Mundo de 2018 realizada na Rússia. Após aplicação de aulas com reflexões sobre o conto, experimentação prática da modalidade esportiva e encenação do combate ocorrido no livro, bem como depoimentos dos alunos sobre a experiência de usar uma literatura narrativa na Educação Física, pudemos chegar a conclusão que é possível utilizar essa ferramenta para ensino de determinados conteúdos, e a atribuição de sentido na prática se dá através do desenvolvimento e relacionamento na prática docente
Nitrate photolysis in ice and snow: A critical review of its multiphase chemistry
No full text18 pages, 15 figures, 2 tablesNitrate, a member of the oxidized nitrogen family (NOy), is one of the primary species involved in the nitrogen cycle and thus plays a key role in ecosystem processes, globally. It exists as nitrate salts and as nitric acid (HNO3) in both aerosols and the gas phase. It is formed from the NO3 radical/N2O5 or directly from the oxidation of NO2 and is lost by photolysis, OH oxidation, and deposition. In regions covered with snow/ice it has a significant impact on air quality, atmospheric oxidizing capacity, greenhouse gas concentrations, and paleoclimate/isotopic data. Snow/ice environments can, at seasonal maximum, comprise ∼30% of Earth's surface area while 10% is covered with ice/snow found at the polar cryosphere. Nitrate makes up 75–100% of the nitrogen budget deposited from the atmosphere and measured at the Arctic and Antarctica. Its concentrations in Greenland ice have risen by a factor of 2–3, reflecting the long-ranged transport of increased anthropogenic NOx (NO + NO2) emissions.
The polar cryosphere is an active medium for the movement of traces gases, such as nitrate, between the snowpack/sea-ice and overlying atmosphere. Field, laboratory, and modeling efforts have quantitatively shown that the exchange of trace species between the snowpack and the air above is governed by photochemistry in combination with air moving gases between these two matrices. Polar tropospheric chemistry and dynamics immensely impact processes governing chemical composition, isotopic signatures, oxidizing capacity, and thus regional climate. This study presents a comprehensive review of laboratory and modeling efforts – contextualized by field measurements – that have elucidated physicochemical processes governing nitrate photochemistry and its impact on the polar snowpack. Specifically, after an Introduction to nitrate photochemistry in ice, we discuss the: 1) initial Arctic field measurements that sparked interest in ice photolysis in the polar regions; 2) suite of follow-up field studies that catalyzed laboratory and snow-chamber investigations that gave deeper understanding of the effects of snow/ice – air trace gas exchange due to nitrate photochemistry; 3) complementary laboratory, snow-chamber investigations; and 4) a detailed review of recent nitrate ice photolysis laboratory experiments and the potential impact of utilizing laboratory and computational models to study the role of nitrate in the nitrogen cycle.Peer reviewe
Le risque d'effraction psychique par le contre-transfert en thérapie : à propos du cas d'une adolescente psychotique dans le cadre d'un dispositif boxe-peinture
No full textNational audienceThis article explores the risk of psychic break-in by countertransference in psychotherapy, exploration based on the case of a psychotic adolescent who was admitted in a psychotherapeutic apparatus combining boxing and painting. The author sets out his theoretical framework, referring the notion of break-in to the concept of “skin-ego” described by Didier Anzieu. He then presents the therapeutic apparatus, in which the patient composes with his internal world, in order to prepare the creative movements. The presentation of Eloïse's case provides an opportunity to examine a number of the clinician's body reactions to these movements, reactions that can be experienced as a beak-in in this sensitive and important process in the case of psychotic subjects.Cet article explore le risque d’effraction psychique par le contre-transfert en psychothérapie, à partir du cas d’une adolescente psychotique accueillie dans un dispositif associant boxe et peinture. L’auteur précise son cadrage théorique, en rapprochant la notion d’effraction de celle de « moi-peau » décrite par Didier Anzieu. Il présente ensuite le dispositif thérapeutique, au cours duquel le patient compose avec son monde interne afin de préparer les mouvements créateurs. L’exposé du cas d’Eloïse permet d’interroger plusieurs réactions psychocorporelles du clinicien accompagnant ces mouvements, réactions qui peuvent être vécues comme une effraction dans ce processus sensible et important dans le cas de sujets psychotiques
A mechanism for biologically induced iodine emissions from sea ice
No full text© Author(s) 2015. Ground- and satellite-based measurements have reported high concentrations of iodine monoxide (IO) in coastal Antarctica. The sources of such a large iodine burden in the coastal Antarctic atmosphere remain unknown. We propose a mechanism for iodine release from sea ice based on the premise that micro-algae are the primary source of iodine emissions in this environment. The emissions are triggered by the biological production of iodide (I-) and hypoiodous acid (HOI) from micro-algae (contained within and underneath sea ice) and their diffusion through sea-ice brine channels, ultimately accumulating in a thin brine layer (BL) on the surface of sea ice. Prior to reaching the BL, the diffusion timescale of iodine within sea ice is depth-dependent. The BL is also a vital component of the proposed mechanism as it enhances the chemical kinetics of iodine-related reactions, which allows for the efficient release of iodine to the polar boundary layer. We suggest that iodine is released to the atmosphere via three possible pathways: (1) emitted from the BL and then transported throughout snow atop sea ice, from where it is released to the atmosphere; (2) released directly from the BL to the atmosphere in regions of sea ice that are not covered with snowpack; or (3) emitted to the atmosphere directly through fractures in the sea-ice pack. To investigate the proposed biology-ice-atmosphere coupling at coastal Antarctica we use a multiphase model that incorporates the transport of iodine species, via diffusion, at variable depths, within brine channels of sea ice. Model simulations were conducted to interpret observations of elevated springtime IO in the coastal Antarctic, around the Weddell Sea. While a lack of experimental and observational data adds uncertainty to the model predictions, the results nevertheless show that the levels of inorganic iodine (i.e. I2, IBr, ICl) released from sea ice through this mechanism could account for the observed IO concentrations during this timeframe. The model results also indicate that iodine may trigger the catalytic release of bromine from sea ice through phase equilibration of IBr. Considering the extent of sea ice around the Antarctic continent, we suggest that the resulting high levels of iodine may have widespread impacts on catalytic ozone destruction and aerosol formation in the Antarctic lower troposphere.Peer Reviewe
Creating a Cinema of Boxing in Day of the Fight (Stanley Kubrick, 1951)
No full textLe premier film de Stanley Kubrick est un film de boxe. Il s’agit de Day of the Fight, un court métrage documentaire de 1951 sur le boxeur et acteur irlando-américain William Walter Cartier. Auparavant photographe chez Look Magazine (1945-1950), Stanley Kubrick développe dans le film son style esquissé dans un reportage journalistique pour lequel il a pris plus de 1 200 photos de Walter Cartier. Ce film de boxe contribue alors à la construction de son statut d’auteur et Day of the Fight donne le coup d’envoi à son esthétique singulière de la violence. Œuvre de transition entre deux formes d’art, la photographie et le cinéma, le film de boxe permet le déploiement de la fascination de Stanley Kubrick pour la confrontation physique. Le jeune réalisateur influencé par le film noir exploite la nature transgressive du sport présente dès les débuts du cinéma. Au-delà de la supposée violence de la boxe, Day of the Fight capture l’intimité du boxeur grâce à un regard homoérotique anticonformiste.Stanley Kubrick's first movie is a boxing film. It is Day of the Fight, a 1951 short documentary on the Irish-American boxer and actor William Walter Cartier. Previously a photographer for Look Magazine (1945-1950), Stanley Kubrick develops in the film his cinematographic style sketched in a photojournalistic report for which he took more than 1200 photographs of William Walter Cartier. This boxing film contributes to the construction of his status as an author and Day of the Fight kicks off his singular aesthetic of violence. As a transitional work between two art forms, photography and cinema, the boxing film allows the unfolding of Stanley Kubrick's fascination for physical confrontation. The young director, inspired by film noir, exploits the transgressive nature of the sport, which has been present since the beginnings of cinema. Beyond the supposed violence of boxing, Day of the Fight captures the male body and the intimacy of the boxer through a non-conformist homoerotic gaze
Monotonic Increase of Nitrite Yields in the Photolysis of Nitrate in Ice and Water between 238 and 294 K
No full textThe quantum yield, φ, of nitrite formation in the 302 nm band photolysis of fluid or frozen aqueous nitrate solutions increases monotonically with temperature over the range 238−294 K. The presence of formate increases φ 5-fold but does not modify its temperature dependence. Considering that the detection of nitrite as a product is only possible after the initial photofragments (NO_2^- + O) escape the solvent cage and that the diffusivity of ice, D_(ice), is about 6 orders of magnitude smaller than that of supercooled water, D_(aq), at the same temperature, we infer that nitrate photodecomposition takes place in similar liquidlike media at all temperatures. We found that the nitrite dispersed into the bulk is subsequently degraded by OH radicals, another primary photoproduct that can be scavenged by formate. The fact that experimental φ values in ice are actually larger than those derived from linear φ vs D_(aq)T^(1/2) extrapolation of aqueous phase data, as expected for cage processes in homogeneous media, suggests that the photochemically relevant properties of the quasi-liquid layer covering ice below the normal melting point resemble those of bulk supercooled water, but other effects, such as the dissipation of excess photon energy into the medium, may also play a role
An Inexpensive, Widely Available Material for 4 wt % Reversible Hydrogen Storage Near Room Temperature
No full textInterpretation of Aura satellite observations of CO and aerosol index related to the December 2006 Australia fires
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