Stochastic methods for modeling hydrodynamics of dilute gases

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (leaf 18).When modeling small scale sub-micron gas flows, continuum methods, i.e. Navier Stokes equations, no longer apply. Molecular Dynamics (MD) approaches are then more appropriate. For dilute gases, where particles travel in straight lines for the overwhelming majority of the time, MD methods are inefficient compared to kinetic theory approaches because they require the explicit calculation of each particle's trajectory. An effective way to model the hydrodynamics of dilute gases is a stochastic particle method known as Direct Simulation Monte Carlo (DSMC). In DSMC the motion and collision of particles are decoupled to increase computational efficiency. The purpose of this thesis is to evaluate a variant of the DSMC algorithm, in which particles have discrete velocities. The most important modification to the DSMC algorithm is the treatment of collisions between particles with discrete velocities in a way which ensures strict conservation of momentum and energy. To achieve that an algorithm that finds all possible pairs of discrete post-collision velocities given a pair of discrete pre-collision velocities was developed and coded.(cont.) Two important discretization ingredients were introduced: the number of discrete velocities and the maximum discrete velocity allowed. A number of simulations were performed to compare the discrete DSMC (IDSMC) and the regular DSMC method. Our results show that the difference between the two methods is small when the allowed discrete velocity spectrum extends to high speeds. In this case the error is fairly insensitive to the number of discrete velocities used. On the other hand, when the maximum velocity allowed is small compared to the most probably particle speed (approximately equivalent to the speed of sound), large errors are observed (in our case up to 450% in the stress).by Tristan J. Hayeck.S.B

The preparation of some derivatives of choline

Thesis (M.A.)--Boston Universit

Interfacial photochemistry at the ocean surface is a global source of organic vapors and aerosols

The surface of the oceans acts as a global sink and source for trace gases and aerosol particles. Recent studies suggest that photochemical reactions at this air/water interface produce organic vapors, enhancing particle formation in the atmosphere. However, current model calculations neglect this abiotic source of reactive compounds and account only for biological emissions. Here we show that interfacial photochemistry serves as a major abiotic source of volatile organic compounds (VOCs) on a global scale, capable to compete with emissions from marine biology. Our results indicate global emissions of 46.4-184 Tg C yr-1 of organic vapors from the oceans into the marine atmosphere and a potential contribution to organic aerosol mass of more than 60% over the remote ocean. Moreover, we provide global distributions of VOC formation potentials, which can be used as simple tools for field studies to estimate photochemical VOC emissions depending on location and season

Author Correction: Interfacial photochemistry at the ocean surface is a global source of organic vapors and aerosols

[no abstract available

Heterogeneous photochemistry of dicarboxylic acids on mineral dust

SSCI-VIDE+CARE+CEM:CGOInternational audienceDicarboxylic acids have low volatilities and hence are present mostly in the particulate phase, including the surface of dust particles. Mineral dust, globally the mostemitted aerosol, has photocatalytic properties that can initiate photo-induced heterogeneous chemistry of organic compounds, which is still poorly characterized. Weinvestigated the photochemistry offive dicarboxylic acids (DCA) i.e., succinic (butanedioic) acid, glutaric (pentanedioic) acid, adipic (hexanedioic) acid, pimelic(heptanedioic) acid and suberic (octanedioic) acid on Arizona test dust (ATD) particles upon UV-A light irradiation (0–1.4 mW cm−2). Gas-phase products weremonitored by a high-resolution proton-transfer-reaction mass spectrometer (PTR-ToF-MS), and surface sorbed products were extracted and analyzed by ultra-high-performance liquid chromatography coupled to a heated electrospray ionization high-resolution mass spectrometer (UHPLC-HESI-HRMS). Monoacids and aldehydeswere the main observed and quantified gaseous products. In contrast, shorter chain DCA and highly oxygenated products were found at the surface of the dustparticles. Interestingly, the photochemistry of these DCAs presented an even-odd alternation concerning their heterogeneous reactivity, with odd-numbered carbondiacids being more reactive than their even-numbered homologous ones. We present and discuss a reaction mechanism for the C4–C8DCA heterogeneous photo-oxidation catalysed by TiO2/Fe2O3-rich dust particles. Our results suggest that photochemical processing on dust surfaces should be regarded as a possible efficient pathway for altering their surface properties impacting ice nucleation and cloud condensation propertie

Refletindo sobre a violência

O presente artigo trata a questão da violência como uma prática corrente desde a antigüidade, e faz um esboço sobre como o conceito desta é tratado por alguns autores, principalmente após o processo civilizatório do homem, além de ponderar sobre as relações estabelecidas entre violência, classe social e o mito da não-violência

Refletindo sobre a violência

O presente artigo trata a questão da violência como uma prática corrente desde a antigüidade, e faz um esboço sobre como o conceito desta é tratado por alguns autores, principalmente após o processo civilizatório do homem, além de ponderar sobre as relações estabelecidas entre violência, classe social e o mito da não-violência

Real-Time Detection of Gas-Phase Organohalogens from Aqueous Photochemistry Using Orbitrap Mass Spectrometry

SSCI-VIDE+CARE+MRT:CEM:SPR:CGOInternational audienceMarine short-lived halogenated compounds, emitted from algae, phytoplankton, and other marine biota, significantly affect both the troposphere and the stratosphere. Here, we show that such compounds might also be photochemically produced through photosensitized reactions in surface water. Gas-phase products were detected and identified by high-resolution mass spectrometry, more particularly by means of an atmospheric pressure chemical ionization source coupled to an Orbitrap mass spectrometer. Under simulated solar irradiation, halogenated organic compounds were produced and detected in the gas phase when a proxy of dissolved organic matter, i.e., 4-benzoylbenzoic acid, was excited into its triplet state. We present a mechanism explaining the formation of a variety of such halogenated compounds. These photochemical reactions take place at the air/sea interface and are, therefore, a potential source of short-lived halogenated compounds in the atmosphere, participating in the tropospheric halogen cycle

Rastros do traumático: reverberações da violência sexual infantil no sujeito adulto

This article is based on concerns about the impacts of the trauma of sexual violence experienced in childhood and its consequences in adult life. As an object of study, we present the investigation of a letter published in open media access to information whose victim managed, in adult life, to denounce the perpetrator of sexual violence, in which the plot of his report brought the possibility of analyzing the discursive elements aiming at the theoretical elucidation of the notion of trauma through reading the psychoanalytic theory of Freud and Ferenczi. The objective was to expose theoretical constructions about trauma from the psychoanalytic perspective initiated with the study of hysteria carried out by Freud, seeking to understand the traumatic traces of sexual violence in the psychic organization of the subjects, above all, considering the developments and symptomatic manifestations in the life of the adult victim of sexual violence in childhood. In this way, the analysis of the published letter, which gives voice to the subject, is situated as an object for accessing the unconscious supported by the perspective that all research in psychoanalysis is clinical, even if the field is not clinical, as it supports the method of research that promotes access to understanding the impacts of trauma on the psyche. Research in Psychoanalysis made it possible to trace the singularity of the subject that promotes the problematization that is relevant to understanding the social phenomenon of sexual violence and its implications in clinical practice. In this scenario, it proved to be essential to understand the reverberations in adult subjects regarding sexual violence experienced in childhood, placing emphasis on the effects of denial, on the defense mechanisms created unconsciously by the victim to try to deal with the traumatic event, expanding the perspective of analysis for understanding of the subject and his symptoms for the redefinition of the remainder that persists from the trauma, the traces of the traumatic event.Este artigo parte da inquietação sobre os impactos do trauma da violência sexual vivenciada na infância e seus desdobramentos na vida adulta. Como objeto de estudo, apresenta-se a investigação de uma carta publicada em meios abertos de acesso à informação, cuja vítima conseguiu, na vida adulta, denunciar o autor da violência sexual, na qual o enredo de seu relato trouxe a possibilidade da análise dos elementos discursivos, visando à elucidação teórica da noção de trauma pelas leituras nas teorias psicanalíticas de Freud e de Ferenczi. Objetivou-se expor construções teóricas sobre o trauma a partir da perspectiva psicanalítica iniciada com o estudo da histeria feito por Freud, buscando compreender os rastros traumáticos da violência sexual na organização psíquica dos sujeitos, sobretudo considerando os desdobramentos e as manifestações sintomáticas na vida do adulto vítima de violência sexual na infância. Dessa forma, a análise da carta publicada, que dá voz ao sujeito, situa-se como objeto para acesso ao inconsciente amparada pela perspectiva de que toda pesquisa em psicanálise é clínica, mesmo que o campo não seja o clínico, por sustentar o método de pesquisa que promove o acesso à compreensão dos impactos do trauma no psiquismo. A pesquisa em Psicanálise permitiu rastrear a singularidade do sujeito que promove a problematização que interessa à compreensão do fenômeno social da violência sexual e a implicação na prática clínica. Nesse cenário, revelou-se imprescindível compreender as reverberações nos sujeitos adultos sobre a violência sexual vivenciada na infância, dando ênfase aos efeitos do desmentido e aos mecanismos de defesa criados inconscientemente pela vítima para tentar lidar com o traumático, ampliando a perspectiva de análise para o entendimento do sujeito e de seus sintomas para a ressignificação sobre o resto que persiste do trauma, os rastros do traumático