7,544 research outputs found
Deep anisotropic dry etching of silicon microstructures by high-density plasmas
No full textThis thesis deals with the dry etching of deep anisotropic microstructures in monocrystalline silicon by high-density plasmas. High aspect ratio trenches are necessary in the fabrication of sensitive inertial devices such as accellerometers and gyroscopes. The etching of silicon in fluorine-based plasmas is isotropic. To obtain anisotropy the addition of sidewall passivation is necessary. This is achieved with both oxygen passivation at low temperatures and fluorocarbon passivation at room temperature. A quantitative approach was pursued to explain the etching mechanism. The etch results were analysed using the measured plasma species fluxes and the surface composition. Moreover, the transport of the plasma species in narrow anisotropic structures is a fundamental factor determining the etch rate and the profile evolution. The experimental methods such as the etching equipment, plasma diagnostics, surface analysis and sample preparation are described in chapter 2. Three etching processes were investigated: the cryogenic etching process with oxygen passivation at low temperatures, the Bosch process with fluorocarbon passivation at room temperature and the novel triple pulse process that was developed in our laboratory. The polymer deposition mechanism and the characteristic role of the ions are also explained. The cryogenic etching process is discussed in chapter 3. Fluorine radicals, oxygen radicals and ion bombardment are responsible for the three main sub-processes, that is, etching, sidewall passivation and depassivation of the trench bottom, respectively. Etching experiments with an extremely low ion-to-radical flux ratio were used to reveal the etching mechanism. Crystal orientation dependent etching leading to Si(111) crystal facets is observed in a surface kinetics controlled regime. By varying the plasma conditions it is possible to adjust the etching mechanism from fluorine-limited to ion-limited. Controlled etching is obtained because the etching is tuned from aspect ratio dependent in the fluorine-limited domain to aspect ratio independent in the ion-limited domain. The transport of radicals in high aspect ratio trenches is an important limiting factor and was investigated with special structures. The etch results are described by an analytic model that is based on the surface site balance of fluorine and oxygen radicals. The results are further explained with a Monte Carlo simulation model. The Bosch process is clarified in chapter 4. The anisotropy of the etched structures is controlled by balancing the etching and passivation pulse. However, the maximal obtainable aspect ratio is limited by convergence of the trench sidewalls due to excessive passivation. The maximal obtainable aspect ratio increases if the ion-to-radical flux ratio increases. The transport of ions is an important limiting factor in the depassivation of the bottom of the trench. Divergence of the ion beam leads to a reduction of the ion flux, so that the fluorocarbon passivation is insufficiently removed near the base of the sidewalls. The average ion angle was measured and correlated to the maximal obtainable aspect ratio. The Bosch process was improved at the depassivation side with the triple pulse process and at the passivation side with preferential sidewall deposition. The triple pulse process that is described in chapter 5 has the aim to improve the depassivation in deep trenches. The three main sub-processes are decoupled using a separate depassivation pulse directly after the etching and passivation pulses. The fluorocarbon passivation is efficiently removed with low-pressure, high-density, oxygen-based plasmas. The investigated plasma chemistries include O2, CO2 and SO2. The triple pulse process leads to better profile control with a straight trench bottom. However, the maximal obtainable aspect ratio is comparable to the Bosch process because a larger etch depth and a small lateral etch cancel out. The polymer deposition mechanism is treated in chapter 6 with the aim to understand the fluorocarbon passivation in deep trenches. The deposition on plane surfaces and on special structures was investigated to distinguish between the radical-induced and ion-enhanced components. A simple analytical model, which explains the main deposition characteristics, was developed. Preferential sidewall deposition is obtained for higher ion fluxes and higher bias voltages where sputtering plays an important role. In this case no fluorocarbon passivation has to be removed from the bottom of the trench. The trench profile was optimised in the Bosch process by tuning the bias voltage during etching and passivation independently. It resulted in perfectly anisotropic trenches but the maximal obtainable aspect ratio was still limited by a small lateral etch. The characteristic role of the ions in the etching mechanism is explained in chapter 7. Ion-induced etching of both SiC in a SF6-O2 plasma and Si in a Cl2 plasma were investigated. The impact of the ions on the profile evolution can be examined more explicitly because spontaneous chemical reactions are absent for these plasma-material systems. The etching mechanism varies from fluorine-limited to ion-limited depending on the radical-to-ion flux ratio. Microtrenches are observed for an ion-limited etching mechanism. Fluorine-limited SiC etching is aspect ratio dependent in contrast to ion-limited SiC etching, which is aspect ratio independent. The etching of high aspect ratio SiC structures is limited by the positive sidewall taper. This is presumably caused by insufficient removal of the thin fluorocarbon layer on the surface. Si etching in a Cl2 plasma is always aspect ratio independent in contrast to SiC etching because of the low reaction probability. The conclusions and recommendations of this thesis are given in chapter 8.Applied Science
Exhumation history of eastern Ladakh revealed by Ar-40/Ar-39 and fission-track ages: the Indus River-Tso Morari transect, NW Himalaya
No full textFission-track and Ar-40/Ar-39 ages place time constraints on the exhumation of the North Himalayan nappe stack, the Indus Suture Zone and Molasse, and the Transhimalayan Batholith in eastern Ladakh (NW India). Results from this and previous studies on a north-south transect passing near Tso Morari Lake suggest that the SW-directed North Himalayan nappe stack (comprising the Mata, Tetraogal and Tso Morari nappes) was emplaced and metamorphosed by c. 50-45 Ma, and exhumed to moderately shallow depths (c. 10 km) by c. 45-40 Ma. From the mid-Eocene to the present, exhumation continued at a steady and slow rate except for the root zone of the Tso Morari nappe, which cooled faster than the rest of the nappe stack. Rapid cooling occurred at c. 20 Ma and is linked to brittle deformation along the normal Ribil-Zildat Fault concomitant with extrusion of the Crystalline nappe in the south. Data from the Indus Molasse suggest that sediments were still being deposited during the Miocene
Integrated high-spatial resolution 40Ar/39Ar geochronology, stable isotope geochemistry, and structural analysis of extensional detachment systems : case studies from the Porsgrunn-Kristiansand Shear Zone (S-Norway) and the Shuswap Metamorphic Core Complex (Canada).
No full textAbstract
Reconstructing the tectonic and kinematic history of orogens and their major fault systems requires a quantitative understanding of the timing and duration over which these fault systems were active. This study aims at understanding the often complex 40Ar/39Ar geochronological data obtained from deformed mylonitic rocks and examines the relationship between defonnation, recrystallization, and argon, oxygen, and hydrogen isotope exchange in muscovite and to some extent amphibole. Textures, as well as compositions and in situ UV-laser ablation and furnace step heating 40Ar/39Ar data from different extensional shear zones demonstrate that when combined with adequate sample characterization, cooling ages can be distinguished from neo- or recrystallization ages. Deformed muscovite porphyroclasts and recrystallized muscovite from the Pogallo Shear Zone (Ivrea Zone, southern Alps) reveal variable intra-grain 40Ar/39Ar ages with internal age variations of more than 60 m.y. The wide age range within compositionally homogeneous grains is consistent with diffusion-dominated argon loss controlled by observable intra-grain microstructures. In contrast, intra-grain 40Ar/39Ar ages of muscovite fish from Proterozoic mylonite of the Porsgrunn-Kristiansand Shear Zone (Southern Norway) and Eocene detachment mylonite of the Shuswap metamorphic core complex (British Columbia, Canada) display only minor age dispersion. Infra- grain recrystallization microstructures of compositionally-zoned, early syntectonic muscovite fish from extensional detachment mylonite at the Porsgrunn-Kristiansand Shear Zone record 40Ar/39Ar ages of deformation increments that bracket the duration of greenschist facies mylonitization. Texturally controlled in situ UV-laser 40Ar/39Ar dating of muscovite cores (891.9 ±2.9 Ma) and recrystallized rims (881.0 ±3.0 Ma) successfully resolves age variations between intra-grain deformation microstructures in muscovite fish and constrains the time scales of extensional detachment faulting to 10.9 ±5.9 m.y. Extensional detachment faulting and exhumation of lower crustal basement rocks along the Porsgrunn-Kristiansand Shear Zone hence occurred well after the main phase of Sveconorwegian high temperature thrusting and crustal shortening at -4 120-1100 Ma as determined by 40Ar/39Ar geochronology of amphibole.
Spatially resolved sampling in mylonitic detachment quartzite of the Shuswap metamorphic core complex indicates that muscovite recrystallized between 49.0 - 47.9 Ma in the presence of meteoric water strongly depleted in deuterium. In situ 40Ar/39Ar geochronology reveals very homogeneous intra-grain 40Ar/39Ar distributions consistent with grain-scale recrystallization and synkinematic argon and hydrogen exchange. Several lines of evidence suggest that for at least 1-2 m.y. during the Early Eocene meteoric waters precipitated onto elevations of 4060 ± 250 m to 4320 ± 250 m some 1000 m higher than today's highest peaks in the area.
The approach of combining X-ray element mapping and careful microstructural characterization with high-spatial resolution in situ UV-laser 40Ar/39Ar geochronology and hydrogen and oxygen isotope geochemistry represents a significant advance in understanding 40Ar/39Ar data from shear zone minerals. The results of this thesis underline that this approach provides a widely applicable tool to establish the rates and time scales of tectonically controlled exhumation in eroding mountain belts and bears potential for determining the paleoelevation of eroded mountain ranges.
Résumé
La reconstitution de l'histoire tectonique et cinématique des orogènes et de leurs principaux systèmes de failles nécessite d'avoir une approche quantitative de leur chronologie et de leur durée de fonctionnement. Le but de cette étude est de déchiffrer les données géochronologiques 40Ar/39Ar, souvent complexes, obtenues sur des roches mylonitiques intensément déformées; il s'agit aussi d'examiner dans la muscovite, et dans une certaine mesure l'amphibole, les relations entre la déformation, la recristallisation, et les échanges isotopiques en argon, oxygène, et hydrogène. Les textures, compositions et données 40Ar/39Ar obtenues par ablation laser ultraviolet (UV) in situ et par chauffage par paliers, montrent que les âges de refroidissement peuvent être distingués des âges de néo- ou recristallisation, quand ils sont couplés avec un échantillonnage adéquat à l'échelle du minéral. Des porphyroclastes déformés de muscovite et des muscovites recristallisées en provenance de la zone de cisaillement de Pogallo (Zone d'Ivrée, Alpes du Sud) donnent des âges 40Ar/39Ar variables pour un même grain, avec des variations internes de plus de 65 Ma. Cet intervalle d'âge dans des minéraux de composition homogène est cohérent avec une perte d'argon contrôlée par des microstructures à l'intérieur même des grains, principalement par diffusion. Par opposition, les âges intra grains 40Ar/39Ar de "mica fish" en provenance des mylonites Protérozoïques de la zone de cisaillement de Porsgrurm-Kristiansand (sud de la Norvège), ainsi que des mylonites du détachement Eocène du dôme métamorphique de Shuswap (Colombie-Britannique, Canada), montrent seulement de très faibles dispersions. Les microstructures de recristallisations intra-grains de "mica fish" zonés et précocement syntectoniques, en provenance de mylonites du détachement en extension de la zone de cisaillement de Porsgrunn-Kristiansand, «enregistrent des âges de déformation qui encadrent dans le temps la durée de la mylonitisation en faciès schiste vert. La datation 40Ar/39Ar par ablation laser UV in situ, contrôlée par la texture minéralogique, de coeurs de muscovites (891.2 ±2.9 Ma) et de bordures de recristallisation (880.2 ±2.8 Ma), résolvent le problème des variations d'âge entre les microstructures de déformation intra-grain des "mica fish" ; la durée de l'épisode de détachement en extension est ainsi de 11.0 Ma. L'activité du détachement en extension et l'exhumation des roches du bloc inférieure le long de la zone de cisaillement de Porsgrunn-Kristiansand se sont donc produites bien après la phase de chevauchement haute température et de raccourcissement crustal de l'orogène Svéconorvégienne vers environ 1120-1100 Ma (âge 40Ar/39Ar sur amphibole).
L'échantillonnage haute résolution à l'échelle du minéral de quartzites mylonitiques dans le détachement du dôme métamorphique de Shuswap montre que la muscovite a recristallisé entre 49.0 et 47.9 Ma, en présence d'eau météorique extrêmement appauvrie en Deutérium. La géochronologie 40Ar/39Ar in situ révèle des distributions 40Ar/39Ar très homogènes, cohérentes avec les phénomènes de recristallisation à l'échelle du grain, et les échanges syn-cinématiques d'argon et d'hydrogène. Plusieurs indices concordants suggèrent que cette eau météorique a précipité à des altitudes de 3900 à 4500 m pendant au moins 1-2 Ma, ce qui implique que cette partie de la cordillère nord-américaine était à des altitudes considérablement plus élevées pendant l'Eocène Inférieur qu'à l actuel.
La combinaison de la cartographie des éléments par rayon X et de la caractérisation microstructurale précise des minéraux, associée à la haute résolution spatiale de la géochronologie 40Ar/39Ar par ablation laser UV in situ, et à la géochimie des isotopes de l'hydrogène et de l'oxygène, représente une avancée significative dans la compréhension des données 40Ar/39Ar des minéraux issus de zones de cisaillement. Les résultats de cette thèse démontrent que cette approche procure un outil valable dans la détermination des taux d'exhumation tectonique lors de l'érosion des chaînes de montagne, des échelles de temps associées, ainsi que dans l'estimation de leur paléoaltitudes.
Résumé large public
La topographie du globe terrestre dépend largement des processus de formation des chaînes de montagne. Ces reliefs, ou orogènes, exercent de plus une influence importante sur l'évolution climatique globale, à la base de vives discussions en sciences de la terre et en sciences sociales. La compréhension de ces processus nécessite un effort multidisciplinaire, de manière à saisir les relations entre la dynamique interne du globe (croûte et manteau terrestre) et ses manifestations à la surface (chaînes de montagne). Dans la plupart des cas, de précieuses informations relatives aux conditions de formation de ces chaînes sont conservées dans ce qu'on appelle des zones de cisaillement d'échelle orogénique. Ces zones de cisaillement concentrent les déformations liées aux déplacements continus observés dans la croûte et le manteau terrestre en relation directe avec les déformations à la surface; elles peuvent ainsi accommoder des déplacements de plusieurs centaines de kilomètres. Etudier des chaînes de montagnes anciennes et les utiliser comme modèles pour les chaînes actuelles oblige à connaître avec précision la chronologie de leur formation et de leur démantèlement. Cette thèse présente des données géochimiques et géochronologiques obtenues par la cartographie haute résolution des minéraux, et montre les difficultés rencontrées lors des tentatives de datation de ces zones de cisaillement. L'analyse in situ de micas blancs par ablation laser ultraviolet est à la base d'une nouvelle variante de la méthode de datation 40Ar/39Ar; elle permet en effet de mettre en relation des informations de type structural, d'échelle plurikilométrique, et microstructural, à l'échelle micrométrique des grains, avec les informations géochronologiques contenues dans le minéral. Par conséquent, la géochronologie 40Ar/39Ar in situ donne un nouvel aperçu, auparavant inconnu, de l'histoire des orogènes et de leurs déformations complexes. Les données géochronologiques 40Ar/39Ar provenant de plusieurs zones de cisaillement montrent que cette déformation se fait sur des échelles de temps pouvant atteindre 10 millions d'années. Par opposition, les résultats de la géochronologie 40Ar/39Ar sur la chaîne Shuswap, située dans la cordillère nord- américaine, montrent que le soulèvement des roches fortement métamorphisées au coeur de l'orogène se fait en moins de 1.1 millions d'années, temps extrêmement rapide à l'échelle des temps géologiques. Ces divergences dans les données géochronologiques sont dues en partie au défaut de résolution spatiale de l'échantillonnage à l'échelle du minéral, mais également peuvent être liées à différentes histoires orogéniques. Des progrès importants dans la détermination de ces évolutions peuvent être réalisés par l'analyse couplée de systèmes isotopiques différents. En raison des ses caractères structuraux et isotopiques uniques, le couplage des résultats obtenus par la méthode 40Ar/39Ar avec ceux issus de l'étude des isotopes de l'hydrogène est à la base d'une nouvelle méthode qui a permis de retrouver la paléotopographie de la chaîne Shuswap. Les analyses des isotopes stables dans les zones de cisaillement d'âge Eocène Inférieur indiquent que les altitudes dans la cordillère nord-américaine étaient au moins 1000 mètres plus importantes qu'aujourd'hui, et que ces zones de cisaillement enregistrent des variations climatiques et topographiques depuis l'Eocène Inférieur
Variscan Sm-Nd and Ar-Ar ages of eclogite facies rocks from the Erzgebirge, Bohemian Massif
No full textAssessment of Models for Near Wall Behavior and Swirling Flows in Nuclear Reactor Sub-system Simulations
No full textAccurate simulation of turbulence remains one of the most challenging problems in nuclear reactor analysis and design. Due to limitations in computing resources, Reynolds averaged Navier Stokes models (RANS) continue to play an important role in reactor simulations. The Consortium for advanced simulations of light water reactors (CASL) is a Department of Energy technology hub that is investing in research and developmentof a state-of-the-art computational fluid dynamics capabilityto meet the challenges of turbulent simulation of nuclear reactors. In this presentation, we assess several RANS eddy viscosity models appropriate for single-phase incompressible turbulent flows. Specifically, we compare the single equation Splalart-Allmaras to several variations of the model. The assessment takes into consideration elements of full system reactor cores such as complex geometries, heterogeneous meshes, swirling flow, near wall flow behavior, heat transfer and robustness issues. The goal of this strategically oriented assessment is to provide an accurate and robust turbulent simulation capability for the CASL community. Metrics of performance will be constructed by comparing different models on a strategically chosen set of problems that represent reactor core sub-systems
O zarubežnoj dejatel'nosti professora M.A. Kumaxova
No full textOn professor M.A. Kumakhov's work and research abroad (in Russian)
Professor Mukhadin A. Kumakhov and the author collaborated in the area of Northwest Caucasian languages under a period from 1991 to 2008. The fruitful collaboration at Lund and Malmö universities resulted in three joint monographs and a number of articles, which is outlined in the article. Mukhadin A. Kumakhov became Honorary Doctor of the Philosophical Faculty of Lund University in 1998
Bringing clouds into our lab!: The influence of turbulence on early stage rain droplets
No full textWe are investigating a droplet-laden flow in an air-filled turbulence chamber, forced by speaker-driven air jets. The speakers are running in a random manner; yet they allow us to control and define the statistics of the turbulence. We study the motion of droplets with tunable size in a turbulent flow, mimicking the early stages of raindrop formation. 3D Particle Tracking Velocimetry (PTV) is chosen as the experimental method to track the droplets and collect data for statistical analysis. Thereby it is possible to study the spatial distribution of the droplets in turbulence using the so-called Radial Distribution Function (RDF), a statistical measure to quantify the clustering of particles. Additionally, this technique allows us to measure velocity statistics of the droplets and the influence of the turbulence on droplet trajectories, both individually and collectively. In this contribution, we will present velocity statistics of the droplets and quantify their clustering using the RDF for different turbulence conditions
The Story about the constructed SARS COV-2 Virus - A Review of three Research Groups
No full textAbstract
A literature research on synthetic recombinant SARS Coronavirus was made to answer two questions. Is the SARS CoV-2 virus designed in a laboratory? And why has the SARS CoV-2 such a high mutation rate? A total of 12 research articles, 2 reviews and 10 experimental studies were attributed to three Research Groups, the Wadsworth Center New York, the Vanderbilt Medical Center, and the Chapel Hill North Carolina. The research papers were published between 1991 and 2014. All 12 research papers reported the successful construction of recombinant SARS Coronaviruses based on RNA reverse genetic and molecular techniques. The Research group from the Medical Center at Vanderbilt University proved how an engineered SARS Coronavirus with an impaired Exonuclease resulted in a progeny virus with high mutation rate. Furthermore, the review showed that a zoonotic-human transmission was just possible with specific genetic manipulations at the SARS CoV virus genome through selection of virus species for recombination, and targeted manipulation at non-structural virus domains. But importantly, the studies showed that a SARS Coronavirus cross-species infection such as between zoonotic and humans or between different animal species without the exchange of the virus spike protein domain with the host-specific receptor-binding domain (RBD) and additional point mutations was not possible. Therefore, the SARS CoV-2 was deliberately constructed to overcome the receptor limiting factor for animal-human infection. Interestingly, the review revealed that the study purpose of constructed recombinant SARS CoV changed from the scientific research point of view to vaccine production and development. Competing interests for all reviewed studies by grants from private investors such as the Gates Foundation and vaccine production companies were part of the discussion. Keywords: SARS CoV-2, Covid19, Spike protein, gene sequencing, Vanderbilt University, University North Carolina, Wadsworth Research Center, New York Health Department, Coronavirus, Bill & Melinda Gates Foundation, WHO, Pfizer, Merck, Novartis, AlphaVaxThe author declares no competing interests.
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The force of law as a social problem
No full textIn this paper, the author aims to respond to the urgings in the book “The Force of Law” by Frederick Schauer breaking from the paradigm of analytical jurisprudence, insofar as the University of Virginia philosopher states having found sociological bases for his own logical/reconstructive architecture. The author, on the one hand, intend to develop a critique of Schauer’s approach that is not merely theoretical, but sociological as well; on another hand, Hart’s thesis on force in law—strongly criticized by contemporary analytical philosophers—is not therefore rebuffed by sociological analysis but somehow finds confirmation. In a nutshell, whether the use of force is sociologically necessary to control isolated resistance to the rules shared by the majority, or to reinforce a law, that aims to trigger necessary social change, but such a strong limitation of human freedom must be justified; and this legitimacy can only derive from the need for Justic
Home and family in the novels 'The White Guard' by M.A. Bulgakov and 'The Suicide' by M.A. Aldanov: A look at the revolution from the 'inside' and the 'outside'
No full textThe sociocultural content of the concept of family hearth under the conditions of the revolutionary events of 1917 described in the novels “The Suicide” (‘Samoubiistvo’) by M.A. Aldanov and “The White Guard” (‘Belaya gvardiya’) by M.A. Bulgakov was revealed.
The relevance of the study is determined by the fact that the concepts of home and family are the basic components of the sociocultural consciousness of any society.
The study was performed with the aim of identifying key motifs in the description of home, as well as similarities and differences in the linguistic representation of this concept when describing two periods in the history of Russia (during the pre-revolutionary and revolutionary times) from the position of the author as an eyewitness to the events and the author as an emigrant.
The following conclusions were made: in the descriptions of home of the pre-revolutionary Russia in the novels “The White Guard” by M.A. Bulgakov and “The Suicide” by M.A. Aldanov, the motifs of the well-being, stability, and continuity of generations are emphasized. In the episodes depicting the revolutionary events, the linguistic representation of home and family changes considerably: the motifs of doom, regret about the lost, surrealism, and tenuous imaginings become evident.
The results obtained are important for linguistic analysis of some passages of the text needed for the adequate perception of the novels “The White Guard” by M.A. Bulgakov and “The Suicide” by M.A. Aldanov
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