8,851 research outputs found
M.A. Just et P.A. Carpenter, The psychology of reading and language comprehension
No full textRacle Gabriel. M.A. Just et P.A. Carpenter, The psychology of reading and language comprehension . In: Communication et langages, n°73, 3ème trimestre 1987. pp. 125-126
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
Low-temperature behavior of natural kalsilite with P31c symmetry: An in situ single-crystal X-ray diffraction study
No full textThe low-temperature behavior of a natural kalsilite (ideal formula KAlSiO4) with P31c symmetry has been investigated by in situ single-crystal diffraction. A series of intensity data collections and structural refinements have been performed at 298, 250, 200, 150, and 100 K on decreasing temperature, and 175, 225, and 275 K on increasing T. The variations of the unit-cell parameters of kalsilite as a function of T are continuous, and show no evidence of any phase transitions or thermo-elastic anomalies in this temperature range. An expansion is observed along [0001] with decreasing temperature. The axial and volume thermal expansion coefficients ({alpha}j = lj-1{middle dot}{partial}lj/{partial}T, {alpha}V = V-1{middle dot}{partial}V/{partial}T) between 298 and 100 K, calculated by weighted linear regression through the data points, are {alpha}a = {alpha}b = 1.30(6){middle dot}10-5, {alpha}c = -1.5(1){middle dot}10-5, {alpha}V = 1.1(2){middle dot}10-5 K-1. The main structural change on decreasing temperature is a cooperative anti-rotation of tetrahedra forming the six-membered rings lying parallel to (0001). This tetrahedral rotation is coupled with a change in the distances between the extra-framework cations and the framework O atoms. A small decrease in the tetrahedral tilts perpendicular to [0001] is responsible for the negative thermal expansion along [0001]; the implications of these mechanisms for thermal expansion in nephelines and kalsilites are discussed
The Year 2000 classification of the agglutinated foraminifera
No full textA reclassification of the agglutinated foraminifera (subclass Textulariia) is presented, consisting of four
orders, 17 suborders, 27 superfamilies, 107 families, 125 subfamilies, and containing a total of 747
valid genera. One order (the Loftusiida Kaminski & Mikhalevich), five suborders (the Verneuilinina
Mikhalevich & Kaminski, Nezzazatina, Loftusiina Kaminski & Mikhalevich, Biokovinina, and
Orbitolinina), two families (the Syrianidae and the Debarinidae) and five subfamilies (the
Polychasmininae, Praesphaerammininae Kaminski & Mikhalevich, Flatschkofeliinae, Gerochellinae
and the Scythiolininae Neagu) are new. The classification is modified from the suprageneric scheme
used by Loeblich & Tappan (1992), and incorporates all the new genera described up to and including
the year 2000. The major differences from the Loeblich & Tappan classification are (1) the use of
suborders within the hierarchical classification scheme (2) use of a modified Mikhalevich (1995)
suprageneric scheme for the Astrorhizida (3) transfer of the Ammodiscacea to the Astrorhizida (4)
restriction of the Lituolida to forms with simple wall structure (5) supression of the order
Trochamminida, and (6) inclusion of the Carterinida within the Trochamminacea (7) use of the new
order Loftusiida for forms with complex inner structures (8) broadening the definition of the
Textulariida to include perforate forms that are initially uniserial or planispiral. Numerous minor
corrections have been made based on the recent literature
The relation of basic needs to the classroom situation
No full textThere is no abstract available for this research paper.Thesis (M.A.
Lattice defects in lawsonite : a TEM investigation
No full textLattice defects in lawsonite have been studied by transmission electron microscopy. It is proposed that twinning and easy glide systems are 1/2[1 10].110; the easy glide planes are coincident with twin planes. This mineral displays high sensitivity to the electron beam, even at low temperatures. In situ precipitates appear as a consequence of beam irradiation. The precipitation takes places first on dislocations, then on twin boundaries and then in the matrix, causing 'coffee-bean' contrast features typical of precipitates. The studies were performed at low temperature (∼ 110 K) in order to investigate the low temperature displacive transitions from space group Cmcm to Pmcn and P21cn and elucidate their microscopic character. No characteristic microstructural texture, such as antiphase domains associated with the transition, were observed, however. This is probably due to the high mobility of protons under the electron beam. The development of regularly spaced dislocations along twin planes is hypothesized as the only evidence that a phase transition takes place at a nanoscale
Quantitative foraminiferal and palynomorph biostratigraphy of the Paleogene in the southwestern Barents Sea
No full textThe stratigraphic distribution of both foraminifera and dinoflagellate cysts is recorded from the
Paleocene to Eocene Torsk Formation in 12 petroleum exploration wells drilled in the southwestern
Barents Sea. The foraminiferal assemblages are wholly agglutinated, and are referred to outer shelf to
middle bathyal environments. A quantitative analysis of biostratigraphic events, mainly last
occurrences (first downhole occurrences), is performed by means of the Ranking and Scaling (RASC)
program. This procedure combined with conventional stratigraphic treatment has enabled us to
establish the most likely order of microfossil events, and to propose a new quantitative zonal scheme
for the southwestern Barents Sea.
In the studied wells the following six zones and subzones are distinguished (in ascending order):
BSP 1, Psmmosphaera fusca – Hyperammina rugosa, late early to early late Paleocene; BSP 2,
Spiroplectammina spectabilis early late Paleocene; BSP 3A, Reticulophragmium pauperum, middle late
Paleocene; BSP 3B, Haplophragmoides aff. eggeri, latest Paleocene; BSP 4, Spiroplectammina navarroana,
earliest Eocene; BSP 5, Reticulophragmium amplectens, early to middle Eocene. Owing to the
occurrence of cosmopolitan deep-water agglutinated foraminifera, the new zonal scheme compares
well with previous zonations developed for the Paleogene of the mid-Norwegian shelf, the North Sea
and Labrador Shelf
Assessment 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
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