12 results
Illite-Smectite Mixed-Layer Minerals in Felsic Volcaniclastic Rocks from Drill Cores, Kakkonda, Japan
- Atsuyuki Inoue, Alain Meunier, Daniel Beaufort
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- Journal:
- Clays and Clay Minerals / Volume 52 / Issue 1 / February 2004
- Published online by Cambridge University Press:
- 01 January 2024, pp. 66-84
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Crystallization processes of the illite-smectite (I-S) mixed-layer mineral series during alteration of felsic vitric materials in volcaniclastic sediments through two drill holes (IT-2 and IT-8) near the Kakkonda active geothermal system, Japan, were examined by optical microscopy, scanning and transmission electron microscopy (SEM and TEM), electron microprobe analysis, X-ray diffraction (XRD), and oxygen isotope analysis. Temperatures measured through the drill holes increased nearly linearly with depth up to 317°C at the bottom (1700 m) of IT-8. Homogenization temperature measurements of fluid inclusions indicated that the alteration occurred at temperatures similar to the present temperatures. In selected volcaniclastic rocks, excluding andesitic rocks and black shales, clay minerals occurred as glass replacements and pore fillings as seen under SEM and optical microscopy, and exhibited predominantly euhedral hexagonal and elongated forms under TEM, implying that they precipitated in situ through hydrolytic reactions of glass and fluid. Based on XRD examination, I-S minerals showed a sigmoidal variation in illite layer percentage (%I) in the range of ∼150 to 220°C and R0 I-S minerals with intermediate %I between 20 and 40% rarely occurred (where R is the Reichweite parameter). The chemical composition also showed a specific variation with depth. Intermediate clays including smectite and I-S minerals are enriched in Al compared to those reported previously from hydrothermal alteration of almost equivalent parent rocks. The oxygen isotope data indicated that the reacting solution was percolating groundwater in the shallow levels and with fossil seawater in the deeper levels. Furthermore, calculating the fluid/rock (W/R) ratio from the isotope variations revealed that the alteration occurred at a nearly constant W/R ratio condition irrespective of %I. Consequently, the observed specific variations in structure and chemical composition of I-S minerals reflect the compositional variations of fluid participating in the crystallization at given temperatures under the conditions of a given original rock and constant W/R ratio. High pH and Na-rich solutions generated by progressive hydrolytic reactions between felsic glass and groundwater favored the precipitation of Al-rich smectite up to ∼150°C and was followed by precipitation of an aluminous R1 I-S mineral with few intermediate R0 I-S minerals at higher temperatures. The crystallization obeys Ostwald’s step rule behavior of smectite illitization processes under a high geothermal gradient.
Clay Minerals in Basalt-Hawaiite Rocks From Mururoa Atoll (French Polynesia). I. Mineralogy
- Antoine Mas, Alain Meunier, Daniel Beaufort, Patricia Patrier, Patrick Dudoignon
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- Journal:
- Clays and Clay Minerals / Volume 56 / Issue 6 / December 2008
- Published online by Cambridge University Press:
- 01 January 2024, pp. 711-729
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Clay minerals in chilled or brecciated margins (altered glass) and massive inner crystalline parts (mesostasis) of three basalt-hawaiite bodies from Mururoa Atoll (French Polynesia) have been studied in order to compare their chemical and mineralogical compositions. Polyphase assemblages comprise di- and trioctahedral phases, both of which consist of non-expandable layers (chlorite, celadonite) and two types of expandable layers (saponite and Fe-rich smectite or ‘nontronite-like’ material). The presence of the Fe-rich clays is supported by the presence of the X-ray diffraction 060 peak at 1.51–1.52 Å and of the infrared absorption bands at 875 and 822 cm−1 (Fe3+-Al-OH and Fe3+-Fe3+-OH groups, respectively). The chemical composition of the Fe-rich smectites does not fit with the theoretical nontronite field. The layer charge averages 1 per Si4O10 making these Fe-rich smectites close to ‘celadonite-type’ clays. This could explain the presence of mixed-layer celadonite-smectite. Plotted in an M+/4Si vs. Fe/sum octahedral cations diagram, the chemical compositions of clay minerals in the mesostasis form a continuous field limited by the celadonite-high-charge nontronite-like smectite and chlorite end-members. The clay assemblages are different from those formed in hydrothermal systems or low-grade metamorphic conditions which are characterized by the sequence: saponite → randomly ordered chlorite-smectite mixed-layered minerals (MLMs) → corrensite → chlorite. The systematic presence of Fe-rich clays either in the altered chilled margins or in the massive inner parts of the basalt-hawaiite bodies (high-charge nontronite-like smectite and mixed-layer nontronite-celadonite) makes the Mururoa sea-mount a potential terrestrial analogue for Mars surface exploration.
Clay Mineralogy and Chemical Composition of Bentonites from the Gourougou Volcanic Massif (Northeast Morocco)
- Mohamed Ddani, Alain Meunier, Mohamed Zahraoui, Daniel Beaufort, Mohamed El Wartiti, Claude Fontaine, Boubker Boukili, Benacer El Mahi
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- Journal:
- Clays and Clay Minerals / Volume 53 / Issue 3 / June 2005
- Published online by Cambridge University Press:
- 01 January 2024, pp. 250-267
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The Gourougou volcanic massif (northeastern Morocco) is actively prospected for bentonite deposits. Five bentonites originating from different environments were selected for the present study: hydrothermal alteration of obsidian perlite glass inside the volcanoes themselves (Providencia and Tribia deposits); alteration of pyroclastic flows in a marine shallow water to lagoonal lacustrine environment (Ibourhardayn deposit); ash falls in marine or lacustrine systems (Moulay Rachid and Melg el Ouidan (formerly Camp Berteau) deposits). All of these bentonites were probably formed from volcanic glass originating from a rhyolitic magma at different stages of differentiation as shown by slight variations of REE and incompatible element abundances. The crystal-chemical characteristics of the smectite vary according to alteration conditions: beidellite predominates in hydrothermal systems, whereas montmorillonite predominates in lagoonal and lacustrine environments, and mixed-layer beidellite-montmorillonite in the sea-water-altered pyroclastic flows. All these dioctahedral smectites exhibit a heterogeneous distribution of charge as shown by the presence of partially expandable (1 EG) or non- expandable (0 EG) layers in the K-saturation state. The proportion of the collapsed or partially expandable layers is not related to the average layer charge or to the cation exchange capacity. This militates for an overall heterogeneous charge distribution. Compared to other natural or experimental alteration systems of similar rhyolitic glass, the formation of beidellite or montmorillonite appears to be controlled by the amounts of Mg in the system.
Illite-Smectite Mixed-Layer Minerals in the Hydrothermal Alteration of Volcanic Rocks: II. One-Dimensional HRTEM Structure Images and Formation Mechanisms
- Takashi Murakami, Atsuyuki Inoue, Bruno Lanson, Alain Meunier, Daniel Beaufort
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- Journal:
- Clays and Clay Minerals / Volume 53 / Issue 5 / October 2005
- Published online by Cambridge University Press:
- 01 January 2024, pp. 440-451
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Smectite illitization was investigated in felsic volcaniclastic rocks from a drill core near the Kakkonda active geothermal system, Japan, using high-resolution transmission electron microscopy (HRTEM) that provided one-dimensional structure images of mixed-layer illite-smectite (I-S) minerals normal to [M0]. Simulated images of a rectorite-like structure revealed that smectite can be distinguished from illite in mixed-layer I-S by HRTEM if the basal spacing of smectite is larger than that of illite. The larger basal spacing of smectite, 1.3 nm under HRTEM, was obtained by intercalation of dodecylammonium ions into smectitic interlayers. In simulated and observed images normal to [hk0], tetrahedral (T) and octahedral (O) cation planes are imaged as dark lines, an illitic interlayer as a bright line, and a smectitic interlayer as a dark line sandwiched between two bright lines.
The samples are from depths of 435 m (5% I; R0), 635 m (35% I; R0), 656 m (62% I; R1), and 756 m (85% I; R3) where % I is the percentage of illite layers in a sample and R is the Reichweite parameter. Sample 435 consisted mostly of smectite, and illite layers occurred, though small in amount, as M1 units (module of type 1, defined as consisting of two polar T-O-T silicate layers with one central illitic interlayer and two, half smectitic interlayers at the outermost surface; the number corresponds to that of central illitic interlayers). The M1 units were dominant and isolated and consecutive smectite layers (>2) were present in sample 635. Sample 656 consisted mostly of packets of M1 units of 1 to 5 layers containing M2 to M5 units occasionally. Isolated or consecutive smectite layers (>2) were not present in 656. Illite layers occurred almost entirely as M1 units in samples 435, 635 and 656, and the number of M1 units increased with increase in % I. Sample 756 was characterized by the presence of M2 to M10 units accompanied by smectitic interlayers at the external surface and the absence of M1 units and isolated smectite layers. The HRTEM data strongly suggest that illitization in a hydrothermal system occurs by precipitation of M1 units for mixed-layer I-S minerals up to 60% I. This does not require the presence of precursor smectite. Illitization of I-S minerals with >60% I proceeds by precipitation of various types of Mn (n ⩾ 2) units. Illite occurs only as Mn (n ⩾ 1) units throughout illitization.
Clay Minerals in Basalt-Hawaiite Rocks From Mururoa Atoll (French Polynesia). II. Petrography and Geochemistry
- Alain Meunier, Antoine Mas, Daniel Beaufort, Patricia Patrier, Patrick Dudoignon
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- Journal:
- Clays and Clay Minerals / Volume 56 / Issue 6 / December 2008
- Published online by Cambridge University Press:
- 01 January 2024, pp. 730-750
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The clay minerals formed in chilled margins and massive crystallized inner parts of three basalt-hawaiite bodies of Mururoa Atoll (French Polynesia) exhibit contrasting textures. Glass alteration textures are observed around fractures crosscutting the quenched margins: Fe-rich clays grow inward into the glass (retreating surface) while Mg-rich clays grow outward (open space). The textures of clay deposits filling the diktytaxitic voids (mesostasis) in the massive inner parts of the three volcanic bodies are different: unoriented clay matrix with embedded euhedral apatite and pyroxene microcrysts (submarine flow); pallisadic clays coating the void walls and the crystal surfaces of apatite and K-feldspar microcrysts (subaerial flow); and clay muffs covering all the apatite needles, with the central part of the void remaining empty (dike). The unoriented texture could result from the alteration of a glass precursor concomitant with the olivine phenocrysts (clay pseudomorphs). However, such an alteration implies important chemical transfers which are not observed. The pallisadic and muff textures form through heterogeneous nucleation on the solid surfaces and crystal growth from a saline solution. No glass precursor existed. As the center of the diktytaxitic voids in the dike is empty, the residual liquid was probably boiling. The amounts of light rare earth elements (LREE), Sr, and the most incompatible elements are greater in clays from diktytaxitic voids relative to the amounts formed in the altered glass of the chilled margins. Thus, diktytaxitic clays formed from a residual liquid which gave either an evolved glass or a saline solution after cooling (fractionation process). The δ18O variation vs. loss on ignition (LOI) indicates that sea water was involved either in rock alteration or magma contamination. This is confirmed by the 87Rb/86Sr ratio of bulk rocks and clay fractions from the quenched and massive inner parts of the three volcanic bodies which do not fit with the 11.5 Ma isochron indicating that the Rb-Sr system was not closed at any stage during the magmatic history.
Application of chemical geothermometry to low-temperature trioctahedral chlorites
- Atsuyuki Inoue, Alain Meunier, Patricia Patrier-Mas, Cecile Rigault, Daniel Beaufort, Philippe Vieillard
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- Clays and Clay Minerals / Volume 57 / Issue 3 / June 2009
- Published online by Cambridge University Press:
- 01 January 2024, pp. 371-382
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Low-temperature chlorites formed in diagenetic to low-grade metamorphic environments generally have greater Si contents and larger numbers of octahedral vacancies, and smaller Fe+Mg contents than higher-grade metamorphic chlorites. The compositional variations are characterized approximately by four end-member components: Al-free trioctahedral chlorite, chamosite, corundophilite, and sudoite. The solid solution is considered to be a random mix of cations and vacancies in the octahedral sites. Using the compositions of chlorites from Niger, Rouez, and Saint Martin diagenetic-hydrothermal series, a new, more convenient geothermometer, applicable to low-T chlorites is proposed and comparison made with geothermometers proposed previously. The chlorites studied contain appreciable amounts of Fe(III) (>14% of the total Fe), determined by Mössbauer spectroscopy. The calculations under which all Fe was regarded as ferrous gave considerable overestimates for the formation temperature, irrespective of the geothermometer used. This problem was reduced by taking into account the presence of Fe(III) in the octahedral sites. The geothermometer from this study gave more reasonable estimates than the geothermometers proposed by Walshe (1986) and Vidal et al. (2001), particularly in the case of the Niger chlorites which crystallized in the lowest-temperature conditions. The ordered-site substitution model of solid solution developed by Vidal et al. (2001) predicted satisfactorily the formation temperature of the Rouez chlorites and of some of the Saint Martin chlorites, suggesting that the chlorite compositions are controlled by the
exchange at low-T conditions while they are controlled by Tschermak exchange at higher temperatures. The decreasing number of vacancies with temperature are poorer in Fe-rich than in Fe-poor chlorites. Furthermore, the ordered-site occupation of cations and vacancies in trioctahedral chlorite occurs concomitantly with the compositional changes ruled by increasing temperature conditions.
Illite-Smectite Mixed-Layer Minerals in the Hydrothermal Alteration of Volcanic Rocks: I. One-Dimensional XRD Structure Analysis and Characterization of Component Layers
- Atsuyuki Inoue, Bruno Lanson, Maria Marques-Fernandes, Boris A. Sakharov, Takashi Murakami, Alain Meunier, Daniel Beaufort
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- Journal:
- Clays and Clay Minerals / Volume 53 / Issue 5 / October 2005
- Published online by Cambridge University Press:
- 01 January 2024, pp. 423-439
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For a series of mixed-layer illite-smectite (I-S) minerals from a drillhole near the Kakkonda geothermal field, one-dimensional structure analysis by X-ray diffraction (XRD) was performed using Casaturated specimens in both air-dried and ethylene glycol-solvated states. The expandability characteristics of component layers were also examined by means of alkylammonium exchange and Li saturation. The K content in the illite layers was 1.5–1.7/O20(OH)4 in the I-S series from 3 to 85% of I-layer content (% I). The layer charge of the smectite layer varied slightly within the range of 0.3–0.5/O10(OH)2 by alkylammonium exchange experiments and the expandability was independent of the beidellite content within a range of 0–0.5 by the Li-saturation test. The degree of long-range ordering represented by Reichweite (R) parameters varied from R0 to R3 via R1 and R2 with increase in % I. The I-S samples contained <10% vermiculite as the third component and the vermiculite content tended to decrease with progressive illitization.
In contrast to the smectitic R0 samples (<10% I), more illitic R0 (e.g. 35% I) and >R1 I-S samples showed complicated expandability with alkylammonium exchange. The XRD patterns of dodecylammonium-exchanged I-S samples can be interpreted by random interstratification of several types of sub-units such as layer-doublets, layer-triplets and layer-quartets present in the crystallites. This interpretation is consistent with the variation in the occurrence probabilities of layer-multiplets calculated from the junction probabilities and the proportions of layers. Because the interpretation indicates that I-S is a stack of various types of the sub-units, the smectite illitization can be described by a systematic change in the type and proportion of the sub-units constituting crystallites.
Effects of metacognitive training (MCT) on social cognition for schizophrenia spectrum and related psychotic disorders: a systematic review and meta-analysis
- Adèle Hotte-Meunier, Danielle Penney, Daniel Mendelson, Élisabeth Thibaudeau, Steffen Moritz, Martin Lepage, Geneviève Sauvé
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- Journal:
- Psychological Medicine / Volume 54 / Issue 5 / April 2024
- Published online by Cambridge University Press:
- 29 September 2023, pp. 914-920
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Background
Individuals with schizophrenia spectrum and related psychotic disorders (SSD) experience significant impairments in social cognition that impede functioning. Social cognition is a multidimensional construct consisting of four domains: 1. theory of mind, 2. emotion processing, 3. attributional style and 4. social perception. Metacognitive training (MCT) is an intervention designed to target cognitive biases in psychosis containing two modules addressing social cognition.
MethodsA systematic review and meta-analysis was conducted to investigate the effects of MCT on social cognition and two of its domains: theory of mind and emotion processing. Ten electronic databases were scoured from 2007 to 1 February 2022 for MCT studies reporting social cognition outcomes for people with SSD (1050 identified, 282 assessed). Effect sizes were calculated using Cohen's d in R.
ResultsNine studies were included in the meta-analysis (nMCT = 212, ncontrol = 194). MCT had a small but positive effect on global social cognition (d = 0.28 [95% CI 0.07–0.49]) and theory of mind (d = 0.27 [95% CI 0.01–0.52]). MCT showed no evidence of an effect on emotion processing (d = 0.03 [95% CI –0.26 to 0.32]).
ConclusionMCT has a small but significant effect on social cognition for people with SSD. Our results add to other recent meta-analyses showing significant effects of MCT on clinically relevant outcomes such as positive symptoms, cognitive biases and cognitive insight. We recommend that future studies on MCT report outcomes on all four domains of social cognition.
Trial RegistrationPROSPERO (in the process of registration) available at https://www.crd.york.ac.uk/prospero/#recordDetails
A Ten-Year Review of Carbapenemase Producing Enterobacterales (CPE) in London, United Kingdom
- Bharatkumar Patel, Katie Hopkins, Daniele Meunier, Peter Staves, Susan Hopkins, Neil Woodford
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- Journal:
- Infection Control & Hospital Epidemiology / Volume 41 / Issue S1 / October 2020
- Published online by Cambridge University Press:
- 02 November 2020, pp. s6-s7
- Print publication:
- October 2020
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Background: To determine the pattern of CPE observed in a single region in the United Kingdom. Methods: From 2009 to 2018, clinical laboratories in England were requested to send suspected CPE from all sites to the national reference laboratory for confirmation and investigation of carbapenem resistance mechanism(s). Isolates of Enterobacterales from London laboratories and confirmed to have 1 or more carbapenemase genes were included in the analysis. Result: Between 2009 and 2018, 5,133 isolates were confirmed to produce a carbapenemase; at least 1 CPE was identified in every London Laboratory and hospital. Confirmations increased from 28 isolates in 2009 to 1857 in 2018 and with a sharp rise after the introduction of the ‘PHE toolkit’ in 2013 (Fig. 1). Most CPE (2655, 51.7%) were from rectal screens (the 3 most frequently identified carbapenemase families were OXA-48–like in 1,263 isolates, NDM in 971 and IMP in 128), 631 (12.3%) were from urine samples, 180 (3.5%) from blood cultures, 103 (2.0%) from sputum specimens and the remainder (1564, 30.5%) were swabs, fluids and tissues from various body sites. Moreover, 51 CPE (1%) were identified from environmental swabs. Isolates were predominantly Klebsiella spp (2,525, 49%; 2,088 were K. pneumoniae), followed by Escherichia coli (1,434, 27.9%), Enterobacter spp (746, 14.5%; 605 were E. cloacae complex), and Citrobacter spp (349, 6.8%); 10 other species contributed smaller numbers. Within the carbapenemase families, OXA-48-like enzymes predominated overall (2303, 44.9%), followed by NDM (1822, 35.5%), IMP (313, 6.1%), VIM (207, 4.0%), NDM+OXA-48-like (205, 4.0%), and KPC (196, 3.8%). The first detection of a CPE with 2 distinct enzymes occurred in 2012 (OXA-48-like and NDM) and since then 235 co-detections have been identified; 233 related to OXA-48-like with another gene. Conclusion: The first CPE isolate in London was identified in 2003, a Klebsiella spp with a VIM enzyme. The number of isolates submitted to the national reference laboratory has continued to increase year on year. VIM and NDM carbapenemases predominated in the early years, because of their association with several outbreaks; these have now been overwhelmed by OXA-48-like detections and outbreaks. The increasing numbers of CPE with a combination of a metallo- and a non-metallo carbapenemase increases the therapeutic challenges to treat infected patients. Bacteremia caused by CPE remains rare, suggesting that infection prevention and control efforts are having some impact. However, as colonization prevalence increases, the number of clinical infections will rise in the future unless control measures to limit transmission and spread are improved.
Funding: None
Disclosures: None
Direct-Write Microfabrication of Single-Chamber Solid Oxide Fuel Cells with Interdigitated Electrodes
- Melanie Kuhn, Teko Napporn, Michel Meunier, Daniel Therriault, Srikar Vengallatore
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- Journal:
- MRS Online Proceedings Library Archive / Volume 972 / 2006
- Published online by Cambridge University Press:
- 26 February 2011, 0972-AA07-09-BB08-09
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- 2006
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Miniaturized single-chamber solid-oxide fuel cells (SC-SOFC) are a promising class of devices for portable power generation required in the operation of distributed networks of microelectromechanical systems (MEMS) in harsh environments. The single-face configuration, which consists of interdigitated (comb-like) array of electrodes on an yttria-stabilized zirconia (YSZ) electrolyte substrate, is of particular interest because of the ease of high-temperature microfluidic packaging and integration with MEMS. The primary design consideration for this configuration is the minimization of electrode widths and inter-electrode spacings to dimensions on the order of a few micrometers. This is necessary to minimize polarization resistance and increase fuel cell efficiency. Achieving these geometries using standard microfabrication methods is difficult because of the thickness, porosity, and complex chemistries of the electrodes. Here, we report the development of an innovative and rapid method for manufacturing SC-SOFCs with interdigitated electrodes using robot-controlled direct-writing. The main steps consist of: (i) formation of inks (or suspensions) using anode (NiO-YSZ) and cathode (lanthanum strontium manganite) powders, (ii) pressure-driven extrusion of inks through a micronozzle using a robot-controlled platform, and (iii) sequential sintering to form the fuel cell. The first-generation SC-SOFC device, with electrode widths of 130 μm and inter-electrode spacing of 300 μm, has been manufactured using direct-write microfabrication. The electrodes have been extensively characterized using electron microscopy and x-ray diffraction to assess porosity and to confirm phase identity. The primary process parameters in this approach are the particle size and size distribution, rheological properties of the suspension, extrusion pressure, nozzle size, stage velocity, and sintering conditions. As the first step in the development of detailed process-structure-performance correlations for the fuel cells, we have studied the effects of extrusion pressure (in the range 30-40 bar) and stage velocity (in the range 0.2-2.0 mm/s) on the geometry and size of electrodes, for fixed suspension viscosity and nozzle diameter. An optimal combination of speed and pressure has been identified and catalogued in the form of process maps. Similarly, the particle size distribution of the anode and cathode powders is found to have a significant effect on the microstructure, especially porosity, of the sintered electrodes. The implications of these results for the design of the next generation of SC-SOFC, with reduced electrode dimensions and improved electrochemical performance, will be discussed.
Viscous fingering in non-Newtonian fluids
- ANKE LINDNER, DANIEL BONN, EUGENIA CORVERA POIRÉ, MARTINE BEN AMAR, JACQUES MEUNIER
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- Journal of Fluid Mechanics / Volume 469 / 25 October 2002
- Published online by Cambridge University Press:
- 15 October 2002, pp. 237-256
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We study the viscous fingering or Saffman–Taylor instability in two different dilute or semi-dilute polymer solutions. The different solutions exhibit only one non-Newtonian property, in the sense that other non-Newtonian effects can be neglected. The viscosity of solutions of stiff polymers has a strong shear rate dependence. Relative to Newtonian fluids, narrower fingers are found for rigid polymers. For solutions of flexible polymers, elastic effects such as normal stresses are dominant, whereas the shear viscosity is almost constant. Wider fingers are found in this case. We characterize the non-Newtonian flow properties of these polymer solutions completely, allowing for separate and quantitative investigation of the influence of the two most common non-Newtonian properties on the Saffman–Taylor instability. The effects of the non-Newtonian flow properties on the instability can in all cases be understood quantitatively by redefining the control parameter of the instability.
Ge Island evolution during growth, in-situ anneal, and Si capping in an industrial CVD reactor
- Roger Loo, Philippe Meunier-Beillard, Didier Dentel, Michael Goryll, Danielle Vanhaeren, Lili Vescan, Hugo Bender, Matty Caymax, Wilfried Vandervorst
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- Journal:
- MRS Online Proceedings Library Archive / Volume 664 / 2001
- Published online by Cambridge University Press:
- 17 March 2011, A8.8
- Print publication:
- 2001
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Si based nanostructures such as Ge or Si1-xGex dots embedded in Si receive a lot of attention. This interest is driven by the reduction of device sizes as well as by their possible use in opto-electronic applications, as a possible solution to improve the radiative light emission. In this paper we give a detailed overview of the growth kinetics as observed for Ge growth in a standard production oriented chemical vapor deposition system. The island morphology and density are controlled by varying the growth conditions or by applying a thermal anneal after the island growth. Island densities up to 2.3x1010 cm−2 have been obtained for depositions at 650°C. With increasing deposition time, the usual change-over from monomodal to bimodal island distribution is pointed out and this change-over depends on the critical island diameter, which decreases with decreasing growth temperature. Applying a thermal budget after the island growth initiates Ge surface diffusion and Si diffusion from the substrate through the islands. This results in an enhancement of the island diameter and height, and also in a reduction of island density. Furthermore, depending on the island distribution after Ge deposition, a transition from pyramid to dome or visa versa is observed after the in-situ anneal. Optical device structures require a Si cap layer. However, Si capping at 700°C, leads to a nearly total dissolution of small islands and a truncation of bigger dome-shaped islands. This can be prevented by reducing the deposition temperature and by changing the Si gas source. Clear island luminescence, is observed up to 200K and lies in the spectral range of 1.35-1.50μm, which is interesting from the point of view of applications. In particular, this shows the potential of this material system for opto-electronic device applications. In spite of the fact that the observed PL intensity is comparable to the best reported values, we could further enhance it by a thermal treatment in a H2 plasma.
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