Molecular Simulations of Supercritical Fluid Permeation through Disordered Microporous Carbons

International audienceFluid transport through microporous carbon-based materials is inherent in numerous applications, ranging from gas separation by carbon molecular sieves to natural gas production from coal seams and gas shales. The present study investigates the steady-state permeation of supercritical methane in response to a constant cross-membrane pressure drop. We performed dual control volume grand canonical molecular dynamics (DCV-GCMD) simulations to mimic the conditions of actual permeation experiments. To overcome arbitrary assumptions regarding the investigated porous structures, the membranes were modeled after the CS1000a and CS1000 molecular models, which are representative of real microporous carbon materials. When adsorption-induced molecular trapping (AIMT) mechanisms are negligible, we show that the permeability of the microporous material, although not significantly sensitive to the pressure gradient, monotonically decreases with temperature and reservoir pressures, consistent with diffusion theory. However, when AIMT occurs, the permeability increases with temperature in agreement with experimental data found in the literature

Two-Dimensional Spectroscopy of Extended Molecular Systems: Applications to Energy Transport and Relaxation in an α-Helix

A simulation study of the coupled dynamics of amide I and amide II vibrations in an α-helix dissolved in water shows that two-dimensional (2D) infrared spectroscopy may be used to disentangle the energy transport along the helix through each of these modes from the energy relaxation between them. Time scales for both types of processes are obtained. Using polarization-dependent 2D spectroscopy is an important ingredient in the method we propose. The method may also be applied to other two-band systems, both in the infrared (collective vibrations) and the visible (excitons) parts of the spectrum.

Hard sphere fluids in annular wedges: density distributions and depletion potentials

We analyze the density distribution and the adsorption of solvent hard spheres in an annular slit formed by two large solute spheres or a large solute and a wall at close distances by means of fundamental measure density functional theory, anisotropic integral equations and simulations. We find that the main features of the density distribution in the slit are described by an effective, two--dimensional system of disks in the vicinity of a central obstacle. For large solute--solvent size ratios, the resulting depletion force has a straightforward geometrical interpretation which gives a precise "colloidal" limit for the depletion interaction. For intermediate size ratios 5...10 and high solvent packing fractions larger than 0.4, the explicit density functional results show a deep attractive well for the depletion potential at solute contact, possibly indicating demixing in a binary mixture at low solute and high solvent packing fraction.Comment: 39 page

Síntese e caracterização de Nanocompósitos Esfoliados de Poliestireno: Hidróxido Duplo Lamelar via polimerização in situ

Nanocompósitos Esfoliados de Poliestireno (PS) e Hidróxido Duplo Lamelar (HDL) composto por zinco, alumínio e dodecil sulfato de sódio, como ânion interlamelar, foram sintetizados via polimerização in situ. O efeito de diferentes composições de HDL (0,5, 1, 3 e 5% em massa) foi avaliado. Os nanocompósitos obtidos foram caracterizados através de ensaios de Difração de Raios X (DRX), Espectroscopia no Infravermelho por Transformada de Fourier (FTIR), Microscopia Eletrônica de Transmissão (MET) e Análise Termogravimétrica (TGA). Os resultados obtidos através das análises de DRX e MET mostraram que todos os nanocompósitos produzidos apresentaram morfologia esfoliada. Os resultados das TGA, quando se utilizam 50% de perda de peso como ponto para comparação, apresentaram ganhos significativos de estabilidade térmica para todas as composições dos nanocompósitos em comparação ao poliestireno puro. Este comportamento possibilita uma vasta gama de aplicação destes novos materiais em diversos campos da indústria e pesquisa.</jats:p

Design, fabrication, and characterization of new materials based on zirconia doped with mixed rare earth oxides: Review and first experimental results

Monazite is one of the most valuable natural resources for rare earth oxides (REOs) used as dopants with high added value in ceramic materials for extreme environments applications. The complexity of the separation process in individual REOs, due to their similar electronic configuration and physical–chemical properties, is reflected in products with high price and high environmental footprint. During last years, there was an increasing interest for using different mixtures of REOs as dopants for high temperature ceramics, in particular for ZrO2‐based thermal barrier coatings (TBCs) used in aeronautics and energy co‐generation. The use of mixed REOs may increase the working temperature of the TBCs due to the formation of tetragonal and cubic solid solutions with higher melting temperatures, avoiding grain size coarsening due to interface segregation, enhancing its ionic conductivity and sinterability. The thermal stability of the coatings may be further improved by using rare earth zirconates with perovskite or pyrochlore structures having no phase transitions before melting. Within this research framework, firstly we present a review analysis about results reported in the literature so far about the use of ZrO2 ceramics doped with mixed REOs for high temperature applications. Then, preliminary results about TBCs fabricated by electron beam evaporation starting from mixed REOs simulating the real composition as occurring in monazite source minerals are reported. This novel recipe for ZrO2‐based TBCs, if optimized, may lead to better materials with lower costs and lower environmental impact, as a result of the elimination of REOs extraction and separation in individual lanthanides. Preliminary results on the compositional, microstructure, morphological, and thermal properties of the tested materials are reported

Femoral Head Avascular Necrosis Due to Brucella Infection: A Case Report

Brucellosis remains a widespread disease in endemic regions worldwide and is not adequately controlled. It is a common zoonotic disease worldwide, a systemic infection, and a major health problem in endemic countries. Femoral head avascular necrosis (FHAVN) as a consequence of brucellosis is exceedingly unusual and has seldom been recorded. The case reports a 21-year-old female patient was hospitalized due to severe pain in both lower limbs, particularly in the anterior portion of the hip joint, accompanied by a low-grade fever persisting for six months. Movement of the right hip was painful, and the patient limped at the beginning of walking after a few steps. Rheumatoid factor and antinuclear antibody test results were negative. The right hip joint was aspirated, and a small quantity of fluid was sent for Gram staining and culture. Synovial joint fluid culture confirmed Brucella abortus infection after four weeks. The source of infection in the present case was the consumption of raw milk. Based on laboratory tests and radiographic images, FHAVN was diagnosed. Owing to misdiagnosis, she had not received standard treatment for brucellosis in the previous months. The patient was diagnosed early, and she was in the third stage. After the patient received medical treatment, the left and right hip joints partly recovered. The right hip joint required replacement; however, the patient refused. Attending physicians should consider brucellosis as an alternative to arthritis for hip joint pain in Brucella-endemic locations. Medication-based therapy may be effective for early avascular necrosis, emphasizing the need for early diagnosis and treatment

Wheat Poisoning of Cattle.

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Trait phenomenological control predicts experience of mirror synaesthesia and the rubber hand illusion

In hypnotic responding, expectancies arising from imaginative suggestion drive striking experiential changes (e.g., hallucinations) — which are experienced as involuntary — according to a normally distributed and stable trait ability (hypnotisability). Such experiences can be triggered by implicit suggestion and occur outside the hypnotic context. In large sample studies (of 156, 404 and 353 participants), we report substantial relationships between hypnotisability and experimental measures of experiential change in mirror-sensory synaesthesia and the rubber hand illusion comparable to relationships between hypnotisability and individual hypnosis scale items. The control of phenomenology to meet expectancies arising from perceived task requirements can account for experiential change in psychological experiments