Isotropic Liquid Crystal Elastomers as Exceptional Photoelastic Strain Sensors

A family of acrylate-based isotropic Liquid Crystal Elastomers (LCEs) exhibit stress- and strain-optic coefficients orders of magnitude greater than conventional polymeric and photoelastic materials. The three materials, composed of liquid crystalline and nonliquid crystalline monomers, show no nematic phase at any temperature. One of the materials has previously been synthesized with nematic symmetry, but here is instead templated with isotropic symmetry, demonstrating a previously unrealized idea proposed by de Gennes in 1969. Uniaxial strains applied to each material induce nematic ordering which we quantify using dye-absorption spectra and polarized Raman Spectroscopy. We deduce the coupling constants between the nematic liquid crystal order parameter and applied strain varies between 0.37 ± 0.02 and 0.66 ± 0.02—values large compared to other LCE systems. The combination of high strain-optic coefficients (0.048 ± 0.003 to 0.11 ± 0.01) and high compliances (245 ± 18 to 1900 ± 100 GPa–1) demonstrates that isotropic LCEs are exciting candidates for photoelastic coatings for assessing deformations across soft devices and biomaterials

L anurie par Intoxication au Mercure ( A Report de 15 cas )

15 cases of acute renal failure follow ing ingestion of bichloride of mercury were studied at Pahlavi medical center, university of Teheran, between"n196? and 1972. All the patients admitted suicide attempts. All had oliguria and uremia except one, in whom oliguria was moderate without azotemia. There were four deaths among the 15 patients, tgastrointestinal hernorrage; secondery infection and the prolonged acute uremia probably were the cause of death in another one. Early administration of B. A. L. and early frequent hemodialysis helps to support the patient through the period of oliguria and possibly to remove the mercury B. A. L. Complex. Although the mortality of mercury intoxication has decreased, gast rointestinal hemorrages and secondery infections make its prognosis still unfavorable.hree of them with

Effect of photonic band gap on the propagation of reflected pulse from a slab doped with two-level and three-level atoms

In this paper the effect of photonic band gap on the group velocity of reflected pulse from a dielectric slab doped with two-level or three-level atoms has been investigated. It is assumed that the slab is sandwiched between a uniform medium (like vacuum) and a one-dimensional photonic crystal. It is shown that the reflected pulse from the slab doped with two-level (three-level) atoms will be superluminal (subluminal) if the carrier frequency of the incident Gaussian pulse is in the photonic band gap. In contrast, for the incident pulse with the carrier frequency at the edge of photonic band gap, the reflected pulse from the slab doped with two-level (three-level) atoms is subluminal (superluminal)

Topological binding and elastic interactions of microspheres and fibres in a nematic liquid crystal

We present a detailed analysis of topological binding and elastic interactions between a long, and micrometer-diameter fiber, and a microsphere in a homogeneously aligned nematic liquid crystal. Both objects are surface treated to produce strong perpendicular anchoring of the nematic liquid crystal. We use the opto-thermal micro-quench of the laser tweezers to produce topological defects with prescribed topological charge, such as pairs of a Saturn ring and an anti-ring, hyperbolic and radial hedgehogs on a fiber, as well as zero-charge loops. We study the entanglement and topological charge interaction between the topological defects of the fiber and sphere and we observe a huge variety of different entanglement topologies and defect-mediated elastic bindings. We explain all observed phenomena with simple topological rule: like topological charges repel each other and opposite topological charges attract. These binding mechanisms not only demonstrate the fascinating topology of nematic colloids, but also open a novel route to the assembly of very complex topological networks of fibers, spheres and other objects for applications in liquid crystal photonics

Creation and topological charge switching of defect loops on a long fibre in the nematic liquid crystal

We demonstrate new type of topological defects on a homeotropic fibre aligned perpendicular to the nematic director in a planar nematic cell. Contrary to expectations we can create defect loops which are encircling the fibre along its short axis and are strongly tilted with respect to the fibre. Such loops are always accompanied by two topological solitons, which emanate from the loop and propagate to the left- and right-hand side of the fibre. Unlike previously reported closed loops of either positive and negative charge, encircling the fibre parallel to the nematic director, these loops can carry either positive or negative charge, or can be charge neutral and very stable. We show how to switch the charge of individual loops from positive to neutral and negative charge by adding unit monopoles of appropriate topological charge. We demonstrate new type of interaction of dipolar colloids with these new topological entities on a fibre

Ferric methanesulfonate as an effective and environmentally sustainable lixiviant for Zn extraction from sphalerite (ZnS)

Zinc is currently extracted from sphalerite (ZnS) by either sintering-smelting or roasting-leaching. These high-temperature processes produce environmentally hazardous sulfur dioxide gas. Hence, sustainable zinc extraction calls for direct leaching at low temperatures. Here, we show that ferric methanesulfonate is a high performing lixiviant for this purpose. Using 0.8 M ferric methanesulfonate, 99.3% Zn was extracted from 106-150 μm sphalerite particles after leaching at 70 °C for 96 h. Elemental sulfur, rather than sulfur dioxide, was produced as a by-product. When compared to common inorganic lixiviants such as ferric sulfate or ferric chloride, ferric methanesulfonate demonstrates greater extraction efficiency and is less corrosive, less toxic, and does not release harmful gases. Mineralogical, microscopical, and compositional characterization of reaction products confirmed the formation of a core-shell structure consisting of a sphalerite core and a sulfur shell, and the manifestation of a coupled dissolution-reprecipitation mineral replacement mechanism. Efficient zinc extraction was facilitated by the interconnected pores in sulfur, which provided pathways for mass transfer between the lixiviant and sphalerite core. The precipitation of anglesite (PbSO4), which in some instances caused surface passivation through the infilling of sulfur shells, suggests that Pb2+ concentration should be controlled when applying ferric methanesulfonate for Zn extraction

Dynamics of topological monopoles annihilation on a fibre in a thick and thin nematic layer

We study topological defect annihilation on a glass fibre with homeotropic surface anchoring of nematic liquid crystal molecules. The fibre is set parallel to the nematic director of a planar cell with variable thickness and we create pairs of Saturn ring and Saturn anti-ring using the laser tweezers. In thick cells we observe in the whole region of defect separation a Coulomb-like pair attraction with no background force, $F\propto 1/d^{\alpha}$ with $\alpha \approx 2\pm 0.3$. In cells with thickness comparable to glass fibre diameter, we observe the Coulomb-like attraction only at small separations of the defect pair. For separations larger than the fibre diameter, the pair interaction force is independent of separation. This string-like force is attributed to the formation of defect lines, connecting both monopoles and are indeed visible only on extremely confined fibre, where the fibre diameter is practically equal to the nematic layer thickness. Numerical simulations confirm the formation of defect lines connecting both rings

Mechanisms of Surface Passivation during Galena Leaching by Hydrogen Peroxide in Acetate and Citrate Solutions at 25–50 °C

Organic solutions are promising lixiviants for fast and environmentally sustainable Pb extraction from ore minerals at low temperatures. However, engineering of novel leaching flowsheets has been hindered by poor understanding of the leaching mechanism, particularly the formation of surface-passivating phases. Here, we studied leaching of galena (PbS), the most abundant Pb ore mineral, in citrate and acetate solutions at 25–50 °C. The results show faster and higher Pb extraction in citrate solutions than in acetate solutions. For example, leaching of 53–106 μm galena particles at 35 °C for 2 h achieved 69.3% Pb extraction in a pH 7 citrate solution but only 30.1% in a pH 3 acetate solution. Investigation of solid residues by SEM, EDS, quantitative powder X-ray diffraction, and Raman spectroscopy proved the formation of a porous yet poorly permeable layer of anglesite during acetate leaching by pseudomorphic replacement of galena and subsequent overgrowth, hindering further leaching after 55.6% Pb extraction. In contrast, in citrate solutions, no anglesite was observed, but the formation of an impermeable thin Pb-oxide layer caused surface passivation after 87.1% Pb extraction. Our experimental results and thermodynamic calculations suggest that Pb-citrate complexes [e.g., Pb2(C6H5O7)22–, Pb(C6H5O7)24–, and Pb(C6H5O7)−] are far more effective than Pb-acetate complexes [e.g., Pb(CH3COO)+ and Pb(CH3COO)2] in suppressing the precipitation of anglesite because of the high solubility of Pb-citrate complexes in sulfate-rich solutions. This work provides a scientific basis for developing greener approaches such as in situ leaching and heap leaching for recovering Pb from galena-bearing ores

Studies of Inclusion Complexes of Dichloromethane in Cryptophanes by Exchange Kinetics and 13 C NMR in Solution and the Solid State

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