Topological Defects in Nematic Droplets of Hard Spherocylinders

Using computer simulations we investigate the microscopic structure of the singular director field within a nematic droplet. As a theoretical model for nematic liquid crystals we take hard spherocylinders. To induce an overall topological charge, the particles are either confined to a two-dimensional circular cavity with homeotropic boundary or to the surface of a three-dimensional sphere. Both systems exhibit half-integer topological point defects. The isotropic defect core has a radius of the order of one particle length and is surrounded by free-standing density oscillations. The effective interaction between two defects is investigated. All results should be experimentally observable in thin sheets of colloidal liquid crystals.Comment: 13 pages, 16 figures, Phys. Rev.

Modeling adsorption in metal-organic frameworks with open metal sites : propane/propylene separations

We present a new approach for modeling adsorption in metal-organic frameworks (MOFs) with unsaturated metal centers and apply it to the challenging propane/propylene separation in copper(II) benzene-1,3,5-tricarboxylate (CuBTC). We obtain information about the specific interactions between olefins and the open metal sites of the MOP using quantum mechanical density functional theory. A proper consideration of all the relevant contributions to the adsorption energy enables us to extract the component that is due to specific attractive interactions between the pi-orbitals of the alkene and the coordinatively unsaturated metal. This component is fitted using a combination of a Morse potential and a power law function and is then included into classical grand canonical Monte Carlo simulations of adsorption. Using this modified potential model, together with a standard Lennard-Jones model, we are able to predict the adsorption of not only propane (where no specific interactions are present), but also of propylene (where specific interactions are dominant). Binary adsorption isotherms for this mixture are in reasonable agreement with ideal adsorbed solution theory predictions. We compare our approach with previous attempts to predict adsorption in MOFs with open metal sites and suggest possible future routes for improving our model

Utjecaj desflurana i sevoflurana na razine oksidativnog stresa u tkivima štakora

General anaesthetics are often used in patients who are under oxidative stress due to a critical illness or surgical trauma. Some anaesthetics may worsen oxidative stress and some may act as antioxidants. The aim of this study was to evaluate liver, brain, kidney, and lung tissue oxidative stress in rats exposed to desflurane and sevoflurane and in unexposed rats. The animals were divided in three groups: control (received only air); sevoflurane (8 %), and desflurane (4 %). After four hours of exposure, we evaluated the levels of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), Cu, and Zn. Exposure to either of the anaesthetics significantly increased lung MDA levels compared to control (Mann-Whitney U test; P<0.05), probably because it is the tissue directly exposed to anaesthetic gases. Oxidative stress and antioxidant activity in other tissues varied between the desflurane and sevoflurane groups. Our results suggest that anaesthesiologist should not only be aware of the oxidative or antioxidative potential of anaesthetics they use, but should also base their choices on organs which are the most affected by their oxidative actionkisikovih radikala tako i zbog smanjene aktivnosti obrambenih sustava koji se mogu oduprijeti njihovu djelovanju. Stoga su saznanja o antioksidativnom kapacitetu anestetika koji se primjenjuju prije nekoga kirurškog zahvata vrlo važna i od velikog su kliničkog značenja. Sevofl uran i desfl uran su inhalacijski anestetici koji se učestalo rabe u svrhu uvođenja bolesnika u anesteziju. Cilj ovog istraživanja bio je utvrditi razine oksidativnog stresa u različitim tkivima štakora i usporediti razlike u odgovoru tkiva na izlaganje navedenim anesteticima. U tu svrhu razine oksidativnog stresa izmjerili smo u jetri, mozgu, bubrezima i plućima štakora podijeljenih u tri eksperimentalne skupine. Kontrolna skupina udisala je samo zrak, dok su druge dvije skupine izložene 8 %-tnomu sevofl uranu te 4 %-tnomu desfl uranu tijekom 4 h. Nakon završetka obrade životinje su žrtvovane i uzimani su im uzorci tkiva za biokemijske analize. Mjerena je razina malondialdehida (MDA), aktivnst enzima superoksid dismutaze (SOD) i glutation peroksidaze (GSH-Px) te razine bakra i cinka. Izloženost anesteticima izazvala je oksidativni stres u plućima, na što upućuje značajno povišena razina MDA (Mann-Whitney U-test P<0.05) izmjerena u plućnom tkivu štakora obiju izloženih skupina u odnosu na kontrolu. Plućno je tkivo u odnosu na ostala tkiva podložnije štetnim utjecajima reaktivnih kisikovih radikala vjerojatno stoga što je ono prvo izloženo plinovitim anesteticima nakon njihova ulaska u organizam. Razine oksidativnog stresa i antioksidativne aktivnosti koje smo izmjerili u ostalim tkivima bile su različite te su ovisile o primijenjenom anestetiku. Na osnovi dobivenih rezultata možemo zaključiti da bi se zbog različitog odgovora tkiva izbor anestetika trebao provoditi na individualnoj osnovi

The “Realstruktur” of the system La2-xSrxCu1-yRuyO4-δ studied by rietveld and extended X-ray absorption fine structure spectroscopy†

The structure of the layered perovskite-related system La2-xSrxCu1-yRuyO4-δ was investigated by Rietveld refinement calculations of X-ray diffraction data and EXAFS analysis of the Ru−K and Cu−K absorption edge. Both methods complement one another as they yield information about long-range ordering and the local environment of a specific element, respectively. Rietveld calculations have revealed remarkable changes of the interatomic distances with the composition, e.g., the degree of elongation of the Cu/Ru−O6 octahedra. To get more detailed information about the local structure we have performed EXAFS studies for selected samples with y = 0, 0.2, 0.4, 0.6, 0.8, and 1. We were able to achieve consistent results both from the Ru−K and Cu−K edge data. As an element specific method, extended X-ray absorption fine structure (EXAFS) spectroscopy is capable of distinguishing between different possible arrangements of the La/Sr and Cu/Ru atoms. We found that La and Sr are distributed statistically on the A cation position. For the B cations a small enrichment of Cu in the Ru surrounding (and vice versa) could be detected. For a given value of y this enrichment increases with increasing La content. This indicates a partial ordering of Ru and Cu within the perovskite layers. Oxygen vacancies (δ > 0) were found to be located exclusively in the Cu surrounding. Coordination numbers less than 5 reveal that a part of the copper ions is coordinated in a square planar way. Distances derived from EXAFS and XRD data show a good agreement; still, the former are usually smaller by 0.01−0.03 Å. The distance Cu−La/Sr was found to be smaller by 0.05 Å than the distance Ru−La/Sr. Apart from this, no significant differences could be detected for the distances between the various combinations of elements

Highly Ordered Porous Zirconias from Surfactant-Controlled Syntheses: Zirconium Oxide−Sulfate and Zirconium Oxo Phosphate

The syntheses and characterization of mesostructured hexagonally ordered surfactant composites using zirconium sulfate ions as inorganic precursor species are described. On the basis of the mesostructured zirconium sulfate surfactant composites, two porous MCM-41 analogues have been synthesized:  zirconium oxide−sulfate and zirconium oxo phosphate. For the zirconium oxo phosphates, a special postsynthetic treatment has been developed. The pore arrangements and wall structures were characterized by XRD, nitrogen adsorption, EXAFS, and TEM. The porous zirconia based materials show hexagonal arrangements of uniformly sized pores and amorphous pore walls. Both zirconium oxide−sulfate and zirconium oxo phosphate show remarkable thermal stability up to 500 °C. Therefore, the surfactant has been completely removed from the structures by calcination. So far, this is the highest thermal stability compared to other porous transition metal oxides prepared via surfactant-controlled synthesis

Iron (III) Oxide within Mesoporous MCM-48 Silica Phases: Synthesis and Characterization

Using multiple cycles of wet impregnation, drying and calcination procedures it was possible to form haematite nanoparticles within the pore system of mesoporous MCM-48 silica phase. A decoration/coating of the inner surface of the silica walls was indicated by a reduction of the BET surface area, the pore radius as well as HRTEM and EDX investigations. Existence of small, slightly disordered iron (III) oxide nanoparticles was proved by X-ray absorption spectroscopic measurements