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Small Cavities (small + cavity)
Selected AbstractsAtomic structure of pyramidal defects in GaN:Mg: Influence of annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2006Z. Liliental-Weber Abstract The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Annealing of the MOCVD layers lead to slight increase of the defect size and an increase of the room temperature photoluminescence intensity. Positron annihilation confirms presence of vacancy clusters of different sizes triggered by the Mg doping in as-grown samples and decrease of their concentration upon annealing at 900 and 1000 °C. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Luminescent Zn and Cd Coordination PolymersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2004Chao Jiang Abstract The hydrothermal reactions of Zn(ClO4)2·6H2O and Cd(ClO4)2·6H2O with 1,3-bis(2H -tetrazol-5-yl)benzene in an aqueous ethanol and an aqueous methanol/pyridine medium, respectively, yielded a 3D and a 2D metal-organic coordination framework [Zn(1,3-BTB)] (1) and [Cd(1,3-BTB)2(Py)2(H2O)2] [Cd[Cd(Py)(H2O)]2(1,3-BTB)2] (2) (1,3-BTB = 1,3-ditetrazolylbenzene, Py = pyridine), respectively. Species 1 possesses an open network structure with no guest molecules residing in its small cavities. The structural characterisation of 2 shows a 2D layered framework consisting of nano-sized polytube structures which are stacked one on top of another in the (110) plane giving small channels along the b and c axes. Additionally, compounds 1 and 2 exhibit strong fluorescence at room temperature in the solid state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Structure and composition of CO2/H2 and CO2/H2/C3H8 hydrate in relation to simultaneous CO2 capture and H2 productionAICHE JOURNAL, Issue 6 2009Rajnish Kumar Gas hydrates from a (40/60 mol %) CO2/H2 mixture, and from a (38.2/59.2/2.6 mol %) CO2/H2/C3H8 mixture, were synthesized using ice powder. The gas uptake curves were determined from pressure drop measurements and samples were analyzed using spectroscopic techniques to identify the structure and determine the cage occupancies. Powder X-ray diffraction (PXRD) analysis at ,110°C was used to determine the crystal structure. From the PXRD measurement it was found that the CO2/H2 hydrate is structure I and shows a self-preservation behavior similar to that of CO2 hydrate. The ternary gas mixture was found to form pure structure II hydrate at 3.8 MPa. We have applied attenuated total reflection infrared spectroscopic analysis to measure the CO2 distribution over the large and small cavities. 1H MAS NMR and Raman were used to follow H2 enclathration in the small cages of structure I, as well as structure II hydrate. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Habitat and Microhabitat of Mediterranean Clingfishes (Teleostei: Gobiesociformes: Gobiesocidae)MARINE ECOLOGY, Issue 1 2000Robert Hofrichter Abstract. This study addresses the habitat and microhabitat of the seven species of gobiesocid fish in the Mediterranean Sea. It is shown that Lepadogaster lepadogaster is closely adapted to large pebbles and boulder fields of rounded stones with a smooth surface. L. candollei is more euryecious and, in addition to inhabiting boulder fields also, occurs close to seagrass meadows, in small cavities and in association with sea urchins. Diplecogaster bimaculata is also euryecious and extends to greater depths. It lives on sand and muddy bottoms as well as on coralline grounds. At some locations this species is found in high abundance during the spawning season under empty bivalve shells or flat stones. Apletodon dentatus is the rarest species of Gobiesocidae in the Mediterranean Sea. It has a close association with seagrass or large brown algae (Cystoseira). Juveniles of A. incognitus are either associated with sea urchins or inhabit Posidonia meadows. Adults prefer the vicinity of seagrass meadows under empty bivalve shells and stones overgrown with red algae. Gouania wildenowi is stenoecious and is restricted to the interstices of roundish coarse gravel near the waterline. Opeatogenys gracilis is also stenoecious and lives only on the leaves of Posidonia and Cymodocea seagrass. The colourations of the different species and their variations are described and discussed. [source] Experimental Investigation of thermal convection in an inclined narrow gap IIPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Daniel Rubes In the past decade the development in micro technology has experienced great progress, what made the knowledge of the flow behavior in small cavities fundamentally interesting. Our experimental contribution describes the measured temperature and velocity fields in a fluid containing inclined cavity with the dimensions 17 × 6 × 24 mm3 (w × d × h). Using PIV/T, we can determine the velocity and temperature distribution in the cavity simultaneously. The chamber is illuminated with a white light sheet of 1 mm. A 20% glycerin-water mixture is examined. The lower side is heated to 46.2°C, while the upper side has a constant temperature of 26°C. In this work we present the measured velocity and temperature fields of the fluid at different angles of the cavity orientation with respect to the direction of gravity in the stationary state. This is a continuation of last years presentation [1] in the sense that the temperature difference has been substantially increased. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] NMR spectroscopic characterization of metoprolol/cyclodextrin complexes in aqueous solution: Cavity size dependencyJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2004Yoichi Ikeda Abstract The inclusion complex formation of a water-soluble ,1 -selective adrenoreceptor antagonist Metoprolol (Met) with ,-cyclodextrin (,-CyD), ,-cyclodextrin (,-CyD), ,-cyclodextrin (,-CyD), and 2-hydroxypropyl-,-cyclodextrin (HP-,-CyD) in aqueous solution was studied by ultraviolet (UV), circular dichroism (CD), and nuclear magnetic resonance (NMR) spectroscopies and the modes of interaction were assessed. Continuous variation plots revealed that Met forms the inclusion complexes with ,-CyD, ,-CyD, and HP-,-CyD in a stoichiometry of 1:1, whereas ,-CyD forms the 2:1 complex where two Met molecules are included in one ,-CyD cavity. NMR spectroscopic studies, including ROESY and GROESY techniques, clearly indicated that ,-CyD with the small cavity includes the methoxyethylbenzene moiety of Met molecule shallowly in the cavity, depositing the benzene and the methoxy moieties around the secondary and primary sides, respectively, of the cavity. In the case of the ,-CyD complex, the methoxyethylbenzene moiety is more deeply included in the cavity, and it is feasible that Met may be able to enter from both primary and secondary hydroxyl sides of the cavity, forming the 1:1 complex. On the other hand, two Met molecules are included probably in an antiparallel orientation in the large ,-CyD cavity, and the benzene moieties of Met are in contact with each other. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:1659,1671, 2004 [source] Change in dimerization mode by removal of a single unsatisfied polar residue located at the interfacePROTEIN SCIENCE, Issue 9 2000P. R. Pokkuluri Abstract The importance of unsatisfied hydrogen bonding potential on protein-protein interaction was studied. Two alternate modes of dimerization (conventional and flipped form) of an immunoglobulin light chain variable domain (VL) were previously identified. In the flipped form, interface residue Gln89 would have an unsatisfied hydrogen bonding potential. Removal of this Gln should render the flipped dimer as the more favorable quaternary form. High resolution crystallographic studies of the Q89A and Q89L mutants show, as we predicted, that these proteins indeed form flipped dimers with very similar interfaces. A small cavity is present in the Q89A mutant that is reflected in the ,100 times lower association constant than found for the Q89L mutant. The association constant of Q89A and Q89L proteins (4 × 106 M,1 and > 108 M,1) are 10- and 1,000-fold higher than that of the wild-type protein that forms conventional dimers clearly showing the energetic reasons for the flipped dimer formation. [source] | ||||||||||