974 resultados para enhanced dynamic wedges, gel dosimetry, interplay effects, x-ray computed tomography, radiation therapy, Monte Carlo simulations, BEAMnrc, DOSXYZnrc


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The asymmetric dicopper(II) title complex with a [Cu2(μ-O2CMe)22+ core was isolated from the reaction between Cu2(μ-O2CMe)4(H2O)2 and bipy in EtOH in the presence of NH4PF6 and has been characterized by X-ray diffraction analysis.

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Inovirus is a helical array of agr-helical protein asymmetric units surrounding a DNA core. X-ray fibre diffraction studies show that the Pf1 species of Inovirus can undergo a reversible temperature-induced transition between two similar structural forms having slightly different virion helix parameters. Molecular models of the two forms show no evidence for altered interactions between the protein and either the solvent or the viral DNA; but there are significant differences in the shape and orientation of the protein asymmetric unit, related to the changes in the virion parameters. Normal modes involving libration of whole asymmetric units are in a frequency range with appreciable entropy of libration, and the structural transition may be related to changes in libration.

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An air-stable and water-soluble diastereomeric half-sandwich ruthenium(I1) complex, [Ru(s-MeCsH4Pr'-p)(H*O)-(L*)] (C104) (l), has been isolated and structurally characterized [HL* = (27)-(a methylbenzyl)salicylaldimine,2-HOC6H4CH-NCHMePhI. Complex 1, Czd-I3oNO&lRu, crystallizes in the noncentric triclinic space group P1 with a = 9.885(1) A, b = 10.185(1) A, c = 14.187(2) A, a = 110.32(1)', 6 = 102.17(1)', y = 102.41(1)O, V=1243( 1) A3, and 2 = 2. The X-ray structure shows the presence of two diastereomers in a 1:l ratio having RR,,,SCand SR,,,&c onfigurations. The Ru-OHz bond distances are considerably long, and the values for RR, - a~n d SRu-1isomers are 2.1 19(5) and 2.203(5) A, respectively. The aqua complex (1) exists as a single diastereomer in solution,and it forms stable adducts with P-, N-, and halide-donor ligands. The stereochemical changes associated with adduct-forming reactions follow an inversion order: PPhs >> P(OMe)3 > pyridine bases >> halides (I, Br, Cl) >H20.

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The structures of Ca0.5Ti2P3O12 and Sr0.5Ti2P3O12, low-thermal-expansion materials, have been refined by the Rietveld method using high-resolution powder X-ray diffraction (XRD) data. The assignment of space group R[3 with combining macron] to NASICON-type compounds containing divalent cations is confirmed. 31P magic-angle spinning nuclear magnetic resonance (MASNMR) data are presented as supporting data. A comparison of changes in the polyhedral network resulting from the cation distribution, is made with NaTi2P3O12 and Nb2P3O12. Factors that may govern thermal expansion in this family of compounds are discussed.

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X-ray diffraction line profile analysis (XRDLPA) techniques have been applied to investigate the deformed microstructure of a recently developed boron modified two-phase titanium alloy Ti-6Al-4V. The alloy was hot compressed at 750 degrees C up to 50% height reduction at two different strain rates (10(-3) S-1 and 1 S-1). Microstructural parameters like average domain size, average microstrain within the domain and dislocation density of the two phases were determined using X-ray diffraction line profile analysis. The results indicate an increase in the microstrain and dislocation density for the alpha-phase and decrease for the beta-phase in the case of boron modified alloys as compared to the normal material. Microstructural modifications viz, the grain refinement and the presence of hard, brittle TiB particles in the case of boron modified alloy are held responsible for the observed difference in the dislocation density. (C) 2010 Elsevier Inc. All rights reserved.

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Edge-sharing bioctahedral (ESBO) complexes [Ru-2(OMe)(O2CC6H4-p-X)3(1-MeIm)(4)](ClO4)2 (X = OMe (1a), Me (1b)) and [Ru-2(O2CC6H4-P-X)(4)(1-MeIm)(4)](ClO4)(2) (X = OMe (2a), Me (2b)) are prepared by reacting Ru2Cl(O(2)CR)(4) with 1-methylimidazole (1-MeIm) in methanol followed by treatment with NaClO4. Complex 2a and the PF6- salt (1a') of 1a have been structurally characterized. Crystal data for 1a.1.5MeCN. 0.5Et(2)O: triclinic, P (1) over bar, a = 13.125(2) Angstrom, b = 15.529(3) Angstrom, c 17.314(5) Angstrom, a; 67.03(2)degrees, beta 68.05(2)degrees, gamma = 81.38(1)degrees, V 3014(1) Angstrom(3), Z = 2. Crystal data for 2a: triclinic, P (1) over bar, a 8.950(1) Angstrom, b = 12.089(3) Angstrom, c = 13.735(3) Angstrom, alpha 81.09(2)degrees, beta = 72.27(1)degrees, gamma = 83.15(2)degrees, V = 1394(1) Angstrom(3), Z = 1. The complexes consist of a diruthenium(III) unit held by two monoatomic and two three-atom bridging ligands. The 1-MeIm ligands are at the terminal sites of the [Ru-2(mu-L)(eta(1):mu-O(2)CR)(eta(1):eta(1):mu-O(2)CR)(2)](2+) core having a Ru-Ru single bond (L = OMe or eta(1)-O(2)CR). The Ru-Ru distance and the Ru-O-Ru angle in the core of 1a' and 2a are 2.49 Angstrom and similar to 76 degrees. The complexes undergo one-electron oxidation and reduction processes in MeCN-0.1 M TBAP to form mixed-valence diruthenium species with Ru-Ru bonds of orders 1.5 and 0.5, respectively.

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The total synthesis of the unusual sesquiterpene (+/-)-myltayl-4(12)-ene 3 starting from the readily available cyclogeraniol 5 and the single-crystal X-ray structure of the 4-nitrobenzoate 12 of the noralcohol 11 are described.

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A team of unmanned aerial vehicles (UAVs) with limited communication ranges and limited resources are deployed in a region to search and destroy stationary and moving targets. When a UAV detects a target, depending on the target resource requirement, it is tasked to form a coalition over the dynamic network formed by the UAVs. In this paper, we develop a mechanism to find potential coalition members over the network using principles from internet protocol and introduce an algorithm using Particle Swarm Optimization to generate a coalition that destroys the target is minimum time. Monte-Carlo simulations are carried out to study how coalition are formed and the effects of coalition process delays.

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The complex [Cu-II (theo)(2)(H2O)(3)].2H(2)O (theo = theophylline) was obtained from aqueous solution. The crystals belong to the monoclinic system, space group P2(1)/n, and are reflection twins about the (001) face. The structure was solved using data from a twinned crystal and refined to final R and R(W) values of 0.069 and 0.064, respectively. Copper has a square-pyramidal coordination with two thee molecules coordinating through N(7) at equatorial positions. The remaining sites are occupied by water molecules. O(6) of one of the thee molecules is at the other axial site at a longer distance of 3.18 Angstrom. This could lead to an alternate (4+1+1) octahedral coordination geometry for Cu-II. The packing is stabilized by stacking interactions between the theophylline moieties at an average separation of 3.46 Angstrom.

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The title complex has been prepared from a reaction of [Ru2O(O22CMe)2 (MeCN)4(PPH3)2](ClO4)2 with N,N-dimethyl-1,2-diaminoethane (dmen) in MeOH. The crystal structure of [Ru2O(O2CMe)2(dmen)2(PPh3)2](ClO4)2.MeOH shows the presence of a [Ru2(mu-O)(mu-O2CMe)2]2+ core. The terminal ligands on each metal are a PPh3 and a bidentate chelating dmen. The Ru-Ru distance and Ru-O-Ru angle in the core are 3.271(2) angstrom and 120.9(4)-degrees. The more electron-donating site of the dmen ligand is bonded at the terminal sites trans to the mu-oxo ligand. The complex displays a visible absorption band at 566 nm (epsilon, 6960 M-1 cm-1) in MeCN and undergoes a nearly reversible one-electron oxidation at 1.02 V and an irreversible reduction at -0.52 V (vs SCE) in MeCN-0.1 M [NBu4n](ClO4).

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Anomalous X-ray scattering (AXS) has been applied to study the structure of amorphous platinum disulfide, Pt1-xS2, prepared by the precipitation process. The local atomic arrangement in amorphous Pt1-xS2 was determined by the least-squares variational method so as to reproduce the experimental differential interference function at the Pt L(III) absorption edge by the AXS method as well as the ordinary interference function by MoK alpha. The structural unit in amorphous Pt1-xS2 is found to be a PtS6 octahedron, similar to that in crystalline PtS2. These octahedra share both their corners and edges, while only edge-sharing linkages occur in crystalline PtS2.

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The anomalous X-ray scattering (AXS) method using Cu and Mo K absorption edges has been employed for obtaining the local structural information of superionic conducting glass having the composition (CuI)(0.3)(Cu2O)(0.35)(MoO3)(0.35). The possible atomic arrangements in near-neighbor region of this glass were estimated by coupling the results with the least-squares analysis so as to reproduce two differential intensity profiles for Cu and Mo as well as the ordinary scattering profile. The coordination number of oxygen around Mo is found to be 6.1 at the distance of 0.187 nm. This implies that the MoO6 octahedral unit is a more probable structural entity in the glass rather than MoO4 tetrahedra which has been proposed based on infrared spectroscopy. The pre-peak shoulder observed at about 10 nm(-1) may be attributed to density fluctuation originating from the MoO6 octahedral units connected with the corner sharing linkage, in which the correlation length is about 0.8 nm. The value of the coordination number of I- around Cu+ is estimated as 4.3 at 0.261 nm, suggesting an arrangement similar to that in molten CuI.

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Cyclization of compound 5c in trifluoroacetic acid/hexamethylenetetramine produces Tröger's base analogue 6c in 75% yield with 70% diastereoselectivity.

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Synchrotron-based X-ray diffraction was used to study the phase diagrams and determine the compressibilities of the pyrochlore rare-earth titanates Ho2Ti2O7, Y2Ti2O7 and Tb2Ti2O7 to 50GPa. The bulk moduli of the cubic phase of these materials were calculated to be 213 +/- 2, 204 +/- 3 and 199 +/- 1GPa, respectively. The onset of a structural phase change from cubic to monoclinic was observed near 37, 42 and 39GPa, respectively. The bulk modulus for the high pressure monoclinic phase of Y2Ti2O7 has been determined to be 185 +/- 3GPa.

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Unusually long (>14 cm) crystalline needles grow from 4-(3-bromopropyloxy)salicylaldehyde 1 presumably as a consequence of Br ... Br interactions; the powdered form of 1 shows one order of magnitude greater SHG activity realtive to urea.