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81.
Nonlinear Dynamics - We study the Kuramoto–Sakaguchi model composed by N identical phase oscillators symmetrically coupled. Ranging from local (one-to-one, $$R=1$$ ) to global (all-to-all,... 相似文献
82.
Wolfgang Bauer Rene Bellwied John Harris Gary Westfall 《Acta Physica Hungarica A》2004,21(2-4):99-100
83.
Digital image processing is applied to X-ray element maps and back-scattered electron (BSE) images obtained with scanning
electron microscopy-energy dispersive X-ray analysis (SEM-EDX), to quantify and identify salts and porosity with depth in
porous media. Until now, only salt chemical composition with depth has been characterised and salt mineral composition inferred,
so that no salt quantification was possible. The method we present can be used stand-alone or integrated with other techniques
to fill certain gaps in our knowledge. It can be used to quantify texture and porosity of clay minerals, with implications
in petroleum research. Also, salts may be identified and quantified with depth in porous media; this is important when selecting
among salt extraction procedures in order to conserve cultural heritage. Finally, the method can help in interpreting salt
weathering processes and links between stone decay forms at different scales, with consequences for geomorphology.
To demonstrate the method, salt and pore percentages with depth are determined in two limestone types from monuments in the
Aunis province, SW France: i) Crazannes sparite, showing alveolisation and black crust, and ii) La Pallice micrite, suffering
from micro-delamination. In most of the micrites no salts are identified. Porosity data show that micro-fissures are confined
between the surface and 9 mm depth in LPAM5, the only micrite with loading salts with depth (NaCl = 1.9% at the surface versus
1.4% at 18 mm; and Na2SO4 · H2O and MgCl2 ∼ 0.02% in the first 3 mm). In the sparites, those samples with no crust display an alveolisation zone with lower porosity
and higher diversity and percentage of salts. In CRZM6, the stone crust-alveolisation front lies at a depth of 9 mm. In the
crust, porosity is lower than in the alveolisation zone (12%). Salt concentration, by contrast, is higher in the crust (2.91%
versus 0.14% in the alveolisation zone).
Received September 1, 2000 Revision November 2, 2001 相似文献
84.
Rene G. Rodriguez Daniel J. V. Pulsipher Lisa D. Lau Endrit Shurdha Joshua J. Pak Michael H. Jin Kublinder K. Banger Aloysius F. Hepp 《Plasma Chemistry and Plasma Processing》2006,26(2):137-148
Thin films of CuInS2 were grown on various substrates at a temperature of 523 K from two metal-organic precursors using radiofrequency plasma enhanced chemical vapor deposition (PECVD). Two precursor molecules, with different solubility properties, were dissolved in appropriate solvents and sprayed into the plasma region in the PECVD chamber. The resulting films were examined for atomic composition, growth rate, crystalline orientation, and uniformity. Films made from each precursor differed in thickness, atomic composition, and crystallinity. The uniformity of the film was fairly good from near the edge to the center of the substrate, and evidence for a chalcopyrite-like structure was found in several samples deposited from one of the precursor molecules. 相似文献
85.
Antunez-de-Mayolo G Antunez-de-Mayolo A Antunez-de-Mayolo P Papiha SS Hammer M Yunis JJ Yunis EJ Damodaran C Martinez de Pancorbo M Caeiro JL Puzyrev VP Herrera RJ 《Electrophoresis》2002,23(19):3346-3356
Alu elements, the largest family of interspersed repeats, mobilize throughout the genomes of primates by retroposition. Alu are present in humans in an excess of 500 000 copies per haploid genome. Since some of the insertion alleles have not reached fixation, they remain polymorphic and can be used as biallelic DNA marker systems in investigations of human evolution. In this study, six polymorphic Alu insertional (PAI) loci were used as genetic markers. These markers are thought to be selectively neutral. The presence of these six PAIs was determined by a polymerase chain reaction (PCR)-based assay in 1646 individuals from 47 populations from around the world. Examination of the populations by plotting the first and second principal components, shows the expected segregation of populations according to geographical vicinity and established ethnic affinities. Centroid analysis demonstrated that sub-Sahara populations have experienced higher than average gene flow and/or represent larger populations as compared to groups in other parts of the globe and especially to known inbreed populations. This is consistent with greater heterogeneity and diversity expected of source groups. In addition, maximum likelihood (ML) analyses were performed with these 47 populations and a hypothetical ancestral group lacking the insertion in all six loci. Analysis of our data supports the Out of Africa hypothesis. African populations and admixed groups of African descent formed a single monophyletic group with a basal placement on the tree, which grouped closest to the hypothetical ancestor. 相似文献
86.
A new chemical preparation of silver iodate AgIO3 is given. The crystal structure has been determined by single-crystal X-ray diffraction methods and refined to a finalR value of 0.051 for 1280 independent reflections. The unit cell is orthorhombic witha = 7.265(2), b = 15.17(4), c = 5.786(2)A?,Z = 8. The space group isPbc21. IO3 groups and AgO6 octaedra form a compact bidimensional framework perpendicular to theb axis. 相似文献
87.
Stuart Clough John Gupton Adepeju Ligali Matthew Roberts David Driscoll Scott Annett Alisa Hewitt Matthew Hudson Edward Jackson Robert Miller Bradley Norwood Rene Kanters Hadley Wyre Heather Petruzzi 《Tetrahedron》2005,61(31):7554-7561
The highly stereoselective conversions of (Z)-3-aryl-3-chloropropenals to (E)-3-alkoxy-3-arylpropenals, to (E)-3-aryl-3-morphorlinopropenals, and to vinamidinium salts are reported. The stereochemical assignments were based on 2D-NMR experiments. 相似文献
88.
Michele Daney Rene Lapouyade Monique Mary Henri Bouas-Laurent 《Journal of organometallic chemistry》1975,92(3):267-274
A detailed study of the stereochemistry of alkylation of 9-ethyl- and 9-isopropyl-10-lithio-9,10-dihydroanthracenes by alkyl halides (R′ = Me, Et, i-Pr) is reported. The reaction is under kinetic control. cis-9-Ethyl-10-isopropyl-9,10-dihydroanthracene has been found more stable than the trans isomer. If we take into account the stereoelectronic factor, which favors axial attack, and the main steric interactions in the transition state, stereochemistry seems to be mainly controlled by the competition between axial-axial and peri interactions. 相似文献
89.
The synthesis, structure, and reactivity of a series of low-coordinate Fe(II) diketiminate amido complexes are presented. Complexes L(R)FeNHAr (R = methyl, tert-butyl; Ar = para-tolyl, 2,6-xylyl, and 2,6-diisopropylphenyl) bind Lewis bases to give trigonal pyramidal and trigonal bipyramidal adducts. In the adducts, crystallographic and (1)H NMR evidence supports the existence of agostic interactions in solid and solution states. Complexes L(R)FeNHAr may be oxidized using AgOTf, and the products L(R)Fe(NHAr)(OTf) are characterized with (19)F NMR spectroscopy, UV/vis spectrophotometry, solution magnetic measurements, elemental analysis, and, in one case, X-ray crystallography. In the structures of the iron(III) complexes L(R)Fe(NHAr)(OTf) and L(R)Fe(OtBu)(OTf), the angles at nitrogen and oxygen result from steric effects and not pi-bonding. The reactions of the amido group of L(R)FeNHAr with weak acids (HCCPh and HOtBu) are consistent with a basic nitrogen atom, because the amido group is protonated by terminal alkynes and alcohols to give free H(2)NAr and three-coordinate acetylide and alkoxide complexes. The trends in complex stability give insight into the relative strength of bonds from three-coordinate iron to anionic C-, N-, and O-donor ligands. 相似文献
90.
Rene J. LeBlanc Christopher T. Williams 《Journal of molecular catalysis. A, Chemical》2004,220(2):207-214
The adsorption of the chiral modifier cinchonidine on platinum in ethanol as a function of temperature has been studied with surface-enhanced Raman spectroscopy (SERS). The temperature range chosen was from 30 to 70 °C, within which both the activity and selectivity of cinchonidine-modified Pt catalysts have been shown to change dramatically. Platinum surfaces were modified with 260 μM cinchonidine in ethanol, and examined both in pure ethanol and in the modifying solution itself. Adsorbed cinchonidine under pure ethanol was found to partially desorb as the temperature was raised, accompanied by an increase in the average tilt of the quinoline group with respect to the surface. In contrast, the presence of solution-phase cinchonidine resulted in an increase in the cinchonidine surface coverage and average tilt as temperature was raised. In a previous study [J. Mol. Catal. A 212 (2004) 277] we showed that hydrogen causes a dramatic enhancement in the SERS response of adsorbed cinchonidine. This was attributed to a conversion of cinchonidine to 10,11-dihydrocinchonidine on the Pt surface and a more flat orientation of the quinoline group. In both pure ethanol and in 260 μM cinchonidine, the presence of hydrogen causes a significant decrease in the alkaloid SERS bands at temperatures above 40 °C. In addition, the average tilt of the quinoline group increases significantly at these elevated temperatures. The temperature-dependence of 10,11-dihydrocinchonidine adsorption was also investigated, and is almost identical to that observed for cinchonidine in the presence of hydrogen. This lends further support to the conclusion that cinchonidine is being hydrogenated on the Pt surface in the presence of hydrogen. The significant changes observed on the cinchonidine-modified Pt surface above 40 °C correlate well with reported decreases in enantioselectivity and turn-over frequency at similar temperatures during ethyl pyruvate hydrogenation. 相似文献