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101.
X-ray scattering has been studied above the critical ordering temperature, Tc (133°C), in b.c.c. α-phase V2D. At 140 and 200°C quite weak diffuse intensity was observed centered on the reciprocal lattice points of the ordered superlattice. This intensity is due to short-range order among deuterium atoms which induces a local or short-range modulation of the parent vanadium lattice and suggests the possibility of local octahedral D—D fluctuations building up well above Tc. 相似文献
102.
Cyclobutylchlorocarbene can be intercepted by simple alkenes in successful competition with intramolecular ring expansion and hydride migration reactions. 相似文献
103.
The iron-dextran complex 总被引:4,自引:0,他引:4
104.
Catherine E. Housecroft Ronald Snaith Karen Moss Robert E. Mulvey Marion E. ONeill Kenneth Wade 《Polyhedron》1985,4(11):1875-1881
Cluster bond enthalpies, EL(BB), and orders, n?(BB), for the structurally characterised closo anions, BnHn2? (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships EL(BB) (kJ mol?1) = 1.766 × 1011 [L(BB)]?4.0 and EL(BB) (kJ mol?1) = 318.8[n?(BB)]0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, EI, have been calculated using the relationships EI(BB) = 297.9 I(BB) and EI(BH) = 374.8I(BH) (enthalpies in kJ mol?1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of EL and Σ EL generally exceed those of EI and Σ EI by some 8% and calculated values of I generally exceed those of n? by a greater amount, the trends in these parameters for the series of BnHn2? anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ EI values suggest that the anions are all of comparable stability, the ΣEL values clearly show B6H62?, B10H102? and B12H122? to be more stable than B8H82?, B9H92? and B11H112?. The interatomic distances in B7H72? and in the unknown B5 H52? are estimated and used to assess their relative stabilities. The EL values suggest that B7 H72? is of comparable stability to B8H82? etc., but show B5H52? as relatively unstable. The EI values suggest that both of these anions should be relatively stable members of the series of closo anions. 相似文献
105.
[reaction: see text] Photolysis of 3-(2,2,2-triphenylethoxy)-3-chlorodiazirine gives 2,2,2-triphenylethoxychlorocarbene which fragments with 1,2-phenyl migration and loss of CO and Cl(-) to yield the 1,1,2-triphenylethyl cation and thence 1,1,2-triphenylethene by proton loss. However, ps and fs laser flash photolysis provides evidence that up to 25% of the alkene product stems from carbocation that arises directly from excited diazirine rather than from the carbene. 相似文献
106.
Barbara Moss Douglas L. Dorset J. C. Wittmann B. Lotz 《Journal of Macromolecular Science: Physics》2013,52(1-4):99-118
Epitaxial growth produces oriented crystal projections where a long unit cell axis is parallel to the major crystal face rather than perpendicular to it and thus provides a favorable condition for electron diffraction data collection which minimizes perturbations due to elastic crystal bending. Even though the crystals are not so perfect as those produced by solution growth, the intensity data from them have been useful for the quantitative crystal structure analysis of several molecular organic compounds and linear polymers as discussed in this review. 相似文献
107.
Abstract Recent observation of the acoustic saturation and of phonon echoes in crystalline quartz after light irradiation with fast neutrons indicates that there are the same low-energy atomic tunnelling systems as in Si02 glass. We report measurements of the diffuse X-ray scattering and of the lattice parameter change from neutron irradiated quartz single crystals studying the strength and symmetry of strain defects and their local correlations. For dose 3 × 1018 n/cm2 the diffuse scattering close to the Bragg peaks together with the lattice parameter change shows that the neutrons create defective regions with a volume change of 29 mean atomic volumes. The distortion field of these regions shows no high symmetry. The radius of the heavily strained region is ~ 10 Å. For higher doses the regions grow a little bit but mainly new defective regions are built. According to the various volume fractions of defective regions at various doses the first strong amorphous halo at about K≈ 1.5 A?1 was detected. Since this amorphous scattering is isotropic and during annealing the regions disappear mainly without changing their size we are led to the conclusion that the defective regions are glass-like in nature. So the size of the tunnelling system has to be smaller than 20 Å. 相似文献
108.
109.
Philip S. Hall Graham E. Jackson John R. Moss David A. Thornton Paul F. M. Verhoeven Gareth M. Watkins 《光谱学快报》2013,46(7):1247-1267
Abstract The infrared spectra (4000 - 50 cm?1) of the square planar rhodium(I) complexes cis-[Rh(CO)2 (pyridine) (X)] (X = Cl, Br) and their isotopomers with pyridine-d 5 and 13CO have been determined. Assignments are based on earlier studies on pyridine and its complexes and on the shifts in infrared bands which are caused by the isotopic substitutions employed. Normal coordinate analysis following the procedure of Becher and Mattes has been used to confirm the empirical assignments. The two v(RhC) bands are observed near 490 and 450 cm?1. v(RhN) is found near 210 cm?1 and v(RhX) occurs at 310 (X = Cl) and 235 (X = Br) cm?1. At frequencies below 200 cm?1, the bands are assigned to bending modes in the following sequence: δ (RhN) > δ (CRhC) > δ (RhCl) > γ (RhCl) > γ (RhN). 相似文献
110.
P. M.C. de Oliveira S. Moss de Oliveira D. Stauffer S. Cebrat A. Pękalski 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):245-254
We discovered a dynamic phase transition induced by sexual
reproduction. The dynamics is a pure Darwinian rule applied to diploid
bit-strings with both fundamental ingredients to drive Darwin's
evolution: (1) random mutations and crossings which act in the sense of
increasing the entropy (or diversity); and (2) selection which acts in
the opposite sense by limiting the entropy explosion. Selection wins
this competition if mutations performed at birth are few enough, and
thus the wild genotype dominates the steady-state population. By slowly
increasing the average number m of mutations, however, the
population suddenly undergoes a mutational degradation precisely at a
transition point mc. Above this point, the “bad”
alleles (represented by 1-bits) spread over the genetic pool of the
population, overcoming the selection pressure. Individuals become
selectively alike, and evolution stops. Only below this point, m < mc, evolutionary life is possible.
The finite-size-scaling behaviour of this transition is
exhibited for large enough “chromosome” lengths L, through
lengthy computer simulations. One important and surprising observation
is the L-independence of the transition curves, for large L.
They are also independent on the population size. Another is that mc is near unity, i.e. life cannot be stable with much more
than one mutation per diploid genome, independent of the chromosome
length, in agreement with reality. One possible consequence is that an
eventual evolutionary jump towards larger L enabling the storage
of more genetic information would demand an improved DNA copying
machinery in order to keep the same total number of mutations per
offspring. 相似文献