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排序方式: 共有59条查询结果,搜索用时 78 毫秒
21.
Vadavi R Conrad ED Arbuckle DI Cameron TS Essoun E Aquino MA 《Inorganic chemistry》2011,50(23):11862-11864
[Ru(2)(μ-O(2)CCH(3))(4)(MeOH)(2)](PF(6)) reacts with chiral diphosphines (R,R)- and (S,S)-chiraphos, leading to disassembly and production of the enantiomers Λ-[Ru(η(2)-O(2)CCH(3))(η(2)-(R,R)-chiraphos)(2)](PF(6)) and Δ-[Ru(η(2)-O(2)CCH(3))(η(2)-(S,S)-chiraphos)(2)](PF(6)) in high yield and purity. X-ray crystallography and solid-state circular dichroism (CD) show that only the indicated isomers are present in the solid state. Solution CD measurements also indicate their predominance in solution. 相似文献
22.
Hiroyuki Sasabe Cornelius T. Moynihan 《Journal of Polymer Science.Polymer Physics》1978,16(8):1447-1457
Structural relaxation in poly(vinyl acetate) (PVAc) in and slightly above the glass-transition region has been studied by monitoring the time dependence of enthalpy using differential scanning calorimetry and the frequency dependence of electric polarization by dielectric loss measurements. The results have been analyzed to yield the kinetic parameters characterizing the structural relaxation and are compared with similar analyses of previously published shear compliance and volume relaxation experiments. Relaxation of enthalpy, electric polarization, volume, and shear stress in PVAc all appear to be characterized by somewhat different relaxation times. The difference between the volume and enthalpy relaxation times, coupled with the fact that PVAc exhibits a Prigogine–Defay ratio greater than unity, is evidence for a previously proposed connection between the thermodynamics and kinetics of structural relaxation in terms of an order parameter model. 相似文献
23.
The influence of glass composition on the crystal growth kinetics of heavy metal fluoride glasses 总被引:1,自引:0,他引:1
The kinetics of crystallization of two heavy metal fluoride glasses, ZrF4---BaF2---LaF3---AlF3---LiF and ZrF4---BaF2---LaF3---AlF3---LiF---PbF2, which are of potential use as core and clad materials for fiber optic waveguides, have been studied by differential scanning calorimetry. The devitrification processes follow the Johnson-Mehl-Avrami relation, and the values of the kinetic parameters for isothermal and non-isothermal techniques are in excellent agreement. The crystallization activation energies for these glasses are about two-thirds those previously reported for a ternary ZrF4---BaF2---LaF3 glass. The implications of the experimental results for glass stability against devitrifications are discussed. 相似文献
24.
[Cu2(μO2CCH3)4(H2O)2], [CuCO3·Cu(OH)2], [CoSO4·7H2O], [Co((+)-tartrate)], and [FeSO4·7H2O] react with excess racemic (±)- 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate {(±)-PhosH} to give mononuclear CuII, CoII and FeII products. The cobalt product, [Co(CH3OH)4(H2O)2]((+)-Phos)((−)-Phos) ·2CH3OH·H2O (7), has been identified by X-ray diffraction. The high-spin, octahedral CoII atom is ligated by four equatorial methanol molecules and two axial water molecules. A (+)- and a (−)-Phos− ion are associated with each molecule of the complex but are not coordinated to the metal centre. For the other CoII, CuII and FeII samples of similar formulation to (7) it is also thought that the Phos− ions are not bonded directly to the metal. When some of the CuII and CoII samples are heated under high vacuum there is evidence that the Phos− ions are coordinated directly to the metals in the products. 相似文献
25.
Richard Moynihan 《Probability Theory and Related Fields》1976,35(2):177-187
Let C be a collection of particles, each of which is independently undergoing the same Markov chain, and let d be a metric on the state space. Then, using transition probabilities, for distinct p, q in C, any time t and real x, we can calculate F
pq
(t)
(x) = Pr [d (p,q)t]. For each time t 0, the collection C is shown to be a probabilistic metric space under the triangle function
. In this paper we study the structure and limiting behavior of PM spaces so constructed. We show that whenever the transition probabilities have non-degenerate limits then the limit of the family of PM spaces exists and is a PM space under the same triangle function. For an irreducible, aperiodic, positive recurrent Markov chain, the limiting PM space is equilateral. For an irreducible, positive recurrent Markov chain with period p, the limiting PM space has at most only [p/2]+2 distinct distance distribution functions. Finally, we exhibit a class of Markov chains in which all of the states are transient, so that P
ij(t)0 for all states i, j, but for which the {F
pq
tt
} all have non-trivial limits and hence a non-trivial limiting PM space does exist. 相似文献
26.
Emmanuel N. Zevgolis Charalabos Zografidis Theodora Perraki Eamonn Devlin 《Journal of Thermal Analysis and Calorimetry》2010,100(1):133-139
This article refers to the mineralogical composition and phase transformations of Greek nickeliferous laterites and to their
metallurgical behaviour, during preheating and reduction with carbon monoxide. Transformation of goethite to hematite and
decomposition of chlorite and serpentine, were identified during preheating. Higher iron metallization was achieved for the
ore in which goethite is the main iron mineral and reduction goes up to 95%, whereas it goes up to 50% for the ore in which
hematite is the main iron mineral. The higher reducibility, however, seems to be due to the higher specific surface area of
the goethitic type of ore. 相似文献
27.
28.
Zueva EM Sameera WM Piñero DM Chakraborty I Devlin E Baran P Lebruskova K Sanakis Y McGrady JE Raptis RG 《Inorganic chemistry》2011,50(3):1021-1029
Six [Fe(8)(μ(4)-O)(4)(μ-4-R-pyrazolato)(12)X(4)] complexes containing an identical Fe(8)(μ(4)-O)(4) core have been structurally characterized and studied by M?ssbauer spectroscopy. In each case, an inner μ(4)-O bridged Fe(III) cubane core is surrounded by four trigonal bipyramidal iron centers, the two distinct sites occurring in a 1:1 ratio. The M?ssbauer spectrum of each of the clusters consists of two quadrupole doublets, which, with one exception (X = NCS, R = H), overlap to give three absorption lines. The systematic variation of X and R causes significant changes in the M?ssbauer spectra. A comparison with values for the same clusters computed using density functional theory allows us to establish an unequivocal assignment of these peaks in terms of a nested model for the overlapping doublets. The changes in M?ssbauer parameters (both experimental and computed) for the 1-electron reduced species [Fe(8)(μ(4)-O)(4)(μ-4-Cl-pyrazolato)(12)Cl(4)](-) are consistent with a redox event that is localized within the cubane core. 相似文献
29.
Heisenberg’s explanation of how two coupled oscillators exchange energy represented a dramatic success for his new matrix
mechanics. As matrix mechanics transmuted into wave mechanics, resulting in what Heisenberg himself described as “…an extraordinary
broadening and enrichment of the formalism of the quantum theory”, the term resonance also experienced a corresponding evolution.
Heitler and London’s seminal application of wave mechanics to explain the quantum origins of the covalent bond, combined with
Pauling’s characterization of the effect, introduced resonance into the chemical lexicon. As the Valence Bond approach gave
way to a soon-to-be dominant Molecular Orbital method, our understanding of the term resonance, as it might apply to our understanding
the chemical bond, has also changed. 相似文献
30.