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31.
Seymour Siegel Robert J. Champetier A. R. Calloway 《Journal of polymer science. Part A, Polymer chemistry》1966,4(9):2107-2120
The ultraviolet (λ = 2537 A.) photolysis of a degassed mixed phenyl and methyl polysiloxane liquid is examined in terms of gas and crosslinking yields. Results are compared to the published values obtained by ionizing irradiation of this type of molecule. It is shown that ultraviolet radiation is less efficient by two orders of magnitude in producing decomposition (i.e., gaseous products) than is ionizing radiation. The comparisons for crosslinking efficiencies are less certain, but the yields seem to have much more similar values in this case based on a spectroscopic estimation of crosslinking (i.e., analysis for substituted phenylcyclohexadiene formation). The gas quantum yields were ?H2 = 2.6 × 10?5, ?CH4 = 0.63 × 10?5, ?C2H6 ≈ 0.12 × 10?5, and ?C2H2 ≈ 0.06 × 10?5. 相似文献
32.
The unimolecular reactions that give rise to mass spectra are controlled by spatial relationships and energy considerations. In molecules that contain a heteroatom, elimination reactions, involving bond-making as well as breaking, are often prominent, e.g. loss of water from alcohols. The ease of such reactions depends on spatial relationships in the molecule, and the resultant ion intensities in the spectra of geometric isomers can consequently be correlated with differences in geometry and hence furnish a basis for assigning structures. Processes that do not involve bond-making do not have such rigorous geometric requirements, but depend rather on attainment of a transition state defined in terms of a minimum energy content. Common product ions from stereoisomeric hydrocarbons seem often to arise via a common transition state. When this condition holds, the difference between the enthalpies of the isomers is reflected in the relative appearance potentials and–though the cause-and-effect relationship here is less direct and more readily obscured by other factors–relative intensities of the common product derived from the isomers. In both classes of processes, the spectra of stereoisomers can be simplified and made more distinctive by lowering source temperature and ionizing voltage. 相似文献
33.
Charles M. Newman 《Constructive Approximation》1991,7(1):389-399
LetV(t) be the even function on (–, ) which is related to the Riemann xi-function by (x/2)=4
–
exp(ixt–V(t))dt. In a proof of certain moment inequalities which are necessary for the validity of the Riemann Hypothesis, it was previously shown thatV'(t)/t is increasing on (0, ). We prove a stronger property which is related to the GHS inequality of statistical mechanics, namely thatV' is convex on [0, ). The possible relevance of the convexity ofV' to the Riemann Hypothesis is discussed.Communicated by Richard Varga. 相似文献
34.
David J. Barsky Geoffrey R. Grimmett Charles M. Newman 《Probability Theory and Related Fields》1991,90(1):111-148
Renormalization arguments are developed and applied to independent nearest-neighbor percolation on various subsets of
d
,d2, yielding:
Corollaries of these results include uniqueness of the infinite cluster for such 's and sufficiency of the following for proving continuity of the full-space phase transition: showing that percolation in the full-space at densityp implies percolation in the half-space at thesame density. 相似文献
| Equality of the critical densities,p c (), for a half-space, quarter-space, etc., and (ford>2) equality with the limit of slab critical densities. |
| Continuity of the phase transition for the half-space, quarter-space, etc.; i.e., vanishing of the percolation probability, (p), atp=p c (). |
35.
Sibilant groove place and width were initially examined during [s] [s] in isolation and in CV and VC syllables. The [s] was found to be produced through a 6- to 8-mm-wide groove near the front of the alveolar ridge by one talker and near the back of the ridge by the other. [s] was produced through a 10- to 12-mm groove behind the posterior border of the alveolar ridge by both. In the second experiment three subjects used visual articulatory feedback to vary sibilant groove width and place systematically. One subject was able to do this with comparatively few retrials; one had difficulty with certain targeted grooves; one had difficulty with many targeted grooves. The noises generated were replayed to 14 listeners who labeled them as "s," "probably s," "probably sh," or "sh." They usually heard the sound as [s] when the grooves were narrow and near the front of the alveolar process, [s] when the groove was wider and behind the alveolar process. Noise through grooves that matched natural speech places and widths usually produced higher listener recognition scores. Exceptions were found when the subjects had unusual difficulty in achieving stipulated groove widths and places. 相似文献
36.
37.
38.
R. P. A. C. Newman 《General Relativity and Gravitation》1981,13(3):257-282
Results are established concerning perturbations of each empty Robertson-Walker space-time (M, g) with a nonvanishing cosmological constant. The perturbed space-times have the general form (
) with
an extension ofM, and
lying in an open neighborhood of g in a type ofW
m
topology. These results indicate that large classes of such perturbations give rise to space-times which suffer from one of two types of incompleteness. 相似文献
39.
C. M. Newman 《Communications in Mathematical Physics》1981,79(1):133-140
The renormalized, dimensionless 4-point coupling constant of scalar one dimensional field theories is maximized uniquely by the critical point theories (obtainable as the scaling limit of 4 models). The renormalized coupling constant of certain scalar one dimensional lattice field theories is maximized uniquely (for fixed correlation length) by the corresponding spin-1/2 model.Alfred P. Sloan Research Fellow, on leave from Indiana University. Research supported in part by NSF Grant MCS 77-20683 and by the U.S.-Israel Binational Science Foundation 相似文献
40.
C.G. Newman B.N. Diel D.P. Paquin M.A. Ring 《Journal of organometallic chemistry》1977,137(3):281-286
Methylation of SiH4, MeSiH3, Si2H6, GeH4 and B2H6, but not of PH3 or AsH3, was observed during reaction (230–324°C) with GaMe3. The products from the SiH4 and Si2H6 reactions were MeSiH3, Me2SiH2 and Me3SiH. The GeH4-derived products were similar, with Me4Ge also being formed. The only methylated products from B2H6 was BMe3. The silane reactions were surface-catalyzed (presumably by surface hydroxyl groups), while those of GeH4 and B2H6 may have occurred via gas-phase free radical processes. 相似文献