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91.
Helium clustering and bubble growth have been studied in Ni and Ni-1 at % Ti through positron lifetime measurements. Helium pressure in the bubble as well as bubble concentration have been estimated and compared for the cases of Ni and Ni-1 at % Ti. The results seem to indicate enhanced helium trapping due to substitutional Ti impurity in the host Ni. 相似文献
92.
S. N. Yedave P. D. Kodali S. T. Bendre R. Viswanathan S. M. Kanetkar S. M. Chaudhari S. B. Ogale 《Solid State Communications》1989,70(12):1131-1135
Ion-implantation-induced structural modifications in Y1Ba2Cu3O7−δ superconductor are examined by a grazing angle X- ray diffraction technique. By employing a range of grazing angles from 0.3° to 10° it is shown that 100 KeV Ar+ inplantation of the superconductor leads to amorphization as well as modification of grain size and orientation at dose values lower than 1016 ions/ cm2. At the dose of 5 × 1016 ions/ cm2 the X-ray diffraction intensity is a factor of 6 less as compared to the original pellet, though the lines themselves are sharp. This shows coexistence of perovskite grains and amorphous matrix. 相似文献
93.
Dispersion equations for the ordinary and extraordinary cyclotron waves propagating perpendicular to the magnetic field in
metals in the critical region where the wavelength is comparable to the electron Larmor radius are derived as an infinite
but rapidly converging power series expansion in δ( = Ω/Ω-M). Numerical studies for the cyclotron wave propagation near the first seven resonances are carried out. The non-local behaviour
of those waves in the critical region 01 ⩽ kR ⩽ 3-0 is studied. For the ordinary waves the first few resonances show significant
dispersion than those near higher resonances which are dispersion-free. Only one extraordinary wave propagates near the fundamental
cyclotron frequency. For the higher resonances, two modes propagate near each of the resonant frequencies, of which one mode
remains constant for all values ofkR whereas the second mode shows significant dispersion. But beyond the fifth resonance both the modes are dispersion free. 相似文献
94.
Bo Pan Kalyanaraman Viswanathan Charles E. Hoyle Robert B. Moore 《Journal of polymer science. Part A, Polymer chemistry》2004,42(8):1953-1962
The photoinitiated grafting of maleic anhydride (MAH) onto polypropylene with the use of benzophenone (BP) as the initiator has been investigated. In comparison with the process of thermally initiated grafting with peroxide as the initiator, photoinitiated grafting affords a higher grafting efficiency. The efficient photografting sensitized by BP can be explained by two possible mechanistic processes: the sensitization of the formation of the excited triplet state of MAH by BP and electron transfer followed by proton transfer between MAH and the benzopinacol radical, which may operate together. In the former case, the generated MAH excited triplet state abstracts a hydrogen from the polymer substrate to initiate grafting. A rate constant of 3.6 × 109 M ?1 s ?1 has been determined by laser flash photolysis for the process of quenching the excited triplet state of BP with ground‐state MAH. In comparison, the rate constant for the quenching of the excited triplet state of BP by hydrogen abstraction has been determined to be 4.1 × 105 M ?1 s ?1. In a study of photografting using a model compound, 2,4‐dimethylpentane, as a small‐molecule analogue of polypropylene, the loss of BP was significantly reduced upon the addition of MAH, and this is consistent with the proposed mechanistic processes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1953–1962, 2004 相似文献
95.
S. S. Obayd B. S. M. Rao S. T. Bendre R. Viswanathan S. M. Chaudhari S. M. Kanetkar S. B. Ogale 《Journal of Radioanalytical and Nuclear Chemistry》1991,153(2):117-123
High-Tc superconductor YBa2Cu3O7 was irradiated by thermal neutrons. Significant effects on the critical temperature were found. The changes were also investigated by X-ray diffraction technique.65Cu (n, )66Cu was the only reason for the degradation in superconducting properties. The existence of an isotope effect is argued. 相似文献
96.
97.
Viswanathan R Prabhakaran EN Plotkin MA Johnston JN 《Journal of the American Chemical Society》2003,125(1):163-168
The scope of aryl radical additions to the nitrogen of azomethines is described. Aryl, trifluoromethyl alkyl, and alpha,beta-unsaturated ketimines engage in regioselective aryl-nitrogen bond formation via 5-exo cyclizations of an aryl radical to azomethine nitrogen. Selectivity for carbon-nitrogen over carbon-carbon bond formation is generally high (>95:5) and competes only with direct aryl radical reduction by stannane (0-10%). Alpha-ketoimines are a promising new class of carbon radical acceptors for which no competitive aryl radical reduction is observed. The reaction conditions are pH-neutral and are therefore among the mildest methods available for amination of an aromatic ring. The ketimines examined did not suffer from competitive reduction by stannane, offering an advantage over the use of diazo and azide functional groups as nitrogen sources for carbon radicals. The free radical-mediated aryl amination was sequenced with the O'Donnell phase transfer-catalyzed enantioselective alkylation strategy of glycinyl imine to provide either enantiomer of indoline alpha-amino acids with high ee. These new constrained phenyl alanine derivatives are now readily available for evaluation across a variety of applications. 相似文献
98.
T. Viswanathan F. Gomez K. B. Wagener 《Journal of polymer science. Part A, Polymer chemistry》1994,32(13):2469-2477
Acyclic dience metathesis (ADMET) depolymerization of functionalized furan-based polymers prepared via aqueous ring-opening polymerization of 7-oxanobornenes has been investigated. Results indicate that while very high molecular weight poly [exo-N-methyl-7-oxabicyclo [2.2.1] hept-2,5-diene-2,3-dicarboximide] can be depolymerized to oligomers with ease, poly [2,3-dicarbomethoxy-7-oxabicyclo [2.2.1] hept-2,5-diene] is more resistant to depolymerization under similar conditions. This difference may be due to differential interaction of the carbonyls in the side chains with the metal atom of the catalyst in the proposed metallacyclobutane intermediate. ADMET depolymerization of poly [2,3-bis (trifluoromethyl)-7-oxabicyclo [2.2.1] hept-2,5-diene] was feasible, however, the extent of depolymerization was decreased due to the use of a coordinating solvent (THF) used during the depolymerization process. © 1994 John Wiley & Sons, Inc. 相似文献
99.
A procedure is described for the estimation of fluorine in microgramme quantities by the steam-distillation of the samples with sulphuric or phosphoric acid. Traces of the acid carried over are precipitated from the distillate as silver or barium salts, in order to eliminate their interference in the subsequent titration of fluorine. The results obtained compare favourably with those of the conventional perchloric acid method. By avoiding the latter, the present method offers the advantage of both safety and simplicity. 相似文献
100.
Viswanathan R Mutnick D Johnston JN 《Journal of the American Chemical Society》2003,125(24):7266-7271
The first examples of the azacyclopentenyl carbinyl radical isomerization are described within a series of enantiomerically enriched 2-substituted indolines, a substructure found extensively in both heterocyclic and natural product chemistry. The isomerization was identified by the varying loss of enantiomeric enrichment (ee) of imines during aryl radical cyclizations to azomethine nitrogen. Independent modification of the steric and electronic nature of the ring substituents revealed the full spectrum of sensitivity to these variables and ultimately defined the use of these effects as gating elements. An example is also given in which a 1,4-amino group transfer is effected via the isomerization mechanism. Analogies are drawn between the title isomerization and the azacyclopropyl carbinyl radical isomerization that has been studied in both chemical and biological contexts. 相似文献