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1.
Mingyang Zhao Warren T. Ford Stefan H. J. Idziak Nicholas C. Maliszewskyj Paul A. Heiney 《Liquid crystals》1994,16(4):583-599
The hexa-4-dodecyloxybenzoyl derivative 1 of azacrown [18]-N6 was originally reported to have a 'tubular' mesophase on the basis of its large central ring and 6-fold symmetry. Starting in the mesophase, annealing of 1 under a cover slip results in formation of a new crystalline phase that melts directly to an isotropic liquid at the temperature previously observed for the mesophase to isotropic transition. Thus the phase behaviour of 1 is kinetically controlled. The analogous hexa-3,4-bisdodecyloxybenzoyl derivative 2 of azacrown [18]-N6 has no kinetic limitations to its phase changes and has an enantiotropic columnar liquid crystalline phase. We have synthesized side chain copolysiloxanes with a (CH2)11 spacer and 75-84 per cent by weight of the same 4-dodecyloxybenzoyl-[18]-N6 mesogen. The polysiloxanes also display a liquid crystalline phase. 相似文献
2.
Three fixtures for conducting laboratory fretting fatigue tests are described and their respective testing methods and the
results of the analysis are compared. Each of these fixtures has been used to investigate the effects of various parameters
of interest in fretting fatigue. These fixtures include a unique apparatus in which all load applied to the specimen is transferred
to the fretting pads, an apparatus similar to many found in the literature where partial load transfer occurs across the pads,
and a simplified dovetail fixture in which the clamping load, P, and the shear load, Q, are varied in phase. Select test conditions from prior experiments performed on identical material and resulting in similar
lives ranging from one to ten million cycles from these fixtures are identified. The various testing conditions were used
to compute the unique stress field for each case. The resulting contact stresses were used to calculate crack initiation based
criteria, and to calculate stress intensity factors. The three fixtures were shown to be able to accommodate a range of loads,
fretting pad contours, and specimen geometries that produced a variety of stress fields. A crack-initiation-based criterion
was shown to predict the failure lives of thinner specimens accurately. The stress intensity factor calculations showed the
possibility of a crack arresting for a stress field that decays rapidly and the possibility of a local minimum for K as a function of depth. The fixtures are shown to be complementary in generating data for development of robust fretting
fatigue models that use these criteria. 相似文献
3.
Nicholas W. DeLuca Yossef A. Elabd 《Journal of Polymer Science.Polymer Physics》2006,44(16):2201-2225
The direct methanol fuel cell (DMFC) has the potential to replace lithium‐ion rechargeable batteries in portable electronic devices, but currently experiences significant power density and efficiency losses due to high methanol crossover through polymer electrolyte membranes (PEMs). Numerous publications document the synthesis and characterization of new PEMs for the DMFC. This article reviews this research, transport phenomena in PEMs, and experimental techniques used to evaluate new PEMs for the DMFC. Although many PEMs do not show significant improvements over Nafion®, the benchmark PEM in DMFCs, experimental results show that several new PEMs exhibit lower methanol crossover at similar proton conductivities and/or higher DMFC power densities. These results and recommendations for future research are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Parts B: Polym Phys 44: 2201–2225, 2006 相似文献
4.
A simple and versatile method for the synthesis of acetals from aldehydes and ketones using bismuth triflate 总被引:1,自引:0,他引:1
Leonard NM Oswald MC Freiberg DA Nattier BA Smith RC Mohan RS 《The Journal of organic chemistry》2002,67(15):5202-5207
Acetals are obtained in good yields by treatment of aldehydes and ketones with trialkyl orthoformate and the corresponding alcohol in the presence of 0.1 mol % Bi(OTf)3.4H2O. A simple procedure for the formation of acetals of diaryl ketones has also been developed. The conversion of carbonyl compounds to the corresponding 1,3-dioxolane using ethylene glycol is also catalyzed by Bi(OTf)3.4H2O (1 mol %). Two methods, both of which avoid the use of benzene, have been developed. 相似文献
5.
Chester M. Mikulski William Henry Louis L. Pytlewski Nicholas M. Karayannis 《Transition Metal Chemistry》1977,2(1):135-140
Summary Complexes (2 : 1) of diethyl benzoylphosphonate (debp) with 3d metal perchlorates were synthesized and characterized by means of i.r. and electronic spectral, magnetic susceptibility and conductance measurements. In new complexes of the types [M(debp)2(OClO3)(OH2)](ClO4) (M = Fe, Co, Zn) and [Fe(debp)2(OClO3)(OH2)](ClO4)2, both debp ligands function as bidentate chelating agents, coordinating through the P=O and C=O oxygens. In contrast, in the manganese(II) and nickel(II) complexes, which are of the [M(debp)2(OClO3)(OH2)2](ClO4) type, one debp acts as a bidentate chelating ligand, while the second debp is unidentate, coordinating only through the P=O oxygen. Hexacoordination in the new cationic complexes is completed by coordination of aqua and unidentate perchlorato ligands, which are in competition for sites in the inner coordination sphere of the central metal ion with the weak debp ligand. On the other hand, debp, owing to its bulkiness, and especially the presence of the benzoyl substituent, introduces sufficiently severe steric hindrance during coordination. As a result of this, the formation of [M(debp)3]n+ tris-chelate cationic complexes with the 3 d metal ions under study does not seem to be possible. 相似文献
6.
Using recently developed theoretical techniques it has been possible to achieve an exact variational solution of the Schrödinger equation within a modest basis set or one-eleltron functions. The full configuration interaction for this system included a total of 256473 1A1 spin-and space-adapted configurations. Comparison with many-body perturbation theory proves to be quite interesting. 相似文献
7.
Multivalent cations can cause DNA to condense from its extended state in solution into high-density toroid-shaped particles. Developing methods to control the size and size distribution of DNA toroids is an important goal for the development of artificial gene delivery systems. Here we demonstrate that changes in salt conditions, prior to condensation by multivalent cations, can significantly affect DNA condensation. Specifically, millimolar concentrations of MgCl2 are shown to cause the formation of toroid clusters, whereas NaCl at the same ionic strength does not. 相似文献
8.
[reaction: see text] A novel solid-phase synthesis of 1,2-dialkoxyindoles on SynPhase lanterns is described. A unique C-C bond formation involving a nucleophilic displacement of a solid-bound aryl fluorine by dimethyl malonate afforded the arylnitro methyl ester, which upon treatment with tin(II) chloride dihydrate gave the N-hydroxyindolone. Alkylation of the N-hydroxyindolones afforded the corresponding N-hydroxy-2-alkoxyindoles, which were further alkylated to give the 1,2-dialkoxyindole. A library of 64 (8R(1) x 8R(2)) discrete 1,2-dialkoxyindoles was prepared using a color encoding technique on SynPhase A-series lanterns. 相似文献
9.
Nitropyridines reacted with an excess of vinyl Grignard reagent to produce 4- or 6-azaindoles. Improved yields were obtained when a halogen atom was present at the position alpha to the nitrogen atom in the pyridine ring. 相似文献
10.
Pygmalion S. Lianis Nestor A. Rodios Nicholas E. Alexandrou 《Journal of heterocyclic chemistry》1988,25(4):1099-1102
Mesitonitrile oxide reacts with C ≡ N bond of (aryl)(9-fluorenylidene)acetonitriles 1 forming in very good yields the corresponding 1,2,4-oxadiazoles 2. Analogously also proceeds the reaction of mesitonitrile oxide with 9-fluorenylidenemalonodinitrile (3) with the formation of bis-1,2,4-oxadiazole derivative 4. 相似文献