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61.
Ryan M. Tipker Jake A. Muldoon Daniel H. Pham Balazs R. Varga Russell P. Hughes David S. Glueck Gary J. Balaich Arnold L. Rheingold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2022,134(1):e202110753
Tetrahedral main-group compounds are normally configurationally stable, but P-epimerization of the chiral phosphiranium cations syn- or anti-[Mes*P(Me)CH2CHPh][OTf] (Mes*=2,4,6-(t-Bu)3C6H2) occurred under mild conditions at 60 °C in CD2Cl2, resulting in isomerization to give a syn-enriched equilibrium mixture. Ion exchange with excess [NBu4][Δ-TRISPHAT] (Δ-TRISPHAT=Δ-P(o-C6Cl4O2)3) followed by chromatography on silica removed [NBu4][OTf] and gave mixtures of syn- and anti-[Mes*P(Me)CH2CHPh][Δ-TRISPHAT]?x[NBu4][Δ-TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P-C cleavage to yield a hyperconjugation-stabilized carbocation, pyramidal inversion promoted by σ-interaction of the P lone pair with the neighboring β-carbocation, and ring closure with inversion of configuration at P. 相似文献
62.
Chen X Zhang L Zhou K Davies E Sugden K Bennion I Hughes M Hine A 《Optics letters》2007,32(17):2541-2543
Using an optical biosensor based on a dual-peak long-period fiber grating, we have demonstrated the detection of interactions between biomolecules in real time. Silanization of the grating surface was successfully realized for the covalent immobilization of probe DNA, which was subsequently hybridized with the complementary target DNA sequence. It is interesting to note that the DNA biosensor was reusable after being stripped off the hybridized target DNA from the grating surface, demonstrating a function of multiple usability. 相似文献
63.
Suzanne K. Estok Thomas A. Hughes IV Mary K. Carroll Ann M. Anderson 《Journal of Sol-Gel Science and Technology》2014,70(3):371-377
Silica aerogels were prepared using the precursor tetraethylorthosilicate (TEOS) via a rapid supercritical extraction (RSCE) method. Multiple consistent batches of monolithic TEOS-based aerogels were fabricated via an 8-h RSCE process. Fabricating TEOS-based aerogels with an RSCE method offers some distinct advantages. One advantage is the relative simplicity of the RSCE approach: liquid precursors are mixed and poured into a metal mold in a hydraulic hot-press, where gelation, aging and extraction of liquid from the pores occur. The precursor recipe employs TEOS, ethanol, water, oxalic acid to catalyze hydrolysis, and ammonia to catalyze the subsequent polycondensation reactions. Another advantage is that reaction of TEOS to form sol gels yields ethanol as a byproduct. A process that releases ethanol, rather than methanol (as in tetramethylorthosilicate (TMOS)-based aerogels) may be more appealing for commercial applications, involving scale-up of the process. The significantly lower cost of TEOS, compared to TMOS, is a considerable advantage. The TEOS-based RSCE aerogels are mesoporous and optically translucent, have bulk densities of 0.099(±0.003) g/cm3 and surface areas of 460(±10) m2/g. Signals observed in infrared and Raman spectra of the aerogels are consistent with Si–O framework bonds. Using scanning electron microscopy imaging, the surface morphology of the aerogel samples was imaged at magnifications up to 150 kX. 相似文献
64.
65.
It is usually assumed that the holding current of an amorphous semiconductor threshold switch is not strongly dependent on the circuit surrounding the switch. This paper shows that the holding current is in fact controlled by both the series resistance and the parallel capacitance, according to two simple inequalities. In order to obtain low holding currents a large series resistor and minimum parallel capacitance are required, and in this way a holding current of 10 μA has been observed. Data are also presented on the effects of device dimensions and temperature on the on-state I-V curves and holding current. 相似文献
66.
Abe K Akagi T Anthony PL Antonov R Arnold RG Averett T Band HR Bauer JM Borel H Bosted PE Breton V Button-Shafer J Chen JP Chupp TE Clendenin J Comptour C Coulter KP Court G Crabb D Daoudi M Day D Dietrich FS Dunne J Dutz H Erbacher R Fellbaum J Feltham A Fonvieille H Frlez E Garvey D Gearhart R Gomez J Grenier P Griffioen KA Hoibraten S Hughes EW Hyde-Wright C Johnson JR Kawall D Klein A Kuhn SE Kuriki M Lindgren R Liu TJ Lombard-Nelsen RM Marroncle J Maruyama T Maruyama XK McCarthy J Meyer W 《Physical review letters》1995,74(3):346-350
67.
Chromate conversion coatings are used on aluminium alloys, primarily for their renowned corrosion resistant properties. Although these coatings are in common industrial use, neither the protection mechanisms, nor the coating interation with the intermetallic precipitation phases are fully understood. Macroscopic models have been developed in order to represent the galvanic cells present in aluminium alloys due to the presence of such intermetallic particles. Particles modelled include CuAl2, FeAl3 and Cu2FeAl7, all know to be cathodic to the aluminium matrix. Variations in deposition, both in composition and thickness, are indicative of the mechanisms of deposition over each phase. Characterisation of the coating deposition was carried out using X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, Auger electron spectroscopy, scanning electron microscopy with X-ray analysis. Depositional characteristics have been determined for each phase. The coating on the intermetallic phases is primarily Al oxide, and is significantly thinner than the coating on the matrix. This coating on the matrix consists mainly of a mixed Cr/Al oxide. The coating on the intermetallic phases was only one tenth the thickness of the matrix coating, and contained higher levels of Fe, Al and O. Matrix coating chemistry predominated with Cr, O, Fe and N, indicative of a chromate conversion coating. The mechanism for reduced rates of deposition over intermetallic phases was found to be affected by fluorine ion attack leading to intermetallic de-alloying and decomposition of Fe(CN)62− accelerator into amide groups on the matrix. 相似文献
68.
Application of amorphous silicon field effect transistors in addressable liquid crystal display panels 总被引:1,自引:0,他引:1
A. J. Snell K. D. Mackenzie W. E. Spear P. G. LeComber A. J. Hughes 《Applied Physics A: Materials Science & Processing》1981,24(4):357-362
It is shown that thin-film field effect transistors (FETs) made from amorphous (a-) silicon deposited by the glow-discharge
technique have considerable potential as switching elements in addressable liquid crystal display panels. The fabrication
of the elements and their characteristics with steady and pulsed applied potentials are discussed in some detail. Two important
points are stressed: (i) a-Si device arrays can be produced by well-established photolithographic techniques, and (ii) satisfactory
operation at applied voltages below 15VV is possible. Small experimental 7×5 transistor panels have been investigated and
it is shown that with the present design up to 250-way multiplexing could be achieved. The reproducibility of FET characteristics
is good and in tests so far no change has been observed after more than 109 switching operations. 相似文献
69.
Grosnick D Wright SC Bolton RD Cooper MD Frank JS Hallin AL Heusi PA Hoffman CM Hogan GE Mariam FG Matis HS Mischke RE Piilonen LE Sandberg VD Sanders GH Sennhauser U Werbeck R Williams RA Wilson SL Hofstadter R Hughes EB Ritter MW Highland VL McDonough J 《Physical review letters》1986,57(26):3241-3244
70.
We study the multiplicative structure of rings of coinvariants for finite groups. We develop methods that give rise to natural
monomial bases for such rings over their ground fields and explicitly determine precisely which monomials are zero in the
ring of coinvariants. We apply our methods to the Dickson, upper triangular and symmetric coinvariants. Along the way, we
recover theorems of Steinberg [17] and E. Artin [1]. Using these monomial bases we prove that the image of the transfer for
a general linear group over a finite field is a principal ideal in the ring of invariants.
This research is supported in part by the Natural Sciences and Engineering Research Council of Canada 相似文献