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101.
Christopher M. Timperley Robin M. Black Michael Bird Ian Holden Joanna L. Mundy Robert W. Read 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):2027-2046
Syntheses of diols of structure [HOCH2CH2S]2(CH2)n in 86–95% yield from the sodium salt of 2-mercaptoethanol and Br(CH2)nBr (n = 1 to 5) or in 60–90% yield from 2-chloroethanol and NaS(CH2)nSNa (n = 2 to 5) are described. The diol [HOCH2CH2SCH2CH2]2O was prepared in 82% yield from the sodium salt of 2-mercaptoethanol and [ClCH2CH2]2O, and in 88% yield from 2-chloroethanol and [HSCH2CH2]2O. Mono- and bis-sulfoxides and bis-sulfones of these species were prepared in generally high yield by treatment with an equivalent of KIO4 in aqueous methanol, two equivalents of NaIO4 in aqueous methanol, or four equivalents of H2O2 in trifluoroacetic acid respectively. The compounds are important analytical standards for investigating the fate of the chemical warfare agents sesquimustard Q and oxygen mustard T in environmental samples. 相似文献
102.
John Read 《Mathematical Methods in the Applied Sciences》1996,19(2):87-129
In this paper we employ concepts from Banach space geometry in order to examine the problem of approximating the optimal distributed control of vibrating media whose motion is governed by a wave equation with a 2n-order self-adjoint and positive-definite linear differential operator. We show that this geometrical approach, arrived at via duality theory, provides the exact framework in which the approximation problem must be placed in order to get the correct convergence results, for it is here that the necessary and sufficient conditions for the approximate norm or time minimal control can be fully developed. Using the theory of Asplund, we are also able to improve the traditional weak* convergence results for the more difficult case of L∞ controls. Finally, we consider certain numerical examples which help illustrate our theoretical results. 相似文献
103.
Laser induced fluorescence spectra of HoS have been obtained using a Broida oven and a ring dye laser. Dispersed fluorescence spectra showed transitions from a common upper state, A[14.79]8.5 to the v = 0 and 1 vibrational levels of three low lying states, labelled X8.5, W[0.25]7.5 and V[0.98]7.5 (the states are labelled [10−3T0]Ω according to their energy and Ω assignment). High resolution excitation spectra were obtained for all six transitions and a rotational analysis yielded the following principal constants, in cm−1, for the X, W and V states, respectively: T0 = 0, 251.8713(31), 980.6969(37); Be = 0.121903(42), 0.121729(37), 0.122561(34); ΔG1/2 = 463.8811(46), 462.9411(45), 461.2084(127). For the A state, T0 = 14794.6987(28) cm−1 and B0 = 0.112596(29) cm−1. The three low lying states are shown to arise from the Ho2+[4f10(5I8)6s]S2− configuration in accord with Ligand Field Theory predictions. The atomic origin of each of the three low lying electronic states was determined from the observed resolved hyperfine structure. 相似文献
104.
105.
A method of writing very high frequency line and dot pattems, in excess of 10,000 lines/mm, is described. This method uses a very small diameter, 10 to 20 nm, beam of electrons to sensitize a 100-nm thick layer of electron resist. The line and dot patterns are produced by etching the sensitized resist. Moiré fringe patterns occur when the line arrays are observed in the scanning electron microscope. Moiré fringes with excellent contrast have been produced at magnifications as high as 1900x. This capability permits e-beam moiré to be employed in micromechanics. Examples of line arrays, dot arrays and moiré fringe patterns on a brass disk and on a tensile specimen fabricated from glass-fiber-reinforced plastic are demonstrated to introduce the possibilities for micromechanics applications. 相似文献
106.
107.
Ronald C. Read 《Discrete Mathematics》2008,308(10):1826-1829
We show that the number of chains of given length in a graph G can be easily found from the Tutte polynomial of G. Hence two Tutte-equivalent graphs will have the same distribution of chain lengths. We give two applications of this latter statement.We also give the dual results for the numbers of multiple edges with given muliplicities. 相似文献
108.
Recent measurements of a 2D electron gas subjected to microwave radiation reveal a magnetoresistance with an oscillatory dependence on the ratio of radiation frequency to cyclotron frequency. We perform a diagrammatic calculation and find radiation-induced resistivity oscillations with the correct period and phase. Results are explained via a simple picture of current induced by photoexcited disorder-scattered electrons. The oscillations increase with radiation intensity, easily exceeding the dark resistivity and resulting in negative-resistivity minima. At high intensity, we identify additional features, likely due to multiphoton processes, which have yet to be observed experimentally. 相似文献
109.
Blanchard A Graham RS Heinrich M Pyckhout-Hintzen W Rciher D Likhtman AE McLeish TC Read DJ Straube E Kohlbrecher J 《Physical review letters》2005,95(16):166001
The process of retraction in entangled linear chains after a fast nonlinear stretch was detected from time-resolved but quenched small angle neutron scattering (SANS) experiments on long, well-entangled polyisoprene chains. The statically obtained SANS data cover the relevant time regime for retraction, and they provide a direct, microscopic verification of this nonlinear process as predicted by the tube model. Clear, quantitative agreement is found with recent theories of contour length fluctuations and convective constraint release, using parameters obtained mainly from linear rheology. The theory captures the full range of scattering vectors once the crossover to fluctuations on length scales below the tube diameter is accounted for. 相似文献
110.
[reaction: see text] A chemoenzymatic synthesis of ADP-D-glycero-beta-D-manno-heptose (ADP-D,D-Hep) is described in which D,D-Hep 7-phosphate is converted to ADP-D,D-Hep by two biosynthetic enzymes. This strategy allows access to the 6'-deuterated analogue, which upon incubation with the epimerase showed complete retention of the isotopic label at the 6'-position. This provides evidence for a direct oxidation mechanism in which the hydride initially transferred to the NADP+ cofactor is subsequently returned to the same carbon in a nonstereospecific manner. 相似文献