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251.
[formula: see text] We report here the first examples of a [1,5] sigmatropic rearrangement in a 4a-alkyl-4a-hydrocarbazol-4-one to yield a 3-alkylcarbazol-4-one with a re-aromatized indole nucleus. The reaction of 1-methyl-3-substituted-indole-2-carbene complexes 1 with terminal alkynes yields 3,4a-dialkyl-1-methoxy-9-methylcarbazol-4-ones 2. These 4a-substituted carbazolones thermally rearrange to cleanly give the more highly aromatic 3,3-dialkyl-1-methoxy-9-methylcarbazol-4-ones 3. This reaction provides a convenient entry to the Aspidosperma family of alkaloids, which contain a 3,3-disubstituted carbazole nucleus. 相似文献
252.
Irradiation of thioxanthenethione with the alkyl- and alkoxysubstituted butatrienes a-d gives the thietanes a-d the cyclobutanethione is formed as a byproduct. Free radical addition of iC3H7SH to a predominantly occurs via terminal attack of the thiyl radical on the π-system. 相似文献
253.
A multivariate data analysis procedure that uses singular value decomposition and the Ho-Kashyap algorithm is proposed to obtain calibration constants for x-ray fluorescence spectrometry. These calibration constants can be used to obtain results from experimental data by means of a simple dot product calculation. The method was tested on experimental data from the literature. Comparison of results showed that the method performs at least as well or better than the Rasberry-Heinrich method or its modifications. The method can be used to express calibration results obtained with a theoretically based program in such a way that they can be used conveniently in routine applications. 相似文献
254.
R. J. de Kock P. A. H. M. Hol H. Bos 《Fresenius' Journal of Analytical Chemistry》1964,205(1):371-381
Summary A method is presented for the determination of the degree of unsaturation of polyethylene samples by means of infrared spectroscopy. The required extinction coefficients for the vinyl, vinylidene and transvinylene absorption bands, at 910, 885 and 963 cm–1 resp. are determined on films prepared from mixtures of suitable unsaturated hydrocarbons with n-hexatriacontane or polyethylene. The degree of unsaturation found is in perfect agreement with ICl-titration data.
A preliminary publication on this subject has appeared in Polymer Letters 2, 339 (1964). 相似文献
Zusammenfassung Eine Methode zur Bestimmung des Grades der Ungesättigtheit von Polyäthylenproben durch IR-Spektroskopie wird vorgeschlagen. Die gesuchten Extinktionskoeffizienten für die Vinyl-, Vinyliden- und trans- Vinylen-Absorptionsbanden bei 910, 885, und 963 cm–1 werden auf Filmen bestimmt, die aus Gemischen entsprechender ungesättigter Kohlenwasserstoffe mit n-Hexatriacontan oder Polyäthylen hergestellt werden.Der gefundene Grad der Ungesättigtheit stand in bester Übereinstimmung mit den nach der JCl-Methode gefundenen Werten.
A preliminary publication on this subject has appeared in Polymer Letters 2, 339 (1964). 相似文献
255.
Facile Surfactant‐Free Synthesis of p‐Type SnSe Nanoplates with Exceptional Thermoelectric Power Factors
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Dr. Guang Han Dr. Srinivas R. Popuri Dr. Heather F. Greer Dr. Jan‐Willem G. Bos Prof. Wuzong Zhou Prof. Andrew R. Knox Dr. Andrea Montecucco Dr. Jonathan Siviter Dr. Elena A. Man Dr. Martin Macauley Prof. Douglas J. Paul Prof. Wen‐guang Li Dr. Manosh C. Paul Dr. Min Gao Dr. Tracy Sweet Prof. Robert Freer Dr. Feridoon Azough Dr. Hasan Baig Dr. Nazmi Sellami Prof. Tapas K. Mallick Prof. Duncan H. Gregory 《Angewandte Chemie (International ed. in English)》2016,55(22):6433-6437
A surfactant‐free solution methodology, simply using water as a solvent, has been developed for the straightforward synthesis of single‐phase orthorhombic SnSe nanoplates in gram quantities. Individual nanoplates are composed of {100} surfaces with {011} edge facets. Hot‐pressed nanostructured compacts (Eg≈0.85 eV) exhibit excellent electrical conductivity and thermoelectric power factors (S2σ) at 550 K. S2σ values are 8‐fold higher than equivalent materials prepared using citric acid as a structure‐directing agent, and electrical properties are comparable to the best‐performing, extrinsically doped p‐type polycrystalline tin selenides. The method offers an energy‐efficient, rapid route to p‐type SnSe nanostructures. 相似文献
256.
A long, smooth cylinder is dragged through a water surface to create a cavity with an initially cylindrical shape. This surface void then collapses due to the hydrostatic pressure, leading to a rapid and axisymmetric pinch-off in a single point. Surprisingly, the depth at which this pinch-off takes place does not follow the expected Froude(1/3) power law. Instead, it displays two distinct scaling regimes separated by discrete jumps, both in experiment and in numerical simulations (employing a boundary integral code). We quantitatively explain the above behavior as a capillary wave effect. These waves are created when the top of the cylinder passes the water surface. Our work thus gives further evidence for the nonuniversality of the void collapse. 相似文献
257.
258.
The aim of this work is to predict sound pressure in front of wall facings based on periodic sound scattering surface profiles. The method involves investigating plane wave reflections randomly incident upon an uneven surface. The waveguide approach is well suited to the geometries usually encountered in industrial workplaces. This method simplifies the profile geometry by using elementary rectangular volumes. The acoustic field in the profile interstices can then be expressed as the superposition of waveguide modes. In past work, walls considered are of infinite dimensions and are subjected to a periodic surface profile in only one direction. We therefore generalise this approach by extending its applicability to “double-periodic” wall facings. Free-field measurements have been taken and the observed agreement between numerical and experimental results supports the validity of the waveguide method. 相似文献
259.
The Lagrangian velocity statistics of dissipative drift-wave turbulence are investigated. For large values of the adiabaticity (or small collisionality), the probability density function of the Lagrangian acceleration shows exponential tails, as opposed to the stretched exponential or algebraic tails, generally observed for the highly intermittent acceleration of Navier-Stokes turbulence. This exponential distribution is shown to be a robust feature independent of the Reynolds number. For small adiabaticity, algebraic tails are observed, suggesting the strong influence of point-vortex-like dynamics on the acceleration. A causal connection is found between the shape of the probability density function and the autocorrelation of the norm of the acceleration. 相似文献
260.
Adrie J.J. Bos Nigel R.J. Poolton Jakob Wallinga Aurélie Bessière Pieter Dorenbos 《Radiation measurements》2010,45(3-6):343-346
Energy-resolved optically stimulated luminescence (OSL) spectra and thermoluminescence (TL) glow curves of a powder sample of YPO4:Ce3+,Sm3+ were measured to investigate the nature of the trapping centre and to locate its energy level relative to the valence and conduction bands of the YPO4 host. The high-temperature glow peak could unequivocally be assigned to Sm2+ (thus Sm3+ acts as an electron trap). The trap depth of this centre, as derived from the OSL excitation spectra, is in good agreement with the Dorenbos model prediction. The OSL excitation spectra also reveal excited states of Sm2+ well below the conduction band. These excited states produce a broadening of the high-temperature TL glow peak and also cause the activation energy determined by the Hoogenstraten method to underestimate the trap depth. 相似文献