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排序方式: 共有93条查询结果,搜索用时 728 毫秒
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Aequationes mathematicae - We establish a new refinement of the right-hand side of the Hermite–Hadamard inequality for simplices, based on the average values of a convex function over the... 相似文献
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Synthesis,Characterisation and Crystal Structures of Two Bi‐oxadiazole Derivatives Featuring the Trifluoromethyl Group
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Marcos A. Kettner Prof. Dr. Thomas M. Klapötke Tomasz G. Witkowski Felix von Hundling 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4238-4241
The synthesis, characterisation, and crystal structure determination of the closely related compounds 3,3′‐bi‐(5‐trifluoromethyl‐1,2,4‐oxadiazole) and 5,5′‐bi‐(2‐ trifluoromethyl‐1,3,4‐oxadiazole) are reported. These two compounds are known for their bioactivity; however, in this study they serve as model compounds to evaluate the suitability of the heterocyclic oxadiazole ring system for energetic materials when the fluorine atoms in the exocyclic CF3 groups are substituted successively by nitro groups. Quantum chemical calculations for the bi‐1,3,4‐ oxadiazole derivatives with difluoronitromethyl, fluorodinitromethyl, and trinitromethyl groups have been carried out and predict promising energetic performances for both explosive and propulsive applications. 相似文献
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Dr. Dennis Fischer Dr. Jennifer L. Gottfried Prof. Dr. Thomas M. Klapötke Prof. Dr. Konstantin Karaghiosoff Dr. Jörg Stierstorfer Dipl.‐Ing. Tomasz G. Witkowski 《Angewandte Chemie (International ed. in English)》2016,55(52):16132-16135
Herein we present the preparation and characterization of three new bispyrazolyl‐based energetic compounds with great potential as explosive materials. The reaction of sodium 4‐amino‐3,5‐dinitropyrazolate ( 5 ) with dimethyl iodide yielded bis(4‐amino‐3,5‐dinitropyrazolyl)methane ( 6 ), which is a secondary explosive with high heat resistance (Tdec=310 °C). The oxidation of this compound afforded bis(3,4,5‐trinitropyrazolyl)methane ( 7 ), which is a combined nitrogen‐ and oxygen‐rich secondary explosive with very high theoretical and estimated experimental detonation performance (Vdet (theor)=9304 m s?1 versus Vdet(exp)=9910 m s?1) in the range of that of CL‐20. Also, the thermal stability (Tdec=205 °C) and sensitivities of 7 are auspicious. The reaction of 6 with in situ generated nitrous acid yielded the primary explosive bis(4‐diazo‐5‐nitro‐3‐oxopyrazolyl)methane ( 8 ), which showed superior properties to those of currently used diazodinitrophenol (DDNP). 相似文献
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Dimethylthioarsinic anhydride: a standard for arsenic speciation 总被引:1,自引:0,他引:1
Dimethylthioarsinic acid (DMTAV) has recently been identified in biological, dietary and environmental matrices. The relevance of this compound to the toxicity of arsenic in humans is unknown and further exposure assessment and metabolic studies are difficult to conduct because of the unavailability of a well characterized standard. The synthesis of DMTAV was accomplished by the reaction of dimethylarsinic acid (DMAV) with hydrogen sulfide. The initial reaction product produced is DMTAV but multiple products over the course of the reaction are also observed. Therefore, a chromatographic separation was developed to monitor the reaction progress via LC-ICP-MS. In this synthesis, conversion of DMAV to DMTAV was not taken to completion to avoid the production of side products. The product was isolated from the starting material by standard organic techniques. Single crystal diffraction demonstrated that solid DMTAV is present in the form of the oxygen-bridged dimethylthioarsinic anhydride. Dissolution of the anhydride in water produces the acid form of DMTAV and the aqueous phase DMTAV provided a characteristic molecular ion of m/z 155 by LC-ESI-MS. The synthesis and isolation of dimethylthioarsinic anhydride provides a stable crystalline standard suitable for identification, toxicological study and exposure assessment of dimethylthioarsinic acid. 相似文献
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H. Baumhacker G. Brederlow E. Fill R. Volk S. Witkowski K. J. Witte 《Applied physics. B, Lasers and optics》1995,61(4):325-332
In this paper, the design procedure and the performance of the single beam Asterix IV high-power iodine laser emitting at = 1315 nm is described. It has been developed on the basis of a 10-years experience with the 1 TW Asterix III laser-system and with the support of a 1-D and a 3-D pulse propagation code. Special emphasis has been put on achieving a high overall system efficiency and a beam intensity profile as homogeneous as possible. Presently, Asterix IV provides output pulses with durations from 0.2 to several ns. At a duration of 0.4 ns, the pulse power is 3 TW and at a duration of 5 ns the pulse energy reaches 2.1 kJ. Under these conditions, the laser can be fired every twenty minutes. 相似文献
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Emily C. Hernández Allan Witkowski Sylvia Daunert Leonidas G. Bachas 《Mikrochimica acta》1995,120(1-4):63-72
The present study explores the attractiveness of combining flow-injection (FI) with lead hydride generation atomic absorption spectrometry (AAS) to improve the selectivity and sensitivity of analysis. Lead hydride was generated in three acid-oxidant media: HNO3-(NH4)2S2O8, lactic acid-K2Cr2O7 and HNO3-H2O2. The effect of chemical parameters (acid-oxidant concentration and NaBH4 concentration) was investigated and the performance of each generation medium in terms of interferences, sensitivity and detection limits was compared with that obtained in batch mode. In all cases improved sensitivity (HNO3-H2O2, 0.8 ng Pb; lactic acid-K2Cr2O7, 0.2 ng Pb; (NH4)2S2O8-HNO3, 4ng Pb) was obtained, most notably in HNO3-H2O2, which provided 12 times higher sensitivity than in batch mode and sharper absorption peaks. Furthermore, interference by Cu and Ni was lower in the proposed FI-HG system. Compared with the batch mode, about 10 to 100 times higher concentrations of interferent are tolerated in the sample. The use of FI also allows work at a lower NaBH4 concentration. The method was applied to the determination of lead in water samples with a sampling frequency of 180 samples per hour. In terms of both sensitivity and freedom from interferences, lactic acid-K2Cr2O7 was the best of the generation media tested.On leave from the School of Environmental Studies, Jadavpur University, Calcutta 700032, India 相似文献