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排序方式: 共有113条查询结果,搜索用时 171 毫秒
61.
Holger Kohlmann PD Dr. Nadine Kurtzemann Richard Weihrich Thomas Hansen 《无机化学与普通化学杂志》2009,635(15):2399-2405
A novel gas pressure cell for in situ neutron powder diffraction has been developed. It is based on a single crystal sapphire tube as a sample holder, allows a 360° unobstructed access by the neutron beam and has little background contribution. This device was used to study the hydrogenation of α‐MgPd3, which undergoes a hydrogen driven rearrangement from a ZrAl3 to a AuCu3 type structure. Deuterium could be located and a strong preference of [Pd6] voids was found in α‐MgPd3D0.79 under 5 bar and in α‐MgPd3D0.94 under 20 bar deuterium pressure. The crystal structure may be described as a new defect superstructure variant of the NaCl type. In situ thermal analysis under 5 bar hydrogen pressure showed that both the hydrogen uptake of α‐MgPd3, which is complete at temperatures below 450 K, and the transformation to the hydride of cubic β‐MgPd3, starting around 550 K, are exothermic. This completion of the hydrogenation‐dehydrogenation series of MgPd3 suggests, that the rearrangement of the metal structure proceeds by a hydrogen assisted gliding mechanism with a shift vector of [110]. This is also supported by quantum chemical calculations, which show a decohesion of the intermetallic structure upon hydrogenation accompanied by the appearance of Pd–H bonding interactions. 相似文献
62.
PD Dr. Holger Kohlmann 《无机化学与普通化学杂志》2010,636(11):2046-2046
63.
PD Dr. Thomas G. Mayerhöfer Dr. Andrei V. Pipa Prof. Dr. Jürgen Popp 《Chemphyschem》2019,20(21):2748-2753
As derived by Max Planck in 1903 from dispersion theory, Beer's law has a fundamental limitation. The concentration dependence of absorbance can deviate from linearity, even in the absence of any interactions or instrumental nonlinearities. Integrated absorbance, not peak absorbance, depends linearly on concentration. The numerical integration of the absorbance leads to maximum deviations from linearity of less than 0.1 %. This deviation is a consequence of a sum rule that was derived from the Kramers-Kronig relations at a time when the fundamental limitation of Beer's law was no longer mentioned in the literature. This sum rule also links concentration to (classical) oscillator strengths and thereby enables the use of dispersion analysis to determine the concentration directly from transmittance and reflectance measurements. Thus, concentration analysis of complex samples, such as layered and/or anisotropic materials, in which Beer's law cannot be applied, can be achieved using dispersion analysis. 相似文献
64.
Stephan Berner Andreas B. Schmidt Mirko Zimmermann Dr. Andrey N. Pravdivtsev Dr. Stefan Glöggler Prof. Dr. Dr. h.c. Jürgen Hennig PD Dr. Dominik von Elverfeldt Prof. Dr. Jan-Bernd Hövener 《ChemistryOpen》2019,8(6):728-736
The signal enhancement provided by the hyperpolarization of nuclear spins of biological molecules is a highly promising technique for diagnostic imaging. To date, most 13C-contrast agents had to be polarized in an extra, complex or cost intensive polarizer. Recently, the in situ hyperpolarization of a 13C contrast agent to >20 % was demonstrated without a polarizer but within the bore of an MRI system. This approach addresses some of the challenges of MRI with hyperpolarized tracers, i. e. elevated cost, long production times, and loss of polarization during transfer to the detection site. Here, we demonstrate the first hyperpolarization of a biomolecule in aqueous solution in the bore of an MRI at field strength of 7 T within seconds. The 13C nucleus of 1-13C, 2,3-2H2-succinate was polarized to 11 % corresponding to a signal enhancement of approximately 18.000. Interesting effects during the process of the hydrogenation reaction which lead to a significant loss of polarization have been observed. 相似文献
65.
66.
PD Dr. O. Müller 《Mathematical Methods of Operations Research》1972,16(2):B7-B16
Zusammenfassung Die Fallstudie behandelt das Problem der Dimensionierung der verschiedenen Teile einer sehr komplexen Anlage für mehrstufige Produktion. Die Programmierung erfolgte in FORTRAN. Anhand der Fallstudie werden einige wesentliche Punkte herausgearbeitet, die für den Erfolg von Simulationsprojekten wesentlich sind, nämlich: klare Zielsetzung, Simulation von Teilbereichen, so daß in kürzester Zeit Resultate vorliegen.
Summary The case-study deals with the problem of the size of various parts of a very complex plant lay-out for multi-step production. The programming was done in FORTAN. Based on the case-study a few points were worked out which are essential for the success of simulation-projects, to wit: clear statement of purpose; simulation of partial scopes, which produce short-term results.相似文献
67.
First measurement of the left-right cross section asymmetry in Z boson production by e+e- collisions
Abe K Abt I Acton PD Adolphsen CE Agnew G Alber C Alzofon DF Antilogus P Arroyo C Ash WW Ashford V Astbury A Aston D Au Y Axen DA Bacchetta N Baird KG Baker W Baltay C Band HR Baranko G Bardon O Barrera F Battiston R Bazarko AO Bean A Beer G Belcinski RJ Bell RA Ben-David R Benvenuti AC Berger R Berridge SC Bethke S Biasini M Bienz T Bilei GM Bird F Bisello D Blaylock G Blumberg R Bogart JR Bolton T Bougerolle S Bower GR Boyce RF Brau JE Breidenbach M Browder TE Bugg WM Burgess B Burke D 《Physical review letters》1993,70(17):2515-2520
68.
Barrett AG Braddock DC de Koning PD White AJ Williams DJ 《The Journal of organic chemistry》2000,65(2):375-380
The double allylboration of aldehydes using 1, 3-bis(diisopinocampheylboryl)-2-methylenepropanes (R,R)-3 and (S, S)-3 under Brown's salt-free conditions provides C(2)-symmetric 3-methylenepentane-1,5-diols 1 in excellent enantiomeric excess. The absolute stereochemistry of the products was confirmed by a single-crystal X-ray study of bis-Mosher ester 6g. Desymmetrization and further functionalization of diol 1a were achieved by treatment of the bis-BOC carbonate 13 with IBr in toluene at -80 degrees C to give cyclic iodocarbonate 14 as a single diastereomer. This methodology is also applicable in natural product synthesis; enantiomerically pure spiroketals 1,7-dioxaspiro[5.5]undecanes 18 and 25, the latter representing an expedient synthesis of the AB ring system of the spongistatins 20, were easily accessed from simple starting materials in excellent yields and selectivities. 相似文献
69.
Dr. Felix Anke Dr. Susanne Boye Dr. Anke Spannenberg Dr. Albena Lederer Prof. Dr. Detlef Heller PD Dr. Torsten Beweries 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(35):7889-7899
Dehydropolymerisation of methylamine borane (H3B⋅NMeH2) using the well-known iron amido complex [(PNP)Fe(H)(CO)] (PNP=N(CH2CH2PiPr2)2) ( 1 ) gives poly(aminoborane)s by a chain-growth mechanism. In toluene, rapid dehydrogenation of H3B⋅NMeH2 following first-order behaviour as a limiting case of a more general underlying Michaelis–Menten kinetics is observed, forming aminoborane H2B=NMeH, which selectively couples to give high-molecular-weight poly(aminoborane)s (H2BNMeH)n and only traces of borazine (HBNMe)3 by depolymerisation after full conversion. Based on a series of comparative experiments using structurally related Fe catalysts and dimethylamine borane (H3B⋅NMe2H) polymer formation is proposed to occur by nucleophilic chain growth as reported earlier computationally and experimentally. A silyl functionalised primary borane H3B⋅N(CH2SiMe3)H2 was studied in homo- and co-dehydropolymerisation reactions to give the first examples for Si containing poly(aminoborane)s. 相似文献
70.
1‐Butyl‐4‐methylpyridinium hexachloridotantalate(V), [BMPy][TaCl6] ( 1 ), tetrakis(1‐butyl‐4‐methylpyridinium) bis(hexachloridotantalate(V) (μ‐oxido)‐decachloridotantalate(V), [BMPy]4[(TaCl6)2(Ta2OCl10)] ( 2 ), and bis(1‐ethyl‐3‐methylimidazolium)‐(μ‐oxido)‐decachloridoditantalate(V), [EMIm]2[Ta2OCl10] ( 3 ) were synthesized and characterized by single‐crystal X‐ray diffraction and vibrational spectroscopy. Compounds 1 and 3 crystallize in the monoclinic space group P21/c (no. 14), whereas compound 2 crystallizes in the triclinic space group P (no. 2). All compounds are built up by the mentioned bulky organic cations and octahedral [TaCl6]– respective linear [Ta2OCl10]2– anions. Coulomb interactions are dominant between the ionic species. FT‐IR and FT‐Raman spectra were recorded and interpreted, especially with respect to the inorganic species [TaCl6]– (Oh) and [Ta2OCl10]2– (Ci symmetry, approximately D4h). The melting temperatures of compounds 1 – 3 are given. 相似文献