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261.
Brinkmann C García F Morey JV McPartlin M Singh S Wheatley AE Wright DS 《Dalton transactions (Cambridge, England : 2003)》2007,(16):1570-1572
While the nucleophilic substitution reaction of manganocene [Cp(2)Mn] with Li(hpp) (1 : 1 equivalents) gives the neutral dimer [CpMn(hpp)]2 (1), further substitution of the Cp ligands leads to the unusual dimeric manganate cage compound [LiMn(hpp)3]2 (2), generated by the dimerisation of a simple tris-organomanganate monomer. 相似文献
262.
263.
Kentgens AP Bart J van Bentum PJ Brinkmann A van Eck ER Gardeniers JG Janssen JW Knijn P Vasa S Verkuijlen MH 《The Journal of chemical physics》2008,128(5):052202
The predominant means to detect nuclear magnetic resonance (NMR) is to monitor the voltage induced in a radiofrequency coil by the precessing magnetization. To address the sensitivity of NMR for mass-limited samples it is worthwhile to miniaturize this detector coil. Although making smaller coils seems a trivial step, the challenges in the design of microcoil probeheads are to get the highest possible sensitivity while maintaining high resolution and keeping the versatility to apply all known NMR experiments. This means that the coils have to be optimized for a given sample geometry, circuit losses should be avoided, susceptibility broadening due to probe materials has to be minimized, and finally the B(1)-fields generated by the rf coils should be homogeneous over the sample volume. This contribution compares three designs that have been miniaturized for NMR detection: solenoid coils, flat helical coils, and the novel stripline and microslot designs. So far most emphasis in microcoil research was in liquid-state NMR. This contribution gives an overview of the state of the art of microcoil solid-state NMR by reviewing literature data and showing the latest results in the development of static and micro magic angle spinning (microMAS) solenoid-based probeheads. Besides their mass sensitivity, microcoils can also generate tremendously high rf fields which are very useful in various solid-state NMR experiments. The benefits of the stripline geometry for studying thin films are shown. This geometry also proves to be a superior solution for microfluidic NMR implementations in terms of sensitivity and resolution. 相似文献
264.
Johan van den Bergh Weidong Zhu Freek Kapteijn Jacob A. Moulijn Kenji Yajima Kunio Nakayama Toshihiro Tomita Shuichi Yoshida 《Research on Chemical Intermediates》2008,34(5-7):467-474
The permeation of CO2 and CH4 and their binary mixtures through a DDR membrane has been investigated over a wide range of temperatures and pressures. The synthesized DDR membrane exhibits a high permeance and maintains a very high selectivity for CO2. At a total pressure of 101 kPa, the highest selectivity for CO2 in a 50∶50 feed mixture was found to be over 4000 at 225 K. This is ascribed to the higher adsorption affinity, as well as to the higher mobility for the smaller CO2 molecules in the zeolite, preventing the bypassing of the CH4 through the membrane. An engineering model, based on the generalized Maxwell-Stefan equations, has been used to interpret the transport phenomena in the membrane. The feasibility of DDR membranes as applied to CO2 removal from natural gas or biogas is anticipated. 相似文献
265.
Kox MH Stavitski E Groen JC Pérez-Ramírez J Kapteijn F Weckhuysen BM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(6):1718-1725
A combination of optical and fluorescence microscopy was used to study the morphology of micro‐ and mesoporous H‐ZSM‐5 zeolite crystals (17×4×4 μm) and to evaluate, in a spatially resolved manner, the effect of mesoporosity, introduced via desilication, on catalytic performance. For this purpose, the oligomerization of various styrene molecules was used as a model reaction, in which the carbocation intermediates formed in the zeolite pores act as reporter molecules. In situ confocal fluorescence measurements after the template removal process showed that the crystals generally consist of three different subunits that have pyramidal boundaries with each other. Examination of these crystals during styrene oligomerization revealed differences in the catalytic activity between the purely microporous and the combined micro‐ and mesoporous crystals. The introduction of intracrystalline mesoporosity limits the formation to dimeric carbocation intermediates and facilitates the transport of styrene molecules inside the zeolite volume. This leads to a more uniform coloration and fluorescence pattern of the crystals. Moreover, the oligomerization of various styrene compounds, which differ in their reactivity, provides a good way of estimating the Brønsted acid strength in a spatially resolved manner, showing a nonhomogeneously distributed Brønsted acidity over the volume of the crystals. More detailed information on the structure of the ZSM‐5 crystals was revealed for mesoporous crystals during the oligomerization of 4‐methoxystyrene. This reaction induced an “explosion” of the crystal leading to the formation of a complex system with at least eight different subunits. Finally, polarized‐light microscopy was used to unravel the pore geometry in these individual building blocks. The observed differences in catalytic behavior between micro‐ and mesoporous ZSM‐5 crystals are strengthened by the microspectroscopic techniques employed, which show that upon desilication the crystal morphology is affected, the product distribution is changed towards less conjugated carbocation intermediates, and that a gradient in Brønsted acid strength appears to be present. 相似文献
266.
Inside Back Cover: Six‐Coordinate Group 13 Complexes: The Role of d Orbitals and Electron‐Rich Multi‐Center Bonding (Angew. Chem. Int. Ed. 41/2015)
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267.
Yu.V. Pyatkov Yu.E. Penionzhkevich W.H. Trzaska O.I. Osetrov A.A. Alexandrov I.A. Alexandrova J. Äystö K.-Th. Brinkmann S.V. Khlebnikov V.F. Kushniruk A.V. Kuznetsov V.G. Lyapin V.A. Maslov M. Mutterer Z. Radivojevich V.A. Rubchenya Yu.G. Sobolev G.P. Tiourine D.N. Vakhtin 《The European Physical Journal A - Hadrons and Nuclei》2001,10(2):171-175
A pronounced fine structure (FS) in the form of distinct peaks was observed in neutron gated mass spectra from the decay of
the 278110 composite system produced in the reaction 238U + 40Ar (243 MeV) at an initial excitation energy E
* > 70 MeV. The FS peaks are located in the vicinity of mass numbers 70-80, 100, and 130, which correspond to those of magic
nuclei (clusters). In the data there is also evidence for a new type of decay -- collinear cluster tripartition of an excited
nucleus.
Received: 8 August 2000 / Accepted: 2 February 2001 相似文献
268.
In this communication, the Digital Image Compression (DIC) – PIV system is introduced. The present system allows the measurement
of mean and RMS velocities in turbulent flow fields, using JPEG digital image compression technique for on-line recording
of thousands of images. The decompression and subsequent analysis of the images, performed by means of digital cross-correlation
technique, is carried out off-line. Errors incurred by the application of the compression method are assessed and discussed.
The effect of the compression is firstly analysed by linearly traversing (synthetic) computer-generated PIV-images at constant
velocity. Secondly, accurate LDA measurements and data from direct numerical simulation (DNS) are used as a basis for the
analysis in a low Reynolds number open water channel flow. The results show that excellent agreement between LDA and DIC–PIV
measurements for mean and RMS velocities can be achieved using a compression factor up to 12.
Received: 27 August 1996 / Accepted: 15 December 1998 相似文献
269.
D. Brinkmann J.E. Golub S.W. Koch P. Thomas K. Maschke I. Varga 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):145-148
A two-band model of a disordered semiconductor is used to analyze dynamical interaction induced weakening of localization
in a system that is accessible to experimental verification. The results show a dependence on the sign of the two-particle
interaction and on the optical excitation energy of the Coulomb-correlated electron-hole pair.
Received 4 September and Received in final form 26 November 1998 相似文献
270.
M. Abdel-Bary S. Abdel-Samad K. -Th. Brinkmann H. Clement J. Dietrich E. Doroshkevich S. Dshemuchadse K. Ehrhardt A. Erhardt W. Eyrich A. Filippi H. Freiesleben M. Fritsch W. Gast A. Gillitzer J. Gottwald H. J?ger B. Jakob R. J?kel L. Karsch K. Kilian H. Koch M. Krapp J. Kre? E. Kuhlmann A. Lehmann S. Marcello S. Mauro P. Michel K. Móller H. P. Morsch L. Naumann N. Paul C. Pizzolotto Ch. Plettner S. Reimann M. Richter J. Ritman E. Roderburg A. Schamlott P. Sch?nmeier W. Schroeder M. Schulte-Wissermann T. Sefzick M. Steinke G. Y. Sun A. Teufel W. Ullrich G. J. Wagner M. Wagner R. Wenzel A. Wilms P. Wintz P. Wüstner P. Zupranski 《The European Physical Journal A - Hadrons and Nuclei》2010,44(1):7-22