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931.
932.
933.
Ludwig R 《Angewandte Chemie (International ed. in English)》2001,40(10):1808-1827
Water is of fundamental importance for human life and plays an important role in many biological and chemical systems. Although water is the most abundant compound on earth, it is definitely not a simple liquid. It possesses strongly polar hydrogen bonds which are responsible for a striking set of anomalous physical and chemical properties. For more than a century the combined importance and peculiarity of water inspired scientists to construct conceptual models, which in themselves reproduce the observed behavior of the liquid. The exploration of structural and binding properties of small water complexes provides a key for understanding bulk water in its liquid and solid phase and for understanding solvation phenomena. Modern ab initio quantum chemistry methods and high-resolution spectroscopy methods have been extremely successful in describing such structures. Cluster models for liquid water try to mimic the transition from these clusters to bulk water. The important question is: What cluster properties are required to describe liquid-phase behavior? 相似文献
934.
Kroke E Völger KW Klonczynski A Riedel R 《Angewandte Chemie (International ed. in English)》2001,40(9):1698-1700
935.
936.
Klein H Jackstell R Wiese KD Borgmann C Beller M 《Angewandte Chemie (International ed. in English)》2001,40(18):3408-3411
937.
Trung Ngoc Le Alexander M. Mebel Ralf I. Kaiser 《Journal of computational chemistry》2001,22(13):1522-1535
The potential energy surface for the reaction of the ground‐state carbon atom [C(3Pj)] with the propargyl radical [HCCCH2(X2B1)] is investigated using the G2M(RCC,MP2) method. Numerous local minima and transition states for various isomerization and dissociation pathways of doublet C4H3 are studied. The results show that C(3Pj) attacks the π system of the propargyl radical at the acetylenic carbon atom and yields the n‐C4H3(2A′) isomer i3 after an 1,2‐H atom shift. This intermediate either splits a hydrogen atom and produces singlet diacetylene, [HCCCCH ( p1 )+H] or undergoes (to a minor amount) a 1,2‐H migration to i‐C4H3(2A′) i5 , which in turn dissociates to p1 plus an H atom. Alternatively, atomic carbon adds to the triple C?C bond of the propargyl radical to form a three‐member ring C4H3 isomer i1 , which ring opens to i3 . Diacetylene is concluded to be a nearly exclusive product of the C(3Pj)+HCCCH2 reaction. At the internal energy of 10.0 kcal/mol above the reactant level, Rice–Ramsperger–Kassel–Marcus calculations show about 91.7% of HCCCCH comes from fragmentation of i3 and 8.3% from i5 . The other possible minor channels are identified as HCCCC+H2 and C2H+HCCH. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1522–1535, 2001 相似文献
938.
Gyeong‐Man Kim Ralf Lach Goerg Hannes Michler Young‐Wook Chang 《Macromolecular rapid communications》2005,26(9):728-733
Summary: The mechanical deformation processes of poly(methyl methacrylate)/ montmorillonite nanocomposites and their electrospun fibers were investigated by in situ tensile tests under a transmission electron microscope depending on their morphology. While the polymer nanocomposites deformed in a brittle manner, i.e., crazing, the electrospun polymer nanocomposite fibers deformed through a shear flow process leading to “nanonecking” due to the strong overlap of stress fields caused by nanopores within the fiber under a uniaxial tensile load. This unique change in deformation behavior provides the possibility that the intrinsic brittle material could be manipulated to be ductile without sacrificing its other attractive properties through a well‐controlled electrospinning process.
939.
In this paper, fiber motion near a planar wall was investigated using a planar shear flow apparatus. Fibers were placed (one
at a time) perpendicular to the flow direction at various locations throughout the flow field. The location and orientation
of each fiber versus time was measured, using an image processing system, until the fiber aligned with the flow direction.
When the centroid of the fiber was located at distances greater than a fiber length from the wall, Jeffery's equations governing
particle motion were verified. For distances less than a fiber length and greater than a fiber diameter from the wall, the
fiber experienced an increased rate of rotation. In this regime, the motion of the fiber could be described by Jeffery's equations
if an increased effective shear rate was used. The effective shear rate was found to increase logarithmically with decreasing
separation distance. The wall effect was higher for longer aspect ratio fibers and was also a function of orientation; fibers
oriented perpendicular to the wall rotated faster than those oriented parallel to the wall at the same separation distance.
Once the fiber aligned with the flow direction, it ceased to rotate within the field of view. In this orientation, the wall
had a stabilizing effect on the fiber. In efforts to relate the increase in shear rate to the aspect ratio of the fiber and
the separation distance between the fiber and a solid wall, a translation model based on the work of De Mestre and Russel
was explored. This model allows one to quantify the increase in shear rate experienced by the fiber due to the presence of
a wall or obstruction in the flow field. However, the model has its limitations and care should be taken when applying this
model outside its realm of validity. When compared to experimental data, the translation model provides a very good estimate
of the increased shear rate experienced by the fiber when it is located less than 2/3 of a fiber length from a planar wall.
Received: 20 April 2000 Accepted: 28 September 2000 相似文献
940.
Ralf Hofmann 《Physics letters. [Part B]》2001,520(3-4):254-256
Using an OPE modification, which takes non-perturbative non-locality into account, the difference and sum of vector and axial-vector correlators are evaluated in euclidean position space. For distances up to 0.8 fm the calculated behavior is close to the instanton liquid result and the ALEPH data, in contrast to the implications of the conventional OPE. 相似文献