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排序方式: 共有139条查询结果,搜索用时 13 毫秒
11.
Dipl.‐Chem. Jan Tillmann Dipl.‐Chem. Josef Heinrich Wender Dr. Ute Bahr Dr. Michael Bolte Dr. Hans‐Wolfram Lerner Prof. Dr. Max C. Holthausen Prof. Dr. Matthias Wagner 《Angewandte Chemie (International ed. in English)》2015,54(18):5429-5433
Silicon analogues of the most prominent carbon nanostructures, namely, hollow spheroidals such as C60 and the fullerene family, have been unknown to date. Herein we show that discrete Si20 dodecahedra, stabilized by an endohedral guest and valence saturation, are accessible in preparative yields through a chloride‐induced disproportionation reaction of hexachlorodisilane in the presence of tri(n‐butyl)amine. X‐ray crystallography revealed that each silicon dodecahedron contains an endohedral chloride ion that imparts a net negative charge. Eight chloro substituents and twelve trichlorosilyl groups are attached to the surface of each cluster in a strictly regioregular arrangement, a thermodynamically preferred substitution pattern according to quantum‐chemical assessment. Our results demonstrate that the wet‐chemical self‐assembly of a complex, monodisperse Si nanostructure is possible under mild conditions starting from simple Si2 building blocks. 相似文献
12.
Utesch T Daminelli G Mroginski MA 《Langmuir : the ACS journal of surfaces and colloids》2011,27(21):13144-13153
Bone morphogenetic protein-2 (BMP-2) plays a crucial role in osteoblast differentiation and proliferation. Its effective therapeutic use for ectopic bone and cartilage regeneration depends, among other factors, on the interaction with the carrier at the implant site. In this study, we used classical molecular dynamics (MD) and a hybrid approach of steered molecular dynamics (SMD) combined with MD simulations to investigate the initial stages of the adsorption of BMP-2 when approaching two implant surfaces, hydrophobic graphite and hydrophilic titanium dioxide rutile. Surface adsorption was evaluated for six different orientations of the protein, two end-on and four side-on, in explicit water environment. On graphite, we observed a weak but stable adsorption. Depending on the initial orientation, hydrophobic patches as well as flexible loops of the protein were involved in the interaction with graphite. On the contrary, BMP-2 adsorbed only loosely to hydrophilic titanium dioxide. Despite a favorable interaction energy between protein and the TiO(2) surface, the rapid formation of a two-layer water structure prevented the direct interaction between protein and titanium dioxide. The first water adlayer had a strong repulsive effect on the protein, while the second attracted the protein toward the surface. For both surfaces, hydrophobic graphite and hydrophilic titanium dioxide, denaturation of BMP-2 induced by adsorption was not observed on the nanosecond time scale. 相似文献
13.
Ast S Müller H Flehr R Klamroth T Walz B Holdt HJ 《Chemical communications (Cambridge, England)》2011,47(16):4685-4687
The new π-conjugated 1,2,3-triazol-1,4-diyl fluoroionophore 1 generated via Cu(I) catalyzed [3 + 2] cycloaddition shows high fluorescence enhancement factors (FEF) in the presence of Na(+) (FEF=58) and K(+) (FEF=27) in MeCN and high selectivity towards K(+) under simulated physiological conditions (160 mM K(+) or Na(+), respectively) with a FEF of 2.5 for K(+). 相似文献
14.
Florian Hatesuer Tillmann Groth Mark Reichwage Dieter Mewes Andrea Luke 《Heat and Mass Transfer》2011,47(8):921-931
Twin-screw multiphase pumps are employed increasingly to convey multiphase mixtures of crude oil, accompanying fluids, associated
gas and solid particles. They are positive displacement pumps and suitable for handling products containing liquid accompanied
by large amounts of gas. Experimental investigations on the conveying characteristic, namely measuring the delivered volume
flow as a function of the pressure difference, provide results for selected mixtures. By means of the on hand work, the influence
of sorption phenomena occurring due to pressure variations alongside the conveying process on the conveying characteristics
of twin-screw pumps delivering mixtures of oil and gases is measured. The employed gases are air and carbon dioxide, which
differ strongly in solubility in oil. All experiments are conducted in a closed loop test facility, where oil and gas volume
flows are mixed before the inlet and separated after the outlet of the multiphase pump. In order to simulate the influence
of the suction side pressure drop in the reservoir on the conveying characteristic, packed beds are employed as oil-filed
model. Sorption processes inside of the oil-field model and within the multiphase pump affect the conveying behaviour significantly.
The two-phase flow in the inlet and outlet pipe is visualised by means of a capacitance tomography system. Results show that
the oil fraction of the total delivered volume flow is decreased due to desorption at the pump inlet. The gas fraction at
the pump outlet is further decreased due to absorption. Experimental results are compared to calculated solubilities of the
on-hand gases in oil and to the theoretically derived gas volume flow fraction expected at the multiphase pump. 相似文献
15.
Heinz Günther Tillmann 《Archiv der Mathematik》1964,15(1):332-334
Ohne ZusammenfassungHerrnHellmuth Kneser zum 65. Geburtstag gewidmet 相似文献
16.
W. Wittmann K. Tillmann H. J. Andrä P. Dobberstein 《Zeitschrift für Physik A Hadrons and Nuclei》1972,257(4):279-287
The complete finestructure beat frequency patterns ofn 3 P states of4He I (n=3–7) are measured by observation of zero field quantum beats using the beam-foil technique. The results provide a new experimental value for the 73 P 2–73 P o separation, confirm the beat amplitude ratios to be in accord with theory and allow comparison with the results of other techniques. 相似文献
17.
A new lower bound on the complexity of a 3-manifold is given using the ${\mathbb Z }_2$ -Thurston norm. This bound is shown to be sharp, and the minimal triangulations realising it are characterised using normal surfaces consisting entirely of quadrilateral discs. 相似文献
18.
Ideas from string theory and quantum field theory have beenthe motivation for new invariants of knots and 3-dimensionalmanifolds which have been constructed from complex algebraicstructures such as Hopf algebras [17, 22], monoidal categorieswith additional structure [24], and modular functors [14, 23].These constructions are closely related. Here we take a unifyingcategorical approach based on a natural 2-dimensional generalisationof a topological field theory in the sense of Atiyah [1], andshow that the axioms defining these complex algebraic structuresare a consequence of the underlying geometry of surfaces. 相似文献
19.
20.
Quantum dynamical simulations for the laser-controlled isomerization of 1-(2-cis-fluoroethenyl)-2-fluorobenzene mounted on adamantane are reported based on a one-dimensional electronic ground-state potential and dipole moment calculated by density functional theory. The model system 1-(2-cis-fluoroethenyl)-2-fluorobenzene supports two chiral and one achiral atropisomers upon torsion around the C-C single bond connecting the phenyl ring and ethylene group. The molecule itself is bound to an adamantyl frame which serves as a model for a linker or a surface. Due to the C3 symmetry of the adamantane molecule, the molecular switch can have three equivalent orientations. An infrared picosecond pulse is used to excite the internal rotation around the chiral axis, thereby controlling the chirality of the molecule. In order to selectively switch the molecules--independent of their orientations-- from their achiral to either their left- or right-handed form, a stochastic pulse optimization algorithm is applied. A subsequent detailed analysis of the optimal pulse allows for the design of a stereoselective laser pulse sequence of analytical form. The developed control scheme of elliptically polarized laser pulses is enantioselective and orientation-selective. 相似文献