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101.
H. Schneider C. Schnbein K. Schwarz M. Walther 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
We have studied the transport properties of electrons in asymmetric quantum well structures upon far-infrared optical excitation of carriers from the lowest subband into the continuum. Here the photocurrent consists of a coherent component originating from ballistic transport upon excitation, and of an incoherent part associated with asymmetric diffusion and relaxation processes, which occur after the coherence has been lost. The signature of the coherent contribution is provided by a sign reversal of the photocurrent upon changing the excitation energy. This sign reversal arises from the energy-dependent interference between continuum states, which have a twofold degeneracy characterized by positive and negative momenta. The interference effect also allows us to estimate the coherent mean free path (
nm at 77
K). In specifically designed device structures, we use both the coherent and incoherent components in order to achieve a pronounced photovoltaic infrared response for detector applications. 相似文献
102.
M. Ekström O. Hartmann A. Marelius R. Wäppling E. Schreier S. Henneberger A. Kratzer G.M. Kalvius 《Hyperfine Interactions》1997,104(1-4):281-285
Muon spin rotation (μSR) data on a single crystalline sample of Dy have been obtained as function of temperature and applied
hydrostatic pressure. The discontinuity observed in our new data at the phase transition at 85 K strongly suggests that the
muons occupy tetrahedral interstitial sites, with a contact field BC=-2.5 T at the lowest temperatures.
Measurements with applied pressures up to 0.8 GPa show that the magnitude of the local fields increases with pressure at 0.3
GPa, and that the muon signal in the antiferromagnetic phase has essentially disappeared at 0.8 GPa.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
103.
H.Walther 《Chinese Journal of Lasers》1994,3(3):193-213
ExperimentswithsingleatomsincavitiesandtrapsH.Walther(SektionPhysikderUniversitatMunchenandMax-Planck-InstitutfurQuantenoptik... 相似文献
104.
Hansjoachim Walther 《Discrete Applied Mathematics》2002,120(1-3):263-274
A face F of a polyhedral graph G(V,E,F) is an a1,a2,…,al-face if is an l-gon and the degrees d(xi) of the vertices xiV incident with in the cyclic order are ai,i=1,2,…,l. The lexicographic minimum b1,b2,…,bl such that is a b1,b2,…,bl-face is the type of . All polyhedral graphs having only one type of faces are listed. It is proved that the set of triangulations having only faces of different types is non-empty and finite. 相似文献
105.
Hans-Otto Walther 《Journal of Dynamics and Differential Equations》2007,19(3):593-622
Automatic soft landing is modeled by a differential equation with state-dependent delay. It is shown that in the model soft
landing occurs for an open set of initial data, which is determined by means of a smooth invariant manifold.
相似文献
106.
Dendronized Hyperbranched Macromolecules: Soft Matter with a Novel Type of Segmental Distribution
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Priv.‐Doz. Dr. Albena Lederer Prof. Dr. Walther Burchard Tobias Hartmann Johannes S. Haataja Dr. Nikolay Houbenov Andreas Janke Dr. Peter Friedel Dr. Ralf Schweins Dr. Peter Lindner 《Angewandte Chemie (International ed. in English)》2015,54(43):12578-12583
Dendronization of a hyperbranched polyester with different generation dendrons leads to pseudo‐dendritic structures. The hyperbranched core is modified by the divergent coupling of protected monomer units to the functional groups. Compared to dendrimers, the synthetic effort is significantly less, but the properties are very close to those of high‐generation dendrimers. The number of functional groups, molar mass, and rheology behavior even in the early generation (G1–G4) pseudo‐dendrimers strongly resembles the behavior of dendrimers in higher generations (G5–G8). Comparison of the segmental and internal structure with perfect dendrimers is performed using SANS, dynamic light scattering and viscosity analysis, microscopy and molecular dynamics simulation. The interpretation of the results reveals unique structural characteristics arising from lower segmental density of the core, which turns into a soft nano‐sphere with a smooth surface even in the first generation. 相似文献
107.
Thomas Heuser Elisabeth Weyandt Dr. Andreas Walther 《Angewandte Chemie (International ed. in English)》2015,54(45):13258-13262
Switchable self‐assemblies respond to external stimuli with a transition between near‐equilibrium states. Although being a key to present‐day advanced materials, these systems respond rather passively, and do not display autonomous dynamics. For autonomous behavior, approaches must be found to orchestrate the time domain of self‐assemblies, which would lead to new generations of dynamic and self‐regulating materials. Herein, we demonstrate catalytic control of the time domain of pH‐responsive peptide hydrogelators in a closed system. We program transient acidic pH states by combining a fast acidic activator with the slow, enzymatic, feedback‐driven generation of a base (dormant deactivator). This transient state can be programmed over orders of magnitude in time. It is coupled to dipeptides to create autonomously self‐regulating, dynamic gels with programmed lifetimes, which are used for fluidic guidance, burst release, and self‐erasing rapid prototyping. 相似文献
108.
109.
The Cage Structure of IndanCHF3 is Based on the Cooperative Effects of CH⋅⋅⋅π and CH⋅⋅⋅F Weak Hydrogen Bonds
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Dr. Laura B. Favero Weixing Li Lorenzo Spada Dr. Luca Evangelisti Giorgio Visentin Prof. Dr. Walther Caminati 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):15970-15973
The structural and energetic features of the C?H???π interaction and the internal dynamics of the CHF3 group change drastically in going from benzene?CHF3 to indan?CHF3, according to the analysis of the rotational spectrum of the latter complex generated in a supersonic expansion. 相似文献
110.
Pavol Brunovský Alexander Erdélyi Hans-Otto Walther 《Journal of Dynamics and Differential Equations》2004,16(2):393-432
A delay differential equation is presented which models how the behavior of traders influences the short time price movements of an asset. Sensitivity to price changes is measured by a parameter a. There is a single equilibrium solution, which is non-hyperbolic for all a>0. We prove that for a< 1 the equilibrium is asymptotically stable, and that for a>1 a 2-dimensional global center-unstable manifold connects the equilibrium to a periodic orbit. Its birth at a=1 is not of Hopf type and seems part of a Takens–Bogdanov scenario. 相似文献