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981.
Various metal oxides were investigated using laser pulse photo-electromotive force measurements. This method is possible if the band gap of these oxides is smaller than the laser radiation energy. The sign of the photovoltage and its decay rate depend on the specific surface potential, which is influenced by adsorption layers. The adsorption of acids and bases on ZnO, TiO2, -Fe2O3 and -Fe2O3 microcrystals shows the dependence of the photovoltage on the type of space charge layer on the surface of the oxides. Oxides with a depletion layer exhibit a rising photovoltage with rising pH, whilst oxides with an accumulation layer at the surface exhibit the opposite behaviour. 相似文献
982.
Pierre Corfdir Oliver Marquardt Ryan B. Lewis Chiara Sinito Manfred Ramsteiner Achim Trampert Uwe Jahn Lutz Geelhaar Oliver Brandt Vladimir M. Fomin 《Advanced materials (Deerfield Beach, Fla.)》2019,31(3)
Phase coherence in nanostructures is at the heart of a wide range of quantum effects such as Josephson oscillations between exciton–polariton condensates in microcavities, conductance quantization in 1D ballistic transport, or the optical (excitonic) Aharonov–Bohm effect in semiconductor quantum rings. These effects only occur in structures of the highest perfection. The 2D semiconductor heterostructures required for the observation of Aharonov–Bohm oscillations have proved to be particularly demanding, since interface roughness or alloy fluctuations cause a loss of the spatial phase coherence of excitons, and ultimately induce exciton localization. Experimental work in this field has so far relied on either self‐assembled ring structures with very limited control of shape and dimension or on lithographically defined nanorings that suffer from the detrimental effects of free surfaces. Here, it is demonstrated that nanowires are an ideal platform for studies of the Aharonov–Bohm effect of neutral and charged excitons, as they facilitate the controlled fabrication of nearly ideal quantum rings by combining all‐binary radial heterostructures with axial crystal‐phase quantum structures. Thanks to the atomically flat interfaces and the absence of alloy disorder, excitonic phase coherence is preserved even in rings with circumferences as large as 200 nm. 相似文献
983.
Fei Wang Patrick Altschuh Lorenz Ratke Haodong Zhang Michael Selzer Britta Nestler 《Advanced materials (Deerfield Beach, Fla.)》2019,31(26)
Polymeric porous media (PPM) are widely used as advanced materials, such as sound dampening foams, lithium‐ion batteries, stretchable sensors, and biofilters. The functionality, reliability, and durability of these materials have a strong dependence on the microstructural patterns of PPM. One underlying mechanism for the formation of porosity in PPM is phase separation, which engenders polymer‐rich and polymer‐poor (pore) phases. Herein, the phase separation in polymer solutions is discussed from two different aspects: diffusion and hydrodynamic effects. For phase separation governed by diffusion, two novel morphological transitions are reviewed: “cluster‐to‐percolation” and “percolation‐to‐droplets,” which are attributed to an effect that the polymer‐rich and the solvent‐rich phases reach the equilibrium states asynchronously. In the case dictated by hydrodynamics, a deterministic nature for the microstructural evolution during phase separation is scrutinized. The deterministic nature is caused by an interfacial‐tension‐gradient (solutal Marangoni force), which can lead to directional movement of droplets as well as hydrodynamic instabilities during phase separation. 相似文献
984.
Ayaka Kamada Aviad Levin Zenon Toprakcioglu Yi Shen Viviane Lutz‐Bueno Kevin N. Baumann Pezhman Mohammadi Markus B. Linder Raffaele Mezzenga Tuomas P. J. Knowles 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(9)
Protein‐based fibers are used by nature as high‐performance materials in a wide range of applications, including providing structural support, creating thermal insulation, and generating underwater adhesives. Such fibers are commonly generated through a hierarchical self‐assembly process, where the molecular building blocks are geometrically confined and aligned along the fiber axis to provide a high level of structural robustness. Here, this approach is mimicked by using a microfluidic spinning method to enable precise control over multiscale order during the assembly process of nanoscale protein nanofibrils into micro‐ and macroscale fibers. By varying the flow rates on chip, the degree of nanofibril alignment can be tuned, leading to an orientation index comparable to that of native silk. It is found that the Young's modulus of the resulting fibers increases with an increasing level of nanoscale alignment of the building blocks, suggesting that the mechanical properties of macroscopic fibers can be controlled through varying the level of ordering of the nanoscale building blocks. Capitalizing on strategies evolved by nature, the fabrication method allows for the controlled formation of macroscopic fibers and offers the potential to be applied for the generation of further novel bioinspired materials. 相似文献
985.
This work deals with the closed‐loop robust stability of nonlinear model predictive control (NMPC) coupled with an extended Kalman filter (EKF). First, we point out the gaps between the practical formulations and theoretical research. Then, we show that the estimation error dynamics of an EKF are input‐to‐state stable (ISS) in the presence of nonvanishing perturbations. Moreover, a target setting optimization problem is proposed to solve the target state corresponding to the desired set points, which are used in the objective function in NMPC formulation. Thus, the objective function is a Lyapunov function candidate, and the input‐to‐state practical stability (ISpS) of the closed‐loop system can be established. Moreover, we see that the stability property deteriorates because of the estimation error. Simulation results of the proposed scheme are presented.Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
986.
Population ageing is, in the first instance, a demographic phenomenon; although its consequences go far beyond demography. But the future trends of ageing are not yet known and many of the consequences of ageing will depend on the future speed and extent of ageing. Here we summarize what is already known and what is not yet known about future ageing trends in different parts of the world. We do this through the means of new probabilistic population forecasts. The section ‘New Regional and Global Probabilistic Population Forecasts’ presents the results of those forecasts. They confirm the earlier finding (Lutz et al., Nature, 412(6846), 543–545, 2001a) that it is highly likely that the world’s population growth will come to the end during this century. The following four sections present results for proportions of populations 60+, old age dependency ratios, proportions 80+ and average ages. In the section ‘New Measures of Ageing’, we analyse a new measure of ageing that takes life expectancy changes into account. 相似文献
987.
Mehlhorn M Gawronski H Nedelmann L Grujic A Morgenstern K 《The Review of scientific instruments》2007,78(3):033905
A newly established combination of a femtosecond laser with a low temperature scanning tunneling microscope is described, which facilitates one to analyze femtochemistry on metal surfaces in real space. The combined instrument enables focusing the laser to some tens of micrometers and guiding it reproducibly into the tunneling gap with the aid of in situ movable mirrors. Furthermore, a method to determine the focus size on the sample is presented. The focus size is used to calculate the electron and phonon temperatures at the surface. Despite the additional noise introduced by laser operation the vertical resolution of the microscope lies below 1 pm. The potential of the instrument is demonstrated on para-chloronitrobenzene clusters adsorbed on Au(111). Single chloronitrobenzene molecules diffuse upon femtosecond laser irradiation; some smaller clusters rotate by multiples of 30 degrees ; clusters of less compact form rearrange to close-packed clusters. 相似文献
988.
Rusdorf S Brunnett G Lorenz M Winkler T 《IEEE transactions on visualization and computer graphics》2007,13(1):15-25
In this paper, we report on the realization of an immersive table tennis simulation. After describing the hardware necessities of our system, we give insight into different aspects of the simulation. In particular, the developed methods for collision detection and physical simulation are presented. The design of the virtual opponent is of crucial importance to realize an enjoyable game. Therefore, we report on the implemented game strategy and the animation of the opponent. Since table tennis is one of the fastest sports, the synchronization of the human player's movements and the visual output on the projection wall is a very challenging problem to solve. To overcome the latencies in our system, we designed a prediction method that allows high speed interaction with our application 相似文献
989.
990.
The semi-empirical molecular orbital method AM1 has been used as a tool for the prediction of radical intermediates and crosslink structures that may be of importance in the direct laser excitation of siloxanes. Special emphasis was put on configuration interaction (Cl) in order to calculate energies and geometries of excited triplet states as well as potential curves of triplet reactions. Heats of formation of intermediates and reaction enthalpies of monomolecular fragmentation reactions of T1 excited states of 2-phenyl-1,1,1,2,3,3,3-heptamethyltrisiloxane and octamethyltrisiloxane were calculated. In the former case bimolecular reactions were also considered. Dissociation of a methyl group was found to be the most probable monomolecular fragmentation. Consecutive reactions of the silyl radical formed lead to crosslink structures like Si? CH2? Si and Si? C6H4? Si. Biphenyl- and phenylcyclohexadienyls are the most probable crosslink structures of bimolecular reactions with phenyl exciplexes as intermediates. Experimental evidence is given for these crosslink structures. 相似文献