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排序方式: 共有395条查询结果,搜索用时 703 毫秒
61.
Gabriella Josefsson Fredrik Berthold E. Kristofer Gamstedt 《International Journal of Solids and Structures》2014
Nanocomposites, reinforced by different types of cellulose fibrils, have gained increased interest the last years due to the promising mechanical properties. There is a lack of knowledge about the mechanical properties of the cellulose fibrils, and their contribution to the often claimed potential of the impressive mechanical performance of the nanocomposites. This paper investigates the contribution from different types of cellulose nanofibril to the overall elastic properties of composites. A multiscale model is proposed, that allows back-calculation of the elastic properties of the fibril from the macroscopic elastic properties of the composites. The different types of fibrils used were nanofibrillated cellulose from wood, bacterial cellulose nano-whiskers and microcrystalline cellulose. Based on the overall properties of the composite with an unaged polylactide matrix, the effective longitudinal Young’s modulus of the fibrils was estimated to 65 GPa for the nanofibrillated cellulose, 61 GPa for the nano whiskers and only 38 GPa for the microcrystalline cellulose. The ranking and absolute values are in accordance with other studies on nanoscale morphology and stiffness estimates. Electron microscopy revealed that in the melt-processed cellulose nanofibril reinforced thermoplastics, the fibrils tended to agglomerate and form micrometer scale platelets, effectively forming a microcomposite and not a nanocomposite. This dispersion effect has to be addressed when developing models describing the structure–property relations for cellulose nanofibril composites. 相似文献
62.
Image-potential states in front of a clean Cu (100) surface were investigated by time- and angle-resolved two-photon photo-emission
(2PPE). We observe a previously unknown quasi-elastic relaxation channel, which efficiently couples states with different
quantum numbers, n, and parallel momenta, k∥. This process of resonant interband scattering (RIS) is independent of sample temperature and shows a close relationship
to the pure dephasing of image-potential states.
Received: 1 October 2001 / Revised version: 24 October 2001 / Published online: 23 November 2001 相似文献
63.
Alexander Pichler Alfred George Friedrich Seiler Julio Srulijes Berthold Sauerwein 《Shock Waves》2009,19(5):413-421
Doppler picture velocimetry (DPV) is a tool for visualizing and measuring the flow velocity distribution of tracer particles
in a laser light sheet. A frequency sensitive Michelson interferometer, tuned for detecting the velocity distribution by the
Doppler effect, visualizes the velocity information of tracer particles crossing an illuminating laser light sheet as interference
fringe patterns. Many efforts have been done to evaluate best these DPV patterns, in order to obtain the frequency distribution
and, by applying the Doppler formula, the velocity profile of the tracers. The first processing method, developed in 1982,
relied on manual processing of the pictures by the user, due to the unavailability of suitable high performance picture processing
algorithms. This drawback made DPV being considered as a rather time-consuming measurement technique with limited accuracy,
compared to existing commercial velocity measurement systems (e.g. PIV). This is no more the state of the art: The new DPV
analysis software, presented in this paper, allows automated processing of the interference fringe samples obtained by two
images, a reference picture without frequency shift and a Doppler picture containing the frequency shift, using single beam
velocimetry. Based on Fast Fourier transformation (FFT), the presented algorithm determines the corresponding velocity profile
(in pseudo colours) within only a few seconds on a standard personal computer without user intervention. 相似文献
64.
Robin F. Weitkamp Beate Neumann Dr. Hans-Georg Stammler Prof. Dr. Berthold Hoge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(21):6460-6464
The reaction of the strong monophosphazene base with the weakly acidic phenol leads to the formation of a phenol–phenolate anion with a moderately strong hydrogen bond. Application of the more powerful tetraphosphazene base (Schwesinger base) renders the isolation of the corresponding salt with a free phenolate anion possible. This compound represents the first species featuring the free phenolate anion [H5C6-O]−. The deprotonation of phenol derivatives with tetraphosphazene bases represents a great way for the clean preparation of salts featuring free phenolate anions and in addition allows the selective syntheses of hydrogen bonded phenol-phenolate salts. This work presents a phosphazenium phenolate salt with a redox potential of −0.72 V and its capability for the selective activation of the chemically inert greenhouse gas SF6. The performed two-electron reduction of SF6 leads to phosphazenium pentafluorosulfanide ([SF5]−) and fluoride salts. 相似文献
65.
66.
Berthold Stech 《Zeitschrift fur Physik C Particles and Fields》1997,75(2):245-251
An explicit model is presented which gives the momentum transfer-dependent ratios of form factors of hadronic currents. For the unknown Isgur-Wise function and its generalization for transitions to light particles a simple phenomenological Ansatz is added. The model allows a calculation of all form factors in terms of mass parameters only. It is tested by comparison with experimental data, QCD sum rules and lattice calculations. 相似文献
67.
Matzanke Berthold F. Bill Eckard Müller Gertraud I. Winkelmann Günther Trautwein Alfred X. 《Hyperfine Interactions》1989,47(1-4):311-327
Hyperfine Interactions - Iron limited growth of microbes results in derepression of siderophore receptor and transport-systems which can be utilized for controlled and specific siderophore... 相似文献
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