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81.
The multiaxial elongational rheometer equipped with rotary clamps is modified such that in addition to simple, equibiaxial and multiaxial elongations also tests with new modes of elongation can be performed. As an example, polyisobutylene is elongated with a ratio of the principal strain rates of
and magnitudes of the maximum strain rate
, 0.04 and 0.08 s–1. As a test result, the first elongational viscosityµ
1
(t) is obtained which follows closely the linear viscoelastic shear viscosity
. In contrast, the second elongational viscosityµ
2
(t) remains below
. By means of a further modification of the rheometer, the test modes can be varied during the deformation period. This allows one to investigate the influence of a well-defined rheological pre-history on the following rheological behaviour. As an example a variation ofm = 0.5 2 was performed. The measured normal-stress differences superpose from the single steps of deformation similar to the linear viscoelastic prediction.Dedicated to Prof. F. R. Schwarzl on the occasion of his 60th birthday 相似文献
82.
Summary Experimental data are presented which show the variation with time of the shear stress and primary normal stress difference during shear flow with a stepfunction shear rate; the material (Melt I at 150 °C) is a low-density polyethylene melt for which stress-growth and elastic recovery data in elongational flow experiments have been previously reported. A method of comparing the data with the predictions of the rubberlike-liquid constitutive equations is given, based on the use of a specially-chosen rate-of-strain invariantI
IV, defined in [4.1]. From this comparison, it is shown that the disagreement between theory and experiment is about the same for shear flow and for elongational flow, and that the extent of disagreement does not exceed 10% for short-duration flows such thatI
IV
t 3.
With 7 figures and 2 tables 相似文献
Zusammenfassung Es werden Meßergebnisse über die zeitliche Änderung der Schubspannung und der ersten Normalspannungsdifferenz bei Scherfließen einer LDPE-Schmelze (Schmelze I bei 150 °C) vorgelegt. Der zeitliche Spannungsverlauf bei und die elastische Erholung nach Dehnfließen sind für dieses Material bereits früher mitgeteilt worden. Hier wird das Verhalten der Schmelze bei Scherung und bei Dehnung mit den Voraussagen der rubberlike liquid-Zustandsgleichung verglichen, wobei eine speziell gewählte InvarianteI IV der Deformationsgeschwindigkeit verwendet wird (definiert in [4.1]). Der Vergleich zeigt Abweichungen von Theorie und Experiment, die für Scher- und Dehnfließen etwa gleich groß sind. Die Abweichungen liegen unter 10%, wenn für das Produkt ausI IV und der Deformationszeitt der WertI IV t = 3 nicht überschritten wird.
With 7 figures and 2 tables 相似文献
83.
Multiple crack propagation in a strip caused by thermal shock 总被引:1,自引:0,他引:1
H. -A. Bahr H. -J. Weiss
H. G. Maschke
F. Meissner
《Theoretical and Applied Fracture Mechanics》1988,10(3):219-226The time-dependent stress intensities due to quenching are calculated by the boundary element method for an array of parallel and equal spaced edge cracks in a long strip. Analyzed is the sequence of crack pattern formation. The predicted patterns have essential features in common with the experimental ones. This tends to support a recently developed approach for analyzing single and multiple crack growth under thermal shock. 相似文献
84.
Pugnat P. Ballou R. Schott M. Husek T. Sulc M. Deferne G. Duvillaret L. Finger M. Finger M. Flekova L. Hosek J. Jary V. Jost R. Kral M. Kunc S. Macuchova K. Meissner K. A. Morville J. Romanini D. Siemko A. Slunecka M. Vitrant G. Zicha J. 《The European Physical Journal C - Particles and Fields》2014,74(8):1-7
Recent Planck measurements show some CMB anomalies on large angular scales, which confirms the early observations by WMAP. We show that an inflationary model, in which before the slow-roll inflation the Universe is in a superinflationary phase, can generate a large-scale cutoff in the primordial power spectrum, which may account for not only the power suppression on large angular scales, but also a large dipole power asymmetry in the CMB. We discuss an implementation of our model in string theory. 相似文献
85.
S. Amini Z. Sun G. A. Meininger K. E. Meissner 《The European physical journal. Special topics》2014,223(10):2023-2033
Quantum Dot (QD)/microsphere structures supporting Whispering Gallery Modes (WGMs) are attached to Atomic Force Microscope (AFM) cantilevers for characterization of the evanescent field around the QD/microsphere and utilization of the evanescent field for sensing at the apical surface of live cells. Following laser excitation, QD emission couples to WGMs that circumnavigate the microsphere via total internal reflection at the internal surfaces of the microsphere. The resulting evanescent field is characterized utilizing the high spatial control of an AFM in approaching a dye monolayer on a test surface. The measured evanescent field extends approximately 50 nm from the microsphere surface, matching theoretical predictions. This system was then used to sense the accumulation of integrin and formation of focal adhesions at the apical surface of cells. 相似文献
86.
87.
88.
89.
The coupling of antiferromagnetic spin excitations and propagating holes has been studied theoretically on a square lattice in order to investigate the dependence of antiferromagnetic order on hole doping, being of relevance, e.g., for the Cu–3 d9 system in antiferromagnetic CuO2-planes of high-Tc superconductors. An effective Hamiltonian has been used, which results from a 2D Hubbard model (hopping integral t) with holes and with strong on-site Coulomb repulsion U. Bare antiferromagnetic excitations and holes with energies of the same order of magnitude t2/U are interacting via a coupling term being proportional to t and allowing holes to hop by emitting and absorbing spinwaves. In terms of a self-consistent one-loop approximation the renormalization of the spectral function both of holes and antiferromagnetic spin excitations are calculated. 相似文献
90.
Kenith E. Meissner Carvel Holton William B. Spillman Jr. 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):377
We present a study of the basic optical properties of colloidal CdSe/ZnS core/shell quantum dots entrained in a microstructured optical fiber. Quantum dots suspended in heptane were pulled into the holes surrounding the solid core of a microstructured optical fiber of the holey fiber class via capillary action and are found to remain in the fiber. In this experiment, a laser coupled into the fiber photoexcited quantum dots along the length of the fiber. Quantum dot emission was observed to couple into the fiber core and propagate along the fiber. To investigate the use of such a system in fiber-based light generation or amplification, a second laser overlapping the low-energy portion of the quantum dot emission was simultaneously coupled into the fiber. We observed apparent amplification of this light when photoexciting the quantum dots well above their bandedge. 相似文献