900 research outputs found
Optical imaging of the effect of in-plane fields on cholesteric liquid crystals
Sharon A. Jewell and J. Roy Sambles, Physical Review E, Vol. 78, article 012701 (2008). Copyright © 2008 by the American Physical Society.The effects of in-plane electric fields on the director structure of cholesteric liquid crystals has been imaged in three dimensions using fluorescence confocal polarizing microscopy. The results show that a liquid crystal lying outside the electrode gap can be significantly affected by stray fields occurring above the electrode surface, resulting in a 90° rotation of the cholesteric helix. Distinct differences between the behavior of cholesterics with positive and negative dielectric anisotropies are observed
Helium irradiation effects in polycrystalline Si, silica, and single crystal Si
Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6âkeV helium ion irradiation of a thin (â55ânm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change
Tracking of fluorescently labeled polymer particles reveals surface effects during shear-controlled aggregation
Surface chemistry is believed to be the key parameter affecting the aggregation and breakage of colloidal suspensions when subjected to shear. To date, only a few works dealt with the understanding of the role of the physical and chemical properties of the particlesâ surface upon aggregation under shear. Previous studies suggested that surface modifications strongly affect polymer particlesâ adhesion, but it was very challenging to demonstrate this effect and monitor these alterations upon prolonged exposure to shear forces. More importantly, the mechanisms leading to these changes remain elusive. In this work, shear-induced aggregation experiments of polymer colloidal particles have been devised with the specific objective of highlighting material transfer and clarifying the role of the softness of the particleâs surface. To achieve this goal, polymer particles with a coreâshell structure comprising fluorescent groups have been prepared so that the surfaceâs softness could be tuned by the addition of monomer acting as a plasticizer and the percentage of fluorescent particles could be recorded over time via confocal microscopy to detect eventual material transfer among different particles. For the first time, material exchange occurring on the soft surface of coreâshell polymer microparticles upon aggregation under shear was observed and proved. More aptly, starting from a 50% labeled/nonlabeled mixture, an increase in the percentage of particles showing a fluorescent signature was recorded over time, reaching a fraction of 70% after 5 h
The Iteratively Regularized Gau{\ss}-Newton Method with Convex Constraints and Applications in 4Pi-Microscopy
This paper is concerned with the numerical solution of nonlinear ill-posed
operator equations involving convex constraints. We study a Newton-type method
which consists in applying linear Tikhonov regularization with convex
constraints to the Newton equations in each iteration step. Convergence of this
iterative regularization method is analyzed if both the operator and the right
hand side are given with errors and all error levels tend to zero. Our study
has been motivated by the joint estimation of object and phase in 4Pi
microscopy, which leads to a semi-blind deconvolution problem with
nonnegativity constraints. The performance of the proposed algorithm is
illustrated both for simulated and for three-dimensional experimental data
Ice XII in its second regime of metastability
We present neutron powder diffraction results which give unambiguous evidence
for the formation of the recently identified new crystalline ice phase[Lobban
et al.,Nature, 391, 268, (1998)], labeled ice XII, at completely different
conditions. Ice XII is produced here by compressing hexagonal ice I_h at T =
77, 100, 140 and 160 K up to 1.8 GPa. It can be maintained at ambient pressure
in the temperature range 1.5 < T < 135 K. High resolution diffraction is
carried out at T = 1.5 K and ambient pressure on ice XII and accurate
structural properties are obtained from Rietveld refinement. At T = 140 and 160
K additionally ice III/IX is formed. The increasing amount of ice III/IX with
increasing temperature gives an upper limit of T ~ 150 K for the successful
formation of ice XII with the presented procedure.Comment: 3 Pages of RevTeX, 3 tables, 3 figures (submitted to Physical Review
Letters
A Monte Carlo study of leading order scaling corrections of phi^4 theory on a three dimensional lattice
We present a Monte Carlo study of the one-component model on the
cubic lattice in three dimensions. Leading order scaling corrections are
studied using the finite size scaling method. We compute the corrections to
scaling exponent with high precision. We determine the value of the
coupling at which leading order corrections to scaling vanish. Using
this result we obtain estimates for critical exponents that are more precise
than those obtained with field theoretic methods.Comment: 20 pages, two figures; numbers cited from ref. 23 corrected, few
typos correcte
Molecular dynamics study of orientational order and rotational melting in clusters of TeF 6
Molecular dynamics simulations of the behavior of molecules in crystalline clusters of TeF 6 were carried out on systems of 100, 150, 250, and 350 molecules. Several diagnostic functions were applied to investigate whether rotational melting occurred before translational melting. These functions included the coefficient of rotational diffusion D Ξ ( T ), the âorientational Lindemann indexâ ÎŽ Ξ ( T ), the âorientational angular distribution functionâ Q (Ξ, T ), and the âorientational pair-correlation functionâ g Ξ ( r, T ). All indicators implied that rotational melting occurred before translational melting, that it began with the outermost molecules, and that its onset for smaller clusters was at lower temperatures than for larger clusters. Results also showed that the rotational transition coincided with the transition from a lower symmetry phase (monoclinic) to cubic, a phenomenon that had been noted by others to occur with some regularity for systems of globular molecules.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43961/1/10053_2005_Article_BF01426586.pd
Formulaic Language in Native and Second Language Speakers: Psycholinguistics, Corpus Linguistics, and TESOL
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/89473/1/j.1545-7249.2008.tb00137.x.pd
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