96 research outputs found
Critical slowing in lipid bilayers
No full textUltrasonic attenuation spectra (100 kHz to 2 GHz) and complex dielectric spectra (300 kHz to 40 GHz) of aqueous solutions of 1,2-dimyristoyl-L-3-phosphatidylcholine vesicles are reported and are discussed in view of their behavior near the main phase transition of the lipid. The relaxation terms in the spectra are assigned to the domain structure fluctuations of the membranes, the structural isomerization of alkyl chains, the axial diffusion of lipid molecules within the membrane, and the reorientational motions of the zwitterionic phospholipid headgroups. The relaxation times of the alkyl chain isomerization and of the headgroup motions on the bilayer surfaces show a steplike change at the transition temperature, T-m. The axial diffusion and the domain fluctuations exhibit substantial effects of slowing near T-m as characteristic for critically demixing liquids at their consolute point
Critical fluctuations in the domain structure of lipid membranes
No full textBetween 100 kHz and 2 GHz ultrasonic attenuation spectra of two aqueous solutions of vesicles from 1,2-dimyristoyl-L-3-phosphatidylcholine have been measured at 13 temperatures around the main phase transition temperature of the membranes. The spectra are analyzed in terms of an asymptotic high frequency background contribution and three relaxation terms. Two of these terms can be represented by a discrete relaxation time, respectively, the other one extends over a significantly broader frequency range than a Debye-type relaxation term. It was found to nicely follow the predictions of the Bhattacharjee-Ferrell model of three-dimensional critical fluctuations. This finding has been additionally verified by measurements of the scaling function and by an analysis of the relaxation rate of order parameter fluctuations following from the fit of the experimental scaling function data to the theoretical form. Theoretical arguments are presented to indicate why the three-dimensional theory applies so well to the quasi-two-dimensional membrane system. (C) 2003 American Institute of Physics
Impaired Color Discrimination in Alzheimer Disease Dementia
No full textBödeker S, Halstenberg E, Schulz P, et al. Impaired Color Discrimination in Alzheimer Disease Dementia. Alzheimer Disease and Associated Disorders. 2021;36(1):22-28.OBJECTIVE: Patients with Alzheimer disease dementia (ADD) often show impaired orientation and navigation. Signage offers an opportunity to compensate for these deficits, communicate information efficiently and facilitate wayfinding. Certain properties of signs such as colors and contrasts may beneficially affect the uptake and processing of information particularly in ADD patients.; METHODS: Thirty-six healthy older adults and 30 ADD patients performed a computerized color perception task that required discriminating different color combinations. The effects of different contrast features on performance accuracy and speed in the 2 experimental groups were examined by nonparametric mixed analysis of variances.; RESULTS: Analyses revealed a significant effect of contrast polarity on reaction times, significant effects of group on reaction times and errors as well as a marginally significant interaction of group*color on errors. All participants benefitted from positive contrast polarity (ie, dark target on lighter background) as indicated by increased performance speed. Furthermore, ADD patients reacted slower and less accurate than healthy controls, but showed higher accuracy at black-white and red-yellow than at blue-green color combinations.; CONCLUSIONS: Our findings suggest the implementation of signs with positive contrast polarity to ensure faster reactions. In addition, certain color combinations may enhance accuracy, particularly in patients with ADD. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved
Long path length UV-Vis spectroscopy with low solubility ligands to determine formation constants with various lanthanide metal ions
No full textHonors paper Department of Chemistry and Biochemistry; Includes bibliographical references (Leaf: 42
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