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Optical Changes (optical + change)

Distribution by Scientific Domains

Polymers and Materials Science	42%

Selected Abstracts

Extraction of Stimulus-Selective Intrinsic Optical Signals From the Cat Visual Cortex

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 6 2009
Midori Nagai Non-member
Abstract Optical imaging based on intrinsic optical signals has been widely utilized in studies on the functional organization of various areas of the brain. Because of the small size of the optical signals and the large amount of background noise that is present, it is critical to be able to separate the stimulus-driven optical change from the background. In this study, we propose a novel method and apply it to the analysis of the orientation preference structure in cat area 17. The three criteria used to determine the activation included the amplitude of the optical change in the optical intensity, the statistical significance level of the change, and the temporal relationship between the optical change and the visual stimulation. In the activated region extracted by the new method, 82.4 ± 8.2% of the cells were electrophysiologically responsive to the stimuli that evoked the optical change. This was significantly higher than the 46.4 ± 7.1% value obtained when the activation region was extracted by the most widely used method, i.e. a differential map between two complementary stimuli, such as orthogonal orientations. Our newly proposed method provides a robust and an effective way to reduce manual operations used in the signal extraction process. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

Conjugated-Polymer/DNA Interpolyelectrolyte Complexes for Accurate DNA Concentration Determination,

ADVANCED MATERIALS, Issue 7 2006
W. Hong
Precise determination of DNA concentration without the health risks of intercalating dyes is possible via the optical changes that arise from DNA-induced aggregation of cationic conjugated polyelectrolytes. Addition of DNA to a conjugated electrolyte containing two fluorophores results in aggregation and fluorescence quenching, inducing a measurable and quantifiable shift from blue- to green-light emission (see figure and inside cover). [source]

New Cyclic Olefin Copolymer for the Preparation of Thermally Responsive Luminescent Films

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2009
Filippo Donati
Abstract Polymer films with optical properties as indicators to thermal stress were obtained through the controlled dispersion of moderate amounts (,0.1 wt.-%) of the 4,4,-bis(2-benzoxazolyl)stilbene (BBS) dye into a new semicrystalline ethylene-norbornene (E - co - N, N content of 15.3 mol.-%) copolymer characterized by a glass transition temperature (Tg) of about 64,°C. All the pristine films showed optical characteristics coming from noninteracting BBS chromophores. In contrast permanent optical changes were detected after film annealing at a T,,,Tg due to the variation of the BBS supramolecular structure. The easy modulation of the optical features of polymer films by thermal perturbations suggests applications as threshold temperature visual indicators in thermoplastic materials. [source]

Gold Nanoparticles Functionalized by a Dextran-Based pH- and Temperature-Sensitive Polymer

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 5 2010
Weipeng Lv
Abstract A dextran-based dual-sensitive polymer is employed to endow gold nanoparticles with stability and pH- and temperature-sensitivity. The dual-sensitive polymer is prepared by RAFT polymerization of N -isopropylacrylamide from trithiocarbonate groups linked to dextran and succinoylation of dextran after polymerization. The functionalized nanoparticles show excellent stability under various conditions and can be stored in powder-form. UV and DLS measurements confirm that the temperature-induced optical changes and aggregation behaviors of the particles are strongly dependent on pH. [source]

HgTe segregation process in HgCdTe studied by E1 reflectance peak positions

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006
M. Pociask
Abstract Long term diffusion processes near the Cd1,xHgxTe surface influences the electronic structure as is shown in this paper. Measurements of reflectivity and surface characterisation by means of scanning electron microscopy (SEM) were performed for samples with x = 0.4 and x = 0.62. The optical results were compared with the reflectivity spectra obtained 22 years ago using the same samples. We discuss the observed dramatic changes in the optical changes upon the SEM and comparative analysis. E1 + , reflectance peak position corresponds to binary HgTe in both recently investigated samples. That method reflection is sensitive to no more than 120 µm the upper depth of investigated samples. The measurements of the E1 reflectance peak has proven to be a helpful and convenient tool for mercury telluride segregation near the HgCdTe surface and may be used to determine composition and age of HgCdTe. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Behavioural environments and niche construction: the evolution of dim-light foraging in bees

BIOLOGICAL REVIEWS, Issue 1 2009
William T. Wcislo
Abstract Most bees forage for floral resources during the day, but temporal patterns of foraging activity vary extensively, and foraging in dim-light environments has evolved repeatedly. Facultative dim-light foraging behaviour is known in five of nine families of bees, while obligate behaviour is known in four families and evolved independently at least 19 times. The light intensity under which bees forage varies by a factor of 108, and therefore the evolution of dim-light foraging represents the invasion of a new, extreme niche. The repeated evolution of dim-light foraging behaviour in bees allows tests of the hypothesis that behaviour acts as an evolutionary pacemaker. With the exception of one species of Apis, facultative dim-light foragers show no external structural traits that are thought to enable visually mediated flight behaviour in low-light environments. By contrast, most obligate dim-light foragers show a suite of convergent optical traits such as enlarged ocelli and compound eyes. In one intensively studied species (Megalopta genalis) these optical changes are associated with neurobiological changes to enhance photon capture. The available ecological evidence suggests that an escape from competition for pollen and nectar resources and avoidance of natural enemies are driving factors in the evolution of obligate dim-light foraging. [source]