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Intensity Gradient (intensity + gradient)

Distribution by Scientific Domains

Life Sciences	28%

Selected Abstracts

Evaluation of fluorescent probe surface intensities as an indicator of transdermal permeant distributions using wide-area two-photon fluorescence microscopy

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2003
Betty Yu
Abstract The application of high-speed two-photon fluorescence microscopy (HTPM) to examine transdermal transport processes has enabled the noninvasive visualization of permeant spatial distributions over a larger, more clinically relevant wide area of the skin. Earlier studies demonstrated that the transdermal fluorescent probe distribution over a 2,×,2 mm skin area was well represented by a significantly reduced sampling of the 400 microscale skin sites (100,×,100 ,m) constituting the wide area. In the present study, the 400 microscale skin sites are considered individually, and the site-to-site variability in permeant distributions is used as a model to reflect the range in experimentally measured skin permeabilities resulting from the inherent stratum corneum structural heterogeneity. The correlation established between the permeant surface intensity and the corresponding permeant intensity gradient at each skin site provides an indication of the potential for screening transdermal permeant distributions solely based on the evaluation of microscale permeant surface intensities. The strong linear correlation between the intensity gradient and the surface intensity for the hydrophilic model permeant, sulforhodamine B, demonstrated that surface intensities provide a robust indicator of the corresponding transdermal probe distributions at the microscale. For the hydrophobic model permeant, rhodamine B hexyl ester, however, weak correlations were observed between these two parameters. This result suggests that the stratum corneum microscale surface intensity does not validly capture the corresponding intensity gradients for the entire range of skin permeabilities typically encountered as a result of the inherent stratum corneum heterogeneity. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2354,2365, 2003 [source]

Interpenetrating Polymer Networks with Spatially Graded Morphology Controllable by UV-Radiation Curing

MACROMOLECULAR SYMPOSIA, Issue 1 2006
Hideyuki Nakanishi
Abstract Interpenetrating Polymer Networks (IPNs) composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) were synthesized from a precursor mixture by using dissimilar photo-cross-link reactions. When the reation yields exceeded a certain threshold, the mixture was quenched from one-phase region into two-phase region, leading to phase separation. Upon irradiation with strong UV-light, an intensity gradient was formed along the propagating direction of the exciting light, generating a gradient of quench depth via the spatial inhomogeneity of the cross-link reactions. As a consequence, a gradient of the characteristic length scales was continuously generated from the top to the bottom of the mixture. The resulting three-dimensional (3-D) morphology was in-situ observed at different depths of the mixture by using a laser-scanning confocal microscope (LSCM). From this 3-D observation, it was found that phase separation was accelerated at the bottom of the mixture and proceeded in an autocatalytic fashion. The mechanism for the formation of the graded morphology was discussed in conjunction with the kinetics of the autocatalytic phase separation. [source]

Investigations on the Photoinitiator-free Photopolymerization of Acrylates by Vibrational Spectroscopic Methods

MACROMOLECULAR SYMPOSIA, Issue 1 2005
Tom Scherzer
Abstract Photopolymerization of acrylates without photoinitiators was carried out by irradiation with short-wavelength UV light from excimer lamps with an emission at 222 or 172 nm. Basic investigations on the reactivity of various acrylates and on the conditions under which they can be UV-cured were performed by real-time FTIR-ATR spectroscopy. Depending on the molar extinction coefficients of a specific acrylate at the wavelength of irradiation, the absorption of the light within the coating leads to a pronounced intensity gradient which significantly influences polymerization rate and conversion. Accordingly, it limits the maximum thickness of the layer that can be cured (ranging from some hundreds of nanometres up to some micrometers). In addition to the basic studies, thin acrylate coatings were also cured on pilot scale. The actual conversion in the layer after UV irradiation was directly monitored by in-line NIR reflection spectroscopy, and the resulting coatings were characterized by FTIR spectroscopy and hardness measurements. [source]

Evaluation of fluorescent probe surface intensities as an indicator of transdermal permeant distributions using wide-area two-photon fluorescence microscopy

A re-examination of the expected effects of disturbance on diversity

OIKOS, Issue 3 2000
Robin L. Mackey
Disturbance is often cited as one of the main factors determining patterns of species diversity. Several models have predicted qualitatively that species richness should be highest at intermediate intensities and/or frequencies of disturbances, but none indicate whether this effect should be strong (statistically accounting for much variability in diversity) or only subtle. Empirical evidence on the point is very mixed. This study examines Markov models of the dynamics of six real communities. We derive the predicted changes in species richness and evenness when these communities are subjected to quantified disturbance frequency and intensity gradients. We also use several different sampling intensities (i.e. numbers of individuals counted) to determine how this affects richness-disturbance relationships. Our models predict that peaked responses of diversity to disturbance should be less common than monotonic ones. Species richness should vary, on average, by only 3% over gradients of no disturbance to complete disturbance. In the most extreme case, richness varied two-fold over this gradient. Moreover, richness may increase monotonically, decrease monotonically, or be a peaked function of disturbance, interacting in a non-intuitive fashion with both the sampling intensity and the community in question. These results are broadly consistent with a review of published richness-disturbance relationships. Evenness varies somewhat more strongly along disturbance gradients, but the effect is still small. We conclude that extant models provide little reason to believe that disturbance should play more than a subtle role in determining patterns of diversity in nature, contrary to most contemporary literature. [source]

Tanzanian Forest Edge Microclimatic Gradients: Dynamic Patterns,

BIOTROPICA, Issue 1 2001
William D. Newmark
ABSTRACT Air temperature, vapor pressure deficit, and light intensity microclimatic gradients were examined along four forest edge and four paired forest interior transects in the East and West Usambara Mountains, Tanzania. Between 14 August 1995 and 11 August 1998, 287, 282, and 196 air temperature, vapor pressure deficit, and light intensity gradients, respectively, were measured along the four forest edge and four interior transects. The relationship between microclimate and distance from the forest edge was examined using piecewise linear regression. All microclimatic gradients were classified into one of nine shapes based on the sign and the size of the two estimated slopes. The relative frequency in the shapes of 65 percent of air temperature gradients, 52 percent of vapor pressure deficit gradients, and 62 percent of light intensity gradients along forest edge transects exceeded the relative frequency of these same shapes along forest interior transects, indicating that a majority of the forest edge microclimatic gradients measured were influenced by edge effects. Yet this result also indicated that approximately one-third of all air temperature and light intensity gradients and nearly one-half of all vapor pressure deficit gradients recorded during this study were affected by factors independent of edge effects per se, and that forest edge microclimatic gradients were temporally nonconstant. For air temperature and vapor pressure deficit gradients, low spatial but high temporal variation existed in estimated edge width and the relative change in microclimate between the forest edge and interior. For light intensity gradients, both high spatial and temporal variability characterized estimated edge width and relative change in microclimate between the forest edge and interior. The pooled mean edge width and relative change in microclimate between die forest edge and interior across the four forest edge transects for air temperature, vapor pressure deficit, and light intensity gradients were 94.1 m and 2.00°C, 82.6 m and 0.29 kPa, and 60.5 m and 10.6 joules/sec/m2, respectively. These results suggest that forest edge microclimatic gradients in general may be inherently dynamic and nonconstant. [source]