Light-related photosynthetic characteristics of freshwater rhodophytes

Photosynthetic characteristics in response to irradiance were analysed in 21 field and culture populations of thirteen freshwater red algal species applying two distinct techniques (chlorophyll fluorescence and oxygen evolution). Photosynthesis-irradiance (PI) curves indicated adaptations to low irradiances in all species analysed, essentially characterized by occurrence of photoinhibition, low values of the saturation parameter (I-k < 225 mu mol m(-2) s(-1)) and compensation irradiance (I-c < 20 mu mol m(-2) s(-1)) and relatively high values of the effective quantum yield of photosystem II (Delta F/F'(m) >= 45). These characteristics have been reported in freshwater red algae and were confirmed from data based on the two techniques, indicating they are typically shade-adapted plants. on the other hand, some species (e.g. Batrachospermum delicatulum) can tolerate high irradiances (up to 2400 mu mol m(-2) s(-1)), suggesting they have mechanisms that enable them to avoid photodarnage of the photosynthetic apparatus. One of these mechanisms is the increase in dissipation of excessive energy captured by reaction centres after exposure to continuous irradiance, as reflected by the non-photochemical quenching fluorescence parameter in dark/light induction curves. Photo-inhibition occurred in all algae tested by both techniques. Light acclimation was evident particularly in field populations, as revealed by lower values of the saturation parameter (Ik) and the compensation irradiance (I-c) and higher values of Delta F/F'(m) in algae under low irradiances (shaded or heavily shaded stream segments), and vice-versa. Forms living within the boundary layer (e.g. crusts), in a region of reduced current velocity, tended to be more shade-adapted than semi-erect plants (e.g. non-mucilaginous or mucilaginous filaments), as indicated by highest values of photosynthetic efficiency (alpha = 0.31) and effective quantum yield (Delta F/F'(m) = 0.88) under natural conditions. Higher photo- synthetic rates (P-max) for the same species or population were observed under culture than field conditions when measured with the oxygen evolution technique, whereas the opposite trend was observed using chlorophyll fluorescence. (c) 2005 Elsevier B.V. All rights reserved.

Light and scanning electron microscopic study of the palatine mucosa of nine-banded armadillo (Dasypus novemcinctus)

The three-dimensional structure of the lamina propria of the hard and soft palatine mucosa of the nine-banded armadillo was observed by scanning electron microscopy. Sodium hydroxide cell maceration method was applied to demonstrate the architecture of the connective tissue papillae. The palatine mucosa of the armadillo had a triangular shape and measured appr. 6.5 cm length. The hard palate showed 9 transverse palatine plicae while the soft palate was smooth. In the 10% NaOH treated specimens, the lamina propria of the hard palatine mucosa showed numerous connective tissue papillae with a general finger-like shape. These structures were composed by a meshwork of collagen fibers arranged in several directions. on the other hand, the connective tissue papillae of the soft palate mucosa were scattered and small. Numerous openings of glandular ducts with circular or elliptical shape were located in the interplicae area and in the soft palate.

Electron scattering and effects of sources of light on photoconductivity of SnO2 coatings prepared by sol-gel

Electro-optical properties of sol-gel derived 2 mol% antimony or niobium doped tin dioxide films have been measured. The electron density has been calculated considering all the relevant scattering mechanisms and experimental conductivity data measured in the range -197 to 25 degrees C. The results support the hypothesis that both ionised impurity scattering and grain boundary scattering have comparable effects in the resistivity of coatings, for free electron density congruent to 5 x 10(18) cm(-3). We have measured variation of photoconductivity excitation with wavelength using xenon and deuterium lamp as light sources. Results show that the main band in the photoconductivity spectrum is dependent on the spectral light source emission, the excitation peak reaching 5 eV (deuterium lamp). This band is due to the recombination process involving oxygen species and photogenerated electron-hole pairs. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Highly intense violet-blue light emission at room temperature in structurally disordered SrZrO3 powders

Violet-blue photoluminescence was produced at room temperature in a structurally disordered SrZrO3 perovskite structure with a 350.7 nm excitation line. The intensity of this emission was higher than that of any other perovskites previously studied. The authors discuss the role of structural order-disorder that favors the self-trapping of electrons and charge transference, as well as a model to elucidate the mechanism that triggers photoluminescence. In this model the wide band model, the most important events occur before excitation. (c) 2007 American Institute of Physics.

MODEL FOR ASYMPTOTIC D-STATE PARAMETERS OF LIGHT-NUCLEI - APPLICATION TO HE-4

A simple method for calculating the asymptotic D-state observables for light nuclei is suggested. The method exploits the dominant clusters of the light nuclei. The method is applied to calculate the He-4 asymptotic D to S normalization ratio rho(alpha) and the closely related D-state parameter D2alpha. The study predicts a correlation between D2alpha and B(alpha), and between rho(alpha) and B(alpha), where B(alpha) is the binding energy of He-4. The present study yields rho(alpha) congruent-to -0.14 and D2alpha congruent-to -0.12 fm2 consistent with the correct experimental eta(d) and the binding energies of the deuteron, triton, and the alpha particle, where eta(d) is the deuteron D-state to S-state normalization ratio.

Light-induced relief gratings and a mechanism of metastable light-induced expansion in chalcogenide glasses

We report on a metastable light-induced volume expansion in Ge25+xGa10-xS65 glasses under irradiation with band gap (UV) light, which can result in recording of relief gratings on their surface in the case of irradiation with two interfering beams. We propose a mechanism for the expansion, which is based on the light-induced change in the polarizability of secondary (van der Waals type) bonds and the effect of this change on primary (covalent type) bonds of the glass. The effect is suggested to be due to an interference of electrons, which belong to a chalcogen atom and participate in the formation of secondary and primary bonds, respectively. We suggest that a minimum point of the Lennard-Jones potential, which corresponds to the equilibrium position of a chalcogen atom is shifted in the course of irradiation to a larger interatomic distance. This shift causes a volume expansion and allows a diffusion of chalcogen atoms into the irradiated area. We show that light-induced polymerization of the glass network is an important attribute of the light-induced volume expansion.

Obtaining a light-like planar gauge

In the usual and current understanding of planar gauge choices for Abelian and non-Abelian gauge fields, the external defining vector n(mu), can either be space-like (n(2) < 0) or time-like (n(2) > 0) but not light-like (n(2) = 0). In this work we propose a light-like planar gauge that consists of defining a modified gauge-fixing term, L-GF, whose main characteristic is a two-degree violation of Lorentz covariance arising from the fact that four-dimensional space-time spanned entirely by null vectors as basis necessitates two light-like vectors, namely n(mu) and its dual m(mu), with n(2) = m(2) = 0, n . m not equal 0, say, e.g. normalized to n . m = 2.

Light microscopy and computer three-dimensional reconstruction of the blood capillaries of the enamel organ of rat molar tooth germs

We performed a light microscope and a computer three-dimensional reconstruction study of serial sections of the molar enamel organ of 3- and 5-day-old rats perfused with Indian ink through the arterial system. The tooth germs were fixed in Bouin's solution, embedded in paraffin, sectioned and stained with haematoxylin and eosin. For the three-dimensional reconstruction, light micrographs of the serial sections were digitized, and aligned using the serial EM Align software downloaded from http://synapses.bu.edu/tools/. After alignment, the boundaries of the India-ink-filled blood vessels were manually traced with a mouse using the software IGL trace (version 1.26b), also downloaded from the above website. After tracing, a three-dimensional representation of the blood vessel contours was generated in a VRML format and visualized with the help of the software Cortona Web3D viewer (version 4.0) downloaded from http://www.parallelgraphics.com/products/cortona. Our results showed that in regions where ameloblasts are polarized the capillaries are arranged in three distinct levels: (1) penetrating and leaving capillaries in relation to the outer enamel epithelium; (2) capillaries crossing and branching inside the stellate reticulum; and (3) capillaries branching and anastomosing profusely within the stratum intermedium, thereby forming an extensive capillary plexus intimately associated with the cells of the stratum intermedium. The existence of a conspicuous capillary plexus intermingled with cells of the stratum intermedium, as shown in our results, suggests that some molecules produced by cells of the stratum intermedium could be released into the capillary plexus and thereafter carried to the dental follicle.