Search results for "visual_art.visual_art_medium"
showing 10 items of 2982 documents
Periphyton pigment analyses using paper chromatography
1983
Paper chromatography was used to study the community structure, the proportion of degraded chlorophylls to the total pigment content, and the chlorophyll and carotenoid content of the epilithic periphyton algae from Lake Tahoe, California-Nevada. Analyses were made using both samples directly from the lake and cultured periphytic algae. The extraction was made with boiling 100% methanol; two dimensional chromatography was used to separate the pigments. The relative contribution of different pigment fractions to total light absorption by the complete periphyton extract was estimated by planimetric integration of absorption curves. From the pigment structure, estimates were made of the propor…
Pigment-pigment interactions and secondary structure of reconstituted algal chlorophyll a/b-binding light-harvesting complexes of Chlorella fusca wit…
1995
Earlier we have shown by in vitro reconstitution experiments that the pigment composition of the chlorophyll alb-binding light-harvesting complex of the green alga Chlorella fusca could be altered in a relatively broad range (Meyer and Wilhelm 1993). In this study we used these reconstituted complexes of different pigment loading to analyze the excitonic interactions between the pigment molecules and the secondary structure by means of circular dichroism spectra in the visible and the far UV spectral regions, respectively. We found that, in contrast to the expectations, the pigment composition and pigment content hardly affected the circular dichroism spectra in the visible spectral region.…
Water-depth effects in photosynthetic pigment content of the benthic algae Dictyota dichotoma and Udotea petiolata
1981
Abstract The effect of water depth on the light-harvesting pigments contents in Dictyota dichotoma (Hudson) Lamouroux and Udotea petiolata (Turra) Borgesen was studied. Both species showed higher photosynthetic-pigments contents with increased depth or shade. The ratios of chlorophyll c /chlorophyll a and chlorophyll b / chlrophyll a in D. dichotoma and U. petiolata were lower in light-exposed samples. In D. dichotoma , the ratios of fucoxanthin to chlorophyll a increased with depth or shade; however, it is worth noting that the 0 m (sun) samples showed the highest values. On the other hand, total carotenoids to chlorophyll a ratios in U. petiolata increased with depth.
Theory-based improvements of continuous polymer fractionation demonstrated for poly(carbonate)
1992
For the first time, a quantitative theoretical analysis (liquid/liquid phase equilibria treated by means of the continuous thermodynamics) of the operating characteristics of continuous polymer fractionation (CPF) was performed. The results of these calculations were compared with data published for CPF of polyethylene. It turned out that the efficiency of the conventional CPF corresponds to approximately two theoretical plates only. For this reason, several improvements, suggested by theoretical considerations, were realized experimentally, for which purpose the system dichloromethane/diethylene glycol/bisphenol-A polycarbonate was chosen. The pulsating sieve-bottom column was replaced by …
Characterisation of Diarylheptanoid- and Flavonoid-type Phenolics in Corylus avellana L. Leaves and Bark by HPLC/DAD-ESI/MS
2013
Introduction The leaves of Corylus avellana L. (common hazel, Betulaceae), a plant with a wide distribution in Europe, have been used in folk medicine for various diseases, but phytochemical exploration of C. avellana is still incomplete. To the best of our knowledge there is no previous report concerning diarylheptanoids in C. avellana, although these compounds show a frequent occurrence among Betulaceae plants. Objective To improve existing online chromatographic methods for the investigation of the phenolic compounds in C. avellana leaves and bark, focusing on diarylheptanoid-type molecules. Methods Dried and powdered leaves and bark of C. avellana were extracted with increasing polarity…
Polydispersity effects on the phase diagram of the system chloroform/poly-l-(lactic acid)/poly(methyl methacrylate) and morphology of PLA/PMMA films
2000
Abstract Cloud point curve, critical composition and several critical coexistence curves were measured at 25°C for the ternary system poly- l -(lactic acid) (PLA), poly(methyl methacrylate) (PMMA) — where both polymers exhibit broad molecular weight distributions — and the common solvent chloroform. In contrast to the situation encountered in the absence of the second polymer both branches of the critical coexistence curves are located without any doubt inside the miscibility gap as defined by the cloud point curve. This unexpected experimental finding is corroborated by model calculations on the basis of continuous thermodynamics. The removal of solvent from the ternary mixtures yields fil…
Combretastatin Analogs via Hydration of Stilbene Derivatives
1993
Hydration of the double bond of some stilbene congeners of Picea abies bark by TiCl4·NaBH4 reagent is described. Five racemic 1,2-diphenylethanol derivatives (9–13), structurally related to (R)-(·)-combretastatin [(R)-1], have been obtained and characterized mainly by 13C- and 1H-NMR as well as mass spectrometry. The antileukemic activity of each compound has preliminarily been tested by the mouse leukemia L1210 system. Compound 10 has been synthesized by Friedel-Crafts acylation.
Effect of Processing Conditions on the Degradation and on the Recycling of Polycarbonate
2003
Polycarbonate, like other polycondensation polymers, can be easily recycled without significant loss of properties only with careful drying. Indeed, the presence of humidity strongly decreases the molecular weight of the polymer by hydrolytic chain scission. In this paper, the degradation and the recycling of an extrusion grade polycarbonate sample has been investigated considering mainly the effect of the humidity. Some degradation is observed also for the material reprocessed in dry conditions and due to the thermomechanical stress acting on the melt. The chain scission is strongly reduced if the processing is carried out under nitrogen flow. In these conditions less degradation effects …
Self-organized nanostructures of poly(4-vinylpyridine), polyaniline and polyamides due to metal complexation
2002
Comb-shaped supramolecules are constructed using flexible polymers and semi-rigid conjugated undoped or doped conjugated polymers upon complexing Zinc dodecyl benzene sulphonate, Zn(DBS) 2 . Self-organized nanostructures are formed in the bulk due to competing attractive interactions (coordination or water mediated hydrogen bonding) and repulsive polar/nonpolar interactions, showing characteristic long periods of ca. 30 A.
Mechanical Behavior of Concrete Columns Confined by Laterally Pre-Tensioned FRP
2011
This paper presents the results of an experimental investigation of concrete columns confined by a wound pre-tensioned carbon filament yarn. Yarn winding equipment was developed in the Institute of Polymer Mechanics with the ability to set the desired pre-tension force and thereby producing confined concrete specimens with different initial lateral pressure. It is shown that initial lateral pressure increases the axial stress at which intense internal cracking of the concrete develops.