PHOTOCHEMISTRY OF TYPE I ACID-SOLUBLE CALF SKIN COLLAGEN: DEPENDENCE ON EXCITATION WAVELENGTH

Although previous studies have demonstrated that the predominant photochemistry of type I collagen under 254 nm irradiation may be attributed either to direct absorption by tyrosine/phenylalanine or to peptide bonds, direct collagen photochemistry via solar UV wavelengths is much more likely to involve several age- and tissue-related photolabile collagen fluorophores that absorb in the latter region. In this study, we compare and contrast results obtained from irradiation of a commercial preparation of acid-soluble calf skin type I collagen in solution with UVC (primarily 254 nm), UVA (335–400nm) and broad-band solar-simulating radiation (SSR; 290^1–00nm). Excitation spectroscopy and analysis of photochemically induced disappearance of fluorescence (fluorescence fading) indicates that this preparation has at least four photolabile fluorescent chromophores. In addition to tyrosine and L-3,4-dihydroxyphenylalanine, our sample contains two other fluorophores. Chromophore I, with emission maximum at 360 nm, appears to be derived from interacting aromatic moieties in close mutual proximity. Chromophore II, with broad emission at430–435 nm, may be composed of one or more age-related molecules. Collagen fluorescence fading kinetics are sensitive to excitation wavelength and to conformation. Under UVC, chromophore I fluorescence disappears with second-order kinetics, indicating a reaction between two proximal like molecules. Adherence to second-order kinetics is abrogated by prior denaturation of the collagen sample. A new broad, weak fluorescence band at400–420 nm, attributable to dityrosine, forms under UVC, but not under solar radiation. This band is photolabile to UVA and UVB wavelengths. Amino acid analysis indicates significant destruction of aromatic amino acids under UVC, but not under UVA or SSR. When properly understood, collagen fluorescence fading phenomena may act as a sensitive molecular probe of structure, conformation and reactivity.     

Replacing Synthetic with Microbial Surfactants as Collectors in the Treatment of Aqueous Effluent Produced by Acid Mine Drainage,Using the Dissolved Air Flotation Technique

Dissolved air flotation (DAF) is a well-established separation process employing micro bubbles as a carrier phase. The application of this technique in the treatment of acid mine drainage, using three yeast biosurfactants as alternative collectors, is hereby analyzed. Batch studies were carried out in a 50-cm high acrylic column with an external diameter of 2.5 cm. High percentages (above 94%) of heavy metals Fe(III) and Mn(II) were removed by the biosurfactants isolated from Candida lipolytica and Candida sphaerica and the values were found to be similar to those obtained with the use of the synthetic sodium oleate surfactant. The DAF operation with both surfactant and biosurfactants, achieved acceptable turbidity values, in accordance with Brazilian standard limits. The best ones were obtained by the biosurfactant from C. lipolytica, which reached 4.8 NTU. The results obtained with a laboratory synthetic effluent were also satisfactory. The biosurfactants removed almost the same percentages of iron, while the removal percentages of manganese were slightly higher compared with those obtained in the acid mine drainage effluent. They showed that the use of low-cost biosurfactants as collectors in the DAF process is a promising technology for the mining industries.     

Imminent fracture detection in graphite/epoxy using acoustic emission

An experiment designed to detect incipient failure in graphite/epoxy tensile specimens is described. Tests using eighteen samples of six different graphite/epoxy compositions in six-ply balanced [0/+45/?45], laminates indicate that a failure precursor does exist. This precursor takes the form of a sudden reduction in the acoustic-emission output at 99 percent of the ultimate tensile load, and evidence indicates that the reduction is the result of a change in the fundamental failure mechanism. The shape of the acoustic-emission countrate curve is analyzed and found to correlate well with micro-mechanical fracture activity.     

A multi-analytical approach to studying binding media in oil paintings

This article presents a multi-analytical approach to investigating the drying, polymerisation and oxidative degradation of linseed oil, which had undergone various treatments known to be undertaken during the nineteenth century in preparation for painting. The oil was mechanically extracted from the same seed lot then processed by different methods: water washing, heat treatments, and the addition of driers, with and without heat. The oil was prepared in 1999 within the framework of the MOLART project. We compared thermogravimetric analysis (TG), which yields macromolecular information, with gas-chromatography mass-spectrometry (GC/MS) and direct exposure mass spectrometry (DE-MS), which provide molecular information. This comparison enabled us to elucidate the role of pre-treatment on the composition of the oil. TG and oxygen uptake curves registered at a constant temperature helped us to identify the different physical behaviour of the oil samples, thus highlighting the presence of hydrolysed, oxidised and crosslinked fractions, as a consequence of the different pre-treatments. GC/MS was used to characterise the soluble and non-polymeric fraction of the oil, to calculate the ratios of palmitic to stearic acid (P/S), and azelaic to palmitic acid (A/P), and to further evaluate the effects of oil pre-treatments. DE-MS using chemical ionisation with CH₄, enabled us to establish the chemical composition of the oil in different stages of ageing. DE-MS proved to be a useful tool for a simultaneous semi-quantitative characterisation of the free fatty acids, monoglycerids, diglycerides and triglycerides present in each sample. The combination of thermal analysis with GC/MS and DE-MS enabled a model to be developed, which unravelled how oil pre-treatments produce binders with different physical–chemical qualities.     

Effects of traditional processing methods of linseed oil on the composition of its triacylglycerols

Different oil processing methods were performed, which included washing with water and treatment with lead-based driers, with and without heating to different temperatures, giving a set of 7 oils to be investigated. The effects of the traditional processing methods of linseed oil on its triacylglycerol (TAG) composition were studied, using the following analytical methods: high performance size exclusion chromatography (HPSEC), Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry (HPLC-APCI-MS), direct temperature resolved mass spectrometry (DTMS), matrix assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), and electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). A decrease of the initial cis-double bonds and the formation of trans-double bonds upon heating of the oils was observed. Heating a lead and oil mixture to 150 degrees C, or heating the oil alone to 300 degrees C led to the highest degree of oxidation. A difference was observed for the oxidation patterns for oils with and without the addition of lead. Furthermore, levels of oxygen incorporation were higher when lead was added to the oil. High temperature treatment of the oils resulted in an increased average molecular weight. The changes in the initial conformation of the double bond systems observed with FTIR were supported by HPLC-APCI-MS measurements that showed the formation of a number of new isomeric TAGs in the heated oil compared to freshly pressed, untreated oil. Oligomerisation up to hexamers was observed with HPSEC, and MALDI-TOF-MS. The formation of oligomers up to trimers only, however, was observed with ESI-FTICR-MS. Incorporation of oxygen was mainly observed with MALDI-TOF-MS and ESI-FTICR-MS whereas with DTMS and FTIR hardly any evidence was found for this.     

Random chain scission of polystyrene in electron irradiated solution

Main-chain scission was the predominant effect when dilute solutions of three linear polystyrenes in 1-methylnaphthalene and polybenzyl oligomer received up to 2000 megaroentgen of 1.5-MeV electrons. Values of energy per scission were independent of dose and of the same magnitude as literature values in dioxane and benzene solutions when compared at the same dose rate. In all cases as irradiation progressed, M_w/M_n approached a value of 2 and M_z/M_w approached a value of 1.5 characteristic of a random distribution. Starting from one initial distribution, random numbers were used to simulate random chain scission. A 500 MR (megaroentgen) distribution calculated in this manner matched the experimental distribution after a 500 MR irradiation.     

Van Gogh’s Painting Grounds: Quantitative Determination of Bulking Agents (Extenders) Using SEM/EDX

A pre-concentration procedure using cloud point extraction is presented for the determination of uranium in natural water using molecular absorption spectrometry. The ligand used was 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) and the micellar phase was obtained using the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) and centrifugation. Interferences were eliminated using a masking solution containing trans-1,2-cyclohexanediaminetetraacetic acid (CDTA), sodium fluoride and sulphosalicylic acid. The optimization step was performed using a two-level factorial design and a Doehlert matrix, involving the factors pH, centrifugation time and buffer concentration. The method allows the determination of uranium in water samples with a detection limit of 0.15 μg L⁻¹, a quantification limit of 0.50 μg L⁻¹ and a precision expressed as relative standard deviation of 1.8 and 2.3% for uranium concentrations of 5 and 10 μg L⁻¹, respectively (n = 8). The accuracy was confirmed by analysis of two certified samples of natural water. This method was applied to the determination of uranium in superficial water samples collected at a uranium mine in Brazil. For five samples analyzed, the concentration of uranium varied between 1.1 and 18.1 μg L⁻¹. Tests of addition/recovery were performed for all these samples, and the results varying between 98 and 105% also proved that this procedure is not affected by the matrix and can be applied satisfactorily to the determination of uranium in water samples.     

Acoustic-emission fatigue analyzer

A new technique has been developed for acoustic-emission fatigue monitoring which facilitates the interpretation of dynamic micromechanical failure processes in materials, through the use of a new method for data presentation. In contrast to conventional acoustic-emission fatigue records in which the emission rate is plotted as a function of the number of fatigue cycles, the new technique produces a graph in which each acoustic event is plotted within a coordinate system of load vs. number of cycles. This approach results in the simultaneous recording of the relationship between sample load, acoustic-emission rate and number of fatigue cycles. Monitoring of 300M steel has established that it is possible to distinguish between fatigue-crack propagation, fatigue-crack closure and testing-machine noise using a single transducer.     

Bin covering algorithms in the second stage of the lot to order matching problem

We formulate the problem of effectively assigning semiconductor fabrication wafer lots to customer orders of various sizes, or the lot-to-order matching problem, as an integer programming problem. Our goal in this paper is to develop an efficient, practical method for solving this problem for various performance measures. Because of its complexity we decompose the problem into a knapsack problem coupled with a generalized bin-covering problem, and solve these subproblems sequentially using heuristic methods. We restrict our attention to solution methods for the less-common second subproblem, and analyze the performance of several heuristics using a data set representative of real situations in a semiconductor back-end. Based on this analysis, we show that these heuristics perform significantly better than current industrial practice in the context of the overall problem.