Improved methods for the isolation and study of the C18, C20 and C22 monoethylenic fatty acid isomers of biological samples: Hg adducts,HPLC, AgNO3-TLC/FID,and ozonolysis

The monoethylenic isomers of C₁₈, C₂₀ and C₂₂ chain lengths of the depot fat of a nonhominid primate (cynomolgus monkeys,Macaca fascicularis), fed a partially hydrogenated herring oil (IV=76.0) for 30 months, were examined by 2 different approaches. The first isolation method involved preparative gas liquid chromatography and argentation thin layer chromatography (TLC). The second sequence involved a chain-length fractionation system based on the TLC of the methoxy-bromomercuri quence involved a chain-length fractionation system based on the TLC of the methoxy-bromomercuri adducts of the total methyl esters to isolate groups of acids of common degrees of unsaturation, and then high performance liquid chromatography on a reverse-phase column. In both cases, the monoethylenic isomer distribution was determined by ozonolysis in BF₃/MeOH. Comparable results were obtained with the 2 methods. The second approach is recommended for small biological samples, especially for those containing a relatively high proportion of di- and other polyethylenic isomers which might interfere. Presented in part at the AOCS annual meeting, New Orleans, May 1981.     

Viscosity measurements of liquids under pressure by using the quartz crystal resonators

A quartz crystal viscometer has been developed for measuring viscosity in liquids under pressure. It employs an AT-cut quartz crystal resonator of fundamental frequency 3 MHz inserted in a variable-volume vessel designed for working up to 80 MPa. Viscosity is determined by two methods from resonance frequency and bandwidth measurements along up to eight different overtones. The resonance frequency allows an absolute measurement of the viscosity but leads to an accuracy limited to 5% whereas the bandwidth technique which works in a relative way provides an accuracy of 2%. The techniques were tested by carrying out measurements in two pure compounds: heptane and toluene. Measurement results demonstrate the feasibility of the technique in this viscosity range. The apparatus was also used to determine the viscosity of n-decane with dissolved methane. The results obtained with these mixtures reveal the applicability of the apparatus for reservoir fluids study.     

Influence of temperature and surfactant on Escherichia coli inactivation in aqueous suspensions treated by moderate pulsed electric fields

This research employed a conductometric technique to estimate the inactivation kinetics of Escherichia coli cells in aqueous suspensions (1 wt.%) during simultaneous pulsed electric fields (PEF) and thermal treatments. The electric field strength was E = 5 kV/cm, the effective PEF treatment time t_PEF was within 0–0.2 s, the pulse duration t_i was 10^− 3 s, the medium temperature was 30–50 °C, and the time of thermal treatment t_T was within 0–7000 s. The damage of E. coli was accompanied by cell size decrease and release of intracellular components. The synergy between PEF and thermal treatments on E. coli inactivation was clearly present. The non-ionic surfactant Triton X-100 additionally improved its inactivation. The characteristic damage time followed the Arrhenius law within the temperature range 30–50 °C with activation energies W = 94 ± 2 kJ mol^− 1 and W = 103 ± 5 kJ mol^− 1 with and without the presence of surfactant, respectively. Relations between cell aggregation, cell ζ-potentials and presence of surfactant were analysed.     

Coalescence of multiple flaws in a rock-model material in uniaxial compression

A number of specimens made of gypsum with three and 16 flaws have been prepared and tested in compression. Results from these experiments are compared with observations from similar specimens with two flaws. The comparisons indicate that the cracking pattern observed in specimens with multiple flaws is analogous to the pattern obtained in specimens with two flaws. Two types of cracks initiate from the tips of the flaws: wing cracks and secondary cracks. Wing cracks are tensile cracks that initiate at an angle with the flaw and propagate in a stable manner towards the direction of maximum compression. Secondary cracks are shear cracks that initially propagate along their own plane in a stable manner. Two types of secondary cracks are possible: coplanar or quasi-coplanar, and oblique. As the load is increased, wing cracks propagate in a stable manner and secondary cracks may propagate in an unstable manner and produce coalescence, which occurs when two flaws are linked together. Nine types of coalescence have been observed, and each type is characteristic of a particular flaw geometry. The stresses at which wing and secondary cracks initiate and coalescence occurs strongly depend on the geometry of the flaws and on the number of the flaws; as the flaw inclination angle increases, the spacing increases, or the number of flaws decreases, initiation and coalescence stresses increase.     

THE X-RAY MEASUREMENT OF AXIAL AND HOOP RESIDUAL STRESSES IN MICROCOMPOSITE SPECIMENS

Thermal residual stresses were measured in microcomposites (Le., the elementary cell of a composite) using the X-ray diffraction method In order to overcome the geometry problem caused by this type of specimen, three different theoretical methods were applied to analyze the X-ray results. The first method was used previously for larger microcomposites (φ = 140 μm) and cannot be applied successfully here due to the small size of our specimen (φ = 20 μm). The two other methods (three-dimensional methods) have been used successfully and lead to similar results. The effects of the interphase type and thickness were studied. However, the uncertainty on thermal residual stress values are still at about 20%.     

Structure,homogeneity ranges,magnetic, and electrical properties of the ordered Laves phases RENi4Mg with MgCu4Sn type structure

New ordered Laves phases RENi₄Mg (RE = Sc, Sm, Tb–Lu) were synthesized from the elements in sealed tantalum ampoules in an induction furnace. Six of the structures were refined on the basis of X-ray single crystal data. The diffraction experiments gave hint for small homogeneity ranges RE_1+xNi₄Mg_1?x. Magnetic susceptibility measurements show Curie–Weiss behavior for RE = Gd, Dy, Ho, Tm, Yb and the resulting effective magnetic moments suggest both stable trivalent states for all RE and a non-magnetic state for Ni. Gd_1+xNi₄Mg_1?x (x ≈ 0.12) orders antiferromagnetically at a Néel temperature of T_N = 4.6(5) K. Resistivity measurements reflect the metallic nature of these compounds.     

Isolation and characterization of copolymers of beta-lactoglobulin, alpha-lactalbumin, kappa-casein, and alphas1-casein generated by pressurization and thermal treatment of raw milk

Raw skim milk was submitted to high pressure (300 to 600 MPa) and temperature (4 to 70 degrees C) treatments for 2 or 5 min. The combined effects of pressure and temperature on milk proteins induced structural changes and polymer and copolymer formation characterized by anion-exchange and size-exclusion fast protein liquid chromatography and electrophoretic techniques. Approximately half of the beta-lactoglobulin formed polymers, and the other half formed large copolymers, mainly with kappa-casein, alpha-lactalbumin via intermolecular disulfide bond exchange, and alpha(s1)-casein via physicochemical interactions, in proportions of 1.0:0.7:0.3:0.1, respectively. Minor whey proteins (serum albumin, immunoglobulins, and lactoferrin) also participated in the formation of the copolymers but to a lesser extent. Two populations of the copolymers were found with apparent molecular masses ranging from 440 to 2000 kDa for the first and more than 2000 kDa for the second. On the contrary, for heated milks the aggregation kinetics obtained by combination of high pressure and thermal treatment were very fast, as no intermediates such as dimers and small size oligomers were observed after pressurization, whatever the temperature studied. Lactosylation of proteins as well as proteolysis were very limited. A beta-casein amino-terminal peptide of 22 kDa was specifically recovered in milk samples treated under the more drastic conditions (500 MPa/55 degrees C per 5 min and 600 MPa/70 degrees C per 5 min) and might have been generated by neutral proteases such as elastase released from somatic cells present in milk. No casein was released from the micelle whatever the combination of high pressure and temperature studied.     

How to visualize the spider mite silk?

Tetranychus urticae (Acari: Tetranychidae) is a phytophagous mite that forms colonies of several thousand individuals. Like spiders, every individual produces abundant silk strands and is able to construct a common web for the entire colony. Despite the importance of this silk for the biology of this worldwide species, only one previous study suggested how to visualize it. To analyze the web structuration, we developed a simple technique to dye T. urticae'silk on both inert and living substrates. Fluorescent brightener 28 (FB) (Sigma F3543) diluted in different solvents at different concentrations regarding the substrate was used to observe single strands of silk. On glass lenses, a 0.5% dimethyl sulfoxide solution was used and on bean leaves, a 0.1% aqueous solution. A difference of silk deposit was observed depending the substrate: rectilinear threads on glass lenses and more sinuous ones on bean leaves. This visualizing technique will help to carry out future studies about the web architecture and silk used by T. urticae. It might also be useful for the study of other silk-spinning arthropods. Microsc. Res. Tech. 2009. © 2009 Wiley-Liss, Inc.