The fatty acids of wax esters and sterol esters from vernix caseosa and from human skin surface lipid

Separation of sterol esters from wax esters in the lipids of vernix caseosa and adult human skin surface was accomplished by column chromatography on MgO. The fatty acids of the sterol esters and wax esters of both samples were separated into saturates and monoenes, and examined in detail by gas liquid chromatography (GLC). The saturated fatty acids of the wax esters of vernix caseosa and of adult human skin surface were remarkably similar. They ranged in chain length from at least C₁₁ to C₃₀, six skeletal types being present: straight even, straight odd, iso, anteiso, other monomethyl branched and dimethyl branched. A large number of patterns of monoenes were observed, each pattern consisting of desaturation of a specific chain at Δ6 or Δ9 plus its extension or degradation products. The mole per cent of the total Δ6 and Δ9 patterns of wax ester fatty acid monoenes of vernix caseosa were 87% and 12%, respectively, and 98% and 1%, respectively, for adult human skin surface lipid. The sterol ester fatty acids of vernix caseosa were much different from those of adult human skin surface: vernix caseosa saturates were largely branched and of lengths greater than C₁₈, whereas the saturates of adult human surface lipid resembled the wax ester fatty acids. Of the vernix caseosa monoene patterns, the mole per cent was 30% Δ6 and 70% Δ9, whereas of the adult human skin surface sterol ester fatty acids 89% were Δ6 and 11% Δ9. Chain extension was particularly pronounced in the sterol ester fatty acid monoenes of vernix caseosa amounting to 7–8 C₂ units in some cases. The fatty acids of the sterol esters of both vernix caseosa and adult human skin surface appear to be derived from the sebaceous gland and from the keratinizing epidermis, but those of the wax esters are from the sebaceous glands only.     

Fischer–Tropsch synthesis: Deactivation of promoted and unpromoted cobalt–alumina catalysts

The loss in activity of Pt-promoted and unpromoted 25 wt% Co–Al₂O₃ catalysts has been compared under identical conditions except for adjustment of the space velocity to give the same initial CO-conversion. Both catalysts underwent a 200 h period of rapid, initial decline in CO conversion and then a slower, linear decline during the next 1000 h. Pt-promotion did not alter the cobalt dispersion (or average particle size) from that of the unpromoted catalyst but did increase the amount of cobalt that was reduced. When compared not by time-on-stream, but by the moles of Co converted per unit weight of catalyst, both the Pt-promoted and unpromoted catalysts decline in activity at the same rate.     

Studies on the lipids of sheep red blood cells. II. The incorporation of phosphorus into phospholipids of HK and LK cells

The incorporation of inorganic phosphate (as NaH₂PO₄) into the phospholipids of sheep red blood cells was studied in vitro in blood samples from five highpotassium (HK) and five low-potassium (LK) sheep. The erythrocytes from HK sheep incorporated more activity in 4 hr than those from the LK sheep. However no activity was incorporated into the major phospholipids of the cells (phosphatidyl ethanolamine, phosphatidyl serine, and sphingomyelin) of either group. The phosphatidic acid fraction was labeled in both groups and to a significantly greater extent in the HK samples. However the highest activity in the phospholipid of sheep red-cells was located in three unknown compounds not previously detected. Their specific activities were the same in the HK and the LK samples although they were present in slightly larger amounts in the HK samples. In general, incorporation was at a rather low level, and from stoichiometric considerations it was concluded that the metabolism in the red-cell phospholipids could not be directly involved in the active transport of ions across the cell membrane. This work also confirmed a previous report that no quantitative differences exist among the major phospholipid classes in the two types of cells.     

Skeletonized hybrid liposomes

Summary Giant hybrid liposomes of polymerizable lipid and cholesterol were prepared by the hydration method and were polymerized by UV irradiation. The obtained giant liposomes were freeze-dried and washed with chloroform to skeletonize the frame structure of the polymerized membrane. The skeletonized liposomes were directly confirmed by scanning electron microscopy. The single-layered and fully spherical liposome frame were easily confirmed by the stereo-pair of the obtained micrographs.     

Cure kinetics of a low epoxide/hydroxyl group-ratio bisphenol a epoxy resin–anhydride system by infrared absorption spectroscopy

An infrared absorption spectroscopy study of the curing kinetics of a low (1.12) epoxide/hydroxyl-group ratio bisphenol A epoxy resin—phthalic anhydride system is reported. A full infrared peak assignment to molecular vibrational modes is given for the range 400 to 4000 cm^?1, and the optical density behavior of all peaks during reaction is discussed in detail. Proposed rival reaction mechanisms are considered and their respective kinetic behavior discussed. The reaction was found to follow consecutive-step addition esterification and simultaneous addition etherification, and epoxide—hydroxyl group and carboxylic acid dimer hydrogen bonding was found to occur. The reaction behavior supports a proposed hydroxyl group-limited inhomogeneous bulk reaction mechanism of a colloid type.     

Nearly-Linear Work Parallel SDD Solvers,Low-Diameter Decomposition,and Low-Stretch Subgraphs

We present the design and analysis of a nearly-linear work parallel algorithm for solving symmetric diagonally dominant (SDD) linear systems. On input an SDD n-by-n matrix A with m nonzero entries and a vector b, our algorithm computes a vector \(\tilde{x}\) such that \(\|\tilde{x} - A^{+}b\|_{A} \leq\varepsilon\cdot\|{A^{+}b}\|_{A}\) in \(O(m\log^{O(1)}{n}\log {\frac{1}{\varepsilon}})\) work and \(O(m^{1/3+\theta}\log\frac{1}{\varepsilon})\) depth for any θ>0, where A ⁺ denotes the Moore-Penrose pseudoinverse of A. The algorithm relies on a parallel algorithm for generating low-stretch spanning trees or spanning subgraphs. To this end, we first develop a parallel decomposition algorithm that in O(mlog ^O(1) n) work and polylogarithmic depth, partitions a graph with n nodes and m edges into components with polylogarithmic diameter such that only a small fraction of the original edges are between the components. This can be used to generate low-stretch spanning trees with average stretch O(n ^α ) in O(mlog ^O(1) n) work and O(n ^α ) depth for any α>0. Alternatively, it can be used to generate spanning subgraphs with polylogarithmic average stretch in O(mlog ^O(1) n) work and polylogarithmic depth. We apply this subgraph construction to derive a parallel linear solver. By using this solver in known applications, our results imply improved parallel randomized algorithms for several problems, including single-source shortest paths, maximum flow, minimum-cost flow, and approximate maximum flow.     

The effect of platinum and silver deposits in the photocatalytic oxidation of resorcinol

The effects of platinum (Pt) and silver (Ag) metallisation in the photocatalytic oxidation of resorcinol at pH 3 ± 0.5 have been investigated. The photocatalytic degradation of resorcinol was significantly improved by Pt/TiO₂, while the presence of Ag/TiO₂ enhanced the initial photocatalytic degradation rate of resorcinol slightly. Likewise, the photocatalytic mineralisation of resorcinol continued to be enhanced by Pt/TiO₂, but it was retarded when Ag/TiO₂ was used.

The function of Pt and Ag deposits on the surface of TiO₂ has been found to be markedly influenced by the interaction of resorcinol and its degradation products with the metal deposits. The presence of Pt or Ag on the surface of TiO₂ altered the distribution of degradation products of resorcinol as well as the production of photoactive species for the photocatalytic oxidation of resorcinol. The X-ray photoelectron spectroscopy (XPS), zeta potential and transmission electron microscopy (TEM) analyses have indicated that the contrasting effect of Pt and Ag deposits were governed by the oxidation states and the catalytic property of metal deposits. In addition to that, it has been found that the roles of metal deposits are specific and should not be generalised.     

Cure kinetics of a high epoxide/hydroxyl group-ratio bisphenol a epoxy resin—anhydride system by infrared absorption spectroscopy

An infrared absorption spectroscopy study of the curing (gelation and postcure) kinetics of a high (4.7) epoxide/hydroxyl group-ratio diglycidyl ether of bisphenol A (DGEBA)–mixed anhydride epoxy resin system is reported. Peak assignments to molecular vibrational modes are given for the range 400–4000 cm^?1, and the optical density behavior of all peaks during reaction is discussed in detail. Chemical reaction was found to follow consecutive-step addition esterification and simultaneous addition etherification. Epoxide hydroxyl-group and carboxylic acid dimer hydrogen bonding was found to occur. The gelation phase of reaction is complex, exhibiting rapid initial hydroxyl–anhydride reactions followed by S-shaped kinetics approaching an incompletely reacted limit. Postcure exhibits functional group kinetic behavior similar to that occurring in low epoxide/hydroxyl group-ratio bisphenol A epoxy resin–phthalic anhydride systems and produces similar final chemical structures. The reaction behavior of low and high epoxide/hydroxyl group-ratio bisphenol A epoxy resin–anhydride systems arises from an hydroxyl group-limited inhomogeneous reaction mechanism involving bisphenol A epoxy resin molecular aggregates. The importance of free hydroxyl group content is discussed.     

Studies of water-soluble oligomers formed in emulsion copolymerization

A polymer chain transfer agent was synthesized by the reaction between poly(vinylbenzyl chloride) latex particles and 2-aminoethanethiol in a basic environment. In subsequent emulsion polymerization reactions, low molecular weight species were formed when waterborn oligomeric radicals diffused to the surface of these seed particles. These low molecular weight oligomers were separated by membrane filtration and their composition and molecular weight weight were analyzed by FTIR and mass spectroscopy. The measured composition results were compared with those that were calculated from the copolymerization equation. The molecular weights were compared with earlier experimental results that were obtained by isolation of oligomers formed when a water-soluble inhibitor was added to a reacting emulsion. Three seeded emulsion copolymerization systems, that is, styrene–acrylic acid, styrenemethacrylic acid, and styrene–methyl methacrylate, were investigated. The distribution of monomer in the water phase and in the copolymer particles was analyzed. The results show that the oligomer compositions for different copolymerization systems can be approximated reasonable well by the copolymerization equation, using the reactivity ratios obtained from bulk copolymerization. The length of the oligomer radicals formed depends on their composition and the properties of the polymer particles, such as surface charge, composition, size, and concentration. © 1994 John Wiley & Sons, Inc.     

Densification and Sintering Kinetics in Sintered Silicon Nitride

The sintering sequence of Y₂O₃-Al₂O₃-doped Si₃N₄ was investigated with respect to the relationship between densification, α→β transformation, and microstructural development. Quenching studies were performed to reveal these interactions during a complete sintering cycle. Isothermal studies were conducted to examine the sintering kinetics and compared to Kingery's liquid-phase sintering model. The bulk density increased to ≥90% of theoretical density with only minor transformation taking place. Major transformation occurred in a late sintering stage and was accompanied by the development of elongated grains. The kinetic order of the densification process, taking into account an appropriate correction, was larger than any of the rate exponents predicted by the Kingery model, indicating that other single or mixed mechanisms were active.