Sintering of the Mechanochemically Activated Powders of Hexagonal Boron Nitride

Pressureless sintering of hexagonal boron nitride (BN) was performed using a powder activated by mechano-chemical treatments. Physical properties of the sintered BN bodies depend on the type of starting powder and the conditions of the treatments. The BN body, which was obtained at 2000°C using an appropriate activated powder, was 99 wt% pure and was excellent in mechanical and physical properties, in spite of its low density (1.64 g/cm³).     

Prooxidant effects of inorganic chromium compounds in the autoxidation of methyl linoleate

The prooxidant property of inorganic chromium compounds was determined in methyl linoleate free from natural antioxidants and metals. Prooxidant properties of inorganic chromium compounds appeared in order of sodium chromate > chromium (VI)-oxide > chromium chloride > potassium chromate > chromium (III)-oxide > potassium dichomate. In comparison with the control, additions of chromium compounds induced different amounts of autoxidation products derived from methyl linoleate, such as small amounts of hydroperoxides and conjugated dienes and large amounts of hydroxy groups,α,β,γ,δ-unsaturated carbonyls, isolatedtrans double bonds, polymers, and free radicals. From these analytical data, the catalysis of chromium compounds in the autoxidation of methyl linoleate seemed to be based on their abilities of abstracting a hydrogen from methyl linoleate and decomposing hydroperoxides derived from the autoxidation of methyl linoleate.     

Bis-(monoacylglyceryl) phosphate and acyl phosphatidylglycerol isolated from human livers of lipidosis induced by 4,4′-diethylaminoethoxyhexesterol

Bis-(monoacylglyceryl) phosphate and acyl phosphatidylglycerol were isolated from the liver of two patients with lipidosis induced by 4,4′-diethylaminoethoxyhexesterol. Identification was based upon the results of alkaline hydrolysis, acetolysis, IR spectrometry, and upon the determination of molar ratio of phosphorus-glycerol-ester. The contents of the bis-(monoacylglyceryl) phosphate were 10 and 16% total phospholipid phosphorus in them. The bis-(monoacylglyceryl) phosphate contained mainly docosahexaenoic (42%), oleic (29%), and linoleic acid (14%) and had the hemolytic activity of ca. one-eighth lysolecithin from egg yolk. Acidic lipids from the liver also were found to contain a lipid which is less polar than bis-(monoacylglyceryl) phosphate. The results of lipid analysis showed that the lipid possessed the structure of an acyl phosphatidylglycerol, and its content was ca. 2% total phospholipid phosphorus. Accumulation of 4,4′-diethylaminoethoxyhexesterol and its derivatives was found in clinical cases by thin layer chromatography and IR spectrometry. This fact suggested that human liver has an ability to metabolize the drug.     

Autoxidation of ethyl eicosapentaenoate and docosahexaenoate

The extent of oxidation of ethyl esters of eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) was compared quantitatively with that of ethyl linoleate (Lo) and ethyl linolenate (Ln) by oxygen uptake and formation of conjugated diene, hydroperoxide and secondary oxidation products. EPA and DHA esters were oxidized rapidly even at 5 C in the dark after an induction period of 3–4 days, while the induction periods of Ln and Lo esters were 20 days and more than 60 days, respectively. Oxygen uptake of EPA and DHA esters after the induction period was 5.2 and 8.5 times faster than that of ethyl Ln, respectively. Hydroperoxides of EPA and DHA esters are much less stable than those of ethyl Lo. The peroxide value is not necessarily a good indication of oxidation in these polyenoic acids because a considerable amount of secondary products is formed at the early stage of oxidation. Polymers were found to be major secondary products in these polyenoic esters.     

Radiation-induced oxidative degradation of isotactic polypropylene

Gas evolution, oxygen consumption, and change of mechanical properties were studied for the γ-ray irradiation of isotactic polypropylene from ⁶⁰Co under various conditions, such as vacuum, air, and oxygen at room temperature. For irradiation under vacuum, G(H₂) = 2.9 and G (CH₄) = 0.09; the G values for other gases were very small. In the presence of oxygen, G(H₂) was the same, and the G values for other hydrocarbons were two times those under vacuum. The G values of oxidative products and oxygen consumption were G(CO₂) = 2.5, G(CO) = 1.1, and G(O₂) = 50 at oxygen pressure of 500 torr and were dependent on oxygen pressure. With irradiation under vacuum at 2–3 Mrad, mechanical properties scarcely changes immediately after irradiation but degrade gradually with storage time in air at room temperature.     

Control of molecular weight distribution of isotactic polypropylene obtained by a MgCl2-supported TiCl4 catalyst

It is of great importance in propene polymerization to control molecular weight and molecular weight distribution as well as isotacticity. Propene polymerization was carried out with an isospecific MgCl₂/TiCl₄-Cp₂TiMe₂ catalyst in the presence of various kinds of external Lewis bases. It was found that the molecular weight distribution of the isotactic polymer could be controlled while retaining high activity, high isospecificity and high molecular weight only by changing the kind and/or amount of the Lewis bases. © 1997 Elsevier Science Ltd.     

Adaptive interpolation scheme for NURBS curves with the integration of machining dynamics

This paper develops a comprehensive interpolation scheme for non-uniform rational B-spline (NURBS) curves, which does not only simultaneously meet the requirements of both constant feedrate and chord accuracy, but also real-time integrates machining dynamics in the interpolation stage. Although the existing work in this regard has realized the importance to simultaneously consider chord error and machining dynamics, none has really incorporated these in one complete interpolation scheme. In this paper, machining dynamics is considered for three aspects: sharp corners or feedrate sensitive corners on the curves, components with high frequencies or frequencies matching machine natural ones and high jerks. A look-ahead module was developed for detecting and adaptively adjusting the feedrate at the sharp corners. By Fast Fourier Transform (FFT) analysis with a moving window in the interpolation stage identified were some special frequency components such as those containing high frequencies or with frequencies matching machine natural ones. Then, the notch filtering or time spacing method was used to eliminate these components. To more completely reduce feedrate and acceleration fluctuations, the jerk-limited algorithm was also developed. Finally, the interpolated feedrate was further smoothened with B-spline fitting method and the NURBS curves were re-interpolated with the smoothened feedrate. During the interpolation, the chord error was repeatedly checked and confined in the prescribed tolerance. Two NURBS curves were used as examples to test the feasibility of the developed interpolation scheme.     

Self-organized porous TiO2 and ZrO2 produced by anodization

The present work investigates the electrochemical formation of self-organized high aspect ratio TiO₂ and ZrO₂ nanotube layers. The formation and growth of a self-organized porous layer can be achieved directly by anodization without any templates in fluoride containing electrolytes. The morphology of the porous layers is affected by the electrochemical conditions such as the electrolyte composition, the pH and the exact polarization treatment (such as the potential sweep rate from the open-circuit potential to the anodizing potential). For Ti, nanotube layers are formed with diameters varying from approx. 20 nm to 100 nm and lengths from approx. 0.25 μm to 2.5 μm depending on the electrolytes and pH. On the other hand, for Zr, tubes of 50 nm in diameter and up to approx. 17 μm in length can be grown—a key parameter in this case is the potential sweep rate. The large difference between Ti and Zr in the achievable thickness of nanotube layers indicates a difference in the growth mechanism which may be based on the different chemical dissolution rates of electrochemically formed oxides.     

Quantitative structural analysis of twin boundary in alpha-Zn7Sb2O12 using HAADF STEM method

The structure and composition of the 1/4{110} twin boundary in alpha-Zn7Sb2O12 have been determined by using quantitative high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) analysis. The noise in the experimental HAADF STEM images is reduced by using the maximum entropy method and average processing, and the parameters used in dynamical simulations are experimentally determined. From the analysis, it has been found that octahedral sites in the twin boundary slightly shift parallel to the [110] direction, and a reduction of the Sb concentration at the octahedral sites on the plane adjacent to the twin boundary was detected. The reduction was measured from three regions in the same twin boundary, and the Sb concentrations were 4 +/- 3, 8 +/- 3 and 19 +/-2 at% from 33 at%.     

A new scaling algorithm for the maximum mean cut problem

We present a new scaling algorithm for the maximum mean cut problem. The mean of a cut is defined by the cut capacity divided by the number of arcs crossing the cut. The algorithm uses an approximate binary search and solves the circulation feasibility problem with relaxed capacity bounds. The maximum mean cut problem has recently been studied as a dual analogue of the minimum mean cycle problem in the framework of the minimum cost flow problem by Ervolina and McCormick. A networkN=(G, lower, upper) with lower and upper arc capacities is said to be -feasible ifN has a feasible circulation when we relax the capacity bounds by ; that is, we use (lower(a)- , upper(a)+) bounds instead of (lower(a), upper(a)) bounds for each arca A. During an approximate binary search we maintain two bounds,LB andUB, such thatN is LB-infeasible andUB-feasible, and we reduce the interval size (LB, UB) by at least one-third at each iteration. For a graph withn vertices, m arcs, and integer capacities bounded byU, the running time of this algorithm is O(mn log(nU). This time bound is better than the time achieved by McCormick and Ervolina under thesimilarity condition (that is,U=O(n^o(1))). Our algorithm can be naturally used for the circulation feasibility problem, and thus provides a new scaling algorithm for the minimum cut problem.Research supported by a grant-in-aid of the Ministry of Education, Science and Culture of Japan.