Ring‐opening polymerization of D,L‐lactide by rare earth 2,6‐dimethylaryloxide

Ring‐opening polymerization of D,L ‐lactide (LA) has been successfully carried out by using rare earth 2,6‐dimethylaryloxide (Ln(ODMP)₃) as single component catalyst or initiator for the first time. The effects of different rare earth elements, solvents, monomers and catalyst concentration as well as polymerization temperature and time on the polymerization were investigated. The results show that La(ODMP)₃ exhibits higher activity to prepare poly(D,L ‐lactide) (PLA) with a viscosity molecular weight of 4.5 × 10⁴ g mol^?1 and the conversion of 97 % at 100 °C in 45 min. The catalytic activity of Ln(ODMP)₃ has following sequence: La > Nd > Sm > Gd > Er > Y. A kinetic study has indicated that the polymerization is first order with respect to both monomer and catalyst concentration. The apparent activation energy of the polymerization of LA with La(ODMP)₃ is 69.6 kJ mol^?1. The analyses of polymer ends indicate that the LA polymerization proceeds according to ‘coordination–insertion’ mechanism with selective cleavage of the acyl–oxygen bond of the monomer. Copyright © 2004 Society of Chemical Industry     

HiSQL: A Front-end Query System for Historical Relational Databases

The paper describes a prototype system called HiSQL (Historical SQL) which extends the functionality of SQL in manipulating historical data, by providing functions for spatial and temporal processing. Conceptually the paper is divided into three parts: the first part deals with the design and architecture of the system; the second part introduces a case study (the defters); and the third part describes specific functions for spatial and temporal processing of serial documents. The paper concludes with a comparison between HiSQL and SQL and suggestions for further work. This revised version was published online in August 2006 with corrections to the Cover Date.     

新型重整催化剂的研究——Pt／L中沸石酸碱性的作用

Ｐｔ／ＫＬ、Ｐｔ／ＢａＫＬ及Ｐｔ／ＨＬ上的铂与沸石的酸碱位发生相互作用，导致催化剂上存在不同电子状态和粒度分布的铂位，从而产生有着完全不同催化作用、不同抗硫性能的两类催化剂，即以碱性沸石为载体的“单功能”催化剂和以酸性沸石为载体的“双功能”催化剂。在Ｐｔ／ＫＬ、Ｐｔ／ＢａＫＬ催化剂上，存在着对硫敏感的具有环化脱氢功能和对硫不敏感的仅具有脱氢功能的两类铂活性位。     

Best L1 Piecewise Monotonic Data Modelling

Let us consider n data measurements of a univariate process that have been altered by random errors. We assume that an underlying model function has a substantially smaller number of turning points than the observed ones. We propose algorithms that make least the sum of the moduli of the errors by requiring k monotonic sections, alternately increasing and decreasing, in the sequence of the smoothed values. The main difficulty in this calculation is that the optimal positions of the joins of the monotonic sections have to be found automatically among so many combinations that it is impossible to test each one separately. Moreover, the calculation seems to be very intractable to general optimization techniques because O(n^k) local minima can occur. It is shown that dynamic programming can be used for separating the data into optimal disjoint sections of adjacent data, where each section requires a single L₁ monotonic calculation. This procedure is highly efficient, requiring at most O(kn²) computer operations and O(n) best L₁ monotonic calculations to subranges of data for a global minimum.     

Supercritical fluid extraction of daphne (Laurus nobilis L.) seed oil

Laurus nobilis L., commonly known as daphne tree, is an evergreen that belongs to the Lauraceae family. Daphne trees produce grape-sized shiny purplish berries having three parts: flesh, skin, and an inner kernel (single seed). This study examines supercritical CO₂ (SC-CO₂) extraction of oil from daphne seeds. The oil yield of ground seeds varied from 14 to 28% depending on the method and particle size used for oil recovery. Yields were similar for both petroleum ether and SC-CO₂ extraction. The extraction yield decreased significantly with increasing particle size. The amount of extract collected increased exponentially with increasing SC-CO₂ pressure. The highest extraction yield was obtained at the highest temperature studied, 75°C. More than 45% of the oil was lauric acid. SC-CO₂ is a viable technique to obtain high-purity L. nobilis L. seed oil, which is a potential ingredient for the cosmetic industry.     

Oxygen glow discharge experiment to remove deposited layers and to release trapped hydrogen isotopes in HT-7 superconducting tokamak

An experiment to remove re-deposited layers and to release hydrogen using a glow discharge in oxygen (O-GDC) has been performed in the HT-7 superconducting tokamak. In the absence of magnetic fields, the O-GDC wall conditioning had produced rapid, controlled co-deposit removal. Average removal rates, 5.2 × 10²² H-atoms/h, 5.65 × 10²¹ D-atoms/h and 5.53 × 10²² C-atoms/h, respectively, were obtained during 145 min O-GDC experiment in the pressure range 0.5-1.5 Pa. The corresponding removal rate of co-deposited films was ∼1.19 μm/day (26.5 g/day for carbon) based on an area of 12 m². Compared to thermo-oxidation and O-ICR experiment, high pressure O-GDC wall conditioning promoted the oxidation and improved the C and D atoms removal. In the O-GDC experiment, the removal rates of H-atoms and D-atoms as H₂O, HDO and D₂O were higher than that of H₂ and D₂ by factors of about 20 and 50, respectively. During the 145 min O-GDC experiment, about 14.5% O-atoms were converted into carbon oxides and hydroxides, and about 5.37 × 10²² O-atoms were adsorbed on the walls corresponding to a coverage of 4.5 × 10²¹ O/m² on an wall area of 12 m². In a 100 min helium glow discharge (He-GDC) following the O-GDC experiment, 1.53 × 10²² O-atoms, about 28.5% oxygen retained on the walls, were removed. The removal rate of H-atoms in He-GDC cleaning after O-GDC experiment was lower than that in He-GDC cleaning before O-GDC experiment, which indicates that the O-GDC wall conditioning had effectively reduced hydrogen retention on the walls.     

L波段窄脉宽500W固态功放组件的设计

介绍了作者研制的应用于固态雷达发射机上的L波段500W固态功放组件的工作原理、用途及其主要技术指标。描述了功放组件的设计过程和测试结果。该功放组件在窄脉宽条件下实现了快速上升沿,性能优良,工作稳定可靠。     

Equilibrium Moisture Characteristics of High Oleic Sunflower Seeds and Kernels

The equilibrium moisture content (EMC) characteristics of high oleic sunflower seeds and kernels between 10 and 55°C were determined by equilibrating the samples to known relative humidities (RH) above saturated salt solutions. EMC of the kernels was lower than that of seeds in the range of 11 to 96% ERH and at 25 and 40°C. Hysteresis effect was found for the EMC properties of seeds and kernels at 25°C. Four EMC-ERH models (modified Henderson, Chung-Pfost, Halsey, and Guggenheim-Anderson-de Boer) and their estimated parameters were evaluated for goodness of fit. GAB and Halsey equations showed the best fitting of experimental data although GAB equation adjusted for temperature described the EMC data the best. Components of the seed as oil content or hull/kernel ratio did not explain the slight differences in EMC found between the varieties.     

Formation of ordered microporous films with water as templates from poly(D,L‐lactic‐co‐glycolic acid) solution

Recently a method that uses water droplets at the air–solution interface as an ordered template was reported for the preparation of ordered micrometer‐size honeycomb structures. Here we show that the method can also be used for formation of honeycomb‐like porous films from random copolymers with certain hydrophilicity, besides those polymers with defined structures such as block copolymers, starlike homopolymers, amd amphiphilic polymers. This demonstrates that the stabilization of water droplets is the key factor for the regular structure. Also we indicate that size and structure of the films can be regulated by such variables as concentration and atmospheric humidity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1846–1850, 2003