Nylon 4,I: an amorphous polyamide

The melt polymerization of nylon 4, I was studied, starting with nylon-salt and nylon prepolymers (η_inh=0.25). With nylon-salt only low molecular polymers were obtained, while with prepolymers the inherent viscosity could be raised to 0.77 (3h, 270°, vac.). The cyclization of tetra methylene diamine to pyrrolidine seem to be the major disturbing factor. The polymer is glassy and could easily be melt pressed. The torsion modulus of the material at 20°C was high (1.8 10⁹ Pa) and remained high to near its T_g (138°C).     

Reproducibility of simplified techniques for the measurement of 51Cr-EDTA clearance

The aim of this study was to assess the reproducibility of a number of simplified clearance methods using chromium-51 ethylenediamine tetraacetic acid (51Cr-EDTA) and to compare these with the multiple blood sample technique. Twenty-four healthy volunteers were enrolled into the study. The test was performed twice, 1 week apart and under similar physiological conditions. After intravenous injection of the tracer, 13 blood samples were taken between 5 and 240 min. The reference clearance was calculated after adapting a bi-exponential fit on the whole plasma disappearance curve. Simplified methods included the slope intercept method using different combinations of blood samples (2 and 4 h; 2, 3 and 4 h; 1.5, 2, 3 and 4 h; 1.5, 2 and 3 h) and several single clearance methods (Constable 3 h; Groth 3 h; Groth 4 h). The standard deviation of the differences between the first and second measurements were similar for all methods, confirming the comparable reproducibility of these methods.     

Generalized inverse approach for static behaviour of constrained structures

The problem of structure subjected to certain external causes is established by a mathematical system consisting of equilibrium equations and prescribed constraint conditions. The satisfaction of constrained trajectories depends on an exact calculation of constraint forces required for satisfying the constraints. Most work related to this subject calculate the constraint forces using a numerical approach including undetermined Lagrange multipliers. However, the Lagrange multipliers method has difficulty in handling systems subjected to several tens of constraints. Starting from the difference in potential energy of structures with and without constraints, this study derives the equilibrium equation of constrained structures. It is shown that the derived equations coincide with the results obtained from previous work. The effectiveness and simplicity of the proposed method are illustrated through the static control of continuous structure and the reanalysis of a simple truss structure with a floating substructure. Copyright © 2005 John Wiley & Sons, Ltd.     

三端双向晶闸管的功耗计算和Tjmax预测

三端双向晶闸管用于控制AC电源负载。在大多数应用中,三端双向晶闸管会消耗大量电能,因而需要考虑散热。同时必须计算散热器的大小并预测最高结点温度Tjmax。散热设计和分析是设计和开发过程的基本部分。散热设计需要几个计算阶段,涉及到功率、热阻和温度升高。本文介绍的便是这些计算。     

Characteristics of Lead Magnesium Niobate Thin Film Prepared by Sol-Gel Processing Using a Complexing Agent

The effects of a complexing agent on the synthesis of a Pb(Mg_1/3Nb_2/3)O₃ (PMN) solution and the dielectric properties of a PMN thin film were investigated. When triethanolamine (TEA) was used as a complexing agent, a homogeneous and stable precursor solution was synthesized in air and a crack-free thin film with the nearly pure perov-skite phase and an average grain size of 0.2–0.4 μm was prepared by heating at 800°C for 5 min. The PMN thin film showed a relative permittivity of 1800 and tan δ of 0.01 at room temperature. The voltage dependence of polarization for the thin film was also presented.     

Overexpression of cyclin D1 and cdk4 in tumorigenesis of sporadic hepatoblastomas

We have shown previously that normal B cells share, with Epstein-Barr virus-transformed and malignant B cells, the ability to activate the alternative pathway (AP) of complement in vitro, resulting in the deposition of C3 fragments on the cell surface. Complement receptor type 2 (CR2, CD21) has been implicated directly as the site for formation of an AP convertase, which provides nascent C3b for deposition at secondary sites on the B-cell surface. In the present study, we have examined C3 fragment deposition in vitro in more detail by (1) assessing the importance of locally generated C3b for the deposition process, (2) investigating whether CR2 is the sole requirement for conferring AP activation capacity on a cell, and (3) determining whether CR2's function, as an AP activator, has different structural requirements from ligand binding. Increasing the availability of native C3, by increasing the serum (NHS) concentration, resulted in enhanced C3 fragment deposition on the B cells, whereas use of factor 1-depleted NHS, which showed massive fluid phase C3 conversion during the incubation, diminished the deposition. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting of untreated and hydroxylamine-treated lysates from B cells, after in vitro activation, revealed that the majority of C3 fragments (primarily iC3b and C3dg) had been covalently bound to the cell surface. Transfection of COS cells with wild-type CR2 or a deletion mutant lacking 11 of the molecule's 15 homologous domains, but retaining the ligand-binding site, revealed that expression of intact CR2 conferred a 12-fold increase in AP-activating capacity on these cells, while no increase in AP activity was apparent on cells transfected with the mutant CR2.     

Buttockectomy as a limbsaving procedure for locally advanced soft tissue sarcoma of the buttock region

Cord blood was obtained from 164 neonates at birth and investigated for the presence of aflatoxins. 14 of the samples were neonates without jaundice and 150 from neonates with jaundice. There was significant reduction (P > 0.05) in birth weight of jaundiced neonates with aflatoxin. Neonates with jaundice have high mean concentration of aflatoxin B1 (32.3 ng/ml and 35.6 ng/ml). Aflatoxin G1 was not detected in any of the groups. The rate of detection was higher in wet (81.8%) than dry season (50.0%). These findings show that neonates are exposed to aflatoxin prenatally and that high incidence of jaundice occurred in the wet warm months.     

Stress and "storm and stress" in early adolescence: The relationship of negative events with dysphoric affect.

The theory that adolescence is universally a time of emotional turmoil has been disproved, yet research indicates higher rates of negative affect among adolescents than preadolescents. This study evaluates the relationship of distressed affect in early adolescence to the experience of stressful life events. 483 5th–9th graders provided experience sampling reports on their daily emotional states; data on recent major events in the child's life were obtained from the child and a parent. Findings indicate that older students in this age range encountered more negative events than younger ones, including more peer, school, and family events, and that experience of multiple negative events had a stronger association with daily negative affect among the older students. These findings suggest that the higher rates of daily distress experienced in adolescence may be partly attributable to the greater number of negative life events encountered by some youths. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Pneumatic Biped “Lucy” Actuated with Pleated Pneumatic Artificial Muscles

This paper reports on the bipedal robot Lucy which is actuated by pleated pneumatic artificial muscles. This novel actuator is very suitable to be used in machines which move by means of legs. Besides its high power to weight ratio the actuator has an adaptable passive behavior, meaning the stiffness of the actuator can be changed on-line. This allows to change the natural frequency of the system while controlling angular joint positions. The main control concept intended for Lucy is joint trajectory control while selecting appropriate actuator compliance characteristics in order to reduce control efforts and energy consumption which is of great importance towards the autonomy of legged robots. Presently Lucy has made her first steps with the implementation of basic control strategies.The pleated pneumatic artificial muscle and its characteristics will be discussed briefly and the design of Lucy which is made modular on mechanical as well as electronic hardware level will be described in detail. To pressurize the muscles, a lightweight valve system has been developed which will be presented together with the fundamental control aspects of a joint actuated with two antagonistically setup artificial muscles. Additionally the first experimental results will be shown and briefly discussed.Björn Verrelst (1972) Study of Mechanical Engineering at the Vrije Universiteit Brussel, graduated in 1996. Since 1998 researcher and teaching assistant at the Vrije Universiteit Brussel. The focus of his research is the use of pneumatic artificial muscles in the walking biped Lucy for dynamically balanced walking.Ronald Van Ham (1976) Study of Electro-Mechanical Engineering at the Vrije Universiteit Brussel, graduated in 1999. Since 1999 researcher and teaching assistant at the Vrije Universiteit Brussel. The focus of his research is the use of adaptable compliance of pneumatic artificial muscles in the walking biped Lucy.Bram Vanderborght (1980) Study of Mechanical Engineeringat the Vrije Universiteit Brussel, graduated in 2003. Since 2003 researcher at the Vrije Universiteit Brussel, supported by the Fund for Scientific Research Flanders (Belgium). The focus of his research is the use of adaptable compliance of pneumatic artificial muscles in the dynamically balanced biped Lucy.Frank Daerden (1966) Study of Mechanical Engineering at the Vrije Universiteit Brussel. Ph.D. in Applied Sciences, Vrije Universiteit Brussel, 1999. Research and teaching assistant at the Vrije Universiteit Brussel, 1991–1999. Doctor-Assistant at the dept. of Mechanical Engineering, Vrije Universiteit Brussel since 1999, visiting Professor since 2003.Dirk Lefeber (1956) Study of Civil Engineering at the Vrije Universiteit Brussel. Ph.D. in Applied Sciences, Vrije Universiteit Brussel, 1986. Professor at the dept. of Mechanical Engineering, head of the Multibody Mechanics Research Group, Vrije Universiteit Brussel.Jimmy Vermeulen (1973) Study of Mechanical Engineering at the Vrije Universiteit Brussel. Ph.D. in Applied Sciences, Vrije Universiteit Brussel, 2004. Research and teaching assistant at the Vrije Universiteit Brussel, 1996–2004. Post-Doctoral researcher at the dept. of Mechanical Engineering, Vrije Universiteit Brussel since 2004. The focus of his research is trajectory generation and control of dynamically balanced legged robots.     

Chemistry of ice surfaces. Elementary reaction steps on ice studied by reactive ion scattering

This Account describes a recent study of reactions on ice surfaces with the emphasis on the mechanistic features of elementary reactions steps. Cs(+) reactive ion scattering (Cs(+) RIS) and low-energy sputtering (LES) techniques monitor the reactions by detecting the molecules and ions on the ice surface. The types of reactions include molecule diffusion and migration, proton transfer, and some simple reactions on frozen water and alcohol surfaces. Ice surface reactions exhibit unique behaviors due to a kinetic constraint, resulting in the isolation of reaction intermediates, preferential stabilization of charged species, and diversity of reaction products.