Positive inotropic responses in cardiac muscles: influence of stimulation frequency and species

Inotropic responses to cumulative additions of methoxamine (10(-7) to 3 X 10(-4) M), isoproterenol (10(-9) to 10(-5) M), or calcium (2 to 32 mM) were measured in isolated rat left atria and papillary muscles and rabbit right ventricular papillary muscles at three stimulation frequencies. Cardiac muscles were incubated in oxygenated Chenoweth-Koelle solution (2 mM calcium) at 37 degrees C. The basal developed force (BDF) before and maximum developed force (MDF) after challenge with methoxamine and isoproterenol were inversely related to stimulation frequency in rat preparations. BDF was directly related to stimulation rate in rabbit papillary muscles while MDF was independent of the rate. Drug-induced increases in force (MDF - BDF) were independent of stimulation frequency in rat and inversely related to stimulation frequency in rabbit. Responses to calcium were similar to the observed adrenergic responses. Also, force-frequency relationships of the rat and rabbit preparations were not similar in the absence and presence of these agonists. These data show that inotropic responses by rat and rabbit hearts are not affected similarly by stimulation frequency and this may reflect a species difference in the utilization of extracellular calcium for contraction.     

Parallel Computation and Indefinite Summation: a MAPLE Application for the Rational Case

The problem of computing a closed form for sums of special functions arises in many parts of mathematical and computer science, especially in combinatorics and complexity analysis. Here we discuss two algorithms for indefinite summation of rational functions, due to Abramov (1975) and Paule (1993). We describe some improvements and a parallel implementation on a workstation network in MAPLE (read: parallel Maple). Our best implementation achieves a speedup of up to eight over the fastest available sequential implementation. Finally, further applications of parallel computing in this field are outlined.     

M8300多相织机的机电开口装置

和传统的高速织造系统相比，瑞士Sulzer公司研制的多相织机在价格上是很有竞争力的。为了形成几个和组织结构相对应的平行梭口，并能使这些梭口沿着经纱方向运动，采用了特殊的经纱定位器，使经纱连续地沿着轴向前后移动。这些运动和织造转子是同步的。对动力系统的要求很高，即使是几个毫米的小偏差也必须以极高的精度来解决。本文将介绍解决这一问题的实用方法。经纱定位器由带液压放大器的线性电机驱动。电机轴的设定值应和织物组织循环相对应。电机轴的实际位置通过高效传感器来测定，并借助数字信号处理器来控制。所需的控制曲线可用这一系统自动生成。     

Young’s modulus and fatigue behavior of plasma-sprayed alumina coatings

The fatigue behavior and Young’s modulus of plasma-sprayed gray alumina on low-carbon steel substrates were investigated. The investigation of the properties of composites that were defined as “coating-substrate” composites included measurements of the microhardness profile, the residual stress on the top of the coating, and the residual stress profile in the substrate. Fatigue samples were periodically loaded as a cantilever beam on a special testing machine. Failed samples were observed with a scanning electron microscope to determine the failure processes in the coating. The Young’s modulus of the coating was measured by the four-point bending method. Samples were tested both in tension and compression under low (300 N) and high (800 N) loads. The authors’ experiments revealed that the average fatigue lives of coated specimens were nearly two times longer than those of the uncoated specimens. The measurements of Young’s modulus of the coating yielded values that varied between 27 and 53 GPa, with an average value of 43 GPa. Loading in tension caused a decrease in the Young’s modulus of the coating, while loading in compression led to an increase in Young’s modulus. The increase in the lifetime of coated samples was likely due to compressive residual stresses in the substrate, originating during the spray process. The failure of the coating was due to several processes, among which the most important were splat cracking, splat debonding, and the coalescence of cracks through the voids in the coating.     

Modellgetriebene Softwareentwicklung auf Basis von Open-Source-Werkzeugen – reif für die Praxis?

Zusammenfassung Der Hype um die Ideen der modellgetriebenen Softwareentwicklung legt sich langsam. Vor- und Nachteile dieser neuen Vorgehensweise sind inzwischen bekannt, so dass sie durchaus eine geeignete Option für die Softwareentwicklung ist. Modellgetriebene Softwareentwicklung stellt heute keinen geheimnisvollen Ansatz mehr dar, welcher nur für akademische Forschungsprojekte geeignet ist, sondern kann auch für gro?e, zeitkritische Projekte eingesetzt werden. MDA (Model Driven Architecture) ist die Sicht der OMG (Object Management Group) auf die Theorien der modellgetriebenen Softwareentwicklung und es gibt zahlreiche Werkzeuge, die diese OMG-Spezifikation umsetzen. Eine treibende Kraft hinter dieser Entwicklung ist die Open-Source-Gemeinde, welche Werkzeuge auf Basis der Ideen modellgetriebener Softwareentwicklung implementiert hat. Dieser Beitrag stellt einige der interessantesten Open-Source-Werkzeuge für die modellgetriebene Softwareentwicklung vor und bewertet diese bezüglich Konformit?t zur MDA, deren Einsatzreife sowie deren Eigenschaften und Einschr?nkungen.     

Determination of phenolic antioxidants in polyethylene with dissolution by n-heptane in an autoclave

A new procedure for quantitative analysis of phenolic antioxidants in polyolefins was tested. Thereby polyethylene samples were dissolved in pure n-heptane or in n-heptane/isopropanol mixture (1 000/5, v/v) in an autoclave at 160–170°C under elevated pressure. After precipitation of the polymer by cooling to room temperature, the obtained solution was either directly analysed by means of HPLC equipped with an UV-detector, or the supernatant solvent used for the extraction was evaporated in vacuum at room temperature and the residue redissolved in acetonitrile. The concentration of antioxidants in the solution was determined by isocratic HPLC. The advantage of this procedure is the short time of about 2 h needed for analysis and the good reproducibility of results (σ = 3–5%).     

Contribution to the study of the pseudobinary Zr1Nb–Oxygen phase diagram by local oxygen measurements of Zr1Nb fuel cladding after high temperature oxidation

This work is concerned with measurement of oxygen concentrations and construction of the pseudobinary Zr1Nb–O phase diagram, acceptable for diffusion models predicting the oxidation behavior of Zr1Nb fuel cladding during thermal transients such as LOCA. Oxygen concentrations were measured in existing phases in the wall of Zr1Nb nuclear fuel cladding tubes after the high-temperature oxidation. The oxygen concentrations at the α/α + β phase boundary in the α-Zr(O) layer have been determined using WDS method. Oxygen concentrations in the prior β-Zr were measured using two experimental methods (SIMS and TEA). Consequently, the ceiling of the oxygen concentration in β-Zr has been assessed based on the results of SIMS, TEA, and microhardness measurements. Eventually, the experimental results were compared to the pseudobinary Zr1Nb–O phase diagram, calculated using CALPHAD software, with satisfactory agreement. The effect of hydrogen was also examined.     

Effect of C,Ti, Zr and B alloying on fracture mechanisms in hot-rolled Fe–40 (at.%)Al

This paper reports a study of fracture behavior of FeAl-based intermetallic alloys with the addition of carbon, titanium, zirconium and boron (Fe–40Al–1C, Fe–40Al–1Ti and Fe–40Al–Zr–B). The alloys were prepared by modified processing technology of vacuum induction melting and hot rolling in special stainless steel sheath. Tensile and fracture toughness tests were carried out at 20 °C, 400 °C, 600 °C, 700 °C and 800 °C. The alloy showed best fracture toughness and tensile properties with Zr and B addition. The fracture toughness at 600 °C was comparable with values in stainless steels and nickel-based superalloys. The fractographic analysis revealed the change of fracture micromechanisms with temperature. Moreover, under specific conditions, the fracture micromechanisms were different in tensile and fracture toughness specimens.     

Phase stability and elasticity of C15 transition-metal intermetallic compounds

First-principles quantum mechanical calculations based on the local-density-functional theory have been performed to study the electronic, physical, and metallurgical properties ofC15 intermetallicsMV2 (M = Zr, Hf, or Ta). The elastic constants ofC15 HfV₂ + Nb were measured by the resonant ultrasound spectroscopy technique. The phase stability ofC15 HfV₂ + Nb was studied by specific heat measurements and by TEM in a low- temperature specimen holder. The total energies and their lattice volume dependence were used to obtain the equilibrium lattice constants and bulk modulus. The band structures at the X- point near the Fermi level were employed to understand the anomalous temperature dependence of the shear modulus of theC15 intermetallics. It was found that the double degeneracy with a linear dispersion relation of electronic levels at the X- point near the Fermi surface is mainly responsible for theC15 anomalous elasticity. The density of states at the Fermi level,N(E _F), and the Fermi surface geometry were obtained to understand the low- temperature phase instability ofC15 HfV₂ and ZrV₂ and the stability ofC15 TaV₂. It is proposed that the largeN(E _F) and Fermi surface nesting are the physical reasons for the structural instability of theC15 HfV₂ and ZrV₂ at low temperatures. The relationship between the anomalous elasticity and structural instability ofC15 HfV₂ and ZrV₂ are also discussed.     

Differences in pre‐service teachers' knowledge and readiness to use ICT in education

The aim of this paper is to provide insights into differences between pre‐service teachers based on the areas of technological pedagogical content knowledge (TPACK) and the areas of theory of planned behaviour (TPB) in the context of using information and communication technology in education. The target group consisted of 267 first‐year pre‐service teachers at 3 Finnish universities. Differences between pre‐service teachers were outlined using cluster analysis based on their knowledge of different TPACK areas (the respondents' weak and strong areas). To see how the TPB areas aligned with the 4 TPACK clusters, 1‐way analysis of variance was used. Statistically significant differences between the 4 clusters were found in all the TPB areas except subjective norms. These results provide insights into the differences among pre‐service teachers in the context of TPACK and the TPB. They also suggest that instead of considering pre‐service teachers as one homogenous group, we need to understand the variations among their abilities and knowledge in order to be able to provide them with support they need within teacher education.