高强度高压绝缘子产品质量与其结构性能的重要关系——制造者和用户应共同掌握的规则和指标(第一部分)

在世界范围内生产的电瓷绝缘子具有区别很大的质量指标。作者愿借助于本文阐述高强度高压绝缘子的产品质量与其结构性能的关系。作为质量保证 ,不仅要求一系列关键性的材料性能指标 ,而且要用普通的方法对结构性能进行可靠的判定。对各种高压绝缘子瓷进行结构比较 ,则在材料质量上的明显区别变得清晰可见。同时 ,借助于新开发的矾土瓷为例 ,阐述高强度和长期稳定的瓷质材料的结构指标要求 ,且使用户理解并进行监督     

Coaxial jet melt-spinning of glassy alloy ribbons

A chill block melt-spinning process is described for the manufacture of continuous metallic ribbons of uniform geometry. Ribbons wider than those obtained by conventional melt-spinning in air are formed by stabilization of the molten alloy puddle through the use of a gas stream coaxial with the molten alloy jet impinging on the moving substrate surface. The dependence of ribbon geometry on process parameters for coaxial jet casting is similar to that found in conventional chill block melt-spinning except that somewhat greater molten alloy spreading may occur in the former process. Stress relaxation and the surface geometry of ribbons cast using the coaxial jet technique is found to be similar to that of vacuum and helium-cast samples having the same dimensions.     

Myxedema ascites

A 74-year-old man presented with mental obtundation and massive ascites without evidence of significant impairment of liver function. Thyroid function studies suggested hypothyroidism. Aspirated ascitic fluid had the characteristics of an exudate. Thyroid replacement therapy resulted in rapid clinical improvement with resolution of the ascites. Prompt recognition of myxedema ascites may prevent the inappropriate use of diuretic agents, therapeutic paracentesis, and sometimes unnecessary laparotomy.     

Effect of carrier system on the yield of human oocytes and embryos as assessed by survival and developmental potential after vitrification

The present study was undertaken to examine the effect of a cooling regimen during vitrification on survival and morphological appearance of human oocytes after warming and the developmental potential of day 3 embryos. Aged human oocytes that had failed to fertilize and human embryos derived from abnormally fertilized zygotes that showed one pronucleus or three or more pronuclei were used as models in this study. In the first part of the study, 928 aged human oocytes that had failed to fertilize were vitrified. The viability of oocytes after vitrification using the hemi-straw system was slightly higher than it was using the cryoloop after warming (85.4% (410 of 480) versus 80.6% (361 of 448)), but the difference was not significant. In the second part of the study, 266 embryos were vitrified. The survival of day 3 embryos after vitrification was improved by using a mixture of ethylene glycol and dimethyl sulphoxide in combination with the hemi-straw system method rather than the cryoloop method (89.7% (122 of 136) versus 83.8% (109 of 130)), but the difference was again not significant. The potential for development up to compaction on day 4 in embryos vitrified using the hemi-straw system method was significantly higher (37.7%) than it was in embryos vitrified using the cryoloop (29.4%; chi(2), P = 0.002). The hemi-straw system and cryoloop methods of vitrification are both successful, easy to perform, and demonstrate the ability of both carriers to vitrify different stages of development (oocytes and day 3 embryos). In addition, the success of both methods appears to be related to the rate of cooling and the lower concentration of cryoprotectant used.     

Nitrogen as an alloying element in some metallic glasses

Glassy alloy ribbons containing nitrogen as an alloying element have been produced by chill block melt-spinning master alloys which were specially pre-melted for enhanced nitrogen content. Alloying substantial amounts of Cr, a potent nitride former, has been found to greatly increase the amount of nitrogen in solution. In turn, thermal stability of the Cr-bearing metallic glasses has been found to increase as much as 31 K with only a 0.5 at% nitrogen addition. No analogous changes in glassy alloy embrittlement or Curie temperature have been observed. However, although weak, the response of Curie temperature to annealing in the Cr-bearing metallic glasses was found to be affected by the presence of nitrogen. Thus, nitrogen appears to be a viable alloying element in some metallic glasses and may have a potent effect on some properties.     

Ribbon-Substrate adhesion dynamics in chill block melt-spinning processes

Rapidly quenched ribbons made directly from the melt by chill block melt-spinning exhibit a variable ribbon-substrate adhesion distance, especially during the start of a run. The present work reports on experimental parameters which affect the ribbon-substrate adhesion dynamics. Frame-by-frame measurements of ribbon-substrate adhesion distance in high speed movies were taken for a variety of melt-spin process conditions. The results are interpreted in terms of interfacial temperature, compositional compatibility, and stresses between the melt or ribbon and the substrate. Calculated interfacial thermal profiles are used to visualize adhesion dynamics qualitatively. It is shown that the interface thermal and compositional factors considered in the present investigation are a key to the nature of ribbon-substrate adhesion dynamics in chill block melt-spinning processes.     

Effects of elemental additions and superheat on melt surface tension and metallic glass embrittlement

Additions of antimony, selenium, tellurium and some other alloying elements to iron-nickel base alloys have been investigated with regard to effects on melt surface tension and resultant metallic glass formation and characteristics. Surface tension of the molten alloys has been measured as a function of composition and melt temperature using a variation of the maximum bubble pressure method. The density of molten Fe₄₀Ni₄₀B₂₀ alloy has been measured as a function of temperature. Attempts to chill block melt-spin and alloys of the present investigation into metallic glass ribbons were largely successful. A few compositions were partially crystalline in the as-cast state and even fewer were not castable at all. The amorphous structure of ribbons made was assessed by X-ray diffraction, differential scanning calorimetry, and embrittlement temperatures for one hour anneals. A correlation has been established between changes in melt surface tension and metallic glass embrittlement temperature with the addition of surface active elements.     

Time–frequency multiresolution of fault-generated transient signals in transmission lines using a morphological filter

The ongoing transformation of electrical power systems highlights the weaknesses of the protection schemes of traditional devices because they are designed and configured according to traditional characteristics of the system. Therefore, this work proposes a new methodology to study the fault-generated high frequency transient signals in transmission lines through multiresolution analysis. The high frequency components are determined by a new digital filtering technique based on mathematical morphology theory and a spectral energy index. Consequently, wide spectra of signals in the time–frequency domain are obtained. The performance of this method is verified on an electrical power system modeled in ATP-Draw, where simulation and test signals are developed for different locations, fault resistances, inception angles, high frequency noises, sampling frequencies, types of faults, and shapes of the structuring element. The results show the characteristics of the fault such as the traveling wave frequency, location, and starting time.     

Exact optimal grillage layouts — Part I: Combinations of free and simply supported edges

In the first instalment of this three-part study, a comprehensive treatment of analytically derived, exact optimal grillage layouts for combinations of simply supported and free edges is given. In part two, grillages with combinations of simply supported, clamped and free edges will be considered.Notation k constant in specific cost function - M beam bending moment - r radius of circular edge - R ⁺,R ^–,S ⁺,S ^–,T optimal regions - x, x _j coordinate along a beam (j) - slope of the adjoint deflection at pointD in directionDA - t, v coordinates along the free edge - adjoint deflection - angle between long beams and free edge - angle between free and simply supported edges - curvature of the adjoint deflection - , angles for layouts with circular edge - total weight (cost) of grillage - coordinate along a beam in anR ⁺ region - distance defined in Fig. 3     

New Effective Ways Toward Solving the Problem of Contamination of Porcelain Insulators

The use of special coating organic materials for imparting hydrophobic properties to the surface of high-voltage porcelain insulators exposed to environmental contamination is described. The surface hydrophobization technique makes it possible to improve the electric performance of insulators and prevent current leakage under industrial conditions and opens ways toward designing insulators safe against flashover and insulation assemblies resistant to aging.