高熵合金在钎焊和表面工程领域的应用研究进展

随着合金制造水平的提高及性能要求的复杂化,高熵合金逐渐引起极大的关注.目前在材料加工领域内的研究主要集中于钎焊和表面工程两大方向.在钎焊领域,高熵合金可以作为钎焊填充材料应用于高温和低温钎焊,本文归纳了合金高熵化的相关经验参数,阐述了第一性原理计算和相图计算等模拟计算手段在高熵合金填充材料设计领域内的应用;详细介绍了高熵合金钎料在镍基高温合金、陶瓷-金属异种材料、低温封装等连接领域的最新研究进展.同时,分析了工艺参数对高熵合金钎料钎焊接头组织与性能的影响.在表面工程领域,论述了高熵合金薄膜/涂层的应用方向与制备手段,总结了在高温防护涂层、硬质保护层以及其他应用领域的研究进展.同时归纳了高熵合金在钎焊和表面工程领域研究和应用中存在的问题,而未来将在降低钎料熔点、提高焊缝高温力学性能以及发展共晶高熵合金钎料/涂层等领域进一步提高研究水平.     

Emulsifying Properties of Food Proteins: Bovine Mi cellar Casein

The capacity of micellar casein isolated from bovine milk to stabilize oil in water (0:w) emulsions was studied. Emulsion surface area per unit mass of protein, i.e., emulsifying activity (EA), was highest at a protein concentration of 1% and o:w ratio of 1:9. The surface concentration of micellar casein was related to the o:w ratio being highest at an o:w of 4:6. Interfacial surface area decreased at pH 6.7 reflecting micellar stability and improved with increasing pH apparently because of destabilization of the casein micelle. Emulsion stability was high when the EA was high. The apparent viscosity of the emulsions was inversely related to EA.     

Determination of Principal Axes ot Truss Towers

The paper is concerned with the determination of the principal axes of geometrically non linear truss towers by a microcomputer. A knowledge of the principal axes may be used at the planning and design stage to advantageously orient the tower with respect to the dominant wind direction. The principal axes may also be used for the assessment of the truss tower's sensitivity to wind direction. A scale for the evaluation of this sensitivity is proposed in the paper. The sensitivity of a structure to lateral load direction depends on the structure's geometry and topology. An example is presented that shows how sensitivity of a space truss can the affected by the by the modifications of its geometry and topology.     

ON THE OPTIMALITY OF DISKS OF UNIFORM CREEP STRENGTH AGAINST BRITTLE RUPTURE

Axisymmetric rotating disks of uniform brittle rupture under creep conditions are considered. The similarity of deviators, according to the flow theory, and the time hardening hypothesis combined with the Kachanov-Sdobyrev brittle rupture rule are used as the governing equations for the unsteady creep problem. The concept of a fully damaged design method is applied, when the appropriate iteration of the thickness (the decision variable) is introduced such that the local condition of the Kachanov type ( ↓x_i t_r) = 0 (the objective) to be satisfied for each x_i under the constant volume condition (the constraint). In general, the disk of uniform creep strength, with geometry changes neglected, is found either as optimal or non-optimal with respect to the lifetime. In case of non-stationary loading (due to prestressing), and the geometric constraints allowed for, an additional small improvement of the lifetime is obtained when shape corrections are imposed upon the disk of uniform creep rupture strength     

INFLUENCE OF CONSTRUCTION OF POWER LOSSES IN A SUPERCONDUCTING A.C. GENERATOR SCREENING SYSTEM

ABSTRACT

Results of calculations of a power losses in a superconducting a.c. generator screening system during asymmetrical load are given. The main variants of screening system are considered. The influence of the screening system parameters on the power losses in particular shells of the rotor is discussed     

ANTIOXIDANT ACTIVITIES OF ENDEMIC SIDERITIS LEPTOCLADA AND MENTHA DUMETORUM AQUEOUS EXTRACTS USED IN TURKEY FOLK MEDICINE

Total phenolic contents, hydroxyl radicals and one 1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activities, antioxidant capacities and reducing powers of Sideritis leptoclada, which is an endemic plant to Turkey, and Mentha × dumetorum were investigated in water extracts. Total phenolic contents were detected to be 0.32 µg gallic acid/µg dry biomass in the presence of 1.33 and 9.82 µg/mL, respectively. Fifty percent scavenging activities of hydroxyl and DPPH radical were determined with 0.03 and 0.16 mg/mL extracts of S. leptoclada and 0.21 and 1.6 mg/mL extracts of Mxdumetorum. In addition, total antioxidant capacities of S. leptoplada were also higher than Mxdumetorum and there was a significant difference between the controls. The result of this study suggests that extracts of S. leptoclada and Mxdumetorum can be used as potential source of natural antioxidants and as a possible food supplement or in the pharmaceutical industry.

PRACTICAL APPLICATIONS

The research is focused on the determination of new potential plant sources of antioxidants that can be used as food. Antioxidants are vital substances that possess the ability to protect the body from damage caused by reactive oxygen species induced oxidative stress. In this study, infusions in boiled water of Sideritis leptoclada , which is a plant endemic to Turkey, and Mentha x dumetorum have high levels of antioxidant capacity. The results of the study show that extracts of S. leptoclada and Mxdumetorum can be used as a supplement agent to increase in quality of food and for the pharmaceutical industry.     

CONTENT OF BASIC COMPONENTS AND VOLATILE OILS IN GREEN DILL AS DEPENDING ON THE HEIGHT AND USABLE PARTS OF PLANTS

The aim of the present study was to establish the content of basic chemical components (dry matter, ash, reducing sugars, total sugars, starch, dietary fiber, total nitrogen, protein nitrogen, ascorbic acid, titratable acidity) and volatile oils in dill plants. The investigated material consisted of the following parts of dill plants: leaf blade, petiole, whole leaf, stem and whole plants harvested at the plant height of 20, 30, 40, 50 and 60 cm. Differences in the level of the analyzed components depending on the part of dill plants to a great degree exceeded these depending on the plant height. The highest content of all components was ascertained in the leaf blade. The smallest contents of dry matter, ash, starch, dietary fiber, total nitrogen and protein nitrogen, total acids and L‐ascorbic acid were found in the stem, and of sugars and volatile oils in the petiole. With the growth of plants, all analyses showed decreasing tendencies in the content of ash, total nitrogen and protein nitrogen, variation in the level of dry matter, sugars, starch and L‐ascorbic acid, and an increasing tendency in the content of dietary fiber, total acids and volatile oils, with the exception of stems, where the level of volatile oils was stable.     

STABILITY AND OPTIMIZATION OF ELASTICALLY CLAMPED HELICAL SPRINGS UNDER TENSION

In this paper, the problem of stability and optimization of an elastically clamped helical spring subject to a tensile force is considered. The force is assumed to change the direction and the point of application during buckling; its behaviour is determined by four parameters. Some particular cases of loadings are investigated in detail. An initial geometry of a spring (a distribution of helix angle and radius of a spring) with a given initial length H_o is sought which ensures the maximal value of a critical loading under equality and inequality constraints. In the paper the variational as well as parametrical optimization problems are considered.