微合金化对U-Co金属玻璃形成能力的影响

U-Co系具有较宽非晶成分区间,但其玻璃形成能力(GFA)较差。针对该体系的U_(69.2)Co_(30.8)合金,选择不同类型的元素M(M=Sn,Si,Be,Cu,Pd,Y,Zr)进行微合金化,采用铜辊甩带方法制备U_(69)Co_(30)M_1非晶合金条带样品,结合X射线衍射与差示扫描量热技术研究了微合金化对合金GFA的影响。结果表明,Sn添加对U-Co合金的GFA具有明显改善作用,Si次之,Be、Cu影响不大,Pd、Y、Zr起到恶化效果。结合合金熔化行为的改变和GFA与M元素的熔点、电负性、原子尺寸及M-C混合焓等参数的关联性分析,初步揭示出微合金化对U-Co合金GFA的影响机制,其本质应该与改变合金液体稳定性和晶化驱动力有关。     

Conversion of light paraffins for preparing small olefins over ZSM-5 zeolites

The conversion of C₃-C₉ paraffins to small olefins over ZSM-5 zeolite is investigated. The small olefins are primary products and are usually converted into other more stable secondary products such as aromatics on the ZSM-5 zeolites. Thermally treated HZSM-5, K/HZSM-5 and Ba/HZSM-5 catalysts were developed and favourable oxidative conditions were introduced for the conversion process to maximize selective conversion of light paraffins to small olefins at the relatively low temperature of 873 K. The role of K and Ba is to minimize bimolecular hydrogen transfer reactions and enhance the dehydrogenation activity of the catalysts. Meanwhile, the oxygen in the gas phase is effective to improve the olefin selectivity and yield. C₂-C₄ olefin selectivities of 70.4 and 66.8% have been obtained for propane andn-hexane feed-stocks, respectively, at a temperature of 873 K.     

Effect of bare metal surface on the dissolution in aqueous citrate solutions of magnetite films on carbon steel

The potential–time dependence of magnetite under varying conditions of pH and Fe2 concentration and of magnetite layers on carbon steel with initially exposed small bare metal areas have been studied. The experiments simulate the case of magnetite scales partially removed from surfaces in the course of chemical cleaning when coupling conditions occur with area ratios variable with time. The interpretation is based on an equivalent electric circuit composed of internal current generators of faradaic origin and capacitors simulating the electric double layer at the metal/solution and oxide/solution interfaces.     

Intelligent systems integration: Guiding Principles, examples and lessons learned

The adoption of support systems based on computational intelligence (CI) techniques in nuclear power plants presents a number of challenges that need to be addressed in order to maximise the added value of this type of systems. This paper tackles issues related to the integration of CI systems and identifies three different levels of integration that should be taken into consideration. These are the data level, the operational level, and the functional level. The data level includes all aspects of data communication between the CI system, the plant instrumentation, and the other computerized support systems present at the plant. The operational level includes all those aspects of integration that influence the way in which the operator interacts with the CI system, with a clear emphasis on Human System Interface (HSI) integration. The functional level includes those aspects of integration that deal with the functionality of the CI system and how this can support or be combined with the functionality offered by other support systems with the aim of exploiting synergistic effects and achieving new functions. Additionally, the paper identifies a set of guiding principles of integration that can be applied at all three levels of integration. Examples taken from experiences gathered at the OECD Halden Reactor Project are also included.     

The influence of equilibration time on the physical properties of B2O3PbOFe2O3 glasses

The 20Fe₂O₃ 80[3B₂O₃·PbO] glasses equilibrated at 1250°C, for times ranging between 0.5 and 10 hrs are studied by X-rays, electron-microscope, Mössbauer effect, electron paramagnetic resonance and magnetic measurements. The iron valence states as well as the distribution of iron ions in the glass matrix are analysed.     

Reliability Growth and Duane Learning Curves

This paper examines Duane learning curves for reliability improvement between successive reliability tests. A constant failure rate ratio between successive tests gives curved lines on a Duane plot. Gordon's observation that dominant failures appear exponentially with test time leads to exponential failure rate ratio models. These models, although not the only possible ones, give results that agree well with observations from practice.     

Sequential Destruction Method for Monte Carlo Evaluation of System Reliability

Circumstances favoring the use of Monte Carlo methods for evaluating the reliability of large systems are discussed. A new method, that of Sequential Destruction (SD) is introduced. The SD method requires no preparatory topological analysis of the system, and remains viable when element failure probabilities are small. It applies to a variety of reliability measures and does not require element failures to be s-independent. The method can be used to improve the performance of selective sampling techniques. Substantial variance reductions, as well as computational savings, are demonstrated using a sample system with more than 100 elements.     

Measurement of the parameters of the acoustic emission when metals are stretched acoustic measurements

The particular features of the measurement of the continuous acoustic emission when metals are stretched are considered. It is shown that the measured physical quantity should be the intensity of the acoustic radiation. Sources of systematic error are indicated, namely, the rigidity of the testing machine, the rate of displacement of the mobile crossarm, and the dimensions and shape of the samples. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 64–68, May, 2006.     

Effects of various baffle designs on acoustic characteristics in combustion chamber of liquid rocket engine

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-frequency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.