掺镉纳米SnO2的热稳定性,电导及气敏性能

本文研究了ＣｄＯ掺杂对纳米ＳｎＯ２粉料的热稳定性，电导及气敏特性的影响。结果表明，以非晶状态均匀分散在ＳｎＯ２颗粒表面的ＣｄＯ能阻止ＳｎＯ２之间的相互扩散，提高了纳米ＳｎＯ２的热稳定性；固溶于ＳｎＯ２昌粒中的ＣｄＯ量（Ｃｄ／Ｓｎ〈０．０５）很小，但对元件的电导影响显著；纳米级的晶粒尺寸（〈６ｎｍ）及ＣｄＯ的掺杂大大改善了ＳｎＯ２的气敏特性。     

加速器磁场测量的霍尔多探头装置

描述了用于加速器磁场测量的霍尔多探头装置,它包括一个具有三只恒温盒(内有58只霍尔片)的测磁长臂,高精度磁场检定系统以及数据自动获取系统。分别叙述了霍尔片的定位、恒温、校准、数据采集、处理等内容。并提出了多探头装置测量中霍尔片稳定性的重要性。给出了在我们条件下的一些具体数据。本装置已应用在兰州重离子研究装置(HIRFL)的建造过程中,实践证明它能有效地高质量地满足加速器磁场测量的要求。     

The Stability of Rare Earth-Iron-Nitrides Sm_2(Fe,M)_(17)N_y,Permanent Magnets

The effects of the partial substitution of element M(M=Cr,V,Mn,x=0.05;Zr,Ga,x=0.017;Si,x=0.15;Co,x=0.10)for Fe in samarium-iron-nitride Sm_2(Fe_(1-x)M_x)_(17)N_y compounds on their stabilitiesand Curie temperatures have been studied.It is found that Co,Ga can raise the Curie temperature of thecompounds.The initial decomposition temperatures cannot be raised significantly by all the studied elementsexcept Co.The result contradicts the formation enthalpy consideration.The final decomposition tempera-tures can be raised by all of the substitution elements.The effects of atmospheres on their decomposition be-havior were also studied.The results show that oxidation is the major reason for magnetic deterioration ofthe powder heated in air.Compared with nitrogen atmosphere,argon or vacuum helps to delay the decompo-sition of the compounds.     

On formalism and stability of switched systems

In this paper,we formulate a uniform mathematical framework for studying switched systems with piecewise linear partitioned state space and state dependent switching.Based on known results from the the...     

冷热循环工艺中冷热转移速率对LY12铝合金尺寸稳定性的影响

研究了冷热转移速率对LY1 2铝合金微屈服强度和残余应力的影响。结果表明 ,提高冷热转移速率易使材料中形成稳定的位错组态 ,从而有利于提高微屈服强度 ;对于圆柱和圆环试样 ,提高冷热转移速率不利于降低残余应力。分析认为 ,冷热转移速率应根据工件几何形状和尺寸进行相应调整。     

Nanocomposites of CsPbBr3 perovskite quantum dots embedded in Gd2O3:Eu3+ hollow spheres for LEDs application

Gd₂O₃:Eu³⁺@CsPbBr₃ quantum dots (QDs) mesoporous hollow nanocomposites with good luminescent properties and high stability were built. Among which, the hollow Gd₂O₃:Eu³⁺ spheres and CsPbBr₃ QDs were prepared by urea homogeneous precipitation and hot-injection method, respectively. Finally, the Gd₂O₃:Eu³⁺@CsPbBr₃ QDs shell–core compounds were constructed through mechanical stirring. The structure, morphology, stability and luminescent properties were studied by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry/thermogravity (DSC/TG), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence excitation/photoluminescence (PLE/PL) and life decay tools. Compared to the original CsPbBr₃ QDs, Gd₂O₃:Eu³⁺@CsPbBr₃ QDs display better photostability, thermal stability and current stability. The resulting Gd₂O₃:Eu³⁺@CsPbBr₃ QDs composite exhibits good yellow emission. The Gd₂O₃:Eu³⁺@CsPbBr₃ QDs mixed silicone resin was directly coated on the blue LED chip, then the w-LED device with the color coordinate of (0.31, 0.32) was successfully assembled. The Gd₂O₃:Eu³⁺@CsPbBr₃ QDs compounds with excellent luminescent properties and stability are expected to be widely used in lighting and display areas.     

Stability of AB5-type hydrogen storage alloys

In this paper, we deduced an empirical equation for predicting the stabilities of the hydrides of AB₅-type compounds with the consideration of the effects of geometrical factor and electric factor. The theoretical curves derived from this equation are in good agreement with the test results of La_1−xCa_xNi₅, Ml_1−xCa_xNi₅ and La_1−xCe_xNi₅ compounds. With this model, we can easily interpret the phenomenon that the initial partial substitution of R by Ca in R_1−xCa_xNi₅ (R is rare earth metal) compounds cause an increase of hydrogen desorption pressure to a maximum value, whereas in the range of larger Ca content x the hydrogen desorption pressure decreases with increasing x.     

ON THE DYNAMICS OF THE COMBUSTION OF SINGLE CHAR PARTICLES

Diffusion and reaction models of varying complexity are used to study the stability of the combustion of single char particles. In contrast to past studies which have considered only the reaction of carbon with oxygen, both the heterogeneous reactions of carbon with oxygen and carbon dioxide and the homogeneous oxidation of carbon monoxide are taken into account in the formulation of the mathematical models. Emphasis is placed on the investigation of the feasibility of occurrence of oscillatory combustion. Our results show that high rates of the C-O₂ reaction and high concentration of O₂ in the ambient favor the occurrence of multiple steady states and oscillatory solutions, but the appearance of oscillatory instability is suppressed by the homogeneous reaction in the gas phase and the presence of CO and CO₂ in the ambient. The parametric investigation of the problem reveals, in agreement with the results of past studies, that the heat capacity of the porous solid, the Lewis number, and the thickness of the stagnant film are three key parameters for the occurrence of the oscillatory response of the system. Reasonably large values of solid heat capacity practically eliminate the possibility of oscillatory combustion, but an appropriate combination of large values of stagnant film thickness and small Lewis numbers may offset the effect of solid heat capacity     

Multivariable adaptive control: A survey

Adaptive control is a control methodology capable of dealing with uncertain systems to ensure desired control performance. This paper provides an overview of some fundamental theoretical aspects and technical issues of multivariable adaptive control, and a thorough presentation of various adaptive control schemes for multi-input–multi-output systems, literature reviews on adaptive control foundations and multivariable adaptive control methods, and related technical problems. It covers some basic concepts and issues such as certainty equivalence, stability, tracking, robustness, and parameter convergence. It discusses some of the most important topics of adaptive control: plant uncertainty parametrization, stable controller adaptation, and design conditions for different adaptive control schemes. The paper also presents a detailed study of well-developed multivariable model reference adaptive control theory and design techniques. It provides an introduction to multivariable adaptive pole placement and adaptive nonlinear control, and it concludes by identifying some open research problems.     

Robust and stable flow shop scheduling with unexpected arrivals of new jobs and uncertain processing times

In real scheduling problems, some disruptions and unexpected events may occur. These disruptions cause the initial schedule to quickly become infeasible and non-optimal. In this situation, an appropriate rescheduling method should be used. In this paper, a new approach has been proposed to achieve stable and robust schedule despite uncertain processing times and unexpected arrivals of new jobs. This approach is a proactive–reactive method which uses a two-step procedure. In the first step an initial robust solution is produced proactively against uncertain processing times using robust optimization approach. This initial robust solution is more insensitive against the fluctuations of processing times in future. In the next step, when an unexpected disruption occurs, an appropriate reactive method is adopted to deal with this unexpected event. In fact, in the second step, the reactive approach determines the best modified sequence after any unexpected disruption based on the classical objective and performance measures. The robustness measure is implemented in the reactive approach to increase the performance of the real schedule after disruption. Computational results indicate that this method produces better solutions in comparison with four classical heuristic approaches according to effectiveness and performance of solutions.