An On-Line Library of Extended High-Temperature Expansions of Basic Observables for the Spin-S Ising Models on Two- and Three-Dimensional Lattices

We present an on-line library of unprecedented extension for high-temperature expansions of basic observables in the Ising models of general spin S, with nearest-neighbor interactions. We have tabulated through order ²⁵ the series for the nearest-neighbor correlation function, the susceptibility and the second correlation moment in two dimensions on the square lattice, and, in three dimensions, on the simple-cubic and the body-centered cubic lattices. The expansion of the second field derivative of the susceptibility is also tabulated through ²³ for the same lattices. We have thus added several terms (from four up to thirteen) to the series already published for spin S = 1/2, 1, 3/2, 2, 5/2, 3, 7/2, 4, 5, .     

The Susceptibility of the Square Lattice Ising Model: New Developments

We have made substantial advances in elucidating the properties of the susceptibility of the square lattice Ising model. We discuss its analyticity properties, certain closed form expressions for subsets of the coefficients, and give an algorithm of complexity O(N⁶) to determine its first N coefficients. As a result, we have generated and analyzed series with more than 300 terms in both the high- and low-temperature regime. We quantify the effect of irrelevant variables to the scaling-amplitude functions. In particular, we find and quantify the breakdown of simple scaling, in the absence of irrelevant scaling fields, arising first at order |T–T_c|^9/4, though high-low temperature symmetry is still preserved. At terms of order |T–T_c|^17/4 and beyond, this symmetry is no longer present. The short-distance terms are shown to have the form (T–T_c)^p (log |T–T_c|)^q with pq². Conjectured exact expressions for some correlation functions and series coefficients in terms of elliptic theta functions also foreshadow future developments.     

Combustion Behaviour of Nitrocellulose and its Complexes with Copper Oxide. Hot stage microscopic studies

Complexes of nitrocellulose (NC – low and high nitrogen content) with copper oxide (CuO) have been synthesized and studied for morphological behaviour on heating from room temperature to 500°C with the help of hot stage microscopy (HSM). During decomposition, NC:CuO complexes show contraction of fibrous boundaries followed by mass movement of matrix, with the evolution of brown yellow colour gas at higher temperatures as compared to NC alone. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies of physico-chemical properties and fractal dimensions of selected high-temperature superconductor surfaces

Properties relating to porosity of solids (fractal dimensions, surface roughness parameters) were evaluated from atomic force microscopy (AFM) and nitrogen adsorption-desorption isotherms measured at 77 K for selected high-temperature [(RE) Ba₂Cu₃O_7−x, RE=Y, Sm] superconductors. Adsorption capacity, specific surface area, fractal dimensions were determined from adsorption-desorption isotherms. The adsorption isotherms of all samples were S-shaped and belong to type II according to the IUPAC classification. A linear relationship was demonstrated between the fractal coefficients calculated by using the two methods and values of adsorption capacity of monolayer.     

Industrial need for accurate thermophysical data and for reliable prediction methods

Intelligent design of chemical-process equipment requires accurate thermophysical property values for pure components and mixtures including solutions. Databases used by practicing engineers should include the best numbers available and estimated uncertainties of these numbers. Many important property values have not been measured and must be estimated. Care should be exercised in selecting the estimation method. Property values that are a function of temperature, pressure, and/or composition can be correlated using appropriate equations. Such equations and the number of adjustable parameters in these equations should be selected with care. Examples of determining uncertainties, estimation techniques used, and correlating equations are given.     

Copper(II)–Ammonia Complexation Equilibria in Aqueous Solutions at Temperatures from 30 to 250°C by Visible Spectroscopy

The spectra of copper(II)–ammonia solutions in 2 mol-kg^–1 NH₄NO₃(aq) were recorded as a function of pH with a new UV–visible flow cell, capable of operating at conditions up to 325°C and 300 bars. Equilibrium constants for the formation of copper(II)–ammonia complexes Cu(NH₃)_n ²⁺, 1 n 4, from 30 to 150°C were determined by evolving factor analysis and nonlinear least-squares regression. Measurements at higher temperatures were limited by thermal decomposition of NH₄NO₃(aq). The formation constants of Cu(NH₃)_n ²⁺ decrease with temperature, consistent with extrapolations of literature data from measurements below 100°C. Measurements above 150°C were carried out in 0.5 mol-kg^–1 CF₃SO₃H (aq), at the very high ammonia concentrations required to avoid the precipitation of CuO(s). The spectra are consistent with Cu(NH₃)₄ ²⁺ as the predominant species, based on extrapolations of peak maxima and molar absorptivities from lower temperatures. Shifts in the spectra of Cu²⁺ and the Cu(NH₃)_n ²⁺ species to higher wavelength and increases in molar absorbance with increasing temperature are discussed in terms of the structure of the complexes.     

截面折变非对称型长周期光栅高温应变特性

研究了基于高频CO_2激光脉冲单侧写入的截面折变非对称型长周期光纤光栅(LPFG)高温特性及其在高温环境中的轴向应变特性。理论和实验表明在200～1000℃之间长周期光纤光栅的谐振峰漂移呈线性趋势;同时,在高温环境中其谐振峰随轴向应变也呈线性漂移,且不同谐振峰的温度和应变灵敏度也不同。利用这种新型长周期光纤光栅独特的高温应变特性可用一根光纤光栅实现对高温和应变的同时测量。     

碱金属离子共掺Sr3Ga2Ge4O14∶Dy3+发光性能研究

本文采用高温固相法制备了一系列新型Sr_3-xGa₂Ge₄O₁₄∶xDy³⁺(x=0~0.40)(摩尔分数)及Sr_2.68Ga₂Ge₄O₁₄∶0.16Dy³⁺,0.16M⁺(M=Li、Na、K)荧光粉。EDS能谱分析证实该荧光粉中存在Sr、Ga、Ge、O、Dy元素。系列Sr_3-xGa₂Ge₄O₁₄∶xDy³⁺在350 nm光激发下产生了以568 nm为主波长,对应于⁴F_9/2→⁶H_13/2跃迁的强黄光发射。荧光粉的发射光谱显示,其发射强度随Dy³⁺浓度的增加而变化,且当x=0.16时达到最强。共掺杂碱金属M(M=Li、Na、K)作为电荷补偿离子,其中Li⁺对增加Dy³⁺的发射强度效果最明显,使得荧光粉的发射强度提高到没有电荷补偿离子时的2倍。此外,随着Dy³⁺掺杂浓度的提高,荧光粉的荧光寿命不断减少。最后探讨了荧光粉Sr_2.68Ga₂Ge₄O₁₄∶0.16Dy³⁺,0.16Li⁺的CIE色度坐标和热稳定性,其CIE色度坐标为(0.371 9,0.404 6),位于黄色区域,在453 K的发光强度约为其室温发光强度的95.5%。因此,Dy³⁺,Li⁺共掺杂Sr_3-xGa₂Ge₄O₁₄荧光粉是潜在的显示器件和白光LED器件候选材料。     

Tb3+掺杂钒磷酸盐蓝绿发光调控及发光机理研究

本文采用高温固相方法合成了不同掺杂浓度的YVO4∶Tb3+、YPO4∶Tb3+和YV1-xPxO4∶Tb3+系列荧光粉,利用差示扫描量热法(DSC)分析了高温固相合成过程中的化学反应,确定将1 350℃作为高温合成温度.利用XRD表征了材料物相结构,结果显示材料物相单一,均为四方晶系结构.研究了 YVO4∶Tb3+、YPO4∶Tb3+和YV1-xPxO4∶Tb3+系列荧光粉室温下的发光性质.受晶体场影响,紫外激发下YVO4∶Tb3+中Tb3+发光主要以5D3→7FJ(J=6,5,4,2)跃迁发光为主,发光显示为蓝光;P元素的增加改变了 YV1-xPxO4∶Tb3+晶体场环境,增强了基质与5D3、5D4能级间的多声子弛豫及5D3 →5D4能级间的交叉弛豫,5D4→7FJ'(J'=6,5,4,3)发射逐渐占优,发光呈现蓝、青、绿发光变化;掺杂浓度对YPO4∶Tb3+发光调控作用显著,随着掺杂浓度增加,Tb3+的5 D3与5 D4能级间的交叉弛豫作用增强,5D3发光减弱,5D4发光增强,通过调整掺杂浓度实现材料发光由青光到绿光的调控.综上,通过基质组分及掺杂浓度调节,可实现Tb3+掺杂钒磷酸盐体系蓝绿发光调控.