排序方式: 共有63条查询结果,搜索用时 62 毫秒
51.
通过真空电弧熔炼、长时间真空热处理的方法获得了单相NaZn13-型LaFe13-xSix(1.2≤x≤2.2)化合物,并测量了它们的磁化强度与磁场和温度的关系,用Maxwell关系式计算出在不同磁场下化合物的熵变ΔS。用Landau的二级相变理论及平均场近似下的标度律,分析拟合了LaFe13-xSix化合物ΔS与H之间的关系,对于具有一级和二级相变的材料,发现均存在ΔS∝H2/3的关系,只是拟合得到的参数不同。采用熵变峰值拟合得到的参数能够反映材料中一级磁性相变的程度,研究磁场诱导的熵变与磁场的关系可以为磁制冷研制提供指导。 相似文献
52.
离子液体在气体分离中的应用 总被引:1,自引:0,他引:1
离子液体是一类“可设计溶剂”,具有极低的蒸气压,几乎不挥发以及选择性溶解能力,近年来在气体分离领域得到了广泛的关注。本文综述了CO2和SO2等酸性气体、低碳链烷烃、烯烃和炔烃等有机气体,以及H2、O2、CO、N2、Ar、Xe等其他气体在离子液体中的溶解性能,归纳了气体在离子液体中的溶解机理和溶解规律,分析了离子液体结构与溶解度、分离性质的定性关系,其中具有胺基、胍基等碱性基团的功能化离子液体对CO2、SO2等酸性气体具有良好的溶解性,含有不饱和基团的离子液体通过π-π相互作用可以改善烯烃在离子液体中的溶解度,炔烃则易溶于氢键碱性较强的离子液体;并介绍了离子液体/气体二元体系分子模拟、溶解度关联模型以及离子液体固定化用于气体分离等工作的研究进展,探讨了离子液体气体分离研究存在的问题和未来发展方向。 相似文献
53.
1.引言1963年,Dahlquist以一类线性问题为模型提出了A-稳定性概念,此后有关如何判断方法是否A-稳定或确定其稳定域的研究十分活跃,袁兆鼎等~[1]中对此有详细的讨论.Burrage与Butcher[2]以一类非线性问题为模型,就一般线性方法引入了代数稳定性概念.Butcher[4]探讨了代数稳定性与A-稳定性间的内在联系.为确保代数稳定性蕴涵A-稳定性,Butcher[5]进一步要求代数稳定性定义中涉及的矩阵G是正定的。然而这样一来,正如李寿佛[6]中指出的那样,许多AN稳定且按[4… 相似文献
54.
2-芳基丙酸类手性药物色谱拆分的热力学研究 总被引:4,自引:0,他引:4
以0.5%和1.0%(体积分数)正丙醇-50 mmol/L磷酸盐缓冲液(pH 6.41)为流动相,温度74~313 K,在Chiral-AGP柱手性固定相上,考察了萘普生和布洛芬对映体在手性柱上的保留和分离行为。在实验范围内,温度升高对分离不利,随着温度的升高,对映体的保留时间、分离度和选择性因子都减少;萘普生对映体的分离度均比布洛芬大;流动相含1.0%正丙醇时,萘普生对映体和布洛芬对映体达到完全分离应控制的最高温度分别为298和288 K。用ln k对1/T作图得到的Van’t Hoff曲线都具有良好的 相似文献
55.
Min Li Zongbi Bao Baogen Su Huabin Xing Yiwen Yang Qilong Ren 《Journal of separation science》2013,36(18):3093-3100
The chiral separation of citalopram base by supercritical fluid chromatography on a semipreparative Chiralpak AD column was studied with the use of three alcohol‐type modifiers (methanol, ethanol, and 2‐propanol) with different volume percentages (5, 10, and 15%). The best separation was achieved when 10% 2‐propanol was used in the presence of 0.1% diethylamine as additive. Under these conditions, the resolution reached 2.15 and the selectivity was 1.388. In addition, other parameters that affected the retention and separation properties, i.e. temperature, pressure, and density, were studied in detail. At the same pressure, a decrease in the temperature improved the enantioselectivity as the experimental temperature range was below the isoelution temperature. However, the temperature dependence of the retention factor was complicated. As a rule, the retention factor decreased when the temperature increased at the same density. A satisfactory regression of the logarithm of the retention factor versus density and temperature was obtained using a simplified lattice‐fluid model. Surprisingly, the relationship between the Henry constant and density can be accurately correlated by using the same quadratic equation. 相似文献
56.
阮保庚 《数学物理学报(A辑)》1999,19(3):313-317
构造了仅由两个参量确定的方法类RK,(μ,δ),一切节点属于区间[0,1]且至少2s-1阶相容的s级RK的方法,如Radau|A,Radau||A,Gauss方法等,均是其特例.此类方法的代数稳定性与A-稳定性均等价于参量的μ的非负性,这一准则改进了Burrage的如下结论:一个满足简化条件B(s)和C(s)的s级RK的方法代数稳定的必要条件是它至少2s—1阶相容.基于此类方法构造了高阶指数拟合的RK公式,且公式是代数稳定的,因而适于求解非线性stiff问题.特别,当用k(k>1)步方法求解stiff问题时,用拟会得当的RK公式确定k-1个附加初值是行之有效的. 相似文献
57.
用K(d,n)表示Kautz网络,该网络由于具有优良的拓扑性质而频频出现在文献中被广泛研究,本文针对该网络中的路和宽距离得到如下结论:设x和y是中两个不同的顶点,P是一条最短(x,y)-路,Q是一条最短(y,x)-路,那么(1)如果P和Q相交于不同于x和y的内部结点,那么|P|+|Q|〉n;(2)PUQ最多由3个圈的并组成;(3)如果有d(x,y)≥n-d+3,那么(d-1)-宽距离dd—1(K(d,n):x,y)=n+1.作为结论(3)的一个应用,本文表明,如果d≥3和他≤d-2,那么独立数al,d-1(K(d,n))=αt,d(K(d,n))=d^n+d^n-1,其中l=1,2,…,n. 相似文献
58.
Xiaoping Zheng Fashen Li Baogen Shen 《Journal of magnetism and magnetic materials》2009,321(23):3842-3846
The effect of Pr substitution for Dy on the magnetization, magnetostriction, anisotropy and spin reorientation of a series of Tb0.3Dy0.7−xPrx(Fe0.9Al0.1)1.95 alloys (x=0, 0.1, 0.20, 0.25, 0.30, 0.35) at room temperature has been investigated. It was found that the magnetization and magnetostriction of the homogenized Tb0.3Dy0.7−xPrx(Fe0.9Al0.1)1.95 alloys decreases drastically with increasing x and the magnetostrictive effect disappears for x>0.2, but the spontaneous magnetostriction λ111 increases approximately linearly with increasing x. Moreover, the magnetostriction exhibits slightly bigger value at x=0.1 than the free alloys and is saturated more easily with the magnetic field H, showing that a small amount of Pr substitution is beneficial to a decrease in the magnetocrystalline anisotropy. The analysis of the Mössbauer spectra indicated that the easy magnetization direction in the {1 1 0} plane deviates slightly from the main axis of symmetry with Pr concentration x, namely spin reorientation. Comparing with the Al substitution, the effect of Pr substitution for Dy on the spin reorientation is smaller. 相似文献
59.
Zhiguo Zhang Fangnan Liu Jingwen Chen Kai Zhou Zongbi Bao Baogen Su Qiwei Yang Qilong Ren Yiwen Yang 《Tetrahedron letters》2019,60(43):151191
A visible-light induced direct amidation of benzoylformic acids with tertiary amines has been explored. Tertiary amines underwent N-dealkylative amidation with α-keto acid in the presence of [Ir{dFCF3ppy}2(bpy)]PF6 and Cs2CO3, affording the corresponding α-ketoamides in good yields under mild conditions. This transformation exhibits a wide substrate scope and provides a facile synthetic approach to α-ketoamides. 相似文献
60.