共查询到18条相似文献,搜索用时 921 毫秒
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考虑一类演化方程ut=au∂2k+1(其中a是常数,u∂2k+1=∂2k+1u/∂x2k+1,k=1,2……)的有限差分解法。构造了两类具有高稳定性的显式差分格式。并用引入耗散项的方法建立了两类半显式差分格式,它们是无条件稳定的且可显式地进行计算。 相似文献
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本文构造了解色散方程u1=auxxx的若干三层恒稳的半显式差分格式。第Ⅰ、Ⅱ类格式的局部截断误差的阶为O(τ2+h2+(τ2)/(h3));而第Ⅲ、Ⅳ类格式的局部截断误差的阶为O(τ2+h4+((τ)/(h))2+τh)。用判别稳定性的Von Neumann准则可证明:第Ⅰ、Ⅱ类格式及当参数α≤1时的第Ⅲ、Ⅳ类格式都是无条件稳定的,并且当必须的边界条件给定时它们可以显式地进行计算。 相似文献
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采用溶胶凝胶法制备了Ti1-xCrxO2±δ体系系列样品.利用扫描电子显微镜(SEM),X射线光电子能谱(XPS),粉末X射线衍射分析(XRD)方法研究了Ti1-xCrxO2±δ系列样品的颗粒尺寸、形貌、组分化学态、相关系和固溶区范围;并利用超导量子干涉磁强计对样品的磁性能进行了研究.采用Rietveld结构精修的方法研究了Cr的不同掺杂量对TiO2晶体结构的影响,研究表明,1000℃烧结的样品的固溶区范围是x=0—0.03,为金红石单相;随着Cr掺杂量的增加,金红石相晶胞参数规律性地减小;当x>0.03,为金红石相和CrO2相两相共存.综合XRD和磁性测量结果,500℃烧结的样品的固溶区范围是x=0—0.02,为锐钛矿单相;随着Cr掺杂量的增加,锐钛矿相晶胞参数规律性地减小;当x≥0.04,为锐钛矿相和绿铬矿相(Cr2O3)两相共存.XPS实验结果表明,500℃和1000℃退火的样品中Cr都是以Cr+3和Cr+6两种化学态存在,1000℃烧结的样品中可能有更多的Cr3+转化为Cr6+.根据M-H和M-T曲线的测试结果发现,本文500℃烧结的Ti1-xCrxO2±δ体系样品当x=0—0.02时,为室温铁磁性.当x≥0.04时,由铁磁相和顺磁相所组成,在低温下有较强的铁磁性;室温下主要是顺磁相,铁磁相只占据很小的体积分数.
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1-xCrxO2±δ体系')" href="#">Ti1-xCrxO2±δ体系
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二维非定常Sine-Gordon方程辛算法及其孤子数值模拟 总被引:1,自引:1,他引:0
在矩形域[-a,a]×[-a,a]内对微分算子L=(ə2)/(əx2)+(ə2)/(əy2)用5点差分格式将二维非定常Sine Gordon方程离散化为一个2×7992阶非线性Hamilton系统.对该系统使用Euler中心格式,得到一个非线性方程组.对此方程组建立迭代解法并给出了这个迭代方法的收敛条件和收敛速度.Sine Gordon方程单孤子和双孤子的数值模拟试验显示该辛算法是有效的. 相似文献
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提出两差分格式求解时间分数阶亚扩散方程.两个格式都是绝对稳定的,收敛阶均为O(τq+h2),其中q(q=2-β或2)与方程解的光滑性有关,β(0 < β < 1)是分数阶导数的阶、τ和h分别是时间和空间方向步长.数值实验验证了理论结果的正确性,并与其他方法进行比较,显示了本文方法的有效性和精确性. 相似文献
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合成了三个系列稀土掺杂镝乙酰丙酮(Hacac)邻菲咯啉(phen)三元配合物RExDy1-x(acac)3phen(RE=La,Y,Gd;x=0,0.10,0.20,0.30,0.50,0.70,0.90,1.00),通过紫外光谱、红外光谱、X射线粉末衍射对配合物进行了表征。对各系列配合物进行荧光光谱研究,发现La3+、Y3+、Gd3+对Dy3+离子均有荧光增敏作用,它们对Dy3+离子的荧光增强顺序为I(La3+)>I(Y3+)≈I(Gd3+)。当x=0.10~0.30,所有掺杂配合物的荧光强度都大于未掺杂的配合物Dy(acac)3phen的荧光强度。 相似文献
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D. Bahadur Sheelavathi Kollali C.N.R. Rao M.J. Patni C.M. Srivastava 《Journal of Physics and Chemistry of Solids》1979,40(12):981-985
FMR measurements have been carried out on several members of the Ln1−xSrxCoO3 (Ln = Rare earth) system. The results show that geff in these systems is around 1.25 independent of x as well as the rare earth ion. It is suggested that this unusual value of geff is due to the localized intermediate-spin Co3+ ions (t52g e1g) located at the top of the π* band. 相似文献
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V. A. Smirnov 《Physics letters. [Part B]》2001,500(3-4):330-337
The dimensionally regularized massless non-planar double box Feynman diagram with powers of propagators equal to one, one leg off the mass shell, i.e., with p12=q2≠0, and three legs on shell, pi2=0, i=2,3,4, is analytically calculated for general values of q2 and the Mandelstam variables s,t and u (not necessarily restricted by the physical condition s+t+u=q2). An explicit result is expressed through (generalized) polylogarithms, up to the fourth order, dependent on rational combinations of q2,s,t and u, and simple finite two- and three-fold Mellin–Barnes integrals of products of gamma functions which are easily numerically evaluated for arbitrary non-zero values of the arguments. 相似文献
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Jamila Ghamri Herv Baussart Michel le Bras Jean-Marie Leroy 《Journal of Physics and Chemistry of Solids》1989,50(12):1237-1244
The mixed oxides BixEu1−xVO4 and BiyGd1−yVO4 crystallize in a zircon-type structure, for 0 <x < 0.6 and 0 < y < 0.64, and in a fergusonite-type structure, for 0.94 < x < 1 and 0.93 < y < 1. A process of competition between the dominant and the constrained effects of the lone-pair 6s2 of Bi3+ is discussed. The diffuse reflectance spectroscopic studies of these mixed oxides are presented. The observed broad bands are attributed to charge transfer processes and the sharp peaks in the BixEu1−xVO4 spectra are ascribed to intra-configurational 4f – 4ftransitions of the Eu3+ ion. The broad absorption shift in BiLnVO4 (Ln : Eu and Gd) compounds to the longer wavelengths range, when Bi is introduced in the LnVO4 lattice, is ascribed to charge transfer processes in a Bi-VO4 center and are interpreted assuming a Jahn-Teller effect in the excited state of Bi3+. The concept of an internal pressure of Bi3+ ions is also used to explain the broad A-band shifts. 相似文献
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A universal feature of 1/f-type fluctuation is numerically observed in the system-size n dependence of the transmission amplitude tn in various one-dimensional disordered systems. The power spectrum P(f) of the transmission coefficient T(n)=|tn|2 exhibits the power law of 1/f2, irrespective to the type of disorder of the system whether it is of short-range or of long-range correlation. That of the phase θt(n) of tn also does the universal power law of 1/f1.4. 相似文献
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K. Yoshida F. Nakamura Y. Tanaka Y. Maeno T. Fujita 《Physica C: Superconductivity and its Applications》1994,230(3-4):371-377
A structural transition to a low-temperature tetragonal (TLT) phase occurs below Td2≈60 K in La2−xBaxCuO4 only around x=0.125, accompanied by sharp suppression of superconductivity. In this study we investigated the effects of partial substitution of smaller divalent cations for Ba2+ ions (Ba2+ > Sr2+ > Ca2+) on these anomalous low-temperature properties. The suppression of superconductivity is strongly affected by the appearance of the TLT phase for this carrier concentration. We also show that the variations of Td2 and Tc are quantitatively scaled by the averaged size of cations at the La site. This dependence can be interpreted as chemical effects acting effectively as applied pressure. We discuss how our observation is related to recent reports which claim that the TLT structure itself does not necessarily destroy the superconductivity. 相似文献
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We show that the HERA data for the inclusive structure function F2(x,Q2) for x10−2 and 0.045Q245 GeV2 can be well described within the color dipole picture, with a simple analytic expression for the dipole–proton scattering amplitude, which is an approximate solution to the non-linear evolution equations in QCD. For dipole sizes less than the inverse saturation momentum 1/Qs(x), the scattering amplitude is the solution to the BFKL equation in the vicinity of the saturation line. It exhibits geometric scaling and scaling violations by the diffusion term. For dipole sizes larger than 1/Qs(x), the scattering amplitude saturates to one. The fit involves three parameters: the proton radius R, the value x0 of x at which the saturation scale Qs equals 1 GeV, and the logarithmic derivative of the saturation momentum λ. The value of λ extracted from the fit turns out to be consistent with a recent calculation using the next-to-leading order BFKL formalism. 相似文献