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铅稳定同位素在环境污染示踪中的应用和进展 总被引:2,自引:0,他引:2
从国内外大量研究实例出发,论述了铅同位素示踪在环境污染研究中的应用和进展。包括大气降尘、水系沉积物、土壤—植物体系这三个方面的相关理论以及最新的研究成果,并得出了不同研究对象中铅污染的来源、迁移以及富集的一些规律。 相似文献
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A full-transparent zone plate(FTZP), which can reuse the wave blocked in the focusing of the Fresnel zone plate(FZP), is proposed to improve the efficiency of terahertz(THz) focusing without aberration. We find that the substrate thickness of the FTZP has a great influence on the focusing intensity, which results from the Fabry–Perot effect. The focusing efficiency of FTZPs could be about twice as high as that of FZPs, but the widths of both focus spots are comparable with the wavelength. The experimental results are in good agreement with the simulation. 相似文献
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倾斜封闭腔内对流换热问题是非线性非平衡系统中研究的热点问题之一.本文采用高精度数值方法对倾斜方腔内流体热对流进行了直接数值模拟,研究了腔体倾角在0°—180°之间变化时,倾角的不同变化过程对流场非线性演化、传热效率以及流动分岔的影响.所考虑的Rayleigh数范围为103—106.结果表明:表征传热效率的Nusselt数对Rayleigh数、Prandtl数及倾斜角度均具有较强依赖性,在较高Rayleigh数时, Nusselt数会在80°和100°附近产生较大幅度的变化;高Rayleigh数下流场及温度场的演变更为复杂,腔体内存在1—3个对流强度不等的涡卷;低Rayleigh数下腔体倾角接近90°时流动状态为热传导状态.当腔体倾角介于70°—110°之间时,在Rayleigh数Ra∈(4949, 314721)内存在解的两条稳定分支. 相似文献
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This paper is concerned with the initial-boundary value problem for damped wave equations with a nonlinear convection term in the multi-dimensional half space R n + : u tt u + u t + divf (u) = 0, t > 0, x = (x 1 , x ′ ) ∈ R n + := R + × R n 1 , u(0, x) = u 0 (x) → u + , as x 1 → + ∞ , u t (0, x) = u 1 (x), u(t, 0, x ′ ) = u b , x ′ = (x 2 , x 3 , ··· , x n ) ∈ R n 1 . (I) For the non-degenerate case f ′ 1 (u + ) < 0, it was shown in [10] that the above initialboundary value problem (I) admits a unique global solution u(t, x) which converges to the corresponding planar stationary wave φ(x 1 ) uniformly in x 1 ∈ R + as time tends to infinity provided that the initial perturbation and/or the strength of the stationary wave are sufficiently small. And in [10] Ueda, Nakamura, and Kawashima proved the algebraic decay estimates of the tangential derivatives of the solution u(t, x) for t → + ∞ by using the space-time weighted energy method initiated by Kawashima and Matsumura [5] and improved by Nishihkawa [7]. Moreover, by using the same weighted energy method, an additional algebraic convergence rate in the normal direction was obtained by assuming that the initial perturbation decays algebraically. We note, however, that the analysis in [10] relies heavily on the assumption that f ′ (u) < 0. The main purpose of this paper isdevoted to discussing the case of f ′ 1 (u b ) ≥ 0 and we show that similar results still hold for such a case. Our analysis is based on some delicate energy estimates. 相似文献
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利用等效变换和重正化群变换的方法,在Sierpinskigasket晶格上研究了具有近邻和次近邻相互作用Gaussian模型的临界性质,求出了临界温度和关联长度临界指数.结果表明:在相变点近邻相互作用K1和次近邻相互作用K2之间满足一定的关系,这种关系对铁磁体和反铁磁体都适用.并且考虑次近邻相互作用后,临界温度和临界指数都不发生改变. 相似文献
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This article is concerned with the global existence and large time behavior of solutions to the Cauchy problem for a parabolic-elliptic system related to the Camassa-Holm shallow water equation {ut+(u^2/2)x+px=εuxx, t〉0,x∈R, -αPxx+P=f(u)+α/2ux^2-1/2u^2, t〉0,x∈R, (E) with the initial data u(0,x)=u0(x)→u±, as x→±∞ (I) Here, u_ 〈 u+ are two constants and f(u) is a sufficiently smooth function satisfying f" (u) 〉 0 for all u under consideration. Main aim of this article is to study the relation between solutions to the above Cauchy problem and those to the Riemann problem of the following nonlinear conservation law It is well known that if u_ 〈 u+, the above Riemann problem admits a unique global entropy solution u^R(x/t) u^R(x/t)={u_,(f′)^-1(x/t),u+, x≤f′(u_)t, f′(u_)t≤x≤f′(u+)t, x≥f′(u+)t. Let U(t, x) be the smooth approximation of the rarefaction wave profile constructed similar to that of [21, 22, 23], we show that if u0(x) - U(0,x) ∈ H^1(R) and u_ 〈 u+, the above Cauchy problem (E) and (I) admits a unique global classical solution u(t, x) which tends to the rarefaction wave u^R(x/t) as → +∞ in the maximum norm. The proof is given by an elementary energy method. 相似文献
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