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Two novel 25,27-dihydroxy-26,28-bis(3-phenylthiapropxy)-calix[4]arene(3) and 25,27-dihydroxy-26,28-bis(3-phenylthiapropoxy)-5,11,17,23-tetra-tert-butylcalix[4] arene (4) were synthesized for the evaluation of their ion-selectivity in ion-selective electrodes(ISEs).ISEs based on 3 and 4 as neutral ionophores were prepared,and their selectivity coefficients for Ag^ (lg KAg,M^pot)were investigated against other alkali metal,alkaline-earth metal,aluminum,thallium(Ⅰ),Lead and some transition metal ions using the separate solution method (SSM).These ISEs showed excellent Ag^ seletivity over most of the interfering cations examined,except for Hg^2 and Fe^2 having relative smaller interference(lg KAg,M^pot≤-2.1). 相似文献
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We consider finite element operators defined on ``rough' functions in a bounded polyhedron in . Insisting on preserving positivity in the approximations, we discover an intriguing and basic difference between approximating functions which vanish on the boundary of and approximating general functions which do not. We give impossibility results for approximation of general functions to more than first order accuracy at extreme points of . We also give impossibility results about invariance of positive operators on finite element functions. This is in striking contrast to the well-studied case without positivity.
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Takahashi K Kodama R Tanaka KA Hashimoto H Kato Y Mima K Weber FA Barbee TW Da Silva LB 《Physical review letters》2000,84(11):2405-2408
A laser self-focused channel formation into overdense plasmas was observed using a soft x-ray laser probe system with a grid image refractometry (GIR) technique. 1.053 &mgr;m laser light with a 100 ps pulse duration was focused onto a preformed plasma at an intensity of 2x10(17) W/cm (2). Cross sections of the channel were obtained which show a 30 &mgr;m diameter in overdense plasmas. The channel width in the overdense region was kept narrow as a result of self-focusing. Conically diverging density ridges were also observed along the channel, indicating a Mach cone created by a shock wave due to the supersonic propagation of the channel front. 相似文献
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This paper considers a posteriori error estimates by averaged gradients in second order parabolic problems. Fully discrete
schemes are treated. The theory from the elliptic case as to when such estimates are asymptotically exact, on an element,
is carried over to the error on an element at a given time. The basic principle is that the elliptic theory can be extended
to the parabolic problems provided the time-step error is smaller than the space-discretization error. Numerical illustrations
confirming the theoretical results are given. Our results are not practical in the sense that various constants can not be
estimated realistically. They are conceptual in nature.
AMS subject classification (2000) 65M60, 65M20, 65M15 相似文献
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Lars Wahlbin 《Numerische Mathematik》1974,23(4):289-303
The Galerkin method, together with a second order time discretization, is applied to the periodic initial value problem for $$\frac{\partial }{{\partial t}}(u - (a(x)u_x )_x ) + (f(x,u))_x = 0$$ . Heref(x, ·) may be highly nonlinear, but a certain cancellation effect is assumed for∫f(x, u) x u. Optimal order error estimates inL 2,H 1, andL ∞ are derived for a general class of piecewise polynomial spaces. 相似文献
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Stability and analyticity estimates in maximum-norm are shown for spatially discrete finite element approximations based
on simplicial Lagrange elements for the model heat equation with Dirichlet boundary conditions. The bounds are logarithm free
and valid in arbitrary dimension and for arbitrary polynomial degree. The work continues an earlier study by Schatz et al.
[5] in which Neumann boundary conditions were considered.
Received November 1998 / Revised version received August 11, 1999 / Published online July 12, 2000 相似文献
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ThetheoryofnonlinearpolymerizationwasinitiatedbyFlory[1]andStockmayer[2].Forsimplifyingtheevaluationofaveragepolymerquantities,manyotherstatisticalmethodssuchastheprobabilityofgeneratingfunctionmethod[3],thelawoftotalprobabilitymethod[4,5]andtheothermethods[6… 相似文献
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