Surface composition of ordered intermetallic compounds PtBi and PtPb

The surface composition of bulk electrodes made from the ordered intermetallic phases PtBi and PtPb has been studied by ex-situ X-ray photoelectron spectroscopy (XPS) after being subjected to various electrochemical treatments. Analysis of the freshly polished surfaces showed that in the surface and near surface regions the less-noble metals; Bi and Pb are oxidized to a significant extent (28% and 41%, respectively). Upon cycling to increasingly positive potentials, the fraction of oxidized to metallic forms of Bi and Pb decreased gradually to reach the minimal values of 7% and 6% at +400 mV vs. Ag/AgCl (saturated KCl). The observed decrements are due to leaching of surface oxides; Bi₂O₃ on PtBi and PbCO₃ or Pb(OH)₂ on PtPb. When the potential sweep was extended to more positive values, there was a linear decrease in the surface concentration of the less-noble metal, along with a slight increase in the amount of the species in their oxidized state (Bi₂O₃ for PtBi and PbSO₄ for PtPb). Leaching of Bi from the electrode surface occurs in accordance to the Pourbaix diagram for elemental bismuth, indicating no significant increase in stability arising from the formation of an intermetallic phase with platinum. In the case of PtPb, however, the Pb starts to dissolve away at potentials significantly more positive (+800 mV) than what was anticipated from the Pourbaix diagram. The results obtained here are in accord with our previous observations on the effects of electrochemical pre-treatment on these intermetallic phases for the electrocatalytic oxidation of formic acid and other potential fuel cell fuels.     

Positive solutions of a system of non-autonomous fractional differential equations

Existence of positive solutions for the following system of fractional differential equations:

     

半群的模糊理论研究进展

介绍半群的模糊理论研究的基本内容、方法,重点介绍半群的模糊理想、模糊同余以及目前半群的模糊理论研究进展。     

Quasi-Differential Posets and Cover Functions of Distributive Lattices II: A Problem in Stanley’s <Emphasis Type="Italic">Enumerative Combinatorics</Emphasis>

A distributive lattice L with 0 is finitary if every interval is finite. A function f:₀₀ is a cover function for L if every element with n lower covers has f(n) upper covers. All non-decreasing cover functions have been characterized by the author ([2]), settling a 1975 conjecture of Richard P. Stanley. In this paper, all finitary distributive lattices with cover functions are characterized. A problem in Stanleys Enumerative Combinatorics is thus solved. 2000 Mathematics Subject Classification. 06A07, 06B05, 06D99, 11B39     

PERIODIC BOUNDARY VALUE PROBLEMS FOR IMPULSIVE INTEGRO-DIFFERENTIAL EQUATIONS OF MIXED TYPE IN BANACH SPACES

1.IntroductionInthispaper,weinvestigatetheperiodicboundaryvalueproblem(PBVP)forfirstordernonlinearimpulsiveintegro-differentialeauationsofmixedtypeinaBanachspaceE:wherefEC[JxExExE,E],J=[0,2r]ticECIE,E](k=1,2,',m:KECID,R ],D={(t,s)EJxJ:t2s},HEC[JxJ,R ],R denotesthesetofallnonnegativenumbers,and0相似文献   

A Simple System with Topological Entropy Infinit

Ｌｅｔ（Ｘ，ｄ）ｂｅａｍｅｔｒｉｃｓｐａｃｅ，ａｎｄｆ：Ｘ→Ｘｂｅａｕｎｉｆｏｒｍｌｙｃｏｎｔｉｎｕｏｕｓｍａｐ．Ｗｈｅｎ（Ｘ，ｄ）ｉｓａｃｏｍｐａｃｔｍｅｔｒｉｃｓｐａｃｅ，ｐｅｏｐｌｅｂｅｌｉｅｖｅｔｈａｔｆｈａｓｐｏｓｉｔｉｖｅｔｏｐｏｌｏｇｉ...     

THE DESIGN AND ANALYSIS OF ALGORITHM OF MINIMUM COST SPANNING TREE

ＴＨＥＤＥＳＩＧＮＡＮＤＡＮＡＬＹＳＩＳＯＦＡＬＧＯＲＩＴＨＭＯＦＭＩＮＩＭＵＭＣＯＳＴＳＰＡＮＮＩＮＧＴＲＥＥ￥（徐绪松，刘大成，吴丽华）ＸｕＸｕｓｏｎｇ；ＬｉｕＤａｃｈｅｎｇ；ＷｕＬｉｈｕａ（ＳｃｈｏｏｌｏｆＭａｎａｇｅｍｅｎｔ，ＷｕｈａｎＵｎｉ...     

图的割宽问题

本文建立了Ｈａｒｐｅｒ型割宽下界估计式，由此求出了轮形图Ｗｎ、完全二部图Ｋ（ｍ，ｎ）、圈幂Ｃｎｒ、格子图：Ｐｍ×Ｐｎ、Ｐｍ×Ｃｎ、Ｃｍ×Ｃｎ以及乘积图：Ｋｍ×Ｐｎ、Ｋｍ×Ｃｎ、Ｃｍｓ×Ｃｎｒ、Ｋｍ×Ｋｎ和强乘积图Ｐｍ　Ｐｎ的割宽。     

Differentiability with respect to parameters of solutions to convex programming problems

We consider a family of convex programming problems that depend on a vector parameter, characterizing those values of parameters at which solutions and associated Lagrange multipliers are Gâteaux differentiable.These results are specialized to the problem of the metric projection onto a convex set. At those points where the projection mapping is not differentiable the form of Clarke's generalized derivative of this mapping is derived.     

Ternary Operations as Primitive Notions for Constructive Plane Geometry VI

In this paper we provide quantifier-free, constructive axiomatizations for several fragments of plane Euclidean geometry over Euclidean fields, such that each axiom contains at most 4 variables. The languages in which they are expressed contain only at most ternary operations. In some precisely defined sense these axiomatizations are the simplest possible.