Broad-band infrared ellipsometry measurements of the c-axis response of underdoped YBa2Cu3O7−δ: Spectroscopic distinction between the normal-state pseudogap and the superconducting gap

We present broad-band infrared ellipsometry measurements of the c-axis dielectric response of underdoped YBa₂Cu₃O_7−d single crystals. Our data provide a clear spectroscopic distinction between the normal-state pseudogap and the superconducting gap. In particular, they establish that different energy scales are underlying the respective redistributions of spectral weight. Furthermore, our data are suggestive of a mutual competition between the two gaps and thus of an extrinsic nature of the pseudogap with respect to superconductivity.     

Estimating quadrature errors for analytic functions using kernel representations and biorthogonal systems

Summary. For analytic functions the remainder term of quadrature rules can be represented as a contour integral with a complex kernel function. From this representation different remainder term estimates involving the kernel are obtained. It is studied in detail how polynomial biorthogonal systems can be applied to derive sharp bounds for the kernel function. It is shown that these bounds are practical to use and can easily be computed. Finally, various numerical examples are presented. Received March 11, 1998 / Revised version January 22, 1999/ Published online November 17, 1999     

An illustrated theory of hyperbolic virtual polytopes

The paper gives an illustrated introduction to the theory of hyperbolic virtual polytopes and related counterexamples to A.D. Alexandrov’s conjecture.      

Continuum models of two-dimensional random droplets

We study the statistical mechanical properties of a two-dimensional assembly of free particles coupled to a mechanical reservoir. The particles-reservoir interaction is modelised by an Hamiltonian depending on the convex hull of the particles only. We concentrate on models whose energy is the sum of an area-term, a perimeter term and possibly a term preventing the particles occupying the interior of the convex hull. The range of coupling constants insuring a thermodynamic behaviour, as well as the associated free energy per particle are exactly determined.Work partially supported by the Swiss National Foundation for Scientific Research.     

Mutually permutable subgroups and group classes

We consider the product AB of two finite mutually permutable subgroups A, B and find some subnormal subgroups of the product. This leads to local and otherwise generalized statements about products of supersolvable groups.Received: 19 May 2004     

An axiomatic semantics for nested concurrency

We give transformation rules for the concurrent parts of Hoare's language CSP, transforming concurrent CSP programs into nondeterministic, sequential programs.On the basis of these transformations we define an axiomatic semantics for CSP with nested concurrency.This axiomatic system includes a rule for binary, associative process composition, enabling modular verification dealing with parts of concurrent systems as well as full programs.The proof system is fully abstract, in the sense that the internal structure of processes is irrelevant in the specification inasmuch it is not externally observable.An outline of a verification of a recursive, concurrent sorter is given as an example.     

Some variants of Cauchy's method with accelerated fourth-order convergence

In this paper, we present some variants of Cauchy's method for solving non-linear equations. Analysis of convergence shows that the methods have fourth-order convergence. Per iteration the new methods cost almost the same as Cauchy's method. Numerical results show that the methods can compete with Cauchy's method.     

Smoothed hat functions in subdivision

Following the general idea of smoothing through convolution, we discuss schemes for smoothing hat functions on the three-directional and the four-directional mesh. The smoothing masks–which in the four-directional case are matrix masks–have the same support as the refinement mask for the hat functions. Several smoothing schemes are presented, and in some cases the smoothness properties of the smoothed functions are analysed. In particular, the results for the four-directional case follow new and original lines of research.     

D2及高浓度H2／CH4辉光放电

D_2辉光放电实验的目的旨在进一步了解辉光放电清除水的机制,弄清辉光放电清洗时,高本底H_2与质谱仪中离子源反应生成H_2影响质谱仪分析的情况。实验是在FY-I装置(异形截面环流器)上进行的,装置结构见文献[2]。实验安排与预试环上进行的实验大致相同。重水(D_2O)在相对净化的氢纯化器内电解后,生成D_2(氘)经压电晶体阀控制输入。