Analytic evaluation of multicenter integrals for gaussian-type orbitals

This work contains the evaluation of multicenter integrals with Cartesian Gaussian functions occurring in ||||² These integrals have to be used if it is necessary to calculate the lower bounds for eigenvalues with the method of the minimization of the variance [1], Considering the varianceF() = ||H||² - (H!| )², the integrals from (HY, Y) are well known in contrast to those for ||H ||².     

Lists of face-regular polyhedra

We introduce a new notion that connects the combinatorial concept of regularity with the geometrical notion of face transitivity. This new notion implies finiteness results in the case of bounded maximal face size. We give lists of structures for some classes and investigate polyhedra with constant vertex degrees and faces of only two sizes.     

How to achieve world-wide mutual recognition of calibration and test results – or: Who accredits the accreditor?

 The ongoing globalization of the economy demands cost- and time-effective conformity assessment procedures through mutual cross-border recognition of calibration and test results. Accreditation is an important tool to ensure the technical competence of laboratories performing calibrations and tests. The question, however, arises as to which mechanisms should be applied to achieve technical equivalence of accreditations throughout the world as a basis for mutual recognition of agreements. To avoid third party "accreditation of accreditors", accreditation bodies have established a specific procedure of regional technical cooperation in order to create a climate of confidence resulting in formal mutual recognition agreements. Key elements of this cooperation are the harmonization of operation procedures in addition to existing international standards, a continuos programme of interlaboratory comparisons, and an extensive procedure for mutual peer assessments. The present article provides detailed information on such cooperation within the European region as an example, describes the present situation with respect to mutual recognition agreements within Europe, and gives a brief look into the future with respect to inter-regional cooperation. Received: 28 September 1996 Accepted: 2 November 1996     

On the production of \pi^{+}_{} \pi^{+}_{} pairs in pp collisions at 0.8 GeV

Data accumulated recently for the exclusive measurement of the pp $ \rightarrow$ pp $ \pi^{+}_{}$ $ \pi^{-}_{}$ reaction at a beam energy of 0.793GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the pp $ \rightarrow$ nn $ \pi^{+}_{}$ $ \pi^{+}_{}$ reaction channel. The latter is expected to be the only $ \pi$ $ \pi$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $ \pi$ $ \pi$ production process. No single event has been found, which meets all conditions for being a candidate for the pp $ \rightarrow$ nn $ \pi^{+}_{}$ $ \pi^{+}_{}$ reaction. This gives an upper limit for the cross-section of 0.16μb (90% C.L.), which is more than an order of magnitude smaller than the cross-sections of the other two-pion production channels at the same incident energy.     

Hyperbolic automorphisms of free groups

We prove that an automorphism \not o : F ? F {\not o} : F \to F of a finitely generated free group F is hyperbolic in the sense of Gromov if it has no nontrivial periodic conjugacy classes. This result was previously claimed (but not proved) in [BF1].     

Molecular-level helical stack of a nucleotide-appended oligo(p-phenylenevinylene) directed by supramolecular self-assembly with a complementary oligonucleotide as a template

The nucleotide-appended oligo(p-phenylenevinylene), {bis[2,5-bis(2-methoxyethoxy)-1,4-phenylene]bis(2,1-ethenediyl-1,4-phenylenemethylene)}bis(2'-deoxy-3'-thymidylic acid) (8), has been synthesized, and self-assembly of the single-component 8 and binary self-assembly of 8 with a complementary single-stranded 20-meric oligodeoxyadenylic acid (9) have been examined in aqueous solutions. Atomic force microscopy (AFM), UV-visible (UV-vis), and circular dichroism (CD) measurements revealed that right-handed helical stacks with 6.4- and 5.1-nm diameters self-assemble from the binary components of 8 and 9 as a template depending on the residual stoichiometry of the two components (thymine (T):adenine (A) = 1:1 and T:A = 2:1, respectively). The concentration of 9 was found to strongly influence the CD spectra of 8 in aqueous solutions. Consequently, we concluded that the one side of the thymine moieties in the stacked assemblies of 8 complexes with a single chain of 9. Complementary T-A base pairs thus formed and induced helical stack of the oligo(p-phenylenevinylene)s in the binary self-assembly. In contrast, self-assembly of the single-component 8 and binary self-assembly of 8 with the noncomplementary 20-meric oligothymidylic acid (10) produced no remarkable formation of fibrous structures like helical stacks.