A Geometric characterization of the perfect Suzuki-Tits ovoids

We characterize in a geometrical way those Suzuki-Tits ovoids which are defined over a perfect fieidK (or equivalently living inside a self polar symplectic quadrangle). We simplify our axioms in the particular cases that (1) the associated Suzuki group has exactly two orbits in the set of lines ofPG(3,K), and (2) the ovoid is finite.Senior Research Associate at the Belgian National Fund for Scientific Research     

Systems with outer constraints. Gupta-Bleuler electromagnetism as an algebraic field theory

Since there are some important systems which have constraints not contained in their field algebras, we develop here in aC*-context the algebraic structures of these. The constraints are defined as a groupG acting as outer automorphisms on the field algebra , :G Aut , _G Inn , and we find that the selection ofG-invariant states on is the same as the selection of states onM(G ) by (U _g)=1gG, whereU _g M (G )/ are the canonical elements implementing _g . These states are taken as the physical states, and this specifies the resulting algebraic structure of the physics inM(G ), and in particular the maximal constraint free physical algebra . A nontriviality condition is given for to exist, and we extend the notion of a crossed product to deal with a situation whereG is not locally compact. This is necessary to deal with the field theoretical aspect of the constraints. Next theC*-algebra of the CCR is employed to define the abstract algebraic structure of Gupta-Bleuler electromagnetism in the present framework. The indefinite inner product representation structure is obtained, and this puts Gupta-Bleuler electromagnetism on a rigorous footing. Finally, as a bonus, we find that the algebraic structures just set up, provide a blueprint for constructive quadratic algebraic field theory.     

Accreditation of reference material producers: the example of IRMM's Reference Materials Unit

The potential approaches for third-party assessment of reference material producers are revisited and the activities of the Reference Materials (RM) Unit of the Institute for Reference Materials and Measurements (IRMM) to obtain accreditation to ISO Guide 34 and ISO 17025 are described. Accreditation was related to the Unit as all matrix RM activities of the institute are concentrated there. A management system was established that allows sufficient flexibility to be applicable to a wide range of RMs while being precise enough to ensure compliance with ISO Guides 30, 31 and especially 34 and 35. Accreditation was achieved in 2004 with independent scopes for testing and RM production and was confirmed and extended in 2005. The key aspects of the RM Unit's management system for RM production are presented. Presented at BERM-10, April 2006, Charleston, SC, USA     

Microarray-based in vitro evaluation of DNA oligomer libraries designed in silico.

We report on the microarray-based in vitro evaluation of two libraries of DNA oligonucleotide sequences, designed in silico for applications in supramolecular self-assembly, such as DNA computing and DNA-based nanosciences. In this first study which is devoted to the comparison of sequence motif properties theoretically predicted with their performance in real-life, the DNA-directed immobilization (DDI) of proteins was used as an example of DNA-based self-assembly. Since DDI technologies, DNA computing, and DNA nanoconstruction essentially depend on similar prereguisites, in particular, large and uniform hybridization efficiencies combined with low nonspecific cross-reactivity between individual sequences, we anticipate that the microarray approach demonstrated here will enable rapid evaluation of other DNA sequence libraries.     

Schwefel(IV)-Verbindungen als Liganden. II. Die Kristall- und Molekülstruktur von Pentacarbonyl-(schwefeldioxid)chrom

Sulfur(IV) Compounds as Ligands. II. The Crystal and Molecular Structure of Pentacarbonyl--(sulfur dioxide)chromium The structure of pentacarbonyl(sulfurdioxide)chromium ( 1 ) has been determined from single crystal X-ray data. The compound crystallizes with eight formula units in the rhombic unit cell (space group Pbn2₁) of the dimensions a = 657.8(2) pm, b = 1245.2(4) pm, c = 2177.4(5) pm (at 180 K). The sulfur dioxide is η¹-coplanar coordinated, the Cr? S distance is 219 pm, the shortest bond reported so far between chromium(0) and sulfur. The Cr? C(ax) bond (189 pm) was found only marginally shorter than the Cr? C(eq) bonds (190 pm) providing proof of the high π-acceptor capacity of SO₂.     

Modelling and mutation studies on the histamine H1-receptor agonist binding site reveal different binding modes for H1-agonists: Asp116 (TM3) has a constitutive role in receptor stimulation

Summary A modelling study has been carried out, investigating the binding of histamine (Hist), 2-methylhistamine (2-MeHist) and 2-phenylhistamine (2-PhHist) at two postulated agonistic binding sites on transmembrane domain 5 (TM5) of the histamine H₁-receptor. For this purpose a conformational analysis study was performed on three particular residues of TM5, i.e., Lys²⁰⁰, Thr²⁰³ and Asn²⁰⁷, for which a functional role in binding has been proposed. The most favourable results were obtained for the interaction between Hist and the Lys²⁰⁰/Asn²⁰⁷ pair. Therefore, Lys²⁰⁰ was subsequently mutated and converted to an alanine, resulting in a 50-fold decrease of H₁-receptor stimulation by histamine. Altogether, the data suggest that the Lys²⁰⁰/Asn²⁰⁷ pair is important for activation of the H₁-receptor by histamine. In contrast, analogues of 2-PhHist seem to belong to a distinct subclass of histamine agonists and an alternative mode of binding is proposed in which the 2-phenyl ring binds to the same receptor location as one of the aromatic rings of classical histamine H₁-antagonists. Subsequently, the binding modes of the agonists Hist, 2-MeHist and 2-PhHist and the H₁-antagonist cyproheptadine were evaluated in three different seven--helical models of the H₁-receptor built in homology with bacteriorhodopsin, but using three different alignments. Our findings suggest that the position of the carboxylate group of Asp¹¹⁶ (TM3) within the receptor pocket depends on whether an agonist or an antagonist binds to the protein; a conformational change of this aspartate residue upon agonist binding is expected to play an essential role in receptor stimulation.Abbreviations 2-MeHist 2-methylhistamine - 2-PEA 2-pyridyl-ethylamine - 2-PhHist 2-phenylhistamine - CHO Chinese hamster ovary - E_int interaction energy - E_str strain energy - GES global energy structure - gpH₁R guinea pig H₁-receptor - GPCR G-protein coupled receptor - Hist histamine - N proximal nitrogen - N tele nitrogen - TM transmembrane domain - WT wild type