Search

Abstract A search is made for charged Higgs bosons predicted by Two-Higgs-Doublet extensions of the Standard Model (2HDM) using electron-positron collision data collected by the OPAL experiment at $\sqrt{s}=189\mbox{--}209\ \mbox{GeV}$ , corresponding to an integrated luminosity of approximately 600 pb−1. Charged Higgs bosons are assumed to be pair-produced and to decay into $\mathrm{q} \bar{\mathrm{q}}$ , τν τ or AW±. No signal is observed. Model-independent limits on the charged Higgs-boson production cross section are derived by combining these results with previous searches at lower energies. Under the assumption $\mathrm{BR} (\mathrm{H}^{\pm} \to \tau\nu_{\tau}) + \mathrm{BR} (\mathrm{H}^{\pm} \to \mathrm{q} \bar{\mathrm{q}}) = 1$ , motivated by general 2HDM type II models, excluded areas on the $[m_{\mathrm{H}^{\pm}} , \mathrm{BR} (\mathrm {H}^{\pm} \to \tau\nu_{\tau})]$ plane are presented and charged Higgs bosons are excluded up to a mass of 76.3 GeV at 95 % confidence level, independent of the branching ratio BR(H±→τν τ). A scan of the 2HDM type I model parameter space is performed and limits on the Higgs-boson masses $m_{\mathrm{H}^{\pm}}$ and m A are presented for different choices of tanβ.

Thin garnet films can be used as magneto-optical sensors or for the realization of optical isolators or modulators in integrated optics. For this purpose, it is desirable to use cheap substrates like SiO2, instead of, e.g., crystalline Y3Fe5O12(YIG). In the following, we describe the ablation of thin YIG films on SiO2substrates (with cuts of (1120), (1010), (001) and amorphous) using pulsed laser deposition, after which an additional annealing step was used to crystallize the garnet. A previously undescribed anomaly occurred in the produced samples. When measuring the rotation of the direction of polarization (PR) of light transmitting through them, we observed large oscillations in the wavelength spectra of the PR. This did not occur with all types of substrates and depended on the applied magnetic field, but due to the huge rotation angles observed (up to 2° for a 160 nm thin YIG layer), this cannot be ascribed to the Faraday effect (FE). Here, we show that this behavior can be explained by using a simple layer system and taking the birefringence of the substrates into account. TEM images of the real samples were used to set up the layer system, which consists of a thin YIG layer, an intersection area between YIG and the substrate and the crystalline SiO2. Further investigations concerning the dependence on the magnetic field or the qualitative mechanical tension can be assigned to the proposed model in a satisfactory way, by using a simple mathematical matrix model for layered systems. [ABSTRACT FROM AUTHOR]

Brachiopods are a phylum of shell-forming sessile marine invertebrates which have existed since the early Cambrian. Two very different biomaterial design strategies for their shells evolved early in their history. Both strategies use hybrid fibre composites, however, one is based on mineral fibres embedded in ~2 wt.% of organic biopolymer sheaths and the inorganic fibres are calcite single crystals. In the second strategy the fibres are biopolymers and are reinforced with Ca-phosphate nanoparticles to form a fibrous nanocomposite. Here the organic component (chitin) dominates. The Ca-phosphate nanoparticle-reinforcement strategy is not unlike that in vertebrate bone, however, the microscale structure is laminated with alternating laminae which have a different degree of mineralization. The calcitic shells feature an outer compact layer of calcite micro- and nanoparticles protecting the inner fibrous layer from the outside. Transmission electron microscopy of the fibrous layer reveals intercrystalline and intracrystalline biopolymers. The calcitic shell material is stiff with nano-indentation E-moduli of 63±8 GPa and relatively hard (Vickers microhardness up to 400 HV 0.0005/10 and nanohardness 4±0.5 GPa). Compared to inorganic calcite the microhardness is doubled and the nanohardness increases by 60%. We attribute this increased hardness to intracrystalline biopolymers. The nano-indentation E-moduli of the chitinophosphatic shells range from 3 to 55 GPa as a result of the varying degree of mineralization between their laminae, and similarly their nanohardness varies between 0.1 and 3 GPa. For brachiopods burrowing inside the sediment, the alternation of non-mineralized laminae with thin, more strongly mineralized laminae provides abrasion-resistance, hardness and longitudinal stiffness while it preserves the flexibility provided by the organic component for bending movements. [ABSTRACT FROM AUTHOR]

It is proved that for every positive integer k, every n-connected graph G of sufficiently large order contains a set W of k vertices such that G— W is ( n-2)-connected. It is shown that this does not remain true if we add the condition that G( W) is connected. [ABSTRACT FROM AUTHOR]