221 research outputs found

    CO adsorption on neutral iridium clusters

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    The adsorption of carbon monoxide on neutral iridium clusters in the size range of n = 3 to 21 atoms is investigated with infrared multiple photon dissociation spectroscopy. For each cluster size only a single v(CO) band is present with frequencies in the range between 1962 cm-1 (n = 8) and 1985 cm-1 (n = 18) which can be attributed to an atop binding geometry. This behaviour is compared to the CO binding geometries on clusters of other group 9 and 10 transition metals as well as to that on extended surfaces. The preference of Ir for atop binding is rationalized by relativistic effects on the electronic structure of the later 5d metals

    Search for CP Violation in D^0--> K_S^0 pi^+pi^-

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    We report on a search for CP violation in the decay of D0 and D0B to Kshort pi+pi-. The data come from an integrated luminosity of 9.0 1/fb of e+e- collisions at sqrt(s) ~ 10 GeV recorded with the CLEO II.V detector. The resonance substructure of this decay is well described by ten quasi-two-body decay channels (K*-pi+, K*0(1430)-pi+, K*2(1430)-pi+, K*(1680)-pi+, Kshort rho, Kshort omega, Kshort f0(980), Kshort f2(1270), Kshort f0(1370), and the ``wrong sign'' K*+ pi-) plus a small non-resonant component. We observe no evidence for CP violation in the amplitudes and phases that describe the decay D0 to K_S^0 pi+pi-.Comment: 10 pages, 3 figures, also available at http://w4.lns.cornell.edu/public/CLNS/, submitted to PR

    A Measurement of the Decay Asymmetry Parameters in \Xi_{c}^{0}\to \X^{-}\pi^{+}

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    Using the CLEO II detector at the Cornell Electron Storage Ring we have measured the Ξc0\Xi_c^{0} decay asymmetry parameter in the decay Ξc0Ξπ+\Xi_c^{0} \to \Xi^{-} \pi^+. We find αΞc0αΞ=0.26±0.18(stat)0.04+0.05(syst)\alpha_{\Xi_c^{0}} \alpha_{\Xi} = 0.26 \pm 0.18{(stat)}^{+0.05}_{-0.04}{(syst)}, using the world average value of αΞ=0.456±0.014\alpha_{\Xi} = -0.456 \pm 0.014 we obtain αΞc0=0.56±0.39(stat)0.09+0.10(syst)\alpha_{\Xi_c^{0}} = -0.56 \pm 0.39{(stat)}^{+0.10}_{-0.09}{(syst)}. The physically allowed range of a decay asymmetry parameter is 1<α<+1-1<\alpha<+1. Our result prefers a negative value: αΞc0\alpha_{\Xi_c^{0}} is <0.1<0.1 at the 90% CL. The central value occupies the middle of the theoretically expected range but is not yet precise enough to choose between models.Comment: 10 pages postscript, also available through http://w4.lns.cornell.edu/public/CLN

    Measurement of the Mass Splittings between the bbˉχb,J(1P)b\bar{b}\chi_{b,J}(1P) States

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    We present new measurements of photon energies and branching fractions for the radiative transitions: Upsilon(2S)->gamma+chi_b(J=0,1,2). The masses of the chi_b states are determined from the measured radiative photon energies. The ratio of mass splittings between the chi_b substates, r==(M[J=2]-M[J=1])/(M[J=1]-M[J=0]) with M the chi_b mass, provides information on the nature of the bbbar confining potential. We find r(1P)=0.54+/-0.02+/-0.02. This value is in conflict with the previous world average, but more consistent with the theoretical expectation that r(1P)<r(2P); i.e., that this mass splittings ratio is smaller for the chi_b(1P) triplet than for the chi_b(2P) triplet.Comment: 11 page postscript file, postscript file also available through http://w4.lns.cornell.edu/public/CLN

    Equations for the estimation of strong ground motions from shallow crustal earthquakes using data from Europe and the Middle East : vertical peak ground acceleration and spectral acceleration

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    This article presents equations for the estimation of vertical strong ground motions caused by shallow crustal earthquakes with magnitudes M w 5 and distance to the surface projection of the fault less than 100km. These equations were derived by weighted regression analysis, used to remove observed magnitude-dependent variance, on a set of 595 strong-motion records recorded in Europe and the Middle East. Coefficients are included to model the effect of local site effects and faulting mechanism on the observed ground motions. The equations include coefficients to model the observed magnitude-dependent decay rate. The main findings of this study are that: short-period ground motions from small and moderate magnitude earthquakes decay faster than the commonly assumed 1/r, the average effect of differing faulting mechanisms is similar to that observed for horizontal motions and is not large and corresponds to factors between 0.7 (normal and odd) and 1.4 (thrust) with respect to strike-slip motions and that the average long-period amplification caused by soft soil deposits is about 2.1 over those on rock sites

    Trends in autoionization of Rydberg states converging to the 4s threshold in the Kr-Rb⁺-Sr²⁺ isoelectonic sequence: theory and experiment

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    We have measured the photoabsorption spectra of the Kr-like ions Rb+ and Sr2+ at photon energies corresponding to the excitation of 4s-np resonances using, the dual laser plasma photoabsorption technique. Dramatic changes in the line profiles, with increasing ionization and also proceeding along the Rydberg series of each ion, are observed and explained by the trends in 4s-transition amplitudes computed within a framework of configuration-interaction Pauli-Fock calculations. Total photoionization cross sections show very good agreement with relative absorption data extracted from the measured spectra

    Common variants near MC4R are associated with fat mass, weight and risk of obesity.

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    To identify common variants influencing body mass index (BMI), we analyzed genome-wide association data from 16,876 individuals of European descent. After previously reported variants in FTO, the strongest association signal (rs17782313, P = 2.9 x 10(-6)) mapped 188 kb downstream of MC4R (melanocortin-4 receptor), mutations of which are the leading cause of monogenic severe childhood-onset obesity. We confirmed the BMI association in 60,352 adults (per-allele effect = 0.05 Z-score units; P = 2.8 x 10(-15)) and 5,988 children aged 7-11 (0.13 Z-score units; P = 1.5 x 10(-8)). In case-control analyses (n = 10,583), the odds for severe childhood obesity reached 1.30 (P = 8.0 x 10(-11)). Furthermore, we observed overtransmission of the risk allele to obese offspring in 660 families (P (pedigree disequilibrium test average; PDT-avg) = 2.4 x 10(-4)). The SNP location and patterns of phenotypic associations are consistent with effects mediated through altered MC4R function. Our findings establish that common variants near MC4R influence fat mass, weight and obesity risk at the population level and reinforce the need for large-scale data integration to identify variants influencing continuous biomedical traits
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