Multi-hadron states in Lattice QCD spectroscopy

The ability to reliably measure the energy of an excited hadron in Lattice QCD simulations hinges on the accurate determination of all lower-lying energies in the same symmetry channel. These include not only single-particle energies, but also the energies of multi-hadron states. This talk deals with the determination of multi-hadron energies in Lattice QCD. The group-theoretical derivation of lattice interpolating operators that couple optimally to multi-hadron states is described. We briefly discuss recent algorithmic developments which allow for the efficient implementation of these operators in software, and present numerical results from the Hadron Spectrum Collaboration.Comment: 5 pages, 3 figures, talk given at Hadron 2009, Tallahassee, Florida, December 1, 200

The heavy quark's self energy from moving NRQCD on the lattice

We present a calculation of the heavy quark's self energy in moving NRQCD to one-loop in perturbation theory. Results for the energy shift and external momentum renormalisation are discussed and compared with non-perturbative results. We show that the momentum renormalisation is small, which is the result of a remnant of re-parameterisation invariance on the lattice.Comment: Talk given at Lattice2004(heavy), Fermilab, June 21-26, 200

Rotational Dynamics of Organic Cations in CH3NH3PbI3 Perovskite

Methylammonium lead iodide (CH3NH3PbI3) based solar cells have shown impressive power conversion efficiencies of above 20%. However, the microscopic mechanism of the high photovoltaic performance is yet to be fully understood. Particularly, the dynamics of CH3NH3+ cations and their impact on relevant processes such as charge recombination and exciton dissociation are still poorly understood. Here, using elastic and quasi-elastic neutron scattering techniques and group theoretical analysis, we studied rotational modes of the CH3NH3+ cation in CH3NH3PbI3. Our results show that, in the cubic (T > 327K) and tetragonal (165K < T < 327K) phases, the CH3NH3+ ions exhibit four-fold rotational symmetry of the C-N axis (C4) along with three-fold rotation around the C-N axis (C3), while in orthorhombic phase (T < 165K) only C3 rotation is present. Around room temperature, the characteristic relaxation times for the C4 rotation is found to be ps while for the C3 rotation ps. The -dependent rotational relaxation times were fitted with Arrhenius equations to obtain activation energies. Our data show a close correlation between the C4 rotational mode and the temperature dependent dielectric permittivity. Our findings on the rotational dynamics of CH3NH3+ and the associated dipole have important implications on understanding the low exciton binding energy and slow charge recombination rate in CH3NH3PbI3 which are directly relevant for the high solar cell performance

STR-805: EXPERIMENTAL EVALUATION OF THE ROBUSTNESS OF WT CONNECTIONS UNDER QUASI-DYNAMIC LOAD

Flexible (simple) shear connections commonly used in steel-framed buildings are very economical and are relatively easy to fabricate. These connections are used for shear resistance, but recent studies have shown that they are capable of sustaining an interaction of rotational and axial load demand necessary for steel-framed building structures to help resist collapse in the event of unanticipated damage scenarios. The objective of this paper is to outline and discuss an experimental effort designed to evaluate the robustness of flexible WT connections. The experimental program included twelve full-scale tests of a system consisting of two wide flange beams connected to a central wide flange column stub by means of the WT connections. Three, four, and five bolt configurations were tested. The system was subjected to a quasi-dynamic loading scenario simulating the loss of a central support column. The experimental testing provides important information regarding the ability of these connections to sustain large rotational demands in conjunction with axial tension forces generated through geometric stiffness (catenary) effects when subjected to rapidly applied vertical loads

STR-806: EXPERIMENTAL EVALUATION OF THE ROBUSTNESS OF SINGLE PLATE SHEAR CONNECTIONS UNDER QUASI-DYNAMIC LOAD

Flexible (simple) shear connections commonly used in steel-framed buildings are very economical and are relatively easy to fabricate. These connections are used for shear resistance, but recent studies have shown that they are capable of sustaining an interaction of rotational and axial load demand necessary for steel-framed building structures to help resist collapse in the event of unanticipated damage scenarios. The objective of this paper is to outline and discuss an experimental effort designed to evaluate the robustness of single plate shear connections under a quasi-dynamic loading scenario simulating the loss of a central column. The experimental program included eleven full-scale tests of a system consisting of two wide flange beams connected to a central wide flange column stub by means of the shear plate connections. Three, four, and five bolt configurations were tested, and two of the tests utilized galvanized bolts. The experimental testing provides important information regarding the ability of these connections to sustain large rotational demands in conjunction with axial tension forces generated through geometric stiffness (catenary) effects when subjected to rapidly applied vertical loads

The excited hadron spectrum in lattice QCD using a new method of estimating quark propagation

Progress in determining the spectrum of excited baryons and mesons in lattice QCD is described. Large sets of carefully-designed hadron operators have been studied and their effectiveness in facilitating the extraction of excited-state energies is demonstrated. A new method of stochastically estimating the low-lying effects of quark propagation is proposed which will allow reliable determinations of temporal correlations of single-hadron and multi-hadron operators.Comment: 5 pages, 4 figures, talk given at Hadron 2009, Tallahassee, Florida, December 1, 200