Exclusive Leptoproduction of rho^0 Mesons from Hydrogen at Intermediate Virtual Photon Energies

Measurements of the cross section for exclusive virtual-photoproduction of rho^0 mesons from hydrogen are reported. The data were collected by the HERMES experiment using 27.5 GeV positrons incident on a hydrogen gas target in the HERA storage ring. The invariant mass W of the photon-nucleon system ranges from 4.0 to 6.0 GeV, while the negative squared four-momentum Q^2 of the virtual photon varies from 0.7 to 5.0 GeV^2. The present data together with most of the previous data at W > 4 GeV are well described by a model that infers the W-dependence of the cross section from the dependence on the Bjorken scaling variable x of the unpolarized structure function for deep-inelastic scattering. In addition, a model calculation based on Off-Forward Parton Distributions gives a fairly good account of the longitudinal component of the rho^0 production cross section for Q^2 > 2 GeV^2.Comment: 10 pages, 6 embedded figures, LaTeX for SVJour(epj) document class. Revisions: curves added to Fig. 1, several clarifications added to tex

Double-Spin Asymmetry in the Cross Section for Exclusive rho^0 Production in Lepton-Proton Scattering

Evidence for a positive longitudinal double-spin asymmetry = 0.24 +-0.11 (stat) +-0.02 (syst) in the cross section for exclusive diffractive rho^0(770) vector meson production in polarised lepton-proton scattering was observed by the HERMES experiment. The longitudinally polarised 27.56 GeV HERA positron beam was scattered off a longitudinally polarised pure hydrogen gas target. The average invariant mass of the photon-proton system has a value of = 4.9 GeV, while the average negative squared four-momentum of the virtual photon is = 1.7 GeV^2. The ratio of the present result to the corresponding spin asymmetry in inclusive deep-inelastic scattering is in agreement with an early theoretical prediction based on the generalised vector meson dominance model.Comment: 10 pages, 4 embedded figures, LaTe

Whatever happened to repeat victimisation?

Crime is concentrated at the individual level (hot dots) as well as at area level (hot spots). Research on repeat victimisation affords rich prevention opportunities but has been increasingly marginalised by policy makers and implementers despite repeat victims accounting for increasing proportions of total crime. The present paper seeks to trigger a resurgence of interest in research and initiatives based on the prevention of repeat victimisation.N/

Developing 1D nanostructure arrays for future nanophotonics

There is intense and growing interest in one-dimensional (1-D) nanostructures from the perspective of their synthesis and unique properties, especially with respect to their excellent optical response and an ability to form heterostructures. This review discusses alternative approaches to preparation and organization of such structures, and their potential properties. In particular, molecular-scale printing is highlighted as a method for creating organized pre-cursor structure for locating nanowires, as well as vapor–liquid–solid (VLS) templated growth using nano-channel alumina (NCA), and deposition of 1-D structures with glancing angle deposition (GLAD). As regards novel optical properties, we discuss as an example, finite size photonic crystal cavity structures formed from such nanostructure arrays possessing highQand small mode volume, and being ideal for developing future nanolasers

A mass spectrometer system for analysis of polar stratospheric aerosols

A balloon-borne mass spectrometer system has been flown successfully to determine the chemical composition of polar stratospheric aerosols over northern Scandinavia. The experiment combines an aerodynamic lens which collimates the aerosols into a narrow beam, a small sphere in which they evaporate, and a mass spectrometer for gas analysis. High-speed differential pumping by two liquid helium pumps effectively lowers the presence of ambient gases without affecting the particles of the beam. Field measurements and aerosol studies inside a large cryo-chamber have shown that the concept of particle focusing, evaporation and subsequent mass spectrometric gas analysis is a reliable technique to determine the molecular composition of aerosols especially in polar stratospheric clouds. (C) 2002 American Institute of Physics

A mass spectrometer system for analysis of polar stratospheric aerosols

A balloon-borne mass spectrometer system has been flown successfully to determine the chemical composition of polar stratospheric aerosols over northern Scandinavia. The experiment combines an aerodynamic lens which collimates the aerosols into a narrow beam, a small sphere in which they evaporate, and a mass spectrometer for gas analysis. High-speed differential pumping by two liquid helium pumps effectively lowers the presence of ambient gases without affecting the particles of the beam. Field measurements and aerosol studies inside a large cryo-chamber have shown that the concept of particle focusing, evaporation and subsequent mass spectrometric gas analysis is a reliable technique to determine the molecular composition of aerosols especially in polar stratospheric clouds. (C) 2002 American Institute of Physics