Exclusive Production of Neutral Vector Mesons at the Electron-Proton Collider HERA

The first five years of operation of the multi-purpose experiments ZEUS and H1 at the electron-proton storage ring facility HERA have opened a new era in the study of vector-meson production in high-energy photon-proton interactions. The high center-of-mass energy available at this unique accelerator complex allows investigations in hitherto unexplored kinematic regions, providing answers to long-standing questions concerning the energy-dependence of the rho, omega, phi, and J/psi production cross sections. The excellent angular acceptance of these detectors, combined with that of specialized tagging detectors at small production angles, has permitted measurements of elastic and inelastic production processes for both quasi-real photons and those of virtuality exceeding the squared mass of the vector meson. This report provides a quantitative picture of the present status of these studies, comparing them to the extensive measurements in this field at lower energies and summarizing topical developments in theoretical work motivated by the new data.Comment: This replacement serves to correct an error in Eq. 3.41. An improved version of this review will appear in book form as Nr. 140 in the series Springer Tracts in Modern Physics on 6.October. 90 pages including 34 figure

Flutter of asymmetrically swept wings

Two formulations of the oblique wing flutter problem are presented; one formulation allows only simple wing bending deformations and rigid body roll as degrees of freedom, while the second formulation includes a more complex bending-torsional deformation together with the roll freedom. Flutter is found to occur in two basic modes. The first mode is associated with wing bending-aircraft roll coupling and occurs at low values of reduced frequency. The second instability mode closely resembles a classical bending-torsion wing flutter event. This latter mode occurs at much higher reduced frequencies than the first. The occurrence of the bending-roll coupling mode is shown to lead to lower flutter speeds while the bending-torsion mode is associated with higher flutter speeds. The ratio of the wing mass moment of inertia in roll to the fuselage roll moment of inertia is found to be a major factor in the determination of which of the two instabilities is critical

Cross-Correlation of the Cosmic Microwave Background with Radio Sources: Constraints on an Accelerating Universe

We present a new limit on the cosmological constant based on the absence of correlations between the cosmic microwave background (CMB) and the distribution of distant radio sources. In the cosmological constant-cold dark matter models currently favored, such correlations should have been produced via the integrated Sachs-Wolfe effect, assuming that radio sources trace the local (z=1) matter density. We find no evidence of correlations between the COBE 53Hz microwave map and the NVSS 1.4 GHz radio survey. The implied 95% CL limit on the cosmological constant is Lambda < 0.74, in marginal agreement with the values suggested by recent measurements of the CMB anisotropy and type-IA supernovae observations, 0.6 < Lambda < 0.7. If the cosmological model does lie in this range, then the integrated Sachs-Wolfe effect should be detectable with upcoming CMB maps and radio surveys.Comment: 5 pages; 3 figures; submitted to PR

Cosmic concordance and the fine structure constant

Recent measurements of a peak in the angular power spectrum of the cosmic microwave background appear to suggest that geometry of the universe is close to being flat. But if other accepted indicators of cosmological parameters are also correct then the best fit model is marginally closed, with the peak in the spectrum at larger scales than in a flat universe. Such observations can be reconciled with a flat universe if the fine structure constant had a lower value at earlier times, which would delay the recombination of electrons and protons and also act to suppress secondary oscillations as observed. We discuss evidence for a few percent increase in the fine structure constant between the time of recombination and the present.Comment: 12 Page