Avoided crossing resonances: structural and dynamical aspects

We examine structural and dynamical properties of quantum resonances associated with an avoided crossing and identify the parameter shifts where these properties attain maximal or extreme values, first at a general level, and then for a two-level system coupled to a harmonic oscillator, of the type commonly found in quantum optics. Finally the results obtained are exemplified and applied to optimize the fidelity and speed of quantum gates in trapped ions.Comment: 4 pages, 1 figur

Flexible Parametrization of Generalized Parton Distributions: The Chiral-Odd Sector

We present a physically motivated parameterization of the chiral-odd generalized parton distributions. The parametrization is an extension of our previous one in the chiral-even sector which was based on the reggeized diquark model. While for chiral even generalized distributions a quantitative fit with uncertainty estimation can be performed using deep inelastic scattering data, nucleon electromagnetic, axial and pseudoscalar form factors measurements, and all available deeply virtual Compton scattering data, the chiral-odd sector is far less constrained. While awaiting the analysis of measurements on pseudoscalar mesons exclusive electroproduction which are key for the extraction of chiral odd GPDs, we worked out a connection between the chiral-even and chiral-odd reduced helicity amplitudes using Parity transformations. The connection works for a class of models including two-components models. This relation allows us to estimate the size of the various chiral odd contributions and it opens the way for future quantitative fits.Comment: 35 pages, 18 figures, text changes, corrected typos, added fig.

Effect of tail-fin span on stability and control characteristics of a Canard-controlled missile at supersonic Mach numbers

An experimental wind-tunnel investigation was conducted at Mach numbers from 1.60 to 3.50 to obtain the longitudinal and lateral-directional aerodynamic characteristics of a circular, cruciform, canard-controlled missile with variations in tail-fin span. In addition, comparisons were made with the experimental aerodynamic characteristics using three missile aeroprediction programs: MISSILE1, MISSILE2, and NSWCDM. The results of the investigation indicate that for the test Mach number range, canard roll control at low angles of attack is feasible on tail-fin configurations with tail-to-canard span ratios of less than or equal to 0.75. The conards are effective pitch and yaw control devices on each tail-fin span configuration tested. Programs MISSILE1 and MISSILE2 provide very good predictions of longitudinal aerodynamic characteristics and fair predictions of lateral-directional aerodynamic characteristics at low angles of attack, with MISSILE2 predictions generally in better agreement with test data. Program NSWCDM provides good longitudinal and lateral-directional aerodynamic predictions that improve with increases in tail-tin span

Mode stability in delta Scuti stars: linear analysis versus observations in open clusters

A comparison between linear stability analysis and observations of pulsation modes in five delta Scuti stars, belonging to the same cluster, is presented. The study is based on the work by Michel et al. (1999), in which such a comparison was performed for a representative set of model solutions obtained independently for each individual star considered. In this paper we revisit the work by Michel et al. (1999) following, however, a new approach which consists in the search for a single, complete, and coherent solution for all the selected stars, in order to constrain and test the assumed physics describing these objects. To do so, refined descriptions for the effects of rotation on the determination of the global stellar parameters and on the adiabatic oscillation frequency computations are used. In addition, a crude attempt is made to study the role of rotation on the prediction of mode instabilities.The present results are found to be comparable with those reported by Michel et al. (1999). Within the temperature range log T_eff = 3.87-3.88 agreement between observations and model computations of unstable modes is restricted to values for the mixing-length parameter alpha_nl less or equal to 1.50. This indicates that for these stars a smaller value for alpha_nl is required than suggested from a calibrated solar model. We stress the point that the linear stability analysis used in this work still assumes stellar models without rotation and that further developments are required for a proper description of the interaction between rotation and pulsation dynamics.Comment: 8 pages, 4 figures, 3 tables. (MNRAS, in press