Coulomb scattering of quantum dipoles in QED

We calculate the total scattering cross-section of a dynamical quantum electrically neutral dipole in QED of the infinitely heavy charge and of the infinitely heavy dipole in the leading order in electromagnetic coupling constant.Comment: 7 pages, no figure

On the Determination of ∣Vub∣|V_{ub}| from Inclusive Semileptonic Decay Spectra

We propose a model independent method to determine $|V_{ub}|$ from the energy spectrum of the charged lepton in inclusive semileptonic $B$ decays. The method includes perturbative QCD corrections as well as nonperturbative ones.Comment: LaTeX, 19 pages, 8 figures appended after \end{document} as uu-encoded and compressed .eps files, uses epsf, Technion-PH-94/9, CERN-TH.7308/9

Further Discoveries of 12CO in Low Surface Brightness Galaxies

Using the IRAM 30m telescope we have obtained seven new, deep CO J(1-0) and J(2-1) observations of low surface brightness (LSB) galaxies. Five of the galaxies have no CO detected to extremely low limits (0.1-0.4 K km/s at J(1-0)), while two of the galaxies, UGC 01922 and UGC 12289, have clear detections in both line transitions. When these observations are combined with all previous CO observations taken of LSB systems, we compile a total of 34 observations, in which only 3 galaxies have had detections of their molecular gas. Comparing the LSB galaxies with and without CO detections to a sample of high surface brightness (HSB) galaxies with CO observations indicates that it is primarily the low density of baryonic matter within LSB galaxies which is causing their low CO fluxes. Finally, we note that one of the massive LSB galaxies studied in this project, UGC 06968 (a Malin-1 `cousin'), has upper limits placed on both M_H2 and M_H2/M_HI which are 10-20 times lower than the lowest values found for any galaxy (LSB or HSB) with similar global properties. This may be due to an extremely low temperature and metallicity within UGC 06968, or simply due to the CO distribution within the galaxy being too diffuse to be detected by the IRAM beam.Comment: 18 pages, 8 figures, 4 tables. Accepted by Ap

Calculation of 1/m^3 terms in the total semileptonic width of D mesons.

We calculate the 1/$m^3_c$ corrections in the inclusive semileptonic widths of $D$ mesons. We show that these are due to the novel penguin type operators that appear at this level in the transition operator. Taking into account the nonperturbative corrections leads to the predicted value of the semileptonic width significantly lower than the experimental value. The $1/m^3_c$ worsen the situation or at the very least, within uncertainty, give small contribution. We indicate possible ways out. It seems most probable that violations of duality are noticeable in the energy range characteristic to the inclusive decays in the charm family. Theoretically these deviations are related to divergence of the high-order terms in the power expansion in the inverse heavy quark mass.Comment: Final version accepted for publication in Physical Review D (19 pages, 5 figures appended as two PS files at the end of the LATEX file

Aspects Of Heavy Quark Theory

Recent achievements in the heavy quark theory are critically reviewed. The emphasis is put on those aspects which either did not attract enough attention or cause heated debates in the current literature. Among other topics we discuss (i) basic parameters of the heavy quark theory; (ii) a class of exact QCD inequalities; (iii) new heavy quark sum rules; (iv) virial theorem; (v) applications (|V_cb| from the total semileptonic width and from the B->D* transition at zero recoil). In some instances new derivations of the previously known results are given, or new aspects addressed. In particular, we dwell on the exact QCD inequalities. Furthermore, a toy model is considered that may shed light on the controversy regarding the value of the kinetic energy of heavy quarks obtained by different methods.Comment: 67 pages, 6 Figures; plain LaTeX. Changes: Some equations in Sect.4 related to spin-nonsinglet sum rules are corrected. The references are updated

Energy dissipation of a friction damper: experimental validation

Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised orcontrolled. In this work one of the positive sides of friction is investigated: friction damping. The frictioninherently present in a system can be positively used to increase the total damping or alternatively, a frictiondamper can be designed. Friction dampers can be a cheap and efficient way to reduce the vibration levels ofa wide range of mechanical systems.In the present paper the conclusions of previous analytic and numericalresults regarding friction damping are validated with results of laboratory experiments, where the energydissipated through friction is measured. The test set-up consists of a mass sliding on parallel ball-bearings,where additional friction is created by a sledge attached to the mass, which is pre-stressed against a frictionplate. No care has been taken to ensure pure dry (Coulomb) friction. Nevertheless, the measured energydissipation is in good agreement with the theoretical results for Coulomb friction

Energy dissipation of a friction damper: experimental validation

Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised orcontrolled. In this work one of the positive sides of friction is investigated: friction damping. The frictioninherently present in a system can be positively used to increase the total damping or alternatively, a frictiondamper can be designed. Friction dampers can be a cheap and efficient way to reduce the vibration levels ofa wide range of mechanical systems.In the present paper the conclusions of previous analytic and numericalresults regarding friction damping are validated with results of laboratory experiments, where the energydissipated through friction is measured. The test set-up consists of a mass sliding on parallel ball-bearings,where additional friction is created by a sledge attached to the mass, which is pre-stressed against a frictionplate. No care has been taken to ensure pure dry (Coulomb) friction. Nevertheless, the measured energydissipation is in good agreement with the theoretical results for Coulomb friction