On the forces transmitted to a vibrating cylinder by a blowing fluid

Summary The measuring apparatus used for experimental wind tunnel studies is described together with the test procedure and salient results. After an analysis of the results, a mechanical model is developed to explain the nature of the phenomenon.

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Sommario Si descrive l'apparato di misura utilizzato per le ricerche sperimentali eseguite in camera a vento al fine di determinare le forze esercitate da una vena fluida su un cilindro libero di vibrare. Si espongono le modalità di prova ed i risultati più salienti. Dopo un'analisi dei risultati si elabora un modello meccanico per interpretare la natura del fenomeno.

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This study forms part of a project that has been carried out jointly by A. Salvi & C. SpA and the Institute of Applied Mechanics, Milan Polytechnic. The Institute of Applied Mechanics received a CNR subsidy to take part in this project.     

Universality of One-Dimensional Fermi Systems,I. Response Functions and Critical Exponents

The critical behavior of one-dimensional interacting Fermi systems is expected to display universality features, called Luttinger liquid behavior. Critical exponents and certain thermodynamic quantities are expected to be related among each other by model-independent formulas. We establish such relations, the proof of which has represented a challenging mathematical problem, for a general model of spinning fermions on a one dimensional lattice; interactions are short ranged and satisfy a positivity condition which makes the model critical at zero temperature. Proofs are reported in two papers: in the present one, we demonstrate that the zero temperature response functions in the thermodynamic limit are Borel summable and have anomalous power-law decay with multiplicative logarithmic corrections. Critical exponents are expressed in terms of convergent expansions and depend on all the model details. All results are valid for the special case of the Hubbard model.     

Evidence for the production of thermal muon pairs with masses above 1 GeV/c 2 in 158 A GeV indium-indium collisions

The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c ² produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c ², rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c ² to be of largely partonic origin, when radial flow has not yet built up.     

Study of DyFe12−xMx compounds by57Fe and161Dy Mössbauer spectroscopy

DyFe_12?xM_x (M=Si,Ti,Cr) were studied with⁵⁷Fe and¹⁶¹Dy Mössbauer spectroscopy. The deduced coupling constants J_RFe of these compounds are about equal. It is found that Si is substituting one particular Fe-site, while Cr is substituting Fe randomly. In DyFe₁₀Si₂ two Fe-sites favour a c-axis anisotropy, while the third one favours the basal plane.     

Functional Integral Construction of the Massive Thirring model: Verification of Axioms and Massless Limit

We present a complete construction of a Quantum Field Theory for the Massive Thirring model by following a functional integral approach. This is done by introducing an ultraviolet and an infrared cutoff and by proving that, if the “bare” parameters are suitably chosen, the Schwinger functions have a well defined limit satisfying the Osterwalder-Schrader axioms, when the cutoffs are removed. Our results, which are restricted to weak coupling, are uniform in the value of the mass. The control of the effective coupling (which is the main ingredient of the proof) is achieved by using the Ward Identities of the massless model, in the approximated form they take in the presence of the cutoffs. As a byproduct, we show that, when the cutoffs are removed, theWard Identities have anomalies which are not linear in the bare coupling. Moreover, we find for the interacting propagator of the massless theory a closed equation which is different from that usually stated in the physical literature.