The Nambu–Jona–Lasinio model of light nuclei

The Nambu–Jona–Lasinio model of the deuteron suggested by Nambu and Jona–Lasinio (Phys. Rev. 124 (1961) 246) is formulated from the first principles of QCD. The deuteron appears as a neutron–proton collective excitation, i.e. a Cooper np–pair, induced by a phenomenological local four–nucleon interaction in the nuclear phase of QCD. The model describes the deuteron coupled to itself, nucleons and other particles through one–nucleon loop exchanges providing a minimal transfer of nucleon flavours from initial to final nuclear states and accounting for contributions of nucleon–loop anomalies which are completely determined by one–nucleon loop diagrams. The dominance of contributions of nucleon–loop anomalies to effective Lagrangians of low–energy nuclear interactions is justified in the large N _C expansion, where N _C is the number of quark colours. Received: 10 March 2000     

Surface tension effects in the zero gravity inflow of a drop into a fluid

As a drop of fluid is deposited on the surface of a miscible fluid (that we call the solvent), it undergoes a strong pulling due to its surface rupture and it acquires a kinetic energy independently of gravity. For the drop and the solvent being of the same fluid we observe a drop injection at an initial velocity which scales as the square root of the surface tension of the drop against air. Once injected, the drop develops a transverse instability giving rise to an expanding ring. Viscosity terminates the process and stops the ring. We show that the final ring height follows a scaling law whereas two asymptotical scaling regimes can be identified for the ring radius. Received 31 August 1999     

Symmetry alteration of ensemble return distribution in crash and rally days of financial markets

We select the n stocks traded in the New York Stock Exchange and we form a statistical ensemble of daily stock returns for each of the k trading days of our database from the stock price time series. We study the ensemble return distribution for each trading day and we find that the symmetry properties of the ensemble return distribution drastically change in crash and rally days of the market. In crash and rally days, the distribution becomes asymmetric. In particular for crashes the positive tail is steeper than the negative one whereas the reverse is observed in rally days. Received 25 February 2000     

New investigation of the decay of the high-spin isomer in 151Er

The decay of the T _1/2 = 420 ns isomer in ¹⁵¹Er has been reinvestigated. The multipolarities of the decaying transitions have been established by measuring the electron conversion coefficients. An I ^π = 67/2⁻ assignment is proposed for this isomer with a π[h ₁₁^2/4 d ₃^2/1 d ₅^2/−1]⊗ν[f _7/2 h _9/2 h ₁₁^2/−1] configuration.     

Experimental evidence and consequences of rare events in quantum tunneling

Tiny spatial fluctuations of tunnel barrier parameters are shown to have dramatic consequences on the statistical properties of quantum tunneling. A direct experimental evidence is provided that the tunnel current through metal-oxide junctions, imaged at a nanometric scale, exhibits broad statistical distributions extending over more than 4 orders of magnitude. Striking effects of broad current distributions are shown: the total tunnel transmission is dominated by few highly transmitting sites and the typical current density varies strongly with the size of the junction. Moreover, self-averaging of the tunnel current fluctuations occurs only for unexpectedly large junction areas. Received 1 April 1999     

Accurate masses of unstable rare-earth isotopes by ISOLTRAP

Direct mass measurements of neutron-deficient rare-earth isotopes in the vicinity of ¹⁴⁶Gd were performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. This paper reports on the measurement of more than 40 isotopes of the elements praseodymium, neodymium, promethium, samarium, europium, dysprosium and holmium, that have been measured with a typical accuracy of m 14 keV. An atomic mass evaluation has been performed taking into account other experimental mass values via a least-squares adjustment. The results of the adjustment are discussed. Received: 18 April 2000 / Accepted: 12 July 2000     

Interfacial reaction kinetics

We study irreversible A-B reaction kinetics at a fixed interface separating two immiscible bulk phases, A and B. Coupled equations are derived for the hierarchy of many-body correlation functions. Postulating physically motivated bounds, closed equations result without the need for ad hoc decoupling approximations. We consider general dynamical exponent z, where is the rms diffusion distance after time t. At short times the number of reactions per unit area, , is 2nd order in the far-field reactant densities . For spatial dimensions dabove a critical value , simple mean field (MF) kinetics pertain, where Q_b is the local reactivity. For low dimensions , this MF regime is followed by 2nd order diffusion controlled (DC) kinetics, , provided . Logarithmic corrections arise in marginal cases. At long times, a cross-over to 1st order DC kinetics occurs: . A density depletion hole grows on the more dilute A side. In the symmetric case (), when the long time decay of the interfacial reactant density, , is determined by fluctuations in the initial reactant distribution, giving . Correspondingly, A-rich and B-rich regions develop at the interface analogously to the segregation effects established by other authors for the bulk reaction . For fluctuations are unimportant: local mean field theory applies at the interface (joint density distribution approximating the product of A and B densities) and . We apply our results to simple molecules (Fickian diffusion, z=2) and to several models of short-time polymer diffusion (z>2). Received 8 June 1998 and Received in final form 10 September 1999     

Strong amplified spontaneous emission and lasing from a narrow-gap RF-excited Ar-He-Xe gas mixture

The performance of a RF excited cw atomic xenon laser at wavelengths of 2.03 μm and 2.65 μm was studied theoretically and experimentally as a function of electrode distance. Results for inter-electrode distances from 2 to 0.25 mm are presented. A high pumping rate resulted in strong 40 mW cw amplified spontaneous emission at 2.65 μm wavelength from the configuration with the smallest distance of 0.25 mm between the electrodes. The maximum laser output of 2.7 W (0.24 W/cm³) was obtained with an active medium volume of 2×15×370 mm³ whereas the maximum specific output of 1.9 W/cm³ was received for an active medium volume of 0.25×2.25×370 mm³. A fluid model of the RF discharge was developed to analyze the laser behavior for different distances between the electrodes. Received: 30 November 1999 / Revised version: 21 April 2000 / Published online: 6 September 2000     

Raman spectroscopy of optical phonons as a probe of GaN epitaxial layer structural quality

We report on Raman scattering measurements of all Raman-active phonons in wurtzite and zinc blende structure GaN epilayers grown on GaAs (001), GaAs (111)A, and GaAs (111)B oriented substrates by means of molecular beam epitaxy (MBE). Raman spectra are taken from these epilayers at room temperature and 77 K in backscattering geometry. The measured values of the phonon frequencies are in agreement with other studies and with lattice dynamic calculations of phonon modes in GaN zinc blende and wurtzite structures. We show that crystal quality is much better in samples grown on GaAs (111) substrates than in samples grown on GaAs (001) substrates. The observation of disorder-activated modes gives information about sample quality. Comparison of the spectra from different thickness epilayers shows that the GaN is more highly disordered close to the substrate, particularly for the (001) substrates. Received 16 July 1999     

Charmonium suppression by gluon bremsstrahlung in p-A and A-B collisions

Prompt gluons are an additional source for charmonium suppression in nuclear collisions, in particular for nucleus-nucleus collisions. These gluons are radiated as bremsstrahlung in N-N collisions and interact inelastically with the charmonium states while the nuclei still overlap. The spectra and mean number <n _g> of the prompt gluons are calculated perturbatively and the inelastic cross section σ_abs ^Ψg is estimated. The integrated cross sections σ(A B →J/ψX) for p-A and A-B collisions and the dependence on transverse energy for S-U and Pb-Pb can be described quantitatively with some adjustment of one parameter <n _g>σ_abs ^Ψg. Received: 20 August 1999