Model for nucleon valence structure functions at allx,allp ⊥ and allQ 2 from the correspondence between QCD and DTU

We propose a simple parametrization of the nucleon valence structure functions at allx, allp _⊥ and allQ ². We use the DTU parton model to fix the parametrization at a reference point (Q ₀ ² =3 GeV²) and we mimic the QCD evolution by replacing the dimensioned parameters of the DTU parton model by functions depending onQ ². Excellent agreement is obtained with existing data.     

Production of a bose einstein condensate of metastable helium atoms

We recently observed a Bose-Einstein condensate in a dilute gas of ⁴He in the 2³S₁ metastable state. In this article, we describe the successive experimental steps which led to the Bose-Einstein transition at 4.7 μK: loading of a large number of atoms in a MOT, efficient transfer into a magnetic Ioffé-Pritchard trap, and optimization of the evaporative cooling ramp. Quantitative measurements are also given for the rates of elastic and inelastic collisions, both above and below the transition. Received 15 October 2001     

Jet model with exclusive parton hadron duality

We discuss a model for hadron jets in hard collisions, in which the observed hadrons originate at the end of a purely hadronic cascade. We assume that this hadronic cascade evolves according to the same laws approximately as a parton cascade in QCD. We obtain a simple relation between hadron and parton final states at an almost exclusive level, which allows in many cases to replace partons by hadrons. As application we discuss jet multiplicities at variable resolution, in particular scaling laws, α _s determination and production of axial vector mesons (A ₁ B, ...).     

A new type of resonances in saturated absorption spectroscopy of 3-level systems

We report the experimental observation of new resonances in saturated absorption spectra of a J = 1 to J = 0 transition of Ne atoms in a static magnetic field. These resonances, which are distinct from the well-known Zeeman and cross-over resonances, result from the modification of stimulated Raman processes by the simultaneous resonant saturation of an optical transition. The light-shifts of the various resonances are also studied.     

Ligand-receptor interactions in chains of colloids: when reactions are limited by rotational diffusion

We discuss the theory of ligand receptor reactions between two freely rotating colloids in close proximity to one other. Such reactions, limited by rotational diffusion, arise in magnetic bead suspensions where the beads are driven into close contact by an applied magnetic field as they align in chainlike structures. By a combination of reaction-diffusion theory, numerical simulations, and heuristic arguments, we compute the time required for a reaction to occur in a number of experimentally relevant situations. We find in all cases that the time required for a reaction to occur is larger than the characteristic rotation time of the diffusion motion tau(rot). When the colloids carry one ligand only and a number n of receptors, we find that the reaction time is, in units of tau(rot), a function simply of n and of the relative surface alpha occupied by one reaction patch alpha = pirC2/(4pir2), where rC is the ligand receptor capture radius and r is the radius of the colloid.     

Ultracold metastable helium: from atoms to exotic molecules

We have written this article in the honor of our friend Vladilen Lethokov, who has produced so many brilliant ideas and results in the field of atomic and molecular physics and with whom we have had frequent unlightening discussions. We hope that the work described here will contribute to illustrate the richness of the field.     

Mechanical Hanle effect

This paper describes an experiment where the Hanle effect in the ground state of an atomic transition is detected, not by a modification of the light absorbed or reemitted by the atoms, but by a modification of the atomic trajectories. The experimental results are compared with the theoretical predictions of two calculations, the first one considering only the steady-state regime, the second one including the effects of the transient phenomena which take place when the atom enters the laser beam.