Radiative Ml capture in light nuclei

The importance of semi-direct processes in E1 and E2 capture reactions has been well documented. Little is known, however, about M1 capture although a vast body of data indicates a non-statistical nature. We discuss here the importance of the semi-direct M1 process and concentrate in particular on recent experimental results claiming that the M 1 strength in²⁹Si isnearly one order of magnitude smaller than in ²⁸Si, the target nucleus. We use shell model arguments to demonstrate that this reduction is indeed consistent with the semi-direct reaction process and that other mechanisms like2p-2h fragmentation and phonon coupling are not likely to be instrumental in elucidating further the non-statistical nature of the²⁸Si+n reaction.     

Ergodicity for a weakly damped stochastic non-linear Schrödinger equation

We study a damped stochastic non-linear Schr?dinger (NLS) equation driven by an additive noise. It is white in time and smooth in space. Using a coupling method, we establish convergence of the Markov transition semi-group toward a unique invariant probability measure. This kind of method was originally developed to prove exponential mixing for strongly dissipative equations such as the Navier-Stokes equations. We consider here a weakly dissipative equation, the damped nonlinear Schr?dinger equation in the one-dimensional cubic case. We prove that the mixing property holds and that the rate of convergence to equilibrium is at least polynomial of any power.     

Photoresponse at the semiconductor-electrolyte junction: Influence of the space charge region width

By varying the potential applied to a semiconductor-electrolyte junction its spectral response is modified. The definition of a reduced parameter from the ratio between two spectral responses at two different potentials is achieved. A quantitative analysis of the behaviour of the illuminated junction is then possible, as well as a comparison with the theoretical Gärtner model without the knowledge of the incident photon flux. The experimental support is provided by the n-GaP-1M HClO₄ junction where the semiconductor presents an indirect and a direct energy transition. Thus a spectral region is determined where the Gärtner model and the experimental spectrum coincide and a value of the minority carrier diffusion length (L=0.31μm) is deduced.     

Core polarization effects and giant quadropole resonances in the A ≈ 90 region

The existence, in A ≈ 90 nuclei, of large E2 core polarization effects evident from experimental and shell model fits to decay rates is examined in two independent model calculations: a linearized Hartree-Fock calculation studying the nuclear response function and a macroscopic model involving excitations of giant quadrupole resonances. Both investigations confirm the need for large renormalization of proton and neutron E2 effective charges consistent with the recently discovered isoscalar and isovector giant quadrupole resonances.     

Effects beyond first-order perturbation theory in the polarization charges forE4 transitions

Recent spectroscopy and electron scattering measurements indicate that severalE4 transitions in thef-p shell are severely retarded compared to shell model estimates. We examine whether core polarization mechanisms could be invoked to explain these anomalousE4 transitions and conclude that open shell effects wellbeyond core polarization are necessary to explain the data.     

Can spin-flip quadrupole resonances be observed?

Shell model calculations ofJ=2⁺,S=0 andS=1 states indicate that the spin flip quadrupole strength is much more fragmented than itsS=0 analog, at least in light nuclei. A sum rule technique is then used to study the coexistence betweenS=0 andS=1 states; it illustrates why theS=0 strength is fairly immune to changes in the noncentral part of the nuclear interaction. In¹⁶O, someE2 spin flip strength is predicted to lie in the 40 MeV region where it could be located by inelastic electron and pion scattering experiments.     

Hydrogen-bond accepting strength of protonated nicotine

Recent crystal structures of nicotine bound to the acetylcholine binding protein (AChBP) ended a long debate confirming that the pyridine nitrogen of nicotine is indeed hydrogen-bonded to receptor residues through a bridging water molecule. Here, we describe the first direct experimental evaluation of the hydrogen-bond affinity of the nicotinium pyridine nitrogen. The equilibrium constant of its association with a phenol is 1 order of magnitude greater than the association of the acetylcholine carbonyl oxygen.