Large enhancement of the sub-barrier fusion probability for a halo nucleus

The fusion-fission cross sections of the 4He+238U and 6He+238U systems have been measured, at Louvain-la-Neuve, for energies around and below the Coulomb barrier, using an array of Si detectors surrounding a UF4 target. The data taken with 4He are in good agreement with previous data and with the coupled channel fusion calculation performed with ECIS. The 6He data show a regular trend with a large enhancement below the barrier which is attributed to the halo structure of the 6He nucleus.     

Determination of the N=16 shell closure at the oxygen drip line

The neutron unbound ground state of (25)O (Z=8, N=17) was observed for the first time in a proton knockout reaction from a (26)F beam. A single resonance was found in the invariant mass spectrum corresponding to a neutron decay energy of 770_+20(-10) keV with a total width of 172(30) keV. The N=16 shell gap was established to be 4.86(13) MeV by the energy difference between the nu1s(1/2) and nu0d(3/2) orbitals. The neutron separation energies for (25)O agree with the calculations of the universal sd shell model interaction. This interaction incorrectly predicts an (26)O ground state that is bound to two-neutron decay by 1 MeV, leading to a discrepancy between the theoretical calculations and experiment as to the particle stability of (26)O. The observed decay width was found to be on the order of a factor of 2 larger than the calculated single-particle width using a Woods-Saxon potential.     

Resilience in reaction-diffusion systems

Reaction-diffusion systems with zero-flux Neumann boundariesare widely used to model various kinds of interaction in, forexample, the scientific fields of ecology, biology, chemistry,medicine and industry. The physical systems within these fieldsare often known to be (conditionally or unconditionally) resilientwith respect to shocks, disturbances or catastrophies in theimmediate environment. In order to be good mathematical modelsof such situations the reaction-diffusion systems must havethe same resilient or asymptotic behaviour as that of the physicalsituation. Three fundamentally different kinds of reaction termsare usually distinguished according to the entry signs of thereaction Jacobian: mutualism, mixed (predator-prey) interactionand competition. The asymptotic stability (in the Poincarésense) of mutualistic systems has already been studied extensively,but the results cannot be generalized (globally) to the othertwo fundamental types, which are not order-preserving. A partial(local) generalization is, however given here for these twotypes, involving simple Jacobian inequalities and knowledge(often prompted by the underlying physical situation) of invariantsets in solution space. The return time of resilient systemsand the approach rate of asymptotically stable solutions arealso estimated.     

The photocurrent response of human cones is fast and monophasic

Background  

The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses.     

Efficient Hydrolysis of RNA by a PNA - Diethylenetriamine Adduct

The introduction of a urea bond linking a protected diethylenetriamine (DETA) unit and the terminal amino group of a resin-bound peptide nucleic acid (PNA) decamer gave access to a PNA - DETA adduct (shown here), which hydrolyzed the target 25-mer RNA rapidly and sequence specifically.