Dynamical heterogeneity close to the jamming transition in a sheared granular material

The dynamics of a bidimensional dense granular packing under cyclic shear is experimentally investigated close to the jamming transition. Measurement of multipoint correlation functions are produced. The self-intermediate scattering function, displaying slower than exponential relaxation, suggests dynamic heterogeneity. Further analysis of four point correlation functions reveal that the grain relaxations are strongly correlated and spatially heterogeneous, especially at the time scale of the collective rearrangements. Finally, a dynamical correlation length is extracted from a spatiotemporal pattern of mobility. Our experimental results open the way to a systematic study of dynamic correlation functions in granular materials.     

Chiral molecular imprinting in liquid-crystalline network<Superscript>⋆</Superscript>

A cholesteric imprinted elastomer was obtained by cross-linking a nematic side-chain polysiloxane around a chiral template. The template was first linked to some functionalised groups of the polymer via hydrogen-bound interactions, then was removed by washing. The sample was macroscopically oriented during the synthesis; so, both a molecular chirality and a supramolecular phase chirality were topologically imprinted inside the network. Batch rebinding experiments, performed in the presence of the template or of the other enantiomer, showed that the imprinted polymer has a pronounced stereo-selectivity towards the template enantiomer. The rebinding capacity appeared to be greater than an unimprinted mesogenic network as well as than an imprinted non mesogenic one.     

Anisotropy of domain wall resistance

The resistive effect of domain walls in FePd films with perpendicular anisotropy was studied experimentally as a function of field and temperature. The films were grown directly on MgO substrates, which induces an unusual virgin magnetic configuration composed of 60 nm wide parallel stripe domains. This allowed us to carry out the first measurements of the anisotropy of domain wall resistivity in the two configurations of current perpendicular and parallel to the walls. At 18 K, we find 8.2% and 1.3% for the domain wall magnetoresistance normalized to the wall width (8 nm) in these two respective configurations. These values are consistent with the predictions of Levy and Zhang.     

Proton-nucleus elastic scattering at 156 MeV

Cross sections for the elastic scattering of 156 MeV protons on eleven targets ranging from ¹²C to ²⁰⁹Bi were measured and an optical model analysis has been performed. The effect of different optical potentials in DWIA inelastic scattering calculations is shown by some examples.     

Excitation of ΔL = 0 spin-flip transitions in the N = 28 isotones by 201 MeV proton inelastic scattering

The effect of the three-nucleon forces on the triton binding energy (E_T) is investigated. Two different types of three-nucleon potentials are considered, one involving 2π-exchange (V_ππF) and the other involving 2σ-exchange (V_SSF) which is an approximation to 3π exchange. Both V_ππF and V_SSF are constructed using the πN scattering amplitude extrapolated to off (pion) mass shell subject to PCAC. The contribution of V_ππF and V_SSF to e_t are calculated in the first-order perturbation using the triton wave function obtained by solving the Faddeev equations with the Reid soft-core potential. The Fujita-Miyazawa force is also investigated as a special case. We find that the effect of V_ππF on E_T is sensitive to the assumed pionic form factor and is small due to cancellation between the πN s-d wave and p-wave contributions. The effect of V_SSF is also found to be small.     

Inequivalence Magnetique Due a la Presence d'un Atome de Phosphore Asymetrique ou Pseudo-Asymetrique

In phosphinous esters of general formula R? PH(O)OR', the asymmetric phosphorus atom induces magnetic non-equivalence in geminal protons and methyl groups. When alkoxy groups also possess an asymmetric carbon, the presence of the two possible diastereoisomers in equal amounts is proven by ³¹P and ¹H NMR. ³¹P NMR reveals that the phosphorus atom in phosphonous esters R? P(O·C₄H₉-s)₂ of racemic sec. butyl alcohol, is a centre of pseudo-asymmetry.     

201 MeV proton excitation of giant resonances in 208Pb: Macroscopic and microscopic analysis

The region of the giant resonances in ²⁰⁸Pb has been investigated by inelastic scattering of 201 MeV protons. To test the analysis, angular distributions were measured for the low-lying 3^?, 5^?, 2⁺ and 4⁺ collective states. The giant isoscalar quadrupole resonance (ISGQR) is split into two structures, one at 9.0 MeV with a full width at half-maximum Γ = 1.0 MeV, the other one at 10.6 MeV (Γ = 2.0 MeV), with fine structures at 8.9, 9.3, 10.1, 10.6 and 11 MeV. A macroscopic analysis using the distorted-wave Born approximation (DWBA) leads for the low-lying collective levels, as well as for the ISGQR, to transition probabilities too small by a factor of two, compared with those obtained in other reactions. Microscopic analysis using the distorted-wave impulse approximation (DWIA), with three different sets of random phase approximation (RPA) transition densities, is in very good agreement with the data. At forward angles, in the 12 to 16 MeV excitation energy region, a strong resonance at 13.5 MeV (Γ = 3.6 MeV) is accounted for by the Coulomb excitation of the isovector giant dipole resonance (IVGDR); at larger angles the results are compatible with the excitation of the isoscalar monopole resonance (ISGMR) located at 13.9 MeV (Γ = 2.6 MeV).A resonance located at 21.5 MeV (Γ = 5.7 MeV) appears as the superposition of an isovector quadrupole resonance (IVGQR) excited by Coulomb interaction and a resonance of multipolarity L = 1 ΔT = 0 (ISGDR “squeezing mode”).     

A Linear Bound on the Complexity of the Delaunay Triangulation of Points on Polyhedral Surfaces

Delaunay triangulations and Voronoi diagrams have found numerous applications in surface modeling, surface mesh generation, deformable surface modeling and surface reconstruction. Many algorithms in these applications begin by constructing the three-dimensional Delaunay triangulation of a finite set of points scattered over a surface. Their running-time therefore depends on the complexity of the Delaunay triangulation of such point sets. Although the complexity of the Delaunay triangulation of points in R³ may be quadratic in the worst case, we show in this paper that it is only linear when the points are distributed on a fixed set of well-sampled facets of R³ (e.g. the planar polygons in a polyhedron). Our bound is deterministic and the constants are explicitly given.     

Individual domain wall resistance in submicron ferromagnetic structures

The resistance generated by individual domain walls is measured in a FePd nanostructure. Combining transport and magnetic imaging measurements, the intrinsic domain wall resistance is quantified. It is found positive and of a magnitude consistent with that predicted by models based on spin scattering effects within the walls. This magnetoresistance at a nanometer scale allows a direct counting of the number of walls inside the nanostructure. The effect is then used to measure changes in the magnetic configuration of submicron stripes under application of a magnetic field.