Classical treatment of molecular collisions: striking improvement of the description of recoil energy distributions using Gaussian weighted trajectories

The Gaussian weighting (GW) procedure, recently used in the classical treatment of molecular collisions, is a practical way of taking into account quantization of product vibrational actions. The goal of this brief communication is to show that the GW procedure may drastically improve the predictions of the recoil energy distribution between final fragments, an observable frequently measured in molecular beam experiments.     

Coulomb excitation of neutron-rich Zn isotopes: first observation of the 2(1)+ state in 80Zn

Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)+ state in 78Zn could be firmly established and for the first time the 2+ --> 0(1)+ transition in 80Zn was observed at 1492(1) keV. B(E2,2(1)+ --> 0(1)+) values were extracted for (74,76,78,80)Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus 78Ni.     

Supercritical ammonia: a molecular dynamics simulation and vibrational spectroscopic investigation

Combining infrared spectroscopy and molecular dynamics simulations, we have investigated the structural and dynamical properties of ammonia from liquid state (T = 220 and 303 K) up to the supercritical domain along the isotherm T = 423 K. Infrared spectra show that the N-H stretching and bending modes are significantly perturbed which is interpreted as a signature of the change of the local environment. In order to compare the experimental spectra with those obtained using molecular dynamics simulation, we have used a flexible four sites model which allows to take into account the anharmonicity in all the vibration modes particularly that of the inversion mode of the molecule. A good agreement between our experimental and calculated spectra has been obtained hence validating the intermolecular potential used in this study to simulate supercritical ammonia. The detailed analysis of the molecular dynamics simulation results provides a quantitative insight of the relative importance of hydrogen bonding versus nonhydrogen bonded interactions that governs the structure of fluid ammonia.     

Sub-poissonian number differences in four-wave mixing of matter waves

We demonstrate sub-Poissonian number differences in four-wave mixing of Bose-Einstein condensates of metastable helium. The collision between two Bose-Einstein condensates produces a scattering halo populated by pairs of atoms of opposing velocities, which we divide into several symmetric zones. We show that the atom number difference for opposing zones has sub-Poissonian noise fluctuations, whereas that of nonopposing zones is well described by shot noise. The atom pairs produced in a dual number state are well adapted to sub-shot-noise interferometry and studies of Einstein-Podolsky-Rosen-type nonlocality tests.     

Domain wall conductivity in La-doped BiFeO3

The transport physics of domain wall conductivity in La-doped bismuth ferrite (BiFeO3) has been probed using variable temperature conducting atomic force microscopy and piezoresponse force microscopy in samples with arrays of domain walls in the as-grown state. Nanoscale current measurements are investigated as a function of bias and temperature and are shown to be consistent with distinct electronic properties at the domain walls leading to changes in the observed local conductivity. Our observation is well described within a band picture of the observed electronic conduction. Finally, we demonstrate an additional degree of control of the wall conductivity through chemical doping with oxygen vacancies, thus influencing the local conductive state.     

On the higher-order Kerr effect in femtosecond filaments

A recent experiment probing the electronic nonlinearity in the femtosecond filament indicated that the optical Kerr effect not only saturates but even changes its sign at high intensities and thus switches from self-focusing to a strongly defocusing regime. Here we examine, through simulations and experiment, some implications of such a behavior. We perform comparative simulations based on the standard model on one hand and on a model implementing the intensity-dependent Kerr effect on the other. Comparison with an experiment provides a strong indication that of these two Kerr-effect models the standard model is better in capturing the observed length of the filament. However, neither of the models can reproduce length and filament radius. Possible implications are discussed.     

Shock-induced crystal-glass transition in solid silica

Solid silica SiO₂ occurs under a variety of forms, α-quartz being the stable one at ambient conditions. Shock wave compression induces in this mineral typical defects which appear at the optical microscope as very straight and narrow (≤1μm) lamellae parallel to {10 n} planes. Transmission electron microscopy on both naturally (meteorite impacts) and experimentally (gun shots) shocked quartz shows that they are thin lamellae of amorphous silica. Theoretical computations show that the shock-induced crystal-amorphous transition results from instabilities of the shear modulus in {10 n} planes for P>10 GPa. The elastic misfit energy in the shock front is relaxed by the nucleation of amorphous and more compressible zones the growth of which is then driven by the propagating shock front. The boundaries delineating these defects are sharp and move at very high speed.     

EXPERIMENTAL CORRELATIONS BETWEEN HLB AND SOLUBILITY PARAMETERS IN OIL-IN-WATER EMULSIONS

The stability of four components emulsions - oil, water, surfactant and cosurfactant - is examined. From a series of stable formulations, prepared with one surfactant family, the correlations between different characteristic parameters - solubility parameters of the oil and of the cosurfactant, surfactant HLB, required HLB of the oil - are checked. The experimental study displays linear relations between some of these parameters. The results allow to predict that the choice of the oil induces the choice of an HLB range for the surfactant and a solubility parameter range for the cosurfactant.     

四(二苯甲酰甲烷)合铕酸二乙铵的激发光谱和荧光光谱

在296和77K测定了四(二苯甲酰甲烷)合铕酸二乙铵[(C2H5)2NH2Eu(DBM)4]的高分辨激发光谱和荧光光谱。光谱数据说明在77K, 配合物含有五种Eu(III)格位。详细分析发光光谱说明, 由于配合物中配位体里的苯基错位产生不同的构型, 形成了不同的Eu(III)物种, 显示出不同的晶体场效应, Eu(III)离子的这种灵敏性可以作为晶体构型探针。     

Thermal conductivity of undoped trans-polyacetylene films

The low temperature variation of the thermal conductivity of transpolyacetylene is reported. The thermal conductivity, which though it is comparable to that of a semi-crystalline polymer at 100 K, varies linearly with the temperature below this temperature. The temperature variation of the phonon mean free path is found to be similar to that of an oriented polyethylene.