Potassium 1,2,4,5-benzenetetracarboxylate,C6H2(CO2K)4·4H2O; its formation,crystal structure,and hydrogen bonding

From an aqueous mixture of 1,2,4,5-benzenetetracarboxylic acid, C₆H₂(CO₂H)₄, and KF we grew crystals first of KHF₂ then of the title compound. An X-ray crystallographic determination of this compound shows a network of C₆H₂(CO ₂ ^– )₄ units linked through hydrogen bonds to water molecules. This is the first reported structure of a benzenecarboxylate anion. Two carboxylate groups are coplanar with the benzene ring, whereas the other two are perpendicular to it.     

Imaging the pair-correlated excitation function: The F+CH4-->HF(v')+CH3(nu=0) reaction

The velocity map ion imaging technique was applied to measure the reaction excitation function for the first time. It was found that the "raw" excitation function was significantly distorted by the density-to-flux transformation of the title reaction. Through a systematic investigation, possible reasons for such a dramatic effect are outlined. In addition, the state-resolved, pair-correlated excitation functions and branching ratios are presented. Effects of imperfect time slicing in the time-sliced velocity imaging technique in general are also discussed.     

Shape of CeO2 nanoparticles using simulated amorphisation and recrystallisation

Evolutionary simulation has been used to generate full atomistic models for CeO2 nanoparticles, which comprise [100]-truncated [111] octahedra in accord with experiments.     

Is the nuclear spin-orbit interaction changing with neutron excess?

The difference in the energies of the lowest states corresponding to the two nodeless single-particle orbitals outside the Z=50 closed proton shell, h(11/2) and g(7/2), increases with neutron excess. We have measured the Sn(alpha,t) reaction for all seven stable even Sn isotopes and found that the spectroscopic factors are constant for these two states, confirming their characterization as single-particle states. The trend in energies is consistent with a decrease in the nuclear spin-orbit interaction. A similar trend, also suggesting a decreasing spin-orbit splitting, is seen in the energies of the neutron single-particle states outside the N=82 core, i(13/2) and h(9/2).     

Controlled vortex-sound interactions in atomic Bose-Einstein condensates

The low temperature dynamics of a vortex in a trapped quasi-two-dimensional Bose-Einstein condensate are studied quantitatively. Precession of an off-centered vortex in a dimple trap, embedded in a weaker harmonic trap, leads to the emission of sound in a dipolar radiation pattern. Sound emission and reabsorption can be controlled by varying the depth of the dimple. In a shallow dimple, the power emitted is proportional to the vortex acceleration-squared over the precession frequency, whereas for a deep dimple, periodic sound reabsorption stabilizes the vortex against radiation-induced decay.     

Zoned microstructure fiber for low-dispersion waveguiding and coupling to photonic crystals

We describe a zoned microstructure fiber that exhibits low dispersion and virtually zero spherical aberration because of its optimized piecewise Gaussian index profile. We present results of a nine-zone design that has an average refractive index of 2.3, a refractive-index contrast of 0.1, a first zone radius of 1.67 microm, and a maximum core radius of 5 microm. It has an in-fiber focal length of 8.88 microm and can focus light to a spot size of radius 315 nm, facilitating efficient coupling between single-mode fiber and photonic crystals.