Excluded volume driven counterion condensation inside nanotubes in a concave electrical double layer model

The physical properties of organic nanotubes attract increasing attention due to their potential benefit in technology, biology and medicine. We study the effect of ion size on the electrical properties of cylindrical nanotubes filled with electrolyte solution within a modified Poisson-Boltzmann (PB) approach. For comparison purposes, small hollow nanospheres filled with electrolyte solution are considered. The finite size of the particles in the inner electrolyte solution is described by the excluded volume effect within a lattice statistics approach. We found that an increased ion size reduces the number of counterions near the charged inner surface of the nanotube, leading to an enlarged electrostatic surface potential. The concentration of counterions close to the inner surface saturates for higher surface charge densities and larger ions. In the case of saturation, the closest counterion packing is achieved, all lattice sites near the surface are occupied and an actual counterion condensation is observed. By contrast, the counterion concentration at the axis of the nanotube steadily increases with increasing surface charge density. This growth is more pronounced for smaller nanotube radii and larger ions. At larger nanotube radii for small ion size counterion condensation may also be observed according to the Tsao criterion, i.e. the counterion concentration at the centre is independent of the number of counterions in the system. With decreasing radius the Tsao condensation effect is shifted towards physiologically unrealistic surface charge densities.     

Measurement of branching fractions and mass spectra of B-->Kpipigamma

We present a measurement of the partial branching fractions and mass spectra of the exclusive radiative penguin processes B-->Kpipigamma in the range m(Kpipi)<1.8 GeV/c(2). We reconstruct four final states: K(+)pi(-)pi(+)gamma, K(+)pi(-)pi(0)gamma, K(S)(0)pi(-)pi(+)gamma, and K(S)(0)pi(+)pi(0)gamma, where K(S)(0)-->pi(+)pi(-). Using 232 x 10(6) e(+)e(-)-->BB events recorded by the BABAR experiment at the SLAC PEP-II asymmetric-energy storage ring, we measure the branching fractions B(B(+)-->K(+)pi(-)pi(+)gamma)=[2.95+/-0.13(stat)+/-0.20(syst)] x 10(-5), B(B(0)-->K(+)pi(-)pi(0)gamma)=[4.07+/-0.22(stat)+/-0.31(syst)] x 10(-5), B(B(0)-->K(0)pi(+)pi(-)gamma)=[1.85+/-0.21(stat)+/-0.12(syst)] x 10(-5), and B(B(+)-->K(0)pi(+)pi(0)gamma)=[4.56+/-0.42(stat)+/-0.31(syst)] x 10(-5).     

Quantum confinement in layer-by-layer deposited colloidal HgTe nanocrystals determined by spectroscopic ellipsometry

We report spectroscopic ellipsometry studies in the energy range of 0.5-5 eV on samples of 1-10 bilayers of polymer and HgTe nanocrystals, which exhibit strong transitions at higher critical points in the dispersion relation. We show that the dispersion relation for nanocrystals can be modelled with the same concepts for critical points as used in semiconductor bulk optics. We find an energy shift of up to 0.4 eV of the critical points to higher energies compared to the HgTe bulk properties, caused by quantum confinement in the nanocrystals, which increases with decreasing nanocrystal size.     

Detecting small flaws near the interface in pulse-echo

Flaw detection near the interface surface is a common problem in many pulse-echo NDT applications due to interference with the interface echo, orders of magnitude above the flaw echoes. Several digital signal processing techniques like deconvolution, Hilbert transform and cepstrum analysis have been proposed to improve axial resolution. However, they require strict linearity, which takes a large portion of the system dynamic range just to fit the interface echo, thus reducing the dynamic range available for flaw detection. This work presents a new alternative based on the time-domain phase analysis of the received signals. Differently from conventional approaches, it works quite well with saturated signals resulting when a high gain is applied to detect small flaws. These can be detected in a range of a fraction of one wavelength from the interface surface, even using narrow-band transducers, as it has been experimentally verified. The method can be easily hardware implemented for real-time processing.     

Sol–gel synthesis of sodium and lithium based materials

Sodium and lithium cobaltates are important materials for thermoelectric and battery applications due to their large thermoelectric power and ability to (de-) intercalate the alkali metal. For these applications, phase pure materials with controlled microstructure are required. We report on the sol?Cgel synthesis of sodium- and lithium-based materials by using acetate precursors. The produced Na_2/3CoO₂, Li(Ni_1/3Mn_1/3Co_1/3)O₂, and Li(Ni_1/2Co_1/2)O₂ powders are phase pure with grain sizes below 1???m. X-ray diffraction and energy-dispersive spectral analyses show that the cation stoichiometry is preserved in the lithium-based compounds. Despite the low temperatures, the sodium content is reduced by 1/3 as compared to the initial value. Chemical phases of the investigated powders are formed in the sol?Cgel route at temperatures typically 100?C200?K lower than those used in the conventional solid-state synthesis of these materials. The suggested sol?Cgel synthesis is a low temperature process suited for production of phase pure and homogeneous materials with volatile cations.     

Determination of 94Nb in radioactive waste using ion exchange chromatography

This paper describes a rapid method of ⁹⁴Nb pre-concentration, separation and purification by using cation and anion exchange resins. The method is suitable for analyzing highly contaminated radioactive waste samples in a relatively short time and high decontamination factors. The use and effectiveness of the method was successfully tested by analysis of samples from nuclear reactor parts such as control rod drive shaft, shielding cassettes, neutron in-core measurement channels (KNI), pressure vessel construction material and fuel cassette construction material samples.     

RbCN3H4: the first structurally characterized salt of a new class of guanidinate compounds

Rubidium guanidinate, RbCN(3)H(4), was synthesized from guanidine and rubidium hydride, and the crystal structure was determined from powder X-ray diffraction (PXRD) data. RbCN(3)H(4) crystallizes in the orthorhombic space group Pnma (No. 62) with four formula units per cell. The guanidinate anions are arranged in double chains running along the b axis, stacked almost perpendicularly to each other to form a three-dimensional network. The rubidium cations, coordinated by 11 N atoms, occupy the vacancies of the network in a zigzag motif along the b axis. Because the PXRD structure of the CN(3) core clearly indicates the N-atom functionalities and the location of the H-atom positions, the latter spatial parameters were determined from Perdew-Burke-Ernzerhof generalized gradient approximation (GGA-PBE) density functional theory calculations. The corresponding ν(NH) stretching modes can be observed in the IR spectrum, and the volume chemistry of RbCN(3)H(4) mirrors the efficient packing of the saltlike phase.