An electrochemical method for fluoride analysis based on a naphthalene urea derivative as a selective receptor

The use of a naphthalene urea derivative as a host molecule for selective fluoride binding allows us to develop a highly selective and sensitive electrochemical method for fluoride analysis without the interference of other halogen atoms. All the parameters affecting the differential pulse voltammetric response of the host molecule used as a fluoride receptor have been optimized and the mechanisms of the electrochemical behavior have been elucidated. The inhibition in the electrochemical signal of the anionic receptor due to the increase of the fluoride amounts allows the determination of F-with an LOD of 3.16 x 10(-6) M with an RSD (%) value lower than 4.8% and an Er (%) value lower than 3.8%.     

Computer aided thermal analysis

Inverse numerical techniques have been applied in a range of different thermal studies in the past. These techniques require measurements of boundary conditions and temperatures at known position within the sample in order to determine thermal properties of the material of interest. Typically, they have been applied to highly specific applications and designs. In the current work the authors have designed a novel instrument in order to measure apparent specific heats of a range of different materials during continuous heating. Measurements of surface heat flux, surface and centre temperatures of the sample were obtained under controlled heating for temperatures of up to 1000°C. Measured data was used to quantify specific and latent heats by employing inverse numerical modelling technique. The instrument was calibrated with calorimetric calibration materials and results were compared with the literature values. The average experimental error was estimated to be approximately 0.9% for the reaction peak temperatures and 1.7% for the latent heats. Detailed experimental and calculation procedures as well as measured results of specific heat and enthalpy for a number of materials are presented here. This revised version was published online in July 2006 with corrections to the Cover Date.     

Progress in anomalous transport research in toroidal magneticconfinement devices

Transport is the outstanding physics issue in the quest for fusion by magnetic confinement. In spite of the intrinsic difficulty, a great deal of progress has been made in the past 25 years. Experiments have gone from being dominated by high anomalous losses, of the order of Bohm diffusion losses, to operation with no anomalous transport. This success is due to a combination of improved experimental infrastructure and the high degree of knowledge on how to control plasma discharges, Both have made it possible to access enhanced confinement regimes and to unravel new effects in confinement physics. Although there is not yet a complete understanding of the dynamical mechanisms underlying the anomalous transport process, there is some understanding of important components such as the ion transport loss mechanism at the plasma core and of the main mechanism for turbulence suppression in the enhanced confinement regimes     

Relativistic particles and the geometry of 4-D null curves

We study actions in (d+1)$(d+1)$-dimensions associated with null curves, mainly when d=3$d=3$, whose Lagrangian is a linear function on the curvature of the particle path, showing that null helices are always possible trajectories of the particles. We find Killing vector fields along critical curves of the action which correspond to the linear and the angular momenta of the particle. They provide two constants of the motion which can be interpreted in terms of the mass and the spin of the system. Moreover, we are able to integrate both the Euler–Lagrange equations and the Cartan equations in cylindrical coordinates around a certain plane.     

Vibronic structure and ion core interactions in Rydberg states of diazomethane: an experimental and theoretical investigation

Vibronic transitions to the 21A2(3py <-- pi) Rydberg state of CH2N2, CD2N2, and CHDN2 were recorded by 2 + 1 REMPI spectroscopy, and kinetic energy distributions (eKE) of photoelectrons from ionization of selected vibronic levels were determined by velocity map imaging. Normal-mode frequencies were obtained for the 21A2(3py) Rydberg state and for the cation. Mixed levels of the 21A2(3py) and 21B1(3pz) of the three isotopologs were identified by photoelectron imaging and analyzed. The equilibrium geometries and harmonic vibrational frequencies of the electronic states of neutral diazomethane were calculated by CCSD(T)/cc-pVTZ, and B3LYP/6-311G(2df,p). The latter method was also used to calculate isotope shifts for the ground-state neutral and cation. Geometry and frequencies of the ground state of the cation were calculated by CCSD(T)/cc-pVTZ, using the unrestricted (UHF) reference. The equilibrium structures, frequencies, and isotope shifts of the 21A2(3py) and 21B1(3pz) Rydberg states were calculated by EOM-EE-CCSD/6-311(3+,+)G(2df). In all cases where comparisons with experimental results were available, the agreement between theory and experiment was very good allowing a full analysis of trends in structure and vibrational frequencies in going from the neutral species to the excited Rydberg states, 21A2(3py) and 21B1(3pz), and the cation. Although the 21A2(3py) and 21B1(3pz) states have planar C2v symmetry like the ion, they exhibit differences in geometry due to the specific interactions of the electron in the 3py and 3pz orbitals with the nuclei charge distributions of the ion core. Moreover, trends in normal-mode frequencies in the ground states of the neutral and ion and the 21A2(3py) and 21B1(3pz) Rydberg states are consistent with removing an electron from the bonding piCN-orbital, which also has an antibonding character with respect to NN. To explain the observed trends, the vibrational modes are divided into two groups that involve displacements mainly (i) along the CNN framework and (ii) in the CH2 moiety. Trends in the first group are due mostly to the effect of the lower CN and NN bond orders, whereas those in the second group are due to the interaction between the positively charged hydrogens and the Rydberg electron density, and the hybridization of the carbon. Within each group, marked differences in behavior between the in-plane and out-of-plane modes are observed.     

Mass spectrometric imaging of peptide release from neuronal cells within microfluidic devices

Microfluidic devices are well suited for manipulating and measuring mass limited samples. Here we adapt a microfluidic device containing functionalized surfaces to chemically stimulate a small number of neurons (down to a single neuron), collect the release of neuropeptides, and characterize them using mass spectrometry. As only a small fraction of the peptides present in a neuron are released with physiologically relevant stimulations, the amount of material available for measurement is small, thereby requiring minimal sample loss and high-sensitivity detection. Although a number of detection schemes are used with microfluidic devices, mass spectrometric detection is used here because of its high information content, allowing the characterization of the released peptide complement. Rather than using an on-line approach, off-line analysis is used; after collection of the peptides onto a surface, mass spectrometric imaging interrogates that surface to determine the peptides released from the cell. The overall utility of this scheme is demonstrated using several device formats with measurement of neuropeptides released from Aplysia californica bag cell neurons.     

A Fock space coupled cluster study on the electronic structure of the UO(2), UO(2) (+), U(4+), and U(5+) species

The ground and excited states of the UO(2) molecule have been studied using a Dirac-Coulomb intermediate Hamiltonian Fock-space coupled cluster approach (DC-IHFSCC). This method is unique in describing dynamic and nondynamic correlation energies at relatively low computational cost. Spin-orbit coupling effects have been fully included by utilizing the four-component Dirac-Coulomb Hamiltonian from the outset. Complementary calculations on the ionized systems UO(2) (+) and UO(2) (2+) as well as on the ions U(4+) and U(5+) were performed to assess the accuracy of this method. The latter calculations improve upon previously published theoretical work. Our calculations confirm the assignment of the ground state of the UO(2) molecule as a (3)Phi(2u) state that arises from the 5f(1)7s(1) configuration. The first state from the 5f(2) configuration is found above 10,000 cm(-1), whereas the first state from the 5f(1)6d(1) configuration is found at 5,047 cm(-1).     

Pressure effects on viscosity and flow stability of polyethylene melts during extrusion

In the present work, the effects of pressure on the viscosity and flow stability of four commercial grade polyethylenes (PEs) have been studied: linear-low-density polyethylene copolymer, high-density polyethylene, metallocene polyethylenes with short-chain branches (mPE-SCB), and metallocene polyethylenes with long chain branching (mPE-LCB). The range of shear rates considered covers both stable and unstable flow regimes. “Enhanced exit-pressure” experiments have been performed attaining pressures of the order of 500×10⁵ Pa at the die exit. The necessary experimental conditions have been clearly defined so that dissipative heating can be neglected and pressure effects isolated. The results obtained show an exponential increase in both shear and entrance-flow pressure drop with mean pressure when shear rate is fixed and as long as flow is stable. These pressure effects are described by two pressure coefficients, β_S under shear and, β_E under elongation, that are calculated using time–pressure superposition and that are independent of mean pressure and flow rate. For three out of four PE, pressure coefficient values can be considered equal under shear and under elongation. However, for the mPE-LCB, the pressure coefficient under elongation is found to be about 30% lower than under shear. Flow instabilities in the form of oscillating flows or of upstream instabilities appear at lower shear rates as mean pressure increases. Nevertheless, the critical shear stress at which they are triggered remains independent of mean pressure. Moreover, it is found that the β_S values obtained for stable flows do not differ much from the values obtained during upstream instability regimes, and differ really from pressure effects observed under oscillating flow and slip conditions.