A continuum thermodynamical approach to electrochemical systems

This work focuses on formulating constitutive models for the bulk and double layer regions of an electrochemical system based on the fundamentals of modern continuum thermodynamics. Particularly, the constitutive models proposed accounting for transport phenomena in electrochemical systems by emphasizing the possibility of cross-coupling between two or more phenomena. Upon deriving a set of thermodynamic restrictions from the Müller-Liu approach of the second law of thermodynamics and axioms of constitutive theory, non-equilibrium quantities are examined in detail, and constitutive answers of the bulk and double layer regions are discussed. Moreover, the conditions for the thermodynamic equilibrium are evaluated for each region as well as the occurrence of dissipative mechanisms. Besides offering a proper formulation for non-equilibrium electrochemical systems, the approach described in this work can be easily extended to more complex chemical systems.     

Full-wavelet approach for fluorescence diffuse optical tomography with structured illumination

We present a fast reconstruction method for fluorescence optical tomography with structured illumination. Our approach is based on the exploitation of the wavelet transform of the measurements acquired after wavelet-patterned illuminations. This method, validated on experimental data, enables us to significantly reduce the acquisition and computation times with respect to the classical scanning approach. Therefore, it could be particularly suited for in vivo applications.     

Time-resolved spectrophotometer for turbid media based on supercontinuum generation in a photonic crystal fiber

We describe an instrument for the time-resolved spectroscopy of turbid media that is based on supercontinuum generation in a photonic crystal fiber. The light injected into the sample consists of subpicosecond pulses that cover 550-1000 nm at 85 MHz at an average power of as much as 40 mW. A spectrometer coupled to a multianode photomultiplier tube is used to detect the light simultaneously in 16 wavelength channels, with a resolution of 5-20 nm/channel, depending on the grating. Time-correlated single-photon counting is used to produce time-dispersion curves, which one fits to the diffusion equation to determine absorption and reduced scattering coefficients. We tested the instrument by measuring the time-resolved diffuse reflectance of epoxy phantoms and by performing in vivo measurements on volunteers. The results were similar to those obtained with previous discrete wavelength systems, whereas the full spectrum (610-810 nm) acquisition time was as short as 1 s owing to the parallel acquisition.     

Towards quantum superpositions of a mirror: an exact open systems analysis

We analyze the recently proposed mirror superposition experiment of Marshall, Simon, Penrose, and Bouwmeester, assuming that the mirror's dynamics contains a nonunitary term of the Lindblad-type proportional to -[q,[q,rho]], with q the position operator for the center of mass of the mirror, and rho the statistical operator. We derive an exact formula for the fringe visibility for this system. We discuss the consequences of our result for tests of environmental decoherence and of collapse models. In particular, we find that with the conventional parameters for the continuous spontaneous localization model of state vector collapse, maintenance of coherence is expected to within an accuracy of at least 1 part in 10(8). Increasing the apparatus coupling to environmental decoherence may lead to observable modifications of the fringe visibility, with time dependence given by our exact result.     

Pulsed laser deposition of tungsten and tungsten oxide thin films with tailored structure at the nano- and mesoscale

Nanostructured thin films synthesized by assembling atoms or clusters present a structure characterized by a modulation at the nanoscale and by a large effective area, which can be exploited for the tailoring of specific structural or electronic properties. These systems are appealing for functional applications, e.g. in sensing and catalysis. We have investigated the deposition of tungsten and tungsten oxide thin films with a wide range of morphologies by exploiting nanosecond pulsed laser deposition (PLD) in an inert background atmosphere (He, Ar and Kr). We show that the non-dimensional ratio of the target-to-substrate distance to the time integrated visible plume length, which depends on the gas mass and pressure and on the substrate position, permits to select morphologies ranging from a compact structure with a density similar to bulk, to a film with an open, low density foam-like mesostructure and a high fraction of voids.     

NATAS 1976

Events

NATAS 1976     

X-ray crystal structure of the clathrate compound tetrakis[(benzonitrile)(triphenylphosphorane)nickel(0)] · 2 toluene · ~1 n-hexane · ~1 cycloocta-1,5-diene

The preparation and the chemical properties of the clathrate compound tetrakis[(benzonitrile)(triphenylphosphorane)nickel(0)] · 2 toluene · ~1 n-hexane · ~1 cycloocta-1,5-diene are described. The crystal and molecular structure of this compound were determined from X-ray diffractometer data. The structure was solved by direct and Fourier methods and refined by least-squares techniques to R = 0.117 for 3441 independent reflections. The crystals are monoclinic, space group P2₁, with Z = 2, in a unit cell of dimensions a 14.680(7), b 28.198(18), c 15.482(8) Å, β = 118.43(8)°. Eight (NiP(C₆H₅)₃ · NCC₆H₅) formula units are present as two tetrameric molecules in the unit cell. Each Ni atom of the tetramer is linked by σ bonds to a P and N atom and by π bonds to the NC group of another benzonitrile molecule. The coordination of the nickel atoms is roughly trigonal. The nickel and N atoms form an eight-membered ring with a boat conformation. The NCC groups of the benzonitrile residues are bent and the NC distances indicate a high degree of double bond character for all these bonds. The triphenylphosphorane groups adopt a “propeller”-like conformation. Four solvent molecules 2 toluene, 1 n-hexane, and ~1 cycloocta-1,5-diene per asymmetric unit are present in the unit cell.     

Comparative study of the thermal analyses of some transition metal(II) maleates and fumarates

The thermal decompositions of maleates and fumarates of Cu(II) and Zn(II) have been studied by employing simultaneous non-isothermal techniques (DTG, DTA and TG). The end-products are the corresponding metal oxides, as characterized by chemical analysis and X-ray diffraction. Comparison of theTm values led to the stability sequences Cu(F)>Cu(M); Zn(F)>Zn(M) and Cu(M)≈ Cu(F); Zn(F)>Zn(M) for dehydration and decomposition, respectively.