Characterization of laser-induced plasmas by emission spectroscopy with curve-of-growth measurements. Part I: Temporal evolution of plasma parameters and self-absorption

Laser-induced plasmas have been characterized by emission spectroscopy, including the measurement of curves of growth. The plasmas have been generated in air at atmospheric pressure using an infrared Nd:YAG laser from a set of Fe–Ni alloys with varying Fe concentrations. The procedure used provides, in addition to the apparent temperature T and electron density N_e, a parameter N′l (the atom number density for 100% concentration times the length of the plasma along the line-of-sight), relevant to obtain the self-absorption and the intensity of the emission lines. The temporal evolution of the plasma parameters has been deduced from the measurement and fitting of the curves of growth. A fast temporal decrease of N′l is obtained for ions, whereas a gradual increase takes place for neutral atoms. The temporal evolution of the line intensity in the optically thin limit and the self-absorption of neutral atom and ion lines have been obtained experimentally and calculated from the evolution of the plasma parameters. The usefulness of the curve-of-growth method in measurements with time integration, in spite of the fast variation of the plasma parameters, has been demonstrated.     

Stable carbon and nitrogen isotopes and quality traits of fossil cereal grains provide clues on sustainability at the beginnings of Mediterranean agriculture

We present a novel approach to study the sustainability of ancient Mediterranean agriculture that combines the measurement of carbon isotope discrimination (Delta(13)C) and nitrogen isotope composition (delta(15)N) along with the assessment of quality traits in fossil cereal grains. Charred grains of naked wheat and barley were recovered in Los Castillejos, an archaeological site in SE Spain, with a continuous occupation of ca. 1500 years starting soon after the origin of agriculture (ca. 4000 BCE) in the region. Crop water status and yield were estimated from Delta(13)C and soil fertility and management practices were assessed from the delta(15)N and N content of grains. The original grain weight was inferred from grain dimensions and grain N content was assessed after correcting N concentration for the effect of carbonisation. Estimated water conditions (i.e. rainfall) during crop growth remained constant for the entire period. However, the grain size and grain yield decreased progressively during the first millennium after the onset of agriculture, regardless of the species, with only a slight recovery afterwards. Minimum delta(15)N values and grain N content were also recorded in the later periods of site occupation. Our results indicate a progressive loss of soil fertility, even when the amount of precipitation remained steady, thereby indicating the unsustainable nature of early agriculture at this site in the Western Mediterranean Basin. In addition, several findings suggest that barley and wheat were cultivated separately, the former being restricted to marginal areas, coinciding with an increased focus on wheat cultivation.     

Structuring bubbles and foams in gelatine solutions within a circular microchannel device

A flow-focusing device with circular cross-section to produce monodispersed air bubbles and foams in several gelatine solutions is presented. Four flow regimes were studied by varying the gas pressure: dripping, bi-disperse bubbly, bubbly and foam flows. Bubble formation at the flow-focusing exit is discussed in detail and compared with that in rectangular microchannels. The bubble volume was shown to depend on the viscosity of the gelatine solution but not on the surface tension. For the bubbly flow, the frequency of bubble formation in this geometry was similar to that found in rectangular microchannels. For the foam flow the frequency was independent of the pressure. Study in the outlet microchannel for the bubbly and foam flows showed that the gas flow followed a power law with the applied pressure. Finally, the viscous resistance was measured and a pressure drop law was determined for each regime.     

Synthesis and photoinitiated polymerization of diacrylate derivates of halobenzoates

The synthesis, characterization, mesomorphism and photoinitiated polymerization of new thermotropic derivatives of bis{4-[6-(acryloyloxy)hexyloxy]halobenzoate}-1,4-phenylene were studied. Halogen incorporation in the mesogenic unit decreases the stability of the mesophases of monomers containing three aromatic rings. The monomer MIII exhibits a nematic phase which has been macroscopically oriented by surface pre-treatment and fixed by photopolymerization in situ, yielding a uniaxially crosslinked network. The molecular ordering of liquid crystalline diacrylate films was visualized by examining the fracture surface by scanning electron microscopy. These films exhibit a fine texture, illustrating the presence of an oriented layered structure.     

Determination of the local electron number density in laser-induced plasmas by Stark-broadened profiles of spectral lines: Comparative results from Hα, Fe I and Si II lines

Measurements of the local electron density in laser-induced plasma have been carried out from the Stark-broadened profiles of three reference lines (H_α, Fe I and Si II). The plasma has been generated from a Fe–Si sample in air using a Nd:YAG laser. Compatible values of the local electron density have been obtained from the three lines. The experiment is based on the use of an imaging spectrometer, the capability for spatial resolution of a charge-coupled device and the application of a spatial deconvolution procedure to the spectra. Distributions of the emission coefficient have been obtained, showing that the three lines are emitted from different regions of the plasma. The implications in the apparent electron density values obtained in spatially-integrated measurements are discussed: similar values are obtained for the H_α and Si II lines, while the Fe I line leads to a 25% lower value.     

Titanocene-phosphine derivatives as precursors to cytotoxic heterometallic TiAu2 and TiM (M = Pd, Pt) compounds. Studies of their interactions with DNA

A series of tri- and bimetallic titanium-gold, titanium-palladium, and titanium-platinum derivatives of the general formulas [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)(AuCl)}(2)]·2THF [n = 0 (1); n = 2 (2); n = 3 (3)] and [TiCl(2){η(5)-C(5)H(4)κ-(CH(2))(n)PPh(2)}(2)(MCl(2))]·2THF [M = Pd, n = 0 (4); n = 2 (5); n = 3 (6) ; M = Pt, n = 0 (7); n = 2 (8); n = 3 (9)] have been synthesized and characterized by different spectroscopic techniques and mass spectrometry. The molecular structures of compounds 1-9 have been investigated by means of density functional theory calculations. The calculated IR spectra of the optimized structures fit well with the experimental IR data obtained for 1-9. The stability of the heterometallic compounds in deuterated solvents [CDCl(3), dimethyl sulfoxide (DMSO)-d(6), and mixtures 50:50 DMSO-d(6)/D(2)O and 1:99 DMSO-d(6)/D(2)O at acidic and neutral pH] has been evaluated by (31)P and (1)H NMR spectroscopy showing a higher stability for these compounds than for Cp(2)TiCl(2) or precursors [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)}(2)]. The new compounds display a lower acidity (1-2 units) than Cp(2)TiCl(2). The decomposition products have been identified over time. Complexes 1-9 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and DU-145 human prostate cancer cells. TiAu(2) and TiPd compounds were highly cytotoxic for these two cell lines. The interactions of the compounds with calf thymus DNA have been evaluated by thermal denaturation (1-9) and by circular dichroism (1, 3, 4, and 7) spectroscopic methods. All of these complexes show a stronger interaction with DNA than that displayed by Cp(2)TiCl(2) at neutral pH. The data are consistent with electrostatic interactions with DNA for TiAu(2) compounds and for a covalent binding mode for TiM (M = Pd, Pt) complexes.     

The direct method in time-dependent bending of thermoelastic plates

The initial-boundary value problems with Dirichlet and Neumann boundary conditions arising in the theory of bending of thermoelastic plates with transverse shear deformation are reduced to time-dependent boundary integral equations by means of the Somigliana representation formulas. The solvability of these equations is then investigated in Sobolev-type spaces.     

Weak solutions for time‐dependent boundary integral equations associated with the bending of elastic plates under combined boundary data

The existence, uniqueness, stability, and integral representation of distributional solutions are investigated for the equations of motion of a thin elastic plate with a combination of displacement and moment‐stress components prescribed on the boundary. Copyright © 2004 John Wiley & Sons, Ltd.