Mobile Bipolaron—Strong Coupling Approach

We explore the properties of the bipolaron in a 1D Holstein–Hubbard model with dynamical quantum phonons. We apply strong coupling theory to investigate the intersite bipolaron. We investigate the influence of the Hubbard interaction on the bipolaron binding energy, effective mass, and phase diagram. We compare our analytic results to recent numerical calculations [1]. In the intermediate and strong coupling regimes, a bipolaron is stable beyond the naive stability limit U ₀ = 2g ². The intersite bipolaron has a significantly reduced mass compared to the single site bipolaron, and is stable in the strong coupling regime up toU _c 4g ².     

Linear regulators and observers

The design of a regulator system using a constant gain observer in the feedback loop is discussed. By examining the poles of the closed-loop plant and observer, it is explicitly clear that the closed-loop response is jointly determined by the plant and observer poles and zeros.     

Ridge formation for AlGaAs GRINSCH lasers by Cl2reactive ion etching

Optical storage applications for AlGaAs power lasers require single-mode laser operation and well-controlled beam divergence. For AlGaAs GRIN separate confinement heterostructure (GRINSCH) ridge lasers, these optical characteristics are sensitive to the precise ridge geometry of the laser. Directional reactive ion etching with Cl₂ and in situ monitoring of the etch with highly attenuated laser interferometry provide the excellent process control required during formation of the ridge. The process is described, and results are presented for lasers that were fabricated using this technique     

Efficient coupling into and out of high-Q resonators

The temporal-coupled-mode theory is directly applied to the design of devices that feature a resonator with a high quality factor. For the temporal-coupled-mode theory we calculate the decay rate of the resonator to determine the transmission properties of the device. The analysis using the decay rates requires little computational effort, and therefore the optimum device properties can be determined quickly. Two examples, a wavelength filter and a resonator crossing, are presented to illustrate the use of the analysis.     

Structural study of thin MgO layers on Ag(001) prepared by either MBE or sputter deposition

Growth, morphology and structure of thin MgO films prepared on Ag(001) substrates by different preparation procedures have been investigated by AES, LEED and modulated electron emission. Oxide layers were prepared by Mg MBE in an oxygen atmosphere or sputter deposition from bulk MgO target. In both cases stoichiometric MgO forms, which initially grows in a rocksalt tetragonally distorted structure. For 3-ML films, 3.6% expansion of the interlayer spacing along the growth axis has been measured. The misfit strain progressively reduces as the film thickness increases, and the equilibrium spacing is completely recovered at 8–10 ML thickness. In spite of the similarity in structure and strain, different deposition procedures lead to different film morphology. Sputter deposited films only partially cover the substrate. Fractional coverage (50%) has been evaluated for the 3-ML thick film, and full coverage only occurs at approximately 10 ML thickness. The MBE procedure results in almost complete layers. Fourfold broadening of spot profiles has been observed in LEED patterns of both MBE and sputter deposited films, indicating the occurrence of a similar large-scale atomic arrangement and surface morphology.     

Two versions of the threshold contact model in two dimensions

Two versions of the threshold contact process–ordinary and conservative–are studied on a square lattice. In the first, particles are created on active sites, those having at least two nearest neighbor sites occupied, and are annihilated spontaneously. In the conservative version, a particle jumps from its site to an active site. Mean-field analysis suggests the existence of a first-order phase transition, which is confirmed by Monte Carlo simulations. In the thermodynamic limit, the two versions are found to give the same results.     

Silver uptake byAgaricus bisporus from an artificially enriched substrate

The champignon mushroomAgaricus bisporus was cultivated on compost (wheat and rye straw, hens' manure, gypsum, urea and peat) artificially fortified with silver nitrate added at four different concentrations (0.01, 0.1, 1.0 and 10.3 mg/kg) and 0 mg/kg (control) on a dry weight basis. The method of measurement was flame atomic absorption spectrophotometry after dry ashing of the samples at 420° C and dissolving the residue in 1M nitric acid. The highest concentration of silver, reaching between 120±30–150±36 mg/kg on a dry weight basis, was observed in fruit bodies grown on the most contaminated substrate containing 10.3 mg added Ag/kg dry weight. The silver concentration in caps/stalks/whole fruit bodies ofA. bisporus was positively correlated (r=0.72; P<0.001) with an increasing level of fortification of the substrate. The bioconcentration factor (BCF) of silver in caps/stalks/whole fruit bodies ofA. bisporus was inversely correlated (?0.44<r<?0.36; 0.001<p<0.01) with the silver concentration of the contaminated substrate. The highest silver BCF value of 120–230 has been observed in caps and stalks of mushrooms grown on a substrate enriched with 0.01 mg Ag/kg dry weight. Silver ion added to the substrate in concentrations up to 10.3 mg/kg on a dry weight basis exhibited no observable toxic effect against the mycelial growth and fruiting of A.bisporus.     

An iterative sensory procedure to select odor-active associations in complex consortia of microorganisms: application to the construction of a cheese model

The aim of this study was to develop and validate an iterative procedure based on odor assessment to select odor-active associations of microorganisms from a starting association of 82 strains (G1), which were chosen to be representative of Livarot cheese biodiversity. A 3-step dichotomous procedure was applied to reduce the starting association G1. At each step, 3 methods were used to evaluate the odor proximity between mother (n strains) and daughter (n/2 strains) associations: a direct assessment of odor dissimilarity using an original bidimensional scale system and 2 indirect methods based on comparisons of odor profile or hedonic scores. Odor dissimilarity ratings and odor profile gave reliable and sometimes complementary criteria to select G3 and G4 at the first iteration, G31 and G42 at the second iteration, and G312 and G421 at the final iteration. Principal component analysis of odor profile data permitted the interpretation at least in part, of the 2D multidimensional scaling representation of the similarity data. The second part of the study was dedicated to 1) validating the choice of the dichotomous procedure made at each iteration, and 2) evaluating together the magnitude of odor differences that may exist between G1 and its subsequent simplified associations. The strategy consisted of assessing odor similarity between the 13 cheese models by comparing the contents of their odor-active compounds. By using a purge-and-trap gas chromatography-olfactory/mass spectrometry device, 50 potent odorants were identified in models G312, G421, and in a typical Protected Denomination of Origin Livarot cheese. Their contributions to the odor profile of both selected model cheeses are discussed. These compounds were quantified by purge and trap-gas chromatography-mass spectrometry in the 13 products and the normalized data matrix was transformed to a between-product distance matrix. This instrumental assessment of odor similarities allowed validation of the choice of G312 as the best 10-strain ecosystem.     

Industrial Hydrogenation Process Monitoring Using Ultra-compact Near-Infrared Spectrometer and Chemometrics

The hydrogenation process of soybean oil is monitored through time-consuming methodologies that demand sample preparation and produce chemical residues. Thus, it is necessary to develop faster low-cost waste-free instrumentation methodologies. The aim of this work was to evaluate an ultra-compact near-infrared spectrometer in tandem with the partial least squares regression (PLSR) or support vector regression (SVR) in the control of the hydrogenation process. Models were used to predict the saturated fatty acids (SFA), unsaturated fatty acids (UFA), monounsaturated fatty acids (MUFA), trans fatty acids (TFA), polyunsaturated fatty acids (PUFA), and the iodine value (IV). The values predicted by the PLSR and SVR models were compared to the experimental values obtained by gas chromatography. A methodology for feature selection was also assessed, which was able to reduce by up to 85% the variables used in the models without loss of performance. The values obtained for root mean square error of cross validation, root mean square error of calibration, root mean square error of prediction, and r ² remained very close for both PLSR and SVR. Regarding RSD, all values were above 5% for the PLSR models, whereas for the SVR, the RSD presented values lower than 5% for IV and UFA. It is worth noting that the spectrometer used has low cost, effortless assembly, and easy handling, which allows its use in any environment. Through the results obtained, it was demonstrated that the ultra-compact NIRS spectrometer in tandem with PLSR or SVR represent an alternative to monitor the industrial hydrogenation process of soybean oil.