Exciton-contribution to the reflection spectrum at high excitation intensities in CdS

We report measurements of changes in reflection spectrum of CdS due to increasing the density of photoexcited carriers at temperatures above the critical temperature for electron-hole liquid formation. The contribution of the exciton resonance is seen to decrease and analysis of the lineshape indicates that this decrease is due to exciton-exciton collision and a change in exciton polarizability. These results are consistent with a transition from exciton to free electron-hole plasma (Mott transition) at a density of n ～ 2.5 x 10¹⁷ cm^-3.     

Metabolomics data exploration guided by prior knowledge

In metabolomics research, it is often important to focus the data analysis to specific areas of interest within the metabolome. In this paper, we describe the application of consensus principal component analysis (CPCA) and canonical correlation analysis (CCA) as a means to explore the relation between metabolome data and (i) biochemically related metabolites and (ii) an amino acid biosynthesis pathway. CPCA searches for major trends in the behavior of metabolite concentrations that are in common for the metabolites of interest and the remainder of the metabolome. CCA identifies the strongest correlations between the metabolites of interest and the remainder of the metabolome.CPCA and CCA were applied to two different microbial metabolomics data sets. The first data set, derived from Pseudomonas putida S12, was relatively simple as it contained metabolomes obtained under four environmental conditions only. The second data set, obtained from Escherichia coli, was much more complex as it consisted of metabolomes obtained under 28 different environmental conditions. In case of the simple and coherent P. putida S12 data set, CCA and CPCA gave similar results as the variation in the subset of the selected metabolites and the remainder of the metabolome was similar.In contrast, CCA and CPCA yielded different results in case of the E. coli data set. With CPCA the trends in the selected subset - the phenylalanine biosynthesis pathway - dominated the results. The main trends were related to high and low phenylalanine productivity, and the metabolites showing a similar behavior in concentration were metabolites regulating the phenylalanine biosynthesis route in the subset and metabolites related to general amino acid metabolism in the remainder of the metabolome. With CCA, neither subset truly dominated the data analysis. CCA described the differences between the wild type and the overproducing strain and the differences between the succinate and glucose grown cells. For the difference between the wild type and the overproducing strain, metabolites from the beginning and the end of aromatic amino acid pathways like erythrose-4-phosphate, tryptophan, and phenylalanine were important for the selected metabolites.CCA and CPCA proved to be complementary data analysis tools that enable the focusing of the data analysis on groups of metabolites that are of specific interest in relation to the remainder of the metabolome. Compared to an ordinary PCA, focusing the data analysis on biologically relevant metabolites lead especially for the complex E. coli data to a better biological interpretation of the data.     

Influence of dentin pre-treatment with NaOCl on the morphology of adhesive interface of self-etching adhesive systems

The aim of this in vitro study was to evaluate the influence of pre-treatment using NaOCl in the morphology of dentin/resin interface. The three self-etching adhesive systems were selected: One-Up Bond F (Tokuyama, Tokyo, Japan), Prime & Bond NT/NRC (Dentsply, Konstanz, Germany) and Clearfil SE Bond (Kuraray, Osaka, Japan). Nine dentin disks were used in this study. Half disk was treated strictly following manufacturers’ instructions (control groups). The other half was treated with a solution of 2.5% NaOCl (experimental groups). After the bonding protocols were accomplished, a low viscosity resin (Flow-it/Jeneric Pentron) was inserted and light-cured. Specimens were prepared for SEM. Morphological aspects were observed, comparing both the groups. The analysis of the photomicrographs revealed formation of a hybrid layer for both controls groups along the interface. The experimental groups showed a resin/dentin interface more irregular and produced topographical features with funnel-shaped dentin tubules. Areas with absence of hybrid layer formation were observed, mainly for One-Up Bond F, although tubules their lateral branches were filled with Prime & Bond NT/NRC and Clearfil Se Bond adhesive systems. It was concluded that the use of NaOCl influenced negatively in the formation of the hybrid layer, mainly for the One-Up Bond F.     

Tri‐block copolymers of polyethylene glycol and hyperbranched poly‐3‐ethyl‐3‐(hydroxymethyl)oxetane through cationic ring opening polymerization

Tri‐block copolymers of linear poly(ethylene glycol) (PEG) and hyperbranched poly‐3‐ethyl‐3‐(hydroxymethyl)oxetane (poly‐TMPO) are reported. The novel dumb‐bell shaped polyethers were synthesized in bulk with cationic ringopening polymerization utilizing BF₃OEt₂ as initiator, via drop‐wise addition of the oxetane monomer. The thermal properties of the materials were successfully tuned by varying the amount of poly‐TMPO attached to the PEG‐chains, ranging from a melting point of 54 °C and a degree of crystallinity of 76% for pure PEG, to a melting point of 35 °C and a degree of crystallinity of 12% for the polyether copolymer having an average of 14 TMPO units per PEG chain. The materials are of relatively low polydispersity, with M_n/M_w ranging from 1.2 to 1.4. The materials have been evaluated for usage with the energetic oxidizer ammonium dinitramide. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6191–6200, 2009     

On the dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide: a frustrated solvent

We have found that the dissolution of cellulose in the binary mixed solvent tetrabutylammonium acetate/dimethyl sulfoxide follows a previously overlooked near-stoichiometric relationship such that one dissolved acetate ion is able to dissolve an amount of cellulose corresponding to about one glucose residue. The structure and dynamics of the resulting cellulose solutions were investigated using small-angle X-ray scattering (SAXS) and nuclear magnetic resonance techniques as well as molecular dynamics simulation. This yielded a detailed picture of the dissolution mechanism in which acetate ions form hydrogen bonds to cellulose and causes a diffuse solvation sheath of bulky tetrabutylammonium counterions to form. In turn, this leads to a steric repulsion that helps to keep the cellulose chains apart. Structural similarities to previously investigated cellulose solutions in aqueous tetrabutylammonium hydroxide were revealed by SAXS measurement. To what extent this corresponds to similarities in dissolution mechanism is discussed.     

Two-phase Flow Dynamics at the Interface Between GDL and Gas Distributor Channel Using a Pore-Network Model

Transport in Porous Media - For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to...     

Naphthenic acids as indicators of crude oil biodegradation in soil,based on semi‐quantitative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Crude oil contaminated soil cores were collected from a basin that contained oily solids left from three decades of oil production. Hydrocarbon biomarker analyses revealed that the soil extracts were moderately biodegraded compared with the non‐degraded source oil. The degree of biodegradation also decreased with core depth (7 cm to 1 m). These data were correlated to compositional changes observed in acidic NSO‐compounds that were selectively ionized and mass resolved by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FT‐ICR MS). Among the NSO‐compounds ionized, the increase in naphthenic acid concentration (e.g., acyclic and alicyclic carboxylic acids) best correlated with the increase in biodegradation (e.g., from non‐degraded to moderately degraded) as determined by the hydrocarbon biomarker analyses. The most biodegraded surface extracts (7 cm) exhibited an 80% increase in the abundance of acids relative to the source oil. Use of an internal standard allowed the semi‐quantitative determination of the total naphthenic acid concentration, which decreased significantly (P < 0.05) with soil depth. Furthermore, the shift to higher double bond equivalents (DBEs), from acyclic to alicyclic acids, indicated that the increase in acids in the soil extracts was predominately due to biotic processes. This work demonstrates the potential of ESI FT‐ICR MS as a semi‐quantitative tool to monitor the production of naphthenic acids during crude oil biotransformation in the environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Enhanced detection of gold nanoparticles in agarose gel electrophoresis

Gel electrophoresis is a powerful tool in gold nanoparticle (AuNP) research. While the technique is sensitive to the size, charge, and shape of particles, its optimal performance requires a relatively large amount of AuNP in the loading wells for visible detection of bands. We here describe a novel and more sensitive method for detecting AuNPs in agarose gels that involves staining the gel with the common organic fluorophore fluorescein, to produce AuNP band intensities that are linear with nanoparticle concentration and almost an order of magnitude larger than those obtained without staining the gel.     

Dynamics of H2 dissociation on the 1/2 ML c(2 × 2)-Ti/Al(100) surface

The dissociation of H(2) on Ti-covered Al surfaces is relevant to the rehydrogenation and dehydrogenation of the NaAlH(4) hydrogen storage material. The energetically most stable structure for a 1/2 monolayer of Ti deposited on the Al(100) surface has the Ti atoms in the second layer with a c(2 × 2) structure, as has been confirmed by both low-energy electron diffraction and low-energy ion scattering experiments and density functional theory studies. In this work, we investigate the dynamics of H(2) dissociation on a slab model of this Ti/Al(100) surface. Two six-dimensional potential energy surfaces (PESs) have been built for this H(2) + Ti/Al(100) system, based on the density functional theory PW91 and RPBE exchange-correlation functionals. In the PW91 (RPBE) PES, the lowest H(2) dissociation barrier is found to be 0.65 (0.84) eV, with the minimum energy path occurring for H(2) dissociating above the bridge to top sites. Using both PESs, H(2) dissociation probabilities are calculated using the classical trajectory (CT), the quasi-classical trajectory (QCT), and the time-dependent wave-packet methods. We find that the QCT H(2) dissociation probabilities are in good agreement with the quantum dynamics results in the collision energy range studied up to 1.0 eV. We have also performed molecular beam simulations and present predictions for molecular beam experiments. Our molecular beam simulations show that H(2) dissociation on the 1/2 ML Ti/Al(100) surface is an activated process, and the reaction probability is found to be 6.9% for the PW91 functional and 1.8% for the RPBE at a nozzle temperature of 1700 K. Finally, we have also calculated H(2) dissociation rate constants by applying transition state theory and the QCT method, which could be relevant to modeling Ti-catalyzed rehydrogenation and dehydrogenation of NaAlH(4).     

Bimetallic coordination networks based on Al(acacCN)3: a building block between inertness and lability

The Al(III) complex of 3-cyanopentane-2,4-dionate (acacCN) features peripheric nitrile groups which may coordinate to silver cations. As the Al(acacCN)(3) building block ranges between inertness and lability, its reactivity towards Ag(I) salts depends on the solvent and the weakly or non-coordinating counter anions; an impressive range of different extended structures has been encountered. With AgPF(6), the original building block is retained and hexafluorophosphate remains uncoordinated. A highly symmetric 3D crystalline solid forms in the presence of trichloromethane, and with benzene a tetrasolvate with large solvent-filled voids is obtained. Two different classes of reaction products with silver triflate have been observed. In addition to networks incorporating Al(acacCN)(3), partial solvolysis may lead to a dinuclear methoxide-bridged derivative. The resulting Al(2)(μ-OMe)(2) core may be perceived as a four-connected node in a self-interpenetrating 3D network. Earlier studies reported transmetalation for the reaction of Al(acacCN)(3) with AgNO(3) and we find the same reactivity for silver tetrafluoroborate. Full degradation of the Al(III) building block with formation of [Ag(acacCN)] is observed.