Nafion resin–silica nanocomposite solid acid catalysts. Microstructure–processing–property correlations
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Boron-doping effects in carbon nanotubes
When nanotubes form in a carbon arc, the presence of boron results in long boron-doped carbon nanotubes which are generated as dominant zigzags. Metallic behaviour is observed, in contrast to carbon nanotubes, which are semi-conducting.
Effects of Molecular Variables and Architecture on the Rheological Behavior of Dendritic Polymers
Comparisons of simple shear, oscillatory, and creep flow rheological behaviors are presented for several poly(propylenimine) dendrimers (DAB), hyperbranched (HBP) polyesters, and poly(ether−imide) (PEI) HBPs. Variables examined include molecular weight, degree of branching, nature of peripheral groups, and molecular a…
Riboflavin (VB2) photosensitized oxidation of 2′-deoxyguanosine-5′-monophosphate (dGMP) in aqueous solution: a transient intermediates study
The use of time-resolved 337 nm and 248 nm laser flash photolysis with transient absorbance detection has shown direct evidence of electron transfer from dGMP to the triplet state of riboflavin (3RF*). dGMP was used as a DNA model system in order to study the damaging potential of photoexcited riboflavin. The evidence…
Mechanical properties of clay-polyimide (BTDA-ODA) nanocomposites via ODA-modified organoclay
Clay–polyimide [3,3′, 4,4′-benzophenone tetracarboxylic dianhydride–4,4′-oxydianiline (BTDA–ODA)] nanocomposites were synthesized from ODA-modified montmorillonite (organoclay) and poly(amic acid). The layered silicates of organoclay were intercalated by polyimide (BTDA–ODA), as confirmed by X-ray diffraction and by t…
The aromatic pathways of porphins, chlorins and bacteriochlorins
The aromatic pathways of free-base porphins, chlorins and bacteriochlorins have been studied by calculating the nuclear magnetic shieldings at selected points outside the molecules. The strengths of the induced ring currents for a given magnetic field have been obtained by using the aromatic ring current shieldings (A…
Synthesis conditions for hexagonal mesoporous silica layers
Hexagonal mesoporous silica layers were prepared by the sol–gel route using silicon alkoxides as silica precursors and alkyltrimethylammonium bromides to form the templating liquid crystal mesophase. The synthesis conditions required to obtain well-ordered crack-free layers were investigated. Thin layers exhibiting th…
Rapid synthesis of mesoporous SBA-15 molecular sieve by a microwave–hydrothermal process
Ordered, hydrothermally stable mesoporous molecular sieve SBA-15 with hexagonal channel porosity has been synthesized for the first time under microwave–hydrothermal conditions from aged precursor gel within 15 min at 373 K; the crystallized product has been characterized using X-ray diffraction, nitrogen adsorption–d…
In situ Raman spectroscopy applied to electrochemical scaling. Determination of the structure of vaterite
The Raman spectrum of vaterite prepared by electrochemical scaling in carbonically pure water is presented and analysed following the rules of group theory. It is shown that only one of the three crystallographic determinations already proposed for the structure of vaterite is compatible with the results obtained. The…
The HPr Kinase from Bacillus subtilis Is a Homo-oligomeric Enzyme Which Exhibits Strong Positive Cooperativity for Nucleotide and Fructose 1,6-Bisphosphate Binding
Carbon catabolite repression allows bacteria to rapidly alter the expression of catabolic genes in response to the availability of metabolizable carbon sources. In Bacillus subtilis, this phenomenon is controlled by the HPr kinase (HprK) that catalyzes ATP-dependent phosphorylation of either HPr (histidine containing…
Raman scattering study of a phase transition in tantalum pentoxide
Ta2O5 ceramics and crystals were prepared and analyzed using Raman spectroscopy in the temperature range 25–873 K. The low-energy phonon bands (ν < 100 cm−1) of Ta2O5 are assigned to external modes originating from the interaction between different Ta polyhedra and TaOn5 − 2n Ta6O126+ clusters. The temperature and po…
Phase transition of dissociatively adsorbed oxygen on Ag(001)
We show that dissociative oxygen adsorption on Ag(001) induces below room temperature a missing row $2\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}$ reconstruction of the substrate. As demonstrated by the analysis of the photoelectron diffraction patterns, the oxygen atoms sit thereby in a $c(2\ifmmode\times\else…
Electronic components and materials.
Electronic components and materials are systematically presented, including the categories, develop cause and especially the latest new development.
Gold nanoparticles from self-assembled gold(i) amine precursors
The reaction of AuCl(THT) (1) with long chain primary amines (CnH2n+1NH2; n = 8, 12, 16) leads to the formation of the complexes AuCl(NH2R) (R = C8H17, 2; C12H25, 3; C16H33, 4) which are characterized by classical methods and shown to self-organize in the solid state into a fibrous material; decomposition of the compl…
Collagen model peptides: Sequence dependence of triple-helix stability
The triple helix is a specialized protein motif, found in all collagens as well as in noncollagenous proteins involved in host defense. Peptides will adopt a triple-helical conformation if the sequence contains its characteristic features of Gly as every third residue and a high content of Pro and Hyp residues. Such m…
Insights into the formation of hydroxyl ions in calcium carbonate: temperature dependent FTIR and molecular modelling studies
This paper describes the use of temperature dependent FTIR spectroscopy and molecular modelling studies to establish the origin and the nature of surface hydroxyl ions on calcium carbonate. It has been demonstrated that two types (Type I, corresponding to a band at 3690 cm−1 and Type II, corresponding to a band at 364…
Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer
The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/talc) has been investigated. The release of water from Mg(OH)2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial s…
Hydrolysis–condensation reactions of TEOS in the presence of acetic acid leading to the generation of glass-like silica microspheres in solution at room temperature
The generation of dense silica microspheres (density 2.14 ± 0.02 g cm−3; 95–98% of theoretical value) from the hydrolysis and condensation reactions of Si(OC2H5)4 (TEOS) in the presence of a fixed concentration of acetic acid and water (TEOS ∶ CH3COOH ∶ H2O = 1 ∶ 4 ∶ 4) were studied by FTIR absorption spectroscopy, pa…
Colloidal quantum dots. From scaling laws to biological applications
Abstract Over a twenty-year period, condensed matter physicists and physical chemists have elucidated a series of scaling laws which successfully describe the size dependence of solid state properties [1,2]. Often the experiments were performed under somewhat exotic conditions, for instance on mass-selected clusters i…
A Domain Wall Model for Hysteresis in Piezoelectric Materials
This paper addresses the modeling of hysteresis and nonlinear constitutive relations in piezoelectric materials at moderate to high drive levels. Hysteresis and nonlinearities are due to the domain structure inherent to the materials and both aspects must be addressed to attain the full potential of the materials as s…