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The dissociative chemisorption of oxygen on Ir(110) has been investigated using supersonic molecular beam techniques. The initial probability of dissociative chemisorption (in the limit of zero surface coverage) as a function of incident kinetic energy between 1 and 28 kcal/mol and surface temperature from 85 to 1000 K is reported. For beam kinetic energies less than approximately 4 kcal/mol, the measured values of the initial probability of dissociative chemisorption are explained by a trapping-mediated adsorption mechanism. In this adsorption regime initial probabilities of dissociative chemisorption decrease with both increasing beam energy and surface temperature. The trapping probability of oxygen into the physically adsorbed state on Ir(110) as a function of incident beam energy is presented. For beam kinetic energies greater than ∼4 kcal/mol, a direct chemisorption mechanism dominates. In the direct adsorption regime, initial probabilities of dissociative chemisorption increase with increasing beam energy, and they are dependent on surface temperature, with the dependence decreasing with increasing surface temperature. This behavior is attributed to direct chemisorption into a molecularly chemisorbed state, from which there is a thermally activated kinetic competition between desorption and dissociation. A pseudo-steady-state kinetic model including physically adsorbed oxygen, molecularly chemisorbed oxygen, and atomically chemisorbed oxygen is applied to find that the activation barrier to desorption from the physically adsorbed molecular state is 1.6±0.1 kcal/mol higher than the barrier to conversion to the molecularly chemisorbed state. The activation barrier for desorption from the molecularly chemisorbed state is 1.5±0.15 kcal/mol greater than the barrier to dissociation from this state. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates repulsive interactions of potassium in rhenium using temperature programmed desorption, work-function measurements and optical second-harmonic generation. Evaluation of the validity of available electrostatic models for explaining simultaneously both sets of data; Activation energy for desorption in the limit of zero coverage.

Presents a study which examined the strength of rare-earth and transition-metal exchange coupling in R[sub2]iron[sub14]boride compounds. Experimental details; Results and discussion; Conclusions.

Presents a study which examined the crystallographic and magnetic properties of the compounds Ho2iron[sub14-x]manganese[subx]carbon. Experimental details; Results and discussion; Conclusions.

In this study, polysaccharide-producing bacteria were isolated from slimes collected from two Finnish and one Spanish paper mill and the exopolysaccharides (EPSs) produced by 18 isolates were characterised. Most of the isolates, selected on the bases of slimy colony morphology, were members of the family Enterobacteriaceae most frequently belonging to the genera Enterobacter and Klebsiella including Raoultella. All of the EPSs analysed showed the presence of charged groups in the form of uronic acid or pyruvate revealing the polyanionic nature of these polysaccharides. Further results of the carbohydrate analysis showed that the EPS produced by nine of the enterobacteria was colanic acid. [ABSTRACT FROM AUTHOR]

Presents a study that examined high-field magnetization in coupled holmium and cobalt magnetic sublattice. Methodology; Determination of the spontaneous magnetization of the compound; Evaluation of the hysteresis in the magnetization curves.

Abstract: Recently, it has been shown that using a single-site catalytic system it is possible to tailor entanglement density in the amorphous region of a semi-crystalline polymer, such as polyethylene, with a molar mass greater than 1 million g/mol. The synthesized polymer can be processed in its solid-state, along uniaxial and biaxial directions. It also shows strong heating rate dependence on melting invoking kinetics in randomization of chains from crystal to amorphous phase. With the help of solid-state NMR the distinction between amorphous regions of the synthesized and commercially available ultra-high molar mass polyethylene is made. For example, the polymer synthesized under the controlled conditions, using a homogeneous single-site catalytic system, shows faster motion of methylene units from the noncrystalline to the crystalline regions compared to commercially available nascent polyethylene synthesized using a Ziegler–Natta (Z–N) catalyst. The differences in chain diffusion, and the resultant 13C polarization transfer from the noncrystalline to the crystalline region, are attributed to the difference in entanglement density arising from the polymerization method employed. The two polyethylene samples investigated are of similar molar mass and crystallinity. Conformational changes caused by deformation of the two samples have been characterized and co-relationship with the entanglement density has been established. [Copyright &y& Elsevier]

Clones of a genomic library of Bifidobacterium adolescentis were grown in minimal medium with sucrose as sole carbon source. An enzymatic fructose dehydrogenase assay was used to identify sucrose-degrading enzymes. Plasmids were isolated from the positive colonies and sequence analysis revealed that two types of insert were present, which only differed with respect to their orientation in the plasmid. An open reading frame of 1,515 nucleotides with high homology for sucrose phosphorylases was detected on these inserts. The gene was designated SucP and encoded a protein of 56,189 Da. SucP was heterologously expressed in Escherichia coli, purified, and characterized. The molecular mass of SucP was 58 kDa, as estimated by SDS-PAGE, while 129 kDa was found with gel permeation, suggesting that the native enzyme was a dimer. The enzyme showed high activity towards sucrose and a lower extent towards α-glucose-1-phosphate. The transglucosylation properties were investigated using a broad range of monomeric sugars as acceptor substrate for the recombinant enzyme, while α-glucose-1-phosphate served as donor. d- and l-arabinose, d- and l-arabitol, and xylitol showed the highest production of transglucosylation products. The investigated disaccharides and trisaccharides were not suitable as acceptors. The structure of the transglucosylation product obtained with d-arabinose as acceptor was elucidated by NMR. The structure of the synthesized non-reducing dimer was α-Glcp(1→1)β-Araf. [ABSTRACT FROM AUTHOR]

The article reports on results of a study of the modulation of fibroblast behaviour by enzymatically-tailored pectins. A description of the experimental set-up and measurement method is presented. The study concluded that grafted-engineered pectins modulate fibroblast adhesion through serum adhesive protein adsorption/conformation.