AN IN SITU METHOD TO STUDY THE REACTION CATALYZED BY ALKALINE PHOSPHATASE ON DNPP

The reaction catalyzed by alkaline phosphatase on disodium‐p‐nitrophenyl phosphate was studied in a reaction media composed of sucrose (43.5 and 53.5%, w/w) and sucrose (43.5%, w/w) + polysaccharide (10%, w/w) added with agar‐agar (0.5%, w/w) at low temperatures (20, 0 and ?5C). The results show that temperature and concentration of sucrose and sucrose + dextran in the media affect the enzymatic reaction. The presence of 10% dextran (molecular weight of 10⁴ g/mol, w/w) in the reaction medium decreased the reaction rate. This could be explained by the increase in the viscosity of the medium, due to the presence of this polysaccharide. The experimental data were compared with predicted values, calculated from Atkin's theory. The results show that in our experimental conditions described previously, the reaction catalyzed by alkaline phosphatase cannot be predicted by Atkin's theory, probably because the viscosity was not the main parameter governing the reaction.     

TEM and AES investigations of the natural surface nano‐oxide layer of an AISI 316L stainless steel microfibre

The chemical composition, nanostructure and electronic structure of nanosized oxide scales naturally formed on the surface of AISI 316L stainless steel microfibres used for strengthening of composite materials have been characterised using a combination of scanning and transmission electron microscopy with energy‐dispersive X‐ray, electron energy loss and Auger spectroscopy. The analysis reveals the presence of three sublayers within the total surface oxide scale of 5.0–6.7 nm thick: an outer oxide layer rich in a mixture of FeO.Fe₂O₃, an intermediate layer rich in Cr₂O₃ with a mixture of FeO.Fe₂O₃ and an inner oxide layer rich in nickel.     

The Economics of Codification and the Diffusion of Knowledge

The process by which knowledge or information evolves and spreadsthrough the economy involves changing its nature between tacitand codified forms. The process of codification includes threeaspects: model building, language creation and the writing ofmessages. Recent technical changes in several technologies haveimpinged on these three activities and changed the costs andbenefits from each of them, generally lowering the costs ofcodification. Technical changes have also facilitated the diffusionof codified knowledge, which has increased its value. Due tothe temporal relations among the three aspects of codification,the ongoing process in which codification takes place may bepathdependent.     

Cloning and Characterization of the KlDIM1 Gene from Kluyveromyces lactis Encoding the m26A Dimethylase of the 18S rRNA

The KlDIM1 gene encoding the m₂⁶A rRNA dimethylase was cloned from a Kluyveromyces lactis genomic library using a PCR amplicon from the Saccharomyces cerevisiae ScDIM1 gene as probe. The KlDIM1 gene encodes a 320-amino acid protein which shows 81% identity to ScDim1p from S. cerevisiae and 25% identity to ksgAp from Escherichia coli. Complementation of the kasugamycin-resistant ksgA-mutant of E. coli lacking dimethylase activity demonstrates that KlDim1p is the functional homologue of the bacterial enzyme. Multiple alignment of dimethylases from prokaryotes and yeasts shows that the two yeast enzymes display distinctive structural motives including a putative nuclear localization signal. © 1997 John Wiley & Sons, Ltd.     

CONSEQUENCES OF A CONFORMATIONAL CHANGE OF FLEXIBLE MACROMOLECULES ON THE NON-NEWTONIAN BEHAVIOUR OF THEIR SOLUTIONS

The shearthickening behaviour of flexible macromolecules in dilute solutions in a simple shear flow is predicted under the assumption of a transconformation from a random coil to a deformed coil at a critical shear rate. Some numerical results for polydisperse solutions in a constant shear rate flow, and monodisperse and polydisperse solutions in a Poiseuille flow are presented     

Coordination within the Firm and Endogenous Growth

The purpose of the paper is to show how firm organization maychange due to endogenous technical change. The firm is depictedas an organization where a collective knowledge on manufacturing(mastering and improving existing technology) is built throughlearning by doing, requiring coordination between workers withinthe workshop. Two styles of coordination, each of them correspondingto a special design of the division of labor, are modeled: acentralized one, in which knowledge is confined to specializedworkers (engineering office) and a decentralized one, in whichevery worker participates in learning. We show that the relativeefficiency (static and dynamic) of these two styles of coordinationmay change when the differentiation of products, stemming fromendogenous forces, grows: whereas the centralized style is moreefficient when the technological level is low, the decentralizedone becomes more efficient when the technological level is higher.     

Wettability and Work of Adhesion of Nonreactive Liquid Metals on Silica

Wettability of silica by gold, silicon, and lead has been determined by the sessile-drop method. The contact angle, θ, and the work of adhesion, W , have been found to be 143° and 227 mJ·m⁻² for gold at 1353 K, 87° and 869 mJ·m⁻² for silicon at 1723 K, and 120° and 203 mJ·m⁻² for lead at 1000 K. Thermodynamic adhesion between silica and nonreactive pure metals has been analyzed using models for metal-oxide bonds. Models based on the assumption that only van der Waals interactions and/or metal-oxygen chemical bonds exist at the metal-oxide interface are unsuited for explaining the relative variations in the W values. A valid model can be accomplished by using an empirical equation which takes into account both metal-oxygen and metal-oxide chemical bonds. It appears that chemical bonds exist at the interface even for nonreactive metal-ionocovalent oxide systems.