New application of an anchored Ru(II)-N-heterocyclic carbene complex

A new, heterogenized Ru(II)-N-heterocyclic carbene complex was prepared via the method developed by Augustine. The anchored catalyst was characterized by spectros-copic methods and was applied in the hydrogenation of different olefins, aldehydes and ketones. The hydrogenations were performed both in alcohol and in aqueous media on homogeneous and heterogenized complexes. The immobilized complex had a reasonable activity in both conditions and at the same time it was possible to filter out from the reaction mixture and to recycle in several subsequent runs.     

Scientific evidences beyond the application of inactive dry yeast preparations in winemaking

In recent years the use of inactive dry yeast (IDY) preparations such as inactive yeast, yeast autolysates, yeast extracts and yeast hulls or walls have been widely used within the oenological industry to improve either technological processes or the sensory characteristics of wines. Some of these preparations have very specific applications and there are currently many of these products in the market under different brands that promise different ways of improving wine characteristics. Nevertheless, scientific information about the chemistry beyond their use and their action mode is still scarce.The objective of this review is to revise the different applications of specific IDY preparations in winemaking, on the basis of their action mechanisms taking into consideration the scientific information available, underlining the necessity of more scientific work in order to better characterize their chemical composition, their action mechanisms, and the establishment of better criteria for their oenological use.     

Annealing effects of polymers and their underlying molecular mechanisms

This paper indicates that changes in chain mobility, heat capacity, WAXS crystallinity, SAXS long period, SAXS peak intensity, specific volume and morphology as a function of increasing temperature, occur in three fairly distinct annealing ranges (I, II and III) that are more or less the same for all crystallized polymers with a lamellar morphology. It is shown that none of the proposed molecular models to date, including the well-known fold surface premelting model, can satisfactorily account for all the experimental data. However, a new molecular interpretation, based primarily on electron microscopy and SAXS studies of changes such as lateral ‘melting’ from edges of microparacrystallites (mPC) within the lamellae seen at the annealing temperatures can account for the data. With our new molecular interpretation, the effect of temperature increase is established to result in a slight breakup of the laterally aligned mPC within the lamellae at low annealing temperatures in range I, and selective lateral ‘melting’ of the exposed mPC and recrystallization at higher annealing temperatures in ranges II and III, with the recrystallization being very limited in range III. Annealing effects seen in cold- or hot-drawn polymers with a fibrillar morphology can also be readily accounted for by this very general molecular mechanism occurring in the same annealing temperature ranges.     

The effect of temperature and solvent on the polymerization of 2-propenylfuran

Summary 2-Propenylfuran was polymerized by trifluoroacetic acid in various solvents. The reactions were accomplished over the temperature range of -78 to 70°C depending on the solvent used. The kinetics of the polymerization in CCl₄ at 0°C was second order. It was observed that the 2,5-disubstituted furan moiety in the chain grows as the dielectric constant of the solvents decreases and that the percentage of alkylated furan ring in the polymer increases with temperature independently from the solvent used. Both findings are explained by considering the possibility of 2-propenylfuran to propagate either by the C-5 position of the furan ring or by the vinyl bond.     

Splitting phenomena occurring in the martensitic transformation of Cr13 and CrMoV14 stainless steels in the absence of carbide precipitation

Previously unknown splitting phenomena were detected in the martensitic transformation of XCrl3 and XCrMoV14 stainless steels using high resolution dilatometric analysis. These splittings, which are denominatedM _S0 in this article, indicate the martensitic subtransformation of areas of austenite rich in carbon and carbide-forming elements. In contrast to other types of splitting known until now, theM _S0 occur in the absence of carbide precipitation during cooling. From the experimental results obtained in this study, it can be concluded that the splittings resulted from concentration gradients produced in the austenite as a consequence of the partial or total dissolution of M₂₃C₆ carbides during heating. Formerly with the Centre Nacional de Investigaciones Metalúirgicas (CENIM), C.S.I.C     

Effects of carbide-forming elements on the response to thermal treatment of the X45Cr13 martensitic stainless steel

The effects of carbide-forming elements on the response to thermal treatment of the X45Cr13 martensitic stainless steel have been investigated. Heat treatments consisted of austenitizing for 60 s at temperatures ranging from 1000–1250 °C. The higher is the solution treatment temperature, the less M23C6 carbide is left out of solution in the austenite. As a result, the concentration of carbon and alloying elements in the martensite increases and, therefore, an increase in the hardness until a maximum value of 710 HV was found at austenitizing temperatures of 1120 and 1130 °C for the steels X45Cr13 and X45CrMoV14, respectively. At higher austenitizing temperatures, the presence of retained austenite was observed, which leads to a lowering of the hardness value. The higher amount of carbide-forming elements in the X45CrMoV14 determines an increase in retained austenite from 3 vol% to about 30 vol%. Thus, a drop in the hardness value from 710 to 680 and 585 for the steels X45Cr13 and X45CrMoV14, respectively, was found. © 1998 Kluwer Academic Publishers     

Steady state creep in two Ni-Al alloys

Creep of two Ni-AI alloys containing 4.8 and 7.0 wt pct Al was studied in the temperature range 873 to 1073 K and stress range 30 to 400 MPa. The former alloy represents the solid solution of aluminum in nickel, the latter a solid solution strengthened by NI3AI particles. As to its creep behavior the solid solution alloy belongs to the Class n of solid solu-tions,i.e. the creep controlling mechanism is the same as in pure nickel. From the analy-sis of an effective stress dependence of steady state creep rate it follows that the mo-tion of jogged screw dislocations can be considered as the most probable creep control-ling mechanism. The apparent activation energy of creep in the two phase alloy increases with tempera-ture. This effect is caused by changes in the volume fraction of second phase particles and by the onset of climb around particles at high temperatures. At lower temperatures particles are cut by dislocation pairs.     

Isomorphism,form equivalence and sequence equivalence of PD0L forms

It is shown that if two PD0L forms F₁ and F₂ are form equivalent, i.e., generate the same family of languages, then the PD0L sequences E(F₁) and E(F₂) are isomorphic, provided one of the sequences contains a word of length greater than one. This result leads to a simple algorithm of deciding the form equivalence of two PD0L forms F₁ and F₂. Moreover, we obtain the rather surprising result that F₁ and F₂ are form equivalent if and only if they are sequence equivalent, i.e., generate the same family of PD0L sequences (excluding again the trivial case that F₁ and F₂ generate only words of length one).