n/a

n/a

The SiMe3 group (TMS), introduced as a substituent at the cyclopentadienyl ligand, is found to magnify the solubility of the corresponding metal complexes in supercritical carbon dioxide (scCO(2)). This is verified from comparative solubility measurements of the species (eta(5)-Me-3 SiC5H4)MoO2 Cl, 1a, (eta(5)-Me3SiC5H4)(2)ZrCl2, 2a, and (eta(5)-Me3SiC5H4)Co(CO)I-2.0.5(I-2), 3a (newly synthesised), and of their unsubstituted precursors 1b-3b, respectively. In spite of the increased solubility, the chemical, structural and reactivity properties of the TMS derivatives are scarcely affected. Confirmation comes from a detailed study of the cobalt complex 3a that includes X-ray structural determination. The geometry is most similar to that of the precursor 3b while an apparently different Co-CO interaction is observed in the carboxylated analogue [(eta(5)-PhCH2CO2C5H4)Co(CO) I-2, 3c]. The problem is computationally tackled by using the DFT B3LYP method. The optimised geometries of the simplified models of 3a-3c are all very similar. In particular, the computed stretching frequency of the unique CO ligand is consistent with the insignificant influence of the TMS group while it suggests a reduced amount of metal back-donation in 3c. It is inferred that the TMS complexes 1a-3a, while having higher solubility in scCO2, maintain almost unaltered the electronic and chemical features of their parent compounds. In particular, the role of 1a-3a as catalysts, that is well documented for homogeneous solutions, remains unaltered in the very different scCO(2) environment. The assumption is experimentally validated for 1a by performing with the latter two classic catalytic processes. The first process is the oxidation of PPh3 that is achieved by using molecular oxygen as an oxidant. The second example concerns the epoxidation of cyclohexene achieved in presence of tert-butyl hydroperoxide (TBHP).

Energies of two-electron one-photon transitions from initial double K-hole states and the transition energies of competing processes, namely K hyper-satellites, were computed for low-Z elements, using the multi-configuration Dirac–Fock method. Transition rates are also evaluated.

n/a

n/a

Superoxide reductases catalyze the monovalent reduction of superoxide anion to hydrogen peroxide. Spectroscopic evidence for the formation of a dinuclear cyano-bridged adduct after K(3)Fe(CN)(6) oxidation of the superoxide reductases neelaredoxin from Treponema pallidum and desulfoferrodoxin from Desulfovibrio vulgaris was reported. Oxidation with K(3)Fe(CN)(6) reveals a band in the near-IR with lambda(max) at 1020 nm, coupled with an increase of the iron content by almost 2-fold. Fourier transform infrared spectroscopy provided additional evidence with CN-stretching vibrations at 2095, 2025-2030, and 2047 cm(-)(1), assigned to a ferrocyanide adduct of the enzyme. Interestingly, the low-temperature electronic paramagnetic resonance (EPR) spectra of oxidized TpNlr reveal at least three different species indicating structural heterogeneity in the coordination environment of the active site Fe ion. Given the likely 6-coordinate geometry of the active site Fe(3+) ion in the ferrocyanide adduct, we propose that the rhombic EPR species can serve as a model of a hexacoordinate form of the active site.

n/a

n/a

The fluid phase behaviour for the binary systems carbon dioxide+cyclobutanone and propane+cyclobutanone has been determined experimentally, using Cailletet equipment. For both the systems bubble points have been determined for a number of isopleths covering the whole mole fraction range. Additionally, for the binary system carbon dioxide+cyclobutanone dew points and critical points could be observed for a number of overall-compositions rich in carbon dioxide. The temperature and pressure range were, respectively, from 278 to 369K and from 0.1 to 14.0MPa. Correlation of the experimental data of both systems has been performed using the Soave-Redlich-Kwong (SRK) equation of state. Satisfactory results have been achieved using only one binary interaction parameter. © 2003 Elsevier B.V. All rights reserved.

n/a

n/a

In this paper we extend results on Fredholmness of singular integral operators with piecewise continuous coefficients in reflexive rearrangement-invariant spaces \(X(\Gamma)\) with nontrivial Boyd indices \(\alpha_X,\beta_X\) [K98] to the weighted case. Suppose a weight \(w\) belongs to the Muckenhoupt classes \(A_{\frac{1}{\alpha_X}}(\Gamma)\) and \(A_{\frac{1}{\beta_X}}(\Gamma)\). We prove that these conditions guarantee the boundedness of the Cauchy singular integral operator \(S\) in the weighted rearrangement-invariant space \(X(\Gamma,w)\). Under a ``disintegration condition'' we construct a symbol calculus for the Banach algebra generated by singular integral operators with matrix-valued piecewise continuous coefficients and get a formula for the index of an arbitrary operator from this algebra. We give nontrivial examples of spaces, for which this ``disintegration condition'' is satisfied. One of such spaces is a Lebesgue space with a general Muckenhoupt weight over an arbitrary Carleson curve.

Let \(\Gamma\) be an oriented Jordan smooth curve and \(\alpha\) a diffeomorphism of $\Gamma$ onto itself which has an arbitrary nonempty set of periodic points. We prove criteria for one-sided invertibility of the binomial functional operator \(A=aI-bW\) where $a$ and $b$ are continuous functions, \(I\) is the identity operator, \(W\) is the shift operator, \(Wf=f\circ\alpha\), on a reflexive rearrangement-invariant space \(X(\Gamma)\) with Boyd indices \(\alpha_X,\beta_X\) and Zippin indices \(p_X,q_X\) satisfying inequalities
\[
0<\alpha_X=p_X\le q_X=\beta_X<1.
\]

This article is based on the lesson presented in the scope of academy activities in the area of Sociology (at FCT-UNL). It is intended to approach the controversies concerning the relation between technology and society (technological determinism, effect on employment, importance of the social behaviours in the definition of needs for new products and equipment), and on the most recent trends (over all, since middle of the last century) in terms of technological evolution and of its social and cultural change. Finally, this subject was dedicated to the presentation of the main factors that has lead to the development of the contribution of sociology for the training and education in engineering. Thus, one intends to acquire new elements on this area of knowledge also presented in other schools of engineering of other countries (for examples, United States and Holland), and how the theoretical beddings are been developed since the beginning of 20th century on the modalities of work organization that imply a cooperation between engineering and social sciences.

n/a

n/a

n/a

n/a

n/a

n/a

Rheocasting, as a semi-solid process, allows the production of aluminium matrix composites at relatively low temperatures (ca. 580ºC), thus favouring a reduced reactivity at the reinforcement-metal matrix interface. When one considers the possibility of further processing (such as any treatment involving remelting, even if partial) of the material, this trait allows a more rigorous control of the interfaces. Composite samples have been produced using as matrix an Al-7Si-0.3Mg alloy reinforced with SiCp (granulometry: 120 μm; Vr = 0.30). These were rheocast at 583ºC, followed by forging and subsequent water-quenching. A structural characterisation (optical microscopy and XRD) of the as-received matrix material, as well as of the reinforced and non-reinforced rheocast material was performed. The phases identification will provide a basis for the understanding of the further processing where the rheocast material will be used as a raw material to produce functionally graded metal-matrix composites by centrifugal casting.

n/a

n/a