Coupling between liquid flow and heat flow in porous media: A connection between two classical approaches

The presented work addresses exclusively to the transport in the liquid (sub)phases occurring in porous media. By analysing the thermodynamics of the solid-liquid and liquid-gas interfaces present within a porous solid-liquid-gas system, it is shown that the forces acting on two distinct subphases of the liquid, due to the presence of a macroscopic temperature gradient, tend to balance each other. Exact counterbalance of the resulting fluxes implies that liquid flow in porous media under nonisothermal conditions is adequately described by the product of isothermal liquid diffusivity and the gradient of volumetric liquid content.It is shown on the basis of physical arguments that in the coefficient matrix, resulting from the analysis of fluxes and forces along the lines of TIP (Thermodynamics of Irreversible Processes), one coupling term vanishes if the liquid content gradient is chosen as the primary driving force. This does not imply that its cross-coefficient, causing the reduced heat flux arising under isothermal conditions from a gradient in liquid content, tends to be zero. The mechanistic Philip and De Vries formulation is reconsidered and is found to be incomplete and not capable of describing true coupling in the thermodynamic sense. Furthermore, the physical interpretation of the so-called reduced heat flux is discussed.     

Intramolecular cycloaddition reactions of exocyclic nitrones: Application in the total synthesis of terpenes

Exocyclic nitrones smoothly participate in intramolecular cycloaddition reactions to provide bridged and fused polycarbocycles. The exploitation of this methodology in the total syntheses of the sesquiterpenes (±)-7,12-secoishwaran-12-ol (44), (±)-hirsutene (56), (±)-coriolin (68) is also presented.     

Determination of the ethylene oxide adduct S-(2-hydroxyethyl)cysteine by a fluorometric HPLC method in albumin and globin from human blood

A new method has been developed for the quantification of 2-hydroxyethylated cysteine resulting as adduct in blood proteins after human exposure to ethylene oxide, by reversed-phase HPLC with fluorometric detection. The specific adduct is analysed in albumin and in globin. After isolation of albumin and globin from blood, acid hydrolysis of the protein and precolumn derivatisation of the digest with 9-fluorenylmethoxycarbonylchloride, the levels of derivatised S-hydroxyethylcysteine are analysed by RP-HPLC and fluorescence detection, with a detection limit of 8 nmol/g protein. Background levels of S-hydroxyethylcysteine were quantified in both albumin and globin, under special consideration of the glutathione transferase GSTT1 and GSTM1 polymorphisms. GSTT1 polymorphism had a marked influence on the physiological background alkylation of cysteine. While S-hydroxyethylcysteine levels in “non-conjugators” were between 15 and 50 nmol/g albumin, “low conjugators” displayed levels between 8 and 21 nmol/g albumin, and “high conjugators” did not show levels above the detection limit. The human GSTM1 polymorphism had no apparent effect on background levels of blood protein 2-hydroxyethylation. Received: 16 February 1998 / Revised: 27 March 1998 / Accepted: 1 April 1998     

Optical emission spectroscopy in reactive hollow cathode arc discharge plasmas – Local distribution of active species during the deposition of hard carbon films

A low pressure arc plasma discharge from a hollow LaB(6)-cathode with up to 100 A discharge current is used to create plasmas of high density. Typical values for the electron density and temperature in PETRA ( Plasma Engineering and Technology Research Assembly) are n(e)=10(12)-10(13) cm(-3) and T(e)=5-20 eV. The ionization ratio is typically 1-10%. Optical emission spectroscopy has been applied to investigate the processes within the plasma which lead to the deposition of thin carbon films. In these experiments hydrogenated carbon films (a-C:H) have been deposited on Si-substrates by introducing hydrocarbon gases (CH(4), C(2)H(2)) into He- and Ar-plasmas. Space resolved optical emission spectroscopy using an in-situ translation mechanism of the optical fibre has been performed to measure the local concentrations of CH-radicals, carbon ions and of the excitation of He-neutrals. In addition the hydrogen liberated by the dissociation of the hydrocarbon molecules has been measured. The dissociation of the hydrocarbon molecules takes place as a localized process in the vicinity of the reactive gas inlet.     

Compact Ovoids in Quadrangles III: Clifford Algebras and Isoparametric Hypersurfaces

In this third part, we consider those compact quadrangles which arise from isoparametric hypersurfaces of Clifford type and their focal manifolds. Sections 9–11 give a comprehensive introduction to these quadrangles from the incidence-geometric point of view. Section 10 contains also a new (algebraic) proof that these geometries are quadrangles.We determine which of these quadrangles have ovoids or spreads and also whether the normal sphere bundles of the focal manifolds admit sections, or whether they are topologically trivial. We give explicit geometric constructions for spreads, ovoids, and sections.     

Compact Ovoids in Quadrangles II: the Classical Quadrangles

In this second part we consider ovoids in the classical compact connected quadrangles. We solve the problem whether closed ovoids or spreads exist in these quadrangles. In fact we prove a slightly more general result: we determine whether the normal sphere bundles of the point- or line space admit sections, or whether they are topologically trivial. We also give explicit geometric constructions for spreads and ovoids. Some of these spreads are apparently new.