Macro-Scale Dynamic Effects in Homogeneous and Heterogeneous Porous Media

It is known that the classical capillary pressure-saturation relationship may be deficient under non-equilibrium conditions when large saturation changes may occur. An extended relationship has been proposed in the literature which correlates the rate of change of saturation to the difference between the phase pressures and the equilibrium capillary pressure. This linear relationship contains a damping coefficient, \tau, that may be a function of saturation. The extended relationship is examined at the macro-scale through simulations using the two-phase simulator MUFTE-UG. In these simulations, it is assumed that the traditional equilibrium relationship between the water saturation and the difference in fluid pressures holds locally. Steady-state and dynamic numerical experiments are performed where a non-wetting phase displaces a wetting phase in homogeneous and heterogeneous domains with varying boundary conditions, domain size, and soil parameters. From these simulations the damping coefficient can be identified as a (non-linear) function of the water saturation. It is shown that the value of increases with an increased domain size and/or with decreased intrinsic permeability. Also, the value of for a domain with a spatially correlated random distribution of intrinsic permeability is compared to a homogeneous domain with equivalent permeability; they are shown to be almost equal.     

Acoustic Radiation from a Finite Length Cylindrical Shell Excited by an Internal Acoustic Source: Solution Based on a Boundary Element Method and a Matched Asymptotic Expansion

This paper deals with acoustic radiation by a thin elastic shell, closed by two perfectly rigid discs, immersed in water and filled with air. The system is driven by an internal acoustic source. The shell has a length L, is clamped along one of its boundaries and is freely supported along the other boundary. Using the infinite domain Green's function, the radiated acoustic pressure is modeled by a hybrid layer potential (linear combination with nonreal coefficient of a simple layer and a double layer). Using Green's tensor of the in vacuo shell operator, the shell displacement is expressed as the sum of the field generated by the acoustic pressures and that due to boundary sources. Finally, the Green's function of the interior Neumann problem is used to express the acoustic pressure inside the shell in terms of the acoustic source and shell normal displacement: this representation fails for any frequency equal to one of the resonance frequencies of the shell interior. To overcome this, a light fluid approximation, which is allowed because the inner fluid is a gas, is adopted. Around each resonance frequency, an inner approximation is defined which matches the classical outer approximation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Calcium Bis[bis(trimethylsilyl)amino‐triethylgallate] — A Molecule with Ca‐C‐Ga Three‐Center Bonds

The reaction of calcium‐bis[bis(trimethylsilyl)amide] with two equivalents triethylgallium yields nearly quantitatively the addition product. In the solid state the calcium atoms are coordinated by two nitrogen atoms and two ethyl groups, whereas in solution all ethyl substituents are magnetically equivalent even at low temperatures. The Ca‐C‐Ga two‐electron three‐center bonds show mean Ca‐N and Ca‐C distances of 243 and 268 pm, respectively.     

Chemometric investigations on the representativity of soil sampling

Summary The characterization of the heavy metal contents of a soil area is carried out by narrow screening sampling and subsequent analysis. It is possible by means of the univariate variance analysis to detect significant alterations within the tested area. The position and extent of multivariate changes of the features can be characterized more exactly with the help of multivariate statistical methods such as the combination of cluster and discriminant analytical methods or the principal component analysis. The maximum possible distance between two sampling points is determined by calculation of the autocorrelation function of the features. The number of soil samples, which is necessary for precisely determining the heavy metal contents of the investigated area, can be derived therefrom. With the help of the multivariate autocorrelation function the distance for the representative sampling of the multivariate loads by heavy metals can be described.     

Quantitative gel electrophoresis: new records in precision by elaborated staining and detection protocols

Gel electrophoresis (GE) is a very common analytical technique for proteome research and protein analysis. Despite being developed decades ago, there is still a considerable need to improve its precision. Using the fluorescence of Colloidal Coomassie Blue -stained proteins in near-infrared (NIR), the major error source caused by the unpredictable background staining is strongly reduced. This result was generalized for various types of detectors. Since GE is a multi-step procedure, standardization of every single step is required. After detailed analysis of all steps, the staining and destaining were identified as the major source of the remaining variation. By employing standardized protocols, pooled percent relative standard deviations of 1.2-3.1% for band intensities were achieved for one-dimensional separations in repetitive experiments. The analysis of variance suggests that the same batch of staining solution should be used for gels of one experimental series to minimize day-to-day variation and to obtain high precision.     

Biogenesis of the unique 4',5'-dehydronucleoside of the uridyl peptide antibiotic pacidamycin

The pacidamycins belong to a class of antimicrobial nucleoside antibiotics that act by inhibiting the clinically unexploited target translocase I, a key enzyme in peptidoglycan assembly. As with other nucleoside antibiotics, the pacidamycin 4',5'-dehydronucleoside portion is an essential pharmacophore. Here we show that the biosynthesis of the pacidamycin nucleoside in Streptomyces coeruleorubidus proceeds through three steps from uridine. The transformations involve oxidation of the 5'-alcohol by Pac11, transamination of the resulting aldehyde by Pac5, and dehydration by the Cupin-domain protein Pac13.