A New Model for Viscous Dissipation in Porous Media Across a Range of Permeability Values

In this paper a unified mathematical theory for the viscous dissipation term in the governing Brinkman equation is derived. This term has, unlike other models, the correct asymptotic behaviour in both the fully Darcy and Newtonian fluid flow limits.     

alpha-Sarcin catalytic activity is not required for cytotoxicity

Background  

α-Sarcin is a protein toxin produced by Aspergillus giganteus. It belongs to a family of cytotoxic ribonucleases that inactivate the ribosome and inhibit protein synthesis. α-Sarcin cleaves a single phosphodiester bond within the RNA backbone of the large ribosomal subunit, which makes the ribosome unrecognizable to elongation factors and, in turn, blocks protein synthesis. Although it is widely held that the protein synthesis inhibition caused by the toxin leads to cell death, it has not been directly shown that catalytically inactive mutants of α-sarcin are non-toxic when expressed directly within the cytoplasm of cells. This is important since recent studies have cast doubt on whether protein synthesis inhibition is sufficient to initiate apoptosis.     

The internal dynamic modes of charged self-assembled peptide fibrils

Photon correlation spectroscopy is used to study the internal dynamics of self-assembled charged peptide fibrils. Short neutral and charged polymeric aggregates have diffusive modes due to whole macromolecular motion. For long semiflexible fibrils the logarithm of the intermediate scattering function follows a q(2)t(3/4) scaling at long times consistent with a Kratky-Porod free energy and preaveraged Oseen hydrodynamics. Persistence lengths on the order of micrometers are calculated for the peptide fibrils consistent with estimates from the liquid-crystalline phase behavior. Fibril diameters (5-35 nm) calculated from the initial decay of the correlation functions are in agreement with transmission electron microscopy measurements.     

Mixed convection similarity solutions on a horizontal surface

The mixed convection boundary layer on a horizontal plate is considered for the two separate cases when there is a uniform free stream with the plate held fixed and when there is no outer flow but the plate is moving continuously with a uniform velocity along its length. In both cases we assume that power law temperature distribution on the plate which enables the governing equations to be reduced to similarity form. For the first problem we consider the range of buoyancy parameter for which there are dual solutions, showing how these dual solutions arise from a bifurcation and how the lower branch of solutions terminate as the buoyancy parameter tends to zero. For the second problem we show that there is a unique solution for all positive values of the buoyancy parameter and that for negative values the solution terminates at a singular solution with algebraic decay.

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Zusammenfassung Die Grenzschicht an einer horizontalen Platte mit gemischter Konvektion wird für zwei Fälle untersucht: Für eine ruhende Platte bei gleichförmiger Außenströmung und für eine Platte, die sich kontinuierlich mit konstanter Geschwindigkeit in ihrer eigenen Ebene bewegt, ohne Außenströmung. Für beide Fälle wählen wir ein Potenzgesetz für die Temperaturverteilung entlang der Wand, für welche die Grundgleichungen eine Ähnlichkeitslösung zulassen. In der ersten Problemstellung betrachten wir einen Bereich des Auftriebsparameters, für den zweifache Lösungen existieren. Wir zeigen, wie diese doppelten Lösungen aus einer Bifurkation entstehen und wie der untere Lösungszweig endet, wenn der Auftriebsparameter gegen Null strebt. Für die zweite Problemstellung zeigen wir, daß eine eindeutige Lösung existiert für alle positiven Werte des Auftriebsparameters und daß für negative Werte eine singuläre Lösung mit algebraischem Zerfall erreicht wird.

     

Observation of a narrow resonance near the pp threshold

Annihilation and elastic cross-sections of $\text{p}$p have been measured between 400 and 850 MeV/c. In both cross-sections a resonance is observed at a mass of 1939 ± 3 MeV. For its natural width τ ? 4 MeV is obtained.     

On the use of a Pohlhausen method in three dimensional boundary layers

Summary The paper deals with the problem of a three dimensional boundary layer flow on the inner surface of a cone when the flow external to the boundary layer is due to a potential line vortex on the axis of the cone together with a radial flow parallel to the cone generators.The momentum integral equations are solved using a Pohlhausen method. An asymptotic solution of the boundary layer equations is used to overcome the arbitrariness which commonly arises in this type of approach and, together with a discussion of certain other boundary conditions, lays a foundation for the use of the method.

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Zusammenfassung Die Arbeit behandelt das dreidimensionale Grenzschichtproblem der Strömung entlang des Inneren an einem Kegel, wobei die Strömung ausserhalb der Grenzschicht durch einen Potentialwirbel entlang der Kegelachse und durch Radialbewegung entlang der Kegel-Generatoren gebildet wird.Die Momenten-Integral-Gleichung wird mit einer Pohlhausen-Methode gelöst. Eine asymptotische Lösung der Grenzschichtgleichung wird dazu benützt, eine gewisse Willkür zu beseitigen, die gewöhnlich bei solchen Methoden auftritt, und gibt zusammen mit der Diskussion von gewissen Grenzbedingungen die Grundlage der Methode.

     

Automated method for measuring globin adducts of acrylamide and glycidamide at optimized Edman reaction conditions

The general population is exposed to acrylamide, a potential human carcinogen, through food and cigarette smoke. The assessment of human exposure to acrylamide is important in the evaluation of health risks associated with this chemical. Hemoglobin adducts of acrylamide (AA-Hb) and its primary metabolite glycidamide (GA-Hb) are established biomarkers of acrylamide exposure and methods to measure these biomarkers using modified Edman reaction are described. Only limited information about the optimal Edman reaction conditions such as pH or temperature is available for these adducts and the existing methods do not allow automation needed in biomonitoring studies. In this study, the yield of Edman products of AA-Hb and GA-Hb between pH 3-10 and at 35-55 degrees C at different time intervals, and the applicability of liquid-liquid extraction on diatomaceous earth for analyte extraction, were assessed and results were used in a new optimized method. The applicability of our optimized method was assessed by comparing results obtained with a convenience sample from 96 individuals with a conventional method. Maximum yield of Edman products was obtained between pH 6-7, heating the reaction solution at 55 degrees C for 2 h resulted in the same yields as with conventional conditions, and use of diatomaceous earth was found suitable for automated analyte extraction. Using these conditions, no difference was observed between our optimized and a conventional method. The median globin adduct values in the convenience sample are 129 pmol/g globin (range: 27-453 pmol/g globin) and 97 pmol/g globin (range: 27-240 pmol/g globin) for AA-Hb and GA-Hb, respectively. The GA-Hb/AA-Hb ratio decreases significantly with increasing AA-Hb values indicating that measurement of AA-Hb as well as GA-Hb are needed to appropriately assess human exposure to acrylamide.     

Free convection from a horizontal moving sheet

In this paper the free convection flow through a thin rigid hot sheet moving horizontally out of a slot is considered. It is found that there is a similarity formulation of the boundary-layer equations so that the problem reduces to solving a system of coupled ordinary differential equations with suitable boundary conditions. This system of equations is solved numerically for various values of the Prandtl number,Pr, namely 0.45≤Pr≤10000. It is found that for the flow under the sheet there is a reverse flow region near the sheet for small values ofPr, whilst in the case of the flow above the sheet there is no reverse flow region for any value ofPr we have investigated. For the flow under the sheet an asymptotic behaviour, which is valid near the minimum value of the Prandtl number for which it is possible to obtain a numerical solution, is proposed.     

On natural convection from a vertical plate with a prescribed surface heat flux in porous media

This paper presents a theoretical and numerical investigation of the natural convection boundary-layer along a vertical surface, which is embedded in a porous medium, when the surface heat flux varies as (1 +x ²)), where is a constant andx is the distance along the surface. It is shown that for > -1/2 the solution develops from a similarity solution which is valid for small values ofx to one which is valid for large values ofx. However, when -1/2 no similarity solutions exist for large values ofx and it is found that there are two cases to consider, namely < -1/2 and = -1/2. The wall temperature and the velocity at large distances along the plate are determined for a range of values of .Notation g Gravitational acceleration - k Thermal conductivity of the saturated porous medium - K Permeability of the porous medium - l Typical streamwise length - q _w Uniform heat flux on the wall - Ra Rayleigh number, =gK(q _w /k)l/(v) - T Temperature - Too Temperature far from the plate - u, v Components of seepage velocity in the x and y directions - x, y Cartesian coordinates - Thermal diffusivity of the fluid saturated porous medium - The coefficient of thermal expansion - An undetermined constant - Porosity of the porous medium - Similarity variable, =y(1+x ) ^/3/x ^1/3 - A preassigned constant - Kinematic viscosity - Nondimensional temperature, =(T – T )Ra^1/3 k/qw - Similarity variable, = =y(log_e x)^1/3/x ^2/3 - Similarity variable, =y/x ^2/3 - Stream function