Development of an egg-white bioassay for monitoring biotin levels in urine and serum.

This article reports on the development of a simple and cost-effective bioassay for the detection of biotin in urine and serum, based on the very selective binding of avidin and biotin. Avidin was allowed to react without isolating it from egg white. Egg white was treated with the dye HABA, which binds to avidin. Upon subsequent treatment with biotin, HABA is released due to the high affinity of biotin to avidin. The amount of HABA released is proportional to the amount of biotin used.     

Leaf anatomy affects the extraction of photosynthetic pigments by DMSO

Dimethylsulfoxide (DMSO) is a widely used solvent for the extraction of chlorophylls (Chls) from leaves of higher plants. The method is preferred because the time-consuming steps of grinding and centrifuging are not required and the extracts are stable for a long time period. However, the extraction efficiency of this solvent is not comparable among plant species, whereas the particular leaf anatomical characteristics responsible for this unevenness remain unknown. In order to examine the influence of leaf anatomy on the extraction efficiency of DMSO (i.e. the concentration of Chls extracted with DMSO as % of the concentration of Chls extracted with 80% acetone), leaves of 19 plant species with different anatomical characteristics were incubated for 40min in DMSO at 65 degrees C. Under these conditions, heterobaric leaves, which are characterized by the occurrence of bundle sheath extensions in the mesophyll, showed lower extraction efficiency of DMSO compared to homobaric leaves and conifer needles. Microscopical observations of DMSO incubated leaf tissues showed that bundle sheath extensions behave as anatomical barriers which prevent the diffusion of DMSO within heterobaric leaves, even after prolonged incubation with the solvent. The effect was stronger in heterobaric leaves possessing thick bundle sheath extensions. The extraction efficiency of DMSO in these leaves was improved by vacuum infiltration of the samples in the presence of warm (65 degrees C) solvent.     

Temporal Stability of Boundary-Free Shear Flows: The Effects of Diffusion

The stability of boundary-free shear flow is studied for the case of variable viscosity due to binary diffusion across the shear layer. This leads to the main difficulty of this investigation, the direct coupling of the momentum and species equations in both the base state calculations as well as the stability analysis. Linear stability analysis is used to examine the effect of a nonuniform concentration profile on the stability of the flow. It is found that for the flow to be stable for all disturbance wave numbers the Reynolds number has to be zero. This is in agreement with constant viscosity free shear flow stability theory. Increasing the magnitude of concentration gradient (increasing the Schmidt number) destabilizes the flow.     

Low-Dimensional Description of Oscillatory Thermal Convection: The Small Prandtl Number Limit

 Low-dimensional models are derived for transitional, buoyancy-driven flow in a vertical channel with prescribed spatially periodic heating. Stationary characteristic structures (empirical eigenfunctions) are identified by applying proper orthogonal decomposition to numerical solutions of the governing partial differential equations. A Galerkin procedure is then employed to obtain suitable low-order dynamical models. Stability analysis of the fixed points of the low-order systems predicts conditions at the primary flow instability that are in very good agreement with direct numerical solutions of the full model. This agreement is found to hold as long as the low-order system possesses a possible Hopf bifurcation (minimum two-equation) mechanism. The effect of the number of retained eigenmodes on amplitude predictions is examined. Received 25 January 1996 accepted 19 July 1996     

A dissipative particle dynamics study of flow in periodically grooved nanochannels

The effect of periodic rectangular wall roughness on planar nanochannel flow is investigated by dissipative particle dynamics simulation. The wall protrusion length is varied, and its effect on the flow is examined. Analysis of particle trajectories and average residence time reveals temporary trapping of fluid particles inside the rectangular cavities for a considerable amount of time. This trapping affects the density, velocity, pressure, and temperature distribution inside and close to the cavities. Inside the cavities, low‐velocity regions and regions of high density related to high pressure and high temperature are observed. When compared with that of the channel with flat walls case, lower flow velocities, temperatures, and pressures are observed for grooved channels. The reduction of the above quantities is more pronounced as the protrusion length, that is, the roughness characteristic length, decreases. Finally, the relation of friction factor, f, with the flow Reynolds number is discussed. The model predicts = constant in the range . The results of this work are of direct relevance to the design of nanofluidic devices. Copyright © 2011 John Wiley & Sons, Ltd.     

Reverse Brascamp–Lieb inequality and the dual Bollobás–Thomason inequality

Archiv der Mathematik - We prove that if $$f:{\mathbb {R}}^n\rightarrow [0,\infty )$$ is an integrable log-concave function with $$f(0)=1$$ and $$F_1,\ldots ,F_r$$ are linear subspaces of...     

How wall properties control diffusion in grooved nanochannels: a molecular dynamics study

The effect of a geometrically-rough wall, amplified by its degree of wettability and stiffness on diffusion coefficient in cases of fluid flow in nanochannels is studied by non-equilibrium molecular dynamics. Diffusion coefficient values, either inside the grooves or as average channel values are affected by the rough wall characteristics. A significant anisotropy along the directions parallel and normal to the flow is observed inside the grooves, while a critical value of groove length below which this anisotropy is enhanced exists. Wall wettability is the property that affects diffusion the most and could be a means of controlling its behavior.     

Computation of high speed turbulent boundary-layer flows using the k–ϵ turbulence model

The applicability of a finite element-differential method to the computation of steady two-dimensional low-speed, transonic and supersonic turbulent boundary-layer flows is investigated. The turbulence model chosen for the Reynolds shear stress and turbulent heat flux is the K-? two-equation model. Calculations are extended up to the wall and the exact values of the dependent variables at the wall are used as boundary conditions. A number of transformations are carried out and the assumed solutions at a longitudinal station are represented by complete cubic spline functions. In essence, the method converts the governing partial differential equations into a system of ordinary differential equations by a weighted residuals method and invokes an ordinary differential equation solver for the numerical integration of the reduced initial-value problem. The results of the computations reveal that the method is highly accurate and efficient. Furthermore, the accuracy and applicability of the k-? turbulence model are examined by comparing results of the computations with experimental data. The agreement is very good.