Groundwater flow pattern in the vicinity of a salt lake

A numerical model was used to visualize and investigate density-driven flow in the subsurface arising in the vicinity of salt lakes, where saline fluid from the lake meets fresh groundwater. Typical flow patterns are determined for a relevant range of the dimensionless parameters Ra and Co, showing that the Rayleigh-number Ra is the relevant parameter for the emergence of density-driven flow, while the influence of the Co-number is small.     

Passive irrigation and functional morphology of crustacean burrows in a tropical mangrove swamp

Flushing measurements and a resin cast of a burrow inhabited by Sesarma messa and Alpheus cf macklay were taken from a Rhizophoraspp. forest. The burrow had 9 openings and occupied a swamp surface area of 0.64 m². Passive irrigation of the burrow was investigated by recording change in conductivity of burrow water in a chamber 45 cm below the swamp surface during tidal inundation of the swamp. The chamber was completely flushed within approximately one hour, i.e. by a single tidal event. Burrow morphology was determined by means of resin casting. The investigated burrow was of discrete structure, with an overall depth of 1.2 m and a total volume of 68 l, i.e. ca. 9% of the volume of swamp soil. The below ground surface area of chambers and tunnels was 3.8 m². The mean and maximum chamber/tunnel diameter was 7 cm and 11 cm respectively. The soil in the close vicinity of the burrow was extensively penetrated by roots, and any two parts of the burrow were located no further than 20 cm away from each other. By reducing diffusion distances within the soil and by being well flushed, the burrows provide an efficient mechanism for removal of excess salt accumulated in the soil around mangrove roots due to exclusion.     

A Theoretical and Experimental Study of Competition Between Solution and Surface Receptors for Ligand in a Biacore Flow Cell

Rate constants that characterize the kinetics of binding and dissociation between biomolecules carry fundamental information about the biological processes these molecules are involved in. An instrument that is widely used to determine these rate constants is the Biacore. In a Biacore experiment, one of the reactants, which we will call the receptor, is immobilized on a sensor chip. During the binding phase of the experiment the other reactant flows past the chip. After binding, buffer alone is introduced into the flow cell and dissociation is monitored. Often surface-based binding assays are influenced by the transport of the reactant in solution, complicating the determination of the chemical rate constants from the observed binding kinetics. We propose a new way to determine the dissociation rate constant by adding soluble receptor during dissociation. The method is tested first on simulated data and then on Biacore experiments where the lac repressor protein binds and dissociates from a stretch of double stranded DNA containing the lac repressor binding site. With this method we find a dissociation rate constant k_d=0.075 ± 0.005s^-1, a value that is faster than previously obtained from Biacore experiments. In developing our method to analyze these experiments we obtain an expression for the transport limited rate constant for a Biacore experiment when soluble receptor is present during dissociation.     

Simulation of Interstitial Fluid Flow in Ligaments: Comparison among Stokes,Brinkman and Darcy Models

In this paper, we use Stokes, Brinkman and Darcy equations to approximate the porous continuum media of ligament tissues respectively, simulate the flow field with FLUENT software, and study the shear stress on the cell surface due to the interstitial fluid flow. Since the Brinkman equation approaches Stokes equation well in high hydraulic permeability (k_p) condition (k_p ≥1.0×10^-8 m² in our numerical simulation), and it is an approximation to Darcy model in low k_p condition (k_p ≤5.0×10^-12 m² in our numerical simulation), we used the Brinkman model to simulate the interstitial fluid flow in the ligament where k_p is approximately 1.0×10^-16 m². It shows k_p and anisotropic property have a little effect on the flow field, but have a great effect on the shear stress on the membrane of interstitial cells (τ_cell). There is a linear relationship between τ_cell and , when k_p =1.0×10^-16 m² and the maximum τ_cell (τ_cell,max) is approximately 10 Pa. The anisotropic property will affect τ_cell''s distribution on the cell surface. When k_x/k_y>1, low τ_cell dominates the cell, while when k_x/k_y<1, high τ_cell dominants the cell.     

Flow field and oscillatory shear stress in a tuning-fork-shaped model of the average human carotid bifurcation

The oscillatory shear index (OSI) was developed based on the hypothesis that intimal hyperplasia was correlated with oscillatory shear stresses. However, the validity of the OSI was in question since the correlation between intimal thickness and the OSI at the side walls of the sinus in the Y-shaped model of the average human carotid bifurcation (Y-AHCB) was weak. The objectives of this paper are to examine whether the reason for the weak correlation lies in the deviation in geometry of Y-AHCB from real human carotid bifurcation, and whether this correlation is clearly improved in the tuning-fork-shaped model of the average human carotid bifurcation (TF-AHCB). The geometry of the TF-AHCB model was based on observation and statistical analysis of specimens from 74 cadavers. The flow fields in both models were studied and compared by using flow visualization methods under steady flow conditions and by using laser Doppler anemometer (LDA) under pulsatile flow conditions. The TF-shaped geometry leads to a more complex flow field than the Y-shaped geometry. This added complexity includes strengthened helical movements in the sinus, new flow separation zone, and directional changes in the secondary flow patterns. The results show that the OSI-values at the side walls of the sinus in the TF-shaped model were more than two times as large as those in the Y-shaped model. This study confirmed the stronger correlation between the OSI and intimal thickness in the tuning-fork geometry of human carotid bifurcation, and the TF-AHCB model is a significant improvement over the traditional Y-shaped model.     

Relationship Between Regional Brain Angiotensinogen a Local Blood Flow and Volume in the Adrenalectomize Rat: Application of Approach to Quantification of Brain Corticosterone Receptors

Abstract: Prior studies from this laboratory have established that angiotensinogen, the prohormone of angiotensin, is unevenly distributed in the rat brain and that adrenalectomy selectively perturbs levels of the prohormone in regions associated with cardiovascular neural pathways. However, plasma angiotensinogen levies are 10²-10³ times higher in plasma than in brain, so that the observation of a unique distribution of brain angiotensinogen may reflect variable plasma contamination. Studies were therefore undertaken to establish whether adrenalectomy selectively alters regional blood flow, blood volume, or plasma contamination of brain tissue, thereby artifactitiously altering apparent angiotensinogen levels. Radioactive 2-deoxyglucose, iodoantipyrine, and inulin were employed in these analyses. We conclude that variations in blood flow do not explain the selective effects of adrenalectomy, but that a variable extent of residual plasma contamination (remaining after transcardiac perfusion) is partially reflected in our earlier data. However, after correcting for plasma contamination, we still find significant changes in selected areas of the rat brain following adrenalectomy. Finally, our results demonstrate the necessity for direct quantitation of plasma contamination of brain tissue segments. This is shown to have relevance in other situations, such as corticosterone binding globulin contamination of brain corticosterone receptor binding.