Measuring salinity by conductivity

The simple conductivity method described here uses a home-made electrode for determining the salinity of estuarine waters     

Effect of conductivity interfaces

By utilizing an integral equation formulation of Laplace’s equation it is shown that knowledge of the geometry of the conductivity interface, the values of conductivity, and the potentials and gradients on the conductivity interface are sufficient information to determine the infinite media potentials and infinite media potential gradients. The integral equations may be approximated by finite sums and the results can be implemented practically by using a medium size digital computer.     

Bacteria detection utilizing electrical conductivity

Real-time and specific detection of single bacterium remains a fundamental challenge and draws very much attention. Using test patterns composed of interdigitated Au-electrode arrays modified with antibody, the specific and quantitative detection of the electrical conductivity of a single Escherichia coli (E. coli, JM109) has been carried out in this work. The key is to ensure low background current of the antibody-modified test patterns before bacteria detection (<0.7pA in this case) and minimize the residual moisture or hydration after E. coli immobilization, such as via the use of 1-min bake at 50 degrees C prior to electrical measurement. This method holds great potential for future application in the real-time, specific, and quantitative bacterium detection down to a single bacterium cell.     

Theory of the near-wall conductivity

A model describing the phenomenon of the electron current in a plane plasma slab bounded by parallel dielectric walls in the presence of a homogeneous magnetic field perpendicular to the walls and an electric field oriented along the walls is presented. The current flows along the electric field because of the electron collisions with diffusely scattering walls. The model takes into account the presence of Debye layers and the non-Maxwellian character of the electron distribution function. Collisions in the plasma volume are ignored.     

Asymmetric conductivity of engineered porins

Positively charged peptide segments of 16 and 18 residues were inserted at a periplasmic turn of the porin from Rhodobacter blasticus in order to form an electric field-dependent plug. The X-ray diffraction analysis of a mutant confirmed that the structure of the porin had remained intact and that the insert was mobile. Incorporation experiments of single molecules into lipid bilayers showed that the distribution of electric conduction increments depended on the field polarity. The observed distributions are explained if the porin molecules enter the bilayer preferentially with their periplasmic surface first. Furthermore, the conduction of membrane-incorporated porin mutants changed reproducibly on field reversal showing asymmetries of reverse similar 15%, while the wild-type remained constant. This asymmetry is most likely caused by the electric field pressing the charged insert onto the pore eyelet in one field direction and removing it from the eyelet in the other. The results encourage attempts to improve the inserts in order to eventually reach diode characteristics.     

Hydraulic conductivity of tonoplast-freeChara cells

Summary This study is the first trial to measure the osmotic water permeability or the hydraulic conductivity of the plasmalemma alone of a plant cell. For this purpose tonoplast-free cells were prepared from intenodal cells ofChara australis and their hydraulic conductivities were measured by the transcellular osmosis method.The transcellular hydraulic conductivity did not change after removing the tonoplast. The transcellular hydraulic conductivity of the tonoplast-free cells was dependent on the internal osmotic pressure as is the case in the tonoplast-containing normal cells. The hydraulic conductivities for both endosmosis and exosmosis of the tonoplast-free cells were equal to respective values of the normal cells. Consequently the ratio between the inward and outward hydraulic conductivities did not change due to the loss of the tonoplast. The results indicate that the resistance of the tonoplast to water flow is negligibly small as compared with that of the plasmalemma and further that the tonoplast is not a factor responsible for the direction-dependency of hydraulic conductivity. The hydraulic conductivity of the plasmalemma is invariable for wide variations of K⁺ and Ca²⁺ in the cytoplasm.     

The hydraulic conductivity of Matrigel

In this study, we measured the specific hydraulic conductivity (K) of Matrigel at 1% and 2% concentrations as a function of perfusion pressure (0 to 100 mmHg) and compared the results to predictions from two models: a fiber matrix model that predicted K of the gel based upon its composition, and a biphasic model that predicted changes in K caused by pressure induced compaction of the gels. The extent of gel compaction as a function of perfusion pressure was also assessed, allowing us to estimate the stiffness of the gels. As expected, 2% Matrigel had a lower K and a higher stiffness than did 1% Matrigel. Measured values of K of both 1% and 2% Matrigel samples showed good agreement with the predictions of the fiber matrix model. Pressure-induced changes in K were better described by the biphasic model than a model in which uniform compression of the gel was assumed. We conclude that K of multi-component gels, such as Matrigel can be well characterized by fiber matrix models, and that pressure-induced changes in K of such gels can be well characterized by biphasic models.     

Hydraulic conductivity of polymer matrices

We demonstrate that the chondroitin sulfate proteoglycan exhibits enhanced sensitivity to the flow of water compared to other macromolecules which is in accord with their functional role in conferring compressive resistance to cartilage. In order to understand factors that may contribute to its low hydraulic conductivity, a comparative study of hydraulic conductivity, as measured by the sedimentation velocity technique is made of various macromolecules representing variations in charge density, chemical composition, thermodynamic nonideality, size and flexibility. The polymers examined were dextran, poly(ethylene glycol), poly(vinyl alcohol), albumin, and dextran sulfate. The differences in hydraulic conductivity between the various macromolecules could not be explained by conventional theories which included prediction of hydraulic conductivity related to the radius of the molecule regarded as a uniform cylinder, nor the absolute charge density of the molecule and nor to the steric hindrance offered by the macromolecule to the diffusion of tritiated water. A qualitative relationship is established, however, between the noncounterion polymer contribution to osmotic activity and the resistance to water flow for polymers with high osmotic activity.     

High-frequency conductivity of photoionized plasma

The tensor of the high-frequency conductivity of a plasma created via tunnel ionization of atoms in the field of linearly or circularly polarized radiation is derived. It is shown that the real part of the conductivity tensor is highly anisotropic. In the case of a toroidal velocity distribution of photoelectrons, the possibility of amplification of a weak high-frequency field polarized at a sufficiently large angle to the anisotropy axis of the initial nonequilibrium distribution is revealed.     

Hydraulic conductivity of rice roots

A pressure chamber and a root pressure probe technique have been used to measure hydraulic conductivities of rice roots (root Lp(r) per m(2) of root surface area). Young plants of two rice (Oryza sativa L.) varieties (an upland variety, cv. Azucena and a lowland variety, cv. IR64) were grown for 31-40 d in 12 h days with 500 micromol m(-2) s(-1) PAR and day/night temperatures of 27 degrees C and 22 degrees C. Root Lp(r) was measured under conditions of steady-state and transient water flow. Different growth conditions (hydroponic and aeroponic culture) did not cause visible differences in root anatomy in either variety. Values of root Lp(r) obtained from hydraulic (hydrostatic) and osmotic water flow were of the order of 10(-8) m s(-1) MPa(-1) and were similar when using the different techniques. In comparison with other herbaceous species, rice roots tended to have a higher hydraulic resistance of the roots per unit root surface area. The data suggest that the low overall hydraulic conductivity of rice roots is caused by the existence of apoplastic barriers in the outer root parts (exodermis and sclerenchymatous (fibre) tissue) and by a strongly developed endodermis rather than by the existence of aerenchyma. According to the composite transport model of the root, the ability to adapt to higher transpirational demands from the shoot should be limited for rice because there were minimal changes in root Lp(r) depending on whether hydrostatic or osmotic forces were acting. It is concluded that this may be one of the reasons why rice suffers from water shortage in the shoot even in flooded fields.     

Interstitial hydraulic conductivity in a fibrosarcoma

Convective transport of therapeutic agents in solid tumors can be improved through intratumoral infusion. To optimize the convection, we investigated the dependence of the hydraulic conductivity on tissue deformation induced by interstitial fluid pressure gradient during the infusion. Two experimental systems were used in the investigation: 1) one-dimensional perfusion through tumor slices and 2) intratumoral infusion using a needle. With these systems, we found that the apparent hydraulic conductivity (K(app)) could be altered by several orders of magnitude in fibrosarcomas through changes in perfusion conditions. When the perfusion pressure was less than a threshold level, fluid flow in tissues could not be detected. When the perfusion pressure was increased above the threshold level, K(app) depended on perfusion system and pressure. The maximum variation in K(app) in fibrosarcomas reached 80,260-fold in our experiments. The large variation in K(app) could be explained by perfusion pressure-induced tissue deformation. These experimental data suggest that the hydraulic conductivity is very sensitive to tissue deformation and imply that it is possible to improve intratumoral infusion of therapeutic agents through optimization of infusion conditions.     

Effect of conductivity interfaces in electrocardiography

This paper develops numerical techniques for two problems of interest in electrocardiography: (1) the determination of infinite-media surface potential gradients from boundedmedia torso potentials, and (2) the effects of lung-torso, blood mass-torso, and torso-air conductivity interfaces on torso surface potentials. This paper is an extension of a previous paper on the effects of conductivity interfaces which also utilized an integral equation formulation of Laplace's equation. Supported in part by USPHS Grants HE 05716 and HE 11307 and American Heart Grant 67-850.     

Electrical conductivity in a mixed-species biofilm

Geobacter sulfurreducens can form electrically conductive biofilms, but the potential for conductivity through mixed-species biofilms has not been examined. A current-producing biofilm grown from a wastewater sludge inoculum was highly conductive with low charge transfer resistance even though microorganisms other than Geobacteraceae accounted for nearly half the microbial community.     

A technique for measuring the thermal conductivity and evaluating the "apparent conductivity" concept in biomaterials

A simple technique for measuring thermal conductivity of biomaterials is described. The method is based on depositing a pulse of heat into the material of choice, and fitting the subsequent local temperature decay to that predicted by a theoretical model. This transient method is most suitable in situations where frequent measurements of the thermal conductivity are desired. The method was evaluated by calculating the thermal conductivity of several inert materials. The measured conductivities compared well with published values. The developed technique was also used to examine the applicability of the "apparent conductivity" index to combine both conductive and blood-convective thermal effects in living, blood perfused tissues. Using both simulated and experimental results, it was shown that the changes in the apparent conductivity are highly correlated with changes in blood flow. However, quantitative application of this index must be restricted to conditions that are similar to those which existed at the time the apparent conductivity was measured.