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PubMed2001

The influence of storage time on the temperature dependence of the dc electrical conductivity of horn keratin.

The direct current electrical conductivity of horn keratin was measured as a function of temperature, in the temperature range 290-480 K, with a constant heating rate, for samples stored for periods of 2-3 weeks and 5 months. The activation energy of charge conducting process was calculated. The longer storage time reduced the water content, and the electrical conductivity, but increased the activation energy at 290-320 K.

Animals↗
PubMed2004

A study of electrical conductance of meridian in the obese during weight reduction.

This study was designed to investigate the electrical conductance of meridian in the obese during weight reduction. Ten obese including overweight (Body Mass Index, BMI > 26) and 30 healthy (non-overweight) people were recruited from Chung Yuan Christian University. The obese subjects were instructed to follow a weight reduction program that included diet control, exercise and oral intake of Prozac. A device, the design of which is based on the Ryodoraku theorem, was used to measure the electrical conductance of 12 meridians on both sides of the subjects. The results showed that: (1) the average coefficient of variation of the electrical conductances in 24 meridians of the obese group was statistically different from that of the healthy group (p < 0.05); (2) the average coefficient of variation of electrical conductance in the obese after weight reduction was significantly decreased than before the weight reduction program (p < 0.05); (3) the BMI and the electrical conductance of meridian was correlated in the obese (r = -0.77, p < 0.001) as well as in the healthy group (r = -0.92, p < 0.001). These findings suggest that electrical conductance of meridians can be a parameter to monitor weight, especially for obese people.

Adult↗
PubMed1971

Relationship of Electrical Conductance at Two Frequencies to Cold Injury and Acclimation in Cornus stolonifera Michx.

The ratio of electrical conductance measured at two frequencies can be used to predict the cold hardiness of stem sections of Cornus stolonifera Michx. during the first stage of cold acclimation. Electrical conductance at 50 hertz divided by electrical conductance at 100 kilohertz gave a better estimate of hardiness than measurements at either frequency alone. The observed increase in the electrical conductance ratio as hardiness increased is consistent with an increase in membrane permeability. After plants were exposed to nonlethal frost, hardiness increased rapidly, and the relation between the conductance ratio and hardiness changed. This change indicates that ice crystallization induces a significant physiological alteration in the plants. Contrary to expectations, stem sections exposed to lethal temperatures could not consistently be separated from sections exposed to nonlethal temperatures by electrical conductance ratio measurements made immediately after thawing.

Journal Article↗
PubMed2000

A New Method for the Characterization of Electrically Conducting Liquid Bridges.

An electrical conductance technique is employed in investigating the behavior of constant volume liquid bridges when their length is altered. The liquid bridges are edge-pinned between two vertical, identical rods with a variable separation distance. Rods of different radius, material, and edge geometry are examined as they play a role in the response of the system. It is shown that liquid bridge volume and rod radius are the parameters that mainly influence the conductance signal. A mathematical framework is developed for the identification of the geometrical characteristics of liquid bridges explicitly from conductance data. The role of gravity is discussed in both the experiments and the theoretical analysis. The theoretical predictions obtained show a close agreement with measurements. Copyright 2000 Academic Press.

Journal Article↗
PubMed2005

Radiofrequency ablation: importance of background tissue electrical conductivity--an agar phantom and computer modeling study.

PURPOSE: To determine whether radiofrequency (RF)-induced heating can be correlated with background electrical conductivity in a controlled experimental phantom environment mimicking different background tissue electrical conductivities and to determine the potential electrical and physical basis for such a correlation by using computer modeling. MATERIALS AND METHODS: The effect of background tissue electrical conductivity on RF-induced heating was studied in a controlled system of 80 two-compartment agar phantoms (with inner wells of 0.3%, 1.0%, or 36.0% NaCl) with background conductivity that varied from 0.6% to 5.0% NaCl. Mathematical modeling of the relationship between electrical conductivity and temperatures 2 cm from the electrode (T2cm) was performed. Next, computer simulation of RF heating by using two-dimensional finite-element analysis (ETherm) was performed with parameters selected to approximate the agar phantoms. Resultant heating, in terms of both the T2cm and the distance of defined thermal isotherms from the electrode surface, was calculated and compared with the phantom data. Additionally, electrical and thermal profiles were determined by using the computer modeling data and correlated by using linear regression analysis. RESULTS: For each inner compartment NaCl concentration, a negative exponential relationship was established between increased background NaCl concentration and the T2cm (R2= 0.64-0.78). Similar negative exponential relationships (r2 > 0.97%) were observed for the computer modeling. Correlation values (R2) between the computer and experimental data were 0.9, 0.9, and 0.55 for the 0.3%, 1.0%, and 36.0% inner NaCl concentrations, respectively. Plotting of the electrical field generated around the RF electrode identified the potential for a dramatic local change in electrical field distribution (ie, a second electrical peak ["E-peak"]) occurring at the interface between the two compartments of varied electrical background conductivity. Linear correlations between the E-peak and heating at T2cm (R2= 0.98-1.00) and the 50 degrees C isotherm (R2= 0.99-1.00) were established. CONCLUSION: These results demonstrate the strong relationship between background tissue conductivity and RF heating and further explain electrical phenomena that occur in a two-compartment system.

Agar↗
PubMed2005

Effects of concentration, relative permittivity, and temperature on the solution behavior of sodium carboxymethylcellulose as probed by electrical conductivity.

Precise measurements on the electrical conductivity of solutions of sodium salt of carboxymethylcellulose in acetonitrile/water mixed-solvent media containing 10, 20, and 40 vol % of acetonitrile are reported as a function of temperature. The degree of substitution of carboxymethylcellulose used was 0.70, and the concentrations were varied from approximately 1 x 10(-4) to approximately 1 x 10(-2) equiv L(-1). The results showed a decrease in the equivalent conductivity with increasing polyelectrolyte concentration. The applicability of Manning's theory for salt-free polyelectrolyte solutions was examined, and a major discrepancy against the theory was observed. The calculated values of the equivalent conductivity deduced on the basis of this theory were found to be higher than the experimental ones. Possible reasons for this discrepancy have been discussed. The fractions of uncondensed counterions were evaluated, and these were found to depend on the polyelectrolyte concentration. The effects of the temperature and relative permittivity of the medium on the equivalent conductivity as well as on the fraction of uncondensed counterions were also investigated.

Acetonitriles↗
PubMed1993

[The specific electric conductivity of erythrocyte ghosts and hemoglobin in alcoholism].

Changes of electric conductivity of red cell shadows and hemoglobin were measured in 36 alcoholics in various periods of abstinence. Electric conductivity varied as a function of temperature [sigma (T)]. It was compared with viscosity of red cell shadows suspensions and some indexes of red blood. The absolute values of red cell shadows and hemoglobin electric conductivity in alcoholics were higher than in controls in the whole temperature range (34-41 degrees C), being associated with decreased temperature coefficient (delta sigma/delta T). Over the treatment the absolute values of sigma decreased and delta sigma/delta T increased. In normal subjects the curves sigma (T) had a wave within the temperature range 37-38 degrees C which apparently reflected the phasic transition. In alcoholics the wave on the curves sigma (T) either disappeared or showed abnormal variations at 36 and 38 degrees C during the acute period of abstinence. Two weeks later the only variation at 37 degrees C appeared, its intensity increasing with prolongation of abstinent period. The changes seen in the curves sigma (T) correlated with peculiarities of red cell viscosity in the temperature range 34-41 degrees C.

Adult↗
PubMed1993

Relations between on-line electrical conductivity and daily milk production on a low somatic cell count farm.

To study the relation between on-line electrical conductivity and daily milk production, data of 1389 cow days were analyzed. After correction for cow effects and DIM, a rise of 1 mS of the mean electrical conductivity caused a decline of .88 kg/d in milk production. A rise of 1 ln(SCC) unit was associated with an additional decline of .54 kg/d in milk production. In cows without clinical mastitis during the test period, the losses associated with mean electrical conductivity and ln(SCC) were 1.06 and .45 kg/d of milk production, respectively. Electrical conductivity and SCC were associated with daily production loss; the effects were additive. Therefore, electrical conductivity and SCC can be utilized as indirect tests of subclinical mastitis.

Animals↗
PubMed2006

Short communication: genetic correlation between test-day electrical conductivity of milk and mastitis.

Electrical conductivity (EC) of milk is an indicator of mastitis. If EC shows genetic variation and is genetically correlated to mastitis, it could be used in a breeding program that includes selection for improved mastitis resistance. In this study, daily records of EC and mastitis from about 1,500 Holstein cows were analyzed. A bivariate animal model was used for estimation of (co)variance components, including fixed effects of age of calving, herd-test-day, and days in milk, in addition to random additive genetic effects and permanent environmental effects. For EC, the estimated heritability was moderate (0.22 to 0.39), whereas for mastitis, the heritability was low (0.013). The genetic correlation between EC and mastitis was estimated to be 0.75, and genetic improvement of mastitis resistance should be feasible through selection for reduced EC.

Analysis of Variance↗
PubMed2006

Computer simulation of electrical conductivity of colloidal dispersions during aggregation.

The computation approach to the simulation of electrical conductivity of colloidal dispersions during aggregation is considered. We use the two-dimensional diffusion-limited aggregation model with multiple-seed growth. The particles execute a random walk, but lose their mobility after contact with the growing clusters or seeds. The two parameters that control the aggregation are the initial concentration of free particles in the system p and the concentration of seeds psi. The case of psi=1, when all the particles are the immobile seeds, corresponds with the usual random percolation problem. The other limiting case of psi=0, when all the particles walk randomly, corresponds to the dynamical percolation problem. The calculation of electrical conductivity and cluster analysis were done with the help of the algorithms of Frank-Lobb and Hoshen-Kopelman. It is shown that the percolation concentration phi c decreases from 0.5927 at psi=1 to 0 at psi --> 0. Scaling analysis was applied to study exponents of correlation length v and of conductivity t. For all psi>0 this model shows universal behavior of classical 2d random percolation with v approximately t approximately 4/3. The electrical conductivity sigma of the system increases during aggregation reaching up to a maximum at the final stage. The concentration dependence of conductivity sigma(phi) obeys the general effective medium equation with apparent exponent ta(psi) that exceeds t. The kinetics of electrical conductivity changes during the aggregation is discussed. In the range of concentration Pc(phi)<p<0.9527 the time of percolation cluster formation pi c decreases with increasing phi.

Journal Article↗
PubMed1992

The electrical conductivity of phospholipid films as an iodine-sensing mechanism.

The d.c. electrical conductivity of dry phospholipid films is increased by some 8-11 orders of magnitude by the adsorption of iodine vapor. The conductivity of these films has been found to increase as a function of iodine 'vapor pressure' and the quantitative relationship between electrical conductivity and the adsorbed iodine has been determined. Films composed of phospholipids with unsaturated hydrocarbon chains are some three orders of magnitude more electrically conductive than are films of phospholipids containing saturated hydrocarbon chains. Optical spectroscopic measurements show the development of absorption bands centered near 294 nm and 365 nm, upon iodine adsorption. These bands are much more intense for unsaturated phospholipids than for saturated ones. X-ray diffraction studies show that exposure to iodine decreases the thickness of phospholipid bilayers containing unsaturated hydrocarbon chains but does not change the thickness of bilayers containing only saturated chains. The electrical response of the lipid films, upon exposure to iodine, suggests their possible use as iodine sensors.

Biosensing Techniques↗
PubMed1991

Identification of subclinical mastitis with a hand-held electrical conductivity meter.

A hand-held, commercially available instrument for measuring the electrical conductivity of milk (the Milk Checker) has been examined for its usefulness and accuracy in detecting subclinical and clinical mastitis. Foremilk from uninfected quarters had an electrical conductivity of 5.4 to 5.6 millisiemens (mS)/cm. Milk from cows with subclinical Staphylococcus aureus infections had a higher milk conductivity (7.1 to 7.5 mS/cm) but milk from cows with subclinical S uberis infections showed no increase in conductivity (5.3 to 5.6 mS/cm). However, experimental S uberis infections could be detected by a 50 per cent increase in the electrical conductivity of foremilk two milkings before visible signs of mastitis were apparent. The equipment could be a useful advisory/veterinary tool but is unlikely to be used routinely in the milking parlour.

Animals↗
PubMed1995

Electrical conductance and electrode area on sound smooth enamel in extracted teeth.

Electrical conductance measurements are being used experimentally to diagnose caries. Current equipment, e.g. the electronic caries monitor (ECM), uses a probe to scan occlusal fissures. For full-mouth examination this method is rather time-consuming. A method with which only one measurement is needed for an entire (occlusal) surface would be preferable. However, the enlargement of the area being measured will influence the conductance. It was the purpose of this study to investigate the relationship between the electrical conductance of human teeth and the enamel electrode area, and to compare the range of results of surface measurements with those of the scanning method. Twenty-five sound extracted teeth were selected for the study. The reference electrode of the ECM was connected to the roots. The buccal surface was blotted dry, and a coloured dentifrice was syringed in increments onto the surface. After each increment the surface was photographed together with a metric reference, a conductance measurement was performed by holding the ECM probe tip in the dentifrice, and the ECM reading was recorded. For each tooth between 5 and 10 increments were applied and measured. The photographs were digitised and the electrode areas were calculated. A least squares curve fitting procedure yielded a linear relationship between conductance and electrode area (0.88 < or = R2 < or = 1.0, mean R2 = 0.97). For most teeth the threshold for dentinal caries as used for scanning ECM measurements (ECM reading = 6.00) was reached only when the electrode area exceeded 12 mm2. For 6 teeth this conductance was already reached between 5 and 12 mm2.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Caries↗
PubMed2006

Electrical conductivities of the freshly excised cerebral cortex in epilepsy surgery patients; correlation with pathology, seizure duration, and diffusion tensor imaging.

The electrical conductivities (sigma) of freshly excised neocortex and subcortical white matter were studied in the frequency range of physiological relevance for EEG (5-1005 Hz) in 21 patients (ages 0.67 to 55 years) undergoing epilepsy neurosurgery. Surgical patients were classified as having cortical dysplasia (CD) or non-CD pathologies. Diffusion tensor imaging (DTI) for apparent diffusion coefficient (ADC) and fractional anisotropy (FA) was obtained in 9 patients. Results found that electrical conductivities in freshly excised neocortex vary significantly from patient to patient (sigma = 0.0660-0.156 S/m). Cerebral cortex from CD patients had increased conductivities compared with non-CD cases. In addition, longer seizure durations positively correlated with conductivities for CD tissue, while they negatively correlated for non-CD tissue. DTI ADC eigenvalues inversely correlated with electrical conductivity in CD and non-CD tissue. These results in a small initial cohort indicate that electrical conductivity of freshly excised neocortex from epilepsy surgery patients varies as a consequence of clinical variables, such as underlying pathology and seizure duration, and inversely correlates with DTI ADC values. Understanding how disease affects cortical electrical conductivity and ways to non-invasively measure it, perhaps through DTI, could enhance the ability to localize EEG dipoles and other relevant information in the treatment of epilepsy surgery patients.

Action Potentials↗
PubMedDate not supplied

Strategies for molecular designing of novel low-band-gap electrically conducting polymers.

Molecular designing of low-band-gap electrically conducting polymers continues to be a major challenge of the field of electrically conducting polymers. Such polymers are expected to show not only good intrinsic conductivity but also possibly a good transparency in the visible spectrum for their use as infrared sensors/detectors. Low-band-gap polymers can also be of great interest as new polymeric materials for nonlinear optics. Various routes presently followed to achieve this designing with special reference to the donor-acceptor polymers and important results obtained with this route are briefly reviewed.

Biotechnology↗
PubMed1985

Comparison of electrical conductivity of milk with other indirect methods for detection of subclinical mastitis.

Efficacy of detecting subclinical mastitis by electrical conductivity of milk was compared with that of other indirect methods including chloride, sodium, potassium, lactose, bovine serum albumin, and somatic cell count of milk. Quarter samples of foremilk, strippings, and bucket milk were obtained from 75 cows at the afternoon milking over 8 wk. Infection of quarters was ascertained by bacteriological analysis. Electrical conductivity, chloride, and sodium content of milk were more accurate for predicting infection status of quarters than were other variables. Most variables were more accurate in predicting infection when measures were in strippings rather than in foremilk or bucket milk. For measures in strippings, misclassifications by electrical conductivity were 11.2 and 15.5% for false positives and false negatives. The accuracy of the electrical conductivity of milk for detection of subclinical mastitis compared favorably with all indirect methods. Accuracy of detection and adaptability to both manual and automatic cow-side mastitis detection systems indicate that the method has considerable potential as a screening test for subclinical mastitis.

Animals↗
PubMed1996

Monodisperse Electrosprays of Low Electric Conductivity Liquids in the Cone-Jet Mode

An experimental investigation was performed on electrosprays of low electric conductivity liquids (heptane with different amounts of an antistatic additive) that were operated in the cone-jet mode. The effects of liquid flow rate, applied voltage, and liquid electric conductivity on droplet size and spray monodispersity were systematically investigated. The droplet size was found to be dominantly controlled by the liquid flow rate and secondarily by the applied voltage. It showed no dependence on capillary size. For a given liquid, stable and monodisperse electrosprays could be established only within certain ranges of liquid flow rates and applied voltages, that defined a cone-jet domain. This domain was affected by the electric conductivity of the liquid. As the liquid electric conductivity increased, the domain shifted toward smaller flow rates which implies that smaller droplets were generated in the spray. An increase in the capillary diameter caused a narrowing of this domain. Outside the cone-jet domain, electrosprays were unstable and polydisperse with different instability patterns that depended on the applied voltage and the liquid flow rate. Experiments also showed that the droplet size and the spray monodispersity were independent of the electrode configuration, as long as the electrospray was operated at the onset voltage condition, that is defined as the minimum voltage at which the cone-jet mode was established. By using dimensional analysis the controlling variables were combined into a few dimensionless groups and an empirical fit was derived and was shown to correlate well all the experimental data.

Journal Article↗
PubMed1999

Ionic Diffusivity, Electrical Conductivity, Membrane and Thermoelectric Potentials in Colloids and Granular Porous Media: A Unified Model.

Ionic diffusivity, electrical conductivity, membrane and thermoelectric potentials in isotropic and homogeneous colloidal suspensions, and granular porous media saturated by a binary symmetric 1:1 electrolyte are four interrelated phenomena. The microstructure and the surface properties of the solid grains-water interface influence directly these properties. The ionic diffusivities (and the electrical conductivity, respectively) in colloids and porous media have contributions from diffusion (and electromigration, respectively) through the bulk solution occupying the pores, together with electromigration occurring at the grains-water interface in the electrical double layer. Surface diffusion in porous materials has no contribution from concentration gradients along the grains-water interface. Instead, surface diffusion is envisioned as a purely electromigration process due to the membrane potential. The tortuosities of the transport of anions and cations are equal to the bulk tortuosity of the pore space only at high ionic strength. As the ionic strength decreases, the dominant paths for transport of the ion corresponding to the counterion of the electrical double layer shift from the pore space to the solid grains-water interface. Because anions and cations do not move independently, the membrane potential created by the charge polarization alters the velocity of the anions and influences the mutual diffusivity coefficient of the salt in the porous material. An electric potential of thermal origin is also produced in nonisothermal conditions. The ionic contributions to the electrical conductivity are based on a differential effective medium approach. These ionic contributions to the electrical conductivity are used to derive the ionic diffusivities and the membrane and thermoelectric potentials. The influence of the temperature and the presence, in the pore space, of a second immiscible and nonwetting phase is also considered in this model. Porosity is shown to affect the membrane potential. Several predictions of the model are checked with success by comparing the model to a set of experimental data previously published. Copyright 1999 Academic Press.

Journal Article↗