Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CATHODE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1992

Effect of aging the hollow cathode by sputtering on the analytical precision of the hollow cathode discharge emission source.

Sputtering changes the analytical performance of the hollow cathode as an emission source. Proper conditioning (aging) of the hollow with sputtering greatly improves precision. Conditioning decreases the blank emission signal and changes the shape of the hollow. Micrographs which show the evolution of the bottom of the hollow into a stable bulb shape are presented. The blank emission signal decreases with aging of the hollow and approaches a constant value when the hollow is properly conditioned. A short-term stability (n = 5) of approximately 1.8% RSD has been observed frequently. An average long-term stability over several days (n = 45) of 4.5% for Li and 3.5% for Na in the emission signal from microsamples (less than 50 nL) deposited in the hollow cathode discharge source is reported here. Instrumentation, operation, and sample preparation procedures are described.

Electrodes↗
PubMed2003

Electrical characteristics of a split cathodal pacing configuration.

Several electrical configurations can be used for biventricular pacing to achieve cardiac resynchronization. Commercially approved biventricular pacing systems stimulate the RV with an endocardial lead and the LV with a unipolar lead positioned in the cardiac venous circulation using the tip electrodes of both leads linked as a common cathode. The distribution of current with this parallel circuit, split cathodal configuration is dependent on the separate impedances of the two leads. A total of 19 patients with left bundle branch block and congestive heart failure underwent implantation of a cardiac venous lead and standard bipolar right atrial and RV pacing leads. Stimulation thresholds and impedances were measured for the RV and LV in five electrical configurations: (1) unipolar LV from the cardiac venous lead; (2) bipolar LV using the tip electrode in the cardiac vein as the cathode and the ring electrode of the RV lead as the anode; (3) bipolar RV from the RV lead; (4) unipolar split cathodal stimulation of the cardiac venous and RV leads; and (5) bipolar split cathodal stimulation of the cardiac venous and RV leads. Repeat measurements of RV and LV thresholds were made from the pulse generator at 1-year follow-up. The LV stimulation threshold increased from 0.7 +/- 0.5 V in the unipolar configuration to 1.0 +/- 0.8 V in the unipolar split cathodal configuration (P = 0.01) and from 1.0 +/- 0.7 V in the bipolar configuration to 1.3 +/- 0.9 V in the bipolar split cathodal configuration (P < 0.001). The RV stimulation threshold increased from 0.3 +/- 0.2 V in the bipolar configuration to 0.5 +/- 0.2 V in the bipolar split cathodal configuration (P = 0.005). The bipolar impedance measured 874 +/- 299 Omega for the coronary venous lead, 705 +/- 152 for the RV lead, 442 +/- 87 in the split unipolar cathodal configuration, and 516 +/- 64 in the bipolar split cathodal configuration. At 1-year follow-up, the LV stimulation threshold was 1.8 +/- 1.6 in the unipolar split cathodal configuration and 2.4 +/- 1.6 in the bipolar split cathodal configuration (P = 0.003). The RV stimulation threshold at 1 year was 0.7 +/- 0.3 in the unipolar split cathodal configuration and 0.8 +/- 0.3 in the bipolar split cathodal configuration (P = 0.02). The split cathodal configuration significantly increases the apparent stimulation threshold for both the LV and the RV as compared with individual stimulation of either chamber alone. Programming to the bipolar split cathodal configuration further increases the apparent stimulation threshold. These observations support the development of pacing systems with separate LV and RV output circuits for resynchronization therapy.

Adult↗
PubMed2004

The use of air fuel cell cathodes to remove contaminants from spent chromium plating solutions.

Results from experiments using an impregnation-reduction (I-R) Pt / Nafion membrane electrode assembly (MEA) in an air fuel cell cathode to remove contaminants (Cu(II), Ni(II), and Fe(III)) from spent chromium electroplating baths are presented in this study. A platinum-carbon (Pt-C) / Nafion MEA and a Pb planar cathode were also used for comparison. The average removal rates of Cu(II) and Ni(II) were almost the same (0.39 and 0.40 mM hr(-1) (or 0.117 and 0.12 mmol hr(-1)), respectively) but higher than that of Fe(III) (0.16 mM hr(-1), or 0.048 mmol hr(-1)) in accordance with the Nernst-Planck flux equation. The removal rates for the same cation were independent of the cathode used. The average removal rate of each impurity was approximately proportional to the product of its initial concentration and separator area/anolyte volume ratio using Pb cathodes. Under constant current conditions the system using the Pt-C / Nafion cathode needed the highest cell voltage, about 3 V more than needed for the system with the Pt / Nafion cathode. The cell voltage required using the Pt / Nafion cathode was similar to that using the conventional planar Pb cathode. Analyses of cathode deposits by SEM/EDS and XPS techniques indicated they were minimal on the Pb and Pt / Nafion cathode and more apparent on the Pt-C / Nafion cathode. The primary deposits on the Pb cathode were chromium oxides (e.g., Cr2O3) with minor amount of lead chromate (lead dichromate or lead trichromate) and other chromium solids (Cr black). As expected, the dominant deposit on the lead anode surface was PbO2.

Carcinogens, Environmental↗
PubMed2004

Cathode performance as a factor in electricity generation in microbial fuel cells.

Although microbial fuel cells (MFCs) generate much lower power densities than hydrogen fuel cells, the characteristics of the cathode can also substantially affect electricity generation. Cathodes used for MFCs are often either Pt-coated carbon electrodes immersed in water that use dissolved oxygen as the electron acceptor or they are plain carbon electrodes in a ferricyanide solution. The characteristics and performance of these two cathodes were compared using a two-chambered MFC. Power generation using the Pt-carbon cathode and dissolved oxygen (saturated) reached a maximum of 0.097 mW within 120 h after inoculation (wastewater sludge and 20 mM acetate) when the cathode was equal size to the anode (2.5 x 4.5 cm). Once stable power was generated after replacing the MFC with fresh medium (no sludge), the Coulombic efficiency ranged from 63 to 78%. Power was proportional to the dissolved oxygen concentration in a manner consistent with Monod-type kinetics, with a half saturation constant of K(DO) = 1.74 mg of O2/L. Power increased by 24% when the cathode surface areas were increased from 22.5 to 67.5 cm2 and decreased by 56% when the cathode surface area was reduced to 5.8 cm2. Power was also substantially reduced (by 78% to 0.02 mW) if Pt was not used on the cathode. By using ferricyanide instead of dissolved oxygen, the maximum power increased by 50-80% versus that obtained with dissolved oxygen. This result was primarily due to increased mass transfer efficiencies and the larger cathode potential (332 mV) of ferricyanide than that obtained with dissolved oxygen (268 mV). A cathode potential of 804 mV (NHE basis) is theoretically possible using dissolved oxygen, indicating that further improvements in cathode performance with oxygen as the electron acceptor are possible that could lead to increased power densities in this type of MFC.

Bioelectric Energy Sources↗
PubMed1991

Virtual cathode effects during stimulation of cardiac muscle. Two-dimensional in vivo experiments.

We have found that when suprathreshold cathodal stimuli were applied to the epicardium of canine ventricle, impulse propagation originated at a "virtual cathode" with dimensions greater than those of the physical cathode. We report the two-dimensional geometry of the virtual cathode as a function of stimulus strength; the results are compared with the predictions of an anisotropic, bidomain model of cardiac conduction recently developed in our laboratories. Data were collected in six pentobarbital-anesthetized dogs by using a small plaque electrode sewn to the left ventricular epicardium. Arrival times at closely spaced bipolar electrodes oriented radially around a central cathode were obtained as a function of stimulus strength and fiber orientation. The dimensions of the virtual cathode were determined by linear back-extrapolation of arrival times to the time of stimulation. The directional dependence of the conduction velocity was consistent with previous reports: at 1 mA, longitudinal (0 degree) and transverse (90 degrees) velocities were 0.60 +/- 0.03 and 0.29 +/- 0.02 m/sec, respectively. At 7 mA, the longitudinal velocity was 0.75 +/- 0.05 m/sec, whereas there was no significant change in the transverse velocity. In contrast to conduction velocity, the virtual cathode was smallest in the longitudinal orientation and largest between 45 degrees and 60 degrees. Virtual cathode size was dependent on both orientation and stimulus strength: at 0 degree, the virtual cathode was small (approximately 1 mm) and relatively constant over the range of 1-7 mA; at oblique orientations (45 degrees-90 degrees), it displayed a roughly logarithmic dependence on stimulus strength, approximately 1 mm at 1 mA and approximately 3 mm at 7 mA. The bidomain, anisotropic model reproduced both the stimulus strength and the fiber-orientation dependence of the virtual cathode geometry when the intracellular and extracellular anisotropies were 10:1 and 4:1, respectively, but not when the two anisotropies were equal. We suggest that the virtual cathode provides a direct measure of the determinants of cardiac activation; its complex geometry appears to reflect the bidomain, anisotropic nature of cardiac muscle.

Animals↗
PubMed1996

Operating mechanism of the electrolyte cathode atmospheric glow discharge.

Cathode fall ( U(cf)), cathodic current density and atomic emission intensities originating from metal salts in the electrolyte cathode were measured as a function of different discharge parameters. Emission intensities in function of cathode fall indicate a potential barrier in the sputtered mass flux. This means that the primary particles of the cathode sputtering are of positive charge and the cathode fall including its internal variables is the most important factor. The measured current density and the U(cf) as a function of pressure are in accordance with the low pressure data in the literature. The observed decrease of the U(cf) with decreasing pH was explained by a model in that the secondary electron emission coefficient of the cathode (gamma) is controlled through a reaction net of competing reactions of different electron scavengers involving the hydroxonium ions of the cathode solution. The model revealed two different electron emission processes of the electrolyte cathode, an emission coupled with hydrated electrons is dominating below pH 2.5 while a proton-independent emission of poor efficiency is working above pH 3. Our model fits to the reported yields of the ultimate products both in the solution and in the gas phase and offers a calculation of gamma and U(cf) in the function of the cathode acidity. The model provides two other independent gamma calculation methods based on product analysis data.

Journal Article↗
PubMed1995

[Effect of an additional cathode on the electrolytic-polishing of titanium specimens with non-aqueous electrolyte].

The purpose of this study was to polish electrolytically a large maxillary denture base-shaped titanium specimen with non-aqueous electrolyte. The test specimen was prepared by bending a sheet of titanium plate. An additional cathode was made by cutting off part of a cylindrical cathode. The effects of the shape and position of the additional cathode were investigated. Selected factors of the additional cathode were as follows: the connecting point between the additional cathode and the cylindrical cathode, the end position of the additional cathode, and the distance between the additional cathode and the titanium specimen. An acceptable polished titanium surface was obtained when the connecting point was below the electrolyte surface, the end position of the additional cathode was at a similar level to the bottom of the specimen, and the distance between the additional cathode and the specimen was 10 mm.

Dental Polishing↗
PubMed1996

The use of a circumferential cathode improves amplitude of intraoperative electrical transcranial myogenic motor evoked responses.

Measurement of motor evoked responses to transcranial electrical stimulation (tc-MER) is a technique for intraoperative monitoring of motor pathways. Since most anesthetics significantly reduce motoneuronal excitability, optimal stimulation paradigms should be sought. We compared the efficiency of stimulus delivery using two different configurations of the cathode component of the stimulating electrode pair (circumferential: Fz, F3, F4, A1, and A2 versus a single cathode at Fz). The anode was positioned at Cz with both cathode configurations. Fourteen neurologically normal patients undergoing spinal surgery were anesthetized with sufentanil-N2O-ketamine. Partial neuromuscular blockade (single twitch height 25%) was maintained with vecuronium. Compound action potentials to transcranial stimulation with both cathode configurations were recorded from the tibialis anterior muscle. All recordings were completed before spinal manipulation. The median amplitude response using the Fz cathode configuration was 256 microV (10th-90th percentiles: 50-641 microV). With the circumferential cathode configuration, tc-MER amplitude increased to 281 (87-1479) microV (P < 0.01). There was no significant difference in onset latency between electrode configurations. The observed tc-MER amplitude augmentation with the use of a circumferential cathode might allow tc-MER monitoring in those patients who do not have sufficiently reproducible responses when a single cathode is used. A possible explanation is that the circumferential cathode alters the direction of the electrical currents in the cortex, resulting in more efficient depolarization of cortical motor neurons.

Action Potentials↗
PubMed1995

A constant cathodic potential device for faradic stimulation of osteogenesis.

The purpose of this study was to design, develop, and test a device that continuously maintains a constant potential at a cathode with respect to a reference electrode by automatically varying the potential between the cathode and an anode. The ability of the device to maintain a constant cathodic potential with respect to a silver/silver chloride reference electrode is demonstrated in acute testing with a variety of electrodes as well as in chronic testing conducted until battery failure. This constant cathodic potential device permits delivery of current at an optimal cathodic potential for faradic stimulation of osteogenesis which involves a net transfer of charge through biological tissue between, typically, an implanted cathode, the negative electrode where osteogenesis occurs, and either an implanted or a topical anode, the positive electrode required only to complete the electrical circuit. Unlike present devices that maintain a constant direct current between a cathode and an anode but permit potential between said electrodes to vary, this device presents the possible detrimental effects of an undesired electrochemical reaction due to an excessive cathodic potential.

Animals↗
PubMed2000

Cathodic dissolution in the electrocoagulation process using aluminium electrodes.

All the authors working with aluminium electrodes in the electrocoagulation process have shown that a dissolution occurs at the cathode. This result cannot be explained by the electrochemical process in which only the anodes should be dissolved. The most probable reaction is a chemical attack by hydroxyl ions (generated during water reduction) on the aluminium cathode but nobody has proved it in the framework of the electrocoagulation process. So we are interested in determining what kind of reactions occurs at the cathode. For that, we have elaborated a batch pilot apparatus divided into two compartments, allowing measurement of gas formation taking place only in one compartment. The gases measurements were performed by mass spectrometry with helium as carrier gas. To validate our experimental protocol, the first experiments have been done with a stainless steel cathode: in this case, the results have indicated that the amount of created hydrogen is in good agreement with the values calculated using the second Faraday's law. The experiments realised with an aluminium cathode have shown that the hydrogen formation, in these conditions, was higher than those observed with the stainless steel cathode. All our investigations enable us to propose that with an aluminium cathode, hydrogen formation can be separated into two phenomena. The first one is due to an electrochemical reaction (water reduction), and the second one arises from a chemical reaction explaining the dissolution observed at the cathode.

Aluminum↗
PubMed1987

Ventricular tachyarrhythmia initiation in a canine model of recent myocardial infarction. Comparison of unipolar cathodal, anodal and bipolar stimulation.

Ventricular tachyarrhythmia initiation was compared using unipolar cathodal, anodal and bipolar programmed stimulation at 21 sites in 5 normal adult mongrel dogs and 67 noninfarct sites in 16 dogs 3-5 days after experimental myocardial infarction. For this purpose, the minimum number of extrastimuli required for tachyarrhythmia initiation was determined in each pacing mode using twice cathodal threshold current for the drive beats and all extrastimuli except the last. The current and pacing mode were varied for the last extrastimulus (S2, S3 or S4). In the 5 normal dogs, ventricular fibrillation was reproducibly inducible from only 1/21 sites, and only in the cathodal mode. In 15/16 (94%) of the myocardial infarction dogs, a sustained ventricular tachycardia or ventricular fibrillation could be reproducibly initiated with either one (4 dogs), two (5 dogs) or three extrastimuli (6 dogs). Diastolic excitability thresholds were 0.08 +/- 0.03, 0.30 +/- 0.17, and 0.09 +/- 0.04 mA (median +/- SD) for unipolar cathodal, anodal and bipolar pacing, respectively (p less than 0.001 for anodal vs. cathodal and bipolar). The median absolute current required for ventricular tachyarrhythmia initiation was also highest with anodal pacing (0.72 +/- 0.77 mA), versus both the cathodal and anodal modes (0.18 +/- 0.28 and 0.20 +/- 0.28 mA, respectively, each p less than 0.001) but was comparable in all three modes relative to the threshold current (2.0, 2.4 and 2.6 mA for cathodal, anodal and bipolar pacing, respectively) required for initiation. Overall, ventricular tachyarrhythmia initiation was concordant in all three modes at 58/67 (87%) sites and discordant at only 9/67 (13%) sites (p less than 0.001). Moreover, there was no difference in either the pattern of arrhythmia initiated in each of the pacing modes with respect to ventricular tachycardia versus ventricular fibrillation, or in the median current required to initiate ventricular tachycardia (0.30 +/- 0.36 mA) versus ventricular fibrillation (0.31 +/- 0.44 mA; p greater than 0.1). Thus, ventricular tachyarrhythmia initiation was comparable in all three pacing modes with respect to overall success rate, number of ventricular extrastimuli required and the pattern of ventricular tachyarrhythmia initiated. Bipolar pacing with similar size anodal and cathodal electrodes appear to be appropriate for electrophysiologic ventricular tachyarrhythmia studies and are not likely to induce spurious arrhythmias resulting from stimulation at the anodal pole.

Animals↗
PubMed1975

Cathodal proteins from primitive (embryonic) red cells of amphibia. Isolation and characterization.

A group of abundant (15% of the soluble protein) nonhemoglobin proteins was isolated from the primitive (embryonic) red cells found in tadpoles, using the cationic properties of the proteins at pH 8.6 to separate them from hemoglobin and other red cell proteins. The cathodal proteins (CP) were resolved into five components, and the two most predominant proteins were separated and characterized. Purified CP-1b and CP-2 had an amino acid composition similar to that of unfractionated cathodal proteins and to each other, except for small variations in the lysine and half-cystine content. The molecular weight of the purified CP-1b and CP-2 was 13 to 14,000, determined by gel filtration chromatography and electrophoresis in the presence of sodium dodecyl sulfate. Cathodal proteins were immunologically related although there were quantitative differences in reactivity. The concentration of cathodal proteins in primitive (embryonic) red cells was 100 times that in definitive (adult) red cells coincided with the replacement of primitive red cells. The synthesis of the cathodal proteins appeared to continue throughout the life of the primitive red cells; when hemoglobin synthesis declined in primitive red cells, approximately half of the protein synthesized by the cells was cathodal protein. Although the function of the cathodal proteins is as yet unknown, the data suggest that the cathodal proteins are a unique characteristic of erythroid differentiation in early development.

Amino Acids↗
PubMedDate not supplied

Electrochemical effect on denitrification in different microenvironments around anodes and cathodes.

A bio-anode reactor and a bio-cathode reactor were developed to investigate the microenvironments around anodes and cathodes and their effects on denitrification. With an applied current of 40 mA, the oxidation-reduction potentials (ORPs) in the bio-cathode and bio-anode reactors were 100-200 mV lower and 50 mV higher, respectively, than that in the control reactor (a normal bio-reactor). The cathode reaction enhanced denitrification and the anode reaction inhibited denitrification. At 40 mA, the denitrification rate in the bio-cathode reactor was 55.1% higher than that in the control reactor. At 75 mA, the denitrification rate in the bio-anode reactor was just 33.5% of that in control reactor. Electric current of less than 20 mA had no effect on the most probable number (MPN) of denitrifiers, but at 75 mA, the MPN of denitrifiers decreased by 90% in the bio-anode reactor. In the bio-cathode reactor, the MPN of denitrifiers increased more than 100% for the lower ORP environment produced by a cathode reaction at 75 mA.

Bacteria↗
PubMed1975

Cathodic oxygen consumption and electrically induced osteogenesis.

Small amounts of electric current stimulate bone formation in the region of a cathode. The purpose of this experiment is to compare changes in oxygen and hydroxyl ion concentration that occur at the cathode at current levels known to be capable of inducing osteogenesis (10-20 muamps) with those changes that occur at current levels known to be toxic to bone (100 muamps). An oxygen consumption chamber containing an oxygen electrode is fitted with two stainless steel electrodes which are connected to a constant current source. At the cathode, with a current of 100 muamps, oxygen is consumed at nearly stoichiometric rates. At higher current (100 muamps) levels, cathodic oxygen consumption gives way to hydrogen evolution. Cathodic hydroxyl ion production is directly proportional to current. It is concluded from these in vitro experiments that at 10-20 muamps the oxygen tension in the vicinity of the cathode is lowered and the pH is moderately increased. At 100 muamps the oxygen tension is not lowered, but the pH is increased dramatically. If these same changes occur in the vicinity of a cathode in vivo, then lowering the local tissue oxygen tension and raising the local pH may be mechanisms operative in electrically induced bone formation.

Chemical Phenomena↗
PubMed1995

A mathematical model of make and break electrical stimulation of cardiac tissue by a unipolar anode or cathode.

Numerical simulations of electrical stimulation of cardiac tissue using a unipolar extracellular electrode were performed. The bidomain model with unequal anisotropy ratios represented the tissue, and the Beeler-Reuter model represented the active membrane properties. Four types of excitation were considered: cathode make (CM), anode make (AM), cathode break (CB), and anode break (AB). The mechanisms of excitation were: for CM, tissue under the cathode was depolarized to threshold; for AM, tissue at a virtual cathode was depolarized to threshold; for CB, a long cathodal pulse produced a steady-state depolarization under the cathode and hyperpolarization at a virtual anode. At the end (break) of the pulse, the depolarization diffused into the hyperpolarized tissue, resulting in excitation. For AB, a long anodal pulse produced a steady-state hyperpolarization under the anode and depolarization at a virtual cathode. At the end (break) of the pulse, the depolarization diffused into the hyperpolarized tissue, resulting in excitation. For AB stimulation, decay of the hyperpolarization faster than that of the depolarization was necessary. The thresholds for rheobase and diastolic CM, AM, CB, and AB stimulation were 0.038, 0.41, 0.49, and 5.3 mA, respectively, for an electrode length of 1 mm and a surface area of 1.5 mm2. Threshold increased as the size of the electrode increased. The strength-duration curves for CM and AM were similar except when the duration was shorter than 0.2 ms, in which case the AM threshold rose more quickly with decreasing duration than did the CM threshold. CM and AM resulted in similar strength-frequency curves. The model agrees qualitatively, but (in some cases) not quantitatively, with experiments.

Animals↗
PubMed1997

Skin microcirculation during tapwater iontophoresis in humans: cathode stimulates more than anode.

The aim of this controlled study was to evaluate the influence of anode and cathode on skin blood flow by using direct current. Skin microcirculation and skin temperature of 26 healthy subjects (17 men and 9 women, 20-64 years of age) without any vascular diseases were registered when a tapwater iontophoresis was applied. Thermoindifferent water temperature was used to prevent thermic effects on microcirculation. The blood flow measurement was conducted by laser-Doppler flowmetry on the proximal forearm and on the back of the wrist. The skin temperature was measured before and after treatment by an infrared thermometer. In 19 persons there was an intense erythema on the side of the cathode and an only modest one on the side of the anode, while 7 persons showed meager reactions on both sides. The erythema rose strongly from the distal (back of the hand) to the proximal forearm. The comparison of the microcirculation of the arms showed an increase of 120% at the anode and of 700% at the cathode. The differences between the two sides were significant (P < 0.001). After the end of tapwater iontophoresis the skin temperature increased more on the side of the cathode than on the anode side (P < 0.001). The frequency of vasomotion did not change. The vasomotion amplitude increased 67% at the anode (P < 0.05) and 175% at the cathode (P < 0.001). The increased blood flow effect was not age or sex dependent. Although the increased blood flow effect was six times larger on the cathode side, the subjects did not perceive any subjective difference.

Adult↗