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PubMed2005

Theory of cathode trajectory characterization by canonical mapping transformation.

The paraxial lens theory cannot directly be applied to the cathode trajectories inside the gun. This inconvenience makes the interpretation of cathode trajectories difficult since one cannot use the physical concepts familiar in the paraxial lens theory, such as focal length and magnification factor. We have proposed the canonical mapping transformation (CMT) to describe the electron trajectories inside the gun by relating the ray conditions on the cathode surface to those in the crossover plane. The method takes as variables the distance along the surface and the sine of the ray angle with respect to the surface normal to define ray conditions. It has been shown that the CMT can be characterized by a small number of optical parameters. One of the parameters is the 'electron gun focal length', an extension of the image side focal length in the paraxial lens theory. The crossover size of a triode gun can be calculated from the electron gun focal length and the initial transverse energy spread. The calculation predicts the dependence of the crossover size on the grid voltage due to the change in the electron gun focal length. The prediction is compared with the measurement and shows good agreement with it. Since the CMT optical parameters can be calculated from the representative trajectories only and as they predict practically all the necessary source properties of guns, the CMT can be used as a practical tool in the designing of various types of electron guns.

Journal Article↗
PubMed1999

Time dependence of anodal and cathodal refractory periods in cardiac tissue.

Mehra et al. (PACE 1980; 3:526) observed that immediately after implantation of a pacing electrode in a dog heart, the anodal refractory period (RP) is shorter than the cathodal RP, but after several weeks the anodal RP becomes longer than the cathodal RP. We examine this experiment using numerical simulations based on the bidomain model of cardiac tissue and a Beeler-Reuter membrane. Our hypothesis is that accumulation of inexcitable tissue around the electrode following implantation causes the effective size of the electrode to increase and that this increase is the mechanism underlying the change in RP. We calculate that the anodal RP is shorter than the cathodal RP for both large and small electrodes. However, for large electrodes the threshold for anode "break" stimulation is greater than 8 mA. Mehra et al. defined RP experimentally as the interval at which the threshold stimulus strength becomes greater than 8 mA. If we restrict the stimulus current in our calculations to less than 8 mA, we exclude anode break stimulation from our calculation of the RP. In that case, our results are consistent with Mehra et al. and suggest that their observation resulted from their definition of RP.

Animals↗
PubMed2004

High performance liquid chromatography with an electrochemical detector in the cathodic mode as a tool for the determination of p-nitrophenol and assay of acid phosphatase in urine samples.

Utilizing a commercially available helium-purging device and PEEK tubes for all tubing, especially for connection between the mobile phase and pump, high performance liquid chromatography with an electrochemical detector (ECD/HPLC) at the cathodic mode is a simple and precise method for the determination of p-nitrophenol (NP). Studies with cyclic and hydrodynamic voltammetry indicated that 25% aqueous MeOH containing 0.1% (v/v) CF(3)CO(2)H and -0.8 V vs. Ag/AgCl are the best mobile phase and detection potential for cathodic ECD/HPLC. With the present system, the limits of detection and determination were 0.2 and 0.25 microM, respectively, and up to 50 microM, a linear calibration curve was afforded. Within-day precisions for the analysis of 5 and 50 microM NP were 0.8 and 0.7% (n=6), respectively, and between-day precisions (n=6) for these samples were 3.5 and 2.2%, respectively. Compared with the commonly used Bessey-Lowry-Brock method, cathodic ECD/HPLC was useful for the assay of acid phosphatase in urine samples with p-nitrophenyl phosphate disodium salt as a substrate.

Acid Phosphatase↗
PubMed2003

Differential pulse and square-wave cathodic stripping voltammetry of xanthine and xanthosine at a mercury electrode.

The surface activity of xanthine (Xan) and xanthosine (Xano) at a hanging mercury drop electrode (HMDE) was studied using out-of-phase ac and cyclic dc voltammetry. The results show that Xan and Xano were strongly adsorbed and chemically interacted with the charged mercury surface, which is the prerequisite step for applying the cathodic adsorptive stripping voltammetric determination of such biologically important compounds. Differential pulse cathodic adsorptive stripping voltammetry (DPCASV) and square-wave cathodic adsorptive stripping voltammetry (SWCASV) were applied for the ultratrace determination of Xan and Xano compounds. Moreover, a rapid and sensitive controlled adsorptive accumulation of Cu(II) complexes of both compounds provided the basis of a direct stripping voltammetric determination of such compounds to submicromolar and nanomolar levels. Operational and solution conditions for the quantitative ultratrace determination of Xan and Xano were optimized in absence and presence of Cu(II). The calibration curve data were subjected to least-squares refinements. The effects of several types of inorganic and organic interfering species on the determination of Xan or Xano were considered.

Journal Article↗
PubMed2004

Development of a laser ablation-hollow cathode glow discharge emission source and the application to the analysis of steel samples.

A novel atomic emission spectrometry comprising laser ablation as a sampling source and hollow cathode plasma for the excitation of ablated sample atoms is proposed. In this arrangement, a conventional Grimm-type discharge lamp is employed, but the polarity of the power supply is reversed so that the cylindrical hollow tube acts as a cathode and the glow discharge plasma is produced within this tube. A laser is irradiated to introduce sample atoms into the discharge plasma. Ablated atoms are excited by collisions with electrons and gas species, and emit characteristic radiation upon de-excitation. The experiments were conducted only in an atmosphere of helium gas so as to avoid a rapid erosion of the cathode hollow tube. Phase-sensitive detection with a lock-in amplifier was utilized to reject the continuous background emission of the plasma gas and emissions of sputtered atoms from the tube material. The unique feature of this technique is that the sampling and excitation processes can be controlled independently. The proposed technique was employed for the determination of Cr, Mn, and Ni in low-alloyed steel samples. The obtained concentrations are in good agreement with the reported values. The relative standard deviation (RSD), a measure of the analytical precision, was estimated to be 2-9% for Cr, 3-4% for Mn, and 4-11% for Ni determination.

Journal Article↗
PubMed1982

Electrical stimulation of osteogenesis: studies of the cathode effect on rabbit femur.

Three series of experiments were performed to evaluate the effect of 20 microampère constant direct current on rabbit femora. Stainless steel cathodes were introduced into the medullary cavity and anodes were placed subcutaneously. Both femora were operated on in the same manner but only the right femur was stimulated electrically. The osteogenic effect was determined histomorphometrically in two of the series. No difference in osteogenic response between the right and the left femora was found. In the third series, the femora were divided into proportionally equal parts and bone volume, ash-weight and activity of 85Sr were determined. A non-significant increase in new bone formation in the cathodal region of the right femora was noted. Our conclusion is that direct cathodal current has a weak stimulating effect on new bone formation in rabbit femora.

Animals↗
PubMed1990

Clinical management of dentin hypersensitivity using cathode and anode iontophoresis.

A clinical study was undertaken to study the desensitising effect of Anode and Cathode iontophoresis using solutions and gels. A total number of sixty patients were selected, divided into four groups and subjected to the following methods of treatment. a) Anode Iontophoresis using strontium Chloride Solution (9%) b) Anode Iontophoresis using Strontium Chloride gel (9%) c) Cathode Iontophoresis using Sodium Fluoride solution (2%) d) Cathode Iontophoresis using Sodium Fluoride gel (2%) Distilled water was used as the control Sensitivity was evaluated objectively with the help of specially designed apparatus which delivered measurable electrical stimuli. The results showed a statistically significant difference in the reduction of tooth sensitivity using Strontium Chloride (9%) both as a gel and solution as compared to Sodium Fluoride (2%) gel and solution.

Adult↗
PubMed1985

Appearance of a cathodic band in the electrophoretogram of blood creatine kinase isoenzyme-MM fraction during hypoxia in rats.

In electrophoretograms of creatine kinase (CK; EC 2.7.3.2) in patients' blood, a band, presumably of mitochondrial origin, is occasionally observed on the cathodic side of the CK-MM fraction. We studied the implications of this phenomenon in rats exposed to hypoxic conditions. In the hypoxic cardiac muscle, the proportions of CK-MB and CK-MM were not significantly different from controls, but that of the mitochondrial CK was lower. In the corresponding blood, the cathodic mitochondrial CK band appeared, but disappeared as the animals recovered from hypoxia. The CK-MB isoenzyme was increased in the blood of the control rats, as obtained by heart puncture, but no mitochondrial fraction was detected. We believe that changes in myocardial mitochondria during hypoxia are related to the appearance of the cathodic band. Cytoplasmic CK-MB, unlike mitochondrial CK, markedly increased in the rats' blood during the recovery stage rather than during the hypoxia.

Animals↗
PubMed1977

Pseudomonas aeruginosa infection in cystic fibrosis. Relative prevalence of antibodies in serum against cathodic and anodic migrating P. aeruginosa antigens determined by immunoelectrophoretic methods.

Sera from 119 patients with cystic fibrosis were examined for precipitating antibodies against anodic migrating P. aeruginosa antigens by means of crossed immunoelectrophoresis. The presence of precipitins against cathodic migrating P. aeruginosa antigens was investigated by means of classical immunoelectrophoresis. Thirty-six per cent of the sera contained precipitins against both anodic and cathodic antigens, 20% contained only precipitins against anodic antigens, none contained only precipitins against cathodic antigens, and 44% had no demonstrable P. aeurginosa precipitins. The amount of extra information obtained by combining the results of classical immunoelectrophoresis with the results of crossed immunoelectrophoresis was small.

Adolescent↗
PubMedDate not supplied

Cathodic electrochemiluminescence of Ru(bpy)(3)(2+)/Nafion coated on graphite oxide electrode in purely aqueous solution.

Two cathodic electrochemiluminescence (ECL) peaks have been obtained at -0.99 and -1.80 V (vs. SCE), respectively, from Ru(bpy)(3)(2+)/Nafion coated onto a graphite oxide electrode in purely aqueous solution under cyclic voltammetric (CV) conditions, without addition of any reducing or oxidative reagents. These two ECL peaks were found to correlate to initial scan direction, pH, and reversal potential. Nafion played an important role in the generation of these two ECL peaks because no cathodic emission was observed in the system without Nafion. It seems that a part of Ru(bpy)(3) (3+) electrogenerated at positive potential can remain in the Nafion, even at negative potentials. It was con fi rmed that Ru(bpy)(+) was formed at -1.80 V by addition of S(2)O(8) (2-). The ECL peak at -0.99 V is attributed to the reaction of Ru(bpy)(3+) and OH(-). The ECL peak at -1.80 V is probably due to the annihilation reaction of Ru(bpy)(3+) and Ru(bpy)(+).

2,2'-Dipyridyl↗
PubMed1990

Experimental and theoretical dynamics of isoelectric focusing: IV. Cathodic, anodic and symmetrical drifts of the pH gradient.

The production of anodic, cathodic and symmetrical drifts of a pH 3.5-10 gradient formed by isoelectric focusing in polyacrylamide gels is demonstrated experimentally by manipulation of the electrolyte concentrations. Experimental behavior is reproduced by computer simulation of a model mixture of 15 hypothetical carrier ampholytes whose pIs span the pH range 3-10. The mechanism which produces the drifts is elucidated and approaches to minimize such drifts are discussed. The data suggest why most experimentally observed drifts are cathodic.

Computer Simulation↗
PubMed1985

Medullary osteogenesis with platinum cathodes.

Studies of electrical stimulation of osteogenesis with stainless steel electrodes have previously established a dose-response relationship between current and bone growth. Examination of the effect of differing geometric current densities resulted in the conclusion that very little electrode surface area was involved in stimulation and led to the design of a multiport "distributive" cathode. A series of experiments were performed to extend these results to wire and multiport platinum electrodes. As before, a current-bone growth dose-response relationship was found. Peak bone growth was greater than for stainless steel. However, peak bone growth occurred at 2.0 microA (versus 20 microA for stainless steel). Correlation studies suggest that small changes in cathodic potential affect bone growth more than similar size changes in current. Finally, the generally benign local host response to platinum suggests that platinum may be a suitable material for chronic indwelling anodes for stimulation of osteogenesis.

Animals↗
PubMed1995

Mn concentration in organs of rats after implantation of battery cathode material.

The distribution of Mn, originating from MnO2 in miniaturized batteries, was studied in rats. Forty young male Wistar rats were included in a randomized block experiment with body weight, weight gain, relative organ weight, and the concentration of Mn as dependent variables. Mn containing cathode material was implanted subcutaneously and after 1 month, animals were sacrificed and organs collected. Mn levels were determined by ICPES after destruction of the organic matter using microwave energy. Body weight, weight gain, and relative weight of heart, brain, liver, and kidneys were not significantly altered after implantation of cathode material. However, Mn levels were largely increased in the four organs under study. These high levels did not provoke any of the well-known clinical signs associated with Mn intoxication. Effects of Mn in larger farm animals can be considered as insignificant.

Animal Identification Systems↗
PubMed1996

Oxygen equilibria of cathodic eel hemoglobin analysed in terms of the MWC model and Adair's successive oxygenation theory.

Allosteric effects of erythrocytic NTP and proton concentrations on cathodic eel Hb were investigated by precise measurement of Hb-O2 equilibria (including extreme saturation values) and analysis in terms of the MWC two-state model and the Adair four-step oxygenation theory. Stripped cathodic Hb shows a reverse Bohr effect and high sensitivities to ATP and GTP that extend to high pH values (> 8.5). A decrease in pH raises KT and lowers the allosteric constant L, compared to opposite effects in 'normal' Bohr effect Hbs. Phosphates even at low concentrations (GTP/Hb = 0.5) annihilate the reverse Bohr effect. GTP exerts a greater effect than ATP due to greater changes in KT and L, and NTP slightly reduces KR. In the absence of NTP, about 1.1 protons are released on deoxygenation at pH 8.15 (where most protons are released), indicating a pK value of the reverse Bohr group of approximately 8.2 (higher in oxy-Hb and lower in deoxy-Hb). The pH and NTP dependence of the Adair association constants and calculated fractional populations of Hb molecules in different oxygenation stages show that NTP effectors stabilise the T structure and postpone the T-R transition, whereas protons in the absence of NTP have the opposite effect. A molecular mechanism for the reverse Bohr effect is suggested.

Adenosine Triphosphate↗
PubMedDate not supplied

Vulnerability of the right ventricle to cathodal, anodal, and bipolar stimulation at double diastolic threshold strength.

UNLABELLED: The repetitive ventricular response (RVR) to three stimulation techniques (bipolar, cathodal and anodal) was investigated in 35 patients. 26 patients suffered from coronary heart disease and 9 patients from dilative cardiomyopathy. The stimulation study was performed at a ventricular driving rate of 120/min with one and two premature ventricular extrastimuli. We used rectangular impulses of 1.8 ms duration at double diastolic threshold strength. RVR was scored as follows: 0: no RVR, 1: one nonstimulated RVR, 2: two nonstimulated RVR, 3: three nonstimulated RVR, 4: four to ten nonstimulated RVR, 5: more than ten nonstimulated RVR lasting less than 2 minutes, 6: sustained ventricular tachycardia or ventricular fibrillation. We found that with unipolar anodal stimulation the diastolic threshold was significantly greater and the effective refractory period of the right ventricle was significantly shorter as compared to the other stimulation techniques. Between the three different electrode configurations there were no significant differences concerning the number of consecutive ventricular depolarizations following premature stimulation. CONCLUSION: the phenomenon of RVR is not influenced by the stimulation technique (bipolar, cathodal and anodal) at double diastolic threshold.

Adult↗
PubMed1994

Sub-kilohertz flash X-ray generator utilising a glass-enclosed cold-cathode triode.

The construction and fundamental studies are described for a sub-kilohertz X-ray generator for producing low-dose rate flash X-rays. The X-ray tube was a glass-enclosed cold-cathode triode, composed of a tungsten plate target, a rod-shaped graphite cathode, a mesh-type trigger electrode made of tungsten wires, and a glass tube body. The coaxial condenser was charged up to 60 kV by a power supply, and the electric charges in the condenser were discharged to the X-ray tube repetitively when a negative high-voltage pulse was applied to the trigger electrode. The maximum tube voltage before the discharging was equivalent to the initial charged voltage of the condenser, and the maximum tube current was about 0.3 kA with a charged voltage of 60 kV. The X-ray durations were about 1 microsecond, and the X-ray intensity was about 0.47 microC kg-1 at 0.5 m per pulse with a charged voltage of 60 kV. The maximum repetition rate of the X-rays was about 0.4 kHz, and high-speed radiography was performed.

Animals↗
PubMed1990

Cathode-ray tube displays for medical imaging.

This paper will discuss the principles of cathode-ray tube displays in medical imaging and the parameters essential to the selection of displays for specific requirements. A discussion of cathode-ray tube fundamentals and medical requirements is included.

Data Display↗
PubMed1982

Cathodic trypsin-like immunoreactivity in serum: influence of sex, age, renal function, food and diurnal variation.

Radioimmunologically determined cathodic trypsin-like immunoreactivity (TLI) in serum was positively correlated with age (Spearman's rho = 0.40, p less than 0.001) and negatively correlated with estimated creatinine clearance (Spearman's rho = -0.31, p less than 0.01) in healthy adults (37 women, 27 men) under standard conditions. Women had higher TLI concentrations than men (median value 358 micrograms trypsin standard/l compared with 283 micrograms trypsin standard/l, p less than 0.02). A clinically significant uptake of cathodic trypsin from the intestine to the blood is not likely because no change was found in serum concentrations of TLI and the two major protease inhibitors (alpha 1-antitrypsin and alpha 2-macroglobulin) one hour after a standard meal. No diurnal variation of TLI in serum was found in a group of 12 healthy subjects. The results indicate that due consideration must be given to sex, age and renal function of the persons used in reference groups for TLI determination.

Adult↗