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At least 1,261 records · Page 70Linked to original sources
PubMed2006

After-effects of transcranial direct current stimulation (tDCS) on cortical spreading depression.

Abnormal cortical excitability influences susceptibility to cortical spreading depression (CSD) in migraine. Because transcranial direct current stimulation (tDCS) is capable of inducing lasting changes of cortical excitability, we investigated the after-effects of tDCS on the propagation velocity of CSD in the rat. Twenty-five anesthetised rats received either anodal, cathodal or sham tDCS. The stimulation was applied for 20 min at a current strength of 200 microA after the recording of three baseline CSD measurements. Starting 5 min after tDCS, a further three CSDs were elicited and CSD velocity recorded at intervals of 20 min. tDCS and CSD recording was performed under anaesthesia with chloralose and urethane. As compared to the baseline velocity of 3.14 mm/min, anodal tDCS induced a significant increase of propagation velocity during the first post-tDCS recording (3.49 mm/min). In contrast to anodal tDCS, neither cathodal tDCS nor sham tDCS, which consisted of an initial ramped DC stimulation lasting only 20 s, showed a significant effect on CSD propagation velocity. As anodal tDCS is known to induce a lasting increase of cortical excitability in the clinical setting, our results support the notion that CSD propagation velocity reflects cortical excitability. Since cortical excitability and susceptibility to CSD is elevated in migraine patients, anodal tDCS - by increasing cortical excitability - might increase the probability of migraine attack in these patients, even beyond the end of its application.

Animals↗
PubMed2006

Coordination stability between metal/ligands interaction by modern spectroscopic studies: IR, electronic, EPR and cyclic voltammetry of cobalt(II) complexes with organic skeleton containing cyclic ligands.

A comparative investigation of the interaction of two pyrrole-substituted, mixed oxygen and nitrogen donor, macrocycles ligands have been designed and their coordination interaction with cobalt(II) is studied. Cobalt(II) salts combine with a tetradentate and hexadentate macrocyclic nitrogen/oxygen donor ligands and formed novel cobalt(II) complexes which are characterized by elemental analysis, molar conductance, magnetic moments, mass, (1)H NMR, IR, electronic and EPR spectral studies. At the room temperature magnetic moment for cobalt(II) complexes lie in the range 4.70-5.01BM, which is higher than the spin-only value. All the complexes are high-spin type and have three unpaired electrons. Therefore, the electronic confutation and the splitting of the orbital will be t(2g)(5)eg(2). The electrochemical behaviour of the cobalt(II) complexes, the Co(III)/Co(II) couple are observed. Their positive potential indicates that metal in lower oxidation state is strongly bound to these ligands. The difference between the potential of the anodic peak and cathodic peak remains constant in all complexes. Also, the ratio between the cathodic peak current and square root of the scan rate is practically constant for the studied complexes.

Cobalt↗
PubMed2005

Modeling and calculation of field emission enhancement factor for carbon nanotubes array.

To estimate the apex field enhancement factor associated with carbon nanotubes (CNTs) array on a planar cathode surface, the image model of floated sphere between parallel anode and cathode plates was proposed. Firstly, the field enhancement factor of individual CNT was given as the following expression, beta0=h/rho+3.5, where h is the height and rho is the radius of CNTs. Then the field enhancement factor of CNTs array was discussed and the above expression was modified to be beta=h/rho+3.5-W, in which W is the function of the intertube distance R and represents the coulomb field interaction between the CNTs. All results show that the intertube distance of CNTs array critically affects the field emission. When the intertube distance is less than the height of tube, the field enhancement factor will decrease rapidly with decreasing the intertube distance. According to the calculated results and considering the field emission current density, the filed emission is optimal theoretically when the intertube distance is comparable with the height of CNTs.

Electrodes↗
PubMed2004

Sonovoltammetric studies on copper in buffered alkaline solution.

The effect of ultrasound on the voltammetry of copper in alkaline solution is reported. At pH 7 the electrode surface remains active after scanning to ca. +1.0 V (vs. SCE) and the effects of ultrasound show the expected substantial enhancement in limiting current due to improved mass transport under ultrasound. However at pH 9, whereas the silent scan is only slightly altered in gross detail from that obtained at pH 7, the sonicated scan is significantly different. This shows the expected current increase only up until ca. +0.6 V (vs. SCE), where there is a substantial loss of current showing a passivation phenomenon that is enhanced by ultrasound. In addition, during the reverse (reduction) scan under ultrasound an anodic peak appears. This suggests reactivation of the electrode during the cathodic sweep, possibly by reductive removal of a transient species from the electrode/(hydr)oxide interface at a potential where oxidation still occurs. Increasing the pH to 11 further shifts the cathodic peaks in the silent voltammogram.

Journal Article↗
PubMed2006

Ultrasonic effects on electroorganic processes. Part 27. Electroreduction of acrylonitrile at suspended lead particle-electrode.

Ultrasonic effect on the electroreduction of acrylonitrile at suspended lead particle-electrode was examined. The product selectivity for adiponitrile, which was formed as the corresponding hydrodimeric product along with propionitrile as the hydromonomeric one in the cathodic reduction of acrylonitrile, was increased by addition of lead particles as a particle-electrode, and moreover the selectivity was further increased under ultrasonication. This ultrasonic effect is rationalized as due to not only mass transport of lead particles to the feeder cathode but also an increase in the effective surface area of particle-electrode by ultrasonic dispersion. A mechanism for the ultrasonic effect is discussed in detail on the basis of the reaction system.

Acrylonitrile↗
PubMed2006

Synthesis of tungsten nanoparticles by sonoelectrochemistry.

Tungsten nanoparticles have been synthesized by the sonoelectrochemical method. The electrolyte contained the tri-sodium citrate, sodium tungstate, ferrous sulphate, and citric acid. A platinum slice was used as the anode and a titanium-alloy horn as the cathode. Twenty kilohertz ultrasound generated by an ultrasound generator was connected to the titanium-alloy horn as an amplitude converter. Due to the electrochemical reaction and the cavitation effect of the ultrasound, the iron-tungsten aggregates at the cathode were dispersed into the electrolyte and iron atoms were dissolved in the acidic environment. In this way, body-center-cubic (bcc) tungsten nanoparticles have been obtained by controlling the density of the electric current, the ultrasound pulse period and amplitude. Their morphology, structure, and chemical components have been characterized using transmission electron microscope (TEM) and X-ray photoelectron spectrometer (XPS).

Crystallization↗
PubMed2007

Electrosynthesis of hydrogen peroxide via the reduction of oxygen assisted by power ultrasound.

The electrosynthesis of hydrogen peroxide using the oxygen reduction reaction has been studied in the absence and presence of power ultrasound in a non-optimized sono-electrochemical flow reactor (20 cm cathodic compartment length with 6.5 cm inner diameter) with reticulated vitreous glassy carbon electrode (30 x 40 x 10 mm, 10 ppi, 7 cm(2)cm(-3)) as the cathode. The effect of several electrochemical operational variables (pH, volumetric flow, potential) and of the sono-electrochemical parameters (ultrasound amplitude and horn-to-electrode distance) on the cumulative concentration of hydrogen peroxide and current efficiency of the electrosynthesis process have been explored. The application of power ultrasound was found to increase both the cumulative concentration of hydrogen peroxide and the current efficiency. The application of ultrasound is therefore a promising approach to the increased efficiency of production of hydrogen peroxide by electrosynthesis, even in the solutions of lower pH (<12). The results demonstrate the feasibility of at-site-of-use green synthesis of hydrogen peroxide.

Electrochemistry↗
PubMed2005

Electricity generation from swine wastewater using microbial fuel cells.

Microbial fuel cells (MFCs) represent a new method for treating animal wastewaters and simultaneously producing electricity. Preliminary tests using a two-chambered MFC with an aqueous cathode indicated that electricity could be generated from swine wastewater containing 8320 +/- 190 mg/L of soluble chemical oxygen demand (SCOD) (maximum power density of 45 mW/m2). More extensive tests with a single-chambered air cathode MFC produced a maximum power density with the animal wastewater of 261 mW/m2 (200 omega resistor), which was 79% larger than that previously obtained with the same system using domestic wastewater (146 +/- 8 mW/m2) due to the higher concentration of organic matter in the swine wastewater. Power generation as a function of substrate concentration was modeled according to saturation kinetics, with a maximum power density of P(max) = 225 mW/m2 (fixed 1000 omega resistor) and half-saturation concentration of K(s) = 1512 mg/L (total COD). Ammonia was removed from 198 +/- 1 to 34 +/- 1 mg/L (83% removal). In order to try to increase power output and overall treatment efficiency, diluted (1:10) wastewater was sonicated and autoclaved. This pretreated wastewater generated 16% more power after treatment (110 +/- 4 mW/m2) than before treatment (96 +/- 4 mW/m2). SCOD removal was increased from 88% to 92% by stirring diluted wastewater, although power output slightly decreased. These results demonstrate that animal wastewaters such as this swine wastewater can be used for power generation in MFCs while at the same time achieving wastewater treatment.

Animal Husbandry↗
PubMed1996

Characterization of Trichuris skrjabini by isoenzyme gel electrophoresis: comparative study with Trichuris ovis.

Morphological and biometric studies were performed in Trichuris skrjabini (Baskakov, 1924) collected from the caecum of Capra hircus. The LDH (EC 1.1.1.27.), G6PD (EC 1.1.1.49.), GPI (EC 5.3.1.9.), MDH (EC 1.1.1.37) and malic enzyme (ME) (EC 1.1.1.40) isoenzymatic patterns of T. skrjabini were determined by starch gel electrophoresis. The G6PD and GPI isoenzymatic patterns of T. skrjabini displayed two anodic bands for both enzymes: one fast migration band and one band near the origin. This isoenzymatic pattern was interpreted as two gene loci encoding both enzymes. The LDH isoenzymatic pattern of T. skrjabini was characterized by the presence of a cathodically migrating band, while the MDH isoenzymatic pattern showed a very slow cathodic band. These two phenotypes were interpreted as the expression of a homozygous state of a gene locus for LDH and MDH in T. skrjabini. The ME isoenzymatic pattern was characterized by the presence of a single anodic band. Further, comparative isoenzymatic studies were carried out between T. skrjabini and T. ovis. The different G6PD, GPI, LDH, MDH and ME isoenzymatic patterns observed for both species allowed us to distinguish them and therefore to use isoenzymatic patterns as a diagnostic tool to differentiate species of Trichuris.

Animals↗
PubMed1990

Clinical efficacy of dual electrode systems for endocardial cardioversion of ventricular tachycardia: a prospective randomized crossover trial.

In order to eliminate the need for epicardial electrodes, two large transvenous catheter electrodes or one catheter and one extrathoracic patch electrode have been proposed as alternative electrode configurations for defibrillation and ventricular tachycardia cardioversion by implantable cardioverter/defibrillators. We compared the efficacy and safety of endocardial shocks delivered through these two electrode systems in man in a prospective randomized crossover study. Twelve patients with sustained ventricular tachycardia and heart disease undergoing electrophysiologic study were evaluated. A transvenous tripolar cardioversion electrode catheter with a large distal defibrillation electrode (surface area, 400 mm2) and proximal defibrillation electrode (surface area, 800 mm2) was positioned in the right ventricular apex with a cutaneous patch electrode placed on the cardiac apex. Sustained ventricular tachycardia was induced at electrophysiologic study. Shocks were delivered using two catheter electrodes only (right ventricular cathode and right atrial anode = method I), and one catheter electrode and cutaneous patch (right ventricular cathode and cutaneous apical patch anode = method II). Synchronized monophasic shocks were delivered using three preselected protocols based on ventricular tachycardia cycle length and morphology. Initial shock energies were 25 joules for polymorphic ventricular tachycardia and ventricular fibrillation, 15 joules for monomorphic rapid ventricular tachycardia (cycle length less than or equal to 300 msec), and 5 joules for monomorphic slow ventricular tachycardia (cycle length greater than 300 msec). Ventricular tachycardia was reinduced and shock energies titrated until cardioversion threshold was obtained. Identical ventricular tachycardia episodes were treated with both methods at each energy level.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1997

Effect of varying pacing waveform shapes on propagation and hemodynamics in the rabbit heart.

The propagation characteristics of myocardium stimulated with anodal, cathodal, and equiphasic biphasic pacing pulses were examined in Langendorff-perfused rabbit hearts. Conduction velocity measurements were made using an array of bipolar extracellular electrodes, transmembrane potentials recorded using floating intracellular microelectrodes, and hemodynamics measured by fluid-filled catheter transducer systems. Anodal (A) stimulation pulses improved the electrical conduction at all the stimulus amplitudes tested in both longitudinal (e.g., 5 V 2-msec pulse: [A] 54.9 +/- 0.7 cm/sec; cathodal [C] 49.7 +/- 1.5 cm/sec) and transverse (e.g., 5 V 2 msec pulse: [A] 31.3 +/- 1.7 cm/sec; [C] 23.3 +/- 2.9 cm/sec) directions. Microelectrode recordings verified that increased conduction velocities of the anodal pulses were associated with faster upstrokes of the action potentials. The increased threshold associated with anodal pulses may be overcome by using a biphasic (B) waveform, in effect adding a second phase (e.g., 2-msec pulse: [A] 2.03 +/- 1.3 V; [C] 3.85 +/- 1.5 V; [B] 2.15 +/- 0.9 V). The conduction speeds achieved by the biphasic pulses were found to be comparable to the equivalent anodal pulses (e.g., 5 V 2-msec pulse: [B] 55.2 +/- 1.7 cm/sec longitudinal and 32.4 +/- 2.1 cm/sec transverse). It is postulated that the enhanced conduction by anodal and biphasic pulses may be due to preconditioning of the myocardium before stimulation, resulting in more vigorous action potential upstrokes. In preliminary experiments, it was observed that improved conduction elicited by these pulses also resulted in enhanced contractility as measured by shortened electromechanical delays and faster rate of rise of pressure development (dP/dtmax: [A] 25.4 +/- 0.4 mm Hg/sec; [C] 19.4 +/- 0.8 mm Hg/sec; [B] 25.7 +/- 1.2 mm Hg/sec, respectively). Use of novel hybrid pulses involving an anodal component may offer a way for implanted pacemakers to enhance the electro-mechanical response of the heart.

Action Potentials↗
PubMed1999

Effect of electrode polarity on the energy required for transthoracic atrial defibrillation.

Two hundred patients with atrial fibrillation underwent transthoracic cardioversion using adhesive electrodes positioned at the apex and right infraclavicular area, and the apex electrode was randomly selected to serve as the cathode or anode. The mean defibrillation energy requirement with the cathodal configuration was significantly lower than with the anodal configuration.

Adolescent↗
PubMed2002

The effect of pulpward pressure on the response to 50% lidocaine (lignocaine) applied to exposed dentine in cats.

The responses of intradental nerves can be blocked by 50% lidocaine applied to exposed, etched dentine. The aim here was to analyse electrophysiologically the contribution of pulpward pressure to the anaesthetic effect of lidocaine applied to exposed dentine. In 17 adult cats with intact lower canines, approximately 1mm of the coronal tip of the canine was removed and the exposed dentine acid-etched. Pulpward pressure was applied to the exposed dentine through a chamber fixed to the tip of the tooth. Cervical and coronal electrodes of silver wire and Ag/AgCl mixture were placed, the cervical 2mm from the gingival margin of the canine and the coronal into the coronal pulp chamber. The inferior alveolar nerve was surgically exposed and single pulpal nerve fibres responding to electrical stimulation of the canine were identified. The chamber was filled with 50% lidocaine solution, and 0 (atmospheric pressure), 1.3, 5.0 or 10.0 kPa pressure was applied to the chamber for 20 min. Orthodromic and antidromic action potentials were compared before and after the lidocaine application. When lidocaine was applied at 0, 1.3 or 5.0 kPa (n=5 each) for 20 min, all the orthodromic responses to cathodal electrical stimulation with the coronal electrode were blocked. Almost all orthodromic responses (12/15) remained unblocked when the cathodal electrical stimulation was applied with the cervical electrode. Applying 10.0 kPa pressure to the lidocaine solution blocked all the pulpal nerve responses (n=5) to both stimulation modes. The amplitude of the antidromic compound action potential was significantly decreased when the applied pressure was increased. These results suggest that increased pulpward pressure may effectively force anaesthetic solution more rapidly through the dentinal tubules into the pulp.

Action Potentials↗
PubMed1992

Effects of protein concentration on IgE receptor mobility in rat basophilic leukemia cell plasma membranes.

The ability of variations of membrane protein concentrations to modulate the lateral diffusion rate of an exemplary membrane protein has been studied in healthy and osmotically shocked cultured cells of the rat basophilic leukemia cell line, 2H3 subclone. Cell surface protein was redistributed by the method of in situ electrophoresis; exposure to electric fields of 1.25-5 V/cm results in cathodal migration of the majority of the surface proteins on this cell type (Ryan, T. A., J. Myers, D. Holowka, B. Baird, and W. W. Webb. Science [Wash. DC]. 239:61-64). Even in these small fields, the steady-state distribution becomes "crowded" with more than an 80% protein occupancy of accessible membrane area at the cathodal end of these spheroidal cells, and the anodal end becomes significantly depleted. We have employed fringe pattern fluorescence photobleaching with CCD imaging detection to measure lateral diffusion coefficients of the liganded IgE receptor on both crowded and uncrowded regions of individual rat basophilic leukemia cells. We find no significant difference in lateral diffusion rates in these regions. Cells swollen by hypoosmotic stress exhibit faster diffusion overall, with the uncrowded regions having a significantly greater increase in diffusion coefficient than the crowded regions. These results are consistent with the partial or total release of cytoskeletal constraints to membrane protein diffusion induced by osmotic stress.

Animals↗
PubMed2003

Polarographic behavior and determination of finasteride.

The polarographic behavior of finasteride at the dropping mercury electrode (DME) was studied adopting direct current (DC(t)), alternating current (AC(t)) and differential-pulse polarography (DPP) modes. In Britton-Robinson buffer (BRb), finasteride exhibited cathodic waves over the pH range 6-12. At pH 10, a well-defined cathodic wave was obtained. The latter could be characterized as being irreversible, diffusion-controlled and partially affected by adsorption phenomenon. The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented. The current-concentration plots were rectilinear over the ranges 8-40 and 2-30 microg ml(-1) using DC(t) and DPP modes, respectively. The minimum delectability was 0.2 microg ml(-1) (5.4 x 10(-7) M), for the latter. The proposed method was successfully applied to the determination of finasteride in its commercial capsules and the results obtained were in good agreement with those given with a reference method.

Finasteride↗
PubMed2001

Separation and on-line preconcentration by sweeping of charged analytes in electrokinetic chromatography with nonionic micelles.

The separation and on-line preconcentration by sweeping of charged analytes in electrokinetic chromatography using a neutral pseudostationary phase is described. Under neutral or basic conditions, the electrophoretic migration of anionic analytes towards the anode is overcome by a high, cathode-directed electroosmotic flow; hence, they experience net migration towards the cathode, and the system is run at positive polarity mode. The separation and the retention factor, k, are dependent on both the analyte's electrophoretic mobility and its interaction with the pseudostationary phase. The versatility of the sweeping mechanism is then shown in this system. The charged analyte, prepared in a matrix free of the pseudostationary phase, penetrates the pseudostationary phase zone upon application of voltage. Analyte molecules are consequently accumulated and concentrated. As a demonstration, the separation and preconcentration of phenol derivatives using nonionic surfactants of the alkyl polyoxyethylene ether type (Brij 35 and Brij 58) yielded peak height enhancements up to 100-fold. The efficiency of sample stacking was also found to be improved with the use of a high viscosity background solution.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed1987

Theoretical and experimental study of high-performance electrophoretic mobilization of isoelectrically focused protein zones.

In an earlier paper we showed that it is possible to mobilize a train of isoelectrically focused proteins and thus detect them on-tube or off-tube. The mobilization was performed in different ways, for instance electrophoretically by exchanging the anolyte for the catholyte or vice versa. In this paper we treat the electrophoretic mobilization theoretically, originating from the conditions of electroneutrality. The information thus gained was used to design anolytes and catholytes of appropriate compositions for mobilization of focused proteins. The usefulness of these electrode solutions is illustrated by focusing-mobilization experiments performed in free solution in a glass tube of length 110 mm. Since the inside diameter of the tube and its wall thickness were only 0.05 mm, the Joule heat was efficiently removed, which allowed the use of high field strengths (270 V/cm). The focusing time was therefore as short as 6 min. The time required for mobilization was about 15 min (360 V/cm). The mobilized protein zones were detected on-tube by absorbance measurements at 280 nm. The glass tube was treated with non-cross-linked polyacrylamide to eliminate electroendosmosis and adsorption of proteins onto the tube wall. The following conclusions drawn from the theoretical studies were experimentally verified: mobilization toward the anode (cathode) can be accomplished by selecting an anolyte (catholyte) containing a cation (anion) other than the proton (hydroxyl ion); the cation (anion) will then electrophoretically migrate into the separation tube and continuously increase (decrease) the pH from the anodic (cathodic) end of the tube. The pH of the electrode solution toward which the mobilization takes place is critical for off-tube, but not for on-tube detection. With the aid of the electroneutrality condition that applies in isoelectric focusing, one can easily explain the generation of the so-called plateau phenomenon.

Animals↗
PubMed2002

Preparative-scale isoelectric trapping separations using a modified Gradiflow unit.

The Gradiflow BF200 preparative electrophoretic unit (Gradipore), which has been developed for size-based and charge-sign-based protein separations and in which the hydraulic flow path of the recirculating sample stream in the separation cartridge is orthogonal to the electric field, has been modified to carry out binary protein separations using the principles of isoelectric trapping. The disposable separation cartridge contained three isoelectric membranes which, along with the cartridge holder, formed the anode and cathode compartments and the anodic and cathodic separation compartments. The utility of the modified instrument was demonstrated by effecting a binary separation of chicken egg white across an isoelectric point 5.5 isoelectric membrane. The desalting and subsequent binary separation steps proved to be remarkably rapid, due to the favorable combination of short electrophoretic path, high electric field strength and large effective isoelectric membrane surface area.

Isoelectric Focusing↗