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At least 1,279 records · Page 71Linked to original sources
PubMed2003

Modulation of moving phosphene thresholds by transcranial direct current stimulation of V1 in human.

Small moving sensations, so-called moving phosphenes are perceived, when V5, a visual area important for visual motion analysis, is stimulated by transcranial magnetic stimulation (TMS). However, it is still a matter of debate if only V5 takes part in movement perception or other visual areas are also involved in this process. In this study we tested the involvement of V1 in the perception of moving phosphenes by applying transcranial direct current stimulation (tDCS) to this area. tDCS is a non-invasive stimulation technique known to modulate cortical excitability in a polarity-specific manner. Moving and stationary phosphene thresholds (PT) were measured by TMS before, immediately after and 10, 20 and 30 min after the end of 10 min cathodal and anodal tDCS in nine healthy subjects. Reduced PTs were detected immediately and 10 min after the end of anodal tDCS while cathodal stimulation resulted in an opposite effect. Our results show that the excitability shifts induced by V1 stimulation can modulate moving phosphene perception. tDCS elicits transient, but yet reversible effects, thus presenting a promising tool for neuroplasticity research.

Adult↗
PubMed1998

N alpha- and N epsilon-D-galacturonoyl-L-lysine amides: properties and possible occurrence in plant cell walls.

Three representatives of a novel class of amide (isopeptide) glycoconjugates have been synthesised: N alpha-D-galacturonoyl-L-lysine and N epsilon-D-galacturonoyl-L-lysine and N epsilon-D-polygalacturonoyl-L-lysine. Galacturonoyl-lysine amide bonds were labile in 2 M trifluoroacetic acid at 120 degrees and in alkali, but relatively stable in cold acid. The amide bonds were resistant to digestion by Driselase, Pronase and trypsin. The polysaccharide backbone of N epsilon-D-polygalacturonoyl-L-lysine was hydrolysed by Driselase to yield two major ninhydrin-positive compounds which were shown by 1H and 13C NMR spectroscopy to be tri- and tetra-alpha-(1-->4)-D-galacturonoyl-L-lysines. To investigate the possible natural occurrence of N-galacturonoyl isopeptide bonds, we fed cell-suspension cultures of spinach and tomato with D-[6-14C]glucuronic acid, which radio-labels pectic polysaccharides. The radioactive cell walls were digested with, sequentially, Driselase, mild acid, and proteinases. On electrophoresis at pH 2.0, several of the radioactive digestion-products were cathodic. Some of the cathodic products yielded [14C]galacturonic acid upon complete acid hydrolysis. The existence of these products is compatible with the presence of novel N-galacturonoyl isopeptide bonds, which could serve as cross-links in plant cell walls.

Amides↗
PubMed2002

Effect of ultrasound on the removal of copper from the model solutions for copper electrolysis process.

A novel combination of an ultrasonic field with electrolysis for the removal of copper is studied. In the ultrasonic field, cavitation acts as jets and agitates the solution and breaks the barrier layer between the cathode surface and the bulk of the solution, thus increases the metal deposition on the cathode surface. The results show that an ultrasonic field is successful for the removal of low copper concentrations in solution.

Copper↗
PubMed2003

Electrochemical regeneration of Fe2+ in Fenton oxidation processes.

This study is to establish optimal conditions for the minimization of iron sludge produced in Fenton oxidation processes by electro-regenerating Fe(2+) with constant potential (CPM) or constant current mode (CCM). Results indicate that the optimal cathodic potential for Fe(2+) regeneration is -0.1 V vs. the saturated calomel electrode (SCE) in terms of current efficiency. Keeping the initial Fe(3+) concentration ([Fe(3+)](0)) constant, the average current density produced at -0.1 V vs. SCE (CPM) is approximately equal to the optimal current density applied in the CCM. The suitable pH range is below the pH value determined by Fe(3+) hydrolysis. As expected, increasing cathode surface area and solution temperature notably increases Fe(2+) regeneration rate. At the optimal potential, the average current density increases linearly with [Fe(3+)](0), exhibiting a slope of 8.48 x 10(-3)(A/m(2))(mg/L)(-1). The average current efficiency varies with [Fe(3+)](0), e.g., 75% and 96-98% at 100 and > or = 500 mg/L [Fe(3+)](0), respectively. Once reaching 75% of Fe(2+) regeneration capacity, further regeneration becomes difficult due to Fe(3+) mass transfer limitation. Fe(2+) can also be effectively regenerated by dissolving iron sludge at low pH (usually </=1). The unit energy consumption is 2.0-3.0 k Wh per kg Fe(2+) regenerated.

Electrochemistry↗
PubMed2001

Environmental protection and economization of resources by electroorganic and electroenzymatic syntheses.

The electrochemical methodology is an intrinsically environmentally friendly technique. It is especially excellently suited for preventive environmental protection because the practically mass-free electrons are used as reagents. Therefore, it allows the production of organic compounds without the formation of ecologically critical waste which has to be disposed. In addition, toxic waste formation can be prevented by continuous in situ or two-step electrochemical regeneration of heavy metal redox reagents. By using solid polymer electrolytes (ion-exchange membranes), even the use of a supporting electrolyte can be avoided. Thus, product formation can take place in pure methanol without any other chemical present. The consumption of resources can be economized by generating high-value products on both electrodes, anode and cathode (paired electrosynthesis). In certain cases, the same product may be formed on the anode and the cathode (200%-cell). Finally, in electroenzymatic syntheses, two environmentally friendly methods can be combined for the regeneration of the cofactors or the prosthetic groups of redox enzymes.

Chemical Industry↗
PubMed2002

Aniline degradation by Electro-Fenton and peroxi-coagulation processes using a flow reactor for wastewater treatment.

The degradation of 10-30 l of a 1000 ppm aniline solution in 0.050 M Na2SO4 + H2SO4 at pH 3.0 and 40 degrees C by Electro-Fenton and peroxi-coagulation processes at constant current until 20 A has been studied using a pilot flow reactor in recirculation mode with a filter-press cell containing an anode and an oxygen diffusion cathode, both of 100 cm2 area. H2O2 is produced by the two-electron reduction of O2 at the cathode, being accumulated with a current efficiency between 60% and 80% at the first stages of electrolyses performed with a Ti/Pt anode. In the presence of 1 mM Fe2+, less H2O2 is accumulated, but it is not detected using an Fe anode. The Electro-Fenton process with 1 mM Fe2+ and a Ti/Pt or DSA anode yields an insoluble violet polymer, while the soluble total organic carbon (TOC) is gradually removed, reaching 61% degradation after 2 h at 20 A. In this treatment, pollutants are preferentially oxidized by hydroxyl radicals formed in solution from reaction of Fe2+ with H2O2. The peroxi-coagulation process with an Fe anode has higher degradation power, allowing to remove more than 95% of pollutants at 20 A, since some intermediates coagulate with the Fe(OH)3 precipitate formed. Both advanced electrochemical oxidation processes (AEOPs) show moderate energy costs, which increase with increasing electrolysis time and applied current.

Aniline Compounds↗
PubMed1980

Quantitative estimation of abnormal microheterogeneity of serum transferrin in alcoholics.

A qualitative abnormality of the microheterogeneity of serum transferrin, demonstrated by isoelectric focusing, has previously been shown to be a highly specific indication of chronic alcoholism. The abnormality consists of a selective increase of a cathodal transferrin component which is probably caused by a reduction of the sialic acid content. The present study describes a method for quantitative estimation of the abnormal transferrin. The technique was based on analytical isoelectric focusing as the first step followed by direct immunofixation. The immunofixed transferrin was quantified by computerized on-line densitometry, and the transferrin abnormality was calculated as a quotient, where the amount of the cathodal component was expressed as a percentage of the relative total immunofixed transferrin quantity. This method was shown to possess high sensitivity and good reproducibility. In the controls the mean value of the quotient was 3.7%, while in the alcoholics it was 9.5% which was a highly significant difference (p less than 0.001). The possible functional significance of a disturbed sialic acid metabolism in alcoholism is discussed.

Adult↗
PubMed1988

Cryogenic changes in seminal protein of cattle and buffalo.

The effect of subzero temperatures on the electrophoretic pattern of seminal plasma protein of cattle and buffalo was studied. The profiles of the seminal proteins of these two closely related species differed considerably. Cattle had 11 proteins in the anodic system (pH 8.6) and none in the cathodic system (pH 4.3), while buffalo have 19 in the anodic system (pH 8.6) and 2 proteins in the cathodic system (pH 4.3). Freezing of semen at -5 degrees C for 24 h caused aggregation of seminal proteins in both species. A higher aggregation and loss of proteins were observed when freezing was done in liquid nitrogen at -196 degrees C. The effect was more pronounced in buffalo than in cattle. Loss of more seminal plasma proteins due to cryoinjury in buffalo semen may account for its poorer freezability than that of cattle semen.

Journal Article↗
PubMed2001

Corrosion behavior of a welded stainless-steel orthopedic implant.

The corrosion behavior of combinations of materials used in an orthopedic implant: the spherical part (forged or forged and annealed) constituting the head, the weld (tungsten inert gas (TIG) or electron beam (EB) techniques), and the cylindrical part (annealed) constituting the shaft of a femoral prosthesis - has been investigated. Open-circuit potentials, potentiodynamic curves, Tafel slope, mixed potential theory and susceptibility to intergranular attack are electrochemical and chemical procedures selected for this work. Electrochemical measurements using a microelectrode have been made in the following zones: spherical part, cylindrical part, weld, and weld/sphere, and weld/shaft interfaces. To detect intergranular attack, the Strauss test has been used. At the interfaces, corrosion currents, measured (Icorr) and predicted (Icouple) are low, in the order of the pico- to nanoampere. The electrochemical behavior of the electron beam (EB) weld is better than that of the tungsten inert gas (TIG). Welds at interfaces can behave either anodically or cathodically. It is better if welds, which are sensitive parts of the femoral prosthesis, behave cathodically. In this way, the risk of starting localized corrosion (pitting, crevice or intergranular corrosion) from a galvanic couple, remains low. From this point of view, the sample with the EB weld offers the best behavior. All the other samples containing a TIG type of weld exhibit a less favorable behavior. The mechanical treatments (forged, and forged and annealed) of the steel sphere did not show any difference in the corrosion behavior. No intergranular corrosion has been observed at the weld/steel interface for unsensitized samples. With sensitized samples, however, a TIG sample has exhibited some localized intergranular corrosion at a distance of 500 microm along the weld/stainless steel (sphere) interface.

Biocompatible Materials↗
PubMed2001

A nerve stimulation method to selectively recruit smaller motor-units in rat skeletal muscle.

Electrical stimulation of peripheral nerve results in a motor-unit recruitment order opposite to that attained by natural neural control, i.e. from large, fast-fatiguing to progressively smaller, fatigue-resistant motor-units. Yet animal studies involving physiological exercise protocols of low intensity and long duration require minimal fatigue. The present study sought to apply a nerve stimulation method to selectively recruit smaller motor-units in rat skeletal muscle. Two pulse generators were used, independently supplying short supramaximal cathodal stimulating pulses (0.5 ms) and long subthreshold cathodal inactivating pulses (1.5 s) to the sciatic nerve. Propagation of action potentials was selectively blocked in nerve fibres of different diameter by adjusting the strength of the inactivating current. A tensile-testing machine was used to gauge isometric muscle force of the plantaris and both heads of the gastrocnemius muscle. The order of motor-unit recruitment was estimated from twitch characteristics, i.e. peak force and relaxation time. The results showed prolonged relaxation at lower twitch peak forces as the intensity of the inactivating current increased, indicating a reduction of the number of large motor-units to force production. It is shown that the nerve stimulation method described is effective in mimicking physiological muscle control.

Action Potentials↗
PubMed2003

Optimization of aminolevulinic acid delivery by iontophoresis.

UNLABELLED: The objective was to optimize aminolevulinic acid (ALA) electrotransport into and through the skin by adjustment of formulation composition and ionic strength. ALA delivery was investigated as a function of the polarity and concentrations of drug and background electrolyte in the donor solution. The anodal iontophoretic flux of ALA from a 10% solution was compared with the drug's passive flux from the same formulation to which 5% dimethyl sulphoxide (DMSO) had been added. Iontophoresis of the predominantly zwitterionic ALA from the anode is more efficient than that from the cathode. It was possible, though, to increase the electrotransport of ALA by simultaneously delivering the drug from both anode and cathode. Reduction of NaCl concentration in the anode led to a 3- to 4-fold increase in ALA flux. Transport of ALA across the skin and the amount of prodrug delivered into the skin (SC and [epidermis+dermis]) were approximately 4-fold greater with iontophoresis as compared to the passive application of the DMSO formulation. IN CONCLUSION: (a) electroosmosis from the anode is enhanced when the background electrolyte concentration is lowered; and (b) low-level iontophoresis enhances ALA transport across and, more importantly, into the [epidermis+dermis] than a simple formulation incorporating DMSO.

Aminolevulinic Acid↗
PubMed2002

Electrokinetic ion transport through unsaturated soil: 2. Application to a heterogeneous field site.

Results of a field demonstration of electrokinetic transport of acetate through an unsaturated heterogeneous soil are compared to numerical modeling predictions. The numerical model was based on the groundwater flow and transport codes MODFLOW and MT3D modified to account for electrically induced ion transport. The 6-month field demonstration was conducted in an unsaturated layered soil profile where the soil moisture content ranged from 4% to 28% (m3 m(-3)). Specially designed ceramic-cased electrodes maintained a steady-state moisture content and electric potential field between the electrodes during the field demonstration. Acetate, a byproduct of acetic acid neutralization of the cathode electrolysis reaction, was transported from the cathode to the anode by electromigration. Field demonstration results indicated preferential transport of acetate through soil layers exhibiting higher moisture content/electrical conductivity. These field transport results agree with theoretical predictions that electromigration velocity is proportional to a power function of the effective moisture content. A numerical model using a homogeneous moisture content/electrical conductivity domain did not adequately predict the acetate field results. Numerical model predictions using a three-layer electrical conductivity/moisture content profile agreed qualitatively with the observed acetate distribution. These results suggest that field heterogeneities must be incorporated into electrokinetic models to predict ion transport at the field-scale.

Acetates↗
PubMed1998

Electric potentiation of gravikinesis in Paramecium is possibly mediated by filaments.

Sensitivity of Paramecium to mechanical stress including gravitational force is organized along two opposing gradients of membrane channel distribution: depolarizing Ca channels and hyperpolarizing K channels. Mechanoreceptor channels reside in the membrane of the cell soma and are activated, when the weight of the cytoplasm deforms the "lower" plasma membrane. Channel distribution is such as to generate ciliary activation which can counteract sedimentation of the cells: a reduction in downward swimming rate and an augmentation in upward swimming rate. Application of weak DC fields does not only induce the well-known cathodal orientation and swimming of Paramecium toward the cathode (galvano-taxis). We document that swimming velocity is augmented up to 175% as a function of the voltage gradient between 0.3 V/cm and 0.8 V/cm (galvanokinesis). A gradient of 0.3 V/cm was highly effective in raising the common negative gravikinesis of downward swimmers threefold. The gravikinesis of upward swimmers reversed polarity under field stimulation inducing cells to augment sedimentation effects (positive gravikinesis). Both effects of electric-field stimulation on ciliary activation are of the depolarizing type: reduction in the frequency of normally beating cilia. Analysis of the data shows that a voltage-sensitivity of gravireceptor channels would not account for the observed potentiation of negative gravikinesis. It is suggested that a previously described voltage-dependent Ca channel of the soma membrane interferes with a Ca(2+)-sensitive, peripheral filament system, which directly connects to gravireceptor channels.

Animals↗
PubMed1977

Differentiation in vivo and in vitro of pyruvate kinase isozymes in rat muscle.

The M type isozymes of Pyruvate-kinase have been studied by isoelectrofocusing in thin layer acrylamide ampholine gel, during the ontogeny of rat muscle in vivo and during the differentiation in vitro of myoblasts of a line established by Yaffe. In both cases, multiple subbands have been seen; the most acid (pHi 5.2) was the predominant band in myoblasts and in fetal muscle at the 15th day. Several more cathodic bands appear sequentially in vitro as in vivo, one of them corresponding to the "M2" or "K" band (predominant in kidney). The most cathodic band M1 (pHi 7.3), characteristic of the adult muscle, appears at the 9th day of culture in vitro in multinucleated myotubes and at the 20th day of fetal life in vivo. Kinetic results confirm these electrofocusing results, showing in fetal muscle and in myoblasts a sigmoid saturation curve of pyruvate kinase activity with phosphoenolpyruvate as substrate. This allosteric kinetic is progressively replaced by a Michaëlian kinetics in vitro as in vivo. Consequently, the studies in vitro may serve as a model for myogenesis in vivo, and may contribute to the understanding of the significance of the multiple forms of pyruvate-kinase during this myogenesis.

Aging↗
PubMed2002

Development of a novel electro-dialysis based technique for lead removal from silty clay polluted soil.

In this study, a novel electro-dialysis based technique has been developed and used to treat a silty clay soil polluted by lead. The effect of chemical reagents, i.e. tap water at pH 4 (reagent 1) and sodium acetate at pH 5 (reagent 2), on enhancing electro-dialysis extraction of lead from the tested soil was examined. Specimens were prepared by mixing soil with 1000 ppm of lead and were compacted in the dialysate at predetermined dry density and moisture content. Then, specimens were subjected to a predetermined level of current. In the dialysate compartment, anions and cations were removed by charge transport in opposite directions to the anodic and cathodic cells. Meanwhile, in the anodic and cathodic cells, ion concentrations were increased. Thus, concentrated electrolyte streams were produced in alternating cells and cleaned soils were obtained in the dialysate. Both soil pH and lead concentrations were uniformly distributed within the compacted soil specimen during testing. Total lead removal of 80 and 92% was obtained for reagents 1 and 2, respectively. The high removal efficiency was attributed to the separation of electrode reactions from the soil and inclusion of ion selective membranes (ISM), which restrict the movement of counter charged species.

Adsorption↗
PubMed2002

Imaging of the boron doping in silicon using low energy SEM.

Scanning electron imaging of plan views of boron-doped patterns in silicon is examined, together with the mechanism of formation of the electronic contrast in this kind of structures. Main to-date published results are critically reviewed and new data are presented concerning the secondary, backscattered and total-emission electron contrasts, including their qualitative and quantitative behaviour, particularly in the low energy range achieved with the help of the cathode lens (the scanning low energy electron microscopy mode, SLEEM). Surface analysis of the structure by means of Auger electron spectrometer has been performed, too, both before and after ion beam bombardment. The scanning electron microscope micrographs, acquired after the oxide mask removal in HF, are examined in a variety of detection modes, aiming at identification of the signal component primarily bearing the contrast. The energy dependence of the contrasts is presented as well as its change owing to alteration in the vacuum conditions. The most important findings include an extremely high contrast obtained in the SLEEM mode and even more enhanced under medium vacuum conditions at which the carbonaceous layer of surface contamination plays its role. The observed phenomena are partly explained in the frame of the "flat band" model of a passivated surface. The increased contrast in the SLEEM mode is understood as connected with the above-surface electric field of the cathode lens, generating space charge layers inside the semiconductor. In addition, charge carriers, injected via the primary electron beam, are considered as influencing the contrast vs. energy dependence.

Journal Article↗
PubMedDate not supplied

On the application of quantum transport theory to electron sources.

Electron sources (e.g., field emitter arrays, wide band-gap (WBG) semiconductor materials and coatings, carbon nanotubes, etc.) seek to exploit ballistic transport within the vacuum after emission from microfabricated structures. Regardless of kind, all sources strive to minimize the barrier to electron emission by engineering material properties (work function/electron affinity) or physical geometry (field enhancement) of the cathode. The unique capabilities of cold cathodes, such as instant ON/OFF performance, high brightness, high current density, large transconductance to capacitance ratio, cold emission, small size and/or low voltage operation characteristics, commend their use in several advanced devices when physical size, weight, power consumption, beam current, and pulse repletion frequency are important, e.g., RF power amplifier such as traveling wave tubes (TWTs) for radar and communications, electrodynamic tethers for satellite deboost/reboost, and electric propulsion systems such as Hall thrusters for small satellites. The theoretical program described herein is directed towards models to evaluate emission current from electron sources (in particular, emission from WBG and Spindt-type field emitter) in order to assess their utility, capabilities and performance characteristics. Modeling efforts particularly include: band bending, non-linear and resonant (Poole-Frenkel) potentials, the extension of one-dimensional theory to multi-dimensional structures, and emission site statistics due to variations in geometry and the presence of adsorbates. Two particular methodologies, namely, the modified Airy approach and metal-semiconductor statistical hyperbolic/ellipsoidal model, are described in detail in their present stage of development.

Journal Article↗
PubMed2000

A novel in-lens detector for electrostatic scanning LEEM mini-column

A novel principle of an in-lens detector of very slow electrons is described and the detector efficiency discussed. The detector was built into a coaxial column for a Cylindrical Mirror Analyser for Auger electron microanalysis. In order to obtain a very low energy scanned imaging, a cathode lens was formed between the final electrode of the column and a negatively biased specimen. The signal electrons accelerated within the cathode lens field enter the column and after being mirrored back impact a micro-channel-plate based detector fitted around the optical axis. The acceptance of the detector, expressed as a ratio of the number of electrons impacting the detector to the full emission of a cosine source, was calculated to be 0.86 for 1 eV and 0.985 for 10 eV electrons. Then, the efficiency of conversion into output pulses is 0.35 and 0.31, respectively; these parameters are superior to those of conventional SEM detectors for secondary electrons. Micrographs taken at low energies ranging down to units of eV are presented.

Journal Article↗