Transient Potential Research Articles

Simulation of shrinkage induced cracking in cement composite overlays

A random lattice is used to model moisture transport in cement-based composites. Model geometry, and the scaling of the elemental diffusivity terms, are based on a Voronoi discretization of the material domain. Steady-state and transient potential flow problems are simulated, and compared with theory, to demonstrate model accuracy and objectivity with respect to lattice random geometry. A novel routine is described for computing moisture flux values at the random lattice sites. Stress production, and potential shrinkage crack development, are driven by the associated drying processes. The random lattice modeling of moisture movement is coupled with rigid-body-spring networks (RBSN), which account for elasticity, creep, and fracture properties of the material. The RBSN is based on the same Voronoi discretization of the material as used to model moisture movement. Relative humidity contours, stress contours, and crack plots are produced for a cement composite overlay restrained by a mature concrete substrate. That example is based on a set of simulation results reported in the literature.

Elucidation of the Nature of the Conformational Changes of the EF-interhelical Loop in Bacteriorhodopsin and of the Helix VIII on the Cytoplasmic Surface of Bovine Rhodopsin: A Time-resolved Fluorescence Depolarization Study

The conformation of the AB-loop and EF-loop of bacteriorhodopsin and of the fourth cytoplasmic loop (helix VIII) of bovine rhodopsin were assessed by a combination of time-resolved fluorescence depolarization and site-directed fluorescence labeling. The fluorescence anisotropy decays were measured employing a tunable Ti:sapphire laser/microchannel plate based single-photon counting apparatus with picosecond time resolution. This method allows measurement of the diffusional dynamics of the loops directly on a nanosecond time-scale. We implemented the method to study model peptides and two-helix systems representing sequences of bacteriorhodopsin. Thus, we systematically analyzed the anisotropic behavior of four different fluorescent dyes covalently bound to a single cysteine residue on the protein surface and assigned the anisotropy decay components to the modes of motion of the protein and its segments. We have identified two mechanisms of loop conformational changes in the functionally intact proteins bacteriorhodopsin and bovine rhodopsin. First, we found a surface potential-dependent transition between two conformational states of the EF-loop of bacteriorhodopsin, detected with the fluorescent dye bound to position 160. A transition between the two conformational states at 150 mM KCl and 20 °C requires a surface potential change that corresponds to Δσ≈−1.0 e −/bacteriorhodopsin molecule. We suggest, that the surface potential-based switch of the EF-loop is the missing link between the movement of helix F and the transient surface potential change detected during the photocycle of bacteriorhodopsin. Second, in the visual pigment rhodopsin, with the fluorescent dye bound to position 316, a particularly striking pH-dependent conformational change of the fourth loop on the cytoplasmic surface was analyzed. The loop mobility increased from pH 5 to 8. The midpoint of this transition is at pH 6.2 and correlates with the midpoint of the pH-dependent equilibrium between the active metarhodopsin II and the inactive metarhodopsin I state.

Calcium entry via Na/Ca exchange during the action potential directly contributes to contraction of failing human ventricular myocytes.

Prolongation of the Ca2+ transient and action potential (AP) durations are two characteristic changes in myocyte physiology in the failing human heart. The hypothesis of this study is that Ca2+ influx via reverse mode Na+/Ca2+ exchanger (NCX) or via L-type Ca2+ channels directly activates contraction in failing human myocytes while in normal myocytes this Ca2+ is transported into the sarcoplasmic reticulum (SR) to regulate SR Ca2+ stores. Myocytes were isolated from failing human (n=6), nonfailing human (n=3) and normal feline hearts (n=9) and whole cell current and voltage clamp techniques were used to evoke and increase the duration of APs (0.5 Hz, 37 degrees C). Cyclopiazonic acid (CPA 10(-6) M), nifedipine (NIF;10(-6) M) and KB-R 7943 (KB-R; 3x10(-6) M) were used to reduce SR Ca2+ uptake, Ca2+ influx via the L-type Ca2+ current and reverse mode NCX, respectively. [Na+)i was changed by dialyzing myocytes with 0, 10 and 20 mM Na(+) pipette solutions. Prolongation of the AP duration caused an immediate prolongation of contraction and Ca2+ transient durations in failing myocytes. The first beat after the prolonged AP was potentiated by 21+/-5 and 27+/-5% in nonfailing human and normal feline myocytes, respectively (P<0.05), but there was no significant effect in failing human myocytes (+5+/-4% vs. steady state). CPA blunted the potentiation of the first beat after AP prolongation in normal feline and nonfailing human myocytes, mimicking the failing phenotype. NIF reduced steady state contraction in feline myocytes but the potentiation of the first beat after AP prolongation was unaltered (21+/-3% vs. base, P<0.05). KB-R reduced basal contractility and abolished the potentiation of the first beat after AP prolongation (2+/-1% vs. steady state). Increasing [Na+]i shortened AP, Ca2+ transient and contraction durations and increased steady state and post AP prolongation contractions. Dialysis with 0 Na+ eliminated these effects. Ca2+ enters both normal and failing cardiac myocytes during the late portion of the AP plateau via reverse mode NCX. In (normal) myocytes with good SR function, this Ca(2+) influx helps maintain and regulate SR Ca2+ load. In (failing) human myocytes with poor SR function this Ca2+ influx directly contributes to contraction. These studies suggest that the Ca2+ transient of the failing human ventricular myocytes has a higher than normal reliance on Ca2+ influx via the reverse mode of the NCX during the terminal phases of the AP.

An efficient technique for the evaluation of lightning-induced voltage in a cylindrical vessel containing charged oil

This paper proposes a numerical procedure, based on a mixed circuit-field approach to compute the transient and spatial potential distributions inside vessels containing flammable liquids, induced by a direct lightning strike. The circuit model is used to simulate the metallic vessel as an equivalent electrical network, which is solved by the SPICE simulator. In this way, it is possible to compute the transient potential distribution on the external vessel walls. These potential values are the boundary conditions of the partial differential equation system, valid at the inner of the container, which is solved by the finite-difference time-domain method. The model takes into account the transient and nonuniform volume charge density inside the liquid and the temporal accumulation of charges at the air/liquid interface. A validation of the proposed method, in the absence of liquid, is furnished. The transient and spatial distributions of the potential in the container are analyzed in order to detect possible hazards.

Leaky-wave analysis of transient fields due to sources in planarly layered media

The transient field due to canonical sources in planarly layered media is obtained using a leaky-wave analysis. By proper choice of integration paths in both the complex frequency and complex wavenumber planes, transient fields are obtained exactly as a temporal inversion integral over a discrete sum of residues. The residues include both proper and improper surface-wave modes, analytically continued into the complex frequency plane. The method is applicable for all times of interest, although for certain source-receiver locations an early-time period is identified which encompasses the specular reflection from the nearest interface, and during which time the residue series requires special treatment. The presented analysis leads to a computationally simple and efficient method for obtaining transient fields due to sources in layered media. Results are shown for the transient potential due to line and point sources over a grounded dielectric slab, although the technique is applicable to multiple planar layers.

Effects of nifedipine and nickel on plateau potentials generated in submucosal interstitial cells distributed in the mouse proximal colon.

The effects of nifedipine and nickel ions (Ni2+), known inhibitors of L- and T-type voltage-gated Ca-channels respectively, were investigated on plateau potentials recorded from submucosal interstitial cells distributed in the mouse proximal colon. Plateau potentials were generated at a frequency of about 15 times min(-1) and were formed of two components. The primary component had an initial fast rate of rise with a transient potential (rate of rise, 130 mV/s; peak amplitude, 35 mV) and was followed by a secondary plateau component with a sustained potential (amplitude, 25 mV; duration, 2.6 s). Each cell from which recordings were made was injected with neurobiotin. Subsequent morphological examination with a confocal microscope indicated successful visualization of injected cells only in the presence of 18beta-glycylrhetinic acid (an inhibitor of gap junctional connections), suggesting that these cells were dye-coupled with surrounding cells. The cells injected with neurobiotin exhibited an oval-shaped cell body with bipolar processes and were distributed in the submucosal layer, suggesting that they were submucosal interstitial cells of Cajal (ICC-SM). The plateau potentials were not altered by 0.01 microM nifedipine, but were reduced in duration by 0.1 microM nifedipine, and abolished by 1 microM nifedipine. The rate of rise of plateau potentials, but not their amplitude, was reduced by Ni2+ (> 10 microM), with no significant alteration of the membrane potential. In the presence of 100 microM Ni2+, the plateau potentials were changed to a triangular form. Thus, the plateau potentials were formed by two types of voltage-gated channel current: the initial component was produced by a Ni2+-sensitive channel current and the plateau component by a nifedipine-sensitive current. The possible involvement of two different types of voltage-gated Ca2+-channels in the generation of submucosal pacemaker potentials was discussed.

Verifying the Computational Method of Transient Performance with Respect to Grounding Systems based on the FD-TD Method.

Lightning strikes on bulk transmission lines and distribution lines frequently cause serious accidents involving electrical apparatus. It is strongly desired to analyze transient performance in terms of the transient electric potential, transient current, and transient grounding resistance of grounding systems of electrical apparatus in order to establish accident prevention. The transmission line approach, which was brought to practical applicability by Sunde and the electromagnetic field approach based on the method of moments have been conventionally used to analyze the transient performance, however, both are insufficient in general practical usage because the former can only deal with TEM waves and the latter can only analyze grounding systems in homogeneous earth. Hence, one of the authors has already proposed a novel method for computational analysis of transient performance based on the finite-difference time-domain, (FD-TD) method (FD-TD CMTP).This paper presents both experimental results of transient performance with respect to a grounding electrode of a rectangular parallelepiped electrode, which is a model of a foot of the transmission towers, and a square loop electrode, which is an element of a grounding grid, and the calculated results obtained using FD-TD CMTP. The calculated results agree very well with experimental results. This confirms the validity of using FD-TD CMTP to analyze transient performance of grounding systems of electrical apparatus.The FD-TD CMTP is expected to facilitate the rational design of grounding systems.

Charge transfer photodissociation of phenol on Ag(111)

The photochemistry of phenol on Ag(111) has been investigated by post-irradiation temperature programmed desorption (TPD). Ultraviolet (UV) irradiation at 355 and 266 nm was found to affect only the chemisorption layer in direct contact with the metal surface, while leaving the multilayer virtually intact. The main photoinduced reaction was found to be photodissociation of the O–H bond of phenol. Two new peaks were observed at the mass of phenol in the post-irradiation TPD spectrum at 335 K and 455 K. These peaks were assigned to the recombinative desorption of phenoxy with the hydrogen from O–H bond photodissociation and from thermal C–H bond fission, respectively. The photodissociation cross section was measured at different wavelengths and coverages. A charge transfer type photodissociation mechanism was proposed, where hot electrons generated in the substrate by UV photons attach to the affinity level of the adsorbed phenol. The transition to the transient anionic potential then leads to facile dissociation of O–H bond. The affinity level of phenol has been estimated to lie at 3.2–3.5 eV above the Fermi level for the 1 ML case.

2D and 3D transient heat conduction analysis by BEM via particular integrals

Particular integral formulations are presented for 2D and 3D transient potential flow (heat conduction) analysis. The results of the analysis are compared with an alternative formulation developed using the volume integral conversion approach. Although the mathematical foundation of the two methods are different both formulations are shown to produce almost identical results. For the particular integral formulation, the steady-state heat conduction equation is used as the complementary solution and two global shape functions (GSFs) are considered to approximate the transient term of the heat conduction equation. The numerical results for three example problems are given and compared with their analytical solutions.

Membrane properties of principal neurons of the lateral superior olive.

In the lateral superior olive (LSO) the firing rate of principal neurons is a linear function of inter-aural sound intensity difference (IID). The linearity and regularity of the "chopper response" of these neurons have been interpreted as a result of an integration of excitatory ipsilateral and inhibitory contralateral inputs by passive soma-dendritic cable properties. To account for temporal properties of this output, we searched for active time- and voltage-dependent nonlinearities in whole cell recordings from a slice preparation of the rat LSO. We found nonlinear current-voltage relations that varied with the membrane holding potential. Repetitive regular firing, supported by voltage oscillations, was evoked by current pulses injected from holding potentials near rest, but the response was reduced to an onset spike of fixed short latency when the pulse was injected from de- or hyperpolarized holding potentials. The onset spike was triggered by a depolarizing transient potential that was supported by T-type Ca(2+)-, subthreshold Na(+)-, and hyperpolarization-activated (I(H)) conductances sensitive, respectively, to blockade with Ni2+, tetrodotoxin (TTX), and Cs+. In the hyperpolarized voltage range, the I(H), was largely masked by an inwardly rectifying K+ conductance (I(KIR)) sensitive to blockade with 200 microM Ba2+. In the depolarized range, a variety of K+ conductances, including A-currents sensitive to blockade with 4-aminopyridine (4-AP) and additional tetraethylammonium (TEA)-sensitive currents, terminated the transient potential and firing of action potentials, supporting a strong spike-rate adaptation. The "chopper response," a hallmark of LSO principal neuron firing, may depend on the voltage- and time-dependent nonlinearities. These active membrane properties endow the LSO principal neurons with an adaptability that may maintain a stable code for sound direction under changing conditions, for example after partial cochlear hearing loss.

On the transient potential in insulators

The methods currently used to study the bulk and surface transport properties of insulators usually consist of charging the sample by corona or electrons, and monitoring the natural decay of the surface potential or its buildup after a temporary short circuit (return potential). These measurements have become quite easy since the advent of reliable potential probes, but their interpretation still raises delicate problems concerning, among others, the sample conductivity and its field dependence, the sample polarization and the interfacial injection efficiency. A discussion of these contributions shows that a strict experimental protocol is required if significant results are to be obtained. An alternate technique proposed here uses a scanning electron microscope (SEM), but no potential probe. Electrons from the gun of the SEM are injected below the surface of a thin insulating sample, having its rear face grounded, then a beam of lower energy, acting as probe, is scattered by the trapped charge and forms on the screen a mirror-image of the gun. If enough charge is trapped, the field from the image charge carries the injected charge down across the sample depth. This causes the mirror to contract at a rate which is related to the mobility of the electrons in the sample. Therefore, the mobility is obtained with the resolution of the microscope. Preliminary results indicate that the mobility of electrons injected in LDPE ranges by at least two orders of magnitude, depending on the local field and the sample morphology.

The uses of non-steady-state membrane characterisation techniques for the study of transport properties of active layers of nanofiltration membranes: theory with experimental examples

Nanofiltration (NF) is a relatively new membrane process suitable for the separation of solutes of close molecular weight. The rejection mechanisms of nanofiltration membranes have not been reliably identified, yet. The electrostatic repulsion of coions by fixed membrane charge (Donnan exclusion) is considered one of most probable rejection mechanisms. However, practically no direct information on the electrochemical and/or electrokinetic properties of NF membranes is available. The interpretation of conventional electrochemical and/or electrokinetic measurements with NF membranes is complicated by their multilayer structure. Under linear conditions only average membrane transport properties can be obtained from steady-state measurements. Information on the properties of constituent layers can be obtained from non-steady-state and/or non-linear measurements, alone. In this paper the opportunities offered by non-steady-state techniques are explored. Volume flows and changes in solute concentration cannot usually be observed at sufficiently short times when the system is still far away from steady state. Therefore the only suitable response is electrical. It is not immediate due to the concentrational polarisation of boundaries between membrane constituent layers. The theory of transient membrane potential, transient filtration potential and low-frequency electrical impedance is briefly presented. The suitability of various non-steady state techniques for the determination of transport and accumulation properties of constituent layers of NF membranes is discussed and compared with available experimental data on transient membrane potential. It is concluded that each of techniques has its advantages and drawbacks. Therefore, the application of several techniques to the same system is desirable for the minimisation of systematic errors.

Static and Transient Model Analysis on Expansion Behavior of LaCrO3 under an Oxygen Potential Gradient

Doped lanthanum chromites show lattice expansion under high temperature reducing atmospheres. We have proposed a numerical simulation model for analyzing the static and the transient expansion behavior of the doped lanthanum chromites under a stationary oxygen potential gradient or a stepwise change of oxygen potential in the atmosphere. A lanthanum chromite interconnector plate, 100 × 100 × 3 mm, was found to warp under a stable solid oxide fuel cell operating condition. The maximum displacement of the center part normal to the originally flat surface was calculated to be about 0.77 mm. A stepwise change of the atmospheric condition caused a transient oxygen potential gradient in a lanthanum chromite rod, 3 × 3 × 20mm, resulting in a deformation of the sample. The calculated tensile stress coming from the transient deformation was as high as 50 MPa or more. © 2000 The Electrochemical Society. All rights reserved.

New Characteristics of Nonlinear Kinetics in the MnSO4-KBrO3- Diacetone-H2SO4 Oscillating Chemical System

The chemical oscillating reaction of the MnSO4-KBrO3-diacetone-H2SO4 system has been studied in a continuous-flow stirred-tank reactor (CSTR), and the new characteristics of nonlinear kinetics of this oscillating system are reported. The effects of the temperature, flow rate, concentration of reactants and acidity were investigated. Two different oscillating states (bistability) were observed in this system; the transient color, waveform, potential, oscillating amplitude and period of the two states were different. A change in the solution acidity or flow rate can translate one state to the other, and the two states can exist under the same experimental conditions. Potential and spectrophotometric methods were used to track the change in the reaction intermediates, and possible mechanism of this oscillating system is proposed.

Non-steady-state membrane potential: theory and measurements by a novel technique to determine the ion transport numbers in active layers of nanofiltration membranes

To better understand the mechanisms of nanofiltration (NF) and to be able to perform its predictive modelling one needs to know electrochemical properties of membrane active layers. Their determination is complicated by the multilayer structure of NF membranes. Conventional linear steady-state techniques yield information on the membrane average properties (involving both active layer and support) alone. In this paper we develop a theory of non-steady-state membrane potential and analyse the informativeness of various modes of its experimental measurement. In particular, we come to the conclusion that any solution replacement technique is not capable of yielding information on the so-called initial membrane potential in membranes with thin and not too dense active layers due to the presence of unstirred solution layers near the membrane surface. A novel non-steady-state technique (‘dab’ technique) is put forward for the measurements of transient membrane potential. A membrane preliminary equilibrated with an electrolyte solution is touched by a drop of solution of different concentration. Thus, a concentration gradient initially located within a very thin surface layer is created. An electrical response to this is tracked with a pair of reversible electrodes. That makes possible the determination of ion transport numbers within active layers. The potentialities of the new technique are illustrated by sample measurements performed with a composite NF membranes (PES10) and two monolayer membranes (Cellophane and Nafion ®115). The PES10 membrane is shown to have quite a high electrochemical activity. The Nafion ®115 membrane is shown to be macroscopically homogeneous.

Transient and cyclic responses of strain-generated potential in rabbit patellar tendon are frequency and pH dependent.

The goal of this study was to expand understanding of strain-generated potential (SGP) in ligamentous or tendinous tissues. Most SGP studies in the past have focused on cartilage or bone. Herein, rabbit patellar tendon (PT) was used as a model. Each patellar tendon had two Ag/AgCl electrodes inserted at axial positions of 1/4 and 1/2 from patellar to tibial insertions. Each specimen was electrically isolated, gripped in a servohydraulic test system, and then subjected to a short session of uniaxial haversine tension (2.5 percent maximum strain) at a frequency of 0.5, 1.0, 2.0, or 5.0 Hz. A cyclic (sinusoidal) electrical potential superimposed upon a larger transient (exponentially asymptotic) potential was consistently observed. Upon termination of loading, the cyclic SGP ended, and the shifted baseline of the SGP exponentially decayed and asymptotically returned to a residual potential which over all specimens was not different than the original potential. The transient and cyclic SGPs were frequency dependent (P < 0.001, P = 0.06, respectively). To our knowledge, this transient portion of the SGP, although theoretically predicted by Suh (1996, Biorheology, 33, pp. 289-304) and Chen (1996, Ph.D. thesis, University of Wisconsin-Madison) has not been observed in other experiments using different protocols. Additional PTs were dehydrated and the rehydrated in solution at different pH levels. The magnitude of SGPs increased in basic solution (pH 9.5) but diminished in pH 4.7 buffer. This pH dependency suggests that electrokinetics is the dominant mechanism for the transient and cyclic responses of the SGPs, although this study does not provide direct evidence.

Rate-dependent changes in cell shortening, intracellular Ca(2+) levels and membrane potential in single, isolated rainbow trout (Oncorhynchus mykiss) ventricular myocytes.

The effects of increasing stimulation frequency (from 0.2 to 1.4 Hz) on the contractility, intracellular Ca(2+) concentration ([Ca(2+)](i)) and membrane potential of single ventricular myocytes isolated from the heart of rainbow trout (Oncorhynchus mykiss) were measured. Cell shortening, expressed as a percentage of resting cell length, was our index of contractility. The fluorescent Ca(2+) indicator Fura-2 was used to monitor changes in [Ca(2+)](i). Action potentials and L-type Ca(2+) currents (I(Ca)) were recorded using the whole-cell patch-clamp technique. Experiments were performed at 15 degrees C. Increasing the stimulation frequency caused a significant increase in diastolic [Ca(2+)](i) and a significant decrease in diastolic cell length and membrane potential. During systole, there was a significant fall in the amplitude of the [Ca(2+)](i) transient, cell shortening and action potential with a decrease in the duration of the action potential at both 20 % and 90 % repolarisation. Caffeine was used to assess the Ca(2+) content of the sarcoplasmic reticulum. We observed that sarcoplasmic reticulum Ca(2+) load was greater at 1.0 Hz than at 0.6 Hz, despite a smaller electrically evoked [Ca(2+)](i) transient. The amplitude of I(Ca) was found to decrease with increased stimulation frequency. At 0.6 Hz, electrically evoked [Ca(2+)](i) transients in the presence of 10 mmol l(-)(1) caffeine or 10 micromol l(-)(1) ryanodine and 2 micromol l(-)(1) thapsigargin were reduced by approximately 15 %. We have described the changes in contractility, [Ca(2+)](i) and action potential configuration in a fish cardiac muscle system. Under the conditions tested (0.6 Hz, 15 degrees C), we conclude that the sarcoplasmic reticulum contributes at least 15 % of the Ca(2+) associated with the [Ca(2+)](i) transient. The rate-dependent decrease in contraction amplitude appears to be associated with the fall in the amplitude of the [Ca(2+)](i) transient. This, in turn, may be influenced by changes in the action potential configuration via mechanisms such as altered Ca(2+) efflux and Ca(2+) influx. In support of our conclusions, we present evidence that there is a rate-dependent decrease in Ca(2+) influx via I(Ca) but that the Ca(2+) load of the sarcoplasmic reticulum is not reduced at increased contraction frequencies.

Sequential determination of chromium(VI) and chromium(III) by potentiometric flow-injection method.

A simple and rapid potentiometric FIA method for the sequential determination of Cr(VI) and Cr(III) is described, using both a redox electrode detector and a stream of an Fe(III)-Fe(II) potential buffer containing bromide. A three-channel flow system, a carrier stream(water), a reagent stream(H2SO4 solution or Ce(IV) solution containing H2SO4) and the Fe(III)-Fe(II) potential buffer solution, was constructed by equipping a six-way valve between the stream of the reagent solution and the carrier stream. The valve was used to switch the stream of either the H2SO4 solution or the Ce(IV) solution containing H2SO4 in the reagent solution. For the selective determination of Cr(VI) in a mixed sample of Cr(VI) and Cr(III), the valve was switched to flow a reagent stream of the H2SO4 solution into the potential buffer solution. Then, Cr(VI) reacted with the potential buffer, and a peak signal was obtained by the detector. For determining the total chromium, the sum of Cr(VI) and Cr(III), the valve was switched to flow the reagent stream of Ce(IV) solution into the potential buffer solution. Cr(III) in the mixed sample was oxidized to Cr(VI) by Ce(IV) in the reagent stream and a peak signal was obtained by the detector. Cr(III) in the mixed sample was determined by the difference of the peak heights obtained by the two reagent streams. The detection of Cr(VI) was based on the measurement of a large transient potential change due to bromine generated by an oxidaton reaction between Cr(VI) and bromide in the potential buffer solution. The linear relationships between the peak heights and the sample concentration were observed over the range of 1×10-6 to 10×10-6M for Cr(VI) and from 4×10-6 to 4×10-5M for Cr(III) by using a 0.01M Fe(III)-Fe(II) potential buffer containng 0.6M NaBr and 3.6M H2SO4.

Magnetoencephalography of cognitive responses A sensitive method for the detection of age-related changes

Magnetoencephalography (MEG) is a novel, state-of-the-art technique used in clinical neurophysiology, which promises better understanding of brain (days) function. The “whole-head” MEG sensor-array enables a noninvasive visualization of the intracellular currents involved in transmission and processing of information in the working brain, on a millisecond timescale, taking into account all (superficial and deeps) parts of the CNS simultaneously. 3D reconstruction algorithms are used to attribute sources to anatomically defined structures and cortical subdivisions. MEG recording during the performance of a simple decision-making task using a continuous Go-NoGo puradigm (= P300) enables the evaluation of the mechanism of attentional and intellectual capabilities. Many psychiatric disorders are related to a state of confusion or disturbances of thought. This poster presentsa brief report on fundamental and clinical research into cognitive decline during (normal) aging, carried out with our innovative MEG equipement. In healthy subjects asked to discriminate high-piched target tones among standard tones during an oddball detection task, when attention is correctly directed, a particular transient electrical potential is observed, called P300,1 with maximal amplitudes around the vertex. The underlying generators are thought to be located in the medial temporal lobe regions. We recently demonstrated tha MEG signals yeld a more complete image of the complex neuronal intercactions involved in this type of cognitive response, showing a large positive pole over the left precentral and frontal brain regions (Figure 1) and a mirror image pattern in the right hemisphere (not shown).2 We are currently in the process of localizing the sources in a realistic head model. Figure 1. Top: 3D mapping of positive pole of MEG response to target tones. Bottom: averaged tracings in Broca's area for 2 age groups (young [ 300 ms (horizontal scale 100 ms/division). ... Research at our Institute are running programs to explore pathophysiological changes in schizophrenics, abstinent alcoholics, and Alzheimer patients, in comparaison with normal aging in control subjects. This is achieved by plotting amplitude and latency parameters for individual subjects as a function of age (Figure 2). Significant decline is found subjects at the far ends of our age-range. Regression analysis shows a loss of signal of about 15% with a slowing of 10 to up to 20 ms with every decade of life. Preliminary findings indicate that MEG recording are able to evidence age-related changes, as do electrical responses, and that these are already clearly visible before the age of 50 years. The slope of change in signal speak parameters is steeper than described in the literature for a neven wider range of ages and pathopysiological situations.9 Figure 2. A. Scattergram of amplitude (ampl) for target specific MEG response in Broca's area B. Mean amplitude of electrical response (P300, Cz electrode) in young (Δ) and aged ( ) healthy subjects; C. Scattergram of MEG response latency; D. mean latency ...

Simultaneous potentiometric determination of ClO 3−–ClO 2− and ClO 3−–HClO by flow injection analysis using Fe(III)–Fe(II) potential buffer

A rapid potentiometric flow injection technique for the simultaneous determination of oxychlorine species such as ClO 3 −–ClO 2 − and ClO 3 −–HClO has been developed, using both a redox electrode detector and a Fe(III)–Fe(II) potential buffer solution containing chloride. The analytical method is based on the detection of a large transient potential change of the redox electrode due to chlorine generated via the reaction of the oxychlorine species with chloride in the potential buffer solution. The sensitivities to HClO and ClO 2 − obtained by the transient potential change were enhanced 700–800-fold over that using an equilibrium potential. The detection limit of the present method for HClO and ClO 2 − is as low as 5×10 −8 M with use of a 5×10 −4 M Fe(III)–1×10 −3 M Fe(II) buffer containing 0.3 M KCl and 0.5 M H 2SO 4. On the other hand, sensitivity to ClO 3 − was low when a potential buffer solution containing 0.5 M H 2SO 4 was used, but could be increased largely by increasing the acidity of the potential buffer. The detection limit for ClO 3 − was 2×10 −6 M with the use of a 5×10 −4 M Fe(III)–1×10 −3 M Fe(II) buffer containing 0.3 M KCl and 9 M H 2SO 4. By utilizing the difference in reactivity of oxychlorine species with chloride in the potential buffer, a simultaneous determination method for a mixed solution of ClO 3 −–ClO 2 − or ClO 3 −–HClO was designed to detect, in a timely manner, a transient potential change with the use of two streams of potential buffers which contain different concentrations of sulfuric acid. Analytical concentration ranges of oxychlorine species were 2×10 −5–2×10 −4 M for ClO 3 −, and 1×10 −6–1×10 −5 M for HClO and ClO 2 −. The reproducibility of the present method was in the range 1.5–2.3%. The reaction mechanism for the transient potential change used in the present method is also discussed, based on the results of batchwise experiments. The simultaneous determination method was applied to the determination of oxychlorine species in a tap water sample, and was found to provide an analytical result for HClO, which was in good agreement with that obtained by the o-tolidine method and to provide a good recovery for ClO 3 − added to the sample.