Rapid Potential Changes Research Articles

Investigation of degradation mechanisms in PEM fuel cells caused by low-temperature cycles

Environmental influences, especially temperatures below the freezing point, can affect the performance and long-term stability of PEMFCs. Within the scope of this research, a completely new test procedure was developed to characterize PEMFC single cells with respect to their long-term stability at temperature cycles between 80 °C and −10 °C. Using this procedure, the behavior of PEMFC single cells (active surface area of 43.6 cm2) with different cathode-ionomer-to-carbon (I/C) weight ratios (0.5/1.0/1.5) was evaluated. The generated in-situ measurement data clearly demonstrate that the performance of each PEMFC single cell changes individually as a function of the cathode I/C-ratio during the 120 stress cycles. While the MEA with an I/C ratio of 0.5 showed a power loss of ~1.49%, the MEAs with an I/C ratio of 1.0 and 1.5 showed a power loss of about ~7.75% and ~24.7%, respectively. The subsequent post-mortem ex-situ analyses clearly showed how the test procedure and the different I/C-ratios affected the changes in the catalyst layers (CL). The destructive mechanisms responsible for the changes can be divided into two categories: One part was driven by rapid enthalpy change leading to mechanical failure, and the other part, which led to the reduction of cathode CL thickness, was driven by rapid potential changes and potential shifts (overpotentials). This reduction in cathode CL thickness ultimately leads to an accumulation and excessive load of ionomer in the direction of GDL, resulting in a reduction in pore size, a shift in the core reaction area, and high O2 transport resistance.

Electrochemical sensing of tumor suppressor protein p53–deoxyribonucleic acid complex stability at an electrified interface

Electrochemical biosensors have the unique ability to convert biological events directly into electrical signals suitable for parallel analysis. Here we utilize specific properties of constant current chronopotentiometric stripping (CPS) in the analysis of protein and DNA–protein complex nanolayers. Rapid potential changes at high negative current intensities (Istr) in CPS are utilized in the analysis of DNA–protein interactions at thiol-modified mercury electrodes. P53 core domain (p53CD) sequence-specific binding to DNA results in a striking decrease in the electrocatalytic signal of free p53. This decrease is related to changes in the accessibility of the electroactive amino acid residues in the p53CD–DNA complex. By adjusting Istr and temperature, weaker non-specific binding can be eliminated or distinguished from the sequence-specific binding. The method also reflects differences in the stabilities of different sequence-specific complexes, including those containing spacers between half-sites of the DNA consensus sequence. The high resolving power of this method is based on the disintegration of the p53CD–DNA complex by the electric field effects at a negatively charged surface and fine adjustment of the millisecond time intervals for which the complex is exposed to these effects. Picomole amounts of p53 proteins and DNA were used for the analysis at full electrode coverage but we show that even 10–20-fold smaller amounts can be analyzed. Our method cannot however take advantage of very low detection limits of the protein CPS detection because low Istr intensities are deleterious to the p53CD–DNA complex stability at the electrode surface. These data highlight the utility of developing biosensors offering novel approaches for studying real-time macromolecular protein dynamics.

Bifurcation-Like Behavior of Electrostatic Potential in LHD

The temporal evolution of the potential is measured with the heavy ion beam probe (HIBP) in the Large Helical Device (LHD). A rapid change in the potential is observed early in the tangential neutral beam injection (NBI) phase, just after the switch from tangential to perpendicular NBI, and in a low-power electron cyclotron heated (ECH) discharge in the LHD. The radial profile of the potential is measured before and after the potential change. This rapid potential change is considered to indicate the bifurcation of the radial electric field in the edge region of the LHD plasma.

Long‐Distance Electron Transfer by G. sulfurreducens Biofilms Results in Accumulation of Reduced c‐Type Cytochromes

So close, but yet so far: G. sulfurreducens c-type cytochromes become reduced as biofilms grow on electrodes beyond a few cell thicknesses, even if the electrode is poised well above the potential required to oxidize all cytochromes. Cytochrome redox state also lags behind rapid potential changes during voltammetry, but only when the films are multiple cell layers thick, as would be expected if diffusional or exchange-based kinetics controls electron transfer between cytochromes.

Study of Accelerated Test Protocol for PEFC Focusing on Carbon Corrosion

Carbon corrosion caused by rapid potential changes is presented. Test results with full-scale single cells suggest rapid voltage changes during start-up and shutdown can accelerate carbon corrosion significantly, without local or global fuel starvation. Impacts of carbon corrosion on material degradation and cell performance decay with various operation modes (e.g. voltage cycles, OCP hold and constant load) are also evaluated. The results indicate voltage cycles by start-up and shutdown, which advances carbon corrosion on cathode, accelerates cell performance decay with electrochemical surface area reduction and mass transport loss on cathode. The voltage cycle testing focusing on carbon corrosion is expected to be one of the promising test protocols for accelerated durability testing.

Repeated coseismic infiltration of meteoric and seawater into deep fault zones: a case study of the Nojima fault zone, Japan

Fluid infiltration into active faults and shear zones is usually studied in middle to upper crustal environment. Circulating fluids deposit fine-grained sediments like clay and carbonate material into cracks within the fault zone. Such crack-fill fine-grained material, calcite veins, and oxidized/weathered open cracks are well observed in the drill cores, from near-surface to a depth of 1800 m, in the Nojima fault zone, Japan, which triggered the 1995 M7.2 Kobe earthquake. Powder X-ray diffraction analysis indicates that the crack-fill fine-grained materials are mainly composed of siderite, calcite, laumontite, and fine-grained clasts of granitic rock. Isotopic analyses of carbonate material within the fine-grained materials and calcite veins reveal variable δ13C (SMOW) values ranging from 19.3‰ to 27.7‰, and δ13C (PDB) values of −4.6‰ to −18.5‰, which are consistent with those of typical meteoric and seawater. 14C dates of 10 calcite vein samples range from 35.0 to 58.4 kyr B.P.Geological, petrological, stable isotopic, and 14C data suggest that these crack-fill fine-grained materials and calcite veins and brown open cracks were developed by the repeated infiltration of O2- and CO2-bearing meteoric and seawater downward into the deep Nojima fault zone during the last 35–60 kyr. We propose a seismic fault suction-pumping model to interpret the infiltration of subsurface waters being carried down into the deep fault zone by rapid potential change during episodes of seismic faulting.

Early Gravi-Electrical Responses in Bean Epicotyls.

The relationship between gravitropism and surface electrical potentials was studied using etiolated epicotyls of adzuki bean (Phaseolus angularis). Early downward curvature (or transient positive gravitropic response) was observed about 1 min after gravistimulation. The downward curvature was closely related to the speed of the subsequent upward curvature. Surface electrical potentials decreased cooperatively in a limited region on the upper side within only 0.5 to 2 min. This is the earliest event found so far to follow gravistimulation of intact epicotyls. The rapid change in the potential had a high correlation with the early downward curvature and also the subsequent negative gravitropism. It is suggested that the rapid potential change plays an important role in gravity perception.

Electron spin resonance studies on a flavoprotein in neutrophil plasma membranes. Redox potentials of the flavin and its participation in NADPH oxidase.

Plasma membrane fractions of stimulated and resting cells were isolated from pig blood neutrophils. The midpoint redox potential (Em) of the membrane-bound flavin was determined potentiometrically by analysis of the flavin free-radical signal by electron spin resonance (ESR) spectroscopy. In both stimulated and resting cells, a peak position of the titration curve gave an Em value of -280 mV at pH 7.0 (Em7). The flavin free radical showed an ESR spectrum at g = 2.004 with a peak to peak width of 19 G, which indicates that the redox intermediate is a neutral semiquinone. Redox titrations were anaerobically examined at 25 degrees C with NADPH in place of dithionite. Addition of NADPH to plasma membranes of stimulated cells resulted in a rapid change in potential, accompanied by the formation of the ESR signal of flavin free radical. Computer simulation of the titration points gave an ambient midpoint potential of -280 mV (Em7). In contrast, those of resting cells showed a very slow change in potential and no g = 2.00 signal formation. Power saturation behavior of the ESR signal showed a marked difference between those of stimulated and resting cells. ESR characteristics of the flavin are discussed in relation to the membrane-bound NADPH oxidase.

A liquid ion-exchanger alternative to KCl for filling intracellular reference microelectrodes.

We have developed a filling solution for silanised microelectrodes consisting of potassium tetrakis (p-chlorophenyl) borate in octanol. Microelectrodes filled with this reference liquid ion-exchanger (RLIE) have equal selectivities to Na and K, and give the same membrane potential as do KCl-filled microelectrodes. The RLIE microelectrodes are more stable, less damaging to the cell membrane and do not leak Cl- ions. Their high resistance, however, makes them unsuitable for recording rapid potential changes or for passing current.

Direct demonstration of the involvement of chloroplasts in the rapid light-induced potential change in tonoplast-free cells of Chara australis. Replacement of Chara chloroplasts with spinach chloroplasts.

To directly demonstrate the involvement of chloroplasts in the rapid light-induced potential change we removed chloroplasts by centrifuging tonoplast-free cells of Chara australis. Chloroplast-free cells showed no signs of a potential change on illumination. When a chloroplast-free Chara cell was perfused with a suspension of chloroplasts isolated from other cells of Chara australis, it regained its ability to generate the rapid potential change induced by light. Chloroplasts were isolated from spinach leaves by a method which preserves the chloroplast envelope; thus ensuring the ability to assimilate CO2. When these chloroplasts were introduced into a transparent Chara cell containing no chloroplasts, normal rapid hyperpolarization was induced on illumination. When spinach chloroplasts were treated with a medium of very low osmotic potential, no O2 evolution was detected, but even with these chloroplasts rapid light-induced hyperpolarization was observed. We concluded that chloroplasts are essential for the rapid light-induced potential change and that chloroplasts can be replaced with those of another species, so far as the light-induced potential change is concerned.

Some factors involved in the thalamic control of spontaneous barbiturate spindles.

1. The origin of thalamic and cortical spontaneous spindles was studied in cats anaesthetized with sodium pentobarbital.2. Complete removal of all cortical grey matter left the thalamic rhythmic spindle activity unchanged.3. Removal of the entire thalamus or pronounced oedema in the thalamus abolished completely the spindle activity in the corresponding hemisphere.4. In a neuronally isolated cortical area, a fast, low voltage background activity appeared, interrupted by occasional irregular rapid potential changes (sharp waves) of high voltage. Regular spindle rhythms were seldom observed unless excited by a depolarizing drug. Spontaneous spindles did not invade the isolated cortex via a bridge of intact cortical tissue.5. With increasingly larger destruction of the thalamus in a rostro-caudal direction, the activity in the post-cruciate cortex did not change until the anterior third of the thalamus was encroached upon. A transverse section in front of the thalamus nearly eliminated the cortical spindles.6. Complete removal of the mid line and intralaminar nuclei left the spontaneous rhythmic activity of the lateral thalamic nuclei and of the frontal cortex principally unchanged.7. Removal of the laterally located thalamic nuclei, including the n. ventralis posterolateralis (VPL), abolished virtually all spontaneous spindle activity of the frontal cortex, including the post-cruciate area.8. Local cortical cooling reduced the amplitude but not the frequency of the cortical spindles.9. Cooling of the whole brain reduced both the amplitude and the frequency of the spindles. At low temperatures, all spindle activity in the cortex disappeared, and occasional sharp waves occurred, as with de-afferentation.10. It is concluded that the rhythm of the cortical spontaneous barbiturate spindles is generated exclusively by thalamic neurones. The electromotive force of the corticographic waves, however, has a cortical origin.

THE OCCURRENCE OF RAPID POTENTIAL CHANGES IN THE ELECTROENCEPHALOGRAM

Medical Journal of AustraliaVolume 1, Issue 15 p. 465-467 Original Article THE OCCURRENCE OF RAPID POTENTIAL CHANGES IN THE ELECTROENCEPHALOGRAM† M. H. Draper, M. H. Draper Department of Human Physiology and Pharmacology, University of AdelaideSearch for more papers by this authorR. S. Edgar, R. S. Edgar Department of Human Physiology and Pharmacology, University of AdelaideSearch for more papers by this authorW. A. Dibden, W. A. Dibden Department of Human Physiology and Pharmacology, University of AdelaideThe work is being carried out under grants from the National Health and Medical Research Council.Search for more papers by this author M. H. Draper, M. H. Draper Department of Human Physiology and Pharmacology, University of AdelaideSearch for more papers by this authorR. S. Edgar, R. S. Edgar Department of Human Physiology and Pharmacology, University of AdelaideSearch for more papers by this authorW. A. Dibden, W. A. Dibden Department of Human Physiology and Pharmacology, University of AdelaideThe work is being carried out under grants from the National Health and Medical Research Council.Search for more papers by this author First published: 01 April 1948 https://doi.org/10.5694/j.1326-5377.1948.tb98886.xCitations: 1 †Read at a meeting of the Medical Sciences Club of South Australia on October 5, 1946. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume1, Issue15April 1948Pages 465-467 RelatedInformation