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PubMedDate not supplied

On the electrical properties of dislocations in ZnS using electric force microscopy.

A combination of electric force microscopy (EFM) and noncontact atomic force microscopy (AFM) was used to study microscratching-induced dislocations in sphaleritic ZnS single crystals. Dislocation bands predominantly consisting of either anion-type (S) or cation-type (Zn) dislocations were induced by scratching along either [111] or [111] on a (110) surface. A significant difference of local distortions in electrical potential between the S(g) and Zn(g) dislocation bands was observed from the EFM images. Electric charges of these dislocations were determined quantitatively and the results were compared with theoretical models.

Journal Article↗
PubMed1982

Electric properties and structure of DNA-restriction fragments from measurements of the electric dichroism.

The electric dichroism of 17 homogeneous DNA fragments, ranging in size from 43 to 4362 base-pairs, has been analyzed in high electric fields. The orientation of the small fragments can be described in terms of an induced dipole moment, whereas the large fragments are oriented according to a constant dipole mechanism. In the intermediate size range, DNA orients according to an induced dipole mechanism at low field strengths and according to a constant dipole mechanism at high field strengths. From these observations we propose an orientation mechanism with a saturating induced dipole. The induced dipole observed at low field strengths is saturated at a field strength Eo within a transition range Em to give a constant dipole moment at high field strengths. These parameters together with the polarizability and the limit reduced dichroism are evaluated by a least-squares analysis of the experimental data. Eo and Em are found to decrease with increasing chain length from Eo approximately 40 kV/cm (Em approximately 14 kV/cm) at 65 base-pairs to 10 kV/cm (6 kV/cm) at 194 base-pairs. The polarizability is found to increase with the square of the chain length, whereas the saturated dipole increases with chain length N at low N and goes to a limit value at high N. The temperature dependence of the orientation parameters is found to be very small. The values obtained for the limit dichroism are between -1.0 and -1.3 for chain lengths between 60 and 1000 base-pairs, whereas values around -1.4 are observed at chain lengths greater than 1000 base-pairs. These data indicate that electric fields extend the contour of DNA strands at high chain lengths from a weakly bent to a more linear form. The variations of the limit dichroism observed for short fragments suggest sequence-dependent differences in the secondary structure of the helix. The experimental results are compared with numerical calculations based on simple polyelectrolyte models. For short fragments the magnitude of several electrochemical parameters can be adequately explained by a polarization of the ion cloud around the DNA molecules. However, these polyelectrolyte models do not adequately describe the observed chain length dependence of the orientation phenomena.

Base Composition↗
PubMed1986

Dielectric behavior of polyelectrolytes. IV. Electric polarizability of rigid biopolymers in electric fields.

The equilibrium Kerr effect of a system of mobile charges constrained to the surface of biomacromolecules is calculated. Cylindrical and spherical geometries are considered. For the cylinder we determine the anisotropy of electric polarizability as a function of length, temperature, and number of charged species in the low-field regime, and the fraction of the maximum induced dipole in the field direction for higher electric fields. The results are compared to experimental data for DNA oligomers taken from the literature. With spherical geometry we calculate the fractional induced dipole moment as a function of electric field strength and from this deduce the orientation function. The field dependence of the orientation function is compared to experimental data in the literature for bovine disk membrane vesicles.

DNA↗
PubMed2005

Reversible and persistent electrical bistability in single crystals of a self-assembled pi-conjugated tetraaryl system: a submicrometer scale electrical characterization.

A new pi-conjugated electroactive 4,4'-bipyridinium that bears two pyridazone self-complementary units was prepared and characterized. The new system readily assembles and forms at least two stable charge-transfer crystalline structures having a thermal population of unpaired electrons. The crystals of one phase exhibit electrical bistability, displaying either high (ON) and low (OFF) conductivity, at the same applied bias, depending on the electrical history of the system. The relation between the supramolecular structure of the crystals and their electrical properties is also discussed.

Journal Article↗
PubMed2007

Reversible vesicle restraint in response to spatiotemporally controlled electrical signals: a bridge between electrical and chemical signaling modes.

Microelectronic devices employ electrons for signaling whereas the nervous system signals using ions and chemicals. Bridging these signaling differences would benefit applications that range from biosensing to neuroprosthetics. Here, we report the use of localized electrical signals to perform an operation common to chemical signaling in the nervous system. Specifically, we employ electrical signals to restrain vesicles reversibly. We perform this operation using the stimuli-responsive aminopolysaccharide chitosan that is able to electrodeposit onto cathode surfaces in response to localized electrical stimuli. We show that surfactant-vesicles and liposomes can be co-deposited with chitosan and are entrapped (i.e., restrained) within the deposited film's matrix. Vesicle co-deposition could be controlled spatially and temporally using microfabricated wafers with independent electrode addresses. Finally, we show that vesicles restrained within the deposited chitosan matrix can be mobilized under mildly acidic conditions (pH <6.5) that resolubilize chitosan. Potentially, the ability to restrain and mobilize chemical signals that are segregated within vesicles may allow microfluidic systems to access the rich diversity offered by chemical signaling.

Animals↗
PubMed2005

Superpositions of chiral states in the presence of electric dipole, magnetic dipole, and electric quadrupole interactions.

This paper is a straightforward generalization of Maierle-Harris proposal regarding parity implications on the superpositions of chiral states of a molecule. It is shown that the inclusion of electric quadrupole and magnetic dipole interactions removes several of restrictions on the preparation of superpositions of mid R:L and mid R:R states of a chiral molecule. It is also found that the dephasing of mid R:L and mid R:R superpositions, due to the spontaneous emission from the chiral molecule, has opposing contributions from electric quadrupole-magnetic dipole and electric dipole interactions.

Journal Article↗
PubMed2006

Multiscale modelling of human gastric electric activity: can the electrogastrogram detect functional electrical uncoupling?

During recent years there has been a growing interest in the assessment of gastric electrical health through cutaneous abdominal recordings. The analysis of such recordings is largely limited to an inspection of frequency dynamics, and this has raised doubts as to whether functional gastric electrical uncoupling can be detected using this technique. We describe here a computational approach to the problem in which the equations governing the underlying physics of the problem have been solved over an anatomically detailed human torso geometry. Cellular electrical activity was embedded within a stomach tissue model, and this was coupled to the torso using an equivalent current source approach. Simulations were performed in which normal and functionally uncoupled (through the introduction of an ectopic antral pacemaker) gastric slow wave activity was present, and corresponding cutaneous electrogastrograms were produced. These were subsequently analysed using the currently recommended techniques, and it was found that the functionally uncoupled situation was indistinguishable from normal slow wave activity using this approach.

Computer Simulation↗
PubMed1993

The electrical geometry, electrical properties and synaptic connections onto rat V motoneurones in vitro.

1. We have developed a tissue slice preparation which allows the study of the actions of single presynaptic neurones onto single trigeminal motoneurones in the immature rat. Our aim in this first stage of the work has been to assess the validity of this preparation as a model for responses obtained in vivo from trigeminal motoneurones in adult rats. We have quantified the integrative properties of the motoneurones and also the variability in transmission at synapses of single presynaptic neurones onto the motoneurones. This data has then been compared to similar published data obtained from adult (rat) trigeminal motoneurones in vivo. 2. Quantitative reconstructions were made of the morphology of three motoneurones which had been labelled with biocytin by intracellular injection. The neurones gave off six to nine dendrites, of mean length 522 microns (S.D. = 160; n = 22), which branched on average 10.5 times to produce 11.45 end-terminations per dendrite (S.D. = 8.57; n = 22). The mean surface area of the dendrites was 0.92 x 10(4) microns2 (S.D. = 0.67; n = 22), and, for individual cells, the ratio of the combined dendritic surface area to the total neuronal surface area ranged from 98.3 to 99.2% (n = 3). At dendritic branch points the ratio of the summed diameters of the daughter dendrites to the 3/2 power against the parent dendrite to the 3/2 power was 1.09 (S.D. = 0.21; n = 217), allowing branch points to be collapsed into a single cylinder. The equivalent cylinder diameter of the combined dendritic tree remained approximately constant over the proximal 25-40% of the equivalent electrical length of the dendritic tree and then showed tapering. The tapering could be ascribed to termination of dendrites at different electrical distances from the soma. 3. Electrical properties were determined for a total of eighty-seven motoneurones, all with membrane potentials more negative than 60 mV (mean = 66.0 mV; S.D. = 5.2) and spikes which overshot zero (mean spike amplitude = 77 mV; S.D. = 10.5; n = 87). The spikes were followed by after-hyperpolarizations (AHPs) of mean amplitude 2.2 mV (S.D. = 1.7; n = 47), and mean duration 54.1 ms (S.D. = 9.5; n = 47). The mean input resistance of the neurones was 7.5 M omega (S.D. = 2.5; n = 69), the mean membrane time constant was 3.5 ms (S.D. = 2.2; n = 35), and the mean rheobase was 1.6 nA (S.D. = 1.1; n = 56).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1976

[The effect of low-frequency electric stimulation of the caudate nucleus on the electrical activity of the cortex and on the sleep-wakefulness cycle].

In cats, the effect of low-frequency electric stimulation of the caudate nucleus on electric activity of neo- and archipaleocortex and on wakefulness-sleep cycle, was studied. The data obtained suggest: 1) at threshold and suprathreshold single electric shocks applied to the caudate nucleus they evoked potential occurs more readily in the sensorimotor area of the neocortex than in the dorsal hippocampus. At 2-6/sec stimulation the evoked potentials in the hippocampus are facilitated and become very stable, whereas in the sensorimotor cortex the most obvious responses occur at the 6-8/sec frequency. However, the evoked potentials are variable in the sensorimotor cortex, and at prolonged 8-12/sec stimulation spindle activity soon develops; 2) behavioral correlate of the synchronized activity in the neo- and archipaleocortical structures during low-frequency stimulation of the caudate nucleus, may involve development of drowsiness with the cessation of stimulation, however, both the EEG and behavioral signs of the drowsiness disappear. The onset of drowsiness following withdrawal of the caudate stimulation, is a rare phenomenon only occurring because of an occasional coincidence of the stimulation with the spontaneous onset of natural sleep; 3) low-frequency caudate stimulation entailing the ECoG synchronization does not cause the transition of paradoxical phase into the slow-wave phase of sleep, and as soon as the stimulation ceases its normal structure recovers. However, if the stimulation of the caudate nucleus is repeated several times in one paradoxical phase, this would shorten the subsequent slow-wave phase and accelerate the onset of the next paradoxical phase; 4) prolonged low-frequency stimulation of the caudate nucleus causing the ECoG synchronization results in a considerable change of wakefulness-sleep cycle in the post-stimulation period: a decrease in the total time of slow-wave sleep due to shortening of its different phases, and an increase in the total amount of paradoxical sleep because of the onset of its phases is rendered more frequent. This effect is more obvious in the first half of the 8-hr cycle.

Animals↗
PubMed2003

[Polish regulations on maximum admissible intensities for electric and magnetic frequencies of 60 Hz and the European Union recommendations for electrical power engineering].

Electric and magnetic fields of 50 Hz from electric power devices affect not only workers, but also the general population, as these devices are also located in populated areas, hence the duality of regulations on maximum admissible intensities. This paper presents these regulations and discusses in detail the changes of 2001. Based on the Polish regulations, hygienic evaluation of electric power devices has been attempted. The Polish regulations on the 50 Hz electromagnetic fields were compared with relevant international regulations of CENELEC and the European Union recommendations. Our maximum admissible intensities have been found to conform with the international standards.

Electromagnetic Fields↗
PubMed1989

[Study of the informative value of Holter ECG monitoring and exercise test in ventricular arrhythmia in patients with ischemic heart disease and a high degree of myocardial electric instability, based on the data of programmed electric stimulation of the heart ventricles].

A total of 118 individuals were investigated to assess the value of Holter's ECG monitoring and bicycle ergometry for the identification of coronary patients predisposed to dangerous arrhythmias. Programmed ventricular stimulation was carried out: 1, 2 and 3 electric stimuli from the apex and/or outflow pathway of the right ventricle were applied in the presence of a pacemaker operating at 100 and 140 imp/min rates. The analysis of 24-hour ECG records demonstrated a correlation between some parameters (number of different ventricular extrasystole configurations, presence of high-grade ventricular arrhythmias) and the magnitude of myocardial electric instability, as shown by electric stimulation. An emergence or essential increase in ectopic ventricular activity during bicycle ergometry is not a precursor of myocardial instability at programmed pacemaker stimulation. At the same time, the absence of ventricular arrhythmias in response to stress does not exclude high-grade myocardial instability, detectable at programmed pacemaker stimulation.

Adult↗
PubMedDate not supplied

[Effect of dispersion of electric parameters of bacterial cells on their orientation in alternating electric fields].

On the basis of electrophysical model of bacterial cell frequency relationship of orienting force moment acting on it in the alternating electric field has been calculated. Dependence of relative value of the moment on electric and geometrical parameters of the model was calculated. It has been shown that the account of frequency dispersion of the electric parameters brings about a change in the course of frequency relationship of the orienting moment in the range of low and mean frequencies. The data obtained agree with electrooptic measurements performed on E. coli cells.

Bacterial Physiological Phenomena↗
PubMed1989

A temporal analysis of testosterone-induced changes in electric organs and electric organ discharges of mormyrid fishes.

The electric organ discharge (EOD) of several species of mormyrid fishes within the genus Brienomyrus is sexually dimorphic during the breeding season: the duration of the male's EOD is much longer than the duration of the female's (for a review see Hopkins, 1986). The mormyrid used here, Brienomyrus sp., exhibits similar alterations in the duration of the triphasic EOD after treatment with testosterone, as do other members of this genus (for reviews see Bass, 1986a,b). In this experiment, animals were intraperitoneally implanted with pellets of either 11-ketotestosterone or 17 a-methyltestosterone, and the time course of the changes in the duration of each of the three phases of the EOD were quantified. Additionally, the time course of changes in the morphology of the electric organ, after testosterone treatment, was also quantified using electron microscopic techniques. The results suggest that the change in the duration of the first phase of the EOD is due exclusively to the change in the thickness of the electrocyte body: this is consistent with a model proposed by Bennett and Grundfest (1961) for the electrogenesis of a triphasic EOD. Changes in the duration of the second and third phases of the EOD are highly correlated with the changes in the surface area of the posterior and anterior faces of the electrocyte, respectively. The results support the hypothesis that gonadal steroid hormone-induced changes in the EOD are due to structural changes in the electrocyte's membranes, and that all of the observed changes in the discharge of this system can be explained by the action of steroid hormones on the peripheral target cells (electrocytes).

Action Potentials↗
PubMed1993

Rapid heat production associated with excitation of electric organs of the electric eel.

By constructing a new type of thermal detector, rapid production of heat was demonstrated during the rising phase of the action potential of the eel electric organs evoked by direct electric stimulation. Following the indirect (synapse-mediated) action potential of the organs, the existence of very large and variable production of heat of unknown origin was revealed.

Action Potentials↗
PubMed1998

Effects of 17alpha-methyltestosterone on sexually dimorphic characters in the weakly discharging electric fish, Brienomyrus niger (Günther, 1866) (Mormyridae): electric organ discharge, ventral body wall indentation, and anal-Fin ray bone expansion.

Adult males of African weakly discharging electric fish (family: Mormyridae) are distinguished from juveniles and adult females by a dorsally directed indentation of the posterior ventral body wall and by massive bone expansion of the bases of a select number of anal-fin rays. These sexually dimorphic structures seem to facilitate the anal-fin reflex that is displayed during courtship when the male envelopes its anal fin around the female's to form a common spawning pouch. Expanded bone could provide additional surface for muscle attachment and thus assist in part with the courtship sequence. Based on the fact that the expression of the male sexually dimorphic electric organ discharge (EOD) is under androgen control, and that the female EOD can be masculinized through testosterone administration, we hypothesized that androgens should also drive anal-fin ray bone expansion in male mormyrids and equally effect male-like changes in treated juveniles and adult females. Exogenous androgen treatment (17alpha-methyltestosterone) of adult female Brienomyrus niger resulted in a male-like EOD, and male-typical structural transformations (body wall indentation and anal-fin ray bone expansion). Some of these changes were immediate and receded following hormone withdrawal (EOD), while others developed more slowly and were apparently permanent (indentation and bone formation). 17alpha-Methyltestosterone administration affected only those targets in females that are normally involved in the male's reproductive behavior, i.e., its courtship signal (EOD) and two morphological features (body-wall indentation and bone expansion). Rays of the dorsal or caudal fins were never affected.

Animals↗
PubMedDate not supplied

Electric signaling behavior and the mechanisms of electric organ discharge production in mormyrid fish.

Mormyrid fish communicate and navigate using electric organ discharges (EODs). The EOD is highly stereotyped and provides information on sender identity, including species, sex, reproductive condition, and possibly relative status and individual identity. By contrast, the sequence of pulse intervals (SPI) is variable and plays more of a role in signaling behavioral states. Various types of SPI displays may be produced, including tonic patterns such as 'random' and 'regularized', and phasic patterns such as 'bursts' and cessations'. Certain displays have been linked to specific behaviors such as aggression, submission, courtship and active exploration. In addition, interacting pairs of fish may produce stereotyped displays involving the relative timing of their EODs. The EOD waveform is controlled by the morphological and physiological properties of cells in the electric organ termed electrocytes. Differences in the innervation, morphology, size and membrane characteristics of electrocytes have been directly linked to species and sex differences in the EOD. The generation of each EOD is initiated in the medullary command nucleus (CN), which thereby determines the timing of EOD output. CN does not have any properties of a pacemaker, but rather appears to integrate descending inputs that affect the probability of EOD production. The precommand nucleus (PCN) provides a major source of excitatory input to CN and is itself inhibited by corollary discharge feedback following the production of each EOD. Changes in the activity of PCN and its inhibitory feedback neurons modify EOD output, and therefore drive the generation of SPI patterns. Current studies are addressing the mechanisms underlying the generation of these patterns and preliminary results suggest that different types of signals may be controlled by distinct components of the electromotor system. This is similar to findings in other electrogenic teleosts, suggesting that it may be a general feature in the motor control of signaling behavior.

Action Potentials↗
PubMed2005

Effect of sample and substrate electric properties on the electric field enhancement at the apex of SPM nanotips.

Finite element (FE) models were built to define the optimal experimental conditions for tip-enhanced Raman spectroscopy (TERS) of thin samples. TERS experimental conditions were mimicked by including in the FE models dielectric or metallic substrates with thin dielectric samples and by considering the wavelength dependence of the dielectric properties for the metallic materials. Electromagnetic coupling between the substrate/sample and the SPM tips led to dramatic changes of both the spatial distribution and magnitude of the scattered electric field which depended on the substrate dielectric permittivity and excitation wavelength. Raman scattering as high as 10(8) with a spatial resolution of approximately 8 nm was estimated for gold SPM tips and gold substrate when excitation is performed at 532 nm (near-resonance wavelength). For dielectric samples (approximately 4 nm thick), the enhancement of Raman scattering intensity is estimated at approximately 10(5); this does not depend significantly on the sample dielectric permittivity for dielectric samples. These results suggest that TERS experimental conditions should be estimated and optimized for every individual application considering the geometric factors and electric properties of the materials involved. Such optimizations could enlarge the range of applications for TERS to samples eliciting weaker intrinsic Raman scattering, such as biological samples.

Algorithms↗