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Results for “Magnetic Fields”

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At least 19 recordsLinked to original sources
PubMed1977

Mössbauer investigation of deoxymyoglobin in a high magnetic field. Orientation of the electric field gradient and magnetic tensors.

We have examined the Mössbauer spectra of deosymyoglobin in a 6 T magnetic field in the temperature range 4.2-195 K. Spectra were fitted by the least-squares method using a phenomenological model in which the internal magnetic hyperfine field was assumed to be related to the applied field by a temperature dependent tensor õmega. The results indicate that õmega has axial symmetry and a principal axis system aligned with that of the electric field gradient (efg). The principal component of the latter is negative and lies on the symmetry axis of õmega. Our fits indicate that of efg asymmetry parameter is eta = 0.7, with no appreciable temperature dependence. Both axial and transverse components of õmega have the expected 1/T temperature dependence for T greater than 20 K. Our experimentally determined value of eta, combined with published single crystal zero-field measurements, constrains the efg-heme relative orientation to two possibilities. In neither of these is an efg principal axis near to the heme normal.

Animals↗
PubMed1977

The trajectories of particles suspended in electrolytes under the influence of crossed electric and magnetic fields. Possible explanation of the sensitivity of organism to magnetic fields.

We observed that particles, suspended in an electrolyte and brought into crossed magnetic and electric fields of low intensities, will deviate in the central part of the electrophoresis chamber of a standard Zeiss Cytopherometer with a component vertical to both fields. The direction and magnitude, however, were sharply at variance with what would be expected by the action of the Lorentz force (EMF) on the surface of the particles. The magnitude of the deviation depends upon the magnetic and electric field strength, the ion concentration of the suspension medium and the geometry of the chamber. The movement of the particles is due to streaming of the electrolyte which is mainly caused by inhomogeneities of the electric field in the electrophoresis chamber. The magnitude of the effect is high enough to occur physiological conditions. Magneto-electrophoretic streaming might eventually act as a transducer mechanism which could explain the ability of some animals to orientate themselves in the geomagnetic field.

Electricity↗
PubMedDate not supplied

[Motor activity of mice in a magnetic field of varying intensity].

Mice were exposed to a constant magnetic field of 250-4,000 oersted and alternative magnetic field of 100 oersted and a frequency of 100 Hz. The animals showed changes in the motor activity whose level and pattern depended on the field intensity. An exposure to a constant magnetic field of 1000 oersted inhibited significantly motor activity of mice. The motor activity was slightly activated during an exposure to a constant magnetic field of 500 oersted and immediately after an exposure to a constant magnetic field of 4000 oersted and to an alternative magnetic field of 100 oersted and a frequency of 100 Hz.

Animals↗
PubMed1978

Electron transfer and spin exchange contributing to the magnetic field dependence of the primary photochemical reaction of bacterial photosynthesis.

The yield phiT of triplet products "PR" generated in reaction centers of Rhodopseudomonas sphaeroides in which the "primary" acceptor is reduced had been found to depend on external magnetic fields. The magnetic field dependence varies, however, between different reaction center preparations. By means of a theoretical description of the primary electron transfer processes and hyperfine coupling-induced electron spin motion the factors influencing the magnetic field behaviour of the triplet products are studied. The following quantities characteristic of the primary electron transfer in photosynthesis have a strong effect on phiT: (1) the rate constants of reversible electron transfer between the initially excited singlet state of the reaction center and an intermediate radical ion pair state; (2) the rate constants of irreversible electron transfer of the radical pair to the ground and excited triplet state of the reaction center; (3) the electron exchange interactions between the radical pair and the "primary" acceptor. From the observed magnetic field dependence of phiT estimates for these quantities are obtained. A temperature dependence of the magnetic field behaviour of phiT and a magnetic field effect on the fluorescence quantum yield of the reaction center are predicted.

Bacteriochlorophylls↗
PubMedDate not supplied

Modification of electron-beam dose distributions by transverse magnetic fields.

By applying a transverse magnetic field to a dosimetry phantom, an incident high-energy electron beam is made to follow a spiral path in the course of slowing down. Certain levels, determined by the electron energy and the magnetic field strength, will be traversed several times by the same electrons. The net result of this process is an enhancement of the depth dose in relation to the entrance dose, and a more sharply defined depth of penetration. Experiments with 50- and 55-MeV electrons traversing a 20.5-kG field are shown to support the predictions of a detailed Monte Carlo calculation.

Electrons↗
PubMed1976

[Change in the evoked potentials of the brain exposed to a constant magnetic field].

The influence of the constant magnetic field (CMF) upon the cerebral and cerebellar cortex potentials evoked by the sciatic stimulation was studied in rats. During the exposure to the CMF there occurred an increase of the evoked potentials in amplitude and the appearance of additional waves in their structure. The effect was enhanced with increase in the intensity of magnetic field within the range of 500-4000 oe.

Animals↗
PubMed1979

Biological effects of magnetic fields: studies with microorganisms.

Five bacteria and one yeast were grown in magnetic fields of 50-900 gauss with frequencies of 0-0.3 HZ and square, triangular, or sine waveform. Growth of these microorganisms could be stimulated or inhibited depending upon the field strength and frequency of the pulsed magnetic field. Spore germination and mutation frequency were unaffected by the magnetic fields used in this study.

Bacillus subtilis↗
PubMed1977

Magnetic field effects on radical pair intermediates in bacterial photosynthesis.

We have investigated the effects of magnetic fields on the formation and decay of excited states in the photochemical reaction centers of Rhodopseudomonae sphaeroides. In chemically reduced reaction centers, a magnetic field decreases the fraction of the transient state PF that decays by way of the bacteriochlorophyll triplet state PR. At room temperature, a 2-kG field decreases the quantum yield of Pr by about 40%. In carotenoid-containing reaction centers, the yield of the carotenoid triplet state which forms via PR is reduced similarly. The effect of the field depends monotonically on field-strength, saturating at about 1 kG. The effect decreases at lower temperatures, when the yield of PR is higher. Magnetic fields do not significantly affect the formation of the triplet state of bacteriochlorophyll in vitro, the photooxidation of P870 in reaction centers at moderate redox potential, or the decay kinetics of states PF and PR. The effect of magnetic fields support in view that state PF is a radical pair which is born in a singlet state but undergoes a rapid transformation into a mixture of singlet and triplet states. A simple kinetic model can account for the effects of the field and relate them to the temperature dependence of the yield of PR.

Free Radicals↗
PubMed1977

Influence of a 1400-gauss magnetic field on the radiosensitivity and recovery of EMT6 cells in vitro.

EMT6 mouse mammary tumour cells in vitro were exposed to an almost uniform 1400-gauss magnetic field during or after irradiation with 120 kV X-rays. Exposure of unirradiated control cultures to this field for up to 48 hours did not alter the viability or growth of the cells. Exposure of exponentially-growing cultures to the magnetic field during irradiation did not alter the survival curve. Exposure of exponentially-growing culturesto the magnetic field between two doses of 500 rad of X-rays did not alter significantly the pattern or magnitude of the recovery from sub-lethal damage. Exposure of plateau phase cultures to the magnetic field after irradiation did not alter significantly the pattern or magnitude of recovery from potentially-lethal damage. The effects of a short exposure to an almost uniform magnetic field of this strength on the production and repair of radiation damage appear to be minimal in this system.

Cell Line↗
PubMed1975

Visually evoked magnetic fields of the human brain.

Magnetic field variations from the human brain produced by visual stimulation have been observed in a normal laboratory setting with a superconducting quantum interference device and no magnetic shielding of the subject. Previously unknown temporal and spatial features of the field near the scalp are reported.

Brain↗
PubMedDate not supplied

[The effects of weak magnetic fields on bacteria].

A stationary device was constructed for conducting experiments in a weak magnetic field. A ferromagnetic screen was used to produce in the working volume a magnetic-field of 26 nT. The effect of a weak magnetic field on the following bacteria was studied: E. coli communior, B. prodigiosum, Staphylococcus aureus 209, and Bac. anthracoides. Cultivation of the bacteria in these conditions for a long time resulted in changes of their tinctorial, morphological, cultural, and biochemical properties.

Bacillus cereus↗
PubMedDate not supplied

High energy electron radiotherapy in a magnetic field.

We propose the use of high energy electrons in a strong local magnetic field as the ionizing beam in radiation therapy. A high kinetic energy insures that the electrons will penetrate to deep-seated tumor masses. A high magnetic field of several tesla in the region encompassing the tumor will confine the high energy electrons to the tumor volume before the scattering of the beam becomes excessive, thus producing an enhanced electron "Bragg peak" and highly localized strong radiation dose. The conclusions are based on a detailed Monte Carlo model which includes Landau straggling, multiple scattering, and the space dependence of the magnetic field.

Electrons↗
PubMedDate not supplied

[Movement of dissolved oxygen in a constant magnetic field].

Some regularities of the movement of liquid-solved oxygen in the constant magnetic field have been studied. Redistribution and specific dynamics of the changes of pO2 in a vessel with a physiological solution under the effect of the magnetic field are shown. The data obtained make us to believe that when interpreting the results of biological experiments applying magnets movement of oxygen in the magnetic field should be taken into account as well as possible change of metabolic processes in this case.

Magnetics↗
PubMed1976

Thermostability of the erythrocytes of mice exposed to the action of a magnetic field.

The authors investigated the thermostability of the erythrocytes os strain CBA mice exposed to the action of a magnetic field formed by the poles of a rotating permanent magnet of 20 mT (200 GAUSS) induction. The erythrocytes of animals which spent 17 weeks in the magnetic field were significantly less heat resistance than those of the control animals. The effect on animals kept in the magnetic field during embryoyenesis and infancy and then left 3 months outside it was even more pronounced.

Animals↗
PubMed1978

RF magnetic field penetration, phase shift and power dissipation in biological tissue: implications for NMR imaging.

The magnetic field penetration, phase shift and power deposition in planar and cylindrical models of biological tissue exposed to a sinusoidal time-dependent magnetic field have been investigated theoretically over the frequency range 1 to 100 MHz. The results are based on measurements of the relative permittivity and resistivity dispersions of a variety of freshly excised rat tissue at 37 and 25 degrees C, and are analysed in terms of their implications for human body nuclear magnetic resonance (NMR) imaging. The results indicate that at NMR operating frequencies much greater than about 30 MHz, magnetic field amplitude and phase variations experienced by the nuclei may cause serious distortions in an image of a human torso. The maximum power deposition envisaged during an NMR imaging experiment on a human torso is likely to be comparable to existing long-term safe exposure levels, and will depend ultimately on the imaging technique and NMR frequency employed.

Animals↗
PubMedDate not supplied

[Bioelectrical activity of the neuromuscular and sympathetic systems exposed to a constant magnetic field].

The experiments on an isolated frog neuromuscular preparation gave evidence that an exposure to stable magnetic fields of 1000-4000 Oe did not influence the time parameters, amplitude and pattern of the action potentials of the gastrocnemius muscle induced by ischiatic nerve stimulation with single impulses. Similar results were obtained from an analysis of electric responses of the upper cervical sympathetic mode to the stimulation of preganglionar fibers in in situ experiments on urethane anesthesized rabbits subjected to a total exposure of a stable magnetic field (500-3000 Oe). In addition, an exposure to a stable magnetic field of 4000 Oe brought about a decrease of the level of depression of the action potential of muscles after conditioning tetanus.

Action Potentials↗
PubMedDate not supplied

[Effect of a magnetic field on Escherichia coli].

The decontaminating effect of the pulsing magnetic field on the E. coli infected reclaimed water was studied on two installations. The magnetic field intensity was 500 and 1000-1500 ersted and the microbial load was 1, 10 and 100 thous. microbial units per 1 ml. It was found that the magnetic treatment of water had a noticeable bactericidal effect. This indicated that the method can be used for decontamination of reclaimed water.

Disinfection↗