Orientation of paramecium swimming in a static magnetic field: Dependence on membrane lipid fluidity

We studied the swimming orientation of the ciliated protozoan Paramecium aurelia in a static magnetic field (0.78 T). P. aurelia is a complex of species termed syngens, whose cell morphology appears similar on microscopic examination. In the magnetic field, the cells of some syngens gradually changed their swimming orientation so that they were swimming perpendicular or parallel to the magnetic field, although such sensitivity to magnetic fields differs between syngens. When the temperature of the cell suspension was raised, the magnetic sensitivity of the cells was decreased. On the other hand, when the cells were cultured beforehand at a high temperature, their magnetic sensitivity was increased. These results raise the possibility that membrane lipid fluidity, which is inversely proportional to the membrane lipid order, contributes to the magnetic orientation of syngens. In this study, measurements of membrane lipid fluidity obtained using fluorescence image analysis with the lipophilic dye, laurdan (6-lauroyl-2-dimethylaminonaphtalene), showed that the degree of membrane lipid fluidity was correlated with the differences in magnetic orientation between syngens. That is, the syngens with decreased membrane fluidity showed an increased degree of magnetic orientation. Therefore, the membrane lipid order is a key factor in the magnetic orientation of Paramecium swimming.     

Orientation of chlorophyll in vivo. Studies with magnetic field oriented chlorella

The streptomycetes have a bacterial-type cell wall and a mycelial growth habit. Although the exact taxonomic relationship to yeasts or fungi and the bacteria is unknown, a great similarity to bacteria is assumed. $\text{Streptomyces erythreus}$ CA340 (Abbott) is found to possess a multienzyme complex making fatty acids. The crude enzyme complex is stimulated by FMN; is inhibited by iodoacetamide; is excluded and partially purified (ca. 70-fold) by Sephadex G-200; is most active at pH 7.5; is most stable in 0.5 M phosphate buffer. Thus, $\text{S. erythreus}$ CA340 and possibly all streptomycetes have a major biochemical similarity to yeasts and fungi.     

Effect of a permanent magnetic field on the formation of lipid bilayers

Effect of the constant magnetic field (MF) by the induction of 1.1 T on formation kinetics of bilayer lipid membranes (BLM) from egg lecithin in decane was discovered. Under the effect of MF oriented in parallel to the lipid film place the rate of BLM formation decreases, while at its perpendicular orientation it is accelerated. The stationary value of BLM capacity decreases under MF effect at both orientations. The discovered changes in the rate of BLM formation under MF effect seem to be related to the effect of MF on liquid crystalline structure of colour lipid film.     

Nonlinear analysis of lipid tubules by nonlocal beam model

Postbuckling, nonlinear bending and nonlinear vibration analyses are presented for lipid tubules. The lipid tubule is modeled as a nonlocal micro/nano-beam which contains small scale effect. The material properties are assumed to be size-dependent. The governing equation is solved by a two-step perturbation technique. The numerical results reveal that the small scale parameter e₀a reduces the postbuckling equilibrium paths, the static large deflections and natural frequencies of lipid tubules. In contrast, it increases the nonlinear to linear frequency ratios slightly for the lipid tubule with immovable end conditions.     

Orientation by magnetic field in leaf-cutter ants, Atta colombica (Hymenoptera: Formicidae)

Leaf‐cutter ants (Atta colombica) use trail following to travel between foraging sites and the home nest. However, this combination of pheromone and visual cues is likely to be complemented by a directional reference system such as a compass, used not only when foraging but also during colony formation, where foraging trails degrade or where ants become displaced. One candidate system is the magnetic polarity compass. We tested the orientation of leaf‐cutter ants under a magnetic field of reversed‐polarity, with the prediction that the ants would show 180° deflection compared with control ants in an unchanged geomagnetic field. When the sun's disc was unobstructed by clouds, orientation was the same as that of control ants, implying that magnetic cues were not used to orient. However, when the sky was overcast, ants in the experimental treatment significantly shifted their mean orientation both in comparison with controls and reversed‐polarity ants under the sun. Although a total reversal in orientation was not induced, the results demonstrate that Atta respond to magnetic reversal in the absence of sunlight cues, and suggest a role for magnetic cues in determining direction during orientation.     

Pumping action on blood by a magnetic field

We report here an analysis of pumping of blood by means of a non-invasive circulatory-assist device using the principle of Magnetohydrodynamics. This study shows that such a pump would require the application of a slowly moving axial magnetic field of strength of about 10⁸ amp turns/m (approximately 10⁶ oersteds). The results indicate that the temperature rise on account of induced currents is within permissible range.     

An instrument for sorting of magnetic microparticles in a magnetic field gradient.

BACKGROUND: The goal of our bioassay technique is to demonstrate high throughput, highly parallel, and high sensitivity quantitative molecular analysis that will expand current biomedical research capabilities. To this end, we have built and characterized a magnetophoresis instrument using a flow chamber in a magnetic field gradient to sort magnetic microparticles by their magnetic moment for eventual use as biological labels. METHODS: The flow chamber consists of a sample inlet, differential sheath streams, and eight outlets for collecting the microparticles after they have traversed the chamber. Magnetic microparticles are injected into the flow chamber that is positioned in a linear magnetic field gradient. The trajectory for each microparticle is determined by its total magnetic moment and size. The resulting populations of monodispersed magnetic microparticles in the different outlet bins are sorted by their magnetic moment; with the highest magnetic moments being deflected the furthest. RESULTS: We have characterized the system for sorting both superparamagnetic and ferromagnetic microparticles with approximate diameters of 8 microm and 4.0-4.9 microm, respectively. To characterize the instrument, we used microparticles with a known size distribution and varied the transit time through the chamber. This is equivalent to varying the magnetic moment, while allowing us to hold the particle properties constant from run-to-run. We demonstrated the ability to reproducibly change the distribution of the particles in the collection bins by varying transit time in good agreement with theory. We identified hydrodynamic instabilities responsible for causing dispersion in the flow. Improvements to the flow chamber hydrodynamics such as reducing the aspect ratio between the sample inlet and the chamber depth and stabilizing the sheath flow resulted in narrow sorting distributions. We measured a sorting reproducibility (percentage of particles returning to their original bin upon resorting individual populations) of 84-89%. CONCLUSIONS: We have developed a simple magnetophoresis system for reproducibly sorting magnetic microparticles. This technique will permit the use of microparticles with a wide range of magnetic moments to create a wide range of magnetic labels. Careful consideration of system design and operational parameters enables reliable and reproducible sorting of microparticles with varying size and magnetic content.     

Cutaneous microcirculation is not altered by a weak 50 Hz magnetic field.

Electromagnetic hypersensitivity (EH) is an increasing problem in modern industrial societies. As crawling sensations are frequently mentioned by EH patients alterations in cutaneous microcirculation possibly linked to exposure to magnetic fields might be involved in the development of such sensations and further dysesthesias. In seven healthy volunteers and in three persons convinced to suffer from EH the microcirculation of the right thumb was determined by laser-Doppler-flowmetry (LDF) during exposure to circularly polarized 50 Hz magnetic flux densities of 96 mT. During field exposure the LDF values remained constant. The LDF ratio "field on/field off" was found to be 1.03 +/- 0.03. In contrast, reactive hyperemia and hyperventilation caused significant changes in the LDF values of volunteers as well as of EH patients. Following arterial congestion of the forearm microcirculation of the thumb was clearly increased during reperfusion, and the LDF values were elevated up to 2.02 +/- 0.36. 10 deep breaths caused a significant decrease in the LDF values up to 0.63 +/- 0.18. In conclusion, reactive hyperemia and hyperventilation caused clear alterations of cutaneous microcirculation, whereas, 50 Hz magnetic fields had no influence on cutaneous microcirculation.     

Orientation of lutein in a lipid bilayer - revisited

Lutein is present in the human retina and lens, where it plays a protective role. As lutein is associated with the lipid matrix of biomembranes, the role depends on its membrane location. Experimental studies predicted two orientations of lutein in a phosphatidylcholine (PC) bilayer: vertical and horizontal. Using a molecular dynamics simulation, we observed, in two different PC bilayers, both orientations of lutein, and in each bilayer, a single change from vertical to horizontal orientation or vice versa. Both orientations were stabilized by hydrogen bonding of lutein OH groups with mainly carbonyl but also phosphate oxygen atoms of PC.     

Correction of lipid metabolism in rats with limited mobility by an alternating magnetic field of infra-low frequency

The effect of changing magnetic field at the frequency of 8 Hz and intensity at 4.1 A/M on rats lipid metabolism state in the exposition of continuous hypokinesia was investigated. It was found that changing magnetic field of such parameters greatly restricted the development of hyperlipidemia of rats with a low level of mobile activity.     

Ion sepation by a curved magnetic field in a multicomponent plasma

It is shown that a curved magnetic field can be used to separate ions in a multicomponent plasma. Without selective ion preheating, the separation over one cycle is inefficient: the separated ion fractions will only be enriched with ions of the corresponding isotopes. Selective ion cyclotron resonance heating makes it possible to achieve essentially a complete separation of the ions.     

Inhibition of pentylenetetrazole-induced seizure in mice by using a 4 Hz magnetic field: a comparative study with a 60 Hz magnetic field

We investigated the comparative effects of 4 and 60 Hz magnetic fields on pentylenetetrazole (PTZ)-induced seizure in mice. For this study, we measured the latent time to seizure, seizure duration, and lethality induced by PTZ in mice exposed to 4 and 60 Hz magnetic fields (MF) for 30 min. Compared to sham-exposed controls, the latent time to tail twitching and seizure in the 4 Hz MF group was significantly decreased while the latent time to seizure in the 60 Hz MF group was significantly increased. The seizure duration in the 4 Hz MF group was significantly decreased while that in the 60 Hz MF group was significantly increased. More importantly, while the mice exposed to a 60 Hz MF experienced significantly increased lethality after seizure convulsion, those exposed to a 4 Hz MF showed no lethality, with a shortening of the duration of seizure. This beneficial effect of a 4 Hz MF on seizure has the same implication as the anti-oxidative effects of a 4 Hz MF observed in our previous work. The results of our current and previous works indicate that a 4 Hz MF may be used as a therapeutic physical agent for the treatment of oxidative stress-induced diseases, including seizure, with or without chemical drugs.     

Generation of auroral kilometric radiation by a finite-size source in a dipole magnetic field. Part II

Propagation and amplification of extraordinary electromagnetic waves in a dipole magnetic field in a narrow 3D plasma cavity in which a weakly relativistic electron beam propagates along the magnetic field in the direction of the gradient of the magnetic field strength is investigated. The domain of wave vectors at the starting point for which the wave amplification factors at the output of the density cavity reach their maximum values is found, and the amplification factor as a function of the wave frequency is determined. It is shown that the longitudinal velocity of fast electrons, which enables generation of waves in a broader frequency range, plays an important role in the formation of the spectrum of the auroral kilometric radiation (AKR). In this case, waves with the largest amplification factors at the output of the cavity have frequencies exceeding the cutoff frequency of the background plasma at the wave generation altitude. The global inhomogeneity of the magnetic field and plasma density, which governs the residence time of the waves in the amplification region, plays a key role in the formation of the AKR spectrum. It is shown that this time is the main factor determining the energy of the waves emerging from the source.     

Effect of a magnetic field on ascorbate system in mice.

The effect exerted on the ascorbate system due to the exposure of mice to the constant magnetic field associated with MRI methods has been examined. The mice were exposed to magnetic field 1.00 T strength for 0.2 h, 3 h, or 24 h. The ascorbyl free radical in tissues was measured in vitro, which in vivo corresponds to the level of ascorbic acid. Only in a group of mice where the ascorbyl free radical was measured 24 h following their exposure to magnetic field 1.00 T strength for 24 hours, was the level of free radical in tissues significantly decreased.     

Measurements of potential differences in human subjects induced by motion in a superconducting magnetic field.

We have attempted to measure the electromotive forces (emfs) induced in human beings moving at a constant speed in a highly dense magnetic field. Experiments were initially conducted on a set of models, and then directly on human subjects. The models consisted of single circular loops of Tygon tubing (I.D., 0.635 cm; O.D., 0.9525 cm) filled with normal saline solution, with circumferences of 20, 40, 60, 80, and 100 cm. The models were connected to an amplifier via silver/silver-chloride electrodes. Each saline loop was mounted on a movable platform, with the plane of the loop perpendicular to the platform's axis; the platform was enabled to move at known constant speeds into and out of the bore of a 1.89-T magnet. The human subjects were then substituted for the saline loops, with the long axis parallel to the direction of motion, and with standard EKG electrodes placed at 180 degrees successively on the ankle, calf, lower thigh, upper thigh, chest, and head. In all cases, for human subjects and models, the peak induced voltage was directly proportional to the speed of movement and the square of the circumference of the bounded cross-sectional areas. Thus, for the saline loops, the correlation coefficient between induced voltage and circumference was .998, and for human subjects, .947. Under the loose assumption that for equal circumferences the bounded areas in human subjects were equal to those in the circular loops, the induced emfs in human subjects were consistently about 13% greater than those in the loops. At a mean speed of 1.18 m/s, the chest had a peak induced voltage of 260 mV, while the voltage at the ankle had a peak of 19.8 mV. The experimental data were used to estimate the corresponding induced-current density at the pericardium, 17 mA/m2. We conclude for a human subject moving at constant speed along the body's long axis into a magnetic field that Faraday's law is closely followed for various cross-sections of the body. Further, in those cases in which the magnetic field and its gradient are not well-established, one can use saline-filled loops to estimate approximate values of voltages induced in human subjects.     

磁场抑制肿瘤的机理

综述了磁场抑制肿瘤的机理。磁场可以抑制肿瘤组织的供血与代谢,损伤肿瘤细胞的DNA,诱导肿瘤细胞凋亡,以及增强机体对肿瘤的免疫作用等。     

A calculation of the magnetic field of a nerve action potential.

The magnetic field outside an isolated axon is calculated using transmembrane potential data to specify the boundary conditions to a solution of Laplace's equation. It is shown that the contribution to the magnetic field from the current inside the membrane is two orders of magnitude larger than that from the external current. The contribution from current within the membrane is negligible. Comparisons are made between waveforms calculated for a crayfish lateral axon and those measured for a frog sciatic nerve. This calculation suggests that the magnetic field measured outside nerves can be used to determine their internal current without puncturing the nerve membrane.     

Pressure profiles of a plasma confined by the magnetic field of a ring current

Pressure profiles p(ψ) marginal with respect to convective instability in a toroidal tubular plasma confined by the magnetic field of an internal levitated ring current and external ring currents are studied as functions of the shape of the magnetic separatrix. Configurations are found in which the maximum plasma pressure in a finite-width layer near the plasma boundary decreases by two orders of magnitude at the expense of artificially raising the effective length (characterized by the integral ∮dl/B) of the magnetic field lines near the separatrix surface. It is shown that, in the case of a straight cylindrical tubular plasma, which is the limiting case of a toroidal configuration with an arbitrarily large aspect ratio, the sufficient condition for the plasma to be MHD stable against both convective and kink perturbations is satisfied for local values β≤0.4. __________ Translated from Fizika Plazmy, Vol. 26, No. 6, 2000, pp. 519–528. Original Russian Text Copyright ￠ 2000 by Popovich, Shafranov.