磁分离仪分离磁性细菌的新方法

磁性细菌胞内可以产生磁性颗粒,因此具有趋磁性,基于这种特性,利用磁分离的原理,本研究开发了一种磁性细菌分离仪,提供了一种分离磁性细菌的新方法。以氧化亚铁硫杆菌为例,使用磁性细菌分离仪进行分离,可以得到强磁菌和弱磁菌。利用透射电镜观察,强磁菌胞内磁性颗粒明显多于弱磁菌;半固体平板磁泳实验也表明强磁菌趋磁性明显强于弱磁菌。各项实验结果表明磁性细菌分离仪可以有效地分离磁性细菌,这是一种分离磁性细菌的新方法,将促进磁性细菌分离培养的研究。     

Making magnetic yeast

This study demonstrates that normal yeast cells can be magnetized, and identifies local redox control via carbon metabolism and iron supply as key factors involved in magnetization.     

Avian magnetic compass can be tuned to anomalously low magnetic intensities

The avian magnetic compass works in a fairly narrow functional window around the intensity of the local geomagnetic field, but adjusts to intensities outside this range when birds experience these new intensities for a certain time. In the past, the geomagnetic field has often been much weaker than at present. To find out whether birds can obtain directional information from a weak magnetic field, we studied spontaneous orientation preferences of migratory robins in a 4 µT field (i.e. a field of less than 10 per cent of the local intensity of 47 µT). Birds can adjust to this low intensity: they turned out to be disoriented under 4 µT after a pre-exposure time of 8 h to 4 µT, but were able to orient in this field after a total exposure time of 17 h. This demonstrates a considerable plasticity of the avian magnetic compass. Orientation in the 4 µT field was not affected by local anaesthesia of the upper beak, but was disrupted by a radiofrequency magnetic field of 1.315 MHz, 480 nT, suggesting that a radical-pair mechanism still provides the directional information in the low magnetic field. This is in agreement with the idea that the avian magnetic compass may have developed already in the Mesozoic in the common ancestor of modern birds.     

Carbon coated magnetic nanoparticles for local drug delivery using magnetic implants

Bioferrofluids obtained from carbon coated iron nanoparticles are promising candidates for magnetic drug delivery. The carbon cages render the particles biocompatible, and provide a good support for drug adsorption. We propose a method in which gold plated permanent magnets are implanted directly in the affected organ, close to the tumour, by endoscopic techniques. The bioferrofluid charged with the chemotherapeutic agent is injected and the particles attracted to the magnet, then desorption of the drug takes place at the tumoral region. This method seems to be more promising, costless and effective than that based on the application of external magnetic fields. Preliminary results of drug adsorption and a preclinical experimental animal model are described.     

多信道脑部磁刺激仪的磁场有限元仿真

利用外部的交变磁场,可以对大脑神经系统进行无创刺激.用有限元分析软件--ANSYS对多信道脑部磁刺激仪在不同工作模式下产生的磁场进行了模拟,并将其与实验测量值进行了比较.结果表明,两者之间的误差小于6%,ANSYS能有效模拟多信道磁刺激仪所产生的磁场.通过对仿真结果进行分析得出：改变多信道磁刺激仪工作线圈的位置,可以调整所产生磁场的位置及形状;增加刺激靶位置邻近的工作线圈个数,可以有效改善磁刺激的深度.     

Effect of the magnetic field curvature on magnetic islands in tokamaks

The effect of the magnetic field curvature on magnetic islands in a tokamak is analyzed. It is demonstrated that the original investigation of this effect by Kotschenreuther et al. (1985) is inconsistent: on the one hand, the authors made the correct assumption that this is an ideal effect and, on the other hand, they described it in terms of the parameters characteristic of the “resistive ordering” approach, which is incompatible with the ideal approximation. More recent studies of the magnetic curvature effect have produced further ambiguities; as a result, a branch of the theory of magnetic islands has arisen that is based on the supposition that the effect under discussion can be described in terms of the Glasser-Greene-Johnson parameter D_R. This branch is shown to be erroneous, because the parameter D_R describes the plasma response to magnetic field perturbations on spatial scales of about the dimension of the linear resistive layer, while the characteristic spatial scale of the magnetic islands is much longer. It is concluded that the correct theory developed here for the magnetic curvature effect makes more optimistic predictions about its stabilizing role.     

Local geometrical properties of magnetic configurations with nested equilibrium magnetic surfaces

The complete set of universal local relationships between geometrical (the curvature and torsion of the force lines of the magnetic field and the field complementary to it) and magnetic (|B|, |?Φ|, b · (? × b), and the local shear s) quantities in currentless magnetic configurations comprising a system of equilibrium nested magnetic surfaces, including those with several magnetic axes, is derived. Possible applications of these relationships are discussed.     

Destruction of hyperbolic magnetic axes in steady three-dimensional toroidal magnetic structures

A study is made of the boundary regions of magnetic structures formed either near the last closed flux surface of the main magnetic configuration in a stellarator or near magnetic islands in more general toroidal confinement systems with topologically equivalent sheared magnetic configurations. With a relatively simple approximate analytic model based on the perturbation method, it was possible not only to reproduce earlier results on the destruction of hyperbolic magnetic axes in the three-dimensional toroidal magnetic configurations under consideration but also to obtain some new results, in particular, to analytically estimate the sizes of the separatrix regions of stochastic magnetic fields that arise in the main stellarator configuration and also near the inner chains of magnetic islands in any magnetic configuration under consideration. It is notable that the boundary region of the main stellarator magnetic configuration is a multiply connected structure, the outer part of which is largely governed by the current distribution in the magnetic system creating this configuration.     

Separation of magnetic affinity biopolymer adsorbents in a Davis tube magnetic separator

A Davis tube (a matrix-free, flow-through magnetic separator used mainly in mineral processing) has been tested for separation of magnetic affinity biopolymer adsorbents from larger volumes of suspensions. Both magnetic chitosan and magnetic cross-linked erythrocytes could be efficiently separated from litre volumes of suspensions. Up to 90% adsorbent recovery was achieved under optimised separation conditions.     

Cytogenetic effects of 50 Hz magnetic fields of different magnetic flux densities

Cytogenetic investigations were performed in human peripheral blood lymphocytes following exposure to 50 Hz magnetic fields alone or in combination with the chemical mutagen mitomycin C or with X-rays. It was found that magnetic fields up to 2500 microT did not significantly influence the chromosome aberration and sister chromatid exchange frequency. Also, the combined treatments failed to indicate the presence of any synergistic, potentiating, or antagonistic effect between the ELF magnetic fields and the mutagens. However, there were two exceptions: Cells exposed to 504 microT magnetic fields before and during cultivation displayed a statistically significant decrease in sister chromatid exchange frequency. Also, when cells were cultivated in the presence of 88.4 microT magnetic fields following X-ray exposures there was a significant increase in chromosome aberration frequency compared to X-ray exposure alone.     

The magnetic diver microgasometer

A magnetic diver microgasometer operated at the constant pressure is described and its application and limitations are evaluated. By the aid of a thin quartz fiber which supports the ampulla the stable equilibrium between bouyancy and magnetic forces is maintained. The control and the sensitivity being independent of the gas volume in the ampulla, reasonably large divers with a low loss of gas can be used. Consequently a sufficient stability is achieved for the measurements of gas changes in the range of 1 × 10⁻⁶ μl/hr.     

Melatonin and magnetic fields

There is public health concern raised by epidemiological studies indicating that extremely low frequency electric and magnetic fields generated by electric power distribution systems in the environment may be hazardous. Possible carcinogenic effects of magnetic field in combination with suggested oncostatic action of melatonin lead to the hypothesis that the primary effects of electric and magnetic fields exposure is a reduction of melatonin synthesis which, in turn, may promote cancer growth. In this review the data on the influence of magnetic fields on melatonin synthesis, both in the animals and humans, are briefly presented and discussed.