The characteristics of iron in high frequency magnetic fields

Not many years ago it was quite generally believed that iron was unable to follow rapid magnetic changes. Experiments which showed an apparent decrease in the permeability of the iron with an increase in the frequency of the magnetic cycle furnished a basis for a theory that iron was magnetically sluggish. Further and more accurate experiments proved, however, that the effects which had previously been ascribed to a peculiarity of the material were in reality caused by eddy currents in the sample. Theoretical calculations were made which demostrated that eddy currents in an iron test piece increased as the square of the frequency and that for even the lower frequencies it was necessary to use quite thin laminations in magnetic circuits in order to eliminate deleterious effects. Furthermore, it was found that due to eddy currents and the magnetic properties of iron, the magnetization in high frequency fields was confined to a thin surface layer of the piece. This “Magnetic Skin Effect” reduced the cross section of the iron which was magnetically active even though the laminations were extremely thin. Careful experimental measurements compared with theoretical calculations proved that the real permeability of iron remained unchanged at frequencies up to about 10⁶ and that previous results had been is serious error due to neglect of the factors mentioned. This fact having been established, efforts were made to see what practical use could be made of iron in high frequency work and to that end some extensive experimental investigations of the saturation curves and core losses were made upon specimens laminated as thinly as was commercially practicable. The resulting data have furnished a basis for design.It is a demostrated fact that the permeability of all metals is unity for the magnetic cycles imposed upon them by heat and light waves. In the region between frequencies of about 10⁶, where the true permeability of iron is practically the same as at zero frequency, and frequencies of about 10¹⁰ where the true permeability of iron approaches unity, the experimental values of μ decrease smoothly with the frequency. What happens to μ in the range of frequencies between the lingest heat waves and the shortest Hertzian waves which have yet been made is a question which has many interesting features but which has not yet yielded to the experimenter.     

磁法勘探大别山区探矿中的应用

本论文介绍了安徽省大别山区铁矿磁异常数据的处理及解释。论文首先对网格化的野外原始磁异常数据进行滤波处理,以消除测量的偶然误差和近地表不均匀磁性体的干扰。然后,对上述预处理后的磁异常数据进行解析延拓,本论文作了三个不同高度的向上延拓及两个不同高度的向下延拓。通过上述数据处理,结果表明,利用这种滤波和解析延拓方法对确定地下异常体与预测成矿区是很有成效的。     

Growth and decay of phosphorescence in calcium sulphide by a photoelectric method

The phosphorescence of the calcium sulphide was excited by light and the intensity of the combined radiation of all stimulated wave-lengths was measured as a function of time by means of photoelectric cell, the current from which was amplified by a special vacuum tube amplifier. The amplified currents deflected a galvanometer, the deflection of which was found to be strictly proportional to the intensity of the light falling on the cell.Decay curves for different durations of excitation of the sample were obtained, the decay in intensity during the first thirty seconds after excitation being automatically recorded. Similar curves were obtained for identical durations of excitation at various temperatures of the sample. The effects of several different binders for the calcium sulphide powder were also investigated. A single empirical equation for sulphide in a given binder was obtained, by means of which the intensity of the phosphorescence can be computed for any time after excitation begins, and for any temperature within the range studied.     

Microstripes for transport and separation of magnetic particles

We present a simple technique for creating an on-chip magnetic particle conveyor based on exchange-biased permalloy microstripes. The particle transportation relies on an array of stripes with a spacing smaller than their width in conjunction with a periodic sequence of four different externally applied magnetic fields. We demonstrate the controlled transportation of a large population of particles over several millimeters of distance as well as the spatial separation of two populations of magnetic particles with different magnetophoretic mobilities. The technique can be used for the controlled selective manipulation and separation of magnetically labelled species.     

Properties and applications of magnetic liquids

Ferromagnetic materials such as iron, cobalt, and nickel lose their strong magnetic properties when heated to a temperature above that called the Curie temperature, a temperature which is different for different materials. For all known ferromagnetic materials this temperature is always below that of the corresponding melting points of the materials and thus intrinsic ferromagnetic liquids are not known to exist. The term magnetic liquid (or ferrofluid) as used today does not refer to an intrinsic ferromagnetic liquid but to a stable colloidal suspension of small particles of a ferromagnetic material.     

Geometrical optimization of microstripe arrays for microbead magnetophoresis

Manipulation of magnetic beads plays an increasingly important role in molecular diagnostics. Magnetophoresis is a promising technique for selective transportation of magnetic beads in lab-on-a-chip systems. We investigate periodic arrays of exchange-biased permalloy microstripes fabricated using a single lithography step. Magnetic beads can be continuously moved across such arrays by combining the spatially periodic magnetic field from microstripes with a rotating external magnetic field. By measuring and modeling the magnetophoresis properties of thirteen different stripe designs, we study the effect of the stripe geometry on the magnetophoretic transport properties of the magnetic microbeads between the stripes. We show that a symmetric geometry with equal width of and spacing between the microstripes facilitates faster transportation and that the optimal period of the periodic stripe array is approximately three times the height of the bead center over the microstripes.     

Transverse Propagation of Transient Electromagnetic Waves in a Non-homogeneous Half-space

The problem of a transient, transverse electromagnetic wave incident on a non-homogeneous half space is considered. Solutions are obtained by both the Laplace transform technique (LT) and the method of characteristics (MOC). The former method yields an infinite number of exact solutions in closed-form provided that the dielectric and permeability parameters are distributed as power laws in the spacial coordinate. A method for systematically generating these solutions is given. The method of characteristics, in numerical form, provides approximate solutions along the curved characteristics. Agreement between the two methods is excellent, except for a certain anomalous class of inhomogeneities. Finally, certain quasi-static solutions, involving a variety of inhomogeneities, are demonstrated.     

On the origin of microbial magnetoreception

A broad range of organisms, from prokaryotes to higher animals, have the ability to sense and utilize Earth''s geomagnetic field—a behavior known as magnetoreception. Although our knowledge of the physiological mechanisms of magnetoreception has increased substantially over recent decades, the origin of this behavior remains a fundamental question in evolutionary biology. Despite this, there is growing evidence that magnetic iron mineral biosynthesis by prokaryotes may represent the earliest form of biogenic magnetic sensors on Earth. Here, we integrate new data from microbiology, geology and nanotechnology, and propose that initial biomineralization of intracellular iron nanoparticles in early life evolved as a mechanism for mitigating the toxicity of reactive oxygen species (ROS), as ultraviolet radiation and free-iron-generated ROS would have been a major environmental challenge for life on early Earth. This iron-based system could have later been co-opted as a magnetic sensor for magnetoreception in microorganisms, suggesting an origin of microbial magnetoreception as the result of the evolutionary process of exaptation.     

Glutaraldehyde enhanced dielectrophoretic yeast cell separation

We introduce a method for improved dielectrophoretic (DEP) discrimination and separation of viable and nonviable yeast cells. Due to the higher cell wall permeability of nonviable yeast cells compared with their viable counterpart, the cross-linking agent glutaraldehyde (GLT) is shown to selectively cross-link nonviable cells to a much greater extent than viable yeast. The DEP crossover frequency (cof) of both viable and nonviable yeast cells was measured over a large range of buffer conductivities (22 μS∕cm–400 μS∕cm) in order to study this effect. The results indicate that due to selective nonviable cell cross-linking, GLT modifies the DEP cof of nonviable cells, while viable cell cof remains relatively unaffected. To investigate this in more detail, a dual-shelled oblate spheroid model was evoked and fitted to the cof data to study cell electrical properties. GLT treatment is shown to minimize ion leakage out of the nonviable yeast cells by minimizing changes in cytoplasm conductivity over a large range of ionic concentrations. This effect is only observable in nonviable cells where GLT treatment serves to stabilize the cell cytoplasm conductivity over a large range of buffer conductivity and allow for much greater differences between viable and nonviable cell cofs. As such, by taking advantage of differences in cell wall permeability GLT magnifies the effect DEP has on the field induced separation of viable and nonviable yeasts.     

考虑假货威胁的品牌制造商双渠道策略研究

考虑由一个品牌商品制造商和一个传统零售商组成的两级供应链系统,制造商具有开启电子直销渠道的选择,然而电子渠道具有假货渗透的风险。文章采用Stackelberg博弈方法来分析品牌商品制造商的双渠道策略及对传统零售商经营决策的影响,并进一步分析了消费者剩余和社会福利的变化。研究结果表明,只有当电子渠道假货渗透率和假货质量在一定范围内,品牌商品制造商倾向双渠道经营来增加自身利润,而超出这个范围单渠道经营对品牌商品制造商更有利。然而,在这个范围内,消费者剩余和社会福利增加。更重要的是,电子渠道假货的存在会加重渠道冲突,是电子直销渠道损害传统零售商利润的又一重要因素。     

What is the magnetic permeability of iron?

This paper is a review of the changes brought about in the magnetic properties of “iron” during the period 1870 to 1928 and shows the absurdity of using “iron” as a standard for comparison. The latest (1928) value for the initial permeability (μ₀) of “iron” is given as 1150, its maximum permeability (μ_max) as 61,000, and its hysteresis loss (W_h) as 300 ergs per cubic centimeter per cycle for B = 10,000 gausses. The corresponding values prior to 1900 were: μ₀ = 250 μ_max = 2600, W_h = 3,000.     

In vitro studies on ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid for T2 MRI contrast agent

Ultrasmall superparamagnetic iron oxide nanoparticles coated with gummic acid have been investigated as possible constituents of aqueous ferrofluids for biomedical applications and especially for MRI contrast agent. The structural characteristics and the size of the nanoparticles have been analyzed as well as the magnetic properties. In order to evaluate any possible capabilities as a contrast agent, the relaxation time, T2, of hydrogen protons in the colloidal solutions of nanoparticles have been measured in order to gain information on the relaxation behavior compared to other MRI contrast agents. The in vitro cytotoxicity of the obtained magnetic nanoparticles of iron oxide coated with gummic acid was investigated by two separate methods (MTT and FACS analysis) and by using three different normal and transformed cell lines. Our results showed that the synthesized nanoparticles had no toxic effect on any of the cell lines used.     

Magnetic losses in remanent state ferrites

Magnetic loss in remanent state ferrites¹ has generally been described through the artifice of a magnetic loss tangent (tanδ_m = μ^″?μ′). This characterization is not directly relatable to intrinsic material parameters. The results presented in this paper indicate that magnetic loss in the remanent state can be related to intrinsic material parameters by describing the ferrite mathematically by a complex “average” permeability tensor. The “average” permeability includes the effects of magnetocrystalline anistropy, remanent magnetization, linewidth and an average demagnetizing field appropriate to the distribution of magnetic domains. Experimental examples are given showing that excellent agreement is obtained between theoretically predicted and measured losses.     

Oxidative stress and disturbance in antioxidant balance in beta thalassemia major

Repeated blood transfusion in beta thalassemia major patients may lead to peroxidative tissue injury by secondary iron overload. In the present study, 72 children with beta thalassemia major were included. Serum levels of total lipid peroxides, Iron, Total Iron Binding Capacity, Copper, Zinc, Vitamin E, plasma Total Antioxidant Capacity, activity of Erythrocyte Superoxide Dismutase, were measured. The findings were compared with 72 age matched healthy controls irrespective of sex. A significant increase in the levels of lipid peroxide and Iron (p<0.001), whereas, significant decrease in the levels of vitamin-E, Total Antioxidant Capacity and Total Iron Binding Capacity (p<0.001) was observed. Serum Zinc was significantly increased (p<0.001) with significant decrease in the levels of copper (p<0.001). Non Significant increase in the activity of Erythrocyte Superoxide Dismutase (p>0.05) was found in the patients when compared with controls. This suggest that oxidative stress and reduced antioxidant defense mechanism play an important role in pathogenesis of beta thalassemia major.     

Unconventional Hall effect induced by Berry curvature

Berry phase and Berry curvature play a key role in the development of topology in physics and do contribute to the transport properties in solid state systems. In this paper, we report the finding of novel nonzero Hall effect in topological material ZrTe₅ flakes when the in-plane magnetic field is parallel and perpendicular to the current. Surprisingly, both symmetric and antisymmetric components with respect to magnetic field are detected in the in-plane Hall resistivity. Further theoretical analysis suggests that the magnetotransport properties originate from the anomalous velocity induced by Berry curvature in a tilted Weyl semimetal. Our work not only enriches the Hall family but also provides new insights into the Berry phase effect in topological materials.     

Role of Iron and Copper in the Pathogenesis of Parkinson’s Disease

Parkinson’s disease (PD) is an old age disorder of basal ganglia which involves oligomerization of α-synuclein protein and formation of intercellular inclusions known as “Lewy bodies” in substantia nigra and caudate nuclei in brain which is progressive in nature. It is second most prevalent neurodegenerative disorder characterized by tremor at rest, muscle rigidity, slowness of movement (bradykinesia, akinesia), and changes in posture (instability). Both excess and deficiency in levels of transition metals (especially iron, copper) can be detrimental to the central nervous system. Abnormalities in iron (Fe) and copper (Cu) metabolism have been reported to produce oxidative stress which is one of the major cause in pathogenesis of PD. In the present study 35 PD patients and 33 controls of Northern Indian population were included and serum levels of Fe, Cu and ceruloplasmin (Cp) were measured. Serum Fe (p < 0.01) and Cu (p < 0.01) levels were found to be significantly decreased in PD, whereas there was no significant change in Cp levels in PD patients as compared to controls. These results suggest the existence of a defect in iron which over the time, may hasten the entry of iron into the brain and decrease iron in the extracellular compartment in PD patients.     

The operating characteristics of small grid-controlled hot-cathode arcs or thyratrons

The grid current required to fire a thyratron has been shown to depend theoretically upon the shape of the grid current characteristic before firing as well as upon the grid circuit constants.The three-element FG-17 and the four-element FG-95 and FG-98 thyratrons have been investigated.Anomalies where excessively large grid currents were required to start the arc, occurring below certain values of temperature and plate potential, have been found and are described in some detail.Although the argon-filled FG-98 was found to be free from temperature effects over the operating range, positive shield grid potentials introduced anomalies at low plate potentials.Even though the plate and shield potentials and the temperature were kept within the recommended optimum range, it was found that for minimum grid currents at firing the negative grid impedance of these tubes necessitated a grid resistance of 100 to 1000 megohms.     

Quantum anomalous Hall effect

Hall efect is a well-known electromagnetic phenomenon that has been widely applied in the semiconductor industry.he quantum Hall efect discovered in two-dimensional electronic systems under a strong magnetic ield provided new insights into condensed mater physics,especially the topological aspect of electronic states.he quantum anomalous Hall efect is a special kind of the quantum Hall efect that occurs without a magnetic ield.It has long been sought ater because its realization will signiicantly facilitate the studies and applications of the quantum Hall physics.In this paper,we review how the idea of the quantum anomalous Hall efect was developed and how the efect was inally experimentally realized in thin ilms of a magnetically doped topological insulator.