Induction Of External Magnetic Field Research Articles

Триплеттриплетная аннигиляция молекулярных электронных возбуждений вблизи диамагнитной металлической микрочастицы в переменном магнитном поле

A mathematical model of the spinselective reaction of triplettriplet annihilation of molecules on the surface of a spherical microparticle or a cylindrical rod of micrometer radius in an alternating magnetic field transformed by conducting microparticles is presented. Based on these models, the calculations of the integral and local rates of magnetically sensitive molecular processes were performed. It has been shown that in the local nearsurface regions of the conducting microparticles in an alternating magnetic field, the rate of spinselective bimolecular reactions changes. The comparison of the nanoand microsphere showed that with the external magnetic field induction value B0 = 1 T, the maximum resulting field at the equator of the particle was equal to 12 mT and 100 mT, respectively. It was also revealed that for nanoand microcylinders with a similar value of the external magnetic field induction B0 = 1 T, the maximum resulting field at the point (R,0) of the 2d magnetic pole was equal to 12 mT and 1.5 T, respectively. The amplitude of the magnetic effect for different times and particle sizes was equal to +1 % and 2 %. For a silver microcylinder with a radius R = 25 μm, there was switching from a purely negative magnetic effect at the time t = 0 ns to an effect with positive and negative parts. For the case of a silver cylinder of radius R = 30 μm and external magnetic field frequency ω = 5∙108 s1, an increase in the amplitude of the positive part of the magnetic effect curve from 0.25 % to 1 % was observed when the time instant changed from t = 0 ns, which corresponds to the maximum of the external magnetic field, up to t = 3.68 ns when the resulting field of the microwire reaches its maximum. This work may be of interest to physicists and chemists involved in science in the field of chemical physics, physics of magnetic phenomena, spinselective reactions and spintronics.

Magnetic field and nuclear spin influence on the DNA synthesis rate

The rate of a chemical reaction can be sensitive to the isotope composition of the reactants, which provides also for the sensitivity of such “spin-sensitive” reactions to the external magnetic field. Here we demonstrate the effect of the external magnetic field on the enzymatic DNA synthesis together with the effect of the spin-bearing magnesium ions (^{25}Mg). The rate of DNA synthesis monotonously decreased with the external magnetic field induction increasing in presence of zero-spin magnesium ions (^{24}Mg). On the contrary, in the presence of the spin-bearing magnesium ions, the dependence of the reaction rate on the magnetic field induction was non-monotonous and possess a distinct minimum at 80–100 mT. To describe the observed effect, we suggested a chemical scheme and biophysical mechanism considering a competition between Zeeman and Fermi interactions in the external magnetic field.

Magnetic induced terahertz modulation characteristics based on ferromagnetic nematic liquid crystals

In recent years, solid state terahertz (THz) modulators have obtained rapid progress with the widespread use of two-dimensional (2D) materials in the field of THz; however, challenges remain in preparing flexible THz modulators. In this study, flexible ferromagnetic nematic materials were prepared by doping thermotropic nematic liquid crystals 5CB into magnetic fluids, and the influence of water was reduced by a self-made cyclic olefin copolymer (COC) microfluidic chip. THz modulation characteristics of magnetic fluid and ferromagnetic nematic liquid crystal (FNLC) under the induction of external magnetic field were compared using a THz time domain spectroscopy system. Under the action of a 91 mT magnetic field, the magnetic fluid has a maximum modulation depth (MD) of 54%. Under the same magnetic field, the maximum MD of the FNLC materials increase to 78% because of the rearrangement of Fe3O4 nanoparticles induced by the topological defect of the liquid crystal. We demonstrate that the magneto-optical effect is significantly enhanced in the ferromagnetic nematic liquid crystal hybrid system. This strategy of doping thermotropic nematic liquid crystals to enhance the magneto-optical effect has great potential for THz filtering, modulation, and sensing applications.

Modulating negative magnetoresistance via inducing vacancy for regulates electron transport under magnetic ambient conditions

The introduction of external magnetic field is one of the most widely studied strategies for photogenerated carrier separation in recent years. However, magnetic materials have great disadvantages in terms of photocatalytic performance. Semiconductor materials with magnetic properties are also extremely rare. It is extremely peculiar to research the magnetism of semiconductor photocatalyst triggered by vacancy. Here, the first example of ferromagnetic Bi2S3 is achieved by controlled Bi vacancy (Bi2S3-VBi). The magnetism properties depends largely on the spin polarization of p electrons in S atoms, and its magnetic moment is mainly distributed on S atoms around cation vacancies. Under the induction of external magnetic field, the tunneling of spin-polarized electrons in S-2p orbital makes Bi2S3-VBi have negative magnetoresistance effect. The ferromagnetic arrangement of Bi2S3-VBi particles can reduce the resistivity and increase the tunneling of electrons. Meanwhile, Lorentz force generated by external magnetic field acts reversely on photogenerated electrons and holes, thus effectively inhibiting the recombination of carriers in photocatalyst. Moreover, the influence of Bi vacancy on Bi2S3 magnetism is investigated by DFT calculation. This study provides a new strategy for effective carrier separation in photocatalysis.

Preparation of Fe3O4/Ag3VO4/Au nanocomposite coated with Caerophyllum macropodum extract modified with oleic acid for theranostics agent in medical imaging

Today, theranostics is one of the most important research areas in medicine. They have a special focus on the simultaneous use of an agent for diagnosis and treatment. This study aimed to synthesize a multifactorial nanocomposite consisting of Fe3O4/Ag3VO4/Au three-component coated with C. macropodum extract modified with oleic acid for theranostics and conjugated with methotrexate. In the method, the effect of coating and modified fatty acid was investigated in the design of nanoparticles. The C. macropodum extract improves the effect of methotrexate. Also, C. macropodum extract in high temperature decomposes. Oleic acid increases its stability and does not allow it to decompose soon. The final sample was confirmed by MTT, MRI, and CT scanning. VSM results showed that the resulting nanocomposite has good magnetic properties for MRI, CT, and methotrexate delivery under external magnetic field induction. Biocompatibility and cytotoxicity of nanocomposites use the MTT method, the results clearly showed its non-toxicity. The conclusion of different tests indicated that the new design is very suitable for process CT scanning and MRI.

DC vacuum breakdown in an external magnetic field

The subject of the present theoretical and experimental investigations is the effect of the external magnetic field induction on dark current and a possibility of breakdown. The generalization of the Fowler–Nordheim equation makes it possible to take into account the influence of a magnetic field parallel to the cathode surface on the field emission current. The reduction in the breakdown voltage due to the increment in electron-impact ionization was theoretical predicted. Experimentally shown that the presence of a magnetic field about a tenth as a large as the cutoff magnetic field (Hull, 1921) reduces the breakdown voltage by 10% to 20% for practically all cathodes no matter what their surface treatment.

Plasma Parameters in the Reactor with Simultaneous Magnetron Discharge and Inductive Radio-Frequency Discharge in the Presence of External Magnetic Field

A plasma reactor that contains vacuum–arc and magnetron sputtering sources and radio-frequency discharge that generates high-density plasma in the presence of external magnetic field is developed, constructed, and optimized. The reactor can be used for deposition of various functional coatings with ion stimulation. The parameters of the inductive radio-frequency discharge generated in the presence of external magnetic field that serves as a source of assisting ions are optimized. It is shown that the working interval of the induction of external magnetic field corresponds to the resonant excitation of the coupled helicon and Trivelpiece–Gold waves. The effect of magnitude and configuration of magnetic field on the parameters of gas-discharge plasma and ion current in the substrate region is studied in the presence of separately and simultaneously initiated magnetron and inductive discharges. The effect of ion flux that is incident on the films in the course of growth on the structure of functional coatings is analyzed.

Classical solutions of the Vlasov–Poisson equations with external magnetic field in a half-space

We consider the first mixed problem for the Vlasov–Poisson equations with an external magnetic field in a half-space. This problem describes the evolution of the density distributions of ions and electrons in a high temperature plasma with a fixed potential of electric field on a boundary. For arbitrary potential of electric field and sufficiently large induction of external magnetic field, it is shown that the characteristics of the Vlasov equations do not reach the boundary of the halfspace. It is proved the existence and uniqueness of classical solution with the supports of charged-particle density distributions at some distance from the boundary, if initial density distributions are sufficiently small.

Stationary solutions of the Vlasov–Poisson system for two-component plasma under an external magnetic field in a half-space

We consider the first mixed problem for the Vlasov–Poisson equations with an external magnetic field in a half-space. This problem describes the evolution of the density distributions of ions and electrons in a high temperature plasma with a fixed potential of electric field on a boundary. For a sufficiently large induction of external magnetic field there are constructed stationary solutions supported on some distance from the hyperplane x 1 = 0.

Multistable current states in high-temperature superconducting composites

Conditions for current instabilities that arise in high-temperature superconducting composites with essentially nonlinear dependences of the critical current densities and resistivity on the temperature and magnetic induction have been studied. The analysis has been conducted in terms of zero-dimensional models, which has made it possible to formulate general physical mechanisms behind the formation of currents states in superconducting composites according to the external magnetic field induction, cooling conditions, and the properties of the superconductor and cladding. The possible existence of current and temperature stable steps, as well as stable steps of the electric field strength, in the absence of the superconducting–normal transition, has been demonstrated. Reasons for instabilities under multistable current states have been discussed.

Magnetic field assisted μ-solid phase extraction of anti-inflammatory and loop diuretic drugs by modified polybutylene terephthalate nanofibers

A magnetic nanocomposite consisting of nanoparticles–polybutylene terephthalate (MNPs–PBT) was electrospun and used as an extracting medium for an on-line μ-solid phase extraction (μ–SPE)–high performance liquid chromatography (HPLC) set–up with an ultraviolet (UV) detection system. Due to the magnetic property of the prepared nanofibers, the whole extraction procedure was implemented under an external magnetic field to enhance the extraction efficiencies. The developed method along with the synthesized nanocomposite were found to be appropriate for the determination of trace levels of selected drugs including furosemide, naproxen, diclofenac and clobetasol propionate in the urine sample. The prepared MNPs-PBT electrospun nanocomposite was characterized using the scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and Fourier transform infrared (FT–IR) spectroscopy. The prepared magnetic fibers showed high porosity, which was another driving force for the extraction efficiency enhancement. Major parameters affecting the extraction efficiency of the selected drugs were optimized. The limits of detections (LOD) of the studied drugs were in the range of 0.4–1.6 μg L−1 and the limits of quantification (LOQ) were 1–4 μg L−1 under the optimized conditions. Relative standard deviation (RSD%) for three replicates at three concentration levels of 6, 100 and 400 μg L−1 were 5.9–8.0% while acceptable linear range with two orders of magnitude was obtained (R2 = 0.99). The method was validated by the determination of the selected drugs in urine samples and the results indicated that this method has sufficient potential for enrichment and determination of the desired drugs in the urine sample. The relative recovery values were found to be in the range of 78–91%. Implementing the developed on–line μ–SPE method under the external magnetic field induction, led to higher extraction efficiencies for the selected drugs with various diamagnetic properties.

Magnetic Field Operation and Shielding of a G-M Cryocooler

The operation conditions of Gifford-McMahon (G-M) cryocoolers are limited by the external magnetic field induction. A G-M coldhead with the cooling power of 1.5 W at 4.2 K (RDK-415 by SHI) has been tested in an axisymmetric inhomogeneous magnetic field created by a conduction cooled superconducting magnet, which is able to generate up to 10 T. The tests revealed that the second-stage cooling power decreases by 29% at 1.0 T and by 42% at 1.6 T. The coldhead demonstrated abnormal operation in the magnetic field higher than some threshold value. The threshold field depends on the second-stage temperature. The stacks of YBCO tapes for the second-stage region and an iron shell for the motor region were tested as a magnetic shield. The magnetic field induction fluctuation on the refrigerator surface caused by periodical movement of magnetic regenerator in the inhomogeneous magnetic field is reported.

Effective Giromagnetic Ratios in Artifical Nuclear Magnetization Pumping of the Noble Gases Mix

Dynamic of the nuclear magnetization of the two noble gases mix was studied in this research. Nuclear magnetization pumped along the induction of external magnetic field. Vector of nuclear magnetization is given a tilt by the week rotational magnetic field, which makes NMR for noble gases. Interaction between the nuclear magnetic moments of the different noble gases adducted to shifts at the frequency of nuclear moments precession in external magnetic field. Effective gyromagnetic ratios of the nuclear of noble gases is defined and it different from the tabulated value. There is theoretical calculation of effective gyromagnetic ratios in this research.

Higher harmonics generation in relativistic electron beam with virtual cathode

The study of the microwave generation regimes with intense higher harmonics taking place in a high-power vircator consisting of a relativistic electron beam with a virtual cathode has been made. The characteristics of these regimes, in particular, the typical spectra and their variations with the change of the system parameters (beam current, the induction of external magnetic field) as well as physical processes occurring in the system have been analyzed by means of 3D electromagnetic simulation. It has been shown that the system under study demonstrates the tendency to the sufficient growth of the amplitudes of higher harmonics in the spectrum of current oscillations in the VC region with the increase of beam current. The obtained results allow us to consider virtual cathode oscillators as promising high power mmw-to-THz sources.

Multifunctional 1D magnetic and fluorescent nanoparticle chains for enhanced MRI, fluorescent cell imaging, and combined photothermal/chemotherapy.

While the assembled 1D magnetic nanoparticle (NP) chains have demonstrated synergistic magnetic effects from the individual NPs, it is essential to prepare new 1D NP chains that can combine the magnetism with other important material properties for multifunctional applications. This paper reports the fabrication and multifunctional investigation of a new type of 1D NP chains that combine the magnetic properties with fluorescent properties, photothermal conversion ability, and drug carrier function. The building block NPs are composed of magnetic Fe(3)O(4) nanocrystals clustered in the core and fluorescent carbon dots embedded in the mesoporous carbon shell with hydroxyl/carboxyl groups anchored on their surface. These NPs can assemble under the induction of external magnetic field and form stable 1D NP chains of diameter ∼ 90 nm and length ∼ 3 μm via the hydrogen bonding and π-π stacking linkage of the carbon shell. The resulted 1D hybrid NP chains not only demonstrate much higher magnetic resonance imaging (MRI) contrasting ability than the dispersed building block NPs, but also enter into intracellular region and light up the B16F10 cells under a laser excitation with strong and stable fluorescence. While the mesoporous carbon shell provides high drug loading capacity, the embedded fluorescent carbon dots convert near-infrared (NIR) light to heat, and hence kill the tumor cells efficiently and enhance the drug release rate to further improve the therapeutic efficacy under NIR irradiation. Such designed 1D magnetic-fluorescent hybrid NP chains with enhanced MRI contrast, fluorescent imaging ability, and combined chemo-/photothermal therapeutic ability have great potential for various biomedical applications.

Maximum allowable currents in YBa2Cu3O7 superconducting tapes as a function of the coating thickness, external magnetic field induction, and cooling conditions

Maximum allowable (ultimate) currents stably passing through an YBa2Cu3O7 superconducting current-carrying element are determined as a function of a silver (or copper) coating thickness, external magnetic field induction, and cooling conditions. It is found that if a magnetic system based on yttrium ceramics is cooled by a cryogenic coolant, currents causing instabilities (instability onset currents) are almost independent of the coating thickness. If, however, liquid helium is used as a cooling agent, the ultimate current monotonically grows with the thickness of the stabilizing copper coating. It is shown that depending on cooling conditions, the stable values of the current and electric field strength preceding the occurrence of instability may be both higher and lower than the a priori chosen critical parameters of the superconductor. These features should be taken into account in selecting the stable value of the operating current of YBa2Cu3O7 superconducting windings.

A theoretical study of the impact of magnetic field of Hall current on the parameters of a high-current vacuum-arc discharge

It is demonstrated that the magnetic field of Hall current in a short high-current vacuum-arc discharge significantly distorts the external axial magnetic field and affects the distribution of current density in the discharge gap. This effect decreases with increasing external magnetic field, with decreasing arc current, and with decreasing ratio of the length of discharge gap to its transverse dimension. A 2D magnetohydrodynamic mathematical model is used to calculate the discharge parameters for different values of induction of external magnetic field. The calculation results are compared with similar results obtained using a 1.5D model in which the impact made by magnetic field of Hall current is ignored. It is inferred that the simpler 1.5D model may be employed in calculations of parameters of vacuum arc in a wide range of variation of arc current and of induction of external magnetic field.

Determining the angular position of a moving object

The angular position of a moving object may be determined from the measured vector for the acceleration due to gravity, the external magnetic field induction, and the magnetic induction from a source of alternating magnetic field.

Magnetic field-assisted hydrothermal growth of chain-like nanostructure of magnetite

Chain-like nanostructures consisted of more than 10 magnetite nanoparticles with an average size of 80 nm were hydrothermally prepared at 200 °C under a 0.18 T external magnetic field. Magnetic measurement results revealed that the chain-like structure showed higher saturation magnetization M s, remnant magnetization M r, coercivity H c and reduced magnetization M r/ M s, compared with those of randomly distributed magnetite nanoparticles prepared without the induction of external magnetic field. Possible reasons responsible for the changes of the above magnetic parameters were tentatively discussed.

The green function method in the theory of nuclear and electron spin polarization. II. The first approximation and its application in the CIDEP theory

The present paper deals with a further development of the method of calculating nuclear and electron spin polarization based on the Green function formalism specifying the character of the relative motion in a pair of radical centers. In the first approximation with respect to the exchange interaction influence the calculations of the desired quantities are reduced to matrix operations. A theory of chemical polarization of electrons serves to illustrate the method. Calculations of this effect in micellar radical pairs are performed. It is shown that quantum oscillations are possible here depending on the magnitude of the external magnetic field induction.