Action Of External Magnetic Field Research Articles

Study on the response of the winding direction of multi-layer CORC cable to its electromagnetic characteristics

A Conductor on Round Core (CORC) cable wound with a high-temperature superconductor is an important cable concept for high-current density applications. It is widely used in large power systems because of its advantages of good flexibility and high engineering current density. However, the complex design structure of CORC cable makes it very difficult to understand its electromagnetic properties (such as AC loss). In particular, the different winding directions of each layer in multi-layer cable have a great influence on its electromagnetic characteristics. In this paper, the H-method is used to solve the electromagnetism and mechanics equations. The influence of the winding direction of CORC cable on its electromagnetic field distribution characteristics, AC loss, and mechanical variation under the action of external magnetic field is investigated. The AC loss study of single-layer cable reveals that when the applied magnetic field is increased from 0.01 to 0.02 and 0.03 T, the AC loss peak of the cable increases by 107 and 103 orders of magnitude, respectively, indicating that the effect of low applied magnetic field on the AC loss of the cable is more significant. For multi-layer cables, cables with opposite winding directions have a greater depth of current density penetration than cables with the same winding direction. In addition, the mechanical variations of multi-layer cables with different winding orientations are explored. The results show that the Mises stress in the cable with the same winding direction is about 32% higher than that of the cable with the opposite winding direction, which indicates that the method of winding the cable in the opposite direction between adjacent layers of tape can avoid excessive mechanical stress.

Magnetic-field-induced spin reorientation in TmFeO<sub>3</sub> single crystals

TmFeO<sub>3</sub> exhibits rich physical properties such as magneto-optical effect, multiferroicity, and spin reorientation, making it possess significant research value in condensed matter physics and materials science. In this study, we utilize a time-domain terahertz magneto-optical spectroscopy system to investigate the changes in spin resonance frequency of TmFeO<sub>3</sub> single crystal at <i>T</i> = 1.6 K under external magnetic fields in a range of 0–7 T. The TmFeO<sub>3</sub> sample is grown in an optical floating zone furnace and its crystallographic orientation is determined by using back-reflection Laue X-ray photography with a tungsten target. The measurement setup is a self-built time-domain terahertz magneto-optical spectroscopy system, with magnetic fields in a range of 0–7 T, temperatures in a range of 1.6–300 K, and a spectral range of 0.2–2.0 THz. A pair of 1 mm-thick ZnTe nonlinear crystals is used to generate and detect terahertz signals through optical rectification and electro-optic sampling technique. The system variable temperature and magnetic field are controlled by a superconducting magnet. In experiments, a linearly polarized terahertz wave is vertically incident on the sample surface, and its magnetic component <i>H</i><sub>THz</sub> is parallel to the sample surface. By rotating the sample, the angle (<i>θ</i>) between macroscopic magnetic moment <i> <b>M</b> </i> and <i>H</i><sub>THz</sub> can be tuned, achieving selective excitations of the two modes, that is, <i>θ</i> = 0 for q-AFM mode and 90° for q-FM mode. Terahertz absorption spectrum results indicate that as the magnetic field increases, the quasi-ferromagnetic resonance (q-FM) of TmFeO<sub>3</sub> single crystal shifts towards high frequencies, and quasi-antiferromagnetic resonance (q-AFM) transits to q-FM under low critical magnetic fields (2.2–3.6 T). Through magnetic structure analysis and theoretical fitting, it is confirmed that the magnetic moment of the single crystal undergoes magnetic field induced spin reorientation. This study is helpful in better understanding of the regulation mechanism of the internal magnetic structure of rare earth ferrite under the combined action of external magnetic field and temperature field, and also in developing related spin electronic devices.

Propagation Characteristics of Terahertz Waves in Magnetized Dusty Plasma

The propagation characteristics, including reflectivity, transmissivity, and absorptivity, of terahertz (THz) waves in magnetized dusty plasmas sheath are investigated theoretically by the analytic method. Both the right-and left-hand circularly polarized (RCP and LCP) waves are considered. The calculation results illustrate that external magnetic field, plasma slab thickness, electron collision frequency, dust particles, and electron relaxation rate can affect the propagation characteristics of THz waves in plasmas. When dust particles are absent, a strong external magnetic field will cause the transmissivity of RCP waves to produce a transmissivity valley at the lower frequency band. Due to the action of external magnetic field and dust particles, a transmissivity peak appears at the lower frequency band for RCP waves. Increasing the density or radius of dust particles can cause an increase in transmissivity peak. For LCP waves, the transmissivity increases monotonously as the frequency of THz wave increases, whether the dust particles exist or not. These simulation results may provide a significant theoretical basis for solving the problem of “blackout.”

Principles of nuclear magnetic resonance and its applications in medication

There is no doubt that the Nuclear Magnetic Resonance is one of the most fascinating inventions in modern era. Nuclear magnetic resonance is the physical process of nucleus in the body, which align with the direction of magnetic field under the action of external magnetic field, resonant absorb the radio frequency pulse of a certain frequency. NMR spectroscopy is a branch of spectroscopy in which the resonant frequency is in the RF band and the corresponding transition is a transition of the nuclear spin on the magnitude of the nuclear energy. With its large-scale application in various aspects, people’s life was facilitated greatly. In the field of medication, as a new imaging technique, it has no negative effect on human health, and high-resolution image could be produced without any radiation. Millions of patients and injuries could get the correct diagnosis and lead a healthy life later on thanks to it.

Fluorinated polyether grafted TiO2 magnetic composite material for oil-water separation of crude oil emulsion

In order to solve the problem of demulsification of oil-water emulsion, a new type of highly efficient and recyclable magnetic fluorine-containing polyether composite demulsifier (Fe3O4@Ti-F) was synthesized. Fe3O4@Ti-F was prepared by one-pot method to combine magnetic nanomaterial TiO2 with Fe3O4 and graft fluorinated polyether. The successful synthesis of Fe3O4@Ti-F was confirmed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray diffraction (XPS). The demulsification performance of Fe3O4@Ti-F was evaluated by using the self-made crude oil emulsion as the experimental object. The demulsification mechanism of the demulsifier and the influence of external factors such as temperature and pH on the demulsification performance of the demulsifier were discussed, and the amount of TiO2 in the preparation process was determined. The results show that the demulsification efficiency of 50:50 (v/v %) W/O emulsion can reach 90.83% when the dosage of Fe3O4@Ti-F is 600 mg/L, the temperature is 65 °C and the time is 30 min. In the neutral acid environment, the demulsification rate of the demulsifier is above 80%. In addition, Fe3O4@Ti-F has been proved to have good magnetic effect. Under the action of external magnetic field, it can be recovered and recycled from the two-phase system for 4 times, and its demulsification efficiency is still above 60%. Fe3O4@Ti-F will have broad application prospects in the field of oil-water separation in an energy-saving way.

Kinematically exact formulation of large deformations of gradient elastic beams

Budiansky’s nonlinear shell theory is particularized to a 2D setting, and thereupon generalized to a fully nonlinear, statically and kinematically exact, theory of strain-gradient elasticity of beams. The governing equations are displayed in their weak and strong forms. A suitable finite element is used to accommodate the new degrees of freedom emanating from the theory and several numerical examples with large geometrical nonlinearities are displayed showing the relative influence of the strain gradient. The numerical apparatus is then applied to permanently magnetized bodies under the action of external magnetic fields.

Study on energy extraction in the process of combustion plasma plume deflection controlled by MHD

This paper presents a new method of extracting electric energy in the process of realizing thrust vector by magnetron gas plasma. Based on the model scramjet, the combustion plasma scheme is adopted, during the experiment, Cs2CO3 was put into a high-temperature environment to excite its own properties, so as to obtain the product Under the action of external magnetic field, it is verified that electric energy can be extracted in the process of plasma jet deflection, and the results are analyzed from the mechanism. Finally, the specific numerical results of magnetic field intensity and outgoing gas temperature are obtained, the average extraction voltage is 600 mV, indicating that ionized seeds enhance the ionization degree of gas. In the process of gas plasma jet of magnetic control scramjet, the scheme of extracting energy is feasible.

Theoretical Modeling of Magnetoactive Elastomers on Different Scales: A State-of-the-Art Review.

A review of the latest theoretical advances in the description of magnetomechanical effects and phenomena observed in magnetoactive elastomers (MAEs), i.e., polymer networks filled with magnetic micro- and/or nanoparticles, under the action of external magnetic fields is presented. Theoretical modeling of magnetomechanical coupling is considered on various spatial scales: from the behavior of individual magnetic particles constrained in an elastic medium to the mechanical properties of an MAE sample as a whole. It is demonstrated how theoretical models enable qualitative and quantitative interpretation of experimental results. The limitations and challenges of current approaches are discussed and some information about the most promising lines of research in this area is provided. The review is aimed at specialists involved in the study of not only the magnetomechanical properties of MAEs, but also a wide range of other physical phenomena occurring in magnetic polymer composites in external magnetic fields.

Magnetically recoverable flower-like Sn3O4/SnFe2O4 as a type-II heterojunction photocatalyst for efficient degradation of ciprofloxacin

Photocatalysis is an important method for degradation of antibiotics. However, the rapid recombination of photoinduced carriers limits the photoactivity. In addition, due to the small particles size of photocatalyst, it is difficult to recycle, leading to secondary pollution to environment and limited practical application. In this work, the Sn3O4/SnFe2O4 (SN/SFO) heterojunction photocatalysts were synthesized by a simple ultrasonic assisted calcination method. The prepared SN/SFO composite was analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Their photocatalytic activities to ciprofloxacin (CIP) degradation were investigated under visible light. Among SN/SFO composites with different mass ratios, SN/SFO-25% composite showed the highest degradation efficiency, and the rate constant value of SN/SFO-25% is 4.87 and 3.02 times faster than pure SFO and SN, respectively. The improved photocatalytic performance of SN/SFO can be attributed to the construction of type II heterojunction, which inhibited the recombination of electron-hole pairs. In addition, the flower-like morphology causes many pores in the material and brings more exposed surface area, which favors, to some extent, multi-reflection, enhanced sunlight absorption and boosted photocatalytic reaction. More importantly, the SN/SFO composite was easy to be separated and recovered under the action of external magnetic field. This work is expected to provide design opportunities for the construction of highly efficient magnetic photocatalysts with type-II scheme for photocatalytic degradation of CIP in water environments.

Macro-mechanical properties of magnetorheological fluids based on body-centered cubic structure

This paper addresses the problem that the microstructure model of magnetorheological fluid established by traditional single-chain or multi-chain dense rows is unable to accurately describe the rheological behavior and the sudden change of macroscopic mechanical properties under the action of an applied magnetic field, and analyzes the stable cluster-like structure formed by a specific volume fraction of magnetorheological fluids in a micro-narrow channel under the action of external magnetic field and extrusion pressure. This paper also establishes the equations of motion and dynamics of magnetic particles under the action of external magnetic field, analyzes the dynamic evolution of particle microstructure, performs numerical simulations of two-dimensional chaining using Matlab, and establishes a microscopic observation test bench for comparison and verification; and it establishes a model of complex cluster-like structure of magnetorheological fluids body-centered cubic, and analyzes the system energy, stability and force of the body-centered cubic structure based on the minimum system energy theory and Hertzian contact theory; and further establishes a shear yield stress model based on the body-centered cubic microstructure to analyze the macroscopic mechanical properties of magnetorheological fluids, thereby enriching the theoretical system of extrusion strengthening of magnetorheological fluids in the microscale.

Aqueous Adsorptive Removal of Bisphenol A Using Tripartite Magnetic Montmorillonite Composites

The adsorption of bisphenol A into untreated montmorillonite clay, doped titanium composite and cationic polymer modified tripartite magnetic montmorillonite composite was investigated under different conditions. The magnetic property of the modified adsorbent was ascertained by action of external magnetic field on the materials when dispersed in aqueous media. The XRD results for the unmodified and modified adsorbents showed that interlayer spacing of the clay material increases due to intercalation of the precursor molecules. The textural properties of the adsorbents from BET analysis showed that pore size and specific surface area of the tripartite magnetic composite was calculated to be 288.08 m2/g while that of the unmodified clay was 90.39 m2/g. The TGA results showed the tripartite magnetic composite was more stable with the lowest percentage mass loss compared to the unmodified montmorillonite. The tripartite magnetic composite showed higher adsorption capacity. Adsorption was best described by the Freundlich isotherm model, which confirmed that the adsorption process was multilayer coverage unto the uneven surface of the adsorbents. Kinetic treatment of the adsorption data confirmed the the process followed a pseudo-second-order kinetic model and predominantly chemisorption process. The standard Gibb’s free energy computed for the adsorbents showed that the adsorption processes were favourably spontaneous with highly negative energy values of −336.70, −533.76 and −1438.38 KJ/mol, respectively, for the unmodified montmorillonite, doped titanium composite and the tripartite magnetic composite. It was observed that the addition of cationic aromatic moiety to the clay material increased pollutant-adsorbent interactions and improved adsorption capacity for micro-pollutants in a simulated industrial effluent.

Improving spreadability of molten metal in MIG welding-brazing of aluminum to steel by external magnetic field

A modified metal inert gas (MIG) welding-brazing process of aluminum and steel with the assistance of external magnetic field (EMF) was proposed in this study. An alternative EMF along the welding direction was used to promote the arc and the droplet to swing along the weld width direction by producing an alternative electromagnetic force perpendicular to the welding direction. The effect of the excitation current level and frequency on weld bead appearance, spreadability of molten metal and the welding process stability was investigated by experimental observation. As the excitation current level increased, the width of the weld seam was increased and the spreadability of the molten metal was enhanced. When it was beyond a critical level, the arc stability was disrupted. Excessive excitation current caused the excessive inclination of the arc especially in base current stage, which was extremely easy to result in arc extinguishing. When the frequency of the excitation current changed from 2 Hz to 15 Hz, the weld width was decreased. If the excitation current exceeded 15 Hz, the weld width kept constant. The wetting angle of the aluminum metal was decreased as the optimized EMF was applied. Besides, the tensile strength of the joint was enhanced due to the enhancement of spreading of molten metal under the action of EMF.

Investigations of microscopic mechanisms in exciplex-based devices with isomers of mCBP and CBP as donors via magneto-electroluminescence

The mCBP and CBP are two kinds of isomers containing carbazole groups and often used as the device hosts for fluorescence and phosphorescence emission. However, there are little studies on the microscopic mechanisms of exciplex-type devices based on mCBP or CBP. In this paper, the isomers of mCBP and CBP are used as donors and the PO-T2T is selected as an acceptor. The two kinds of exciplex-based devices are fabricated according to a mass ratio of 1∶1, which are respectively referred to as device 1 (Dev. 1) and device 2 (Dev. 2). Their magneto-electroluminescence (MEL) curves are measured at different working temperatures and various injection currents. It is found that the low field effects of the MEL curves from Dev. 1 are dominated by the <i>B</i>-mediated reverse intersystem crossing (RISC) process at room temperature, and as the operational temperature decreases, the MEL line-shapes change gradually from RISC to the intersystem crossing (ISC) process. Conversely, the low field effects of the MEL curves of Dev. 2 are governed by the <i>B</i>-mediated ISC process at room temperature, and the ISC process first weakens then strengthens with temperature decreasing. The high field effects of the MEL curves of Dev. 1 and Dev. 2 are both dominated by the <i>B</i>-mediated triplet-charge annihilation (TQA) process at room temperature, but those of Dev. 2 at 20 K present the <i>B</i>-mediated triplet-triplet annihilation (TTA) process. The completely opposite low-field line-shapes of MEL traces from Dev. 1 and Dev. 2 can be attributed to their different structures of mCBP and CBP, which lead to the higher and lower triplet state exciton energy, respectively. The higher triplet exciton energy of the mCBP donor causes the triplet exciplex energy to be confined effectively, which promotes the RISC process (EX<sub>1</sub> ← EX<sub>3</sub>) in Dev.1. Contrarily, the lower triplet exciton energy of the CBP donor causes the triplet exciplex to experience an energy loss process (EX<sub>3</sub> → T<sub>1</sub>, CBP) , resulting in the suppressed RISC process in Dev. 2. Consequently, the overlapped effects of the ISC process of polaron pairs and the RISC process of exciplex in Dev. 2 under the action of external magnetic field display the ISC-determined process at room temperature. Moreover, the temperature-dependent change in the microscopic process of Dev. 1 such as the conversion from RISC to ISC is because decreasing temperature is not conducive to the occurrence of the RISC process of exciplex states due to its endothermic property. The low-temperature TTA process occurring in Dev. 2 is due to the suppressed energy loss process of triplet exciplex via the Dexter energy transfer from the triplet exciplex to the triplet exciton of CBP donor. In addition, when the mass ratio of mCBP donor to PO-T2T acceptor varies from 1∶4 to 1∶1 to 4∶1, the RISC process of MEL curves of devices turns stronger and stronger, which is because the devices tend more to balance, favoring the RISC process. A higher external quantum efficiency is obtained in the mCBP:PO-T2T host than in the CBP:PO-T2T host when fluorescent guest material of TBRb is used as a dopant in these two exciplex-based devices, which verifies the importance of the effective confinement of triplet exciplex energy in improving the luminescence efficiency. Note that via the MEL detection technology, the current- and temperature-dependent microscopic processes and their reasonable interpretations and device performances from exciplex-based devices with the isomers of mCBP and CBP as donors have not been reported in the literature. This work provides experimental and theoretical references for fabricating the high-efficiency exciplex-based organic light-emitting devices.

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C18 ) Precursors, C18 -(CO)n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (-CO) Groups.

The bonding character, electron delocalization, and aromaticity of the cyclo[18]carbon (C18 ) precursors, C18 -(CO)n (n=6, 4, and 2), have been studied by combining quantum chemical calculations and various electronic wavefunction analyses with different physical bases. It was found that C18 -(CO)n (n=6, 4, and 2) molecules exhibit alternating long and short C-C bonds, and have out-of-plane and in-plane dual π systems (πout and πin ) perpendicular to each other, which are consistent with the relevant characteristics of C18 . However, the presence of carbonyl (-CO) groups significantly reduced the global electron conjugation of C18 -(CO)n (n=6, 4, and 2) compared to C18 . Specifically, the -CO group largely breaks the extensive delocalization of πin system, and the πout system is also affected by it but to a much lesser extent; as a consequence, C18 -(CO)n (n=6, 4, and 2) with larger n shows weaker overall aromaticity. Mostly because of the decreased but still apparent πout electron delocalization in the C18 -(CO)n (n=6, 4, and 2), a notable diatropic induced ring current under the action of external magnetic field is observed, demonstrating the clear aromatic characteristic in the molecules. The correlation between C18 -(CO)n (n=6, 4, and 2) and C18 in terms of the gradual elimination of -CO from the precursors showed that the direct elimination of two CO molecules in C18 -(CO)n (n=6, 4, and 2) has a synergistic mechanism, but it is kinetically infeasible under normal conditions due to the high energy barrier.

Preparation of magnetically retrievable flower-like AgBr/BiOBr/NiFe2O4 direct Z-scheme heterojunction photocatalyst with enhanced visible-light photoactivity

The rapid recombination of electrons and holes is the main reason affecting the performance of photocatalyst, and the difficulty in recovery of photocatalyst also impedes its practical application. Herein, the magnetically recoverable flower-like AgBr/BiOBr/NiFe2O4 (AB/BOB/NFO) ternary heterojunction photocatalyst was successfully constructed. The phase composition, morphology, the absorption of visible light of the samples, and the surface chemical environment of samples were tested by XRD, SEM, UV–vis, and XPS, respectively. Compared with pure BiOBr and BiOBr/NFO, AB/BOB/NFO showed improved photocatalytic degradation effect for RhB. 25% AB/BOB/NFO showed the best degradation performance of 100% in 90 min, which was about 3.6 times that of pure BOB. The enhanced photoactivity of AB/BOB/NFO heterojunction photocatalyst can be ascribed to the wider absorption range of visible light and the inhibited recombination of photogenerated electros and holes. Additionally, the flower-like morphology assembled by nanosheets provides more active sites and improve light absorption through reflecting multiple times and plays roles in improving the photocatalytic performance. It was also found that the AB/BOB/NFO heterojunction photocatalyst has excellent magnetic recovery ability under the action of external magnetic field. The photostability of AB/BOB/NFO heterojunction photocatalyst was also investigated, and a direct Z - type electron hole transfer mechanism was proposed according to the energy band structure. These advances provide a new way to improve the photoactivity of magnetic recyclable photocatalysts, and the as-synthesized flower-like AB/BOB/NFO has broad promising application in water environment remediation.

Information storage in permalloy modulated magnetic nanowires

A long piece of magnetic material shaped as a central cylindrical wire (diameter d=50 nm) with two wider coaxial cylindrical portions (diameter D=90 nm and thickness t=100 nm) defines a bimodulated nanowire. Micromagnetism is invoked to study the equilibrium energy of the system under the variations of the positions of the modulations along the wire. The system can be thought of as composed of five independent elements (3 segments and 2 modulations) leading to 2^5=32 possible different magnetic configurations, which will be later simplified to 4. We investigate the stability of the configurations depending on the positions of the modulations. The relative chirality of the modulations has negligible contributions to the energy and they have no effect on the stability of the stored configuration. However, the modulations are extremely important in pinning the domain walls that lead to consider each segment as independent from the rest. A phase diagram reporting the stability of the inscribed magnetic configurations is produced. The stability of the system was then tested under the action of external magnetic fields and it was found that more than 50 mT are necessary to alter the inscribed information. The main purpose of this paper is to find whether a prototype like this can be complemented to be used as a magnetic key or to store information in the form of firmware. Present results indicate that both possibilities are feasible.

Electrochemical Enhanced Detection of Uric Acid Based on Peroxidase‐like Activity of Fe3O4@Au

AbstractFe3O4@Au nanomaterials were prepared by the self‐assembly method. An enzyme‐free, ultrasensitive electrochemical detection of uric acid was achieved based on the peroxidase‐like activity of Fe3O4@Au. The proposed procedure has exhibited excellent catalytic activities and achieved significant enhancements of the current responses to uric acid. The detection range was from 0.1 to 10 mmol/L, and the limit of detection was 0.087 μmol/L. Under the action of external magnetic field, the magnetic particles can be easily separated from the bottom liquid, which has the advantages of simple operation and high separation efficiency. Moreover, this detection method combining a simulated enzyme and electrochemical can enhance the effective output of the overall electrochemical signal without modifying the electrode, and excellent reproducibility can be achieved. Compared to colorimetric assay, the electrochemical one has higher sensitivity and selectivity, and was further applied in ultrasensitive detection of uric acid in food samples. In short, the proposed electrochemical assay has great potential in the fields of food quality control and biomedical analysis.

Application of magnetic nanoparticles Fe304 in the field of orthopedics and medicine

Magnetic nanoparticle Fe304 have super paramagnetic, biological cell compatibility, low toxicity, antibiosis and bacteriostasis, drug loading, sustained release and thermal effect. Using magnetic nanoparticies Fe304 as magnetic source, magnetic masoporous glass two-dimensional bone framework was synthesized under the action of external magnetic field, which provides growth space for bone repair, cell proliferation and metabolism, and contribute to mineralizing. The same time, The application of graphene, especially magnetic nanoparticles Fe304, in bone materials, bone repair and relatedmedicalfields was discussed.

Isolated Dirac string induced by interaction between positive and negative monopoles

<sec>Based on the three-dimensional spinor Gross-Pitaevskii (GP) equation, the dynamic behavior of the Bose-Einstein condensate under the action of a time-dependent periodic external magnetic field is studied. The results show that the Bose-Einstein condensate with spin-1 in a ferromagnetic state will undergo topological deformation under the action of an external magnetic field periodically varying with time. When the two zero points of the magnetic field enter into the condensate, the density pattern of the spin-up state forms small convexities protruding upward and downward on the <i>z</i>-axis, respectively. As the two zero points of the magnetic field gradually coincide in the condensate, the upward and downward protruding convexities are elongated. Finally, the spin-up state in the shape of a line is distributed on the <i>z</i>-axis, which is consistent with the scenario of the isolated Dirac string predicted by theoretical analysis. </sec><sec>As far as we know, magnetic monopole can be divided into positive monopole and negative monopole. The positive magnetic monopole means that all magnetic induction lines are emitted from the center of the circle. And only the Dirac string points to the center of the circle. The negative monopole is that all the magnetic induction lines point from the outside to the center of the circle, and only the Dirac string emits from the center of the circle. Magnetic monopole is a topological defect in vector field, which accords with both quantum mechanics and gauge invariance of electromagnetic field. </sec><sec>Single magnetic monopole has been studied a lot in theory, and its analogues have been observed in experiment. But multiple monopoles and the interaction between them are still rarely studied. In this paper, multiple monopoles are produced based on the fact that the periodic magnetic field has multiple zeros. We use a new periodic magnetic field to generate a positive and negative magnetic monopole. Due to the strong external magnetic field, the vorticity in the condensate is consistent with the magnetic field of the monopole. Finally, by calculating the superfluid vorticity of the condensate, the characteristic diagram of the magnetic monopole is obtained. The results show that the condensate forms a pair of positive and negative magnetic monopoles at the two zero points of the magnetic field, corresponding to the two small convexities protruding upward and downward on the <i>z</i>-axis of the spin-up state, respectively. As the two zero points of the magnetic field coincide, the two Dirac strings in the positive and negative magnetic monopole gradually approach to each other, and after about 5 ms, they are completely connected, finally forming an isolated Dirac string. This result provides a new idea for further studying the isolated Dirac strings.</sec>

Rheological implications of the inclusion of ferrofluids and the presence of uniform magnetic field on heavy and extra-heavy crude oils

This study embraces the evaluation of the rheological and magneto-rheological properties of heavy and extra-heavy crude oils by applying nanotechnology and magnetism as technological solutions in reducing viscosity. Mixtures of heavy oils with ferrofluids were used to study the viscous effects induced by the action of external magnetic fields. The rheological evaluation covered rotational and oscillatory tests as a function of time and temperature. In the magneto-rheological characterization, there were analyzed the magnetoviscous effects. The results revealed that the crude oils are viscoelastic materials that follow the Generalized Maxwell Model over a wide range of temperatures (-5 to 60 °C). It was also proved that the synergy between the carrier liquid and the nanoparticles promoted a significant reduction of viscosity (~98–99%) and viscoelasticity, which was directly related to the simultaneous action of the solvent and the asphaltene adsorption onto the nanoparticles surface. Critical concentrations of nanoparticles (0.2 wt% and 0.6 wt%) were proved to promote the maximum decrease in viscosity (additional ~ 0.3–0.5% or 1000-3000 cP) and the elastic storage modulus, which was crucial evidence of their effect on hindering the aggregation mechanisms of asphaltenes. In the heavy oil–ferrofluid mixtures, a magneto-rheological effect was demonstrated. The magnetic field attenuated the initial relaxation processes, leading to an increase in the viscosity and shear stress. The phenomenon was attributed to the formation of magnetic chains, such as that observed in magneto-rheological fluids. These results were supported by Scanning Electron Microscopy, which showed the formation of magnetic-field induced thick columnar assemblies of nanoparticles-asphaltene complexes.