Field Generation Research Articles

Terahertz field generation from laser interaction with spherical nano-particles: effect of external magnetic field

Terahertz field generation from laser interaction with spherical nano-particles: effect of external magnetic field

SVM-based fast 3D pore-scale rock-typing and permeability upscaling for complex rocks using Minkowski functionals

The rapid advancement of digital core analysis has greatly promoted the research progress of flow and transport in porous media. However, complex analytical process with exceeding computational load impedes the application on large data volume. Considering the strong heterogeneity of the underground porous media, the integration of pore-scale information into continuum scale is widely concerned for the future development of digital physical analysis. For hierarchical porous structures, pore-scale rock-typing and upscaling of petrophysical properties is a promising solution towards the issue, and morphological and topological descriptors associating data clustering methods are popularly utilized. However, the size of the regional support through which the parameter fields are generated heavily affects the descriptive capacities of the parameters and the following partitioning process. We propose in this work a robust integrated pore-scale rock-typing and upscaling technology for 3D porous structures which uses Minkowski functionals as the descriptive parameters. A fast-computational method utilising fast Fourier transform has been applied for efficient generation of the parameter fields. A comparative study between the two different classification methods of Support Vector Machine (SVM) and Gaussian Mixture Model (GMM) has been conducted on two complex artificial porous systems and a laminated sandstone through various regional support sizes. Throughout the test, SVM has illustrated obvious advantage of overcoming regional support size effect even with limited labelling information. The Upscaling of permeability on the natural sandstone sample based on the rock type distribution has demonstrated excellent accuracy comparing with full scale direct computation.

Microplastic removal from water using modified maifanite with rotating magnetic field affected

Magnetic separation of microplastics from water is a new generation technology that is cost effective and environmentally friendly, and can avoid secondary pollution. The influence of magnetic Maifanite on polystyrene removal from water was investigated under a magnetic field action time, solution pH, magnetic carrier dosage, and polystyrene concentration, using a developed rotating magnetic field generator. Additionally, the polystyrene removal mechanism by the rotating magnetic field was revealed based on characterization and process simulation. The results showed that Maifanite can increase the number of surface adsorption sites and improve the adsorption performance after high temperature and acid impregnated modification. Specifically, the surface morphology of the modified Maifanite exhibited skirted stripes and a multilayered pore structure. And the specific surface area increased from 3.26 to 20.83 m2/g. The removal process is based on chemical adsorption, supplemented by physical adsorption. The magnetic carrier is tightly wrapped around the polystyrene surface by π bonds between the metal and hydroxy groups, ensuring agglomeration strength. Additionally, the rotating magnetic field generator designed can provide a rotating dynamic magnetic field, and the magnetic particles in the mixed system present a multi-directional helical motion trajectory, thus the walking displacement increases and the capture time decreases. And the probability of collision with non-magnetic particles and the formation of magnetic agglomerates are greatly increased. Thus the adsorption and removal of microplastics are enhanced theoretically. The polystyrene removal efficiency from water using modified Maifanite by rotating magnetic field affected increased by 19.49 %, reaching 98.46 %, and stabilizing at 86.53 % over 25 operation cycles. This study holds promise for advancing magnetic separation technology for microplastics from water.

Linear perturbations of the Bloch type of space-periodic magnetohydrodynamic steady states. III. Asymptotics of branching

The previous paper of this series presented the results of a numerical investigation of the dependence of the dominant growth rates of Bloch eigenmodes on the diffusivity parameters (the molecular viscosity ν and molecular magnetic diffusivity η) in three linear stability problems: the kinematic dynamo problem, and the hydrodynamic and MHD stability problems for steady spaceperiodic flows and MHD states. The dominant eigenmodes (i.e., the stability modes, whose growth rates are maximum over the wave vector q of the planar wave involved in the Bloch modes) comprise branches. In some branches, the dominant growth rates are attained for constant half-integer q. In all the three stability problems for parity-invariant steady states, offshoot branches, stemming from the branches of this type, were found, in which the dominant growth rates are attained for q depending on ν and/or η. We consider now such a branching of the dominant magnetic modes in the kinematic dynamo problem, where an offshoot stems from a branch of neutral eigenmodes for q = 0, and construct power series expansions for the offshoots and the associated eigenvalues of the magnetic induction operator near the point of bifurcation. We show that the branching occurs for the molecular magnetic diffusivities, for which the two eigenvalues of the eddy diffusivity operator become imaginary, and magnetic field generation by the mechanism of the negative eddy diffusivity ceases. The details of branching in the other linear stability problems under consideration are distinct.

The Rosensweig instability at the interface between ferrofluids and immiscible fluids

In this study, the Rosensweig instability at the interface between ferrofluids and other immiscible fluids is systematically studied. Stable water based ferrofluids with saturated magnetization as high as 25.4 kA/m are successfully synthesized. The surface tension, density and viscosity of water based ferrofluids used in this study are systematically and scientifically studied. Concentrated coils magnetic field generator is constructed to evaluate the experimental results of Rosensweig instability at the interface between ferrofluids and immiscible fluids. Combined with the theoretical results, the simulation results are obtained from our model to evaluate the Rosensweig instability at the interfaces. The well accordance between experimental results and the theoretical simulation results indicates that the Rosensweig instability is easily generating at interfaces between ferrofluids and oils than the interfaces between ferrofluids and air. This result could be attributed to the surface tension and buoyance of liquids on the ferrofluids.

Tunable Tesla-Scale Magnetic Attosecond Pulses through Ring-Current Gating.

Coherent control over electron dynamics in atoms and molecules using high-intensity circularly polarized laser pulses gives rise to current loops, resulting in the emission of magnetic fields. We propose, and demonstrate with ab initio calculations, "current-gating" schemes to generate direct or alternating-current magnetic pulses in the infrared spectral region, with highly tunable waveform and frequency, and showing femtosecond-to-attosecond pulse duration. In optimal conditions, the magnetic pulse can be highly isolated from the driving laser and exhibits a high flux density (∼1 T at a few hundred nanometers from the source, with a pulse duration of 787 attoseconds) for application in forefront experiments of ultrafast spectroscopy. Our work paves the way toward the generation of attosecond magnetic fields to probe ultrafast magnetization, chiral responses, and spin dynamics.

Resistive field generation in intense proton beam interaction with solid targets

The Brown–Preston–Singleton (BPS) stopping power model is added to our previously developed hybrid code to model ion beam–plasma interaction. Hybrid simulations show that both resistive field and ion scattering effects are important for proton beam transport in a solid target, in which they compete with each other. When the target is not completely ionized, the self-generated resistive field effect dominates over the ion scattering effect. However, when the target is completely ionized, this situation is reversed. Moreover, it is found that Ohmic heating is important for higher current densities and materials with high resistivity. The energy fraction deposited as Ohmic heating can be as high as 20%–30%. Typical ion divergences with half-angles of about 5°–10° will modify the proton energy deposition substantially and should be taken into account.

Neural network based generation of a 1-dimensional stochastic field with turbulent velocity statistics

We define and study a fully-convolutional neural network stochastic model, NN-Turb, which generates a 1-dimensional field with some turbulent velocity statistics. In particular, the generated process satisfies the Kolmogorov 2/3 law for the second order structure function. It also presents negative skewness across scales (i.e. Kolmogorov 4/5 law) and exhibits intermittency as characterized by skewness and flatness. Furthermore, our model is never in contact with turbulent data and only needs the desired statistical behavior of the structure functions across scales for training.

Computer simulation of two phase power-law nanofluid of blood flow through a curved overlapping stenosed artery with induced magnetic field: entropy generation optimization

PurposeThe purpose of this study is to determine the impact of two-phase power law nanofluid on a curved arterial blood flow under the presence of ovelapped stenosis. Over the past couple of decades, the percentage of deaths associated with blood vessel diseases has risen sharply to nearly one third of all fatalities. For vascular disease to be stopped in its tracks, it is essential to understand the vascular geometry and blood flow within the artery. In recent scenarios, because of higher thermal properties and the ability to move across stenosis and tumor cells, nanoparticles are becoming a more common and effective approach in treating cardiovascular diseases and cancer cells.Design/methodology/approachThe present mathematical study investigates the blood flow behavior in the overlapped stenosed curved artery with cylinder shape catheter. The induced magnetic field and entropy generation for blood flow in the presence of a heat source, magnetic field and nanoparticle (Fe3O4) have been analyzed numerically. Blood is considered in artery as two-phases: core and plasma region. Power-law fluid has been considered for core region fluid, whereas Newtonian fluid is considered in the plasma region. Strongly implicit Stone’s method has been considered to solve the system of nonlinear partial differential equations (PDE’s) with 10–6 tolerance error.FindingsThe influence of various parameters has been discussed graphically. This study concludes that arterial curvature increases the probability of atherosclerosis deposition, while using an external heating source flow temperature and entropy production. In addition, if the thermal treatment procedure is carried out inside a magnetic field, it will aid in controlling blood flow velocity.Originality/valueThe findings of this computational analysis hold great significance for clinical researchers and biologists, as they offer the ability to anticipate the occurrence of endothelial cell injury and plaque accumulation in curved arteries with specific wall shear stress patterns. Consequently, these insights may contribute to the potential alleviation of the severity of these illnesses. Furthermore, the application of nanoparticles and external heat sources in the discipline of blood circulation has potential in the medically healing of illness conditions such as stenosis, cancer cells and muscular discomfort through the usage of beneficial effects.

Gradient tungsten-doped Bi3TiNbO9 ferroelectric photocatalysts with additional built-in electric field for efficient overall water splitting

Bi3TiNbO9, a layered ferroelectric photocatalyst, exhibits great potential for overall water splitting through efficient intralayer separation of photogenerated carriers motivated by a depolarization field along the in-plane a-axis. However, the poor interlayer transport of carriers along the out-of-plane c-axis, caused by the significant potential barrier between layers, leads to a high probability of carrier recombination and consequently results in low photocatalytic activity. Here, we have developed an efficient photocatalyst consisting of Bi3TiNbO9 nanosheets with a gradient tungsten (W) doping along the c-axis. This results in the generation of an additional electric field along the c-axis and simultaneously enhances the magnitude of depolarization field within the layers along the a-axis due to strengthened structural distortion. The combination of the built-in field along the c-axis and polarization along the a-axis can effectively facilitate the anisotropic migration of photogenerated electrons and holes to the basal {001} surface and lateral {110} surface of the nanosheets, respectively, enabling desirable spatial separation of carriers. Hence, the W-doped Bi3TiNbO9 ferroelectric photocatalyst with Rh/Cr2O3 cocatalyst achieves an efficient and durable overall water splitting feature, thereby providing an effective pathway for designing excellent layered ferroelectric photocatalysts.

Vorticity generation in cosmology and the role of shell crossing

There is no source for cosmic vorticity within the cold dark matter cosmology. However, vorticity has been observed in the universe, especially on the scales of clusters, filaments, galaxies, etc. Recent results from high-resolution general relativistic N-body simulation show that the vorticity power spectrum dominates over the power spectrum of the divergence of the peculiar velocity field on scales where the effective field theory of large-scale structure breaks down. Incidentally, this scale also corresponds to the scale where shell-crossing occurs. Several studies have suggested a link between shell crossing in the dark matter fluid and the vorticity generation in the universe, however, no clear proof of how it works within general relativity exists yet. We describe for the first time how vorticity is generated in a universe such as ours with expanding and collapsing regions. We show how vorticity is generated at the boundary of the expanding and collapsing regions. Our result indicates that the amplitude of the generated vorticity is determined by the jump in gradients of the gravitational potential, pressure and the expansion rate at the boundary. In addition, we argue that the presence of vorticity in the matter fields implies a non-vanishing magnetic part of the Weyl tensor. This has implications for the generation of Maxwell's magnetic field and the dynamics of clusters. The impact of accelerated expansion of the universe and the existence of causal limit for massive particles are discussed

Multichromatic supercontinuum polarization shaping applied to photoelectron holography

We present a supercontinuum pulse shaping method specifically designed for the generation of polarization-tailored multichromatic femtosecond laser fields. By combining a 4f-polarization pulse shaper with a custom-made polarizer kit, we independently modulate different spectral bands of a white-light supercontinuum in amplitude, phase, and polarization. The scheme is highly modular, scalable to any number of bands supported by the input spectrum and aims at the physically motivated design of specific laser fields tailored to the relevant transitions and dynamics of the quantum system. The power and versatility of the scheme is showcased in three different scenarios based on atomic multiphoton ionization employing polarization-tailored trichromatic pulse sequences. (1) We demonstrate the creation of an -type free electron wave packet and reconstruct its 3D momentum distribution by a waveplate-free shaper-based photoelectron tomography technique. (2) We utilize the holographic properties of the wave packet to study time-resolved and phase-sensitive ultrafast dynamics of bound states. (3) We investigate the field-free time-evolution of a photoelectron wave packet in the continuum. Our results on an atomic model system demonstrate the great potential of the modular shaping scheme for a wide range of applications on more complex quantum systems, including polyatomic molecules, nanoscopic structures and solids.

Simulation and Generation of the In-born Strong Magnetic Environment During Railgun Launch

The in-born strong magnetic environment during the launch process of the railgun is a potential risk for ammunition applications. Currently, there are no mature means to simulate the magnetic field environment to provide a platform for the electromagnetic safety test of ammunition. Given this problem, a strong magnetic environment generation system was designed. By establishing the theoretical model of the magnetic field generated, the difficulty of generating specific waveforms of strong magnetic fields was broken through. Besides, the strong magnetic field generator’s multi-physical field response was analyzed by using the FEM method, and its stability of structure and temperature was evaluated. Finally, the strong magnetic environment generation experiment was conducted, where the in-born magnetic field during the launch process of the railgun was generated successfully. As a result, the strong magnetic environment generation system can generate the expected strong magnetic fields. The magnetic flux density is 10 T, and the pulse width is 6.1 ms.

Pulsed Magnetic Field Generator for Enhancing Cell Membrane Permeability In Vitro

Pulsed Magnetic Field Generator for Enhancing Cell Membrane Permeability In Vitro

Magnetic field-enhanced orifice traversal of droplets: Minimizing surface adhesion for improved efficiency

In this article, we propose the feasibility of replacing traditional materials with ferrofluid droplets to actively regulate their behavior as they traverse an orifice in the presence of an external magnetic field. The traversal behavior of the droplet is investigated using both rectangular and curved orifice boundaries. We employed a simplified multiphase lattice Boltzmann method (SMLBM) to simulate the flow field and interface, which considerably improves computational efficiency. For magnetic field generation, a self-correction procedure is coupled with SMLBM. For curved boundaries, we used our recently developed immersed boundary approach, which can specify wetting boundary conditions for both stationary and moving boundaries, in the same way as flat boundaries are handled. To check the validity of our methods, we first simulated three benchmark phenomena and compared our results with experimental and numerical findings. This research includes orifice geometries, including straight and curved boundaries, and investigates the dynamic behavior of droplets traversing through narrow opening, increased orifice thicknesses, and large diameter droplets passing through confined and multiple orifices. All simulations are initially carried out without the use of magnetic fields, then the experiments are repeated and compared with the addition of a uniform magnetic field. It is found that, in the absence of a magnetic field, the droplets can successfully pass only through wide orifices. However, for narrow or thick orifices, a significant portion of droplet volume adheres to the orifice walls, causing an apparent decrease in falling velocity. In contrast, the addition of a magnetic field enables the droplet to efficiently traverse through even narrower and thicker orifices, attaining faster speeds and reduced mass loss. Furthermore, the influence of Reynold number and magnetic field strengths on the droplet velocity, its wetting dynamics, and relative shedding area are also discussed in detail.

Formation of activity scenarios based on generative artificial intelligence services

The work is dedicated to describing a methodology for generating activity scenarios based on causal networks formed using generative artificial intelligence. The methodology is based on the use of a bidirectional algorithm for generating causal networks. According to this algorithm, two networks are formed and then combined – the first network starts from a node corresponding to the initial state of the problem (the root cause), and the second network corresponds to the goal that needs to be achieved. The article demonstrates the possibility of constructing such causal networks based on the use of a generative transformer like ChatGPT, and provides an example of scenario generation in the subject field of mobile communication. The methodology combines tools for text analysis and the formation of causal networks, followed by the selection and ranking of narrative chains based on the analysis of these networks

Magnetogenesis in Non-Local Models during Inflation

The generation of magnetic fields during the inflation in an electromagnetic model with a non-local form factor in Maxwell’s action is studied. The equations of motion for the electromagnetic field are derived and solved. It is found that the conformal symmetry breaking due to the non-local form factor does not lead to the generation of magnetic fields during the inflation in the absence of an interaction with the inflaton field. If such a coupling takes place, then the presence of the form factor inhibits the generation of primordial magnetic fields compared to the case where the non-local form factor is absent.

Origin and properties of polychromatic directional emission from sodium atoms

The parametric and nonparametric nonlinear processes responsible for generation of directional infrared radiation in sodium vapors, excited to the 4D5/2 energy level by resonant laser radiation, are identified by the transfer of orbital angular momentum from the pump radiation to the generated fields. We show that the optical fields generated by amplified spontaneous emission (ASE) simultaneously participate in several loops of four-wave mixing (FWM) generating new directional emission. The measured spectral linewidth of the FWM emission at 819.7 nm sets an upper limit to the linewidth of two fields resulting from ASE at 2338.6 and 9093.0 nm, assuming their spectra are uncorrelated. Understanding details of the new-field generation is central to applications such as directional laser guide stars, stand-off magnetometry, and entangled field generation.

Magneto-Mechanical Actuation Induces Endothelial Permeability.

Cancer treatment is one of the major health problems that burden our society. According to the American Cancer Society, over 1.9 million new cancer cases and ∼0.6 million deaths from cancer are expected in the US in 2023. Therapeutic targeting is considered to be the gold standard in cancer treatment. However, when a tumor grows beyond a critical size, its vascular system differentiates abnormally and erratically, creating a heterogeneous endothelial barrier that further restricts drug delivery into tumors. While several methods exist, these prompt tumor migration and the appearance of new metastatic sites. Herein, we propose an innovative method based on magneto-mechanical actuation (MMA) to induce endothelial permeability. This method employs FDA-approved PEGylated superparamagnetic iron oxide nanoparticles (PEG-SPIONs) and alternating nonheating magnetic fields. MMA lies in the translation of magnetic forces into mechanical agitation. As a proof of concept, we developed a 2D cell culture model based on human umbilical vein endothelial cells (HUVEC), which were incubated with PEG-SPIONs and then exposed to different magnetic doses. After adjusting the particle concentration, incubation times, and parameters (amplitude, frequency, and exposure time) of the magnetic field generator, we induced actin filament remodeling and subsequent vascular endothelial-cadherin junction disruption. This led to transient gaps in cell monolayers, through which fluorescein isothiocyanate-dextran was translocated. We observed no cell viability reduction for 3 h of particle incubation up to a concentration of 100 μg/mL in the presence and absence of magnetic fields. For optimal permeability studies, the magnetic field parameters were adjusted to 100 mT, 65 Hz, and 30 min in a pulse mode with 5 min OFF intervals. We found that the endothelial permeability reached the highest value (33%) when 2 h postmagnetic field treatment was used. To explain these findings, a magneto-mechanical transduced stress mechanism mediated by intracellular forces was proposed. This method can open new avenues for targeted drug delivery into anatomic regions within the body for a broad range of disease interventions.

Systematic investigation of MoS2-metal sulfides (Metal = In, Sn, Cu, Cd) heterostructure via metal-sulfur bond for photocatalytic CO2 reduction

Heterojunctions between MoS2 and metal sulfides (Metal = In, Sn, Cu, Cd) were successfully constructed via the metal-sulfur bond, and their application of CO2 photoreduction into chemical values could address the problem of global warming effectively. Among all MoS2/metal sulfides, the same lamellar morphology between MoS2 and In2S3 could be ascribed for the high photocatalytic performance, which revealed the high specific surface area and benefitted for the generation of build-in electric field, thus leading to the outstanding separation and migration ability. In the opposite, the dissatisfactory photoreduction performance was emerged on the heterostructure between rod-like morphology of CdS and lamellar MoS2. Moreover, the feature of small gap between valence band minimum and Fermi level in In2S3 was remained in MoS2/In2S3 composite, which could promote more carriers to be excited. Hence, the optimal MoS2/In2S3 composite reached 10.09 μmol·h−1·g−1 of CO, 68.41 μmol·h−1·g−1 of CH4 and 6.66 μmol·h−1·g−1 of CH3OH, and the mix-coordination of CO2 adsorption and the carbene pathway over MoS2/In2S3 was revealed via in-situ DRIFTS.