Frequency Of Oscillating Field Research Articles

300-Times-Increased Diffusive Skyrmion Dynamics and Effective Pinning Reduction by Periodic Field Excitation.

Thermally induced skyrmion dynamics, as well as skyrmion pinning effects, in thin films have attracted significant interest. While pinning poses challenges in deterministic skyrmion devices and slows down skyrmion diffusion, for applications in non-conventional computing, both pinning of an appropriate strength and skyrmion diffusion speed are key. Here, periodic field excitations are employed to realize an increase of the skyrmion diffusion by more than two orders of magnitude. Amplifying the excitation, a drastic reduction of the effective skyrmion pinning, is reported, and a transition from pinning-dominated diffusive hopping to dynamics approaching free diffusion is observed. By tailoring the field oscillation frequency and amplitude, a continuous tuning of the effective pinning and skyrmion dynamics is demonstrated, which is a key asset and enabler for non-conventional computing applications. It is found that the periodic excitations additionally allow stabilization of skyrmions at different sizes for field values that are inaccessible in static systems, opening up new approaches to ultrafast skyrmion motion by transiently exciting moving skyrmions.

Influence of alternating magnetic field on non-newtonian blood perfusion and transport of nanoparticles in tissues with embedded blood vessel during hyperthermia

In this paper, we consider the impact of an alternating magnetic field on axisymmetric non-Newtonian nanofluid flow and nanoparticle (magnetite or iron-platinum) transport through a blood vessel and surrounding tissue during hyperthermia therapy. The geometrical domain of the problem is divided into four regions; the blood vessel region, cancerous and non-cancerous muscle or prostate regions, and a fat region. Each of the tissue regions is considered to be a saturated porous material that admits fluid flow, which is given by the Darcy-Brinkman-Forchheimer model. The Quemada model is used to describe the non-Newtonian nature of blood in each region. The resulting unsteady coupled governing equations and corresponding boundary and initial conditions are numerically solved by using the finite element method with Taylor-Hood elements. A physically realistic range of parameter values are used when numerically solving the governing equations. Using the obtained numerical solution, the effects of magnetic field amplitude and oscillation frequency, inlet nanoparticle solid volume fraction and nanoparticle diameter on nanofluid velocity, temperature, pressure and nanoparticle distribution are examined. The results determined that more heat generation is achieved with a larger volume fraction of injected nanoparticles and higher magnetic field amplitude. Also, heat generation is maximized by using nanoparticles with a diameter near 15nm and a magnetic field oscillation frequency near 4×104s-1. Thus, the present study provides an improved understanding of the factors influencing the effectiveness of intravenous magnetic hyperthermia cancer therapy in muscle and prostate tissues. The heat generated by the considered nanoparticles under an alternating magnetic field can be more accurately predicted and controlled using the two-phase non-Newtonian model of fluid flow and convective heat and mass transfer that is investigated herein.

Two-phase model of intravenous magnetic nanoparticle hyperthermia in muscle and prostate tumours

In this work, we investigate heat transfer phenomena in muscle and prostate tissues during magnetic hyperthermia cancer therapy with intravenously-injected maghemite nanoparticles. The resulting suspension of nanoparticles in blood is considered to be a non-Newtonian nanofluid, and a two-phase model that considers Brownian and thermophoretic effects is considered. The geometrical domain is comprised of a blood vessel region, cancerous and non-cancerous (prostate or muscle) tissue regions, and a region of fat tissue. The mixed finite element technique is utilized for solving the governing equations and their associated initial and boundary conditions; triangular quadratic elements are chosen for the temperature, velocity and nanoparticle volume fraction approximations, whereas triangular linear elements are selected for the pressure approximation. Based on this numerical solution, we examine the impact of the nanoparticle volume fraction at the inlet of the blood and magnetic field oscillation frequency on heat transfer and nanoparticle transport. The findings of this study indicate that in the prostate and muscle tissue cases, the nanoparticle distribution non-uniformity and the tissue and blood vessel temperatures are increased, and the average pressure is reduced, by increasing the inlet nanoparticle concentration and magnetic field oscillation frequency. In the muscle tissue case, the mean flow velocity can be increased by increasing the inlet nanoparticle concentration and decreasing the magnetic field oscillation frequency. Based on these findings, recommendations are made for improving the effectiveness of magnetic nanoparticle hyperthermia in cancerous muscle and prostate tissues. The research conducted in this work is motivated by the need for a better understanding of the factors impacting nanoparticle transport in tissues and heat generation during magnetic hyperthermia. Using the mathematical model developed herein, tissue temperatures attained under intravenous magnetic hyperthermia treatment can be accurately predicted.

Mechanism and characteristics of sound scattering modulation by underwater low frequency oscillating vortex flow field

The scattering of sound waves by underwater vortex flow filed is the basic problem of sound waves propagating in complex flow fields, which has important significance in implementing underwater target detection and sound imaging of flow field. The theoretical analysis model and numerical calculation method are established for the problem of sound scattering modulation in underwater low frequency oscillating vortex flow fields, and the generation mechanism and time frequency and space characteristics of the scattering modulation sound field are explored. Firstly, based on the wave equation of the moving medium, in the first-order approximation the wave equation is decomposed into the flow-sound coupling term and the non flow-sound coupling term by introducing a potential function, and the flow-sound coupling term is analyzed in the frequency domain, revealing the underwater oscillating vortex flow field. Secondly, the discontinuous Galerkin numerical calculation method is used to solve the wave equation of the moving medium, and the sound propagation process in the underwater low frequency oscillating vortex flow field is numerically simulated. Under the condition of low Mach number, the effects of incident sound frequency, the oscillation frequency of the vortex flow field, and the scale of the vortex core on the time-frequency and space characteristics of the scattering modulating sound fields of vortex flow field are analyzed, and theoretical analysis model is used to explain the characteristics. The research results show that under the condition of low Mach number, the scattering of sound wave by oscillating vortex flow field can produce a scattering modulated sound field containing the harmonic of oscillating frequency side frequency modulation. The amplitude of the scattered sound pressure changes periodically with time, and the forward scattering is much stronger than the backward scattering. The fundamental frequency scattering modulation is much stronger than the frequency doubling scattering modulation. With the increase of the frequency of the incident sound wave and the scale of the vortex core, the intensity of the scattering modulating sound field increases, and the spatial distribution of the total scattering sound field has symmetry and an obvious main lobe, the main lobe is gradually sharpened, the azimuth angle of the main lobe is close to the propagation direction of the incident wave. When the frequency ratio is much greater than 1, the vortex flow field oscillation frequency has little effect on the spatial distribution of the sound field intensity of scattering modulating sound field.

Simplified P-representation operator correspondence applied to quantum systems with generalized Kerr nonlinearity

A simplified operator correspondence scheme is derived to address nonlinear quantum systems within the framework of the [Formula: see text]-representation. The simplified method is applied to a general nonlinear quantum oscillator model that has been used in the literature to describe nonlinear quantum optical and matter wave systems. The [Formula: see text]-representation evolution equation for the model is derived for arbitrary nonlinearity exponents. It is shown that in the high temperature case, the [Formula: see text]-representation is sufficient to describe the model and its associated systems such that there is no need to use alternative, mathematically more involved representations. Systems with quadratic and cubic nonlinearities are considered in more detail. Distributions for the energy levels and photon and particle numbers are obtained within the framework of the [Formula: see text]-representation. Moreover, the electrical field oscillation frequency dependency is studied numerically when interpreting the model as model for quantum optical nonlinear oscillators.

Dynamic Phenomena in Mixed Spin-1 and Spin-1/2 Ising Bilayer System: Effective-Field Theory Based on Glauber Type Stochastic Dynamics

The dynamic compensation and dynamic hysteresis features of the mixed bilayer Ising system (MBIS) consist of spin-1 and spin-1/2 on a bilayer square lattice and have been studied extensively with the use of the effective-field theory and Glauber type stochastic dynamic. Firstly, the thermal variations of the total magnetization were investigated in order to find the compensation types of the MBIS. The six compensation types were found to be the Q-, R-, P-, N-, S-, and L-types. Then, the effects of the temperature, interlayer coupling constant, crystal field, and oscillating field frequency on the dynamic magnetic hysteresis properties were widely studied.

Different sensitivities of two optical magnetometers realized in the same experimental arrangement

In this article, operation of optical magnetometers detecting static (DC) and oscillating (AC) magnetic fields is studied and comparison of the devices is performed. To facilitate the comparison, the analysis is carried out in the same experimental setup, exploiting nonlinear magneto-optical rotation. In such a system, a control over static-field magnitude or oscillating-field frequency provides detection of strength of the DC or AC fields. Polarization rotation is investigated for various light intensities and AC-field amplitudes, which allows to determine optimum sensitivity to both fields. With the results, we demonstrate that under optimal conditions the AC magnetometer is about ten times more sensitive than its DC counterpart, which originates from different response of the atoms to the fields. Bandwidth of the magnetometers is also analyzed, revealing its different dependence on the light power. Particularly, we demonstrate that bandwidth of the AC magnetometer can be significantly increased without strong deterioration of the magnetometer sensitivity. This behavior, combined with the ability to tune the resonance frequency of the AC magnetometer, provide means for ultra-sensitive measurements of the AC field in a broad but spectrally-limited range, where detrimental role of static-field instability is significantly reduced.

An investigation of competition on the dynamic magnetic properties of the core/shell nanowire

In this study, we investigate the dynamic magnetic properties of Ising-type core/shell nanowires (NW) for different spin systems. The model of NW X(Spin-1/2)@Y with Y = Spin-1/2, Spin-1 and Spin-3/2 are considered for discussing an effect of the nature of shell particle on the dynamic properties. The mean-field theory and Glauber-type stochastic dynamics have been successfully applied to this, and the results of the dynamic magnetic properties for the core/shell NW are obtained. Different shell spin states are employed to the analysis of dynamic magnetic behavior for core/shell NW. Results of numerical calculation for the magnetization and coercivity curves are discussed for the effect of shell particles, shell interaction and oscillating field frequency. All results present that dynamic magnetic properties of the NW strongly dependent on the shell particle and the shell interaction.

Estimation of the Lyman-α signal of the EFILE diagnostic under static or radiofrequency electric field in vacuum

The electric field induced Lyman-α emission diagnostic aims to provide a non intrusive and precise measurement of the electric field in plasma, using a beam of hydrogen atoms prepared in the metastable 2s state. The metastable particles are obtained by means of a proton beam extracted from a hydrogen plasma source, and neutralised by interaction with vaporised caesium. When a 2s atom enters a region where an electric field is present, it undergoes a transition to the 2p state (Stark mixing). It then quickly decays to the ground level, emitting Lyman-α radiation, which is collected by a photomultiplier. The transition rate is proportional to the square of the magnitude of the electric field, and depends on the field oscillation frequency (with peaks around 1 GHz). By measuring the intensity of the Lyman-α radiation emitted by the beam it is possible to determine the magnitude of the field in a defined region. In this work, an analysis of the behaviour of the diagnostic under static or radiofrequency electric field is presented. Electric field simulations obtained with a finite element solver of Maxwell equations, combined with theoretical calculations of the Stark mixing transition rate, are used to develop a model for the interpretation of photomultiplier data. This method shows good agreement with experimental results for the static field case, and allows to measure the field magnitude for the oscillating case.

Dynamic hysteresis loops of the spin-2 bilayer Ising model

Based on the mean-field theory and Glauber-type stochastic dynamics, the dynamic hysteresis loops (DHLs) of the spin-2 Ising model are studied on the bilayer square lattice. The DHLs are given for different values of temperature, crystal-field, exchange interaction and oscillating field frequency. It is found that the physical parameters have a strong effect on the shape and number of the DHLs. The results are compared with some theoretical and experimental works and found in a qualitatively good agreement.

The influence of external field on the lubricity of mineral oil for railway transport

The use of mineral oil is associated with its gradual operational degradation caused by its natural aging and contamination with various impurities. As the concentration of impurities increases, the number of active surface molecules which determine the operational properties of mineral oils decreases. A promising method of recovery of the operational properties of oils is the treatment with an electric field, which makes it possible to enhance the activity of surfactants in the tribo-contact area. This statement is proved through the improvement of the wettability of the bronze surface with mineral oils after their treatment with an electrostatic field. However, the method of electrical treatment is associated with the need to increase the requirements for the purity of liquids, especially to the presence of water, which requires creating an oil pre-treatment system. As an alternative, a method of electrical treatment with special field parameters is proposed enabling to accelerate the coalescence process. The major parameter that accelerates the coalescence process is the electric field oscillation frequency. The results of the study give grounds for choosing the optimal field parameters.

Generation of a longitudinal current by a transverse electromagnetic field in collisional degenerate plasma

From the Vlasov–Boltzmann kinetic equation for a collisional degenerate plasma, the electron distribution function is constructed in the quadratic approximation in the electric field strength. A formula for calculating the electric current is derived. It is shown that nonlinearity leads to the rise of a longitudinal electric current directed along the wave vector. The longitudinal current is orthogonal to the known transverse classical current obtained in the linear analysis. When the collision frequency tends to zero, all results obtained for a collisional plasma pass into the corresponding results for a collisionless plasma. The case of small wavenumbers is considered. It is shown that, when the collision frequency tends to zero, the expression for the current passes into the corresponding expression for the current in a collisionless plasma. Graphic analysis of the real and imaginary parts of the current density is performed. The dependence of the electromagnetic field oscillation frequency and electron–plasma-particle collision frequency on the wavenumber is studied.

The dynamic critical properties of the spin-2 Ising model on a bilayer square lattice

The spin-2 Ising model is investigated for the ferromagnetic/ferromagnetic (FM/FM), antiferromagnetic/ferromagnetic (AFM/FM) and antiferromagnetic/antiferromagnetic (AFM/AFM) interactions on the two-layer square lattice by using the Glauber-type stochastic dynamics. The system is in contact with a heat bath at temperature T, and the exchange of energy with the heat bath occurs via one-spin flip. By employing the Master equation and Glauber transition rates, the dynamic equations of the system are obtained. These equations are solved by using the numerical methods. First, we investigate the average order parameters as a function of the time to find the phases in the system. Then, the temperature-dependence of the dynamic order parameters is examined to obtain the dynamic phase transition temperatures. The dynamic phase diagrams are presented on the different planes. According to the values of the system parameters, a variety of dynamic critical points such as tricritical point, triple point, quadruple point, critical end point, double critical end point, zero-temperature critical point, multicritical point and tetracritical point are obtained. The reentrant behavior is seen in the system for the AFM/AFM interaction. Finally, we also investigate the influence of the oscillating field frequency on the dynamic phase diagrams in detail.

The effects of magnetic fields on photoelectron‐mediated spacecraft potential fluctuations

AbstractPreviously, we have experimentally studied photoelectron‐mediated spacecraft potential fluctuations associated with time‐dependent external electric fields. In this paper, we investigate the effects of magnetic fields on such spacecraft potential fluctuations. A magnetic field is created above the UV‐illuminated surface of a spacecraft model to alter the escape rate of photoelectrons. The packet of the observed potential oscillations becomes less positive with increasing magnetic field strength because more of the emitted photoelectrons are returned to the surface. As a result, the photoelectric charging time is increased, corresponding to a decrease in the response frequency of the photoemitting surface. The amplitude of the potential oscillations decreases when the response frequency becomes lower than the electric field oscillation frequency. A test particle simulation is validated with the laboratory experiments and applied to estimate the photoelectron escape rate from the Van Allen Probes spacecraft, showing that the photoelectron current is reduced by as much as 30% when magnetic field strength is 1200 nT. Based on our laboratory results and computer simulations, we discuss the effects of magnetic fields on the spacecraft potential fluctuations observed by the Van Allen Probes.

On determination possibility of the total electron content of the interplanetary path from distortions of an ultrashort radio pulse

The character and features of dispersion distortions of an ultrashort radio pulse in the form of a sinusoidal train propagating along the spacecraft-Earth interplanetary path are theoretically analyzed. It is established that the instantaneous field oscillation frequency in the distorted pulse is completely determined by the value of the total electron content of the path. It is shown that, theoretically, one of the main characteristics of the solar wind can be measured from the frequency of the detected signal.

Interaction of electromagnetic H-wave with thin metal film

It is shown that for thin metal films whose thickness does not exceed that of the skin layer the problem can be solved analytically for arbitrary boundary conditions. The transmission, reflection, and absorption coefficients are analyzed as functions of the angle of incidence of the electromagnetic wave, thickness of the layer, specular reflectivity, and field oscillation frequency.

GABAergic synapse properties may explain genetic variation in hippocampal network oscillations in mice

Cognitive ability and the properties of brain oscillation are highly heritable in humans. Genetic variation underlying oscillatory activity might give rise to differences in cognition and behavior. How genetic diversity translates into altered properties of oscillations and synchronization of neuronal activity is unknown. To address this issue, we investigated cellular and synaptic mechanisms of hippocampal fast network oscillations in eight genetically distinct inbred mouse strains. The frequency of carbachol-induced oscillations differed substantially between mouse strains. Since GABAergic inhibition sets oscillation frequency, we studied the properties of inhibitory synaptic inputs (IPSCs) received by CA3 and CA1 pyramidal cells of three mouse strains that showed the highest, lowest and intermediate frequencies of oscillations. In CA3 pyramidal cells, the frequency of rhythmic IPSC input showed the same strain differences as the frequency of field oscillations. Furthermore, IPSC decay times in both CA1 and CA3 pyramidal cells were faster in mouse strains with higher oscillation frequencies than in mouse strains with lower oscillation frequency, suggesting that differences in GABAA-receptor subunit composition exist between these strains. Indeed, gene expression of GABAA-receptor β2 (Gabrb2) and β3 (Gabrb2) subunits was higher in mouse strains with faster decay kinetics compared with mouse strains with slower decay kinetics. Hippocampal pyramidal neurons in mouse strains with higher oscillation frequencies and faster decay kinetics fired action potential at higher frequencies. These data indicate that differences in genetic background may result in different GABAA-receptor subunit expression, which affects the rhythm of pyramidal neuron firing and fast network activity through GABA synapse kinetics.

GABAa Receptor Heterogeneity Modulates Dendrodendritic Inhibition

In the olfactory bulb, mitral and tufted cells receive GABAergic inhibition at dendrodendritic synapses with granule cells. Recent studies have revealed a remarkable variability in the subunit composition of GABA(a) receptors in dendrodendritic microcircuits, with differential expression patterns of the alpha1 and alpha3 subunits in different subtypes of mitral and tufted cells. In particular, all mitral cells express the alpha1 subunit, whereas GABA(a)alpha3 is restricted to a subgroup of mitral cells, as well as to several subtypes of tufted cells. To assess the functional relevance of this heterogeneity, we investigated a mouse strain carrying a genetic deletion of the alpha1 subunit. Elimination of GABA(a)alpha1 was partially compensated for in mitral cells by receptors containing the alpha3 subunit, substantially decreasing the frequency of spontaneous inhibitory postsynaptic currents, as well as prolonging their decay time. Evoked inhibition between granule and mitral cells was slower to rise and decay and had smaller amplitude in alpha1 mutants. Remarkably, these changes in synaptic inhibition were accompanied by a significant reduction in the frequency of field oscillations. Therefore, the subunit composition of GABA(a) receptors strongly influences rhythmic activities in the olfactory bulb network. Together, these data indicate that dendrodendritic circuits in the external plexiform layer segregate into parallel pathways involving distinct GABA(a) receptors that are expressed by different subtypes of mitral and tufted cells.

CoII Molecular Square with Single-Molecule Magnet Properties

A new tetranuclear cobalt(II) molecular square in which adjacent Co(II) centers are linked by a mu(2)-bridging oxygen atom and a N-N bridge along the edges of the square has been designed for single-molecule magnets (SMMs) with high anisotropy barriers. The overall intramolecular ferromagnetic coupling at low temperature combined with the slow relaxation at static zero fields suggests a SMM behavior for this molecular square. The zero-field cooled magnetization (ZFCM) and field cooling magnetization (FCM) at 10 Oe illustrate the nonreversibility and bifurcation below 4.5 K. The deviations of magnetization from the saturated value in strong applied fields demonstrate the participation of low-lying excited states. The peaks of the out-of-phase signals are observed corresponding to coincidence of the applied ac field oscillation frequency with the relaxation rate.

On the interaction of a beam of polar molecules with a static and a resonant RF field as a source of molecular interferences

A molecular beam interference model is presented based on a two-state interaction between a polar molecule and a resonant RF field as it occurs in the so-called C-field of a typical molecular beam electric resonant spectrometer. The treatment shows the onset of interferences in the beam transmission spectra as well as in its transverse profile. It is demonstrated how the molecular interferences are originated by the wavefunction phase shift introduced by the resonant RF field. Furthermore it is shown that for a given beam velocity and oscillating field frequency the fringes’ visibility depends on the strength of the RF field, i.e. the Rabi frequency, in the transmission spectra. Likewise the presence of a RF field gradient in the perpendicular beam direction gives rise to a peak structure in the transverse beam profile. The theoretical model was applied to simulate a variety of beam transmission spectra under resonant conditions as well as some experimental data already published by our group showing a satisfactory agreement between experimental and simulated data. Finally, the potentiality of this internal state molecular interferometer to carry out studies in matter-wave interferometry is remarked.