Local Field Values Research Articles

Large-scale Linear Magnetic Holes with Magnetic Mirror Properties in Hybrid Simulations of Solar Wind Turbulence

Magnetic holes (MHs) are coherent magnetic field dips whose size ranges from fluid to kinetic scale, ubiquitously observed in the heliosphere and in planetary environments. Despite the long-standing effort in interpreting the abundance of observations, the origin and properties of MHs are still debated. In this Letter, we investigate the interplay between plasma turbulence and MHs, using a 2D hybrid simulation initialized with solar wind parameters. We show that fully developed turbulence exhibits localized elongated magnetic depressions, whose properties are consistent with linear MHs frequently encountered in space. The observed MHs develop self-consistently from the initial magnetic field perturbations by trapping hot ions with large pitch angles. Ion trapping produces an enhanced perpendicular temperature anisotropy that makes MHs stable for hundreds of ion gyroperiods, despite the surrounding turbulence. We introduce a new quantity, based on local magnetic field and ion temperature values, to measure the efficiency of ion trapping, with potential applications to the detection of MHs in satellite measurements. We complement this method by analyzing the ion velocity distribution functions inside MHs. Our diagnostics reveal the presence of trapped gyrotropic ion populations, whose velocity distribution is consistent with a loss cone, as expected for the motion of particles inside a magnetic mirror. Our results have potential implications for the theoretical and numerical modeling of MHs.

Optical characterization of nanosecond-pulsed discharge in liquid nitrogen

We report the optical characterization of nanosecond-pulsed plasma ignited directly in liquid nitrogen. Using imaging and optical emission spectroscopy, we estimate neutral temperatures and densities, as well as local electric field values, and the obtained results indicate that the discharge develops via streamer (‘electronic’) mechanism. We show that millimeter-scale plasma propagates in liquid nitrogen at velocities of ∼500 km s−1 with the corresponding required local electric fields as high as 25 MV cm−1, while the estimated local electric fields in the ‘core’ of the discharge are around 6–8 MV cm−1 (corresponding to reduced electric field values of 600–1000 Td). The neutral and electron densities in the ‘main body’ of the discharge were estimated using broadened argon lines, indicating that the neutral densities in the near-electrode region are around 1020 cm−3 (tens of atmospheres), while the maximum recorded temperature is just a few tens of degrees above the surrounding liquid. Electron densities were estimated to be ∼1017 cm−3, about two orders of magnitude lower than those measured for water discharge.

Synthesis features, structure, magnetometry and NMR spectroscopy of nanowires of various types

Various types of nanowires obtained by matrix synthesis --- homogeneous (from iron) and heterogeneous (layered) --- have been studied. A technique for obtaining arrays of layered nanowires with alternating thin layers of magnetic and non-magnetic metals (Co/Cu, Ni/Cu) has been developed and described. Microscopy methods (SEM and TEM with elemental analysis) have been used to study the topography of the resulting structures, the diameters of nanowires and the thicknesses of individual layers, and the features of interlayer interfaces. Methods of synthesis of nanowires with thin layers and clear boundaries are proposed --- dilution of the electrolyte, use of a reference electrode, control of the leaked charge. Layered nanowires have been studied by magnetometry methods and it has been shown that the magnetic properties of an array of layered nanowires (in particular, the direction of the axis of light magnetization in the Co/Cu-NP array) depend not only on the aspect ratio of the magnetic layer, but also on the ratio of the thickness of the magnetic metal layer to the thickness of a non-magnetic spacer (copper layer). The nuclear magnetic resonance (NMR) method was used to study two types of nanowires. The NMR method (on 59-Co nuclei) studied the layer structures of Co/Cu: it is shown that in nanowires with layers of smaller thickness (and, accordingly, with a large contribution of interfaces), a large proportion of Co atoms coordinated by Cu atoms is observed. The high proportion of atoms coordinated by copper suggests that an admixture of copper enters the cobalt layers. Homogeneous iron nanowires (NMR on 57-Fe nuclei) were compared with bulk iron samples. A shift of the line towards high frequencies (by 0.3 MHz) was detected, indicating an increase in the field by about 0.2 T. A significant broadening of the line and a decrease in the spin-lattice relaxation time may indicate a significant variation in the local magnetic field values. Keywords: nanowires, matrix synthesis, microscopy, elemental analysis, magnetic properties, NMR.

Penetration of non-uniform electromagnetic field into conducting body

The study is based on the exact analytical solution for the general conjugation problem of three-dimensional quasi-stationary field at a flat interface between dielectric and conducting media. It is determined that non-uniform electromagnetic field always decreases in depth faster than uniform field. The theoretical conclusion is confirmed by comparing the results of analytical and numerical calculations. The concept of strong skin effect is extended to the case when penetration depth is small not only compare to the characteristic body size, but also when the ratio of the penetration depth to the distance from the surface of body to the sources of the external field is small parameter. For strong skin effect in its extended interpretation, the influence of external field non-uniformity to electromagnetic field formation both at the interface between dielectric and conducting media and to the law of decrease field in conducting half-space is analyzed. It is shown, at the interface the expressions for the electric and magnetic intensities in the form of asymptotic series in addition to local field values of external sources contain their derivatives with respect to the coordinate perpendicular to the interface. The found expressions made it possible to generalize the approximate Leontovich impedance boundary condition for diffusion of non-uniform field into conducting half-space. The difference between the penetration law for the non-uniform field and the uniform one takes place in the terms of the asymptotic series proportional to the small parameter to the second power and to the second derivative with respect to the vertical coordinate from the external magnetic field intensity at the interface.

Research of New Thermoelectric Materials Based on Multicomponent Semiconductor Compounds

This paper presents the results of studies of new thermoelectric materials, obtained on the basis of multicomponent semiconductor compounds with a crystal structure of chalcopyrite and delafossite, by methods of nuclear magnetic resonance in a local field (63.65Cu NMR) and nuclear quadrupole resonance (63.65Cu NQR). The values of local magnetic fields at the location of the resonant copper nuclei and the parameters of nuclear quadrupole interactions in chalcopyrite (CuFeS2) and copper aluminate (CuAlO2) are determined. The search for new thermoelectric materials is caused by the low operating efficiency of industrial thermoelectric converters based on bismuth and lead tellurides, which have been used for half a century.

Soft magnetic FeCo films produced by green chemistry technique

The saturation magnetizations, local magnetic anisotropy field and coercivity values of FeCo film plated under various processing conditions have been investigated to optimize soft magnetic properties. Herein, we introduce a very promising processing technique based on the electrodeless deposition of FeCo film with carbohydrates as reducing agents. The produced FeCo film demonstrated significantly better saturation magnetization values and less contaminations, compared to those for the sample preparing with conventional reducing agent (sodium hypophosphite). The surface morphology and coercivities of FeCo films are dependent on the iron content and type of reducing agent. The coercive force values range from 12 up to 30 Oe and the saturation magnetization from 150 to 240 emu/g depending on the bath composition and deposition parameters. Maximum of saturation magnetization magnitude is reached for FeCo film with 30% cobalt. The local anisotropy field value of FeCo alloys increases with a decrease in Fe content for all reducing agent types.

Full-Maxwell Simulations of Very Fast Transients in GIS: Case Study to Compare 3-D and 2-D-Axisymmetric Models of 1100 kV Test Setup

Development and type testing of gas-insulated switchgear (GIS) disconnectors are supported with the simulation-based analyses of very fast transients (VFTs) that are associated with the disconnector switching operations. In order to analyze local field values in the entire GIS geometry, the full-Maxwell approach needs to be involved for simulating the VFT generation process. According to power substation layout studies, 90 ${}^{\circ }$ -angled GIS disconnectors are often used in GIS projects, since they offer most layout options and, at the same time, require the lowest number of GIS components. This implies that the test setups are asymmetric, thus the direct use of the full-Maxwell approach requires 3-D models, the application of which is considered to be highly demanding from a numerical point of view. The paper shows a comparison of the results obtained from full-Maxwell numerical simulations for a development test setup of 1100 kV GIS. The analyses are conducted for full 3-D geometry and for the corresponding 2-D-axisymmetric geometry. Example simulations of the VFT overvoltage (VFTO) waveforms are presented for both geometries, together with a comparison of the numerical effort needed for solving the associated field equations. The presented approach based on the 2-D-axisymmetric GIS model allows one to significantly reduce the numerical effort involved to support design work and development tests.

Reduced-Order Model Accounting for High-Frequency Effects in Power Electronic Components

This paper proposes a reduced-order (RO) model of power electronic components based on the proper orthogonal decomposition. Starting from a full-wave finite-element model and several snapshots (solutions at different frequencies), the RO model is constructed. Local field values (e.g., magnetic flux density, electric current density, magnetic field, or electric field) and global quantities (e.g., characteristic complex impedance and Joule losses) can be determined for the intermediate frequencies with a very low computational cost and high accuracy. Particular attention is paid to the choice of the most suitable snapshots by means of three different greedy algorithms, the performance of which is compared. We adopt an automatic greedy algorithm that depends only on the RO model.

Effect of texturing on polarization switching dynamics in ferroelectric ceramics

Highly (100),(001)-oriented (Ba0.85Ca0.15)TiO3 (BCT) lead-free piezoelectric ceramics were fabricated by the reactive templated grain growth method using a mixture of plate-like CaTiO3 and BaTiO3 particles. Piezoelectric properties of the ceramics with a high degree of texture were found to be considerably enhanced compared with the BCT ceramics with a low degree of texture. With increasing the Lotgering factor from 26% up to 94%, the piezoelectric properties develop towards the properties of a single crystal. The dynamics of polarization switching was studied over a broad time domain of 8 orders of magnitude and was found to strongly depend on the degree of orientation of the ceramics. Samples with a high degree of texture exhibited 2–3 orders of magnitude faster polarization switching, as compared with the ones with a low degree of texture. This was rationalized by means of the Inhomogeneous Field Mechanism model as a result of the narrower statistical distribution of the local electric field values in textured media, which promotes a more coherent switching process. The extracted microscopic parameters of switching revealed a decrease of the critical nucleus energy in systems with a high degree of texture providing more favorable switching conditions related to the enhanced ferroelectric properties of the textured material.

Scattered-Field Formulation for Stratified Dispersive Layers and the Near-Field Accuracy Assessment

A scattered-field formulation for finite-difference time-domain (FDTD) computation of stratified dispersive layers with a unified treatment of layers simply as any other scatterers is presented. We verified the resulting calculated local field values to the analytic solutions to assess the percentile error in the calculations. The near-field accuracy of less than 5% is achieved for an oblique incident angle at 45°.

Analytically Modeling the Asymmetric Double Gate Tunnel FET

This paper proposes an analytical model for the asymmetric double-gate (ADG) TFET operation. Two-dimensional Poisson equation is solved based on the depletion approximation [1,2]. The two-dimensional potential function is given by appropriate boundary conditions. Internal electric field is calculated from the potential model and tunnel current is numerically calculated using the Kane’s tunnel current generation model [3,4]. We used the commercial TCAD simulator in order to examine the analytical model [5]. Schematic of ADG-TFET device structure is shown in Fig. 1. It is assumed that p-type source and n-type drain regions are highly doped. Channel region is a p-type with the doping level of Na . tox denotes the gate oxide thickness and tsi denotes the semiconductor film thickness. Hereafter, we call the top gate “front gate” and the bottom gate “back gate”. Potential profile of the channel region is derived from the following two-dimensional Poisson equation based on the depletion approximation. Equation (1) where q denotes the elemental charge and εsi denotes the permittivity of semiconductor. Here, we assume the following potential function with the cubic function of coordinate y [1]. Equation (2) where four factors a(x), b(x), c(x), and d(x) are functions of coordinate x. We introduce the following boundary conditions for the potential in solving eq. (1). Equation (3) where ψf(x) and ψb(x) stand for front and back surface potentials at y=0 and y=t si, respectively. Vfg,fb and Vbg,fb are the front-gate and the back-gate flat-band voltages, respectively. Vfg and Vbg are the front- and back-gate voltages, respectively. εox is the permittivity of gate insulator. Drain current of ADG TFET is numerically calculated by integrating carriers tunneling from the valence band of the source region to the conduction band of the channel region. We can calculate the drain current (IDS ) using the carrier generation rate (G) due to the band-to-band tunnel process. Equation (4) where we use the Kane’s model for the carrier generation rate (G) [3,4]. Equation (5) where |E| (=(Ex 2+Ey 2)1/2 ) is the electric field strength, A and B are constants given byEquation (Si) Equation (Ge) We perform the TCAD simulation [5] in order to examine the validity of the analytical model. In device simulations for Si-based TFETs, we assume the gate material with the work function of 4.1 eV for the front- and the back-gate electrodes. Figure 2 shows the calculated potential profiles at y=0nm, 2.5nm, and 5.0nm for tsi =10nm. Using the potential function revealed in Fig. 2, local electric field values are calculated along with the x direction and the y direction separately. The potential function analytically given and resulting electric fields successfully reproduced those given by TCAD simulations (not shown here). We found a slight difference of potential profile near the surface around the source junction for a relatively low-doping source region because of the depletion in the source region [6]. We also calculated drain current characteristics. Figure 3 demonstrates ID-Vfg characteristics for tsi =10nm and 20nm, where the condition of Lg >2ts is satisfied. In Fig. 5, the model basically reproduces the TCAD result. On the other hand, the model doesn’t well reproduce TCAD-based ID-Vgf characteristics for tsi =30nm and 100nm (not shown here), where Lg <2tsi . This difference stems from the linear approximation of the in-depth electric field in the model. As the condition of Lg >2tsi is important in the future, this is not a crucial issue of the model. In addition, we confirmed the model proposed here is available for Ge-based TFET (not shown here).

Downscaling at submicrometer scale of the gap width of interdigitated Ba0.5Sr0.5TiO3 capacitors.

The goal of this work was to study the influence of shrinking the gap width between the fingers of interdigitated tunable capacitors (IDCs). Voltage control of the capacitance was achieved with a 500-nm-thick Ba0.5Sr0.5TiO3 film which is in paraelectric state at room temperature. Eight devices with finger spacing ranging from 3 μm down to 0.25 μm were fabricated by the sol-gel deposition technique, electron beam patterning, and gold evaporation. The equivalent capacitance, quality factor, and tunability of the devices were measured subsequently by vector network analysis from 40 MHz to 40 GHz and for a dc bias voltage varying from -30 V to +30 V. This experimental study mainly shows that a decrease of the gap below 1 μm 1) introduces a frequency dependence of the capacitance caused by resonance effects with the finger inductance; 2) degrades the quality factor above 20 GHz, and 3) optimizes the tunability of the devices by enhancing the local electric field values. As a consequence, some trade-offs are pointed out related to the goal of ultra-thin ferroelectric film which can be voltage controlled by means of finger-shaped electrodes with deep submicrometer spacing.

Criteria for the evaluation of the technical state of the long-lived metal of HPP equipment based on acoustic structuroscopy

The criteria for the maintenance evaluation of long-lived metal of the equipment of heat power plants during the acoustic structuroscopy of weld joints of vapor pipelines and boiler drums are described. The data on the change of the structural state of metal during long-term operation of heat-resistant steels are given. The dependences of the criteria versus the values of local fields of internal stresses of a crystal lattice are given. The relationship between the integrated criterion and the durability of heat-resistant steels is presented.

Additional electromagnetic waves in a uniaxial crystal with anisotropy fluctuations

It has been shown that the inclusion of orientational fluctuations of the axes of nonpolar axially symmetric molecules leads to a spatial dispersion of the permittivity of a uniaxial crystal. Expressions for the local field, polarization, and principal values of the permittivity tensor of the crystal have been derived. An estimate has been made of the wavelength above which the contribution to the spatial dispersion of orientational fluctuations of the molecular axes dominates. The phase velocities of the ordinary and extraordinary electromagnetic waves in a uniaxial crystal have been determined. It has been demonstrated that additional slow extraordinary electromagnetic waves can exist near the zeros of the principal values of the permittivity tensor of the crystal in particular ranges of angles between the wave vector and the optic axis of the crystal.

Generalized mean field approximation for parallel dynamics of the Ising model

.The dynamics of the non-equilibrium Ising model with parallel updates is investigated using a generalized mean field approximation that incorporates multiple two-site correlations at any two time steps, which can be obtained recursively. The proposed method shows significant improvement in predicting local system properties compared to other mean field approximation techniques, particularly in systems with symmetric interactions. Results are also evaluated against those obtained from Monte Carlo simulations. The method is also employed to obtain parameter values for the kinetic inverse Ising modeling problem, where couplings and local field values of a fully connected spin system are inferred from data.

Step scaling and the Yang-Mills gradient flow

The use of the Yang-Mills gradient flow in step-scaling studies of lattice QCD is expected to lead to results of unprecedented precision. Step scaling is usually based on the Schr\"odinger functional, where time ranges over an interval [0,T] and all fields satisfy Dirichlet boundary conditions at time 0 and T. In these calculations, potentially important sources of systematic errors are boundary lattice effects and the infamous topology-freezing problem. The latter is here shown to be absent if Neumann instead of Dirichlet boundary conditions are imposed on the gauge field at time 0. Moreover, the expectation values of gauge-invariant local fields at positive flow time (and of other well localized observables) that reside in the center of the space-time volume are found to be largely insensitive to the boundary lattice effects.

Impedance analysis and tunability of BaTiO3–chitosan composites: Towards active dielectrics for flexible electronics

Composite thick films BaTiO3–chitosan with different BaTiO3 additions (1% and 10%) were prepared. The electric response was investigated by Impedance Spectroscopy technique in terms of equivalent electric circuits. The dielectric non-linear properties (tunability) showed a remarkable increase with increasing the BaTiO3 addition by comparison with pure chitosan. The presence of ferroelectric particles into the chitosan matrix plays a twofold role resulting in increasing tunability: (i) increase the values of local fields in the polymer matrix by local field engineering, (ii) contribute with its own tunability to increase the field-variation of the effective permittivity. The present results show a simple approach for generating tunable flexible structures.

Infinite-time average of local fields in an integrable quantum field theory after a quantum quench.

The infinite-time average of the expectation values of local fields of any interacting quantum theory after a global quench process are key quantities for matching theoretical and experimental results. For quantum integrable field theories, we show that they can be obtained by an ensemble average that employs a particular limit of the form factors of local fields and quantities extracted by the generalized Bethe ansatz.

On one-point functions for sinh-Gordon model at finite temperature

Using fermionic basis we conjecture the exact formulae for the expectation values of local fields in sinh-Gordon model. The conjecture is checked against previously known results.

Direct simulation of extinction in a slab of spherical particles

The exact multiple sphere superposition method is used to calculate the coherent and incoherent contributions to the ensemble-averaged electric field amplitude and Poynting vector in systems of randomly positioned nonabsorbing spherical particles. The target systems consist of cylindrical volumes, with radius several times larger than length, containing spheres with positional configurations generated by a Monte Carlo sampling method. Spatially dependent values for coherent electric field amplitude, coherent energy flux, and diffuse energy flux, are calculated by averaging of exact local field and flux values over multiple configurations and over spatially independent directions for fixed target geometry, sphere properties, and sphere volume fraction. Our results reveal exponential attenuation of the coherent field and the coherent energy flux inside the particulate layer and thereby further corroborate the general methodology of the microphysical radiative transfer theory. An effective medium model based on plane wave transmission and reflection by a plane layer is used to model the dependence of the coherent electric field on particle packing density. The effective attenuation coefficient of the random medium, computed from the direct simulations, is found to agree closely with effective medium theories and with measurements. In addition, the simulation results reveal the presence of a counter-propagating component to the coherent field, which arises due to the internal reflection of the main coherent field component by the target boundary. The characteristics of the diffuse flux are compared to, and found to be consistent with, a model based on the diffusion approximation of the radiative transfer theory.