Null Field Research Articles

The null and force-free electromagnetic field

This paper describes the electrodynamics of a null and force-free field in completely geometric terms. As was previously established in Menon (2020 Class. Quantum Grav. 37 245006), solutions to force-free electrodynamics are governed by the existence of certain special types of foliations of spacetime. Here the nature of the foliations in a coordinate-free formalism in the null case is prescribed. All of the general results are illustrated by constructing a new null, force-free electrodynamic field in a Friedmann–Lemaitre–Robertson–Walker spacetime.

The Geomagnetic Field (GMF) Modulates Nutrient Status and Lipid Metabolism during Arabidopsis thaliana Plant Development.

The Geomagnetic field (GMF) is a typical component of our planet. Plant perception of the GMF implies that any magnetic field (MF) variation would induce possible metabolic changes. In this work was we assessed the role of the GMF on Arabidopsis thaliana Col0 mineral nutrition and lipid metabolism during plant development. We reduced the local GMF (about 40 μT) to Near Null Magnetic Field (NNMF, about 30 nT) to evaluate the effects of GMF on Arabidopsis in a time-course (from rosette to seed-set) experiment by studying the lipid content (fatty acids, FA; and surface alkanes, SA) and mineral nutrients. The expression of selected genes involved in lipid metabolism was assessed by Real-Time PCR (qPCR). A progressive increase of SA with carbon numbers between 21 and 28 was found in plants exposed to NNMF from bolting to flowering developmental stages, whereas the content of some FA significantly (p < 0.05) increased in rosette, bolting and seed-set developmental stages. Variations in SA composition were correlated to the differential expression of several Arabidopsis 3-ketoacyl-CoAsynthase (KCS) genes, including KCS1, KCS5, KCS6, KCS8, and KCS12, a lipid transfer protein (LTPG1) and a lipase (LIP1). Ionomic analysis showed a significant variation in some micronutrients (Fe, Co, Mn and Ni) and macronutrients (Mg, K and Ca) during plant development of plants exposed to NNMF. The results of this work show that A. thaliana responds to variations of the GMF which are perceived as is typical of abiotic stress responses.

Liquid argon scintillation response to electronic recoils between 2.8–1275 keV in a high light yield single-phase detector

We measure the liquid argon scintillation response to electronic recoils in the energy range of $2.82$ to $1274.6~{\rm keV}$ at null electric field. The single-phase detector with a large optical coverage used in this measurement yields $12.8 \pm 0.3 ~ (11.2 \pm 0.3)~{\rm photoelectron/keV}$ for $511.0$-${\rm keV}$ $\gamma$-ray events based on a photomultiplier tube single photoelectron response modeling with a Gaussian plus an additional exponential term (with only a Gaussian term). It is exposed to a variety of calibration sources such as $^{22}{\rm Na}$ and $^{241}{\rm Am}$ $\gamma$-ray emitters, and a $^{252}{\rm Cf}$ fast neutron emitter that induces quasimonoenergetic $\gamma$ rays through a $(n, n'\gamma)$ reaction with $^{19}{\rm F}$ in polytetrafluoroethylene. In addition, the high light detection efficiency of the detector enables identification of the $2.82$-${\rm keV}$ peak of $^{37}{\rm Ar}$, a cosmogenic isotope in atmospheric argon. The observed light yield and energy resolution of the detector are obtained by the full-absorption peaks. We find up to approximately $25\%$ shift in the scintillation yield across the energy range and $3\%$ of the energy resolution for the $511.0$-${\rm keV}$ line. The Thomas-Imel box model with its constant parameter $\varsigma=0.033 ^{+0.012} _{-0.008}$ is found to explain the result. For liquid argon, this is the first measurement on the energy-dependent scintillation yield down to a few ${\rm keV}$ at null field and provides essential inputs for tuning the argon response model to be used for physics experiments.

Kundt spacetimes in the Einstein-Gauss-Bonnet theory

We systematically investigate the complete class of vacuum solutions in the Einstein-Gauss-Bonnet gravity theory which belong to the Kundt family of non-expanding, shear-free and twist-free geometries (without gyratonic matter terms) in any dimension. The field equations are explicitly derived and simplified, and their solutions classified into three distinct subfamilies. Algebraic structures of the Weyl and Ricci curvature tensors are determined. The corresponding curvature scalars directly enter the invariant form of equation of geodesic deviation, enabling us to understand the specific local physical properties of the gravitational field constrained by the EGB theory. We also present and analyze several interesting explicit classes of such vacuum solutions, namely the Ricci type III spacetimes, all geometries with constant-curvature transverse space, and the whole pp-wave class admitting a covariantly constant null vector field. These exact Kundt EGB gravitational waves exhibit new features which are not possible in Einstein's general relativity.

Moving away from the near-horizon attractor of the extreme Kerr force-free magnetosphere

We consider force-free magnetospheres around the extreme Kerr black hole. In this case there is no known exact analytic solution to force free electrodynamics which is stationary, axisymmetric and magnetically-dominated. However, any stationary, axisymmetric and regular force-free magnetosphere in extreme Kerr black hole approaches the same attractor solution in the near-horizon extreme Kerr (NHEK) limit with null electromagnetic field. We show that by moving away from the attractor solution in the NHEK region, one finds magnetically-dominated solutions in the extreme Kerr black hole with finite angular momentum outflow. This result is achieved using a perturbative analysis up to the second order.

THREE-DIMENSIONAL NUMERICAL SIMULATION OF A VERTICAL THERMAL TANK

In this study, the results obtained by the numerical simulation presented in this paper are compared with the results obtained experimentally by Oliveski (2000) for a vertical cylindrical thermal reservoir with internal diameter of 0.42m and internal height of 0.57m (79L). In the simulation using Ansys software, for the same parameters of the problem, a study to evaluate the degree of mesh refinement was performed based on the methodology used by Adolfo (2015). The boundary conditions adopted were: Flow: Transient; Buoyancy Model: Boussinesq Approximation; Step of time used: 1s; Wall Condition: Top Non slip / adiabatic; Base: h = 06 [Wm ^ 2 / K]; Lateral: h = 10 [Wm ^ 2 / K]; Initial tank conditions: Null velocity field and initial temperature of approximately 355.15 K. Total simulated flow time: 18,000 s. For the external temperature, contour condition used in the simulation, the ambient temperature was used as a function of time through the graph provided by Oliveski. Three meshes were compared based on the methodology used by Adolfo (2015) in his studies. These have 1,512,143 and 7,997,663, 851,837 and 4,379,079, 271,898 and 1,308,368, number of nodes and elements, respectively. For the turbulence model adopted, the SST (Shear Stress Transport) model was used. The simulations took approximately 58 days to complete. The residue sought in the iterations was at least 0.001, with a maximum of 100 iterations for each time step. For the behavior of the temperature field in the tank over time the formation of the stratified temperature profile was observed, as described in Oliveski's work, and also that the thermal stratification occurs only in the lower region and that in the upper region the water becomes temperature is almost constant. In terms of mean temperature in the tank, the simulation is very close to the results shown by Savicki (2007). However, in terms of temperature profile along the height of the tank, this behavior is shown to be different. Another fact is that the height of the thermocline found in this simulation was considerably higher than that shown in the Savicki simulation. Therefore, the results obtained were validated with the experimental results presented by Oliveski and the numerical results presented by Savicki. It has been confirmed that the mesh with the second refinement level is already sufficiently capable of generating satisfactory results.

Effect of null aether field on weak deflection angle of black holes

We study light rays in the static and spherically symmetric gravitational field of the null aether theory (NAT). To this end, we employ the Gauss-Bonnet theorem to compute the deflection angle formed by a NAT black hole in the weak limit approximation. Using the optical metrics of the NAT black hole, we first obtain the Gaussian curvature and then calculate the leading terms of the deflection angle. Our calculations indicate how gravitational lensing is affected by the NAT field. We also illustrate that the bending of light stems from global and topological effects.

Studies of structural and electrical properties of lead-free ceramic: Bi(Ba0.25Ti0.25Fe0.5)O3

Bismuth barium ferric titanate Bi(Ba0.25Ti0.25Fe0.5)O3 has been fabricated through a conventional solid-state reaction route. By means of various experimental techniques, the material has been characterized in different experimental conditions. Study of crystal structure using X-ray diffraction data determines the tetragonal system. The detailed studies of dielectric, impedance, conductivity of Bi(Ba0.25Ti 0.25Fe0.5)O3 in a broad range of temperature (25 – 380°C) and frequency (1kHz –1MHz) have provided a range of exciting results on structure and correlation properties, conduction mechanism, etc. The existence of ferroelectricity in the material is confirmed by the polarization-electric field loop analysis. At low-frequencies and high- temperatures, space charge polarization and the Maxwell–Wagner dielectric relaxation have been observed. The grain and grain boundary effects in the ceramic sample have been studied from the Nyquist plots. The study of temperature-frequency dependence of transport properties (conductivity) of the specimen has established type of conduction mechanism in it. The coefficient of magneto-electric coupling of the studied sample is found to be 3.79 mV cm−1Oe−1 at null magnetic field.

Contact metric three manifolds and Lorentzian geometry with torsion in six-dimensional supergravity

We introduce the notion of εη-Einstein ε-contact metric three-manifold, which includes as particular cases η-Einstein Riemannian and Lorentzian (para) contact metric three-manifolds, but which in addition allows for the Reeb vector field to be null. We prove that the product of an εη-Einstein Lorentzian ε-contact metric three-manifold with an εη-Einstein Riemannian contact metric three-manifold carries a bi-parametric family of Ricci-flat Lorentzian metric-compatible connections with isotropic, totally skew-symmetric, closed and co-closed torsion, which in turn yields a bi-parametric family of solutions of six-dimensional minimal supergravity coupled to a tensor multiplet. This result allows for the systematic construction of families of Lorentzian solutions of six-dimensional supergravity from pairs of εη-Einstein contact metric three-manifolds. We classify all left-invariant εη-Einstein structures on simply connected Lie groups, paying special attention to the case in which the Reeb vector field is null. In particular, we show that the Sasaki and K-contact notions extend to ε-contact structures with null Reeb vector field but are however not equivalent conditions, in contrast to the situation occurring when the Reeb vector field is not light-like. Furthermore, we pose the Cauchy initial-value problem of an ε-contact εη-Einstein structure, briefly studying the associated constraint equations in a particularly simple decoupling limit. Altogether, we use these results to obtain novel families of six-dimensional supergravity solutions, some of which can be interpreted as continuous deformations of the maximally supersymmetric solution on Sl˜(2,R)×S3.

Homogeneous fields: Double expansion method, 3D printing/CNC realization, and verification by atomic magnetometry

In low-field magnetic resonance applications there is often an interest in creating homogeneous magnetic fields over unusual geometries, particularly when quantum magnetometers are involved. In this paper a design method is proposed, where both the surface current and magnetic field are expanded to find current coefficients that cancel out higher order field terms. Two coils are designed using this double expansion methodology: (1) a tuning field for a half-meter-long atomic magnetometer array and (2) a null field for a magnetometer to operate adjacent to an excitation solenoid. The field verification of the former shows the accuracy of CNC milling and the method proposed; a close analysis of the field signature in the latter revealed the limitations of 3D printing for precise scientific applications. Both coils are designed to be fifth-order error systems or better.

The Geomagnetic Field Is a Contributing Factor for an Efficient Iron Uptake in Arabidopsis thaliana.

The Earth’s magnetic field, defined as the geomagnetic field (GMF), is an unavoidable environmental factor for all living organisms. Variation in the GMF intensity was found to affect the content of some nutrients and their associated channels and transporters in Arabidopsis thaliana. In this work, we observed that reduction of the GMF to near null magnetic field (NNMF) affects the accumulation of metals in plant tissues, mainly iron (Fe) and zinc (Zn) content, while the content of others metals such as copper (Cu) and manganese (Mn) is not affected. Accordingly, Fe uptake genes were induced in the roots of NNMF-exposed plants and the root Fe reductase activity was affected by transferring GMF-exposed plant to NNMF condition. Under Fe deficiency, NNMF-exposed plants displayed a limitation in the activation of Fe-deficiency induced genes. Such an effect was associated with the strong accumulation of Zn and Cu observed under NNMF conditions. Overall, our results provide evidence on the important role of the GMF on the iron uptake efficiency of plants.

Modeling the fringe field of permanent magnet multipoles using numerical simulations.

Permanent magnet multipoles (PMMs) are widely used in accelerators to either focus particle beams or confine plasma in ion sources. The real magnetic field created by PMMs is calculated by magnetic field simulation software and then used in particle tracking codes by means of a three dimensional magnetic field map. A common alternative is to use the so-called "hard-edge" model, which gives an approximation of the magnetic field inside the PMM assuming a null fringe field. This work proposes an investigation of the PMM fringe field properties. An analytical model of the PMM magnetic field is developed using the Fourier multipole expansion. A general axial potential function with a unique parameter λ, able to reproduce the actual PMM magnetic field (including its two fringe fields) with an explicit dependence on the PMM length, is proposed. An analytical first order model including the axial fringe field is derived. This simple model complies with the Maxwell equations [curl(B) = 0 and div(B) = 0] and can replace advantageously the "hard-edge" model when fast analytical calculations are required. The higher order analytical multiple expansion model quality is assessed by means of χ2 estimators. The general dependence of the potential function parameter λ is given as a function of the PMM geometry for quadrupole, hexapole, and multipole, allowing one to use the developed model in simulation programs where the multipole geometry is an input parameter.

On rational electromagnetic fields

We employ a recently developed method for constructing rational electromagnetic field configurations in Minkowski space to investigate several properties of these source-free finite-action Maxwell (“knot”) solutions. The construction takes place on the Penrose diagram but uses features of de Sitter space, in particular its isometry group. This admits a classification of all knot solutions in terms of S3 harmonics, labeled by a spin 2j∈N0, which in fact provides a complete “knot basis” of finite-action Maxwell fields. We display a j=1 example, compute the energy for arbitrary spin-j configurations, derive a linear relation between spin and helicity and characterize the subspace of null fields. Finally, we present an expression for the electromagnetic flux at null infinity and demonstrate its equality with the total energy.

The surface wave phenomenon on an impedance half-plane

The excitation of surface waves on an impedance half–plane is investigated by considering the complex integral of scattering. The poles of the split function are examined with respect to some criteria, obtained from an inhomogeneous plane wave. It is shown that two poles of the complex integral lead to null fields. The surface wave expressions were derived according to the remaining two poles. The diffraction of the surface waves at the edge discontinuity of the half-plane is studied by using the theory, developed for grazing incidence. The uniform representation of the diffracted field is performed according to the uniform theory for evanescent waves. The behaviors of the obtained field expressions were examined numerically.

Measurement of the scintillation efficiency for low energy nuclear- and electronic-recoils in liquid argon detector for WIMP search

A liquid argon (LAr) scintillation detector is known to offer several attractive features to search for WIMP dark matter. A key quantity in this search is the conversion efficiencies of nuclear- and electronic-recoils (NR and ER) energy deposition into the scintillation signal. Two measurements are performed to study these properties: (1) scintillation efficiency for a few tens of keV NR under electric fields up to 3 kV/cm; (2) efficiency for ER ranging from a few keV to 1 MeV at null field. We present the results of these measurements and discuss the LAr response based on traditional models.

Rigging Technique for 1-Lightlike Submanifolds and Preferred Rigged Connections

We extend the rigging technique to null submanifolds of a Lorentzian manifold, which allows us to construct two connections: the induced connection and the rigged connection. We study the relationship between them after changing the rigging and the existence and uniqueness of a preferred rigged connection, i.e., a rigged connection which coincides with the induced connection. As an application, we derive some integral formulas for compact null hypersurfaces with a preferred rigged connection and we obtain some consequences. For instance, we show that if the null mean curvature is zero, then the transverse null mean curvature vector field is orthogonal to any Killing vector field at some point.

Design and Validation of the Invariant Imbedded T-Matrix Scattering Model for Atmospheric Particles with Arbitrary Shapes

Light scattering by non-spherical particles is an important factor influencing atmospheric radiative transfer. To accurately simulate the scattering properties of non-spherical particles, the Invariant Imbedded T-matrix method (IIM T-Matrix) is developed by combining the Lorenz–Mie theory and invariant imbedding technique. In this model, the non-spherical particle is regarded as an inhomogeneous sphere and discretized into multiple spherical layers in the spherical coordinate system. The T-matrix of the inscribed sphere is firstly calculated by the Lorenz–Mie theory, and then taking it as the initial value, the T-matrix is updated layer by layer by using the invariant imbedding technique. To improve the computational efficiency, the model is further parallelized by the OpenMP technique. To verify the simulation accuracy of the IIM T-Matrix method, the results of the model are compared with those of the EBCM (Extended Boundary Condition Method) T-Matrix method, DDA (Discrete Dipole Approximation) and MRTD (Multi-Resolution Time Domain). The results show that the scattering phase matrix simulated by the IIM T-Matrix method closely agrees with that of the well-tested models, indicating that the IIM T-Matrix method is a powerful tool for the light scattering simulation of non-spherical particles. Since the IIM T-Matrix method is derived from the volume integral equation, compared to the T-Matrix method which is based on surface integral principles (i.e., “EBCM” or the “null field method”), it can be applied to the scattering calculations of particle with arbitrary shapes and inhomogeneous compositions, which can greatly expand the application scope of the T-Matrix method.

Influence of microwave photo-excitation on the transport properties of the high mobility GaAs/AlGaAs 2D electron system

ABSTRACTWe examined the influence of the microwave power on the diagonal resistance in the GaAs/AlGaAs two dimensional electron system (2DES), in order to extract the electron temperature and determine microwave induced heating as a function of the microwave power. The study shows that microwaves produce a small discernable increase in the electron temperature both at null magnetic field and at finite magnetic fields in the GaAs/AlGaAs 2DES. The heating effect at null field appears greater in comparison to the examined finite field interval, although the increase in the electron temperature in the zero-field limit appears smaller than theoretical predictions.

Principal configurations around umbilics of spacelike surfaces in null hypersurfaces of [formula omitted

We study the principal configurations around an isolated η-umbilical point on a generic spacelike surface S immersed in a null hypersurface M of Minkowski space R14 relative to a well-defined null vector field η orthogonal to the surface S. In the particular case of M being a null rotation hypersurface of R14 we also recover the local Darbouxian principal configurations around that kind of η-umbilical points.

Integral equation‐based nonoverlapping domain decomposition method for electromagnetic scattering analysis of PEC targets in half‐space environment

AbstractAn integral equation‐based nonoverlapping domain decomposition method (IE‐NDDM) is proposed for efficient and accurate scattering analysis of electrically large PEC targets in a half‐space environment. Taking the condition that there are null fields as well as current inside PEC objects in the original problem, a novel explicit transmission condition is proposed to ensure continuity of electric currents between adjacent subdomains. Moreover, to deal with this situation that targets located in half‐space environment, the stratified‐medium dyadic Green's function is adopted. Numerical examples are provided to demonstrate the correctness and the performance of the proposed method. In detail, an analysis about electromagnetic scattering respect to the altitude of the target away from half‐space interface, the incident direction of plane wave, and the material parameters of the lower half‐space is presented; furthermore, the convergence behavior of the proposed method is studied.