Magnetic Field Oscillations Research Articles

Local deformation in a hydrogel induced by an external magnetic field

The aim of this study is to prove the feasibility of a system able to apply local mechanical loading on cells seeded in a hydrogel for tissue engineering applications. This experimental study is based on a previously developed artificial cartilage model with different concentrations of poly(vinyl alcohol) (PVA) that simulates the cartilage extracellular matrix (ECM). Poly(l-lactic acid) (PLLA) microspheres with dispersed magnetic nanoparticles (MNPs) were produced with an emulsion method. These microspheres were embedded in aqueous PVA solutions with varying concentration to resemble increased viscosity of growing tissue during regeneration. The ability to induce a local deformation in the ECM was assessed by applying a steady or an oscillatory magnetic field gradient to different PVA solutions containing the magnetic microparticles, similarly as in ferrogels. PLLA microparticle motion was recorded, and the images were analyzed. Besides, PVA gels and PLLA microparticles were introduced into the pores of a polycaprolactone scaffold, and the microparticle distribution and the mechanical properties of the construct were evaluated. The results of this experimental model show that the dispersion of PLLA microparticles containing MNPs, together with cells in a supporting gel, will allow applying local mechanical stimuli to cells during tissue regeneration. This local stimulation can have a positive effect on the differentiation of seeded cells and improve tissue regeneration.

Exploiting the magnetoelectric effect in piezoelectric/conductor composites for sensing static magnetic fields

ABSTRACTIn this work, static magnetic field sensors based on the interaction between the Lorentz force and the direct piezoelectric effect were developed and characterized. The major components of these solid-state sensors are a piezoelectric/conductor laminar composite, formed by a PZT-5A ferroelectric ceramic disk placed between two thin conductive silver layers, and a single coil to generate a controllable oscillatory magnetic field. Design parameters, such as the length and number of turns of the coil, were investigated, and a spatial field resolution of 0.24 Oe/mm was typically observed.

Adiabatic Edge Channel Transport in a Nanowire Quantum Point Contact Register.

We report on a prototype device geometry where a number of quantum point contacts are connected in series in a single quasi-ballistic InAs nanowire. At finite magnetic field the backscattering length is increased up to the micron-scale and the quantum point contacts are connected adiabatically. Hence, several input gates can control the outcome of a ballistic logic operation. The absence of backscattering is explained in terms of selective population of spatially separated edge channels. Evidence is provided by regular Aharonov-Bohm-type conductance oscillations in transverse magnetic fields, in agreement with magnetoconductance calculations. The observation of the Shubnikov-de Haas effect at large magnetic fields corroborates the existence of spatially separated edge channels and provides a new means for nanowire characterization.

Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions

We study the Josephson current in long ballistic superconductor-monolayer graphene-superconductor junctions. As a first step, we have developed an efficient computational approach to calculate the Josephson current in tight-binding systems. This approach can be particularly useful in the long-junction limit, which has hitherto attracted less theoretical interest but has recently become experimentally relevant. We use this computational approach to study the dependence of the critical current on the junction geometry, doping level, and an applied perpendicular magnetic field $B$. In zero magnetic field we find a good qualitative agreement with the recent experiment of M. Ben Shalom et al. [Nat. Phys. 12, 318 (2016)] for the length dependence of the critical current. For highly doped samples our numerical calculations show a broad agreement with the results of the quasiclassical formalism. In this case the critical current exhibits Fraunhofer-like oscillations as a function of $B$. However, for lower doping levels, where the cyclotron orbit becomes comparable to the characteristic geometrical length scales of the system, deviations from the results of the quasiclassical formalism appear. We argue that due to the exceptional tunability and long mean free path of graphene systems a new regime can be explored where geometrical and dynamical effects are equally important to understand the magnetic field dependence of the critical current.

Onsager rule, quantum oscillation frequencies, and the density of states in the mixed-vortex state of cuprates

The Onsager rule determines the frequencies of quantum oscillations in magnetic fields. We show that this rule remains intact to an excellent approximation in the mixed-vortex state of the underdoped cuprates even though the Landau level index $n$ may be fairly low, $n\sim 10$. The models we consider are fairly general, consisting of a variety of density wave states combined with $d$-wave superconductivity within a mean field theory. Vortices are introduced as quenched disorder and averaged over many realizations, which can be considered as snapshots of a vortex liquid state. We also show that the oscillations ride on top of a field independent density of states, $\rho(B)$, for higher fields. This feature appears to be consistent with recent specific heat measurements [C. Marcenat, et al. Nature Comm. {\bf 6}, 7927 (2015)]. At lower fields we model the system as an ordered vortex lattice, and show that its density of states follows a dependence $\rho(B)\propto \sqrt{B}$ in agreement with the semiclassical results [G. E. Volovik, JETP Lett. {\bf 58}, 469 (1993)].

Triboelectric motion sensor combined with electromagnetic induction energy harvester

We investigate the possibility of combining electromagnetic induction and triboelectricity for creating a low-friction floating magnet-based sensor system to detect motion and harvest energy from small vibrations or oscillatory magnetic fields. We designed a system with low friction such that the energy harvester based on electromagnetic induction is not influenced by the triboelectric transduction mechanism. An enclosed system combining a triboelectric and electromagnetic mechanism which responds to vibrations or changes in magnetic fields was designed. The system comprises an aluminum-covered magnet placed inside a tube covered by metallized fluorinated ethylene propylene. The sliding action between the metal and the polymer causes triboelectric charging. The magnet acts as a carrier for the aluminum surface, but is also used to induce a voltage in a copper coil, thus allowing one to detect the same mechanical motion utilizing two different technological principles. The main advantage of our design is an enhanced sensing mechanism based on the triboelectrical signal that does not require one to interpret the complicated electromagnetically induced signal that may occur for complex magnet geometries.

Quantum simulations of nuclei and nuclear pasta with the multiresolution adaptive numerical environment for scientific simulations

Neutron star and supernova matter at densities just below the nuclear matter saturation density is expected to form a lattice of exotic shapes. These so-called nuclear pasta phases are caused by Coulomb frustration. Their elastic and transport properties are believed to play an important role for thermal and magnetic field evolution, rotation and oscillation of neutron stars. Furthermore, they can impact neutrino opacities in core-collapse supernovae. In this work, we present proof-of-principle 3D Skyrme Hartree-Fock (SHF) simulations of nuclear pasta with the Multi-resolution ADaptive Numerical Environment for Scientific Simulations (MADNESS). We perform benchmark studies of $^{16} \mathrm{O}$, $^{208} \mathrm{Pb}$ and $^{238} \mathrm{U}$ nuclear ground states and calculate binding energies via 3D SHF simulations. Results are compared with experimentally measured binding energies as well as with theoretically predicted values from an established SHF code. The nuclear pasta simulation is initialized in the so-called waffle geometry as obtained by the Indiana University Molecular Dynamics (IUMD) code. The size of the unit cell is 24\:fm with an average density of about $\rho = 0.05 \:\mathrm{fm}^{-3}$, proton fraction of $Y_p = 0.3$ and temperature of $T=0\:$MeV. Our calculations reproduce the binding energies and shapes of light and heavy nuclei with different geometries. For the pasta simulation, we find that the final geometry is very similar to the initial waffle state. In the present pasta calculations spin-orbit forces are not included but will be added in the future. Within the MADNESS framework, we can successfully perform calculations of inhomogeneous nuclear matter. By using pasta configurations from IUMD it is possible to explore different geometries and test the impact of self-consistent calculations on the latter.

Observations of ULF waves on the ground and ionospheric Doppler shifts during storm sudden commencement

AbstractUsing data from ground‐based magnetometers and HF Doppler sounder, we study ultralow frequency (ULF) waves excited during the storm sudden commencement (SSC) on 8 March 2012 and find possible evidence on the link between ULF waves and ionospheric Doppler shifts. Pc1–Pc2 ULF waves are observed from 11:04 to 11:27 UT after the SSC by ground stations of L shell ranging from 1.06 to 2.31, mapping to the topside ionosphere. There are weak responses in this frequency range in the power spectra of ionospheric Doppler shift. From 11:19 to 11:23 UT, oscillations of magnetic field in a lower frequency range of Pc3–Pc4 are observed and are well correlated with the trace of Doppler shift. It is thus suggested that ionospheric Doppler shift can response to ULF oscillations in magnetic field in various frequency ranges, especially in the frequency range of Pc3–Pc4 and below. This paper demonstrates a new mechanism of magnetosphere‐ionosphere coupling.

Middle‐ and low‐latitude ionosphere response to 2015 St. Patrick's Day geomagnetic storm

AbstractThis paper presents a study of the St Patrick's Day storm of 2015, with its ionospheric response at middle and low latitudes. The effects of the storm in each longitudinal sector (Asian, African, American, and Pacific) are characterized using global and regional electron content. At the beginning of the storm, one or two ionospheric positive storm effects are observed depending on the longitudinal zones. After the main phase of the storm, a strong decrease in ionization is observed at all longitudes, lasting several days. The American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed. At low latitudes, using spectral analysis, we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field (PPEF) and of the disturbance dynamo electric field (DDEF) on the basis of ground magnetic data. Concerning the PPEF, Earth's magnetic field oscillations occur simultaneously in the Asian, African, and American sectors, during southward magnetization of the Bz component of the interplanetary magnetic field. Concerning the DDEF, diurnal magnetic oscillations in the horizontal component H of the Earth's magnetic field exhibit a behavior that is opposed to the regular one. These diurnal oscillations are recognized to last several days in all longitudinal sectors. The observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models.

Understanding the residual patterns of timing solutions of radio pulsars with a model of magnetic field oscillation

We explain some phenomena existing generally in the timing residuals: amplitude and sign of the second derivative of a pulsar's spin-frequency ($\ddot\nu$), some sophisticated residual patterns, which also change with the time span of data segments. The sample is taken from Hobbs et al.\,(2010), in which the pulsar's spin-frequency and its first derivative have been subtracted from the timing solution fitting. We first classify the timing residual patterns into different types based on the sign of $\ddot\nu$. Then we use the magnetic field oscillation model developed in our group \citep{zhang12a} to fit successfully the different kinds of timing residuals with the Markov Chain Monte Carlo method. Finally, we simulate the spin evolution over 20 years for a pulsar with typical parameters and analyze the data with the conventional timing solution fitting. By choosing different segments of the simulated data, we find that most of the observed residual patterns can be reproduced successfully. This is the first time that the observed residual patterns are fitted by a model and reproduced by simulations with very few parameters. From the distribution of the different residual patterns in the $P-\dot P$ diagram, we argue that (1) a single magnetic field oscillation mode exists commonly in all pulsars throughout their lifetimes; (2) there may be a transition period over the lifetimes of pulsars, in which multiple magnetic field oscillation modes exist.

Planetary period oscillations in Saturn's magnetosphere: Further comments on the relationship between post-equinox properties deduced from magnetic field and Saturn kilometric radiation measurements

We discuss the planetary period oscillations (PPOs) observed by the Cassini spacecraft in Saturn's magnetosphere, in particular the relationship between the properties of the PPOs in the post-equinox interval as observed in magnetic field data by Andrews et al. (2012) and Provan et al. (2013, 2014) and in Saturn kilometric radiation (SKR) emissions by Fischer et al. (2014, 2015), whose results are somewhat discrepant. We show that differences in the reported PPO periods, a fundamental property which should be essentially identical in the two data sets, can largely be accounted for by the phenomenon of dual modulation of the SKR emissions in polarization-separated data, in which the modulation associated with one hemisphere is also present in the other. Misidentification of the modulations results in a reported reversal in the SKR periods in the initial post-equinox interval, south for north and vice versa, relative to the magnetic oscillations whose hemispheric origin is more securely identified through the field component phase relations. Dual modulation also results in the apparent occurrence of phase-locked common periods in the northern and southern SKR data during later intervals during which two separate periods are clearly discerned in the magnetic data through beat modulations in both phase and amplitude. We further show that the argument of Fischer et al. (2015) concerning the phase relation between the magnetic field oscillations and the SKR modulations is erroneous, the phase difference between them revealing the local time (LT) of the upward field-aligned current of the PPO current system at times of SKR modulation maxima. Furthermore, this LT is found to vary significantly over the Cassini mission from dawn, to dusk, and to noon, depending on the LT of apoapsis where the spacecraft spends most time. These variations are consistent with the view that the SKR modulation is fundamentally a rotating system like the magnetic perturbations, though complicated by the strong LT asymmetry in the strength of the sources, and rule out a mainly clock-like (strobe) modulation as argued by Fischer et al. (2015), for which no physical mechanism is suggested. We also elucidate the nature of the magnetic periods, criticized by Fischer et al. (2015), which have previously been derived in ∼100–200 day post-equinox intervals between abrupt changes in PPO properties, and further show that their argument that the magnetic phase data provide evidence for the occurrence of common phase-locked magnetic oscillations in some intervals is fallacious. The most important consequence of our results, however, is that they demonstrate the essential compatibility of the post-equinox magnetic field and SKR data, despite the contrary results published to date. They also show that due to the dual modulation effect in polarization-separated SKR data, analysis and interpretation may contain more subtleties than previously realized. Joint examination of the combined magnetic and SKR data clearly provides greater insight and enhanced confidence compared with analyses of these data sets individually.

Comment on “A new approach to Saturn's periodicities” by J. F. Carbary

The phenomenon of “planetary period oscillations” in Saturn’s magnetosphere was first observed by the Voyager spacecraft via modulations near the planetary rotation period in the intensity of radio emissions at kilometer wavelengths [Warwick et al., 1981; Desch and Kaiser, 1981], together with related oscillations in particles and magnetic fields in situ within the magnetosphere [Carbary and Krimigis, 1982; Espinosa and Dougherty, 2000]. Subsequent remote observations of Saturn kilometric radiation (SKR) by the Ulysses spacecraft showed that the period can change by of order ~1% over yearly intervals, such that the modulations cannot be connected directly to the rotation of the body of the planet [Galopeau and Lecacheux, 2000]. A more recent Cassini discovery has been that two such variable modulations are generally present in SKR data, with periods of ~10.6 and ~10.8 h during Saturn southern summer conditions early in themission [Kurth et al., 2008; Gurnett et al., 2009a], though later becoming closer together, more variable, and with intervals of only one detectable period postequinox [Provan et al., 2014; Fischer et al., 2014; Cowley and Provan, 2015]. As will be indicated below, in subsequent discussions these two periods have generally been taken to correspond to planetary period oscillation (PPO) phenomena associated with the Northern and Southern Hemispheres of the planet. In a recent paper, however, Carbary [2015] has suggested a “new approach” to these findings, pointing out the simple fact via a number of elementary demonstrations that if a single sinusoidal oscillation is modulated in amplitude, frequency, or phase, its frequency spectrum is no longer monochromatic andmay become split into a number of peaks near that of the principal period, suggested to correspond to the observed dual PPO modulations. The simplest illustrative example is that of a signal S(t) consisting of a “carrier” of frequency ω2 whose amplitude is modulated by a sinusoid of frequency ω1, for which it can be shown by elementary trigonometry that

Radial profile of sunspot magnetic field on the SDO data

The spatial distribution of the vertical (with respect to the surface photosphere) magnetic field in a sunspot plays an important role in modeling the temperature-density characteristics of sunspot, in the calculation of its total energy, in the study of magnetic field oscillations of sunspots and in many others tasks. A number of radial field distributions, such as the Broxon’s formula, is discussed in the literature, but the generally accepted, “canonical” profile of the vertical field in a sunspot does not exist on today. Magnetograms obtained with the HMI device of the Solar Dynamic Observatory (Scherrer et al. in Sol. Phys. 275(1–2):207–227, 2012), due to their high spatial resolution, provide a good opportunity to get closer to solving this problem. We have studied 30 regular round-shaped unipolar sunspots, situated near the center of the solar disk, without any changes of their configuration or the magnetic field strength during a day or two. Four radial cuts were taken on the magnetograms for each of these 30 sunspots. The magnetic field strength measured along a cut was normalized to the maximum value of the field in the sunspot, all distances are measured in units of the radius of the umbra of the sunspot. It is shown that the radial profile of the vertical field averaged over all studied sunspots has a smooth bell-shaped form and can be well described by the analytic formula for a magnetic monopole, with the depth of immersion into the convective zone of the Sun close to the radius of the sunspot umbra.

Interplay between quantum confinement and Fulde–Ferrell–Larkin–Ovchinnikov phase in superconducting nanofilms

In superconducting nanofilms the energy quantization induced by the confinement in the direction perpendicular to the film splits the band of single-electron states into series of subbands. The quantum size effect leads to the experimentally observed oscillations of the critical magnetic field with increasing nanofilm thickness. Here, we study the influence of the quantum confinement on the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase in superconducting nanofilms. We show that the range of the magnetic fields for which the FFLO phase is stable oscillates as a function of the film thickness with the phase shift equal to one half of the period corresponding to the critical magnetic field oscillations. Due to the multiband character of the system a division of the FFLO phase stability region appears leading to a phase diagram which is qualitatively different than the one corresponding to a single-band situation. The number of subregions created in such manner depends on the number of bands participating in the formation of the paired state.

Sporadic Geomagnetic Pulsations at Frequencies of up to 15 HZ in the Magnetic Storm of November 7–14, 2004: Features of the Amplitude and Polarization Spectra and their Connection with Ion–Cyclotron Waves in the Magnetosphere

We study the dynamics of the geomagnetic-pulsation spectra at unusually high frequencies (including the frequencies exceeding the Schumann resonance frequency 8 Hz), which were detected for the first time at the Novaya Zhizn’ midlatitude station (the McIlwain parameter L = 2.6) at the time of a strong magnetic storm on November 07–14, 2004. To interpret the observed pulsation frequencies, we used the data from the NOAA low-orbit satellites which recorded localized precipitations of energetic protons (with energies of 30 to 80 keV) and calculations of the singlepass cyclotron amplification of electromagnetic ion–cyclotron waves. Amplitude and polarization characteristics of the radiation spectra at frequencies of up to 15 Hz at the Novaya Zhizn’ and Lovozero stations (L = 5.2) are compared. It is shown that the magnetic field oscillations in the frequency range 7–15 Hz correlate with proton precipitations and proton auroras at geomagnetic latitudes 50°–57° (L = 2.42–3.37). It is also shown that for a high anisotropy of the pitch-angle distribution of the ring-current protons at such low geomagnetic latitudes, the frequency spectrum of observed high-frequency radiation agrees well with the calculated location of the maximum of the single-pass cyclotron amplification of electromagnetic ion–cyclotron waves. Analysis of the data and calculation results has led to the conclusion that inherently the recorded signals are a high-frequency counterpart of the Pc1 pulsations and are due to the generation of ion–cyclotron waves in the magnetosphere at unusually low latitudes, which are probably stipulated by the shift of the plasma pause to these latitudes during a strong magnetic storm.

Electromagnetic properties of neutrinos: three new phenomena in neutrino spin oscillations

In studies of neutrino electromagnetic properties we discuss three very inter- esting aspects related to neutrino spin oscillations. First we consider neutrino mixing and oscillations in the mass and flavour bases under the influence of a constant magnetic field with nonzero transversal and longitudinal components. Then we discuss the effect of neutrino spin oscillations induced by electroweak interactions of neutrino with mov- ing matter in case there is matter transversal current or polarization. In the final part of the paper we discuss recently developed approach to description of neutrino spin and spin-flavour oscillations in a constant magnetic field that is based on the use of the exact neutrino stationary states in the magnetic field.

Taming the Dynamical Sign Problem in Real-Time Evolution of Quantum Many-Body Problems.

Current nonequilibrium MonteCarlo methods suffer from a dynamical sign problem that makes simulating real-time dynamics for long times exponentially hard. We propose a new "inchworm algorithm," based on iteratively reusing information obtained in previous steps to extend the propagation to longer times. The algorithm largely overcomes the dynamical sign problem, changing the scaling from exponential to quadratic. We use the method to solve the Anderson impurity model in the Kondo and mixed valence regimes, obtaining results both for quenches and for spin dynamics in the presence of an oscillatory magnetic field.

Geodesic acoustic mode investigation in the spherical Globus-M tokamak using multi-diagnostic approach

The results of a multi-diagnostic approach for geodesic acoustic mode (GAM) studies in the spherical torus Globus-M are presented. The GAM oscillations of radial electric field, plasma density and magnetic field were simultaneously observed. The spatial structures of crucial plasma parameters are exhibited and discussed. The intermittent character of the GAM manifests itself as a modulation at two time-scales: equilibrium time scale and the characteristic time for limit-cycle oscillations. The mutual influence of GAM oscillations and turbulence is demonstrated by bicoherence analysis.

Dynamics of magnetic single domain particles embedded in a viscous liquid

Kinetic equations for magnetic nano particles dispersed in a viscous liquid are developed and analyzed numerically. Depending on the amplitude of an applied oscillatory magnetic field, the particles orient their time averaged anisotropy axis perpendicular to the applied field for low magnetic field amplitudes and nearly parallel to the direction of the field for high amplitudes. The transition between these regions takes place in a narrow field interval. In the low field region, the magnetic moment is locked to some crystal axis and the energy absorption in an oscillatory driving field is dominated by viscous losses associated with particle rotation in the liquid. In the opposite limit, the magnetic moment rotates within the particle while its easy axis being nearly parallel to the external field direction oscillates. The kinetic equations are generalized to include thermal fluctuations. This leads to a significant increase of the power absorption in the low and intermediate field regions with a pronounced absorption peak as function of particle size. In the high field region, on the other hand, the inclusion of thermal fluctuations reduces the power absorption. The illustrative numerical calculations presented are performed for magnetic parameters typical for iron oxide.

Multifrequency compressional magnetic field oscillations and their relation to multiharmonic toroidal mode standing Alfvén waves

AbstractThe power spectrum of the compressional component of magnetic fields observed by the Van Allen Probes spacecraft near the magnetospheric equator in the dayside plasmasphere sometimes exhibits regularly spaced multiple peaks at frequencies below 50 mHz. We show by detailed analysis of events observed on two separate days in early 2014 that the frequencies change smoothly with the radial distance of the spacecraft and appear at or very near the frequencies of the odd harmonics of mutiharmonic toroidal mode standing Alfvén waves seen in the azimuthal component of the magnetic field. Even though the compressional component had a low amplitude on one of the selected days, its spectral properties are highlighted by computing the ratio of the spectral powers of time series data obtained from two spatially separated Van Allen Probes spacecraft. The spectral similarity of the compressional and azimuthal components suggests that the compressional component contains field line resonance characteristics.