Field Signatures Research Articles

Down‐tail mass loss by plasmoids in Jupiter's and Saturn's magnetospheres

AbstractRecent estimates of the plasma mass‐loss rates by the formation and down‐tail propagation of plasmoids observed in the plasma sheet in Jupiter's and Saturn's magnetosphere fall short of inner moon source rates by at least an order of magnitude. Here we argue that on the time scale between large‐scale disconnection events, ~15 h at Jupiter and ~45 h at Saturn, mass‐loaded closed flux tubes will typically have stretched out a few hundred planetary radii down tail at speeds ~100–200 km s−1. Consequently, the “plasmoids” of order ~10 planetary radii in length observed at closer planetary distances represent only a small planetward portion of the overall structure that is disconnected and lost down tail. Plasmoid mass‐loss estimates are then revised upward by around an order of magnitude, becoming comparable to the moon source values. Additional “hidden,” e.g., small‐scale, mass‐loss processes of comparable strength may not then be required. The essentially continuous azimuthally flowing source plasma in the dusk sector is shown to correspond to a plasma sheet layer adjacent to the magnetopause of width typically ~10% of the distance to the magnetopause in that local time sector. This physical picture also provides a simple explanation for the asymmetry in the plasmoid bipolar field signature observed at both Jupiter and Saturn and predicts that the apparent plasmoid length will increase with distance down tail to a limit beyond a few hundred planetary radii where the full ~100–200 planetary radii structures will be observed.

PEMFC stack diagnosis based on external magnetic field measurements

A new diagnosis method based on the measurement of the magnetic field surrounding a PEMFC stack was developed. The method relies on the measurements of the magnetic field signature generated by the current distribution in the PEMFC. It is possible to estimate an averaged 2D current density identification by solving an inverse problem, based on the relationship between the currents and a magnetic field. In this work, 30 sensors fixed around the stack are used to perform the cartography within a second. This technique was implemented on a PEMFC stack consisting of 30 cells with a large active area of 220 cm 2 and was capable to capture the current density change from a healthy state to a faulty one. Our approach is robust and allows us to distinguish between either membrane drying or electrode flooding by varying the air stoichiometry.

Field signature for apparently superluminal particle motion

In the context of Stueckelberg's covariant symplectic mechanics, Horwitz and Aharonovich [1] have proposed a simple mechanism by which a particle traveling below light speed almost everywhere may exhibit a transit time that suggests superluminal motion. This mechanism, which requires precise measurement of the particle velocity, involves a subtle perturbation affecting the particle's recorded time coordinate caused by virtual pair processes. The Stueckelberg framework is particularly well suited to such problems, because it permits pair creation/annihilation at the classical level. In this paper, we study a trajectory of the type proposed by Horwitz and Aharonovich, and derive the Maxwell 4-vector potential associated with the motion. We show that the resulting fields carry a signature associated with the apparent superluminal motion, providing an independent test for the mechanism that does not require direct observation of the trajectory, except at the detector.

Halo velocity profiles in screened modified gravity theories

Screened modified gravity predicts potentially large signatures in the peculiar velocity field that makes it an interesting probe to test gravity on cosmological scales. We investigate the signatures induced by the Symmetron and a Chameleon $f(R)$ model in the peculiar velocity field using $N$-body simulations. By studying fifth force and halo velocity profiles we identify three general categories of effects found in screened modified gravity models: a fully screened regime where we recover $\Lambda$CDM to high precision, an unscreened regime where the fifth force is in full operation, and, a partially screened regime where screening occurs in the inner part of a halo, but the fifth force is active at larger radii. These three regimes can be pointed out very clearly by analyzing the deviation in the maximum cluster velocity. Observationally, the partially screened regime is of particular interest since an uniform increase of the gravitational force - as present in the unscreened regime - is degenerate with the (dynamical) halo mass estimate, and, thus, hard to detect.

Magnetospheric signatures of ionospheric density cavities observed by Cluster

AbstractWe present Cluster measurements of large amplitude electric fields correlated with intense downward field‐aligned currents, observed during a nightside crossing of the auroral zone. The data are reproduced by a simple model of magnetosphere‐ionosphere coupling which, under different conditions, can also produce a divergent electric field signature in the downward current region, or correlation between the electric and perturbed magnetic fields. We conclude that strong electric field associated with intense downward field‐aligned current, such as this observation, is a signature of ionospheric plasma depletion caused by the downward current. It is also shown that the electric field in the downward current region correlates with downward current density if a background field is present, e.g., due to magnetospheric convection.

Conjugate observations of traveling convection vortices associated with transient events at the magnetopause

AbstractTraveling convection vortices (TCVs) are generally produced by field‐aligned currents (FACs) at high latitudes associated with transient changes of the magnetopause. This paper presents multipoint conjugate observations of transient events at the magnetopause measured in space and on the ground. The transient events showing radial fluctuation of the magnetopause in association with sudden increases in solar wind dynamic pressure were detected by both the Time History of Events and Macroscale Interactions during Substorms and the Geostationary Operational Environmental Satellite spacecraft. Geomagnetic signatures seen as TCVs in response to the transient events were observed by the ground magnetometer array in Greenland and Canada and their conjugate locations in Antarctica including recently developed Antarctic magnetometers, mostly located along the 40° magnetic meridian. This new conjugate network provides a unique opportunity to observe geomagnetic field signatures over a relatively large region in both hemispheres. This study focuses mainly on the spatial and temporal features of the TCVs in the conjugate hemispheres in relation to the transient events at the magnetopause. The TCV events are characterized by their single or twin vortex, of which the centers are located approximately at 72°–76° magnetic latitude, propagating either dawnward or duskward away from local noon. While interhemispheric conjugacy is expected with an assumption that TCV signatures are created by FACs directed in both hemispheres, our observations suggest that there might be more complex mechanisms contributing the asymmetrical features, perhaps due to field line mapping and/or conductivity differences.

CHROMOSPHERIC DIAGNOSIS WITH Ca II LINES: FORWARD MODELING IN FORWARD SCATTERING. I

This paper shows the first synthetic tomography of the quiet solar chromosphere formed by spatial maps of scattering polarization. It has been calculated for the CaII 8498, 8542 and 3934 A lines by solving the NLTE (non-local thermodynamical equilibrium) RT (radiative transfer) problem of the second kind in a 3D atmosphere model obtained from realistic MHD (magneto-hydrodynamical) simulations. Maps of circular polarization were calculated neglecting atomic polarization. Our investigation focuses on the linear polarization signals induced by kinematics, radiation field anisotropy and Hanle effect in forward-scattering geometry. Thus, instead of considering slit profiles at the limb as normally done in the study of the second solar spectrum, we synthetize and analyze spatial maps of polarization at disk center. It allows us to understand the spatial signatures of dynamics and magnetic field in the linear polarization for discriminating them observationally. Our results suggest new ideas for chromospheric diagnosis that will be developed throughout a serie of papers. In particular, Hanle Polarity Inversion Lines and dynamic Hanle diagrams are two concepts introduced in the present work. We find that chromospheric dynamics and magnetic field topology create spatial fingerprints in the polarization maps that trace the dynamic situation of the plasma and the magnetic field. Based on such spatial features we reconstruct the magnetic field intensity in the middle chromosphere along grooves of null linear polarization. We finally address the problems of diagnosing Hanle saturation and kinematic amplification of scattering signals using Hanle diagrams.

Developing a spectral library of mangrove species of Indian east coast using field spectroscopy

Development of a spectral library is a prerequisite for the higher order classification of satellite data and hyperspectral image analysis to map any ecosystem with rich diversity. In this study, sampling methodology, collection of field and laboratory spectral signatures and post-processing methodologies were investigated for developing an exclusive spectral library of mangrove species using hyperspectral spectroscopic techniques. Canopy level field spectra and leaf level laboratory spectra were collected for 34 species (25 true and 9 associated mangroves) from two different mangrove ecosystems of the Indian east coast. Post-processing steps such as removal of water vapour absorption bands, correction of drifts which occur due to the thermal properties of the instrument during data collection and smoothing of spectra for its further utilisation were applied on collected spectra. The processed spectra were then compiled as spectral library.

Electrostatic supersolitons and double layers at the acoustic speed

Supersolitons are characterized by subsidiary extrema on the sides of a typical bipolar electric field signature or by association with a root beyond double layers in the fully nonlinear Sagdeev pseudopotential description. It has been proven that supersolitons may exist in several plasmas having at least three constituent species, but they cannot be found in weakly nonlinear theory. Another recent aspect of pseudopotential theory is that in certain plasma models and parameter regimes solitons and/or double layers can exist at the acoustic speed, having no reductive perturbation counterparts. Importantly, they signal coexistence between solitons having positive and negative polarity, in that one solution can be realized at a time, depending on infinitesimal perturbations from the equilibrium state. Weaving the two strands together, we demonstrate here that one can even find supersolitons and double layers at the acoustic speed, as illustrated using the model of cold positive and negative ions, in the presence of nonthermal electrons following a Cairns distribution. This model has been discussed before, but the existence and properties of supersolitons at the acoustic speed were not established at the time of publication.

Improved formula for localized corrosion using field signature method

Field signature method (FSM) is based on a potential drop (PD) technique and has been applied for nearly three decades for online metal pipe corrosion monitoring in many industrial areas. However, the detection precision of FSM for localized corrosion is still very low because the current field distribution in the measured pipe will be changed during the corrosion process but the formula used to assess corrosion-depth at present ignores the changes. This paper proposed an improved formula to calculate localized corrosion. The theoretical analysis and experimental results verified that the evaluation accuracy of FSM for localized corrosion can be greatly improved by this new formula.

Observation of a retreating x line and magnetic islands poleward of the cusp during northward interplanetary magnetic field conditions

AbstractWhen the interplanetary magnetic field is northward, reconnection occurs in each hemisphere on lobe field lines, poleward of the cusp. We have identified a case where the Cluster spacecraft crossed the magnetopause and encountered a tailward retreating x line. The x line is identified by the encounter of both a tailward and sunward jet, as well as Hall magnetic field signatures in the out‐of‐plane direction. Additionally, we find no signatures of electron heating and hypothesize that the spacecraft is too close to the x line to observe the accelerated electrons. Using two spacecraft, we are able to resolve the velocity of the structure, which moves near the magnetosheath speed. The speed of the x line is also consistent with the asymmetric reconnection theory. To our knowledge, this is the first time the speed of a retreating x line has been measured directly. Additionally, we observe ion distribution functions with counterstreaming populations, suggesting that a second x line formed sunward of the original one, leading to a magnetic island.

SiO2 versus chelating agent@ iron oxide nanoparticles: interactions effect in nanoparticles assemblies at low magnetic field

Hydrophilic magnetic nanoparticles present many interest for various medical applications due to their unique properties: immunoassays, imaging and hyperthermia. With regards to their applicability in the biomedical field, colloidal stability is a key parameter related to nanoparticle surface functionalization. In this paper, we report the water transfer of hydrophobic oleic acid coated iron oxide nanoparticles comparing two methodologies to obtain water dispersible iron oxide nanoparticles: exchange ligands with small strong chelating agent (caffeic acid) and SiO2 shell passivation. Both strategies are leading to stable aqueous ferrofluid but differing by their interactions. The non linear magnetic behavior at high and low magnetic field and second derivative signature of water dispersed superparamagnetic Fe304 nanoparticles samples are studied using conventional SQUID equipment and miniaturized detector MIAplex® device. We demonstrated those samples differing only by their interparticle interactions present different magnetic behavior at very low magnetic field whereas at high magnetic field both samples are very similar.

FORMATION AND DECAY OF RUDIMENTARY PENUMBRA AROUND A PORE

We analyze the evolution of a pore in the active region NOAA 10940 using the data obtained by the Hinode satellite on 2007 February 3. The pore we analyzed showed the formation of a rudimentary penumbra structure, succeeded by an abrupt disappearance after about 5 hr. The pore had an approximate radius of 3.5 Mm and a total magnetic flux of 3.0 × 1019 Mx, which is a little smaller than the necessary magnetic flux for penumbral formation supposed by Rucklidge et al. (1-1.5 × 1020 Mx). Our observation describes a rare phenomenon which was in the unstable phase between a pore and a sunspot. The area of the dark umbra gradually decreased when the rudimentary penumbral filaments formed the penumbral structure, meaning that the penumbra develops at the expense of the umbral magnetic flux. This statement was confirmed by a rough estimation of the magnetic flux variation observed by the Hinode Fe I magnetogram. Five hours after the formation phase, the decay phase began. In this decaying phase, multiple opposite polarity patches are found to appear in the exterior of the pore (a different location from the penumbra formation site). We interpret these opposite polarities as signatures of the horizontal magnetic field, which preferably appears in the course of the unstable reconfiguration of the magnetic field structure. During the course of the disappearance of the penumbra, the horizontal penumbral field seems to become vertical because of the dark umbral area that recovered by about 10%.

X-ray emission from star-forming galaxies – signatures of cosmic rays and magnetic fields

The evolution of magnetic fields in galaxies is still an open problem in astrophysics. In nearby galaxies the far-infrared-radio correlation indicates the coupling between magnetic fields and star formation. The correlation arises from the synchrotron emission of cosmic ray electrons traveling through the interstellar magnetic fields. However, with an increase of the interstellar radiation field (ISRF), inverse Compton scattering becomes the dominant energy loss mechanism of cosmic ray electrons with a typical emission frequency in the X-ray regime. The ISRF depends on the one hand on the star formation rate and becomes stronger in starburst galaxies, and on the other hand increases with redshift due to the evolution of the cosmic microwave background. With a model for the star formation rate of galaxies, the ISRF, and the cosmic ray spectrum, we can calculate the expected X-ray luminosity resulting from the inverse Compton emission. Except for galaxies with an active galactic nucleus the main additional contribution to the X-ray luminosity comes from X-ray binaries. We estimate this contribution with an analytical model as well as with an observational relation, and compare it to the pure inverse Compton luminosity. Using data from the Chandra Deep Field Survey and far-infrared observations from ALMA we then determine upper limits for the cosmic ray energy. Assuming that the magnetic energy in a galaxy is in equipartition with the energy density of the cosmic rays, we obtain upper limits for the magnetic field strength. Our results suggest that the mean magnetic energy of young galaxies is similar to the one in local galaxies. This points toward an early generation of galactic magnetic fields, which is in agreement with current dynamo evolution models.

High-accuracy evaluation of pitting corrosion in field signature method

High-accuracy evaluation of pitting corrosion in field signature method

Research on the Shaft-Frequency Electric Field Character of Ship’s Physical Scale Model

By signature gathering system, the shaft-frequency electric field of ship’s physical scale model is measured. At the same time, the mechanism of the corrosion related to shaft-frequency electric field is also described. Results show that the shaft-frequency electric field signature arises around a vessel and transmits in the surrounding seawater due to the current flow from impressed current cathodic protection (ICCP) system and the current flow resulting from the corrosion of dissimilar metals during propeller rotation, which contains both shaft fundamental and harmonics. The signature character of electric field is more and more marked with the shaft rotation speed increasing. The amplitude of electric shaft-frequency electric field by modulating the current of ICCP system is 10 times greater than that of corrosion current. It is proved that the using a 1:100 physical scale model of a vessel to study the shaft-frequency electric field character is an effective method and provided an new way.

Larmor electric field observed at the Earth's magnetopause by Polar satellite

We present, for the first time, observational evidence of a kinetic electric field near the X-line associated with asymmetric reconnection at the Earth's dayside magnetopause using Polar observations. On March 29, 2003, Polar satellite detected an asymmetric collisionless reconnection event. This event shows a unipolar Hall electric field signature and a simple deviation from the guide field during the magnetopause crossing, with the absence of an ion plasma jet outflow indicating that the magnetopause crossing was near the X-line. As expected from particle-in-cell simulations by Malakit et al. (Phys. Rev. Lett. 111, 135001 (2013)), an earthward pointing normal electric field appears in the magnetospheric side of the ion diffusion region. The electric field satisfies two necessary conditions for the existence of the finite ion Larmor radius effect: (1) the ion Larmor radius (rg2) is larger than the distance between the stagnation point and the edge of the ion diffusion region in the strong magnetic field side (δS2) and (2) the spatial extent of the kinetic electric field (δEL) is of the order of the ion Larmor radius. Furthermore, it is shown that the peak value of the Larmor electric field is comparable to the predicted value. The observation of the Larmor electric field can be valuable in other analyses to show that the crossing occurred near the X-line.

Monitoring the Petrol Engine Oil Viscosity: Investigation of the Capability of the Metal Magnetic Memory Technology

An engine lubrication system is one of the main factors which influence engine life span, and it can be easily determined based on the viscosity of the engine oil. The current and common technology for monitoring and the determination of the engine oil viscosity using the oil analysis method is found to be uneconomical and ineffective. On the same vein, this paper presents an investigation of the capability of the Metal Magnetic Memory (MMM) technology in the processes of monitoring and detecting the variation of petrol engine lubricant viscosity via in-situ operation. A few investigations were conducted on a Robin Engine 126 cc EX 13D single cylinder of four strokes with water cooling. One multi-grade engine lubricant oil condition has been put to the test; namely, SAE 15W-40. During the investigation of the petrol engine oil viscosity, the magnetic field signal is captured when the engine oil in-service age is 0 km (fresh oil), 250 km, 500 km, 750 km and 1,000 km, with the crankshaft rotational speed of 2500 rpm at three different locations such as at the Bottom Dead Centre (BDC), oil sump A (engine oil inlet), and oil sump B. The lubrication condition in the petrol engine is successfully monitored based on the magnetic field signatures generated by the interaction between the piston surface and the layer of the lubricant during the time when the engine was in operation. The generated MMM signatures were captured using a type 2 scanning device with two ferroprobe sensors and a length measuring sensor and recorded by the TSC-3M-12 type device. The waveform signatures captured were displayed as length domain signal and then were analysed using the MATLAB software to determine the magnetic field energy (EH). In addition, the real viscosity value at room temperature was determined using the Haake Viscotester 6 L, each time after the magnetic field signal was captured. The results of these studies have shown that the magnetic field energy (EH) is inversely proportional to engine oil viscosity. Finally, the MMM technology can be utilised in promoting economic development and effective planning of the maintenance schedule of the petrol engine oil.

Time-domain response of the ARIANNA detector

The Antarctic Ross Ice Shelf Antenna Neutrino Array (ARIANNA) is a high-energy neutrino detector designed to record the Askaryan electric field signature of cosmogenic neutrino interactions in ice. To understand the inherent radio-frequency (RF) neutrino signature, the time-domain response of the ARIANNA RF receiver must be measured. ARIANNA uses Create CLP5130-2N log-periodic dipole arrays (LPDAs). The associated effective height operator converts incident electric fields to voltage waveforms at the LDPA terminals. The effective height versus time and incident angle was measured, along with the associated response of the ARIANNA RF amplifier. The results are verified by correlating to field measurements in air and ice, using oscilloscopes. Finally, theoretical models for the Askaryan electric field are combined with the detector response to predict the neutrino signature.

Precise Magnetic Sensors for Navigation and Prospection

Navigation, position tracking, search for unexploded ammunition, and geophysical prospection of magnetic or conducting ore are key applications where very small magnetic field signatures and field increments should be detected in the presence of the Earth’s magnetic field, typically 50,000 nT. The industry calls for a new generation of portable vectorial magnetic sensors with a precision better than 0.1 nT. This error requirement includes not only sensor noise but also linearity, cross-field error, hysteresis, and perming and also temperature drift of the sensitivity and mainly the offset drift. For application on moving platform, the sensors should also have fast response. We will show that these requirements can be met only by fluxgate sensors. On the other hand, mass market requires cheap, low-power, and small magnetic sensors for portable gadgets; the typical application is compass in mobile phone, with precision of several degrees, corresponding to a 100-nT precision. For these applications, anisotropic magnetoresistance (AMR) sensor is dominant, while integrated fluxgates may penetrate the high-end market.