Large Field Strength Research Articles

Geochemical, mineralogical and chronological studies of mafic-intermediate dykes in the Jiaodong Peninsula: implications for Late Mesozoic mantle source metasomatism and lithospheric thinning of the eastern North China Craton

ABSTRACT The Late Mesozoic tectonic evolution of the eastern North China Craton (NCC) remains controversial. In this study, a suite of Early Cretaceous mafic-intermediate dyke swarms found in the same section in the Jiaodong Peninsula, eastern NCC, were used to trace the nature of lithospheric mantle and crust–mantle interaction. Zircon U-Pb dating demonstrates that these dykes emplaced into the Jiaodong Peninsula during the same period (112–121 Ma). Diorite dykes have SiO2 contents of 52.7–54.1 wt.%, Na2O+K2O contents of 5.77–6.10 wt.%, a limited range of MgO (4.43–5.13 wt.%), Cr (64.8–85.5 ppm) and Ni (23.6–27.7 ppm), and a narrow range of (87Sr/86Sr)i isotopic ratios (0.709240–0.709246), ƐNd(t) values (−20.0 to −19.1) and ƐHf(t) values (ca. −23.9). Lamprophyre and dolerite dykes have low contents of SiO2 (50.5–55.4 wt.%) and Na2O+K2O (4.88–7.28 wt.%), high contents of Al2O3 (14.6–15.8 wt.%), MgO (5.83–8.60 wt.%), Cr (210–292 ppm) and Ni (114–149 ppm), and a narrow range (87Sr/86Sr)i isotopic ratios (0.709134–0.709788), ƐNd(t) values (−19.9 to −17.4) and ƐHf(t) values (−22.1 to −15.1). Both intermediate and mafic dykes exhibit strong large ion lithophile elements (LILE) enrichment and high field strength element (HFSE) depletion. These geochemical characteristics demonstrate that the magma was primarily derived from relatively low degrees of the partial melting of garnet-lherzolite mantle, which was modified by fluids from a subducting oceanic slab with marine sediments. Both the mafic dykes and intermediate dykes originated from the same magma source and formed in different stages of magma fractionation crystallization. The magma experienced the fractional crystallization of clinopyroxene and more ferromagnesian minerals in a hydrous condition, thus forming mafic dykes. Then, the residual calc-alkaline liquids upwelled into a low-H2O and low-pressure environment, in which more plagioclase crystallized from liquid, thus increasing the degree of differentiation and producing the Ca- and Al-rich diorite dyke. Combined with Late Mesozoic mantle-derived mafic-intermediate dykes and crust-derived volcanic rocks in the region, the eastern NCC has experienced considerable lithospheric thinning along with regional extensional tectonics, which was caused by the prolonged thermo-mechanical-chemical erosion on the lithosphere induced by the rollback of the subducted paleo-Pacific plate.

The dominant exploration area from three-dimensional crosswell electromagnetic modeling in the time domain

ABSTRACT We analyze the sensitivity of a three-dimensional crosswell electromagnetic (EM) system based on finite-difference time-domain modeling. To reinforce the simulation accuracy of low-frequency electromagnetic propagation in a small space, we limit the boundary reflection energy by suppressing the numerical dispersion of convolutional perfectly matched layers. The numerical simulation results for an isotropic medium indicate that an anomalous conductivity will induce a large magnetic field strength disturbance at the receiving coils in the X- and Z-directions, and a relatively large absolute sensitivity is observed at the receiving coils in the Y-direction. The three-component signals are most sensitive to high-resistance anomalies. Through an experiment that involved moving an anomalous conductivity disturbance, comparison plots of dynamic residual hydrocarbon monitoring between wells and depth determinations of anomalous conductivities are provided. The optimal acquisition depth interval of the receiving coil in the homogeneous medium is given, and the effective exploration area and optimal modeling region of the crosswell EM system are obtained.

Mineralogical and geochemical characterization of radioactive minerals and rare earth elements in granitic pegmatites at G. El Fereyid, South Eastern Desert, Egypt

The present work deals with the mineralogical and geochemical investigations of radioactive minerals and rare earth elements associated with granitic pegmatites at Gabal El Fereyid area exposed in the south Eastern Desert of Egypt. The study area is occupied by tonalite and monzogranites, the latter is intruded by pegmatites with a distinctive distribution of economically important mineralization. The studied pegmatitic bodies occur as veins that are ranging in size from few meters to 25 m long and their width usually less than 7 m; although small pockets are present. The latter display zoning structure (concentric layering) consisting of feldspar-rich zones enveloping pockets of mica (mainly muscovite) and all zoning internal quartz core. Field work using gamma spectroscopy measurements over these pegmatites shows that some bodies are radiometrically anomalous, especially the muscovite-rich zones. The mineralogy and geochemistry (trace and rare earth elements contents) of the radioactive zones in such pegmatites were achieved.Mineral characterization of the highly radioactive zones shows enrichment in thorite, uranothorite, ishikawaite, samarskite and fergusonite minerals. The spectrometric measurements of the studied pegmatites show that they possess the highest content of radioelements as well. They show enrichment in large ion lithophile elements (LILE; Pb, Rb, Sr) and high field strength elements (HFSE; Y, Zr, Th, U, Nb) and depletion in K, P and Ti. The studied granitic pegmatites indicate moderate to large negative Eu anomaly and show clear M-type tetrad effect of REE.The mineralogical and geochemical signature of investigated pegmatites represents a NYF-type (Niobium–Yttrium–Fluorine family), whereas the enrichment of rare element is an indication of high degrees of fractional crystallization of a suite of volatile-rich magmas. Uranium and thorium mineralization in the studied pegmatite are related to magmatic (syngenetic) origin with hydrothermal (epigenetic) input. The magmatic mineralization is evidenced by occurrence of thorite and zircon, whereas the hydrothermal activity is represented by alteration of feldspars and formation of pyrite and iron oxides associated with the radioactive minerals.The high levels of radioactivity and rare earth elements mineralization in the studied granitic pegmatite bodies make them a target to exploration and to enlarge the potentiality of the highly mineralized localities.

Heat transfer and flow regimes in quasi-static magnetoconvection with a vertical magnetic field

Numerical simulations of quasi-static magnetoconvection with a vertical magnetic field are carried out up to a Chandrasekhar number of $Q=10^{8}$ over a broad range of Rayleigh numbers $Ra$. Three magnetoconvection regimes are identified: two of the regimes are magnetically constrained in the sense that a leading-order balance exists between the Lorentz and buoyancy forces, whereas the third regime is characterized by unbalanced dynamics that is similar to non-magnetic convection. Each regime is distinguished by flow morphology, momentum and heat equation balances, and heat transport behaviour. One of the magnetically constrained regimes appears to represent an ‘ultimate’ magnetoconvection regime in the dual limit of asymptotically large buoyancy forcing and magnetic field strength; this regime is characterized by an interconnected network of anisotropic, spatially localized fluid columns aligned with the direction of the imposed magnetic field that remain quasi-laminar despite having large flow speeds. As for non-magnetic convection, heat transport is controlled primarily by the thermal boundary layer. Empirically, the scaling of the heat transport and flow speeds with $Ra$ appear to be independent of the thermal Prandtl number within the magnetically constrained, high-$Q$ regimes.

A project of advanced solid-state neutron polarizer for PF1B instrument at Institut Laue-Langevin.

Among polarizers based on the neutron reflection from Super-Mirrors (SMs), solid-state neutron-optical devices have many advantages. The most relevant is the 5-10 times smaller size along the neutron beam direction compared to more traditional air-gap devices. An important condition for a good SM polarizer is the matching of the substrate SLD (Scattering Length Density) with the SM coating SLD for the spin-down component. For traditional Fe/Si SM on the Si substrate, this SLD step is positive when a neutron goes from the substrate to the SM, which leads to a significant degradation of the polarizer performance in the small Q region. This can be solved by replacing single-crystal Si substrates by single-crystal sapphire or quartz substrates. The latter shows a negative SLD step for the spin-down neutron polarization component at the interface with Fe and, therefore, avoid the total reflection regime in the small Q region. In order to optimize the polarizer performance, we formulate the concept of sapphire V-bender. We perform ray-tracing simulations of sapphire V-bender, compare results with those for traditional C-bender on Si, and study experimentally V-bender prototypes with different substrates. Our results show that the choice of substrate material, polarizer geometry, as well the strength and quality of magnetizing field have dramatic effect on the polarizer performance. In particular, we compare the performance of polarizer for the applied magnetic field strength of 50 mT and 300 mT. Only the large field strength (300 mT) provides an excellent agreement between the simulated and measured polarization values. For the double-reflection configuration, a record polarization >0.999 was obtained in the neutron wavelength band of 0.3-1.2 nm with only 1% decrease at 2 nm. Without any collimation, the polarization averaged over the full outgoing capture spectrum, 0.997, was found to be equal to the value obtained previously using only a double polarizer in the "crossed" (X-SM) geometry. These results are applied in a full-scale polarizer for the PF1B instrument.

Sauter–Schwinger effect with a quantum gas

The creation of particle–antiparticle pairs from vacuum by a large electric field is at the core of quantum electrodynamics. Despite the wide acceptance that this phenomenon occurs naturally when electric field strengths exceed Ec ≈ 1018 V m−1, it has yet to be experimentally observed due to the limitations imposed by producing electric fields at this scale. The high degree of experimental control present in ultracold atomic systems allow experimentalists to create laboratory analogs to high-field phenomena. Here we emulated massive relativistic particles subject to large electric field strengths, thereby quantum-simulated particle–antiparticle pair creation, and experimentally explored particle creation from ‘the Dirac vacuum’. Data collected from our analog system spans the full parameter regime from low applied field (negligible pair creation) below the Sauter–Schwinger limit, to high field (maximum rate of pair creation) far in excess of the Sauter–Schwinger limit. In our experiment, we perform direct measurements on an analog atomic system and show that this high-field phenomenon is well-characterized by Landau–Zener tunneling, well known in the atomic physics context, and we find full quantitative agreement with theory with no adjustable parameters.

Flipping Molecules over on TiO2 Surfaces with Light and Electric Fields.

Light excitation of the sensitizer [Ru(NH3)5(eina)](PF6)2, where eina is ethyl isonicotinate, anchored to anatase TiO2 nanocrystallites interconnected in a mesoporous thin film and immersed in CH3CN resulted in spectroscopic changes consistent with both excited-state injection and sensitizer reorientation, termed flipping. When the light irradiation was removed, the sensitizers flipped back over. Such flipping was absent when the carboxylic acid derivative of the sensitizer was utilized or when SnO2/TiO2 core/shell materials were employed in place of TiO2. The flipping was attributed to the torque on the sensitizer in the electric field generated by the injected electrons. Pulsed light excitation was utilized to time-resolve flipping and charge recombination with this and the per-deuterated complex (ND3)5RuII(eina)|TiO2. In all cases, charge recombination was more rapid when the oxidized sensitizer was flipped over, behavior consistent with stronger electronic coupling. Kinetic isotope effects of 26.7 and 0.12 were determined for charge recombination and for flipping, respectively. Spectro-electrochemical measurements showed that thermal reduction of TiO2 with an applied potential also initiated flipping yet required much larger field strengths. The data show that the electric fields created at illuminated semiconductor interfaces are sufficient to reorientate molecules anchored to its surface.

Magnetic field strengths of hot Jupiters from signals of star–planet interactions

Evidence of star-planet interactions in the form of planet-modulated chromospheric emission has been noted for a number of hot Jupiters. Magnetic star-planet interactions involve the release of energy stored in the stellar and planetary magnetic fields. These signals thus offer indirect detections of exoplanetary magnetic fields. Here we report the derivation of the magnetic field strengths of four hot Jupiter systems using the power observed in Ca II K emission modulated by magnetic star-planet interactions. By approximating the fractional energy released in the Ca II K line we find that the surface magnetic field values for the hot Jupiters in our sample range from 20 G to 120 G, ~10-100 times larger than the values predicted by dynamo scaling laws for planets with rotation periods of ~2 - 4 days. On the other hand, these value are in agreement with scaling laws relating the magnetic field strength to the internal heat flux in giant planets. Large planetary magnetic field strengths may produce observable electron-cyclotron maser radio emission by preventing the maser from being quenched by the planet's ionosphere. Intensive radio monitoring of hot Jupiter systems will help confirm these field values and inform on the generation mechanism of magnetic fields in this important class of exoplanets.

On-Chip Dispersion Measurement of the Quadratic Electro-Optic Effect in Nonlinear Optical Polymers Using a Photonic Integrated Circuit Technology

A novel method to determine the dispersion of the quadratic electro-optic effect in nonlinear optical materials by using a silicon-on-insulator microring resonator is presented. The microring consists of a silicon slot waveguide enabling large dc electric field strength at low applied voltages. The dispersion of third-order hyperpolarizability of a linear conjugated dye is approximated by using a two-level model for the off-resonant spectral region. As an example, the dispersion of the resonance wavelength of the resonator filled with a dye doped polymer was measured in dependence of the applied dc voltage. The polymer was poly (methylmethacrylate) doped with $\text{5 wt}\%$ disperse red 1 (DR1), and the measurements have been carried out at the telecommunication wavelength band around $\text{1550 nm}$ (optical C -band). The described measurements represent a new technique to determine the dispersion of the third-order susceptibility and molecular hyperpolarizability of the material filled into the slot of the ring-resonator.

The low-Ti high-temperature dacitic volcanism of the southern Paraná-Etendeka LIP: Geochemistry, implications for trans-Atlantic correlations and comparison with other Phanerozoic LIPs

The low-Ti silicic volcanic units of the Paraná-Etendeka Large Igneous Province (LIP) have a high volume (~20,000 km3) and are widespread in South America and Africa. In this paper we present a geochemical investigation of conduit- and lava flow-related metaluminous dacitic volcanic rocks from three areas outcropping in southern Brazil. Trace-element abundances are close to those observed from the low-Ti basaltic parental melts and interbedded basaltic andesites. Assimilation and fractional crystallization models suggest significant fractionation (>60%) from basaltic melts with assimilation involving sources with variable large ion lithophiles (LIL) and high field strength (HFS) elements. Variation in Zr/Nb ratios of the silicic volcanic rocks is interpreted to be related to the source characteristics. An effective magma drainage system through structurally controlled conduits was sustained at high magmatic temperatures (~1000–1100 °C), low viscosities of ~106–104 Pa s and water contents from 0.5–1.3 wt%. Melt structures with RAI < 1 are in agreement with field descriptions of an effusive emplacement, erupting domes, coulees, lobes, and extensive SR-type lavas. Trans-Atlantic correlations indicate some compositional overlaps with the Grootberg and Wereldsend quartz latites of Namibia, but the much higher Pb contents of the Namibian quartz latites, five to ten times greater than for the Brazilian dacites, and higher Pb/Cu ratios, suggest a greater degree of assimilation/fractionation of Pb-rich material, such as shale, slate or schist, for the Namibian silicic rocks. After comparing Phanerozoic silicic units related to LIPs, we propose they can be separated into three main types: (1) large volume, high-temperature, water-poor metaluminous rocks, (2) small volume, lower temperature, more hydrous peraluminous to peralkaline rocks; and (3) high-temperature peraluminous rocks with cordierite and garnet, derived from partial melting of metapelitic basement.

Building Arc Crust: Plutonic to Volcanic Connections in an Extensional Oceanic Arc, the Southern Alisitos Arc, Baja California

AbstractThe ∼50 km long Rosario segment of the Cretaceous Alisitos oceanic arc terrane provides undeformed three-dimensional exposures of the upper 7 km of an oceanic extensional arc, where crustal generation processes are recorded in both the volcanic and underlying plutonic rocks. These exceptional exposures allow for the study of the physical and chemical links between the rock units and help constrain the differentiation processes active during the growth and evolution of arc crust. This study focuses on the southern third of the Rosario segment, previously referred to as the southern volcano-bounded basin, and its plutonic underpinnings. Upper crustal rocks in the Rosario segment consist of a 3–5 km thick volcanic–volcaniclastic section with hypabyssal intrusions. Plutons intrude these units at various levels along-strike, but at each intrusive contact the transition is complete over a distance of &lt;150 m, where stoped volcanic blocks are present. There is striking compositional overlap in whole-rock and mineral chemistry between the plutonic and volcanic units, suggesting a comagmatic source. Whole-rock geochemistry shows coherent trends in major and trace elements in mafic to intermediate compositions, but less coherent trends above 63 wt % SiO2. Units are predominantly low-K with flat rare earth element patterns, and show large ion lithophile element enrichment and high field strength element depletion. Initial Nd and Pb isotope ratios overlap for all units and imply no cratonic continental involvement. This agrees with low Sr/Y ratios of all rock types, indicative of thin, immature oceanic arc crust. Modeling results show that closed-system fractional crystallization drove crustal differentiation from mafic to intermediate compositions, but open-system processes likely occurred to produce some of the felsic compositions. Differentiation occurred in a two-step fractionation process. Step 1, from basaltic andesite to andesite, fractionated an anhydrous gabbroic cumulate (∼40% crystallization). Step 2, from andesite to rhyolite, fractionated a hydrous amphibole cumulate (∼65% crystallization, total), which is similar to what fluid dynamical models suggest for production of rhyolite (between 50–70% crystallization). Our results can be used as a reference model for differentiation processes relating to the growth of the middle and upper crust within active extensional arc systems. The Rosario segment plutonic rocks may be analogous to the low-velocity zone (Vp = 6·0–6·5 km s–1) imaged within the extensional Izu–Bonin arc. The chemistry of the plutonic and volcanic rocks is most similar to those of volcanic rocks in the Izu–Bonin active rift.

Second harmonic generation from complementary triangular Au metamaterials

Sub-wavelength square array of a triangular Au platelet and its complementary structure (i.e. that of a triangular hole in a square film of Au) are compared in terms of second harmonic generation efficiency for fundamental light in the near infrared and visible region of spectrum for normal incidence. Electric field strength around the convex corners of a triangular particle is at least 10 times larger than the one around the concave corners of triangular hole in the complementary structure. Nevertheless the SHG intensity at the respective resonant frequency is found to be comparable, which are numerically estimated by an overlap integral of nonlinear polarization and electric field at the SHG frequency in the nonlinear optical scattering theory originally proposed by Roke et al. (Phys. Rev. B 70, 115106 (2004)). The reason is due to the large electric field strength at the sides of the triangular hole at the resonance frequency, which compensates the suppressed electric field at the concave corners in the overlap integral.

Magnetic Properties and Flow Angle of the Inverse Evershed Flow at Its Downflow Points

Abstract We determined the direction and strength of the photospheric and lower chromospheric magnetic field in the umbra and penumbra of a sunspot from inversions of spectropolarimetric observations of photospheric lines at 617 nm and 1565 nm and the chromospheric Ca ii IR line at 854 nm, respectively. We compare the magnetic field vector with the direction of 75 flow channels that harbor the chromospheric inverse Evershed effect (IEF) near their downflow points (DFPs) in the sunspot’s penumbra. The azimuth and inclination of the IEF channels to the line of sight (LOS) were derived from spatial maps of the LOS velocity and line–core intensity of the Ca ii IR line and a thermal inversion of the Ca ii IR spectra to obtain temperature cubes. We find that the flow direction of the IEF near the DFPs is aligned with the photospheric magnetic field to within about ±15°. The IEF flow fibrils make an angle of 30°–90° to the local vertical with an average value of about 65°. The average field strength at the DFPs is about 1.3 kG. Our findings suggest that the IEF in the lower chromosphere is a field-aligned siphon flow, where the larger field strength at the inner footpoints together with the lower temperature in the penumbra causes the necessary gas pressure difference relative to the outer footpoints in the hotter quiet Sun with lower magnetic field strength. The IEF connects to magnetic field lines that are not, like in the case of the regular Evershed flow, but which continue upward into the chromosphere, indicating an “uncombed” penumbral structure.

Gallium Oxide Field Effect Transistors — Establishing New Frontiers of Power Switching and Radiation-Hard Electronics

Ga2O3 has gained worldwide interests for next-generation power electronics because its large critical field strength stemming from an ultra-wide bandgap promises miniaturized circuits and systems with high conversion efficiency. Intense pursuit of Ga2O3 power devices stimulated by early demonstrations of high-voltage Ga2O3 field effect transistors (FETs) has brought about tremendous advancements in this new technology, whose strong radiation tolerance and high thermal stability also befit harsh-environment applications. In this paper, we review the various types of depletionand enhancement-mode Ga2O3 FETs — which have predominantly been lateral devices — for power switching and radiation-hard electronics. The development of vertical Ga2O3 transistors based on a low-cost, highly-manufacturable ion implantation doping process will also be discussed.

First Map of Coherent Low‐Frequency Continuum Radiation in the Sky

AbstractLightning discharges and radio transmitters emit low‐frequency (∼3–300 kHz) electromagnetic waves with large electric field strengths and stable phases. This phase stability makes it possible to map the source locations of lightning and transmitters in the sky. Electromagnetic waves with smaller electric field strengths generally exhibit a reduced phase stability, caused by numerous simultaneous physical processes that blend into an underlying continuum radiation trapped inside the Earth‐ionosphere cavity. It is therefore currently not known whether the source locations of continuum radiation can be determined. Here we show the first map of coherent continuum radiation in the sky above an array of high‐precision radio receivers. The source locations of the coherent continuum radiation are found at elevation angles ∼30∘−60∘ above the horizon. The identified source locations are attributed to intermittent radio transmitters that emit electromagnetic waves with electric field strengths ∼2 orders of magnitude below the instrumental noise floor. The results demonstrate that it is possible to simultaneously map the signals from coherent continuum radiation, lightning discharges, and radio transmitters in the sky. This work thereby lays the foundation toward the discovery of many more coherent source locations of low‐frequency electromagnetic waves in the sky. It is expected that the identified source locations vary with time as a result of the impact of solar variability on the D‐region ionosphere. Future studies have therefore the potential to contribute to a novel remote sensing and an improved understanding of the D‐region ionosphere, influenced by the near‐Earth space environment.

Double-gap plate–plate magnetorheology

A double-gap magnetorheological (MR) cell is designed, constructed, and validated using finite element method magnetostatics simulations, computational fluid dynamics calculations, and experimental data with Newtonian fluids and conventional MR fluids for a range of particle concentrations and external magnetic field strengths. This new cell is a generalization of the twin-gap device. It is capable of reaching very large magnetic field strengths and shear rates, avoiding normal force overload. More importantly, it is optimized for magnetic field homogeneity.

The primordial magnetic field in our cosmic backyard

We reconstruct for the first time the three dimensional structure of magnetic fields on cosmological scales, which were seeded by density perturbations during the radiation dominated epoch of the Universe and later on were evolved by structure formation. To achieve this goal, we rely on three dimensional initial density fields inferred from the 2M++ galaxy compilation via the Bayesian BORG algorithm. Using those, we estimate the magnetogenesis by the so called Harrison mechanism. This effect produced magnetic fields exploiting the different photon drag on electrons and ions in vortical motions, which are exited due to second order perturbation effects in the Early Universe. Subsequently we study the evolution of these seed fields through the non-linear cosmic structure formation by virtue of a magneto-hydrodynamics simulation to obtain a 3D estimate for the structure of this primordial magnetic field component today. At recombination we obtain large scale magnetic field strengths around , with a power spectrum peaking at about in comoving scales. At present we expect this evolved primordial field to have strengths above ≈10 and ≈10 in clusters of galaxies and voids, respectively. We also calculate the corresponding Faraday rotation measure map and show the magnetic field morphology and strength for specific objects of the Local Universe. These results provide a reliable lower limit on the primordial component of the magnetic fields in these structures.

Re-igniting the afterglow plasma column of an AC powered gliding arc discharge in atmospheric-pressure air

The stability and re-ignition characteristics of the plasma column of an alternating current (AC) powered gliding arc discharge operating in atmospheric-pressure air were investigated for better plasma-mode controlling and optimized applications. By modulating the AC power supply and the air flow field, the states of afterglow plasma column were varied. When pulsating the AC power supply sequence, re-ignitions of the afterglow columns were introduced and their characteristics were studied using simultaneous high-speed photography and electrical measurements. Two re-ignition types were observed in the afterglow column with different decay times (the temporal separation of two sequential pulsed AC power trains). For a short decay time (&amp;lt;200 μs at 10 l/min air flow), the afterglow column can be recovered mildly without current spikes, which is called a glow re-ignition event. If the decay time is so long that the electric field strength becomes larger than 120 kV/m, the re-ignition event occurs with current spikes and bright emissions, which is called a spark re-ignition event. A quasi-equilibrium model is proposed to estimate the chemical compositions in the plasma column and to explain the observed phenomena. It infers that the chemical dissociation and ionization processes enhanced by vibrationally excited nitrogen molecules are dominating in the afterglow plasmas and thereby the electrons can survive a long time to keep the conductivity of the afterglow column, forming a glow re-ignition event. Whereas under large electric field strength (&amp;gt;120 kV/m), the electron impact ionization becomes dominant to trigger the spark re-ignition event.

Magnetic fields at the onset of high-mass star formation

Context. The importance of magnetic fields at the onset of star formation related to the early fragmentation and collapse processes is largely unexplored today. Aims. We want to understand the magnetic field properties at the earliest evolutionary stages of high-mass star formation. Methods. The Atacama Large Millimeter Array is used at 1.3 mm wavelength in full polarization mode to study the polarized emission, and, using this, the magnetic field morphologies and strengths of the high-mass starless region IRDC 18310-4. Results. Polarized emission is clearly detected in four sub-cores of the region; in general it shows a smooth distribution, also along elongated cores. Estimating the magnetic field strength via the Davis-Chandrasekhar-Fermi method and following a structure function analysis, we find comparably large magnetic field strengths between ~0.3–5.3 mG. Comparing the data to spectral line observations, the turbulent-to-magnetic energy ratio is low, indicating that turbulence does not significantly contribute to the stability of the gas clump. A mass-to-flux ratio around the critical value 1.0 – depending on column density – indicates that the region starts to collapse, which is consistent with the previous spectral line analysis of the region. Conclusions. While this high-mass region is collapsing and thus at the verge of star formation, the high magnetic field values and the smooth spatial structure indicate that the magnetic field is important for the fragmentation and collapse process. This single case study can only be the starting point for larger sample studies of magnetic fields at the onset of star formation.

New Magnetostrictive Transducer Designs for Emerging Application Areas of NDE.

Magnetostrictive transduction has been widely utilized in nondestructive evaluation (NDE) applications, specifically for the generation and reception of guided waves for the long-range inspection of components such as pipes, vessels, and small tubes. Transverse-motion guided wave modes (e.g., torsional vibrations in pipes) are the most common choice for long-range inspection applications, because the wave motion is in the plane of the structure surface, and therefore does not couple well to the surrounding material. Magnetostrictive-based sensors for these wave modes using the Wiedemann effect have been available for several years. An alternative configuration of a sensor for generating and receiving these transverse-motion guided waves swaps the biasing and time-varying magnetic field directions. This alternative design is a reversed Wiedemann effect magnetostrictive transducer. These transducers exhibit a number of unique features compared with the more conventional Wiedemann sensor, including: (1) the use of smaller rare earth permanent magnets to achieve large, uniform, and self-sustained bias field strengths; (2) the use of more efficient electric coil arrangements to induce a stronger time-varying magnetic field for a given coil impedance; (3) beneficial non-linear operating characteristics, given the efficiency improvements in both magnetic fields; and (4) the ability to generate unidirectional guided waves when the field arrangement is combined with a magnetically soft ferromagnetic strip (patch). Reversed Wiedemann effect magnetostrictive transducers will be presented that are suitable for different inspection applications, one using electromagnetic generation and reception directly in a ferromagnetic material, and another design that integrates a magnetostrictive patch to improve its efficiency and enable special operating characteristics.