Improvement of the Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Inversion Code

A spectral line inversion code, Very Fast Inversion of the Stokes Vector (VFISV), has been used since 2010 May to infer the solar atmospheric parameters from the spectropolarimetric observations taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. The magnetic filling factor, the fraction of the surface with a resolution element occupied by magnetic field, is set to have a constant value of 1 in the current version of VFISV. This report describes an improved inversion strategy for the spectropolarimetric data observed with HMI for magnetic field strengths of intermediate values in areas spatially not fully resolved. The VFISV inversion code has been modified to enable inversion of the Stokes profiles with two different components: one magnetic and one nonmagnetic. In this scheme, both components share the atmospheric components except for the magnetic field vector. In order to determine whether the new strategy is useful, we evaluate the inferred parameters inverted with one magnetic component (the original version of the HMI inversion) and with two components (the improved version) using a Bayesian analysis. In pixels with intermediate magnetic field strengths (e.g., plages), the new version provides statistically significant values of filling fraction and magnetic field vector. Not only does the fitting of the Stokes profile improve, but also the inference of the magnetic parameters and line-of-sight velocity are obtained uniquely. The new strategy is also proven to be effective for mitigating the anomalous hemispheric bias in the east–west magnetic field component in moderate field regions.

Low-field Onset of Wannier-Stark Localization in a Polycrystalline Hybrid Organic Inorganic Perovskite

Control over light propagation in a material by applying external fields is at the heart of photonic applications. Here, we demonstrate ultrafast modulation of the optical properties in the room temperature polycrystalline MAPbI3 perovskite using phase-stable terahertz pulses, centered at 20 THz. The biasing field from the THz pulse creates extreme localization of electronic states in the ab plane – Wannier-Stark localization. This quasi-instantaneous reduction of dimensionality (from 3D to 2D) causes a marked change in the absorption shape, enabling the modulation depth to be tens of percent at moderate field strengths (3 MV/cm). The notably low-field onset results from a narrow electronic bandwidth, a large relevant lattice constant, and the coincidence of the two along the same direction in this tetragonal perovskite. We show that the transient optical response is in fact dominated by the least dispersive direction of the electronic band structure, facilitating a substantial modulation despite the arbitrary arrangement of the individual crystallites. The demonstration of THz-field-induced optical modulation in a solution-processed, disordered, and polycrystalline material is of substantial potential significance for novel photonic applications.

Vertexes in Kinetic Space-Matter With Local Stresses Instead of Localized Particles With Distant Gravitation

Due to the fact that negative energies have no existence in physical reality, the advanced mechanics of purely positive energies should describe gravitational interactions and collisions in monistic terms of extended kinetic energies and their local stresses. Such non-Newtonian mechanics of continuous inertial densities reinforces the Cartesian concept of matter-extension in the metric formalism of Einstein-Grossmann with a supplemental (dark, aether) fraction of bi-vertex mass-energy distributions. Local accelerations or decelerations of mono-vertex material densities in a multi-vertex distribution of complete kinetic energy arise under its constant integral due to nonlocal organization of continuous densities. Such integral conservation of the distributed mass-energy occurs instantaneously throughout the whole continuum of correlated densities and metric stresses despite the time-varying contributions of complementary mono-vertex and bi-vertex fractions. Under the nonlocal organization of purely kinetic (positive) mass-energy, geodesic self-heating and self-cooling of the pulsating space-matter conserve the integral energy in the two-fraction virial theorem for the averaged motion of visible mono-vertexes in the presence of invisible bi-vertex (interference, dark) mass-energy. Metric stresses of such material space are subordinate to nonlocal self-government of continuously distributed kinetic energy, including the relativistic rest-energy of General Relativity. These mutually consistent or correlated stresses in inertial space-time-energy create timelessly coordinated self-accelerations, observed for dense material volumes as distant gravitational pulls. In order to falsify/verify the nonlocal self-organization of adaptive kinetic energy, the monistic mechanics of self-consistent inertial densities and metric stresses can suggest moderate field changes in the temporal redshift, cycles of geodetic falls and takeoffs in pulsating kinetic organizations, and the calculated acceleration of the expanding Metagalaxy in its current phase of geodesic self-cooling.

Estimating trajectories of meteors: an observational Monte Carlo approach – II. Results

ABSTRACT In the first paper of this series, we examined existing methods of optical meteor trajectory estimation and developed a novel method which simultaneously uses both the geometry and the dynamics of meteors to constrain their trajectories. We also developed a simulator which uses an ablation model to generate realistic synthetic meteor trajectories which we use to test meteor trajectory solvers. In this second paper, we perform simulation validation to estimate radiant and velocity accuracy, which may be achieved by various meteor observation systems as applied to several meteor showers. For low-resolution all-sky systems, where the meteor deceleration is generally not measurable, the multi-parameter fit method assuming a constant velocity better reproduces the radiant and speed of synthetic meteors. For moderate field of view systems, our novel method performs the best at all convergence angles, while multi-parameter fit methods generally produce larger speed errors. For high-resolution, narrow field of view systems, we find our new method of trajectory estimation reproduces radiant and speed more accurately than all other methods tested. The ablation properties of meteoroids are commonly found to be the limiting factor in velocity accuracy. We show that the true radiant dispersion of meteor showers can be reliably measured with moderate field of view (or more precise) systems provided appropriate methods of meteor trajectory estimation are employed. Finally, we compare estimated and real angular radiant uncertainty and show that for the solvers tested the real radiant error is on average underestimated by a factor of two.

Modeling of Electron Transfer in Graphene on SiC Substrate

The results of simulation of electron transfer processes in a single graphene layer on a SiC substrate are presented. High mobility of charge carriers with respect to all known materials makes graphene to be a promising candidate for applications in new semiconductor devices. The prevalence of electron–electron scattering over other types of scattering in the range of moderate field energies in a single graphene layer is established by modeling using the Monte Carlo method.

Co/Cu/Co Pseudo Spin-Valve System Prepared by Magnetron Sputtering with Different Argon Pressure

Thin Co films were fabricated by DC magnetron sputtering. The effect of argon pressure on the microstructure, surface morphology and magnetic properties of the samples was systematically studied. It was found that with the increase of argon pressure, the sharpness of the crystalline texture of the samples declines, the roughness of film surfaces and the coercivity of the films increase. Based on these results, a Co/Cu/Co pseudo spin-valve system was designed and the corresponding structures were fabricated. The difference in coercivity of magnetic layers was obtained by deposition of the Co layers at different Ar pressures. Change of the resistance of this trilayer is induced at a moderate field by the spin rotation in the soft layer with lower coercivity.

SCIENCE WITH THE HARD X-RAY MODULATION TELESCOPE

The hard X-ray modulation telescope (HXMT) is a slat-collimated instrument sensitive in the 1–250 keV energy band. It will use the direct demodulation technique to conduct an all sky imaging survey with both high sensitivity and high spatial resolution. The moderate field of view also allows for sensitive spectroscopic and timing observations of bright sources in the pointed mode. The wide energy coverage and large collecting area in the hard X-ray band (nearly 5000 cm2 effective area at 30–100 keV) make HXMT a unique instrument for some scientific goals. Here we give brief discussion about scientific objectives that can be addressed with HXMT, involving black holes at a variety of scales and equations of states of matter at extreme conditions.