Domains of Magnetic Pressure Balance in Parker Solar Probe Observations of the Solar Wind

The Parker Solar Probe (PSP) spacecraft is performing the first in situ exploration of the solar wind within 0.2 au of the Sun. Initial observations confirmed the Alfvénic nature of aligned fluctuations of the magnetic field B and velocity V in solar wind plasma close to the Sun, in domains of nearly constant magnetic field magnitude ∣ B ∣, i.e., approximate magnetic pressure balance. Such domains are interrupted by particularly strong fluctuations, including but not limited to radial field (polarity) reversals, known as switchbacks. It has been proposed that nonlinear Kelvin–Helmholtz instabilities form near magnetic boundaries in the nascent solar wind leading to extensive shear-driven dynamics, strong turbulent fluctuations including switchbacks, and mixing layers that involve domains of approximate magnetic pressure balance. In this work we identify and analyze various aspects of such domains using data from the first five PSP solar encounters. The filling fraction of domains, a measure of Alfvénicity, varies from median values of 90% within 0.2 au to 38% outside 0.9 au, with strong fluctuations. We find an inverse association between the mean domain duration and plasma β. We examine whether the mean domain duration is also related to the crossing time of spatial structures frozen into the solar wind flow for extreme cases of the aspect ratio. Our results are inconsistent with long, thin domains aligned along the radial or Parker spiral direction, and compatible with isotropic domains, which is consistent with prior observations of isotropic density fluctuations or flocculae in the solar wind.

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.

Emergent supersymmetry on the edges

The WZW models describe the dynamics of the edge modes of Chern-Simons theories in three dimensions. We explore the WZW models which can be mapped to supersymmetric theories via the generalized Jordan-Wigner transformation. Some of such models have supersymmetric Ramond vacua, but the others break the supersymmetry spontaneously. We also make a comment on recent proposals that the Read-Rezayi states at filling fraction \nu=1/2,~2/3ν=1/2,2/3 are able to support supersymmetry.

Ce Filling Limit and Its Influence on Thermoelectric Performance of Fe3CoSb12-Based Skutterudite Grown by a Temperature Gradient Zone Melting Method

CoSb3-based skutterudite is a promising mid-temperature thermoelectric material. However, the high lattice thermal conductivity limits its further application. Filling is one of the most effective methods to reduce the lattice thermal conductivity. In this study, we investigate the Ce filling limit and its influence on thermoelectric properties of p-type Fe3CoSb12-based skutterudites grown by a temperature gradient zone melting (TGZM) method. Crystal structure and composition characterization suggests that a maximum filling fraction of Ce reaches 0.73 in a composition of Ce0.73Fe2.73Co1.18Sb12 prepared by the TGZM method. The Ce filling reduces the carrier concentration to 1.03 × 1020 cm−3 in the Ce1.25Fe3CoSb12, leading to an increased Seebeck coefficient. Density functional theory (DFT) calculation indicates that the Ce-filling introduces an impurity level near the Fermi level. Moreover, the rattling effect of the Ce fillers strengthens the short-wavelength phonon scattering and reduces the lattice thermal conductivity to 0.91 W m−1 K−1. These effects induce a maximum Seebeck coefficient of 168 μV K−1 and a lowest κ of 1.52 W m−1 K−1 at 693 K in the Ce1.25Fe3CoSb12, leading to a peak zT value of 0.65, which is 9 times higher than that of the unfilled Fe3CoSb12.

Turbulent Flow through and over a Compact Three-Dimensional Model Porous Medium: An Experimental Study

There are several natural and industrial applications where turbulent flows over compact porous media are relevant. However, the study of such flows is rare. In this paper, an experimental investigation of turbulent flow through and over a compact model porous medium is presented to fill this gap in the literature. The objectives of this work were to measure the development of the flow over the porous boundary, the penetration of the turbulent flow into the porous domain, the attendant three-dimensional effects, and Reynolds number effects. These objectives were achieved by conducting particle image velocimetry measurements in a test section with turbulent flow through and over a compact model porous medium of porosity 85%, and filling fraction 21%. The bulk Reynolds numbers were 14,338 and 24,510. The results showed a large-scale anisotropic turbulent flow region over and within the porous medium. The overlying turbulent flow had a boundary layer that thickened along the stream by about 90% and infiltrated into the porous medium to a depth of about 7% of the porous medium rod diameter. The results presented here provide useful physical insight suited for the design and analyses of turbulent flows over compact porous media arrangements.

Ultrasensitive Biosensor with Hyperbolic Metamaterials Composed of Silver and Zinc Oxide

We propose a hyperbolic metamaterial-based surface plasmon resonance (HMM-SPR) sensor by composing a few pairs of alternating silver (Ag) and zinc oxide (ZnO) layers. Aiming to achieve the best design for the sensor, the dependence of the sensitivity on the incidence angle, the thickness of the alternating layer and the metal filling fraction are explored comprehensively. We find that the proposed HMM-SPR sensor achieves an average sensitivity of 34,800 nm per refractive index unit (RIU) and a figure of merit (FOM) of 470.7 RIU−1 in the refractive index ranging from 1.33 to 1.34. Both the sensitivity (S) and the FOM show great enhancement when compared to the conventional silver-based SPR sensor (Ag-SPR). The underlying physical reason for the higher performance is analyzed by numerical simulation using the finite element method. The higher sensitivity could be attributed to the enhanced electric field amplitude and the increased penetration depth, which respectively increase the interaction strength and the sensing volume. The proposed HMM-SPR sensor with greatly improved sensitivity and an improved figure of merit is expected to find application in biochemical sensing due to the higher resolution.

Controlling the amount of acoustic absorption by using clusters of hard cylinders

The viscothermal absorption of a cluster of hard cylinders periodically arranged in air is directly related with the filling fraction of the underlying lattice. In this work, we present a comprehensive study of the viscous absorption of clusters with circular external shape. The study has been performed by using a homogenization theory in which the clusters have been represented by a single fluid-like cylinder with effective parameters. The validity of the homogenization approach has been supported with numerical experiments in which the viscosity of the actual cluster is calculated with an improved version of the boundary element method. The simulations have been performed by embedding the clusters in a multimode impedance tube. For example, for a circular cluster containing 817 hard cylinders distributed in a hexagonal lattice with filling ratio of 0.836, the absorptive factor calculated with the homogenization approach is 41.5%, which underestimates by about 1% the value obtained with the complete cluster.

Left ventricular diastolic dysfunction in primary hypertension and ischemic heart disease-evaluation by doppler echocardiography

Background: Congestive heart failure caused by a predominant abnormality in diastolic function is both common and causes significant morbidity and mortality. The objective of the study was to evaluate application of doppler echocardiography in determining left ventricular diastolic dysfunction in ischemic heart disease and essential hypertension.Methods: Present study is based on analysis of 75 patients of hypertension and 60 patients of IHD (UA, AMI, IMI) admitted to Bapuji and Chigateri general hospital during December 2019 to November 2020. Detailed history and physical examination were done. Every patient was subjected to ECG, CXR, routine investigations and Doppler Echo cardiography.Results: A total of 75 patients of primary hypertension were studied. 37 patients showed diastolic dysfunction with E/A ratio <1, with increased atrial filling fraction. Out of 37 patients, 24 showed LVH and 13 cases did not have LVH. A total of 60 patients of ischemic heart disease were studied. 23 patients showed diastolic dysfunction with E/A ratio <1, with increased atrial filling fraction and prolonged isovolumetric relaxation time.Conclusions: Our findings suggest that myocardial damage in patients with HTN and IHD affects diastolic dysfunction before systolic dysfunction. Doppler echocardiography is a valuable non-invasive method to detect left ventricular diastolic impairment and the intentional assessment of diastolic function is advisable for early detection of LV dysfunction before clinical symptoms appear.

The Influence of Clamping, Structure Geometry, and Material on Seismic Metamaterial Performance

Diverting and controlling the impact of elastic vibrations upon an infrastructure is a major challenge for seismic hazard mitigation and for the reduction of machine noise and vehicle vibration in the urban environment. Seismic metamaterials (SMs), with their inherent ability to manipulate wave propagation, provide a key route for overcoming the technological hurdles involved in this challenge. Engineering the structure of the SM serves as a basis to tune and enhance its functionality, and inspired by split rings, swiss-rolls, notch-shaped, and labyrinthine designs of elementary cells in electromagnetic and mechanical metamaterials, we investigate altering the structure geometries of SMs with the aim of creating large bandgaps in a subwavelength regime. Interestingly, clamping an SM to the bedrock creates a zero frequency stopband, but further effects can be observed in the higher frequency regime due to their specific geometry. We show that square stiff inclusions perform better in comparison to circular ones while keeping the same filling fraction. En route to enhancing the bandgap, we have also studied the performance of SMs with different constituent materials; we find that steel columns, as inclusions, show large bandgaps, however, the columns are too large for steel to be a feasible material in practical or financial terms. Non-reinforced concrete would be preferable for industry level scaling up of the technology because, concrete is cost-effective, easy to cast directly at the construction site and easy to provide arbitrary geometry of the structure. As a part of this study, we show that concrete columns can also be designed to exhibit bandgaps if we cast them within a soft soil coating surrounding the protected area for various civil structures like a bridge, building, oil pipelines, etc. Although our motivation is for ground vibration, and we use the frequencies, lengthscales, and material properties relevant for that application, it is notable that we use the equations of linear elasticity, and our investigation is more broadly relevant in solid mechanics.

Dispersion Diagram of Trigonal Piezoelectric Phononic Structures with Langasite Inclusions

The dispersion relation of elastic Bloch waves in 1-3 piezoelectric phononic structures (PPnSs) with Langasite (La3Ga5SiO14) inclusions in a polymeric matrix is reported. Langasite presents promising material properties, for instance good temperature behaviour, high piezoelectric coupling, low acoustic loss and high quality factor. Furthermore, Langasite belongs to the point group 32 and has a trigonal structure. Thus, the 2-D bulk wave propagation in periodic systems with Langasite inclusions cannot be decoupled into XY and Z modes. The improved plane wave expansion (IPWE) is used to obtain the dispersion diagram of the bulk Bloch waves in 1-3 PPnSs considering the classical elasticity theory and D3 symmetry. Full band gaps are obtained for a broad range of frequency. The piezoelectricity enhances significantly the band gap widths and opens up a narrow band gap in lower frequencies for a filling fraction of 0.5. This study should be useful for surface acoustic wave (SAW) filter and 1-3 piezocomposite transducer design using PPnSs with Langasite.