Frequency-dependent damping in propagating slow magneto-acoustic waves

Propagating slow magneto-acoustic waves are often observed in polar plumes and active region fan loops. The observed periodicities of these waves range from a few minutes to few tens of minutes and their amplitudes were found to decay rapidly as they travel along the supporting structure. Previously, thermal conduction, compressive viscosity, radiation, density stratification, and area divergence, were identified to be some of the causes for change in the slow wave amplitude. Our recent studies indicate that the observed damping in these waves is frequency dependent. We used imaging data from SDO/AIA, to study this dependence in detail and for the first time from observations we attempted to deduce a quantitative relation between damping length and frequency of these oscillations. We developed a new analysis method to obtain this relation. The observed frequency dependence does not seem to agree with the current linear wave theory and it was found that the waves observed in the polar regions show a different dependence from those observed in the on-disk loop structures despite the similarity in their properties.Comment: accepted for publication in Ap

Propagating Disturbances along fan-like coronal loops in an active region

Propagating disturbances are often observed in active region fan-like coronal loops. They were thought to be due to slow mode MHD waves based on some of the observed properties. But the recent studies involving spectroscopy indicate that they could be due to high speed quasi-periodic upflows which are difficult to distinguish from upward propagating slow waves. In this context, we have studied a fan loop structure in the active region AR 11465 using simultaneous spectroscopic and imaging observations from Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode and Atmospheric Imaging Assembly (AIA) on board SDO. Analysis of the data shows significant oscillations at different locations. We explore the variations in different line parameters to determine whether the waves or flows could cause these oscillations to improve the current understanding on the nature of these disturbances.Comment: 12 pages, 6 figures. Accepted for publication in RA

Omnipresent long-period intensity oscillations in open coronal structures

Quasi-periodic propagating disturbances in coronal structures have been interpreted as slow magneto-acoustic waves and/or periodic upflows. Here we aim to understand their nature from the observed properties using a three-hour imaging sequence from AIA/SDO in two different temperature channels. We also compare the characteristics with a simple wave model. We searched for propagating disturbances in open-loop structures at three different locations; a fan loop-structure off-limb, an on-disk plume-like structure and the plume/interplume regions in the north pole of the sun. In each of the subfield regions chosen to cover these structures, the time series at each pixel location was subjected to wavelet analysis to find the different periodicities. We then constructed powermaps in three different period ranges. We also constructed space-time maps for the on-disk plume structure to estimate the propagation speeds in different channels. We find propagating disturbances in all three structures. Powermaps indicate that the power in the long-period range is significant up to comparatively longer distances along the loop than that in the shorter periods. This nature is observed in all three structures. A detailed analysis on the on-disk plume structure gives consistently higher propagation speeds in the 193 \AA channel and also reveals spatial damping along the loop. The amplitude and the damping length values are lower in hotter channels, indicating their acoustic dependence. These properties can be explained very well with a propagating slow-wave model. We suggest that these disturbances are more likely to be caused by propagating slow magneto-acoustic waves than by high-speed quasi-periodic upflows. We find that intensity oscillations in longer periods are omnipresent at larger heights even in active regions.Comment: accepted for publication in A &

The effects of rotational flow, viscosity, thickness, and shape on transonic flutter dip phenomena

The transonic flutter dip phenomena on thin airfoils, which are employed for propfan blades, is investigated using an integrated Euler/Navier-Stokes code and a two degrees of freedom typical section structural model. As a part of the code validation, the flutter characteristics of the NACA 64A010 airfoil are also investigated. In addition, the effects of artificial dissipation models, rotational flow, initial conditions, mean angle of attack, viscosity, airfoil thickness and shape on flutter are investigated. The results obtained with a Euler code for the NACA 64A010 airfoil are in reasonable agreement with published results obtained by using transonic small disturbance and Euler codes. The two artificial dissipation models, one based on the local pressure gradient scaled by a common factor and the other based on the local pressure gradient scaled by a spectral radius, predicted the same flutter speeds except in the recovery region for the case studied. The effects of rotational flow, initial conditions, mean angle of attack, and viscosity for the Reynold's number studied seem to be negligible or small on the minima of the flutter dip

A complete description of the magnetic ground state in spinel vanadates

Capturing the non-collinear magnetic ground state of the spinel vanadates AV$_2$O$_4$ (A= Mn, Fe and Co) remains an outstanding challenge for state-of-the-art ab-initio methods. We demonstrate that both the non-collinear spin texture, as well as the magnitude of local moments, are captured by a single value of the on-site Hubbard $U$ of 2.7~eV in conjunction with the local spin density approximation (LSDA+$U$), provided the source term (i.e., magnetic monopole term) is removed from the exchange-correlation magnetic field ${\bf B}_{XC}$. We further demonstrate that the magnetic monopole structure in ${\bf B}_{XC}$ is highly sensitive to the value of $U$, to the extent that the interplay between on-site localization and local moment magnitude is qualitatively different depending on whether the source term is removed or not. This suggests that in treating strongly correlated magnetic materials within the LSDA+$U$ formalism, subtraction of the unphysical magnetic monopole term from the exchange-correlation magnetic field is essential to correctly treat the magnetic ground state.Comment: 4 pages, 3 figure

മുത്തുകൃഷി

Pearl cultur

Soft tissue neoplasms: a clinicopathological study

Background: The current WHO classification has categorized soft tissue tumours into benign, malignant and so-called intermediate neoplasms. Soft tissue sarcoma comprises <1% of adult cancers. The aim of the study was to clinically correlate soft tissue neoplasms and study the histomorphological features of various malignant soft tissue tumors.Methods: This was a retrospective study conducted in a tertiary care hospital in Mangalore, India from January 2019 to June 2020. Clinical details of all cases of soft tissue neoplasms retrieved from the medical records of our institution. Data collected included age, gender, presenting symptoms, site and size of soft tissue neoplasms and clinical diagnosis. Pathological diagnosis of these tumours was made and details recorded.Results: A total of 113 cases of soft tissue neoplasms were collected. 94.4% benign and 18.6 %. malignant tumours were present. 77% cases presented with swelling whereas 23% presented with pain. Majority of benign soft tissue tumours were located in the trunk (36.9%) and the most common type was lipomas (66.38%). Malignant soft tissue tumours showed male to female ratio of 1.33:1. Most predilection was noted for the extremities (42.8%) and leiomyosarcomas were the most common type (38%).Conclusions: The incidence of malignant soft tissue tumours is rare. Majority of the cases were noted in the extremities. Leiomyosarcoma was the most common type, in our study. Lipomas were the most common benign soft tissue tumours, and majority of the benign tumours were located in the trunk.

Nanoscale quantum dot infrared sensors with photonic crystal cavity

We report high performance infrared sensors that are based on intersubband transitions in nanoscale self-assembled quantum dots combined with a microcavity resonator made with a high-index-contrast two-dimensional photonic crystal. The addition of the photonic crystal cavity increases the photocurrent, conversion efficiency, and the signal to noise ratio (represented by the specific detectivity D*) by more than an order of magnitude. The conversion efficiency of the detector at Vb=–2.6 V increased from 7.5% for the control sample to 95% in the PhC detector. In principle, these photonic crystal resonators are technology agnostic and can be directly integrated into the manufacturing of present day infrared sensors using existing lithographic tools in the fabrication facility

The effects of transients on photospheric and chromospheric power distributions

We have observed a quiet Sun region with the Swedish 1-meter Solar Telescope (SST) equipped with CRISP Imaging SpectroPolarimeter. High-resolution, high-cadence, H$\alpha$ line scanning images were taken to observe different layers of the solar atmosphere from the photosphere to upper chromosphere. We study the distribution of power in different period-bands at different heights. Power maps of the upper photosphere and the lower chromosphere show suppressed power surrounding the magnetic-network elements, known as "magnetic shadows". These also show enhanced power close to the photosphere, traditionally referred to as "power halos". The interaction between acoustic waves and inclined magnetic fields is generally believed to be responsible for these two effects. In this study we explore if small-scale transients can influence the distribution of power at different heights. We show that the presence of transients, like mottles, Rapid Blueshifted Excursions (RBEs) and Rapid Redshifted Excursions (RREs), can strongly influence the power-maps. The short and finite lifetime of these events strongly affects all powermaps, potentially influencing the observed power distribution. We show that Doppler-shifted transients like RBEs and RREs that occur ubiquitously, can have a dominant effect on the formation of the power halos in the quiet Sun. For magnetic shadows, transients like mottles do not seem to have a significant effect in the power suppression around 3 minutes and wave interaction may play a key role here. Our high cadence observations reveal that flows, waves and shocks manifest in presence of magnetic fields to form a non-linear magnetohydrodynamic system.Comment: 11 pages, 11 Figures, 4 movies (will be available online in ApJ). ApJ (accepted