561 research outputs found
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
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 &
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
Comparison of Accuracy Measures for RS Image Classification using SVM and ANN Classifiers
The accurate land use land cover (LULC) classifications from satellite imagery are prominent for land use planning, climatic change detection and eco-environment monitoring. This paper investigates the accuracy and reliability of Support Vector Machine (SVM) classifier for classifying multi-spectral image of Hyderabad and its surroundings area and also compare its performance with Artificial Neural Network (ANN) classifier. In this paper, a hybrid technique which we refer to as Fuzzy Incorporated Hierarchical clustering has been proposed for clustering the multispectral satellite images into LULC sectors. The experimental results show that overall accuracies of LULC classification of the Hyderabad and its surroundings area are approximately 93.159% for SVM and 89.925% for ANN. The corresponding kappa coefficient values are 0.893 and 0.843. The classified results show that the SVM yields a very promising performance than the ANN in LULC classification of high resolution Landsat-8 satellite images
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 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
Effect of Lutein in the expression of PPARα and LDLR in hypercholesterolemic male Wistar Rats
Background: Hyperlipidemia is a well known risk factor for cardiovascular disease, especially atherosclerotic coronary artery disease. Peroxisome proliferator activated receptor α (PPARα), a member of this nuclear receptor family, has emerged as an important player in this scenario, with evidence supporting a central co-ordinated role in the regulation of fatty acid oxidation, lipid and lipoprotein metabolism and inflammatory and vascular responses, all of which would be predicted to reduce atherosclerotic risk. The low-density lipoprotein (LDL) receptor (LDLR) is the primary pathway for removal of cholesterol from the circulation, and its activity is meticulously governed by intracellular cholesterol levels. Hence in this study we investigated the effect of Lutein on PPARα and LDLR expression in liver of wistar rats.Methods: Male Wistar rats were divided into 6 groups of 6 each. Group I served as control. Group II III, IV, V and VI rats were received high cholesterol diet. Group III was treated with Atorvastatin 5mg/kg. Group IV, V and VI rats were treated with 25mg/kg, 50mg/kg and 100mg/kg of Lutein. After 16 weeks, liver tissue samples were collected from all the groups of animals to evaluate the expression of PPARα and LDLR.Results: The expression of Peroxisome proliferator activated receptor α and low-density lipoprotein (LDL) receptor (LDLR) was significantly increased in Lutein treated hypercholesterolemic male wistar rats.Conclusions: The results of this study indicate that Lutein activates LDL receptor and PPARα in hypercholesterolemic male wistar rats
Prevalence of thyroid dysfunction and its association with controlled and uncontrolled type 2 diabetes mellitus in northern Andhra Pradesh population: a retrospective study
Background: The two important endocrinopathies, diabetes mellitus and thyroid dysfunction are interrelated to each other where the correlation is poorly understood. The thyroid dysfunction is more frequent in diabetics than general population. The present study was aimed to know the prevalence of thyroid dysfunction in type 2 diabetes mellitus (T2DM) and its association with controlled and uncontrolled T2DM.Methods: A retrospective study of 600 T2DM patients between 13-60 years of age with known thyroid status were included and the following parameters were examined: age, sex, body mass index (BMI), fasting blood sugar (FBS), HbA1C, free triiodothyronine (fT3), free tetraiodothyronine (fT4) and thyroid stimulating hormone (TSH).Results: The prevalence of thyroid dysfunction in T2DM patients was found to be 26.5% whereas 9% in healthy controls. Significantly elevated levels of FBS, HbA1C and TSH were observed whereas the levels of fT3, fT4 were found to be low in patients when compared to controls. Subclinical hypothyroidism (SCH) in diabetics (both controlled and uncontrolled) was more prevalent (15%) than it was found in healthy controls (5%). Similarly, overt hypothyroidism was also found to be high in diabetic patients (6%) as compared to healthy controls (2%). Significant difference (p <0.05) in the levels of TSH was found between group I (Controlled T2DM) and II (uncontrolled T2DM patients), also between groups II and III (Controls). Group II patients were found to have significant low levels of fT3 as compared to other two groups (Group I and III) (p<0.005).Conclusions: As SCH is more frequent in T2DM diabetes mellitus and untreated SCH patients have higher rate of complications, periodical screening is advised for thyroid dysfunction to prevent micro vascular and cardiovascular complications
Low-stress mechanical properties and fabric hand of cotton and polylactic acid fibre blended knitted fabrics
Low-stress mechanical behavior of cotton-rich/polylacticacid blended fabrics has been investigated and the results arecompared with cotton and polylactic acid fibre fabrics. Thepolylactic acid fibres are mixed with cotton fibres in two differentproportions, namely 20% and 35% and spun into 14.76 tex (40sNe) yarn. The yarns are then knit into single jersey structurefollowed by chemical pretreatments and relaxation. The relaxedfabrics are tested for low-stress mechanical properties usingKawabata evaluation system for fabrics (KES-F) and the handvalues are calculated. The results show that the addition of PLAfibres to cotton enhances the smoothness and softness of theblended fabrics. The total hand value of the fabrics rangesbetween 3.2 and 3.5
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