Nature of Quiet Sun Oscillations Using Data from the Hinode, TRACE, and SOHO Spacecraft

We study the nature of quiet-Sun oscillations using multi-wavelength observations from TRACE, Hinode, and SOHO. The aim is to investigate the existence of propagating waves in the solar chromosphere and the transition region by analyzing the statistical distribution of power in different locations, e.g. in bright magnetic (network), bright non-magnetic and dark non-magnetic (inter-network) regions, separately. We use Fourier power and phase-difference techniques combined with a wavelet analysis. Two-dimensional Fourier power maps were constructed in the period bands 2??C?4?minutes, 4??C?6?minutes, 6??C?15?minutes, and beyond 15?minutes. We detect the presence of long-period oscillations with periods between?15 and 30?minutes in bright magnetic regions. These oscillations were detected from the chromosphere to the transition region. The Fourier power maps show that short-period powers are mainly concentrated in dark regions whereas long-period powers are concentrated in bright magnetic regions. This is the first report of long-period waves in quiet-Sun network regions. We suggest that the observed propagating oscillations are due to magnetoacoustic waves, which can be important for the heating of the solar atmosphere.     

Dynamics of Coronal Bright Points as Seen by Sun Watcher Using Active Pixel System Detector and Image Processing (SWAP), Atmospheric Imaging Assembly (AIA), and Helioseismic and Magnetic Imager (HMI)

The Sun Watcher using Active Pixel system detector and Image Processing (SWAP) onboard the PRoject for OnBoard Autonomy-2 (PROBA2) spacecraft provides images of the solar corona in EUV channel centered at 174 Å. These data, together with the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO), are used to study the dynamics of coronal bright points. The evolution of the magnetic polarities and associated changes in morphology are studied using magnetograms and multi-wavelength imaging. The morphology of the bright points seen in low-resolution SWAP images and high-resolution AIA images show different structures, whereas the intensity variations with time show similar trends in both SWAP 174 Å and AIA 171 Å channels. We observe that bright points are seen in EUV channels corresponding to a magnetic flux of the order of 10¹⁸ Mx. We find that there exists a good correlation between total emission from the bright point in several UV–EUV channels and total unsigned photospheric magnetic flux above certain thresholds. The bright points also show periodic brightenings, and we have attempted to find the oscillation periods in bright points and their connection to magnetic-flux changes. The observed periods are generally long (10?–?25 minutes) and there is an indication that the intensity oscillations may be generated by repeated magnetic reconnection.     

Spectroscopic Observation of Oscillations in the Corona During the Total Solar Eclipse of 22 July 2009

We performed high resolution spectroscopy of the solar corona during the total solar eclipse of 22 July 2009 in two emission lines: the green line at 5303 ? due to Fe xiv and the red line at 6374 ? due to Fe x, simultaneously from Anji (latitude 30°28.1′ N; longitude 119°35.4′ E; elevation 890 m), China. A two-mirror coelostat with 100 cm focal length lens produced a 9.2 mm image of the Sun. The spectrograph using 140 cm focal length lens in Littrow mode and a grating with 600 lines per millimeter blazed at 2 μm provided a dispersion of 30 m? and 43 m? per pixel in the fourth order around the green line and third order around the red line, respectively. Two Peltier cooled 1k × 1k CCD cameras, with a pixel size of 13 μm square and 14-bit readout at 10 MHz operated in frame transfer mode, were used to obtain the time sequence spectra in two emission lines simultaneously. The duration of totality was 341 s, but we could get spectra for 270 s after a trial exposure at an interval of 5 s. We report here on the detection of intensity, velocity, and line width oscillations with periodicity in the range of 25 – 50 s. These oscillations can be interpreted in terms of the presence of fast magnetoacoustic waves or torsional Alfvén waves. The intensity ratios of green to red emission lines indicate the temperature of the corona to be 1.65 MK in the equatorial region and 1.40 MK in the polar region, relatively higher than the expected temperature during the low activity period. The width variation of the emission lines in different coronal structures suggests different physical conditions in different structures.     

Dynamic Behavior of Small Scale Nailed Soil Slopes

The shaking table tests are conducted on small scale nailed embankment slopes to study their behavior under dynamic conditions. Medium grained local sand with a water content of 3% is used in the study. The embankment slope is constructed using the controlled-volume compaction method. Three slope angles, 30°, 35° and 40° with a constant slope height of 18 cm are considered for the embankment. Each slope is reinforced with six number of hollow aluminum nails in two rows. The ratio of the length of nail to slope height (0.82) is same for all model slopes. The nails are inserted at three different inclinations. Three strain gauges are glued to each nail to obtain local strains during shaking. The accelerations at the base and the crest of the model slopes are monitored to find the acceleration responses of the embankments during the input ground motions. The numerical simulation of the model tests is performed by a commercial program called FLAC. The results of the numerical analyses are found to be reasonably close to the corresponding experimental results.     

Propagation of axi-symmetric relativistic shock waves

Solutions in series for the propagation of relativistic shock waves with axial symmetry are obtained in this paper. We assume that the gaseous elements move almost radially and that the disturbance moves through a cold gas at rest wherein the nucleon number density and the energy density obey an exponential law of distance from a given plane. The motion is sustained by continuous explosions in the central region liberating energy varying as the cube of time. Also, we assume the equation of state of the moving elements as that of photonic gas.     

A plasticity model for the mechanical behaviour of anisotropically consolidated clay

An incremental plasticity theory has been developed to describe the mechanical behaviour of anisotropically consolidated clays. The theory removes some of the shortcomings of the existing critical state models by incorporating the effects of the initial anisotropy due to a known depositional stress history and its subsequent alteration during further plastic deformation under a general stress system. From the extensive comparisons with the reported results in the literature, it is established that the model is satisfactory in predicting the various aspects of drained as well as undrained behaviour of K₀-consolidated clays.     

A qualitative assessment of seismic risk along the Peninsular coast of India, south of 19°N

Many earthquakes have been recorded from the coastal margin of the Indian peninsular shield during the last 200 years. Largely made up of Precambrian assemblages with variable cover of Jurassic to Quaternary sedimentary rocks and Cretaceous-Eocene volcanics, the peninsular shield was long held to be aseismic. Recent measurements, however, show that this continental fragment is being pushed northeastward by the Carlsberg and Central Indian ridges; and the Indo-Myanmar subduction zone is exerting vigorous slab pull towards the east. Repeated cycles of sea level change during the Quaternary have also induced continuing hydro-isostatic adjustment due to variable melt water loading in the Bay of Bengal and the Arabian sea. All these forces produce space-time fluctuations of strain around many small to large faults, which occur in the upper crust of the shield. Some of the faults have been intermittently active (during the past 100 kyr); others were active earlier. Although the Shillong plateau and the associated hill ranges of northeastern India and Myanmar are subject to the maximum seismic hazard, the peninsular coast is also vulnerable to intermittent seismicity. We present illustrative evidence of some active faults, which are recognisable (a) on coastal land by displaced Pleistocene weathered cover, hot springs, leakages of native mercury and allochthonous geochemical anomalies of base metals and (b) offshore below the inner shelf by horst-shaped uplifted segments and intra-formational slump folds on and below the top shallow seismic (3.5 kHz) reflector. On the other hand, there are long stretches of the east coast at Vishakhapatnam and Manappad Point, which do not show active faults. Step-like marine terraces, which occur up to+6 m above the low tide level (LTL) preserve records of relative sea level fluctuations during the Holocene and the Last Interglacial. In such sectors, absence of tectonic disturbance during the last 100 ka is also corroborated by lateral continuity of shallow seismic reflectors below the inner shelf over many kilometers. Since authentic historical (200–1000 years B.P.) records of seismicity along the Peninsular coast are virtually unavailable, the likely recurrence interval between earthquakes in each sector cannot be gauged. We, therefore, propose a scale of seismic risk, based on geometry of the mappable faults and available seismic records of the last two centuries. These could be used in combination to rank the densely populated coastal tracts sector-wise.     

Nature and distribution of manganese nodules from three sediment domains of the Central Indian Basin,Indian Ocean

Manganese nodules from the Central Indian Basin (5°–10°S) vary in abundance, morphology, mineralogy, and chemistry with water depth and sediment type. Nodules from the southern region, dominated by siliceous sediment, differ markedly from northern and central regions, dominated by terrigenous and terrigenous-siliceous mixed sediments, respectively. Effects of lysocline and sediment diagenesis are envisaged for trace metal enrichment in rough nodules of the southern region. Influence of deep ocean bottom currents have been postulated for the atypical trace metal enrichment of the smooth nodules from other regions. While nodules from other areas of sub-equatorial CIB are grown hydrogenetically, present area nodules show diagenetic influence.     

Effect of alcohol and polyglycol ether frothers on foam stability,bubble size and coal flotation

The frothers of alcohol family (MIBC and Alpha-terpineol) were compared with polyglycol ethers (DF-1012) in terms of two phase characterization parameters like foamability, foam stability, surface activity and bubble size distribution. In this research, fundamental two phase frother characterization parameters were linked with three phase coal flotation behavior.     

Interpretations of self potential anomalies due to localised causative bodies

Summary Some direct methods of interpretation of SP anomalies that may arise from localised causative bodies have been developed in this paper. The models of the current sources that have been considered here are the cases of 1. single vertical dipole, 2. a pair of similar and similarly situated vertical dipoles and 3. an inclined dipole. A set of three master curves has been prepared in terms of which the interpretation in the first and the third case is complete. With an additional assumption that the distance between the dipoles is small, the second case also is completely solved with the help of the same set of master curves.Published under the kind permission of the Director General, Geological Survey of India, Calcutta.