Detection of ionospheric perturbation due to a soft gamma ray repeater SGR J1550-5418 by very low frequency radio waves

The properties of cylindrical and spherical dust acoustic (DA) solitary and shock waves in an unmagnetized electron depleted dusty plasma consisting of inertial dust fluid and ions featuring Tsallis statistics are investigated by employing the reductive perturbation technique. A Korteweg-de Vries Burgers (KdVB) equation is derived and its numerical solution is obtained. The effects of ion nonextensivity and dust kinematic viscosity on the basic features of DA solitary and shock waves are discussed in nonplanar geometry. It is found that nonextensive nonplanar DA waves behave quite differently from their one-dimensional planar counterpart.     

Unique Observation of a Solar Flare by Lunar Occultation During the 2010 Annular Solar Eclipse Through Ionospheric Disturbances of VLF Signals

Very Low Frequency (VLF) radio waves propagate through the Earth-ionosphere waveguide. Irregularities caused by excess or deficient extreme ultra-violet and X-rays, which otherwise sustain the ionosphere, change the waveguide properties and hence the signals are modified. We report the results of monitoring of the NWC transmitter (19.8?kHz) by a receiver placed at Khukurdaha (22°27′N, 87°45′E) during the partial solar eclipse (75?%) of 15th January, 2010. The propagation path from the transmitter to the receiver crosses the annular eclipse belt. We got a clear depression in the data during the period of the eclipse. Most interestingly, there was also a X-ray flaring activity in the sun on that day which reached its peak (C-type) right after the time when the eclipse reached its maximum. We saw the effects of the occultation of this flare in our VLF signal since a part of the X-ray active region was clearly blocked by the moon. We quantitatively compared by using analogies with previous observations and found best fitting parameters for the time when the flare was occulted. We then reconstructed the VLF signal in the absence of the occulted flare. To our knowledge, this is the first such incident where the solar flare was observed through lunar occultation and that too during a partial eclipse.     

A LiDAR study of the effective size of cirrus ice crystals over Chung-Li,Taiwan

In this paper, we estimated the effective size of ice crystals in cirrus clouds using fall velocity derived from LiDAR (light detection and ranging) measurements at Chung-Li (24.58°N, 121.1°E), Taiwan. Nine shapes of the ice crystals, viz. hexagonal plates, hexagonal columns, rimed long columns, crystals with sector-like branches, broad-branched crystals, stellar crystal with broad arms, side planes, bullet rosettes and assemblages of planar poly-crystals of specific dimensions have been analyzed. The results show that the lidar derived most probable mean effective size of ice crystals is 340±180 μm with a dominant size range of 200–300 μm. The lidar derived mean effective size of cirrus crystals are parameterized in terms of cloud mid-height temperature as well as optical depth. The discussed method will be useful to study the most probable effective size distribution of ice crystals in cirrus cloud.     

Studies of accretion flows around rotating black holes – III. Shock oscillations and an estimation of the spin parameter from QPO frequencies

In the present communication of our series of papers dealing with the accretion flows in the pseudo-Kerr geometry, we discuss the effects of viscosity on the accretion flow around a rotating black hole. We find the solution topologies and give special attention to the solutions containing shocks. We draw the parameter space where standing shocks are possible and where the shocks could be oscillating and could produce quasi-periodic oscillations (QPOs) of X-rays observed from black hole candidates. In this model, the extreme locations of the shocks give the upper limits of the QPO frequencies  (ν_QPO)  which could be observed. We show that both the viscosity of the flow and the spin of the black hole a increase the QPO frequency while, as expected, the black hole mass reduces the QPO frequencies. Our major conclusion is that the highest observed frequency gives a strict lower limit of the spin. For instance, a black hole exhibiting  ν_QPO∼ 400  and  700 Hz  must have the spin parameters of   a > 0.25  and  >0.75  , respectively, provided viscosity of the flow is small. We discuss the implications of our results in the light of observations of QPOs from black hole candidates.     

First report of trace fossils from Palaeogene succession (Namunagarh grit) of Andaman and Nicobar islands

The Namunagarh grit of Eocene age in South Andaman island is a submarine fan deposit where sedimentation occurred in deep marine environment mainly by turbidity currents. The mudstone and fine-grained sandstone of the turbidite sequence yielded three ichnogenera viz Thalassinoides, Teichichnus and Lorenzinia. Typically shallow marine Thalassinoides burrows co-occur with deep water burrows represented by Teichichnus and Lorenzinia, indicating a dominant control of substrate, availability of food and rate of sedimentation against bathymetry on distribution of trace fossils. Trace fossils are particularly abundant in the mudstones pointing to a strong lithofacies control. A well-oxygenated muddy bottom with a low rate of sedimentation is envisaged. An order in the succession of traces could be deciphered. Simply constructed burrows of Thalassinoides appeared initially followed by complex structures of Teichichnus and ornate Lorenzinia.     

Some auroral properties from far ultraviolet observations

Recent far ultraviolet spectra of four nightside auroras observed with the extreme ultraviolet (e.u.v.) spectrometer abroad the STP 78?1 satellite (Bowyer et al., 1981) are discussed in terms of two secondary electron flux distribution models. One of these is based on calculations published by Rees and Maeda (1973) and the other on electron flux observations. Using the 1084 Å NII line as the norm, the relative intensities of several lines in the range 900–1400 Å could be fitted equally well by either model, indicating that some of these emission ratios are somewhat independent of the energy dependence of the secondary electron flux. The ratio of the NI 1243 Å to 1084 Å emission is seen to yield an effective correlation for the other observed emissions and a reasonably consistent estimate of the penetration depth of the aurora.     

Earthquake analysis of concrete gravity dams including dam-water-foundation rock interaction

A general procedure for analysis of the response of concrete gravity dams, including the dynamic effects of impounded water and flexible foundation rock, to the transverse (horizontal) and vertical components of earthquake ground motion is presented. The problem is reduced to one in two dimensions, considering the transverse vibration of a monolith of the dam. The system is analysed under the assumption of linear behaviour for the concrete, foundation rock and water. The complete system is considered as composed of three substructures—the dam, represented as a finite element system, the fluid domain, as a continuum of infinite length in the upstream direction, and the foundation rock region as a viscoelastic half-plane. The structural displacements of the dam are expressed as a linear combination of Ritz vectors, chosen as normal modes of an associated undamped dam-rock system. The effectiveness of this analytical formulation lies in its being able to produce excellent results by considering only a few Ritz vectors. The generalized displacements due to earthquake motion are computed by synthesizing their complex frequency responses using Fast Fourier Transform procedures. The stress responses are calculated from the displacements. An example analysis is presented to illustrate results obtained from this analytical procedure. Computation times for several analyses are presented to illustrate the effectiveness of the procedure.     

Oriented transformation of grunerite to clinoferrosilite at 775° C and 500 bars Argon pressure

A member of the grunerite series (Fe_6.685Mn_0.142Ca_0.110Mg_0.096) (Si_7.968Al_0.016)O₂₂(OH)₂, has been transformed to clinoferrosilite, amorphous silica and water at 775° C and 500 bars Argon pressure. Single crystal photographs of an oriented intergrowth of the amphibole and pyroxene show that the clinoferrosilite retains the cristallographic a, b and c axes of the original grunerite in the I2/m orientation and has the cell dimensions: a=9.77, b=9.08, c=5.30 Å, =109.5°; space group P2₁/c. Mössbauer resonance spectroscopy confirmed the identity of the olinoferrosilite.A transformation mechanism requires a minimum of ionic movements in an acceptor region (7/8 of the total crystal), where pyroxene is formed by expulsion of protons and acceptance of Fe²⁺ ions; simultaneous destruction of donor regions provide the Fe²⁺ ions, the residue being silica and water. The formation of metastable clinoferrosilite rather than fayalite and quartz indicates the strong structural control imposed by the host grunerite structure on the nature of the transformation products.     

Strong site preference of Co2+ in olivine,Co1.10Mg0.90SiO4

The crystal structure and site preference of Co²⁺ in a synthetic Co_1.10Mg_0.90SiO₄ olivine have been determined from single crystal X-ray diffraction data collected on an automatic diffractometer. The R factor is 0.044 for 612 reflections. The site occupancies are: Ml site: Co 0.730±0.006; Mg 0.270; M2 site: Co 0.370, Mg 0.630. The Gibbs free energy change, ΔG° for the ion-exchange reaction between M1 and M2 sites is ?4.06 kcals/mole, assuming ideal mixing at each set of sites. This energy may be called ‘site preference energy’ of Co²⁺ in olivine. The strong preference of Co²⁺ for the M1 site can be quantitatively explained by two competing forces: preference of ions larger than Mg²⁺ for the M2 site and stronger covalent bonding of transition metal ions at the M1 site. For Fe²⁺, Mg²⁺, these two effects nearly neutralize each other, explaining the lack of considerable cation-ordering in Fe-Mg olivines.