Radio-continuum study of the nearby sculptor group galaxies. Part 3: NGC 7793 at λ=12.2, 6 and 3 cm

We re-examine a series of archived centimetre radio-continuum observations (λ=16, 6 and 3 cm) focusing on NGC?7793 using the Australia Telescope Compact Array. These new images are both very sensitive (σ=0.011 mJy/beam) and feature reasonably high angular resolution (down to <3″). Using these images, a total of 76 discrete radio sources are identified, of which 57 have been classified. We also studied the radio component of the micro-quasar NGC7793-S26 which shows two distinct regions of somewhat steep spectral index (α) between ?0.3 and ?0.7.     

Prospect for UV observations from the Moon

Space astronomy in the last 40 years has largely been done from spacecraft in low Earth orbit (LEO) for which the technology is proven and delivery mechanisms are readily available. However, new opportunities are arising with the surge in commercial aerospace missions. We describe here one such possibility: deploying a small instrument on the Moon. This can be accomplished by flying onboard the Indian entry to the Google Lunar X PRIZE competition, Team Indus mission, which is expected to deliver a nearly 30 kgs of payloads to the Moon, with a rover as its primary payload. We propose to mount a wide-field far-UV (130–180 nm) imaging telescope as a payload on the Team Indus lander. Our baseline operation is a fixed zenith pointing but with the option of a mechanism to allow observations of different attitudes. Pointing towards intermediate ecliptic latitude (50^° or above) ensures that the Sun is at least 40^° off the line of sight at all times. In this position, the telescope can cover higher galactic latitudes as well as parts of Galactic plane. The scientific objectives of such a prospective are delineated and discussed.     

A study of halo orbits at the Sun–Mars L1 Lagrangian point in the photogravitational restricted three-body problem

Photogravitational Restricted Three-Body Problem (PGRTBP) is considered and halo orbits are generated in the vicinity of the Sun–Mars L₁ Lagrangian point. Deviation of properties such as time period, size and velocity variation in the halo orbits with Sun as a source of radiation are discussed. With increase in solar radiation pressure, the halo orbits are found to elongate and move towards the Sun and the time period of the halo orbits is found to increase. The variation in the behaviour of invariant manifolds with change in radiation pressure is also computed and it is found that as the radiation pressure increases, the transition from Mars-centric path to heliocentric path is delayed. Certain implications of the velocity profile of the invariant manifolds are also discussed.     

Nonlinear effects associated with the finite frequency pump kinetic Alfvén wave and turbulent spectrum in solar wind

The paper contains a numerical simulation of the nonlinear coupling between the kinetic Alfvén wave and the ion acoustic wave for an intermediate β-plasma (m _e/m _i?β?1). For this study, we have introduced the nonlinear ponderomotive force (due to the finite frequency (ω ₀<ω _ci) kinetic Alfvén wave) in the derivation of the ion acoustic wave. The main aim of the present paper is to study the nonlinear effects associated with the different driving finite frequencies (ω ₀<ω _ci) of the pump kinetic Alfvén wave on the formation of localized structures and a turbulent spectrum applicable to the solar wind around 1 AU. As a result, we found that the different driving frequencies of the pump kinetic Alfvén wave affect the formation of the localized structures. We have also studied the turbulent scaling which follows (～k ^?3.6) for ω ₀/ω _ci≈0.2, (～k ^?3.4) for ω ₀/ω _ci≈0.3 and (～k ^?3.2) for ω ₀/ω _ci≈0.4, at small scales. Further, we have also found that different finite driving frequencies of the pump kinetic Alfvén wave affect the turbulence scaling at small scales, which may affect the heating of the plasma particles in solar wind. The present study is correlated with the observation made by the Cluster spacecraft for the solar wind around 1 AU.     

Modified Jeans instability of magnetized viscous spin 1/2 quantum plasma with resistive effects and Hall current

Properties of ion acoustic solitons head-on collision in an ultracold neutral plasma composed of ion fluid and non-Maxwellian electron distributions are investigated. For this purpose, the extended Poincare-Lighthill-Kuo (PLK) method is employed to derive coupled Kortweg-de Vries (KdV) equations describing the system. The nonlinear evolution equations for the colliding solitons and corresponding phase shifts are investigated both analytically and numerically. It is found that the polarity of the colliding solitons strongly depends on the type of the non-Maxwellian distribution (via nonthermal or superthermal electron distributions). Especially the phase shift due to solitons collision is strongly influenced by the non-Maxwellian distribution. A new critical nonthermal parameter β _c , characterizing the nonthermal electron distribution, and which is not present for superthermal particle distributions, allows the existence of double polarity of the solitons. The phase shift increases below β _c for compressive solitons, but it decreases above β _c for rarefactive soliton. For superthermal distribution the phase shift increases rapidly for low spectral index κ, whereas for higher values of κ, the phase shift decreases smoothly and becomes nearly stable for κ>10. Around β _c and small values of κ, the deviation from the Maxwellian state is strongest, and therefore the phase shift has unexpected behavior due to the presence of more energetic electrons that are represented by the non-Maxwellian distributions. The nonlinear structure, as reported here, could be useful for controlling the solitons that may be created in future ultracold neutral plasma experiments.     

Nonlinear evolution of kinetic Alfvén wave and turbulent spectra: effect of initial conditions

Using the 2D numerical simulation we have studied the nonlinear evolution of kinetic Alfvén wave (KAW) in intermediate β plasmas (β?m _e /m _i ?1). The coupled equations of kinetic Alfvén wave (KAW) and ion acoustic wave (IAW) have been studied with different initial conditions using (1) periodic perturbation, (2) Gaussian perturbation and (3) random perturbation. We have studied the effect of initial conditions on the filament formation and on the turbulent scaling laws. The scale size of the localized structures is also obtained under different conditions.     

Formation of the localized structures and the generation of turbulence by 3-dimensional kinetic Alfvén waves in solar wind plasmas

In the present paper, we have investigated nonlinear interaction of three dimensional kinetic Alfvén wave with perpendicularly propagating magnetosonic wave for intermediate β-plasma (m _e /m _i ?β?1). We have developed the set of dimensionless equations in the presence of ponderomotive nonlinearity due to three dimensional kinetic Alfvén wave in the dynamics of perpendicularly propagating magnetosonic wave. Numerical simulation has been carried out to study the effect of nonlinear coupling of three dimensional kinetic Alfvén wave with perpendicularly propagating magnetosonic wave on power spectrum for the plasma parameters applicable to solar wind around 1 AU. Relevance of the obtained results is pointed out with observation received by Cluster spacecraft for the solar wind around 1 AU.     

Transport and mobilization of multiwall carbon nanotubes in quartz sand under varying saturation

In this study, a series of sand packed columns were used to investigate the mobility of multiwall carbon nanotubes (MWCNTs) in unsaturated porous media under unfavorable conditions for deposition. The flow through column experiments were designed to assess water content, flow rate, and grain size effect on the mobility of MWCNTs. It was found that variation in water content had no significant effect on retention of MWCNTs until it was lowered to 16 % effective saturation. Thick water films, high flow rate, and repulsive forces between MWCNTs and porous media made MWCNTs highly mobile. Different porous media grain sizes (D ₅₀ = 150–300 μm) were used in this study. The mobility of MWCNTs slightly decreased in finer grain sands, which was deemed to be an effect of increase in surface area and the number of depositional sites, in combination with low-pore water velocity. However, physical straining was not observed in selected fine-grain sands and aspect ratio of MWCNTs had low impact on mobility. Variations in pore-water velocity were produced by both changes in water saturation and in flow rate. At high pore-water velocities, the MWCNTs were generally mobile. However, for the combination of low-pore water velocity with either low water saturation or small grain size, some retention of MWCNTs was observed. Hence, low velocity in combination with flow through smaller pores increased MWCNT deposition.     

Stability investigation of hill cut soil slopes along National highway 222 at Malshej Ghat,Maharashtra

The section of about 12 km of National highway 222 passing through the Malshej Ghat experience frequent slope failure due to complex geological condition, heavy rainfall and slope geometry. The area is part of Western Ghat Deccan trap and slope masses are made of basalt and its weathered crust (debris/soil). The soil slope failure problem mainly occur in rainy seasons due to induced pore water pressure and reduced strength of the slope mass. The present study has been carried out to investigate the slope forming material and assess the stability of soil slopes by numerical approach. For the identification of the vulnerable zones, field study has been carried out and five vulnerable soil slopes identified namely MGS1, MGS2, MGS3, MGS4 and MGS5 on the basis of degree of weathering and slope geometry. The laboratory experiments were carried out to determine the strength properties of the geomaterials. All the input variables acquired from the field and laboratory experiments have been used for numerical simulation, which was performed with the help of limit equilibrium method (LEM) and finite element method (FEM). Numerical analysis provides understanding of the slope behaviour and illustrates that MGS1 and MGS3 are stable slopes, MGS2 and MGS4 are critically stable, whereas, slope MGS5 is unstable. This study recommend the protection of soil slopes and suggest that more detailed investigation is required for long term remedial measures to prevent risk of damage in Malshej Ghat.     

Assessment of Durability and Weathering State of Some Igneous and Metamorphic Rocks Using Micropetrographic Index and Rock Durability Indicators: A Case Study

Weathering and durability are the key factors of the rock in the suitability and usefulness of different construction materials, building materials and engineering structures. A single test never predicts the entire factor for suitability of rock stone and aggregate in different uses. Thus, variety of physical, mechanical and chemical tests and indices of rocks are widely used to estimate and evaluate the rocks for the suitability of the required purpose. In all the cases, knowledge of durability and weathering properties are the most important along with the strength of the rock. Micropetrographic index and rock durability indicators (dynamic and static) are the one of the best methods to evaluate the rock for weathering and durability. To estimate these indices, variety of tests are performed such as petrographic examination test, point load index, sulfate soundness test, water absorption test, modified aggregate impact value test and test for specific gravity. Slake durability index and impact strength index tests were also performed for correlation with static and dynamic rock durability indicators due to its application and usefulness in the durability and strength of the rock materials. Micropetrographic index was obtained by petrographic examination test and correlated with all the physical and mechanical properties used for find out the durability indicators. The present study is to express the usefulness of these three indices in the classification of weathering and durability classes and estimation of durability indices by slake durability index, impact strength index and micropetrographic index.