On the Large-Scale Diffuse Magnetic Field of the Sun

Although the sunspots migrate towards the equator, the large-scale weak diffuse magnetic fields of the Sun migrate poleward with the solar cycle, the polar field reversing at the time of the sunspot maxima. We apply the vector model of Dikpati and Choudhuri (1994, Paper I) to fit these observations. The dynamo layer at the base of the convection zone is taken to be the source of the diffuse field, which is then evolved in the convection zone subject to meridional circulation and turbulent diffusion. We find that the longitudinally averaged observational data can be fitted reasonably well both for positive and negative values of the alpha-effect by adjusting the subsurface meridional flow suitably. The model will be extended in a future paper to include the decay of active regions as an extra source of the diffuse field, which may be necessary to explain the probable phase lag between B-tau and B-phi at lower latitudes.

On the large-scale diffuse magnetic field of the sun - II. The contribution of active regions

Dikpati and Choudhuri (1993, 1995) developed a model for the poleward migration of the weak diffuse magnetic field on the Sun's surface. This field was identified with the poloidal component produced by the solar dynamo operating at the base of the convection zone, and its evolution was studied by considering the effects of meridional circulation and turbulent diffusion. The earlier model is extended in this paper by incorporating the flux from, the decay of tilted active regions near the solar surface as an additional source of the poloidal field. This extended model can now explain various low-latitude features in the time-latitude diagram of the weak diffuse fields. These low-latitude features could not be accounted for in the earlier model, which was very successful in modeling the behavior at high latitudes. The time-latitude diagrams show that regions of a particular polarity often have 'tongues' of opposite polarity. Such tongues can be produced in the theoretical model by incorporating fluctuations in the source term arising out of the decaying active regions.

Finding India’s place in the Sun –Prospects for harnessing solar thermal energy

In this article, we describe our ongoing efforts in addressing the environment and energy challenges facing the world today. Tapping solar thermal energy seems to be the right choice for a country like India. We look at three solar-thermal technologies in the laboratory — water purification/distillation, Stirling engine, and air-conditioning/refrigeration.

Pulsed plasma treatment of polluted gas using wet/low temperature corona reactors

pplication of pulsed plasma for gas cleaning is gaining prominence in recent years mainly from the energy consideration point of view. Normally, gas treatment is carried out, at or above room temperature, by a conventional dry type corona reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the exhaust/flue gas mixture. The authors report some interesting results of the treatment of such stable gases with pulsed plasma at very low ambient temperature. Also reported in the paper is an improvement in DeNO/DeNOx efficiency using unconventional wet-type reactors, designed and fabricated by the authors, operating at different ambient temperatures. Apart from laboratory tests on simulated gas mixtures, field tests were also carried out on the exhaust gas of a 8 kW diesel engine. Further, an attempt was made to test the feasibility of a helical wire as a corona electrode in place of the conventional straight wire electrode. A comparative analysis of the various tests is presented together with a note on the energy consideration

DeNOx Study in Diesel Engine Exhaust Using Barrier Discharge Corona Assisted by V2O5/TiO2 Catalyst

A plasma-assisted catalytic reactor was used to remove nitrogen oxides (NOx) from diesel engine exhaust operated under different load conditions. Initial studies were focused on plasma reactor (a dielectric barrier discharge reactor) treatment of diesel exhaust at various temperatures. The nitric oxide (NO) removal efficiency was lowered when high temperature exhaust was treated using plasma reactor. Also, NO removal efficiency decreased when 45% load exhaust was treated. Studies were then made with plasma reactor combined with a catalytic reactor consisting of a selective catalytic reduction (SCR) catalyst, V2O5/TiO2. Ammonia was used as a reducing agent for SCR process in a ratio of 1:1 to NOx. The studies were focused on temperatures of the SCR catalytic reactor below 200°C. The plasma-assisted catalytic reactor was operated well to remove NOx under no-load and load conditions. For an energy input of 96 J/l, the NOx removal efficiencies obtained under no-load and load conditions were 90% and 72% respectively at an exhaust temperature of 100°C.

Pulsed plasma treatment of polluted gas using wet/low temperature corona reactors

Application of pulsed plasma for gas cleaning is gaining prominence in recent years mainly from the energy consideration point of view. Normally, gas treatment is carried out, at or above room temperature, by a conventional dry type corona reactor. However, this treatment is still inadequate in the removal of certain stable gases present in the exhaust/flue gas mixture. The authors report some interesting results of the treatment of such stable gases with pulsed plasma at very low ambient temperature. Also reported in the paper is an improvement in DeNO/DeNOx efficiency using unconventional wet-type reactors, designed and fabricated by the authors, operating at different ambient temperatures. Apart from laboratory tests on simulated gas mixtures, field tests were also carried out on the exhaust gas of a 8 kW diesel engine. Further, an attempt was made to test the feasibility of a helical wire as a corona electrode in place of the conventional straight wire electrode. A comparative analysis of the various tests is presented together with a note on the energy consideration

Corona treatment for NOx reduction from stationary diesel engine exhaust: Impact of nature of energization and exhaust composition

A detailed study on the removal of oxides of nitrogen (NOx) from the exhaust of a stationary diesel engine was carried out using non-thermal plasma (dielectric barrier discharge) process. The objective of the study was to explore the effect of different voltage energizations and exhaust composition on the NOx removal process. Three types of voltage energizations, namely AC, DC and Pulse were examined. Due to the ease of generation of high voltage AC/DC electrical discharges from automobile/Vehicular battery supply for possible retrofitting in exhaust cleaning circuit, it was found relevant to investigate individual energisation cases in detail for NOx removal. AC and Pulse energisations exhibit a superior NOx removal efficiency compared to DC energisation. However,Pulse energisation is found to be more energy efficient. Experiments were further carried out with filtered/ unfiltered (raw) exhaust under pulse energisations. The results were discussed with regard to NOx removal, energy consumption and formation of by-products.

Design of corona control rings for EHV/UHV line hardwares and substations

The components of EHV/UHV lines and substations can produce significant corona. To limit the consequent Radio Interference and Audible Noise on these systems, suitable corona control rings are employed. The shapes of these rings could vary from circular to rectangular with smooth bends. Many manufacturers seem to adopt trial and error method for arriving at the final design. As such neither the present testing standard nor the final design adopted consider the practical scenario like corona produced by deposition of dirt, bird droppings, etc. The present work aims to make a first step in addressing this practically important problem. This requires an accurate evaluation of the electric field and a reliable method for the evaluation of corona inception. Based on a thorough survey of pertinent literature, the critical avalanche criteria as applicable to large electrodes, has been adopted. Taking the rain drop on the surface as the biggest protrusion, conducting protrusions modeled as semi-ellipsoid is considered as representative for deposition of dust or the boundary of bird droppings etc. Through examples of 4 00 kV and 765 kV class toroidal corona rings, the proposed method is demonstrated. This work is believed to be useful to corona ring manufacturers for EHV/UHV systems.

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 -aEuro parts per thousand 4 minutes, 4 -aEuro parts per thousand 6 minutes, 6 -aEuro parts per thousand 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.

TURBULENT PUMPING OF MAGNETIC FLUX REDUCES SOLAR CYCLE MEMORY AND THUS IMPACTS PREDICTABILITY OF THE SUN'S ACTIVITY

Prediction of the Sun's magnetic activity is important because of its effect on space environment and climate. However, recent efforts to predict the amplitude of the solar cycle have resulted in diverging forecasts with no consensus. Yeates et al. have shown that the dynamical memory of the solar dynamo mechanism governs predictability, and this memory is different for advection- and diffusion-dominated solar convection zones. By utilizing stochastically forced, kinematic dynamo simulations, we demonstrate that the inclusion of downward turbulent pumping of magnetic flux reduces the memory of both advection- and diffusion-dominated solar dynamos to only one cycle; stronger pumping degrades this memory further. Thus, our results reconcile the diverging dynamo-model-based forecasts for the amplitude of solar cycle 24. We conclude that reliable predictions for the maximum of solar activity can be made only at the preceding minimum-allowing about five years of advance planning for space weather. For more accurate predictions, sequential data assimilation would be necessary in forecasting models to account for the Sun's short memory.

Correlation between corona current and radio interference due to high voltage insulator string

The Radio Interference (RI) from electric power transmission line hardware, if not controlled, poses serious electromagnetic interference to system in the vicinity. The present work mainly concerns with the RI from the insulator string along with the associated line hardware. The laboratory testing for the RI levels are carried out through the measurement of the conducted radio interference levels. However such measurements do not really locate the coronating point, as well as, the mode of corona. At the same time experience shows that it is rather difficult to locate the coronating points by mere inspection. After a thorough look into the intricacies of the problem, it is ascertained that the measurement of associated ground end currents could give a better picture of the prevailing corona modes and their intensities. A study on the same is attempted in the present work. Various intricacies of the problem,features of ground end current pulses and its correlation with RI are dealt with. Owing to the complexity of such experimental investigations, the study made is not fully complete nevertheless it seems to be first of its kind.

Can Superflares Occur on Our Sun?

Recent observations of Sun-like stars, similar to our Sun in their surface temperature (5600-6000 K) and slow rotation (rotational period > 10 d), using the Kepler satellite by Maehara et al. (2012, Nature, 485, 478) have revealed the existence of superflares (with energy of 10(33)-10(35) erg). From statistical analyses of these superflares, it was found that superflares with energy of 10(34) erg occur once in 800 yr, and superflares with 10(35) erg occur once in 5000 yr. In this paper, we examine whether superflares with energy of 10(33)-10(35) erg could occur on the present Sun through the use of simple order-of-magnitude estimates based on current ideas related to the mechanisms of the solar dynamo. If magnetic flux is generated by differential rotation at the base of the convection zone, as assumed in typical dynamo models, it is possible that the present Sun would generate a large sunspot with a total magnetic flux of similar to 2 x 10(23) Mx (= G cm(2)) within one solar cycle period, and lead to superflares with an energy of 10(34) erg. To store a total magnetic flux of similar to 10(24) Mx, necessary for generating 10(35) erg superflares, it would take similar to 40 yr. Hot Jupiters have often been argued to be a necessary ingredient for the generation of superflares, but we found that they do not play any essential role in the generation of magnetic flux in the star itself, if we consider only the magnetic interaction between the star and the hot Jupiter. This seems to be consistent with Maehara et al.'s finding of 148 superflare-generating solar-type stars that do not have a hot Jupiter-like companion. Altogether, our simple calculations, combined with Maehara et al.'s analysis of superflares on Sun-like stars, show that there is a possibility that superflares of 10(34) erg would occur once in 800 yr on our present Sun.

Surface Degradation of Silicone Rubber Nanocomposites Due to DC Corona Discharge

Corona discharge is recognized as one of the mechanisms that can influence the surface hydrophobicity of Silicone Rubber (SR) because of the chemical changes that occur on its surface. In this study SR samples were exposed to positive and negative DC corona for 25 and 50 hours using a needle-plane electrode system. Hydrophobicity changes were monitored using a sessile drop contact angle measurement facility. The physical changes on the surface were studied using Scanning Electron Microscopy (SEM) and surface roughness measurements. The effect of positive dc corona was found to be different from that of negative dc corona. Significant surface degradation and loss of hydrophobicity was found in the case of negative dc corona exposed samples. Significant improvement in the above mentioned properties were obtained by adding small quantities of nSIL into the SR matrix.

Sun skink diversification across the Indian-Southeast Asian biogeographical interface

Aim Widespread, transcontinental vertebrate groups represent ideal systems for biogeographical studies, because they can shed light on a wide range of questions relating to species diversification across the geographical template. We combined extensive geographical and genetic sampling from across multiple biogeographical realms to examine the timing and location of diversification in Asian sun skinks, a clade characterized by problematic species boundaries and a particularly enigmatic evolutionary history. Location Indian subcontinent, the Philippines, Southeast Asia and Sundaland. Methods We sequenced one mitochondrial and nine nuclear genes for most species in the genus Eutropis, and estimated phylogenetic relationships and divergence times using coalescent methods. To investigate the location of diversification events, we also estimated ancestral geographical ranges using several methods. Finally, we explored patterns of genetic diversity within several poorly understood, but widely distributed species. Results Divergence-time estimates indicate that Eutropis began to diversify during the Eocene. Biogeographical reconstructions show that species diversification was associated with dispersal into three biogeographical realms: India, Sundaland and the Philippines. Main conclusions The results of this study clarify several questions related to the evolutionary history of Eutropis, and place them in the context of classic Southeast Asian biogeography. Our study represents one of the first to compile a heavily sampled multilocus dataset ranging across international boundaries in southern Asia that have historically prevented a unified understanding of biogeographical and evolutionary processes involving the Indian subcontinent, mainland southern Asia and the island archipelagos of Southeast Asia.