The solar dynamo with meridional circulation

We show that meridional circulation can have a profound influence on dynamo models for the solar cycle. Motivated by the observed tilt angles of sunspot groups we assume that the generation of the poloidal field takes place near the surface, while a shear layer of radial differential rotation produces the toroidal field at the bottom of the convection zone. Both layers are coupled by a circulation with a poleward directed flow in the upper part and an equatorward flow in the deep layers of the convection zone. The circulation forces the toroidal field belts (which are responsible for the surface activity) to move equatorward. This leads to butterfly diagrams in qualitative agreement with the observations, even if the dynamo wave would propagate poleward in the absence of circulation. This result opens the possibility to construct models for the solar cycle which are based on observational data (tilt angles, differential rotation, and meridional circulation).

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 30A degrees 28.1' N; longitude 119A degrees 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 mu m 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 x 1k CCD cameras, with a pixel size of 13 mu m 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 Alfv,n 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.

Modelling transport processes during microwave heating: A review

The review is concerned with models that analyze transport:processes that occur during microwave heating. Early models on microwave. heating used Lambert's law to describe the microwave power absorption. Over the last decade, models for transport processes have been developed with the microwave power derived from Maxwell's equations. Those models, primarily based on plane waves, have been used for analyzing microwave heating of solids, liquids, emulsions, microwave thawing and drying. The models illustrate phenomena such a resonances, hot spots, edge and runaway heating. The literature on microwave sintering, susceptor heating and microwave assisted synthesis is largely experimental in nature and only key issues are highlighted. To fully appreciate the models for microwave heating, a section on the theory of electromagnetic wave propagation is included, where expressions for the electric field in dielectric slabs and cylinders are presented.

Alfven resonances and forced reconnection

The correspondence between the forced magnetic reconnection induced by perturbing the boundary of the simple Taylor model and the surface-wave-induced magnetic reconnection given by Alfven resonance theory is pointed out explicitly by showing that the theory of forced magnetic reconnection is actually embedded in the Alfven resonance theory. The advantages of viewing the forced reconnection as surface-wave-induced reconnection are briefly discussed in the context of the formation of small-scale structures at the magnetospheric boundary and solar coronal heating.

A portable battery-operated chip thermocycler based on induction heating

A microchip thermocycler, fabricated from silicon and Pyrex #7740 glass, is described. Usual resistive heating has been replaced by induction heating, leading to much simpler fabrication steps. Heating and cooling rates of 6.5 and 4.2 degreesC/s, respectively have been achieved, by optimising the heater dimensions and heating frequency (similar to200 kHz). Four devices are mounted on a heater, resulting in low power consumption (similar to 1.4 W per device on the average). Using simple on-off electronic temperature control, a temperature stability within -0.2 degreesC is achieved. Features such as induction heating, good temperature control, battery operation, and low power consumption make the device suitable for portable applications, particularly in polymerase chain reaction (PCR) systems. (C) 2002 Elsevier Science B.V. All rights reserved.

Constraints on the solar internal magnetic field from a buoyancy driven solar dynamo

We report here results from a dynamo model developed on the lines of the Babcock-Leighton idea that the poloidal field is generated at the surface of the Sun from the decay of active regions. In this model magnetic buoyancy is handled with a realistic recipe - wherein toroidal flux is made to erupt from the overshoot layer wherever it exceeds a specified critical field B-C (10(5) G). The erupted toroidal field is then acted upon by the alpha-effect near the surface to give rise to the poloidal field. In this paper we study the effect of buoyancy on the dynamo generated magnetic fields. Specifically, we show that the mechanism of buoyant eruption and the subsequent depletion of the toroidal field inside the overshoot layer, is capable of constraining the magnitude and distribution of the magnetic field there. We also believe that a critical study of this mechanism may give us new information regarding the solar interior and end with an example, where we propose a method for estimating an upper limit of the difusivity within the overshoot layer.

Microwave heating in multiphase systems: evaluation of series solutions

The 1D electric field and heat-conduction equations are solved for a slab where the dielectric properties vary spatially in the sample. Series solutions to the electric field are obtained for systems where the spatial variation in the dielectric properties can be expressed as polynomials. The series solution is used to obtain electric-field distributions for a binary oil-water system where the dielectric properties are assumed to vary linearly within the sample. Using the finite-element method temperature distributions are computed in a three-phase oil, water and rock system where the dielectric properties vary due to the changing oil saturation in the rock. Temperature distributions predicted using a linear variation in the dielectric properties are compared with those obtained using the exact nonlinear variation.

Optimization of off-oriented Ge substrates for MOVPE-grown GaAs solar cells

GaAs/Ge heterostructures having abrupt interfaces were grown on 2degrees, 6degrees, and 9degrees off-cut Ge substrates and investigated by cross-sectional high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy, photoluminescence spectroscopy and electrochemical capacitance voltage (ECV) profiler. The GaAs films were grown on off-oriented Ge substrates with growth temperature in the range of 600-700degreesC, growth rate of 3-12 mum/hr and a V/III ratio of 29-88. The lattice indexing of HRTEM exhibits an excellent lattice line matching between GaAs and Ge substrate. The PL spectra from GaAs layer on 6degrees off-cut Ge substrate shows the higher excitonic peak compared with 2degrees and 9degrees off-cut Ge substrates. In addition, the luminescence intensity from the GaAs solar cell grown on 6degrees off-cut is higher than on 9degrees off-cut Ge substrates and signifies the potential use of 6degrees off-cut Ge substrate in the GaAs solar cells industry. The ECV profiling shows an abrupt film/substrate interface as well as between various layers of the solar cell structures.

Solution combustion synthesis of gamma(L)-Bi(2)MoO(6) and photocatalytic activity under solar radiation

The facile method of solution combustion was used to synthesize gamma(L)-Bi(2)MoO(6). The material was crystallized in a purely crystalline orthorhombic phase with sizes varying from 300 to 500 nm. Because the band gap was 2.51 eV, the degradation of wide variety of cationic and anionic dyes was investigated under solar radiation. Despite the low surface area (< 1 m(2)/g) of the synthesized material, gamma(L)-Bi(2)MoO(6) showed high photocatalytic activity under solar radiation due to its electronic and morphological properties. (C) 2011 Elsevier Ltd. All rights reserved.

Toward a Mean Field Formulation of the Babcock-Leighton Type Solar Dynamo. I. α-Coefficient versus Durney's Double-Ring Approach

We develop a model of the solar dynamo in which, on the one hand, we follow the Babcock-Leighton approach to include surface processes, such as the production of poloidal field from the decay of active regions, and, on the other hand, we attempt to develop a mean field theory that can be studied in quantitative detail. One of the main challenges in developing such models is to treat the buoyant rise of the toroidal field and the production of poloidal field from it near the surface. A previous paper by Choudhuri, Schüssler, & Dikpati in 1995 did not incorporate buoyancy. We extend this model by two contrasting methods. In one method, we incorporate the generation of the poloidal field near the solar surface by Durney's procedure of double-ring eruption. In the second method, the poloidal field generation is treated by a positive α-effect concentrated near the solar surface coupled with an algorithm for handling buoyancy. The two methods are found to give qualitatively similar results.

Full Sphere Axisymmetric Simulations of the Solar Dynamo

We explore a full sphere (2D axisymmetric) kinematic solar dynamo model based on the Babcock-Leighton idea that the poloidal field is generated in the surface layers from the decay of tilted bipolar solar active regions. This model incorporates the helioseismically deduced solar rotation profile and an algorithm for buoyancy motivated from simulations of flux tube dynamics. A prescribed deep meridional circulation plays an important role in the advection of magnetic flux. We specifically address the parity issue and show that – contrary to some recent claims – the Babcock-Leighton dynamo can reproduce solar-like dipolar parity if certain reasonable conditions are satisfied in the solar interior, the most important requirement being that the poloidal field of the two hemispheres be efficiently coupled across the equator.

The origin of the solar magnetic cycle

After summarizing the relevant observational data, we discuss how a study of flux tube dynamics in the solar convection zone helps us to understand the formation of sunspots. Then we introduce the flux transport dynamo model and assess its success in modelling both the solar cycle and its departures from strictly periodic behaviour.

Hotspots of solar potential in India

Solar hotspots are the regions characterized by an exceptional solar power potential suitable for decentralized commercial exploitation of energy. Identification of solar hotspots in a vast geographical expanse with dense habitations helps to meet escalating power demand in a decentralized, efficient and sustainable manner. This communication focuses on the assessment of resource potential with variability in India derived from high resolution satellite derived insolation data. Data analysis reveals that nearly 58% of the geographical area potentially represent the solar hotspots in the country with more than 5 kWh/m(2)/day of annual average Global insolation. A techno-economic analysis of the solar power technologies and a prospective minimal utilization of the land available within these solar hotspots demonstrate their immense power generation as well as emission reduction potential. The study evaluates the progress made in solar power generation in the country especially with the inception of an ambitious National Solar Mission (NSM) also termed as `Solar India'. The organizational aspects of solar power generation with focus on existing policy elements are also addressed so as to probe the actual potential of the identified solar hotspots in meeting the NSM targets and beyond. (C) 2011 Elsevier Ltd. All rights reserved.