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Summary: At present, the demand for wireless communications is growing tremendously. Cognitive radio network plays an important role in making the spectrum to be used effectively. Uncertainty in channels and interference were generally occurs that reduced the system efficiency. To overcome the load usage problem, the proposed system of spectrum sensing and scheduling algorithms is introduced, where the available spectrums are sensed or detected and scheduled to load the free spectrum. Spectrum sensing is a cognitive radio basic function to thwart the harmful interference with licensed users and detect the available spectrum for enhancing the spectrum's utilization. In the proposed technique, initially, the spectrum sharing and sensing method is put forward to raise the throughput and quality of service necessity. At this time, spectrum sharing in common with scheduling process is presented, where the available spectrum, the load is scheduled and sensed to free the spectrum. Here, the modified spider monkey optimization (MSMO) technique is used for spectrum sensing and detecting free spectrums, thereby enhancing the energy efficiency of the available spectrum. This technique will found the optimal solution and increases the expectation of some decisions. Modified round robin algorithm is used for scheduling load. In this algorithm, every packet flow has its packet queue presented in the network interface controller. The performance analysis is finally measured using metrics such as throughput, handoff, success probability, and false alarm probability. [ABSTRACT FROM AUTHOR]

Summary: Wireless communication is an emerging technology in recent days which involves the transmission of data or information over a wide range of distance. The wireless network is capable of using the unlicensed spectrum for the transmission of data for various applications like medical, science, and industries. There are cases where the licensed spectrum is not utilized up to the level. In such cases, the cognitive radio network (CRN) technology allows cognitive devices to sense it and further enables the dynamic access of the scarce resource for proper utilization. However, the excessive number of bandwidth access may lead to the occurrence of interferences among the system. This is the major issue faced in all CRNs. To resolve this, effective band scheduling mechanism in CRN has been proposed. In this research, efficient spectrum sensing is performed using stochastic optimization algorithm called Salp Swarm Optimization Algorithm (SSOA). This SSOA algorithm utilizes the best fitness function through three phases such as leaving, contention and joining of bands and provides a list of nonacquired list of bands. From the list of bands, the best band with majority bandwidth has been selected using Round Robin (RR) Algorithm. Here, the load system is allotted dynamically. Based on the load factor, the spectrum is scheduled. As a matter of fact, the whole spectrum scheduling methodology depends primarily on the base contributions made by the operation of spectrum sensing. Finally, the performance analysis is estimated for the throughput, settling time, number of bands occupied by base station (BS), and the bands occupied by each BS. From the performance analysis, the proposed system attains better results than other conventional approaches. [ABSTRACT FROM AUTHOR]

Efforts are made to demonstrate high-resolution observations of the solar atmosphere using spatial interferometry. Covering the telescope pupil with a Fizeau mask consisting of two small circular apertures separated by a vector distance known as the baseline is the first step towards interferometric imaging. A mask with two circular holes of diameter 7 cm each and separated by a distance of 19 cm is placed in the pupil plane of the Multi-application solar telescope at Udaipur solar observatory. The fringe pattern observed in the image plane signifies the presence of solar structures with sizes smaller than the fringe period. The study is extended with baselines of 29 cm and 38 cm. It is observed that an increase in the baseline causes a reduction in the fringe period and the fringe contrast. Observations are carried out in two spectral lines/bands, centered at 656.3 nm and 861.0 nm using filters of bandwidth 1 nm and 330 nm, respectively. The effect of bandwidth on the fringe visibility is also discussed based on the bandwidth decorrelation function. [ABSTRACT FROM AUTHOR]

Multi Application Solar Telescope (MAST), a telescope for the detailed study of solar activity, was operationalized at the Udaipur Solar Observatory (USO) of Physical Research Laboratory (PRL), on 16 June 2015. This article traces the history of the conceptualization to realization of MAST and describes its salient features. MAST is an off-axis Gregorian-Coudé telescope with a 50 cm aperture. The first light backend instruments include a narrow band polarimetric imager to map the photospheric and chromospheric magnetic fields and a multi-slit spectro-polarimeter. An adaptive optics system is also being developed for the on-line corrections of the image distortions produced by atmospheric seeing. The main objective of MAST is to obtain high spatial and temporal resolution observations of solar photospheric and chromospheric activity, with the ultimate goal of predicting space weather. [ABSTRACT FROM AUTHOR]

The electric current exists because of the non-potential magnetic field in solar active regions. We present the evolution of net current in the solar active region NOAA 10930 as the sum of shear current and twist current by using 27 high-resolution vector magnetograms obtained with Hinode/SOT-SP during 9 - 15 December 2006. This active region was highly eruptive and produced a large number of flares ranging from B to X class. We derived local distribution of shear and twist current densities in this active region and studied the evolution of net shear current (NSC) and net twist current (NTC) in the N-polarity and S-polarity regions separately. We found the following: i) The twist current density was dominant in the umbrae. ii) The footpoint of the emerging flux rope showed a dominant twist current. iii) The shear current density and twist current density appeared in alternate bands around the umbrae. iv) On the scale of the active region, NTC was always larger than NSC. v) Both NTC and NSC decreased after the onset of an X3.4 class flare that occurred on 13 December 2006. [ABSTRACT FROM AUTHOR]

A major flare (of class X3.4) occurred on 2006 December 13 in the active region NOAA 10930. This flare event has remained interesting to solar researchers for studies related to particle acceleration during the flare process and the reconfiguration of magnetic fields as well as fine-scale features in the active region. The energy released during flares is also known to induce acoustic oscillations in the Sun. Here, we analyze the line-of-sight velocity patterns in this active region during the X3.4 flare using the Dopplergrams obtained by the Global Oscillation Network Group (GONG) instrument. We have also analyzed the disk-integrated velocity observations of the Sun obtained by the Global Oscillation at Low Frequency (GOLF) instrument on board the Solar and Heliospheric Observatory spacecraft as well as full-disk collapsed velocity signals from GONG observations during this flare to study any possible connection between the flare-related changes seen in the local and global velocity oscillations in the Sun. We apply wavelet transform to the time series of the localized velocity oscillations as well as the global velocity oscillations in the Sun spanning the flare event. The line-of-sight velocity shows significant enhancement in some localized regions of the penumbra of this active region during the flare. The affected region is seen to be away from the locations of the flare ribbons and the hard X-ray footpoints. The sudden enhancement of this velocity seems to be caused by the Lorentz torce driven by the "magnetic jerk" in the localized penumbral region. Application of wavelet analysis to these flare-induced localized seismic signals shows significant enhancement in the high-frequency domain (5 < v < 8 mHz) and a feeble enhancement in the p-mode oscillations (2 < v < 5 mHz) during the flare. On the other hand, the wavelet analysis of GOLF velocity data and the full-disk collapsed GONG velocity data spanning the flare event indicates significant post-flare enhancements in the high-frequency global velocity oscillations in the Sun, as evident from the wavelet power spectrum and the corresponding scale-average variance. The present observations of the flare-induced seismic signals in the active region in context of the driving force are different as compared to previous reports on such cases. We also find indications of a connection between flare-induced localized seismic signals and the excitation of global high-frequency oscillations in the Sun. [ABSTRACT FROM AUTHOR]

Analysis of a time series of high spatial resolution vector magnetograms of the active region NOAA 10930 available from the Solar Optical Telescope SpectroPolarimeter on board Hinode revealed that there is a mixture of upward and downward currents in the two footpoints of an emerging flux rope. The flux emergence rate is almost the same in both the polarities. We observe that along with an increase in magnetic flux, the net current in each polarity increases initially for about three days after which it decreases. This net current is characterized by having exactly opposite signs in each polarity while its magnitude remains almost the same most of the time. The decrease of the net current in both the polarities is due to the increase of current having a sign opposite to that of the net current. The dominant current, with the same sign as the net current, is seen to increase first and then decreases during the major X-class flares. Evolution of non-dominant current appears to be a necessary condition for flare initiation. The above observations can be plausibly explained in terms of the superposition of two different force-free states resulting in a non-zero Lorentz force in the corona. This Lorentz tbrce then pushes the coronal plasma and might facilitate the magnetic reconnection required for flares. Also, the evolution of the net current is found to follow the evolution of magnetic shear at the polarity inversion line. [ABSTRACT FROM AUTHOR]

The active region NOAA (National Oceanic and Atmospheric Administration) AR 10486 which appeared on the solar disc in 2003 October produced a lot of space weather related activity. Here, we report on the co-spatial evolution of the photospheric Doppler enhancements and the chromospheric Hα flare ribbons observed during the 4B/X17.2 class solar flare of 2003 October 28 in this active region. These velocity enhancements exactly match the Hα brightness enhancements in space, and are delayed by approximately 1 min in time. Hα brightness attains a maximum nearly at the same time as the peak seen in light curves in high-energy emission observed by KORONAS ( Kuznetsov et al. 2006 ). [ABSTRACT FROM AUTHOR]

A Multi-Application Solar Telescope (MAST) is proposed to be installed at the lake site (Lake Fatehsagar) of Udaipur Solar Observatory (USO) in India. The lake site Observatory of USO is located on a small island in the middle of the lake. To determine the optimum size of the MAST (for use with an adaptive optics system), it was decided to quantify the seeing conditions prevailing at the lake site during the different months of the year. For this purpose, we have used short-exposure (3 ms) high-resolution Hα (6563 Å) images (spatial scale of ∼0.55 arc sec per pixel) of the Sun taken in burst mode with the 15-cm refractor Spar telescope located at the lake site of USO. Spectral ratio technique as reported by von der Lühe (, J. Opt. Soc. Am. A1, 510) has been used to estimate the Fried’s parameter ( r 0) at this site, which gives the quantitative measure of astronomical seeing. This study has been carried out daily on an hourly basis during 4:30 – 10:30 UT over the months January – June of the years 2005 and 2006 to understand the diurnal and seasonal variations in r 0 at this site. It is noteworthy that the lake was almost dry during the observing period in 2005, while it overflowed during our observations in 2006 because of abundant monsoon rains. The seeing in the presence of water shows improvement in r 0 by about 1.0 cm with respect to the previous year’s dry condition and mean r 0 varies between 4.0 and 4.5 cm as evident from the data obtained between January and June, 2006. [ABSTRACT FROM AUTHOR]

Modern solar telescope designs are different from the conventional concept of vacuum telescopes. These new designs are "open" telescopes which try to minimize the temperature difference between various parts of the telescope and the ambient air. In this paper, we address a few issues related to the thermal response and imago quality of such insolated mirrors. We estimate the distortion produced by thermal and material inhomogeneities and present limiting values of allowable temperature differences and percentage change of expansion coefficients for different aperture diameters, for typical materials under best possible seeing conditions, We predict the evolution of surface temperature of an insolated mirror using a simplified theoretical approach and show that it is compatible with the experimental values to a large extent. The results indicate the possibility of avoiding active cooling of the mirror surfaces, at least for primary mirrors with aperture diameter less than or equal to 50 cm. [ABSTRACT FROM AUTHOR]

High-resolution MDI magnetograms are used to study the pattern of moving magnetic inhomogeneities in sunspots. We examine the inward and outward moving features in sunspots. The velocity of these features is small in the umbra while it is about 0.5 km s-1 in the outer penumbra. The inward and outward moving features may be the possible origin for the long-term fluctuations of magnetic field strength in sunspots. [ABSTRACT FROM AUTHOR]

The length scale and life time of the transition region network cells were studied using He ii λ304 filtergrams. The temporal structure function was calculated from spatially aligned He ii λ304 images. The estimated life time of the network cell was about 27 hr. We compared this life time with the life time of photospheric magnetic network and of the extrapolated magnetic network. The spatial structure function was calculated from the He ii λ304 filtergrams. The calculated spatial structure function saturates at ∼ 25 000 km. The transition region network elements are bigger in size than the photospheric magnetic network element. The magnetic network element equals the size of the He ii λ304 network element when the photospheric magnetic field is extrapolated to a height of 3000 km above the photosphere where the magnetic fluxes are deployed. The derived value of the diffusion speed of the network elements was 0.098 km s-1. [ABSTRACT FROM AUTHOR]

Near simultaneous coronal EUV images were used to show that the He ii λ304 network brightening is independent of coronal EUV radiation. We studied the quantitative relation between the intensity of He ii λ304 network brightening with the associated magnetic elements. An almost linear relationship was found between the He ii λ304 network brightening and the magnetic field for a field strength higher than 10 G with exceptions at neutral lines and in the intra-network. We also calculated the most probable formation height of He ii λ304 network elements using the potential extrapolation of the photospheric magnetic field. The results show that He ii λ304 network elements form at or around 3000 km above the height of the layer at which the sources of magnetic flux are deployed. [ABSTRACT FROM AUTHOR]

The supramolecular nonbonded C-H···X interactions between formyl hydrogens and ortho-halogen atoms (Br/Cl) have been exploited to achieve conformational control in the solid state of dimethylsubstituted iso- and terephthaladehydes (1-3) for unprecedented diphotocyclization. It is shown that the dihalogen substitution also contributes to the stability of the benzocyclobutenols relative to their precursor photoenols, so that the solid-state photolysis of dialdehydes 2b, 2c, and 3b leads to diphotocycIization to afford respectable yields of bis-benzocyclobutenols. [ABSTRACT FROM AUTHOR]

The rapid growth of industry and transport within this contemporary progress, there was sufficient consideration given to air quality monitoring; but conventional air quality monitoring methods are inefficient to produce adequate spatial and temporal resolutions of the air quality information by cost-effective also the period time clarifications. During the paper, we propose a distinct methodology to achieve the air quality monitoring system, using this fog computing-based Internet of Things (IoT). In this paper proposed an embedded system, where sensors collect the air quality information within period time and send it over the fog nodes. Every fog node may be an extraordinarily virtualized program hosted at a committed computing node implemented with a connection interface. Data gathered by Microprocessor based IoT sensing things do not seem to be causing on into the cloud server to the process. Preferably, they do send through the adjacent fog node to get quick, including high-rise rate service. Though, fog node will refine non-actionable data (e.g., regular device measurement) also forward them to the Cloud for lengthy run storage and batch analytics. The Cloud may be a convenient location to run world analytics at information gathered from commonly shared devices over sustained periods (months, years). General purpose processor (microprocessor) and IoT cloud platforms were involved in developing this whole infrastructure and model for analysis. Empirical outcomes reveal that this advanced method is responsible for sensing air quality, which serves to expose the modification patterns regarding air quality through a certain level. [ABSTRACT FROM AUTHOR]

We report on the rapid variations of solar magnetic fields that appear to be enhanced significantly above the background variability, at a few locations within the solar active regions, as observed with the Michelson Doppler Imager (MDI) on board the SOHO spacecraft. The pressure fluctuations estimated to arise from this variability far exceed the general level of acoustic pressure fluctuations. The equivalent mechanical flux that could be generated from these rapid magnetic variations is more than adequate for the heating of the active region chromosphere and corona. [ABSTRACT FROM AUTHOR]

The Multi-application Solar Telescope is a 50 cm off-axis Gregorian telescope that has been installed at the lake site of Udaipur Solar Observatory. For quasi-simultaneous photospheric and chromospheric observations, a narrow-band imager has been developed as one of the back-end instruments for this telescope. Narrow-band imaging is achieved using two lithium niobate Fabry-Perot etalons working in tandem as a filter. This filter can be tuned to different wavelengths by changing either voltage, tilt, or temperature of the etalons. To characterize the etalons, a Littrow spectrograph was set up in conjunction with a 15 cm Carl Zeiss Coudé solar telescope. The etalons were calibrated for the solar spectral lines Fe i 6173 Å, and Ca ii 8542 Å. In this work, we discuss the characterization of the Fabry-Perot etalons, specifically, the temperature and voltage tuning of the system for the spectral lines proposed for observations. We present the details of the calibration set-up and various tuning parameters. We also present solar images obtained using the system. [ABSTRACT FROM AUTHOR]

The distribution of acoustic power over sunspots shows an enhanced absorption near the umbra - penumbra boundary. Previous studies revealed that the region of enhanced absorption coincides with the region of strongest transverse potential field. The aim of this paper is to i) utilize the high-resolution vector magnetograms derived using Hinode SOT/SP observations and study the relationship between the vector magnetic field and power absorption and ii) study the variation of power absorption in sunspot penumbrae due to the presence of spine-like radial structures. It is found that i) both potential and observed transverse fields peak at a similar radial distance from the center of the sunspot, and ii) the magnitude of the transverse field, derived from Hinode observations, is much larger than the potential transverse field derived from SOHO/MDI longitudinal-field observations. In the penumbra, the radial structures called spines (intra-spines) have stronger (weaker) field strength and are more vertical (horizontal). The absorption of acoustic power in the spine and intra-spine shows different behavior, with the absorption being larger in the spine as compared to the intra-spine. [ABSTRACT FROM AUTHOR]

The outer atmosphere of the sun - called the corona - has been observed during total solar eclipse for short periods (typically < 6 min), from as early as the eighteenth century. In the recent past, space-based instruments have permitted us to study the corona uninterruptedly. In spite of these developments, the dynamic corona and its high temperature (1-2 million K) are yet to be fully understood. It is conjectured that their dynamic nature and associated energetic events are possible reasons behind the high temperature. In order to study these in detail, a visible emission line space solar coronagraph is being proposed as a payload under the small-satellite programme of the Indian Space Research Organisation. The satellite is named as Aditya-1 and the scientific objectives of this payload are to study: (i) the existence of intensity oscillations for the study of wavedriven coronal heating; (ii) the dynamics and formation of coronal loops and temperature structure of the coronal features; (iii) the origin, cause and acceleration of coronal mass ejections (CMEs) and other solar active features, and (iv) coronal magnetic field topology and three-dimensional structures of CMEs using polarization information. The uniqueness of this payload compared to previously flown space instruments is as follows: (a) observations in the visible wavelength closer to the disk (down to 1.05 solar radii); (b) high time cadence capability (better than two-images per second), and (c) simultaneous observations of at least two spectral windows all the time and three spectral windows for short durations. [ABSTRACT FROM AUTHOR]

A filament disappearance event was observed on 22 May 2008 during our recent campaign JOP 178. The filament, situated in the Southern Hemisphere, showed sinistral chirality consistent with the hemispheric rule. The event was well observed by several observatories, in particular by THEMIS. One day, before the disappearance, Hα observations showed up- and down-flows in adjacent locations along the filament, which suggest plasma motions along twisted flux rope. THEMIS and GONG observations show shearing photospheric motions leading to magnetic flux canceling around barbs. STEREO A, B spacecraft with separation angle 52.4°, showed quite different views of this untwisting flux rope in He ii 304 Å images. Here, we reconstruct the three-dimensional geometry of the filament during its eruption phase using STEREO EUV He ii 304 Å images and find that the filament was highly inclined to the solar normal. The He ii 304 Å movies show individual threads, which oscillate and rise to an altitude of about 120 Mm with apparent velocities of about 100 km s−1 during the rapid evolution phase. Finally, as the flux rope expands into the corona, the filament disappears by becoming optically thin to undetectable levels. No CME was detected by STEREO, only a faint CME was recorded by LASCO at the beginning of the disappearance phase at 02:00 UT, which could be due to partial filament eruption. Further, STEREO Fe xii 195 Å images showed bright loops beneath the filament prior to the disappearance phase, suggesting magnetic reconnection below the flux rope. [ABSTRACT FROM AUTHOR]

A variety of allylic and benzylic alcohols are oxidized to their respective carbonyl compounds with IBX under solvent-free conditions at ca. 60–70 °C. It has also been found that some of the aromatic aldehydes also undergo oxidation when heated with IBX at 90 °C under solvent-free conditions; notably, this transformation does not occur under the otherwise identical but heterogeneous conditions. [Copyright &y& Elsevier]

We propose a criterion for extending the parameter search method (Krishnakumar and Venkatakrishnan, 1997) of estimating the point spread function to solar data. In the parameter search method, the number of pixels with negative intensity values in the restored object is used as an estimator for determining the unknown parameters of the point spread function. As a solar image has a high background, the restored object does not contain negative values, thereby making the method unsuitable for solar data. We propose to use the intrinsic contrast of solar features as a criterion for identifying the unknown parameter. We validate our method through simulations. This method can not be used for image restoration but can be used for monitoring daytime seeing. [ABSTRACT FROM AUTHOR]

The Multi-Application Solar Telescope (MAST) is a 50 cm off-axis Gregorian telescope that has recently become operational at the Udaipur Solar Observatory (USO). An imaging spectropolarimeter is being developed as one of the back-end instruments of MAST to gain a better understanding of the evolution and dynamics of solar magnetic and velocity fields. This system consists of a narrow-band filter and a polarimeter. The polarimeter includes a linear polarizer and two sets of liquid crystal variable retarders (LCVRs). The instrument is intended for simultaneous observations in the spectral lines 6173 Å and 8542 Å, which are formed in the photosphere and chromosphere, respectively. In this article, we present results from the characterization of the LCVRs for the spectral lines of interest and the response matrix of the polarimeter. We also present preliminary observations of an active region obtained using the spectropolarimeter. For verification purposes, we compare the Stokes observations of the active region obtained from the Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) with that of MAST observations in the spectral line 6173 Å. We find good agreement between the two observations, considering the fact that MAST observations are limited by seeing. [ABSTRACT FROM AUTHOR]

Context. The photospheric Evershed flow is a distinct characteristic of penumbrae that is closely associated with the photometric and magnetic structure of sunspots. Aims. We analyse the properties of an anomalous flow in the photosphere in a sunspot penumbra and compare it with those of the regular Evershed flow. Methods. High-resolution spectropolarimetric observations of active region NOAA 11271 were obtained with the spectro-polarimeter (SP) on board Hinode. We used the magnetic field properties derived by aMilne-Eddington inversion. In addition, we used Ca II H images obtained by the broad-band filter instrument to study the low chromospheric response to the photospheric structure and Dopplergrams from the Helioseismic and Magnetic Imager to follow the evolution of the photospheric flows. Results. We detect a blueshifted feature that appeared on the limb-side penumbra of a sunspot and that was present intermittently during the next two hours. It exhibited a maximum blueshift of 1.6 km s-1, an area of 5.2 arcsec2, and a maximum uninterrupted lifetime of 1 h. The blueshifted feature, when present, lies parallel to redshifts. Both blue- and redshifts flank a highly inclined or horizontal magnetic structure that is radially oriented in the penumbra. The low-cadence SP maps reveal changes in size, radial position in the penumbra, and line-of-sight (LOS) velocity of the blueshifted feature, from one scan to the next. There was an increase of nearly 500 G in the field strength with the onset of the blueshifts, particularly when the LOS velocity in the feature exceeded 1.5 km s-1. There was only a marginal reduction in the field inclination of about 10° with the increase in blueshifts. In the chromosphere, intense, arc-shaped brightenings were observed close to the location of the photospheric blueshifts, which extend from the edge of the umbral core to the penumbra-quiet Sun boundary. The intensity of these brightenings exceeds the background intensity by 30% to 65% with the strongest and largest brightenings observed about 30 min after the strongest blueshifts were detected at the photosphere. The close spatial proximity of the two phenomenon strongly suggests a causal relationship. Conclusions. The blueshifted feature represents plasma motion that could be related to a magnetic structure that rises in the solar atmosphere and subsequently reconnects with the ambient chromospheric magnetic field of the sunspot or an inverse Evershed flow, which would be unique in the photosphere. This transient phenomena is presumably related to the dynamic stability of the sunspot because the corresponding umbral core separated two days later at the location of the blueshifts and fragmented subsequently. [ABSTRACT FROM AUTHOR]

Abstract: During the maximum of Solar Cycle 23, large active regions had a long life, spanning several solar rotations, and produced large numbers of X-class flares and CMEs, some of them associated to magnetic clouds (MCs). This is the case for the Halloween active regions in 2003. The most geoeffective MC of the cycle (Dst=−457) had its source during the disk passage of one of these active regions (NOAA 10501) on 18 November 2003. Such an activity was presumably due to continuous emerging magnetic flux that was observed during this passage. Moreover, the region exhibited a complex topology with multiple domains of different magnetic helicities. The complexity was observed to reach such unprecedented levels that a detailed multi-wavelength analysis is necessary to precisely identify the solar sources of CMEs and MCs. Magnetic clouds are identified using in situ measurements and interplanetary scintillation (IPS) data. Results from these two different sets of data are also compared. [Copyright &y& Elsevier]

This paper addresses some of the issues related to externally occulted solar coronagraph; vignetting and achievable resolution due to an external occulter. The analytical expression by Evans (J Opt Soc Am 38:1083-1085, ) is used to perform the initial calculations. An expression for the vignetting for a given external occulter and field angle is derived. The values obtained with the derived expression are verified with those obtained by ZEMAX an Optical design software. The degradation in angular resolution of the system due to vignetting is also presented and an empirical relation to calculate the normalized resolution for a given amount of vignetting is obtained. [ABSTRACT FROM AUTHOR]

We present G-band and Ca ii H filtergrams of two sunspot light bridges in NOAA AR 10953 taken from the 50-cm Solar Optical Telescope onboard the Japanese space satellite Hinode on 1 May 2007. The two light bridges differ in structure, with one of them resembling the filamentary penumbra and the other possessing a dark central lane running along the axis of the bridge having a width of 170 km, which is close to the diffraction limit of the telescope. Velocity measurements of the light bridges using proper motion displacements of inhomogeneities, averaged over the entire time series, show a nonuniform flow with velocities peaking at 250 and 180 m s−1 for the two bridges, respectively. We report observations of an archlike structure over one of the light bridges in the Ca images. Brightness enhancements are seen traveling along this arch as well as along the light bridge. Observations suggest that these enhancements over light bridges could possibly be a signature of lower chromospheric heating. [ABSTRACT FROM AUTHOR]

A low-order Adaptive Optics (AO) system is being developed at the Udaipur Solar Observatory and we present in this paper the status of the project, which includes the image stabilization system and calibration of wavefront sensor and deformable mirror. The image stabilization system comprises of a piezo driven tip-tilt mirror, a high speed camera (955 fps), a frame grabber system for sensing the overall tilt and a Linux based Intel Pentium 4 control computer with Red Hat Linux OS. The system operates under PID control. In the closed loop, an rms image motion of 0.1-0.2 arcsec was observed with the improvement factor varying from 10-20 depending on the external conditions. Error rejection bandwidth of the system at 0 dB is 80-100 Hz. In addition to that, we report the on-going efforts in the calibration of lenslet array and deformable mirror for sensing and correcting the local tilt of the wavefront. [ABSTRACT FROM AUTHOR]

The Solar Vector Magnetograph (SVM) at Udaipur Solar Observatory saw its first light in April 2005. The retrieval of vector fields from the imaging spectro-polarimetric observational data requires a substantial amount of computer post-processing. The GUI-based data reduction and analysis software have been developed to make the data processing pipeline user-friendly and less time-consuming. In this paper we describe these software packages. [ABSTRACT FROM AUTHOR]

Adaptive Optics (AO) systems improve the resolution of ground based telescopes and allow for long exposure images. Their performance depends on the seeing conditions at the time of observations. In this paper, we evaluate the performance of an AO system under various seeing conditions through simulations. Then we present the wave-front sensing and correction schemes that would be used in the first phase of the AO system to be developed at the Udaipur Solar Observatory. [ABSTRACT FROM AUTHOR]

We employ high-resolution filtergrams and polarimetric measurements from Hinode to follow the evolution of a sunspot for eight days starting on 2007 June 28. The imaging data were corrected for intensity gradients, projection effects, and instrumental stray light prior to the analysis. The observations show the formation of a light bridge at one corner of the sunspot by a slow intrusion of neighboring penumbral filaments. This divided the umbra into two individual umbral cores. During the light bridge formation, there was a steep increase in its intensity from 0.28 to 0.7 IQS in nearly 4 hr, followed by a gradual increase to quiet-Sun (QS) values in 13 hr. This increase in intensity was accompanied by a large reduction in the field strength from 1800 G to 300 G. The smaller umbral core gradually broke away from the parent sunspot nearly two days after the formation of the light bridge, rendering the parent spot without a penumbra at the location of fragmentation. The penumbra in the fragment disappeared first within 34 hr, followed by the fragment whose area decayed exponentially with a time constant of 22 hr. In comparison, the parent sunspot area followed a linear decay rate of 0.94 Mm2 hr–1. The depleted penumbra in the parent sunspot regenerated when the inclination of the magnetic field at the penumbra-QS boundary became within 40° from being completely horizontal and this occurred near the end of the fragment's lifetime. After the disappearance of the fragment, another light bridge formed in the parent which had similar properties as the fragmenting one, but did not divide the sunspot. The significant weakening in field strength in the light bridge along with the presence of granulation is suggestive of strong convection in the sunspot, which might have triggered the expulsion and fragmentation of the smaller spot. Although the presence of QS photospheric conditions in sunspot umbrae could be a necessary condition for fragmentation, it is not a sufficient one. [ABSTRACT FROM AUTHOR]