Pointing of HAGAR telescope mirrors

An array of seven atmospheric Cherenkov telescopes was commissioned at a high altitude site in Hanle in the Ladakh region of the Himalayas. The array called HAGAR has been designed to observe celestial γ-rays of energy >100 GeV. Each telescope is altitude-azimuth mounted and carries seven parabolic mirrors whose optic axes are co-aligned with the telescope axis. The telescopes point and track a celestial source using a PC-based drive control system. Two important issues in positioning of each HAGAR telescope are pointing accuracy of telescope axis and co-alignment of mirrors’ optic axes with the telescope axis. We have adopted a three pronged strategy to address these issues, namely use of pointing models to improve pointing accuracy of the telescopes, RA-DEC scan technique to measure the pointing offsets of the mirrors and mechanical fine-tuning of off-axis mirrors by sighting a distant stationary light source. This paper discusses our efforts in this regard as well as the current status of pointing and monitoring of HAGAR telescopes.     

Anthropogenic arsenic menace in Delhi Yamuna Flood Plains

Arsenic, one of the most poisonous chemical elements, was analyzed in the waters of the host of the 2010 Commonwealth Games, i.e., New Delhi. The study revealed shocking outcomes with arsenic concentrations well beyond the safe limits set by WHO, and a maximum concentration up to 180 ppb was found in the groundwater. Analysis of around 120 water samples collected extensively along the Yamuna Flood Plain showed that more than 55% had arsenic contamination beyond the WHO limit of 10 ppb. The maximum value of arsenic in coal and fly ash from Rajghat coal-based thermal power plant contained 200 and 3,200 ppb, respectively. Moreover, the ore petrography of coal samples shows the presence of arsenopyrite mineral. Maximum concentration of arsenic contamination is found within a 5-km radius from power plants. In the perspective of Delhi, arsenic contamination is purely anthropogenic due to coal-based thermal power plants, which had already shown toxic arsenic, fluorine and China-type coal effects. The presence of such power plants in coal field locations, e.g., West Bengal and Bangladesh, could release the arsenic due to combustion in superthermal power plants, thus accentuating the arsenic concentration besides the natural arsenic coming from the foreland basins of the Himalaya in Indian sub-continent.     

On the affinity of Chuaria–Tawuia complex: A multidisciplinary study

In this study, biometric and structural engineering tool have been used to examine a possible relationship within Chuaria–Tawuia complex and micro-FTIR (Fourier Transform Infrared Spectroscopy) analyses to understand the biological affinity of Chuaria circularis Walcott, collected from the Mesoproterozoic Suket Shales of the Vindhyan Supergroup and the Neoproterozoic Halkal Shales of the Bhima Group of peninsular India. Biometric analyses of well preserved carbonized specimens show wide variation in morphology and uni-modal distribution. We believe and demonstrate to a reasonable extent that C. circularis most likely was a part of Tawuia-like cylindrical body of algal origin. Specimens with notch/cleft and overlapping preservation, mostly recorded in the size range of 3–5 mm, are of special interest. Five different models proposed earlier on the life cycle of C. circularis are discussed. A new model, termed as ‘Hybrid model’ based on present multidisciplinary study assessing cylindrical and spherical shapes suggesting variable cell wall strength and algal affinity is proposed. This model discusses and demonstrates varied geometrical morphologies assumed by Chuaria and Tawuia, and also shows the inter-relationship of Chuaria–Tawuia complex.Structural engineering tool (thin walled pressure vessel theory) was applied to investigate the implications of possible geometrical shapes (sphere and cylinder), membrane (cell wall) stresses and ambient pressure environment on morphologically similar C. circularis and Tawuia. The results suggest that membrane stresses developed on the structures similar to Chuaria–Tawuia complex were directly proportional to radius and inversely proportional to the thickness in both cases. In case of hollow cylindrical structure, the membrane stresses in circumferential direction (hoop stress) are twice of the longitudinal direction indicating that rupture or fragmentation in the body of Tawuia would have occurred due to hoop stress. It appears that notches and discontinuities seen in some of the specimens of Chuaria may be related to rupture suggesting their possible location in 3D Chuaria.The micro-FTIR spectra of C. circularis are characterized by both aliphatic and aromatic absorption bands. The aliphaticity is indicated by prominent alkyl group bands between 2800–3000 and 1300–1500 cm⁻¹. The prominent absorption signals at 700–900 cm⁻¹ (peaking at 875 and 860 cm⁻¹) are due to aromatic CH out of plane deformation. A narrow, strong band is centred at 1540 cm⁻¹ which could be COOH band. The presence of strong aliphatic bands in FTIR spectra suggests that the biogeopolymer of C. circularis is of aliphatic nature. The wall chemistry indicates the presence of ‘algaenan’—a biopolymer of algae.     

Modeling of particle breakage in a smooth double roll crusher

A model has been developed to describe the breakage behavior of particle breakage in a smooth double roll crusher. In addition to this, an empirical relationship has been obtained between Hardgrove Grindability Index (HGI) of material and breakage parameters. The model uses matrix method of breakage process analysis. Experiments were carried out in a laboratory scale smooth double roll crusher using different materials. The model has been verified experimentally and gives product size distribution after breakage which matches with the experimental distribution well within the satisfactory range.     

Mathematical analysis of a chaotic model in relevance to monsoon ISO

Mathematical analysis of a predominantly bimodal chaotic attractor, Lu system, was carried out to investigate a possible application of the model as a prototype of monsoon intra-seasonal oscillation (ISO). Bifurcation structures of the system are explored as the system parameter c and the forcing parameter F are varied. Stability criteria of equilibrium points of the forced Lu system are also explored in detail. A sensitivity study is carried out, by changing forcing parameter F, to explore relationships between some of the derived variables of the model and, based on such relationships, an empirical rule is used for extended range prediction. Analogous variables are also derived from the ISO data and prediction results are compared. Application of the prediction rule of regime transition to the observed ISO and chaotic model data is purely based on the bimodal characteristics of ISO and neglects some of the intricate mechanisms therein. We have found that a forced Lu system can be a good prototype in the prediction of peak anomaly of the monsoon ISO when growth rates around a threshold value are taken as predictors.     

Chronometry and formation pathways of gypsum using Electron Spin Resonance and Fourier Transform Infrared Spectroscopy

Gypsum is an authigenic precipitate that forms under periods of accentuated aridity and occurs widely in arid zones. However its use in quantitative paleoclimatology has been limited due to the absence of a method to determine the timing of its formation. We present here the results of a feasibility study that demonstrates that the timing of the formation event of gypsum can be estimated using Electron Spin Resonance (ESR) analysis. We used well documented samples from White Sands in New Mexico, USA, the Thar Desert, India and lakes in the Simpson Desert and Mallee Region, Australia and found that ESR ages could be obtained using radiation sensitive SO₄^?, SO₃^? radicals and a photobleachable signal O₃^?. ESR signals were consistent with control ages based on contextual information. These suggest that the dating signals (SO₄^?, SO₃^?) are stable over time scales >100 ka. We propose that this stability of the SO₄^? signals over geological time scales arises due to hydrogen bonding between the water proton and the SO₄^? radical and that the suitability of these radiation-induced radicals comes from their being a part of the host matrix. Further, ESR along with Fourier Transform Infrared (FT-IR) Spectroscopy methods additionally inform on the geochemical pathways for gypsum formation and help elucidate complex formation processes even in samples that appeared unambiguous gypsum precipitates. Thus, the presence of Hannebachite (CaSO₃.½H₂O) and Mn²⁺ in Thar and Australian samples suggested a reducing environment such that low valence sulfur reacted with CaCO₃ to form hannebachite and eventually gypsum. The presence of sulfur, partially as sulfite in Thar gypsum samples suggested that redox cycles were mediated by microbial activity. Absence of these features in White Sands samples suggested oxic conditions during gypsum precipitation.     

Production of Laccase from Coriolus versicolor and Its Application in Dye Decolorization in Combination with UV/H2O2 Technique

The relative ability of Coriolus versicolor to grow on coir fiber as a ligninocellulosic material was examined. Addition of yeast extract to the culture increased laccase activity, which was further enhanced to the level of 1976 U/L by addition of 1 mM copper sulfate. Laccase thus produced was used without further purification for the decolorization of various dye solutions. Decolorization efficiency was compared with the conventional environment friendly oxidation technique using hydrogen peroxide in the presence of UV radiations. Laccase showed good decolorization in most of the cases. Excellent results were achieved when the dye solution was treated successively with laccase and UV/H₂O₂ wherein more than 80% decolorization was achieved. This value is remarkably higher than that attained either by the enzyme or UV/H₂O₂ photolysis alone.     

LITHIUM IN STONE METEORITES AND STONY IRONS

Lithium contents have been determined by neutron activation analysis in 54 meteorites distributed as: C (9), H (13), L (10), LL (3), E (2), achondrites (11), and stony irons (6). Among the undifferentiated meteorites Li contents range from 1 to 3 ppm. Li contents are higher in Ca-rich achondrites and mesosiderites than in Ca-poor achondrites and pallasites respectively. Among achondrites, Li correlates positively with Ca and Al and inversely with Mg. A minor Li-rich phase might be associated with the plagioclase component of achondrites. In several meteorites Li concentration is determined in magnetic and nonmagnetic fractions, chondrules, and light and dark components (for the gas-rich meteorites).     

Nonlinear Drift–Alfvén Waves in Relativistically Hot Multicomponent Plasmas and Their Relevance to the Fine Structure of Pulsar Radioemissions

A set of equations which governs the nonlinear dynamics of drift–Alfvén waves in an inhomogeneous relativistic electron-positron plasma with a small admixture of heavy ions is derived. It is shown that these equations admit a stationary solution in the form of a two-scale dipolar vortex. The conditions for the existence of such structures are discussed. It is shown that the presence of heavy ions in are lativistic electron-positron plasma significantly reinforces the spatial localization of the solitary waves which results in the appearance of exponentially localized vortex structures. It is also shown that the small scale micropulse structure of radio pulsar radiation (e.g., in the case of the pulsar PSR 0905+08) can be interpreted as a signature of the vortex structure in the outer region of the pulsar polar magnetosphere. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nonlinearly coupled electromagnetic ion-cyclotron and magnetosonic waves in astrophysical plasmas

A set of three nonlinearly coupled equations governing the interaction between electromagnetic ion-cyclotron and magnetosonic waves is derived. In appropriate limiting cases, the set yields simplified equations. On the other hand, the full set of equations is used to derive a general dispersion relation for the parametric interaction of electromagnetically modulated ion-cyclotron wave packets. An analytical expression for the growth rate of the electromagnetic modulational instability is presented. The relevance of our investigation to non-thermal electromagnetic fluctuations in astrophysical and cometary plasmas is pointed out.