Exotic bulk viscosity and its influence on neutron star r-modes     

Debarati Chatterjee  Debades Bandyopadhyay 《Astrophysics and Space Science》2007,308(1-4):451-455

We investigate the effect of exotic matter in particular, hyperon matter on neutron star properties such as equation of state (EoS), mass-radius relationship and bulk viscosity. Here we construct equations of state within the framework of a relativistic field theoretical model. As hyperons are produced abundantly in dense matter, hyperon–hyperon interaction becomes important and is included in this model. Hyperon–hyperon interaction gives rise to a softer EoS which results in a smaller maximum mass neutron star compared with the case without the interaction. Next we compute the coefficient of bulk viscosity and the corresponding damping time scale due to the non-leptonic weak process including Λ hyperons. Further, we investigate the role of the bulk viscosity on gravitational radiation driven r-mode instability in a neutron star of given mass and temperature and find that the instability is effectively suppressed.   相似文献   

Solar activity forecast with a dynamo model     

Jie Jiang  Piyali Chatterjee  Arnab Rai Choudhuri 《Monthly notices of the Royal Astronomical Society》2007,381(4):1527-1542

Although systematic measurements of the Sun's polar magnetic field exist only from mid-1970s, other proxies can be used to infer the polar field at earlier times. The observational data indicate a strong correlation between the polar field at a sunspot minimum and the strength of the next cycle, although the strength of the cycle is not correlated well with the polar field produced at its end. This suggests that the Babcock–Leighton mechanism of poloidal field generation from decaying sunspots involves randomness, whereas the other aspects of the dynamo process must be reasonably ordered and deterministic. Only if the magnetic diffusivity within the convection zone is assumed to be high (of order  10¹² cm² s⁻¹  ), we can explain the correlation between the polar field at a minimum and the next cycle. We give several independent arguments that the diffusivity must be of this order. In a dynamo model with diffusivity like this, the poloidal field generated at the mid-latitudes is advected toward the poles by the meridional circulation and simultaneously diffuses towards the tachocline, where the toroidal field for the next cycle is produced. To model actual solar cycles with a dynamo model having such high diffusivity, we have to feed the observational data of the poloidal field at the minimum into the theoretical model. We develop a method of doing this in a systematic way. Our model predicts that cycle 24 will be a very weak cycle. Hemispheric asymmetry of solar activity is also calculated with our model and compared with observational data.  相似文献   

Short-term periodicity in proton fluences during solar cycle 22     

T. K. Das  T. K. Nag  T. N. Chatterjee 《Solar physics》1996,168(2):385-388

The data of proton fluences measured in three ranges of energy values (1 MeV, 10MeV, and 100 MeV) in the current solar cycle 22 have been analysed to detect periodicities. Power spectral analysis of the time series of the data of proton fluences shows a periodicity of 74 days, which conforms to that of other kinds of solar activity as reported by earlier authors, thus indicating the intimate relationship of proton emission with solar activity.  相似文献   

AGRO-CLIMATIC PERSPECTIVE ON IRRIGATION IN WEST BENGAL,INDIA: A DISTRICT LEVEL ANALYSIS     

Nandini Chatterjee Ph.D. 《Singapore journal of tropical geography》1991,12(1):12-30

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On the existence of a long range correlation in the Geomagnetic Disturbance storm time (Dst) index     

Adrija Banerjee  Amaresh Bej  T. N. Chatterjee 《Astrophysics and Space Science》2012,337(1):23-32

The Dst (Disturbance storm time) index is a measurement of earth geomagnetic activity and is widely used to characterize the geomagnetic storm. It is calculated on the basis of the average value of the horizontal component of the earth’s magnetic field at four observatories, namely, Hermanus (33.3° south, 80.3° in magnetic dipole latitude and longitude), Kakioka (26.0° north, 206.0°), Honolulu (21.0° north, 266.4°), and San Juan (29.9° north, 3.2°) and is expressed in nano-Teslas. The strength of the low-latitude surface magnetic field is inversely proportional to the energy content of the ring current around earth caused by solar protons and electrons, which increases during geomagnetic storms. Thus a negative Dst index value indicates that the earth’s magnetic field is weakened which is specifically the case during solar storms. Predicting Dst index is a difficult task due to its structural complexity involving a variety of underlying plasma mechanism. For characterizing and forecasting this complex time series, a formal model must be established to identify the specific pattern of the series. Persistent demand for a fool proof model of Geomagnetic Dst index prompted us to investigate the Dst Time Series mechanism with a very recent technique called Visibility Algorithm and it is observed that the Dst time series follows the same model that of a Stochastic Fractional Brownian motion having long range correlation.  相似文献   

Nonplanar ion acoustic solitary waves with superthermal electrons and positrons     

Deb Kumar Ghosh  Prasanta Chatterjee  Biswajit Sahu 《Astrophysics and Space Science》2012,341(2):559-565

The properties of cylindrical and spherical ion acoustic solitary waves (IASWs) are investigated in a three-component unmagnetized, collisionless plasma consisting of warm ion fluid and superthermally distributed electrons and positrons in a nonplanar cylindrical or spherical geometry. Using the reductive perturbation technique, the nonplanar cylindrical and spherical Korteweg-de Vries (KdV) equations are derived. The effects of spectral index of electron and positron, and other plasma parameters are studied. It is found that both negative as well as positive solitary potential structures are formed in nonplanar geometries. The numerical solution shows that amplitude of the soliton is large in spherical geometry in comparison with cylindrical geometry. Numerical results indicate that the amplitude of the soliton is large in spherical geometry in comparison with cylindrical geometry.  相似文献   

Trace element geochemistry of scheelite and rutile from metaturbidite-hosted quartz vein gold deposits, Meguma Terrane, Nova Scotia, Canada: genetic implications   总被引：3，自引：0，他引：3  

Jaroslav Dostal  Daniel J. Kontak  A. K. Chatterjee 《Mineralogy and Petrology》2009,97(1-2):95-109

Scheelite and rutile from several metaturbidite-hosted gold-bearing quartz vein deposits of the Meguma Terrane of Nova Scotia were analyzed for trace elements including rare earth elements, niobium and tantalum. Scheelites have high concentrations of Sr, Nb, Y and rare earth elements (REE) with bell-shaped chondrite-normalized REE patterns accompanied by both positive and negative Eu anomalies. They also have high Nb/Ta ratios (80–300). Three distinct trace element types of the scheelites are interpreted to reflect chemical differences in the pulses of hydrothermal fluids. Hydrothermal rutiles have high contents of W (up to 4.2 wt.% WO₃), are rich in Ta compared to Nb and have a very low Nb/Ta ratio (~0.3). Hydrothermal fluids which produced both scheelite with a high Nb/Ta and rutile with a low Nb/Ta ratio are an efficient medium for fractionation of this ratio although these two minerals play an important role during the process.  相似文献   

Post-stack seismic inversion and attribute analysis in shallow offshore of Krishna-Godavari basin,India     

Baisakhi Das  Rima Chatterjee  Dip Kumar Singha  Rajan Kumar 《Journal of the Geological Society of India》2017,90(1):32-40

Seismic attributes such as: amplitude envelope, instantaneous phase and cosine of instantaneous phase of 2D post-stack seismic data facilitates structural and stratigraphic interpretation of shallow marine offshore, Krishna-Godavari basin. Two seismic sections namely, X and Y oriented N-S passing through wells W-1 andW-2 respectively are considered for seismic attribute analysis and porosity prediction. The gamma ray log trend indicates deposition of cleaning upward sediment. Coarsening upward, clayey-silty-sandy bodies, making a series of about 50-60 m thickness, have been evidenced from the gamma ray log. An extensional structural style comprising growth faults is associated with the progradational style of deposition. Four seismic zones have been distinguished. These zones differ in amplitude, frequency and continuity of the reflectors. Channel sands of Cretaceous age of Raghavapuram shale are identified in well log, seismic section and its acoustic impedance section. Major stratigraphic horizons along with faults extending to basement are marked with the help of attribute analysis. Porosity is mapped from transformation of acoustic impedance. The shales/unconsolidated sediments measure a high porosity with low impedance and the more porous sands are in an intermediate range. The predicted impedance and porosity values may be erroneous beyond the drilled depth because of non availability of well log data for calibration.  相似文献   

Groundwater arsenic contamination and its health effects in India   总被引：2，自引：0，他引：2  

Dipankar Chakraborti  Mohammad Mahmudur Rahman  Bhaskar Das  Amit Chatterjee  Dipankar Das  Biswajit Nayak  Arup Pal  Uttam Kumar Chowdhury  Sad Ahmed  Bhajan Kumar Biswas  Mrinal Kumar Sengupta  Md. Amir Hossain  Gautam Samanta  M. M. Roy  Rathindra Nath Dutta  Khitish Chandra Saha  Subhas Chandra Mukherjee  Shyamapada Pati  Probir Bijoy Kar  Adreesh Mukherjee  Manoj Kumar 《Hydrogeology Journal》2017,25(4):1165-1181

During a 28-year field survey in India (1988–2016), groundwater arsenic contamination and its health effects were registered in the states of West Bengal, Jharkhand, Bihar and Uttar Pradesh in the Ganga River flood plain, and the states of Assam and Manipur in the flood plain of Brahamaputra and Imphal rivers. Groundwater of Rajnandgaon village in Chhattisgarh state, which is not in a flood plain, is also arsenic contaminated. More than 170,000 tubewell water samples from the affected states were analyzed and half of the samples had arsenic >10 μg/L (maximum concentration 3,700 μg/L). Chronic exposure to arsenic through drinking water causes various health problems, like dermal, neurological, reproductive and pregnancy effects, cardiovascular effects, diabetes mellitus, diseases of the respiratory and gastrointestinal systems, and cancers, typically involving the skin, lungs, liver, bladder, etc. About 4.5% of the 8,000 children from arsenic-affected villages of affected states were registered with mild to moderate arsenical skin lesions. In the preliminary survey, more than 10,000 patients were registered with different types of arsenic-related signs and symptoms, out of more than 100,000 people screened from affected states. Elevated levels of arsenic were also found in biological samples (urine, hair, nails) of the people living in affected states. The study reveals that the population who had severe arsenical skin lesions may suffer from multiple Bowens/cancers in the long term. Some unusual symptoms, such as burning sensation, skin itching and watering of eyes in the presence of sun light, were also noticed in arsenicosis patients.  相似文献   

Isotope–geochemical characterization and geothermometrical modeling of Uttarakhand geothermal field,India     

Sitangshu Chatterjee  Uday Kumar Sinha  Archana. S. Deodhar  Md. Arzoo Ansari  Nathu Singh  Ajay Kumar Srivastava  R. K. Aggarwal  Ashutosh Dash 《Environmental Earth Sciences》2017,76(18):638

Uttarakhand geothermal area, located in the central belt of the Himalayan geothermal province, is one of the important high temperature geothermal fields in India. In this study, the chemical characteristics of the thermal waters are investigated to identify the main geochemical processes affecting the composition of thermal waters during its ascent toward the surface as well as to determine the subsurface temperature of the feeding reservoir. The thermal waters are mainly Ca–Mg–HCO₃ type with moderate silica and TDS concentrations. Mineral saturation states calculated from PHREEQC geochemical code indicate that thermal waters are supersaturated with respect to calcite, dolomite, aragonite, chalcedony, quartz (SI > 0), and undersaturated with respect to gypsum, anhydrite, and amorphous silica (SI < 0). XRD study of the spring deposit samples fairly corroborates the predicted mineral saturation state of the thermal waters. Stable isotopes (δ¹⁸O, δ²H) data confirm the meteoric origin of the thermal waters with no oxygen-18 shift. The mixing phenomenon between thermal water with shallow ground water is substantiated using tritium (³H) and chemical data. The extent of dilution is quantified using tritium content of thermal springs and non-thermal waters. Classical geothermometers, mixing model, and multicomponent fluid geothermometry modeling (GeoT) have been applied to estimate the subsurface reservoir temperature. Among different classical geothermometers, only quartz geothermometer provide somewhat reliable estimation (96–140 °C) of the reservoir temperature. GeoT modeling results suggest that thermal waters have attained simultaneous equilibrium with respect to minerals like calcite, quartz, chalcedony, brucite, tridymite, cristobalite, talc, at the temperature 130 ± 5 °C which is in good agreement with the result obtained from the mixing model.  相似文献