Forming supermassive black holes like J1342+0928 (invoking dark matter) in early universe     

C. Sivaram  Arun Kenath  O. V. Kiren 《Astrophysics and Space Science》2018,363(2):40

Recent discovery of J1342+0928 using data from the WISE telescope and ground based surveys indicate presence of a supermassive black hole (SMBH) having a mass of 800 million solar mass at a redshift of about 7.6. This imply that the black hole grew to this mass only 690 million years after the universe started expanding. Here we suggest that formation of such SMBH’s so early in the universe is consistent with our present understanding of the phenomena involved by invoking dark matter (DM).  相似文献   

Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics     

Bhal Chandra Joshi  Prakash Arumugasamy  Manjari Bagchi  Debades Bandyopadhyay  Avishek Basu  Neelam Dhanda Batra  Suryarao Bethapudi  Arpita Choudhary  Kishalay De  L. Dey  A. Gopakumar  Y. Gupta  M. A. Krishnakumar  Yogesh Maan  P. K. Manoharan  Arun Naidu  Rana Nandi  Dhruv Pathak  Mayuresh Surnis  Abhimanyu Susobhanan 《Journal of Astrophysics and Astronomy》2018,39(4):51

Radio pulsars show remarkable clock-like stability, which make them useful astronomy tools in experiments to test equation of state of neutron stars and detecting gravitational waves using pulsar timing techniques. A brief review of relevant astrophysical experiments is provided in this paper highlighting the current state-of-the-art of these experiments. A program to monitor frequently glitching pulsars with Indian radio telescopes using high cadence observations is presented, with illustrations of glitches detected in this program, including the largest ever glitch in PSR B0531+21. An Indian initiative to discover sub-\(\mu \)Hz gravitational waves, called Indian Pulsar Timing Array (InPTA), is also described briefly, where time-of-arrival uncertainties and post-fit residuals of the order of \(\mu \)s are already achievable, comparable to other international pulsar timing array experiments. While timing the glitches and their recoveries are likely to provide constraints on the structure of neutron stars, InPTA will provide upper limits on sub-\(\mu \)Hz gravitational waves apart from auxiliary pulsar science. Future directions for these experiments are outlined.  相似文献   

Lissajous motion near Lagrangian point $$ L_{2} $$ in radial solar sail     

Arun Kumar Yadav  Badam Singh Kushvah  Uday Dolas 《Journal of Astrophysics and Astronomy》2018,39(6):72

An attempt was made to study the dynamics close to the collinear libration point \( L_{2} \) of the radial solar sail circular-restricted three-body problem (RSCRTBP) in the Sun–Jupiter System, where the third massless body is a solar sail. We analyse the qausi-periodic (Lissajous solutions) orbits about the libration point \( L_{2} \). The Lindstedt–Poincaré approximation for the qausi-periodic orbits was used for numerical simulations. We utilized linear quadratic regulator (LQR) to stabilize the full nonlinear model, and linear state-feedback controller was designed to stabilize the trajectory.  相似文献   

Ecological variables influencing the diversity and distribution of macrolichens colonizing <Emphasis Type="Italic">Quercus leucotrichophora</Emphasis> in Uttarakhand forest     

Shashi Upadhyay  Arun K. Jugran  Yogesh Joshi  Renu Suyal  Ranbeer S. Rawal 《山地科学学报》2018,15(2):307-318

Ecological variables play a significant role in determining the diversity and distribution of any living organism on earth. Lichens are not exceptional and are quite sensitive in comparison to other organisms; hence the present study focuses on the impact of ecological variables on the diversity and distribution of epiphytic macrolichens colonizing Quercus leucotrichophora across eight different sites (50 m × 50 m) in Thal Ke Dhar forest, Kumaun Himalaya, Uttarakhand, India. For sampling of macrolichens, 200 trees (25 trees from each site) of Q. leucotrichophora were selected from each site and five quadrats of 5 cm × 10 cm (1000 quadrats in totality) were drawn at the tree trunk. From all the sampled trees, a total of 54 species of epiphytic macrolichens belonging to 18 genera and five families were recorded. Various ecological variables, namely altitude, aspect, slope, diameter at breast height (DBH), and lopping percent (partial cutting of the twigs as disturbance), were also analyzed to investigate their influence on macrolichen species composition and distribution pattern in the study area. For the determination of relationships between these variables, statistical analysis, namely Pearson’s Correlation Coefficient, Polynomial regression analysis and Principal Component Analysis (PCA) were performed. Out of all variables, lopping was significantly correlated to species richness of epiphytic macrolichens (0.712*, p<0.05) and it was confirmed by Pearson’s Correlation Coefficient. Despite of having high anthropogenic pressure or impact through lopping, the maximum number of macrolichen species was recorded at elevation 2267 meter above sea level (m asl). The present study revealed that besides other ecological variables, lopping practices can act as a key parameter in controlling the diversity and distribution not only of epiphytic macrolichens but also of other life forms such as bryophytes, pteridophytes, insects, birds etc. and can be either negatively or positively correlated.  相似文献   

X-ray observation of XTE J2012+381 during the 1998 outburst     

S. Naik  P. C. Agrawal  B. Paul  A. R. Rao  S. Seetha  K. Kasturirangan 《Journal of Astrophysics and Astronomy》2000,21(1-2):29-38

The outburst of X-ray transient source XTE J2012+381 was detected by the RXTE All-Sky Monitor on 1998 May 24th. Following the outburst, X-ray observations of the source were made in the 2–18 keV energy band with the Pointed Proportional Counters of the Indian X-ray Astronomy Experiment (IXAE) on-board the Indian satellite IRS-P3 during 1998 June 2nd–10th. The X-ray flux of the source in the main outburst decreased exponentially during the period of observation. No large amplitude short-term variability in the intensity is detected from the source. The power density spectrum obtained from the timing analysis of the data shows no indication of any quasi-periodic oscillations in 0.002–0.5 Hz band. The hardness ratio i.e. the ratio of counts in 6–18 keV to 2–6 keV band, indicates that the X-ray spectrum is soft with spectral index >2. From the similarities of the X-ray properties with those of other black hole transients, we conclude that the X-ray transient XTE J2012+381 is likely to be a black hole.  相似文献   

Large Area X-Ray Proportional Counter (LAXPC) Instrument on AstroSat and Some Preliminary Results from its Performance in the Orbit     

P. C. Agrawal  J. S. Yadav  H. M. Antia  Dhiraj Dedhia  P. Shah  Jai Verdhan Chauhan  R. K. Manchanda  V. R. Chitnis  V. M. Gujar  Tilak Katoch  V. N. Kurhade  P. Madhwani  T. K. Manojkumar  V. A. Nikam  A. S. Pandya  J. V. Parmar  D. M. Pawar  Jayashree Roy  B. Paul  Mayukh Pahari  Ranjeev Misra  M. H. Ravichandran  K. Anilkumar  C. C. Joseph  K. H. Navalgund  R. Pandiyan  K. S. Sarma  K. Subbarao 《Journal of Astrophysics and Astronomy》2017,38(2):30

Large area X-ray propositional counter (LAXPC) instrument on AstroSat is aimed at providing high time resolution X-ray observations in 3–80 keV energy band with moderate energy resolution. To achieve large collecting area, a cluster of three co-aligned identical LAXPC detectors, is used to realize an effective area in access of \({\sim }6000\,\hbox {cm}^{2}\) at 15 keV. The large detection volume of the LAXPC detectors, filled with xenon gas at \({\sim }\)2 atmosphere pressure, results in detection efficiency greater than 50%, above 30 keV. In this article, we present salient features of the LAXPC detectors, their testing and characterization in the laboratory prior to launch and calibration in the orbit. Some preliminary results on timing and spectral characteristics of a few X-ray binaries and other type of sources, are briefly discussed to demonstrate that the LAXPC instrument is performing as planned in the orbit.  相似文献   

Integrating value-chain approach with participatory multicriteria analysis for sustainable planning of a niche crop in Indian Himalayas     

Sudeshna Maya SEN  Arun KANSAL 《山地科学学报》2019,(10)

The value-chain approach(VCA)was used for exploring how a niche crop,namely large cardamom(Amomum subulatum Roxb.),can be developed sustainably to increase incomes and enhance rural livelihoods in the mountains.Large cardamom is a high-value,agro-climatically suitable,and non-perishable spice crop grown in the Himalayan region.Originating in Sikkim,the crop is important to the local economy and is sold in both domestic and international markets;however,its production in India has been declining significantly in recent years.Using VCA and participatory methods of data collection the study helped elicit value chain actors'perspectives on various reasons for the decline as well as potential strategies to improve the cardamom value chain.The results present the multiple environmental and climatic(e.g.water stress),social(e.g.women participation)and institutional(e.g.lack of trust between actors)challenges and corresponding upgrading strategies.Through participatory multi-criteria analysis(MCA),the strategies were prioritized based on the overall preferences of multiple stakeholders.The analysis considered eight criteria and 25 options,or strategies,and found that that marketability and profitability were the most important criteria,and increasing cardamom production,the most important optiontrait.Stakeholder discussions along with sensitivity analysis also showed how these options could be implemented and revealed how criteria preferences can change with expert inputs.This combination of VCA and MCA,because it supports participatory decision-making and balances multiple dimensions of sustainable development,can be effectively deployed in planning for agricultural development in the mountains.  相似文献   

Modeling Short-Term Spatial and Temporal Variability of Groundwater Level Using Geostatistics and GIS   总被引：1，自引：0，他引：1  

Deepesh Machiwal  Amit Mishra  Madan K. Jha  Arun Sharma  S. S. Sisodia 《Natural Resources Research》2012,21(1):117-136

Continuous depletion of groundwater levels from deliberate and uncontrolled exploitation of groundwater resources lead to the severe problems in arid and semi-arid hard-rock regions of the world. Geostatistics and geographic information system (GIS) have been proved as successful tools for efficient planning and management of the groundwater resources. The present study demonstrated applicability of geostatistics and GIS to understand spatial and temporal behavior of groundwater levels in a semi-arid hard-rock aquifer of Western India. Monthly groundwater levels of 50 sites in the study area for 36-month period (May 2006 to June 2009; excluding 3 months) were analyzed to find spatial autocorrelation and variances in the groundwater levels. Experimental variogram of the observed groundwater levels was computed at 750-m lag distance interval and the four most-widely used geostatistical models were fitted to the experimental variogram. The best-fit geostatistical model was selected by using two goodness-of-fit criteria, i.e., root mean square error (RMSE) and correlation coefficient (r). Then spatial maps of the groundwater levels were prepared through kriging technique by means of the best-fit geostatistical model. Results of two spatial statistics (Geary’s C and Moran’s I) indicated a strong positive autocorrelation in the groundwater levels within 3-km lag distance. It is emphasized that the spatial statistics are promising tools for geostatistical modeling, which help choose appropriate values of model parameters. Nugget-sill ratio (<0.25) revealed that the groundwater levels have strong spatial dependence in the area. The statistical indicators (RMSE and r) suggested that any of the three geostatistical models, i.e., spherical, circular, and exponential, can be selected as the best-fit model for reliable and accurate spatial interpolation. However, exponential model is used as the best-fit model in the present study. Selection of the exponential model as the best-fit was further supported by very high values of coefficient of determination (r ² ranging from 0.927 to 0.994). Spatial distribution maps of groundwater levels indicated that the groundwater levels are strongly affected by surface topography and the presence of surface water bodies in the study area. Temporal pattern of the groundwater levels is mainly controlled by the rainy-season recharge and amount of groundwater extraction. Furthermore, it was found that the kriging technique is helpful in identifying critical locations over the study area where water saving and groundwater augmentation techniques need to be implemented to protect depleting groundwater resources.  相似文献   

A composite study of the MJO influence on the surface air temperature and precipitation over the Continental United States   总被引：1，自引：1，他引：0  

Shuntai Zhou  Michelle L’Heureux  Scott Weaver  Arun Kumar 《Climate Dynamics》2012,38(7-8):1459-1471

The influence of the MJO on the continental United States (CONUS) surface air temperature (SAT) and precipitation is examined based on 30?years of daily data from 1979–2008. Composites are constructed for each of the eight phases of the Wheeler-Hendon MJO index over 12 overlapping three-month seasons. To ensure that the MJO signal is distinguished from other patterns of climate variability, several steps are taken: (a) only days classified as “MJO events” are used in the composites, (b) statistical significance of associated composites is assessed using a Monte Carlo procedure, and (c) intraseasonal frequencies are matched to the unfiltered data. Composites of other fields are also shown in order to examine how the SAT and precipitation anomalies are associated with large-scale circulations providing a link between the tropics and extratropics. The strongest and most significant MJO effects on SAT are found during the northern winter seasons. When enhanced convection is located over the equatorial Indian Ocean, below-average SAT tends to occur in New England and the Great Lakes region. As enhanced tropical convection shifts over the Maritime continent, above-average SAT appears in the eastern states of the US from Maine to Florida. The MJO influence on precipitation is also significant during northern winter seasons. When enhanced convection is located over the Maritime continent, more precipitation is observed in the central plains of the US. Enhanced precipitation also occurs over the west coast of the US when convective activity is stronger over the Indian Ocean. During the northern summer and fall, the MJO impact on precipitation is mainly significant at lower latitudes, over Mexico and southeastern US.  相似文献   

Connection of stratospheric QBO with global atmospheric general circulation and tropical SST. Part I: methodology and composite life cycle     

Bohua Huang  Zeng-Zhen Hu  James L. Kinter III  Zhaohua Wu  Arun Kumar 《Climate Dynamics》2012,38(1-2):1-23

The stratospheric quasi-biennial oscillation (QBO) and its association with the interannual variability in the stratosphere and troposphere, as well as in tropical sea surface temperature anomalies (SSTA), are examined in the context of a QBO life cycle. The analysis is based on the ERA40 and NCEP/NCAR reanalyses, radiosonde observations at Singapore, and other observation-based datasets. Both reanalyses reproduce the QBO life cycle and its associated variability in the stratosphere reasonably well, except that some long-term changes are detected only in the NCEP/NCAR reanalysis. In order to separate QBO from variability on other time scales and to eliminate the long-term changes, a scale separation technique [Ensemble Empirical Mode Decomposition (EEMD)] is applied to the raw data. The QBO component of zonal wind anomalies at 30?hPa, extracted using the EEMD method, is defined as a QBO index. Using this index, the QBO life cycle composites of stratosphere and troposphere variables, as well as SSTA, are constructed and examined. The composite features in the stratosphere are generally consistent with previous investigations. The correlations between the QBO and tropical Pacific SSTA depend on the phase in a QBO life cycle. On average, cold (warm) SSTA peaks about half a year after the maximum westerlies (easterlies) at 30?hPa. The connection of the QBO with the troposphere seems to be associated with the differences of temperature anomalies between the stratosphere and troposphere. While the anomalies in the stratosphere propagate downward systematically, some anomalies in the troposphere develop and expand vertically. Therefore, it is possible that the temperature difference between the troposphere and stratosphere may alter the atmospheric stability and tropical deep convection, which modulates the Walker circulation and SSTA in the equatorial Pacific Ocean.  相似文献