Solving the graceful exit problem in superstring cosmology     

Sukanta Bose 《Journal of Astrophysics and Astronomy》1997,18(4):381-387

We briefly review the status of the “graceful exit” problem in superstring cosmology and present a possible resolution. It is shown that there exists a solution to this problem in two-dimensional dilaton gravity provided quantum corrections are incorporated. This is similar to the recently proposed solution of Rey. However, unlike in his case, in our one-loop corrected model the graceful exit problem is solved for any finite number of massless scalar matter fields present in the theory.  相似文献   

Observations of AGNs using PACT     

D. Bose  V. R. Chitnis  P. R. Vishwanath  P. Majumdar  M. A. Rahman  B. B. Singh  A. C. Gupta  B. S. Acharya 《Astrophysics and Space Science》2007,309(1-4):111-117

We report our observations on 4 AGNs viz, Mkn 421, Mkn 501, 1ES1426+428 and ON231 belonging to a sub-class called blazars. The observations were carried out using the Pachmarhi Array of Cherenkov Telescopes and span about 6 years period from 2000 to 2005. We discuss our methods of analysis adopted to extract the gamma ray signal from cosmic ray background. We present our results on the emission of TeV gamma rays from these objects. Also, we report on the status of the new high altitude experiment, a 7 telescope array at Hanle in the Himalayas at an altitude of about 4200 m above mean sea level for detecting celestial gamma-rays.  相似文献   

A Review of “Geographies of Media and Communication”     

Pablo S. Bose 《The Professional geographer》2013,65(1):145-146

Contemporary cartographic research on mapmaking and map use has a broad mandate and, as a consequence, researchers need a broad suite of methods. Consistent with research developments in other geographic subdisciplines, cartographic researchers now use qualitative methods. They offer the advantage of bringing research closer to the problem-solving realms of mapmakers and map users. Our purpose here is to discuss an array of qualitative methods for mapmaking and map use. Questionnaires, interviews, and protocol methods are used to gather verbal data about mapmaking and map use. Ethnographies produce data from direct observation of mapmakers and users. Maps also are sources for document analysis. We use examples of published cartographic research to elaborate on each of these methods.  相似文献   

Gamma (γ)-Ray Activity as a Tool for Identification of Hidden Ejecta Deposits Around Impact Crater on Basaltic Target: Example from Lonar Crater, India     

T. Bose  S. Misra  S. Chakraborty  K. Reddy 《Earth, Moon, and Planets》2013,111(1-2):31-46

Geophysical techniques based on radioactivity measurements are not generally used for exploration of asteroid impact craters. Our studies on the field and laboratory measurements of radioactivity on samples from the Lonar crater, India, show that this technique could be an important method for mapping the distribution of ejecta around the deeply excavated impact craters particularly when these structures are formed on relatively old target rocks/palaeosol. The Lonar ejecta shows ~1.3 times higher γ-ray count rates in the field on average compared to the underlying palaeosol and ~1.9 times higher values over the target basalt while measured by a portable Geiger–Müller pulse counter. The absorbed γ-dose rate (D) of the Lonar samples, computed from ²³²Th, ²³⁸U, and ⁴⁰K abundances in these samples, also show that the ejecta has distinct bulk dose rates (average ~8.42 nGy h^?1) as compared to those of the palaeosol (~18.34 nGy h^?1), target basalt (~11.97 nGy h^?1), and the impact-melts and spherules (~14 nGy h^?1). Therefore, radioactivity mapping of the terrestrial and planetary impact craters by direct methods has importance in mapping ejecta distributions around these structures.  相似文献   

Microstructural Variation in Quartzofeldspathic Mylonites: Example from Schirmacher Hills, East Antarctica     

Santanu Bose  Sudipta Sengupta 《Gondwana Research》2001,4(4):581-582

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Identification of a surface layer structure and analysis of humidity data in two weather situations at Jodhpur (26°18′N, 73°04′E), India,during MONTBLEX 1990     

N.?Das  M.?Bose  U.?K.?DeEmail author 《Journal of Earth System Science》2004,113(1):73-87

The Monsoon Trough Boundary Layer Experiment held in 1990 was a multi-institutional effort to probe the atmospheric boundary layer over the monsoon trough over northern India. For this experiment, four micrometeorological towers were set up at four different locations along the normal position of the trough. One such tower of 30m height was located at Jodhpur (26‡18′N, 73‡04′E), Rajasthan. The fast and slow response data available during the experiment have been used in the present study to determine a suitable layer-structure of the surface layer for evaluation of sensible heat flux using the multilayer hypothesis of Kramm (1989).  相似文献   

Isoseismals for the Kutch earthquake of 26th January 2001     

A. Sinvhal  P. R. Bose  V. Prakash  A. Bose  A. K. Saraf  H. Sinvhal 《Journal of Earth System Science》2003,112(3):375-383

Damage observed during the Kutch earthquake of 26th January 2001 is classified according to the type of structure. This damage pattern has been used to draw the isoseismal map on the basis of the intensity scale given in IS 1893-2002 which covers only traditional one to two storey houses. Having thus estimated intensities, and observed damage to other types of structures, a new criterion was adopted which is included in this paper. Areas that showed maximum damage to structures have been assigned maximum intensity X.  相似文献   

Observations of NO2 and O3 during thunderstorm activity using visible spectroscopy     

D.B. Jadhav  A.L. Londhe  S. Bose 《大气科学进展》1996,13(3):359-374

Simultaneous observations for the total column densities of NO2, O3 and H2O were carried on using the porta-ble Spectrometer (438-450 nm and 400-450 nm) and the visible Spectrometer (544.4-628 nm) during premonsoon thunderstorms and embedded hail storm activity at Pune (18o32’N & 73o51’E), India. These observations confirm the fact that there is an increase in O3 and NO2 column densities during thunderstorms. The increase in O3 was observed following onset of thunderstorm, while the increase in NO2 was observed only after the thunder flashes occur. This implies that the production mechanisms for O3 and NO2 in thunderstorm are different. The observed column density of NO2 value (1 to 3 × 1017molecules · cm-2) during thunderstorm activity is 10 to 30 times higher than the value (1 × 1016molecules · cm-2) of a normal day total column density. The spectrometric observations and observations of thunder flashes by electric field meter showed that 6.4 × 1025molecules / flash of NO2 are produced. The increased to-tal column density of ozone during thunderstorm period is 1.2 times higher than normal (clear) day ozone concentra-tion. The multiple scattering in the clouds is estimated from H2O and O2 absorption bands in the visible spectral re-gion. Considering this effect the calculated amount of ozone added in the global atmosphere due to thunderstorm ac-tivity is 0.26 to 0.52 DU, and the annual production of ozone due to thunderstorm activity is of the order of 4.02 × 1037 molecules /year. The annual NO2 production may be of the order of 2.02 × 1035molecules / year.  相似文献   

Determination of Mercury in Thirty‐three International Stream Sediment and Soil Reference Samples by Direct Mercury Analyser     

Nitish Kumar Roy  Surya Sankar Bose 《Geostandards and Geoanalytical Research》2008,32(3):331-335

Mercury was determined in thirty‐three international stream sediment and soil reference samples (eleven Chinese soils, GSS‐1 to GSS‐11; twelve Chinese stream sediments, GSD‐1A to GSD‐12; four Canadian stream sediments STSD‐1 to STSD‐4; South African stream sediments, SARM‐42, SARM‐46 and SARM‐47; Japanese stream sediments, JSd‐1 to JSd‐3) by direct mercury analyser. Samples were taken in 500 μl quartz boats, placed in an auto sampler and processed (drying time 60 s at 300 °C; decomposition time 120 s at 850 °C; waiting time 45 s). The instrument was calibrated in the low (0‐50 ng) and high ranges (50‐500 ng) with two reference materials GSS‐5 and GXR‐2 (USGS). Using the calibration line, reference samples were analysed for Hg. The results of the determinations agreed with the recommended values of RMs in all cases except JSd‐1. The RSD calculated for the RMs was found to be within 20%. The detection limit was 1 ng g^?1.  相似文献   

A three-dimensional wake impingement model and applications on tandem oscillating foils     

Moqin He  Brain Veitch  Neil Bose  Bruce Colbourne  Pengfei Liu 《Ocean Engineering》2007,34(8-9):1197-1210

Potential flow based vortex numerical methods have been widely used in aerodynamics and hydrodynamics. In these methods, vortices shed from lifting bodies are traced by using vortex filaments or dipole panels. When the wake elements encounter a downstream body, such as a rudder behind a propeller or a stator behind a rotor, a treatment is necessary to divert the wake elements to pass by the body. This treatment is vital to make wake simulations realistic and to satisfy the non-penetration condition during wake body interaction. It also helps to avoid pure numerical disturbances such as when a vortex filament or an edge of a dipole panel passes through the collection point of a body element; this is a singularity for induced velocity and it will introduce a large numerical disturbance. This necessary treatment for three-dimensional problems with geometrical complexity has not been found to date. In this study, a wake impingement model was developed to divert wake elements to slip over the body surface, model the vortex/body interaction, and predict forces on fluctuating components. The model was also tested on configurations of oscillating foils in tandem with an existing panel method code. Simulation results with the wake impingement model are shown to be in closer agreement with limited published experimental data than those without the model. With the established wake impingement model, force fluctuations on the after body due to the wake vortex impingement were investigated based on a series of simulations. The series varied several parameters including distance between two foils, oscillating frequency, span, rear foil pitch angle, swap angle and vertical position.  相似文献