Cosmic microwave background power spectrum estimation with non-circular beam and incomplete sky coverage     

Sanjit Mitra  Anand S. Sengupta  Subharthi Ray  Rajib Saha  Tarun Souradeep 《Monthly notices of the Royal Astronomical Society》2009,394(3):1419-1439

Over the last decade, measurements of the cosmic microwave background (CMB) anisotropy have spearheaded the remarkable transition of cosmology into a precision science. However, addressing the systematic effects in the increasingly sensitive, high-resolution, 'full' sky measurements from different CMB experiments poses a stiff challenge. The analysis techniques must not only be computationally fast to contend with the huge size of the data, but the higher sensitivity also limits the simplifying assumptions which can then be invoked to achieve the desired speed without compromising the final precision goals. While maximum likelihood is desirable, the enormous computational cost makes the suboptimal method of power spectrum estimation using pseudo-C _l unavoidable for high-resolution data. The debiasing of the pseudo-C _l needs account for non-circular beams, together with non-uniform sky coverage. We provide a (semi)analytic framework to estimate bias in the power spectrum due to the effect of beam non-circularity and non-uniform sky coverage, including incomplete/masked sky maps and scan strategy. The approach is perturbative in the distortion of the beam from non-circularity, allowing for rapid computations when the beam is mildly non-circular. We advocate that it is computationally advantageous to employ 'soft' azimuthally apodized masks whose spherical harmonic transform die down fast with m . We numerically implement our method for non-rotating beams . We present preliminary estimates of the computational cost to evaluate the bias for the upcoming CMB anisotropy probes  ( l _max∼ 3000)  , with angular resolution comparable to the Planck surveyor mission. We further show that this implementation and estimate are applicable for rotating beams on equal declination scans, and can possibly be extended to simple approximations to other scan strategies.  相似文献   

On a possible mechanism of low surface magnetic field structure of quark stars     

Nandini Nag  Sutapa Ghosh  Roni Saha  Somenath Chakrabarty 《Astrophysics and Space Science》2009,323(2):123-133

Following some of the recent articles on hole super-conductivity and related phenomena by Hirsch (Phys. Lett. A 134:451, 1989; Phys. Rev. B 68:184502, 2003a; Phys. Rev. B 71:184521, 2005a and Phys. Lett. A 345:453, 2005b) a simple model is proposed to explain the observed low surface magnetic field of the expected quark stars. It is argued that the diamagnetic moments of the electrons circulating in the electro-sphere induce a magnetic field, which forces the existing quark star magnetic flux density to become dilute. For the sake of completeness, we have also included the analyses of instability at the normal-super-conducting interface due to excess accumulation of magnetic flux lines. The instability at the interface has also been studied numerically.   相似文献   

The Indian monsoon and its economic impact     

Dr. K. R. Saha  D. A. Mooley  S. Saha 《GeoJournal》1979,3(2):171-178

Indian economy is vitally linked with the monsoon because of its water resources. A large part of the country gets more than 75% of the annual rainfall during the four months, June to September.The production of foodgrains depends fairly closely on the amount and distribution of monsoon rainfall over the country. Further the generation of hydro-electric power from monsoon rain water has been traced over the last 20 years. While hydro-electric power constitutes about 40% of power from all sources, with proper surveys and planning additional hydro-electric power projects this percentage could, perhaps, be further substantially increased. The distinct advantage of hydro-electric power over all other types of power is that its source, i.e. monsoon water, is perennial, although it shows some fluctuations from year to year. The power of the monsoon winds at four and two stations on the West coast and in the interior resp. has been assessed on the basis of five years hourly wind data. The wind at New Kandla on the West coast has a good potentiality for power. The wind power could be used for electricity, grinding corn and drawing water. On the debit side, Indian economy suffers heavy losses due to floods and droughts almost every year.The population of India is increasing at a much faster rate than the total foodgrains production and soon the country may be facing a serious economic crisis. A large part of the monsoon water which is currently unutilized should be held at suitable locations for irrigation and possible power generation.  相似文献   

Some observations on brittle-ductile toggle     

Dilip Saha 《Journal of Earth System Science》1995,104(3):419-431

In low temperature deformation of polymineralic rocks the constituent minerals often show contrasting deformation mechanisms. In naturally deformed arkoses, feldspathic quartzites and grits under greenschist to almandine-amphibolite fades condition, feldspar deforms by microboudinage (rigid-brittle behaviour), while quartz flows by a combination of dislocation creep, pressure solution and solution transfer. Boudin segments develop and separate in a phased sequential manner while quartz matrix flows in a ductile manner, indicating a brittle-ductile toggle during progressive deformation. Both the pressure solution and dislocation creep flows are volume-conservative. Therefore, a net volume increase during the above deformations is a necessity, unless compensated by a solution-transfer process. Hydrofracturing probably played a role in microboudinage formation as the ambient level of differential stress is estimated to be low around 45–75 MPa. To develop a synthetic flow law for the above type of deformation in arkoses, one needs to consider the significance of different rate-controlling mechanisms. As feldspar pull-aparts are syntectonically filled with quartz or metamorphic minerals crystallizing during progressive deformation, successive microboudin segmentation will depend on how fast/slow the matrix quartz moves to the open crack or the sealing takes place by transfer of appropriate solute components by pressure solution or solution transfer, the real rate-controlling process.  相似文献   

Evolution of India’s monsoon climate through geological times     

Kshudiram Saha 《Journal of Earth System Science》1993,102(1):241-247

Using the theory of plate tectonics and a concept of climate analogs, the paper speculates that a monsoon type of climate with warm and wet summer and cold and dry winter might have first appeared over the northern part of India when during its northward drift across the Tethys Ocean (now the Indian Ocean) it was located over the subtropical belt of the southern hemisphere some 60 million years before present (BP). The monsoon climate gradually evolved and extended to other parts of India as the Indian plate after crossing the equator about SO million years BP moved further northward and collided against the north Asian plate giving rise to the Himalayas along the northern boundary of India some 40 million years BP. Recent studies suggest that despite short and long period fluctuations, no major secular change or trend has taken place in the monsoon climate of India since then.  相似文献   

Internal geometry of a thrust sheet,eastern Proterozoic belt,Godavari Valley,South India     

Dilip Saha 《Journal of Earth System Science》1990,99(2):339-355

A small thrust sheet, named Pedda Gutta thrust sheet, consisting of calcareous to cherty argillites and cherts, and juxtaposed against tidal-intertidal cross-bedded quartzites and stromatolitic and sileceous limestone in the eastern Proterozoic belt, Godavari Valley, exhibits structures comparable in style to those of the external zone of a fold-thrust mountain belt. A wide spectrum of periodic and aperiodic mesoscopic folds varying from upright ones with rounded hinges and attenuated limbs, through noncylindrical kinks to whalebacks and sheath-like forms have developed within the small volume of the thrust sheet, the preserved thickness of which is of the order of 50 metres (comparable in scale to cleavage duplexes). Cleavage development is also heterogeneous across the width of the sheet. Displacement transfer from faults to folds and vice-versa is a common feature. On the basis of the distribution of the mesoscopic structures of varying style within the sheet and localization of fault rocks, three slices (wedges) have been recognized, each bounded on the east by a thrust which is steep at the current erosion level but interpreted to be of listric form making the thrust network comparable in architecture, though not in scale, to a hinterland (west) dipping imbricate fan.  相似文献   

Comparison of Water Quality and the Chemical Nature of the Sediments of River and Wells at Bhagalpur,India     

S. Kumar  L. C. Saha 《洁净——土壤、空气、水》1991,19(4):411-417

Bottom sediments of a river and of two sites of well showed significant changes in relation to different water factors. Comparatively, organic carbon, organic matter and free CaCO₃ concentration were higher in the Sutapatti well than at other sites which may affect the quality of potable water considerably.  相似文献   

String cosmological model in the presence of a magnetic flux     

Bijan Saha  Mihai Visinescu 《Astrophysics and Space Science》2008,315(1-4):99-104

A Bianchi type I string cosmological model in the presence of a magnetic flux is investigated. A few plausible assumptions regarding the parametrization of the cosmic string and magneto-fluid are introduced and some exact analytical solutions are presented.  相似文献   

Soil-Physiography relationship in Mahanadi Delta (Part) using Landsat Imagery     

S. Chatterjee  L. M. Pande  S. K. Subramanian  S. K. Saha  C. J. Thampi 《Journal of the Indian Society of Remote Sensing》1990,18(4):15-23

Visual Interpretation of Landsat Imagery (TM-FCC) on 1∶250,000 scale covering 2410 sq km in a part of Mahandi Delta, Kataka district, Orissa was carried out for delineating the physiographic units. The major physiographic units identified and delineated were ‘Delta plain’ and ‘Coastal plain’. These units were further subdivided on the basis of image elements. The abstraction level attained was ‘Family’ based on Soil Taxonomy. The soils of the beach were classified as Typic Ustipsamments; old coastal plain as fine, Typic Haplaquept and coarse loamy Aquic Ustifluvent; Tidal flat as fine Typic Haplaquept and fine loamy Aquic Ustifluvent; mud flat as fine Typic Haplaquept; Levee-plain complex as Typic Ustipsamment and fine loamy Typic Ustorthent; old Delta plain as fine Udic Ustochrept and Aeric Haplaquept and recent delta plain as fine loamy and coarse loamy Typic Ustorthent. The soils are mixed in mineralogy and Isohyperthermic in temperature regime.  相似文献   

Some problems of interpreting the correlations between the modal variables in granitic rocks     

A. K. Saha  C. Bhattacharyya  S. Lakshmipathy 《Mathematical Geology》1974,6(3):245-258

Correlation coefficients of modal variables from several suites of granitic rocks have been calculated and tested for significance using the Chayes-Kruskal and Chayes methods. The results show that although Chayes' remaining-space transformation does, in general, weaken the original proportion correlations, the positive and low-negative original proportion correlations tend to increase in absolute value because of a tendency of positive increment of the covariance by such transformation. However, no satisfactory procedure for choosing the variable to be transformed (V₂)could be determined, and testing of the significance of remaining-space correlations is found to be highly problematic. It is shown also that the Vistelius-Sarmanov procedure of calculation of correlation coefficients from closed-table data does not effectively eliminate the closure effect. It is concluded that assigning statistical significance to the correlation coefficients between modal variables is, in general, unsatisfactory, except where the number of variables 8,the sample size is large (say, 30),and there is no negative element in the variance vector of the corresponding open variables.  相似文献