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Search Results: 1 - 10 of 484781 matches for " S. C. Chakravarty "
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A Novel Approach to Study Regional Ionospheric Variations Using a Real-Time TEC Model  [PDF]
S. C. Chakravarty
Positioning (POS) , 2014, DOI: 10.4236/pos.2014.51001

Since IGY (International Geophysical Year), through coordinated global observations, ionospheric research has been carried out by many countries. This effort primarily helped in the design and operation of HF radio wave communication systems. The Indian region covers a highly variable part of the equatorial electrojet and EIA (Equatorial Ionisation Anomaly) phenomena making its predictability difficult. With the advent of satellite communication and navigation, the need for accurate ionospheric TEC (Total Electron Content) models at global and regional scales has been stressed. The GAGAN (GPS Aided Geo Augmented Navigation) project jointly undertaken by the Indian Space Research Organisation (ISRO) and the Airport Authority of India (AAI) aims at effectively utilising the Global Navigational Satellite System (GNSS) to determine position coordinates accurately for aircraft precision landing applications. For this purpose the range errors are estimated by using a ground network of TEC stations spread over Indian region. The near simultaneous data collected from these dual frequency GPS stations can be used to generate the geo-referenced TEC values for various applications. The author has developed necessary algorithm and associated computer programmes for a real-time vertical TEC (VTEC) model based on TEC data collected from the GAGAN ground based network stations. The model has been tested and sample results presented here show that it adequately provides for the latitudinal resolution of 1° for the entire longitude span and also for two longitude blocks (73 - 83 & 83 - 93°E) separately. Cubic spline and bilinear interpolation techniques are used for filling up temporal and spatial data gaps. The model provides tabulated output of hourly average VTEC data with latitude for ready use, as well as graphical displays of VTEC maps and contours for monitoring purpose. The real-time model and its extensions are also being used for detailed scientific studies; examples of these show small day to day variability of VTEC without any change in solar activity and indication of the change in the shape of the VTEC diurnal curve with season. The present model will be used for further studies to derive the monthly average variation of the diurnal pattern and the relationship between VTEC peak amplitudes with changes in solar activity. The

S. Chakravarty* and J. C. Kalita
International Journal of Pharmaceutical Sciences and Research , 2012,
Abstract: Nalbari district is situated in between 26°N and 27oN latitude and 92oE and 97oE longitude. It lies between Kamrup and Barpeta district of lower Assam. Nalbari has a population of 1138184 (2001 census). An ethnobotanical Survey was conducted in 2010 in selected villages to explore the medicinal plant used by the villagers to cure Diabetes. This villages are inhabited by Boros, Koch, Muslim communities. The indigenous knowledge of local traditional healers and native plants used by the villagers to cure Diabetes were collected using a questionnaire and personal interviews. Total 30 villagers in the age group of 30-68 years were interviewed out of which 3 were local healers. The investigation reveals 35 species of plants belonging to 28 families which are used to cure Diabetes. It is found that the whole plant is used for curing the ailment but mostly fresh juice, powder, fresh leaves, paste or decoction in water remains the most preferred method of preparation. Most plants are very effective remedy when used in a combination or singly. The present study throws light on the traditional knowledge of the villagers regarding medicinal plant which can be used against Diabetes which is largely unexplored.
Hidden Order in the Cuprates
S. Chakravarty,R. B. Laughlin,D. K. Morr,C. Nayak
Physics , 2000, DOI: 10.1103/PhysRevB.63.094503
Abstract: We propose that the enigmatic pseudogap phase of cuprate superconductors is characterized by a hidden broken symmetry of d(x^2-y^2)-type. The transition to this state is rounded by disorder, but in the limit that the disorder is made sufficiently small, the pseudogap crossover should reveal itself to be such a transition. The ordered state breaks time-reversal, translational, and rotational symmetries, but it is invariant under the combination of any two. We discuss these ideas in the context of ten specific experimental properties of the cuprates, and make several predictions, including the existence of an as-yet undetected metal-metal transition under the superconducting dome.
Deletion/inversion in the X-chromosome and increased telomeric associations in a female with primary amenorrhea
Multani, Asha S.;Shah, Vinod C.;Singh, Divya;Chakravarty, Nivedita;Chinoy, Niloufer J.;Pathak, Sen;
Brazilian Journal of Genetics , 1997, DOI: 10.1590/S0100-84551997000300025
Abstract: we describe a new case of a partial interstitial deletion and inversion of the long arm of the x-chromosome associated with a high incidence of telomeric associations in an 18-year old female who showed underdeveloped secondary sex characteristics, including small breasts and primary amenorrhea. her karyotype was considered to be 46,x,del(xq13 ? q22)inv(x)(q23-q27). the buccal mucosal cells showed absence of a typical barr body, and the 5?-bromo-2-deoxyuridine incorporation studies revealed that neither the normal x-nor the abnormal x-chromosome was late replicating. the case is being presented for its extreme rarity
Low temperature in-situ reaction sintering of zircon: Alumina composites trough spark plasma sintering
Anjali M.C.,Biswas P.,Chakravarty D.,Hareesh U.S.
Science of Sintering , 2012, DOI: 10.2298/sos1203323a
Abstract: Pure Zircon and Zircon: Alumina (ZrSiO4: α-Al2O3) composite powders were subjected to densification studies employing spark plasma sintering (SPS). Physico chemical and microstructural properties of the samples were evaluated and compared with that of conventionally sintered (CRH-Constant Ramp and Hold) compacts. Density measurements and microstructural evaluation revealed a low temperature densification of Zircon: Alumina at temperatures as low as 1300°C by SPS. Increase of temperature to 1350°C had shown negligible changes in density and on further heating the sample melts at 1400°C as a result of excessive formation of liquid phase. However, pure zircon could not be densified in the absence of alumina under SPS conditions. It is evident that addition of alumina enhances partial low temperature decomposition of zircon under the influence of plasma generated during SPS. Mullite formed as a result of this insitu reaction between alumina and silica acts as a bonding phase as revealed by the X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Electron disperse scanning (EDS) analysis.
The neurology of eclampsia : some observations.
Chakravarty A,Chakrabarti S
Neurology India , 2002,
Abstract: Nineteen patients admitted with diagnosis of eclampsia in a large general hospital between 1996 - 1999, were analyzed. Eight patients were referred to neurologists for assessment and management. All these patients had recurrent generalized seizures. Five patients developed visual disturbance. Neuroimaging (CT and/or MRI) revealed symmetrical occipital lesions in all. One patient had a large pontine lesion. Seizure control was achieved in all with intravenous phenytoin. All patients recovered fully without any residual neurological deficit and their radiological brain lesions resolved completely, in all except one case. The neurological manifestations and neuroimaging features in cases of eclampsia have been reviewed. A brief note on the pathogenesis of the cerebral lesions is included and the controversial aspect of seizure control in eclampsia highlighted.
Primary degenerative cerebellar ataxias in ethnic Bengalees in West Bengal: Some observations
Chakravarty A,Mukherjee S
Neurology India , 2003,
Abstract: Seventy cases of primary degenerative cerebellar ataxias in ethnic Bengalees from southern West Bengal, India, were studied by the authors. Of these, 50 cases were of the familial type (hereditary ataxias) encountered in 23 families and the remaining 20 were of sporadic onset. 18 cases (from 11 families) were of 'probable' autosomal recessive (AR) inheritance, 12 cases (8 families) had Friedreich's type ataxia (FA), 4 cases (2 families) had FA type ataxia with retained reflexes and in 2 cases (1 family) the exact phenotypic characterization could not be made. AR inheritance in these cases seemed most likely in view of the occurrence in a single generation with unaffected parents and history of consanguinity in many of the families studied. Genotypic confirmation of FA type ataxia and its variants could not be done in any case due to the non-availability of technology for studying the FA locus but some common dominant ataxia genotypes could be excluded. Thirty-two cases (from 12 families) with autosomal dominant ataxias (ADCA) were studied. Genotype analysis revealed 4 families with SCA2 genotype, 5 families with SCA3 and 3 families where genotypic characterization could not be made (phenotypically 2 were of ADCA I and 1 of ADCA II). No clear preponderance of one particular genotype of SCA over another could be demonstrated in our ethnic Bengalee patients. We also noted significant intra and inter-family variations in phenotypes within the same genotypic form as well as overlapping of clinical signs between different genotypes. Slow saccades and peripheral neuropathy were not seen consistently in our ethnic Bengalee subjects with SCA2 genotype. Similarly, extrapyramidal features, ophthalmoplegias and distal amyotrophy were seen in some but not all families with the SCA3 genotype. Phenotypic expression appeared to be an inconsistent marker of the SCA genotype in our patients. Of the 20 sporadic cases with cerebellar ataxia, genotype analysis revealed 2 cases with SCA1 and 1 with SCA2. Some of the sporadic ataxia cases had extracerebellar involvement and may warrant classification as Multiple System Atrophy. In all the 3 subjects with genotype characterization, phenotype correlation was lacking. The clinical pattern of hereditary ataxias in ethnic Bengalees seems to be somewhat different from that seen in Western India. The need for clinical and genetic studies of ataxias in different specific ethnic populations of India has been stressed.
Spectral Anomaly and High Temperature Superconductors
L. Yin,S. Chakravarty
Physics , 1995, DOI: 10.1142/S0217979296000349
Abstract: Spectral anomaly for interacting Fermions is characterized by the spectral function $A([k-k_F],\omega)$ satisfying the scaling relation $A(\Lambda^{y_1} [k-k_F],\Lambda^{y_2}\omega)= \Lambda^{y_A}A([k-k_F],\omega)$, where $y_1$, $y_2$, and $y_A$ are the exponents defining the universality class. For a Fermi liquid $y_1=1$, $y_2=1$, $y_A=-1$; all other values of the exponents are termed anomalous. In this paper, an example for which $y_1=1$, $y_2=1$, but $y_A=\alpha-1$ is considered in detail. Attractive interaction added to such a critical system leads to a novel superconducting state, which is explored and its relevance to high temperature cuprate superconductors is discussed.
First mesospheric turbulence study using coordinated rocket and MST radar measurements over Indian low latitude region
H. Chandra, H. S. S. Sinha, U. Das, R. N. Misra, S. R. Das, J. Datta, S. C. Chakravarty, A. K. Patra, N. Venkateswara Rao,D. Narayana Rao
Annales Geophysicae (ANGEO) , 2008,
Abstract: A campaign to study turbulence in the mesosphere, over low latitudes in India, using rocket-borne measurements and Indian MST radar, was conducted during July 2004. A rocket-borne Langmuir probe detected a spectrum of electron density irregularities, with scale sizes in the range of about 1 m to 1 km, in 67.5–78.0 km and 84–89 km altitude regions over a low latitude station Sriharikota (13.6° N, 80.2° E). A rocket-borne chaff experiment measured zonal and meridional winds about 30 min after the Langmuir probe flight. The MST radar located at Gadanki (13.5° N, 79.2° E), which is about 100 km west of Sriharikota, also detected the presence of a strong scattering layer in 73.5–77.5 km region from which radar echoes corresponding to 3 m irregularities were received. Based on the region of occurrence of irregularities, which was highly collisional, presence of significant shears in zonal and meridional components of wind measured by the chaff experiment, 10 min periodicity in zonal and meridional winds obtained by the MST radar and the nature of wave number spectra of the irregularities, it is suggested that the observed irregularities were produced through the neutral turbulence mechanism. The percentage amplitude of fluctuations across the entire scale size range showed that the strength of turbulence was stronger in the lower altitude regions and decreased with increasing altitude. It was also found that the amplitude of fluctuations was large in regions of steeper electron density gradients. MST radar observations showed that at smaller scales of turbulence such as 3 m, (a) the thickness of the turbulent layer was between 2 and 3 km and (b) and fine structures, with layer thicknesses of about a km or less were also embedded in these layers. Rocket also detected 3-m fluctuations, which were very strong (a few percent) in lower altitudes (67.5 to 71.0 km) and small but clearly well above the noise floor at higher altitudes. Rocket and radar results also point to the possibility of existence of thin layers of turbulence (<450 m). The turbulence parameters estimated from rocket-borne measurements of electron density fluctuations are consistent with those determined from MST radar observed Doppler spectra and the earlier works.
Health Care and Women's Empowerment: The role of Self Help Groups
S Chakravarty,A N Jha
Health, Culture and Society , 2012, DOI: 10.5195/hcs.2012.56
Abstract: Over the last couple of decades the concept of Self Help Groups (SHGs) and its potential as an effective tool to alleviate poverty and empower women has garnered considerable interest worldwide. Considering the importance given by policy makers across various nations to the group approach while conceptualizing, formulating and implementing any scheme or programme for the welfare of marginalized and underprivileged sections of the society (especially women), we identified the need to critically examine and explore the role of SHGs in the empowerment of women with a special emphasis on health status. To date, the functioning of SHGs has essentially been viewed only from an economic perspective. The existing approach puts encourages the economic development of women, with SHGs a mechanism to achieving this. However, how these economic benefits are being translated into the change in women’s status, particularly their health status, remains unexplored and ultimately unaddressed. This working research paper attempts to review the scope and limitations of SHGs in improving women’s health and empowerment based upon empirical work undertaken in the Jharkhand state of India. Our paper also explores the extent to which SHGs can be involved in attaining better health status for women, and thereby point the way for further research.
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