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Search Results: 1 - 10 of 27836 matches for " Tapan Kumar Das "
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Computational Identification of Conserved microRNAs and Their Targets in Tea (Camellia sinensis)  [PDF]
Akan Das, Tapan Kumar Mondal
American Journal of Plant Sciences (AJPS) , 2010, DOI: 10.4236/ajps.2010.12010
Abstract: MicroRNAs (miRNAs) are a class of ~22 nucleotides long non coding RNA molecules which play an important role in gene regulation at the post transcriptional level. The conserved nature of miRNAs provides the basis of new miRNA identification through homology search. In an attempt to identify new conserved miRNAs in tea, previously known plant miRNAs were used for searching their homolog in a tea Expressed Sequence Tags and full length nucleotide sequence database. The sequences showing homolog no more than four mismatches were predicted for their fold back structures and passed through a series of filtration criteria, finally led us to identify 13 conserved miRNAs in tea belonging to 9 miRNA families. A total of 37 potential target genes in Arabidopsis were identified subsequently for 7 miRNA families based on their sequence complementarity which encode transcription factors (8%), enzymes (30%) and transporters (14%) as well as other proteins involved in physiological and metabolic processes (48%). Overall, our findings will accelerate the way for further researches of miRNAs and their functions in tea.
Market Risk Beta Estimation using Adaptive Kalman Filter
Atanu Das,,Tapan Kumar Ghoshal
International Journal of Engineering Science and Technology , 2010,
Abstract: Market risk of an asset or portfolio is recognized through beta in Capital Asset Pricing Model (CAPM). Traditional estimation techniques emerge poor results when beta in CAPM assumed to be dynamic and follows auto regressive model. Kalman Filter (KF) can optimally estimate dynamic beta where measurement noise covariance and state noise covariance are assumed to be known in a state-space framework. This paper applied Adaptive Kalman Filter (AKF) for beta estimation when the above covariances are not known and estimated dynamically. The technique is first characterized through simulation study and then applied to empirical data from Indian security market. A odification of the used AKF is also proposed to take care of the problems of AKF implementation onbeta estimation and simulations show that modified method improves the performance of the filter measured by RMSE.
Many-body approach to low-lying collective excitations in a BEC approaching collapse
Anindya Biswas,Tapan Kumar Das
Physics , 2008, DOI: 10.1088/0953-4075/41/23/231001
Abstract: An approximate many-body theory incorporating two-body correlations has been employed to calculate low-lying collective multipole frequencies in a Bose-Einstein condensate containing $A$ bosons, for different values of the interaction parameter $\lambda=\frac{Aa_{s}}{a_{ho}}$. Significant difference from the variational estimate of the Gross-Pitaevskii equation has been found near the collapse region. This is attributed to two-body correlations and finite range attraction of the realistic interatomic interaction. A large deviation from the hydrodynamic model is also seen for the second monopole breathing mode and the quadrupole mode for large positive $\lambda$.
Salt tolerant culturable microbes accessible in the soil of the Sundarban Mangrove forest, India  [PDF]
Subhajit Das, Minati De, Raghab Ray, Dipnarayan Ganguly, Tapan kumar Jana, Tarun Kumar De
Open Journal of Ecology (OJE) , 2011, DOI: 10.4236/oje.2011.12004
Abstract: Sundarban Mangrove forest is highly productive marine ecosystem where halophilic microbes actively participate in bio-mineralization and biotransformation of minerals. The population of aerobic halophilic microbes was studied to determine their distribution with the availability of different physicochemical parameters with increasing depth of this forest sediment. The present study revealed that microbes present in the top soil region were less tolerant to fluctuation in salinity than the middle and bottom segment. Microbes isolated from bottom segment showed higher growth rate in anaerobic condition. A decreasing trend of total microbial population and organic carbon content of soil were found with increase in depth. In contrary a reverse profile was found for salinity. A significant stratification was found to exist among microbial population and the salty nature of the soil of Sundarban Mangrove forest.
Arsenic: it's extent of pollution and toxicosis: An animal perspective
Debashis Roy,Tapan Kumar Das,Shalini Vaswani
Veterinary World , 2013, DOI: 10.5455/vetworld.2013.53-58
Abstract: Arsenic poisoning is now considered as one of the biggest environmental disaster and a major public health issue. Incidence of arsenicpoisoning has been reported from many parts of the world. While Bangladesh and West Bengal (India) account for the most of the incidence, occasional reports from Mexico, Taiwan and mainland China have also appeared.It is a natural metalloid found in low concentrations in virtually every part of the environment as it is used in a wide variety of industrial applications, from computers to fireworks. Ground water arsenic is the major source of poisoning in animals and human. About 80% of ingested arsenic is absorbed and metabolized in liver and then excreted through urine and faeces while upon chronic exposure, it is deposited in liver, kidney and skin. Human populations are also being exposed to this poison by consuming the milk of affected animal.Inorganic forms of arsenic are more toxic compared to organic forms. Acute toxicity is rare in nature in comparison to chronic toxicity, which is prevalent in contaminated areas. Most non-ruminants are more susceptible to intoxication than ruminants. Chronic exposure of arsenic in animals and human beings causes severe adverse effects in the form of lowered immunity, diseases and production performances. [Vet World 2013; 6(1.000): 53-58]
Pair-correlation properties and momentum distribution of finite number of interacting trapped bosons in three dimension
Anindya Biswas,Barnali Chakrabarti,Tapan Kumar Das
Physics , 2010, DOI: 10.1063/1.3488650
Abstract: We study the ground state pair-correlation properties of a weakly interacting trapped Bose gas in three dimension by using a correlated many-body method. Use of the van der Waals interaction potential and an external trapping potential shows realistic features. We also test the validity of shape-independent approximation in the calculation of correlation properties.
Behavior of heat capacity of an attractive Bose-Einstein Condensate approaching collapse
Sanchari Goswami,Tapan Kumar Das,Anindya Biswas
Physics , 2011, DOI: 10.1103/PhysRevA.84.053617
Abstract: We report calculation of heat capacity of an attractive Bose-Einstein condensate, with the number N of bosons increasing and eventually approaching the critical number Ncr for collapse, using the correlated potential harmonics (CPH) method. Boson pairs interact via the realistic van der Waals potential. It is found that the transition temperature Tc increases initially slowly, then rapidly as N becomes closer to Ncr . The peak value of heat capacity for a fixed N increases slowly with N, for N far away from Ncr . But after reaching a maximum, it starts decreasing when N approaches Ncr . The effective potential calculated by CPH method provides an insight into this strange behavior.
Thermodynamic properties of ultracold Bose gas: transition exponents and universality
Sanchari Goswami,Tapan Kumar Das,Anindya Biswas
Physics , 2010, DOI: 10.1007/s10909-013-0860-3
Abstract: We report exact numerical calculation of chemical potential, condensate fraction and specific heat of $N$ non-interacting bosons confined in an isotropic harmonic oscillator trap in one, two and three dimensions, as also for interacting bosons in a 3D trap. Quasi phase transitions are observed in all these cases, including one-dimension, as shown by a rapid change of all the thermodynamic quantities at the transition point. The change becomes more rapid as $N$ increases in 2D and 3D cases. However with increase in $N$, the sudden change in the nature of specific heat, gets gradually wiped out in 1D, while it becomes more drastic in 2D and 3D. The sudden change in the nature of condensate fraction and chemical potential as $N$ increases becomes more drastic even in 1D. Defining transition exponents, which characterize the nature of a thermodynamic quantity at the transition point of a quasi phase transition, we evaluate them by careful numerical calculation very near the transition temperature. These exponents are found to be independent of the size of the system and whether the bosons are interacting or not, demonstrating their universality property.
A Depth Wise Diversity of Free Living N2 Fixing and Nitrifying Bacteria and Its Seasonal Variation with Nitrogen Containing Nutrients in the Mangrove Sediments of Sundarban, WB, India  [PDF]
Subhajit Das, Dipnarayan Ganguly, Tushar Kanti Maiti, Abhishek Mukherjee, Tapan Kumar Jana, Tarun Kuma De
Open Journal of Marine Science (OJMS) , 2013, DOI: 10.4236/ojms.2013.32012
Abstract:

Mangrove provides a unique ecological niche to different microbes which play various roles in nutrient recycling as well as various environmental activities. The highly productive and diverse microbial community living in mangrove ecosystems continuously transforms dead vegetation and recycle nitrogen, phosphorus, sulphur and other nutrients that can later be used by the plants. Mangrove ecosystems are rich in organic matter, and however, in general, they are nutrient-deficient ecosystems, especially of nitrogen and phosphorus. The present study investigated depth wise variation of Nitrifying bacteria, Nitrogen fixing bacteria, total bacterial population along with nitrate-nitrogen, nitrite-nitrogen and other physicochemical parameters of soil during pre-monsoon, monsoon and post-monsoon periods at three different sampling stations of mangrove sediments viz. deep forest region, rooted region and unrooted region. The microbial population was also found maximum in the deep forest sediment relative to the other two sites. Populations of cultureable microbes were found maximum in surface soil and decreased with increase in depth in Sundarban mangrove environment. A decreasing trend of total microbial load, nitrifying and nitrogen fixing bacteria with increase in depth were recorded throughout the year. Present study revealed the relationship among depth integrated variations of physicochemical components (viz. soil temperature, pH, salinity, nitrite nitrogen and nitrate nitrogen concentration) and total microbial load, nitrifying and nitrogen fixing bacteria microbial populations.

Depth profile exploration of enzyme activity and culturable microbial community from the oxygen-starved soil of Sundarban mangrove forest, India  [PDF]
Subhajit Das, Tapan Kumar Jana, Minati De, Tusher Kanti Maiti, Abhishek Mukherjee, Dipnarayan Ganguly, Tarun Kumar Sarkar, Tarun Kumar De
Open Journal of Ecology (OJE) , 2011, DOI: 10.4236/oje.2011.13009
Abstract: Populations of culturable microbes and activities of dehydrogenase & ?-D glucosidase were found maximum in surface soil and decreased with increase in depth in Sundarban mangrove environment.The maximum (13.529 X 106 C.F.U g-1 dry weight of soil) and minimum (11.547 X 106 C.F.U g-1 dry weight of soil) total microbial popu- lations in surface soil were recorded during po- st-monsoon and monsoon respectively. At 60 cm depth, the lower (6.396 X 106 C.F.U g-1 dry weight of soil) and higher (8.003 X 106 C.F.U g-1 dry weight of soil) numbers of total microbial populations were observed during monsoon and post-monsoon respectively. A decreasing trend of total microbial load, enzyme activities and nutrient status with organic carbon were found with increase in depth throughout the year. Present study revealed the relationship among depth integrated variations of physico-chemical compo- nents (viz. soil temperature, pH, moisture, orga- nic-C, .nitrogen, and available-P) and microbial populations as well as activity of dehydrogenase and ?-D glucosidase enzymes.
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