Showing papers by "Indian Institute of Technology Kharagpur published in 2005"

Biodiesel production from mahua (Madhuca indica) oil having high free fatty acids

Abstract: A technique to produce biodiesel from mahua oil ( Madhuca indica ) having high free fatty acids (19% FFA) has been developed. The high FFA level of mahua oil was reduced to less than 1% by a two-step pretreatment process. Each step was carried out with 0.30–0.35 v/v methanol-to-oil ratio in the presence of 1% v/v H 2 SO 4 as an acid catalyst in 1-hour reaction at 60°C. After the reaction, the mixture was allowed to settle for an hour and methanol–water mixture that separated at the top was removed. The second step product at the bottom was transesterified using 0.25 v/v methanol and 0.7% w/v KOH as alkaline catalyst to produce biodiesel. The fuel properties of mahua biodiesel were found to be comparable to those of diesel and conforming to both the American and European standards.

Drought forecasting using stochastic models

Abstract: Drought is a global phenomenon that occurs virtually in all landscapes causing significant damage both in natural environment and in human lives. Due to the random nature of contributing factors, occurrence and severity of droughts can be treated as stochastic in nature. Early indication of possible drought can help to set out drought mitigation strategies and measures in advance. Therefore drought forecasting plays an important role in the planning and management of water resource systems. In this study, linear stochastic models known as ARIMA and multiplicative Seasonal Autoregressive Integrated Moving Average (SARIMA) models were used to forecast droughts based on the procedure of model development. The models were applied to forecast droughts using standardized precipitation index (SPI) series in the Kansabati river basin in India, which lies in the Purulia district of West Bengal state in eastern India. The predicted results using the best models were compared with the observed data. The predicted results show reasonably good agreement with the actual data, 1–2 months ahead. The predicted value decreases with increase in lead-time. So the models can be used to forecast droughts up to 2 months of lead-time with reasonably accuracy.

Solar influence on the Indian summer monsoon during the Holocene

Abstract: [1] The large (8%) changes in the past seasonal insolation have a well-documented influence on the Indian summer monsoon. However, the effect of the small (<1%) decade to century scale solar variability is less certain. Evidence is emerging that Earth's climate is sensitive to small changes in solar output on centennial time scale during the Holocene. Comparison of a recently published proxy record for sunspot activity with our newly-revised higher-resolution record of the Indian summer monsoon winds reveals multiple intervals of weak summer monsoon during the Holocene at multidecadal to centennial scales. Weak summer monsoon winds correlate with reduced solar output. Our results suggest that small changes in solar irradiance can bring pronounced changes in the tropical monsoon. The multidecade to century scale variations in the monsoon winds were much larger in the early Holocene coincident with increased sunspot numbers.

Power system frequency estimation using least mean square technique

Abstract: Frequency is an important parameter in power system monitoring, control, and protection. A least mean square (LMS) algorithm in complex form is presented in this paper to estimate power system frequency where the formulated structure is very simple. The three-phase voltages are converted to a complex form for processing by the proposed algorithm. To enhance the convergence characteristic of the complex form of the LMS algorithm, a variable adaptation step-size is incorporated. The performance of the new algorithm is studied through simulations at different situations of the power system.

Texture image retrieval using new rotated complex wavelet filters

Abstract: A new set of two-dimensional (2-D) rotated complex wavelet filters (RCWFs) are designed with complex wavelet filter coefficients, which gives texture information strongly oriented in six different directions (45/spl deg/ apart from complex wavelet transform). The 2-D RCWFs are nonseparable and oriented, which improves characterization of oriented textures. Most texture image retrieval systems are still incapable of providing retrieval result with high retrieval accuracy and less computational complexity. To address this problem, we propose a novel approach for texture image retrieval by using a set of dual-tree rotated complex wavelet filter (DT-RCWF) and dual-tree-complex wavelet transform (DT-CWT) jointly, which obtains texture features in 12 different directions. The information provided by DT-RCWF complements the information generated by DT-CWT. Features are obtained by computing the energy and standard deviation on each subband of the decomposed image. To check the retrieval performance, texture database D1 of 1856 textures from Brodatz album and database D2 of 640 texture images from VisTex image database is created. Experimental results indicates that the proposed method improves retrieval rate from 69.61% to 77.75% on database D1, and from 64.83% to 82.81% on database D2, in comparing with traditional discrete wavelet transform based approach. The proposed method also retains comparable levels of computational complexity.

Effect of viscous dissipation on the mixed convection heat transfer from an exponentially stretching surface

Abstract: The mixed convection flow and heat transfer from an exponentially stretching vertical surface in a quiescent fluid is analyzed using similarity solution technique. Wall temperature and stretching velocity are assumed to have specific exponential function forms. The influence of buoyancy along with viscous dissipation on the convective transport in the boundary layer region is analyzed in both aiding and opposing flow situations. The flow is governed by the mixed convection parameter Gr/Re2. The velocity and temperature inside the boundary layer are observed to be influenced by the parameters like Prandtl number Pr, Gebhart number Gb. Significant changes are observed in non-dimensional skin friction and heat transfer coefficients due to viscous dissipation in the medium. The flow and temperature distributions inside the boundary layer are analyzed and the results for non-dimensional skin friction and heat transfer coefficients are discussed through computer generated plots.

Analysis and modeling of fixed bed column operations on As(V) removal by adsorption onto iron oxide-coated cement (IOCC).

Abstract: Fixed-bed column studies were undertaken to evaluate the performance of iron oxide-coated cement (IOCC) in removing As(V), from aqueous environment, under varying operating conditions. Investigations revealed IOCC to be a very efficient media for the removal of As(V) from water. The Bohart and Adams sorption model was employed to determine characteristic parameters such as depth of exchange zone, time required for exchange zone to move its own height, adsorption rate, and adsorption capacity, useful for process design. The IOCC media effectively removed As(V) from a 2 mg/L solution with a maximum adsorption capacity of 505.3 mg/L. Predicted data points obtained using a Freundlich isotherm model were compared against experimental data points determined in the dynamic process. The effects of important design parameters such as flow rate and influent concentration on the As(V) breakthrough curves were also investigated. The bed depth service time (BDST) model was extended to the prediction of service times of columns operated at different flow rates and influent concentrations and these predicted values were compared with the experimental values. The columns were regenerated by eluting the bound As(V) with 10% NaOH after the adsorption studies.

Low-temperature synthetic route for boron carbide

Abstract: Boron carbide is one of the hardest materials with diamond-like mechanical properties, and is already used for a variety of applications including armor plating, blasting nozzles, and mechanical seal faces, as well as for grinding and cutting tools. It is produced on an industrial scale by classical carbothermal reduction of boric oxides at high temperatures, but the formation of pure boron carbide in processed forms, such as films and fibers, is difficult. As an alternative to high-temperature powder techniques, there is recently great interest in the development of polymer precursors to produce ceramic materials. The aim of the present work is to develop a cost effective and low-temperature manufacturing process to synthesize boron carbide from cheap and easily available raw materials. The initial objective of our research is the design and synthesis of a new type of boron–carbon polymer, which would serve as precursor for boron carbide. The polymeric precursor is synthesized by the reaction of boric acid and polyvinyl alcohol that after pyrolysis at 400 °C and 800 °C gives boron carbide. The polymeric precursor and its pyrolyzed products are characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). X-ray diffraction shows that boron carbide (B 4 C) obtained from this method has an orthorhombic crystal structure. It is a unique low-temperature (∼400 °C) synthetic route for boron carbide.

Dynamics of Solvation and Rotational Relaxation of Coumarin 153 in Ionic Liquid Confined Nanometer-Sized Microemulsions

Abstract: The effects of confinement of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate on solvation dynamics and rotational relaxation of Coumarin 153 (C-153) in Triton X-100/cyclohexane microemulsions have been explored using steady-state and picosecond time-resolved emission spectroscopy. The steady-state and rotational relaxation data indicate that C-153 molecules are incorporated in the core of the microemulsions. The average rotational relaxation time increases with increase in w ([bmim][BF4]/[TX-100]) values. The solvent relaxation in the core of the microemulsion occurs on two different time scales and is almost insensitive to the increase in w values. The solvent relaxation is retarded in the pool of the microemulsions compared to the neat solvent. Though, the retardation is very small compared to several-fold retardation of the solvation time of the conventional solvent inside the pool of the microemulsions.

On the parameters to assess the glass forming ability of liquids

Abstract: A new parameter has been proposed to assess the glass forming ability of liquids and its effectiveness is compared with the existing parameters. The new parameter ( α = T x / T l ), which incorporates both the factors of stability of the liquid (a low T l ) and the thermal stability of glass (a high T x ), has good correlation with the critical cooling rate for glass formation in a wide variety of glass forming alloys. This parameter can even be used for those glass forming alloys, which do not show a clear glass transition temperature. It has also been shown that the heating rate used during differential scanning calorimetry has negligible effect on the different glass forming parameters.

Secondary Structure Sensitivity of Hydrogen Bond Lifetime Dynamics in the Protein Hydration Layer

Abstract: The heterogeneous nature of a protein surface plays an essential role in its biological activity and molecular recognition, and this role is mediated at least partly through the surrounding water molecules. We have performed atomistic molecular dynamics simulations of an aqueous solution of HP-36 to investigate the correlation between the dynamics of the hydration layer water molecules and the lifetimes of protein - water hydrogen bonds. The nonexponential hydrogen bond lifetime correlation functions have been analyzed by using the formalism of Luzar and Chandler, which allowed identification of the quasi-bound states in the surface and quantification of the dynamic equilibrium between quasi-bound and free water molecules in terms of time-dependent rate of interconversion. It is noticed that, irrespective of the structural heterogeneity of different segments of the protein, namely the three a-helices, the positively charged amino acid residues form longer-lived hydrogen bonds with water. The overall relaxation behavior of protein-water hydrogen bonds is found to differ significantly among the three helices of the protein. Study of water number density fluctuation reveals that the hydration layer of helix-3 is much less rigid, which can be correlated with faster structural relaxation of the hydrogen bonds between its residues and water. This also agrees excellently with faster translational and rotational motions of water near helix-3, and hence the lower rigidity of its hydration layer. The lower rigidity of the helix-3 hydration layer also correlates well with the biological activity of the protein, as several of the active-site residues of HP-36 are located in helix-3.

Spatial and temporal drought analysis in the Kansabati river basin, India

Abstract: The identification, monitoring and characterization of droughts are of great importance in water resources planning and management. To investigate the spatial and temporal relationships of drought occurrence, the Standardized Precipitation Index (SPI) (calculated from the probability distribution of precipitation using a two‐parameter gamma function) was used. The SPIs were applied at the local scale using monthly rainfall data for the period of 1965–2001 from five raingauge stations in the basin. The basin is divided into 25 grid‐cells of 13 × 13 km with each grid correspondence to approximately 4% of total area. The inverse distance weighting (IDW) approach is used for the spatial interpolation of rainfall at each grid point. Drought severity is then assessed from the estimated gridded SPI values at multiple time scales. The spatial and temporal characteristics of SPI are used to develop drought severity – area – frequency curves that can assess the severity of the localized drought within the ...

On using visibility correlations to probe the Hi distribution from the dark ages to the present epoch – I. Formalism and the expected signal

Abstract: Redshifted 21-cm radiation originating from the cosmological distribution of neutral hydrogen (H i) appears as background radiation in low-frequency radio observations. The angular and frequency domain fluctuations in this radiation carry information concerning cosmological structure formation. We propose that correlations between visibilities measured at different baselines and frequencies in radio-interferometric observations be used to quantify the statistical properties of these fluctuations. This has an inherent advantage over other statistical estimators in that it deals directly with the visibilities which are the primary quantities measured in radio-interferometric observations. Also, the visibility correlation has a very simple relation with the power spectrum. We present estimates of the expected signal for nearly the entire post-recombination era, from the dark ages to the present epoch. The epoch of reionization, where H I has a patchy distribution, has a distinct signature where the signal is determined by the size of the discrete ionized regions. The signal at other epochs, where H I follows the dark matter, is determined largely by the power spectrum of dark matter fluctuations. The signal is strongest for baselines where the antenna separations are within a few hundred times the wavelength of observation, and an optimal strategy would preferentially sample these baselines. In the frequency domain, for most baselines the visibilities at two different frequencies are uncorrelated beyond Δν ∼ 1 MHz, a signature which, in principle, would allow the HI signal to be easily distinguished from the continuum sources of contamination.