Swarnendu Sen

Optimization of fermentation conditions for cellulase production by Bacillus subtilis CY5 and Bacillus circulans TP3 isolated from fish gut

Background. Microbial and fungal cellulases are known to hydrolyse cellulose, which is ingested as plant mate rial by herbivorous/omnivorous fishes. Microbial enzymes have enormous advantage of being produced in large quantities by established fermentation techniques. The present investigation aims to optimize the environmental and nutritional parameters for fermentation to enhance cellulase production by two bacterial strains isolated from fish gastrointestinal tracts. Materials and methods. Two bacterial strains, Bacillus subtilis CY5 and Bacillus circulans TP3, isolated from the gastrointestinal tracts of common carp, Cyprinus carpio L., and Mozambique tilapia, Oreochromis mossam bicus (Peters, 1852), respectively were identified as potent cellulase producers. Both strains were cultured in tryp tone soya broth for 24 h at 32 ± 2oC, when average viable count of 9.75 · 10 7 cells · mL –1 culture broth was obtained. This was used as the inoculum for the production medium. The fermentation medium was seeded with 1.0%, 2.0%, 3.0%, 4.0%, and 5.0% inoculum (tryptone soya broth) and incubated in static culture at 40oC to stan dardize the inoculum size for fermentation. The effect of different production parameters, such as fermentation condition, moisture, pH, temperature, inoculum size, and nitrogen sources on cellulase production by the isolat ed bacterial strains were studied. Results. Cellulase yield was highest (26 U in B. subtilis and 20.2 U in B. circulans ) in solid-state fermentation (SSF). Enzyme production in both the isolates increased in an optimum pH range of 7.0 to 7.5. Minimum cellulase production was observed at 45oC, while maximum production was obtained at 40oC. To standardize the fermenta tion period for cellulase production, production rate was measured at 12-h intervals up to 120 h. Enzyme produc tion increased for 96 h of fermentation in both strains, and decreased thereafter. The enzyme production increased with increased inoculum size up to 3.0 percentage points. Asparagine as the nitrogen source was most effective in B. subtilis CY5, while beef extract proved useful in optimizing enzyme production by B. circulans TP3. Conclusion. The results of this study will help to standardize the requirements for optimum production of cellu lase by cellulase-producing fish gut bacteria and might contribute towards better fish feed formulation incorpo rating plant ingredients, especially in the larval stages when the enzyme system is not efficient .

Einstein pseudotensor and total energy of the universe

The total energy of the universe has been calculated assuming that it is the sum of the contributions from the matter part and gravitational part. The calculations involve the use of Einstein pseudotensor. Calculations have been carried out in some specific examples of spacetime geometries. In some cases the total energy is indeed zero confirming previous results but in other cases the total energy is nonzero. So Rosen’s idea that the pseudotensorial calculations will lead to the result that the total energy of the universe is zero, is very much model dependent.

Thermomagnetic convection in a square enclosure using a line dipole

We have simulated thermomagnetic convection in a differentially heated square cavity with an infinitely long third dimension. The cavity is under the influence of an imposed two-dimensional magnetic field that conforms to the Maxwell’s equations. Our objective is to characterize the thermomagnetic convection in terms of the geometric length scales, magnetic fluid properties, temperature differences, and strengths of the imposed magnetic fields. Fluid motion occurs due to both the gradients of the magnetic field and the temperature. Colder fluid that has a larger magnetic susceptibility is attracted toward regions with larger field strength during thermomagnetic convection, which displaces warmer fluid of lower susceptibility. The height-averaged Nusselt number Nuav increases with increasing magnetic dipole strength and temperature but decreases with increasing fluid viscosity. Thermomagnetic heat transfer increases when the length scale decreases if the dipole strength of the source magnet is constant. Th...

Flame synthesis of carbon nanofibres and nanofibre composites containing encapsulated metal particles

We have synthesized carbon nanofibres (CNFs) in an ethylene?air flame on a stainless steel substrate. Ten-minute specimens consisted of both nodules and carbon micro-?and nanofibres of various diameters up to . There are two kinds of primary fibres. The first are of ?nm thickness and show numerous kinks along their length. The second variety can have thicknesses of the order of and can grow to a length of . Nanofibre branching is also evident. The inclusion of periodic metal deposits in the nanofibres reveals a strategy by which it might be possible to encapsulate metal particles in order to form connected CNF networks.

An investigation of nonlinear dynamics of a thermal pulse combustor

Nonlinear dynamics of a thermal pulse combustor was investigated using a coupled fourth order lumped combustor model. The effects of optically thin radiation from the combustor gases to the wall are also investigated. The system response changes from steady combustion to extinction through oscillatory combustion as the wall temperature is lowered. The qualitative results suggest a transition to chaos through a period-doubling route prior to extinction. The presence of chaos is also confirmed by quantitative measures like correlation dimension and Lyapunov exponent. The system dynamics is qualitatively similar in presence and absence of radiation. However, inclusion of radiative heat loss leads to extinction at higher temperatures and also increases the predicted range of wall temperatures for which limit cycle behaviour is obtained. A measure for monitoring the proximity of the system to extinction has been developed using the time series data.

Interaction of surface radiation and variable property natural convection in a differentially heated square cavity – a finite element analysis

A finite element solution on the interaction of surface radiation and variable property laminar natural convection is presented. Finite element formulation of the governing equations, associated with variable property natural convection, and incorporation of the radiative boundary conditions has been extensively discussed. The study also aims to highlight the limiting value of the terminal temperature difference (TTD), below which the natural convection heat transfer becomes the sole heat transfer mode, i.e. the effect of surface radiation can be neglected. The effects of variations of emissivity and TTD are also presented.

Lean Blow-Out Prediction in Gas Turbine Combustors Using Symbolic Time Series Analysis

This paper develops a novel strategy for prediction of lean blowout in gas turbine combustors based on symbolic analysis of time series data from optical sensors, where the range of instantaneous data is partitioned into a finite number of cells and a symbol is assigned to each cell. Depending on the cell to which a data point belongs, a symbolic valueisassignedtothedatapoint.Thus,thesetoftimeseriesdataisconvertedtoasymbolstring.The(estimated)state probability vector is computed based on the number of occurrence of each symbol over a given time span. For the purpose of detecting lean blowout in gas turbine combustors, the state probability vector obtained at a condition sufficientlyawayfromleanblowout(referencestate)isconsideredasthereferencevector.Thedeviationofthecurrent state vector from the reference state vector is used as an anomaly measure for early detection of lean blowout. The results showed that the rate of change of the anomaly measure with equivalence ratio changed significantly as the systemapproachedleanblowout.Thischangeinslopeofthecurvewasobservedapproximatelyatasimilarproximity to lean blowout for different operating conditions and, hence, could be used as an early lean blowout precursor. The actual location of the change of slope depended primarily on the choice of reference state. This technique performed satisfactorily over a wide range of premixing.

Heat Transfer and Entropy Generation in a Porous Square Enclosure in Presence of an Adiabatic Block

The present work investigates the thermal aspects of a differentially heated porous square enclosure in the presence of an adiabatic block of different block sizes utilizing Darcy–Rayleigh number in the range of 1–10,000 with Darcy number

Numerical simulation of early stages of oxide formation in molten aluminium–magnesium alloys in a reverberatory furnace

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