Showing papers by "Indian Institute of Science published in 2007"

PIC: Protein Interactions Calculator

Abstract: Interactions within a protein structure and interactions between proteins in an assembly are essential considerations in understanding molecular basis of stability and functions of proteins and their complexes. There are several weak and strong interactions that render stability to a protein structure or an assembly. Protein Interactions Calculator (PIC) is a server which, given the coordinate set of 3D structure of a protein or an assembly, computes various interactions such as disulphide bonds, interactions between hydrophobic residues, ionic interactions, hydrogen bonds, aromatic– aromatic interactions, aromatic–sulphur interactions and cation–n interactions within a protein or between proteins in a complex. Interactions are calculated on the basis of standard, published criteria. The identified interactions between residues can be visualized using a RasMol and Jmol interface. The advantage with PIC server is the easy availability of inter-residue interaction calculations in a single site. It also determines the accessible surface area and residue-depth, which is the distance of a residue from the surface of the protein. User can also recognize specific kind of interactions, such as apolar–apolar residue interactions or ionic interactions, that are formed between buried or exposed residues or near the surface or deep inside.

Red-, blue-, or no-shift in hydrogen bonds: a unified explanation.

Abstract: We provide a simple explanation for X-H bond contraction and the associated blue shift and decrease of intensity in IR spectrum of the so-called improper hydrogen bonds This explanation organizes hydrogen bonds (HBs) with a seemingly random relationship between the X-H bond length (and IR frequency and its intensity) to its interaction energy The factors which affect the X-H bond in all X-H [midline ellipsis] Y HBs can be divided into two parts: (a) The electron affinity of X causes a net gain of electron density at the X-H bond region in the presence of Y and encourages an X-H bond contraction (b) The well understood attractive interaction between the positive H and electron rich Y forces an X-H bond elongation For electron rich, highly polar X-H bonds (proper HB donors) the latter almost always dominates and results in X-H bond elongation, whereas for less polar, electron poor X-H bonds (pro-improper HB donors) the effect of the former is noticeable if Y is not a very strong HB acceptor Although both the above factors increase with increasing HB acceptor ability of Y, the shortening effect dominates over a range of Ys for suitable pro-improper X-Hs resulting in a surprising trend of decreasing X-H bond length with increasing HB acceptor ability The observed frequency and intensity variations follow naturally The possibility of HBs which do not show any IR frequency change in the X-H stretching mode also directly follows from this explanation

Long-lived giant number fluctuations in a swarming granular nematic.

Abstract: Coherently moving flocks of birds, beasts, or bacteria are examples of living matter with spontaneous orientational order. How do these systems differ from thermal equilibrium systems with such liquid crystalline order? Working with a fluidized monolayer of macroscopic rods in the nematic liquid crystalline phase, we find giant number fluctuations consistent with a standard deviation growing linearly with the mean, in contrast to any situation where the central limit theorem applies. These fluctuations are long-lived, decaying only as a logarithmic function of time. This shows that flocking, coherent motion, and large-scale inhomogeneity can appear in a system in which particles do not communicate except by contact.

Ultrafine Single‐Crystalline Gold Nanowire Arrays by Oriented Attachment

Abstract: The mechanism of templateless growth of anisotropic nanostructures consisting of high-symmetry crystals is an important fundamental problem with technological consequences.The bottom-up approach for building nanostructures relies on the ability to produce shape-controlled building blocks and their subsequent assembly into mesoscale architectures. Onedimensional nanostructures in the form of nanowires and nanorods are especially important building blocks owing to the multitude of interesting properties that they exhibit. The literature is replete with techniques for producing high-quality semiconductor nanowires with controlled diameters and roughness for potential use as biosensors, logic circuits, field-effect transistors, and nonvolatile memory elements.

Mechanical properties of wood–fiber reinforced polypropylene composites: Effect of a novel compatibilizer with isocyanate functional group

Abstract: Natural fibers are increasingly being used as reinforcement in commercial thermoplastics due to their low cost, high specific properties and renewable nature. While the maleic anhydride modified polypropylene (MAPP) is most commonly used as compatibilizer to improve interfacial adhesion between hydrophilic wood–fibers and hydrophobic polypropylene, in this study, a novel compatibilizer (m-TMI-g- PP) with isocyanate functional group was synthesized by grafting m-isopropenyl-\alpha,\alpha-dimethylbenzyl-isocyanate (m-TMI) onto isotactic polypropylene (PP) in a twin screw extruder. The effect of filler concentration on the mechanical properties of wood–fiber filled composites, prepared by using m-TMI-g-PP as the compatibilizer, was investigated. The addition of the compatibilizer resulted in greater reinforcement of composites, as indicated by the improvement in mechanical properties. Tensile strength of composites so prepared increased by almost 45%, whereas 85% increase in flexural properties was observed. However the addition of wood–fibers resulted in a decrease in elongation at break and impact strength of the composites.

New insights from a fixed-point analysis of single cell IEEE 802.11 WLANs

Abstract: We study a fixed-point formalization of the well-known analysis of Bianchi. We provide a significant simplification and generalization of the analysis. In this more general framework, the fixed-point solution and performance measures resulting from it are studied. Uniqueness of the fixed point is established. Simple and general throughput formulas are provided. It is shown that the throughput of any flow will be bounded by the one with the smallest transmission rate. The aggregate throughput is bounded by the reciprocal of the harmonic mean of the transmission rates. In an asymptotic regime with a large number of nodes, explicit formulas for the collision probability, the aggregate attempt rate, and the aggregate throughput are provided. The results from the analysis are compared with ns2 simulations and also with an exact Markov model of the backoff process. It is shown how the saturated network analysis can be used to obtain TCP transfer throughputs in some cases.

Sex differences in ageing in natural populations of vertebrates

Abstract: In many long-lived vertebrates (including humans), adult males have shorter lifespans than adult females, partly as a result of higher annual rates of mortality in males and partly owing to sex differences in the rate of ageing. A probable explanation of the evolution of sex differences in ageing is that, in polygynous species, intense intrasexual competition between males restricts the number of seasons for which individual males are able to breed successfully, weakening selection pressures favouring adult longevity in males relative to females. If this is the case, sex differences in adult longevity and in the onset and rate of senescence should be greater in polygynous species than in monogamous ones and their magnitude should be related to the duration of effective breeding males compared with females. Here, we use data from longitudinal studies of vertebrates to show that reduced longevity in adult males (relative to females) is commonly associated with a more rapid decline in male than female survival with increasing age and is largely confined to polygynous species. The magnitude of sex differences in adult longevity in different species is consistently related to the magnitude of sex differences in the duration of effective breeding, calculated across surviving adults. Our results are consistent with the suggestion that sex differences in senescence in polygynous species are a consequence of weaker selection for longevity in males than females.

Predicting Solar Cycle 24 With a Solar Dynamo Model

Abstract: Whether or not the upcoming cycle 24 of solar activity will be strong is being hotly debated. The solar cycle is produced by a complex dynamo mechanism. We model the last few solar cycles by “feeding‿ observational data of the Sun's polar magnetic field into our solar dynamo model. Our results fit the observed sunspot numbers of cycles 21–23 reasonably well and predict that cycle 24 will be about 35% weaker than cycle 23.

Modeling of Formation of Gold Nanoparticles by Citrate Method

Abstract: Properties of nanoparticles are size dependent, and a model to predict particle size is of importance. Gold nanoparticles are commonly synthesized by reducing tetrachloroauric acid with trisodium citrate, a method pioneered by Turkevich et al (Discuss. Faraday Soc. 1951, 11, 55). Data from several investigators that used this method show that when the ratio of initial concentrations of citrate to gold is varied from 0.4 to similar to 2, the final mean size of the particles formed varies by a factor of 7, while subsequent increases in the ratio hardly have any effect on the size. In this paper, a model is developed to explain this widely varying dependence. The steps that lead to the formation of particles are as follows: reduction of Au3+ in solution, disproportionation of Au+ to gold atoms and their nucleation, growth by disproportionation on particle surface, and coagulation. Oxidation of citrate results in the formation of dicarboxy acetone, which aids nucleation but also decomposes into side products. A detailed kinetic model is developed on the basis of these steps and is combined with population balance to predict particle-size distribution. The model shows that, unlike the usual balance between nucleation and growth that determines the particle size, it is the balance between rate of nucleation and degradation of dicarboxy acetone that determines the particle size in the citrate process. It is this feature that is able to explain the unusual dependence of the mean particle size on the ratio of citrate to gold salt concentration. It is also found that coagulation plays an important role in determining the particle size at high concentrations of citrate.

Decentralized energy planning; modeling and application—a review

Abstract: Energy planning is carried out at a centralized level using computer-based modeling. The centralized energy planning models and approaches have already been reviewed in literature. Decentralized energy planning (DEP) is a concept of recent origin with limited applications. Literature shows that different models are being developed and used worldwide. This paper gives an overview of different decentralized energy models used worldwide, their approaches and their applications along with a few emerging energy models. The central theme of the energy planning at decentralized level would be to prepare an area-based DEP to meet energy needs and development of alternate energy sources at least-cost to the economy and environment. Ecologically sound development of the region is possible when energy needs are integrated with the environmental concerns at the local and global levels. Taking into account these features, this paper explains the need of DEP and shows how different types of energy planning and optimization models, supply demand models, regional models, resource models and neural models have been carried, adopted and applied at decentralized level.

Synthesis of inorganic nanomaterials

Abstract: Synthesis forms a vital aspect of the science of nanomaterials. In this context, chemical methods have proved to be more effective and versatile than physical methods and have therefore, been employed widely to synthesize a variety of nanomaterials, including zero-dimensional nanocrystals, one-dimensional nanowires and nanotubes as well as two-dimensional nanofilms and nanowalls. Chemical synthesis of inorganic nanomaterials has been pursued vigorously in the last few years and in this article we provide a perspective on the present status of the subject. The article includes a discussion of nanocrystals and nanowires of metals, oxides, chalcogenides and pnictides. In addition, inorganic nanotubes and nanowalls have been reviewed. Some aspects of core–shell particles, oriented attachment and the use of liquid–liquid interfaces are also presented.

Wintertime aerosol characteristics over the Indo‐Gangetic Plain (IGP): Impacts of local boundary layer processes and long‐range transport

Abstract: [1] The Indo-Gangetic Plain (IGP) encompasses a vast area, (accounting for ∼21% of the land area of India), which is densely populated (accommodating ∼40% of the Indian population). Highly growing economy and population over this region results in a wide range of anthropogenic activities. A large number of thermal power plants (most of them coal fed) are clustered along this region. Despite its importance, detailed investigation of aerosols over this region is sparse. During an intense field campaign of winter 2004, extensive aerosol and atmospheric boundary layer measurements were made from three locations: Kharagpur (KGP), Allahabad (ALB), and Kanpur (KNP), within the IGP. These data are used (1) to understand the regional features of aerosols and BC over the IGP and their interdependencies, (2) to compare it with features at locations lying at far away from the IGP where the conditions are totally different, (3) to delineate the effects of mesoscale processes associated with changes in the local atmospheric boundary layer (ABL), (4) to investigate the effects of long-range transport or moving weather phenomena in modulating the aerosol properties as well as the ABL characteristics, and (5) to examine the changes as the season changes over to spring and summer. Our investigations have revealed very high concentrations of aerosols along the IGP, the average mass concentrations (MT) of total aerosols being in the range 260 to 300 μg m−3 and BC mass concentrations (MB) in the range 20 to 30 μg m−3 (both ∼5 to 8 times higher than the values observed at off-IGP stations) during December 2004. Despite, BC constituted about 10% to the total aerosol mass concentration, a value quite comparable to those observed elsewhere over India for this season. The dynamics of the local atmospheric boundary layer (ABL) as well as changes in local emissions strongly influence the diurnal variations of MT and MB, both being inversely correlated with the mixed layer height (Zi) and the ventilation coefficient (Vc). The share of BC to total aerosols is highest (∼12%) during early night and lowest (∼4%) in the early morning hours. While an increase in the Vc results in a reduction in the concentration almost simultaneously, an increase in Zimax has its most impact on the concentration after ∼1 day. Accumulation mode aerosols contributed ∼90% to the aerosol concentration at ALB, ∼77 % at KGP and 74% at KNP. The BC mass mixing ratio was ∼10% over all three locations and is comparable to the value reported for Trivandrum, a tropical coastal location in southern India. This indicates presence of submicron aerosols species other than BC (such as sulfate) over KGP and KNP. A cross-correlation analysis showed that the changes in MB at KGP is significantly correlated with those at KNP, located ∼850 km upwind, and ALB after a delay of ∼7 days, while no such delay was seen between ALB and KNP. Back trajectory analyses show an enhancement in MB associated with trajectories arriving from west, the farther from to the west they arrive, the more is the increase. This, along with the ABL characteristics, indicate two possibilities: (1) advection of aerosols from the west Asia and northwest India and (2) movement of a weather phenomena (such as cold air mass) conducive for build up of aerosols from the west to east. As the winter gives way to summer, the change in the wind direction and increased convective mixing lead to a rapid decrease in MB.

Multiple minor mergers: formation of elliptical galaxies and constraints for the growth of spiral disks

Abstract: Multiple, sequential mergers are unavoidable in the hierarchical build-up picture of galaxies, in particular for the minor mergers that are frequent and highly likely to have occured several times for most present-day galaxies. However, the effect of repeated minor mergers on galactic structure and evolution has not been studied systematically so far. We present a numerical study of multiple, subsequent, minor galaxy mergers, with various mass ratios ranging from 4:1 to 50:1. The N-body simulations include gas dynamics and star formation. We study the morphological and kinematical properties of the remnants, and show that several so-called “minor” mergers can lead to the formation of elliptical-like galaxies that have global morphological and kinematical properties similar to that observed in real elliptical galaxies. The properties of these systems are compared with those of elliptical galaxies produced by the standard scenario of one single major merger. We thus show that repeated minor mergers can theoretically form elliptical galaxies without major mergers, and can be more frequent than major mergers, in particular at moderate redshift. This process must then have formed some elliptical galaxies seen today, and could in particular explain the high boxiness of massive ellipticals, and some fundamental relations observed in ellipticals. In addition, because repeated minor mergers, even at high mass ratios, destroy disks into spheroids, these results indicate that spiral galaxies cannot have grown only by a succession of minor mergers.

An objective definition of the Indian summer monsoon season and a new perspective on the ENSO–monsoon relationship

Abstract: The concept of an interannually varying Indian summer monsoon season is introduced here, considering that the duration of the primary driving of the Indian monsoon – the large-scale meridional gradient of the deep tropospheric heat source – may vary from one year to another. Onset (withdrawal) is defined as the day when the tropospheric heat source shifts from south to north (north to south). This physical principle leads to a new thermodynamic index of the seasonal mean monsoon. While the traditional measure of seasonal rainfall, averaged from 1 June to 30 September, indicates a breakdown of the ENSO–monsoon relationship in recent decades, it is argued that this breakdown is partly due to the inappropriate definition of a fixed monsoon season. With a new physically based definition of the seasonal mean, the ENSO–monsoon relationship has remained steady over the decades. El Nino (La Nina) events contract (expand) the season, and thus decrease (increase) the seasonal mean monsoon by setting up persistent negative (positive) tropospheric temperature (TT) anomalies over the southern Eurasian region. Thus, we propose a new pathway, whereby the Indian summer monsoon could be influenced by remote climatic phenomena via modification of TT over Eurasia. Diagnostics of the onset and withdrawal processes suggest that onset delay is due to the enhanced adiabatic zubsidence that inhibits vertical mixing of sensible heating from warm landmass during the pre-monsoon months. On the other hand, the major factor that determines whether the withdrawal is early or late is the horizontal advective cooling. Most of the late (early) onsets and early (late) withdrawals are associated with El Nino (La Nina). This link between the ENSO and the monsoon is realized through vertical and horizontal advections associated with the stationary waves in the upper troposphere set up by the tropical ENSO heating.

Multipurpose Reservoir Operation Using Particle Swarm Optimization

Abstract: This paper presents an efficient and reliable swarm intelligence-based approach, namely elitist-mutated particle swarm opti- mization EMPSO technique, to derive reservoir operation policies for multipurpose reservoir systems. Particle swarm optimizers are inherently distributed algorithms, in which the solution for a problem emerges from the interactions between many simple individuals called particles. In this study the standard particle swarm optimization PSO algorithm is further improved by incorporating a new strategic mechanism called elitist-mutation to improve its performance. The proposed approach is first tested on a hypothetical multireservoir system, used by earlier researchers. EMPSO showed promising results, when compared with other techniques. To show practical utility, EMPSO is then applied to a realistic case study, the Bhadra reservoir system in India, which serves multiple purposes, namely irrigation and hydropower generation. To handle multiple objectives of the problem, a weighted approach is adopted. The results obtained demonstrate that EMPSO is consistently performing better than the standard PSO and genetic algorithm techniques. It is seen that EMPSO is yielding better quality solutions with less number of function evaluations.

A study of communication pathways in methionyl- tRNA synthetase by molecular dynamics simulations and structure network analysis

Abstract: The enzymes of the family of tRNA synthetases perform their functions with high precision by synchronously recognizing the anticodon region and the aminoacylation region, which are separated by \approx 70 \AA in space. This precision in function is brought about by establishing good communication paths between the two regions. We have modeled the structure of the complex consisting of Escherichia coli methionyl-tRNA synthetase (MetRS), tRNA, and the activated methionine. Molecular dynamics simulations have been performed on the modeled structure to obtain the equilibrated structure of the complex and the cross-correlations between the residues in MetRS have been evaluated. Furthermore, the network analysis on these simulated structures has been carried out to elucidate the paths of communication between the activation site and the anticodon recognition site. This study has provided the detailed paths of communication, which are consistent with experimental results. Similar studies also have been carried out on the complexes (MetRS + activated methonine) and (MetRS + tRNA) along with ligand-free native enzyme. A comparison of the paths derived from the four simulations clearly has shown that the communication path is strongly correlated and unique to the enzyme complex, which is bound to both the tRNA and the activated methionine. The details of the method of our investigation and the biological implications of the results are presented in this article. The method developed here also could be used to investigate any protein system where the function takes place through long-distance communication.

Spatial mapping of renewable energy potential

Abstract: An energy resource that is renewed by nature and whose supply is not affected by the rate of consumption is often termed as renewable energy. The need to search for renewable, alternate and non-polluting sources of energy assumes top priority for self-reliance in the regional energy supply. This demands an estimat+ion of available energy resources spatially to evolve better management strategies for ensuring sustainability of resources. The spatial mapping of availability and demand of energy resources would help in the integrated regional energy planning through an appropriate energy supply–demand matching. This paper discusses the application of Geographical Information System (GIS) to map the renewable energy potential talukwise in Karnataka State, India. Taluk is an administrative division in the federal set-up in India to implement developmental programmes like dissemination of biogas, improved stoves, etc. Hence, this paper focuses talukwise mapping of renewable energy (solar, wind, bioenergy and small hydroenergy) potential for Karnataka using GIS. GIS helps in spatial and temporal analyses of the resources and demand and also aids as Decision Support System while implementing location-specific renewable energy technologies. Regions suitable for tapping solar energy are mapped based on global solar radiation data, which provides a picture of the potential. Coastal taluks in Uttara Kannada have higher global solar radiation during summer $(6.31 kWh/m^2)$, monsoon $(4.16 kWh/m^2)$ and winter $(5.48 kWh/m^2)$. Mapping of regions suitable for tapping wind energy has been done based on wind velocity data, and it shows that Chikkodi taluk, Belgaum district, has higher potential during summer (6.06 m/s), monsoon (8.27 m/s) and winter (5.19 m/s). Mysore district has the maximum number of small hydropower plants with a capacity of 36 MW. Talukwise computation of bioenergy availability from agricultural residue, forest, horticulture, plantation and livestock indicates that Channagiri taluk in Shimoga district yields maximum bioenergy. The bioenergy status analysis shows that Siddapur taluk in Uttara Kannada district has the highest bioenergy status of 2.004 (ratio of bioresource availability and demand).

Photocatalytic Degradation of Rhodamine Dyes with Nano-TiO2

Abstract: The photocatalytic degradation of various Rhodamine dyes with different functional groups, namely, Rhodamine B (C28H31ClN2O3), Rhodamine 6G (C28H31ClN2O3), Rhodamine Blue (C28H32N2O3), and Rhodamine 6G perchlorate (C28H31ClN2O7) was investigated under UV irradiation. The kinetics of degradation was determined in the presence of two catalysts: commercial Degussa P-25 and TiO2 synthesized by the combustion solution method. The effect of organic solvents (ethanol and acetonitrile) and metal ions (Cu2+, Fe3+, Zn2+, and Al3+) on the photodegradation of Rhodamine B was investigated. The presence of solvents and metal ions significantly reduced the degradation rate. A detailed Langmuir−Hinshelwood kinetic model was developed to explain the effect of Cu2+ on the rate of photodegradation. It was shown that the degradation rate reduces primarily because of a decrease in electron concentration.

Synthesis, Characterization, and Li-Electrochemical Performance of Highly Porous Co3O4 Powders

Abstract: Oxidative precipitation in an aqueous medium of highly self-compacted crystallized Co 3 O 4 dense nanoparticles (4-5 nm) leads to the formation of porous micrometric agglomerates exhibiting a well-defined porosity distribution. Postannealing of these powders induces drastic reorganizations first because of the fast removal of trapped water and then because of the particles sintering, resulting in larger inter-particle voids. Electrochemical behavior of this nanometric material precipitated at moderate temperature is found to be extremely dependent on the way the mixing with the SP conducting carbon is performed; the better performances being obtained by a soft mixing in an organic solvent. This textural effect provides a stable capacity over the first cycles (800 mA·h/g) and reveals a first cycle capacity loss of the same extent as for bulk Co 3 O 4 , implying that the nanotexturation undergone by bulk oxide particles during their first formatting cycle is not responsible for the corresponding initial loss. Through chemical analysis of the electrolyte we found that the long-term capacity fading of our materials can be mainly attributed to the dissolution of the active material within the organic electrolyte.

Solar activity forecast with a dynamo model

Abstract: Although systematic measurements of the Sun’s polar magnetic field exist only from mid-1970s, other proxies can be used to infer the polar field at earlier times. The observational data indicate a strong correlation between the polar field at a sunspot minimum and the strength of the next cycle, although the strength of the cycle is not correlated well with the polar field produced at its end. This suggests that the Babcock–Leighton mechanism of poloidal field generation from decaying sunspots involves randomness, whereas the other aspects of the dynamo process must be reasonably ordered and deterministic. Only if the magnetic diffusivity within the convection zone is assumed to be high (of order 10 12 cm 2 s 1 ), we can explain the correlation between the polar field at a minimum and the next cycle. We give several independent arguments that the diffusivity must be of this order. In a dynamo model with diffusivity like this, the poloidal field generated at the mid-latitudes is advected toward the poles by the meridional circulation and simultaneously diffuses towards the tachocline, where the toroidal field for the next cycle is produced. To model actual solar cycles with a dynamo model having such high diffusivity, we have to feed the observational data of the poloidal field at the minimum into the theoretical model. We develop a method of doing this in a systematic way. Our model predicts that cycle 24 will be a very weak cycle. Hemispheric asymmetry of solar activity is also calculated with our model and compared with observational data.

A singular Moser-Trudinger embedding and its applications

Abstract: Let Ω be a bounded domain in \({\mathbb{R}}^{n}\) , we prove the singular Moser-Trudinger embedding: \(\mathop {\sup\limits_{\parallel u\parallel \leqslant 1\Omega } \int {\frac{{e^{\alpha |u|^{\frac{n} {{n - 1}}} } }}{{|x|^\beta }}} } 0,\beta \in [0,n),u \in W_0^{1,n} (\Omega )\) and \(\parallel u\parallel = \left({\int\limits_\Omega {| abla u|^n } } \right)^\frac{1}{n}\) . We will also study the corresponding critical exponent problem.

Rare earth chromites: a new family of multiferroics

Abstract: Heavy rare earth chromites of the formula LnCrO3 with Ln = Ho, Er, Yb, Lu and Y are shown to be multiferroic, exhibiting canted antiferromagnetism at low temperatures (TN = 113–140 K) and a ferroelectric transition in the 472–516 K range.

Synthesis of Biodiesel from Castor Oil and Linseed Oil in Supercritical Fluids

Abstract: Biodiesel synthesis (transesterification of triglycerides of higher fatty acid to methyl and ethyl esters) from castor oil and linseed oil using methanol and ethanol was investigated at subcritical and supercritical conditions of methanol and ethanol from 200°C to 350°C at 200 bar. The effect of molar ratio of alcohol to oil, temperature, and time was investigated in supercritical methanol and ethanol. The kinetics of the reaction was first order,and the activation energies were determined from the temperature dependence of the rate coefficients. Biodiesel was also synthesized enzymatically with Novozym 435 in supercritical carbon dioxide {(ScCO_2)}. The effect of various parameters such as enzyme loading, alcohol to oil molar ratio, temperature, and time was investigated in these systems. A simplified model, based on the Ping Pong Bi Bi with competitive inhibition mechanism,was proposed to describe the enzymatic transesterification kinetics for castor oil with methanol and ethanol.

Modified SVPWM Algorithm for Three Level VSI With Synchronized and Symmetrical Waveforms

Abstract: The objective of the present work is to improve the output waveform of three level inverters used in high-power applications, where the switching frequency is very low. This is achieved by maintaining the synchronization, half-wave symmetry, quarter-wave symmetry, and three-phase symmetry in the pulsewidth modulation (PWM) waveforms. The principles of achieving synchronization and symmetries in terms of space vectors for three level inverters are presented. A novel synchronized space vector pulsewidth modulation (SVPWM) algorithms is proposed and verified experimentally. The experimental waveforms of the inverter output voltage and motor no load current for different operating conditions of the drive are presented. The performance measure in terms of the weighted total harmonic distortion (THD) of the line voltage is computed for the linear modulation region of the drive for the proposed algorithm and compared with that of synchronized SVPWM and synchronized sine-triangle pulsewidth modulation (SPWM) technique. The comparative results show that consideration of synchronization and symmetry results in improved THD. Another significant feature of the proposed algorithm is that the symmetry and synchronization leads to self-balancing of the direct current (dc) bus capacitor voltages over every one third cycle of the fundamental