Browsing by Author "R.P. Rastogi"

Now showing 1 - 17 of 17

A comparative study on the oscillatory behaviour of isomers of hydroxybenzoic acid with and without methyl ketones
(2009) Masood A. Nath; R.P. Rastogi; M. Peerzada
The oscillatory behaviour of isomers of hydroxybenzoic acid has been studied in 1.0 M H2S04 with and without methyl ketones as mixed substrates. The presence of Br̄ and the critical bromide ion concentration have been found to have a key role in the present study. Moreover, the effect of ketones such as acetone, butanone and pentanone has also been found to affect the oscillatory characteristics such as induction period, time period, frequency and number of oscillations. The oscillations arise in such systems provided the inhibitory reaction and autocatalysis balance each other.
Anomalous behaviour of Belousov-Zhabotinskii oscillators in the presence of Ag+
(1989) R.P. Rastogi; Kiran Mani
Non-Br--controlled Belousov-Zhabotinskii oscillators have been studied. Not only are Br- oscillations suppressed but redox potential oscillations are also subsequently suppressed on addition of sufficient Ag+. Analytical studies show that there is still sufficient BrO3- in the systems at this instant. The redox potential oscillations are revived on addition of BrO3- but not on addition of organic substrate. The phenomenon is general and has been observed in systems having (a) malonic acid+Ce4+, (b) phenol and (c) oxalic acid+acetone/cyclohexone+Ce4+. © 1989.
Belousov-Zhabotinskii reaction systems in the presence of Ag+
(1991) R.P. Rastogi; Kiran Mani; G.P. Misra
Threshold values of [Ag+] for quenching (i) Br- potential oscillation and (ii) redox potential oscillations + Br- oscillations have been determined under aerobic and anaerobic conditions for the (a) malonic acid + Ce4+ + BrO-3 + H2SO4 system, and the (b) oxalic acid + acetone + Ce4+ + BrO-3 + H2SO4 system. Similar experiments on the lower limit of BrO-3 under aerobic/anaerobic conditions are reported. The results show that the mechanism of quenching, so far as the key steps are concerned, is expected to be the same in the two cases. Numerical simulations have been made on the basis of the Field, Körös and Noyes (FKN) mechanisms with the additional step Ag+ + Br- ⇌ AgBr. The analysis shows that the experimental results can be explained quite well if the corresponding forward rate constant, k6, is assumed to lie between 104-105 M-1 s-1, as has been suggested by Ruoff and others. © 1991.
Bifurcation features of the Belousov-Zhabotinskii reaction with mixed organic substrates
(1989) R.P. Rastogi; Sangita Srivastava
Oscillations in the redox potential and Br- concentration, the nature of the phase-plane plot and bifurcation have been reported for a wide range of ketone concentrations in Belousov-Zhabotinskii oscillators containing (1) glucose + acetone; (2) glucose + cyclohexane; (3) fructose + acetone and (4) fructose + cyclohexanone as mixed substrates. Both complex periodic and periodic oscillations are observed. Similarly, limit cycles and folded-limit cycles are obtained. Hopf as well as jug handle bifurcation occurs in specific circumstances. © 1989.
Bifurcation phenomena in Belousov-Zhabotinskii systems
(1987) R.P. Rastogi; G.P. Misra
The BrO3- + Ce4+ + H2SO4 + oxalic acid + cyclohexanone system has been investigated in detail in order to study the nature and character of oscillations. Oscillations in redox potential as well as oscillations in [Br-] confirm the earlier finding that oscillations occur in a fixed range of ketone concentrations. Phase-plane plots at different ranges of cyclohexanone concentrations have been obtained. Near the upper limit of cyclohexanone, limit cycle oscillations are obtained whereas near the lower limit folded limit cycles appear. At the upper limit, cessation of oscillation is accompanied by diminution of amplitude, the time period remaining constant, showing thereby that supercritical Hopf bifurcation occurs at the upper limit. At the lower limit, the nature of the bifurcation points is different since the characteristics of the oscillations (amplitude and time period) during their cessation are different. The difference probably arises on account of different rate equations for bromination in view of widely differing Br2 concentrations at the two levels. The nature of bifurcations in the BrO3- + Ce4+ + oxalic acid + acetone, phenol + BrO3- + H2SO4, and gallic acid + BrO3- + H2SO systems has also been examined for the sake of comparison. © 1987 American Chemical Society.
Bistability and electrokinetic oscillations
(Academic Press Inc., 1999) R.P. Rastogi; G.P. Mishra; P.C. Pandey; Kanchan Bala; K. Kumar
Nonlinear dynamic behavior and electrokinetic oscillations have been investigated for the membrane systems (a) 0.1 N NaCl/KCl parallel with Millipore filter parallel with 0.01 N NaCl/KCl; (b) 0.1 N NaCl/KCl parallel with Whatman Inorganic filter parallel with 0.01 N NaCl/KCl; and (c) 0.1 N NaCl/KCl parallel with silver-coated filter parallel with 0.01 N NaCl/KCl, from the viewpoint of testing the theories for the phenomena and elucidating the mechanism. To achieve these objectives, studies on hydrodynamic permeability, electroosmotic permeability, bistability, and electrokinetic oscillations were undertaken. Relaxation time for buildup and decay of electroosmotic pressures was experimentally determined. Bistability was not observed showing that it is not a prerequisite for oscillations and nonlinear relations between (J(v))(Δρ=0) and ΔΦ involving cubic or higher-order terms are necessary for bistability. The oscillations were studied at different current strengths. The period is found to be independent of current, while amplitude A is found to be linearly related to current I which is the bifurcation parameter. The bifurcation point occurs at ~0.4 mA. Studies have also been made with membranes of different pore size that show that amplitude increases with increase in pore size of the membranes. The validity of the two-variable model of Teorell was examined by comparing the experimental results with computer simulation based on parameters determined experimentally. Theory does not meet expectation and the results suggest that modification of theory is needed. The weakness of the theory has been critically examined.
Critical limits in Belousov-Zhabotinskii reaction system
(1990) R.P. Rastogi; G.P. Misra
It has been reported that in Belousov-Zhabotinskii reaction systems having mixed organic substrate, upper and lower limits of acetone concentration exist between which oscillations occur and beyond which the system is stable. Computer calculations based on the mechanism for bromine-hydrolysis-controlled oscillators as proposed by Field and Boyd show the existence of such limits and the quantitative agreement with experiment is satisfactory. Numerical simulations also predict revival of oscillations by BrO-3 at the upper limits as is observed experimentally. Further, an experimentally observed lower limit of [BrO-3] is also predicted by computer calculations. The conclusions are identical when Field-Boyd (FB) values of Field-Försterling (FF) values of the parameters are used. A seven-variable version of the above model has been also used to simulate conditions for a batch reactor. Here again, the conclusions are similar when FB or FF values are used. © 1990.
Further tests on the bromine hydrolysis controlled model and Cl- perturbation of bromate-driven oscillators
(1992) R.P. Rastogi; G.P. Misra
Experimental results on (i) critical limits of [malonic acid] between which oscillations occur for a Belousov-Zhabotinskii oscillator and (ii) upper limit of [cyclohexanone] for a modified Belousov-Zhabotinskii oscillator with malonic acid + cyclohexanone as mixed organic substrate are reported. Numerical computations show that whereas Oregonator predicts the limits in case (i) the upper limit of [cyclohexanone] observed in case (ii) is not predicted by the Field, Körös, and Noyes (FKN) mechanism or the bromine hydrolysis controlled (BHC) model as such. It is shown that a modified BHC model simulates the upper limit of [cyclohexanone] when the hard core of the FKN mechanism is retained. Studies on the influence of Cl- on the oscillatory behavior in case (i) have been reported. Studies rule out the possibility of quenching at the upper limit of [malonic acid] due to Cl-. Experiments show that, on adding a moderate amount of Cl- during oscillation, the amplitude is shortened. On increasing the amount, the oscillations are quenched for a longer period and even permanently. However, when Cl- is added initially, the onset time is lengthened in agreement with the observation of Jacobs and Epstein (J. Am. Chem. Soc. 1976, 98, 1721). The experimental phase-plane plots confirm these observations and show (1) how the quenching vector moves away from the limit cycle and then falls back on the limit cycle in the case when oscillations are interrupted for a while and (2) how the quenching vector moves away from the limit cycle and falls back on stable focus. Numerical simulation for the oscillatory behavior on addition of Cl- during oscillations has been attempted by including the reaction HBrO2 + Cl- + H+ → HOBr + HOCl in the model. Computer results are in agreement with the experimental behavior when the rate constant is assumed to be 1.0 × 103 M-1 s-1 which is reasonable. Computer calculations for the onset time when Cl- is added initially show that oscillations only stop when Cl- reaches a very high value ∼10-3 M. © 1992 American Chemical Society.
Intrinsic Instability During Combustion of Composite Solid Propellants
(1985) R.P. Rastogi; A.P. Rao; V. Syal
The thermodynamic theory of instability shows that a reacting system with a first order exothermic reaction in a continuously stirred tank reactor (CSTR) can be destabilized under certain conditions. On the other hand thermodynamic analysis shows that the reactor is always stable if an endothermic reaction occurs. Combustion instability in solid propellant rockets using ammonium perchlorate (AP) as an oxidizer, has been examined in the light of current ideas of nonequilibrium thermodynamics. It has been shown that the decomposition of AP, which is autocatalytic, can destabilize the system under certain conditions. © 1985, Walter de Gruyter. All rights reserved.
Life of wetland cyanobacteria under enhancing solar UV-B radiation
(2008) R.P. Sinha; R.P. Rastogi; N.K. Ambasht; D.-P. Häder
The continuing depletion of stratosp.heric ozone layer mainly due to anthropogenically released pollutants such as chlorofluorocarbons (CFCs) has resulted in an increase in solar ultraviolet-B (UV-B; 280-315 nm) radiation reaching to the Earth's surface. UV-B is a small (less than 1% of total energy) but highly active component of solar radiation that can penetrate deep into biologically significant depths in lakes, ponds, rivers and oceans. Photosynthctic prokaryotes such as cyanobacteria are dependent on solar energy and thereby always sense and face the stress of UV-B radiation. UV-B can cause wide ranging effects including mutagenesis, destruction of proteins/enzymes, inhibition of a number of vital metabolic processes and formation of thymine dimers in DNA leading to death of microbes. The degree of damaging effects brought about by UV-B varies in different sp.ecies suggesting the existence of certain protective mechanisms operative in cyanobacteria. A number of sp.ecies counteract the damaging effects of UV-B by synthesizing UV protective compounds such as mycosp.orine-like amino acids (MAAs) and the sheath pigment, scytonemin. These compounds are known to act as natural sunscreens and their synthesis is induced by UV-B radiation. In this article an attempt has been made to highlight some of the notable effects of UV-B radiation on wetland cyanobacteria and the role of photoprotective mechanisms in mitigating the damage.
Nonequilibrium thermodynamics of electrokinetic phenomena
(American Chemical Society, 1993) R.P. Rastogi; R.C. Srivastava; S.N. Singh
[No abstract available]
Nonequilibrium Thermodynamics of Electrokinetic Phenomena
(1993) R.P. Rastogi; R.C. Srivastava; S.N. Singh
[No abstract available]
Nonlinear dynamics of membrane processes: Bistability and oscillations in electrokinetic phenomena
(1995) R.P. Rastogi; G. Srinivas; R.C. Srivastava; P.C. Pandey; A.P. Mishra; A.R. Singh
Bistability and oscillations have been studied for a C1 |membrane|C2 system, where C1 and C2 represent the concentrations of dilute and concentrated solutions of NaCl/KCl. In this context (i) hydrodynamic permeability, (ii) electroosmotic permeability, (iii) streaming current, and (iv) diffusion current (current due to concentration difference on the two sides of the membrane) have been measured to test the assumptions of existing theories. Bistability data do not support the existing theories. The ratio of the slopes does not correspond to C1/C2 as predicted by the theory of Kobatake et al. A semiempirical correlation has been proposed for the interpretation of data. Data on electrokinetic oscillations in (i) a Pyrex membrane-aqueous electrolyte system and (ii) a Millipore filter-aqueous electrolyte system have been reported in order to test certain features of the existing theories. The results show that the time period depends on the geometrical factors describing the system and is independent of the current strength, which is in conformity with the theory of Teorell et al. as well as that of Meares et al. It has been shown that previous theory also leads to an equation of the Van der Pol type. An attempt has been made to examine the correlation between bistability and oscillations. It is found that bistability can occur when electroosmotic permeability is a function of potential difference and conductance is a function of volume flux. On the other hand, oscillations can occur when conductance is a function of volume flux, provided certain dynamic conditions are satisfied. © 1995 by Academic Press, Inc.
Photosynthetic performance of Anabaena variabilis PCC 7937 under simulated solar radiation
(Kluwer Academic Publishers, 2013) S.P. Singh; R.P. Rastogi; R.P. Sinha; D.-P. Häder
In vivo chlorophyll fluorescence analysis reflecting the photosystem II functionality was investigated in the cyanobacterium Anabaena variabilis PCC 7937 under simulated solar radiation in a combination with various cut-off filters (WG 280, WG 295, WG 305, WG 320, WG 335, WG 345, and GG 400) to assess the effects of photosynthetically active radiation (PAR), ultraviolet-A (UV-A), and ultraviolet-B (UV-B) radiations on photosynthesis. The photosynthetic activity (PA) was severely inhibited immediately after 10 min of exposure to high PAR, UV-A, and UV-B radiations compared with low PAR grown control samples. After 1 h of exposure, PA of 17.5 ± 2.9% was detected in the high PAR exposed samples compared with the control, while only a trace or no PA was observed in the presence of ultraviolet radiation (UVR). A recovery of PA was recorded after 2 h of the exposure, which continued for next 4, 8, 12, and 24 h. After 24 h of the exposure, PA of 57.5 ± 1.9%, 36.1 ± 11.7%, 23.5 ± 3.3%, 22.3 ± 5.2%, 20.8 ± 6.7%, 13.2 ± 6.6%, and 21.6 ± 9.5% was observed compared with the control sample in 400, 345, 335, 320, 305, 295, and 280 nm cut-off filters-covered samples, respectively. The relative electron transport rate, measured after 24 h exposure, showed also a disturbance in electron transfer between the two photosystems under the high PAR and UVR treatments relative to the control samples, suggesting the inhibition of photosynthesis. This study suggests that both high PAR and UVR inhibited the photosynthetic performance of A. variabilis PCC 7937 by damaging the photosynthetic apparatus, however, photoprotective mechanisms evolved by the organism allowed an immediate repair of ecologically important machinery, and enabled its survival. © 2013 Springer Science+Business Media Dordrecht.
Sequential oscillations in bromine hydrolysis controlled oscillators in a closed reactor
(1993) R.P. Rastogi; G.P. Misra; Ishwar Das; Archana Sharma
Detailed results on birth, growth including sequential oscillations and decay for ascorbic acid-cyclohexanone-Ce4+-BrO3--H 2SO4 system in a batch reactor are reported. Oscillations are observed within a certain range of temperature and the system is monostable beyond the upper and lower limits of temperature. Results have been interpreted in terms of Field, Körös and Noyes mechanism and bromine hydrolysis controlled model which has been modified for reactions in the closed reactor keeping in view the consecutive reactions associated with ascorbic acid. Numerical simulations indicate the existence of two types of oscillations as experimentally observed when the sequence ascorbic acid → oxalic acid → products is taken into account. There is an indication of time pause which becomes more evident when the sequence ascorbic acid → intermediate (threonic acid) → oxalic acid is taken into consideration. However, quantitative agreement is poor. © 1993 American Chemical Society.
Some novel facets of molecular and supramolecular systems
(1998) R.P. Rastogi; L. Mishra
This article surveys in brief the developments in the building up of supramolecules through non-covalent interactions between molecules and their various applications. The major topics included in the present review are : self-assembly and supramolecules; construction of supramolecules through non-covalent interactions; characterization of supramolecules; molecular recognition and sensors; supramolecular reactivity, catalysis and transport processes; photochemistry of supramolecules, and, drug design and supramolecules.
Ultraviolet radiation-induced generation of reactive oxygen species, DNA damage and induction of UV-absorbing compounds in the cyanobacterium Rivularia sp. HKAR-4
(Elsevier, 2014) R.P. Rastogi; S.P. Singh; A. Incharoensakdi; D.-P. Häder; R.P. Sinha
The effects of ultraviolet radiation (UVR) on certain biochemical processes were studied in the cyanobacterium Rivularia sp. HKAR-4. The generation of reactive oxygen species (ROS) was investigated under 295, 320 and 395nm cut-off filters using the ROS sensing probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA). Contrary to photosynthetically active radiation (PAR) and PAR+UV-A (PA) radiation, ROS signals were more prominent under PAR+UV-A+UV-B (PAB) radiation. The low levels of ROS were also detected in the cells growing under dark as well as normal light conditions. The integrity of genomic DNA, the amplification of 16S rDNA and random amplified polymorphic DNA (RAPD) profile were considerably affected by PAB radiation. The formation of cyclobutane thymine dimers (T<>T) was observed under PAR as well as PA and PAB radiations but the intensity was found to be the highest under UV-B radiation. The formation of T<>T under PAR as well as PA radiation has not previously been reported in cyanobacterial systems. Furthermore, the synthesis of UVR-absorbing/screening compounds such as mycosporine-like amino acids (MAAs) was investigated under PAR and PAB. Dose-dependent induction of MAAs, mycosporine-glycine (MG; λmax310nm) as well as an unknown UV-absorbing compound (λmax 335nm) was observed under both PAR as well as UVR. The concentration of unknown MAA (hereafter, M-335) was higher than MG. Overall, in response to harmful effects of solar UVR, cyanobacteria have developed some photoprotective machinery to overcome its impact to grow in the adverse natural environments. © 2013 South African Association of Botanists.