Analysis of a Chemostat Model with Variable Yield Coefficient

We investigate a chemostat model in which the growth rate is given by a Monod expression with a variable yield coefficient. This model has been investigated by previous researchers using numerical integration. We combine analytical results with path-following methods. The conditions for washout to occur are found. When washout does not occur we establish the conditions under which the reactor performance is maximised at either a finite or infinite residence time. We also determine the parameter region in which oscillations may be generated in the reactor, which was the primary feature of interest to earlier workers on this problem.     

Neutral-current constraints on gauge models of weak and electromagnetic interactions

Sehgal and Hung and Sakurai have recently argued that neutrino-hadron neutral-current couplings must lie in one of two allowed regions in coupling-parameter space. We study this conjecture using realistic BNL ν_μ and ν̄_μ spectra in the elastic ν_μp (ν̄_μp) calculations and also study constraints imposed by theq²-distributions. On comparing to gauge models, we find that the Weinberg-Salam and SU(2)_L×SU(2)_R×U(1) models fall within one allowed region, while a vectorlike SU(3)×U(1) model and a hybrid SU(2)×U(1) model with a (u, b)_R doublet fall in the other region.     

Green synthesis of thiazol-2-ylthiazolidin-4-ones as potential antifungals

Russian Journal of Applied Chemistry - MORE (Microwave oriented reaction enhancement) green methodology was utilized to synthesize benzothiazol/thiazol-2-ylthiazolidin-4-ones and relatively assayed...     

Bifurcation Phenomena for an Oxidation Reaction in a Continuously Stirred Tank Reactor I. Adiabatic Operation

We investigate the steady-state multiplicity exhibited by the reaction of a fuel/air mixture in a continuously stirred tank reactor. The chemical mechanism used is a modification of a scheme due to Sal'nikov. We consider four cases; corresponding to the choice of fuel fraction, inflow temperature, inflow pressure, or precursor decay rate as the primary bifurcation parameter. From the perspective of fire-retardancy, the case when the fuel fraction is varied is the most important. In this case the steady-state diagrams provide a basis for a systematic investigation into the effectiveness of gas-phase active fire retardants.     

Properties of combustion waves in a model with competitive exothermic reactions

We study the properties of travelling combustion waves in a diffusional thermal model with a two-step competitive exothermic-exothermic reaction mechanism. This investigation considers the system in one spatial dimension under adiabatic conditions. Based on the notion of the crossover temperature, the model is examined analytically using the activation energy asymptotic method to predict travelling combustion wave behaviour in the limit of large activation energies. The model is then studied numerically using a shooting-relaxation method over a wide range of parameter values, such as those describing the ratios of enthalpies, pre-exponential factors and activation energies. It is demonstrated that the flame speed as a function of these parameters is a single-valued monotonic function and there are two flame regimes identified—each region representing parameter values when one reaction dominates the other.     

Pulsating instabilities in the Zeldovich–Liñán model

In this paper we numerically study the properties and stability of the travelling combustion waves in Zeldovich–Liñán model in the adiabatic limit in one spatial dimension. The structure and the properties of the combustion waves are found to depend on the recombination parameter, showing the relation between the characteristic times of the branching and recombination reactions. For small (large) values of this parameter the slow (fast) recombination regime of flame propagation is observed. The dependence of flame speed on the parameters of the model are studied in detail. It is found that the flame speed is unique, the combustion wave does not exhibit extinction as the activation energy is increased. The flame speed is a monotonically decreasing function of the activation energy. The results are compared to the prediction of the activation energy asymptotic analysis. It is found that the correspondence is good for the fast recombination regime and large activation energies. Stability of combustion waves is studied by using the Evans function method and direct integration of the governing partial differential equations. It is demonstrated that the combustion waves lose stability due to supercritical Hopf bifurcation. The neutral stability boundary is found in the space of parameters. The pulsating solutions emerging as a result of Hopf bifurcation are investigated. The amplitude of pulsations grow in a root type manner as the activation energy is increased beyond the neutral stability boundary.     

Application of HR-MAS NMR spectroscopy for studying chemotype variations of Withania somnifera (L.) Dunal

Withania somnifera (L.) Dunal (Solanaceae), commonly known as Ashwagandha, is one of the most valued Indian medicinal plants with a number of pharmaceutical and nutraceutical applications. Metabolic profiling has been performed by HR-MAS NMR spectroscopy on fresh leaf and root tissue specimens from four chemotypes of W. somnifera. The HR-MAS NMR spectroscopy of lyophilized defatted leaf tissue specimens clearly distinguishes resonances of medicinally important secondary metabolites (withaferin A and withanone) and its distinctive quantitative variability among the chemotypes. A total of 41 metabolites were identified from both the leaf and root tissues of the chemotypes. The presence of methanol in leaf and root tissues of W. somnifera was detected by HR-MAS NMR spectroscopy. Multivariate principal component analysis (PCA) on HR-MAS (1) H NMR spectra of leaves revealed clear variations in primary metabolites among the chemotypes. The results of the present study demonstrated an efficient method, which can be utilized for metabolite profiling of primary and secondary metabolites in medicinally important plants.     

Chelation controlled reductive amination of cyclic ketones to trans-4-methoxycyclohexylamines: 9-BBN reduction mediated with FeCl3

A novel trans-diastereoselective reductive amination of 4-substituted cyclohexanones is described using 9-BBN as reducing agent in the presence of FeCl₃. The method permits efficient synthesis of structurally diverse 4-trans-alkoxycyclohexylamines.