Gravity effects on partially premixed flames: an experimental-numerical investigation

While premixed and nonpremixed microgravity flames have been extensively investigated, the corresponding literature regarding partially premixed flames (PPFs) is sparse. We report the first experimental investigation of burner-stabilized microgravity PPFs. Partially premixed flames with multiple reaction zones are established in microgravity on a Wolfhard–Parker slot burner in the 2.2 s drop tower at the NASA Glenn Research Center. Microgravity measurements include flame imaging, and thermocouple and radiometer data. Detailed simulations are also used to provide further insight into the steady and transient response of these flames to variations in g. The flame topology and interactions between the various reaction zones are strongly influenced by gravity. The flames widen substantially in microgravity. During the transition from normal to microgravity, the flame structure experiences a fast change and another relatively slower transient change. The fast response is due to the altered advection as the value of g is reduced, while the slow response is due to the changes in the diffusive fluxes. The radiative heat loss from the flames increases in microgravity. A scaling analysis based on a radiation Damköhler number is able to characterize the radiation heat loss.     

Separation and complete analyses of the overlapped and unresolved 1H NMR spectra of enantiomers by spin selected correlation experiments

NMR spectroscopic discrimination of optical enantiomers is most often carried out using (2)H and (13)C spectra of chiral molecules aligned in a chiral liquid crystalline solvent. The use of proton NMR for such a purpose is severely hindered due to the spectral complexity and the significant loss of resolution arising from numerous short- and long-distance couplings and the indistinguishable overlap of spectra from both R and S enantiomers. The determination of all the spectral parameters by the analyses of such intricate NMR spectra poses challenges, such as, unraveling of the resonances for each enantiomer, spectral resolution, and simplification of the multiplet pattern. The present study exploits the spin state selection achieved by the two-dimensional (1)H NMR correlation of selectively excited isolated coupled spins (Soft-COSY) of the molecules to overcome these problems. The experiment provides the relative signs and magnitudes of all of the proton-proton couplings, which are otherwise not possible to determine from the broad and featureless one-dimensional (1)H spectra. The utilization of the method for quantification of enantiomeric excess has been demonstrated. The studies on different chiral molecules, each having a chiral center, whose spectral complexity increases with the increasing number of interacting spins, and the advantages and limitations of the method over SERF and DQ-SERF experiments have been reported in this work.     

Total synthesis of (-)-bitungolide F and determination of its absolute stereochemistry

A highly convergent total synthesis of bitungolide F leading to the assignment of its absolute stereochemistry is described. The key steps include a Horner-Wadsworth-Emmons olefination to construct the C7-C8 bond, a Wittig reaction to introduce the conjugate E,E-olefinic moiety in the molecule, and finally a ring-closing metathesis reaction to construct the six-membered alpha,beta-unsaturated delta-lactone of the molecule. Modified Evans's syn-aldol reaction, using Crimmins's protocol, was used to install the stereochemistries at the C4 and C5 centers. The stereochemistry at C9 was introduced by means of hydroxy-directed reduction of the C9 keto using Evans's protocol.     

Synthesis,anti‐bacterial,anti‐asthmatic and anti‐diabetic activities of novel N‐substituted‐2‐(benzo[d]isoxazol‐3‐ylmethyl)‐1H‐benzimidazoles

Synthesis of a series of novel class of N‐substituted‐2‐(benzo[d]isoxazol‐3‐ylmethyl)‐1H‐benzimidazoles ( 4 ) by the condensation of o‐phenylenediamine ( 1 ) with benzo[d]isoxazol‐3‐yl‐acetic acid ( 2 ) and subsequent reactions with different types of electrophiles have been reported. Some compounds exhibited promising anti‐bacterial activity against Salmonella typhimurium, however poor activity against Staphylococcus aureus. The compound 4t was found to have high activity even at 1 μg/ml compared to Cephalexin against S. aureus. The biological activity against PDE‐IV for potential anti‐asthmatic effect and against DP‐IV and PTP‐1B for potential anti‐diabetic effects was disappointing.     

Spatial trends in uranium distribution in groundwaters of Southwest Punjab,India - A hydrochemical perspective

A hydrochemical study was undertaken in uranium impacted districts of southwest Punjab for evaluating the spatial and vertical trends as well as correlations with other hydrochemical parameters. Results infer that U is present in all samples (12.2–621 µg l⁻¹) and 90% are contaminated. Contour diagram depicts contamination in entire region excepting some pockets in central part of the study area. Shallow zones (<50 m bgl) show higher U compared to deeper ones. Hydrochemistry infers a common source of U for both shallow and deep zones and alkalinity as the governing factor for U mobilization from the sediments.

     

Assessment of recharge source to springs in upper Beas basin of Kullu region,Himachal Pradesh,India using isotopic signatures

Journal of Radioanalytical and Nuclear Chemistry - Environmental stable and radioisotope data of springs located in Kullu region of Himachal Pradesh are interpreted to identify the recharge source...     

The effect of numerical integration on the finite element approximation of linear functionals

In this paper, we have studied the effect of numerical integration on the finite element method based on piecewise polynomials of degree k, in the context of approximating linear functionals, which are also known as “quantities of interest”. We have obtained the optimal order of convergence, O(h^2k){\mathcal{O}(h^{2k})}, of the error in the computed functional, when the integrals in the stiffness matrix and the load vector are computed with a quadrature rule of algebraic precision 2k − 1. However, this result was obtained under an increased regularity assumption on the data, which is more than required to obtain the optimal order of convergence of the energy norm of the error in the finite element solution with quadrature. We have obtained a lower bound of the error in the computed functional for a particular problem, which indicates the necessity of the increased regularity requirement of the data. Numerical experiments have been presented indicating that over-integration may be necessary to accurately approximate the functional, when the data lack the increased regularity.