Novel triterpenoid saponins from Mimusops elengi

Two novel triterpenoid saponins, mimusopin ( 3-O-β-D-glucopyranosyl-2β, 3β, 6β, 23-tetrahydroxyolean-12-en-28-oic acid 28-O--L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)[a-L-rhamnopyranosyl-(1→ 3)]--L-rhamnopyranosyl-(1→2)--L-arabinopyranoside)(1) and mimusopsin 3-O-[β-D-glucopyranosyl-(1→3)β-D-gluco-pyranosyl]-2β, 3β, 6β, 23-tetrahydroxyolean-12-en-28-oic acid 28-O--L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)--L-rhamnopyranosyl-(1→2)--L-arabinopyranoside (2) were isolated from the seeds of Mimusops elengi. Their structures were elucidated by a combination of 2D-NMR (COSY, HOHAHA, HETCOR, HMBC and NOESY), FAB-MS/MS and strategic chemical degradation. In addition, molecular mechanics and dynamics studies showed that the lack of a ¹³C glycosylation shift at the C-4 of the inner rhamnose in 1 could be correlated with distortion in the corresponding torsion angles.     

Calix[n]arenes mediated phase‐transfer catalytic synthesis of purine derivatives

A new route was designed to achieve the synthesis of purine derivatives under phase‐transfer catalysis conditions using calix[n]arenes TAC_nA (n = 4, 6, and 8) as phase‐transfer catalyst for the first time in this particular type of synthesis. The compounds were synthesized in excellent yields (70%–80%) and the structures were established on the basis of consistent IR, ¹H NMR, FAB‐Mass, and elemental analyses data. Their purity has been ascertained by chromatographic resolution using acetonitrile, methanol, and water (50:30:20, v/v) as eluenting system. Moreover, the kinetics of the reaction was studied and it was found to obey first‐order kinetics. Effect of various parameters, namely, temperature, amount of catalyst, stirring speed, and so on was also investigated. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 265–274, 2009     

Asymmetric barrier model for heavy ion fusion and its relation to channel coupling

A new asymmetric parabolic effective fusion barrier model for heavy ion fusion is developed.     

The Effect of Sudden Permeability Changes in Porous Media Filling Box Flows

We report upon experimental and analytical investigations of filling box flows in non-uniform porous media characterized by a sudden change in permeability. The porous medium consists of two layers separated by a horizontal permeability jump and is initially filled with light ambient fluid. A line source located at the top of the upper layer supplies dense contaminated fluid that falls toward the bottom of the domain. Two configurations are studied, i.e., a low-permeability layer on top of a high-permeability layer and vice versa. In the former scenario, the flow dynamics are qualitatively similar to the case of a uniform porous medium. Thus, the analytical formulation of Sahu and Flynn (J Fluid Mech 782:455–478, 2015) can be adopted to compute the parameters of interest, e.g., the plume volume flux. In the latter scenario, the flow dynamics are significantly different from those of the uniform porous medium case; after reaching the permeability jump, some fraction of the dense plume propagates horizontally as a pair of oppositely directed interfacial gravity currents. Meanwhile, the remaining fraction of the plume flows downward into the lower layer where it accumulates along the bottom boundary in the form of a deepening layer of discharged plume fluid. Depending on the permeability ratio of the upper and lower layers and the source conditions, the gravity currents may become temporarily arrested after traveling some finite horizontal length. An analytical prediction for this so-called run-out length is derived, motivated, in part, by the immiscible analysis of Goda and Sato (J Fluid Mech 673:60–79, 2011). Finally, a prediction of the filling box time, consisting of the time required to fill the control volume up to the point of contaminated fluid overflow, is made. These predictions are compared with analog experimental measurements. Generally positive agreement is found when the higher-permeability layer is located below the lower-permeability layer. In the opposite circumstance, the agreement is conditional. If the run-out length of the gravity current is less than the horizontal dimensions of the control volume (or tank in case of the experiments), the agreement is good. By contrast, when the run-out length is large, comparatively poor agreement may be realized: In spite of the higher density of the contaminated fluid, it may occupy the entirety of the upper layer before filling the lower layer.     

Tamarind seed skin-derived fiber-like carbon nanostructures as novel anode material for lithium-ion battery

Demand of low-cost carbonaceous anode materials for lithium-ion batteries has led to the development of anode materials from different bio-sources. In this regard, tamarind seed (skin) was used as a precursor to prepare disordered carbon as an anode material for lithium-ion batteries. The carbon was prepared through simple hydrothermal method and was characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET) measurements, field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) techniques. It exhibited amorphous carbon particles arranged in a fiber-like morphology with high surface area of 508 m² g^?1. The binder content was optimized for the carbon to achieve high and stable capacity. Electrochemical performance of the as-prepared carbon with optimized binder content showed a stable reversible specific capacity of 224 mAhg^?1 after 300 cycles at 1 C-rate. The stable cycling performance of carbon at high current rate is explained by electrochemical impedance spectroscopy (EIS) and FE-SEM data of cycled electrodes. The low cost and stable specific capacity make the carbon as potential anode material for lithium-ion battery.

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Graphical abstract Fiber-like carbon nanostructures from tamarind seed (skin) (TDC) via simple and effective hydrothermal method and its application as a novel anode material for lithium-ion battery.

     

Dielectric constant of graphene-on-polarized substrate: A tight-binding model study

By using the bifurcation theory of planar dynamical systems and the qualitative theory of differential equations, we studied the dynamical behaviours and exact travelling wave solutions of the modified generalized Vakhnenko equation (mGVE). As a result, we obtained all possible bifurcation parametric sets and many explicit formulas of smooth and non-smooth travelling waves such as cusped solitons, loop solitons, periodic cusp waves, pseudopeakon solitons, smooth periodic waves and smooth solitons. Moreover, we provided some numerical simulations of these solutions.     

A model for expansion ratio in liquid-solid fluidized beds

Liquid-solid fluidized beds are used in mineral processing industries to separate particles based on parti- cle size, density, and shape. Understanding the expanded fluidized bed is vital for accurately assessing its performance. Expansion characteristics of the fluidized bed were studied by performing several experi- ments with iron ore, chromite, quartz, and coal samples. Using water as liquid medium, experiments were conducted to study the effects of particle size, particle density, and superficial velocity on fluidized bed expansion. The experimental data were utilized to develop an empirical mathematical model based on dimensional analysis to estimate the expansion ratio of the fluidized bed in terms of particle character- istics, operating and design parameters. The predicted expansion ratio obtained from the mathematical model is in good agreement with the experimental data.