Comparison of Air-Assisted,Vortex-Assisted and Ultrasound-Assisted Dispersive Liquid–Liquid Microextraction for the Determination of BTEX Compounds in Water Samples Prior to GC-FID Analysis

Three new dispersive liquid–liquid microextraction (DLLME) methods, air-assisted (AA-DLLME), vortex-assisted (VA-DLLME) and ultrasound-assisted (UA-DLLME), were compared from the point of view of their analytical application for preconcentration of trace amounts of benzene, toluene, ethylbenzene and xylene isomers (BTEX) in water samples. In all of these methods, no dispersive solvent is required and dispersion of extractant is carried out by air bubbles, vortex and ultrasound for AA-DLLEM, VA-DLLME, and UA-DLLME, respectively. Advantages and disadvantages of these three liquid phase microextraction methods and their capability in dispersion of a similar extractant phase in sample solutions were comprehensively compared. All other extraction parameters, which have an influence on the microextraction, were also investigated and optimized. Under optimized conditions, analytical figures of merit for the three techniques were determined and compared. It was found that the limit of detection of the three methods is almost the same, while AA-DLLME has a wider linear dynamic range and the shortest analysis time. Enrichment factors of 182, 45 and 245 were achieved for AA-DLLEM, VA-DLLME, and UA-DLLME, respectively.     

Isometries, Geodesics and Jacobi Fields of Lorentzian Heisenberg Group

The paper is mainly devoted to determine the groups of isometries of the Heisenberg group endowed with each of the three left invariant Lorentzian metrics which are possible on it; also, an explicit computation of all the isometries for the (two) non flat Lorentzian metrics is done. Moreover, explicit formulas for the geodesic curves and the Jacobi vector fields for each of these three Lorentzian metrics are computed.     

Non-minimal quintessence: Dynamics and coincidence problem

Brans–Dicke scalar–tensor theory provides a conformal coupling of the scalar field with gravity in Einstein’s frame. This model is equivalent to an interacting quintessence in which dark matter is coupled to dark energy. This provides a natural mechanism to alleviate the coincidence problem. We investigate the dynamics of this model and show that it leads to comparable dark energy and dark matter densities today.     

MgO(001) barrier based magnetic tunnel junctions and their device applications

Spintronics has received a great attention and significant interest within the past decades,and provided considerable and remarked applications in industry and electronic information etc.In spintronics,the MgO based magnetic tunnel junction(MTJ) is an important research advancement because of its physical properties and excellent performance,such as the high TMR ratio in MgO based MTJs.We present an overview of more than a decade development in MgO based MTJs.The review contains three main sections.(1) Research of several types of MgO based MTJs,including single-crystal MgO barrier based-MTJs,double barrier MTJs,MgO based MTJs with interlayer,novel electrode material MTJs based on MgO,novel barrier based MTJs,novel barrier MTJs based on MgO,and perpendicular MTJs.(2) Some typical physical effects in MgO based MTJs,which include six observed physical effects in MgO based MTJs,namely spin transfer torque(STT) effect,Coulomb blockade magnetoresistance(CBMR) effect,oscillatory magnetoresistance,quantum-well resonance tunneling effect,electric field assisted magnetization switching effect,and spincaloric effect.(3) In the last section,a brief introduction of some important device applications of MgO based MTJs,such as GMR & TMR read heads and magneto-sensitive sensors,both field and current switching MRAM,spin nano oscillators,and spin logic devices,have been provided.     

Explicit Formulas Associated with Some Families of Generalized Bernoulli and Euler Polynomials

In this paper, we propose and derive several new explicit formulas of the generalized Bernoulli and Euler polynomials in terms of the generalized Stirling numbers of the second kind. A study of some families of the modified generalized Euler polynomials yields an interesting algorithm for calculating the generalized Euler polynomials.     

Two new acridone alkaloids from Glycosmis macrantha

Extraction and chromatographic separation of the extracts of dried stem barks of Glycosmis macrantha lead to isolation of two new acridone alkaloids, macranthanine and 7-hydroxynoracronycine, and a known acridone, atalaphyllidine. The structures of these alkaloids were determined by detailed spectral analysis and also by comparison with reported data.     

Isocyanide‐Based Multicomponent Reaction: One‐Pot Synthesis of New Derivatives of Iminofuranone

The one‐pot multicomponent reaction of alkyl isocyanide, alkylidene‐substituted Meldrum's acid, and arylcarboxylic acids affords new derivatives of iminofuranone in fair yields. The structure of the products was deduced from their spectroscopic data. Two equivalents of the respective isocyanides participate in this reaction.     

Soulamarin, a new coumarin from stem bark of Calophyllum soulattri

The extracts of the stem bark of Calophyllum soulattri gave a new pyranocoumarin, soulamarin (1), together with five other xanthones caloxanthone B (2), caloxanthone C (3), macluraxanthone (4), trapezifolixanthone (5) and brasixanthone B (6) one common triterpene, friedelin (7), and the steroidal triterpene stigmasterol (8). The structures of these compounds were established based on spectral evidence (1D and 2D NMR).     

Peristaltic flow of MHD Jeffrey fluid through finite length cylindrical tube

The present investigation studies the peristaltic flow of the Jeffrey fluid through a tube of finite length. The fluid is electrically conducting in the presence of an applied magnetic field. Analysis is carried out under the assumption of long wavelength and low Reynolds number approximations. Expressions of the pressure gradient, volume flow rate, average volume flow rate, and local wall shear stress are obtained. The effects of relaxation time, retardation time, Hartman number on pressure, local wall she...     

Investigation of new solutions for an extended (2+ 1)-dimensional Calogero-Bogoyavlenskii-Schif equation

We investigate and concentrate on new infinitesimal generators of Lie symmetries for an extended (2+ 1)-dimensional Calogero-Bogoyavlenskii-Schif (eCBS) equation using the commutator table which results in a system of nonlinear ordinary differential equations (ODEs) which can be manually solved. Through two stages of Lie symmetry reductions, the eCBS equation is reduced to non-solvable nonlinear ODEs using different combinations of optimal Lie vectors. Using the integration method and the Riccati and Bernoulli equation methods, we investigate new analytical solutions to those ODEs. Back substituting to the original variables generates new solutions to the eCBS equation. These results are simulated through three- and two-dimensional plots.