Accurate estimation of Brillouin frequency shift in Brillouin optical time domain analysis sensors using cross correlation

Current methods of estimating the Brillouin frequency shift in Brillouin optical time domain analysis sensors are based on curve-fitting techniques. These techniques apply the same weight to all portions of the curve and dutifully fit into the peak and noisy ends of the curve. This makes them very sensitive to noise, initialization of fitting parameters, symmetry, and start and stop frequencies. We introduce a method based on the cross-correlation technique to estimate the central frequency of noisy Lorentzian curves, which is more robust to noise and free from initial settings of fitting parameters.     

The Influence of Copolymerization Condition on Rheology,Morphology and Thermal Behavior of Polypropylene Heterophasic Copolymers

In this work, the polypropylene impact copolymers were synthesized by a modified sequential polymerization process. The copolymerization of ethylene and propylene was carried out between two homopolymerization stages at two different pressures and temperatures and the rheology, morphology and thermal properties of reactor alloys were studied. It is found that the ethylene propylene rubber (EPR) content increased up to 32 wt% by increasing the copolymerization time to 20 min. At a fixed copolymerization time of 10 min, the addition of 50 ppm hydrogen (H₂), increased the EPR content from 9.7 to 12.8 wt%. By doubling H₂ concentration, no considerable change in EPR wt% was observed. It is found that the zero shear viscosity of the alloys is significantly under the influence of EPR wt%, not the molecular weight of matrix. The molecular weight of PP matrices determined by rheological data, mildly decreased from 463000 to 458000 g/mol by increasing the copolymerization time from 10 min to 15 min. At high copolymerization time/high H₂ concentration, a melting peak in the differential scanning calorimetry test around 165°C for isotactic PP and also an endothermic peak around 127°C for the block copolymer with long ethylene segments, is observed. The study of interfacial strength by theoretical emulsion models showed that 15 min copolymerization time is optimum considering EPR wt%.     

Substitution Effect in NICS Values in Tropylium Ion Derivatives: An Ab Initio Study

Hartree–Fock (HF) and hybrid density functional theory (B3LYP) calculations were performed on tropylium ion and 19 of its mono- and diheteroatomic derivatives. The aromaticity in this class of compounds is evaluated based on the nucleus independent chemical shift (NICS) values. The NICS values are calculated at the center of the rings NICS (0) and at 1Å above the molecular plane NICS (1). The geometry optimization and NICS calculations were carried out at the HF/6–311+G?? and at the B3LYP/6–311+G (2d, p) density functional level, respectively. These calculations in the effects of heteroatoms such as N, B, P, and Si are considered on aromaticity, molecular properties, NICS values, and structural parameters.     

Time-Dependent Density of Modified Cosmic Chaplygin Gas with Variable Cosmological Constant in Non-Flat Universe

In this paper we study modified cosmic Chaplygin cosmology with non-zero cosmological constant in non-flat Universe. By using well-known forms of scale factor we obtain time-dependent dark energy density by numerical analysis of non-linear differential equation and fitting curves. We use observational data to fix solution and discuss about stability of our system. First of all we consider cosmological constant as a constant in Einstein equation, and then study possibility of variable cosmological constant.     

Screening method for phthalate esters in water using liquid-phase microextraction based on the solidification of a floating organic microdrop combined with gas chromatography-mass spectrometry

A simple and efficient liquid-phase microextraction (LPME) technique was developed using directly suspended organic microdrop coupled with gas chromatography–mass spectrometry (GC–MS), for the extraction and the determination of phthalate esters (dimethyl phthalate, diethyl phthalate, diallyl phthalate, di-n-butyl phthalate (DnBP), benzyl butyl phthalate (BBP), dicyclohexyl phthalate and di-2-ethylhexyl phthalate (DEHP)) in water samples. Microextraction efficiency factors, such as nature and volume of the organic solvent, temperature, salt effect, stirring rate and the extraction time were investigated and optimized. Under the optimized extraction conditions (extraction solvent: 1-dodecanol; extraction temperature: 60 °C; microdrop volume: 7 μL; stirring rate: 750 rpm, without salt addition and extraction time: 25 min), figures of merit of the proposed method were evaluated. The values of the detection limit were in the range of 0.02–0.05 μg L⁻¹, while the R.S.D.% value for the analysis of 5.0 μg L⁻¹ of the analytes was below 7.7% (n = 4). A good linearity (r² ≥ 0.9940) and a broad linear range (0.05–100 μg L⁻¹) were obtained. The method exhibited enrichment factor values ranging from 307 to 412. Finally, the designed method was successfully applied for the preconcentration and determination of the studied phthalate esters in different real water samples and satisfactory results were attained.     

Dynamical Calculation of Θ+ Mass and Decay width in the Quark Model

In this paper we study the mass splitting and the decay width of pentaquark (Θ⁺) at the ground states in the framework of flux tube, quark delocalization and color screening model. We consider the pentaquark as diquark-triquark configuration and obtained closer values of mass splitting and the decay width of Θ⁺ to the experimental data.     

Phantom Accretion onto the Schwarzschild Anti de-Sitter Black Hole

In this paper we study phantom energy accretion onto the Schwarzschild anti de-Sitter black hole. We obtain critical point where the speed of flow is equal speed of sound. We find that the critical point is near the black hole horizon.     

Phantom Accretion onto the Schwarzschild AdS Black Hole with Topological Defect

In this paper, we have studied phantom energy accretion of prefect fluid onto the Schwarzschild AdS black hole with topological defect. We have obtained critical point during the accretion of fluid on the black hole where the speed of flow is equal speed of sound (Sharif and Abbas in Phantom accretion onto the Schwarzschild de-Sitter black hole, 2011, [gr-qc]). The critical velocities have been computed so that the speed of fluid into the black hole is less than speed of sound. Finally, we have found that the critical point is near the black hole horizon.