Few-mode ring core fiber characteristics: temperature impact

Photonic Network Communications - In this paper, a novel fiber is proposed to support few linearly polarized (LP) modes, with the feature of a circular ring-shaped core filled by liquid. This fiber...     

Heterogeneous polymerization of some methacrylate monomers

It has been found that sodium metabisulphite failed to initiate the polymerization of methyl and butyl acrylates but succeeded in polymerizing methyl, ethyl, and hydroxy propyl methacrylates. All the samples of the poly(hydroxypropyl methacrylates) were crosslinked, even those prepared at low conversions. Gel permeation chromatographic analysis indicated a multinodal molecular weight distribution, suggesting the existence of more than one mechanism occurring in such a heterogeneous system. It has also been proved by electron spin resonance that the polymerization process, using sodium bisulphite as the initiator in such a system, is a radical mechanism. The use of substances such as quartz, glass powder, and kaoline powder enabled the detection of the bisulphite radicals by trapping them. Using ¹³C NMR spectroscopy, the estimated triad fractions from α-methyl peaks and from quaternary carbon peaks of the poly(methyl methacrylates) and poly(ethyl methacrylates) showed that the polymers obtained were all predominantly syndiotactic in structure, as expected. The poly(ethyl methacrylate) samples were found to have a slightly higher syndiotacticity than the poly(methyl methacrylates), also as expected. The greater bulk of the ethyl ester group relative to that of the methyl ester group probably leads to greater steric hindrance in the isotactic and heterotactic triad (i.e., in a mesodyad).     

Polymerization of methyl methacrylate in water in presence of some egyptian sands and quartz pegmatite

The polymerization of methyl methacrylate was carried out in water in presence of some Egyptian sands and quartz pegmatite using sodium bisulphite as initiator. The polymerization was performed at 30, 40, 50 and 60°C using initiator concentrations varying from 0.05 to 0.3 mol/l. The overall rates of polymerization increased from 2.0 × 10^?5 mol/l·s to 4.8 × 10^?5 mol/l·s in presence of quartz pegmatite, to 5 × 10^?5 mol/l·s when Natron sand was used and to 6.4 × 10^?5 mol/l·s in the presence of Ahram sand, as the concentration of each was varied from 0 to 30 g/l. The effect of change of temperature, initiator and monomer concentration on the overall rate of polymerization was studied. The molecular weights were determined viscosimetrically. It was found that the average molecular weights of the obtained polymers increase with the increase of both monomer and initiator concentrations and decrease with rise of temperature. Ahram sand leads to a higher polymer yield and a lower average molecular weight than in case of Natron sand. The stereoregularity of the obtained polymers was determined with a 60 MHz NMR spectrometer.     

Simple and rapid spectrophotometric and titrimetric methods for the determination of ascorbic acid in pharmaceutical preparations

Ascorbic acid in pharmaceutical preparations can be determined by either spectrophotometric or titrimetric methods by its reaction with ferricinium trichloroacetate at pH 3. The latter is quantitatively reduced to ferrocene. This is extracted by chloroform and its concentration calculated from the absorbance at 440 nm. Alternatively, an aqueous solution of ascorbic acid is titrated with that of the blue ferricinium salt which acts as an indicator. Vitamins, minerals, hormones, dextrose and coloured additives do not interfere with the reaction. Both methods are simple, rapid and sensitive.     

Electrospun polyvinyl alcohol membranes incorporated with green synthesized silver nanoparticles for wound dressing applications

Electrospun membranes have the potential to act as an effective barrier for wounds from the external environment to prevent pathogens. In addition, materials with good antibacterial properties can effectively fight off the invading pathogens. In this paper, we report the development of a novel electrospun polyvinyl alcohol (PVA) membrane containing biosynthesized silver nanoparticle (bAg) for wound dressing applications. Plant extract from a medicinal plant Mimosa pudica was utilized for the synthesis of bAg. Synthesized bAg were characterized by Ultraviolet-Visible (UV) Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). The morphology of bAg was obtained from Transmission Electron Microscopy (TEM) and found that they were spherical in morphology with average particle size 7.63?±?1.2?nm. bAg nanoparticles incorporated PVA membranes were characterized using several physicochemical techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD) analysis. Experimental results confirmed the successful incorporation of bAg in PVA fibers. PVA nanofiber membranes incorporated with bAg showed good mechanical strength, excellent exudate uptake capacity, antibacterial activity, blood compatibility and cytocompatibility.

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Synthesis of some new 2‐[(2,3‐dihydroinden‐1‐ylidene) hydrazinyl]‐4‐methylthiazole derivatives for simultaneous dyeing and finishing for UV protective cotton fabrics

Several 2‐[1‐(1,2‐dihydroinden‐3‐ylidene) hydrazono]‐5‐aryldiazo‐4‐methyl‐1,3‐thiazoles were synthesized by reaction of 1‐(1,2‐Dihydroinden‐3‐ylidene) thiosemicarbazide with different hydrazonyl chlorides. The products are water insoluble and UV absorbers, expressed UPF‐rating values, and their H₂O/DMF solutions were used in simultaneous dyeing and resin finishing of cotton fabrics. Results obtained show that finishing of cotton samples in presence of any of that dyes, irrespective of dye concentration, brings about an improvement in percent nitrogen, wrinkle recovery angle (WRA), dyeability, and UV protection rating values along with slight decrease of tensile strength (TS) compared with the untreated samples. Irrespective of dye structure, increasing the dye concentration from 0.5 and up to 1.7% results in an improvement in the percent nitrogen, TS and a remarkable improvement in both the dyeability, UPF‐rating values along with slight decrease in WRA and lower fastness properties of the treated fabrics. The treated fabrics was characterized using energy dispersive X‐ray analysis indicating the entrapped dye within the fabric structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structural characteristics and electrical properties of copper doped manganese ferrite

A series of Mn_1?xCu_xFe₂O₄ ferrite samples with 0.2 ≤ x ≤ 0.5 were prepared using the co-precipitation method. X-ray analysis confirmed the formation of single phase cubic spinel structure for all concentrations. Rietveld refinement revealed that the Mn_1?xCu_xFe₂O₄ with all concentrations of x belongs to normal spinel structure. The lattice parameters decrease leading to the increase in the X-ray density with increasing the copper concentration and this may be due to the difference in the ionic radii between Mn²⁺ and Cu²⁺. The decrease in the crystallite size with increasing the copper content is attributed to the higher formation temperature. The IR absorption spectra analyses were used for the detection and confirmation of the chemical bonds in spinel ferrites. The AC electrical conductivity, real part of the dielectric constant and the loss tangent tan δ were studied as a function of the applied frequency and temperature. It was found that the AC electrical conductivity increased with increasing temperature, this increase may be related to the increase in the drift mobility of the charge carriers, which are localized at ions or vacant sites. The AC conductivity increases with increasing copper concentration which may be ascribed to the decrease in hopping length. The dielectric constant ?′ and dielectric loss showed a decrease with increasing frequency and increase with increasing temperature for all compositions. The dielectric behavior is explained by using the mechanism of polarization process.     

Deterministic and Stochastic Fractional Order Model for Lesser Date Moth

In this paper, a deterministic and stochastic fractional order model for lesser date moth (LDM) using mating disruption and natural enemies is proposed and analysed. The interaction between LDM larvae, fertilized LDM female, unfertilized LDM female, LDM male and the natural enemy is investigated. In order to clarify the characteristics of the proposed deterministic fractional order model, the analysis of existence, uniqueness, non-negativity and boundedness of the solutions of the proposed fractional-order model are examined. In addition, some sufficient conditions are obtained to ensure the local and global stability of equilibrium points. The occurrence of local bifurcation near the equilibrium points is investigated with the help of Sotomayor’s theorem. Numerical simulations are conducted to illustrate the properties of the proposed fractional order model with respect to the intrinsic growth rate of the LDM larvae, natural enemy’s mortality rate, predation rate, sex pheromone trap parameter, fractional order and environmental noise. The impact of mating disruption on lesser date moth is demonstrated. Also, a numerical approximation method is developed for the proposed stochastic fractional-order model.     

Numerical approach to field fluctuations and spectral lineshape in InGaAsP laser diodes

This paper reports on a numerical approach to model the field fluctuations, spectral lineshape and linewidth in semiconductor lasers. The approach is based on numerical solution of the laser rate equations augmented by Langevin noise sources that account for fluctuations in the lasing field. The paper newly examines contributions of intensity and frequency noises to the spectral characteristics of the lineshape and its linewidth over a wide range of injection current. The model is applied to InGaAsP lasers emitting in a wavelength of 1.5 μm as the most representative light sources in optical communication systems. Accuracy of approximated models of calculating linewidth from low‐frequency components of the frequency noise is checked. Effect of non‐linear gain suppression on the lineshape is also explored. The spectral lineshape promotes and the linewidth decreases as the laser is injected far from the near‐threshold region. The lineshape changes mainly with changes in the frequency noise spectrum while the linewidth is sensitive to variation in the low‐frequency levels of both intensity and frequency noises. Copyright © 2004 John Wiley & Sons, Ltd.