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.     

Physical,optical and gamma radiation shielding competence of newly boro-tellurite based glasses: TeO2–B2O3–ZnO–Li2O3–Bi2O3

Herein, a traditional melt quenching method was utilized to synthesize glasses with a nominal chemical composition (80-x)TeO₂-xB₂O₃–5ZnO–5Li₂O₃–10Bi₂O₃: 30≤ x ≤ 80 mol%). The produced sample was coded as TBBZL30 to TBBZL80. X-ray diffraction (XRD) has been employed to test the amorphous nature of the synthesized samples. In the range of 200–500 nm wavelength, UV–Vis spectra for the glasses have been performed. Optical energy gaps ($E_{gap}$) have been determined based on the absorption measurements. With the help of ($E_{gap}$), refractive index (n), molar polarizability (α^M), metallization criterion (M^Cri.), molar refractivity (R^M), static dielectric constant (ε^Sta.), optical dielectric constant (ε^Opt.), reflection loss (R^L) and optical transmission (T^Opt.) have been calculated. For the fabricated boro-tellurite glasses, Phy-X/PSD was used to report some shielding factors for several energies between 15 keV and 15 MeV. The maximum attenuation for all samples took place at 15 keV and the mass attenuation coefficient varied between 52.309 and 57.084 cm²/g. The linear attenuation coefficient (LAC) results demonstrated that TBBZL80 has the highest attenuation than the rest of samples which is due to high content of TeO₂ (containing 80 mol% of TeO₂) whereas TBBZL30 has the lowest attenuation. The LAC for the fabricated samples varied between 230.160 and 351.064 cm-¹ at 15 keV. The minimum effective atomic number (EAN) occurred between 0.8 and 4 MeV and varied between 15.16 and 17.35 for TBBZL30 and 25.10–28.33 for TBBZL80. The addition of TeO₂ was found to enhance the EAN and improved shielding properties for the tested TBBZL glass systems.     

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     

Building performance assessment of user behaviour as a post occupancy evaluation indicator: Case study on youth housing in Egypt

Youth housing prototypes are widely spread all over Egypt as a cheap economic housing for youth which are designed in a number of different shapes. A post occupancy evaluation (POE) has been conducted to one of these prototypes to assess some modifications spontaneously done by users to the original design for the sake of enhancing building performance, e.g., creating new openings to improve lighting and natural ventilation thermal comfort, and making sunshades to control direct sunlight and thermal radiation. These assessments have been validated using simulation techniques i.e. CFD, thermal and daylight simulations, to compare natural ventilation, thermal comfort, and daylight energy efficiency in the original designs to that in the user modified. A wind tunnel test has been conducted to validate the standard k–epsilon turbulence CFD simulation in addition to daylighting in-situ measurements to validate natural lighting. The outcome of this research could be widely used as an important feedback tool in the future designs of the same prototype to evaluate user behaviour role in building performance efficiency. The research showed that some of these behaviours has improved thermal comfort by 60% to 87% from the original design while daylight efficiency has been improved by 31.8% to 41.4% while sensible cooling loads’ improvement ranges from 27.4% to 77.2% for the northern zone and 29.9% to 91.6% for the southern one, and thus, it could be used as a reliable POE feedback tool.     

Enhancing the properties of urea formaldehyde wood adhesive system using different generations of core‐shell modifiers based on hydroxyl‐terminated dendritic poly(amidoamine)s

Different generations of hydroxy‐terminated dendritic poly(amidoamine) (Gn? OH) with ethylenediamine as a core were prepared by successive alternative addition of methylacrylate and the core up to the third generation while employing ethanolamine only in the last step of every full generation. The different generations prepared were used as modifiers for urea‐formaldehyde (UF) resins. The enhanced durability and stabilizing effect of the (Gn? OH)s along with the reduced levels of free formaldehyde and improved mechanical performance of wood joints glued with the modified resins are discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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.     

Simple,green approach for the synthesis of solid support‐embedded PdNPs for ligand exchange

Green approaches have the potential to significantly reduce the costs and environmental impact of chemical syntheses. Here, the authors used green tea (GT) leaf extract to synthesise and anchor palladium nanoparticles (PdNPs) to silica. The synthesised PdNPs in GT extract were characterised by ultraviolet–visible spectroscopy, Fourier‐transform infrared spectroscopy, X‐ray diffraction, and transmission electron microscopy. PdNPs primarily formed as capped NPs dispersed in GT extract before reduction completed after 24 h. This capped phytochemical solution was employed as a green precursor solution to synthesise PdNP‐embedded solid supports. The morphology of PdNPs anchored to silica differed to that of PdNPs in solution. Silica‐embedded PdNPs was employed as a new ligand exchanger to isolate trace polycyclic aromatic sulphur heterocycles from a hydrocarbon matrix. The isolation efficiency of the new, greener ligand exchanger was the same as an efficient chemical ligand exchanger and may, therefore, hold promise for future applications.Inspec keywords: nanofabrication, palladium, visible spectra, transmission electron microscopy, nanoparticles, reduction (chemical), ultraviolet spectra, X‐ray diffraction, Fourier transform infrared spectra, surface morphologyOther keywords: ultraviolet–visible spectroscopy, Fourier‐transform infrared spectroscopy, transmission electron microscopy, phytochemical solution, green precursor solution, PdNP‐embedded solid supports, solid support‐embedded PdNPs, green tea leaf extract, chemical ligand exchanger, anchor palladium nanoparticles, X‐ray diffraction, isolate trace polycyclic aromatic sulphur heterocycles, hydrocarbon matrix, green synthesis, time 24.0 hour, Pd