Ahmed Al-Saie

Light amplification and lasing in a (meta-phenylene vinylene) copolymer

We report on single pass optical gain and lasing measurements on a blue-emitting copolymer, poly(m-phenylene vinylene-co-2,5-dioctyloxy-p-phenylene vinylene) under 0.5 ns pulsed photoexcitation. This soluble copolymer is designed and synthesized for light amplification and lasing applications. Blue photoluminescence is achieved by introduction of the meta linkage of the phenylene rings in the polymer backbone, which reduces the extent of delocalization of π electrons. The large Stokes shift of about 70 nm implies a low reabsorption rate, and leads to easier creation of population inversion and hence to efficient light amplification. A solution of the polymer exhibits amplified spontaneous emission evidenced by spectral narrowing and a superlinear increase of output intensity when it is photoexcited at 337 nm. By means of the variable excitation stripe length method, net gains of 18 and 24 cm−1 are deduced for different pump energies of 71 and 113 μJ, respectively. Moreover, laser emission from the polymer...

STRUCTURE AND MAGNETIC PROPERTIES OF NANOSIZED BaFe2O4 MATERIAL

A mixture of BaO and Fe2O3 was mechanically alloyed followed by subsequent annealing. XRD spectra and magnetization hysteresis curves were obtained for both as-milled and annealed samples. XRD pattern of the as-milled powder indicates the formation of an initial amorphous phase. Upon annealing up to 900°C, the material crystallizes into monoferrite BaFe2O4 phase, accompanied by a dramatic change of the magnetic properties. Moreover, the Ms ≈ 5.8 emu/g, Hc ≈ 1.2 kOe, Mr ≈ 2.4 emu/g and an average crystallites size around 23 nm.

The optical gain and effective stimulated emission cross-section for dimethoxy-PmPV and dimethyl-PmPV-ONV copolymers in toluene solution

We report amplified spontaneous emission from the copolymers poly{m-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(3,4-dimethyloxy phenyl) vinylene]} (dimethoxy-PmPV) and poly{m- phenylene-co-[1,5-dioctyloxy-2,6-naphthylene-bis-2(3,4-dimethyl phenyl) vinylene]} (dimethyl-PmPV-ONV) in toluene. The copolymers are related to poly(phenylene vinylene) and have been synthesized via the Horner?Emmons polycondensation reaction. The optical gain determined from the amplified spontaneous emission intensity is dependent on the excited stripe length. Net gains of 3.4 ? 0.2 and 0.3 ? 0.3 cm?1 were measured for dimethoxy-PmPV and dimethyl-PmPV-ONV respectively under nanosecond pulse excitation. The gain for rhodamine 6G was also measured under the same experimental conditions and was used to determine the stimulated emission cross-sections for both polymers; these were found to be ?se (peak) = 2.3 ? 10?18 cm2 for dimethoxy-PmPV and ?se (peak) = 2 ? 10?20 cm2 for dimethyl-PmPV-ONV.

Synthesis, structure and magnetic properties of nano-sized CoFe204 material

A single and pure CoFe 2 O 4 phase at the nanoscale has been successfully synthesised by a simple combination of milling a mixture of Fe-oxide and Co-oxide followed by annealing at low temperature, i.e., 750°C. X-ray diffraction and magnetic measurements were carried out.

Effect of the preparation route, PEG and annealing on the phase stability of Fe3O4 nanoparticles and their magnetic properties

Fe3O4 nanoparticles are synthesised via two different methods: (1) co-precipitation of Fe2+ and Fe3+ ions and (2) oxidative alkaline hydrolysis of Fe2+ ions under atmospheric pressure using different protective agents (PEG 200 and PEG 3000) and urea as a base. The preparation method and the polyethylene glycol (PEG) used are concurrently affecting the phase stability of the formation of the iron oxides: the co-precipitation method using PEG 200 (E4a) or PEG 3000 (E4b) leads to the formation of different ratios of Fe2O3 and Fe3O4, whereas the oxidative hydrolysis of Fe2+ using PEG 200 gives Fe3O4 (E2) powder as a major product. The average crystallites size of E4a and E4b is almost identical, i.e. around 19 nm but the saturation magnetisation of E4b is three times larger than that of E4a. The sample E2 shows the highest saturation magnetisation value 74 emu/g, with an average crystallites size of 71 nm. Transmission electron microscopy analysis confirmed that the E2 sample shows the presence of needles crystals with typical sizes around 10 and 50 nm and its selected area diffraction (SAD) shows a typical diffraction of the spinel structure of magnetite. On the other hand, E4b sample shows elongated nanoparticles with typical sizes around 24 nm and its SAD confirmed the presence of a mixture of Fe2O3 and Fe3O4 as many dispersed spots were obtained.

Structure and magnetic properties of mechanically milled Pb 3 O 4 -Fe 2 O 3 mixture

A mixture of Fe 2 O 3 and Pb 3 O 4 oxides has been mechanically milled to form the nanosized spinel PbFe 2 O 4 phase. X-ray diffraction pattern of the as milled mixture shows the presence of Fe 2 O 3 peaks in addition to a broad halo around 29° related to the amorphisation of Pb3O4. Annealing at 750°C for 1 h, leads to the formation of new phases as evidenced by the appearance of new peaks. The saturation magnetisation and coercivity values of the as-milled mixture are 1.03 emu/g and 200 Oe, respectively. After annealing, a paramagnetic behaviour with a large hysteresis loop was observed.

Synthesis, crystal structure and magnetic properties of iron oxides nanoparticles for biomedical applications

Magnetic Fe3O4 nanoparticles have been synthesised by two methods: co-precipitation using a range of Fe3+ and Fe27+ raw materials; oxidative hydrolysis using various Fe2+ salts. X-ray diffraction analysis shows that most of the samples prepared by the co-precipitation method resulted in a mixture of two iron oxide phases (Fe2O3 and Fe3O4) with the presence of impurities (unreacted precursors) while using the oxidative hydrolysis method, Fe3O4 was found to be a major product. Magnetic measurements confirm the results obtained by X-ray diffraction. The sample prepared using FeSO4 as precursor in urea and PEG 200 at 40-50°C for 3 hours (nominated as E2) gives an average crystallites size around 70 nm, a saturation magnetisation Ms = 75 emu/g, a remanence of Mr = 12 emu/g and a coercivity of Hc = 110 kOe, which can be a good candidate for biomedical applications.

Synthesis, structure and optical properties of nano-sized doped In2O3 – 10% SnO material

A mixture of In2O3 + 10% SnO was milled under various conditions, followed by subsequent annealing at various temperatures. X-ray diffraction analysis and FTIR measurements were carried out. It is found that after milling, a single (In,Sn)2O3 phase is obtained, indicating the dissolution of Sn into In2O3 lattice and its substitution into In-ionic site.

Evaluation of the mobile content in Magnetospirillum magneticum AMB-1 genome using bioinformatical approaches reveals a new genome size for the magnetosome island

Abstract After completing its sequence/annotation in 2005, Magnetospirillum magneticum AMB-1 had become one of the most important magnetotactic genomes used to facilitate analysis of the magnetosome formation process. In this paper we investigate the genome contents of AMB-1 and other magnetotactic bacteria to demonstrate the size of mobile genome and number of conserved genes in M. magneticum AMB-1. The preliminary analysis presented here shows the mosaic structure of these genomes. 100 genomic islands were identified in AMB-1 by IslandPick. Moreover, the size of AMB-1 magnetosome island (MAI), previously known to be 100 kb, was re-estimated to be in the size range of 110 kb. Thus more genes were included to be part of this GI. The investigation included the use of comparative approaches to elucidate conserved protein coding sequences. 13 CDS were identified to be conserved among three magnetotactic genomes. One CDS (amb3135) was conserved in five magnetotactic genomes. The amino acid sequence for this CDS (amb3135) was used to draw a phylogenetic tree among magnetotactic bacteria. The phylogeny based on amb3135 is in concordance with previous studies indicating a close relationship between strain AMB-1 and other Magnetospirillum species.

Structural and magnetic properties of mechanically milled TiO 2 -Fe 2 O 3 mixture

A mixture of Fe 2 O 3 and TiO 2 oxides has been mechanically milled to form TiFe 2 O 4 spinel phase. X-ray diffraction pattern of the as-milled mixture shows the presence of both Fe 2 O 3 and TiO 2 phases. The broadening of the diffraction peaks and the decrease of their relative intensity are due to the grain size reduction and accumulation of internal strains. Annealing at 750°C leads to an increase of the Fe 2 O 3 peaks intensity and the reduction of TiO 2 amount suggesting a possible diffusion of Ti into Fe 2 O 3 crystal lattice to form Fe 2–x TixO 3 compound. The saturation magnetisation ( Ms ) drops from 2.6 emu/g for the as-milled mixture to 0.8 emu/g after annealing.