Four wave mixing nonlinearity effect in wavelength division multiplexing radio over fiber system

The integration of wireless and optical networks is a potential solution for the increasing capacity and mobility as well as decreasing costs in the access networks. Optical networks are fast, robust and error free, however, there are nonlinearity obstacles preventing them from being perfect media. The performance of wavelength division multiplexing (WDM) in radio over fiber (RoF) systems is found to be strongly influenced by nonlinearity characteristics in side the fiber. The effect of four wave mixing (FWM) as one of the influential factors in the WDM for RoF has been studied here using Optisystem and Matlab. From the results obtained, it is found that the FWM effects have become significant at high optical power levels and have become even more significant when the capacity of the optical transmission line is increased, which has been done by either increasing the channel bit rate, and decreasing the channel spacing, or by the combination of both process. It is found that when the channel spacing is 0.1 nm, 0.2 nm and 0.5 nm the FWM power is respectively, becomes about -59 dBm, -61 dBm and -79 dBm. This result confirms that the fiber nonlinearities play decisive role in the WDM for RoF system. The simulation results obtained here are in reasonable agreement as compared with other numerical simulation results obtained, elsewhere, using different simulation tools

Model electrodes for the electrooxidation of simple alcohols : a DEMS study

Pt is considered as a model for fuel cell electrocatalysts. In the present thesis, I stud-ied the electrooxidation mechanisms of methanol (chapter 3) and ethanol (chapter 4) on different Pt surfaces, using a dual thin-layer flow through cell combined with the mass spectrometer. In chapter 5, Ru quasi single crystal films on different bead Pt surfaces were formed using the resistive heating in a stream of nitrogen. The Ru films were exam-ined by cyclic voltammetry in sulfuric acid and by structure-sensitive underpotential deposition of Cu. Finally, in chapter 6, in order to use bead single crystal in the right ar-rangement (hanging meniscus) on DEMS, a new DEMS flow cell was manufactured and improved for that purpose. The electrooxidation of methanol proceeds via the dual pathway mechanism. The path involving the formation of soluble intermediates such as formaldehyde and formic acid is the direct pathway, while the dehydrogenation of methanol to adsorbed CO fol-lowed by its oxidation to CO2 is referred to as indirect pathway. Methylformate is one of the volatile products formed during the electrooxidation of methanol at Pt surfaces. In all previous articles it is assumed that methylformate formation results from the reaction of formic acid and the excess of methanol, i.e. the detection of methylformate is an indirect way to determine the amount of formic acid produced during the oxidation reaction. However, the probability of esterification reaction is very small because the fast diffusion of the soluble products away from DEMS cell under effect of continuous electrolyte flow. A simple kinetic study of methanol esterification and methylformate hydrolysis in acid media was performed since literature data for the rate of this esterification reaction were not available. The reaction rate constant of methylformate formation was found to be far too low (τ ≈ 40 h at 0.1 mol L-1 methanol), while the time constant of dual-thin layer flow through cell at 1.6 µL s-1 is 5 s. Methylformate therefore is directly formed during oxida-tion of methanol at the electrode surface and not in the solution phase as believed before, with a current efficiency about 1%. The suggested mechanism for methylformate formation, is the nucleophilic attack of adsorbed methanol with another methanol molecule from the solu-tion; note that the nucleophilic power of the oxygen in methanol is higher than that in the water molecule. The current efficiency with respect to CO2 and the surface coverage with methanol adsorbate (COad) have been shown to be independent of the electrolyte flow rate (from 1.6–30 µL s-1); this confirms the parallel pathway mechanism. Poisoning of the catalyst with adsorbed CO is one of the main problems in fuel cells. Ru as a catalyst with Pt promotes the electrooxidation of adsorbed CO according to bi-functional and the electronic mechanism. On such bimetallic surfaces, Ru is preferentially deposited at steps. Using deliberately stepped Pt surfaces as model electrodes, it could be shown that the complete coverage of the step sites with Ru has an inhibiting effect for methanol and ethanol oxidation due to the blockage of the most active sites, i.e. the free step sites are necessary for the first step of C1 and C2 alcohols adsorption and oxidation. For ethanol, the cleavage of C–C bond is the most difficult step in the complete oxi-dation of ethanol to CO2. Also ethanol electrooxidation at Pt surfaces occurs according to different pathways depending on the surface structure. During the electrooxidation under controlled convection, where there is no further oxidation of soluble products at the sur-face, acetaldehyde is the main product at polycrystalline Pt and Pt stepped single crystal surfaces vicinal to the (100) plane. Acetaldehyde is formed at these surfaces over the po-tential range with a current efficiency close to 100%. At Pt stepped single crystals vicinal to the (111) plane, the formation of acetic acid proceeds at lower potentials than that of acetaldehyde production due to the direct reac-tion between adsorbed ethanol and adsorbed hydroxide species. At higher potentials, due the blockage of the surface with adsorbed anions, e.g. acetate and sulfate, only the dehydrogenation of ethanol takes place at (111) planes to produce acetaldehyde. In practical applications, the formation of acetic acid should be avoided because of its inertness whereas, in principle, acetaldehyde can be oxidized to CO2. Therefore, it might be advantageous to use nanoparticles without a large degree of (111) facets as electro-catalyst in fuel cells. Another kind of model electrode would be Ru single crystals modified by Pt. How-ever, since Ru is oxidized by atmospheric oxygen very fast, the usual flame annealing method in air does not work. Attard and co-workers developed a new method for Ru quasi single crystal preparation by forced deposition of Ru multilayer on Pt single crystals followed by resistive heating in a nitrogen atmosphere. In order to characterize this Ru film on different Pt single crystals, Cu UPD is the suitable technique. For Pt(100), the charge density of Cu UPD stripping from Ru quasi-single-crystal electrode is in agreement with the charge density of Cu UPD stripping from clean Pt(100); this suggests the formation of an epitaxial Ru film on the Pt(100) electrode. For the Ru films formed on Pt(111) and Pt(110) surfaces, Cu UPD deposition is inhibited due to strongly adsorbed oxygen species. For Ru films deposited on stepped Pt single crystal vicinal to the (100) plane, it was found that: Because the characteristic Cu UPD stripping peak related to the free Pt sites is absent, the stepped Pt single crystal surfaces are completely covered with Ru film. The charge density for the peak at 185 mV related to Cu UPD stripping from (100) terrace sites decreases linearly with increasing the step density of the Pt single crystal substrate, which confirms the formation of epitaxial Ru films on the Pt surfaces. Preliminary results show that the deposition of a Pt sub-monolayer on the Ru film is pos-sible by galvanic replacement of Cu UPD. In order to be able to use bead single crystals in the hanging meniscus configuration, a new DEMS cell was constructed. The recorded cyclic voltammogrames for different bead Pt single crystals in supporting electrolyte, under hanging meniscus arrangement and at constant flow of electrolyte, are in agreement with literature profiles. This and the calibration constant and corresponding ionic signals for organic molecules oxidation sug-gest that this new cell is well suited for bead single crystals. Compared with the dual thin layer flow through cell, it has the advantage that cleanliness is easier achieved and that less expensive single crystals can be used. The K* values are reproducible and typical to that of the dual thin layer flow through cell under the same experimental conditions. For the electrooxidation of bulk methanol at polycrystalline Pt in the new flow cell, the current efficiency with respect to CO2 is high-er than that in the previous cell design. The reason might be the further oxidation of the soluble intermediates because of a less efficient electrolyte flow in the thin layer between the electrode surface and the glass capillary. Also, the ionic signal of methylformate is not detected under the same experimental conditions due to the small surface area of the working electrode resulting in a small amount of product.</p

Relaxation of ultrasonic waves in ternary TeO2-V2O5-Sm2O3 glasses

Studies were carried out on the attenuation of longitudinal ultrasonic waves in tellurite glasses containing vanadium and samarium oxides with different concentrations, using the pulse echo technique. Glass samples were prepared in the form (composition in mol%): 65 TeO2 - (35 - x) V2O5 - x Sm2O3, where x = 0.1, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mol%. The temperature dependence of the attenuation at ultrasonic frequencies of 2, 4, 6, and 10 MHz in the temperature range 150 to 280 Κ was proved. The shape of the loss peaks, i.e. the relaxation spectra, showed the presence of well-defined peaks at various temperatures depending upon glass composition and operating frequency. It was observed that these loss peaks shift to higher temperatures with increasing frequency suggesting some kind of relaxation process. Activation energies of the relaxation process, and deformation potential were calculated. Results showed that activation energies are strongly dependent on the samarium oxide content. Deformation potential is also frequency- and composition-dependent. Discussion of the results obtained in this study is reported

Application of fluorescence in situ hybridization (FISH) to the analysis of sulfate reducing bacterial community in an oily bench scale reactor

Advances in the field of genomics and meta-genomics have led to rapid and accurate strategies for the monitoring of microbial biodiversity and have revealed its potential for biotechnological applications. In this study, fluorescent in situ hybridization (FISH) as a culture-independent molecular approach using specific CY3-labelled oligonucleotide probes was used to study the dynamics of the sulfate reduction bacterial community (SRB) of the activated sludge from an oily wastewater treatment system. The relative abundance of members of the dominant bacteria in the oily water reactor was determined by FISH for 16S rRNA using EUB338 probes, for detecting general eubacteria, and SRB385 for targeting SRBs and major species of delta-proteobacteria sulfate reducers. The percentage of cells hybridizing with probe EUB338 for the dominant bacteria decreased from 25.85 to 6.25%, while with the SRB385 probe for SRB bacteria, it increased from 7.21 to 10.20% of total cells during the reactor process. These data show that SRB bacteria dominated the active microbial community in the system. It is interesting that delta-proteobacterial SRBs occupied a high percentage and took place in an oily biological system under aerobic conditions.Keywords: Sulfate reducing bacteria, fluorescence in situ hybridization, 16S rRNA oligonucleotide probes, microbial community, dynamic

Synthesis and Characterization of New Fused Heterocyclic Compounds Consisting of Benzodiazepine, Quinoxaline, Benzimidazole and Thiazole Rings

In this study, new heterocyclic compounds were synthesized through the cyclization reactions of o-phenylenediamine (1) with various organic reagents. Benzodiazepine derivatives (2-4) were obtained by reaction of (1) with ethylacetoacetate, malonic acid and acetyl acetone.Treatment of compound (1) with chloroacetamide, chloroacetic acid, p-bromophenacyl bromide and oxalic acid dihydrate afforded quinoxaline derivatives (5-8), respectively. Reaction of compound (1) with benzoic acid, piperonal, cyclohexanone and carbon disulfide resulted in the formation of compounds (9-12), respectively. Finally, reaction of compound (12) with chloroacetic acid in the presence of potassium hydroxide produced compound (13)

A New Derivatives of Benzodiazepine, Imidazole, Isatin, Maleimide, Pyrimidine and 1,2,4-Triazole: Synthesis and Characterization

The synthesis of new benzodiazepine, imidazole, isatin, maleimide, pyrimidine and 1,2,4-triazole derived from 2-amino-4-hydroxy-1,3,5-triazine, via its cyclocondensation reaction with different organic reagents, is described. FT-IR, 1H-NMR and as well as 13C-NMR spectra disclosed the structures of the precursors and heterocyclic derivatives formed

Disposition kinetics, in vitro plasma protein binding and tissue residues of tilmicosin in healthy and experimentally (CRD) infected broiler chickens

Background: Several studies assayed the pharmacokinetics of tilmicosin in broilers at a dosage of (25mg/kg.b.wt.). The aim of this study was to investigate the pharmacokinetics and tissue residues of tilmicosin following single and repeated oral administrations (25mg/kg.b.wt.) once daily for 5 consecutive days in healthy and experimentally Mycoplasma gallisepticum and E. coli infected broilers.Methods: After oral administrations of tilmicosin (25 mg/kg.b.wt.) one ml blood was collected from the right wing vein and tissues samples for determination of tilmicosin concentrations and the disposition kinetics of it by the microbiological assay method using Bacillus subtilis (ATCC 6633) as a test organism.Results: In this study, the plasma concentration time graph was characteristic of a two-compartments open model. Following a single oral administration, tilmicosin was rapidly absorbed in both healthy and experimentally infected broilers with an absorption half-life of (t0.5(ab)) 0.45 and 0.52h, maximum serum concentration (Cmax) was 1.06 and 0.69μg/ml at (tmax) about 2.56 and 2.81h, (t0.5(el)) was 21.86 and 22.91h and (MRT) was 32.15 and 33.71h, respectively; indicating the slow elimination of tilmicosin in chickens. The in-vitro protein binding was 9.72±0.83%. Serum concentrations of tilmicosin following repeated oral administration once daily for five consecutive days, almost peaked 2h after each dose with lower significant values recorded in experimentally infected broiler chickens than in healthy ones.Conclusions: This study showed that tilmicosin was cleared rapidly from tissues. The highest residue values were recorded in the lung followed by liver and kidneys while the lowest values were recorded in spleen, fat and thigh muscles. Five days for withdrawal period of tilmicosin suggested in broilers

Genotype diet interaction in Fayoumi and Rhode Island Red layers and their crosses

Fayoumi and Rhode Island Red (R.I.R.) layers and their two reciprocal crosses were distributed into 2 groups which received different diets in the laying period. The diets had the same calculated energy level and their total protein content differed by less than 1 p. 100, but one of them contained 40 p. 100 barley and the other contained none. With the barley-containing diet, feed consumption, egg mass, egg number and mean egg weight per hen were reduced, but the effects were more marked in the R.LR. line and one of the reciprocal crosses, with a significant genotype x diet interaction for egg mass, average clutch length, total feed intake and its residual component.Des poules Fayoumi et Rhode Island (R.LR.) et leurs 2 croisements réciproques ont été répartis en 2 groupes recevant un régime alimentaire différent en période de ponte. Les 2 régimes avaient la même teneur énergétique et un taux protéique différant de moins de 1 p. 100 mais l’un contenait 40 p. 100 d’orge, l’autre n’en contenait pas. En présence de la ration à base d’orge, la consommation alimentaire et la masse d’oeufs produite par poule, ainsi que le nombre et le poids moyen des oeufs, étaient abaissés, mais les effets étaient plus marqués dans la lignée R.LR. et dans l’un des croisements réciproques, avec une interaction régime x type génétique significative pour la masse d’oeufs, la longueur moyenne des séries de ponte, la consommation alimentaire totale et sa composante « résiduelle »