Possibility for mode-locked operation of a femtosecond UV storage ring free-electron laser using a low-loss Fabry–Perot resonator

A storage ring free-electron laser (SR-FEL) is inherently a self-mode-locked optical system. The gain broadening due to electron energy spread affects the small signal gain in order to determine the output coupling. Here, the dependence of the small signal gain, the optimum output coupling, and pulse duration on both electron energy spread and loss of a Fabry–Perot resonator in UV SR-FEL were investigated. It was shown that the output coupling strongly affects the mode-locked pulse duration and the present picosecond pulses can be shortened to femtosecond ones using a proper low-loss resonator.     

The effect of carrier gas flow rate on the growth of MoS<Subscript>2</Subscript> nanoflakes prepared by thermal chemical vapor deposition

Molybdenum disulfide nanoflakes (MoS₂) are superior material for their semiconducting properties. For bulk and monolayer MoS₂ the band gap changes from indirect-to-direct, respectively. So, it exhibits promising prospects in the applications of optoelectronics and valleytronics, such as solar cells, transistors, photodetectors, etc. In this research, the influence of different Ar flow rates as the carrier gas, is investigated for growing MoS₂ nanoflakes on silicon substrates using one-step thermal chemical vapor deposition by simultaneously evaporating of solid sources like sulfur and molybdenum trioxide powders. The structural and optical properties of the obtained nanoflakes are assessed by using X-ray diffraction pattern, scanning electron microscopy, UV–visible absorption, photoluminescence and Raman spectroscopy. It is shown that, Ar gas flow rate is strongly affects on the final products as few-layer MoS₂ structures. Moreover, the abundance of MoS₂ in comparison to MoO₂ and MoO₃ structures, in the obtained nanoflakes, is influenced by the Ar flow rate.     

Catalytic Oxidation of Indigo Carmine in the Presence of Silver Nanoparticles: Application to Groundwater Analysis

The oxidation of indigo carmine by potassium hexacyanoferrate(III) is catalyzed by trace of silver nanoparticle (AgNP). The reaction is followed UV‐Vis absorption spectrophotometrically by measuring the change in the absorption spectra (λ_max 612 nm). The catalytic oxidation reaction is used for the quantification of indigo carmine. The calibration graph was linear in the concentration range 50 nM—1.8 μM of indigo carmine. The variables affecting the method have been optimized. The method is applied to the determination of indigo carmine in groundwater samples with the satisfactory results.     

Effect of mass transfer limitations on catalyst performance during reduction and carburization of iron based Fischer-Tropsch synthesis catalysts

Existence of intraparticle mass transfer limitations under typical Fischer-Tropsch synthesis has been reported previously,but there is no suitable study on the existence of intraparticle diffusion limitations under pretreatment steps (reduction and activation) and their effect on catalytic performance for iron based catalysts.In this study,Fe-Cu-La-SiO2 catalysts were prepared by co-precipitation method.To investigate the intraparticle mass transfer limitation under reduction,activation and reaction steps,and its effect on catalytic performance,catalyst pellets with different sizes of 6,3,1 and 0.5 mm have been prepared.All catalysts were calcined,pretreated and tested under similar conditions.The catalysts were activated in hydrogen (5%H2in N2) at 450℃ for 3 h and exposed to syngas (H2/CO=1) at 270℃ and atmospheric pressure for 40 h.Afterwards,FTS reaction tests were performed for approximately 120 h to reach steady state conditions at 290℃,17 bar and a feed flow (syngas H2/CO=1) rate of 3 L/h (STP).Using small pellets resulted in higher CO conversion,FT reaction rate and C5+ productivity as compared with larger pellets.The small pellets reached steady state conditions just 20 h after starting the reaction.Whereas for larger pellets,CO conversion,FT reaction rate and C5+ productivity increased gradually,and reached steady state and maximum values after 120 h of operation.The results illustrate that mass transfer limitations exist not only for FTS reaction but also for the reduction and carburization steps which lead to various phase formation through catalyst activation.Also the results indicate that some effects of mass transfer limitations in activation step,can be compensated in the reaction step.The results can be used for better design of iron based catalyst to improve the process economy.     

Mono‐ and binuclear nickel catalysts for 1‐hexene polymerization

Polymerization of 1‐hexene was carried out using a mononuclear (MN) catalyst and two binuclear (BN₁ and BN₂) α‐diimine Ni‐based catalysts synthesized under controlled conditions. Ethylaluminium sesquichloride (EASC) was used as an efficient activator under various polymerization conditions. The highly active BN₂ catalyst (2372 g poly(1‐hexene) (PH) mmol^?1 cat) in comparison to BN₁ (920 g PH mmol^?1 cat) and the MN catalyst (819 g PH mmol^?1 cat) resulted in the highest viscosity‐average molecular weight (M_v) of polymer. Moreover, the molecular weight distribution (MWD) of PH obtained using BN₂/EASC was slightly broader than those obtained using BN₁ and MN (2.46 for BN₂ versus 2.30 and 1.96 for BN₁ and MN, respectively). These results, along with the highest extent of chain walking for BN₂, were attributed to steric, nuclearity and electronic effects of the catalyst structures which could control the catalyst behaviour. Differential scanning calorimetry showed that the glass transition temperatures of polymers were in the range ? 58 to ?81 °C, and broad melting peaks below and above 0 °C were also observed. In addition, longer α‐olefins (1‐octene and 1‐decene) were polymerized and characterized, for which higher yield, conversion and molecular weight were observed with a narrower MWD. The polymerization parameters such as polymerization time and polymerization temperature showed a significant influence on the productivity of the catalysts and M_v of samples.     

Vortex penalization method for bluff body flows

In this work, a penalization method is discussed in the context of vortex methods for incompressible flows around complex geometries. In particular, we illustrate the method in two cases: the flow around a rotating blade for Reynolds numbers 1000 and 10,000 and the flow past a semi‐circular body consisting of a porous layer surrounding a rigid body at Reynolds numbers 550 and 3000. In the latter example, the results are interpreted in terms of control strategy. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of ceria addition and pre-calcination temperature on performance of cobalt catalysts for Fischer-Tropsch synthesis

Summary The effect of ceria addition on the performance of 10 wt.% Co catalysts supported on SiO2 and Al2O3 for Fischer-Tropsch synthesis has been investigated. The catalysts were prepared by impregnation method and characterized by X-ray diffraction technique. The catalytic tests (P = 1 atm, T = 488 K, H2/CO = 2, GHSV=1800 h-1) indicate that with addition of ceria, significant changes in CO conversion and hydrocarbon selectivities are observed. Also, the experiments show that the performance of 10 wt.% Co-CeO2/Al2O3 depends on the ceria concentration as well as on the pre-calcination temperature.     

New olefin block copolymers of ethylene/1-hexene synthesized by iron and zirconocene catalysts in the presence of ZnEt2

Journal of Thermal Analysis and Calorimetry - Development of olefin block copolymers (OBCs) based on new catalytic systems is challenging. We evaluate the performance of rac-ethylenebis(1-η...