Passive control of the flow around a square cylinder using porous media

The passive control of bluff body flows using porous media is investigated by means of the penalization method. This method is used to create intermediate porous media between solid obstacles and the fluid in order to modify the boundary layer behaviour. The study covers a wide range of two‐dimensional flows from low transitional flow to fully established turbulence by direct numerical simulation of incompressible Navier–Stokes equations. A parametric study is performed to illustrate the effect of the porous layer permeability and thickness on the passive control. The numerical results reveal the ability of porous media to both regularize the flow and to reduce the drag forces up to 30%. Copyright © 2004 John Wiley & Sons, Ltd.     

A rapid and precise technique for measuring delta(13)C-CO(2) and delta(18)O-CO(2) ratios at ambient CO(2) concentrations for biological applications and the influence of container type and storage time on the sample isotope ratios

A simple modification to a commercially available gas chromatograph isotope ratio mass spectrometer (GC/IRMS) allows rapid and precise determination of the stable isotopes ((13)C and (18)O) of CO(2) at ambient CO(2) concentrations. A sample loop was inserted downstream of the GC injection port and used to introduce small volumes of air samples into the GC/IRMS. This procedure does not require a cryofocusing step and significantly reduces the analysis time. The precisions for delta(13)C and delta(18)O of CO(2) at ambient concentration were +/-0.164 and +/-0.247 per thousand, respectively. This modified GC/IRMS was used to test the effects of storage on the (18)O and (13)C isotopic ratios of CO(2) at ambient concentrations in four container types. On average, the change in the (13)C-CO(2) and (18)O-CO(2) ratios of samples after one week of storage in glass vials equipped with butyl rubber stoppers (Bellco Glass Inc.) were depleted by 0.12 and by 0.20 per thousand, respectively. The (13)C ratios in aluminum canisters (Scotty II and IV, Scott Specialty Gasses) after one month of storage were depleted, on average, by 0.73 and 2.04 per thousand, respectively, while the (18)O ratios were depleted by 0.38 and 1.20 per thousand for the Scotty II and IV, respectively. After a month of storage in electropolished containers (Summa canisters, Biospheric Research Corporation), the (13)C-CO(2) and (18)O-CO(2) ratios were depleted, on average, by 0.26 and enriched by 0.30 per thousand, respectively, close to the precision of measurements. Samples were collected at a mature hardwood forest for CO(2) concentration determination and isotopic analysis. A comparison of CO(2) concentrations determined with an infrared gas analyzer and from sample voltages, determined on the GC/IRMS concurrent with the isotopic analysis, indicated that CO(2) concentrations can be determined reliably with the GC/IRMS technique. The (13)C and (18)O ratios of nighttime ecosystem-respired CO(2), determined from the intercept of Keeling plots, were -26.11 per thousand (V-PDB) and -8.81 per thousand (V-PDB-CO(2)), respectively.     

Molecular dynamics study on the thermal conductivity and mechanical properties of boron doped graphene

We investigated the effects of boron atoms substitution on the thermal conductivity and mechanical properties of single-layer graphene using the non-equilibrium molecular dynamics (NEMD) simulations. By performing the uniaxial tension simulations, we observed that substituted boron atoms slightly decrease the elastic modulus and tensile strength of graphene. On the other hand, it was observed that only 0.75% concentration of boron atoms in graphene reduces the thermal conductivity of graphene by more than 60% and leads to vanishing chirality effect.     

Effects of nitrogen-containing functional groups of reduced graphene oxide as a support for Pd in selective hydrogenation of cinnamaldehyde

Research on Chemical Intermediates - The importance of electronic and chemical properties of nitrogen-doped reduced graphene oxide (NRGO) has attracted more attention in recent years. Various...     

Microleakage and antibacterial properties of ZnO and ZnO:Ag nanopowders prepared via a sol–gel method for endodontic sealer application

A novel method, recently proved useful for the synthesis of nanoparticles, has been now used for the preparation of very stable silver iodide–trihexyl(tetradecyl)phosphonium chloride ionanofluids. Only the ionic liquid and the AgI bulk powder were needed. Synthesized nanofluids are much more stable than those obtained by simple dispersion of the nanoparticles in the base fluid. The ionanofluids were synthesized at different concentrations (up to 50 % w/w) and characterized in terms of physical, electrical, and thermal properties (density, viscosity, refractive index, electric conductivity, and specific heat capacity). A very high increase in the electric conductivity of the base ionic liquid was expected due to the high concentration of nanoparticles achieved. Nonetheless, it was not found, probably due to the reduction of ions mobility caused by the increase of the viscosity in ionanofluids with concentrations over 20 % w/w. An appropriate characterization of nanoparticles composing the nanofluids was carried out (UV–Vis absorbance, shape and size distribution). The diameter of the particles was measured and calculated by different techniques and approximations, obtaining a value of 2–4 nm. They were spherical, well-defined, and not agglomerated, with a narrow size distribution. The X-ray powder diffraction confirmed that no structural change took place in the transformation of the bulk solid to nanoparticles.     

SMFs-supported Pd nanocatalysts in selective acetylene hydrogenation:Pore structure-dependent deactivation mechanism

In the present study,CNFs,ZnO and Al2O3 were deposited on the SMFs panels to investigate the deactivation mechanism of Pd-based catalysts in selective acetylene hydrogenation reaction.The examined supports were characterized by SEM,NH3-TPD and N2adsorption-desorption isotherms to indicate their intrinsic characteristics.Furthermore,in order to understand the mechanism of deactivation,the resulted green oil was characterized using FTIR and SIM DIS.FTIR results confirmed the presence of more unsaturated constituents and then,more branched hydrocarbons formed upon the reaction over alumina-supported catalyst in comparison with the ones supported on CNFs and ZnO,which in turn,could block the pores mouths.Besides the limited hydrogen transfer,N2 adsorption-desorption isotherms results supported that the lowest pore diameters of Al2O3/SMFs close to the surface led to fast deactivation,compared with the other catalysts,especially at higher temperatures.     

SMFs-supported Pd nanocatalysts in selective acetylene hydrogenation: Pore structure-dependent deactivation mechanism

In the present study, CNFs, ZnO and Al₂O₃ were deposited on the SMFs panels to investigate the deactivation mechanism of Pd-based catalysts in selective acetylene hydrogenation reaction. The examined supports were characterized by SEM, NH₃-TPD and N₂ adsorption-desorption isotherms to indicate their intrinsic characteristics. Furthermore, in order to understand the mechanism of deactivation, the resulted green oil was characterized using FTIR and SIM DIS. FTIR results confirmed the presence of more unsaturated constituents and then, more branched hydrocarbons formed upon the reaction over alumina-supported catalyst in comparison with the ones supported on CNFs and ZnO, which in turn, could block the pores mouths. Besides the limited hydrogen transfer, N₂ adsorption-desorption isotherms results supported that the lowest pore diameters of Al₂O₃/SMFs close to the surface led to fast deactivation, compared with the other catalysts, especially at higher temperatures.     

Chemically bonded multiwalled carbon nanotubes as efficient material for solid phase extraction of some metal ions in food samples

Multiwalled carbon nanotubes chemically functionalized with 2-((3-silylpropylimino) methyl) phenol (SPIMP-MWCNT) and successfully applied for the solid phase extraction (SPE) of some metal ions in food samples. The influences of the analytical parameters including pH, amounts of solid phase, eluent conditions (type, volume and concentrations), sample volume and interference of some metal ions on the recoveries of ions Cu²⁺, Pb²⁺, Fe²⁺, Ni²⁺ and Zn²⁺ ion were investigated. The metal ions retained on SPIMP-MWCNT was eluted using 6?mL of 4?mol?L^?1 HNO₃ solution and their content was determined by flame atomic absorption spectrometry (FAAS) with recoveries more than 95% and relative standard deviations (n?=?5) between 2.4–3.4% for both reproducibility and repeatability. The detection limit of this metal ions was between 1.0–2.6?ng?mL^?1 (3S _b , n?=?10) and their preconcentration factor was 100, while their loading capacity was above 32.9?mg?g^?1 of SPIMP-MWCNT. The proposed method was successfully applied for the preconcentration and determination of analytes in different samples.