A LBM–DEM solver for fast discrete particle simulation of particle–fluid flows

The lattice Boltzmann method (LBM) for simulating fluid phases was coupled with the discrete element method (DEM) for studying solid phases to formulate a novel solver for fast discrete particle simulation (DPS) of particle–fluid flows. The fluid hydrodynamics was obtained by solving LBM equations instead of solving the Navier–Stokes equation by the finite volume method (FVM). Interparticle and particle–wall collisions were determined by DEM. The new DPS solver was validated by simulating a three-dimensional gas–solid bubbling fluidized bed. The new solver was found to yield results faster than its FVM–DEM counterpart, with the increase in the domain-averaged gas volume fraction. Additionally, the scalability of the LBM–DEM DPS solver was superior to that of the FVM–DEM DPS solver in parallel computing. Thus, the LBM–DEM DPS solver is highly suitable for use in simulating dilute and large-scale particle–fluid flows.     

Mass flow rate prediction of pressure–temperature-driven gas flows through micro/nanoscale channels

In this paper, we study mass flow rate of rarefied gas flow through micro/nanoscale channels under simultaneous thermal and pressure gradients using the direct simulation Monte Carlo (DSMC) method. We first compare our DSMC solutions for mass flow rate of pure temperature-driven flow with those of Boltzmann-Krook-Walender equation and Bhatnagar-Gross-Krook solutions. Then, we focus on pressure–temperature-driven flows. The effects of different parameters such as flow rarefaction, channel pressure ratio, wall temperature gradient and flow bulk temperature on the thermal mass flow rate of the pressure–temperature-driven flow are examined. Based on our analysis, we propose a correlated relation that expresses normalized mass flow rate increment due to thermal creep as a function of flow rarefaction, normalized wall temperature gradient and pressure ratio over a wide range of Knudsen number. We examine our predictive relation by simulation of pressure-driven flows under uniform wall heat flux (UWH) boundary condition. Walls under UWH condition have non-uniform temperature distribution, that is, thermal creep effects exist. Our investigation shows that developed analytical relation could predict mass flow rate of rarefied pressure-driven gas flows under UWH condition at early transition regime, that is, up to Knudsen numbers of 0.5.     

Statistical analysis of instantaneous turbulent heat transfer in circular pipe flows

Turbulent heat transfer in circular pipe flow with constant heat flux on the wall is investigated numerically via Large Eddy Simulations for frictional Reynolds number Re _τ  = 180 and for Prandtl numbers in the range 0.1 ≤ Pr ≤ 1.0. In our simulations we employ a second-order finite difference scheme, combined with a projection method for the pressure, on a collocated grid in cylindrical coordinates. The predicted statistical properties of the velocity and temperature fields show good agreement with available data from direct numerical simulations. Further, we study the local thermal flow structures for different Prandtl numbers. As expected, our simulations predict that by reducing the Prandtl number, the range of variations in the local heat transfer and the Nusselt number decrease. Moreover, the thermal flow structures smear in the flow and become larger in size with less sharpness, especially in the vicinity of the wall. In order to characterize the local instantaneous heat transfer, probability density functions (PDFs) for the instantaneous Nusselt number are derived for different Prandtl number. Also, it is shown that these PDFs are actually scaled by the square root of the Prandtl number, so that a single PDF can be employed for all Prandtl numbers. The curve fits of the PDFs are presented in two forms of log-normal and skewed Gaussian distributions.     

Transient characteristics of the InGaP–GaAs–InGaAs–GaAs transistor laser

Transient characteristics of the InGaP–GaAs–InGaAs (quantum well)-GaAs transistor laser are studied. Rate equations are numerically solved to obtain the response of current density and photon density. Expression of resonance frequency $f_{r}$ is obtained by solving the rate equations analytically. It has been found that the $f_{r}$ increases with decreasing spontaneous carrier lifetime and with increasing value of the bias current density.     

An Efficient Synthesis of 8-Hydroxy-6,7-dimethoxy-3-methylisocoumarin (6-O-methylreticulol)

An efficient synthesis of 8-hydroxy-6,7-dimethoxy-3-methylisocoumarin (6-O-methylreticulol), a metabolite of several fungal species possessing phosphodiesterase inhibitor, topoisomerase I inhibitor activities and antitumor efficacy, has been described. 3,4,5-Trimethoxyhomophthalic acid was refluxed with acetic anhydride in dry pyridine and the resulting 2,3,4-trimethoxy-6-(2-oxopropyl)benzoic acid was smoothly cyclodehydrated to 6,7,8-trimethoxy-3-methylisocoumarin using acetic anhydride. Regioselective demethylation of the latter yielded the 6-O-methylreticulol. __________ Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1644–1648, November, 2005.     

Synthesis of 7,8-benzo-9-aza-4-oxabicyclo[3.3.1]nonan-3-ones by sequential ‘condensation–iodolactonization’ reactions of 1,1-bis(trimethylsilyloxy)ketene acetals with isoquinolines

Functionalized 7,8-benzo-9-aza-4-oxabicyclo[3.3.1]nonan-3-ones were prepared by regio- and diastereoselective condensation of 1,1-bis(silyloxy)ketene acetals with isoquinolinium salts and subsequent regioselective and stereospecific iodolactonization.     

Cyclic voltammetric studies of the redox behavior of iron(III)-vitamin B6 complex at carbon paste electrode

Electrochemical redox behavior of Fe-vit B₆ complex is investigated in HEPES buffer in the pH range 5.1–13.1 using cyclic voltammetry. Well-defined anodic and cathodic peaks are observed in the voltammograms at pH 13.1. At pH 8.0, only one cathodic peak and at pH 5.1, only one anodic peak are found. At all the pH values, the peak potential separation is much higher than that of a reversible electrochemical reaction. The peak current ratio (i _pa/i _pc) is less than unity and decreases with the scan rate. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 6, pp. 691–697. The text was submitted by the authors in English.     

3-D finite element modeling of laser cladding by powder injection: effects of laser pulse shaping on the process

This paper introduces a 3-D transient finite element model of laser cladding by powder injection to investigate the effects of laser pulse shaping on the process. The proposed model can predict the clad geometry as a function of time and process parameters including laser pulse shaping, travel velocity, laser pulse energy, powder jet geometry, and material properties. In the proposed strategy, the interaction between powder and melt pool is assumed to be decoupled and as a result, the melt pool boundary is first obtained in the absence of powder spray. Once the melt pool boundary is obtained, it is assumed that a layer of coating material is deposited on the intersection of the melt pool and powder stream in the absence of the laser beam in which its thickness is calculated based on the powder feedrate and elapsed time. The new melt pool boundary is then calculated by thermal analysis of the deposited powder layer, substrate and laser heat flux. The process is simulated for different laser pulse frequencies and energies. The results are presented and compared with experimental data. The quality of clad bead for different parameter sets is experimentally evaluated and shown as a function of effective powder deposition density and effective energy density. The comparisons show excellent agreement between the modeling and experimental results for cases in which a high quality clad bead is expected.     

Catalytic Asymmetric Dearomatization by Visible‐Light‐Activated [2+2] Photocycloaddition

A novel method for the catalytic asymmetric dearomatization by visible‐light‐activated [2+2] photocycloaddition with benzofurans and one example of a benzothiophene is reported, thereby providing chiral tricyclic structures with up to four stereocenters including quaternary stereocenters. The benzofurans and the benzothiophene are functionalized at the 2‐position with a chelating N‐acylpyrazole moiety which permits the coordination of a visible‐light‐activatable chiral‐at‐rhodium Lewis acid catalyst. Computational molecular modeling revealed the origin of the unusual regioselectivity and identified the heteroatom in the heterocycle to be key for the regiocontrol.