Drag Force Calculations in Polydisperse DEM Simulations with the Coarse-Grid Method: Influence of the Weighting Method and Improved Predictions Through Artificial Neural Networks

Transport in Porous Media - Several methods are employed for drag force calculations with the discrete element method depending on the desired accuracy and the number of particles involved. For...     

A highly diastereoselective five-component synthesis of 1-(alkylimino)-5,5-dicyano-3a-aryloctahydro-3-oxacyclobuta[cd]pentalene-1a,2,5a,5b(2H,3aH)-tetracarboxylates

A novel one-pot, five-component synthesis of 1-(alkylimino)-5,5-dicyano-3a-aryloctahydro-3-oxacyclobuta[cd]pentalene-1a,2,5a,5b(2H,3aH)-tetracarboxylates is described. A mixture of phenacyl bromide, malononitrile, isocyanide, and two equivalents of a dialkyl acetylenedicarboxylate undergoes a novel 1:1:1:2 addition reaction at ambient temperature in absolute ethanol to produce diastereoselectively the title compounds in good yields.     

Elastic breakup in uniaxial extension of entangled polymer melts

Five entangled melts, with the number of entanglements per chain ranging from 25 to 160, have been studied to illustrate how cohesive strength can be overcome in either continuous or interrupted extension (i.e., during or after uniaxial stretching). The internal elastic stress due to chain deformation from imposed strain appears to be the cause of the observed yielding behavior that reveals scaling laws. The visual signature of the elastic breakup is the occurrence of nonuniform extension. The yield phenomena may be understood at a force level.     

A high-order Monte Carlo algorithm for the direct simulation of Boltzmann equation

A high-order algorithm of the direct simulation Monte Carlo (DSMC) method, H-DSMC, has been developed to simulate rarefied flow regimes. The mth order Taylor series expansion has been employed to obtain a more generalized form of the time discretization for the collision part of Boltzmann equation. In the purposed algorithm, the higher order collision terms are introduced as well as higher order terms in the time step of the probabilistic coefficients. These newly implemented higher order terms improve the accuracy and efficiency of the solution and enhance the convergence rate quite significantly. Comparison between results of the classic DSMC method and the H-DSMC method shows the promising performance of the introduced technique.     

Numerical simulation of critical heat flux in forced boiling of a flow in an inclined tube with different angles

Journal of Thermal Analysis and Calorimetry - In this paper, the effect of changing tube slope on the critical heat flux for the evaporation of upward saturated flow of a liquid (water) in a...     

Nickel aluminate oxides/hydroxides by pulsed laser ablation of NiAl2O4 powder in water

Submicron-sized NiAl_2+X O₄ fragments and nanocondensates of Ni-doped γ-Al₂O₃, Al-doped NiO and β-Ni(OH)₂ were synthesized simultaneously by pulsed laser ablation of NiAl₂O₄ powder in water and characterized using X-ray/electron diffraction and optical spectroscopy. The NiAl_2+X O₄ is Al-enriched spinel with dislocations and subgrains. The Ni-doped γ-Al₂O₃ spinel has paracrystalline distribution (i.e., with fair constant longitudinal spacing, but variable relative lateral translations) of defect clusters and intimate intergrowth of θ-Al₂O₃ and 2x( \( \overline{1} \) 3 \( \overline{1} \) ) commensurate superstructure. The Al-doped NiO has perfect cubo-octahedron shape and as small as 5 nm in size. The β-Ni(OH)₂ and 1-D turbostratic hydroxide lamellae occurred as a matrix of these oxide nanoparticles. The colloidal suspension containing the composite phases has a minimum band gap of 5.3 eV for potential photocatalytic applications.     

Surface modification, martensitic transformation, and optical properties of hydrogenated ZrO2 nanocondensates via pulsed laser ablation in water

Pulsed laser ablation on Zr plate in water under Q-switch mode and a fluence of 700 and 800 mJ/pulse for a rather high power density of 1.5 and 1.7 × 10¹¹ W/cm², respectively, was employed to fabricate hydrogenated ZrO₂ nanocondensates. X-ray diffraction and transmission electron microscopic observations indicated such nanocondensates are full of {111} and {100} facets and predominantly in monoclinic (m-) rather than cubic- and/or tetragonal (t-) crystal symmetry in particular when fabricated at 700 mJ/pulse. The hydrogenated ZrO₂ nanocondensates underwent martensitic t ?? m transformation at a rather small critical size (ca. 20 nm) due to H⁺ signature and hence oxygen vacancy deficiency in the lattice. The resultant m-phase was free of twin and fault due to site saturation and rather limited growth of the nanosized particles. Spectroscopic characterizations indicated that the nanocondensates have a significant internal compressive stress, (H⁺, Zr²⁺, Zr³⁺) co-signature and hence a smaller band gap of 5.2?C5.3 eV for potential applications in UV region.     

Crystallographic shear of polymorphic TiO<Subscript>2</Subscript> nanocondensates with enhanced Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> dissolution via pulsed laser ablation

TiO₂ nanoparticles with enhanced solid solution of Cr up to 16 wt% in polymorphs of rutile, anatase, brookite, α-PbO₂-type, and occasionally baddeleyite-type were synthesized via pulse laser ablation on ceramic TiO₂ target dissolved with Cr₂O₃ or clamped Cr/Ti plates in air. Analytical electron microscopic observations indicated these nanocondensates have prevalent crystallographic shear (CS) along specific planes to form superstructures. The rutile type typically shows (100) and (010) CS besides the conventional ones rotating about the [111] zone axis as reported for ambient samples. The CS planes are parallel to (001) for anatase, (001) and ([`1] \overline{1} 10) for brookite, whereas (001) and {1[`3] \overline{3} 1} for the α-PbO₂-type TiO₂ with varied extent of Cr dissolution. Surface modification, as a result of Cr dissolution and/or internal stress, was observed for all the polymorphs.