Thermal studies of 2-methyl-1, 2-propanediamine complexes of nickel(II) in the solid state

Summary The complexes, [NiL₂]Br₂ (L=2-methyl-1, 2-propanediamine), [NiL₂(H₂O)₂]SeO₄·2H₂O, [NiL₂]X₂·2H₂O (X=0.5SO₄ or 0.5SeO₄) and [NiL₂(NCS)₂] have been prepared and investigated thermally. Upon heating, [NiL₂]Br₂ exhibits reversible thermochromism from yellow to blue: [NiL₂]X₂·2H₂O (X=0.5SO₄ or 0.5SeO₄) undergoes dehydration accompanied with irreversible thermochromism from yellow to blue yielding [NiL₂X₂], whereas [NiL₂(H₂O)₂]SeO₄·2H₂O (blue) transforms irreversibly into [NiL₂SeO₄] (blue). [NiL₂]X₂ (X=0.5SO₄ or 0.5SeO₄), prepared from their corresponding diaquo complexes by the temperature arrest technique, shows irreversible thermochromism from yellow to blue without showing any peak in the d.t.a./d.s.c. curves. [NiL₂(NCS)₂] (blue) undergoes a thermally induced phase transition without any visual change. All the yellow species are square planar; the blue species are octahedral. These colour changes are due to configurational changes; the phase change in [NiL₂(NCS)₂] is probably due to conformational changes in the diamine chelate rings.     

Natural convection heat transfer and entropy generation in a porous rhombic enclosure: influence of non-uniform heating

Journal of Thermal Analysis and Calorimetry - In this paper, we present a numerical investigation of natural convection heat transfer and entropy generation for a rhombic enclosure with inclination...     

Synthesis of aluminium borate-boron oxide and binary titanium-boron and zirconium-boron oxides from metal alkoxides and (MeO)3B3O3 in non-aqueous solvents

The reaction of metal alkoxides M(OR)4 (M = Ti, Zr; R = organyl) with (MeO)3B3O3 (1 : 0.67) in dry propan-2-one at room temperature led to gels which when dried and calcined in air for 24 h at 500-1000 degrees C afforded bi-phased mixed-oxide materials formulated as 4TiO2 x 3B2O3 and ZrO2 x B2O3 in high ceramic yields and purity; the B2O3 phases of these materials were amorphous. The materials remained amorphous upon calcination at lower temperatures. The TiO2 phase of the 4TiO2 x 3B2O3 was crystalline when calcined at higher temperatures with either anatase (600 degrees C) or rutile (>800 degrees C) being obtained. The ZrO2 phase of the ZrO2 x B2O3 was crystalline when calcined at higher temperatures and was obtained as a metastable tetragonal phase (<700 degrees C) or baddeleylite (>800 degrees C). In a similar reaction, Al(O(i)Pr)3 (2 : 1) gave a bi-phased aluminium borate-boron oxide (Al18B4O(33).7B2O3) after calcination at >700 degrees C. The dried gels and oxide materials were all characterized by elemental analysis, TGA-DSC, and powder XRD.     

On a theorem of Graham

A strengthened form of Gurevich's conjecture was proved by R. L. Graham, which says that for any > 0 and any pair of non-parallel lines L₁ and L₂, in any partition of the plane into finitely many classes, some class contains the vertices of a triangle which has area and two sides parallel to the lines L_i. In this note, using the main idea of Graham, we present a shorter proof of the result.     

An optimal algorithm for finding depth-first spanning tree on permutation graphs

LetG be a connected graph ofn vertices. The problem of finding a depth-first spanning tree ofG is to find a connected subgraph ofG with then vertices andn − 1 edges by depth-first-search. In this paper, we propose anO(n) time algorithm to solve this problem on permutation graphs.     

“Atom” as a complex system: One- and two-dimensional cellular automata simulations

One- and two-dimensional cellular automata (CA) simulations of neutral “atoms,” viewed as “complex” distributions of electron density around a central nucleus, are performed in order to explore CA-based discretized and connectionist approaches to the synthesis and structure-dynamics problems of many-electron systems. A link between CA and the quantum mechanics of atoms is made by taking the Thomas-Fermi theory as an illustrative example. Starting from a nonstationary distribution, the stationary distribution of electron density around a nucleus arises out of a natural stability criterion described through CA rules. © 1996 John Wiley & Sons, Inc.     

Iterative Arylation of Amino Acids and Aliphatic Amines via δ‐C(sp3)−H Activation: Experimental and Computational Exploration

Directed C?H functionalization has been realized as a complementary tool to the traditional approaches for a straightforward access of non‐proteinogenic amino acids; albeit such a process is restricted mostly up to the γ‐position. In the present work, we demonstrate the diverse (hetero)arylation of amino acids and analogous aliphatic amines selectively at the remote δ‐position by tuning the reactivity controlled by ligands. An organopalladium δ‐C(sp³)?H activated intermediate has been isolated and crystallographically characterized. Mechanistic investigations carried out experimentally in conjunction with computational studies shed light on the difference in the mechanistic picture depending on the substrate structure.     

The R-γ transition prediction model

The R_t turbulence closure (Goldberg 2003 Goldberg, U. 2003. “Turbulence Closure with a Topography-parameter-free Single Equation Model.” IJCFD 17 (1): 27–38.[Web of Science ®] , [Google Scholar]) is coupled with an intermittency transport equation, γ, to enable prediction of laminar-to-turbulent flow by-pass transition. The model is not correlation-based and is completely topography-parameter-free, thus ready for use in parallelized Computational Fluid Dynamics (CFD) solvers based on unstructured book-keeping. Several examples compare the R-γ model's performance with experimental data and with predictions by the Langtry–Menter γ-Re_θ transition closure (2009) Langtry, R.B., and F.R. Menter. 2009. “Correlation-Based Transition Modeling for Unstructured Parallelized Computational Fluid Dynamics Codes.” AIAA J 47 (12): 2894–2906.[Crossref] , [Google Scholar]. Like the latter, the R-γ model is very sensitive to freestream turbulence levels, limiting its utility for engineering purposes.