Intermediate Geometry Research Articles

Exponential basis functions in solution of incompressible fluid problems with moving free surfaces

In this paper, a new simple meshless method is presented for the solution of incompressible inviscid fluid flow problems with moving boundaries. A Lagrangian formulation established on pressure, as a potential equation, is employed. In this method, the approximate solution is expressed by a linear combination of exponential basis functions (EBFs), with complex-valued exponents, satisfying the governing equation. Constant coefficients of the solution series are evaluated through point collocation on the domain boundaries via a complex discrete transformation technique. The numerical solution is performed in a time marching approach using an implicit algorithm. In each time step, the governing equation is solved at the beginning and the end of the step, with the aid of an intermediate geometry. The use of EBFs helps to find boundary velocities with high accuracy leading to a precise geometry updating. The developed Lagrangian meshless algorithm is applied to variety of linear and nonlinear benchmark problems. Non-linear sloshing fluids in rigid rectangular two-dimensional basins are particularly addressed.

Cu(II), Ni(II), Zn(II) and Fe(III) complexes containing a N 2O 2 donor ligand: Synthesis, characterization, DNA cleavage studies and crystal structure of [Cu(HL)Cl

A polydentate ligand, H 2L “[1-(5-isopropyl-2-methyl phenoxy)-3-(N-2-hydroxy benzyl-N-((pyridine-2-yl)amino) propan-2-ol]”, containing a N 2O 2 donor moiety was synthesized by refluxing 2-((5-isopropyl-2-methylphenoxy)methyl)oxirane and HBPA (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)amine). This synthesized ligand was used for the preparation of complexes with different metal ions, viz. [Cu(HL)Cl] ( 1), [Ni(HL)Cl] ( 2), [Zn(HL)Cl] ( 3) and [Fe(HL)Cl 2] ( 4). The ligand and metal complexes were characterized by 1H NMR, mass, ESI-MS, elemental analysis, IR, UV–Vis and electron paramagnetic resonance (EPR) spectroscopy. The crystal structure for one of the complexes, [Cu(HL)Cl], was solved from the X-ray crystallography data. The structure of the complex, based on the trigonality index tau, suggests an intermediate geometry between square pyramidal (sp) and trigonal bipyramidal (tb). Both the ligand and the metal complexes show oxidative cleavage of plasmid DNA (pBR322) without addition of any exogenous agent, even at a concentration of 5 μM. The binding constants for these compounds were found to be in the range 5.33–0.065 × 10 5 M −1.

General conformal transformation method based on Schwarz-Christoffel approach

A general conformal transformation method (CTM) is proposed to construct the conformal mapping between two irregular geometries. In order to find the material parameters corresponding to the conformal transformation between two irregular geometries, two polygons are utilized to approximate the two irregular geometries, and an intermediate geometry is used to connect the mapping relations between the two polygons. Based on these manipulations, the approximate material parameters for TE and TM waves are finally obtained by calculating the Schwarz-Christoffel (SC) mappings. To demonstrate the validity of the method, a phase modulator and a plane focal surface Luneburg lens are designed and simulated by the finite element method. The results show that the conformal transformation can be expanded to the cases that the transformed objects are with irregular geometries.

A new N6 hexadentate ligand and a novel heptacoordinated N6O-type Fe(III) compounds: Synthesis, characterization and structure of [Fe(dimpyen)(OH)](A)2 (A = PF6− or ClO4−)

In this contribution, we report the syntheses of a novel N6 donor set ligand, dimpyen=N1,N2-di[(1-methyl-1H-2-imidazolyl) methyl]-N1,N2-di(2-pyridilmethyl)-1,2-ethanediamine. This type of ligand was designed to modulate the properties of the metal ions bound to it. The reaction with Fe(II) gives off a new heptacoordinated iron(III) complex. We study the spectroscopic (UV–Vis), magnetic and electrochemical behavior and also made the structural determination with X-ray diffraction at 134K and a heptacoordinated N6O-type derivative of Fe(III) is reported as well. This complex crystallize as perchlorate or hexafluorophosphate and the formula of these derivatives are [Fe(dimpyen)(OH)](PF6)2 (1) and [Fe(dimpyen)(OH)](ClO4)2 (2) which both crystallize with an intermediate geometry, between pentagonal bipyramidal and monocapped octahedral. The UV–Vis spectra in CH3CN solution show a shoulder at 306nm assigned to one ligand–metal charge-transfer (LMCT) transition, in addition, a weaker and wide band assigned to the charge transfer HO–Fe transition (λmax at 404nm with an extinction coefficient of 818cm−1M−1) is also observed. The magnetic studies corroborate a high-spin iron (III) species in all the temperature range considered. Measurements of cyclic voltammetric confirm a reversible system Fe(III) species, with E1/2=−0.380V/Fc+–Fc, this low potential value explains the high stability of the Fe(III) and the easy oxidation of Fe(II) by atmospheric O2(g) reaction.

Direct Evidence for Methyl Group Coordination by Carbon-Oxygen Hydrogen Bonds in the Lysine Methyltransferase SET7/9

SET domain lysine methyltransferases (KMTs) are S-adenosylmethionine (AdoMet)-dependent enzymes that catalyze the site-specific methylation of lysyl residues in histone and non-histone proteins. Based on crystallographic and cofactor binding studies, carbon-oxygen (CH · · · O) hydrogen bonds have been proposed to coordinate the methyl groups of AdoMet and methyllysine within the SET domain active site. However, the presence of these hydrogen bonds has only been inferred due to the uncertainty of hydrogen atom positions in x-ray crystal structures. To experimentally resolve the positions of the methyl hydrogen atoms, we used NMR (1)H chemical shift coupled with quantum mechanics calculations to examine the interactions of the AdoMet methyl group in the active site of the human KMT SET7/9. Our results indicated that at least two of the three hydrogens in the AdoMet methyl group engage in CH · · · O hydrogen bonding. These findings represent direct, quantitative evidence of CH · · · O hydrogen bond formation in the SET domain active site and suggest a role for these interactions in catalysis. Furthermore, thermodynamic analysis of AdoMet binding indicated that these interactions are important for cofactor binding across SET domain enzymes.

Synthesis, crystal structure, and catalytic studies on dinuclear copper(II) mesocates

Imine based bis-bidentate ligands H2-m-xysal, (L1H2); H2-m-xysal-Cl, (L2H2); H2-m-xysal-Br, (L3H2); H2-m-xysal-OCH3, (L4H2); H2-m-xysal-(t-Bu)2, (L5H2) were synthesized and characterized. These substituted 1,3-bis(hydroxylbenzyl)-diaminoxylene dianion ligands upon treating with copper(II) acetate in 2:2 equivalent of L:M ratio, resulted in a series of binuclear [Cu2(m-xysal)2] neutral complexes 1–5. The crystal structures determined for the complexes 1 and 2 indicate a dinuclear association. The CH⋯π interaction observed between the metal-chelate ring and the hydrogens associated with m-xylene spacer moiety being first in this series of complexes, is demonstrated to stabilize the helical conformation through intramolecular self assembly process. The position of the resonance on the EPR spectra and the absence of ΔMs=±1 feature for the complexes 2, 3, and 5 obtained for room temperature solid state samples revealed that the metal centers though exist in the dinuclear unit, they are separated from each other and possess a non-interacting monomer-type metal–metal association. The Cu(II) centers in all these complexes possessing an intermediate geometry between tetrahedral and square planar, an appropriate catalytic study converting 4-nitrobenzaldehye to corresponding nitroaldol was carried out using complex 5.

Strong Geometrical Dependence of the Absorption of Light in Arrays of Semiconductor Nanowires

We demonstrate experimentally that arrays of base-tapered InP nanowires on top of an InP substrate form a broad band and omnidirectional absorbing medium. These characteristics are due to the specific geometry of the nanowires. Almost perfect absorption of light (higher than 97%) occurs in the system. We describe the strong optical absorption by finite-difference time-domain simulations and present the first study of the influence of the geometry of the nanowires on the enhancement of the optical absorption by arrays. Cylindrical nanowires present the highest absorption normalized to the volume fraction of the semiconductor. The absolute absorption in layers of conical nanowires is higher than that in cylindrical nanowires but requires a larger volume fraction of semiconducting material. Base-tapered nanowires, with a cylindrical top and a conical base, represent an intermediate geometry. These results set the basis for an optimized optical design of nanowire solar cells.

Computational Modeling of the Dehydrogenation of Methylamine

The reaction sequence early in the metabolism of methyl- amine by the dehydrogenase cofactor tryptophan tryptophyl quinone (TTQ) is investigated by a large series of density functional theory calculations. Free energy corrections are calculated at the reactant and intermediate geometries, and solvation effects are estimated by use of the semi-empirical COSMO-RS solvent model. Two competing reac- tion paths are found to have very similar reaction free energies, and the free energies of activation are found to depend heavily on adequate modeling of the solvent.

Synthesis and characterization of aluminum complexes incorporating Schiff base ligands derived from pyrrole-2-carboxaldehyde

The reaction of 1,2-Ethylendiamine-N,N′-bis(1H-pyrrol-2-yl)methylene (L1H), 1,2-benzenediamine-N,N′-bis(1Hpyrrol-2-yl)methylene (L2H) and 3,4-Dimethyl-1,2-benzenediamine-N,N′-bis(1 H-pyrrol-2-yl)methylene (L3H) with one equivalent of AlR2R′ (R = alkyl, R′ = alkyl, Cl) in toluene afforded the monometallic complexes [LAlR′] (1–12). All the complexes were characterized by analytical and spectroscopic methods. Compounds 1, 3, 4, 6, 7, and 11 were characterized bya singlecrystal X-ray structural analyses. Due to the rigidity imposed by the ligand, 1, 3 and 4, with an ethylene “backbone” connecting the two nitrogens, adopt a severely distorted tbp geometry (av. = 0.68). On the other hand 6, 7 and 11, with a phenylene backbone, adopt an intermediate tbp-sqp geometry (av. = 0.43). The study of the X-ray crystal structures suggests that, like group 13 Salen complexes, flexible bridges between the two imine groups favor a tbp geometry while more rigid backbones, like phenylene rings, lead to an intermediate sqp and tbp geometry. Based on the geometrical parameter for previously reported aluminum complexes with Schiff base ligands and those presented herein, it is possible to propose that upon the coordination geometries of five coordinated aluminum complexes are less tbp distorted ( ≈ 1) the catalytic activity on ROP increases.

Automatic setup planning system using a neutral part data exchange format

The task of automatic setup planning includes grouping machining features into setups, selecting setup datum and sequencing the setups. A feasible setup plan satisfies fundamental manufacturing constraints and assures that the part is machined to meet design specification. The objective of this work is to automatically generate and evaluate setup plans for complete machining of a given component while simultaneously considering the feature tolerance relationships, feature dependencies, general manufacturing rules, critical machine spatial constraints and fixturing feasibility. The methodology developed during the present work minimises the number of setups and machining tolerances, decides the setup sequence and generates the setups' information and the intermediate work piece geometry. The component geometry with identified machining features and their access directions is taken as input from a neutral part data exchange format STandard for the Exchange of Product data (STEP) model. The procedure for generation of setup planning results and visualisation of intermediate work piece model is presented and demonstrated with the help of case studies.

Redox-active nickel and cobalt tris(pyrazolyl)borate dithiocarbamate complexes: air-stable Co(ii) dithiocarbamates

A series of new cobalt(II) and nickel(II) tris(3,5-diphenylpyrazolyl)borate (Tp(Ph2)) dithiocarbamate complexes [Tp(Ph2)M(dtc)] (M = Co, dtc = S₂CNEt₂ 1, S₂CNBz₂ 2 and S₂CN(CH₂)₄ 3; M = Ni, dtc = S₂CNEt₂ 4, S₂CNBz₂ 5 and S₂CN(CH₂)₄ 6) have been prepared by the reaction of [Tp(Ph2)MBr] with Nadtc in CH₂Cl₂. IR spectroscopy indicates that the Tp(Ph2) ligand is κ³ coordinated while the dithiocarbamate ligand is κ² coordinated. ¹H NMR and UV-Vis spectroscopy are consistent with high spin, five-coordinate metal centres. X-ray crystallographic studies of 1, 3 and 6 confirm the κ³ coordination of the Tp(Ph2) ligand and reveal an intermediate five-coordinate geometry with an asymmetrically coordinated dithiocarbamate ligand. Electrochemical studies of 1-6 reveal a metal centred reversible one-electron oxidation to M(III). Attempted oxidation of [Tp(Ph2)Co(dtc)] with [FeCpCp(COMe)]BF₄ yields [Co(dtc)₃], Hpz(Ph2) and a further product which may be [Tp(Ph2)CoBp(Ph2)]. DFT calculations indicate that the low redox potentials in these complexes result from a strongly antibonding M-S σ* HOMO.

South Atlantic intermediate water mass geometry for the last glacial maximum from foraminiferal Cd/Ca

[1] Paleoceanographic studies using benthic foraminiferal Cd as a nutrient tracer have provided a robust means of reconstructing glacial Atlantic Ocean water mass geometry, but a paucity of data from the South Atlantic above 1200 m has limited investigation of Antarctic Intermediate Water (AAIW) configuration and formation. A new Cd depth profile from Brazil margin sediments suggests that AAIW penetrated northward at 1100 m to at least 27°S in the glacial Atlantic. It exhibited substantially reduced δ13Cas values, confirming preliminary evidence that this AAIW was unique to the glacial Atlantic and that it formed differently than today, with less atmospheric contact.

Fully substituted carbon centers by diastereoselective spirocyclization: stereoselective synthesis of (+)-lepadiformine C.

Reductive lithiation of N-Boc alpha-amino nitriles generated alpha-amino alkyllithium reagents with unexpected selectivity. The intermediate radical prefers to align with the nitrogen lone pair, and this interaction leads to an A(1,3)-strain effect that biases the conformation of the radical. In cyclohexane rings with alpha-substituents the net effect is an inversion of configuration on reductive lithiation. In the presence of a tethered electrophile the alkyllithium cyclizes to produce a spiro compound, again with inversion of configuration. The overall result is retention of configuration in the cyclization reaction. The same overall selectivity is found with alpha-oxygen alkyllithium cyclizations, but in this case both steps proceed with retention. The difference can be explained by careful consideration of the intermediate geometries. The alpha-amino spirocyclization was utilized in a concise and stereoselective synthesis of lepadiformine C.

Grammar‐based Encoding of Facades

AbstractIn this paper we propose a real‐time rendering approach for procedural cities. Our first contribution is a new lightweight grammar representation that compactly encodes facade structures and allows fast per‐pixel access. We call this grammar F‐shade. Our second contribution is a prototype rendering system that renders an urban model from the compact representation directly on the GPU. Our suggested approach explores an interesting connection from procedural modeling to real‐time rendering. Evaluating procedural descriptions at render time uses less memory than the generation of intermediate geometry. This enables us to render large urban models directly from GPU memory.

Negative tunnel magnetoresistance and differential conductance in transport through double quantum dots

Spin-dependent transport through two coupled single-level quantum dots weakly connected to ferromagnetic leads with collinear magnetizations is considered theoretically. Transport characteristics, including the current, linear and nonlinear conductance, and tunnel magnetoresistance are calculated using the real-time diagrammatic technique in the parallel, serial, and intermediate geometries. The effects due to virtual tunneling processes between the two dots via the leads, associated with off-diagonal coupling matrix elements, are also considered. Negative differential conductance and negative tunnel magnetoresistance have been found in the case of serial and intermediate geometries, while no such behavior has been observed for double quantum dots coupled in parallel. It is also shown that transport characteristics strongly depend on the magnitude of the off-diagonal coupling matrix elements.

Synthesis of a new compound based on tin(II) with intermediate SnX4E and SnX5E geometry

Synthesis of a new compound based on tin(II) with intermediate SnX4E and SnX5E geometry

Triple differential cross sections for the electron-impact ionization ofH2molecules for equal and unequal outgoing electron energies

A comprehensive theoretical and experimental investigation of the triple differential cross sections arising from the electron-impact ionization of molecular hydrogen is made, at an incident electron energy of 35.4 eV, for cases where the outgoing electrons have equal and unequal energies, and for a range of experimental geometries. Generally, good agreement is found between two theoretical approaches and experiment, with the best agreement arising for intermediate geometries with large gun angles and for the perpendicular geometry.

Plastic Buckling of Cylindrical Shells Under Transverse Loading

Thick cylindrical shells under transverse loading exhibit an elephant foot buckling mode, whereas moderately thick cylindrical shells show a diamond buckling mode. There exists some intermediate geometry at which the transition between buckling modes can take place. This behavior is significantly influenced by the radius-to-thickness ratio and the material yield strength, rather than the length-to-radius ratio and the axial force. This paper presents a critical value at which the transition of buckling modes occurs as a function of the radius-to-thickness ratio and the material yield strength. The result shows that the circumferential wave number of the diamond buckling mode increases with decreasing wall thickness. The strain concentration is also intensified for the diamond buckling modes compared with the elephant foot buckling modes.

The Effect of One Valence Electron: Contrasting (PNP)Ni(CO) with (PNP)Ni(NO) to Understand the Half-Bent NiNO Unit

Reaction of a (PNP)Ni radical with NO finishes in the time of mixing to form a 1:1 adduct with a NO stretching frequency of 1654 cm (-1). NMR data of this diamagnetic product indicate C 2 v symmetry, which is contradicted by the X-ray structure, which shows it to be nonplanar at Ni, with a geometry intermediate between planar and tetrahedral; the planar geometry is thus the transition state for fluxionality giving time-averaged C 2 v symmetry. The X-ray structure, together with DFT calculations, reveals that the "half-bent" NiNO unit and the intermediate coordination geometry result from a Ni --> NO charge transfer, which has a nonintegral value, resulting in a continuum between NO (+) (hence Ni (0)) and NO (-) (hence Ni (II)). This is related to the nonaxially symmetric character of the Ni --> NO back-donation caused by the (PNP) environment on Ni. Steric effects of ( t )Bu and even chelate constraints are ruled out as the cause of the unusual electronic and structural features.

Ab initio multireference study of Hetero-Diels-Alder reaction of buta-1,3-diene with alkyl glyoxylates

Hetero-Diels-Alder (HDA) reaction of methyl glyoxylate with buta-1,3-diene has been investigated using multireference methods (complete active space SCF and multi-reference perturbation theory) and compared with several single-reference methods (including DFT) often used in calculations of catalysed [4+2] cycloadditions. Concerted and stepwise mechanisms, found in the literature, are compared. It is shown, that the stepwise mechanism may be a result of choosing unbalanced active space. Such choice leads to very close singlet and triplet states in the intermediate geometry - an artificial effect, that disappears if properly balanced active space is used (here, we use active space of 12 orbitals and 12 electrons). Conclusions concerning the mechanism and usefulness of the applied methodology are drawn, which might be important for theoretical investigation of stereoselectivity and specificity of catalysts for the HDA reaction.