Planar Structures (planar + structure)

Distribution by Scientific Domains
Distribution within Engineering

Selected Abstracts

First-Row Transition Metal Bis(amidinate) Complexes; Planar Four-Coordination of FeII Enforced by Sterically Demanding Aryl Substituents

Christian A. Nijhuis
Abstract The sterically hindered benzamidinate ligand [PhC(NAr)2], (Ar = 2,6- iPr2C6H3) has been employed to prepare bis(amidinate) complexes [{PhC(NAr)2}2M] of the divalent first-row transition metals Cr,Ni (1,5). For Cr (planar), Mn and Co (tetrahedral) the observed structures follow the electronic preference for the metal ion in its highest spin multiplicity, as determined by DFT calculations. Remarkably, the Fe derivative adopts a distorted planar structure while retaining the high-spin (S = 2) configuration. This rare combination is due to reduced interligand steric interactions in the planar vs. the tetrahedral structure, combined with a relatively small electronic preference of FeII for the tetrahedral environment. Thus, the simple bidentate ligand N,N' -diarylbenzamidinate provides a convenient means to make this unusual species accessible for further study. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Stereostructural Determination by a Synthetic and NMR-Based Approach of Three Oxazinins Isolated from Adriatic Mussels

Patrizia Ciminiello
Abstract Two oxazinins, namely oxazinin-5 and -6, along with a related linear precursor (preoxazinin-7) were isolated from toxic mussels collected along the Northern Adriatic coasts in October 2005. Determination of the planar structure of these novel compounds was achieved through extensive NMR spectroscopic analysis, whereas a synthetic approach was crucial for their absolute stereochemical elucidation.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Conjugated Polymer Based on Polycyclic Aromatics for Bulk Heterojunction Organic Solar Cells: A Case Study of Quadrathienonaphthalene Polymers with 2% Efficiency

Shengqiang Xiao
Abstract Polycyclic aromatics offer great flexibility in tuning the energy levels and bandgaps of resulting conjugated polymers. These features have been exploited in the recent examples of benzo[2,1- b:3,4- b']dithiophene (BDT)-based polymers for bulk heterojunction (BHJ) photovoltaics (ACS Appl. Mater. Interfaces2009, 1, 1613). Taking one step further, a simple oxidative photocyclization is used here to convert the BDT with two pendent thiophene units into an enlarged planar polycyclic aromatic ring,quadrathienonaphthalene (QTN). The reduced steric hindrance and more planar structure promotes the intermolecular interaction of QTN- based polymers, leading to increased hole mobility in related polymers. As-synthesized homopolymer (HMPQTN) and donor,acceptor polymer (PQTN - BT) maintain a low highest occupied molecular orbital (HOMO) energy level, ascribable to the polycyclic aromatic (QTN) moiety, which leads to a good open-circuit voltage in BHJ devices of these polymers blended with PCBM ([6,6]-phenyl-C61 -butyric acid methyl ester; HMPQTN: 0.76,V, PQTN - BT: 0.72,V). The donor,acceptor polymer (PQTN - BT) has a smaller optical bandgap (1.6,eV) than that of HMPQTN (2.0,eV), which explains its current (5.69,mA,cm,2) being slightly higher than that of HMPQTN (5.02,mA,cm,2). Overall efficiencies over 2% are achieved for BHJ devices fabricated from either polymer with PCBM as the acceptor. [source]

Miniaturized antenna using half-mode substrate integrated waveguide structure

Cuilin Zhong
Abstract An X-band miniaturized antenna which uses half-mode substrate integrated waveguide structure is designed. We analyzed the electromagnetic field using the cavity model and the electromotive force method. The input impedance, simulated and experimental results of return loss, resonant frequency, and radiation patterns are presented. Its performances are as same as those of the corresponding microstrip antenna, but its size is half of the microstrip antenna. This planar structure can be integrated on the same substrate with other components such as filter and amplifier, and it can also be used to easily form antenna arrays. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3214,3218, 2008; Published online in Wiley InterScience ( DOI 10.1002/mop.23911 [source]

A compact dual-port, dual-band planar microstrip antenna

A. Gadzina
Abstract A compact dual-band, dual-port planar microstrip antenna is described. Its main properties are wide bandwidth, high and constant gain at both frequency bands, and a simple planar structure, which results from etching all patches onto a common substrate. As an example of application an antenna for GSM900/1800 has been realized and described with measured data. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 302,305, 2002; Published online in Wiley InterScience ( DOI 10.1002/mop.10443 [source]

8-Hydroxyquinaldinic acid and its nickel(II) complex

Nobuo Okabe
The molecules of 8-hydroxy­quinolinium-2-carboxyl­ate, C10H7NO3, have a planar structure, in which the carboxyl group is ionized and the ring N atom is protonated. The derived nickel(II) complex, bis(8-hydroxy­quinoline-2-carboxyl­ato-,3O2,N,O8)­nickel(II) trihydrate, [Ni(C10H6NO3)2]·3H2O, contains an octahedral central NiII ion coordinated by the hydroxyl O atom, the ring N atom and the carboxyl­ate O atom of each of the two tridentate ligands, with a perpendicular orientation of the quinoline rings. [source]

The effect of the side chain length of Asp and Glu on coordination structure of Cu2+ in a de novo designed protein

BIOPOLYMERS, Issue 11 2009
Daigo Shiga
Abstract Metal ions in proteins are important not only for the formation of the proper structures but also for various biological activities. For biological functions such as hydrolysis and oxidation, metal ions often adopt unusual coordination structures. We constructed a stable scaffold for metal binding to create distorted metal coordination structures. A stable four stranded ,-helical coiled-coil structure was used as the scaffold, and the metal binding site was in the cavity created at the center of the structure. Two His residues and one Asp or Glu residue were used to coordinate the metal ions, AM2D and AM2E, respectively. Cu2+ bound to AM2D with an equatorial planar coordination structure with two His, one Asp, and H2O as detected by electron spin resonance and UV spectral analyzes. On the other hand, Cu2+ had a slightly distorted square planar structure when it bound two His and Glu in AM2E, due to the longer side-chain of the Glu residue as compared to the Asp residue. Computational analysis also supported the distorted coordination structure of Cu2+ in AM2E. This construct should be useful to create various coordinations of metal ions for catalytic functions. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 907,916, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at [source]

Electronic Structure and Bonding in Neutral and Dianionic Boradiphospholes: R,BC2P2R2 (R=H, tBu, R,=H, Ph)

Dandamudi Usharani
Abstract Classical and non-classical isomers of both neutral and dianionic BC2P2H3 species, which are isolobal to Cp+ and Cp,, are studied at both B3LYP/6-311++G(d,p) and G3B3 levels of theory. The global minimum structure given by B3LYP/6-311++G(d,p) for BC2P2H3 is based on a vinylcyclopropenyl-type structure, whereas BC2P2H32, has a planar aromatic cyclopentadienyl-ion-like structure. However, at the G3B3 level, there are three low-energy isomers for BC2P2H3: 1),tricyclopentane, 2),nido and 3),vinylcyclopropenyl-type structures, all within 1.7,kcal,mol,1 of each other. On the contrary, for the dianionic species the cyclic planar structure is still the minimum. In comparison to the isolobal Cp+ and HnCnP5,n+ isomers, BC2P2H3 shows a competition between ,-delocalised vinylcyclopropenyl- and cluster-type structures (nido and tricyclopentane). Substitution of H on C by tBu, and H on B by Ph, in BC2P2H3 increases the energy difference between the low-lying isomers, giving the lowest energy structure as a tricyclopentane type. Similar substitution in BC2P2H32, merely favours different positional isomers of the cyclic planar geometry, as observed in 1),isoelectronic neutral heterodiphospholes EtBu2C2P2 (E=S, Se, Te), 2),monoanionic heterophospholyl rings EtBu2C2P2 (E=P,, As,, Sb,) and 3),polyphospholyl rings anions tBu5,nCnP5,n (n=0,5). The principal factors that affect the stability of three-, four-, and five-membered ring and acyclic geometrical and positional isomers of neutral and dianionic BC2P2H3 isomers appear to be: 1),relative bond strengths, 2),availability of electrons for the empty 2p boron orbital and 3),steric effects of the tBu groups in the HBC2P2tBu2 systems. [source]

Earthquake behavior of structures with copper energy dissipators

Juan C. De la Llera
Abstract The earthquake behavior of structures with supplemental copper dampers is evaluated in this study. The investigation is divided into two parts: (i) an experimental work with seven pairs of hourglass copper dampers of different aspect ratios and side profiles; and (ii) a parametric study of 6-, 12-, and 25-story planar structures with elastic as well as inelastic behavior in the primary structure and copper dampers. The copper used in this study is electrolytic tough pitch (ETP) copper C11000; probably the most commonly used of all coppers; ductile, with a low-yield, and highly resistant to corrosion. Experimental results demonstrate that all copper plates reached stable angular distortions of the order of ,=25%, which implies transverse distortions in the devices larger than 40mm. The behavior of the devices is highly dependent on the aspect ratio of the plate, h/t, and a recommendation is made to use plates in the range 11 h/t,18. Plates beyond this range exhibit either large stress and strain concentrations in the neck of the device or a strong influence of axial deformations in their cyclic behavior. The inelastic earthquake response of structures with such devices shows that drift reduction factors of the order of 30 to 40% can be achieved with reasonably economic designs. It is also shown that the efficiency of these devices depends on the soil conditions and flexibility of the primary structure. Finally, it is concluded that supplemental copper dampers are a good alternative for drift reduction in a wide range of structural layouts, ranging from coupled shear-wall systems to moment-resisting frames, and for impulsive as well as non-impulsive ground motions. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Syntheses of optically active 2-(2-benzothiazolylimino)-heterazolidines

Alejandro Cruz
The syntheses of compounds 4R, 5R-2-[2-benzothiazolylimino]-3-hydro-4-methyl-5-phenylthiazolidine (5a), 4S,5S-2-[2-benzothiazolylimino]-3,4-dimethyl-5-phenylthiazolidine (5b), 4R,5S-[2-benzothiazolylimino]-3-hydro-4-methyl-5-phenyloxazolidine (5c), 4R,5S-2-[2-benzothiazolyl-imino]-3,4-dimethyl-5-phenyloxazolidine (5d), and 4R,5S-2-[2-benzothiazolylimino]-1,3,4-trimethyl-5-phenylimidazolidine (5e) are reported. The stereochemistry of the reaction products and the X-ray diffraction analyses of compounds 5a,d are discussed. Compounds 5a,d present planar structures. We have found short distances between the thiazolidine S1 atom and the benzothiazole N9 atom for 5a and 5b (2.782 and 2.824 Ĺ, respectively) and the distance between the oxazolidine O1 and the benzothiazole S7 for 5d (2.721 Ĺ). These distances are shorter than the sum of the van der Waals radii. These distances, together with the coplanarity of the heterocycles, seem to indicate the existence of a weak coordination bonding from sp2 oxygen or nitrogen atoms towards the sulfur atom. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:586,593, 2001 [source]

Time-domain sensitivity analysis of planar structures using first-order one-way wave-equation boundaries

Peter A. W. Basl
Abstract An efficient adjoint variable method technique is developed for time-domain sensitivity analysis of planar structures with transmission-line modeling complemented by a first-order one-way wave-equation absorbing boundaries. A backward-running adjoint simulation is derived and solved. The validity of the technique is illustrated through three microstrip circuits. The examples demonstrate the efficiency and accuracy of the technique in comparison with the classical finite-difference approaches to the estimation of the response sensitivities. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Adaptive integral method combined with the loose GMRES algorithm for planar structures analysis

W. Zhuang
Abstract In this article, the adaptive integral method (AIM) is used to analyze large-scale planar structures. Discretization of the corresponding integral equations by method of moment (MoM) with Rao-Wilton-Glisson (RWG) basis functions can model arbitrarily shaped planar structures, but usually leads to a fully populated matrix. AIM could map these basis functions onto a rectangular grid, where the Toeplitz property of the Green's function would be utilized, which enables the calculation of the matrix-vector multiplication by use of the fast Fourier transform (FFT) technique. It reduces the memory requirement from O(N2) to O(N) and the operation complexity from O(N2) to O(N log N), where N is the number of unknowns. The resultant equations are then solved by the loose generalized minimal residual method (LGMRES) to accelerate iteration, which converges much faster than the conventional conjugate gradient method (CG). Furthermore, several preconditioning techniques are employed to enhance the computational efficiency of the LGMRES. Some typical microstrip circuits and microstrip antenna array are analyzed and numerical results show that the preconditioned LGMRES can converge much faster than conventional LGMRES. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009. [source]

On the extension of commercial planar circuit CAD packages to the analysis of two-port waveguide components

Marco Farina
Abstract We introduce a simple algorithm that enables several commercial codes, based on the method of moments (MoM) and developed for the analysis of planar structures, to address the analysis of a class of two-port waveguide components. Its key step is a numerical calibration that can be easily automated. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 113,117, 2003. [source]

FWCIP method for PGB planar structures

T. P. Vuong
Abstract The fast wave concept iterative process (FWCIP) and the boundary element method (BEM) are combined to evaluate the characteristic impedance of a microstrip filter, which is composed of (8×8) metallic via holes array. Simulations, measurements, and previous publications are in good agreement. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 236,246, 2002. [source]

Underwater SLAM in man-made structured environments

David Ribas
This paper describes a navigation system for autonomous underwater vehicles (AUVs) in partially structured environments, such as dams, harbors, marinas, and marine platforms. A mechanically scanned imaging sonar is used to obtain information about the location of vertical planar structures present in such environments. A robust voting algorithm has been developed to extract line features, together with their uncertainty, from the continuous sonar data flow. The obtained information is incorporated into a feature-based simultaneous localization and mapping (SLAM) algorithm running an extended Kalman filter. Simultaneously, the AUV's position estimate is provided to the feature extraction algorithm to correct the distortions that the vehicle motion produces in the acoustic images. Moreover, a procedure to build and maintain a sequence of local maps and to posteriorly recover the full global map has been adapted for the application presented. Experiments carried out in a marina located in the Costa Brava (Spain) with the Ictineu AUV show the viability of the proposed approach. © 2008 Wiley Periodicals, Inc. [source]

Preparation of halogenated derivatives of thiazolo[5,4- d]thiazole via direct electrophilic aromatic substitution

Vladimir Benin
Chlorination and bromination reactions of thiazolo[5,4- d]thiazole led to the generation of its mono- and dihalogenated derivatives. These are the first instances of successful direct electrophilic aromatic substitution in the thiazolo[5,4- d]thiazole ring system. X-ray analysis demonstrates that both 2-bromothiazolo[5,4- d]-thiazole and 2,5-dibromothiazolo[5,4- d]thiazole are planar structures, with strongly manifested ,-stacking in the solid state. Theoretical analysis of the pyridine-catalyzed halogenation (MP2/6-31+G(d) and B3LYP/6-31+G(d) calculations) reveals that introduction of one halogen actually leads to a slightly enhanced reactivity towards further halogenation. Several halogenation mechanisms have been investigated: 1) The direct C-halogenation with N-halopyridine as electrophile; 2) C-halogenation via intermediate N-halogenation, and 3) C-halogenation following an addition - elimination pathway, with intermediate formation of a cyclic halonium ion. The theoretical studies suggest that the direct C-halogenation is the favored mechanism. [source]

Inverted metamorphic sequence in the Sikkim Himalayas: crystallization history, P,T gradient and implications

S. Dasgupta
Abstract The metapelitic rocks of the Sikkim Himalayas show an inverted metamorphic sequence (IMS) of the complete Barrovian zones from chlorite to sillimanite + K-feldspar, with the higher grade rocks appearing at progressively higher structural levels. Within the IMS, four groups of major planar structures, S1, S2 and S3 were recognised. The S2 structures are pervasive throughout the Barrovian sequence, and are sub-parallel to the metamorphic isograds. The mineral growth in all zones is dominantly syn-S2. The disposition of the metamorphic zones and structural features show that the zones were folded as a northerly plunging antiform. Significant bulk compositional variation, with consequent changes of mineralogy, occurs even at the scale of a thin section in some garnet zone rocks. The results of detailed petrographic and thermobarometric studies of the metapelites along a roughly E,W transect show progressive increase of both pressure and temperature with increasing structural levels in the entire IMS. This is contrary to all models that call for thermal inversion as a possible reason for the origin of the IMS. Also, the observation of the temporal relation between crystallization and S2 structures is problematic for models of post-/late-metamorphic tectonic inversion by recumbent folding or thrusting. A successful model of the IMS should explain the petrological coherence of the Barrovian zones and the close relationship of crystallization in each zone with S2 planar structures along with the observed trend(s) of P,T variation in Sikkim and in other sections. A discussion is presented of some of the available models that, with some modifications, seem to be capable of explaining these observations. [source]

Substrate-integrated-waveguide feed network for microstrip antenna arrays

Mohsen Yousefbeigi
Abstract In this article, a low-loss parallel-series feed structure using substrate integrated waveguide (SIW) technology for a single-layer microstrip antenna array is presented. In addition to reduction of feed radiation, the feed network benefits from typical advantages of planar structures such as compactness, low cost, integrability, and mass-producibility. A 2 × 8 microstrip antenna array of size 109 mm × 34 mm fed by the proposed SIW feed system is designed and fabricated. Measurements on the fabricated array verify a minimum gain of 17.5 dBi in the frequency range of 17.4 to 18 GHz. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1619,1621, 2009; Published online in Wiley InterScience ( DOI 10.1002/mop.24412 [source]

Atomic study of molecular wires composed of thiophene oligomers

P. Bai
Abstract In this paper, we study the electron conductance of thiophene oligomers based molecular wires through atomic structures using the first principles method based on density functional theory and nonequilibrium Green's function. The molecular wires are built by sandwiching various thiophene oligomers between two metal electrodes via terminal groups at atomic levels. The effects of alkyl substituents on the thiophene oligomers are modelled by varying inter-ring angles of the oligomers. Thiophene dimers, tetramers and hexamers are used to studied thiophene size effects. The projected orbitals, energy gaps, transmission functions and current,voltage characteristics of the molecular wires are calculated and analyzed. Results show that the molecular wires with the planar structures of thiophene oligomers have larger electron transmission functions, hence better electronic conductance than those with twist structures. The conductance of molecular wires decreases when the chain length of the thiophene oligomer increases. The results can provide guidance for design of thiophene molecular electronic wires and other devices. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

X-ray and neutron structure of 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol (P326); some pitfalls of automatic data collection

Rex A. Palmer
The structure of the crown ether 1,8-(3,6,9-trioxaundecane-1,11-diyldioxy)-9,10-dihydro-10,10-dimethylanthracene-9-ol, C24H30O6·H2O (1), code name P326, the parent compound for a series of derivatives, has been determined by both X-ray diffraction at room temperature and neutron diffraction at very low temperature. The unit cells are very similar at both temperatures and in both cases the crystals exhibit P21 symmetry with Z = 4 (two molecules, A and B, respectively, per asymmetric unit) and pseudosymmetry P21/c. The higher symmetry is broken mainly by the two independent water molecules in the unit cell, some reflections which would be absent in P21/c having strong intensities in both the X-ray and neutron data. In both molecules A and B hydrogen bonds involving the water molecule stabilize the macrocyclic ring structure, one involving the macrocyclic O(9) as a donor. Close contacts between the water and macrocyclic O atoms in each molecule also suggest the presence of two bifurcated hydrogen bonds, involving water HW2 to both O(16) and O(18), and water HW1 to both O(18) and O(20), respectively, with considerable variation in the geometry being present. Both molecules A and B exhibit very close pseudosymmetry across a plane perpendicular to the molecular plane and through atoms C(9) and O(18), and in addition are predominantly planar structures. The X-ray analysis failed to reveal one H atom per water molecule, each being subsequently included after location and refinement in the neutron analysis. [source]

2,4-Di­methoxy­benzoic acid and 2,5-di­methoxy­benzoic acid

Dewey H. Barich
The title compounds (both C9H10O4) have nearly planar structures, and the methyl and/or carboxylic acid groups lie out of the molecular plane, as dictated by steric interactions. 2,5-Di­methoxy­benzoic acid (2,5-DMBA) forms an unusual intramolecular hydrogen bond between the carboxylic acid group and the O atom of the methoxy group in the 2-position [O,O,=,2.547,(2),Ĺ and O,H,O,=,154,(3)°]. 2,4-DMBA forms a typical hydrogen-bond dimer with a neighboring mol­ecule. [source]

Puckering transitions of pseudoproline residues

BIOPOLYMERS, Issue 6 2009
Young Kee Kang
Abstract The puckering transitions of pesudoprolines such as oxazolidine and thiazolidine residues (Oxa and Thz dipeptides) with trans and cis prolyl peptide bonds were explored by optimizations along the endocyclic torsion angle ,1 using quantum-chemical methods in the gas phase and in water. The overall shapes of the potential energy surfaces for Oxa and Thz dipeptides in the gas phase and in water are similar to those for the Pro dipeptide, although there are some differences in relative stabilities of local minima and in barriers to puckering transition. On the whole, the barriers to puckering transition for Oxa and Thz dipeptides are computed to be 0.8,3.2 kcal/mol at the B3LYP/6-311++G(d,p) level in the gas phase and in water, which are lower by 0.5,1.9 kcal/mol than those for the Pro dipeptide. The n , ,* interactions for the delocalization of the lone pair of the prolyl amide nitrogen into the antibonding orbitals that are anti to the lone pair appear to play a role in stabilizing the nonplanar puckered transition states over the corresponding planar structures. The calculated barriers indicate that the down-to-up puckering transition can proceed in the orders Pro < Oxa < Thz in the gas phase and Pro , Oxa < Thz in water. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 444,455, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at [source]