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Similar Geometry (similar + geometry)
Selected AbstractsCircular fractal monopole antenna based on descartes circle theorem for UWB applicationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2008Salman Naeem Khan Abstract An apollonian shaped ultra-wideband circular monopole antenna based on descartes circle theorem is presented. Different self similar geometries from DCT are analyzed and optimized for UWB applications. The proposed design is slightly modified to ensure an overall smooth current distribution limited by the junction point nature of the fractal geometries. The experimental results are compared with conventional circular disk monopole and annular monopole antenna. The measured return loss of the proposed design below ,10 dB is from 2.4 to over 40 GHz and its radiation pattern is omni-directional compared with circular disk and annular antennas in most of its impedance bandwidth. Moreover due to the fractal shape, the proposed design has less weight and wind loading effect. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1605,1608, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23437 [source] Two 18, TiIV,5 -Cp-tris(sec -amido)-type complexes derived from 1H -imidazol-2-yl side-chain functionalized cyclopentadienesACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009Xiaowu Wang Achiral {2-[2-(,5 -cyclopentadienyl)-2-methylpropyl]-1H -imidazolyl-,N1}bis(N,N -diethylamido-,N)titanium(IV), [Ti(C4H10N)2(C12H14N2)], (I), and closely related racemic (SR)-{2-[(,5 -cyclopentadienyl)(phenyl)methyl]-1H -imidazolyl-,N1}bis(N,N -diethylamido-,N)titanium(IV), [Ti(C4H10N)2(C15H12N2)], (II), have been prepared by direct reactions of Ti(NEt2)4 and the corresponding 1H -imidazol-2-yl side-chain functionalized cyclopentadienes. In compound (II), there are two crystallographically independent molecules of very similar geometries connected by a noncrystallographic pseudosymmetry operation akin to a 21 screw axis. All Ti-ligating N atoms in both (I) and (II) are in planar environments, which is indicative of an additional N,Ti p,,d, donation. This fact and the 18, nature of both (I) and (II) are additionally supported by quantum chemical single-point density functional theory (DFT) computations. [source] From small structural modifications to adjustment of structurally dependent properties: 1-methyl-3,5-bis[(E)-2-thienylidene]-4-piperidone and 3,5-bis[(E)-5-bromo-2-thienylidene]-1-methyl-4-piperidoneACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Paul Tongwa The molecules of the title compounds, C16H15NOS2, (I), and C16H13Br2NOS2, (II), are E,E -isomers and consist of an extensive conjugated system, which determines their molecular geometries. Compound (I) crystallizes in the monoclinic space group P21/c. It has one thiophene ring disordered over two positions, with a minor component contribution of 0.100,(3). Compound (II) crystallizes in the noncentrosymmetric orthorhombic space group Pca21 with two independent molecules in the unit cell. These molecules are related by a noncrystallographic pseudo-inversion center and possess very similar geometries. The crystal packings of (I) and (II) have a topologically common structural motif, viz. stacks along the b axis, in which the molecules are bound by weak C,H...O hydrogen bonds. The noncentrosymmetric packing of (II) is governed by attractive intermolecular Br...Br and Br...N interactions, which are also responsible for the very high density of (II) (1.861,Mg,m,3). [source] Density functional study on the structural conformations and intramolecular charge transfer from the vibrational spectra of the anticancer drug combretastatin-A2JOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2009L. Padmaja Abstract Combretastatin-A2 (CA2), a potential anticancer drug in advanced preclinical development, is extracted from the medicinal plant Combretum caffrum. The NIR-FT Raman and FT-IR spectral studies of the molecule were carried out and ab initio calculations performed at the B3LYP/6-31G(d) level to derive the equilibrium geometry as well as the vibrational wavenumbers and intensities of the spectral bands. The vibrational analysis showed that the molecule has a similar geometry as that of cis-stilbene, and has undergone steric repulsion resulting in twisting of the phenyl ring with respect to the ethylenic plane. Vibrational analysis was used to investigate the lowering of the stretching modes, and enhancement of infrared band intensities of the C,H stretching modes of Me2 may be attributed to the electronic effects caused by back-donation and induction from the oxygen atom. Analysis of phenyl ring modes shows that the CA2 stretching mode 8 and the aromatic C,H in-plane bending mode are equally active as strong bands in both IR and Raman spectra, which can be interpreted as the evidence of intramolecular charge transfer (ICT) between the OH and OCH3groups via conjugated ring path and is responsible for bioactivity of the molecule. Copyright © 2008 John Wiley & Sons, Ltd. [source] Use of the wavelet method for analyzing electrochemical noise dataMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2007O. Duran This research paper shows the application of the mathematical tool "wavelet's" to be used in the interpretation and analysis of electrochemical noise signals. The Fast Fourier Transformation (FFT) is one of the most commonly used techniques for analyzing electrochemical noise. But the application of this methodology to the analysis of stochastic signals does not allow their interpretation in a suitable way. The wavelet's methodology carries out the analysis by means of the construction of finite base functions. In several studies, it has been found out that the function that is closest to the electrochemical oscillations is the one called "coiflets," which presents a similar geometry to what it is observed when an ionic,electronic interchange occurs during an electrochemical interphase. The analysis that appears here was implemented using the toolbox "LabViewÔ." [source] Ion dispersion near parallel wire grids in orthogonal acceleration time-of-flight mass spectrometry: predicting the effect of the approach angle on resolutionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2002Mark Lewin Ions experience small deflections in the vicinity of grids in accelerators and ion mirrors in time-of-flight (TOF) mass spectrometers. Recent experiments with an orthogonal acceleration (oa) TOF instrument have verified that the effect can significantly degrade resolution when ions approach grids at an angle deviating from 90,°. The phenomenon becomes significant only when ions have components of velocity at right angles to the wires of the grids. A model is presented in this study to predict this phenomenon for parallel wire grids. The fractional energy spread of ions (calculated in the static TOF-spectrometer frame of reference) scales directly with the approach angle of ions to the grid (as measured from normal approach). The energy spread also scales with the range of angles that is a consequence of the focusing effect in each gap between the wires of the grid. The equations imply that closely spaced parallel wire grids are best for deployment in oa-TOF systems where non-zero approach angles are unavoidable. Such grids are relatively impractical to manufacture and support but rectangular repeat cell grids with relatively few wires at right angles to the source axis are shown experimentally to introduce minimal energy spread. When these grids are rotated by 90,°, the resolution measured in a Q-TOF spectrometer is degraded in approximate agreement with the parallel wire model. A practical implication of this work is that grid transmissions in oa-TOF systems may be significantly increased without loss of resolution. Improvements of ,200% (V-mode) and ,400% (W-mode) in ion transmission were obtained in this study without compromising resolution. This was achieved with ,73% transmission grids and greater potential improvements in transmission are being realised since this study with ,89% transmission grids having similar geometry. Copyright © 2002 John Wiley & Sons, Ltd. [source] 1,1,-Fc(4-C6H4CO2Et)2 and its unusual salt derivative with Z, = 5, catena -[Na+]2[1,1,-Fc(4-C6H4CO2,)2]·0.6H2O [1,1,-Fc = (,5 -(C5H4)2Fe]ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2010John F. Gallagher The neutral diethyl 4,4,-(ferrocene-1,1,-diyl)dibenzoate, Fe[,5 -(C5H4)(4-C6H4CO2Et)]2 (I), yields (II) (following base hydrolysis) as the unusual complex salt poly[disodium bis[diethyl 4,4,-(ferrocene-1,1,-diyl)dibenzoate] 0.6-hydrate] or [Na+]2[Fe{,5 -(C5H4)-4-C6H4CO}2]·0.6H2O with Z, = 5. Compound (I) crystallizes in the triclinic system, space group , with two molecules having similar geometry in the asymmetric unit (Z, = 2). The salt complex (II) crystallizes in the orthorhombic system, space group Pbca, with the asymmetric unit comprising poly[decasodium pentakis[diethyl 4,4,-(ferrocene-1,1,-diyl)dibenzoate] trihydrate] or [Na+]10[Fe{,5 -(C5H4)-4-C6H4CO}2]5·3H2O. The five independent 1,1,-Fc[(4-C6H4CO2),]2 dianions stack in an offset ladder (stepped) arrangement with the ten benzoates mutually oriented cisoid towards and bonded to a central layer comprising the ten Na+ ions and three water molecules [1,1,-Fc = ,5 -(C5H4)2Fe]. The five dianions differ in the cisoid orientations of their pendant benzoate groups, with four having their ,C6H4, groups mutually oriented at interplanar angles from 0.6,(3) to 3.2,(3)° (as ,..., stacked C6 rings) and interacting principally with Na+ ions. The fifth dianion is distorted and opens up to an unprecedented ,C6H4, interplanar angle of 18.6,(3)° through bending of the two 4-C6H4CO2 groups and with several ionic interactions involving the three water molecules (arranged as one-dimensional zigzag chains in the lattice). Overall packing comprises two-dimensional layers of Na+ cations coordinated mainly by the carboxylate O atoms, and one-dimensional water chains. The non-polar Fc(C6H4)2 groups are arranged perpendicular to the layers and mutually interlock through a series of efficient C,H..., stacking contacts in a herringbone fashion to produce an overall segregation of polar and non-polar entities. [source] Orientational disorder and phase transitions in crystals of (NH4)2NbOF5ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2008Anatoly A. Udovenko Ammonium oxopentafluoroniobate, (NH4)2NbOF5, was synthesized in a single-crystal form and the structures of its different phases were determined by X-ray diffraction at three temperatures: phase (I) at 297,K, phase (II) at 233,K and phase (III) at 198,K. The distorted [NbOF5]2, octahedra are of similar geometry in all three structures, with the central atom shifted towards the O atom. The structure of (I) is disordered, with three spatial orientations of the [NbOF5]2, octahedron related by a jump rotation around the pseudo-threefold local axis such that the disorder observed is of a dynamic nature. As the temperature decreases, the compound undergoes two phase transitions. The first is accompanied by full anionic ordering and partial ordering of the ammonium groups (phase II). The structure of (III) is completely ordered. The F and O atoms in the structures investigated were identified via the Nb,X (X = O and F) distances. The crystals of all three phases are twinned. [source] (,)- epi -Inosose-2ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2000Hiroyuki Hosomi The structure of the title compound, C6H10O6, was determined to confirm the position of the keto group in the molecule prepared enantioselectively by a bioconversion from myo -inositol. There are two independent molecules showing similar geometry. [source] Interaction of cyanine dyes with nucleic acids.BIOPOLYMERS, Issue 4 2001Abstract The spectral luminescent properties of two groups of monomethine cyanine dyes were studied in the presence of DNA. The first group included five dyes with 5,6-methylenedioxy-[d]-benzo-1,3-thiazole heterocycle and their unsubstituted analogs. Five monomethine pyrylium cyanines and their N -methyl-pyridine analogs were included in the second group. In each pair the pyrylium and pyridine dyes had similar geometry but differed in charge density distribution. The results presented some evidence in favor of the half-intercalation interaction mode between the studied dyes and DNA. When the benzothiazole residue had the lowest electron donor ability between the two heterocycles in the dye molecule, its substitution with the bulky methylenedioxy group led to a significant decrease in fluorescence enhancement of the dye,DNA complex. On the contrary, when the substituents that create steric hindrance (e.g., methylenedioxy and methyl groups) were introduced into the heterocycle with the higher electron donor ability, the fluorescence enhancement value of the dye,DNA complex was virtually unchanged. The changes in the Stock's shift values upon the formation of the dye,DNA complexes were in agreement with the proposed half-intercalation model. Interestingly, in the dye,DNA complexes the pyrylium dyes probably resided in a place similar to the pyridine ones. It is possible that the benzothiazole (or benzooxazole) ring intercalated between the DNA bases and the pyrylium (or pyridine) residue was located in the DNA groove closer to the phosphate backbone. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 219,227, 2001 [source] | ||||||||||