Search results for "Geometry"
showing 10 items of 4487 documents
Twotrans-4-aminoazoxybenzenes
2001
Two isomeric trans-4-aminoazoxybenzenes, trans-1-(4-aminophenyl)-2-phenyldiazene 2-oxide (alpha, C(12)H(11)N(3)O) and trans-2-(4-aminophenyl)-1-phenyldiazene 2-oxide (beta, C(12)H(11)N(3)O), have been characterized by X-ray diffraction. The alpha isomer is almost planar, having torsion angles along the C(aryl)-N bonds of only 4.9 (2) and 8.0 (2) degrees. The relatively short C(aryl)-N bond to the non-oxidized site of the azoxy group [1.401 (2) A], together with the significant quinoid deformation of the respective phenyl ring, is evidence of conjugation between the aromatic sextet and the pi-electron system of the azoxy group. The geometry of the beta isomer is different. The non-substitute…
Bruhat–Tits Trees and Modular Groups
2019
In this chapter, we give background information and preliminary results on the main link between the geometry and the algebra used for our arithmetic applications: the (discrete-time) geodesic ow on quotients of Bruhat{Tits trees by arithmetic lattices.
Estimation of Vegetation Structure Parameters From SMAP Radar Intensity Observations
2021
In this article, we present a multipolarimetric estimation approach for two model-based vegetation structure parameters (shape A and orientation distribution ψ of the main canopy elements). The approach is based on a reduced observation set of three incoherent (no phase information) polarimetric backscatter intensities (|S HH | 2 , |S HV | 2 , and |S VV | 2 ) combined with a two-parameter (A P and ψ) discrete scatterer model of vegetation. The objective is to understand whether this confined set of observations contains enough information to estimate the two vegetation structure parameters from the L-band radar signals. In order to disentangle soil and vegetation scattering influences on th…
Digital image analysis technique for measuring railway track defects and ballast gradation
2018
Abstract In order to guarantee safety and driving comfort and to maintain an efficient railway infrastructure, the first step is to carefully monitor the track geometry and wear level of the materials constituting the superstructure. To that end diagnostic trains are widely used on main lines, in that they can detect several geometric track parameters and rail wear, but under no circumstances they can yet detect ballast gradation. Due to the practical implications for the planning of maintenance operations on the railway network, this article presents a “DIP” digital image processing technique for measuring the transverse profile and corrugations of the rails as well as ballast gradation. T…
Toward the development of metal-based synthetic nucleases: DNA binding and oxidative DNA cleavage of a mixed copper(II) complex with N-(9H-purin-6-yl…
2009
Abstract The complex [Cu(N9-ABS)(phen) 2 ]·3.6H 2 O, H 2 N9-ABS = N -(9 H -purin-6-yl)benzenesulfonamide and phen = 1,10-phenanthroline, has been synthesized and then characterized with the aid of X-ray diffraction, analytical, and spectroscopic techniques. The geometry of Cu(II) is distorted square pyramidal with the equatorial positions occupied by three N atoms from two phenantroline molecules and one N atom from the adenine ring of the sulfonamide ligand. The interaction of the complex with DNA was studied by means of viscosity measurements and fluorescence spectroscopy. The results pointed to a classic intercalation of the complex between the DNA base pairs. The complex was found to b…
Experimental observations of upstream overdeepening
2005
The issue of morphodynamic influence in meandering streams is investigated through a series of laboratory experiments on curved and straight flumes. Both qualitative and quantitative observations confirm the suitability of the recent theoretical developments (Zolezzi & Seminara 2001) that indicate the occurrence of two distinct regimes of morphodynamic influence, depending on the value of the width ratio of the channel β. The threshold value βR separating the upstream from the downstream influence regimes coincides with the resonant value discovered by Blondeaux & Seminara (1985). Indeed it is observed that upstream influence may occur only in relatively wide channels, while narrower stream…
How to learn a conceptual space
2005
the experiments proposed in the article by steels & belpaeme (s&b) can be considered as a starting point toward a general methodology for the automatic learning of conceptual spaces.
Movement dependent position changes of the antennular flagellum ofPalaemon xiphias (Risso)
1977
The angular positions of the outer flagellum ofPalaemon xiphias were obtained by cinematographic measurements during different phases of locomotion. Contrary to the upright resting position the flagella are stretched forward into a distinct starting position preliminary to any forward movement, and then pushed down with acceleration of swimming speed. These phenomena are discussed in context with comparable behaviour in other decapods and in insects.
Counter-complementarity control of the weak exchange interaction in a bent {Ni(ii)3 complex with a μ-phenoxide-μ-carboxylate double bridge
2019
We have prepared and structurally characterized a novel {Ni3} bent complex bearing a double μ-phenoxide-μ-carboxylate bridge. Both terminal Ni(ii) sites are symmetry related, offering a simplified exchange interaction scheme. DC magnetic data is consistent with a weak antiferromagnetic interaction between the central and terminal Ni(ii) ions. As expected for a Ni(ii) system, local zero-field splitting is observed, which can be experimentally established. Broken symmetry quantum chemical calculations, as well as ab initio CASSCF-SA-SOC computations that support the magnetic experimental data, were also performed. From the analysis of other reported closely related Ni(ii) systems, a counter-c…
Dimeres und Trimers 1-Methyl-1-aza-5-stannabicyclo[3.3.01,5]-octan sulfid [MeN(CH2CH2CH2)2SnS]n, Röntgenstrukturanalyse des Dimeren und Gleichgewicht…
1991
Abstract The crystal structure of the dimeric title compound has been determined and refined to R = 0.0266. The core of the nearly centrosymmetric dimer is formed by an almost perfect [SnS]2 rectangle (Sn-S 2.39 and 2.51 A). The two sulfur atoms of this rectangle establish the connecting edge of two distorted trigonal bipyramids around the two tin atoms (Sn … N 2.55 A). Solutions of the title compound contain in addition to the dimer (σ(119Sn) = −4.6 ppm) about 20% of the trimer (+ 10.3 ppm). By quick crystallization a mixture of both oligomers can be transferred into the solid state.