Search results for "π"

Rapid and eco-friendly synthesis of graphene oxide-silica nanohybrids

2014

La filosofía política de Aristóteles en las Comunidades de Castilla

2020

p. 47-68 El movimiento social y político de las Comunidades de Castilla se puede calificar de un intento de renovación de la monarquía como forma de gobierno. Entre las principales ideas políticas que se debatieron durante este breve período de tiempo que se extiende desde mayo de 1520 al 23 de abril de 1521, se percibe una clara influencia de la filosofía política de Aristóteles. La transmisión de estas ideas se realizó a través de algunos profesores de la Universidad de Salamanca. En lo que se podría denominar corpus doctrinal se aprecia con claridad la presencia de la idea de πόλις, participación, igualdad y libertad políticas del súbdito-ciudadano, el control del ejercicio del poder pol…

A model for the γN → ππN reaction

1996

We have studied the γN → ππN reaction using a model wich includes N, Δ(1232), N*(1440) and N*(1520) intermediate baryonic states and the ρ-meson as a intermediate ππ resonance. The model reproduces fairly well experimental cross sections below Eγ=800 MeV and invariant-mass distributions even at higher energies. One of the interesting findings of study is what the γN → N*(1520) → Δπ process is very important and interferes strongly with the dominant Δ-Kroll-Ruderman term to produce the experimental peak of the kross section. Oset Baguena, Eulogio, Eulogio.Oset@ific.uv.es

Evaluation of building heating loads with dimensional analysis: Application of the Buckingham π theorem

2017

Abstract A detailed assessment of building energy performance requires a large amount of input data concerning building typology, environmental conditions, envelope thermophysical properties, geometry, control strategies, and several other parameters. Notwithstanding, the use of specialized software tools poses many challenges in regards to the retrieval of reliable and detailed information, setting a steep learning curve for engineers and energy managers. To speed up the preliminary assessment phase, it might be more convenient to resort to a simplified model that allows the evaluation of heating energy demand with a good level of accuracy and without excessive computational cost or user e…

On a posteriori error bounds for approximations of the generalized Stokes problem generated by the Uzawa algorithm

2012

In this paper, we derive computable a posteriori error bounds for approximations computed by the Uzawa algorithm for the generalized Stokes problem. We show that for each Uzawa iteration both the velocity error and the pressure error are bounded from above by a constant multiplied by the L2-norm of the divergence of the velocity. The derivation of the estimates essentially uses a posteriori estimates of the functional type for the Stokes problem. peerReviewed

Solution and solid-state studies on the halide binding affinity of perfluorophenyl-armed uranyl–salophen receptors enhanced by anion–π Interactions

2016

The enhancement of the binding between halide anions and a Lewis acidic uranyl-salophen receptor has been achieved by the introduction of pendant electron- deficient arene units into the receptor skeleton. The association and the occurrence of the elusive anion-p interaction with halide anions (as tetrabutylammonium salts) have been demonstrated in solution and in the solid state, providing unambiguous evidence on the interplay of the concerted interactions responsible for the anion binding.

Crystal structure of the borabenzene–2,6-lutidine adduct

2015

In the title compound, C12H14BN, the complete molecule is generated by a crystallographic twofold axis, with two C atoms, the B atom and the N atom lying on the rotation axis. The dihedral angle between the borabenzene and pyridine rings is 81.20 (6)°. As well as dative electron donation from the N atom to the B atom [B—N = 1.5659 (18) Å], the methyl substituents on the lutidine ring shield the B atom, which further stabilizes the molecule. In the crystal, weak aromatic π–π stacking between the pyridine rings [centroid–centroid separation = 3.6268 (9) Å] is observed, which generates [001] columns of molecules.

Coordination complexes of chromium(0) with a series of 1,3-diphenyl-6-arylfulvenes

2018

The synthesis and structural properties of a series of chromium tricarbonyl `piano-stool' complexes bearing substituted pentafulvene ligands were studied. The complexes, tricarbonyl(1,3,6-triphenylfulvene)chromium(0) benzene hemisolvate, [Cr(C24H18)(CO)3]·0.5C6H6 (I), tricarbonyl[1,3-diphenyl-6-(3-vinylphenyl)fulvene]chromium(0), [Cr(C26H20)(CO)3] (II), and tricarbonyl[1,3-diphenyl-6-(pyren-1-yl)fulvene]chromium(0), [Cr(C34H22)(CO)3] (III), each have a distorted octahedral geometry, with the fulvene coordinated in a π–η2:π–η2:π–η2 fashion. Significant deviation of the exocyclic fulvene double bond from the cyclopentadiene plane accompanies coordination. Evidence of non-covalent π–π interact…

Crystal structures of isomeric 3,5-dichloro-N-(2,3-dimethylphenyl)benzenesulfonamide, 3,5-dichloro-N-(2,6-dimethylphenyl)benzenesulfonamide and 3,5-d…

2017

The crystal structures of three isomeric compounds of formula C14H13Cl2NO2S, namely 3,5-dichloro-N-(2,3-dimethylphenyl)-benzenesulfonamide (I), 3,5-dichloro-N-(2,6-dimethylphenyl)benzenesulfonamide (II) and 3,5-dichloro-N-(3,5-dimethylphenyl)benzenesulfonamide (III) are described. The molecules of all the three compounds are U-shaped with the two aromatic rings inclined at 41.3 (6)° in (I), 42.1 (2)° in (II) and 54.4 (3)° in (III). The molecular conformation of (II) is stabilized by intramolecular C—H...O hydrogen bonds and C—H...π interactions. The crystal structure of (I) features N—H...O hydrogen-bonded R 2 2(8) loops interconnected via C(7) chains of C—H...O interactions, forming a thre…

Conformational investigation of α,β‐dehydropeptides. XV: N‐acetyl‐α,β‐dehydroamino acid N ′N ′‐dimethylamides: conformational properties from infrare…

2005

The FTIR spectra were analysed in the region of the nu(s)(N-H), AI(C=O) and nu(s)(Calpha=Cbeta) bands for a series of Ac-DeltaXaa-NMe2, where DeltaXaa = DeltaAla, (Z)-DeltaAbu, (Z)-DeltaLeu, (Z)-DeltaPhe and DeltaVal, to determine a predominant solution conformation of these alpha,beta-dehydropeptide-related molecules. Measurements were taken in CCl4, DCM and MeCN solutions. In the same way, spectra of saturated analogues Ac-Xaa-NMe2, where Xaa = Ala, Abu, Leu, Phe and Val, were investigated. To help interpret the spectroscopic results, conformational maps were calculated by the B3LYP/6-31+G** method. Also, the relative energies of all conformers of the dehydro compounds in vacuo as well as…