Centrality in networks of urban streets

Centrality has revealed crucial for understanding the structural properties of complex relational networks. Centrality is also relevant for various spatial factors affecting human life and behaviors in cities. Here, we present a comprehensive study of centrality distributions over geographic networks of urban streets. Five different measures of centrality, namely degree, closeness, betweenness, straightness and information, are compared over 18 1-square-mile samples of different world cities. Samples are represented by primal geographic graphs, i.e., valued graphs defined by metric rather than topologic distance where intersections are turned into nodes and streets into edges. The spatial behavior of centrality indices over the networks is investigated graphically by means of color-coded maps. The results indicate that a spatial analysis, that we term multiple centrality assessment, grounded not on a single but on a set of different centrality indices, allows an extended comprehension of the city structure, nicely capturing the skeleton of most central routes and subareas that so much impacts on spatial cognition and on collective dynamical behaviors. Statistically, closeness, straightness and betweenness turn out to follow similar functional distribution in all cases, despite the extreme diversity of the considered cities. Conversely, information is found to be exponential in planned cities and to follow a power-law scaling in self-organized cities. Hierarchical clustering analysis, based either on the Gini coefficients of the centrality distributions, or on the correlation between different centrality measures, is able to characterize classes of cities.     

Some new routes for the preparation of 3-amino-2-phenyl-4(1H)-quinolinones from anthranilamides

[reaction: see text] Several new routes for the preparation of 3-amino-2-phenyl-4-1(H)-quinolinone 7a are compared. The most efficient is based on the cyclization of phenacyl anthranilamide 2a in the presence of (poly)phosphoric acid. The mechanisms of the rearrangements involved are discussed on the basis of the structures of isolated heterocyclic intermediates. The best methodology for the preparation of the title compound 7a was verified, and 10 other quinolinones 7 were prepared.     

Rhenium(V) and technetium(V) nitrido complexes with mixed tridentate π-donor and monodentate π-acceptor ligands

Mixed-ligand [M(N)(SNS)(PPh(3))] complexes (M = Tc, Re) (1, 2) were prepared by reaction of the precursor [M(N)Cl(2)(PPh(3))(2)] with ligand 2,2'-dimercaptodiethylamine [H(2)SNS = NH(CH(2)CH(2)SH)(2)] in refluxing dichloromethane/ethanol mixtures. In these compounds, 2,2'-dimercaptodiethylamine acts as a dianionic tridentate chelating ligand bound to the [M≡N](2+) group through the two π-donor deprotonated sulfur atoms and the protonated amine nitrogen atom. Triphenylphosphine completes the coordination sphere, acting as a monodentate ligand. [M(N)(NS(2))(PPh(3))] complexes can assume two different isomeric forms depending on the syn and anti orientations of the hydrogen atom bound to the central nitrogen atom of the SNS ligand with respect to the M≡N moiety. X-ray crystallography of the syn isomer of complex 2 demonstrated that it has a distorted trigonal bipyramidal geometry with the nitrido group and the two sulfur atoms defining the equatorial plane, the phosphorus atom of the monophosphine and the protonated amine nitrogen of the tridentate ligand spanning the two reciprocal trans positions along the axis perpendicular to the trigonal plane. Synthesis of the analogous Tc derivatives with tris(2-cyanoethyl)phosphine, [Tc(N)(SNS)(PCN)] [(PCN = P(CH(2)CH(2)CN)(3)], required the preliminary preparation of the new precursor [Tc(N)(PCN)(2)Cl(2)](2) (3), which was prepared by reacting [n-NBu(4)][Tc(N)Cl(4)] with a high excess of PCN. The crystal structure of compound 3 consists of a noncrystallographic centrosymmetric dimer of Tc(V) nitrido complexes having an octahedral geometry. In this arrangement, the apical positions are occupied by two tris(2-cyanoethyl)phosphine groups and the equatorial positions by the nitrido group whereas the two Cl(-) anions and one cyano ligand belong to the other octahedral component of the dimer. By reacting the new precursor [Tc(N)(PCN)(2)Cl(2)](2) with the ligand H(2)SNS the complex [Tc(N)(SNS)(PCN)] (5) was finally obtained in acetonitrile solution. The new Tc(III) complex trans-[Tc(PCN)(2)Cl(4)][n-NBu(4)] (4) was also isolated from the reaction solution used for preparing complex 3 as side product and characterized by X-ray diffraction. The crystal structure of 4 consists of independent trans-[TcCl(4)(PCN)(2)](-) anions situated on crystallographic centers of symmetry and tetrabutylammonium cations in general positions.     

Cosmological expansion and local systems: a Lemaître–Tolman–Bondi model

We propose a Lemaître–Tolman–Bondi system mimicking a two-body system to address the problem of the cosmological expansion versus local dynamics. This system is strongly bound but participates in the cosmic expansion and is exactly comoving with the cosmic substratum.     

An X-Ray Crystallographic Study of the Novel Aminal bis-(<Emphasis Type="Italic">p</Emphasis>-Ethoxycarbonylphenylamino-)methane

Abstract  The crystal structure of bis-(p-Ethoxycarbonylphenylamino-)methane (1) has been determined by single crystal X-ray diffraction analysis. The bis-aminal (1) molecule is V-shaped and situated on a twofold axis passing through C1 with the phenyl rings forming a dihedral angle of 70.2(1)°. The carboxylate and phenyl groups are coplanar. The crystal structure of 1 is compared with the structure of the closely related aminals, 2–5. Crystal data: 1 C₁₉H₂₂N₂O₄, tetragonal, space group I4 ₁ cd (N.110), a = 20.4760(7) Ǻ, b = 20.4760(7) Ǻ, c = 8.2984(3) ?, and V = 3477.7(2) ?³, for Ζ = 8. Index Abstract  The crystal structure of bis-(p-ethoxycarbonylphenylamino-)methane (1) has been determined by single crystal X-ray diffraction analysis.      

An X-Ray Crystallographic Study of Five Compounds from a Series of 1,x-<Emphasis Type="Italic">bis</Emphasis>-(4-Oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)alkanes

Abstract  

The crystal structures of a series of bis-(4-oxo-3,4-dihydro-1,2,3-benzotriazin-3-yl)alkanes, compounds 5 to 9, have been determined by single crystal X-ray diffraction analysis. The structural parameters of the triazinone rings in the five compounds do not display systematic differences with respect to those reported for a few analogous compounds. The benzotriazinone rings in 5 and 9 are almost perpendicular to the alkylic chain. The molecules in the crystal packing are linked by means of a weak C–H···X H-bond (X = N/O). Compound 6 has two independent molecules in the asymmetric unit; one of the molecules displays disorder within the benzotriazinone moiety linked in position 1 to the propane alkylic group. The disordered molecule displays two conformations of the benzotriazinone linked in position 1 to the propane bridge. Compound 8 also displays disorder within the benzotriazinone moiety linked in position 1 to the pentane alkylic spacer group. The molecules of compound 7, in the crystal packing, also form intra and inter-molecular C–H···X (X = N/O) hydrogen bonds. None of these compounds show any tendency to adopt a folded conformation with intramolecular π–π stacking between benzotriazinone units. Crystal data: 5 C₁₆H₁₂N₆O_2, monoclinic, space group P2 ₁ /c, a = 4.8370(2)?, b = 14.7845(7)?, c = 10.0837(4)?, β = 95.430(2)°, V = 717.88(6)?³, for Ζ = 2; 6 C₁₇H₁₄N₆O_2, triclinic, space group P-1, a = 7.4237(4)?, b = 14.4738(9)?, c = 15.0359(10)?, α = 91.871(3)°, β = 92.147(3)°, γ = 101.233(3)°, V = 1582.2(2)?³, for Ζ = 4; 7 C₁₈H₁₆N₆O_2, monoclinic, space group C2/c, a = 33.8886(10)?, b = 6.4593(2)?, c = 16.0608(6)?, β = 102.298(1)°, V = 3435.0(2)?³, for Ζ = 8; 8 C₁₉H₁₈N₆O_2, triclinic, space group P-1, a = 7.2592(2)?, b = 7.6795(2)?, c = 16.1003(5)?, α = 85.292(1)°, β = 81.367(1)°, γ = 88.377(1)°, V = 884.26(4)?³, for Ζ = 2; 9 C₂₀H₂₀N₆O_2, monoclinic, space group P2 ₁ /c, a = 7.2668(2)?, b = 4.5612(1)?, c = 28.1993(12)?, β = 97.313(2)°, V = 927.07(5)?³, for Ζ = 2.     

Anomalous Behavior in an Effective Model of Graphene with Coulomb Interactions

We analyze by exact Renormalization Group (RG) methods the infrared properties of an effective model of graphene, in which two-dimensional (2D) massless Dirac fermions propagating with a velocity smaller than the speed of light interact with a 3D quantum electromagnetic field. The fermionic correlation functions are written as series in the running coupling constants, with finite coefficients that admit explicit bounds at all orders. The implementation of Ward Identities in the RG scheme implies that the effective charges tend to a line of fixed points. At small momenta, the quasi-particle weight tends to zero and the effective Fermi velocity tends to a finite value. These limits are approached with a power law behavior characterized by non-universal critical exponents.     

A facile “one pot” synthesis of 2,9-disubstituted 8-azapurin-6-ones (3,5-disubstituted 7-hydroxy-3H-1,2,3-triazolo[4,5-d]pyrimidines)

A series of title compounds have been synthesized by utilising benzylazide, cyanoacetamide, ethyl or methyl esters of aliphatic or aromatic carboxylic acids and sodium ethoxide as catalyst.     

The preparation,characterization, and thermal behaviour of some lithium aluminum oxides: Li3AlO3 and Li5AlO4

The purpose of this research was to study the best conditions for the synthesis of the double oxides Li₅AlO₄ and Li₃AlO₃ in the solid state starting from the simple oxides, and to determine their heats of formation. Li₅AlO₄ was obtained from Li₂O₂ or Li₂O and γ-Al₂O₃ in a Li/Al molar ratio of 5∶1, and was characterized by X-ray methods. Lithium orthoaluminate, Li₃AlO₃, was obtained from Li₂O₂ and γ-Al₂O₃ in a molar ratio 3∶1. The postulated formula, Li₃AlO₃, was confirmed by chemical analysis. The temperature ranges in which the compounds are stable were established by the DTA method, and were found to be very limited for Li₃AlO₃ (400–430°) but greater for Li₅AlO₄ (440 — more than 600°). The heats of formation of Li₅AlO₄ and Li₃A10₃, also determined by means of the DTA method, were found to be ?552.3 ± 0.8 kcal/mole and ?416.8 ± 2 kcal/mole, respectively.