The existence spectrum of Meta(K 4 (3) >K 4 (3) − e)

Let H and J1 be both t-uniform hypergraphs. Let J2 be a sub-hypergraph of J1. In this paper, the metamorphosis of a hypergraph decomposition is introduced, denoted by (H, J1 J2)-design, which is a generalization of the concept of metamorphosis of a graph decomposition. Let Meta(J1J2) denote the set of all integers v such that there exists a (Kv((3)), J1J2)-design. We completely determine the set Meta(K4((3))K4((3))-e).     

A convenient method of producing thiophene linked bipyridine oligomers

A series of soluble polybipyridine ligands comprising one to five bipyridine modules sandwiched between rigid carbon-carbon triple bonds substituted by 3,4-dibutylthiophene repeating units was synthesized. Two different protocols have been explored with the idea to use a divergent/convergent approach starting from bisymmetrically and symmetrically substituted bipyridine modules. At each stage of the iteration two bipy/thiophene modules are connected. The use of triethylsilylacetylene and 2-methylbut-3-yn-2-ol insures an easy entry to pivotal building blocks, which could be selectively deprotected from the TES or 2-hydroxyprop-2-yl sites. All cross-coupling reactions are promoted with palladium(0) tetrakistriphenylphosphine under mild conditions.     

Adsorption of 2-amino-5-nitropyridine on the (111) and (210) silver faces

The adsorption isotherms of 2-amino-5-nitropyridine (ANP) on the (111) and (210) silver faces from an aqueous solution of 0.09 M KClO₄ + 0.02 M NaOH were determined at −0.4 V vs. the 1 mol⁻¹ calomel electrode using double-potential-step chronocoulometry. The surface concentration Γ_ANP of ANP was obtained by stepping the applied potential from −0.4 V, where ANP is electroinactive, to −1.2 V, where ANP is electroreduced to 2,5-diaminopyridine. The charge involved in this step, once corrected for the diffusive and capacitive contributions, yields 6FΓ_ANP directly. The maximum surface concentration and standard Gibbs energy of adsorption are equal to 3.6 × 10⁻¹⁰ mol cm⁻² and −35 kJ mol⁻¹ on Ag(111) and 5.2 × 10⁻¹⁰ mol cm⁻² and 42 kJ mol⁻¹ on Ag(210), thus demonstrating the strong effect of surface crystallography on the energetics of ANP adsorption.     

Molecular alignment of rigid rods in nonrigid spherical pores

We have investigated the orientation ordering of two shish-kebab chains confined by spherically harmonic potentials through Monte Carlo simulations and asymptotic analysis. The rigid rod is modeled as shish-kebab chains consisting of tangent hard spheres aligned in the same axis, and the harmonic potential is chosen to model nonrigid cavities. We first show that the interactions between a rod and the spherically harmonic potential are independent of chain orientation, indicating that the alignment of two confined rods arises from the excluded volume interactions alone. In the strong fields, the order parameter of two confined rods converges to different values, depending on the parity of chain length. From asymptotic order parameters, we find that the rods of odd-number beads rotate more freely even under the limiting strong confinement. However, the two rods of even-number beads are essentially trapped in a configuration of perpendicular alignment through intercalation of their central grooves. We attribute the dependence of the parity of chain length to the different locations of the center-of-mass in a rod for these two cases. Furthermore, we compare the shish-kebab chains with different rod models in the simulations, and utilize these models to explore the effect of the local rod smoothness on molecular alignment. Our findings suggest that increasing local rod smoothness enhances the rotational degree of freedom for confined rods, and the effect of local rod roughness emerges under strong enough applied potentials.     

On the modeling of confined buckling of force chains

Buckling of force chains, laterally confined by weak network particles, has long been held as the underpinning mechanism for key instabilities arising in dense, cohesionless granular assemblies, e.g. shear banding and slip-stick phenomena. Despite the demonstrated significance of this mechanism from numerous experimental and discrete element studies, there is as yet no model for the confined buckling of force chains. We present herein the first structural mechanical model of this mechanism. Good agreement is found between model predictions and confined force chain buckling events in discrete element simulations. A complete parametric analysis is undertaken to determine the effect of various particle-scale properties on the stability and failure of force chains. Transparency across scales is achieved, as the mechanisms on the microscopic and mesoscopic domains, which drive well-known macroscopic trends in biaxial compression tests, are elucidated.     

Topological evolution in dense granular materials: A complex networks perspective

One of the great challenges in the science of complex materials – materials capable of emergent behavior such as self-organized pattern formation – is deciphering their “inherent” structural design principles as they deform in response to external loads. We have been exploring the efficacy of techniques from complex networks to the study of dense granular materials as a means to: (i) uncover such design principles and (ii) identify suitable metrics that quantify the evolution of structure during deformation. Herein, we characterize the developing network structure and loss of connectivity in a quasistatically deforming granular medium from the perspective of complex networks. Attention is paid to the evolution of the contact and contact force networks at the local or mesoscopic level, i.e., a particle and its immediate neighbors, as well as the macroscopic level. We explore network motifs and other topological properties at these multiple length scales, in an attempt to find that which best correlates with the constitutive properties of nonaffine deformation and dissipation, spatially and with respect to strain. Key processes or rearrangement events that cause loss of connectivity within the material domain, e.g. microbanding and force chain buckling, are investigated. Network statistics of these processes, previously shown to be major sources of energy dissipation and nonaffine deformation, are then tied to corresponding trends observed in the evolving macroscopic network. It is shown that consideration of the unweighted contact network alone is insufficient to tie dissipation to loss of material connectivity.     

Kinetic and spectroscopic characterization of ACMSD from Pseudomonas fluorescens reveals a pentacoordinate mononuclear metallocofactor

The enzyme alpha-amino-beta-carboxy-muconic-epsilon-semialdehyde decarboxylase (ACMSD) plays an important role in the biodegradation of 2-nitrobenzoic acid in microorganisms and in tryptophan catabolism in humans. We report that the overexpressed ACMSD enzyme from Pseudomonas fluorescens requires a divalent metal, such as Co(II), Fe(II), Cd(II), or Mn(II), for catalytic activity and that neither a redox reagent nor an organic cofactor is required for the catalytic function. The metal ions can be taken up in either cell or cell-free preparations for generating the active form of ACMSD. The kinetic parameters and enzyme specific activity are shown to depend on the metal ion present in the enzyme, suggesting a catalytic role of the metal center. EPR spectrum of Co(II)-ACMSD provides a high-spin (S = 3/2 mononuclear metal ion in a non-heme, noncorrinoid environment with a mixed nitrogen/oxygen ligand field. We observe hyperfine interactions due to 59Co nucleus at temperatures below 5 K but not at higher temperatures. Ten hyperfine lines are present in the g(perpendicular) region, and three equivalent nitrogen hyperfine couplings are required to simulate the resonances in the EPR spectrum. The results for the metal binding site are also assessed using the copper-substituted enzyme, and the EPR spectral assignments for both cobalt and copper proteins give strong support for a distorted trigonal bipyramidal geometry of the metal center. Ultimately, these results suggest for the first time that ACMSD is a metal-dependent enzyme that catalyzes a novel nonoxidative decarboxylation.     

Adaptive control of femtosecond soliton self-frequency shift in fibers

The Raman shift of a subpicosecond soliton in 100 m of fiber is controlled adaptively by pulse shaping before launching into the fiber. We use a deformable-mirror-based shaper to control the spectral phase of the input pulse.     

Spectroscopic and redox properties of novel d6-complexes engineered from all Z-ethenylthiophene-bipyridine ligands

A series of quasilinear dinuclear complexes incorporating ruthenium(II)- and osmium(II)-tris(2,2'-bipyridine) units has been prepared in which the individual metal-containing moieties are separated by 3,4-dibutyl-2,5-diethenylthiophene spacers and end-capped by 3,4-dibutyl-2-ethenylthiophene subunits; related ruthenium(II) and osmium(II) mononuclear complexes have also been prepared where one bpy unit is likewise end-capped by 3,4-dibutyl-2-ethenylthiophene subunits [bpy = 2,2'-bipyridine]. Overall, mononuclear species, labeled here Ru and Os, and dinuclear species, RuRu, OsOs, and RuOs, have been prepared and investigated. Their electrochemical behavior has been studied in CH3CN solvent and reveals ethenylthiophene-centered oxidations (irreversible steps at > +1.37 V vs SCE), metal-centered oxidations (reversible steps at +1.30 V vs SCE for Ru(II/III) and +0.82 V vs SCE for Os(II/III)), and successive reduction steps localized at the substituted bpy subunits. The spectroscopic studies performed for the complexes in CH3CN solvent provided optical absorption spectra associated with transitions of ligand-centered nature (LC, from the bpy and ethenylthiophene subunits) and metal-to-ligand charge-transfer nature (MLCT), with the former dominating in the visible region (400-600 nm). While the constituent ethenylthiophene-bpy ligands are strong fluorophores (fluorescence efficiency in CH2Cl2 solvent, phi em = 0.49 and 0.39, for the monomer and the dimer, respectively), only weak luminescence is observed for each complex in acetonitrile at room temperature. In particular, (i) the complexes Ru and RuRu do not emit appreciably, and (ii) the complexes Os, OsOs, and RuOs exhibit triplet emission of 3Os --> L CT character, with phi em in the range from 10-3 to 10-4. These features are rationalized on the basis of the role of nonemissive triplet energy levels, 3Th, centered on the ethenylthiophene spacer. These levels appear to lie lower in energy than the 3Ru --> L CT triplet levels, and in turn higher in energy than the 3Os --> L CT triplet levels, along the sequence 3Ru --> L CT > 3Th > 3Os --> L CT.