Stochastic incoherence in the response of rebound bursters

At an optimal value of the noise intensity, the maximum variability in rebound burst durations is observed and referred to as a response stochastic incoherence. A general mechanism underlying this phenomenon is given, being different from those reported so far in excitable systems. It is shown to be determined by (i) the monotonic reduction of the hysteresis responsible for bursting caused by noise and consequent transformation of responses from rebound bursts to single spikes, and (ii) a symmetry breaking in distributions of burst durations caused by the existence of the minimum response length. The phenomenon is studied numerically in a Morris-Lecar model for neurons and its mechanism is explained with the use of canonical models describing hard excitation states.     

Olefin polymerization and copolymerization by complexes bearing [ONNO]‐Type salan ligands: Effect of ligand structure and metal type (titanium,zirconium, and vanadium)

A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2′‐(OC₆H₃‐5‐t‐Bu)₂‐NHRNH}Cl₂] (Lig¹TiCl₂: R = C₂H₄; Lig²TiCl₂: R = C₄H₈; Lig³TiCl₂: R = C₆H₁₂) and [Ti{2,2′‐(OC₆H₂‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴TiCl₂) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [ M{2,2′‐(OC₆H₃‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴VCl₂: M = V; Lig⁴ZrCl₂: M = Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1‐octene polymerization after activation by MAO and/or Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄]. The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig¹TiCl₂ << Lig²TiCl₂ < Lig³TiCl₂) and declines after adding additional tert‐Bu group on the aromatic rings (Lig³TiCl₂ < Lig⁴TiCl₂). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et₂AlCl‐activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra‐high molecular weight PE (up to 3588 kg mol^?1) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg mol_v^?1), with high molecular weight (1986 kg mol^?1) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1‐octene copolymers, whereas vanadium catalysts produced product mixtures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2111–2123     

Determination of the Lipophilicity of Twenty-Seven Imidazo[2,1-c][1,2,4]triazine Derivatives with Strong Biological Activity by Reversed-Phase TLC. Comparison with Results Obtained by Use of Computational Algorithms

JPC – Journal of Planar Chromatography – Modern TLC - The lipophilicity, log P, of 27 novel imidazo[2,1-c][1,2,4]triazine derivatives with strong biological activity has been determined...     

Chromogenic macrocyclic derivatives of azoles—synthesis and properties

The synthesis of macrocyclic chromogenic derivatives of pyrrole and imidazole is described. The complexing properties of these compounds with metal cations were investigated spectrophotometrically in acetonitrile. The synthesized crown ethers were also tested as ion carriers in ion-selective membrane electrodes. The X-ray structure of one isomer of 18-membered pyrrole crown ether is reported.     

Aryl h-phosphonates. 14. Synthesis of new nucleotide analogues with phosphonate-phosphate internucleosidic linkage

[reaction: see text] Aryl nucleoside H-phosphonates 3 and aryl nucleoside P-acylphosphonates 4, generated in situ from the appropriate H-phosphonate 1 and acylphosphonate monoesters 2, respectively, reacted rapidly in the presence of tertiary amines to produce in high yields the extended, pyrophosphate analogues, diaryl dinucleoside phosphonate-phosphate derivatives 6. These, depending on a substituent on the alpha-carbon of the phosphonate moiety, either underwent transformation into the dinucleoside phosphonate-phosphate 7 or afforded nucleoside H-phosphonates 8 and aryl nucleoside phosphate 9.     

The ?NH?(C)?Br functionality of heteroaromatic compounds as a synthon for fused dihydrooxazoles

Fused dihydrooxazoles are produced by the reaction of 8‐bromoteophylline (1), 6‐bromo‐2‐pyridone (7), or 2‐bromobenzimidazole (11) with an N‐substituted N‐(2,3‐epoxypropyl)amine. The product derived from 1 undergoes rearrangement to a fused dihydrooxazine while the fused dihydrooxazoles derived from 7 and 11 are stable. J. Heterocyclic Chem., (2011).     

Dynamical mechanism of anticipating synchronization in excitable systems

We analyze the phenomenon of anticipating synchronization of two excitable systems with unidirectional delayed coupling which are subject to the same external forcing. We demonstrate for different paradigms of excitable system that, due to the coupling, the excitability threshold for the slave system is always lower than that for the master. As a consequence the two systems respond to a common external forcing with different response times. This allows us to explain in a simple way the mechanism behind the phenomenon of anticipating synchronization in excitable systems.     

LP and SDP branch-and-cut algorithms for the minimum graph bisection problem: a computational comparison

While semidefinite relaxations are known to deliver good approximations for combinatorial optimization problems like graph bisection, their practical scope is mostly associated with small dense instances. For large sparse instances, cutting plane techniques are considered the method of choice. These are also applicable for semidefinite relaxations via the spectral bundle method, which allows to exploit structural properties like sparsity. In order to evaluate the relative strengths of linear and semidefinite approaches for large sparse instances, we set up a common branch-and-cut framework for linear and semidefinite relaxations of the minimum graph bisection problem. It incorporates separation algorithms for valid inequalities of the bisection cut polytope described in a recent study by the authors. While the problem specific cuts help to strengthen the linear relaxation significantly, the semidefinite bound profits much more from separating the cycle inequalities of the cut polytope on a slightly enlarged support. Extensive numerical experiments show that this semidefinite branch-and-cut approach without problem specific cuts is a superior choice to the classical simplex approach exploiting bisection specific inequalities on a clear majority of our large sparse test instances from VLSI design and numerical optimization.     

Synthesis,characterization and ethylene polymerization by metallasilsesquioxane

Soluble complexes of group (IV) metallocenes anchored on a substituted polyhedral oligomeric silsesquioxane trisilanol support were prepared and characterized. These catalyst precursors formulated as [M(O^O^O)X] are found to be active in polymerization of ethylene at high temperature in combination with ethylaluminum sesquichloride (Et₃Al₂Cl_3, EASC) as co‐catalyst. The polyethylene obtained by these catalysts is linear, crystalline and displays narrow dispersity. The unique low molecular weight PE formed in this reaction exhibits properties comparable to commercial micronized PE waxes that have potential industrial applications in surface coating and ink formulations. Copyright © 2013 John Wiley & Sons, Ltd.