Trapping of phase kinks in polyacetylene

Molecular orbital calculations with full geometry optimization using a semi-empirical tight-binding Hamiltonian for finite molecular models of phase kinks (solitons) in polyacetylene, (CH)_X′ were done. This bond alternation defect extends over many atoms from which only ～30 atoms are energetically important for stabilizing it. The neutral (spin-carying) phase kink is attracted by an energy on the meV scale to carbon atoms joining a non-hydrogen side-group, in contrast to charged phase kinks, where this attraction is estimated to be 100 to 1000 times larger.     

Coulomb effects in the organic charge transfer salt TTT2I3

Madelung energy and simple band structure calculations on different models of the TTT₂I₃ complex indicate, that the iodine chains do not play an active role in the conduction process. The relatively small Coulomb coupling of the iodine chains to the crystal obtained by the Madelung calculations rationalizes the structural findings about the ordering of these chains at low temperatures. The Madelung energy difference between the localized model (with TTT^o and TTT⁺ ions) and delocalized model (with partly charged $\text{TTT}{}^{\mathrm{<mtext>1</mtext><mtext>2+</mtext>}}$ stacks) is large enough to stabilize the former.     

Posterior Simulation with Priors Specified on Functionals

Abstract

Many Bayesian analyses use Markov chain Monte Carlo (MCMC) techniques. MCMC techniques work fastest (per iteration) when the prior distribution of the parameters is chosen conveniently, such as a conjugate prior. However, this is sometimes at odds with the prior desired by the investigator. We describe two motivating examples where nonconjugate priors are preferred. One is a Dirichlet process where it is difficult to implement alternative, nonconjugate priors. We develop a method that allows computation to be done with a convenient prior but adjusts the equilibrium distribution of the Markov chain to be the posterior distribution from the desired prior. In addition to allowing more freedom in choosing prior distributions, the method enables the investigator to perform quick sensitivity analyses, even in nonparametric settings.     

Value Production in a Collaborative Environment

We review some recent endeavors and add some new results to characterize and understand underlying mechanisms in Wikipedia (WP), the paradigmatic example of collaborative value production. We analyzed the statistics of editorial activity in different languages and observed typical circadian and weekly patterns, which enabled us to estimate the geographical origins of contributions to WPs in languages spoken in several time zones. Using a recently introduced measure we showed that the editorial activities have intrinsic dependencies in the burstiness of events. A comparison of the English and Simple English WPs revealed important aspects of language complexity and showed how peer cooperation solved the task of enhancing readability. One of our focus issues was characterizing the conflicts or edit wars in WPs, which helped us to automatically filter out controversial pages. When studying the temporal evolution of the controversiality of such pages we identified typical patterns and classified conflicts accordingly. Our quantitative analysis provides the basis of modeling conflicts and their resolution in collaborative environments and contribute to the understanding of this issue, which becomes increasingly important with the development of information communication technology.     

George Inzelt: a tribute on the occasion of his 75th birthday

Journal of Solid State Electrochemistry -     

Different sensing mechanisms in single wire and mat carbon nanotubes chemical sensors

Chemical sensing properties of single wire and mat form sensor structures fabricated from the same carbon nanotubes (CNT) materials have been compared. Sensing properties of CNT sensors were evaluated upon electrical response in the presence of five vapours as acetone, acetic acid, ethanol, toluene, and water. Diverse behaviour of single wire CNT sensors was found, while the mat structures showed similar response for all the applied vapours. This indicates that the sensing mechanism of random CNT networks cannot be interpreted as a simple summation of the constituting individual CNT effects, but is associated with another robust phenomenon, localized presumably at CNT–CNT junctions, must be supposed.     

Election results and the Sznajd model on Barabasi network

The network of Barabasi and Albert, a preferential growth model where a new node is linked to the old ones with a probability proportional to their connectivity, is applied to Brazilian election results. The application of the Sznajd rule, that only agreeing pairs of people can convince their neighbours, gives a vote distribution in good agreement with reality Received 19 September 2001 and Received in final form 2 November 2001     

Bond length alternation and energy gap in (CH)x. Application of the intermediate exciton formalism

Previous ab initio LCAO Hartree-Fock (HF) self-consistent field (SCF) band structure calculations predicted the alternating all trans (CH)_x (polyacetylene or polyene) to be energetically more stable than the equidistant metallic chain, however, the gap of those calculations was too large (≈7 eV). The present discussion based on semi-empirical PPP hamiltonian explains how electronic correlation neglected in the HF theory reduces this gap to ≈4 eV, while the excitation energy for the creation of excitons is estimated to be below 2 eV. The formalism for this estimation is an intermediate-binding exciton theory with explicit use of numerical Wannier functions. It is concluded that the gap is not due to a spin-density-wave state of the equidistant chain, as expected by Ovchinnikov .     

Cycloaddition reactions with 2,3‐benzodiazepine derivatives

We report here on some 3+2 dipolar cycloaddition reactions of propargyl, allyl and cyano substituted 2,3‐benzodiazepines with in situ generated nitrile oxides and diazomethane. The reactivity of carbon‐nitrogen double bonds of the 5H‐[2,3]benzodiazepine ring system was also noticed.     

Polydopamine as an adhesive coating for open tubular capillary electrochromatography

Polydopamine (PolyD) coating was used as an adhesive layer in the preparation of biological stationary phases for open tubular capillary electrochromatography (OT-CEC). The influence of coating solution freshness, coating time, temperature and dopamine hydrochloride concentration on the PolyD layer formation was studied. The performance of the polyD coating was monitored by measuring the electro-osmotic flow in coated capillaries. Following polyD coating of the capillary, secondary layer material (e.g. cell membrane solutions, phospholipid mixtures or mitochondria) was inserted into the capillary for at least 1?h. The performance of these double-coated capillaries (a polyD layer+a biological material layer) was compared with capillaries containing the respective biological material directly attached to the capillary wall. The study reveals that the presence of polyD layer in fused silica capillaries improves the performance of lipid and membrane fragment coatings in capillaries. At the same time, the thickness of the polyD layer does not have marked impact on the secondary coatings. Analysis with test analytes demonstrated that double-coated capillaries can be applied to study membrane-drug interactions.