Superconducting state in strong coupling

We consider the behavior of the critical temperature in the limit of strong electron-phonon coupling. The peculiar behavior of the order parameter in this limit allows one to evaluate T_c analytically and directly from Eliashberg's equation. We also consider the effect of Coulomb interaction and the contribution of low phonon modes, the role of lattice instabilities and the relative contribution of phonon and non-phonon interactions.     

Dominance relations in polling systems

In this paper we compare several service disciplines commonly used in polling systems. We present a sample path comparison which allows us to evaluate the efficiency of the different policies based on thetotal amount of work found in the systemat any time. The analysis is carried out for a large variety of polling schemes under fairly general conditions and can be used to construct a hierarchy of the different service schemes.     

Organic Conductors – Metals With a Short Mean Free Path

At ambient temperature the organic conductors have a mean free path of the order of a lattice constant. In this temperature range the magnetic susceptibility is enhanced over its Pauli value and the resistivity obeys a T²-law just like at lower T where the conductivity is metallic. We describe a theory based on a quadratic electron-phonon coupling which accounts for these features.     

Locality of reference and the use of sojourn time variance for measuring queue unfairness

Sojourn time variance is widely used as an indication of queue unfairness. We demonstrate that this quantity has a disadvantage, since it is not local to the busy period in which it is measured. We show that RAQFM, a recently proposed queue fairness metric, does possess such a locality property.     

Pseudo-cyclic policies for multi-queue single server systems

In this paper we evaluate the waiting time performance of cycle-time guided algorithms in semi-dynamic polling models. In these models knowledge of the system state is used by the server in the process of on-line determination of the visit pattern. Our main focus is on pseudo-cyclic algorithms which achievefairness by visiting every station exactly once in each cycle.It is shown that in fully symmetric systems the performance ofevery pseudocyclic policy is bounded between the performance of the cycle maximization and the cycle minimization strategies. In particular, stochastic dominance is shown with regard to system workload, implying dominance of mean waiting times. In a fluid approximation model the performance ratio between the two bounding policies is derived and shown to be always between 1 and 3/4 under the gated service regime and between 1 and 1/2 under the exhaustive service regime. Under both regimes, the ratio approaches 3/4 when the number of stations grows to infinity. Simulation results suggest that a similar performance ratio holds for the general (non-symmetric) stochastic model.Further, we study strategies which are guided by the cycle maximization (minimization) criteria, but which do not constrain themselves to pseudo-cyclic orders. It is shown that depending on the switch-over parameters these more dynamic policies may perform much worse than the pseudo-cyclic schemes.     

Composites of hydrophilic polymers and organic nanocrystals enable enhanced robustness

We describe a new family of composite materials, polymer/organic nanocrystal (ONC) hybrids. These were prepared from soluble ONCs based on perylene diimides (PDI) and water‐soluble polymers (sodium alginate and polyvinyl alcohol). Polymer/ONC films were characterized by optical spectroscopy, electron microscopy, and tensile strength studies. The films show enhanced chemical and mechanical stability due to synergy between the constituents. The hybrid films are stable in both water and organic solvents, unlike the individual components. The ONCs we employed possess nonlinear optical activity (second harmonic generation, SHG); they showed improved photostability (stable SHG under laser light) in the hybrids. Tensile strength enhancement (as high as twofold in the film having just 2.4% ONCs by weight) was observed as revealed by mechanical measurements. Hybrids with aligned ONCs were also prepared using simple extrusion via syringe needle followed by gelation. Employing ONCs in polymeric hybrid materials enables facile fabrication in aqueous media, synergy, chemical, mechanical, and photostability as well as useful photofunction (SHG), introducing a versatile class of composite materials.     

OPTIMAL AUSTRALIAN AND JAPANESE HARVESTING OF SOUTHERN BLUEFIN TUNA

A 19-cohort bioeconomic model is developed for the southern bluefin tuna fishery. The fish are long-lived and highly migratory. They are harvested as juveniles by Australia and Japan in Australian waters, and as adults by Japan on the high seas. The potential for conflict between Australian and Japanese fleets therefore exists in the exploitation of the fishery. The model is used to compare Japanese and Australian social rents and harvest levels through time under joint maximization, and under duopoly.     

Origin of delocalization in organic molecular conductors

The delocalization of electron states in one-dimensional metals, such as TTF-TCNQ, accounts for the observed itinerant motion of the electrons at temperatures above about 50 K. This delocalization is related to the extended nature of the molecules in organic metals, which causes the amplitude for forward scattering by the phonons to exceed the amplitude for backward scattering by an order of magnitude. The large forward scattering, which delocalizes the electrons, does not contribute to the resistivity in the delocalized state.     

k‐Nearest neighbors optimization‐based outlier removal

Datasets of molecular compounds often contain outliers, that is, compounds which are different from the rest of the dataset. Outliers, while often interesting may affect data interpretation, model generation, and decisions making, and therefore, should be removed from the dataset prior to modeling efforts. Here, we describe a new method for the iterative identification and removal of outliers based on a k‐nearest neighbors optimization algorithm. We demonstrate for three different datasets that the removal of outliers using the new algorithm provides filtered datasets which are better than those provided by four alternative outlier removal procedures as well as by random compound removal in two important aspects: (1) they better maintain the diversity of the parent datasets; (2) they give rise to quantitative structure activity relationship (QSAR) models with much better prediction statistics. The new algorithm is, therefore, suitable for the pretreatment of datasets prior to QSAR modeling. © 2014 Wiley Periodicals, Inc.     

MC(JBW): Simple but smart Monte Carlo algorithm for free energy simulations of multiconformational molecules

Many of the most common molecular simulation methods, including Monte Carlo (MC) and molecular or stochastic dynamics (MD or SD), have significant difficulties in sampling the space of molecular potential energy surfaces characterized by multiple conformational minima and significant energy barriers. In such cases improved sampling can be obtained by special techniques that lower such barriers or somehow direct search steps toward different low energy regions of space. We recently described a hybrid MC/SD algorithm [MC(JBW)/SD] incorporating such a technique that directed MC moves of selected torsion and bond angles toward known low energy regions of conformational space. Exploration of other degrees of freedom was left to the SD part of the hybrid algorithm. In the work described here, we develop a related but simpler simulation algorithm that uses only MC to sample all degrees of freedom (e.g., stretch, bend, and torsion). We term this algorithm MC(JBW). Using simulations on various model potential energy surfaces and on simple molecular systems (n-pentane, n-butane, and cyclohexane), MC(JBW) is shown to generate ensembles of states that are indistinguishable from the canonical ensembles generated by classical Metropolis MC in the limit of very long simulations. We further demonstrate the utility of MC(JBW) by evaluating the room temperature free energy differences between conformers of various substituted cyclohexanes and the larger ring hydrocarbons cycloheptane, cyclooctane, cyclononane, and cyclodecane. The results compare favorably with available experimental data and results from previously reported MC(JBW)/SD conformational free energy calculations. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1736–1745, 1998