Accurate estimation of the density of states from Monte Carlo transition probability data

This study develops an efficient approach for calculating the density of states from energy transition probability matrices generated from extended sampling Monte Carlo simulations. Direct and iterative variants of the method are shown to achieve high accuracy when applied to the two-dimensional Ising model for which the density of states function can be determined exactly. They are also used to calculate the density of states of lattice protein and Lennard-Jones models which generate more complex nonzero matrix structures. Whereas the protein simulations test the method on a system exhibiting a rugged free energy landscape, the Lennard-Jones calculations highlight implementation details that arise in applications to continuous energy systems. Density of states results for these two systems agree with estimates from multiple histogram reweighting, demonstrating that the new method provides an alternative approach for computing the thermodynamic properties of complex systems.     

Polymer friction-transfer layers as orienting substrates

A variety of polymers were investigated as candidates for the formation of oriented layers by friction transfer. Only polyethylene, the liquid-crystalline Vectrá and fluorinated ethylene-propylene copolymer were found to yield oriented transfer layers. These layers, in turn, were found to induce the oriented growth a variety of species deposited onto them from the melt, solution or vapor phase. The present orientation-inducing friction-transfer layers, however, were found to be inferior to those of poly(tetrafluoroethylene) [PTFE], described previously. © 1994 John Wiley & Sons, Inc.     

Three-phase flow and gravity drainage in porous media

We present a theoretical and experimental treatment of three-phase flow in water-wet porous media from the molecular level upwards. Many three-phase systems in polluted soil and oil reservoirs have a positive initial spreading coefficient, which means that oil spontaneously spreads as a layer between water and gas. We compute the thickness and stability of this oil layer and show that appreciable recovery of oil by drainage only occurs when the oil layer occupies crevices or roughness in the pore space. We then analyze the distribution of oil, water and gas in vertical equilibrium for a spreading system, which is governed byα=γ _ow (ρ _o ?ρ _g )/γ _go (ρ _w ?ρ _o ), whereγ _ow andγ _go are the oil/water and gas/oil interfacial tensions respectively, andρ _g ,ρ _o andρ _w are the gas, oil and water densities respectively. Ifα>1, there is a height above the oil/water contact, beyond which connected oil only exists as a molecular film, with a negligible saturation. This height is independent of the structure of the porous medium. Whenα<1, large quantities of oil remain in the pore space and gravity drainage is not efficient. If the initial spreading coefficient is negative, oil can be trapped and the recovery is also poor. We performed gravity drainage experiments in sand columns and capillary tubes which confirmed our predictions.     

Stable isotopic studies of earthworm feeding ecology in tropical ecosystems of Puerto Rico

Feeding strategies of earthworms and their influence on soil processes are often inferred from morphological, behavioral and physiological traits. We used (13)C and (15)N natural abundance in earthworms, soils and plants to explore patterns of resource utilization by different species of earthworms in three tropical ecosystems in Puerto Rico. In a high altitude dwarf forest, native earthworms Trigaster longissimus and Estherella sp. showed less (15)N enrichment ((15)N = 3-6 per thousand) than exotic Pontoscolex corethrurus ((15)N =7-9 per thousand) indicating different food sources or stronger isotopic discrimination by the latter. Conversely, in a lower altitude tabonuco forest, Estherella sp. and P. corethrurus overlapped completely in (15)N enrichment ((15)N = 6-9 per thousand), suggesting the potential for interspecific competition for N resources. A tabonuco forest converted to pasture contained only P. corethrurus which were less enriched in (15)N than those in the forest sites, but more highly enriched in (13)C suggesting assimilation of C from the predominant C(4) grass. These results support the utility of stable isotopes to delineate resource partitioning and potential competitive interactions among earthworm species. Copyright 1999 John Wiley & Sons, Ltd.     

Dual functions of a novel low-gap polymer for near infra-red photovoltaics and light-emitting diodes

We have synthesised and characterised a new low-gap conjugated polymer, with a broad absorption profile. In blends with a C(70) derivative we demonstrate power conversion efficiencies of 0.76%. We show electroluminescence from the polymer peaking at 956 nm, and quantum efficiency of 0.02% in a blend.     

Die potentiometrische Ferro- und Ferrocyanid-Bestimmung mit Kaliumbromat haben

Ohne Zusammenfassung     

Two-Steps Hantzsch Based Macrocyclization Approach for the Synthesis of Thiazole Containing Cyclopeptides

Macrocyclization via an efficient high-yielding solid-phase intramolecular thioalkylation reaction is described. The reaction of S-nucleophiles with newly generated N-terminal 4-chloromethyl thiazoles led to the desired macrocyclization products 5 in high purities and good overall yields.     

An Experimental Design for Measuring Advertising Payoff

A model is described to assist retail management in developing an effective advertising strategy. The difficulties of advertising decision-making are reviewed and the nature of the particular marketing problem is outlined. It is shown how market research is used to construct an effective appeal and choice of media. An experiment, using a split-plot design, is then performed to estimate the payoff of advertising. This provides a clear framework for developing advertising decisions and for their implementation and control.