Self-Assembly of Patchy Particles into Polymer Chains: A Parameter-Free Comparison between Wertheim Theory and Monte Carlo Simulation

We numerically study a simple fluid composed of particles having a hard-core repulsion, complemented by two short-ranged attractive (sticky) spots at the particle poles, which provides a simple model for equilibrium polymerization of linear chains. The simplicity of the model allows for a close comparison, with no fitting parameters, between simulations and theoretical predictions based on the Wertheim perturbation theory, a unique framework for the analytic prediction of the properties of self-assembling particle systems in terms of molecular parameter and liquid state correlation functions. This theory has not been subjected to stringent tests against simulation data for ordering across the polymerization transition. We numerically determine many of the thermodynamic properties governing this basic form of self-assembly (energy per particle, order parameter or average fraction of particles in the associated state, average chain length, chain length distribution, average end-to-end distance of the chains, and the static structure factor) and find that predictions of the Wertheim theory accord remarkably well with the simulation results

What have we already learned from the CMB?

The COBE satellite, and the DMR experiment in particular, was extraordinarily successful. However, the DMR results were announced about 7 years ago, during which time a great deal more has been learned about anisotropies in the Cosmic Microwave Background (CMB). The CMB experiments currently being designed and built, including long-duration balloons, interferometers, and two space missions, promise to address several fundamental cosmological issues. We present our evaluation of what we already know, what we are beginning to learn now, and what the future may bring.Comment: 20 pages, 3 figures. Changes to match version accepted by PAS

Seasonal Movements and Distribution of Steller’s Eiders (Polysticta stelleri) Wintering at Kodiak Island, Alaska

We used satellite telemetry in 2004–06 to describe the annual movements and habitat use of a segment of the Pacific population of Steller’s Eiders (Polysticta stelleri) that winters at Kodiak Island, Alaska. Information about broad-scale patterns of seasonal distribution and links among annual cycle stages is critical for interpreting population trends and developing conservation strategies. We captured birds in Chiniak Bay at Kodiak Island in late February and early March and monitored the movements after departure from Kodiak Island of 24 satellite-tagged birds: 16 after-second-year (ASY) age class females, one second-year age class female, and seven ASY males. All birds used the same intercontinental migration corridor during spring, but routes and chronology of spring migration appeared to vary by year and among individuals. Sixteen of the 24 birds that were tracked migrated to breeding areas along the Arctic coast of Russia from the Chukotka Peninsula to the Taymyr Peninsula; five birds, assumed to be non-breeding, spent the summer in nearshore waters of Russia and Alaska; and the remaining three birds either died during spring migration or had failed transmitters. Thirteen birds were tracked to molt sites that were broadly distributed along the coast of Alaska. Molt sites included St. Lawrence Island, the Kuskokwim Shoals, Kamishak Bay, and three sites along the Alaska Peninsula. Twelve of these 13 birds returned to Kodiak Island to winter, and a single male wintered on the Alaska Peninsula. Steller’s Eiders marked during winter at Kodiak Island were widely distributed during the breeding season, but a large proportion of marked birds returned to molting and wintering areas in two years of the study.De 2004 à 2006, nous avons recouru à la télémétrie satellitaire pour décrire l’utilisation de l’habitat et les mouvements annuels d’un segment de la population d’eiders de Steller (Polysticta stelleri) dans la région du Pacifique, eiders qui hivernent sur l’île Kodiak, en Alaska. Il est essentiel d’obtenir des données sur les tendances à grande échelle de la répartition saisonnière et des liens entre les divers stades du cycle annuel de ces oiseaux afin d’être en mesure d’interpréter leurs tendances démographiques et d’élaborer des stratégies de conservation. Nous avons capturé des oiseaux dans la baie Chiniak de l’île Kodiak vers la fin février et le début mars. Après notre départ de l’île Kodiak, nous avons surveillé les mouvements de 24 oiseaux pistés par satellite : 16 femelles de plus de deux ans, une femelle de deux ans et sept mâles de plus de deux ans. Tous les oiseaux ont emprunté le même couloir de migration intercontinental au printemps, mais les routes et la chronologie de la migration printanière semblaient varier d’une année à l’autre et d’un individu à l’autre. Seize des24 oiseaux pistés ont migré vers des aires de reproduction situées le long de la côte arctique de la Russie, depuis la presqu’île de Tchoukotkae jusqu’à la presqu’île de Taïmyr; cinq oiseaux, probablement non reproducteurs, ont passé l’été dans les eaux côtières de la Russie et de l’Alaska, tandis que les trois autres oiseaux sont morts pendant la migration printanière ou étaient dotés de transmetteurs défectueux. Treize oiseaux ont été repérés à des sites de mue largement répartis le long de la côte de l’Alaska. Parmi ces sites, notons ceux de l’île Saint-Laurent, du haut-fond de Kuskokwim, de la baie de Kamishak et de trois autres sites le long de la péninsule de l’Alaska. Douze de ces 13 oiseaux sont retournés à l’île Kodiak pour passer l’hiver, et un seul mâle a hiverné dans la péninsule de l’Alaska. Les eiders de Steller qui ont été marqués à l’île Kodiak pendant l’hiver étaient largement répartis pendant la saison de reproduction, mais une grande proportion d’oiseaux pistés sont retournés aux aires de mue et d’hivernage au cours des deux années visées par l’étude

A Comparison of Qualifications Based-Selection and Best Value Procurement for Construction Manager/General Contractor Highway Construction

Faster project delivery and the infusion of contractor knowledge into design are the primary drivers for choosing construction manager/general contractor (CM/GC) project delivery. This paper focuses on the use of qualifications-based (QBS) and best-value (BV) procurement approaches, how and why agencies use each, and their associated opportunities and obstacles. Data for this study were obtained from a majority of federally funded CM/GC projects completed between 2005 to 2015. The findings are that BV and QBS projects characteristics and performance have no statistically significant difference. The choice of BV or QBS coincides with the agency’s CM/GC stage of organizational development and influences of non-agency stakeholders on the CM/GC process. When agencies and the local industry are new to CM/GC, they were found to use BV as it is closer to the traditional procurement culture and it is perceived to result in a fair market project price. Alternatively, agencies and local industry partners with an established history of using CM/GC were found to choose QBS. The low level of design at the time of procurement, means that assumptions relating to risk, production rates, materials sources, etc. may be too preliminary to secure a reliable price. The use of BV procurement was found to pose a risk to innovation and increase negotiation efforts. Qualitative trends from the project data, interviews and literature point to agencies using QBS for the majority of CM/GC project and BV on CM/GC projects with lesser complexity or more highly developed designs at the time of selection

Comments and general discussion on “The anatomical problem posed by brain complexity and size: a potential solution”

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