Comparing and Simplifying Distinct-Cluster Phylogenetic Networks

Phylogenetic networks are rooted acyclic directed graphs in which the leaves are identified with members of a set X of species. The cluster of a vertex is the set of leaves that are descendants of the vertex. A network is “distinct-cluster” if distinct vertices have distinct clusters. This paper focuses on the set DC(X) of distinct-cluster networks whose leaves are identified with the members of X. For a fixed X, a metric on DC(X) is defined. There is a “cluster-preserving” simplification process by which vertices or certain arcs may be removed without changing the clusters of any remaining vertices. Many of the resulting networks may be uniquely determined without regard to the order of the simplifying operations.     

Design of high-χ block copolymers for lithography

This report describes the design and synthesis of a series of lamella-forming, silicon-containing block copolymers (Si-BCPs) and evaluation of these materials as potential candidates for lithographic applications. The interaction parameter χ of each Si-BCP is measured by both the mean-field theory predicted order-disorder transition and by analysis of X-ray scattering profiles. The introduction of more-polar methoxy and less-polar methylsilyl moieties increases χ to about 2–3 times that of the reference material, poly(styrene-block−4-trimethylsilylstyrene). The incremental increases appear to be essentially additive in this family of block copolymers, suggesting that improvements in χ can be predicted from appropriate monomer choice. Perpendicularly oriented thin-films of the ordered Si-BCPs generated by thermally annealing between two “neutral” polymeric surfaces and developed by etching on commercial RIE equipment show excellent image fidelity. These images demonstrate the excellent etch contrast of the Si-BCPs and document improvements in pattern fidelity that are realized with more strongly segregated BCPs. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 344–352     

Ranking of polymorph stability for a pharmaceutical drug using the Noyes-Whitney titration template method

A further refinement to the screening process of candidate selection in early drug development is the selection of a polymorphic form on the bases of solid state stability. The Noyes-Whitney titration template method has been used routinely by others to determine the intrinsic solubility of sparingly soluble materials. This method uses potentiometric measurements whilst titrating over a pH range to determine the pH-solubility profile of a drug substance. Using a novel modification to the conventional Noyes-Whitney titration template method, this paper describes an application for the determination of the relative stability between polymorphic forms of materials. Such an assessment can be deduced from the change in Gibbs energy that accompanies the physical changes in materials when going from a solid to a solution phase and will be shown to be derived from the intrinsic solubility measurements. In addition, it will be shown that solution calorimetry was used to good effect to help in the interpretation of the solubility results.Three crystalline polymorphic modifications, a hydrate and two anhydrate forms, and an amorphous form of a pure drug substance currently in development in GSK were ranked in terms of physical stability. Stability measurements were made as a function of temperature and a phase diagram over a narrow temperature range was constructed.     

Basic flows of a micropolar liquid

Steady plane shear flow, rotation flow, plane wave disturbances, oscillatory boundary layers, and free surface waves in a micropolar liquid are investigated.     

SYNTHESE DE SPIROPHOSPHORANES CONTENANT UNE LIAISON P–C

Abstract

Les réactions des oxa et oxazaspirophosphoranes à liaison P–H (1)–(4) avec les doubles liaisons activées C?C conduisent aux spirophosphoranes à liaison P_VC (9)-(20). Nous considérons les composés (9)-(20) comme des précurseurs de phosphonates. Le mécanisme de ces réactions a été examiné.

The reaction of oxa and oxazaspirophosphoranes containing P–H bond (1)-(4) with C?C activated double bond lead to spirophosphoranes containing P_V-C bond (9)-(20). We consider compounds (9)-(20) as phosphonates precursors. The mechanism of these reactions has been examined.     

Design of photoresists with reduced environmental impact. II. Water‐soluble resists based on photocrosslinking of poly(2‐isopropenyl‐2‐oxazoline)

The performance of water‐ and solvent‐cast, two‐component photoresist films containing poly(2‐isopropenyl‐2‐oxazoline) or poly(2‐isopropenyl‐2‐oxazoline‐co‐styrene) with a photoacid generator has been investigated. These materials afford negative‐tone images after deep‐UV exposure and development in a suitable medium (water or toluene). Resist solutions prepared from polymers containing at least 80 mol % 2‐isopropenyl‐2‐oxazoline may be cast from and developed in pure water. Features of higher quality can be obtained when the resist is cast from 2‐methoxyethanol, probably because side reactions such as partial hydrolysis of the pendant oxazoline rings in aqueous environments are avoided. It was possible to resolve micrometer scale patterns using ca. 200 mJ/cm² of irradiation at 254 nm, followed by heating 2 min at 130°C and development in water alone. Image quality and etch resistance were improved using copolymers containing up to 20 mol % of styrene repeat units. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1225–1236, 1999     

Molecular model of phenolic polymer dissolution in photolithography

The resolution of photolithographic processes has advanced to the point that difficulties, such as line‐edge roughness, associated with phenomena occurring at molecular length scales are becoming important. In order to control these phenomena, it is necessary to understand them. To that end, a numerical model has been used to simulate the dissolution of phenolic polymers in aqueous base. The simulation applies the Critical Ionization Model to a rectangular‐lattice representation of the polymer matrix. The model has been adapted to describe the dissolution process that is responsible for photoresist function. Both continuum and molecular versions of the model are presented. The Continuum Model yields dissolution profiles that approximate the contours of the calculated spatial variations in chemical blocking (blocking profile). An algorithm has been developed to connect individual cells to form polymer chains, and to fill the lattice in a way that produces a Gaussian chain length distribution. The model employs only a single adjustable parameter, the time‐step correction factor (assuming one can measure the probability of ionization once a site encounters the developer). The Molecular Model predicts a dissolution rate that decreases non‐linearly with respect to degree of chemical blocking, as is observed experimentally. Dissolution profiles can be generated with the Molecular Model based either on this calculated dependence of the dissolution rate on blocking fraction or from direct application of the model to a blocking profile. The probabilistic nature of the model introduces edge roughness of the same degree as that observed experimentally. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2103–2113, 1999