100th Anniversary of Macromolecular Science Viewpoint: Opportunities in the Physics of Sequence-Defined Polymers

Polymer science has been driven by ever-increasing molecular complexity, as polymer synthesis expands an already-vast palette of chemical and architectural parameter space. Copolymers represent a key example, where simple homopolymers have given rise to random, alternating, gradient, and block copolymers. Polymer physics has provided the insight needed to explore this monomer sequence parameter space. The future of polymer science, however, must contend with further increases in monomer precision, as this class of macromolecules moves ever closer to the sequence-monodisperse polymers that are the workhorses of biology. The advent of sequence-defined polymers gives rise to opportunities for material design, with increasing levels of chemical information being incorporated into long-chain molecules; however, this also raises questions that polymer physics must address. What properties uniquely emerge from sequence-definition? Is this circumstance-dependent? How do we define and think about sequence dispersity? How do we think about a hierarchy of sequence effects? Are more sophisticated characterization methods, as well as theoretical and computational tools, needed to understand this class of macromolecules? The answers to these questions touch on many difficult scientific challenges, setting the stage for a rich future for sequence-defined polymers in polymer physics

Recent progress in the science of complex coacervation

Complex coacervation is an associative, liquid–liquid phase separation that can occur in solutions of oppositely-charged macromolecular species, such as proteins, polymers, and colloids. This process results in a coacervate phase, which is a dense mix of the oppositely-charged components, and a supernatant phase, which is primarily devoid of these same species. First observed almost a century ago, coacervates have since found relevance in a wide range of applications; they are used in personal care and food products, cutting edge biotechnology, and as a motif for materials design and self-assembly. There has recently been a renaissance in our understanding of this important class of material phenomena, bringing the science of coacervation to the forefront of polymer and colloid science, biophysics, and industrial materials design. In this review, we describe the emergence of a number of these new research directions, specifically in the context of polymer–polymer complex coacervates, which are inspired by a number of key physical and chemical insights and driven by a diverse range of experimental, theoretical, and computational approaches

Evaluation of anomalies observed on film from S-190A flight system calibration test

Due to a persistent problem of scratched film from testing of the Skylab S-190A system, a series of tests were designed to identify the cause of the film scratching. The procedures followed in this test for pretest handling and packaging of the film, the makeup of the rolls for processing, and the results of the processed film evaluation are reported

Compositional redistribution during casting of Hg sub 0.8 Cd sub 0.2 Te alloys

A series of Hg(0.8)Cd(0.2)Te ingots was cast both vertically and horizontally under well-defined thermal conditions by using a two-zone furnace with isothermal heat-pipe liners. The main objective of the experiments was to establish correlations between casting parameters and compositional redistribution and to develop ground-based data for a proposed flight experiment of casting of Hg(1-x)Cd(x)Te alloys under reduced gravity conditions. The compositional variations along the axial and radial directions were determined by precision density measurements, infrared transmission spectra, and X-ray energy dispersion spectrometry. Comparison between the experimental results and a numerical simulation of the solidification process of Hg(0.8)Cd(0.2)Te is described

THE POTENTIAL FOR REVENUE INSURANCE POLICIES IN THE SOUTH

The 1996 Farm Act and the 1994 Crop Insurance Reform Act are recent examples of policy changes that have increased risks for U.S. farmers. New products are emerging to help farmers manage risks. This article examines some of the policy changes, farmer responses, and new risk-sharing products. The focus turns to the new revenue insurance products and their potential in the South. While there are reasons to believe revenue insurance should be attractive in the South, any revenue products that use existing crop insurance rates will face difficulties since poor actuarial performance in the South has resulted in relatively high rates.Agricultural policy, Crop insurance, Revenue insurance, Risk, Southern agriculture, Risk and Uncertainty,

Medical physicists should seek patent protection for new ideas before publishing articles about them

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135069/1/mp8811.pd

PRISM-Based Theory of Complex Coacervation: Excluded Volume versus Chain Correlation

Aqueous solutions of oppositely charged polyelectrolytes can undergo liquid–liquid phase separation into materials known as complex coacervates. These coacervates have been a subject of intense experimental and theoretical interest. Efforts to provide a physical description of complex coacervates have led to a number of theories that qualitatively (and sometimes quantitatively) agree with experimental data. However, this agreement often occurs in a degeneracy of models with profoundly different starting assumptions and different levels of sophistication. Theoretical difficulties in these systems are similar to those in most polyelectrolyte systems where charged species are highly correlated. These highly correlated systems can be described using liquid state (LS) integral equation theories, which surpass mean-field theories by providing information on local charge ordering. We extend these ideas to complex coacervate systems using PRISM-type theories and are able to capture effects not observable in traditional coacervate models, particularly connectivity and excluded volume effects. We can thus bridge two traditional but incommensurate theories meant to describe complex coacervates: the Voorn–Overbeek theory and counterion release. Importantly, we hypothesize that a cancellation of connectivity and excluded volume effects provides an explanation for the ability of Voorn–Overbeek theory to fit experimental data despite its well-known approximations

The NIF LinkOut Broker: A Web Resource to Facilitate Federated Data Integration using NCBI Identifiers

This paper describes the NIF LinkOut Broker (NLB) that has been built as part of the Neuroscience Information Framework (NIF) project. The NLB is designed to coordinate the assembly of links to neuroscience information items (e.g., experimental data, knowledge bases, and software tools) that are (1) accessible via the Web, and (2) related to entries in the National Center for Biotechnology Information’s (NCBI’s) Entrez system. The NLB collects these links from each resource and passes them to the NCBI which incorporates them into its Entrez LinkOut service. In this way, an Entrez user looking at a specific Entrez entry can LinkOut directly to related neuroscience information. The information stored in the NLB can also be utilized in other ways. A second approach, which is operational on a pilot basis, is for the NLB Web server to create dynamically its own Web page of LinkOut links for each NCBI identifier in the NLB database. This approach can allow other resources (in addition to the NCBI Entrez) to LinkOut to related neuroscience information. The paper describes the current NLB system and discusses certain design issues that arose during its implementation

Issues in the Design of a Pilot Concept-Based Query Interface for the Neuroinformatics Information Framework

This paper describes a pilot query interface that has been constructed to help us explore a "concept-based" approach for searching the Neuroscience Information Framework (NIF). The query interface is concept-based in the sense that the search terms submitted through the interface are selected from a standardized vocabulary of terms (concepts) that are structured in the form of an ontology. The NIF contains three primary resources: the NIF Resource Registry, the NIF Document Archive, and the NIF Database Mediator. These NIF resources are very different in their nature and therefore pose challenges when designing a single interface from which searches can be automatically launched against all three resources simultaneously. The paper first discusses briefly several background issues involving the use of standardized biomedical vocabularies in biomedical information retrieval, and then presents a detailed example that illustrates how the pilot concept-based query interface operates. The paper concludes by discussing certain lessons learned in the development of the current version of the interface