Rigorous theory of nuclear fusion rates in a plasma

Real-time thermal field theory is used to reveal the structure of plasma corrections to nuclear reactions. Previous results are recovered in a fashion that clarifies their nature, and new extensions are made. Brown and Yaffe have introduced the methods of effective quantum field theory into plasma physics. They are used here to treat the interesting limiting case of dilute but very highly charged particles reacting in a dilute, one-component plasma. The highly charged particles are very strongly coupled to this background plasma. The effective field theory proves that this mean field solution plus the one-loop term dominate; higher loop corrections are negligible even though the problem involves strong coupling. Such analytic results for very strong coupling are rarely available, and they can serve as benchmarks for testing computer models.Comment: 4 pages and 2 figures, presented at SCCS 2005, June 20-25, Moscow, Russi

Programmable viscoelastic matrices from artificial proteins

Extracellular matrix compliance influences cellular adhesion and migration, proliferation and apoptosis, and differentiation. Much of our current knowledge of the effects of substrate stiffness on cellular behavior is based on elastic substrates, in particular cross‐linked polyacrylamide hydrogels. Biological tissues, however, are viscoelastic and exhibit stress relaxation and energy dissipation on physiologically relevant timescales. While emerging evidence suggests that these physical properties also influence cellular behavior, materials in which viscoelasticity can be precisely engineered are currently lacking. Here, we describe programmable hydrogel matrices assembled from artificial recombinant proteins designed to be cross‐linked by covalent bonds involving cysteine residues, by association of helical domains as coiled coils, or by both mechanisms. Using these proteins, we construct chemical, physical, and chemical‐physical hydrogel networks that deform elastically or viscoelastically depending on the type of cross‐linking (Dooling et al., Adv. Mater., 2016, 28, 4651–4657). In viscoelastic networks, the amount of stress relaxation is tuned by controlling the ratio of physical cross‐linking to chemical crosslinking, and the timescale for stress relaxation is tuned over five orders of magnitude by single point mutations to the coiled‐coil physical cross‐linking domain (Dooling and Tirrell, ACS Cent. Sci., 2016, 2, 812–819). The genetic engineering approach also allows biological activity to be encoded directly within the protein sequence in the form of cell‐adhesive domains and proteolytic cleavage sites. The capacity to program the viscoelasticity and biological activity of hydrogel matrices is anticipated to have applications in studying and engineering cell‐matrix interactions

Material Selection Guidelines to Limit Atomic Oxygen Effects on Spacecraft Surfaces

This report provides guidelines in selecting materials for satellites and space platforms, designed to operate within the Low-Earth orbit environment, which limit the effects of atomic oxygen interactions with spacecraft surfaces. This document should be treated as an introduction rather than a comprehensive guide since analytical and flight technologies continue to evolve, flight experiments are conducted as primary or piggyback opportunities arise, and our understanding of materials interactions and protection methods grows. The reader is urged to consult recent literature and current web sites containing information about research and flight results

LDEF materials results for spacecraft applications: Executive summary

To address the challenges of space environmental effects, NASA designed the Long Duration Exposure Facility (LDEF) for an 18-month mission to expose thousands of samples of candidate materials that might be used on a space station or other orbital spacecraft. LDEF was launched in April 1984 and was to have been returned to Earth in 1985. Changes in mission schedules postponed retrieval until January 1990, after 69 months in orbit. Analyses of the samples recovered from LDEF have provided spacecraft designers and managers with the most extensive data base on space materials phenomena. Many LDEF samples were greatly changed by extended space exposure. Among even the most radially altered samples, NASA and its science teams are finding a wealth of surprising conclusions and tantalizing clues about the effects of space on materials. Many were discussed at the first two LDEF results conferences and subsequent professional papers. The LDEF Materials Results for Spacecraft Applications Conference was convened in Huntsville to discuss implications for spacecraft design. Already, paint and thermal blanket selections for space station and other spacecraft have been affected by LDEF data. This volume synopsizes those results

A model of CP Violation from Extra Dimension

We construct a realistic model of CP violation in which CP is broken in the process of dimensional reduction and orbifold compactification from a five dimensional theories with $SU(3)\times SU(3) \times SU(3)$ gauge symmetry. CP violation is a result of the Hosotani type gauge configuration in the higher dimension.Comment: 5 page