Activities of the NASA sponsored SRI technology applications team in transferring aerospace technology to the public sector Quarterly progress report, 1 Jul. - 30 Sep. 1969

Aerospace technology utilization in air pollution, criminalistics, and public transportatio

Detection of intermediates and kinetic control during assembly of bacteriophage P22 procapsid

Bacteriophage P22 serves as a model for the assembly and maturation of other icosahedral double-stranded DNA viruses. P22 coat and scaffolding proteins assemble in vitro into an icosahedral procapsid, which then expands during DNA packaging (maturation). Efficient in vitro assembly makes this system suitable for design and production of monodisperse spherical nanoparticles (diameter ≈50 nm). In this work we explore the possibility of controlling the outcome of assembly by scaffolding protein engineering. The scaffolding protein exists in monomer-dimer-tetramer equilibrium. We address the role of monomers and dimers in assembly by using three different scaffolding proteins with altered monomer-dimer equilibrium (weak dimer, covalent dimer, monomer). The progress and outcome of assembly was monitored by time-resolved X-ray scattering which allowed us to distinguish between closed shells and incomplete assembly intermediates. Binding of scaffolding monomer activates the coat protein for assembly. Excess dimeric scaffolding protein resulted in rapid nucleation and kinetic trapping yielding incomplete shells. Addition of monomeric wild type scaffold with excess coat protein completed these metastable shells. Thus, the monomeric scaffolding protein plays an essential role in the elongation phase by activating the coat and effectively lowering its critical concentration for assembly

Ice Fog as a Problem of Air Pollution in the Arctic

Extensive field programs were undertaken in Alaska during the winters of 1952-1954 to determine the causes of ice-fog formation. Ice fog forms at temperatures near -30 C and below in populated areas and is particularly troublesome at military installations. It poses no threat to health but seriously restricts visibility. The fog is a direct result of supersaturation of the cold air with water vapor from man-made sources. The only methods of curtailing its formation appear to be restricting vapor emission into the air or confining emission to selected fall stacks. Microphotographs of ice fog particles collected at various temperatures are included

Frozen-droplets aggregation at temperature below -40°C

The onset of the aggregation process of frozen droplets was investigated in laboratory settings. The experiments were conducted in a cloud chamber controlled at temperatures cooler than −40°C, where pure water droplets freeze spontaneously without the need for ice nucleating particles. We present laboratory evidence supporting that the aggregation process can occur for frozen droplet sizes around 10 μm in diameter and at concentrations observed in the cloud chamber of 70 ± 20 cm−3, which can be found in some regions of anvil cirrus. The characteristics and morphology of the aggregates were examined in detail. Additional experiments performed with electrically charged droplets show that the aggregation processes can be significantly accelerated, suggesting that the mechanism of collision and adhesion could be related to electrical forces generated by different charge distributions or dipole interactions between the interacting ice surfaces. The current work aims at advancing our fundamental understanding of the aggregation process of frozen droplets, which is necessary for understanding the cloud microphysical processes.Fil: Pedernera, Débora Analía. Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, Córdoba; ArgentinaFil: Avila, Eldo Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Structure of the Sec13–Sec16 edge element, a template for assembly of the COPII vesicle coat

The crystal structure of a Sec13–Sec16 complex reveals its functions in the early steps of COPII coat complex assembly

Structural puzzles in virology solved with an overarching icosahedral design principle

Viruses have evolved protein containers with a wide spectrum of icosahedral architectures to protect their genetic material. The geometric constraints defining these container designs, and their implications for viral evolution, are open problems in virology. The principle of quasi-equivalence is currently used to predict virus architecture, but improved imaging techniques have revealed increasing numbers of viral outliers. We show that this theory is a special case of an overarching design principle for icosahedral, as well as octahedral, architectures that can be formulated in terms of the Archimedean lattices and their duals. These surface structures encompass different blueprints for capsids with same numbers of structural proteins, as well as for capsid architectures formed from a combination of minor and major capsid proteins, and are conserved within viral lineages. They also apply to other icosahedral structures in nature, and offer alternative designs for man-made materials and nanocontainers in bionanotechnology

Female Reproductive Strategies in the Ruff (Philomachus pugnax)

Traditionally, females have been considered to be strictly monogamous. Today, we know that females in the majority of species actively seek out and mate with several males. Trying to understand female preferences, including what benefits mate choice entails, has been the focus of intense research during the last decades. Females can gain both direct (e.g. access to better territories or paternal care) and indirect (i.e. genetic) benefits. The aim of this thesis is to further our understanding of the female reproductive strategies in the ruff, Philomachus pugnax (Aves, Scolopacidae). The ruff is a lekking wader, where males gather on leks to display to females that come there to mate. Males do not provide any paternal care to the offspring. Lekking systems are ideal for studying indirect benefits of female choice, as females do not gain any direct benefits from males. Females mated with several males and 50% of the broods were fathered by at least two males. The level of genetic similarity between two parents has previously been shown to be an important source of variation in offspring fitness. Males that were less closely related to the female fathered more offspring in broods with multiple paternity, such that females that mated multiply gained in terms of receiving more outbred offspring. There did not, however, appear to be an overall female preference for less closely related males. There are two genetically determined male reproductive strategies in the ruff, that differ in behaviour and morphology. There was no evidence for females taking male strategy into account when choosing a partner. Female post-fertilisation strategies may also influence fitness, e.g. through differential investment in eggs, gender of the offspring and choice of breeding habitat. Females allocated sex in a non-random manner dependent upon body condition, such that females in good condition had more daughters. Females were found to nest in higher than average vegetation and in areas with higher than average abundance of insects, factors likely to influence predation rates on both eggs and young, as well as foraging opportunities for the precocial young. Further, females were faithful to their previous breeding site and usually nested within meters of their previous nest. Hatching success did not, however, affect a female’s decision to return or not