Browsing by Subject "ELASTIC PROPERTIES"

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  • Santos-Perez, Isaac; Oksanen, Hanna M.; Bamford, Dennis H.; Goni, Felix M.; Reguera, David; Abrescia, Nicola G. A. (2017)
    Genome packaging and delivery are fundamental steps in the replication cycle of all viruses. Icosahedral viruses with linear double-stranded DNA (dsDNA) usually pacicage their genome into a preformed, rigid procapsid using the power generated by a virus-encoded packaging ATPase. The pressure and stored energy due to this confinement of DNA at a high density is assumed to drive the initial stages of genome ejection. Membrane-containing icosahedral viruses, such as bacteriophage PRD1, present an additional architectural complexity by enclosing their genome within an internal membrane vesicle. Upon adsorption to a host cell, the PRD1 membrane remodels into a proteo-lipidic tube that provides a conduit for passage of the ejected linear dsDNA through the cell envelope. Based on volume analyses of PRD1 membrane vesicles captured by cryo-electron tomography and modeling of the elastic properties of the vesicle, we propose that the internal membrane makes a crucial and active contribution during infection by maintaining the driving force for DNA ejection and countering the internal turgor pressure of the host These novel functions extend the role of the PRD1 viral membrane beyond tube formation or the mere physical confinement of the genome. The presence and assistance of an internal membrane might constitute a biological advantage that extends also to other viruses that package their linear dsDNA to high density within an internal vesicle. (C) 2016 Elsevier B.V. All rights reserved.
  • Reza, Abdallah; Yu, Hongbing; Mizohata, Kenichiro; Hofmann, Felix (2020)
    Using transient grating spectroscopy (TGS) we measure the thermal diffusivity of tungsten exposed to different levels of 20 MeV self-ion irradiation. Damage as low as 3.2 × 10−4 displacements per atom (dpa) causes a measurable reduction in thermal diffusivity. Doses of 0.1 dpa and above, up to 10 dpa, give a degradation of ̴55% from the pristine value at room temperature. Using a kinetic theory model, the density of irradiation-induced point defects is estimated based on the measured changes in thermal diffusivity as a function of dose. These predictions are compared with point defect and dislocation loop densities observed in transmission electron microscopy (TEM). Molecular dynamics (MD) predictions are combined with the TEM observations to estimate the density of point defects associated with defect clusters too small to be probed by TEM. When these “invisible” defects are accounted for, the total point defect density agrees well with that estimated from TGS for a range of doses spanning 3 orders of magnitude. Kinetic theory modelling is also used to estimate the thermal diffusivity degradation expected due to TEM-visible and invisible defects. Finely distributed invisible defects appear to play a much more important role in the thermal diffusivity reduction than larger TEM-visible dislocation loops. This work demonstrates the capability of TGS, in conjunction with kinetic theory models, to provide rapid, quantitative insight into defect densities and property evolution in irradiated materials.