Thermomechanical properties of graphene: valence force field model approach

Using the valence force field model of Perebeinos and Tersoff [Phys. Rev. B {\bf79}, 241409(R) (2009)], different energy modes of suspended graphene subjected to tensile or compressive strain are studied. By carrying out Monte Carlo simulations it is found that: i) only for small strains ($|\varepsilon| \lessapprox 0.02$) the total energy is symmetrical in the strain, while it behaves completely different beyond this threshold; ii) the important energy contributions in stretching experiments are stretching, angle bending, out-of-plane term and a term that provides repulsion against $\pi-\pi$ misalignment; iii) in compressing experiments the two latter terms increase rapidly and beyond the buckling transition stretching and bending energies are found to be constant; iv) from stretching-compressing simulations we calculated the Young modulus at room temperature 350$\pm3.15$\,N/m, which is in good agreement with experimental results (340$\pm50$\,N/m) and with ab-initio results [322-353]\,N/m; v) molar heat capacity is estimated to be 24.64\,J/mol$^{-1}$K$^{-1}$ which is comparable with the Dulong-Petit value, i.e. 24.94\,J/mol$^{-1}$K$^{-1}$ and is almost independent of the strain; vi) non-linear scaling properties are obtained from height-height correlations at finite temperature; vii) the used valence force field model results in a temperature independent bending modulus for graphene, and viii) the Gruneisen parameter is estimated to be 0.64.Comment: 8 pages, 5 figures. To appear in J. Phys.: Condens. Matte

EGFR oligomerization organizes kinase-active dimers into competent signalling platforms

Epidermal growth factor receptor (EGFR) signalling is activated by ligand-induced receptor dimerization. Notably, ligand binding also induces EGFR oligomerization, but the structures and functions of the oligomers are poorly understood. Here, we use fluorophore localization imaging with photobleaching to probe the structure of EGFR oligomers. We find that at physiological epidermal growth factor (EGF) concentrations, EGFR assembles into oligomers, as indicated by pairwise distances of receptor-bound fluorophore-conjugated EGF ligands. The pairwise ligand distances correspond well with the predictions of our structural model of the oligomers constructed from molecular dynamics simulations. The model suggests that oligomerization is mediated extracellularly by unoccupied ligand-binding sites and that oligomerization organizes kinase-active dimers in ways optimal for auto-phosphorylation in trans between neighbouring dimers. We argue that ligand-induced oligomerization is essential to the regulation of EGFR signalling

Bioelectromagnetics research within an Australian context: the Australian centre for electromagnetic bioeffects research (ACEBR)

Mobile phone subscriptions continue to increase across the world, with the electromagnetic fields (EMF) emitted by these devices, as well as by related technologies such as Wi-Fi and smart meters, now ubiquitous. This increase in use and consequent exposure to mobile communication (MC)-related EMF has led to concern about possible health effects that could arise from this exposure. Although much research has been conducted since the introduction of these technologies, uncertainty about the impact on health remains. The Australian Centre for Electromagnetic Bioeffects Research (ACEBR) is a National Health and Medical Research Council Centre of Research Excellence that is undertaking research addressing the most important aspects of the MC-EMF health debate, with a strong focus on mechanisms, neurodegenerative diseases, cancer, and exposure dosimetry. This research takes as its starting point the current scientific status quo, but also addresses the adequacy of the evidence for the status quo. Risk communication research complements the above, and aims to ensure that whatever is found, it is communicated effectively and appropriately. This paper provides a summary of this ACEBR research (both completed and ongoing), and discusses the rationale for conducting it in light of the prevailing science.Sarah P. Loughran ... Jim Manavis ... Robert Vink ... et al

The architecture of EGFR's basal complexes reveals autoinhibition mechanisms in dimers and oligomers

Our current understanding of epidermal growth factor receptor (EGFR) autoinhibition is based on X-ray structural data of monomer and dimer receptor fragments and does not explain how mutations achieve ligand-independent phosphorylation. Using a repertoire of imaging technologies and simulations we reveal an extracellular head-to-head interaction through which ligand-free receptor polymer chains of various lengths assemble. The architecture of the head-to-head interaction prevents kinase-mediated dimerisation. The latter, afforded by mutation or intracellular treatments, splits the autoinhibited head-to-head polymers to form stalk-to-stalk flexible non-extended dimers structurally coupled across the plasma membrane to active asymmetric tyrosine kinase dimers, and extended dimers coupled to inactive symmetric kinase dimers. Contrary to the previously proposed main autoinhibitory function of the inactive symmetric kinase dimer, our data suggest that only dysregulated species bear populations of symmetric and asymmetric kinase dimers that coexist in equilibrium at the plasma membrane under the modulation of the C-terminal domain

Determining the diffusion coefficient of fluorescent beads through phasor-FLIM

Abbstract not available

Determining complex aggregate distributions of macromolecules using photobleaching image correlation spectroscopy

Aggregation of cell surface receptors is believed to be linked to their biological function. In this paper, we dis-close the explicit formulation for macromolecular aggregation distribution by means of photobleaching Image Correlation Spectroscopy (pbICS)

Characterization of optical polarization converters made by femtosecond laser writing

Recently, new types of silica polarization converters fabricated by femtosecond lasers have been introduced. These devices use spatially arranged nanogratings found under certain femtosecond laser exposure conditions in fused silica to create arbitrary polarization states by shaping spatially and locally the retardance of an incoming beam. Using this principle, radial and azimuthal polarization converters were demonstrated. These devices make use of a large density of femtosecond laser spots, introducing localized defects, affecting the performance of the converter. To optimize the writing and the post-processing annealing step of these kind of devices, here we introduce a novel fluorescence lifetime imaging microscope (FLIM) working with deep UV (240-280 nm) wavelength excitations. Specifically, we demonstrate the potential of this technique and more generally, how it can be used for characterizing a variety of femtosecond laser induced modifications in fused silica. This UV-FLIM can be used with micro-fluidic and bio-samples to characterize temporal characteristics of fluorescence

Characterization of optical polarization converters made by femtosecond laser writing

Recently, new types of silica polarization converters fabricated by femtosecond lasers have been introduced. These devices use spatially arranged nanogratings found under certain femtosecond laser exposure conditions in fused silica to create arbitrary polarization states by shaping spatially and locally the retardance of an incoming beam. Using this principle, radial and azimuthal polarization converters were demonstrated. These devices make use of a large density of femtosecond laser spots, introducing localized defects, affecting the performance of the converter. To optimize the writing and the post-processing annealing step of these kind of devices, here we introduce a novel fluorescence lifetime imaging microscope (FLIM) working with deep UV (240-280 nm) wavelength excitations. Specifically, we demonstrate the potential of this technique and more generally, how it can be used for characterizing a variety of femtosecond laser induced modifications in fused silica. This UV-FLIM can be used with micro-fluidic and bio-samples to characterize temporal characteristics of fluorescence