On leading order gravitational backreactions in de Sitter spacetime

Backreactions are considered in a de Sitter spacetime whose cosmological constant is generated by the potential of scalar field. The leading order gravitational effect of nonlinear matter fluctuations is analyzed and it is found that the initial value problem for the perturbed Einstein equations possesses linearization instabilities. We show that these linearization instabilities can be avoided by assuming strict de Sitter invariance of the quantum states of the linearized fluctuations. We furthermore show that quantum anomalies do not block the invariance requirement. This invariance constraint applies to the entire spectrum of states, from the vacuum to the excited states (should they exist), and is in that sense much stronger than the usual Poincare invariance requirement of the Minkowski vacuum alone. Thus to leading order in their effect on the gravitational field, the quantum states of the matter and metric fluctuations must be de Sitter invariant.Comment: 12 pages, no figures, typos corrected and some clarifying comments added, version accepted by Phys. Rev.

Light propagation in nanorod arrays

We study propagation of TM- and TE-polarized light in two-dimensional arrays of silver nanorods of various diameters in a gelatin background. We calculate the transmittance, reflectance and absorption of arranged and disordered nanorod arrays and compare the exact numerical results with the predictions of the Maxwell-Garnett effective-medium theory. We show that interactions between nanorods, multipole contributions and formations of photonic gaps affect strongly the transmittance spectra that cannot be accounted for in terms of the conventional effective-medium theory. We also demonstrate and explain the degradation of the transmittance in arrays with randomly located rods as well as weak influence of their fluctuating diameter. For TM modes we outline the importance of skin-effect, which causes the full reflection of the incoming light. We then illustrate the possibility of using periodic arrays of nanorods as high-quality polarizers.Comment: 6 pages, 7 figure

On the initial value problem for second order scalar fluctuations in Einstein static

We consider fluctuations in a perfect irrotational fluid coupled to gravity in an Einstein static universe background. We show that the homogeneous linear perturbations of the scalar and metric fluctuations in the Einstein static universe must be present if the second order constraint equations are to be integrable. I.e., the 'linearization stability' constraint forces the presence of these homogeneous modes. Since these linear homogeneous scalar modes are well known to be exponentially unstable, the tactic of neglecting these modes to create a long-lived, almost Einstein universe does not work, even if all higher order (L $>$ 1) modes are dynamically stable.Comment: 8 pages, no figures, changes made to the presentation throughout to emphasize the linear nature of the analysis and the treatment of the irrotational perfect fluid. Conclusions unchanged. Submitted to PR

A unique 3D nitrogen-doped carbon composite as high-performance oxygen reduction catalyst

The synthesis and properties of an oxygen reduction catalyst based on a unique 3-dimensional (3D) nitrogen doped (N-doped) carbon composite are described. The composite material is synthesised via a two-step hydrothermal and pyrolysis method using bio-source low-cost materials of galactose and melamine. Firstly, the use of iron salts and galactose to hydrothermally produceiron oxide (Fe₂O₃) magnetic nanoparticle clusters embedded carbon spheres. Secondly, magnetic nanoparticles diffused out of the carbon sphere when pyrolysed in the presence of melamine as nitrogen precursor. Interestingly, many of these nanoparticles, as catalyst-grown carbon nanotubes (CNTs), resulted in the formation of N-doped CNTs and N-doped carbon spheres under the decomposition of carbon and a nitrogen environment. The composite material consists of integrated N-doped carbon microspheres and CNTs show high ORR activity through a predominantly four-electron pathway.Ramesh Karunagaran, Tran Thanh Tung, Cameron Shearer, Diana Tran, Campbell Coghlan, Christian Doonan, and Dusan Losi

Controlling interferometric properties of nanoporous anodic aluminium oxide

A study of reflective interference spectroscopy [RIfS] properties of nanoporous anodic aluminium oxide [AAO] with the aim to develop a reliable substrate for label-free optical biosensing is presented. The influence of structural parameters of AAO including pore diameters, inter-pore distance, pore length, and surface modification by deposition of Au, Ag, Cr, Pt, Ni, and TiO2 on the RIfS signal (Fabry-Perot fringe) was explored. AAO with controlled pore dimensions was prepared by electrochemical anodization of aluminium using 0.3 M oxalic acid at different voltages (30 to 70 V) and anodization times (10 to 60 min). Results show the strong influence of pore structures and surface modifications on the interference signal and indicate the importance of optimisation of AAO pore structures for RIfS sensing. The pore length/pore diameter aspect ratio of AAO was identified as a suitable parameter to tune interferometric properties of AAO. Finally, the application of AAO with optimised pore structures for sensing of a surface binding reaction of alkanethiols (mercaptoundecanoic acid) on gold surface is demonstrated

A unique synthesis of macroporous N-doped carbon composite catalyst for oxygen reduction reaction

Macroporous carbon materials (MCMs) are used extensively for many electrocatalytic applications, particularly as catalysts for oxygen reduction reactions (ORRs)—for example, in fuel cells. However, complex processes are currently required for synthesis of MCMs. We present a rapid and facile synthetic approach to produce tailored MCMs efficiently via pyrolysis of sulfonated aniline oligomers (SAOs). Thermal decomposition of SAO releases SO2 gas which acts as a blowing agent to form the macroporous structures. This process was used to synthesise three specifically tailored nitrogen (N)-doped MCM catalysts: N-SAO, N-SAO (phenol formaldehyde) (PF) and N-SAO-reduced graphene oxide (rGO). Analysis using Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) analysis confirmed the formation of macropores (100–350 µm). Investigation of ORR efficacy showed that N-SAOPF performed with the highest onset potential of 0.98 V (vs. RHE) and N-SAOrGO showed the highest limiting current density of 7.89 mAcm−2. The macroporous structure and ORR efficacy of the MCM catalysts synthesised using this novel process suggest that this method can be used to streamline MCM production while enabling the formation of composite materials that can be tailored for greater efficiency in many applications.Ramesh Karunagaran, Diana Tran, Tran Thanh Tung, Cameron Shearer and Dusan Losi

Cogranulation of low rates of graphene and graphene oxide with macronutrient fertilizers remarkably improves their physical properties

Published: November 20, 2017The beneficial effects of graphene (GN) and graphene oxide (GO) additives on the physical properties of monoammonium phosphate (MAP) fertilizer granules were investigated. Low doses (0.05 to 0.5% w/w) of GN and GO sheets were cogranulated with MAP and effects on the crushing strength, abrasion and impact resistance of prepared granules were evaluated. Cogranulation with 0.5% w/w GN sheets (MAP-GN) significantly enhanced the mechanical strength of MAP granules (∼18 times improvement) whereas inclusion of same amounts of GO sheets (MAP-GO) improved the strength to a lesser extent (∼8 times improvement). The cogranulation of GN also improved MAP granules resistance to abrasion (>70%) and impact resistance (>75%). Heating MAP-GO granules at 50 °C after granulation is shown to enhance their physical properties in comparison to MAP-GO granules dried under ambient temperatures. The advantages of GN and GO sheets compared with current additives in enhancing the physical properties of MAP granules are explained by their high specific area, superior nanofiller–matrix and adhesion/interlocking ability arising from their unique wrinkled structures and two-dimensional (2D) geometry. These results confirm the potential of GN/GO additives to enhance the physical properties of MAP granules that could be translated to other fertilizers and applied in the industry.Shervin Kabiri, Roslyn Baird, Diana N. H. Tran, Ivan Andelkovic, Mike J. McLaughlin, and Dusan Losi

Novel use of activated carbon fabric to mitigate smoke taint in grapes and wine

Published online 27 February 2022Background and Aims: Grapegrowers and winemakers, around the world, are searching for strategies to mitigate the compositional and sensory consequences of grapevine exposure to smoke from wildfires. This study evaluated the use of activated carbon fabrics as protective coverings to mitigate the uptake of smoke-derived volatile phenols by grapes, and accordingly, the intensity of smoky, ashy characters in wine. Methods and Results: Smoke was applied toMataro grapes, with and without individual bunches being enclosed in bags made fromthree activated carbon fabrics (felt, light cloth and heavy cloth). Winemade fromsmoke-exposed grapes had an elevated concentration of volatile phenols, but the composition ofwinesmade fromgrapes protected by activated carbon fabric was comparable to that of the Control wine; the difference in concentration of guaiacol, o- andm-cresol and/or syringolwas only 1 μg/L. Winemade from smoke-exposed grapes had diminished fruit and prominent smoke characters, whereas the sensory profile of the wines corresponding to activated carbon fabric treatments could not be differentiated from that of the Control wine. Analysis by GC/MS of the activated carbon fabrics following repeated smoke exposure confirmed their adsorption of smoke volatiles. Conclusions: The activated carbon fabrics successfully protected Mataro grapes and wine from being tainted by smoke exposure. Significance of the Study: This study demonstrates a promising new technology for overcoming smoke taint, an issue of major concern for grape and wine producers worldwide.K.L. Wilkinson, R. Ristic, C. Szeto, D.L. Capone, L. Yu and D. Losi

Graphene oxide a new carrier for slow release of plant micronutrients

The environmental problems and low efficiency associated with conventional fertilizers provides an impetus to develop advanced fertilizers with slower release and better performances. Here we report of development of a new carrier platform based on graphene oxide (GO) sheets that can provide a high loading of plant micronutrients with controllable slow release. To prove this concept two micronutrients zinc (Zn) and copper (Cu) were used to load on GO sheets and hence formulate GO-based micronutrients fertilizer. The chemical composition and successful loading of both nutrients on GO sheets were confirmed by X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). The prepared Zn-graphene oxide (Zn-GO) and Cu-graphene oxide (Cu-GO) fertilizers showed a biphasic dissolution behaviour compared to commercial zinc sulphate and copper sulphate fertilizer granules, displaying desirable fast- and slow-release micronutrient release. A visualization method and chemical analysis were used to assess the release and diffusion of Cu and Zn in soil from GO-based fertilizers compared with commercial soluble fertilizers to demonstrate the advantages of GO carriers and show their capability to be used as generic platform for macro- and micro-nutrients delivery. A pot trial demonstrated that Zn and Cu uptake by wheat was higher when using GO-based fertilizers compared to standard zinc or copper salts. This is a first report on the agronomic performance of GO-based slow-release fertilizer.Shervin Kabiri, Fien Degryse, Diana N. H. Tran, Rodrigo C. da Silva, Mike J. McLaughlin and Dusan Losi

Optimisation of phosphate loading on graphene oxide-Fe(iii) composites-possibilities for engineering slow release fertilisers

Current commercially available phosphorus (P) fertilisers, which are highly soluble salts, are susceptible to surface runoff to waterways, and leaching to groundwaters where soils are light/medium textured. Here, we report the synthesis of a graphene oxide (GO)/iron (GO–Fe) composite, a promising carrier for loading P. The GO–Fe carriers loaded with P acted as slow release fertilisers with tunable loading/release properties. The amount of P loaded onto the GO–Fe composite was 15%, similar to commercial products. Investigation of the morphology and spectroscopic and chemical analysis revealed a complex loading mechanism of Fe onto GO. Iron, as an active center for P sorption, could interact with the oxygen functional groups at the edge of GO sheets as well as the π-electron system of the aromatic part of GO. Column perfusion studies, visualisation of P diffusion in soils and chemical analysis of soils after diffusion showed the composites to have slow-release properties. Pot experiments using wheat and our composites resulted in the same yield as using highly soluble commercial fertiliser.Ivan B. Andelkovic, Shervin Kabiri, Rodrigo C. da Silva, Ehsan Tavakkoli, Jason K. Kirby, Dusan Losic and Michael J. McLaughli