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Some UK insurers have been using real-world economic scenarios for more than 30 years. Popular approaches have included random walks, time series models, arbitrage-free models with added risk premiums or 1-year Value at Risk distribution fits. Based on interviews with experienced practitioners as well as historical documents and meeting minutes, this paper traces historical model evolution in the United Kingdom and abroad. We examine the possible catalysts for changes in modelling practice with a particular emphasis on regulatory and socio-cultural influences. We apply past lessons to provide some guidance to the direction of capital market modelling in future, which has been key for business and strategy decisions.
The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (~2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
This paper is a report from the Extreme Events Working Party. The paper considers some of the difficulties in calculating capital buffers to cover potential losses. This paper considers the reasons why a purely mechanical approach to calculating capital buffers may bot be possible or justified. A range of tools and techniques is presented to help address some of the difficulties identified.
The cold, dry, and stable air above the summits of the Antarctic plateau provides the best ground-based observing conditions from optical to sub-millimetre wavelengths to be found on the Earth. Pathfinder for an International Large Optical Telescope (PILOT) is a proposed 2 m telescope, to be built at Dome C in Antarctica, able to exploit these conditions for conducting astronomy at optical and infrared wavelengths. While PILOT is intended as a pathfinder towards the construction of future grand-design facilities, it will also be able to undertake a range of fundamental science investigations in its own right. This paper provides the performance specifications for PILOT, including its instrumentation. It then describes the kinds of projects that it could best conduct. These range from planetary science to the search for other solar systems, from star formation within the Galaxy to the star formation history of the Universe, and from gravitational lensing caused by exo-planets to that produced by the cosmic web of dark matter. PILOT would be particularly powerful for wide-field imaging at infrared wavelengths, achieving near diffraction-limited performance with simple tip–tilt wavefront correction. PILOT would also be capable of near diffraction-limited performance in the optical wavebands, as well be able to open new wavebands for regular ground-based observation, in the mid-IR from 17 to 40 μm and in the sub-millimetre at 200 μm.
A heuristic greedy algorithm is developed for efficiently tiling spatially dense redshift surveys. In its first application to the Galaxy and MassAssembly (GAMA) redshift survey we find it rapidly improves the spatial uniformity of our data, and naturally corrects for any spatial bias introduced by the 2dF multi-object spectrograph. We make conservative predictions for the final state of the GAMA redshift survey after our final allocation of time, and can be confident that even if worse than typical weather affects our observations, all of our main survey requirements will be met.
EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The primary goal of EMU is to make a deep (rms ∼ 10 μJy/beam) radio continuum survey of the entire Southern sky at 1.3 GHz, extending as far North as +30° declination, with a resolution of 10 arcsec. EMU is expected to detect and catalogue about 70 million galaxies, including typical star-forming galaxies up to z ∼ 1, powerful starbursts to even greater redshifts, and active galactic nuclei to the edge of the visible Universe. It will undoubtedly discover new classes of object. This paper defines the science goals and parameters of the survey, and describes the development of techniques necessary to maximise the science return from EMU.
The atomic and electronic structures of multilayer graphene on a monolayer boron nitride (MLBN) have been investigated by using the pseudopotential method and the local density approximation (LDA) of the density functional theory (DFT). We show that the LDA energy band gap can be tuned in the range 41-278 meV for a multilayer graphene by using MLBN as a substrate. The dispersion of the π/π* bands slightly away from the K point is linear with the electron speed of 0.9×106 and 0.93×106 for graphene (MLG)/MLBN and ABA trilayer graphene (TLG)/MLBN systems, respectively. This behaviour becomes quadratic with a relative effective mass of 0.0021 for the bilayer graphene (BLG)/MLBN system. The calculated binding energies are in the range of 10-43 meV per C atom.
Graphyne is a generic name for a family of carbon allotrope two-dimensional structures where sp2 (single and double bonds) and sp (triple bonds) hybridized states coexists. They exhibit very interesting electronic and mechanical properties sharing some of the unique graphene characteristics. Similarly to graphene, the graphyne electronic properties can be modified by chemical functionalization, such as; hydrogenation, fluorination and oxidation. Oxidation is of particular interest since it can produce significant structural damages.
In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics and structural changes of the oxidation of single-layer graphyne membranes at room temperature. We have considered α, β, and γ-graphyne structures. Our results showed that the oxidation reactions are strongly site dependent and that the sp-hybridized carbon atoms are the preferential sites to chemical attacks. Our results also showed that the effectiveness of the oxidation (estimated from the number of oxygen atoms covalently bonded to carbon atoms) follows the α, β, γ-graphyne structure ordering. These differences can be explained by the fact that for α-graphyne structures the oxidation reactions occur in two steps: first, the oxygen atoms are trapped at the center of the large polygonal rings and then they react with the carbon atoms composing of the triple bonds. The small rings of γ-graphyne structures prevent these reactions to occur. The effectiveness of β-graphyne oxidation is between the α- and γ-graphynes.
Diamond was investigated as one of the superior dielectric materials for advanced wakefield accelerators. Both planar and cylindrical wakefield accelerating structures were constructed. An AsTex microwave plasma-enhanced CVD system was modified for synthesis of cylindrical polycrystalline diamond tubes. Cylindrical diamond tubes were successfully synthesized from hydrogen and methane and are characterized with micro Raman, photoluminescence spectroscopy and optical tests. In addition, planar wakefield structures were constructed from commercially available diamond. Wakefield tests on a rectangular diamond structure confirm that diamond can sustain microwave electric field strengths of 0.3 GV/m at its surface without material breakdown.
Transparent films of platinum nanoparticles on graphene nanohybrids were synthesized in a two-step process. Reduction of homogeneously dispersed Pt precursor and graphene in water and solution coating/annealing afforded thin films with high catalytic performance as counter electrodes in dye-sensitized solar cells (DSSC). The requisite dispersant consisting of poly(oxyethylene)-(POE) segments and cyclic imide functionalities allowed the in-situ reduction of dihydrogen hexachloroplatinate by ethanol and the formation of nanohybrids of graphene-supported Pt nanoparticles at 4.0 nm diameter. Characterizations of polymeric dispersants by Fourier-transform infrared spectroscopy, thermogravimetric analysis, and nanohybrids by transmission electron microscope were performed. After screening various compositions of Pt/graphene, the nanohybrid film at the specific ratio of 5/1 by weight was fabricated into a counter electrode (CE) for DSSC by the solution casting method. The evaluation of cell performance demonstrated the most improved power conversion efficiency of 8.00%. This is significant achievement in comparison with 7.14% for the DSSC with the conventional platinum sputtered CE. Furthermore, the solution casting method allows the preparation of transparent CE films that are suitable for using as rear-illuminated DSSC. The approach was proven to be feasible by measuring the cell efficiency under rear light illumination. The power efficiency up to 7.01%, comparable to 8.00% by a normally front illumination, has been accomplished. In contrast, the rear illumination at merely 2.36% efficiency was obtained for the DSSC with sputtered platinum CE. Analyses of cyclic voltammetry, electrochemical impedance spectra were well correlated to the high efficiency of the performance caused by this nanohybrid film.
Graphene is a two-dimensional (2D) hexagonal array of carbon atoms in sp2-hybridized states. Graphene presents unique and exceptional electronic, thermal and mechanical properties. However, in its pristine state graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Because of this there is a renewed interest in other possible two-dimensional carbon-based structures similar to graphene. Examples of this are graphynes and graphdiynes, which are two-dimensional structures, composed of carbon atoms in sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two acetylenic groups) were recently synthesized and they can be intrinsically nonzero gap systems. These systems can be easily hydrogenated and the amount of hydrogenation can be used to tune the band gap value. In this work we have investigated, through fully atomistic molecular dynamics simulations with reactive force field (ReaxFF), the structural and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes. Our results showed that depending on whether the atoms are in the benzenoid rings or as part of the acetylenic groups, the rates of hydrogenation are quite distinct and change in time in a very complex pattern. Initially, the most probable sites to be hydrogenated are the carbon atoms forming the triple bonds, as expected. But as the amount of hydrogenation increases in time this changes and then the carbon atoms forming single bonds become the preferential sites. The formation of correlated domains observed in hydrogenated graphene is no longer observed in the case of graphdiynes. We have also carried out ab initio DFT calculations for model structures in order to test the reliability of ReaxFF calculations.
Hexagonal boron nitride (h-BN), also known as white graphite, is the inorganic analogue of graphite. Single layers of both structures have been already experimentally realized.
In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics of hydrogenation of h-BN single-layers membranes.
Our results show that the rate of hydrogenation atoms bonded to the membrane is highly dependent on the temperature and that only at low temperatures there is a preferential bond to boron atoms. Unlike graphanes (hydrogenated graphene), hydrogenated h-BN membranes do not exhibit the formation of correlated domains. Also, the out-of-plane deformations are more pronounced in comparison with the graphene case. After a critical number of incorporated hydrogen atoms the membrane become increasingly defective, lost its two-dimensional character and collapses. The hydrogen radial pair distribution and second-nearest neighbor correlations were also analyzed.
The advent of graphene created a new era in materials science. Graphene is a two-dimensional planar honeycomb array of carbon atoms in sp2-hybridized states. A natural question is whether other elements of the IV-group of the periodic table (such as silicon and germanium), could also form graphene-like structures. Structurally, the silicon equivalent to graphene is called silicene. Silicene was theoretically predicted in 1994 and recently experimentally realized by different groups. Similarly to graphene, silicene exhibits electronic and mechanical properties that can be exploited to nanoelectronics applications.
In this work we have investigated, through fully atomistic molecular dynamics (MD) simulations, the mechanical properties of single-layer silicene under mechanical strain. These simulations were carried out using a reactive force field (ReaxFF), as implemented in the LAMMPS code. We have calculated the elastic properties and the fracture patterns.
Our results show that the dynamics of the whole fracturing processes of silicene present some similarities with that of graphene as well as some unique features.