The microscopic motion of water is a central question, but gaining experimental information about the interfacial dynamics of water in fields such as catalysis, biophysics and nanotribology is ...challenging due to its ultrafast motion, and the complex interplay of inter-molecular and molecule-surface interactions. Here we present an experimental and computational study of the nanoscale-nanosecond motion of water at the surface of a topological insulator (TI), BiFormula: see textTeFormula: see text. Understanding the chemistry and motion of molecules on TI surfaces, while considered a key to design and manufacturing for future applications, has hitherto been hardly addressed experimentally. By combining helium spin-echo spectroscopy and density functional theory calculations, we are able to obtain a general insight into the diffusion of water on BiFormula: see textTeFormula: see text. Instead of Brownian motion, we find an activated jump diffusion mechanism. Signatures of correlated motion suggest unusual repulsive interactions between the water molecules. From the lineshape broadening we determine the diffusion coefficient, the diffusion energy and the pre-exponential factor.
To fully appreciate the contributions of Professor Watanabe to studies of luminescence, it is important to recall how, during his lifetime, not only have experimental facilities changed dramatically, ...but also there have been (and still are) many conflicting models as to the relevant lattice sites. This current overview summarises some of these factors. Indeed, several powerful early techniques have gone into abeyance, but there is a real potential benefit in resurrecting them. Equally, early key experiments on the existence of long-range interactions are frequently ignored, to the detriment of many models of lattice sites related to luminescence. Despite difficulties with defect site models and understanding luminescence processes, empirical data have nevertheless been effective in many applications from archaeological dating, luminescence dosimetry, and the development of modern phosphors for use across a wide range of modern applications. Improved models that include long-range features will inevitably add to this empirical progress.
The conservation of marine benthic biodiversity is a recognised goal of a number of national and international programs such as the United Nations Convention on Biodiversity (CBD). In order to attain ...this goal, information is needed about the distribution of life in the ocean so that spatial conservation measures such as marine protected areas (MPAs) can be designed to maximise protection within boundaries of acceptable dimensions. Ideally, a map would be produced that showed the distribution of benthic biodiversity to enable the efficient design of MPAs. The dilemma is that such maps do not exist for most areas and it is not possible at present to predict the spatial distribution of all marine life using the sparse biological information currently available. Knowledge of the geomorphology and biogeography of the seafloor has improved markedly over the past 10 years. Using multibeam sonar, the benthic ecology of submarine features such as fjords, sand banks, coral reefs, seamounts, canyons, mud volcanoes and spreading ridges has been revealed in unprecedented detail. This book provides a synthesis of seabed geomorphology and benthic habitats based on the most recent, up-to-date information. Introductory chapters explain the drivers that underpin the need for benthic habitat maps, including threats to ocean health, the habitat mapping approach based on principles of biogeography and benthic ecology and seabed (geomorphic) classification schemes. Case studies from around the world are then presented. They represent a range of seabed features where detailed bathymetric maps have been combined with seabed video and sampling to yield an integrated picture of the benthic communities that are associated with different types of benthic habitat. The final chapter examines critical knowledge gaps and future directions for benthic habitat mapping research.
Reviews and compares the different methodologies currently being used Includes global case studiesProvides geological expertise into what has traditionally been a biological discipline
This book builds the case for a comprehensive social security system to be developed in all countries - to eliminate desperate conditions of poverty, reverse growing inequality and sustain economic ...growth. It gives the history of the rich countries in meeting poverty and shows how the strategies in the poor countries can be greatly improved.
In this work, we use density functional theory to investigate the electronic structure of poly(3,4-ethylenedioxythiophene) (PEDOT) oligomers with co-located AlCl4− anions, a promising combination for ...energy storage. The 1980s bipolaron model remains the dominant interpretation of the electronic structure of PEDOT despite recent theoretical progress that has provided new definitions of bipolarons and polarons. By considering the influence of oligomer length, oxidation or anion concentration and spin state, we find no evidence for many of the assertions of the 1980s bipolaron model and so further contribute to a new understanding. No self-localisation of positive charges in PEDOT is found, as predicted by the bipolaron model at the hybrid functional level. Instead, our results show distortions that exhibit a single or a double peak in bond length alternations and charge density. Either can occur at different oxidation or anion concentrations. Rather than representing bipolarons or polaron pairs in the original model, these are electron distributions driven by a range of factors. Distortions can span an arbitrary number of nearby anions. We also contribute a novel conductivity hypothesis. Conductivity in conducting polymers has been observed to reduce at anion concentrations above 0.5. We show that at high anion concentrations, the energy of the localised, non-bonding anionic orbitals approaches that of the system HOMO due to Coulombic repulsion between anions. We hypothesize that with nucleic motion in the macropolymer, these orbitals will interfere with the hopping of charge carriers between sites of similar energy, lowering conductivity.
Academic studies of imperfections in insulating crystals and glasses initially assumed the sites were simple and isolated. In part this was the result of the original simplistic characterisation and ...modelling. Unfortunately many textbooks, teaching and publications engrained this viewpoint. More detailed techniques invariably showed those ideas to be incorrect, with numerous examples of extremely long range interactions, multi-sites packages, and even phase separations or nanoparticle inclusions. Despite these examples, current defect models still often focus on extremely localised sites. This seems particularly inappropriate, as in many modern applications the materials are heavily doped, and in a powder format. It therefore seems essential to include, or reintroduce, analysis techniques which can reveal both the long range effects, and the variations that exist as a function of powder size and method of production. Where such data exist, they reveal considerable complexity. This overview thus comments on past and future analysis techniques with the sensitivity to enhance detailed models. Site models require, and will benefit from, a wider acceptance of medium and long range interactions. Realistically, many sites exist simultaneously, so models will never be perfect, but improved characterisation can assist not only the science, but also commercial developments. Inevitably there are self citations as we have actively exploited a range of techniques that can reveal evidence of long range defect production and sensitivity to extended lattice perturbations.
•We contrast the early modelling of defect sites with the current attempts.•We identify some anomalies which caused by the long range interactions.•It is hard but essential to change the entrenched views on the defect sites.
A unique combined and multi‐disciplinary wavelength multiplexed spectrometer is described. It is furnished with high‐sensitivity imaging plate detectors, the power to which can be gated to provide ...time‐resolved data. The system is capable of collecting spectrally resolved luminescence data following X‐ray excitation radioluminescence (RL) or X‐ray excited optical luminescence (XEOL), electron irradiation cathodoluminescence (CL) and visible light from light emitting diodes (LEDs) photoluminescence (PL). Time‐resolved PL and CL data can be collected to provide lifetime estimates with half‐lives from microsecond timeframes. There are temperature stages for the high and low temperature experiments providing temperature control from 20 to 673 K. Combining irradiation, time resolved (TR) and TR‐PL allows spectrally‐resolved thermoluminescence (TL) and optically stimulated luminescence (OSL). The design of two detectors with matched gratings gives optimum sensitivity for the system. Examples which show the advantages and multi‐use of the spectrometer are listed. Potential future experiments involving lifetime analysis as a function of irradiation, dose and temperature plus pump‐probe experiments are discussed.
We derive an analytical expression for the intermediate scattering function of a particle on a flat surface obeying the Generalised Langevin equation, with exponential memory friction. Numerical ...simulations based on an extended phase space method confirm the analytical results. The simulated trajectories provide qualitative insight into the effect that introducing a finite memory timescale has on the analytical line shapes. The relative amplitude of the long-time exponential tail of the line shape is suppressed, but its decay rate is unchanged, reflecting the fact that the cutoff frequency of the exponential kernel affects short-time correlations but not the diffusion coefficient which is defined in terms of a long-time limit. The exponential sensitivity of the relative amplitudes to the decay time of the chosen memory kernel is a very strong indicator for the prospect of inferring a friction kernel and the physical insights from experimentally measured intermediate scattering functions.
PDF
