A theoretical and semiemprical correction to the long-range dispersion power law of stretched graphite

In recent years intercalated and pillared graphitic systems have come under increasing scrutiny because of their potential for modern energy technologies. While traditional \emph{ab initio} methods such as the LDA give accurate geometries for graphite they are poorer at predicting physicial properties such as cohesive energies and elastic constants perpendicular to the layers because of the strong dependence on long-range dispersion forces. `Stretching' the layers via pillars or intercalation further highlights these weaknesses. We use the ideas developed by [J. F. Dobson et al, Phys. Rev. Lett. {\bf 96}, 073201 (2006)] as a starting point to show that the asymptotic $C_3 D^{-3}$ dependence of the cohesive energy on layer spacing $D$ in bigraphene is universal to all graphitic systems with evenly spaced layers. At spacings appropriate to intercalates, this differs from and begins to dominate the $C_4 D^{-4}$ power law for dispersion that has been widely used previously. The corrected power law (and a calculated $C_3$ coefficient) is then unsuccesfully employed in the semiempirical approach of [M. Hasegawa and K. Nishidate, Phys. Rev. B {\bf 70}, 205431 (2004)] (HN). A modified, physicially motivated semiempirical method including some $C_4 D^{-4}$ effects allows the HN method to be used successfully and gives an absolute increase of about $2-3$ to the predicted cohesive energy, while still maintaining the correct $C_3 D^{-3}$ asymptotics

Analysis of curtailment at The Geysers geothermal Field, California

Geothermal energy has traditionally been viewed as a baseload energy source, but the rapid growth of intermittent renewable energy has led to a need for more flexibility in power generation to avoid mandatory curtailment imposed by grid operators. This study of curtailment at The Geysers provides insights into the magnitude, duration, frequency, temporal and spatial distribution, and potential causes of curtailment events between 2013 and 2018. Annual levels of curtailment range during this period from 9 to 47 GW h, representing 0.15 to 0.81 % of the net generation. Most curtailments occurred at the power plants connected to a lower capacity transmission line and may result from transmission constriction. There is a clear link between negative pricing and economic curtailment, especially when solar production is higher. Economic curtailment events tend to be only a few hours and vary in magnitude up to almost 300 MW, whereas transmission-related curtailment events can be up to several weeks in duration. It is likely that curtailment of geothermal power will be an increasing concern, and could be mitigated by flexible generation strategies and increases in energy storage. It is critical to know the nature of curtailment events so that flexible generation options can be assessed properly

High-Level Correlated Approach to the Jellium Surface Energy, Without Uniform-Electron-Gas Input

We resolve the long-standing controversy over the surface energy of simple metals: Density functional methods that require uniform-electron-gas input agree with each other at many levels of sophistication, but not with high-level correlated calculations like Fermi Hypernetted Chain and Diffusion Monte Carlo (DMC) that predict the uniform-gas correlation energy. Here we apply a very high-level correlated approach, the inhomogeneous Singwi-Tosi-Land-Sj\"olander (ISTLS) method, and find that the density functionals are indeed reliable (because the surface energy is "bulk-like"). ISTLS values are close to recently-revised DMC values. Our work also vindicates the previously-disputed use of uniform-gas-based nonlocal kernels in time-dependent density functional theory.Comment: 4 pages, 1 figur

Power-law carrier dynamics in semiconductor nanocrystals at nanosecond time scales

We report the observation of power law dynamics on nanosecond to microsecond time scales in the fluorescence decay from semiconductor nanocrystals, and draw a comparison between this behavior and power-law fluorescence blinking from single nanocrystals. The link is supported by comparison of blinking and lifetime data measured simultaneously from the same nanocrystal. Our results reveal that the power law coefficient changes little over the nine decades in time from 10 ns to 10 s, in contrast with the predictions of some diffusion based models of power law behavior.Comment: 3 pages, 2 figures, compressed for submission to Applied Physics Letter

Many-body approach to infinite non-periodic systems: application to the surface of semi-infinite jellium

A method to implement the many-body Green function formalism in the GW approximation for infinite non periodic systems is presented. It is suitable to treat systems of known ``asymptotic'' properties which enter as boundary conditions, while the effects of the lower symmetry are restricted to regions of finite volume. For example, it can be applied to surfaces or localized impurities. We illustrate the method with a study of the surface of semi-infinite jellium. We report the dielectric function, the effective potential and the electronic self-energy discussing the effects produced by the screening and by the charge density profile near the surface.Comment: 11 pages, 4 figure

Batch fabricated dual cantilever resistive probe for scanning thermal microscopy

In this study dual cantilever resistive probes for scanning thermal microscopy (SThM) have been batch fabricated. In the dual probe, one is used as local heater and a second one nearby detects the thermal diffusivity at a microscopic scale. Various types of dual probes have been fabricated in one batch to allow experimental determination of the optimal sensor type for the measurement. Thermal scans with the dual cantilever probes have been performed in atmosphere, and contrast in thermal imaging indicating the difference of thermal conductivity is shown. Test of these probes under vacuum indicates strong thermal coupling through air between the two probes in the dual cantilever probes

Identifying mechanisms influencing the emergence and success of innovation within national economies: a realist approach

This paper uses data from recent OECD (OECD Science, technology and industry scoreboard. OECD Publishing, Paris, 2013b) and Cornell University et al. (The global innovation index 2014. World Intellectual Property Organization, Fontainebleau, 2014) national innovation reports to explain Australia’s poor innovation performance. We adopt a realist approach and apply the technique of retroduction to identify potential causes. While our account is only preliminary, we contend that this technique provides the resources to uncover plausible causes for further, more detailed, causal analysis. We conclude that the retroductive method is one that can be applied to aggregated statistics more generally and could be used by analysts and policy makers in any jurisdiction

Towards operational measures of computer security

Ideally, a measure of the security of a system should capture quantitatively the intuitive notion of ‘the ability of the system to resist attack’. That is, it should be operational, reflecting the degree to which the system can be expected to remain free of security breaches under particular conditions of operation (including attack). Instead, current security levels at best merely reflect the extensiveness of safeguards introduced during the design and development of a system. Whilst we might expect a system developed to a higher level than another to exhibit ‘more secure behaviour’ in operation, this cannot be guaranteed; more particularly, we cannot infer what the actual security behaviour will be from knowledge of such a level. In the paper we discuss similarities between reliability and security with the intention of working towards measures of ‘operational security’ similar to those that we have for reliability of systems. Very informally, these measures could involve expressions such as the rate of occurrence of security breaches (cf rate of occurrence of failures in reliability), or the probability that a specified ‘mission’ can be accomplished without a security breach (cf reliability function). This new approach is based on the analogy between system failure and security breach. A number of other analogies to support this view are introduced. We examine this duality critically, and have identified a number of important open questions that need to be answered before this quantitative approach can be taken further. The work described here is therefore somewhat tentative, and one of our major intentions is to invite discussion about the plausibility and feasibility of this new approach

Where Are the Parasites? [Letters]

First paragraph: The review by E. Post et al. ( Ecological dynamics across the Arctic associated with recent climate change, 11 September 2009, p. 1,355) paid little heed to parasites and other pathogens. The rapidly growing literature on parasites in arctic and subarctic ecosystems provides empirical and observational evidence that climate-linked changes have already occurred. The life cycle of the protostrongylid lungworm of muskoxen, Umingmakstrongylus pallikuukensis, has changed, and the range of that organism and the winter tick, Dermacentor albipictus, has expanded