Topological entropy of realistic quantum Hall wave functions

The entanglement entropy of the incompressible states of a realistic quantum Hall system are studied by direct diagonalization. The subdominant term to the area law, the topological entanglement entropy, which is believed to carry information about topologic order in the ground state, was extracted for filling factors 1/3, 1/5 and 5/2. The results for 1/3 and 1/5 are consistent with the topological entanglement entropy for the Laughlin wave function. The 5/2 state exhibits a topological entanglement entropy consistent with the Moore-Read wave function.Comment: 6 pages, 6 figures; improved computations and graphics; added reference

The quenching of compressible edge states around antidots

We provide a systematic quantitative description of the edge state structure around a quantum antidot in the integer quantum Hall regime. The calculations for spinless electrons within the Hartree approximation reveal that the widely used Chklovskii et al. electrostatic description greatly overestimates the widths of the compressible strips; the difference between these approaches diminishes as the size of the antidot increases. By including spin effects within density functional theory in the local spin-density approximation, we demonstrate that the exchange interaction can suppress the formation of compressible strips and lead to a spatial separation between the spin-up and spin-down states. As the magnetic field increases, the outermost compressible strip, related to spin-down states starts to form. However, in striking contrast to quantum wires, the innermost compressible strip (due to spin-up states) never develops for antidots.Comment: submitted to Phys. Rev. Let

Development of a viable route for lithium-6 supply of DEMO and future fusion power plants

In the European DEMO program, the design development of a demonstration power plant (DEMO) is currently in its pre-conceptual phase. In DEMO, breeding blankets will use large quantities of lithium, enriched in the isotope lithium-6 (6Li), for breeding the tritium needed to feed the DT fusion reaction. Unfortunately, enriched lithium is commercially not available in the required quantities, which is threatening the success of future power plant applications of nuclear fusion. Even if the manufacturing of the breeding blankets is still two decades ahead of us, it is now mandatory to address the topic of lithium-6 supply and to make sure that a viable supply (and reprocessing) route is available when needed. This paper presents an unbiased systems engineering approach assessing a number of available lithium isotope separation methods by defining requirements, rating them systematically and finally calculating a ranking number expressing the value of different methods. As a result, we suggest using a chemical exchange method based on a lithium amalgam system, but including some important improvements leading to a more efficient and ‘clean’ process (the ICOMAX process) in comparison with the formerly used COLEX process. Furthermore, by modelling activities and experiments in the KIT mercury laboratory (HgLab Karlsruhe), it is shown which work has to be done in the next years to make sure that the technical-scale process is available in time to supply DEMO and future fusion power plants by middle of the 21st century

Operational Tritium Inventories in the EU-DEMO Fuel Cycle

The European Demonstration Fusion Power Reactor (EU-DEMO) has to operate in a completely tritium self-sufficient mode after initial start-up, which includes producing excess tritium to allow the start-up of other reactors. The initial start-up inventory is mainly dictated by operational inventories in the fuel cycle (FC). Advances in FC technologies and immediate recycling of a large fraction of the torus exhaust gas in the direct internal recycling loop are expected to contribute greatly to an overall low operational inventory. The remainder of the torus exhaust gas, as well as tritium from the blankets, nevertheless requires treatment in the tritium plant in order to perform the necessary purification and isotope rebalancing. Here, the employed systems still feature significant operational inventories and predominantly require steady-state operation in order to maximize their performance. In this paper the operational tritium inventories in the major FC systems are reported based on the pre-concept FC design. Additionally, major dependencies of these inventories on key design drivers of the FC are discussed. It is predicted that the EU-DEMO FC will be able to operate with an overall tritium inventory of less than 2 kg

Where are the turtles? Looking for Western Chicken Turtles, Deirochelys reticularia miaria, in Mississippi

Turtles are among the world’s most threatened vertebrates, with roughly two-thirds of species listed as threatened or endangered (Buhlmann et al., 2009). Factors such as habitat loss, overharvesting, poaching, disease, and climate change are driving these declines (Stanford et al., 2020), and it is imperative that we carefully monitor turtle populations to determine the extent of declines and prioritize conservation actions for threatened species. Western Chicken Turtles (Deirochelys reticularia miaria Schwartz, 1956) are among the turtles that appear to be experiencing rapid declines. This subspecies is distinct from the other subspecies in morphology (Schwartz, 1956), diet (McKnight et al., 2015c), nesting season (McKnight et al., 2015a, 2018; Carr and Tolson, 2018), and activity season (McKnight et al., 2015a; Bowers 2020). Genetic comparisons are currently limited, but available data also suggest a deep phylogenetic split between the Eastern Chicken Turtle, D. r. reticularia, (Latreille, 1801) and D. r. miaria Schwart, 1956 (Walker and Avise 1998; Hilzinger 2009). Historically, D. r. miaria occurs in Missouri, Oklahoma, Arkansas, Louisiana, Texas, and a small portion of western Mississippi, and the ranges of D. r. miaria and D. r. reticularia are primarily divided by the Mississippi River, which likely acts as a strong barrier to interbreeding

Optical and Electrochemical Properties of Multi-layer Polyelectrolyte Thin Films Incorporating Spherical, Gold Colloid Nanomaterials

Polyelectrolyte multilayer (PEM) films incorporating various types of spherical, gold nanomaterials (NMs) were investigated to assess the existence of electrochemical and/or optical signal enhancement effects directly attributable to embedded NMs and the relationship of these effects to film structure and composition. Specifically, electrostatically assembled films of cationic poly-L-lysine (PLL) and anionic poly(4-styrene sulfonate) (PSS) incorporating one of four types of spherical, gold colloid NMs were constructed on 3-(aminopropyl)trimethoxysilane (3-APTMS)-modified glass substrates for optical studies or 11-mercaptoundecanoic (MUA)-modified gold electrodes for electrochemical studies. The NMs inserted into the PEM films include citrate-stabilized gold nanoparticles, thioctic acid-stabilized gold nanoparticles (TAS-NPs), MUA-modified monolayer protected gold clusters, and hollow gold nanoshells (Au-NSs). Optical sensitivity of the NM-embedded films, in terms of absorbance, surface plasmon band shifts, and the dependence of these optical responses on film thickness, varied depending on the type of NM within the film (e.g., TAS-NPs versus Au-NSs) but exhibited no corresponding electrochemical effects in the diffusional voltammetry of a ferricyanide redox probe. While not correlated to optical responses, the increased Faradaic current achieved during voltammetry at NM-embedded PEM films suggested that electrochemical effects of NMs were less dependent on the type of NMs and were, instead, more related to their location within the film and the electrostatic interactions built into the interfacial chemistry of the films. These results should prove useful for developing strategies constructing thin films with NMs that are specifically designed for optical or electrochemical sensing, taking full advantage of the signal enhancements provided by individual types of NMs

Learned avoidance of trap locations in freshwater turtles

Context. Understanding the effects that learned responses to being captured have on subsequent recapture rates and associated abundance estimates is important for developing accurate descriptions of populations and communities. Although variation in the willingness of individual turtles to be trapped is commonly mentioned in the literature, few studies have experimentally tested learned trap avoidance (or fondness) in turtles. Aims. To determine whether turtles learn to avoid traps, whether repositioning traps will lead to increased capture rates, whether this effect varies among species, and whether such relocations yield more accurate depictions of community structure. Methods. We studied a community of turtles in a small lake in southeastern Kansas that included populations of red-eared slider turtles (Trachemys scripta elegans) and common musk turtles (Sternotherus odoratus). We trapped the lake for 35 consecutive days by using two concurrently deployed groups of traps. One group remained stationary for the duration of the study, whereas traps comprising the other group were moved to new locations on Day 14 and returned to their original locations on Day 28, thus dividing the trapping season into three periods. Key results. For both species, capture rates declined over time. However, traps in the moved group captured more T. s. elegans than did those in the stationary group during the second period and more S. odoratus during the third period. Traps in the moved group also had higher recapture rates in the second period. Population abundance estimates based on captures from the moved group, the stationary group, and the pool of all captures were similar for T. s. elegans, but for S. odoratus the stationary group of traps produced an abundance estimate much lower than those generated from the moved group and the pool of all captures. Conclusions. Both species exhibited learned avoidance of trap locations, but relocating traps had distinct effects on different species, and the accuracy of the observed community structure was improved by relocating traps. Implications. The movement patterns and catchability of individuals of different species within a community must be taken into consideration when developing trapping protocols. Even high-intensity trapping over a long period may not generate an accurate sample of the community if different species use the spatial environment in substantially different ways and learn to avoid trap locations

Fe(I)-Mediated Reductive Cleavage and Coupling of CO_2: An Fe^(II)(μ-O,μ-CO)Fe^(II) Core

THF solutions of a new iron(I) source, [PhBP^(CH2_Cy_3)]Fe ([PhBP^(CH_2Cy_3)] = [PhBP(CH_2P(CH_2Cy)_2)_3]-), effect the reductive cleavage of CO_2 via O-atom transfer at ambient temperature. The dominant reaction pathway is bimetallic and leads to the formation of a structurally unprecedented diiron Fe^(II)(μ-O)(μ-CO)Fe^(II) core. X-ray data are also available to suggest that bimetallic reductive CO_2 coupling to generate oxalate occurs as a minor reaction pathway. These initial observations forecast a diverse reaction landscape between CO_2 and iron(I) synthons

Universality of residence-time distributions in non-adiabatic stochastic resonance

We present mathematically rigorous expressions for the residence-time and first-passage-time distributions of a periodically forced Brownian particle in a bistable potential. For a broad range of forcing frequencies and amplitudes, the distributions are close to periodically modulated exponential ones. Remarkably, the periodic modulations are governed by universal functions, depending on a single parameter related to the forcing period. The behaviour of the distributions and their moments is analysed, in particular in the low- and high-frequency limits.Comment: 8 pages, 1 figure New version includes distinction between first-passage-time and residence-time distribution