2,376 research outputs found
Quantum Monte Carlo study of a positron in an electron gas
Quantum Monte Carlo calculations of the relaxation energy, pair-correlation function, and annihilating-pair momentum density are presented for a positron immersed in a homogeneous electron gas. We find smaller relaxation energies and contact pair-correlation functions in the important low-density regime than predicted by earlier studies. Our annihilating-pair momentum densities have almost zero weight above the Fermi momentum due to the cancellation of electron-electron and electron-positron correlation effects
An efficient k.p method for calculation of total energy and electronic density of states
An efficient method for calculating the electronic structure in large systems
with a fully converged BZ sampling is presented. The method is based on a
k.p-like approximation developed in the framework of the density functional
perturbation theory. The reliability and efficiency of the method are
demostrated in test calculations on Ar and Si supercells
Digitally Optimizing the Information Flows Necessary to Manage Professional Athletes: A Case Study in Rugby Union
Practical case studies elaborating end-to-end attempts to improve the quality of information flows associated with athlete management processes are scarce in the current sport literature. Therefore, guided by a Business Process Management (BPM) approach, the current study presents the outcomes from a case study to optimize the quality of strength and conditioning (S&C) information flow in the performance department of a professional rugby union club. Initially, the S&C information flow was redesigned using integral technology, activity elimination and activity automation redesign heuristics. Utilizing the Lean Startup framework, the redesigned information flow was digitally transformed by designing data collection, management and visualization systems. Statistical tests used to assess the usability of the data collection systems against industry benchmarks using the System Usability Scale (SUS) administered to 55 players highlighted that its usability (mean SUS score of 87.6 ± 10.76) was well above average industry benchmarks of similar systems (Grade A from SUS scale). In the data visualization system, 14 minor usability problems were identified from 9 cognitive walkthroughs conducted with the High-Performance Unit (HPU) staff. Pre-post optimization information quality was subjectively assessed by administering a standardized questionnaire to the HPU members. The results indicated positive improvements in all of the information quality dimensions (with major improvements to the accessibility) relating to the S&C information flow. Additionally, the methods utilized in the study would be especially beneficial for sporting environments requiring cost effective and easily adoptable information flow digitization initiatives which need to be implemented by its internal staff members.</p
Ab initio Random Structure Searching
It is essential to know the arrangement of the atoms in a material in order
to compute and understand its properties. Searching for stable structures of
materials using first-principles electronic structure methods, such as density
functional theory (DFT), is a rapidly growing field. Here we describe our
simple, elegant and powerful approach to searching for structures with DFT
which we call ab initio random structure searching (AIRSS). Applications to
discovering structures of solids, point defects, surfaces, and clusters are
reviewed. New results for iron clusters on graphene, silicon clusters,
polymeric nitrogen, hydrogen-rich lithium hydrides, and boron are presented.Comment: 44 pages, 23 figure
Electronic structure of superconducting graphite intercalate compounds: The role of the interlayer state
Although not an intrinsic superconductor, it has been long--known that, when
intercalated with certain dopants, graphite is capable of exhibiting
superconductivity. Of the family of graphite--based materials which are known
to superconduct, perhaps the most well--studied are the alkali metal--graphite
intercalation compounds (GIC) and, of these, the most easily fabricated is the
CK system which exhibits a transition temperature K. By increasing the alkali metal concentration (through high pressure
fabrication techniques), the transition temperature has been shown to increase
to as much as K in CNa. Lately, in an important recent
development, Weller \emph{et al.} have shown that, at ambient conditions, the
intercalated compounds \cyb and \cca exhibit superconductivity with transition
temperatures K and K respectively, in excess
of that presently reported for other graphite--based compounds. We explore the
architecture of the states near the Fermi level and identify characteristics of
the electronic band structure generic to GICs. As expected, we find that charge
transfer from the intercalant atoms to the graphene sheets results in the
occupation of the --bands. Yet, remarkably, in all those -- and only
those -- compounds that superconduct, we find that an interlayer state, which
is well separated from the carbon sheets, also becomes occupied. We show that
the energy of the interlayer band is controlled by a combination of its
occupancy and the separation between the carbon layers.Comment: 4 Figures. Please see accompanying experimental manuscript
"Superconductivity in the Intercalated Graphite Compounds C6Yb and C6Ca" by
Weller et a
The Rise and Fall of American Queensware 1807-1822
.
This article examines the history of several manufacturers of American queensware in Philadelphia, Pennsylvania, and beyond. Our research reveals that efforts to produce queensware were more extensive and widespread than previously thought. This survey expanded as we discovered references to contemporary queensware potteries in other parts of the United States during the first two decades of the 19th century. In all, 14 queensware-manufacturing ventures are identified and described from Pennsylvania, New Jersey, Ohio, what is now West Virginia, Vermont, and New Hampshire. Much of this research is drawn from period newspaper notices, advertisements, and surviving personal correspondence. The period sources provide a view of the experimental nature of this industry, document the search for raw materials, and describe various aspects of the manufacturing process
The role of care home fees in the public costs and distributional effects of potential reforms to care home funding for older people in England
In England, Local Authorities (LAs) contribute to the care home fees of two-thirds of care home residents aged 65+ who pass a means test. LAs typically pay fees below those faced by residents excluded from state support. Most proposals for reform of the means test would increase the proportion of residents entitled to state support. If care homes receive the LA fee for more residents, they might increase fees for any remaining self-funders. Alternatively, the LA fee might have to rise. We use two linked simulation models to examine how alternative assumptions on post-reform fees affect projected public costs and financial gains to residents of three potential reforms to the means test. Raising the LA fee rate to maintain income per resident would increase the projected public cost of the reforms by between 22% and 72% in the base year. It would reduce the average gain to care home residents by between 8% and 12%. Raising post-reform fees for remaining self-funders or requiring pre-reform self-funders to meet the difference between the LA and self-funder fees, reduces the gains to residents by 28-37%. For one reform, residents in the highest income quintile would face losses if the self-funder fee rises. © 2012 Cambridge University Press
Domestic Queensware in Kensington-Fishtown: Excavating Philadelphia\u27s Waterfront Neighborhoods
Ongoing archaeological excavation undertaken by URS/AECOM along the I-95 corridor in Kensington-Fishtown in Philadelphia have brought to light 18th and 19th century domestic and industrial life along a three-mile section of the Delaware River waterfront. Excavation has revealed over 400 shaft features, yard deposits, and industrial foundations yielding over one million artifacts from a three mile section of the Delaware River waterfront. A small quantity of domestic queensware has been recovered from barrel and wood-lined box privies and from an early 19th century drain feature. The recovery of domestic queensware in Kensington-Fishtown has revealed that this ware had become part of the domestic fabric of early 19th century consumers in this part of the city
Recommended from our members
Electrostatic force driven helium insertion into ammonia and water crystals under pressure
AbstractHelium, ammonia and ice are among the major components of giant gas planets, and predictions of their chemical structures are therefore crucial in predicting planetary dynamics. Here we demonstrate a strong driving force originating from the alternation of the electrostatic interactions for helium to react with crystals of polar molecules such as ammonia and ice. We show that ammonia and helium can form thermodynamically stable compounds above 45 GPa, while ice and helium can form thermodynamically stable compounds above 300 GPa. The changes in the electrostatic interactions provide the driving force for helium insertion under high pressure, but the mechanism is very different to those that occur in ammonia and ice. This work extends the reactivity of helium into new types of compounds and demonstrates the richness of the chemistry of this most stable element in the periodic table.</jats:p
- …