110 research outputs found

    Density functional theory calculations of defect energies using supercells

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    Reliable calculations of defect properties may be obtained with density functional theory using the supercell approximation. We systematically review the known sources of error and suggest how to perform calculations of defect properties in order to minimize errors. We argue that any analytical error-correction scheme relying on electrostatic considerations is not appropriate to derive reliable defect formation energies, especially not for relaxed geometries. Instead we propose finite size scaling of the calculated defect formation energies, and compare the use of this with both fully converged and "Gamma" (Γ) point only k-point integration. We give a recipe for practical DFT calculations which will help to obtain reliable defect formation energies and demonstrate it using examples from III-V semiconductors

    A Combined Signal Approach To Technical Analysis On The S&P 500

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    This paper examines the effectiveness of nine technical trading rules on the S&P 500 from January 1950 to March 2008 (14,646 daily observations).  The annualized returns from each trading rule are compared to a naïve buy-and-hold strategy to determine profitability. Over the 59 year period, only the moving-average cross-over (1,200) and (5,150) trading rules were able to outperform the buy-and-hold trading strategy after adjusting for transaction costs. However, excess returns were generated by employing a Combined Signal Approach (CSA) on the individual trading rules. Statistical significance was confirmed through bootstrap simulations and robustness through sub-period analysis.&nbsp

    Biodiversity patterns of Arctic diatom assemblages in lakes and streams: Current reference conditions and historical context for biomonitoring

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    Comprehensive assessments of contemporary diatom distributions across the Arctic remain scarce. Furthermore, studies tracking species compositional differences across space and time, as well as diatom responses to climate warming, are mainly limited to paleolimnological studies due to a lack of routine monitoring in lakes and streams across vast areas of the Arctic. The study aims to provide a spatial assessment of contemporary species distributions across the circum-Arctic, establish contemporary biodiversity patterns of diatom assemblages to use as reference conditions for future biomonitoring assessments, and determine pre-industrial baseline conditions to provide historical context for modern diatom distributions. Diatom assemblages were assessed using information from ongoing regulatory monitoring programmes, individual research projects, and from surface sediment layers obtained from lake cores. Pre-industrial baseline conditions as well as the nature, direction and magnitude of changes in diatom assemblages over the pastc.200 years were determined by comparing surface sediment samples (i.e. containing modern assemblages) with a sediment interval deposited prior to the onset of significant anthropogenic activities (i.e. containing pre-1850 assemblages), together with an examination of diatoms preserved in contiguous samples from dated sediment cores. We identified several biotypes with distinct diatom assemblages using contemporary diatom data from both lakes and streams, including a biotype typical for High Arctic regions. Differences in diatom assemblage composition across circum-Arctic regions were gradual rather than abrupt. Species richness was lowest in High Arctic regions compared to Low Arctic and sub-Arctic regions, and higher in lakes than in streams. Dominant diatom taxa were not endemic to the Arctic. Species richness in both lakes and streams reached maximum values between 60 degrees N and 75 degrees N but was highly variable, probably reflecting differences in local and regional environmental factors and possibly sampling effort. We found clear taxon-specific differences between contemporary and pre-industrial samples that were often specific to both ecozone and lake depth. Regional patterns of species turnover (beta-diversity) in the pastc.200 years revealed that regions of the Canadian High Arctic and the Hudson Bay Lowlands to the south showed most compositional change, whereas the easternmost regions of the Canadian Arctic changed least. As shown in previous Arctic diatom studies, global warming has already affected these remote high latitude ecosystems. Our results provide reference conditions for future environmental monitoring programmes in the Arctic. Furthermore, diatom taxa identification and harmonisation require improvement, starting with circum-Arctic intercalibrations. Despite the challenges posed by the remoteness of the Arctic, our study shows the need for routine monitoring programmes that have a wide geographical coverage for both streams and lakes

    Abstracts of presentations on plant protection issues at the xth international congress of virology: August 11-16,1996 Binyanei haOoma, Jerusalem, Israel Part 2 Plenary Lectures

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    Oral rehabilitation of maxilla: Technical consideration

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    Oral rehabilitation of edentulous maxilla is particularly difficult because of the lack of bone in correspondence of maxillary sinuses, therefore, the surgeon is forced to place implants in sites where bone is more prevalent. In addition, patients require more frequent oral immediate rehabilitation in order to reduce the discomfort related to wearing a total denture. A viable solution to provide stability and retention of the prosthesis in a short time is represented by the technique of intraoral welding supporting total denture or fixed prosthesis. This goal may be achieved thanks to the technique of welding titanium bars onto implant abutments. In fact, the procedure can be performed directly in the mouth, eliminating the possibility of errors or distortions due to prosthetic procedures. This paper describes a case report and the most recent data regarding long-term success and high predictability of intraorally-welded titanium bar in immediate loading implants.Sin financiación1.711 JCR (2020) Q4, 132/146 Endocrinology & Metabolism0.284 SJR (2020) Q3, 167/232 Endocrinology, Diabetes and MetabolismNo data IDR 2020UE
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