731 research outputs found
Hybrid-functional and quasi-particle calculations of band structures of Mg2Si, Mg2Ge, and Mg2Sn
We perform hybrid functional and quasi-particle band structure calculations
with spin-orbit interaction to investigate the band structures of Mg2Si, Mg2Ge,
and Mg2Sn. For all Mg2X materials, where X = Si, Ge, and Sn, the
characteristics of band edge states, i.e., band and valley degeneracies, and
orbital characters, are found to be conserved, independent of the computational
schemes such as density functional generalized gradient approximation, hybrid
functionals, or quasi-particle calculations. However, the magnitude of the
calculated band gap varies significantly with the computational schemes. Within
density-functional calculations, the one-particle band gaps of Mg2Si, Mg2Ge,
and Mg2Sn are 0.191, 0.090, and -0.346 eV, respectively, and thus severely
underestimated compared to the experimental gaps, due to the band gap error in
the density functional theory and the significant relativistic effect on the
low-energy band structures. By employing hybrid-functional calculations with a
35% fraction of the exact Hartree-Fock exchange energy (HSE-35%), we overcame
the negative band gap issue in Mg2Sn. Finally, in quasi-particle calculations
on top of the HSE-35% Hamiltonians, we obtained band gaps of 0.835, 0.759, and
0.244 eV for Mg2Si, Mg2Ge, and Mg2Sn, respectively, consistent with the
experimental band gaps of 0.77, 0.74, and 0.36 eV, respectively.Comment: 23 pages, including 84 references, 5 tables, 3 figure
Counterintuitive example on relation between ZT and thermoelectric efficiency
The thermoelectric figure of merit ZT, which is defined using electrical
conductivity, Seebeck coefficient, thermal conductivity, and absolute
temperature T, has been widely used as a simple estimator of the conversion
efficiency of a thermoelectric heat engine. When material properties are
constant or slowly varying with T, a higher ZT ensures a higher maximum
conversion efficiency of thermoelectric materials. However, as material
properties can vary strongly with T, efficiency predictions based on ZT can be
inaccurate, especially for wide-temperature applications. Moreover, although ZT
values continue to increase, there has been no investigation of the
relationship between ZT and the efficiency in the higher ZT regime. In this
paper, we report a counterintuitive situation by comparing two materials:
although one material has a higher ZT value over the whole operational
temperature range, its maximum conversion efficiency is smaller than that of
the other. This indicates that, for material comparisons, the evaluation of
exact efficiencies as opposed to a simple comparison of the ZTs is necessary in
certain cases.Comment: 12 pages, 2 tables, 2 figure
Observation of diurnal variations in mesoscale eddy sea-surface currents using GOCI data
The surface current field of a mesoscale eddy in the East Sea (Sea of Japan) was derived from consecutive Geostationary Ocean Color Imager chlorophyll-a (chl-a) concentration images using the normalized maximum cross-correlation method. The estimated current field of the eddy exhibited anticyclonic structure demonstrated by the objective dynamic thresholds of correlation coefficients. The eddy periphery was defined by fitting an ellipse to subjectively selected points from the frontal map of chl-a concentration data. Radial distribution and hourly variation of the current speed around the eddy were presented. In terms of the magnitude and direction, the estimated current field was in good agreement with altimeter-based current field and current vectors from surface drifters. Diurnal variations in the current speeds of the mesoscale eddies showed a quadratic relation to the wind speed
Database Security System for Applying Sophisticated Access Control via Database Firewall Server
Database security, privacy, access control, database firewall, data break masking
Recently, information leakage incidents have occurred due to database security vulnerabilities. The administrators in the traditional database access control methods grant simple permissions to users for accessing database objects. Even though they tried to apply more strict permissions in recent database systems, it was difficult to properly adopt sophisticated access control policies to commercial databases due to performance degradations. This paper proposes a database security system including a database firewall server as an enhanced database access control system which can efficiently enforce sophisticated security policies to provide database with confidentiality using a data masking technique for diverse conditions such as the date, time, SQL string, and table columns to database systems
Surface currents from hourly variations of suspended particulate matter from Geostationary Ocean Color Imager data
Surface currents in Korean coastal regions were obtained using the maximum cross-correlation method applied to hourly suspended particulate matter images from the Geostationary Ocean Color Imager. Preliminary current vectors were filtered out by applying a series of quality-control procedures. The current vectors resulting from the tests were compared with the currents from a numerical model with tide and wind field. It was found that the estimated currents were more similarly to the currents caused by both tide and wind. A high degree of discrepancy was detected in regions of strong tidal currents, where the fundamental assumption of horizontal movement was limited due to the dominant vertical tidal mixing in the shallow region. The hourly rotations of the current vectors within a day were clarified by a comparison of the time-varying orientation angles of tidal ellipses. This study emphasized how to understand the short-term surface flows from hourly high-resolution geostationary satellite images
Native point defects and low -doping efficiency in solid solutions: A hybrid-density functional study
We perform hybrid-density functional calculations to investigate the charged
defect formation energy of native point defects in , , and
their solid solutions. The band gap correction by hybrid-density functional is
found to be critical to determine the charged defect density in these
materials. For , interstitials are dominant and provide
unintentional -type conductivity. Additionally, as the vacancies can
dominate in -poor , -type conductivity is possible for . However, the existence of low formation energy defects such as
and in and their diffusion can cause
severe charge compensation of hole carriers resulting in low -type doping
efficiency and thermal degradation. Our results indicate that, in addition to
the extrinsic doping strategy, alloying of with under
-poor conditions would be necessary to enhance the -type conductivity
with less charge compensation.Comment: Main: 17 pages (including title, abstract, main, references, figure
captions. 4 figures). This manuscript is accepted for publication in JALCOM.
The article will be published as Gold Open Acces
Construction of the Nursing Diagnosis Ontology in Obstetric and Gynecologic Nursing Unit using Nursing Process and SNOMED CT
PURPOSE: This study was performed to propose an ontology methodology based on standardized nursing process as framework in obstetric and gynecologic nursing practice.
METHODS: The instrument used in this study was based on the nursing diagnosis classification established by North American Nursing Diagnosis Association (NANDA) (2009-2011), fifth edition of the Nursing Interventions Classification (NIC) (2008), forth edition of the Nursing Outcomes Classification (NOC) (2008) developed by Iowa State University and systematized nomenclature of medicine clinical terms (SNOMED CT). The nursing records data were collected from electronic medical records of one hospital from August to October 2010.
RESULTS: One hundred and forty-one nursing diagnosis statements used in obstetric and gynecologic nursing unit were linked standardized nursing classifications and constructed nursing diagnosis ontology including interoperability.
CONCLUSION: Not only will this result be helpful to complete nurse's lack of knowledge and experience, it will also help to determine nursing diagnosis logically by using standardized nursing process. It will be utilized as the method to construct ontology including interoperability in other nursing units. It will be presented nursing interventions according to nursing diagnosis and thus will be easier to establish nursing planning. This can provide immediate feedback of the nursing process application
Performance of the tuberculin skin test and interferon-γ release assay for detection of tuberculosis infection in immunocompromised patients in a BCG-vaccinated population
<p>Abstract</p> <p>Background</p> <p>Interferon-γ release assay (IGRA) may improve diagnostic accuracy for latent tuberculosis infection (LTBI). This study compared the performance of the tuberculin skin test (TST) with that of IGRA for the diagnosis of LTBI in immunocompromised patients in an intermediate TB burden country where BCG vaccination is mandatory.</p> <p>Methods</p> <p>We conducted a retrospective observational study of patients given the TST and an IGRA, the QuantiFERON-TB Gold In-Tube (QFT-IT), at Severance Hospital, a tertiary hospital in South Korea, from December 2006 to May 2009.</p> <p>Results</p> <p>Of 211 patients who underwent TST and QFT-IT testing, 117 (55%) were classified as immunocompromised. Significantly fewer immunocompromised than immunocompetent patients had positive TST results (10.3% vs. 27.7%, p 0.001), whereas the percentage of positive QFT-IT results was comparable for both groups (21.4% vs. 25.5%). However, indeterminate QFT-IT results were more frequent in immunocompromised than immunocompetent patients (21.4% vs. 9.6%, p 0.021). Agreement between the TST and QFT-IT was fair for the immunocompromised group (κ = 0.38), but moderate agreement was observed for the immunocompetent group (κ = 0.57). Indeterminate QFT-IT results were associated with anaemia, lymphocytopenia, hypoproteinemia, and hypoalbuminemia.</p> <p>Conclusion</p> <p>In immunocompromised patients, the QFT-IT may be more sensitive than the TST for detection of LTBI, but it resulted in a considerable proportion of indeterminate results. Therefore, both tests may maximise the efficacy of screening for LTBI in immunocompromised patients.</p
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