| 1. |
- Atumi, M.K., et al.
(author)
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Hyperfine interaction of H-divacancy in diamond
- 2020
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In: Results in Physics. - : Elsevier. - 2211-3797. ; 16
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Journal article (peer-reviewed)abstract
- We present a first principles density functional theory study of microscopic properties of hydrogen defect centres in diamond. Several configurations, involving interstitial hydrogen impurities, have been considered either forming with other defects, such as hydrogen defects and vacancies. The atomic structures, and hyperfine parameters of hydrogen result compared with the experimental data on electrically active centres in synthetic diamond. Based on Local density functional theory our calculations are in excellent agreement with one interpretation of electron paramagnetic resonance of hydrogen in diamond.
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| 2. |
- Boernhorst, C., et al.
(author)
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Validity of 24-h recalls in (pre-)school aged children : Comparison of proxy-reported energy intakes with measured energy expenditure
- 2014
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In: Clinical Nutrition. - : CHURCHILL LIVINGSTONE. - 0261-5614 .- 1532-1983. ; 33:1, s. 79-84
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Journal article (peer-reviewed)abstract
- Background & aims: Little is known about the validity of repeated 24-h dietary recalls (24-HDR) as a measure of total energy intake (El) in young children. This study aimed to evaluate the validity of proxy-reported El by comparison with total energy expenditure (TEE) measured by the doubly labeled water (DLW) technique. Methods: The agreement between El and TEE was investigated in 36 (47.2% boys) children aged 4-10 years from Belgium and Spain using subgroup analyses and Bland-Altman plots. Low-energy-reporters (LER), adequate-energy-reporters (AER) and high-energy-reporters (HER) were defined from the ratio of El over TEE by application of age- and sex-specific cut-off values. Results: There was good agreement between means of El (1500 kcal/day) and TEE (1523 kcal/day) at group level though in single children, i.e. at the individual level, large differences were observed. Almost perfect agreement between El and TEE was observed in thin/normal weight children (EI: 1511 kcal/day; TEE: 1513 kcal/day). Even in overweight/obese children the mean difference between El and TEE was only 86 kcal/day. Among the participants, 28(78%) were classified as AER, five (14%) as HER and three (8%) as LER. Conclusion: Two proxy-reported 24-HDRs were found to be a valid instrument to assess El on group level but not on the individual level. (C) 2013 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.
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| 3. |
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| 4. |
- Atumi, M.K., et al.
(author)
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Hyperfine interactions at nitrogen interstitial defects in diamond
- 2013
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:6
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Journal article (peer-reviewed)abstract
- Diamond has many extreme physical properties and it can be used in a wide range of applications. In particular it is a highly effective particle detection material, where radiation damage is an important consideration. The WAR9 and WAR10 are electron paramagnetic resonance centres seen in irradiated, nitrogen-containing diamond. These S = 1/2 defects have C2v and C1h symmetry, respectively, and the experimental spectra have been interpreted as arising from nitrogen split-interstitial centres. Based upon the experimental and theoretical understanding of interstitial nitrogen defect structures, the AIMPRO density functional code has been used to assess the assignments for the structures of WAR9 and WAR10. Although the calculated hyperfine interaction tensors are consistent with the measured values for WAR9, the thermal stability renders the assignment problematic. The model for the WAR10 centre yields principal directions of the hyperfine tensor at variance with observation. Alternative models for both centres are discussed in this paper, but no convincing structures have been found.
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| 5. |
- Bammann, K, et al.
(author)
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The IDEFICS validation study on field methods for assessing physical activity and body composition in children: design and data collection.
- 2011
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In: International journal of obesity (2005). - : Springer Science and Business Media LLC. - 1476-5497 .- 0307-0565. ; 35 Suppl 1
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Journal article (peer-reviewed)abstract
- Objective: To describe the design, measurements and fieldwork of the IDEFICS (Identification and prevention of dietary- and lifestyle-induced health effects in children and infants) physical activity and body composition validation study, and to determine the potential and limitations of the data obtained. Design: Multicentre validation study. Subjects: A total of 98 children from four different European countries (age: 4–10 years). Methods: An 8-day measurement protocol was carried out in all children using a collaborative protocol. Reference methods were the doubly labelled water method for physical activity, and a three- and a four-compartment model for body composition. Investigated field methods were accelerometers, a physical activity questionnaire and various anthropometric measurements. Results: For the validation of physical activity field methods, it was possible to gather data from 83 to 89 children, laying the basis for age- and sex-specific results. The validation of body composition field methods is possible in 64–80 children and allows sex-specific analyses but has only limited statistical power in the youngest age group (o6 years). The amount of activity energy expenditure (AEE) varied between centres, sexes and age groups, with boys and older children having higher estimates of AEE. After normalisation of AEE by body weight, most group-specific differences diminished, except for country-specific differences. Conclusion: The IDEFICS validation study will allow age- and sex-specific investigation of questions pertaining to the validity of several field methods of body composition and physical activity, using established reference methods in four different European countries. From the participant analyses it can be concluded that the compliance for the investigated field methods was higher than that for the reference methods used in this validation study.
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| 6. |
- Camps, I., et al.
(author)
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Elastic and optical properties of Cu2ZnSn(SexS1-x)4 alloys: density functional calculations
- 2012
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In: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 27:11
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Journal article (peer-reviewed)abstract
- Cu2ZnSn(S1 − xSex)4 (CZT(S, Se)) is emerging as a very credible alternative to CuIn1 − xGaxSe2 (CIGS) as the absorber layer for thin film solar cells. The former compound has the important advantage of using abundant Zn and Sn instead of the expensive In and Ga. A better understanding of the properties of CZT(S, Se) is being sought through experimental and theoretical means. Thus far, however, very little is known about the fundamental properties of the CZT(S, Se) alloys. In this work, theoretical studies on the structural, elastic, electronic and optical properties of CZT(S, Se) alloys through first-principles calculations are reported. We use a density functional code (aimpro), along with the Padé parametrization for the local density approximation to the exchange correlation potential. For the alloying calculations we employed 64 atom supercells (approximately cubic) with a 2 × 2 × 2 k-point sampling set. These supercells possess a total of 32 chalcogen species and the CZTSexS1 − x alloys are described by using the ordered alloy approximation. Accordingly, to create a perfectly diluted alloying host, the species type of the 32 chalcogen sites is selected randomly with uniform probability x and 1 − x for Se and S, respectively. Properties of alloys (structural, elastic, electronic and optical) are obtained by averaging the results of ten supercell configurations generated for each composition. For each configuration, lattice vectors and atomic positions were allowed to relax (although enforcing the tetragonal lattice type) and the Murnaghan equation of state was fitted to the total energy data. The results presented here permit a better understanding of the properties of the CZT(S, Se) alloys which in turn result in the design of more efficient solar cells.
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| 7. |
- Carvahlo, A., et al.
(author)
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Electronic structure modification of Si nanocrystals with F(4)-TCNQ
- 2011
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:12
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Journal article (peer-reviewed)abstract
- We use first-principles models to demonstrate how an organic oxidizing agent F(4)-TCNQ (7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane) modifies the electronic structure of silicon nanocrystals, suggesting it may enhance p-type carrier density and mobility. The proximity of the lowest unoccupied level of F(4)-TCNQ to the highest occupied level of the Si nanocrystals leads to the formation of an empty hybrid state overlapping both the nanocrystal and molecule, reducing the excitation energy to similar to 0.8-1 eV in vacuum. Hence, it is suggested that F(4)-TCNQ can serve both as a surface oxidant and as a mediator for hole hopping between adjacent nanocrystals in p-type doped silicon nanocrystal networks
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| 8. |
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| 9. |
- Markevich, Vladimir P., et al.
(author)
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Radiation-induced defect reactions in tin-doped Ge crystals
- 2011
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In: Solid State Phenomena. - 1012-0394 .- 1662-9779. ; 178 - 179, s. 392-397
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Journal article (peer-reviewed)abstract
- We have recently shown that Sn impurity atoms are effective traps for vacancies (V) in Ge:Sn crystals irradiated with MeV electrons at room temperature [V.P. Markevich et al., J. Appl. Phys. 109 (2011) 083705]. A hole trap with 0.19 eV activation energy for hole emission to the valence band (Eh) has been assigned to an acceptor level of the Sn-V complex. In the present work electrically active defects introduced into Ge:Sn+P crystals by irradiation with 6 MeV electrons and subsequent isochronal annealing in the temperature range 50-300 oC have been studied by means of transient capacitance techniques and ab-initio density functional modeling. It is found that the Sn-V complex anneals out upon heat-treatments in the temperature range 50-100 oC. Its disappearance is accompanied by the formation of vacancy-phosphorus (VP) centers. The disappearance of the VP defect upon thermal annealing in irradiated Sn-doped Ge crystals is accompanied by the effective formation of a defect which gives rise to a hole trap with Eh = 0.21 eV and is more thermally stable than other secondary radiation-induced defects in Ge:P samples. This defect is identified as tin-vacancy-phosphorus (SnVP) complex. It is suggested that the effective interaction of the VP centers with tin atoms and high thermal stability of the SnVP complex can result in suppression of transient enhanced diffusion of phosphorus atoms in Ge.
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| 10. |
- Markevich, V.P., et al.
(author)
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Tin-vacancy complex in germanium
- 2011
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109, s. 083705-1
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Journal article (peer-reviewed)abstract
- Electrically active defects introduced into Ge crystals co-doped with tin and phosphorus atoms by irradiation with 6 MeV electrons have been studied by means of transient capacitance techniques and ab-initio density functional modeling. It is shown that Sn atoms are effective traps for vacancies (V) in the irradiated Ge:Sn+P crystals. The electronic structure of Sn-V is unraveled on the basis of hybrid states from a Sn atom and a divacancy. Unlike the case for Si, Sn-V in Ge is not a donor. A hole trap with 0.19 eV activation energy for hole emission to the valence band is assigned to an acceptor level of the Sn-V complex. The Sn-V complex anneals out upon heat-treatments in the temperature range 50–100 °C. Its disappearance is accompanied by the formation of phosphorus-vacancy centers.
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