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- Granville, S, et al.
(författare)
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Optical conductivity and x-ray absorption and emission study of the band structure of MnN films
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:20, s. 205127-
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Tidskriftsartikel (refereegranskat)abstract
- The band structure of MnN films prepared by ion assisted deposition has been investigated by optical conductivity and x-ray absorption and emission spectroscopies. X-ray diffraction and extended x-ray absorption fine structure show the films to be nanocrystalline but phase pure and exhibiting the known antiferromagnetic distorted rocksalt phase. X-ray emission spectroscopy of the N K-edge and x-ray absorption near edge spectroscopy of both the N K- and Mn L-edges are used to probe the occupied and empty densities of states, which compare well with the N(2p) and Mn(3d) partial densities of states calculated using the linearized muffin-tin orbital band structure method. A similar comparison is made between the measured optical conductivity and the calculated contribution from interband transitions. It is possible to associate the main features in the measured spectrum with corresponding ones in the calculated optical function. The major differences between calculated and measured spectra can be understood on the basis of a limited electron mean-free-path in these nanocrystalline films, which broadens the features in the joint density of states and relaxes the momentum conservation requirement. The calculated optical functions are analyzed in detail in terms of their dominant band-to-band contributions and in addition the polarization dependence is predicted. Temperature dependent conductivity measurements are also reported and show a clear metallic behavior and a weak Kondo-like low temperature anomaly.
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| 3. |
- Isaeva, Anna A., et al.
(författare)
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New metal-rich mixed chalcogenides with intergrowth structures : Ni8.21Ge2S2 and Ni8.45Ge2Se2
- 2009
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Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 11:6, s. 1071-1076
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Tidskriftsartikel (refereegranskat)abstract
- New metal-rich mixed nickel germanium chalcogenides, Ni8.21(1)Ge2S2 and Ni8.45(1)Ge2Se2, were synthesized by a high-temperature ceramic technique. Ni8.21Ge2S2 decomposes incongruently at 798(5) degrees C, while Ni8.45Ge2Se2 is stable only between approximately 600(5) degrees C and 813(5) degrees C. Single crystals were grown from a molten flux and by a recrystallization of presynthesized charge. The X-ray diffraction study revealed that Ni8.21Ge2S2 and Ni8.45Ge2S2 are isostructural and crystallize in the tetragonal system (space group 14/mmm, Z = 2) with a = 3.578(1) angstrom, c = 24.687(5) angstrom, and a = 3.601 (1) angstrom, c = 25.427(6) angstrom, respectively. Their crystal structures comprise heterometallic (2)(infinity) [Ni6Ge2] slabs and are closely related to the Ni8.54Ga2Se2 and Ni8.93Sn2S2 structure types. The geometrical changes of structural units upon p-element substitution in all known Ni(10-delta)E(2)Q(2) (E = element of group 13 or 14; Q = chalcogen) compounds are discussed. The relation to the intergrowth structure of Ni5.46GeSe2 is analyzed.
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- Ripsweden, J, et al.
(författare)
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Is training essential for interpreting cardiac computed tomography?
- 2009
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Ingår i: Acta radiologica (Stockholm, Sweden : 1987). - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 50:2, s. 194-200
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Tidskriftsartikel (refereegranskat)abstract
- Background: Cardiac computed tomography (CT) has gained increasing acceptance for diagnosing obstructive coronary artery disease (CAD). Several guidelines have been published on required education for proficiency in the interpretation of these examinations. Purpose: To describe the learning-curve effect of the interpretation of 100 consecutive cardiac CT examinations aimed at diagnosing CAD. The diagnostic accuracy of radiologists and radiographers was also compared. Material and Methods: Two radiologists and two radiographers, all with no prior experience in evaluation of cardiac CT, independently underwent a dedicated training program of 100 examinations randomized into 10 blocks (sessions), with 10 cases in each. They independently evaluated the coronary arteries regarding significant obstructive CAD. After every session, individual feedback on diagnostic accuracy and comparison with the corresponding invasive coronary angiography (currently regarded as the gold standard to detect coronary lesions) was given. The time required for interpretation was recorded. Results: The mean review time decreased ( P<0.0001) successively during the 10 sessions for all the observers together. The first session had a mean review time of 32 min, and the last session 16 min. No significant improvement in sensitivity, specificity, or negative predictive value (NPV) was observed. For positive predictive value (PPV), there was an improvement for the radiologists ( P<0.05), but not for the radiographers. The radiographers had a higher total specificity compared to the radiologists ( P<0.01). Conclusion: The review time for novices in cardiac CT was approximately halved during the first 100 cases, with maintained accuracy. There was a learning-curve effect in PPV for the radiologists. The diagnostic accuracy of dedicated radiographers indicates that they might be considered to be included as part of the evaluation team.
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- Mir-Akbari, H, et al.
(författare)
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Limitations of 64-detector-row computed tomography coronary angiography: calcium and motion but not short experience
- 2009
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Ingår i: Acta radiologica (Stockholm, Sweden : 1987). - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 50:2, s. 174-180
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Tidskriftsartikel (refereegranskat)abstract
- Background: Recently, 64-detector-row computed tomography coronary angiography (CTA) has been introduced for the noninvasive diagnosis of coronary artery disease. Purpose: To evaluate the diagnostic capacity and limitations of a newly established CTA service. Material and Methods: In 101 outpatients with suspected coronary artery disease, 64-detector-row CTA (VCT Lightspeed 64; GE Healthcare, Milwaukee, Wisc., USA) was performed before invasive coronary angiography (ICA). The presence of >50% diameter coronary stenosis on CTA was rated by two radiologists recently trained in CTA, and separately by an experienced colleague. Diagnostic performance of CTA was calculated on segment, vessel, and patient levels, using ICA as a reference. Segments with a proximal reference diameter <2 mm or with stents were not analyzed. Results: In 51 of 101 patients and 121 of 1280 segments, ICA detected coronary stenosis. In 274 of 1280 (21%) segments, CTA had non-diagnostic image quality, the main reasons being severe calcifications (49%), motion artifacts associated with high or irregular heart rate (45%), and low contrast opacification (14%). Significantly more women (43%) had non-diagnostic scans compared to men (20%). A heart rate above 60 beats per minute was associated with significantly more non-diagnostic patients (38% vs. 18%). In the 1006 diagnostic segments, CTA had a sensitivity of 78%, specificity of 95%, positive predictive value (PPV) of 54%, and negative predictive value (NPV) of 98% for detecting significant coronary stenosis. In 29 patients, CTA was non-diagnostic. In the remaining 72 patients, sensitivity was 100%, specificity 65%, PPV 79%, and NPV 100%. The use of a more experienced CTA reader did not improve diagnostic performance. Conclusion: CTA had a very high negative predictive value, but the number of non-diagnostic scans was high, especially in women. The main limitations were motion artifacts and vessel calcifications, while short experience in CTA did not influence the interpretation.
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