| 1. |
- Lif, Hanna M., et al.
(author)
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Persistent discrepancies in orbital morphology after surgical treatment of unicoronal craniosynostosis : a critical image-based analysis
- 2023
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In: Journal of Neurosurgery. - : Journal of Neurosurgery Publishing Group (JNSPG). - 1933-0707 .- 1933-0715. ; 31:6, s. 574-583
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Journal article (peer-reviewed)abstract
- OBJECTIVE: Unicoronal craniosynostosis (UCS) is characterized by complex orbital deformity and is typically treated by asymmetrical fronto-orbital remodeling (FOR) during the 1st year of life. The aim of this study was to elucidate to what extent orbital morphology is corrected by surgical treatment.METHODS: The extent to which orbital morphology was corrected by surgical treatment was tested by analysis of differences in volume and shape between synostotic, nonsynostotic, and control orbits at two time points. In total, 147 orbits were analyzed from patient CT images obtained preoperatively (mean age 9.3 months), at follow-up (mean age 3.0 years), and in matched controls. Semiautomatic segmentation software was used to determine orbital volume. For analysis of orbital shape and asymmetry, geometrical models, signed distance maps, principal modes of variation, and three objective parameters (mean absolute distance, Hausdorff distance, and dice similarity coefficient) were generated by statistical shape modeling.RESULTS: Orbital volumes on both the synostotic and nonsynostotic sides were significantly smaller at follow-up than volumes in controls and significantly smaller both preoperatively and at follow-up than orbital volumes on the nonsynostotic side. Significant differences in shape were identified globally and locally, both preoperatively and at 3 years of age. Compared with controls, deviations were mostly found on the synostotic side at both time points. Asymmetry between synostotic and nonsynostotic sides was significantly decreased at follow-up, but not compared with the inherent asymmetry of controls. On a group level, the preoperative synostotic orbit was mainly expanded in the anterosuperior and anteroinferior regions and smallest on the temporal side. At follow-up, the mean synostotic orbit was still larger superiorly but also expanded in the anteroinferior temporal region. Overall, the morphology of nonsynostotic orbits was more simi-lar to that of controls than to synostotic orbits. However, the individual variation in orbital shape was greatest for nonsynostotic orbits at follow-up.CONCLUSIONS: In this study, the authors presented what is, to their knowledge, the first objective automatic 3D bony evaluation of orbital shape in UCS, defining in greater detail than has been done previously how synostotic orbits differ from nonsynostotic and control orbits, and how orbital shape changes from 9.3 months of age preoperatively to 3 years of age at the postoperative follow-up. Despite surgical treatment, both local and global deviations in shape persist. These findings may have implications for future directions in the development of surgical treatment. Future studies connecting orbital morphology to ophthalmic disorders, aesthetics, and genetics could provide further insight to enable better outcomes in UCS.
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| 2. |
- Arnroth, Lukas, et al.
(author)
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Quantile regression based on the skewed exponential power distribution
- 2023
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In: Communications in statistics. Simulation and computation. - 0361-0918 .- 1532-4141. ; , s. 1-17
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Journal article (peer-reviewed)abstract
- Bayesian quantile regression generally relies on the asymmetric Laplace distribution (ALD) as the error distribution. We consider methods for Lp-quantile regression based on the skewed exponential power distribution (SEPD). Both Bayesian and frequentist estimation procedures are outlined and compared with previous work based on the SEPD. We find that our proposed methods greatly outperform a previous method in terms of quantile estimation. Further, compared with standard quantile regression, we find that our proposed methods generally perform better in terms of root mean square error (RMSE). Empirical evidence of the statistical properties of the proposed models is provided through a simulation study. Further, a real data application illustrates their performance.
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| 3. |
- Butorin, Sergei M., et al.
(author)
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High-resolution X-ray absorption spectroscopy as a probe of crystal-field and covalency effects in actinide compounds
- 2016
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 113:29, s. 8093-8097
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Journal article (peer-reviewed)abstract
- Applying the high-energy resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS), we were able to probe, for the first time to our knowledge, the crystalline electric field (CEF) splittings of the 5f shell directly in the HERFD-XAS spectra of actinides. Using ThO2 as an example, data measured at the Th 3d edge were interpreted within the framework of the Anderson impurity model. Because the charge-transfer satellites were also resolved in the HERFD-XAS spectra, the analysis of these satellites revealed that ThO2 is not an ionic compound as previously believed. The Th 6d occupancy in the ground state was estimated to be twice that of the Th 5f states. We demonstrate that HERFD-XAS allows for characterization of the CEF interaction and degree of covalency in the ground state of actinide compounds as it is extensively done for 3d transition metal systems.
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| 4. |
- Butorin, Sergei M., et al.
(author)
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Local Symmetry Effects in Actinide 4f X-ray Absorption in Oxides
- 2016
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In: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 88:8, s. 4169-4173
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Journal article (peer-reviewed)abstract
- A systematic X-ray absorption study at actinide N-6,(7) (4f -> 6d transitions) edges was performed for light-actinide oxides including data obtained for the first time for NpO2, PuO2 and UO3. The measurements were supported by ab initio calculations based on local-density approximation. with added 5f-5f Coulomb interaction (LDA+U). Improved energy resolution compared to common experiments at actinide L-2,L-3 (2p -> 6d transitions) edges allowed us to resolve the major structures of the 13 unoccupied 6d density of states (DOS) and estimate the crystal-field 116) splittings in the 6d shell directly from the spectra of light-actinide dioxides. The measurements demonstrated an enhanced sensitivity of the N-6,N-7, spectral shape to changes in the compound crystal structure. For nonstoichiometric NpO2-x, the filling of the entire band gap with Np 6d states was observed thus supporting a phase coexistence of Np metal and stoichiometric NpO2 which is in agreement with the tentative Np-O phase diagram.
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| 5. |
- Butorin, Sergei. M., et al.
(author)
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Probing Chemical Bonding in Uranium Dioxide by Means of High- Resolution X-ray Absorption Spectroscopy
- 2016
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:51, s. 29397-29404
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Journal article (peer-reviewed)abstract
- A systematic X-ray absorption study at the U 3d, 4d, and 4f edges of UO2 was performed, and the data were analyzed within framework of the Anderson impurity model. By applying the high-energy-resolution fluorescence-detection (HERFD) mode of X-ray absorption spectroscopy (XAS) at the U 3d(3/2) edge and conducting the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved resulting from reduced core-hole lifetime broadening. This multiedge study enabled a far more effective analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree of the 5f localization in UO2. The results support the covalent character of UO2 and do not agree with the suggestions of rather ionic bonding in this compound as expressed in some publications.
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| 6. |
- Hollmark, Håkan, et al.
(author)
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Exposure of Oxidized Copper Surfaces to Aqueous Na2S Solution Studied with Soft X-Ray Spectroscopy
- 2011
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In: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 158:1, s. C1-C5
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Journal article (peer-reviewed)abstract
- We present results from X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) of oxidized polycrystalline copper surfaces [Cu(I) and Cu(II), respectively] exposed to a 1.0 mM aqueous solution of Na2S (sodium sulfide) for several hours. Scanning electron microscopy reveals that the Cu oxide surfaces attain a much rougher texture upon sodium sulfide exposure, and that the exposed Cu(II) oxide sample exhibits areas with crystallites. The XAS spectra show that sodium sulfide effectively reduces Cu(II) oxide to Cu(I) compounds. The RIXS spectra of the exposed surfaces closely resemble those of the Cu2O reference sample with the notable exception of their Cu LIII,II-RIXS spectra. We conclude that copper evidently forms a Cu(I) compound with oxygen but with a Cu 3d-band of much reduced width, pointing to the possibility of a more complex compound containing both oxygen and sulfur.
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| 7. |
- Hollmark, Håkan, et al.
(author)
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X-ray absorption spectroscopy on electrochemically oxidized Cu exposed to Na2S
- 2011
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In: Corrosion Science. - Amsterdam : Elsevier. - 0010-938X .- 1879-0496. ; 54, s. 85-89
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Journal article (peer-reviewed)abstract
- Copper surfaces have been investigated by X-ray absorption spectroscopy after electrochemical oxidation and subsequent exposure to sulfide solution. Oxide surface layers on bulk copper surfaces were electrochemically grown in anaqueous NaOH solution at two different potentials and the resulting chemical composition was investigated using X-ray absorption spectroscopy. At both potentials the resulting surfaces consisted largely of Cu2O. At the more strongly oxidizing potential, an admixture of Cu2+-containing phases – mostly Cu(OH)2 – was detected. Sulfide exposure of both surfaces was found to completely reduce the surface from Cu2+ to Cu1+ and resulted in the formation of Cu2S with an admixture of Cu2O.
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| 8. |
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| 9. |
- Jin, Shaobo, et al.
(author)
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A Marginal Maximum Likelihood Approach for Extended Quadratic Structural Equation Modeling with Ordinal Data
- 2020
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In: STRUCTURAL EQUATION MODELING: A MULTIDISCIPLINARY JOURNAL. - USA : Taylor & Francis Group. - 1070-5511 .- 1532-8007. ; 27:6, s. 864-873
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Journal article (peer-reviewed)abstract
- The literature on non-linear structural equation modeling is plentiful. Despite this fact, few studies consider interactions between exogenous and endogenous latent variables. Further, it is well known that treating ordinal data as continuous produces bias, a problem that is enhanced when non-linear relationships between latent variables are incorporated. A marginal maximum likelihood-based approach is proposed in order to fit a non-linear structural equation model, including interactions between exogenous and endogenous latent variables in the presence of ordinal data. In this approach, the exact gradient of the approximated observed log-likelihood is calculated in order to attain the approximated maximum likelihood estimator. A simulation study shows that the proposed method provides estimates with low bias and accurate coverage probabilities
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| 10. |
- Kapaklis, Vassilios, et al.
(author)
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Temperature dependence of the electrical resistivity and electronic structure of amorphous Fe100-xZrx films and multilayers
- 2012
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:49, s. 495402-
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Journal article (peer-reviewed)abstract
- The electrical resistivity of amorphous Fe100-xZrx metal alloy films and multilayers has been investigated in a wide temperature and composition range. The overall behavior of the resistivity is consistent with bulk measurements, exhibiting prominent semiconductor-like changes at low temperatures. The transition from positive (metallic) to negative temperature coefficient of resistivity behavior is accompanied by minute changes in magnetoresistance and we can therefore rule out magnetic phase changes as being the cause for the observed changes in the resistivity. Using x-ray absorption and emission spectroscopies we are able to probe the unoccupied and occupied electronic densities of states. The corresponding spectra are found to significantly overlap, as expected for a metallic-like electronic structure and the absence of a band gap. Besides a broadening of the x-ray emission lines expected from an amorphous material, remarkably small differences are observed in the electronic structures when changing the amount of Zr. The resistivity data were modeled and agreement with the Mott variable range hopping model was found, indicating localized electronic states due the disordered structure of the Fe100-xZrx alloys.
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