| 1. |
- Solomonidou, A., et al.
(författare)
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Spectral and emissivity analysis of the raised ramparts around Titan's northern lakes
- 2020
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Ingår i: Icarus. - : Academic Press. - 0019-1035 .- 1090-2643. ; 344
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Tidskriftsartikel (refereegranskat)abstract
- Some of Titan's small northern hemisphere lakes show raised rampart features (which are distinct from raised rims), and appear as SAR-bright mound-like annuli extending away from the lake for up to tens of kilometers from the shoreline. We investigate the infrared and microwave characteristics of these features using Cassini Visual and Infrared Mapping Spectrometer (VIMS) and RADAR data. A spectral comparative analysis is performed among the lakes, their ramparts, and the surrounding regions. We overcome the profound difference in spatial resolution between VIMS and SAR data by using a method that provides overlays between the spectral images and SAR, thus enabling the correct selection of VIMS pixels. The surface properties of the selected areas are obtained using a radiative transfer analysis on the selected VIMS pixels, in addition to emissivity obtained from the RADAR in radiometry mode. Analysis of these combined and co-registered data provides constraints for the formation mechanism(s) of raised ramparts. The results show that the emissivity of the raised ramparts is close to that of Titan's labyrinthic terrains and to that of empty lake floors in the northern polar regions. This is confirmed by the VIMS analysis that also shows that the infrared spectral response of the raised ramparts is very similar to that of some empty lake floors. This suggests that both areas are made from or are covered by a similar material. In addition, two out of the eight lakes with raised ramparts show spectral differences at three specific wavelengths, 1.6, 2.0, and 5.0 mu m, between the ramparts and the surrounding terrain. We hypothesize that this could be due to some component, or mixture of components in the ramparts that is less absorbent at these specific wavelengths, or it could be an effect of different grain sizes. These observations provide first insights into the possible mechanisms leading to the formation of the raised ramparts that are discussed here.
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| 2. |
- Solomonidou, A., et al.
(författare)
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The Spectral Nature of Titan's Major Geomorphological Units : Constraints on Surface Composition
- 2018
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Ingår i: Journal of Geophysical Research - Planets. - : AMER GEOPHYSICAL UNION. - 2169-9097 .- 2169-9100. ; 123:2, s. 489-507
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Tidskriftsartikel (refereegranskat)abstract
- We investigate Titan's low-latitude and midlatitude surface using spectro-imaging near-infrared data from Cassini/Visual and Infrared Mapping Spectrometer. We use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in Cassini Synthetic Aperture Radar data, which exhibit quite similar spectral response to the Visual and Infrared Mapping Spectrometer data. We have identified three main categories of albedo values and spectral shapes, indicating significant differences in the composition among the various areas. We compare with linear mixtures of three components (water ice, tholin-like, and a dark material) at different grain sizes. Due to the limited spectral information available, we use a simplified model, with which we find that each albedo category of regions of interest can be approximately fitted with simulations composed essentially by one of the three surface candidates. Our fits of the data are overall successful, except in some cases at 0.94, 2.03, and 2.79m, indicative of the limitations of our simplistic compositional model and the need for additional components to reproduce Titan's complex surface. Our results show a latitudinal dependence of Titan's surface composition, with water ice being the major constituent at latitudes beyond 30 degrees N and 30 degrees S, while Titan's equatorial region appears to be dominated partly by a tholin-like or by a very dark unknown material. The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titan's surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories. Plain Language Summary Titan, Saturn's moon, has been investigated by the Cassini mission for almost 13 years, unveiling an exotic world with many features similar to Earth. One of the mysteries that still has not been resolved even after that many years of exploration is the nature of its surface composition. Titan is a very complex world with multivariable geology and a very thick and hazy atmosphere that shields the surface from remote sensing observations, prohibiting direct evaluation of its composition. In our study we analyze spectro-imaging data from the Cassini visual and infrared spectrometer. We first infer the atmospheric contribution and then extract true surface properties. We study major geomorphological regions on Titan, which include among other mountains, plains, craters, and dunes. We derive their surface albedo values and shapes that reveal the brightness of the surface and compare them with materials that we expect to find on Titan's surface, such as water ice, tholins (atmospheric products), and a very dark unknown component. The results from this analysis show that Titan presents a pattern in its surface composition distribution with its equator being dominated by organic materials from the atmosphere and a very dark unknown material, while higher latitudes contain more water ice.
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| 3. |
- Solomonidou, A., et al.
(författare)
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The chemical composition of impact craters on Titan : I. Implications for exogenic processing
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 641
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the spectral behavior of nine Titan impact craters in order to constrain their composition. Past studies that have examined the chemical composition of impact craters on Titan have either used qualitative comparisons between craters or combined all craters into a single unit, rather than separating them by geographic location and/or degradation state. Here, we use Visual and Infrared Mapping Spectrometer (VIMS) data and a radiative transfer code to estimate the atmospheric contribution to the data, extract the surface albedos of the impact craters, and constrain their composition by using a library of candidate Titan materials, including essentially water ice, tholin, a dark component, and other possible ices at different grain sizes. Following a general characterization of the impact craters, we study two impact crater subunits, the "crater floor" and the "ejecta blanket". The results show that the equatorial dune craters - Selk, Ksa, Guabonito, and the crater on Santorini Facula - appear to be purely composed of organic material (mainly an unknown dark component). Titan's midlatitude plain craters - Afekan, Soi, and Forseti - along with Menrva and Sinlap, are enriched in water ice within an organic-based mixture. This follows the geographic pattern observed in our previous work with VIMS data, where the uppermost layers of the midlatitude alluvial fans, undifferentiated plains, and labyrinth terrains were found to consist of a mixture of organics and water ice, while the equatorial plains, hummocky terrains, and dunes were found to consist of a mixture of dark material and tholins. Furthermore, we found that the addition of some form of ice improves the fit in the ejecta spectra of Afekan and Sinlap craters. We find no indication for the presence of either NH3 or CO2 ice. Our main results agree with an existing Titan surface evolution scenario, wherein the impact cratering process produces a mixture of organic material and water ice, which is later "cleaned" through fluvial erosion in the midlatitude plains. This cleaning process does not appear to operate in the equatorial regions, which are quickly covered by a thin layer of sand sediment (with the exception of the freshest crater on Titan, Sinlap). Thus, it appears that active processes are working to shape the surface of Titan, and it remains a dynamic world in the present day.
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| 4. |
- Xu, J. H., et al.
(författare)
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Adaptive and Maladaptive Brain Functional Network Reorganization After Stroke in Hemianopia Patients: An Electroencephalogram-Tracking Study
- 2022
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Ingår i: Brain connectivity. - : Mary Ann Liebert Inc. - 2158-0014 .- 2158-0022. ; 12:8, s. 725-739
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Hemianopia after occipital stroke is believed to be mainly due to local damage at or near the lesion site. However, magnetic resonance imaging studies suggest functional connectivity network (FCN) reorganization also in distant brain regions. Because it is unclear whether reorganization is adaptive or maladaptive, compensating for, or aggravating vision loss, we characterized FCNs electrophysiologically to explore local and global brain plasticity and correlated FCN reorganization with visual performance.Methods: Resting-state electroencephalography (EEG) was recorded in chronic, unilateral stroke patients and healthy age-matched controls (n = 24 each). This study was approved by the local ethics committee. The correlation of oscillating EEG activity was calculated with the imaginary part of coherence between pairs of regions of interest, and FCN graph theory metrics (degree, strength, clustering coefficient) were correlated with stimulus detection and reaction time.Results: Stroke brains showed altered FCNs in the alpha- and low beta-band in numerous occipital, temporal brain structures. On a global level, FCN had a less efficient network organization whereas on the local level node networks were reorganized especially in the intact hemisphere. Here, the occipital network was 58% more rigid (with a more "regular" network structure) whereas the temporal network was 32% more efficient (showing greater "small-worldness"), both of which correlated with worse or better visual processing, respectively.Conclusions: Occipital stroke is associated with both local and global FCN reorganization, but this can be both adaptive and maladaptive. We propose that the more "regular" FCN structure in the intact visual cortex indicates maladaptive plasticity, where less processing efficacy with reduced signal/noise ratio may cause the perceptual deficits in the intact visual field (VF). In contrast, reorganization in intact temporal brain regions is presumably adaptive, possibly supporting enhanced peripheral movement perception. Impact statementThe functional connectivity network (FCN) after occipital stroke changes toward a more "regular" pattern. It is maladaptive in the intact occipital region, possibly leading to creating perceptual deficits causing spatiotemporal visual impairments in the "intact" but crowded visual field. The FCN can also be "adaptive," enabling temporal gyrus structures to compensate for the loss of vision.
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| 5. |
- Raty, S., et al.
(författare)
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Non-invasive electrical brain stimulation for vision restoration after stroke: An exploratory randomized trial (REVIS)
- 2021
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Ingår i: Restorative Neurology and Neuroscience. - : IOS Press. - 0922-6028 .- 1878-3627. ; 39:3, s. 221-235
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Tidskriftsartikel (refereegranskat)abstract
- Background: Occipital strokes often cause permanent homonymous hemianopia leading to significant disability. In previous studies, non-invasive electrical brain stimulation (NIBS) has improved vision after optic nerve damage and in combination with training after stroke. Objective: We explored different NIBS modalities for rehabilitation of hemianopia after chronic stroke. Methods: In a randomized, double-blinded, sham-controlled, three-armed trial, altogether 56 patients with homonymous hemianopia were recruited. The three experiments were: i) repetitive transorbital alternating current stimulation (rtACS, n=8) vs. rtACS with prior cathodal transcranial direct current stimulation over the intact visual cortex (tDCS/rtACS, n=8) vs. sham (n = 8); ii) rtACS (n = 9) vs. sham (n = 9); and iii) tDCS of the visual cortex (n = 7) vs. sham (n = 7). Visual functions were evaluated before and after the intervention, and after eight weeks follow-up. The primary outcome was change in visual field assessed by high-resolution and standard perimetries. The individual modalities were compared within each experimental arm. Results: Primary outcomes in Experiments 1 and 2 were negative. Only significant between-group change was observed in Experiment 3, where tDCS increased visual field of the contralesional eye compared to sham. tDCS/rtACS improved dynamic vision, reading, and visual field of the contralesional eye, but was not superior to other groups. rtACS alone increased foveal sensitivity, but was otherwise ineffective. All trial-related procedures were tolerated well. Conclusions: This exploratory trial showed safety but no main effect of NIBS on vision restoration after stroke. However, tDCS and combined tDCS/rtACS induced improvements in visually guided performance that need to be confirmed in larger-sample trials.
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| 6. |
- Koehler, Niklas, et al.
(författare)
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Pretomanid-resistant tuberculosis
- 2023
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Ingår i: Journal of Infection. - : W B SAUNDERS CO LTD. - 0163-4453 .- 1532-2742. ; 86:5, s. 520-524
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Lim, W., et al.
(författare)
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Migration and Luminescence Enhancement Effects of Deuterium in ZnO/ZnCdO Quantum Wells
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92, s. 032103-
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Tidskriftsartikel (refereegranskat)abstract
- ZnO/ZnCdO/ZnO multiple quantum well samples grown on sapphire substrates by molecular beam epitaxy and annealed in situ were exposed to D2 plasmas at 150 °C. The deuterium showed migration depths of ~0.8 µm for 30 min plasma exposures, with accumulation of 2H in the ZnCdO wells. The photoluminescence (PL) intensity from the samples was increased by factors of 5 at 5 K and ~20 at 300 K as a result of the deuteration, most likely due to passivation of competing nonradiative centers. Annealing up to 300 °C led to increased migration of 2H toward the substrate but no loss of deuterium from the sample and little change in the PL intensity. The initial PL intensities were restored by annealing at >=400 °C as 2H was evolved from the sample (~90% loss by 500 °C). By contrast, samples without in situ annealing showed a decrease in PL intensity with deuteration. This suggests that even moderate annealing temperatures lead to degradation of ZnCdO quantum wells.
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| 8. |
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| 9. |
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| 10. |
- Ye, Z, et al.
(författare)
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Fully-automated sarcopenia assessment in head and neck cancer: development and external validation of a deep learning pipeline
- 2023
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Ingår i: medRxiv : the preprint server for health sciences. - : Cold Spring Harbor Laboratory.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- PurposeSarcopenia is an established prognostic factor in patients diagnosed with head and neck squamous cell carcinoma (HNSCC). The quantification of sarcopenia assessed by imaging is typically achieved through the skeletal muscle index (SMI), which can be derived from cervical neck skeletal muscle (SM) segmentation and cross-sectional area. However, manual SM segmentation is labor-intensive, prone to inter-observer variability, and impractical for large-scale clinical use. To overcome this challenge, we have developed and externally validated a fully-automated image-based deep learning (DL) platform for cervical vertebral SM segmentation and SMI calculation, and evaluated the relevance of this with survival and toxicity outcomes.Materials and Methods899 patients diagnosed as having HNSCC with CT scans from multiple institutes were included, with 335 cases utilized for training, 96 for validation, 48 for internal testing and 393 for external testing. Ground truth single-slice segmentations of SM at the C3 vertebra level were manually generated by experienced radiation oncologists. To develop an efficient method of segmenting the SM, a multi-stage DL pipeline was implemented, consisting of a 2D convolutional neural network (CNN) to select the middle slice of C3 section and a 2D U-Net to segment SM areas. The model performance was evaluated using the Dice Similarity Coefficient (DSC) as the primary metric for the internal test set, and for the external test set the quality of automated segmentation was assessed manually by two experienced radiation oncologists. The L3 skeletal muscle area (SMA) and SMI were then calculated from the C3 cross sectional area (CSA) of the auto-segmented SM. Finally, established SMI cut-offs were used to perform further analyses to assess the correlation with survival and toxicity endpoints in the external institution with univariable and multivariable Cox regression.ResultsDSCs for validation set (n = 96) and internal test set (n = 48) were 0.90 (95% CI: 0.90 – 0.91) and 0.90 (95% CI: 0.89 - 0.91), respectively. The predicted CSA is highly correlated with the ground-truth CSA in both validation (r = 0.99,p< 0.0001) and test sets (r = 0.96,p< 0.0001). In the external test set (n = 377), 96.2% of the SM segmentations were deemed acceptable by consensus expert review. Predicted SMA and SMI values were highly correlated with the ground-truth values, with Pearson r β 0.99 (p < 0.0001) for both the female and male patients in all datasets. Sarcopenia was associated with worse OS (HR 2.05 [95% CI 1.04 - 4.04], p = 0.04) and longer PEG tube duration (median 162 days vs. 134 days, HR 1.51 [95% CI 1.12 - 2.08], p = 0.006 in multivariate analysis.ConclusionWe developed and externally validated a fully-automated platform that strongly correlates with imaging-assessed sarcopenia in patients with H&N cancer that correlates with survival and toxicity outcomes. This study constitutes a significant stride towards the integration of sarcopenia assessment into decision-making for individuals diagnosed with HNSCC.SUMMARY STATEMENTIn this study, we developed and externally validated a deep learning model to investigate the impact of sarcopenia, defined as the loss of skeletal muscle mass, on patients with head and neck squamous cell carcinoma (HNSCC) undergoing radiotherapy. We demonstrated an efficient, fullyautomated deep learning pipeline that can accurately segment C3 skeletal muscle area, calculate cross-sectional area, and derive a skeletal muscle index to diagnose sarcopenia from a standard of care CT scan. In multi-institutional data, we found that pre-treatment sarcopenia was associated with significantly reduced overall survival and an increased risk of adverse events. Given the increased vulnerability of patients with HNSCC, the assessment of sarcopenia prior to radiotherapy may aid in informed treatment decision-making and serve as a predictive marker for the necessity of early supportive measures.
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