| 1. |
- Banyai, Istvan, et al.
(författare)
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Simple O-17 NMR method for studying electron self-exchange reaction between UO22+ and U4+ aqua ions in acidic solution
- 2016
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Ingår i: Magnetic Resonance in Chemistry. - : WILEY-BLACKWELL. - 0749-1581 .- 1097-458X. ; 54:6, s. 444-450
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Tidskriftsartikel (refereegranskat)abstract
- O-17 NMR spectroscopy is proven to be suitable and convenient method for studying the electron exchange by following the decrease of O-17-enrichment in (UOO2+)-O-17 ion in the presence of U4+ ion in aqueous solution. The reactions have been performed at room temperature using I=5MClO(4)(-) ionic medium in acidic solutions in order to determine the kinetics of electron exchange between the U4+ and UO22+ aqua ions. The rate equation is given as R = a[H+](-2) + R, where R is an acid independent parallel path. R depends on the concentration of the uranium species according to the following empirical rate equation: R = k(1)[UO2+](1/2)[U4+](1/2) + k(2)[UO2+](3/2)[U4+](1/2). The mechanism of the inverse H+ concentration-dependent path is interpreted as equilibrium formation of reactive UO2+ species from UO22+ and U4+ aqua ions and its electron exchange with UO22+. The determined rate constant of this reaction path is in agreement with the rate constant of UO22+-UO2+, one electron exchange step calculated by Marcus theory, match the range given experimentally of it in an early study. Our value lies in the same order of magnitude as the recently calculated ones by quantum chemical methods. The acid independent part is attributed to the formation of less hydrolyzed U(V) species, i.e. UO3+, which loses enrichment mainly by electron exchange with UO22+ ions. One can also conclude that O-17 NMR spectroscopy, or in general NMR spectroscopy with careful kinetic analysis, is a powerful tool for studying isotope exchange reactions without the use of sophisticated separation processes. Copyright (C) 2015 John Wiley amp; Sons, Ltd.
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| 2. |
- Pajola, Maurizio, et al.
(författare)
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The southern hemisphere of 67P/Churyumov-Gerasimenko : Analysis of the preperihelion size-frequency distribution of boulders >= 7m
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We calculate the size-frequency distribution of the boulders on the southern hemisphere of comet 67P Churyumov-Gerasimenko (67P), which was in shadow before the end of April 2015. We compare the new results with those derived from the northern hemisphere and equatorial regions of 67P, highlighting the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 2 May 2015 at a distance of 125 km from the nucleus. The scale of this dataset is 2.3 m/px; the high resolution of the images, coupled with the favorable observation phase angle of 62 degrees, provided the possibility to unambiguously identify boulders >= 7 m on the surface of 67P and to manually extract them with the software ArcGIS. We derived the size-frequency distribution of the illuminated southern hemisphere. Results. We found a power-law index of -3.6 +/- 0.2 for the boulders on the southern hemisphere with a diameter range of 7-35 m. The power-law index is equal to the one previously found on northern and equatorial regions of 67P, suggesting that similar boulder formation processes occur in both hemispheres. The power-law index is related to gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. In addition, the presence of a larger number of boulders per km(2) in the southern hemisphere, which is a factor of 3 higher with respect to the northern hemisphere, suggests that the southernmost terrains of 67P are affected by a stronger thermal fracturing and sublimating activity, hence possibly causing larger regressive erosion and gravitational events.
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| 3. |
- Piski, Zalán, et al.
(författare)
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Minimálisan invazív, endoszkóppal asszisztált, transcribriform reszekció a koponyaalap rosszindulatú daganatainak sebészetében : [Minimally invasive endoscopic transcribriform resection of malignant lesions of the skull base]
- 2019
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Ingår i: Orvosi Hetilap. - : Akademiai Kiado Rt.. - 0030-6002 .- 1788-6120. ; 160:40, s. 1584-1590
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Forskningsöversikt (refereegranskat)abstract
- Introduction: Malignant tumours of the sinonasal region - including those with invasion of the skull base - necessitate surgical resection. The majority of the cases give an opportunity to perform the procedure via minimally invasive, endoscopic approach, without external, craniofacial surgery.Aim: To assess our clinical experience in treating anterior skull base malignancies, performing minimally invasive endoscopic transcribriform resection.Method: Between February 2015 and July 2017, four male and one female patient underwent minimally invasive, endoscopic skull base procedure. The mean age was 64.6 years (59-70, median: 66). Every surgery was performed via transnasal, endoscopic transcribriform approach. In two cases Kadish C esthesioneuroblastomas, while in one case a T3N0 sinonasal non-differentiated carcinoma, a T1N0 intestinal type adenocarcinoma and a T4N0 squamous cell carcinoma was the indication of surgery, respectively.Results: The mean follow-up time was 22.8 months, between 14 and 46 months. Intraoperative complications did not occur during the procedures. Regarding the postoperative period, liquorrhoea and pneumocephalus occurred in one case. Complications were solved with lumbar drainage. During follow-up, neither residual nor recurrent tumour was observed in our patients.Conclusion: Endoscopic transcribriform resection of the skull base malignancies is a safe and viable alternative to the traditional open approach.
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| 4. |
- Vincent, Jean-Baptiste, et al.
(författare)
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Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 523:7558, s. 63-66
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Tidskriftsartikel (refereegranskat)abstract
- Pits have been observed on many cometary nuclei mapped by spacecraft(1-4). It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments(5,6) andmodels(7,8) cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts(8,9). Alternative mechanisms like explosive activity(10) have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface.
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