Kinder als Experten für Leistungsbewertung

Vor dem Hintergrund der Diskussion um schulische Leistungsbewertung werden Ergebnisse des Forschungsprojektes "LeiHS" vorgestellt, mit dem die Leistungsbewertung und -rückmeldung an Hamburger Schulen untersucht wird. Nachweisbar ist eine hohe Akzeptanz der Bewertung bei Schülern und Eltern. Ein enger Zusammenhang zwischen Schulklima und "Zeugniskultur" lässt sich belegen, der sich insbesondere auf den Umgang mit Berichtzeugnissen auswirkt. Die Auswertung von Interviews mit Grundschulkindern zu deren Berichtszeugnissen zeigt, dass Erwartungen an Transparenz, Textqualität und Hinweise zur Verbesserung des Lernens gerade von jungen Schülerinnen und Schülern formuliert werden, die damit durchaus als Experten für schulische Leistungsbewertung anzusehen sind. (DIPF/ Orig.)Against the background of the debate on the assessment of school achievment, the authors presents results of the research project „LeiHS“, wich investigates the assessment and feedback on achievment at schools in the city of Hamburg. Both students and parents show a high acceptance of assessment as well as a preference for reports in which the grades are accompanied by commentaries on the individual achievment in the different subjekts. It can be shown that there is a close relation between school climate an ‘report culture’, which has a strong influence om dealing with reports giving a written assessment of the student’s work. The evaluation of interviews with primary school students regarding their reports shows that young school girls and boys, in particular, formula legitimate expections regarding transparency, textual quality and tips for an improvement of their learning techniques, thus proving themselves to be experts in the assessment of school achievments. (DIPF/Orig.

The Phanerozoic δ88/86Sr Record of Marine Carbonates : Implications for Seawater Chemistry

In the light of increasing interest in the role of the world’s oceans in future global change, it is important to understand the underlying processes that were responsible for paleoceanographic changes in the geological past. Previous studies working on the geochemistry of ancient marine deposits agree that the seawater chemistry must have been changed throughout the Phanerozoic Eon. In particular, concurrent long-term changes in radiogenic and stable isotope systems, element ratios and concentrations and their correlation with sea-level changes, climate reconstructions, and global mass extinctions suggests common causative mechanisms. However, the geological processes being responsible for the observed changes are still being debated. Specifically, the role of mid ocean spreading rates, dolomitization and sea-level changes are thought to play a major role in paleo-seawater chemistry of major and trace elements. Within this study the first Phanerozoic stable strontium (Sr) isotope seawater record (δ(88/86)Sr-sw) is reconstructed, which is sensitive to imbalances in the Sr input and output fluxes. In a consequent model approach, the radiogenic Sr isotope record (87-Sr/86-Sr)sw and δ(88/86)Sr-sw are used to constrain the marine Phanerozoic Sr budget. On long timescales (~200Myr periodicity), δ(88/86)Sr-sw and modelled Sr carbonate burial rates (F(Sr)carb) follow times of proposed „aragonite seas“ and „calcite seas“, implying that the dominant carbonate mineralogy has an important effect on Sr burial rates. On shorter timescales, minima and maxima in F(Sr)carb are partly correlated to ocean anoxia and glaciations and related sea-level low stands, implying the importance of continental carbonate shelf weathering to the marine Sr budget. In particular, enduring high carbonate burial rates for ~21Myr could be related to seawater anoxia during the end-Permian mass extinctions. Here, bacterial sulphate reduction rates led to toxic and high alkaline deep waters that were intermittently upwelled to the surface ocean, causing massive carbonate precipitation on the seafloor as well as the largest biogeochemical crisis in the Phanerozoic Eon. Ultimately, insights from changes in δ(88/86)Sr-sw significantly improved our understanding of long-term changes in seawater chemistry and the relation of carbonate-related Sr fluxes to sea-level changes, mass extinctions, and global anoxia

Cannabidiol Strengthening of Gastric Tight Junction Complexes Analyzed in an Improved Xenopus Oocyte Assay

Cannabidiol (CBD), the non-psychoactive compound derived from the cannabis plant, has gained attention in recent years as a remedy against gastrointestinal disorders ranging from nausea and inflammation to abdominal pain. Recent advances demonstrated an effect on inflammatory pathways and barrier proteins. However, information on possible direct effects is scarce and needs to be addressed, as applications are currently increasing in popularity. To accomplish this, we have employed Xenopus laevis oocytes as a heterologous expression system for analysis of the direct effects on stomach-specific claudins and further developed tight junction (TJ) protein interaction assays. Human claudin-4, claudin-5, and claudin-18.2 were expressed in Xenopus oocytes, clustered in pairs to form contact areas, and analyzed in a two-cell model approach, including measurement of the contact area and contact strength. CLDN4/5/18 + CLDN4/5/18 oocyte pairs were incubated with 20 µM CBD or with 40 µM CBD and were compared to cells without CBD treatment (ctrl). For interaction analysis, the contact area was measured after 24 h and 48 h. Whereas CBD did not affect the size of the protein interaction area, Double Orbital Challenge experiments revealed an increased contact strength after 24 h incubation with CBD. In addition, the Xenopus oocyte experiments were accompanied by an analysis of claudin-4, -5, and -18 expression in gastric epithelium by immunoblotting and immunohistochemistry. Claudin-4, -5, and -18 were strongly expressed, indicating a major role for gastric epithelial barrier function. In summary, our study shows direct effects of 40 µM CBD on Xenopus oocytes heterologously expressing a stomach-specific claudin combination, indicating a supportive and beneficial effect of CBD on gastric TJ proteins

Der Phanerozoische δ(88/86)Sr Datensatz mariner Karbonate - Implikationen zur Meerwasserchemie

In the light of increasing interest in the role of the world’s oceans in future global change, it is important to understand the underlying processes that were responsible for paleoceanographic changes in the geological past. Previous studies working on the geochemistry of ancient marine deposits agree that the seawater chemistry must have been changed throughout the Phanerozoic Eon. In particular, concurrent long-term changes in radiogenic and stable isotope systems, element ratios and concentrations and their correlation with sea-level changes, climate reconstructions, and global mass extinctions suggests common causative mechanisms. However, the geological processes being responsible for the observed changes are still being debated. Specifically, the role of mid ocean spreading rates, dolomitization and sea-level changes are thought to play a major role in paleo-seawater chemistry of major and trace elements. Within this study the first Phanerozoic stable strontium (Sr) isotope seawater record (δ(88/86)Sr-sw) is reconstructed, which is sensitive to imbalances in the Sr input and output fluxes. In a consequent model approach, the radiogenic Sr isotope record (87-Sr/86-Sr)sw and δ(88/86)Sr-sw are used to constrain the marine Phanerozoic Sr budget. On long timescales (~200Myr periodicity), δ(88/86)Sr-sw and modelled Sr carbonate burial rates (F(Sr)carb) follow times of proposed „aragonite seas“ and „calcite seas“, implying that the dominant carbonate mineralogy has an important effect on Sr burial rates. On shorter timescales, minima and maxima in F(Sr)carb are partly correlated to ocean anoxia and glaciations and related sea-level low stands, implying the importance of continental carbonate shelf weathering to the marine Sr budget. In particular, enduring high carbonate burial rates for ~21Myr could be related to seawater anoxia during the end-Permian mass extinctions. Here, bacterial sulphate reduction rates led to toxic and high alkaline deep waters that were intermittently upwelled to the surface ocean, causing massive carbonate precipitation on the seafloor as well as the largest biogeochemical crisis in the Phanerozoic Eon. Ultimately, insights from changes in δ(88/86)Sr-sw significantly improved our understanding of long-term changes in seawater chemistry and the relation of carbonate-related Sr fluxes to sea-level changes, mass extinctions, and global anoxia.In Anbetracht des zunehmenden Interesses an der Rolle der Weltmeere im zukünftigen globalen Wandel, ist es wichtig die zugrunde liegenden Prozesse für die paläozeanographischen Veränderungen der geologischen Vergangenheit zu verstehen. Die bisherigen geochemischen Arbeiten an alten marinen Ablagerungen stimmen dabei überein, dass sich die Meerwasserchemie im Phanerozoikum geändert haben muss. Insbesondere die langfristigen Veränderungen in radiogenen und stabilen Isotopensystemen, Element-verhältnissen und –konzentrationen, sowie deren Korrelation mit Meeresspiegeländerungen, Klimarekonstruktionen und globalen Massenaussterbeereignissen weisen auf gemeinsame kausale Mechanismen hin. Allerdings sind die dafür verantwortlichen geologischen Prozesse noch in der Diskussion. Insbesondere die Prozesse der Ozeankrustenproduktion an mittelozeanischen Rücken, der Dolomitisierung und Meeresspiegeländerungen werden in Betracht gezogen, eine wichtige Rolle in der Paläo-Meerwasserchemie der Haupt- und Spurenelementen zu spielen. Im Rahmen dieser Studie wurde der erste phanerozoische stabile Strontium (Sr)-Isotopen Datensatz des Meerwassers (δ(88/86)Sr-sw) erstellt, welcher empfindlich auf Ungleichgewichte zwischen den Sr Quellen und Senken reagiert. In einem darauf folgenden Modell-Ansatz wurden die radiogenen (87-Sr/86-Sr) und stabilen (δ(88/86)Sr-sw) Daten verwendet, um das marine phanerozoische Sr Budget zu bilanzieren. Auf langen Zeitskalen (~ 200Mio. Jahre Periodizität) folgen δ88/86Srsw und die modellierten Sr Sedimentationsflüsse (F(Sr)carb) den Perioden von „Aragonit Meeren“ und „Calcit Meeren“, was bedeutet, dass die dominante Karbonatmineralogie einen wichtigen Einfluss auf die Sr Sedimentation hat. Auf kürzeren Zeitskalen sind Minima und Maxima in F(Sr)carb teilweise mit marinen Anoxien sowie Vereisungen und den damit verbundenen Meeresspiegeländerungen korreliert, welches die Bedeutung der kontinentalen Karbonatschelfverwitterung für das Sr Budget anzeigt. Insbesondere die ~21Mio. Jahre anhaltendenden hohen Karbonatsedimentationsraten am Ende des Perms konnten zur Meerwasseranoxie während der Massenaussterbens in Bezug gesetzt werden. Hier führte die bakterielle Sulfatreduktion zu giftigen und stark alkalischen Tiefengewässern, die zeitweise zur Meeresoberfläche aufgetrieben wurden, was zu einer massiven Karbonatausfällung auf dem Meeresboden, sowie zur bisher größten biogeochemischen Krise im Phanerozoikum geführt hat. Letztendlich haben die Erkenntnisse aus den Veränderungen im δ(88/86)Sr-sw unser Verständnis von langfristigen Veränderungen in der Meerwasserchemie, sowie den Zusammenhang zwischen marine Karbonatflüssen zu Meeresspiegeländerungen, Massenaussterben und globaler Anoxie, deutlich verbessert

Results of special mechanical analyses of Luna 16 material

The studies carried out on the Luna 16 regolith have confirmed the data that were already published internationally. By means of activation analysis under irradiation in the reactor, activation analysis with a 14 MeV U-generator, and mass spectroscopy on samples of 10 or 20 mg, six main and 63 trace elements were quantitatively determined and compared with known data

Determination of radiogenic and stable strontium isotope ratios (87Sr/86Sr; δ88/86Sr) by thermal ionization mass spectrometry applying an 87Sr/84Sr double spike

Recent findings of natural strontium isotope fractionation have opened up a new field of research in non-traditional stable isotope geochemistry. While previous studies were based on data obtained by MC-ICP-MS we here present a novel approach combining thermal ionization mass spectrometry (TIMS) with the use of an 87Sr/84Sr double spike (DS). Our results for the IAPSO sea water and JCp-1 coral standards, respectively, are in accord with previously published data. The strontium isotope composition of the IAPSO sea water standard was determined as δ88/86Sr = 0.386(5)‰ (δ values relative to the SRM987), 87Sr/86Sr* = 0.709312(9) n = 10 and a corresponding conventionally normalized 87Sr/86Sr = 0.709168(7) (all uncertainties 2SEM). For the JCp-1 coral standard we obtained δ88/86Sr = 0.197(8)‰, 87Sr/86Sr* = 0.709237(2) and 87Sr/86Sr = 0.709164(5) n = 3. We show that by applying this DS-TIMS method the precision is improved by at least a factor of 2–3 when compared to MC-ICP-MS

The isotope composition of selenium in chondrites constrains the depletion mechanism of volatile elements in solar system materials

Solar nebula processes led to a depletion of volatile elements in different chondrite groups when compared to the bulk chemical composition of the solar system deduced from the Sun's photosphere. For moderately-volatile elements, this depletion primarily correlates with the element condensation temperature and is possibly caused by incomplete condensation from a hot solar nebula, evaporative loss from the precursor dust, and/or inherited from the interstellar medium. Element concentrations and interelement ratios of volatile elements do not provide a clear picture about responsible mechanisms. Here, the abundance and stable isotope composition of the moderately- to highly-volatile element Se are investigated in carbonaceous, ordinary, and enstatite chondrites to constrain the mechanism responsible for the depletion of volatile elements in planetary bodies of the inner solar system and to define a δ(82/78)Se value for the bulk solar system. The δ(82/78)Se of the studied chondrite falls are identical within their measurement uncertainties with a mean of −0.20±0.26‰ (2 s.d., n=14n=14, relative to NIST SRM 3149) despite Se abundance depletions of up to a factor of 2.5 with respect to the CI group. The absence of resolvable Se isotope fractionation rules out a kinetic Rayleigh-type incomplete condensation of Se from the hot solar nebula or partial kinetic evaporative loss on the precursor material and/or the parent bodies. The Se depletion, if acquired during partial condensation or evaporative loss, therefore must have occurred under near equilibrium conditions to prevent measurable isotope fractionation. Alternatively, the depletion and cooling of the nebula could have occurred simultaneously due to the continuous removal of gas and fine particles by the solar wind accompanied by the quantitative condensation of elements from the pre-depleted gas. In this scenario the condensation of elements does not require equilibrium conditions to avoid isotope fractionation. The results further suggest that the processes causing the high variability of Se concentrations and depletions in ordinary and enstatite chondrites did not involve any measurable isotope fractionation. Different degrees of element depletions and isotope fractionations of the moderately-volatile elements Zn, S, and Se in ordinary and enstatite chondrites indicate that their volatility is controlled by the thermal stabilities of their host phases and not by the condensation temperature under canonical nebular conditions