656 research outputs found
Counting Cubic Extensions with given Quadratic Resolvent
Given a number field and a quadratic extension , we give an explicit
asymptotic formula for the number of isomorphism classes of cubic extensions of
whose Galois closure contains as quadratic subextension, ordered by
the norm of their relative discriminant ideal. The main tool is Kummer theory.
We also study in detail the error term of the asymptotics and show that it is
, for an explicit .Comment: 19 page
Cropping School: Wir lernen gemeinsam mit und voneinander - eine kooperative Zusammenarbeit zwischen Landwirten, Wissenschaftlern und Beratern
Im Nordosten von Brandenburg (Deutschland) wird erstmalig das neue Konzept einer "Cropping School" erprobt, welches auf den Ansätzen der "Farmer Field Schools" und der "Stable Schools" basiert. Die Hauptziele der Cropping School bestehen darin i) Landwirte in die Lage zu versetzen, Maßnahmen zur Verbesserung ihrer Anbausysteme selbst durchzuführen sowie ii) eine praxisnahe Alternative zu existierenden Beratungsangeboten entwickeln zu können
Spatial and temporal trends of iron and iron isotope cycling in the Peruvian oxygen minimum zone
Iron (Fe) is a key element in the global ocean’s biogeochemical framework because of its essential role in numerous biological processes. A poorly studied link in the oceanic Fe cycle is the reductive release of Fe from sediments in oxygen depleted ocean regions - the oxygen minimum zones (OMZs). Changing rates of Fe release from OMZ sediments may have the potential to modulate ocean fertility which has far-reaching implications considering the high amplitude oxygen fluctuations throughout earth history as well as the ongoing ocean deoxygenation projected for the near future. In order to explore spatial and temporal trends of Fe cycling in OMZs, we present here Fe isotope and speciation data for surface sediments from a transect across the Peruvian upwelling area, one of the most pronounced OMZs of the modern ocean.
Because of continuous dissimilatory Fe reduction and diffusive loss across the benthic boundary, sediments within the OMZ are strongly depleted in reactive Fe components, and the little reactive Fe left behind has a heavy isotope composition. In contrast, surface sediments below the OMZ are enriched in reactive Fe, with the majority being present as Fe oxides with comparably light isotope composition. This lateral pattern of Fe depletion and enrichment indicates that Fe released from sediments within the OMZ is reoxidized and precipitated at the oxycline. First-order calculations suggest that the amount of Fe mobilized within the OMZ and that accumulated at the boundaries are largely balanced. Therefore, benthic Fe fluxes in OMZs should be carefully evaluated prior to incorporation into global models, as much of the initially released Fe may be reprecipitated prior to vertical or offshore transport.
First XRF core scanning results for partly laminated piston cores from the OMZ boundaries reveal downcore oscillations in the content of reactive Fe and redox-sensitive trace metals that are attributed to past changes in OMZ extension. Ongoing work on these cores will focus on their dating and the downcore investigation of Fe and trace metal records in order to better understand past Fe cycling within the Peruvian OMZ and potential interactions with climate variability
The relationship between young children’s personal values and their teacher-rated behaviors in the classroom
There has been little research on the relationships between children’s personal values and the behaviors that express such values in the school context. In the present study, we examined for the first time with children at this young age, the relations between values and their value-related behaviors, i.e., supportive, disciplined, learning-oriented, and achievement-oriented, in the primary school context. The sample consisted of 952 primary school children (51.5% boys; Mage = 7.93; SD = 0.35). Data used in this study were collected in 2022 in Switzerland. A multilevel analysis confirmed the hypothesis that systematic relationships between values and teacher-rated behaviors can be demonstrated with young children. However, gender was the strongest predictor of teacher-rated children’s classroom behaviors. The results highlight the significance of understanding children’s value-behavior relations, teachers’ possible gender stereotypes of children’s behaviors, and its practical importance in the school context
Early diagenesis of trace metals (V, Mo, U) in sediments of the Peruvian upwelling area: response to oxygen dynamics in the water column
The upwelling area in the eastern equatorial Pacific off Peru is one of the most pronounced oxygen minimum zones
(OMZs) of the modern ocean. Modeling scenarios predict an expansion of the OMZs in the course of global change
in the coming decades. As a consequence, the Peruvian continental margin represents a key locality for studies on
biogeochemical dynamics in the future ocean.
We present pore water and sediment data for redox-sensitive metals (Fe, Mn, V, Mo, and U) that have been collected
along a transect across the Peruvian margin at 11°S. The results are used to evaluate the behavior of trace metals
in a wide range of biogeochemical and hydrodynamic settings.
In the core of the OMZ, where permanently anoxic conditions prevail, redox sensitive metals exhibit diagenetic
behaviors largely consistent with previous studies. Vanadium and Mo are released from Fe oxihydroxides and
subsequently recycled through diffusion across the benthic boundary or trapped through formation of authigenic
V phases and sequestration of Mo by authigenic pyrite. Some U is delivered through diffusion across the benthic
boundary, reduction and precipitation of UO2 and incorporation into phosphorites. The utmost part of the buried U,
however, is delivered in particulate form, most likely as bioauthigenic U which cannot be recycled in the suboxic
waters overlying the anoxic sediments. In contrast to sediments in the core of the OMZ, sediments on the shelf
experience frequent oxygenation episodes related to the passage of internal waves and the regular recurrence of
El Niño events. These oxygenation episodes lead to the re-oxidation and remobilization of authigenic U and V. In
contrast to that, the authigenic accumulation of Mo is favored by the occasional occurrence of slightly oxidizing
conditions. This is most likely due to enhanced formation of sulfur intermediates necessary for pyrite formation
and the increased stability of pyrite, the major Mo sink, under oxidizing conditions, compared to authigenic V and
U phases. Redox oscillations in the Peruvian OMZ thus lead to a discrimination of U against Mo, a mechanism that
should be considered in the interpretation of U/Mo systematics in paleo redox studies. Overall our results provide
valuable constraints on how trace metal inventories of marginal sediments may respond to expanding shelf anoxia
and to short term perturbations of sediment redox conditions
Early diagenesis of redox-sensitive trace metals in the Peru upwelling area – Response to ENSO-related oxygen fluctuations in the water column
Pore water and solid phase data for redox-sensitive metals (Mn, Fe, V, Mo and U) were collected on a transect across the Peru upwelling area (11°S) at water depths between 78 and 2025 m and bottom water oxygen concentrations ranging from ~0 to 93 µM. By comparing authigenic mass accumulation rates and diffusive benthic fluxes, we evaluate the respective mechanisms of trace metal accumulation, retention and remobilization across the oxygen minimum zone (OMZ) and with respect to oxygen fluctuations in the water column related to the El Nino Southern Oscillation (ENSO).
Sediments within the permanent OMZ are characterized by diffusive uptake and authigenic fixation of U, V and Mo as well as diffusive loss of Mn and Fe across the benthic boundary. Some of the dissolved Mn and Fe in the water column re-precipitate at the oxycline and shuttle particle-reactive trace metals to the sediment surface at the lower and upper boundary of the OMZ. At the lower boundary, pore waters are not sufficiently sulfidic as to enable an efficient authigenic V and Mo fixation. As a consequence, sediments below the OMZ are preferentially enriched in U which is delivered via both in situ pre-cipitation and lateral supply of U-rich phosphorites from further upslope. Trace metal cycling on the Peruvian shelf is strongly affected by ENSO-related oxygen fluctuations in bottom water. During periods of shelf oxygenation, surface sediments receive particulate V and Mo with metal (oxyhydr)oxides that derive from both terrigenous sources and precipitation at the retreating oxycline. After the recurrence of anoxic conditions, metal (oxyhydr)oxides are reductively dissolved and the hereby liberated V and Mo are authigenically removed. This alternation between supply of particle-reactive trace metals during oxic periods and fixation during anoxic periods leads to a preferential accumulation of V and Mo compared to U on the Peruvian shelf.
The decoupling of V, Mo and U accumulation is further accentuated by the varying susceptibility to re-oxidation of the different authigenic metal phases. While authigenic U and V are readily re-oxidized and recycled during periods of shelf oxygenation, the sequestration of Mo by authigenic pyrite is favored by the transient occurrence of oxidizing conditions.Our findings reveal that redox-sensitive trace metals respond in specific manner to short-term oxygen fluctuations in the water column. The relative enrichment patterns identified might be useful for the reconstruction of past OMZ extension and large-scale redox oscillations in the geological record
Sim2Real for Environmental Neural Processes
Machine learning (ML)-based weather models have recently undergone rapid
improvements. These models are typically trained on gridded reanalysis data
from numerical data assimilation systems. However, reanalysis data comes with
limitations, such as assumptions about physical laws and low spatiotemporal
resolution. The gap between reanalysis and reality has sparked growing interest
in training ML models directly on observations such as weather stations.
Modelling scattered and sparse environmental observations requires scalable and
flexible ML architectures, one of which is the convolutional conditional neural
process (ConvCNP). ConvCNPs can learn to condition on both gridded and
off-the-grid context data to make uncertainty-aware predictions at target
locations. However, the sparsity of real observations presents a challenge for
data-hungry deep learning models like the ConvCNP. One potential solution is
'Sim2Real': pre-training on reanalysis and fine-tuning on observational data.
We analyse Sim2Real with a ConvCNP trained to interpolate surface air
temperature over Germany, using varying numbers of weather stations for
fine-tuning. On held-out weather stations, Sim2Real training substantially
outperforms the same model architecture trained only with reanalysis data or
only with station data, showing that reanalysis data can serve as a stepping
stone for learning from real observations. Sim2Real could thus enable more
accurate models for weather prediction and climate monitoring.Comment: 4 pages, 3 figures, To be published in Tackling Climate Change with
Machine Learning workshop at NeurIP
Islamismus in der Jugendphase
How do young people find their way into Islamist contexts and towards Islamist positions? The authors conducted biographical-narrative interviews with young people, who held different positions in this field of ideological positions. They look at the actual forms and features of the particular worldviews and processes of (de-)radicalisation and show how individual notions of the self and the world are intertwined with social interaction within families, peergroups, radical groups, or official institutions.Obwohl es mittlerweile eine Vielzahl an Forschung zum Phänomen Islamismus gibt, wurden in nur wenigen Studien Interviews mit jungen Menschen mit islamistischen Orientierungen geführt und systematisch ausgewertet. In diesem Buch gehen die Autorinnen anhand autobiografischer Erzählungen den folgenden Fragen nach: Wie eignen sich junge Menschen islamistische Orientierungen an, wie hängen sie mit biografischen Erfahrungen zusammen und welche Funktion erfüllen sie in den Biografien?
Die Autorinnen zeigen, dass die Orientierungen in jugendphasenspezifische Probleme von Grenzziehung, Handlungskontrolle, sozialer Positionierung und Vergemeinschaftung eingebunden sind und diese Probleme auf verschiedene Weise gelöst werden: Islamismus übernimmt dabei die Funktion der starken Grenze, die Funktion der starken Ordnung oder die Funktion der starken Gemeinschaft
Modelling radiation-induced cell cycle delays
Ionizing radiation is known to delay the cell cycle progression. In
particular after particle exposure significant delays have been observed and it
has been shown that the extent of delay affects the expression of damage such
as chromosome aberrations. Thus, to predict how cells respond to ionizing
radiation and to derive reliable estimates of radiation risks, information
about radiation-induced cell cycle perturbations is required. In the present
study we describe and apply a method for retrieval of information about the
time-course of all cell cycle phases from experimental data on the mitotic
index only. We study the progression of mammalian cells through the cell cycle
after exposure. The analysis reveals a prolonged block of damaged cells in the
G2 phase. Furthermore, by performing an error analysis on simulated data
valuable information for the design of experimental studies has been obtained.
The analysis showed that the number of cells analyzed in an experimental sample
should be at least 100 to obtain a relative error less than 20%.Comment: 19 pages, 11 figures, accepted for publication in Radiation and
Environmental Biophysic
- …