Untersuchung innen und außen berippter, rohrförmiger, gasgekühlter Brennelemente

Die vorliegende Arbeit liefert einen Beitrag zur Entwicklung eines rohrförmigen innen und außen gekühlten Brennelementes für den Reaktortyp Natururan/Graphit/Gas. An sieben hierfür geeigneten Hüllrohren mit Längs-, Quer- und Pfeilrippen wurden mittlere und örtliche Wärmeübergangszahlen und mittlere Druckverlustbeiwerte gemessen. Die Untersuchungen erfolgten bezüglich Kühlgas, Druck, Temperatur, Massenstrom und Heizleistung unter Reaktorbedingungenim Hochdruckgaskreislauf des Instituts für Reaktorbauelemente. Die Aufteilung des Kühlgasmassenstromes in einen turbulenten inneren und äußeren Teilstrom wurde theoretisch berechnet und experimentell überprüft. Zur Beurteilung der einzelnen Rippenformen wurden in einer Rechnung Wärmeleistung, Gebläseleistung, Uran-, Rippenrohr- und Gastemperatur für einen vereinfachten Reaktorkühlkanal mit Originalabmessungen bestimmt. Die höchste Wärmeleistung wird unter Einhaltung aller Grenzen erreicht, wenn das Uranrohr außen und innen mit Pfeilrippenrohren umhüllt wird. Eine nur 11 % geringere Wärmeleistung wird erzielt, wenn das Uranrohr innen mit einem Längsrippenrohr umhüllt wird. Berücksichtigt man, daß beim Längsrippenrohr die erforderliche Gebläseleistung niedriger und die Herstellungskosten bedeutend geringer sind als beim Pfeilrippenrohr, so erkennt man, daß auch Längsrippenrohre als Innenhüllrohre durchaus geeignet sind

First passage time distribution for a random walker on a random forcing energy landscape

We present an analytical approximation scheme for the first passage time distribution on a finite interval of a random walker on a random forcing energy landscape. The approximation scheme captures the behavior of the distribution over all timescales in the problem. The results are carefully checked against numerical simulations.Comment: 16 page

Epstein-Barr virus nuclear antigen 3A protein regulates CDKN2B transcription via interaction with MIZ-1

The Epstein-Barr virus (EBV) nuclear antigen 3 family of protein is critical for the EBV-induced primary B-cell growth transformation process. Using a yeast two-hybrid screen we identified 22 novel cellular partners of the EBNA3s. Most importantly, among the newly identified partners, five are known to play direct and important roles in transcriptional regulation. Of these, the Myc-interacting zinc finger protein-1 (MIZ-1) is a transcription factor initially characterized as a binding partner of MYC. MIZ-1 activates the transcription of a number of target genes including the cell cycle inhibitor CDKN2B. Focusing on the EBNA3A/MIZ-1 interaction we demonstrate that binding occurs in EBV-infected cells expressing both proteins at endogenous physiological levels and that in the presence of EBNA3A, a significant fraction of MIZ-1 translocates from the cytoplasm to the nucleus. Moreover, we show that a trimeric complex composed of a MIZ-1 recognition DNA element, MIZ-1 and EBNA3A can be formed, and that interaction of MIZ-1 with nucleophosmin (NPM), one of its coactivator, is prevented by EBNA3A. Finally, we show that, in the presence of EBNA3A, expression of the MIZ-1 target gene, CDKN2B, is downregulated and repressive H3K27 marks are established on its promoter region suggesting that EBNA3A directly counteracts the growth inhibitory action of MIZ-1

The impact of neuron morphology on cortical network architecture

The neurons in the cerebral cortex are not randomly interconnected. This specificity in wiring can result from synapse formation mechanisms that connect neurons, depending on their electrical activity and genetically defined identity. Here, we report that the morphological properties of the neurons provide an additional prominent source by which wiring specificity emerges in cortical networks. This morphologically determined wiring specificity reflects similarities between the neurons’ axo-dendritic projections patterns, the packing density, and the cellular diversity of the neuropil. The higher these three factors are, the more recurrent is the topology of the network. Conversely, the lower these factors are, the more feedforward is the network’s topology. These principles predict the empirically observed occurrences of clusters of synapses, cell type-specific connectivity patterns, and nonrandom network motifs. Thus, we demonstrate that wiring specificity emerges in the cerebral cortex at subcellular, cellular, and network scales from the specific morphological properties of its neuronal constituents

Self-Similar Liquid Lens Coalescence

A basic feature of liquid drops is that they can merge upon contact to form a larger drop. In spite of its importance to various applications, drop coalescence on pre-wetted substrates has received little attention. Here, we experimentally and theoretically reveal the dynamics of drop coalescence on a thick layer of a low-viscosity liquid. It is shown that these so-called "liquid lenses" merge by the self-similar vertical growth of a bridge connecting the two lenses. Using a slender analysis, we derive similarity solutions corresponding to the viscous and inertial limits. Excellent agreement is found with the experiments without any adjustable parameters, capturing both the spatial and temporal structure of the flow during coalescence. Finally, we consider the crossover between the two regimes and show that all data of different lens viscosities collapse on a single curve capturing the full range of the coalescence dynamics

Numerical evaluation of a novel double-concentric swirl burner for sulfur combustion

A burner system for the efficient and clean combustion of sulfur is introduced, which serves as a key component in a novel solar power cycle using sulfur as chemical storage medium of solar energy. In order to validate the proposed design concept, highly-resolved numerical simulations have been performed. The current setup is operated with a thermal load of 20 kW or power density of 5 MW/m$^{3}$. Two nozzle configurations with different swirl intensities (SI) of the airflow are studied. A large inner recirculation zone is observed for the nozzle with a high SI (HSI), which leads to a strong radial dispersion of the sulfur spray and a broad, short flame in the combustion chamber; although this HSI design is beneficial from the viewpoint of flame stabilization, it causes a large number of sulfur droplets hitting the chamber wall. In contrast, the nozzle design with a low SI (LSI) yields a narrow spray and a long jet flame, with much less droplets hitting the wall. The HSI nozzle shows an overall higher flame temperature compared with the LSI nozzle, which is confirmed to be caused by burning at a higher local fuel equivalence ratio. This is attributed to the strong inner recirculation flow generated by the high swirl intensity, which results in an enhanced evaporation and mixing of sulfur droplets with air. In terms of operability and NOx emission, the LSI burner is preferred due to less sulfur droplets hitting the chamber wall and the lower flame temperature

Multi-Sideband RABBIT in Argon

We report a joint experimental and theoretical study of a three-sideband (3-SB) modification of the "reconstruction of attosecond beating by interference of two-photon transitions" (RABBIT) setup. The 3-SB RABBIT scheme makes it possible to investigate phases resulting from interference between transitions of different orders in the continuum. Furthermore, the strength of this method is its ability to focus on the atomic phases only, independent of a chirp in the harmonics, by comparing the RABBIT phases extracted from specific SB groups formed by two adjacent harmonics. We verify earlier predictions that the phases and the corresponding time delays in the three SBs extracted from angle-integrated measurements become similar with increasing photon electron energy. A variation in the angle dependence of the RABBIT phases in the three SBs results from the distinct Wigner and continuum-continuum coupling phases associated with the individual angular momentum channels. A qualitative explanation of this dependence is attempted by invoking a propensity rule. Comparison between the experimental data and predictions from an R-matrix (close-coupling) with time dependence calculation shows qualitative agreement in the observed trends.Comment: 8 pages, 5 figure

Us and the virus: understanding the COVID-19 pandemic through a social psychological lens

From a social psychological perspective, the COVID-19 pandemic and its associated protective measures affected individuals’ social relations and their basic psychological needs. We aim to identify sources of need frustration (stressors) and possibilities to bolster need satisfaction (buffers). Particularly, we highlight emerging empirical research in areas in which social psychological theorizing can contribute to our understanding of the pandemic’s social consequences: Loneliness, social networks, role conflicts, social identity, compliance, trust, reactance, and conspiracy beliefs. We highlight directions for future social psychological research as the pandemic continues