Institut für Umwelttechnologien und Strahlenschutz (Germany)

Persisting division of the Korean Peninsula has caused scholars to observe that younger generations of South Koreans are becoming less optimistic about reunification. Past studies have found that “Generation Z,” the population born between 1997 and 2012, is characteristically more pessimistic about reunification than older generations, and predict that this trend will continue. They have also found that young women are less hopeful of a reunification than young men. These past studies were conducted on a larger scale through surveys or public polls. In order to achieve a more nuanced discernment on Gen-Z’s attitudes, I conducted ten interviews with South Korean Gen-Z nationals. Despite the small sample size, my study confirms previously identified patterns among the youth. I found that female participants are more skeptical, and that Gen-Z might support reunification under different circumstances. This study also found that Gen-Z holds a South Korean-centric national identity, where North and South Korea are seen as separate entities. They feel no particular obligation to aid North Korea or work towards peninsular reunification. Instead of pursuing reunification, my interviewees felt that the South Korean government should devote its resources to other issues that are more pertinent to them. More importantly, however, this study argues that Gen-Z is flexible in their beliefs and may support reunification if the circumstances were different.

Let $m$ be a bounded function and $\alpha$ a nonnegative parameter. This article is concerned with the first eigenvalue $\lambda\_\alpha(m)$ of the drifted Laplacian type operator $\mathcal L\_m$ given by $\mathcal L\_m(u)= -\operatorname{div} \left((1+\alpha m)\nabla u\right)-mu$ on a smooth bounded domain, with Dirichlet boundary conditions. Assuming uniform pointwise and integral bounds on $m$, we investigate the issue of minimizing $\lambda\_\alpha(m)$ with respect to $m$. Such a problem is related to the so-called "two phase extremal eigenvalue problem" and arises naturally, for instance in population dynamics where it is related to the survival ability of a species in a domain. We prove that unless the domain is a ball, this problem has no "regular" solution. We then provide a careful analysis in the case of a ball by: (1) characterizing the solution among all radially symmetric resources distributions, with the help of a new method involving a homogenized version of the problem; (2) proving in a more general setting, a stability result for the centered distribution of resources with the help of a monotonicity principle for second order shape derivatives which significantly simplifies the analysis.

Most cortical interneurons are generated in the subpallial ganglionic eminences and migrate tangentially to their final destinations in the neocortex. Within the cortex, interneurons follow mainly stereotype routes in the subventricular zone/intermediate zone (SVZ/IZ) and in the marginal zone. It has been suggested that interactions between invading interneurons and locally generated projection neurons are implicated in the temporal and spatial regulation of the invasion process. However, so far experimental evidence for such interactions is lacking. We show here that the chemokine stromal-derived factor 1 (SDF-1; CXCL12) is expressed in the main invasion route for cortical interneurons in the SVZ/IZ. Most SDF-1-positive cells are proliferating and express the homeodomain transcription factors Cux1 and Cux2. Using MASH-1 mutant mice in concert with the interneuron marker DLX, we exclude that interneurons themselves produce the chemokine in an autocrine manner. We conclude that the SDF-1-expressing cell population represents the precursors of projection neurons during their transition and amplification in the SVZ/IZ. Using mice lacking the SDF-1 receptor CXCR4 or Pax6, we demonstrate that SDF-1 expression in the cortical SVZ/IZ is essential for recognition of this pathway by interneurons. These results represent the first evidence for a molecular interaction between precursors of projection neurons and invading interneurons during corticogenesis.

The linear-no-threshold (LNT) controversy covers much more than the mere discussion whether or not "the LNT hypothesis is valid". It is shown that one cannot expect to find only one or even the only one dose-effect relationship. Each element within the biological reaction chain that is affected by ionizing radiation contributes in a specific way to the final biological endpoint of interest. The resulting dose-response relationship represents the superposition of all these effects. Till now there is neither a closed and clear picture of the entirety of radiation action for doses below some 10 mSv, nor does clear epidemiological evidence exist for an increase of risk for stochastic effects, in this dose range. On the other hand, radiation protection demands for quantitative risk estimates as well as for practicable dose concepts. In this respect, the LNT concept is preferred against any alternative concept. However, the LNT concept does not necessarily mean that the mechanism of cancer induction is intrinsically linear. It could hold even if the underlying multi-step mechanisms act in a non-linear way. In this case it would express a certain "attenuation" of non-linearities. Favouring LNT against threshold-, hyper-, or sub-linear models for radiation-protection purposes on the one hand, but preferring one of these models (e.g. for a specific effect) because of biological considerations for scientific purposes on the other hand, does not mean a contradiction.

The aim of this work was to determine the significance of groundwater colloids in far-field radionuclide migration. To this purpose, isotopic data presented in this paper were obtained from several selected Gorleben groundwaters as part of the colloid characterisation programme. The contents of major and minor ions, light isotopes (2H, 3H, 13C, 14C, 18O and 34S), and the U/Th isotopes were measured. Radiocarbon and 13C were measured in dissolved inorganic carbon (DIC), ion the humic acid (HAcolloids) and fulvic acid (FA-solution) fractions of dissolved organic carbon (DOC). The 18O and 34S were also determined in dissolved sulphate phase. The U/Th isotope measurements were carried out on total and surface solid phases, colloid fraction (1-1000 nm particle size, HA) and solution (<1.5 nm, FA). The 3H data using a piston-flow model have yielded groundwater ages of less than 40a before present (BP) for a near surface groundwaters and much older ages for all other deeper organically-rich Gorleben groundwaters. The 14C content of DIC is low and probably influenced by strong dilution with mineralised fossil carbon. The resulting high 14C-model ages (up to 27 ka BP) can only be interpreted as upper limits of the true groundwater ages. The 14C content of the HA fractions is partly very low or partly below detection limit yielding very high 14C-model groundwater ages (up to >30 ka BP) whereas, some of the FA fractions contain higher 14C yielding model groundwater ages more consistent with post-glacial recharge (<12 ka BP). These groundwater ages are consistent with Holocene recharge inferred from the 2H and 18O isotope data. These differences between the HA and FA fractions are also confirmed by the U/Th isotope ratios suggesting different source/histories of the two organic carbon fractions. Thus, it is possible that the FA fraction has originated mainly from the near-surface (soil) source, while the HA fraction derives mainly from organic matter from older sediments such as lignite lenses or from a mixture of an enhanced input of organically-rich water younger than some 12 ka BP and much older lignite source.

Direct alpha spectrometry with three different filter types was investigated for the determination of thorium air concentrations at workplaces in the manufacturing process of discharge lamps containing thoriated tungsten electrodes. The method was compared with neutron activation analysis over an activity range of five orders of magnitude. Within the experimental limits of error, both methods were found to be comparable with respect to sensitivity and accuracy. The advantage of direct alpha spectrometry, however, is that it is less laborious than neutron activation analysis and that it supplies information on the degree of radioactive equilibrium of the thorium series, which is important with regard to the estimation of dose.