Slowness: An Objective for Spike-Timing-Dependent Plasticity?

Slow Feature Analysis (SFA) is an efficient algorithm for learning input-output functions that extract the most slowly varying features from a quickly varying signal. It has been successfully applied to the unsupervised learning of translation-, rotation-, and other invariances in a model of the visual system, to the learning of complex cell receptive fields, and, combined with a sparseness objective, to the self-organized formation of place cells in a model of the hippocampus. In order to arrive at a biologically more plausible implementation of this learning rule, we consider analytically how SFA could be realized in simple linear continuous and spiking model neurons. It turns out that for the continuous model neuron SFA can be implemented by means of a modified version of standard Hebbian learning. In this framework we provide a connection to the trace learning rule for invariance learning. We then show that for Poisson neurons spike-timing-dependent plasticity (STDP) with a specific learning window can learn the same weight distribution as SFA. Surprisingly, we find that the appropriate learning rule reproduces the typical STDP learning window. The shape as well as the timescale are in good agreement with what has been measured experimentally. This offers a completely novel interpretation for the functional role of spike-timing-dependent plasticity in physiological neurons

Regional Disparities in the Training Market: Opportunities for Adolescents to Obtain a Company-Based Training Place Depending on Regional Training Market Conditions

Context: Due to limited geographical mobility, opportunities for adolescents interested in company-based training are primarily dependent on regional training offers. Competition for company-based training among adolescents varies regionally, and thus, the chance to obtain a training contract varies as well. In this article, we investigate the opportunities for adolescents to obtain company-based training depending on regional training market conditions. We assume that the advantages of obtaining a company-based training place exist in areas of decreased competition among interested adolescents. However, the question is whether those advantages will differ between adolescents depending on characteristics such as school achievement, socioeconomic status or migration background. Furthermore, we assume that, above all, market-induced ease-of-access to company-based training exists for occupations that face hiring challenges and indicates less occupational attractiveness. Methods: The transition from school (after 9th and 10th grade) to company-based training is analysed using data from the German National Educational Panel Study (NEPS, starting cohort 4). This dataset is merged with the official regional training market data regarding local supply and demand ratio for training places (called "SDR") in the dual system of Vocational Education and Training in Germany. Logistic regressions are used to predict the probabilities of obtaining a training place. The focus lies on the interaction effects between SDR and adolescents’ education-related characteristics (school certificates and grade point average), socioeconomic characteristics and migration backgrounds. Subgroup-specific analyses of different clusters of hiring challenges for trainee occupations are used to examine whether these effects are valid for all occupations. Findings: The results confirm regional differences in obtaining a training place depending on the SDR. Here, applicant hierarchies according to educational achievement continue to exist if competition for company-based training among adolescents decreases. Beneficiaries are better-qualified adolescents with poorer GPAs. SDR hardly influences social disparities. However, the advantages of obtaining a company-based training place primarily exist for training occupations with hiring challenges when competition for company-based training among adolescents decreases. These occupations have a significantly lower occupational prestige (ISEI-08) compared to occupations with fewer hiring challenges. Conclusion: The results make it clear that market-induced ease-of-access to company-based training is not necessarily an advantage. Because the findings indicate that the advantages pertain mainly to low-prestige occupations, it can be assumed that career-path disadvantages can arise down the road. Future studies should investigate this in more differentiated ways

To what extent do secondary effects shape migrants’ educational trajectories after lower-secondary education?

Research shows a heterogeneous picture of migration-related disparities regarding adolescents’ educational trajectories at the end of lower-secondary education. Among other disparities, migrants face large disadvantages with regard to the transition to vocational education and training (VET). They are, however, also more likely to change to upper-secondary school tracks at the end of lower-secondary education. Using longitudinal data drawn from the German National Educational Panel Study (NEPS, Starting Cohort 4), this study empirically captures patterns in school-leavers’ transition trajectories after lower-secondary education and empirically tests theoretical mechanisms of migration-related educational inequalities. Building on the concept of secondary effects of migrant origin, this study asks to what extent self-selection explains migration-related disparities in the educational trajectories at the end of lower-secondary education. Particular attention is devoted to the extent to which migration-related inequalities in adolescents’ transitions can be explained by differences in (1) rational choice factors and (2) the educational expectations and demands of parents and friends. The results show that rational choice factors and the educational expectations of social groups largely contribute to migration-related educational inequalities. The results provide important starting points for educational policy discussions on strategies and measures to address migration-related inequalities in the transition to VET

Impact of marine sand extraction on benthic communities west off Sylt (SE North Sea)

Ongoing erosion at coasts, beaches and dunes accompanied by a climate change-induced sea-level rise requires extensive protection measures. At the Island of Sylt (SE North Sea) beach nourishments were conducted for almost 50 years to protect the exposed western coast against erosion. Since 1984, the materials for the sand replenishments were dredged from an offshore excavation site approx. 7 km west off Sylt in the German Bight. In this study, we investigate the long-term effects of sand extraction on the local geomorphology, the associated benthic habitats and fauna. Hydroacoustic surveys and grab sampling revealed that after more than 35 years changes in bathymetry (with dredging pits of down to ~15 m below sea floor) and also changes in habitat characteristics are still present. Additionally, the sediment and benthic faunal compositions have changed. A comparison between dredged areas and undisturbed seafloor revealed significant differences in mud content (increasing), the number of individuals and species of macrozoobenthic organisms (decreasing). This indicates that the benthic communities in the dredging areas are in a persistent successional stage. Mud-loving species (e. g. Notomastus latericeus and Kurtiella bidentate) profit from the changed habitats, however sand-preferring organisms (e.g. Pisione remota and Aonides paucibranchiata) largely disappeared. Because of the slow backfill rates, we conclude that a complete backfill of the deep dredging pits is likely to take centuries. The same is expected to apply for the regeneration of the benthic communities. However, since rather coarse-to-medium sand was removed from this area and re-accumulation of this Pleistocene material is not possible because of weak transport rates, a re-establishment of benthic communities that prefer coarser sand seems to be unlikely. Since benthic communities are strongly linked to the habitat characteristics, habitat mapping using hydroacoustic techniques is an efficient and cost-effective measure to monitor the state of regeneration in this study site

Methane turnover and temperature response of methane-oxidizing bacteria in permafrost-affected soils of northeast Siberia

The abundance, activity, and temperature response of aerobic methane-oxidizing bacteria were studied in permafrost-affected tundra soils of northeast Siberia. The soils were characterized by both a high accumulation of organic matter at the surface and high methane concentrations in the water-saturated soils. The methane oxidation rates of up to 835 nmol CH4 h−1 g−1 in the surface soils were similar to the highest values reported so far for natural wetland soils worldwide. The temperature response of methane oxidation was measured during short incubations and revealed maximum rates between 22 °C and 28 °C. The active methanotrophic community was characterized by its phospholipid fatty acid (PLFA) concentrations and with stable isotope probing (SIP). Concentrations of 16:1ω8 and 18:1ω8 PLFAs, specific to methanotrophic bacteria, correlated significantly with the potential methane oxidation rates. In all soils, distinct 16:1 PLFAs were dominant, indicating a predominance of type I methanotrophs. However, long-term incubation of soil samples at 0 °C and 22 °C demonstrated a shift in the composition of the active community with rising temperatures. At 0 °C, only the concentrations of 16:1 PLFAs increased and those of 18:1 PLFAs decreased, whereas the opposite was true at 22 °C. Similarly, SIP with 13CH4 showed a temperature-dependent pattern. When the soils were incubated at 0 °C, most of the incorporated label (83%) was found in 16:1 PLFAs and only 2% in 18:1 PLFAs. In soils incubated at 22 °C, almost equal amounts of 13C label were incorporated into 16:1 PLFAs and 18:1 PLFAs (33% and 36%, respectively). We concluded that the highly active methane-oxidizing community in cold permafrost-affected soils was dominated by type I methanotrophs under in situ conditions. However, rising temperatures, as predicted for the future, seem to increase the importance of type II methanotrophs, which may affect methane cycling in northern wetlands

Persistent effects of sand extraction on habitats and associated benthic communities in the German Bight

Sea-level rise demands for protection measures of endangered coastlines crucial for the local population. At the island of Sylt in the SE North Sea, shoreline erosion is compensated by replenishment with sand dredged from an offshore extraction site. We studied the long-term effects of sand extraction on bathymetry, geomorphology, habitats and benthic fauna. Sand extraction created dredging holes about 1 km in diameter and up to 20 m below the ambient seafloor level. Directly after dredging the superficial sediment layer, inside the pits was dominated by coarse sand and stones. Hydroacoustic surveys revealed only minor changes of bathymetry > 35 years after sand extraction. Obviously, backfill of the dredging pits was very slow, at a rate of a few millimeters per year, presumably resulting from low ambient sediment availability and relatively calm hydrodynamic conditions despite high wave energy during storms. Thus, a complete backfill of the deep extraction sites is likely to take centuries in this area. Hydroacoustic surveys and ground truthing showed that the backfilled material is mainly very fine sand and mud, turning the previously coarse sand surface into a muddy habitat. Accordingly, grab samples revealed significant differences in macrozoobenthos community composition, abundance and species density between recently dredged areas ( 10 years ago) and undisturbed sites (control sites). Overall, dredging turned the original association of sand-dwelling species into a muddy sediment association. Since re-establishment of disturbed benthic communities depends on previous re-establishment of habitat characteristics, the low sedimentation rates indicate that a return to a pre-dredging habitat type with its former benthic community and habitat characteristics is unlikely. Since coarse sand is virtually immobile in this area, a regeneration towards pre-dredging conditions is also unlikely without human interference (e.g., mitigation measures like depositing coarse material on the seafloor to restore the sessile epifauna)

Fluorogenic tagging of protein 3-nitrotyrosine with 4-(aminomethyl)benzenesulfonate (ABS) in tissues: a useful alternative to immunohistochemistry for fluorescence microscopy imaging of protein nitration

Protein tyrosine nitration is a common biomarker of biological aging and diverse pathologies associated with the excessive formation of reactive oxygen and nitrogen species. Recently, we suggested a novel fluorogenic derivatization procedure for the detection of 3-nitrotyrosine (3-NT) using benzylamine derivatives to convert specifically protein or peptide bound 3-NT to a highly fluorescent benzoxazole product. In the current study, we applied this procedure to fluorogenic derivatization of protein 3-NT in sections from adult rat cerebellum in order to: (i) test this method in imaging nitrated proteins in fixed brain tissue sections, and (ii) compare the chemical approach to immunohistochemical labeling with anti-3-NT antibodies. Immunofluorescence analysis of cerebellar sections using anti-3-NT antibodies showed differential levels of immunostaining in the molecular, Purkinje, and granule cell layers of the cerebellar cortex; in agreement with previous reports, the Purkinje cells were most highly labeled. Importantly, fluorogenic derivatization reactions of cerebellar proteins with 4-(aminomethyl)benzenesulfonic acid (ABS) and K3Fe(CN)6 at pH 9, following sodium dithionite (SDT) reduction of 3-NT to 3-aminotyrosine (3-AT), showed a very similar pattern of relative intensity of cell labeling and improved resolution when compared with antibody labeling. Our data demonstrate that ABS-derivatization may be either a useful alternative or a complimentary approach to immunolabeling in imaging protein nitration in cells and tissues, including under conditions of dual labeling with antibodies to cell proteins, thus allowing for cellular co-localization of nitrated proteins and any protein of interest

Image potential states as quantum probe of graphene interfaces

Image potential states (IPSs) are electronic states localized in front of a surface in a potential well formed by the surface projected bulk band gap on one side and the image potential barrier on the other. In the limit of a two-dimensional solid a double Rydberg series of IPSs has been predicted which is in contrast to a single series present in three-dimensional solids. Here, we confirm this prediction experimentally for mono- and bilayer graphene. The IPSs of epitaxial graphene on SiC are measured by scanning tunnelling spectroscopy and the results are compared to ab-initio band structure calculations. Despite the presence of the substrate, both calculations and experimental measurements show that the first pair of the double series of IPSs survives, and eventually evolves into a single series for graphite. Thus, IPSs provide an elegant quantum probe of the interfacial coupling in graphene systems.Comment: Accepted for publication in New Journal of Physic