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Plateau bursting is typical of many electrically excitable cells, such as endocrine cells that secrete hormones and some types of neurons that secrete neurotransmitters. Although in many of these cell types the bursting patterns are regulated by the interplay between voltage-gated calcium channels and calcium-sensitive potassium channels, they can be very different. For example, in insulin-secreting pancreatic β-cells, plateau bursting is characterized by well-defined spikes during the depolarized phase whereas in pituitary cells, bursting features fast, irregular, small amplitude spikes. The latter has been termed “pseudo-plateau bursting” because the spikes are transients around a depolarized steady state rather than stable oscillations in the fast subsystem. In this study we systematically investigate the bursting patterns found in endocrine cell models. We show that this class of voltage and calcium gated conductance based models can be reduced to the polynomial model of Hindmarsh and Rose (25). This reduction preserves the main properties of the biophysical class of models that we consider and allows for detailed bifurcation analysis of the full fast-slow system. Our analysis does not require decomposition of the full system into fast and slow subsystems and reveals properties of endocrine bursting that are not captured by the standard fast-slow analysis.

Future changes in runoff can have important implications for water resources and flooding. In this study, runoff projections from ISI-MIP (Inter-sectoral Impact Model Intercomparison Project) simulations forced with HadGEM2-ES bias-corrected climate data under the Representative Concentration Pathway 8.5 have been analysed for differences between impact models. Projections of change from a baseline period (1981–2010) to the future (2070–2099) from 12 impacts models which contributed to the hydrological and biomes sectors of ISI-MIP were studied. The biome models differed from the hydrological models by the inclusion of CO2 impacts and most also included a dynamic vegetation distribution. The biome and hydrological models agreed on the sign of runoff change for most regions of the world. However, in West Africa, the hydrological models projected drying, and the biome models a moistening. The biome models tended to produce larger increases and smaller decreases in regionally averaged runoff than the hydrological models, although there is large inter-model spread. The timing of runoff change was similar, but there were differences in magnitude, particularly at peak runoff. The impact of vegetation distribution change was much smaller than the projected change over time, while elevated CO2 had an effect as large as the magnitude of change over time projected by some models in some regions. The effect of CO2 on runoff was not consistent across the models, with two models showing increases and two decreases. There was also more spread in projections from the runs with elevated CO2 than with constant CO2. The biome models which gave increased runoff from elevated CO2 were also those which differed most from the hydrological models. Spatially, regions with most difference between model types tended to be projected to have most effect from elevated CO2, and seasonal differences were also similar, so elevated CO2 can partly explain the differences between hydrological and biome model runoff change projections. Therefore, this shows that a range of impact models should be considered to give the full range of uncertainty in impacts studies.

Using comprehensive data for West Germany, this paper investigates the determinants of establishment exit. We find that between 1975 and 2006 the average exit rate has risen considerably. In order to test various 'liabilities' of establishment survival identified in the literature, we analyze the impact of establishment size and put a special focus on differences between young and mature establishments. Our empirical analysis shows that the mortality risk falls with establishment size, which confirms the liability of smallness. The probability of exit is substantially higher for young establishments which are not more than five years old, thus confirming the liability of newness. There also exists a liability of aging since exit rates first decline over time, reaching a minimum at ages 15 to 18, and then rise again somewhat. The determinants of exit differ substantially between young and mature establishments, suggesting that young establishments are more vulnerable in a number of ways. Mit umfangreichen Daten für Westdeutschland untersucht diese Studie die Einflussfaktoren von Betriebsschließungen. Es zeigt sich, dass die durchschnittliche Schließungsrate der Betriebe von 1975 bis 2006 deutlich gestiegen ist. Um verschiedene in der Literatur herausgearbeitete Anfälligkeiten zu überprüfen, analysieren wir den Einfluss der Betriebsgröße sowie Unterschiede zwischen jungen und älteren Betrieben. Die empirische Analyse zeigt, dass das Sterberisiko mit der Betriebsgröße abnimmt, was die 'liability of smallness' bestätigt. Entsprechend der 'liability of newness' ist die Schließungswahrscheinlichkeit deutlich höher für jüngere Betriebe, die maximal fünf Jahre alt sind. Ferner findet sich eine 'liability of aging', da die Schließungswahrscheinlichkeit zunächst mit dem Alter abnimmt, ihr Minimum zwischen 15 und 18 Jahren erreicht und danach wieder etwas zunimmt. Die Einflussfaktoren der Betriebsschließungen unterscheiden sich deutlich zwischen jungen und älteren Betrieben, wobei junge Betriebe in verschiedener Weise gefährdeter sind.

Ordinary linear and generalized linear regression models relate the mean of a response variable to a linear combination of covariate effects and, as a consequence, focus on average properties of the response. Analyzing childhood malnutrition in developing or transition countries based on such a regression model implies that the estimated effects describe the average nutritional status. However, it is of even larger interest to analyze quantiles of the response distribution such as the 5% or 10% quantile that relate to the risk of children for extreme malnutrition. In this paper, we analyze data on childhood malnutrition collected in the 2005/2006 India Demographic and Health Survey based on a semiparametric extension of quantile regression models where nonlinear effects are included in the model equation, leading to additive quantile regression. The variable selection and model choice problems associated with estimating an additive quantile regression model are addressed by a novel boosting approach. Based on this rather general class of statistical learning procedures for empirical risk minimization, we develop, evaluate and apply a boosting algorithm for quantile regression. Our proposal allows for data-driven determination of the amount of smoothness required for the nonlinear effects and combines model selection with an automatic variable selection property. The results of our empirical evaluation suggest that boosting is an appropriate tool for estimation in linear and additive quantile regression models and helps to identify yet unknown risk factors for childhood malnutrition.

An important puzzle in corporate taxation is that effective tax rates have fallen significantly while tax revenue has simultaneously risen in most countries. Moreover, the gross profitability of firms seems to be lower in high-tax countries, even though standard models of international investment would yield the opposite conclusion. We offer an explanation for these stylized facts by setting up a simple two-country model of tax competition with heterogeneous firms. In this model a unique, asymmetric Nash equilibrium can be shown to exist, provided that countries are sufficiently different with respect to their exogenous market conditions. In equilibrium the larger country levies the higher tax rate and attracts the high-cost firms. A simultaneous expansion of both markets intensifies tax competition and causes both countries to reduce their tax rates, despite higher corporate tax bases.

Die mathematische Beschreibung der Grundwasserströmung durch das Darcy-Gesetz ermöglicht es, neben den Grundwasserständen auch die Transportrichtung und die mittlere Transportgeschwindigkeit von Wasserinhaltsstoffen zu ermitteln. Die bei Transportvorgängen in porösen Medien zusätzlich zu diesem konvektiven Transport auftretende Vermischung wurde in ersten Ansätzen von Taylor, 1954 und Aris, 1956 untersucht. Für ein ideales homogenes poröses Medium (z. B. Einkornsande) läßt sich zur Beschreibung der Dispersion als Arbeitshypothese ein zum Fick'schen Diffusionsgesetz äquivalenter Ansatz formulieren. Die in der Natur gemessenen Ausbreitungsvorgänge zeigen, daß diese für die homogene Porenmatrix gefundene Beziehung nur schwer auf den Stofftransport in einem geologisch komplex aufgebauten natürlichen Aquifer übertragen werden kann. In dem vorliegenden Bericht wird versucht, einen kurzen Abriß einer Vorgehensweise zu geben, mit der sich der dispersive Transport im Feld besser beschreiben läßt als allein mit dem Ansatz nach Fick.

This paper documents multivariate forecast disagreement among professional forecasters of the Euro area economy and discusses implications for models of heterogeneous expectation formation. Disagreement varies over time and is strongly counter-cyclical. Disagreement is positively correlated with general (economic) uncertainty. Aggregate supply shocks drive disagreement about the long-run state of the economy while aggregate demand shocks have an impact on the level of disagreement about the short-run outlook for the economy. Forecasters disagree about the structure of the economy and the degree to which individual forecasters disagree with the average forecast tends to persist over time. This suggests that models of heterogeneous expectation formation, which are currently not able to generate those last two features, need to be modified. Introducing learning mechanisms and heterogeneous signal-to-noise ratios could reconcile the benchmark model for disagreement with the observed facts.