Bronze Open-Access
Refine
Year of publication
Document Type
- Article (349)
- Other (51)
- Working Paper (18)
- Review (9)
- Conference Proceeding (3)
- Report (3)
- Part of a Book (2)
- Part of Periodical (2)
- Monograph/Edited Volume (1)
Keywords
- stars: massive (11)
- subdwarfs (11)
- gamma rays: general (10)
- stars: atmospheres (10)
- stars: winds, outflows (9)
- stars: early-type (8)
- ISM: supernova remnants (7)
- stars: abundances (7)
- stars: mass-loss (7)
- Magellanic Clouds (6)
Institute
- Institut für Physik und Astronomie (122)
- Institut für Biochemie und Biologie (70)
- Institut für Geowissenschaften (38)
- Department Psychologie (22)
- Fachgruppe Betriebswirtschaftslehre (21)
- Extern (18)
- Center for Economic Policy Analysis (CEPA) (17)
- Department Linguistik (16)
- Fachgruppe Volkswirtschaftslehre (15)
- Institut für Mathematik (12)
Context. NGC 253 is one of only two starburst galaxies found to emit gamma-rays from hundreds of MeV to multi-TeV energies. Accurate measurements of the very-high-energy (VHE; E> 100 GeV) and high-energy (HE; E > 60 MeV) spectra are crucial to study the underlying particle accelerators, probe the dominant emission mechanism(s) and to study cosmic-ray interaction and transport. Aims. The measurement of the VHE gamma-ray emission of NGC 253 published in 2012 by H.E.S.S. was limited by large systematic uncertainties. Here, the most up to date measurement of the gamma-ray spectrum of NGC 253 is investigated in both HE and VHE gamma-rays. Assuming a hadronic origin of the gamma-ray emission, the measurement uncertainties are propagated into the interpretation of the accelerated particle population. Methods. The data of H.E.S.S. observations are reanalysed using an updated calibration and analysis chain. The improved Fermi-LAT analysis employs more than 8 yr of data processed using pass 8. The cosmic-ray particle population is evaluated from the combined HE-VHE gamma-ray spectrum using NAIMA in the optically thin case. Results. The VHE gamma-ray energy spectrum is best fit by a power-law distribution with a flux normalisation of (1.34 +/- 0.14(stat) +/- 0.27(sys)) x 10(-13) cm(-2) s(-1) TeV-1 at 1 TeV - about 40% above, but compatible with the value obtained in Abramowski et al. (2012). The spectral index Gamma = 2.39 +/- 0.14(stat) +/- 0.25(sys) is slightly softer than but consistent with the previous measurement within systematic errors. In the Fermi energy range an integral flux of F(E > 60 MeV) = (1.56 +/- 0.28(stat) +/- 0.15(sys)) x 10(-8) cm(-2) s(-1) is obtained. At energies above similar to 3 GeV the HE spectrum is consistent with a power-law ranging into the VHE part of the spectrum measured by H.E.S.S. with an overall spectral index Gamma = 2.22 +/- 0.06(stat). Conclusions. Two scenarios for the starburst nucleus are tested, in which the gas in the starburst nucleus acts as either a thin or a thick target for hadronic cosmic rays accelerated by the individual sources in the nucleus. In these two models, the level to which NGC 253 acts as a calorimeter is estimated to a range of f(cal) = 0.1 to 1 while accounting for the measurement uncertainties. The presented spectrum is likely to remain the most accurate measurements until the Cherenkov Telescope Array (CTA) has collected a substantial set of data towards NGC 253.
Retinol-binding protein 4 (RBP4) is the major transport protein for retinol in blood. Recent evidence from genetic mouse models shows that circulating RBP4 derives exclusively from hepatocytes. Because RBP4 is elevated in obesity and associates with the development of glucose intolerance and insulin resistance, we tested whether a liver-specific overexpression of RBP4 in mice impairs glucose homeostasis. We used adeno-associated viruses (AAV) that contain a highly liver-specific promoter to drive expression of murine RBP4 in livers of adult mice. The resulting increase in serum RBP4 levels in these mice was comparable with elevated levels that were reported in obesity. Surprisingly, we found that increasing circulating RBP4 had no effect on glucose homeostasis. Also during a high-fat diet challenge, elevated levels of RBP4 in the circulation failed to aggravate the worsening of systemic parameters of glucose and energy homeostasis. These findings show that liver-secreted RBP4 does not impair glucose homeostasis. We conclude that a modest increase of its circulating levels in mice, as observed in the obese, insulin-resistant state, is unlikely to be a causative factor for impaired glucose homeostasis.
A small fraction of the radiative flux emitted by hot stars is absorbed by their winds and redistributed towards longer wavelengths. This effect, which leads also to the heating of the stellar photosphere, is termed wind blanketing. For stars with variable winds, the effect of wind blanketing may lead to the photometric variability. We have studied the consequences of line driven wind instability and wind blanketing for the light variability of O stars. We combined the results of wind hydrodynamic simulations and of global wind models to predict the light variability of hot stars due to the wind blanketing and instability. The wind instability causes stochastic light variability with amplitude of the order of tens of millimagnitudes and a typical timescale of the order of hours for spatially coherent wind structure. The amplitude is of the order of millimagnitudes when assuming that the wind consists of large number of independent concentric cones. The variability with such amplitude is observable using present space borne photometers. We show that the simulated light curve is similar to the light curves of O stars obtained using BRITE and CoRoT satellites.
One paragraph of the manuscript of the paper has been inadvertently omitted in the very final stage of its compilation due to a technical mistake. Since this paragraph discusses the declustering of the used earthquake catalogue and is therefore necessary for the understanding of the seismicity data preprocessing, the authors decided to provide this paragraph in form of a correction. The respective paragraph belongs to chapter 2 of the paper, where it was placed originally, and should be inserted into the published paper before the second to the last paragraph. The omitted text reads as follows:
Tundra be dammed
(2018)
Increasing air temperatures are changing the arctic tundra biome. Permafrost is thawing, snow duration is decreasing, shrub vegetation is proliferating, and boreal wildlife is encroaching. Here we present evidence of the recent range expansion of North American beaver (Castor canadensis) into the Arctic, and consider how this ecosystem engineer might reshape the landscape, biodiversity, and ecosystem processes. We developed a remote sensing approach that maps formation and disappearance of ponds associated with beaver activity. Since 1999, 56 new beaver pond complexes were identified, indicating that beavers are colonizing a predominantly tundra region (18,293km(2)) of northwest Alaska. It is unclear how improved tundra stream habitat, population rebound following overtrapping for furs, or other factors are contributing to beaver range expansion. We discuss rates and likely routes of tundra beaver colonization, as well as effects on permafrost, stream ice regimes, and freshwater and riparian habitat. Beaver ponds and associated hydrologic changes are thawing permafrost. Pond formation increases winter water temperatures in the pond and downstream, likely creating new and more varied aquatic habitat, but specific biological implications are unknown. Beavers create dynamic wetlands and are agents of disturbance that may enhance ecosystem responses to warming in the Arctic.
On the ambiguity of interaction and nonlinear main effects in a regime of dependent covariates
(2017)
The analysis of large experimental datasets frequently reveals significant interactions that are difficult to interpret within the theoretical framework guiding the research. Some of these interactions actually arise from the presence of unspecified nonlinear main effects and statistically dependent covariates in the statistical model. Importantly, such nonlinear main effects may be compatible (or, at least, not incompatible) with the current theoretical framework. In the present literature, this issue has only been studied in terms of correlated (linearly dependent) covariates. Here we generalize to nonlinear main effects (i.e., main effects of arbitrary shape) and dependent covariates. We propose a novel nonparametric method to test for ambiguous interactions where present parametric methods fail. We illustrate the method with a set of simulations and with reanalyses (a) of effects of parental education on their children’s educational expectations and (b) of effects of word properties on fixation locations during reading of natural sentences, specifically of effects of length and morphological complexity of the word to be fixated next. The resolution of such ambiguities facilitates theoretical progress.
The phenomenon of forced fixations suggests that readers sometimes fixate a word (due to oculomotor constraints) even though they intended to skip it (due to parafoveal cognitive-linguistic processing). We investigate whether this leads readers to look directly at a word but not pay attention to it. We used a gaze-contingent boundary paradigm to dissociate parafoveal and foveal information (e.g., the word phone changed to scarf once the reader's eyes moved to it) and asked questions about the sentence to determine which one the reader encoded. When the word was skipped or fixated only briefly (i.e., up to 100 ms) readers were more likely to report reading the parafoveal than the fixated word, suggesting that there are cases in which readers look directly at a word but their minds ignore it, leading to the illusion of reading something they did not fixate.
Plastid ribosomes are very similar in structure and function to the ribosomes of their bacterial ancestors. Since ribosome biogenesis is not thermodynamically favorable under biological conditions it requires the activity of many assembly factors. Here we have characterized a homolog of bacterial RsgA in Arabidopsis thaliana and show that it can complement the bacterial homolog. Functional characterization of a strong mutant in Arabidopsis revealed that the protein is essential for plant viability, while a weak mutant produced dwarf, chlorotic plants that incorporated immature pre-16S ribosomal RNA into translating ribosomes. Physiological analysis of the mutant plants revealed smaller, but more numerous, chloroplasts in the mesophyll cells, reduction of chlorophyll a and b, depletion of proplastids from the rib meristem and decreased photosynthetic electron transport rate and efficiency. Comparative RNA sequencing and proteomic analysis of the weak mutant and wild-type plants revealed that various biotic stress-related, transcriptional regulation and post-transcriptional modification pathways were repressed in the mutant. Intriguingly, while nuclear- and chloroplast-encoded photosynthesis-related proteins were less abundant in the mutant, the corresponding transcripts were increased, suggesting an elaborate compensatory mechanism, potentially via differentially active retrograde signaling pathways. To conclude, this study reveals a chloroplast ribosome assembly factor and outlines the transcriptomic and proteomic responses of the compensatory mechanism activated during decreased chloroplast function. Significance Statement AtRsgA is an assembly factor necessary for maturation of the small subunit of the chloroplast ribosome. Depletion of AtRsgA leads to dwarfed, chlorotic plants, a decrease of mature 16S rRNA and smaller, but more numerous, chloroplasts. Large-scale transcriptomic and proteomic analysis revealed that chloroplast-encoded and -targeted proteins were less abundant, while the corresponding transcripts were increased in the mutant. We analyze the transcriptional responses of several retrograde signaling pathways to suggest the mechanism underlying this compensatory response.
Background Heart failure (HF) is a complex, chronic condition that is associated with debilitating symptoms, all of which necessitate close follow-up by health care providers. Lack of disease monitoring may result in increased mortality and more frequent hospital readmissions for decompensated HF. Remote patient management (RPM) in this patient population may help to detect early signs and symptoms of cardiac decompensation, thus enabling a prompt initiation of the appropriate treatment and care before a manifestation of HF decompensation. Objective The objective of the present article is to describe the design of a new trial investigating the impact of RPM on unplanned cardiovascular hospitalisations and mortality in HF patients. Methods The TIM-HF2 trial is designed as a prospective, randomised, controlled, parallel group, open (with randomisation concealment), multicentre trial with pragmatic elements introduced for data collection. Eligible patients with HF are randomised (1:1) to either RPM + usual care or to usual care only and are followed for 12 months. The primary outcome is the percentage of days lost due to unplanned cardiovascular hospitalisations or all-cause death. The main secondary outcomes are all-cause and cardiovascular mortality. Conclusion The TIM-HF2 trial will provide important prospective data on the potential beneficial effect of telemedical monitoring and RPM on unplanned cardiovascular hospitalisations and mortality in HF patients.
The presence of extreme horizontal branch (EHB) and blue hook stars in some Galactic globular clusters (GGCs) constitutes one of the remaining mysteries of stellar evolution. While several evolutionary scenarios have been proposed to explain the characteristics of this peculiar population of evolved stars, their observational verification has been limited by the availability of spectroscopic data for a statistically significant sample of such objects in any single GGC. We recently launched the SHOTGLAS project with the aim of providing a comprehensive picture of this intriguing stellar population in terms of spectroscopic properties for all readily accessible GGCs hosting an EHB. In this first paper, we focus on omega Cen, a peculiar, massive GGC that hosts multiple stellar populations. We use non-LTE model atmospheres to derive atmospheric parameters (Te ff, log g and N(He) / N(H)) and spectroscopic masses for 152 EHB stars in the cluster. This constitutes the largest spectroscopic sample of EHB stars ever analyzed in a GGC and represents similar to 20% of the EHB population of omega Cen. We also search for close binaries among these stars based on radial velocity variations. Our results show that the EHB population of omega Cen is divided into three spectroscopic groups that are very distinct in the Te ff helium abundance plane. The coolest sdB-type stars (Te ff. 30 000 K) have a hydrogen-rich atmosphere, populate the theoretical EHB region in the Te ff log g plane, and form 26% of our sample. The hottest sdO-type stars (Te ff & 42 000 K) make up 10% of the sample, have a hydrogen-rich atmosphere and are thought to be in a post-EHB evolutionary phase. The majority of our sample is found at intermediate temperatures and consists of sdOB stars that have roughly solar or super-solar atmospheric helium abundances. It is these objects that constitute the blue hook at V > 18 : 5 mag in the omega Cen color-magnitude diagram. Interestingly, the helium-enriched sdOBs do not have a significant counterpart population in the Galactic field, indicating that their formation is dependent on the particular environment found in omega Cen and other select GGCs. Another major di ff erence between the EHB stars in omega Cen and the field is the fraction of close binaries. From our radial velocity survey we identify two binary candidates, however no orbital solutions could be determined. We estimate an EHB close binary fraction of similar to 5% in omega Cen. This low fraction is in line with findings for other GGCs, but in sharp contrast to the situation in the field, where around 50% of the sdB stars reside in close binaries. Finally, the mass distribution derived is very similar for all three spectroscopic groups, however the average mass (0.38 M fi) is lower than that expected from stellar evolution theory. While this mass conundrum has previously been noted for EHB stars in omega Cen, it so far appears to be unique to that cluster.
Himalayan rivers are frequently hit by catastrophic floods that are caused by the failure of glacial lake and landslide dams; however, the dynamics and long-term impacts of such floods remain poorly understood. We present a comprehensive set of observations that capture the July 2016 glacial lake outburst flood (GLOF) in the Bhotekoshi/Sunkoshi River of Nepal. Seismic records of the flood provide new insights into GLOF mechanics and their ability to mobilize large boulders that otherwise prevent channel erosion. Because of this boulder mobilization, GLOF impacts far exceed those of the annual summer monsoon, and GLOFs may dominate fluvial erosion and channel-hillslope coupling many tens of kilometers downstream of glaciated areas. Long-term valley evolution in these regions may therefore be driven by GLOF frequency and magnitude, rather than by precipitation.
In Germany, the productivity of professional services, a sector dominated by micro and small firms, declined by 40 percent between 1995 and 2014. This productivity decline also holds true for professional services in other European countries. Using a German firm-level dataset of 700,000 observations between 2003 and 2017, we analyze this largely uncovered phenomenon among professional services, the 4th largest sector in the EU15 business economy, which provide important intermediate services for the rest of the economy. We show that changes in the value chain explain about half of the decline and the increase in part-time employment is a further minor part of the decline. In contrast to expectations, the entry of micro and small firms, despite their lower productivity levels, is not responsible for the decline. We also cannot confirm the conjecture that weakening competition allows unproductive firms to remain in the market.
We present a study of the [O III]/[O II] ratios of star-forming galaxies drawn from Multi-Unit Spectroscopic Explorer (MUSE) data spanning a redshift range 0.28 < z < 0.85. Recently discovered Lyman continuum (LyC) emitters have extremely high oxygen line ratios: [O III]lambda 5007/[O II]lambda lambda 3726, 3729 > 4. Here we aim to understand the properties and the occurrences of galaxies with such high line ratios. Combining data from several MUSE Guaranteed Time Observing (GTO) programmes, we select a population of star-forming galaxies with bright emission lines, from which we draw 406 galaxies for our analysis based on their position in the z-dependent star formation rate (SFR) stellar mass (M*) plane. Out of this sample 15 are identified as extreme oxygen emitters based on their [O III]/[O II] ratios (3.7%) and 104 galaxies have [O III]/[O II] > 1 (26%). Our analysis shows no significant correlation between M*, SFR, and the distance from the SFR M, relation with [O III]/[O II]. We find a decrease in the fraction of galaxies with [O III]/[O II] > 1 with increasing M*, however, this is most likely a result of the relationship between [O III]/[O II] and metallicity, rather than between [O III]/[O II] and M. We draw a comparison sample of local analogues with < z > 0.03 from the Sloan Digital Sky Survey, and find similar incidence rates for this sample. In order to investigate the evolution in the fraction of high [O III]/[O II] emitters with redshift, we bin the sample into three redshift subsamples of equal number, but find no evidence for a dependence on redshift. Furthermore, we compare the observed line ratios with those predicted by nebular models with no LyC escape and find that most of the extreme oxygen emitters can be reproduced by low metallicity models. The remaining galaxies are likely LyC emitter candidates.
Although it is theoretically expected that all organic semiconductors support ambipolar charge transport, most organic transistors either transport holes or electrons effectively. Single-layer ambipolar organic field-effect transistors enable the investigation of different mechanisms in hole and electron transport in a single device since the device architecture provides a controllable planar pn-junction within the transistor channel. However, a direct comparison of the injection barriers and of the channel conductivities between electrons and holes within the same device cannot be measured by standard electrical characterization. This article introduces a novel approach for determining threshold gate voltages for the onset of the ambipolar regime from the position of the pn-junction observed by photoluminescence electromodulation (PLEM) microscopy. Indeed, the threshold gate voltage in the ambipolar bias regime considers a vanishing channel length, thus correlating the contact resistance. PLEM microscopy is a valuable tool to directly compare the contact and channel resistances for both carrier types in the same device. The reported results demonstrate that designing the metal/organic semiconductor interfaces by aligning the bulk metal Fermi levels to the highest occupied molecular orbital or lowest unoccupied molecular orbital levels of the organic semiconductors is a too simplistic approach for optimizing the charge injection process in organic field-effect devices.
We report on observations of the pulsar/Be star binary system PSR J2032+4127/MT91 213 in the energy range between 100 GeV and 20 TeV with the Very Energetic Radiation Imaging Telescope Array and Major Atmospheric Gamma Imaging Cherenkov telescope arrays. The binary orbit has a period of approximately 50 years, with the most recent periastron occurring on 2017 November 13. Our observations span from 18 months prior to periastron to one month after. A new point-like gamma-ray source is detected, coincident with the location of PSR J2032+4127/MT91 213. The gamma-ray light curve and spectrum are well characterized over the periastron passage. The flux is variable over at least an order of magnitude, peaking at periastron, thus providing a firm association of the TeV source with the pulsar/Be star system. Observations prior to periastron show a cutoff in the spectrum at an energy around 0.5 TeV. This result adds a new member to the small population of known TeV binaries, and it identifies only the second source of this class in which the nature and properties of the compact object are firmly established. We compare the gamma-ray results with the light curve measured with the X-ray Telescope on board the Neil Gehrels Swift Observatory and with the predictions of recent theoretical models of the system. We conclude that significant revision of the models is required to explain the details of the emission that we have observed, and we discuss the relationship between the binary system and the overlapping steady extended source, TeV J2032+4130.
Thermokarst lakes are prevalent in Arctic coastal lowland regions and sublake permafrost degradation and talik development contributes to greenhouse gas emissions by tapping the large permafrost carbon pool. Whereas lateral thermokarst lake expansion is readily apparent through remote sensing and shoreline measurements, sublake thawed sediment conditions and talik growth are difficult to measure. Here we combine transient electromagnetic surveys with thermal modeling, backed up by measured permafrost properties and radiocarbon ages, to reveal closed-talik geometry associated with a thermokarst lake in continuous permafrost. To improve access to talik geometry data, we conducted surveys along three transient electromagnetic transects perpendicular to lakeshores with different decadal-scale expansion rates of 0.16, 0.38, and 0.58m/year. We modeled thermal development of the talik using boundary conditions based on field data from the lake, surrounding permafrost and a borehole, independent of the transient electromagnetics. A talik depth of 91m was determined from analysis of the transient electromagnetic surveys. Using a lake initiation age of 1400years before present and available subsurface properties the results from thermal modeling of the lake center arrived at a best estimate talk depth of 80m, which is on the same order of magnitude as the results from the transient electromagnetic survey. Our approach has provided a noninvasive estimate of talik geometry suitable for comparable settings throughout circum-Arctic coastal lowland regions.
Vela Jr. (RX J0852.0-4622) is one of just a few known supernova remnants (SNRs) with a resolved shell across the whole electromagnetic spectrum from radio to very-high-energy (>100 GeV; VHE) gamma-rays. Its proximity and large size allow for detailed spatially resolved observations of the source, making Vela Jr. one of the primary sources used for the study of particle acceleration and emission mechanisms in SNRs. High-resolution X-ray observations reveal a steepening of the spectrum toward the interior of the remnant. In this study we aim for a self-consistent radiation model of Vela Jr. which at the same time would explain the broadband emission from the source and its intensity distribution. We solve the full particle transport equation combined with the high-resolution one-dimensional (1D) hydrodynamic simulations (using Pluto code) and subsequently calculate the radiation from the remnant. The equations are solved in the test particle regime. We test two models for the magnetic field profile downstream of the shock: damped magnetic field, which accounts for the damping of strong magnetic turbulence downstream, and transported magnetic field. Neither of these scenarios can fully explain the observed radial dependence of the X-ray spectrum under spherical symmetry. We show, however, that the softening of the spectrum and the X-ray intensity profile can be explained under the assumption that the emission is enhanced within a cone.
The keynote article (Mayberry & Kluender, 2017) makes an important contribution to questions concerning the existence and characteristics of sensitive periods in language acquisition. Specifically, by comparing groups of non-native L1 and L2 signers, the authors have been able to ingeniously disentangle the effects of maturation from those of early language exposure. Based on L1 versus L2 contrasts, the paper convincingly argues that L2 learning is a less clear test of sensitive periods. Nevertheless, we believe Mayberry and Kluender underestimate the evidence for maturational factors in L2 learning, especially that coming from recent research.
The tropical peat swamp forests of South-East Asia are being rapidly converted to agricultural plantations of oil palm and Acacia creating a significant global “hot-spot” for CO2 emissions. However, the effect of this major perturbation has yet to be quantified in terms of global warming potential (GWP) and the Earth's radiative budget. We used a GWP analysis and an impulse-response model of radiative forcing to quantify the climate forcing of this shift from a long-term carbon sink to a net source of greenhouse gases (CO2 and CH4). In the GWP analysis, five tropical peatlands were sinks in terms of their CO2 equivalent fluxes while they remained undisturbed. However, their drainage and conversion to oil palm and Acacia plantations produced a dramatic shift to very strong net CO2-equivalent sources. The induced losses of peat carbon are ~20× greater than the natural CO2 sequestration rates. In contrast, a radiative forcing model indicates that the magnitude of this shift from a net cooling to warming effect is ultimately related to the size of an individual peatland's carbon pool. The continuous accumulation of carbon in pristine tropical peatlands produced a progressively negative radiative forcing (i.e., cooling) that ranged from −2.1 to −6.7 nW/m2 per hectare peatland by 2010 CE, referenced to zero at the time of peat initiation. Peatland conversion to plantations leads to an immediate shift from negative to positive trend in radiative forcing (i.e., warming). If drainage persists, peak warming ranges from +3.3 to +8.7 nW/m2 per hectare of drained peatland. More importantly, this net warming impact on the Earth's radiation budget will persist for centuries to millennia after all the peat has been oxidized to CO2. This previously unreported and undesirable impact on the Earth's radiative balance provides a scientific rationale for conserving tropical peatlands in their pristine state.
Whistler mode exohiss are the structureless hiss waves observed outside the plasma pause with featured equatorward Poynting flux. An event of the amplification of exohiss as well as chorus waves was recorded by Van Allen Probes during the recovery phase of a weak geomagnetic storm. Amplitudes of both types of the waves showed a significant increase at the regions of electron density enhancements. It is found that the electrons resonant with exohiss and chorus showed moderate pitch angle anisotropies. The ratio of the number of electrons resonating with exohiss to total electron number presented in-phase correlation with density variations, which suggests that exohiss can be amplified due to electron density enhancement in terms of cyclotron instability. The calculation of linear growth rates further supports above conclusion. We suggest that exohiss waves have potential to become more significant due to the background plasma fluctuation.