Halogenfrei flammgeschützte Epoxidharzsysteme auf der Basis von Präformulierungen

Es wurden flammgeschützte Epoxidharzsysteme auf der Basis reaktiver, phosphorhaltiger Flammschutzmittel entwickelt. Als Hauptkriterium für die Qualität der flammhemmenden Eigenschaften wurde das Erreichen der UL 94 V0 Klassifizierung gemäß DIN IEC 60695-11-10 gewählt. Darüber hinaus wurde für ausgewählte Systeme der Sauerstoffindex (LOI) ermittelt und als entscheidende Materialeigenschaft die Glasübergangstemperatur mittels DSC bestimmt. Ein Hauptaugenmerk wurde auf die Art und Weise der Einbringung des Flammschutzmittels in das Polymer gelegt. Es wurde insbesondere die Modifizierung der Epoxidharzmonomere durch eine der Formulierung (Abmischen der Harzkomponente mit der Härterkomponente und einem entsprechenden Beschleuniger) zeitlich vorgelagerte Reaktion („Präformulierung“) als Methode der Wahl angewendet. Mittels dieser Präformulierungsreaktion gelang es die reaktiven Flammschutzmittel kovalent an die entsprechenden mehrfunktionellen Epoxidharze zu binden. Nach der Polymerisation wurde das Flammschutzmittel somit integraler Bestandteil des Polymernetzwerkes. Es wurden verschiedene Polymere, die monofunktionelle, phosphorhaltige Verbindungen als Flammschutzmittel enthielten, untersucht und entsprechend ihres Brandverhaltens klassifiziert. Es konnte gezeigt werden, dass 9,10-Dihydro-9-oxa-10-phosphaphenanthren-10-oxid (1) und seine Derivate sehr effektive Flammschutzmittel darstellten. Epoxidharze, die mit diversen Phosphiten und Phosphaten modifiziert wurden, die nicht über eine dem 9,10-Dihydro-9-oxa-10-phosphaphenanthren-10-oxid analoge phosphacyclische Struktur verfügten, wiesen keine ausgeprägten flammhemmenden Eigenschaften auf. Mit steigendem Flammschutzmittelgehalt nahmen die flammhemmenden Eigenschaften der Polymere erwartungsgemäß zu, allerdings sank im Gegensatz die Glasübergangstemperatur der modifizierten Polymere. Da die Glasübergangstemperatur die maximale Einsatztemperatur der Polymere markiert, sind möglichst hohe Glasübergangstemperaturen erstrebenswert. Durch die Ermittlung der Grenzgehalte an Flammschutzmittel, bei denen die UL 94 V0 Klassifizierung gerade erreicht wurde, konnte eine allzu starke Erniedrigung der Glasübergangstemperatur verhindert werden. So konnten mit dem Härter DETDA 80 (Diethyltoluoldiamin) außerdem ein System auf Basis von DEN 438, modifiziert mit 1 erarbeitet werden, das flammhemmend ausgerüstet war und eine sehr hohe Glasübergangstemperatur von 202°C aufwies. Dieses derartig modifizierte Epoxidharzsystem erreichte dabei die UL 94 V0 Klassifizierung ab dem niedrigen, absoluten Phosphorgehalt von 0.61%. Neben monofunktionellen, phosphorhaltigen Flammschutzmitteln wurden auch difunktionelle Phosphorverbindungen zur Präformulierung herangezogen. Diese besaßen den Vorteil, dass sie auch mit dem zweifunktionellen Standardharz DGEBA Präformulierungen ergaben, die effektiv polymerisiert werden konnten ohne zu ungenügenden Netzwerkdichten zu führen. Als Referenzflammschutzmittel wurde das Addukt von 1 an Benzochinon (15) herangezogen, da es sich im asiatischen Raum in den letzten Jahren in der Leiterplattenindustrie etabliert hatte. Es konnten durch den Einsatz der Addukte von Verbindung 1 an Dialdehyde, insbesondere Terephthaldialdehyd, Alternativen zu 15 entwickelt werden, die ebenfalls präformuliert werden konnten und nach der Polymerisation vergleichbare flammgeschützte Polymerkörper lieferten. Die Kompatibilität dieser Systeme mit verschiedenen Härtern wurde erfolgreich demonstriert und die resultierenden Materialeigenschaften verglichen. Um die unterschiedliche Effektivität der präformulierten Phosphorverbindung zu erklären, wurden 1, 2 und 3 sowie 8 und 9 als Reinsubstanzen mittels hochauflösender Sektorfeldmassenspektroskopie untersucht. Hauptaugenmerk wurde dabei auf die Hauptzersetzungsprodukte gelegt. Im Fall von 1 und seinen Derivaten 2 und 3 konnten plausible Fragmentierungs- und Zersetzungsschemata gefunden werden. Als treibende Kraft der dabei ablaufenden Reaktionen wurde die Bildung von stabilem Dibenzofuran identifiziert. Als Nebenprodukt konnte das PO-Radikal im Massenspektrometer hochauflösend nachgewiesen werden. Aufgrund ihrer chemischen Struktur konnten 8 und 9 dieses Radikal nicht bilden. Es wurde dementsprechend bei der Zersetzung im hochauflösenden Sektorfeldmassensprektometer nicht detektiert. Um nicht nur die Zersetzung der molekularen Substanzen zu detektieren, wurden auch gemahlene ausgehärtete Epoxidharzproben mittels thermischer Desorptionsmassenspekrometrie untersucht. Hierzu wurden Epoxidharzmaterialien, basierend auf DDM gehärteten Präformulierungen aus DEN 438 und 1 bzw. 8 herangezogen, sowie unmodifiziertes, DDM gehärtetes DEN 438 als Blindprobe. Es gelang bei der thermischen Zersetzung dieser Polymere konkrete Pyrolysegase zu analysieren. Das 1 modifizierte Polymer setzte PO Radikale frei, während bei der Blindprobe und dem mit 8 modifizierten Harz kein PO detektiert wurde. Die PO Radikale können bei erhöhter Temperatur gasförmig aus dem pyrolysierenden Polymer austreten und in einer Radikalfängerreaktion H- und OH- Radikale abfangen. Da diese hochreaktiven Radikale die thermische Zersetzung des Polymers in Brennstoff bewerkstelligen, zeigt die durch PO verursachte Abfangreaktion flammhemmende Wirkung. Im Gegensatz zu Verbindung 1 und seinen Derivaten, die ihre Wirkung in der Gasphase entfalten können, wirkten Verbindung 8 und vergleichbare Phosphorverbindungen ausschließlich in der kondensierten Phase

Privatizing disability insurance

Public disability insurance (DI) programs in many countries face pressure to reduce their generosity in order to remain sustainable. In this paper, we investigate the welfare effects of giving a larger role to private insurance markets in the face of public DI cuts. Exploiting a unique reform that abolished one part of the German public DI system for younger cohorts, we find that despite significant crowding-in effects, overall private DI take-up remains modest. Private DI tends to be concentrated among high-income, high-education and low-risk individuals. We do not find any evidence of adverse selection on unpriced risk. Finally, we estimate individual insurance valuations via a revealed preferences approach, a key input for welfare calculations. We find that observed willingness-to-pay of many individuals is low, such that providing coverage partly via a private DI market improves welfare. However, we show that distributional concerns as well as individual risk misperceptions can provide grounds for justifying a full public DI mandate

Will forest dynamics continue to accelerate throughout the 21st century in the Northern Alps?

Observational evidence suggests that forests in the Northern Alps are changing at an increasing rate as a consequence of climate change. Yet, it remains unclear whether the acceleration of forest change will continue in the future, or whether downregulating feedbacks will eventually decouple forest dynamics from climate change. Here we studied future forest dynamics at Berchtesgaden National Park, Germany by means of a process-based forest landscape model, simulating an ensemble of 22 climate projections until the end of the 21st century. Our objectives were (i) to assess whether the observed acceleration of forest dynamics will continue in the future, (ii) to analyze how uncertainty in future climate translates to variation in future forest disturbance, structure, and composition, and (iii) to determine the main drivers of future forest dynamics. We found that forest dynamics continue to accelerate in the coming decades, with a trend towards denser, structurally more complex and more species rich forests. However, changes in forest structure leveled off in the second half of the 21st century regardless of climate scenario. In contrast, climate scenarios caused trajectories of tree species change to diverge in the second half of the 21st century, with stabilization under RCP 2.6 and RCP 4.5 scenarios and accelerated loss of conifers under RCP 8.5. Disturbance projections were 3 to 20 times more variable than future climate, whereas projected future forest structure and composition varied considerably less than climate. Indirect effects of climate change via alterations of the disturbance regime had a stronger impact on future forest dynamics than direct effects. Our findings suggest that dampening feedbacks within forest dynamics will decelerate forest change in the second half of the 21st century. However, warming beyond the levels projected under RCP 4.5 might profoundly alter future forest disturbance and composition, challenging conservation efforts and ecosystem service supply. --Raw simulation outputs are extensive in size and can be requested from the corresponding author, Dominik Thom.Funding provided by: European Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000781Award Number: 101001905Funding provided by: Bavarian State Ministry of the Environment and Consumer ProtectionCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100010219Award Number: StMUV TKP01KPB-66747The data is based on simulations of Berchtesgaden National Park using iLand (https://iland-model.org/). Simulations include 22 climate change projections à 20 replicates from year 2020 - 2100. Presented here is the analysis of iLand outputs

Domain-specific neural networks improve automated bird sound recognition already with small amount of local data

1. An automatic bird sound recognition system is a useful tool for collecting data of different bird species for ecological analysis. Together with autonomous recording units (ARUs), such a system provides a possibility to collect bird observations on a scale that no human observer could ever match. During the last decades, progress has been made in the field of automatic bird sound recognition, but recognizing bird species from untargeted soundscape recordings remains a challenge. 2. In this article, we demonstrate the workflow for building a global identification model and adjusting it to perform well on the data of autonomous recorders from a specific region. We show how data augmentation and a combination of global and local data can be used to train a convolutional neural network to classify vocalizations of 101 bird species. We construct a model and train it with a global data set to obtain a base model. The base model is then fine-tuned with local data from Southern Finland in order to adapt it to the sound environment of a specific location and tested with two data sets: one originating from the same Southern Finnish region and another originating from a different region in German Alps. 3. Our results suggest that fine-tuning with local data significantly improves the network performance. Classification accuracy was improved for test recordings from the same area as the local training data (Southern Finland) but not for recordings from a different region (German Alps). Data augmentation enables training with a limited number of training data and even with few local data samples significant improvement over the base model can be achieved. Our model outperforms the current state-of-the-art tool for automatic bird sound classification.An automatic bird sound recognition system is a useful tool for collecting data of different bird species for ecological analysis. Together with autonomous recording units (ARUs), such a system provides a possibility to collect bird observations on a scale that no human observer could ever match. During the last decades, progress has been made in the field of automatic bird sound recognition, but recognizing bird species from untargeted soundscape recordings remains a challenge. In this article, we demonstrate the workflow for building a global identification model and adjusting it to perform well on the data of autonomous recorders from a specific region. We show how data augmentation and a combination of global and local data can be used to train a convolutional neural network to classify vocalizations of 101 bird species. We construct a model and train it with a global data set to obtain a base model. The base model is then fine-tuned with local data from Southern Finland in order to adapt it to the sound environment of a specific location and tested with two data sets: one originating from the same Southern Finnish region and another originating from a different region in German Alps. Our results suggest that fine-tuning with local data significantly improves the network performance. Classification accuracy was improved for test recordings from the same area as the local training data (Southern Finland) but not for recordings from a different region (German Alps). Data augmentation enables training with a limited number of training data and even with few local data samples significant improvement over the base model can be achieved. Our model outperforms the current state-of-the-art tool for automatic bird sound classification. Using local data to adjust the recognition model for the target domain leads to improvement over general non-tailored solutions. The process introduced in this article can be applied to build a fine-tuned bird sound classification model for a specific environment.Peer reviewe

Resolving the SLOSS dilemma for biodiversity conservation: a research agenda

The legacy of the ‘SL > SS principle’, that a single or a few large habitat patches (SL) conserve more species than several small patches (SS), is evident in decisions to protect large patches while down-weighting small ones. However, empirical support for this principle is lacking, and most studies find either no difference or the opposite pattern (SS > SL). To resolve this dilemma, we propose a research agenda by asking, ‘are there consistent, empirically demonstrated conditions leading to SL > SS?’ We first review and summarize ‘single large or several small’ (SLOSS) theory and predictions. We found that most predictions of SL > SS assume that between-patch variation in extinction rate dominates the outcome of the extinction–colonization dynamic. This is predicted to occur when populations in separate patches are largely independent of each other due to low between-patch movements, and when species differ in minimum patch size requirements, leading to strong nestedness in species composition along the patch size gradient. However, even when between-patch variation in extinction rate dominates the outcome of the extinction–colonization dynamic, theory can predict SS > SL. This occurs if extinctions are caused by antagonistic species interactions or disturbances, leading to spreading-of-risk of landscape-scale extinction across SS. SS > SL is also predicted when variation in colonization dominates the outcome of the extinction–colonization dynamic, due to higher immigration rates for SS than SL, and larger species pools in proximity to SS than SL. Theory that considers change in species composition among patches also predicts SS > SL because of higher beta diversity across SS than SL. This results mainly from greater environmental heterogeneity in SS due to greater variation in micro-habitats within and across SS habitat patches (‘across-habitat heterogeneity’), and/or more heterogeneous successional trajectories across SS than SL. Based on our review of the relevant theory, we develop the ‘SLOSS cube hypothesis’, where the combination of three variables – between-patch movement, the role of spreading-of-risk in landscape-scale population persistence, and across-habitat heterogeneity – predict the SLOSS outcome. We use the SLOSS cube hypothesis and existing SLOSS empirical evidence, to predict SL > SS only when all of the following are true: low between-patch movement, low importance of spreading-of-risk for landscape-scale population persistence, and low across-habitat heterogeneity. Testing this prediction will be challenging, as it will require many studies of species groups and regions where these conditions hold. Each such study would compare gamma diversity across multiple landscapes varying in number and sizes of patches. If the prediction is not generally supported across such tests, then the mechanisms leading to SL > SS are extremely rare in nature and the SL > SS principle should be abandoned

Stripes and electronic quasiparticles in the pseudogap state of cuprate superconductors

This article is devoted to a discussion of stripe and electron-nematic order and their connection to electronic properties in the pseudogap regime of copper-oxide superconductors. We review basic properties of these symmetry-breaking ordering phenomena as well as proposals which connect them to quantum-oscillation measurements. Experimental data indicate that these orders are unlikely to be the cause of the pseudogap phenomenon, implying that they occur on top of the pseudogap state which itself is of different origin. Specifically, we discuss the idea that the non-superconducting pseudogap ground state hosts electron-like quasiparticles which coexist with a spin liquid, realizing a variant of a fractionalized Fermi liquid. We speculate on how stripe order in such a pseudogap state might offer a consistent description of ARPES, NMR, quantum-oscillation, and transport data.Comment: 15 pages, 6 figs. Article prepared for a Physica C special issue on "Stripes and Electronic Liquid Crystals

Insights from regional and short-term biodiversity monitoring datasets are valuable: a reply to Daskalova et al. 2021

Reports of major losses in insect biodiversity have stimulated an increasing interest in temporal population changes. Existing datasets are often limited to a small number of study sites, few points in time, a narrow range of land-use intensities and only some taxonomic groups, or they lack standardised sampling. While new monitoring programs have been initiated, they still cover rather short time periods. Daskalova et al. 2021 (Insect Conservation and Diversity, 14, 1-18) argue that temporal trends of insect populations derived from short time series are biased towards extreme trends, while their own analysis of an assembly of shorter- and longer-term time series does not support an overall insect decline. With respect to the results of Seibold et al. 2019 (Nature, 574, 671–674) based on a 10-year multi-site time series, they claim that the analysis suffers from not accounting for temporal pseudoreplication. Here, we explain why the criticism of missing statistical rigour in the analysis of Seibold et al. (2019) is not warranted. Models that include ‘year’ as random effect, as suggested by Daskalova et al. (2021), fail to detect non-linear trends and assume that consecutive years are independent samples which is questionable for insect time-series data. We agree with Daskalova et al. (2021) that the assembly and analysis of larger datasets is urgently needed, but it will take time until such datasets are available. Thus, short-term datasets are highly valuable, should be extended and analysed continually to provide a more detailed understanding of insect population changes under the influence of global change, and to trigger immediate conservation actions

Monitoring Fungal Communities With the Global Spore Sampling Project

Peer reviewe