Efficient polarisation-preserving frequency conversion from a trapped-ion-compatible wavelength to the telecom C band

We demonstrate polarisation-preserving frequency conversion of single-photon-level light at 854 nm, resonant with a trapped-ion transition and qubit, to the 1550-nm telecom C band. A total photon in / fiber-coupled photon out efficiency of $\sim$ 30 % is achieved, for a free-running photon noise rate of $\sim$ 60 Hz. This performance would enable telecom conversion of 854-nm polarisation qubits, produced in existing trapped-ion systems, with a signal-to-noise ratio greater than 1. In combination with near-future trapped-ion systems, our converter would enable the observation of entanglement between an ion and a photon that has travelled more than 100 km in optical fiber: three orders of magnitude further than the state-of-the-art.Comment: 20 pages, 5 figure

On the Scalability of a Partially Premixed Low NOx Hydrogen Burner

Increasingly stringent regulations on nitric oxide (NOx) emissions led to the development of various low and ultra low NOx combustion technologies over the last decades. These technologies are further challenged by the increasing demand for fuel flexibility and rising contribution of non-carbon fuels to the global fuel mix, such as for example hydrogen. Modern burners incorporate complex designs and flow regimes, to address the high burning velocities and temperatures associated with hydrogen and hydrogen rich fuels, allowing stable combustion and low NOx emissions. The development process of such burners requires the scaling of the burner geometry to facilitate simulations and testing at laboratory scale. Scaling is conducted by employing scaling laws, that aim to preserve relevant burner characteristics. The present doctoral thesis investigates the effect of the most commonly used scaling laws, constant velocity and constant residence time scaling, on complex burner designs. Both scaling laws are derived based on "simple" flames that can be defined by a single length and velocity scale. Previous studies have, however, indicated that such global scaling laws fail when applied to complex industrial burners, where flow conditions can vary significantly for different burner regions. The main focus of the present study is, therefore, the analysis of local effects on the combustion and NOx characteristics. The analysis was conducted based on a partially premixed bluff body (PPBB) burner, which incorporates an inner and outer recirculation zone, stagnation point flow, staged fuel injection and varying degree of partial premixing; all typical features of complex, modern burner designs. A numerical model of the PPBB burner was developed and validated against experimental data. The simulation of turbulent combustion processes, including detailed combustion kinetics, heat radiation and NOx formation, at various burner scales is computational demanding. Hence, a compromise between model accuracy and costs is sought after. Considering this, a non reacting flow configuration of the burner was investigated first, which made it possible to conduct the CFD simulations with a wide variety of different turbulence models, ranging from steady state Reynolds averaged (RANS) to transient scale resolving simulations. Varying the complexity of the turbulence model allowed the identification of model requirements and exposed limitations for the cost effective RANS models. The non reactive model was, thereupon, further extended to incorporate species transport, detailed hydrogen combustion kinetics, turbulence chemistry interaction, radiation and NOx formation. The extended model was employed to conduct twelve simulations of different operational conditions, i.e., secondary fuel fraction and thermal loads. Furthermore, a postprocessing routine was developed to incorporate scatter data, obtained from the CFD simulations, in combustion regime diagrams, leading to a more refined representation of the burner characteristics. Finally the burner geometry was scaled based on the constant velocity as well as the constant residence time scaling approach, and CFD simulations at various scales in the range of 10 kW to 500 kW were conducted. The simulations were used to study the effect of the two different scaling laws on the local NOx formation rate and flame characteristics, and to compare the CFD prediction to scaling theory. The fluid domain was, furthermore, decomposed in order to investigate different burner regions, and their contribution to the NOx formation individually. Based on the identified burner regions, work on a reactor network of the PPBB burner was initiated. The non reacting flow simulations showed, for all investigated turbulence models, good agreement between the simulated and the measured recirculation zone length. However, all RANS models generally overpredicted the velocity magnitudes, especially within the inner recirculation zone, while scaling resolving simulations resulted in a reasonable good agreement between simulation and experiment. The predicted NOx emissions, for a wide range of operational conditions, were between +10% and -20% of the measured data, underpredicting them in average by 7%. The model was, furthermore, able to predict the overall NOx trend for varying thermal loads, while it failed to reproduce the effect of a varying secondary fuel fraction on the NOx emissions at low thermal loads, of 10 kW. The detailed analysis of the flame characteristics in CFD based combustion regime diagrams revealed that primary fuel burns in a multi regime mode, mainly in the thin reaction zone regime, spanning a wide range of equivalence ratios, while secondary fuel is burned closer to the global and stoichiometric equivalence ratio. The simulations showed, furthermore, a transition from a fuel lean to a fuel rich mixture in the inner recirculation zone, when the secondary fuel fraction is increased from 0% to 30%. The numerical model was utilized to simulate the burner at various scales in the range of 10 kW to 500 kW. Constant velocity scaling leads to lower Karlovitz numbers and ultimately to a transition, for large parts of the flame, from the thin reaction zone regime to the corrugated flamelet regime. Constant residence time scaling, on the other hand, preserves the global Damköhler number. However, a significant part of the flame follows a constant Karlovitz number, close to unity, which is not expected based on scaling theory. Constant velocity scaling leads due to the larger volumes and residence times to overall higher NOx emissions, with exception of the inner recirculation zone, even though constant residence time leads locally to the larger mean volumetric formation rates. An interesting finding, regarding flame stability, was found for constant velocity scaling, which led to the sudden breakup of the inner recirculation zone at a scale in-between 450 kW and 500 kW, while the flame is stable at 500 kW, when constant residence time scaling is applied

Towards modeling climate effects of energetic particle precipitation

Energetic particles enter Earth’s atmosphere at the poles. The charged particles are either from solar or magnetospheric origin and alter the chemistry of the middle and upper atmosphere. Most importantly, they enhance the production of nitrogen oxides (NOx) and hydrogen oxides (HOx) in the winter mesosphere and lower thermosphere. Both components are powerful ozone destroyers. The impact of HOx on ozone is limited to the mesosphere, because HOx has a short chemical lifetime (up to hours). In contrast, NOx can persist up to several months in the winter polar middle atmosphere and can be transported downward to the stratosphere. Models covering the middle and upper atmosphere underestimate this downward transport. This may lead to an underestimation of potential climate effects from energetic particle precipitation. This thesis investigates the polar winter transport from the lower thermosphere to the stratosphere. Several observational studies confirmed the downward transport (e.g., Randall et al. 2009; Semeniuk et al. 2005). However, it remains unclear which processes cause the transport from the lower thermosphere to the mesosphere. This thesis quantifies, for the first time, the contribution of advection, eddy diffusion and molecular diffusion for the transport through the mesopause. Advection and molecular diffusion dominate the transport through the mesopause. Eddy diffusion has a negligible impact on the transport. However, if eddy diffusion is enhanced as suggested by observations, it can significantly contribute to the transport. This leaves advection being responsible for the underestimation of the downward transport. Gravity waves are the key driver for the advective downwelling in the polar winter mesosphere. This thesis shows that weakening gravity waves enhances the mesospheric transport bringing it close to satellite observations. The altitude of the mesospheric momentum deposition is identified to be key for the polar downwelling. In addition to the analysis of the winter polar downward transport, climate effects of energetic particles are studied. Energetic particle precipitation reduces significantly ozone in the mesosphere and stratosphere. An ozone loss potentially influences the atmospheric temperature and the strength of the polar vortex. It has been shown that large variations in the polar vortex strength can propagate from the stratosphere down to the surface and force the surface temperature (Baldwin and Dunkerton 2001). This thesis presents the climate impact of a mesospheric and of a stratospheric ozone loss. No statistically significant changes in atmospheric winds are found neither for a mesospheric ozone loss nor for a stratospheric ozone loss. Hence, the influence of energetic particles is too weak to force significantly changes in the surface temperature. In summary, this thesis advances the understanding of energetic particle precipitation. Processes relevant for the winter polar downward transport from the lower thermosphere to the stratosphere are identified. Two novel findings are the importance of advection in the thermosphere and the impact of weaker gravity waves on the dynamics of the middle and upper atmosphere. Based on this thesis, large climate effects of energetic particles seem unlikely

Upstream-binding factor is sequestered into herpes simplex virus type 1 replication compartments

Previous reports have shown that adenovirus recruits nucleolar protein upstream-binding factor (UBF) into adenovirus DNA replication centres. Here, we report that despite having a different mode of viral DNA replication, herpes simplex virus type 1 (HSV-1) also recruits UBF into viral DNA replication centres. Moreover, as with adenovirus, enhanced green fluorescent protein-tagged fusion proteins of UBF inhibit viral DNA replication. We propose that UBF is recruited to the replication compartments to aid replication of HSV-1 DNA. In addition, this is a further example of the role of nucleolar components in viral life cycle

Decision making under risk in agriculture : An experimental and survey based analysis

Risk, and risk management are inherent to agricultural production. We distinguish two categories of factors influencing the farmers’ decision on risk management strategy: external and internal factors. Factors external to the farm holding include the geographic, political and climatic environment. Internal factors include personal characteristics and the farmers’ frame of reference. The presented studies in this thesis include analysis of external and internal determinants of the farmers’ risk management decision in the German region North-Rhine-Westphalia focusing on (i) effects of contextualizing experimental risk preference elicitation methods, (ii) determinants of risk management choices amongst livestock farmers, (iii) underlying motives of agritourism farmers and (iv) characteristics of diversifying farmers in the peri-urban context. Four unique case study analyses are conducted. First data collected from agricultural students is used to explore effects of contextualization in experimental risk preference elicitation methods. Second, data collected from livestock farmers is used for a holistic analysis of determinants of risk management choices. Third, agritourism and non-agritourism farmers are interviewed to explore underlying motives of farmers engaging in agritourism activities, and to find distinguishing farm, farmer and household characteristics of both groups. Fourth, data from farmers in the Ruhr-metropolitan area are collected to analyze their diversification decisions in the peri-urban context. The collected data is analyzed using econometric methods. The results show that contextualization of experimental risk preference elicitation methods decreases misspecifications, and improves obtained data quality. Furthermore, the analysis of farmers’ behavior under risk show that the individual farmer’s frame of reference (i.e. risk preferences, perception and past experiences) determines the choice of risk management strategy. Additionally, results show that proximity to urban agglomerations incentivizes farmers to engage in on-farm, non-agricultural diversification. Farmers’ decision to diversify is found to be opportunity driven, leading to the conclusion that improved information with regards to existing and new innovative diversification channels in the farming context is essential to improve rural development

Transport of Nitrogen Oxides through the winter mesopause in HAMMONIA

We analyze the importance of individual transport processes for the winter polar downward transport of nitrogen oxides (NOx) from the thermosphere to the mesosphere. The downward transport of NOx produced by energetic particle precipitation induces chemical alterations in the middle atmosphere and influences ozone chemistry. However, it remains unclear how much each transport process contributes to the downward transport. We use simulations of the atmospheric general circulation and chemistry model HAMMONIA (Hamburg Model of Neutral and Ionized Atmosphere) for the extended winter 2008/2009 with a passive tracer. The model enables us to separate the contributions of advection, eddy and molecular diffusion on the total transport by switching off processes. The results show that molecular diffusion and resolved vertical mixing due to advection effectively transport NOx to the mesosphere. While the impact of molecular diffusion on the transport rapidly decreases below 0.001 hPa, the impact of advection increases. Around the central date of the sudden stratospheric warming in January 2009, advection is strongly enhanced in the thermosphere and mesosphere and the downward transport through the mesopause region is almost entirely driven by advection. Eddy diffusion has limited impact on the transport in the upper mesosphere and negligible impact on the transport in the thermosphere. If eddy diffusion is enhanced as suggested by observations, it can potentially have a larger impact on transport through the mesopause than was previously assumed

BRAVENT – Storskala branntester (del 2): Effekten av ventilasjonsstrategi på røykspredning og trykkontroll i en mock-up skolebygning

In the overall BRAVENT project, the goal is to generate answers and documentation on current issues related to ventilation and fire by examining these with experimental fire tests. The present study aimed to evaluate how different failure mechanisms identified in sub-report 1, "Fire performance for non-fire rated ventilation components" [5], affect the pressure conditions and possible smoke spread in the building. In order to investigate the ventilation system's ability to control pressure balance and smoke spread in the event of a fire, 14 large-scale fire tests with different fuel types were carried out. The tests were conducted in a test building with several rooms representing a classroom, an office and a corridor. The fire tests were designed to investigate relevant fire scenarios for school buildings, but the findings from the tests may also be relevant for other purpose-built buildings. The building was equipped with a full-fledged damper-optimized ventilation system which was sized to serve a total of 450 m2 and thus provide a realistic basis for the fire tests. In sub-report 1, a number of component failures were uncovered when the system was exposed to hot smoke. The failure mechanisms led to the system losing its status and control over the dampers, thus also losing the overview of which air volumes passed through the dampers. The failure of the dampers then led to an imbalance in the ventilation system, also in rooms other than the fire room. In the extreme, this can lead to challenges in connection with escape by making it difficult or impossible to open doors. Smoke spread via the supply air ducts can occur due to smoke backflow if the pressure in the fire compartment exceeds the pressure in the supply air duct. In the experiments, the ventilation system increased to the maximum design airflow rate (Vmax) upon fire detection, and no smoke spread due to backflow of fire smoke in the supply air ducts was observed. It was not tested whether a backflow of smoke could have also been prevented at lower airflow rates than Vmax. Whether the ventilation system maintains sufficiently high pressure in the supply air duct to prevent backflow depends on, among other things, the capacity of the supply air fans, the density of the fire compartment and how quickly the fire develops. The smoke from the fire caused the filter in the unit to gradually clog. In three tests, the filter was clogged so much that the air handling unit could not extract enough air, which created an imbalance in the ventilation system. The new BRAVENT tests show that the size of the fire in relation to the air handling unit's capacity plays an important role in how long the exhaust airflow can be maintained. An air handling unit serving several small fire cells with limited available fuel will be able to maintain the required exhaust air volume longer than an aggregate serving a few large fire cells as the ratio between smoke volume and total air volume changes. Other factors that affect how long the unit can compensate for filter clogging are: • whether the air handling unit is designed for 100% or less simultaneity, i.e. the proportion of rooms that can have the maximum amount of airflow at the same time, • the condition of the filter at the start of the fire, completely new filters were used in each of the fire tests, • whether the ventilation system operates with Vmax or less airflow when a fire alarm is triggered. No smoke spread between the rooms via the exhaust duct was observed. However, since the exhaust airflow rate in one of the tests was significantly reduced to around 50% of the maximum design airflow rate, it is concluded that gradual clogging of the exhaust filter will increase the risk of smoke spreading via the exhaust duct. Clogging of the filters can be avoided by establishing a bypass. Nevertheless, it must then still be documented that all other functions of the ventilation system are safeguarded in the event of a fire. The tests carried out showed that the failure mechanism of some components (measurement errors in dampers, short circuits and clogging of the exhaust filters) can lead to the whole system no longer being able to maintain its function.publishedVersio

Multi-Sensor Data Fusion for Cloud Removal in Global and All-Season Sentinel-2 Imagery

This work has been accepted by IEEE TGRS for publication. The majority of optical observations acquired via spaceborne earth imagery are affected by clouds. While there is numerous prior work on reconstructing cloud-covered information, previous studies are oftentimes confined to narrowly-defined regions of interest, raising the question of whether an approach can generalize to a diverse set of observations acquired at variable cloud coverage or in different regions and seasons. We target the challenge of generalization by curating a large novel data set for training new cloud removal approaches and evaluate on two recently proposed performance metrics of image quality and diversity. Our data set is the first publically available to contain a global sample of co-registered radar and optical observations, cloudy as well as cloud-free. Based on the observation that cloud coverage varies widely between clear skies and absolute coverage, we propose a novel model that can deal with either extremes and evaluate its performance on our proposed data set. Finally, we demonstrate the superiority of training models on real over synthetic data, underlining the need for a carefully curated data set of real observations. To facilitate future research, our data set is made available onlineComment: This work has been accepted by IEEE TGRS for publicatio

HEPPA-II model-measurement intercomparison project : EPP indirect effects during the dynamically perturbed NH winter 2008-2009

We compare simulations from three high-top (with upper lid above 120 km) and five medium-top (with upper lid around 80 km) atmospheric models with observations of odd nitrogen (NOx D NO+NO2), temperature, and carbon monoxide from seven satellite instruments (ACE-FTS on SciSat, GOMOS, MIPAS, and SCIAMACHY on Envisat, MLS on Aura, SABER on TIMED, and SMR on Odin) during the Northern Hemisphere (NH) polar winter 2008/2009. The models included in the comparison are the 3-D chemistry transport model 3dCTM, the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model, FinROSE, the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMO-NIA), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA), the modelling tools for SOlar Climate Ozone Links studies (SOCOL and CAO-SOCOL), and the Whole Atmosphere Community Climate Model (WACCM4). The comparison focuses on the energetic particle precipitation (EPP) indirect effect, that is, the polar winter descent of NOx largely produced by EPP in the mesosphere and lower thermosphere. A particular emphasis is given to the impact of the sudden stratospheric warming (SSW) in January 2009 and the subsequent elevated stratopause (ES) event associated with enhanced descent of mesospheric air. The chemistry climate model simulations have been nudged toward reanalysis data in the troposphere and stratosphere while being unconstrained above. An odd nitrogen upper boundary condition obtained from MIPAS observations has further been applied to medium-top models. Most models provide a good representation of the mesospheric tracer descent in general, and the EPP indirect effect in particular, during the unperturbed (pre-SSW) period of the NH winter 2008/2009. The observed NOx descent into the lower mesosphere and stratosphere is generally reproduced within 20 %. Larger discrepancies of a few model simulations could be traced back either to the impact of the models' gravity wave drag scheme on the polar wintertime meridional circulation or to a combination of prescribed NOx mixing ratio at the uppermost model layer and low vertical resolution. In March-April, after the ES event, however, modelled mesospheric and stratospheric NOx distributions deviate significantly from the observations. The too-fast and early downward propagation of the NO x tongue, encountered in most simulations, coincides with a temperature high bias in the lower mesosphere (0.2-0.05 hPa), likely caused by an overestimation of descent velocities. In contrast, upper-mesospheric temperatures (at 0.05-0.001 hPa) are generally underestimated by the high-top models after the onset of the ES event, being indicative for too-slow descent and hence too-low NOx fluxes. As a consequence, the magnitude of the simulated NOx tongue is generally underestimated by these models. Descending NOx amounts simulated with mediumtop models are on average closer to the observations but show a large spread of up to several hundred percent. This is primarily attributed to the different vertical model domains in which the NOx upper boundary condition is applied. In general, the intercomparison demonstrates the ability of state-of- the-art atmospheric models to reproduce the EPP indirect effect in dynamically and geomagnetically quiescent NH winter conditions. The encountered differences between observed and simulated NOx, CO, and temperature distributions during the perturbed phase of the 2009 NH winter, however, emphasize the need for model improvements in the dynamical representation of elevated stratopause events in order to allow for a better description of the EPP indirect effect under these particular conditions.Peer reviewe

Triggering cognitive dissonance with textual information and images : Data from three experiments with meat-eaters

This article presents data from three experiments in which we triggered and measured cognitive dissonance in meat-eaters. Cognitive dissonance is a well-established concept in the social psychology literature; however, empirical measures are scarce. In all datasets, we used textual information and/or images related to meat consumption as means to trigger cognitive dissonance. Cognitive dissonance data was collected in Study 1 with a Likert scale, whereas Study 2 and 3 used a Semantic Bipolar scale. Each experiment was programmed with Qualtrics and consisted of four conditions. Data was collected online; Study 1 utilized social media to recruit participants while Study 2 and 3 were hosted on Prolific. All datasets contain items on participants’ socio-demographic background, liking of different food products, cognitive dissonance, and a measure of meat avoidance. The data can be used to analyze the effect of information provision on cognitive dissonance and meat avoidance. Moreover, the relationship between socio-demographic variables and cognitive dissonance, as well as other exploratory purposes regarding meat avoidance can be explored. Furthermore, researchers can use the data to investigate differences between Likert scales and Semantic Bipolar scales. This data is related to the paper Can images and textual information lead to meat avoidance? The mediating role of cognitive dissonance