Modelling optical properties of morphologically complex soot aerosols

Soot containing aerosol has both adverse impacts on the Earth\u27s climate and on human health. Monitoring soot sources, transport pathways and sinks on global scale requires satellite-borne remote sensing techniques.A detailed understanding of the soot particle\u27s optical properties is important to improve the interpretation of remote sensing data as well as the use of lidar remote sensing data in chemical transport modelling. The calculations of the optical properties were carried out using the discrete dipole approximation (DDA). Aim of this thesis is to identify key morphological features, which affect the depolarisation ratio.As soot particles age in the atmosphere, condensation of other compounds from the gas phase onto the particles results in soot aggregates coated by liquid-phase material. Initially, the soot particles are coated by a thin film (i.e., the coating follows the shape of the aggregate). As more liquid phase material is added, the coating becomes increasingly spherical. It is found that this transition from film coating to radial growth of spherical shells is an important process affecting the linear depolarisation ratio. If this transition occurs first at relatively high amounts of coating, then the depolarisation ratio tends to be high. Conversely, if the coating becomes already spherical at low amounts of coating material, then the depolarisation ratio of the coated soot particles is much lower.The linear depolarisation ratio of thickly coated aggregates was found to be sensitive to changes in the complex refractive index of the coating material, which represents changes in the chemical composition.These differences in the optical properties, even after averaging over a particle size distribution, are large enough to clearly distinguish the coating materials

Modelling optical properties of morphologically complex aerosols

The interpretation of remote sensing data of atmospheric aerosol particles requires a thorough understanding of the links between microphysical and optical properties. Morphologically complex aerosol models describe the particles’ morphology in detail. Based on the calculations with realistic particle models, simplified models can be devised, which incorporate essential microphysical properties for reproducing the optical properties. In this thesis, such models are developed and tested for soot aerosols, for mineral dust, and for dried and partially dissolved sea salt aerosol.A tunable model for coated soot aggregates is presented, and corresponding uncertainty estimates are performed. One of the main sources of uncertainty for thickly coated soot is the chemical composition of the coating, as represented by its refractive index. These uncertainties are so substantial, they are investigated as a potential source of information. The calculated lidar-measurable (spectral) quantities are distinct for two coating materials.The non-sphericity of a particle is identified as an essential morphological property affecting the linear depolarisation ratio. For coated soot another important property is the amount of carbon interacting with the incident wave, as it affects the absorption cross section. Combining these two insights resulted in the core grey shell dimer (CGS2) model, which is introduced in this thesis.For dry sea salt aerosol different random geometries are investigated, to simultaneously calculate linear depolarisation and extinction-to-backscatter ratio of dried sea salt aerosol particles. The results indicate that convex polyhedra are best suited to represent dried sea salt aerosol particles. Thus, the coated convex polyhedra model is proposed as the basis for modelling dissolving sea salt in a further study. For dissolving sea salt three simplified, equally well-performing models are presented, which identify the change in particle sphericity as a key morphological feature.A spheroidal model with a single refractive index and a single aspect ratio is fitted to laboratory measurements of 131 different dust samples. The scattering of the measurements about the model can mainly be explained by changes in morphology and dielectric properties, and to a lesser degree by the width of the particle size distribution.These results are expected to significantly advance our capacity to exploit and interpret polarimetric remote sensing observations of morphologically complex and chemically heterogeneous aerosol. This will be important for constraining Earth-system climate and air-quality forecasting models, and for evaluating and improving parameterisations of aerosol processes in these environmental modelling system

Pre-schoolers’ images, intergroup attitudes, and liking of refugee peers in Germany

There is extensive research on children’s intergroup attitudes, but their perceptions of refugee children have rarely been studied. We conducted a study with 5- and 6-year-old children (N = 60) in Germany following the arrival of unprecedented large numbers of refugees in 2015 and 2016. Children completed a set of three tasks that measured their perceptions of refugee children (minority group) and German children (majority group): a draw-a-typical-child task (including questions about whether participants wanted to interact with the depicted child), an intergroup attitude task, and a liking task. Results indicate that participants drew similar pictures of and had similar intentions to interact with refugee children and German children. There was mixed evidence for group favouritism: while participants showed similar explicit attitudes towards German and refugee peers, they indicated more liking of German peers. Moreover, children viewed refugee children as a less variable (more homogeneous) group than German children. Opportunities for intergroup contact with refugee peers (i.e., whether participants attended kindergartens with or without refugee children) had no discernible effect on any of the measures. Our findings provide a snapshot of children’s perceptions of refugees in a unique historical context and contribute to research on the development of intergroup attitudes in real-world settings

Wavefront shaping concepts for application in optical coherence tomography - a review

Optical coherence tomography (OCT) enables three-dimensional imaging with resolution on the micrometer scale. The technique relies on the time-of-flight gated detection of light scattered from a sample and has received enormous interest in applications as versatile as non-destructive testing, metrology and non-invasive medical diagnostics. However, in strongly scattering media such as biological tissue, the penetration depth and imaging resolution are limited. Combining OCT imaging with wavefront shaping approaches significantly leverages the capabilities of the technique by controlling the scattered light field through manipulation of the field incident on the sample. This article reviews the main concepts developed so far in the field and discusses the latest results achieved with a focus on signal enhancement and imaging. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Young children consider merit when sharing resources with others

Merit is a key principle of fairness: rewards should be distributed according to how much someone contributed to a task. Previous research suggests that children have an early ability to take merit into account in third-party situations but that merit-based sharing in first-party contexts does not emerge until school-age. Here we provide evidence that three- and five-year-old children already use merit to share resources with others, even when sharing is costly for the child. In Study 1, a child and a puppet-partner collected coins that were later exchanged for rewards. We varied the work-contribution of both partners by manipulating how many coins each partner collected. Children kept fewer stickers in trials in which they had contributed less than in trials in which they had contributed more than the partner, showing that they took merit into account. Few children, however, gave away more than half of the stickers when the partner had worked more. Study 2 confirmed that children related their own work-contribution to their partner’s, rather than simply focusing on their own contribution. Taken together, these studies show that merit-based sharing is apparent in young children; however it remains constrained by a self-serving bias

To Listen Differently, Away from Sonic Certitude: Some Propositions, Some Questions

In this piece, we move through propositions that invite an opening up to how, if at all, an abolitionary listening might take place. The “we” we use is intended to be multi-directional and polyphonic. It is a “we” we use as authors, as readers, and as listeners. Our thinking with and listening to the “uncapturable” seeks to unrepresent monological and univocal narratives of intelligibility, rationality, and social consensus. Rather than strain a hearing, we worry and listen to the very register and sonics of (a) hearing (determinacy, judgement, autonomy). Drawing from the writings and sonic articulations, undulations and intervallic cries of different thinkers and musicians we undo the certainty of voice and sound that the law predicates itself upon, and surrender to unanticipated openness

Double Interferometer Design for Independent Wavefront Manipulation in Spectral Domain Optical Coherence Tomography

Spectral domain optical coherence tomography (SD-OCT) is a highly versatile method which allows for three dimensional optical imaging in scattering media. A number of recent publications demonstrated the technique to benefit from structured illumination and beam shaping approaches, e.g. to enhance the signal-to-noise ratio or the penetration depth with samples such as biological tissue. We present a compact and easy to implement design for independent wavefront manipulation and beam shaping at the reference and sample arm of the interferometric OCT device. The design requires a single spatial light modulator and can be integrated to existing free space SD-OCT systems by modifying the source arm only. We provide analytical and numerical discussion of the presented design as well as experimental data confirming the theoretical analysis. The system is highly versatile and lends itself for applications where independent phase or wavefront control is required. We demonstrate the system to be used for wavefront sensorless adaptive optics as well as for iterative optical wavefront shaping for OCT signal enhancement in strongly scattering media. © 2019, The Author(s)

Challenges and Coping: Perspectives of Syrian and Iraqi Refugee Youth in Germany

Refugee youth constitute around a third of the refugee population in Germany. We studied the experiences of newly arrived Syrian and Iraqi refugee youth, aged 14 to 18 years (N = 20), in Germany. We utilized semi-structured interviews and thematic analysis to investigate (a) the main challenges faced by youth and (b) their main coping resources to deal with these challenges. We grouped challenges into three levels: the individual level, the immediate social level, and the broader societal level. The most frequently mentioned challenges in our sample related to psychological wellbeing, school, friendship, accommodation, and discrimination. Youth reported relying on social support (friends, family, social services) and on themselves (through avoidance, persistence, activity seeking, active engagement) to cope with their challenges. Our findings provide insights into refugee youth’s experiences in Germany, encompassing the acculturative, developmental, and generational aspects of their lives and demonstrating their coping and resilience. We discuss our results in relation to the literature on refugee youth in high income countries

When and how does labour lead to love? The ontogeny and mechanisms of the IKEA effect

We elevate our constructions to a special status in our minds. This ‘IKEA’ effect leads us to believe that our creations are more valuable than items that are identical, but constructed by another. This series of studies utilises a developmental perspective to explore why this bias exists. Study 1 elucidates the ontogeny of the IKEA effect, demonstrating an emerging bias at age 5, corresponding with key developmental milestones in self-concept formation. Study 2 assesses the role of effort, revealing that the IKEA effect is not moderated by the amount of effort invested in the task in 5-to-6-year olds. Finally, Study 3 examines whether feelings of ownership moderate the IKEA effect, finding that ownership alone cannot explain why children value their creations more. Altogether, results from this study series are incompatible with existing theories of the IKEA bias. Instead, we propose a new framework to examine biases in decision making. Perhaps the IKEA effect reflects a link between our creations and our self-concept, emerging at age 5, leading us to value them more positively than others’ creations

Cheating and the effect of promises in Indian and German children

Cheating is harmful to others and society at large. Promises have been shown to increase honesty in children, but their effectiveness has not been compared between different cultural contexts. In a study (2019) with 7- to 12-year-olds (N = 406, 48% female, middle-class), voluntary promises reduced cheating in Indian, but not in German children. Children in both contexts cheated, but cheating rates were lower in Germany than in India. In both contexts, cheating decreased with age in the (no-promise) control condition and was unaffected by age in the promise condition. These findings suggest that there may exist a threshold beyond which cheating cannot be further reduced by promises. This opens new research avenues on how children navigate honesty and promise norms