Launching Delta Alliance, final report of phase 2

Delta Alliance is a network that aims to improve the resilience of the world’s deltas. It provides a foundation and framework for international knowledge sharing and development around delta issues. Phase 2 focussed on three components: developing the Delta Alliance organization, initiating network activities and (development of) research and knowledge sharing projects

Can galaxy growth be sustained through HI-rich minor mergers?

Local galaxies with specific star-formation rates (star-formation rate per unit mass; sSFR~0.2-10/Gyr) as high as distant galaxies (z~1-3), are very rich in HI. Those with low stellar masses, log M_star (M_sun)=8-9, for example, have M_HI/M_star~5-30. Using continuity arguments of Peng et al. (2014), whereby the specific merger rate is hypothesized to be proportional to the specific star-formation rate, and HI gas mass measurements for local galaxies with high sSFR, we estimate that moderate mass galaxies, log M_star (M_sun)=9-10.5, can acquire sufficient gas through minor mergers (stellar mass ratios ~4-100) to sustain their star formation rates at z~2. The relative fraction of the gas accreted through minor mergers declines with increasing stellar mass and for the most massive galaxies considered, log M_star (M_sun)=10.5-11, this accretion rate is insufficient to sustain their star formation. We checked our minor merger hypothesis at z=0 using the same methodology but now with relations for local normal galaxies and find that minor mergers cannot account for their specific growth rates, in agreement with observations of HI-rich satellites around nearby spirals. We discuss a number of attractive features, like a natural down-sizing effect, in using minor mergers with extended HI disks to support star formation at high redshift. The answer to the question posed by the title, "Can galaxy growth be sustained through \HI-rich minor mergers?", is maybe, but only for relatively low mass galaxies and at high redshift.Comment: 6 pages, 3 figures; in final acceptance by A&

Characterisation of Transcription Factor SPL15, an Integrator of Multiple Flowering Time Pathways

The transition from vegetative to reproductive development in plants is tightly controlled to ensure their reproductive success. Plants integrate many different environmental signals to flower at the appropriate time, and complex regulatory networks underlie this decision. In Arabidopsis thaliana, the model organism for plant molecular research, the timing of floral transition is influenced by environmental cues, which include temperature and day length, and by internal factors, including the age of the plant and the levels of the phytohormone gibberellin. During the transition, Arabidopsis switches from producing leaves to producing flowers, a process that includes morphological and identity changes in the shoot apical meristem (SAM). In favourable environmental conditions, such as floral inductive long-days, Arabidopsis accelerates the floral transition and quickly bolts and flowers. In the absence of floral inductive signals, these plants still undergo the floral transition, but do so later after producing many more leaves. The transcription factor SQUAMOSA PROMOTER BINDING PROTEIN LIKE 15 (SPL15) promotes flowering in non-inductive conditions. SPL15 integrates signals from multiple floral induction pathways at the shoot apical meristem and is proposed to directly activate transcription of two other genes with a prominent function in flowering: FRUITFULL (FUL), which encodes a MADS box transcription factor, and MICRORNA172b (MIR172B), which encodes a short non-coding RNA. However, the precise role of SPL15 in floral induction remains unknown. To gain understanding of the importance of SPL15 targets and other downstream components, I genetically assessed their contribution to floral induction. I found that FUL and MIR172B were important for SPL15 function during floral induction. However, in their absence, increased expression of SPL15 still induced early bolting of the inflorescence, but could not induce floral development. These analyses suggested that SPL15 regulates more target genes than FUL and MIR172B during the floral transition. Subsequently, I identified the binding sites of SPL15 in the FUL promoter, and studied the effect of mutating them. This revealed that SPL15 is not the only SPL protein that recognises these sites to regulate floral transition. I therefore propose that during vegetative growth, other SPLs bind there to repress the expression of FUL. Lastly, I set out to identify additional putative target genes of SPL15 by two complementary transcriptome analyses. The resulting high confidence list of putative target genes of SPL15 showed that SPL15 likely regulates several other genes with described functions in floral induction. In addition, SPL15 regulates a set of genes with functions in cell proliferation, which might be relevant for the morphological changes occurring in the SAM during the floral transition. Altogether this thesis has contributed to a better understanding of how SPL15 regulates different stages of the floral transition in A. thaliana under non-inductive conditions

The properties of Low Surface Brightness galaxies

A description is given of the samples of Low Surface Brightness galaxies (LSBs) used for comparison with models of their chemical and spectro-photometric evolution (Boissier et al., this Volume). These samples show the large variation and scatter in observed global properties of LSBs, some of which cannot be modeled without adding starbursts or truncations to their star formation history.Comment: To appear in the Proceedings of the Euroconference on The Evolution of Galaxies: III. From simple approaches to self-consistent models (Kluwer). 4 page

Statistical analysis of time-resolved emission from ensembles of semiconductor quantum dots: Interpretation of exponential decay models

We present a statistical analysis of time-resolved spontaneous emission decay curves from ensembles of emitters, such as semiconductor quantum dots, with the aim of interpreting ubiquitous non-single-exponential decay. Contrary to what is widely assumed, the density of excited emitters and the intensity in an emission decay curve are not proportional, but the density is a time integral of the intensity. The integral relation is crucial to correctly interpret non-single-exponential decay. We derive the proper normalization for both a discrete and a continuous distribution of rates, where every decay component is multiplied by its radiative decay rate. A central result of our paper is the derivation of the emission decay curve when both radiative and nonradiative decays are independently distributed. In this case, the well-known emission quantum efficiency can no longer be expressed by a single number, but is also distributed. We derive a practical description of non-single-exponential emission decay curves in terms of a single distribution of decay rates; the resulting distribution is identified as the distribution of total decay rates weighted with the radiative rates. We apply our analysis to recent examples of colloidal quantum dot emission in suspensions and in photonic crystals, and we find that this important class of emitters is well described by a log-normal distribution of decay rates with a narrow and a broad distribution, respectively. Finally, we briefly discuss the Kohlrausch stretched-exponential model, and find that its normalization is ill defined for emitters with a realistic quantum efficiency of less than 100%.\ud \u

Selling brands while staying “Authentic”: The professionalization of Instagram influencers

While Instagram influencers may have started out as ordinary people documenting their everyday life through a stream of photographs, they are increasingly emerging as an intermediary between advertisers and consumers. This study examines the professionalization of Instagram influencers, combining data from 11 interviews with travel influencers with a visual and textual content analysis of their 12 most recent Instagram posts (N = 132). We show how the increasing professionalization of the influencer steers their relationship with their audience, the advertisers they work with, and the platform Instagram. We argue that, for the Instagram influencer to be perceived as successful, they need to negotiate a tension: they need to appear authentic, yet also approach their followers in a strategic way to remain appealing to advertisers. Although Instagram influencers are seen as more trustworthy than traditional forms of advertising, this tension ultimately leads to a standardization of the content shared by influencers

Mass estimates of rapidly-moving prominence material from high-cadence EUV images

We present a new method for determining the column density of erupting filament material using state-of-the-art multi-wavelength imaging data. Much of the prior work on filament/prominence structure can be divided between studies that use a polychromatic approach with targeted campaign observations and those that use synoptic observations, frequently in only one or two wavelengths. The superior time resolution, sensitivity, and near-synchronicity of data from the Solar Dynamics Observatory's Advanced Imaging Assembly allow us to combine these two techniques using photoionization continuum opacity to determine the spatial distribution of hydrogen in filament material. We apply the combined techniques to SDO/AIA observations of a filament that erupted during the spectacular coronal mass ejection on 2011 June 7. The resulting "polychromatic opacity imaging" method offers a powerful way to track partially ionized gas as it erupts through the solar atmosphere on a regular basis, without the need for coordinated observations, thereby readily offering regular, realistic mass-distribution estimates for models of these erupting structures