Diode-laser pumped, high-repetition-rate, Nd:YLF laser and its frequency conversion

This thesis describes the development of a continuous-wave (cw), diode pumped, repetitively Q-switched Nd:YLF laser, and its application as a pump source for non-linear optical frequency converters and optical parametric oscillators (OPO's), with typical pulse widths of several tens of nanoseconds and repetition rates in the kHz region. At the core of this thesis is the proposal and realisation of a novel rhombic Nd:YLF slab geometry, which is pumped by two 20W cw AlGaAs diode arrays, each focused by means of 3 lenses into a folded resonator path. The novelty of this adaptation is that it uses Yttrium Lithium Fluoride (YLF), known for its comparatively low tensile strength, as the Neodymium host crystal, by addressing and solving the thermal stress fracture problem in YLF for pump powers up to 20W per surface in an end-pumped configuration. With the excellent beam quality, high average output power and short pulses achieved, Nd:YLF has been established as an excellent material for high density, diode pumped, Q-switched lasers at 1047nm. With identical slabs coated for 1321nm operation also available, the performance and laser parameters such as crossection, linewidth and thermal lensing for these two transitions were compared. The pronounced change in the thermal lensing of the 1321nm transition led to an investigation of excited state upconversion (ESA) in Nd:YLF at 1047 and 1321nm under cw and Q-switched operation. The excellent access to the pumped volume made not only a time dependent spectral analysis of the visible and near UV fluorescence bands possible, but also permitted a spatial analysis of the different up-conversion areas. This pump density and laser transition dependent loss mechanism has implications on the end-effect governed lensing, upper state lifetime and Q-switched pulse form. The low threshold, high repetition rate conversion schemes realised during this thesis expanded the spectral cover of the 1mum pump laser from the near UV (349nm) at one end of the spectrum over the green (523.5nm) and 1.5mum region up to the near infrared at 3.445mum. The progress in this area lies not in the well known phase match configuration of the materials used such as KTP, KTA and LBO, but in the adaptation of these nonlinear converters and non-critically phase matched (NCPM) OPO's to achieve high conversion efficiencies at low pulse energies (typically less than 1mJ, 40kW). With average output powers in the green of 3W (~60% conversion from the IR at 6kHz repetition rate), 750mW in the UV, IW at 1.54mum and 280mW at 3.44mum it has been demonstrated that the high average output power of the repetitively Q-switched system can be preserved in the up- and down-converted radiation

Overlooked Diversity of Ultramicrobacterial Minorities at the Air-Sea Interface

Members of the Candidate phylum Patescibacteria, also called Candidate Phyla Radiation (CPR), are described as ultramicrobacteria with limited metabolic capacities. Wide diversity and relative abundances up to 80% in anaerobic habitats, e.g., in groundwater or sediments are characteristic for Candidatus Patescibacteria. However, only few studies exist for marine surface water. Here, we report the presence of 40 patescibacterial candidate clades at air-sea interfaces, including the upper water layer, floating foams and the sea-surface microlayer (SML), a < 1 mm layer at the boundary between ocean and atmosphere. Particle-associated (>3 μm) and free-living (3–0.2 μm) samples were obtained from the Jade Bay, North Sea, and 16S rRNA (gene) amplicons were analyzed. Although the abundance of Cand. Patescibacteria representatives were relatively low (<1.3%), members of Cand. Kaiserbacteria and Cand. Gracilibacteria were found in all samples. This suggests profound aerotolerant capacities of these phylogenetic lineages at the air-sea interface. The presence of ultramicrobacteria in the >3 μm fraction implies adhesion to bigger aggregates, potentially in anoxic niches, and a symbiotic lifestyle. Due to their small sizes, Cand. Patescibacteria likely become aerosolized to the atmosphere and dispersed to land with possible implications for affecting microbial communities and associated processes in these ecosystems.J.R.: C.S., O.W. and this study were funded by the European Research Council project PASSME, grant number GA336408. The picture of seafoam was taken during a campaign funded by the Assemble Plus project MIDSEAS (European Union’s Horizon 2020 research and innovation program, Grant Agreement No. 730984). D.P.R.H. was supported by the European Regional Development Fund/Estonian Research Council funded by “Mobilitas Plus Top Researcher grant MOBTT24”. A.J.P. received funding by the Ministerium für Kultur und Wissenschaft des Landes Nordrhein-Westfalen (“Nachwuchsgruppe Alexander Probst”). The APC was funded by the Open Access Publication Fund of the University of Duisburg-Essen.J.R.: C.S., O.W. and this study were funded by the European Research Council project PASSME, grant number GA336408. The picture of seafoam was taken during a campaign funded by the Assemble Plus project MIDSEAS (European Union’s Horizon 2020 research and innovation program, Grant Agreement No. 730984). D.P.R.H. was supported by the European Regional Development Fund/Estonian Research Council funded by “Mobilitas Plus Top Researcher grant MOBTT24”. A.J.P. received funding by the Ministerium für Kultur und Wissenschaft des Landes Nordrhein-Westfalen (“Nachwuchsgruppe Alexander Probst”). The APC was funded by the Open Access Publication Fund of the University of Duisburg-Essen

Air-Sea CO2-Exchange in a Large Annular Wind-Wave Tank and the Effects of Surfactants

Wind, chemical enhancement, phytoplankton activity, and surfactants are potential factors driving the air-sea gas exchange of carbon dioxide (CO2). We investigated their effects on the gas transfer velocity of CO2 in a large annular wind-wave tank filled with natural seawater from the North Atlantic Ocean. Experiments were run under 11 different wind speed conditions (ranging from 1.5 ms−1 to 22.8 ms−1), and we increased the water pCO2 concentration twice by more than 950 μatm for two of the seven experimental days. We develop a conceptual box model that incorporated the thermodynamics of the marine CO2 system. Surfactant concentrations in the sea surface microlayer (SML) ranged from 301 to 1015 μgL−1 (as Triton X-100 equivalents) with enrichments ranged from 1.0 to 5.7 in comparison to the samples from the underlying bulk water. With wind speeds up to 8.5 ms−1, surfactants in the SML can reduce the gas transfer velocity by 54%. Wind-wave tank experiments in combination with modeling are useful tools for obtaining a better understanding of the gas transfer velocities of CO2 across the air-sea boundary. The tank allowed for measuring the gas exchange velocity under extreme low and high wind speeds; in contrast, most previous parametrizations have fallen short because measurements of gas exchange velocities in the field are challenging, especially at low wind conditions. High variability in the CO2 transfer velocities suggests that gas exchange is a complex process not solely controlled by wind forces, especially in low wind conditions

Genetic diversity in terrestrial subsurface ecosystems impacted by geological degassing

Earth’s mantle releases 38.7 ± 2.9 Tg/yr CO2 along with other reduced and oxidized gases to the atmosphere shaping microbial metabolism at volcanic sites across the globe, yet little is known about its impact on microbial life under non-thermal conditions. Here, we perform comparative metagenomics coupled to geochemical measurements of deep subsurface fluids from a cold-water geyser driven by mantle degassing. Key organisms belonging to uncultivated Candidatus Altiarchaeum show a global biogeographic pattern and site-specific adaptations shaped by gene loss and inter-kingdom horizontal gene transfer. Comparison of the geyser community to 16 other publicly available deep subsurface sites demonstrate a conservation of chemolithoautotrophic metabolism across sites. In silico replication measures suggest a linear relationship of bacterial replication with ecosystems depth with the exception of impacted sites, which show near surface characteristics. Our results suggest that subsurface ecosystems affected by geological degassing are hotspots for microbial life in the deep biosphere

Oxygen Profiles Across the Sea-Surface Microlayer—Effects of Diffusion and Biological Activity

Gas exchange across the air-water interface is strongly influenced by the uppermost water layer (&lt; 1 mm), the sea-surface microlayer (SML). However, a clear understanding about how the distinct physicochemical and biological properties of the SML affect gas exchange is lacking. We used an automatic microprofiler with Clark-type microsensors to measure small-scale profiles of dissolved oxygen in the upper 5 cm of the water column in a laboratory tank filled with natural seawater. We aimed to link changing oxygen concentrations and profiles with the metabolic activity of plankton and neuston, i.e., SML-dwelling organisms, in our artificial, low-turbulence set-up during diel cycles. We observed that temporal changes of the oxygen concentration in near surface water (5 cm depth) could not be explained by diffusive loss of oxygen, but by planktonic activity. Interestingly, no influence of strong neuston activity on oxygen gradients at the air-water interface was detectable. This could be confirmed by a modeling approach, which revealed that neuston metabolic activity was insufficient to create distinct curvatures into these oxygen gradients. Moreover, the high neuston activity in our study contributed only ≤ 7.1% (see Supplementary Table 4) to changes in oxygen concentration in the tank. Overall, this work shows that temporal and vertical variation of oxygen profiles across the air-water interface in controlled laboratory set-ups is driven by biological processes in the underlying bulk water, with negligible effects of neuston activity

Establishing the Secondary Metabolite Profile of the Marine Fungus: Tolypocladium geodes sp. MF458 and Subsequent Optimisation of Bioactive Secondary Metabolite Production

As part of an international research project, the marine fungal strain collection of the Helmholtz Centre for Ocean Research (GEOMAR) research centre was analysed for secondary metabolite profiles associated with anticancer activity. Strain MF458 was identified as Tolypocladium geodes, by internal transcribed spacer region (ITS) sequence similarity and its natural product production profile. By using five different media in two conditions and two time points, we were able to identify eight natural products produced by MF458. As well as cyclosporin A (1), efrapeptin D (2), pyridoxatin (3), terricolin A (4), malettinins B and E (5 and 6), and tolypocladenols A1/A2 (8), we identified a new secondary metabolite which we termed tolypocladenol C (7). All compounds were analysed for their anticancer potential using a selection of the NCI60 cancer cell line panel, with malettinins B and E (5 and 6) being the most promising candidates. In order to obtain sufficient quantities of these compounds to start preclinical development, their production was transferred from a static flask culture to a stirred tank reactor, and fermentation medium development resulted in a nearly eight-fold increase in compound production. The strain MF458 is therefore a producer of a number of interesting and new secondary metabolites and their production levels can be readily improved to achieve higher yield

Health-related quality of life in family caregivers of autistic adults

IntroductionFamily members of autistic individuals often provide support for their autistic relative throughout the lifespan which can lead to massive burden themselves. Reduced health-related Quality of Life (HRQoL) in family caregivers is assumed; however, only a handful studies on the HRQoL of family caregivers providing care to adult relatives exist as opposed to autistic children. Thus, the current study aimed to (i) investigate the current state of physical and mental HRQoL of family caregivers of autistic adults compared to the general population, and (ii) examine caregiver-related (e.g., age, subjective caregiver burden) and care recipient-related variables (e.g., symptom severity, utilization of formal services) explaining variance in the caregivers’ HRQoL.MethodsN = 149 family caregivers completed a nationwide online survey, including the Short-Form Health Survey (SF-8) in order to assess the HRQoL. T-tests were used to compare the HRQoL of family caregivers with the general population. Bivariate correlational and multiple linear regression analyses were conducted in order to identify predictors explaining variance in family caregivers’ HRQoL.ResultsFamily caregivers of autistic adults reported significantly lower physical (M = 46.71, SD = 8.72, Cohen’s d = 0.42) and mental HRQoL (M = 40.15, SD = 11.28, Cohen’s d = 1.35) compared to the general population. Multiple linear regression with the mental HRQoL as the outcome showed a significant model (F(11, 95) = 5.53, p &lt; .001, adj. R2 = .32) with increased subjective burden explaining most of the variance in mental HRQoL (ß = .32, GDW = .141, p &lt; .001). Multiple linear regression analysis with the outcome physical HRQoL did not reveal a statistically significant model (F(11,95) = 1.09, p = .38). However, bivariate analyses also showed a positive correlation with the subjective caregiver burden (r= .20, p &lt; .05).DiscussionFindings highlight the need to consider HRQoL (and caregiver burden) of family caregivers of autistic adults in several healthcare settings to monitor a potential comprised health status in early stages, with the long-term goal to improve family caregivers’ HRQoL

Environmental stress responses and experimental handling artifacts of a model organism, the copepod Acartia tonsa (Dana)

Handling animals during experiments potentially affects the differential expression of genes chosen as biomarkers of sub-lethal stress. RNA sequencing was used to examine whole-transcriptome responses caused by laboratory handling of the calanoid copepod, Acartia tonsa. Salinity shock (S = 35 to S = 5) was used as positive stress control; individuals not exposed to handling or other stressors served as negative stress control. All copepods were grown from eggs to adults without being handled or exposed to any stressors prior the experiment. Survival of nauplii and adults was estimated for up to 10 min of exposure to handling stress and salinity shock. Only adults exhibited decreased survival (44 ± 7% with 10 min of exposure) in response to handling stress and were selected for definitive experiments for RNA sequencing. After 10 min of experimental exposures to handling stress or salinity shock, adults were incubated for 15 min or 24 h at normal culture conditions. A small number of significantly differentially expressed genes (DEGs) were observed 15 min after exposure to handling stress (2 DEGs) or salinity shock (7 DEGs). However, 24 h after exposure, handling stress resulted in 276 DEGs and salinity shock resulted in 573 DEGs, of which 174 DEGs were overlapping between the treatments. Among the DEGs observed 24 h after exposure to handling stress or salinity shock, some commonly-used stress biomarkers appeared at low levels. This suggests that a stress-response was induced at the transcriptional level for these genes between 15 min and 24 h following exposure. Since handling stress clearly affects transcriptional patterns, it is important to consider handling when designing experiments, by either including additional controls or avoiding focus on impacted genes. Not considering handling in gene expression studies can lead to inaccurate conclusions. The present study provides a baseline for studying handling stress in future studies using this model organism and others

Eggs of the copepod Acartia tonsa Dana require hypoxic conditions to tolerate prolonged embryonic development arrest

Additional file 1. Raw data and calculations for all experiments as well as an overview of experiments in this study