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result(s) for
"Hoek, C. J."
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An ecohydrological sketch of climate change impacts on water and natural ecosystems for the Netherlands: bridging the gap between science and society
2012
For policy making and spatial planning, information is needed about the impacts of climate change on natural ecosystems. To provide this information, commonly hydrological and ecological models are used. We give arguments for our assessment that modelling only is insufficient for determining the impacts of climate changes on natural ecosystems at regional scales. Instead, we proposed a combination of hydrological simulations, a literature review and process-knowledge on climate-hydrology-vegetation interactions, to compile a sketch map that indicates climate change effects on a number of ecosystems in the Netherlands. Soon after a first version of our sketch map was published by a Dutch professional journal, copies appeared in policy documents, and also in a commercial and popular atlas of the Netherlands. Moreover, the map led to a question in the Dutch parliament about the sustainability of bog reserves under the future climate. Apparently, there was an urgent need for the information provided by the map. The map shows that climate change will presumably have the largest influence on ecosystems in the Netherlands that depend on precipitation as the major water source, like heathlands, dry grasslands, rain-fed moorland pools and raised bogs. Also highly susceptible are fens in reserves surrounded by deeply drained polders, because such fens depend on the inlet of surface water, of which quality is likely to deteriorate upon climate change. While the map is indicative for directions of change, in view of the uncertainties of our study, no conclusions should be drawn that may have far-reaching consequences, such as giving up certain nature targets that might no longer be feasible in the future climate. Instead, we advise to anticipate the potential threats from climate change by taking a number of adaptation measures that enhance the robustness of nature reserves. To improve climate change projections on hydrology and ecosystems, future research should especially focus on feedbacks of vegetation on the water balance, on processes that directly influence plant performance and on the ecological effects of weather extremes.
Journal Article
Secondary fluorescence near phase boundaries - Typical cases in steel
by
van Hoek, C J G
,
Rijnders, M R
in
Aluminum oxide
,
Energy dispersive X ray spectroscopy
,
Fluorescence
2018
Secondary fluorescence (SF) from across a phase boundary can cause spurious analytical results. Two cases of SF in steel research are presented: Zn in Zn-coated steel across the interface, and Fe in alumina particles embedded in a steel matrix. Wavelength-dispersive X-ray spectrometry (WDS) and energy-dispersive X-ray spectrometry (EDS) measurements were performed both on couples of juxtaposed Fe/Zn as well as equivalent samples that were production-derived (i.e., high-T exposed). Subsequently the SF effect was modelled using CalcZAF to compare the measured profiles with the theoretical ones. For Zn in Fe it is shown that the calculations are in close agreement with the measurements, although some discrepancies need a more detailed research. This work shows the importance of the use of models to support the interpretation of experimental WDS and EDS results on coated steel samples where phase boundaries are involved.
Journal Article
An inter-laboratory comparison of EPMA analysis of alloy steel at low voltage
2012
We present the results of an inter-laboratory comparison of EPMA analysis at low voltage (5-6 kV) of three monophasic alloy steel samples. The aim of the work was to obtain an estimate of the present situation of low-voltage analysis of steel and identify needs for improvement. EPMA analyses of the samples were conducted by seven participant groups using electron microprobes and scanning electron microscopes of different kind, equipped with wavelength- and/or energy-dispersive X-ray spectrometers, and employing their own methodology of analysis. The results using WDS showed essentially an underestimation of the Cr contents, with relative deviations from the reference values ranging from -0.7 % to -17 %, and an overestimation of Fe and Ni, with relative deviations from the reference composition ranging from -4 % to +30 %, and from +14 % to +42 %, respectively. The relative deviations obtained by using EDS showed larger scatter, ranging from -16 % to +54 % for Cr, -0.4 % to +66 % for Fe and from +13 % to +90 % for Ni. Reasons for the differences observed and the scatter of results are discussed.
Journal Article
Spatial planning of a climate adaptation zone for wetland ecosystems
by
Vos, Claire C
,
van der Hoek, Dirk C. J
,
Vonk, Marijke
in
Adaptation
,
Adaptation strategy
,
Adaptive capacity
2010
Here we present a spatial planning approach for the implementation of adaptation measures to climate change in conservation planning for ecological networks. We analyse the wetland ecosystems of the Dutch National Ecological Network for locations where the effectiveness of the network might be weakened because of climate change. We first identify potential dispersal bottlenecks where connectivity might be insufficient to facilitate range expansions. We then identify habitat patches that might have a too low carrying capacity for populations to cope with additional population fluctuations caused by weather extremes. Finally, we describe the spatial planning steps that were followed to determine the best locations for adaptation measures. An essential part of our adaptation strategy is to concentrate adaptation measures in a ‘climate adaptation zone'. Concentrating adaptation measures is a cost-effective planning strategy, rendering the largest benefit per area unit. Measures are taken where abiotic conditions are optimal and measures to enhance the spatial cohesion of the network are taken close to existing areas, thus creating the highest possible connectivity with the lowest area demands. Another benefit of a climate adaptation zone is that it provides a spatial protection zone where activities that will have a negative impact on ecosystem functioning might be avoided or mitigated. The following adaptation measures are proposed within the climate adaptation zone: (1) link habitat networks to enable species to disperse from present to future suitable climate zones, (2) enlarge the carrying capacity by either enlarging the size of natural areas or by improving habitat quality to shorten population recovery after disturbances, (3) increase the heterogeneity of natural areas, preferably by stimulating natural landscape-forming processes, to avoid large synchronised extinctions after extreme weather events. The presented approach can be generalised to develop climate adaptation zones for other ecosystem types inside or outside Europe, where habitat fragmentation is a limiting factor in biodiversity responses to climate change.
Journal Article
Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event
2019
The Galactic Centre contains a supermassive black hole with a mass of four million Suns
1
within an environment that differs markedly from that of the Galactic disk. Although the black hole is essentially quiescent in the broader context of active galactic nuclei, X-ray observations have provided evidence for energetic outbursts from its surroundings
2
. Also, although the levels of star formation in the Galactic Centre have been approximately constant over the past few hundred million years, there is evidence of increased short-duration bursts
3
, strongly influenced by the interaction of the black hole with the enhanced gas density present within the ring-like central molecular zone
4
at Galactic longitude |
l
| < 0.7 degrees and latitude |
b
| < 0.2 degrees. The inner 200-parsec region is characterized by large amounts of warm molecular gas
5
, a high cosmic-ray ionization rate
6
, unusual gas chemistry, enhanced synchrotron emission
7
,
8
, and a multitude of radio-emitting magnetized filaments
9
, the origin of which has not been established. Here we report radio imaging that reveals a bipolar bubble structure, with an overall span of 1 degree by 3 degrees (140 parsecs × 430 parsecs), extending above and below the Galactic plane and apparently associated with the Galactic Centre. The structure is edge-brightened and bounded, with symmetry implying creation by an energetic event in the Galactic Centre. We estimate the age of the bubbles to be a few million years, with a total energy of 7 × 10
52
ergs. We postulate that the progenitor event was a major contributor to the increased cosmic-ray density in the Galactic Centre, and is in turn the principal source of the relativistic particles required to power the synchrotron emission of the radio filaments within and in the vicinity of the bubble cavities.
Radio observations show a bipolar bubble structure of size 140 parsecs by 430 parsecs both above and below the Galactic Centre.
Journal Article
Inflation of 430-parsec bipolar radio bubbles in the Galactic Centre by an energetic event
2019
The Galactic Centre contains a supermassive black hole with a mass of 4 million suns within an environment that differs markedly from that of the Galactic disk. While the black hole is essentially quiescent in the broader context of active galactic nuclei, X-ray observations have provided evidence for energetic outbursts from its surroundings. Also, while the levels of star formation in the Galactic Centre have been approximately constant over the last few hundred Myr, there is evidence of elevated short-duration bursts, strongly influenced by interaction of the black hole with the enhanced gas density present within the ring-like Central Molecular Zone at Galactic longitude |l| < 0.7 degrees and latitude |b| < 0.2 degrees. The inner 200 pc region is characterized by large amounts of warm molecular gas, a high cosmic ray ionization rate, unusual gas chemistry, enhanced synchrotron emission, and a multitude of radio-emitting magnetised filaments, the origin of which has not been established. Here we report radio imaging that reveals bipolar bubbles spanning 1 degree x 3 degrees (140 parsecs x 430 parsecs), extending above and below the Galactic plane and apparently associated with the Galactic Centre. The structure is edge-brightened and bounded, with symmetry implying creation by an energetic event in the Galactic Centre. We estimate the age of the bubbles to be a few million years, with a total energy of 7 x 10^52 ergs. We postulate that the progenitor event was a major contributor to the increased cosmic-ray density in the Galactic Centre, and is in turn the principal source of the relativistic particles required to power the synchrotron emission of the radio filaments within and in the vicinity of the bubble cavities.
The biology of ergothioneine, an antioxidant nutraceutical
by
Paramasivan, Kalaivani
,
Roberts, Timothy J.
,
Pretorius, Etheresia
in
Actinobacteria - chemistry
,
Amino acids
,
Animals
2020
Ergothioneine (ERG) is an unusual thio-histidine betaine amino acid that has potent antioxidant activities. It is synthesised by a variety of microbes, especially fungi (including in mushroom fruiting bodies) and actinobacteria, but is not synthesised by plants and animals who acquire it via the soil and their diet, respectively. Animals have evolved a highly selective transporter for it, known as solute carrier family 22, member 4 (SLC22A4) in humans, signifying its importance, and ERG may even have the status of a vitamin. ERG accumulates differentially in various tissues, according to their expression of SLC22A4, favouring those such as erythrocytes that may be subject to oxidative stress. Mushroom or ERG consumption seems to provide significant prevention against oxidative stress in a large variety of systems. ERG seems to have strong cytoprotective status, and its concentration is lowered in a number of chronic inflammatory diseases. It has been passed as safe by regulatory agencies, and may have value as a nutraceutical and antioxidant more generally.
Journal Article
Safety and immunogenicity of three different formulations of an adjuvanted varicella-zoster virus subunit candidate vaccine in older adults: A phase II, randomized, controlled study
by
Plassmann, Georg
,
Schwarz, Tino F.
,
Heineman, Thomas C.
in
Adjuvant
,
adjuvants
,
Adjuvants, Immunologic - administration & dosage
2014
•We investigated a herpes zoster vaccine candidate at different antigen doses, and with or without the AS01B Adjuvant System.•All adjuvanted vaccine formulations were immunogenic and well-tolerated in adults ≥60 years of age.•Two vaccinations with the adjuvanted vaccine candidate induced a greater immune response than one.•The dose of varicella-zoster virus glycoprotein E impacted humoral but not cellular immune responses.
This study investigated the safety and immunogenicity of different formulations and schedules of a candidate subunit herpes zoster vaccine containing varicella-zoster virus glycoprotein E (gE) with or without the adjuvant system AS01B.
In this phase II, single-blind, randomized, controlled study, adults aged ≥60years (N=714) received one dose of 100μggE/AS01B, two doses, two months apart, of 25, 50, or 100μggE/AS01B, or two doses of unadjuvanted 100μggE/saline. Frequencies of CD4+ T cells expressing ≥2 activation markers following induction with gE were measured by intracellular cytokine staining and serum anti-gE antibody concentrations by ELISA.
Frequencies of gE-specific CD4+ T cells were >3-fold higher after two doses of all gE/AS01B formulations than after one dose of 100μggE/AS01B or two doses of 100μggE/saline. Frequencies were comparable after two doses of 25, 50, or 100μggE/AS01B. Serum anti-gE antibody concentrations were comparable after two doses of 50 or 100μggE/AS01B and higher than in the other groups. Immune responses persisted for at least 36 months. Reactogenicities of all gE/AS01B formulations were similar but greater than with gE/saline.
The three formulations of gE/AS01B were immunogenic and well tolerated in adults aged ≥60years. Two vaccinations with gE/AS01B induced higher immune responses than one and the dose of gE impacted humoral but not cellular immune responses (NCT00434577).
Journal Article
Global distribution of hydrologic controls on forest growth
by
Roebroek, Caspar T. J.
,
Fan, Ying
,
Hoek van Dijke, Anne J.
in
Availability
,
Climate
,
Climate and vegetation
2020
Vegetation provides key ecosystem services and is an important component in the hydrological cycle. Traditionally, the global distribution of vegetation is explained through climatic water availability. Locally, however, groundwater can aid growth by providing an extra water source (e.g. oases) or hinder growth by presenting a barrier to root expansion (e.g. swamps). In this study we analyse the global correlation between humidity (expressing climate-driven water and energy availability), groundwater and forest growth, approximated by the fraction of absorbed photosynthetically active radiation, and link this to climate and landscape position. The results show that at the continental scale, climate is the main driver of forest productivity; climates with higher water availability support higher energy absorption and consequentially more growth. Within all climate zones, however, landscape position substantially alters the growth patterns, both positively and negatively. The influence of the landscape on vegetation growth varies over climate, displaying the importance of analysing vegetation growth in a climate–landscape continuum.
Journal Article
Can large-scale tree cover change negate climate change impacts on future water availability?
by
Roebroek, Caspar T. J.
,
Engel, Freek
,
Hoek van Dijke, Anne J.
in
Afforestation
,
Analysis
,
Availability
2025
The availability of fresh water over land may become increasingly scarce under climate change (CC), and natural and human-induced tree cover changes can further enhance or negate the water scarcity. Previous studies showed that global tree cover change can have large impacts on water availability under current climate conditions, but they did not touch upon the implications of global tree cover change under climate change. Here, we study the hydrological impacts of large-scale tree cover change (climate-induced changes in combination with large-scale afforestation) in a future climate (SSP3-7.0) following an interdisciplinary approach. By combining data from five Coupled Model Intercomparison Project phase 6 (CMIP6) climate models with a future potential tree cover dataset, six Budyko models, and the UTrack moisture recycling dataset, we can disentangle the impacts of climate change and future tree cover change on evapotranspiration, precipitation, and runoff. We quantify per grid cell and for five selected river basins (Yukon, Mississippi, Amazon, Danube, and Murray–Darling) if tree cover changes can enhance or counteract the climate-driven changes in runoff due to their impact on evapotranspiration and moisture recycling. Globally averaged, the impacts of climate change and large-scale tree cover change on runoff can be of similar magnitude with opposite signs. While climate change may increase global runoff, we estimate that tree cover change could reverse this effect, which may result in a limited net impact on global runoff relative to the present climate and current tree cover. Nevertheless, the local changes in runoff due to tree cover change and climate change can be substantial, with increases and decreases of more than 100 mm yr−1. We show that, for approximately 16 % of the land surface, tree cover change can increase the water availability significantly. However, for 14 % of the land surface, both tree cover change and climate change could decrease water availability by more than 5 mm yr−1. For each of the selected catchments, the direction and magnitude of the impacts of climate change and tree cover change can vary, with dominating climate change impacts in all basins except the Mississippi River basin. Our results show that ecosystem restoration projects targeting an altered tree cover should consider the corresponding hydrological impacts to limit unwanted (non-)local reductions in water availability.
Journal Article