https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1131&context=usdoepub

A review of polymer electrolyte membrane fuel cells: Technology, applications,and needs on fundamental research

Patterns, mechanisms, projections, and consequences of tree mortality and associated broad-scale forest die-off due to drought accompanied by warmer temperatures—“hotter drought”, an emerging characteristic of the Anthropocene—are the focus of rapidly expanding literature. Despite recent observational, experimental, and modeling studies suggesting increased vulnerability of trees to hotter drought and associated pests and pathogens, substantial debate remains among research, management and policy-making communities regarding future tree mortality risks. We summarize key mortality-relevant findings, differentiating between those implying lesser versus greater levels of vulnerability. Evidence suggesting lesser vulnerability includes forest benefits of elevated [CO2] and increased water-use efficiency; observed and modeled increases in forest growth and canopy greening; widespread increases in woody-plant biomass, density, and extent; compensatory physiological, morphological, and genetic mechanisms; dampening ecological feedbacks; and potential mitigation by forest management. In contrast, recent studies document more rapid mortality under hotter drought due to negative tree physiological responses and accelerated biotic attacks. Additional evidence suggesting greater vulnerability includes rising background mortality rates; projected increases in drought frequency, intensity, and duration; limitations of vegetation models such as inadequately represented mortality processes; warming feedbacks from die-off; and wildfire synergies. Grouping these findings we identify ten contrasting perspectives that shape the vulnerability debate but have not been discussed collectively. We also present a set of global vulnerability drivers that are known with high confidence: (1) droughts eventually occur everywhere; (2) warming produces hotter droughts; (3) atmospheric moisture demand increases nonlinearly with temperature during drought; (4) mortality can occur faster in hotter drought, consistent with fundamental physiology; (5) shorter droughts occur more frequently than longer droughts and can become lethal under warming, increasing the frequency of lethal drought nonlinearly; and (6) mortality happens rapidly relative to growth intervals needed for forest recovery. These high-confidence drivers, in concert with research supporting greater vulnerability perspectives, support an overall viewpoint of greater forest vulnerability globally. We surmise that mortality vulnerability is being discounted in part due to difficulties in predicting threshold responses to extreme climate events. Given the profound ecological and societal implications of underestimating global vulnerability to hotter drought, we highlight urgent challenges for research, management, and policy-making communities.

/pdf/on-underestimation-of-global-vulnerability-to-tree-mortality-1w5zrntf70.pdf

On underestimation of global vulnerability to tree mortality and forest die‐off from hotter drought in the Anthropocene

https://iopscience.iop.org/article/10.1149/2.1441707jes/pdf

Review—SEI: Past, Present and Future

/pdf/high-resolution-x-ray-computed-tomography-in-geosciences-a-3sj7249knj.pdf

High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications

3.8.2. Temperature Distribution Measurements 4749 3.8.3. Two-Phase Visualization 4750 3.8.4. Experimental Validation 4751 3.9. Modeling the Catalyst Layer at Pore Level 4751 3.10. Summary and Outlook 4752 4. Direct Methanol Fuel Cells 4753 4.1. Technical Challenges 4754 4.1.1. Methanol Oxidation Kinetics 4754 4.1.2. Methanol Crossover 4755 4.1.3. Water Management 4755 4.1.4. Heat Management 4756 4.2. DMFC Modeling 4756 4.2.1. Needs for Modeling 4756 4.2.2. DMFC Models 4756 4.3. Experimental Diagnostics 4757 4.4. Model Validation 4758 4.5. Summary and Outlook 4760 5. Solid Oxide Fuel Cells 4760 5.1. SOFC Models 4761 5.2. Summary and Outlook 4762 6. Closing Remarks 4763 7. Acknowledgments 4763 8. References 4763

Fundamental models for fuel cell engineering.

Different oils, waxes, natural and synthetic resins are in use for conservation and stability enhancement of degraded wood samples X-ray radiography, tomography and thermography studies were carried out at several places as an attempt for the visualization of the conservation procedures Because of the high sensitivity of neutrons in detecting hydrogen-containing materials, the visualization of their distribution can be obtained by means of neutron radiography at the NEUTRA facility of SINQ with good resolution One of the most common conservation preservatives for wood consolidation is the acryl resin “Paraloid B-72” Combined with different solvents in a variety of solvent mixtures, B-72 can be used to address a diversity of absorption, dispersion or evaporation determinants for different wooden objects Therefore, four different acryl resin solvents of the same acryl resin applied to coniferous wood samples (4×4×27 cm) were investigated to determine the uptake and loss processes, followed by measuring sequences of images of the 2-dimensional distribution This was done by creating image sequences showing the process of uptake and loss processes as two-dimensional distribution over about 20 h The resin uptake depends strongly on the solvent, as well on the proportion of the resin in the composition The acryl-ethylacetate composition has the lowest uptake, but the composition of 20% acryl 80% toluol has soaked up almost eight times more Out of these results, a composition of 20% acryl and 80% toluol seems to be the best of the tried compositions, because the greatest part of resin remains and its allocation seems to be the most homogeneous as well

Neutron radiography as visualization and quantification method for conservation measures of wood firmness enhancement

The phase-contrast radiography is an edge-enhancement technique which allows to visualize objects providing very low contrast with the conventional absorption radiography technique The image formation in this case is based on the phase variations transformed to intensity variations in a beam with a high lateral coherence by its transmission of the object Due to the fact that neutrons could not be easily focused in a spot with a micrometric size like X-rays we need a small diaphragm and a large distance between the diaphragm and the sample in order to achieve a good lateral coherence length for the neutron phase-contrast radiographic experiments The main beam parameters which generate some differences between the different beam facilities and influence the phase-contrast effect are the beam divergences and the beam spectra of each beam lines Various examples of phase-contrast imaging performed at neutron beam lines with different beam parameters will be shown The combination of the phase-contrast effect with the effect of image magnification due to the beam divergence which leads to an improvement in the image contrast and resolution will be presented in detail

Improving the image contrast and resolution in the phase-contrast neutron radiography

The knowledge of manufacturing related magnetic property degeneration in electrical steel laminations is essential for selecting correct obstructing material grades and designing efficient electrical machines. Until now these effects stay undiscovered due to the lack of adequate investigation methods that reveal local information on troubling lamination areas. Here we show how the use of a non-destructive testing method based on a neutron grating interferometry setup provides spatially-resolved information about the local bulk domain wall density. Different representative manufacturing techniques are compared in terms of magnetic flux density deterioration such as punching, mechanically cutting by guillotine as well as laser fusion cutting applying industrial high power laser beam sources.

Localized investigation of magnetic bulk property deterioration of electrical steel: Analysing magnetic property drop thorough mechanical and laser cutting of electrical steel laminations using neutron grating interferometry

Neutron Imaging (NI) has been developed in the last decades from a film-based inspection method for non-destructive observations towards a powerful research tool with many new and competitive methods. The most important technical step forward has been the introduction and optimization of digital imaging detection systems. In this way, direct quantification of the transmission process became possible—the basis for all advanced methods like tomography, phase-contrast imaging and neutron microscopy. Neutron imaging facilities need to be installed at powerful neutron sources (reactors, spallation sources, other accelerator driven systems). High neutron intensity can be used best for either highest spatial, temporal resolution or best image quality. Since the number of such strong sources is decreasing world-wide due to the age of the reactors, the number of NI facilities is limited. There are a few installations with pioneering new concepts and versatile options on the one hand, but also relatively new sources with only limited performance thus far. It will be a challenge to couple the two parts of the community with the aim to install state-of-the-art equipment at the suitable beam ports and develop NI further towards a general research tool. In addition, sources with lower intensity should be equipped with modern installations in order to perform practical work best.

https://www.mdpi.com/2313-433X/3/4/52/pdf

Neutron imaging facilities in a global context

Dryout of the liquid coolant film on fuel pins at the top of boiling water reactor (BWR) cores constitutes the type of heat transfer crisis relevant for the conditions of high void fractions. It is a limiting factor in the thermal power, and therefore the economy, of BWRs. Ongoing research on multiphase annular flow, specifically the liquid film thickness, is fundamental not only to nuclear reactor safety and operation but also to that of evaporators, condensers, and pipelines in a general industrial context. We have performed cold neutron tomography of adiabatic air water annular flow in a scaled up model of the subchannel geometry found in BWR fuel assemblies today. All imaging has been performed at the ICON beamline at the neutron spallation source SINQ at the Paul Scherrer Institut in Switzerland. Neutron tomography is shown to excel in investigating the interactions of air water two phase flows with spacer vanes of different geometry. The high resolution, high contrast measurements provide spatial distributions of the coolant on top of the surfaces of the spacer, including the vanes, and in the subchannel downstream of the spacers.

Eberhard Lehmann

Papers

Neutron radiography as visualization and quantification method for conservation measures of wood firmness enhancement

Improving the image contrast and resolution in the phase-contrast neutron radiography

Localized investigation of magnetic bulk property deterioration of electrical steel: Analysing magnetic property drop thorough mechanical and laser cutting of electrical steel laminations using neutron grating interferometry

Neutron imaging facilities in a global context

Cold neutron tomography of annular coolant flow in a double subchannel model of a boiling water reactor