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.

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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.

In this paper the magnetization decay behavior of neutron irradiated MgB2 bulk samples and an estimate of the strength of the introduced pinning centers are presented. The magnetization decay measurements appear much more complex than usual, in fact, they may be logarithmic or not, depending on the values of temperature and magnetic field and, as the region of low temperatures and fields is approached, they are affected by a “noise” that is out of experimental uncertainties. This “noisy” behavior is attributed to the small flux jumps, related to the dendritic flux penetration, widely observed in MgB2 samples. We identify a phase diagram that divides the H-T plane in two regions: one, at relatively low temperatures and fields, where the decay observed is noisy, the other, outside it, where the decay is “clean.” This noisy region extends up to T/Tc≅0.5 and up to a field of some teslas, i.e., in a range of instability much more extended than that found in previous measurements. At high magnetic field the pin...

/pdf/magnetization-decay-in-neutron-irradiated-mgb2-bulk-samples-4ugy9bymo1.pdf

Magnetization decay in neutron irradiated MgB2 bulk samples

Non-destructive neutron radiography is used to study the different processes of liquid transport in Scots pine sapwood and heartwood. The spatial and temporal changes in moisture content and saturation degree, measured at high resolution, are provided for water uptake in longitudinal, radial and tangential directions. Liquid uptake in sapwood, compared to in heartwood, is found to be faster and more homogeneous. Latewood cells are the preferential pathways for longitudinal and tangential uptake in both sapwood and heartwood resulting in strongly non-uniform water fronts. In radial uptake, water accumulates first in the border between growth layers. While the moisture content profiles vary strongly between earlywood and latewood layers, the corresponding swelling strain profiles change smoothly due to the mechanical interaction between the different layers. Long term experiments in laboratory show three phases of uptake: a first fast phase, a second slower phase and a third phase reaching capillary saturation. The main difference between sapwood and heartwood uptake takes place in the first phase when liquid is mainly transported in the lumen, until moisture reaches the top of the sample. After that, both wood types behave similarly, uptake is followed by a slower adsorption in the wood cell walls and liquid redistribution in perpendicular to the uptake direction until the sample is almost totally saturated. These findings are of interest for future studies on durability and treatability of pine sapwood and heartwood. The online version of the original article can be found under doi:10.1617/s11527-013-0112-7. M. Sedighi-Gilani D. Derome (&) Laboratory of Building Science and Technology, Swiss Federal Laboratories for Materials Science and Technology, Uberlandstrasse 128, 8600 Dübendorf, Switzerland e-mail: dominique.derome@empa.ch P. Vontobel E. Lehmann Paul Scherrer Institut, 5232 Villigen, Switzerland J. Carmeliet Chair of Building Physics, ETH Zürich, Hönggerberg, Wolfgang-Pauli-Strasse 15, 8093 Zurich, Switzerland Materials and Structures (2014) 47:1097 DOI 10.1617/s11527-013-0136-z

https://link.springer.com/content/pdf/10.1617%2Fs11527-013-0136-z.pdf

Erratum to: Liquid uptake in Scots pine sapwood and heartwood visualized and quantified by neutron radiography

We report about the method of neutron imaging which can be considered as complement and alternative to the more common X-ray techniques. While the image quality obtained (resolution, dynamic, contrast) is comparable, the particular sensitivity for the investigated materials can differ much. With respect to bronze objects containing Cu, Sn, Zn or Pb in large amounts, the transmission of neutrons is considerably higher than is possible with common X-ray devices. Furthermore, traces of organic materials (corrosion products, resin, wax, oil, lacquer) can be detected accurately. The report describes by means of selected examples how to apply the neutron techniques most efficiently and what infor- mation can be derived from these studies. In addition we describe in brief some alternative analytical tools based on X-ray fluorescence and diffraction that are applicable for material characterization on the surface. The beam lines at PSI’s large-scale facilities can be used on demand if the scientific justification for a dedicated study is submitted in a proposal. (Key words: neutron imaging, bronze objects, tomography, complementarity, X-rays)

Using neutron imaging methods for the non-destructive investigation of large ancient bronze artefacts

Digital thermal neutron imaging (radiography and tomography) is a powerful non-destructive analytical tool and has demonstrated its importance in industrial and research application world-wide. The standardization process, to certify digital thermal neutron imaging as a standard practice in industry, entails standardized test phantoms to be evaluated. Through the evaluation of the phantoms the spatial resolution and contrast of a thermal neutron digital imaging system can be determined in a controlled and standardized manner by accepting good practice in terms of scanning, data processing, data visualization and evaluation. Standard test phantoms are objects with physical features designed to test facility capabilities to reveal these features without any ambiguity. The good practice enables the acceptable assessment of different international digital thermal neutron imaging facilities for spatial resolution and contrast abilities. The purpose of this contribution is to establish good practice for the experimental setup, acquiring of 2-D digital projections, the reconstruction process, the visualization and evaluation of the 3-D digital images of standard test phantoms for spatial resolution and contrast. Results obtained from applying this suggested good practice on contrast standard test phantom will be discussed.

Towards establishment of standardized practice for assessment of spatial resolution and contrast of international digital thermal neutron imaging facilities

It is well known that neutron tomography produces spectacular images of, for instance, interiors of large engineering components and cultural heritage objects, taking advantage of continuous improv...

Eberhard Lehmann

Papers

Magnetization decay in neutron irradiated MgB2 bulk samples

Erratum to: Liquid uptake in Scots pine sapwood and heartwood visualized and quantified by neutron radiography

Using neutron imaging methods for the non-destructive investigation of large ancient bronze artefacts

Towards establishment of standardized practice for assessment of spatial resolution and contrast of international digital thermal neutron imaging facilities

ISIS hosts NEUWAVE-2 Workshop on Energy-Selective Neutron Imaging