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"Roberts, David W."
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Variation partitioning involving orthogonal spatial eigenfunction submodels
When partitioning the variation of univariate or multivariate ecological data with respect to several submodels of spatial eigenfunctions (e.g., Moran's eigenvector maps, MEM) acting as explanatory data, a problem occurs: although the submodels are constructed to be orthogonal to one another, the partitioning based on adjusted
R
2
statistics produces nonzero values in the intersections between spatial submodels. This phenomenon is described and two solutions are proposed. The first solution is to apportion the intersection fractions proportionally to the variation explained by each submodel. The second solution consists in creating a hierarchy among the spatial submodels, in accordance with hierarchy theory. These solutions lead to new partitioning equations that are described in the Appendix. R functions are provided to carry out partitioning with respect to environmental variables and spatial eigenfunction submodels. This development is important for the correct interpretation of spatial modeling results implying explanatory environmental data as well as submodels of spatial eigenfunctions involving two or more spatial scales.
Journal Article
5-aminolevulinic acid induced protoporphyrin IX (ALA-PpIX) fluorescence guidance in meningioma surgery
Introduction
5-aminolevulinic acid induced protoporphyrin IX (5-ALA-PpIX) fluorescence guidance has emerged as a valuable surgical adjunct for resection of intracranial tumors.
Methods
Here we present a focused review on 5-ALA-PpIX fluorescence guidance for meningiomas.
Results
We discuss the clinical studies and specific applications to date as well as the two main intraoperative fluorescence technologies applied to meningiomas.
Conclusions
The use of 5-ALA-PpIX in meningiomas holds promising potential so neurosurgeons can improve surgical outcomes for patients with meningiomas as well as be pioneers in developing improved fluorescence imaging technologies.
Journal Article
Measuring Understory Fire Effects from Space: Canopy Change in Response to Tropical Understory Fire and What This Means for Applications of GEDI to Tropical Forest Fire
The ability to measure the ecological effects of understory fire in the Amazon on a landscape scale remains a frontier in remote sensing. The Global Ecosystem Dynamics Investigation’s (GEDI) LiDAR data have been widely suggested as a critical new tool in this field. In this paper, we use the GEDI Simulator to quantify the nuanced effects of understory fire in the Amazon, and assess the ability of on-orbit GEDI data to do the same. While numerous ecological studies have used simulated GEDI data, on-orbit constraint may limit ecological inference. This is the first study that we are aware of that directly compares methods using simulated and on-orbit GEDI data. Simulated GEDI data showed that fire effects varied nonlinearly through the canopy and then moved upward with time since burn. Given that fire effects peaked in the mid-canopy and were often on the scale of 2 to 3 m in height difference, it is unlikely that on-orbit GEDI data will have the sensitivity to detect these same changes.
Journal Article
Visualization technologies for 5-ALA-based fluorescence-guided surgeries
Introduction
5-ALA-based fluorescence-guided surgery has been shown to be a safe and effective method to improve intraoperative visualization and resection of malignant gliomas. However, it remains ineffective in guiding the resection of lower-grade, non-enhancing, and deep-seated tumors, mainly because these tumors do not produce detectable fluorescence with conventional visualization technologies, namely, wide-field (WF) surgical microscopy.
Methods
We describe some of the main factors that limit the sensitivity and accuracy of conventional WF surgical microscopy, and then provide a survey of commercial and research prototypes being developed to address these challenges, along with their principles, advantages and disadvantages, as well as the current status of clinical translation for each technology. We also provide a neurosurgical perspective on how these visualization technologies might best be implemented for guiding glioma surgeries in the future.
Results
Detection of PpIX expression in low-grade gliomas and at the infiltrative margins of all gliomas has been achieved with high-sensitivity probe-based visualization techniques. Deep-tissue PpIX imaging of up to 5 mm has also been achieved using red-light illumination techniques. Spectroscopic approaches have enabled more accurate quantification of PpIX expression.
Conclusion
Advancements in visualization technologies have extended the sensitivity and accuracy of conventional WF surgical microscopy. These technologies will continue to be refined to further improve the extent of resection in glioma patients using 5-ALA-induced fluorescence.
Journal Article
Vegetation classification by two new iterative reallocation optimization algorithms
This paper presents two new non-hierarchical iterative reallocation optimization algorithms for vegetation classification. The OPTimal PARTitioning algorithm (OPTPART) optimizes the ratio of within-cluster similarity to among-cluster similarity; the OPTimal SILhouette algorithm (OPTSIL) optimizes the difference between the similarity of each sample to the cluster to which it is assigned and its similarity to the most similar cluster. The algorithms were tested on three vegetation datasets (Mt. Field Massif, Tazmania, Australia; Podyj/Thayatal National Park, Austria/Czech Republic; and Shoshone National Forest, Wyoming, USA) using three dissimilarity/distance matrices (Bray-Curtis, chord distance, and Hellinger distance) and compared to five other commonly used or recently introduced vegetation classification algorithms (flexible-β, TWINSPAN, PAM, ISOPAM, and K-means) using eight goodness-of-clustering evaluators. Five of the eight evaluators were species-based and operate on the distribution of individual taxa among clusters; three were community-based and operate on the compositional similarity of clusters. OPTPART was initialized from random partitions and from the results of a flexible-β classification as the initial partition; OPTSIL was initialized from partitions resulting from OPTPART, flexible-β, and K-means classifications. Algorithms were ranked from best to worst on each clustering evaluator for each dissimilarity/distance matrix for each dataset, and summarized by median ranks. OPTPART, SIL/OPT (OPTSIL from an OPTPART initial partition), and SIL/FLEX (OPTSIL from a flexible-β initial partition) ranked 1–3 respectively for results pooled across all three datasets and dissimilarity/distance matrices. OPTPART, SIL/OPT, and SIL/FLEX consistently ranked 1–3 across the individual datasets, although the order varied slightly by dataset.
Journal Article
Liberal Peacebuilding and Global Governance
This book examines the limits to cosmopolitan liberal peacebuilding caused by its preoccupation with the values and assumptions of neoliberal global governance.
The peace people experience is determined by the processes privileged in peacebuilding. This book is about four things that shape the processes involved. First, it is a critique of orthodox postconflict peacebuilding. It takes the position that the present approach, although seemingly hegemonic, is routinely ignored or manipulated by elites and society and converted into a miasma that to some degree wastes the energies and opportunities involved. Second, it is about alternatives which invoke the kind of peace people might seek in postconflict places if they had more control over the process of peacebuilding, a notion referred to here as 'popular peace'. It is thus not the kind of critical work that some describe as 'reflexive anti-liberalism'. Rather, it seeks alternatives that are grounded in the lives of people in postconflict spaces and which also reflect some of the essential values of Liberalism. Third, it is about the role of both informal and formal actors, institutions and practices in the creation of such a peace. For instance, it is concerned with the legitimacy of informal practices that lie beyond Liberal tolerance and which are vital in the pursuit of everyday peace. Fourth, it is about a 'transversal' (rather than vertical or hierarchical) relationship of global and local governance in securing a peace that reflects the needs and values of both. In short, this work is a response to the substantial inconsistencies that appear between peacebuilding rhetoric and everyday outcomes in postconflict places.
This book will be of much interest to students of peacebuilding, post-conflict statebuilding, conflict studies, global governance and International Relations in general.
eBook
Validation and Error Minimization of Global Ecosystem Dynamics Investigation (GEDI) Relative Height Metrics in the Amazon
Global Ecosystem Dynamics Investigation (GEDI) is a relatively new technology for global forest research, acquiring LiDAR measurements of vertical vegetation structure across Earth’s tropical, sub-tropical, and temperate forests. Previous GEDI validation efforts have largely focused on top of canopy accuracy, and findings vary by geographic region and forest type. Despite this, many applications utilize measurements of vertical vegetation distribution from the lower canopy, with a wide diversity of uses for GEDI data appearing in the literature. Given the variability in data requirements across research applications and ecosystems, and the regional variability in GEDI data quality, it is imperative to understand GEDI error to draw strong inferences. Here, we quantify the accuracy of GEDI relative height metrics through canopy layers for the Brazilian Amazon. To assess the accuracy of on-orbit GEDI L2A relative height metrics, we utilize the GEDI waveform simulator to compare detailed airborne laser scanning (ALS) data from the Sustainable Landscapes Brazil project to GEDI data collected by the International Space Station. We also assess the impacts of data filtering based on biophysical and GEDI sensor conditions and geolocation correction on GEDI error metrics (RMSE, MAE, and Bias) through canopy levels. GEDI data accuracy attenuates through the lower percentiles in the relative height (RH) curve. While top of canopy (RH98) measurements have relatively high accuracy (R2 = 0.76, RMSE = 5.33 m), the accuracy of data decreases lower in the canopy (RH50: R2 = 0.54, RMSE = 5.59 m). While simulated geolocation correction yielded marginal improvements, this decrease in accuracy remained constant despite all error reduction measures. Some error rates for the Amazon are double those reported in studies from other regions. These findings have broad implications for the application of GEDI data, especially in studies where forest understory measurements are particularly challenging to acquire (e.g., dense tropical forests) and where understory accuracy is highly important.
Journal Article
Review of clinical trials in intraoperative molecular imaging during cancer surgery
Most solid cancers are treated by surgical resections to reduce the burden of disease. Surgeons often face the challenge of detecting small areas of residual neoplasm after resection or finding small primary tumors for the initial resection. Intraoperative molecular imaging (IMI) is an emerging technology with the potential to dramatically improve cancer surgery operations by allowing surgeons to better visualize areas of neoplasm using fluorescence imaging. Over the last two years, two molecular optical contrast agents received U.S. Food and Drug Administration approval, and several more drugs are now on the horizon. Thus a conference was organized at the University of Pennsylvania to bring together oncologic surgeons from different specialties to discuss the current clinical status of IMI trials with a specific focus on phase 2 and phase 3 studies. In addition, phase 1 and experimental trials were also discussed briefly, to highlight other novel techniques. Our review summarizes the discussions from the conference and delves into the types of cancers discussed, different contrast agents in human trials, and the clinical value being studied.
Journal Article