Dynamic hierarchies in temporal directed networks

The outcome of interactions in many real-world systems can be often explained by a hierarchy between the participants. Discovering hierarchy from a given directed network can be formulated as follows: partition vertices into levels such that, ideally, there are only forward edges, that is, edges from upper levels to lower levels. In practice, the ideal case is impossible, so instead we minimize some penalty function on the backward edges. One practical option for such a penalty is agony, where the penalty depends on the severity of the violation. In this paper we extend the definition of agony to temporal networks. In this setup we are given a directed network with time stamped edges, and we allow the rank assignment to vary over time. We propose 2 strategies for controlling the variation of individual ranks. In our first variant, we penalize the fluctuation of the rankings over time by adding a penalty directly to the optimization function. In our second variant we allow the rank change at most once. We show that the first variant can be solved exactly in polynomial time while the second variant is NP-hard, and in fact inapproximable. However, we develop an iterative method, where we first fix the change point and optimize the ranks, and then fix the ranks and optimize the change points, and reiterate until convergence. We show empirically that the algorithms are reasonably fast in practice, and that the obtained rankings are sensible

Platinum-Gallium (Pt-Ga) Intermetallic Alloys for Propane Dehydrogenation

Natural gas is a source of energy for the United States. The Center for Innovative Strategic Transformation of Alkane Resources (CISTAR) plans to use shale gas extracted from shale rock formations as a bridge fuel to replace coal and oil while the US transitions to renewable energy like solar and wind. After methane, the largest components in shale gas are light alkanes such as ethane and propane. These can be catalytically converted to olefins, which can be further reacted to produce fuels, for example. Olefins from alkanes can be accomplished by dehydrogenation by promoted platinum alloys. This study compares the structure and chemical properties of Pt-Ga alloys on silica (SiO2) and ceria (CeO2) supports to determine if the support plays an important role in this chemistry. The catalysts containing different Pt:Ga ratios were synthesized using incipient wetness impregnation. These catalysts were characterized by in situ X-ray diffraction (XRD) and X-ray adsorption spectroscopy (XAS) to determine if an alloy was formed, and if so, the structure of that alloy. Finally, the catalysts were tested in a fixed bed reactor, where it was found that the silica-supported Pt-Ga alloy has a selectivity of \u3e90% towards propylene. Understanding catalyst design can lead to higher catalytic conversion of substances and potentially an improved selectivity for the formation of preferred products. Pt-Ga on ceria is tested for comparison and there appears to behave differently from that on silica demonstrating the importance of the role of the support on these catalysts

Knowledge Levels, Attitude and Beliefs of Men towards the Digital Rectal Examinations (DRE): A study in Trinidad

Background: Trinidad and Tobago have been ranked as having one of the highest cancer mortality rates in the Caribbean. Prostate cancer was identified as the most common cancer in men, with a higher mortality than any other cancer. At least 1 in 9 men in Trinidad and Tobago will be diagnosed with prostate cancer during his lifetime. Purpose: The purpose of this study is to determine knowledge levels, attitudes, and beliefs of men aged 40 years and over regarding digital rectal examination (DRE). The investigators considered this crucial following the scourge of prostate cancer in Trinidad and Tobago and an apparent lack of the use of the DRE, a noted method of screening for the condition for early detection. Methods: A cross-sectional descriptive study was undertaken using 216 men who were at least 40 years old and who gave their informed consent; these men were attending a central mall in Trinidad in the month of April 2018 when the data was collected. Data was collected using the researchers’ designed, self-administered questionnaire and analysed using SPSS version 20. Result: Results indicate that most men (95.8%) are knowledgeable/very knowledgeable about DRE. Similarly, most (64.6%) of the men have favourable/very favourable attitudes towards DRE while 59.3% of them indicated that their beliefs have little or major influence regarding their participation in DRE. It also showed that the men’s beliefs are associated with their ethnicity (pDiscussion/Recommendation/Conclusion: The findings suggest that perhaps the attitudes and beliefs of men aged 40 years and over attending this mall are better predictors of intentions than their knowledge. This needs to be explored further given the need to curb the prevalence of prostate cancer amongst men in Trinidad and Tobago

Breeding young as a survival strategy during earth’s greatest mass extinction

Studies of the effects of mass extinctions on ancient ecosystems have focused on changes in taxic diversity, morphological disparity, abundance, behaviour and resource availability as key determinants of group survival. Crucially, the contribution of life history traits to survival during terrestrial mass extinctions has not been investigated, despite the critical role of such traits for population viability. We use bone microstructure and body size data to investigate the palaeoecological implications of changes in life history strategies in the therapsid forerunners of mammals before and after the Permo-Triassic Mass Extinction (PTME), the most catastrophic crisis in Phanerozoic history. Our results are consistent with truncated development, shortened life expectancies, elevated mortality rates and higher extinction risks amongst post-extinction species. Various simulations of ecological dynamics indicate that an earlier onset of reproduction leading to shortened generation times could explain the persistence of therapsids in the unpredictable, resource-limited Early Triassic environments, and help explain observed body size distributions of some disaster taxa (e.g., Lystrosaurus). Our study accounts for differential survival in mammal ancestors after the PTME and provides a methodological framework for quantifying survival strategies in other vertebrates during major biotic crises

Book Reviews

Book reviews of: William F. Winter and the New Mississippi: A Biography. By Charles C. Bolton Jackson: University Press of Mississippi, 2013. Pp. vii, 368. Illustrations, map, acknowledgements, notes, index. $35.00 cloth. ISBN: 9781617037870. Born of Conviction: White Methodists and Mississippi’s Closed Society. By Joseph T. Reiff. (New York: Oxford University Press, 2016. Acknowledgements, illustrations, map, notes, index. Pp. xxi, 384.$35 Hardcover. ISBN: 9780190246815). In Katrina’s Wake: The U.S. Coast Guard and the Gulf Coast Hurricanes of 2005. By Donald L. Canney. (Gainesville: University Press of Florida, 2010. Foreword, notes, index. Pp. xv, 228. $27.50 cloth.) Slavery, Race and Conquest in the Tropic: Lincoln, Douglas and the Future of America. By Robert E. May. (New York: Cambridge University Press, 2013. Acknowledgements, illustrations, maps, notes, index. Pp. xi, 296.$80 cloth, $26.99 paper,$22 e-book. ISBN: 9780521132527.) Rivers of Sand: Creek Indian Emigration, Relocation, and Ethnic Cleansing in the American South. By Christopher D. Haveman. (Nebraska: University of Nebraska Press, 2016. Illustrations, preface, acknowledgments, notes on terminology, index. Pp. ix, 414. Trouble in Goshen: Plain Folk, Roosevelt, Jesus, and Marx in the Great Depression. By Fred C. Smith (Jackson: University Press of Mississippi, 2014. Acknowledgements, illustrations, map notes, index. Pp. xi, 214. $60.00 cloth. ISBN: 9781617039560.) Builders of a New South: Merchants, Capital, and the Remaking of Natchez, 1865-1914. By Aaron D. Anderson (Jackson: University Press of Mississippi, 2013. Acknowledgments, illustrations, photographs, notes, graphics, index. Pp. 279.$40 cloth. ISBN: 978-1- 61703-667-5.) Adventurism and Empire: The Struggle for Mastery in the Louisiana- Florida Borderlands 1762-1803. By David Narrett. (Chapel Hill: The University of North Carolina Press, 2015. Acknowledgements, illustrations, notes, index. Pp. xi, 365. $45 cloth,$44.99 e-book. ISBN: 978-1-4696-1833-3.) Empty Sleeves: Amputation in the Civil War South. By Brian Craig Miller. (Athens: University of Georgia Press, 2015. Illustrations, acknowledgments, appendix, notes, index. Pp. xvi, 257. $79.95 cloth,$29.95 paper. ISBN: 0820343327.) Signposts: New Directions in Southern Legal History. By Sally E. Hadden and Patricia Hagler Minter, eds. (Athens and London: The University of Georgia Press, 2013. Acknowledgements, illustrations, index. Pp. xi, 480. $69.95 cloth,$26.95 paper, $26.95 ebook. ISBN: 978-0-8203-4499-7.) The Color of Christ: The Son of God and the Saga of Race in America. By Edward J. Blum and Paul Harvey. (Chapel Hill: University of North Carolina Press, 2012. Pp. 325.$32.50 Cloth. ISBN: 9780807835722.

Red Queen Coevolution on Fitness Landscapes

Species do not merely evolve, they also coevolve with other organisms. Coevolution is a major force driving interacting species to continuously evolve ex- ploring their fitness landscapes. Coevolution involves the coupling of species fit- ness landscapes, linking species genetic changes with their inter-specific ecological interactions. Here we first introduce the Red Queen hypothesis of evolution com- menting on some theoretical aspects and empirical evidences. As an introduction to the fitness landscape concept, we review key issues on evolution on simple and rugged fitness landscapes. Then we present key modeling examples of coevolution on different fitness landscapes at different scales, from RNA viruses to complex ecosystems and macroevolution.Comment: 40 pages, 12 figures. To appear in "Recent Advances in the Theory and Application of Fitness Landscapes" (H. Richter and A. Engelbrecht, eds.). Springer Series in Emergence, Complexity, and Computation, 201

No silver bullet for digital soil mapping: country-specific soil organic carbon estimates across Latin America.

Country-specific soil organic carbon (SOC) estimates are the baseline for the Global SOC Map of the Global Soil Partnership (GSOCmap-GSP). This endeavor is key to explaining the uncertainty of global SOC estimates but requires harmonizing heterogeneous datasets and building country-specific capacities for digital soil mapping (DSM).We identified country-specific predictors for SOC and tested the performance of five predictive algorithms for mapping SOC across Latin America. The algorithms included support vector machines (SVMs), random forest (RF), kernel-weighted nearest neighbors (KK), partial least squares regression (PL), and regression kriging based on stepwise multiple linear models (RK). Country-specific training data and SOC predictors (5 x 5 km pixel resolution) were obtained from ISRIC - World Soil Information. Temperature, soil type, vegetation indices, and topographic constraints were the best predictors for SOC, but country-specific predictors and their respective weights varied across Latin America. We compared a large diversity of country-specific datasets and models, and were able to explain SOC variability in a range between ~ 1 and ~ 60 %, with no universal predictive algorithm among countries. A regional (n = 11 268 SOC estimates) ensemble of these five algorithms was able to explain ~ 39% of SOC variability from repeated 5-fold cross-validation.We report a combined SOC stock of 77.8 +- 43.6 Pg (uncertainty represented by the full conditional response of independent model residuals) across Latin America. SOC stocks were higher in tropical forests (30 +- 16.5 Pg) and croplands (13 +- 8.1 Pg). Country-specific and regional ensembles revealed spatial discrepancies across geopolitical borders, higher elevations, and coastal plains, but provided similar regional stocks (77.8 +- 42.2 and 76.8 +- 45.1 Pg, respectively). These results are conservative compared to global estimates (e.g., SoilGrids250m 185.8 Pg, the Harmonized World Soil Database 138.4 Pg, or the GSOCmap-GSP 99.7 Pg). Countries with large area (i.e., Brazil, Bolivia, Mexico, Peru) and large spatial SOC heterogeneity had lower SOC stocks per unit area and larger uncertainty in their predictions. We highlight that expert opinion is needed to set boundary prediction limits to avoid unrealistically high modeling estimates. For maximizing explained variance while minimizing prediction bias, the selection of predictive algorithms for SOC mapping should consider density of available data and variability of country-specific environmental gradients. This study highlights the large degree of spatial uncertainty in SOC estimates across Latin America. We provide a framework for improving country-specific mapping efforts and reducing current discrepancy of global, regional, and country-specific SOC estimates

Compilation and Network Analyses of Cambrian Food Webs

A rich body of empirically grounded theory has developed about food webs—the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple “niche model,” which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body plans, and trophic roles during the Cambrian radiation. More research is needed to explore the generality of food-web structure through deep time and across habitats, especially to investigate potential mechanisms that could give rise to similar structure, as well as any differences