ECOSYSTEM ENGINEERING AND ENVIRONMENTAL CONTEXT: THE IMPACT OF LEAFTYING CATERPILLARS AND FOLIAGE QUALITY ON THE ARTHROPOD COMMUNITY ASSOCIATED WITH WHITE OAK (Quercus alba L.)

In this study, I investigated how ecosystem engineering by leaftying caterpillars and foliage quality affect the arthropod community associated with white oak (Quercus alba L.). In Chapter 1, I review the literature on ecosystem engineering, shelter building caterpillars, and foliage quality. I examine the origins of the concept of ecosystem engineering, the controversies surrounding it, and the current framework. I review previous studies on shelter building caterpillars, with a special emphasis on those studies performed on oaks. In addition, I review the components of foliage quality in oaks and how these components can influence arthropods, including ecosystem engineers. In Chapter 2, I present the results of a study designed to determine the impact of leaftying caterpillars as ecosystem engineers and foliage quality on the arthropod community associated with white oak. I found that the presence of leaftying caterpillars significantly impacted arthropod communities by altering community structure and increasing arthropod diversity. In addition, I found that the impact of leaftying caterpillars on the arthropod community varied between host plants of different quality, suggesting that environmental context can have an influence on the community impacts of ecosystem engineering

Structuring cooperative nuclear risk reduction initiatives with China

The Stanford Center for International Security and Cooperation engaged several Chinese nuclear organizations in cooperative research that focused on responses to radiological and nuclear terrorism. The objective was to identify joint research initiatives to reduce the global dangers of such threats and to pursue initial technical collaborations in several high priority areas. Initiatives were identified in three primary research areas: 1) detection and interdiction of smuggled nuclear materials; 2) nuclear forensics; and 3) radiological (“dirty bomb”) threats and countermeasures. Initial work emphasized the application of systems and risk analysis tools, which proved effective in structuring the collaborations. The extensive engagements between national security nuclear experts in China and the U.S. during the research strengthened professional relationships between these important communities.Project on Advanced Systems and Concepts for Countering Weapons of Mass Destruction (PASCC)Grant Number N00244-14-I-003

Computer assisted proof of transverse saddle-to-saddle connecting orbits for first order vector fields

In this paper we introduce a computational method for proving the existence of generic saddle-to-saddle connections between equilibria of first order vector fields. The first step consists of rigorously computing high order parametrizations of the local stable and unstable manifolds. If the local manifolds intersect, the Newton–Kantorovich theorem is applied to validate the existence of a so-called short connecting orbit. If the local manifolds do not intersect, a boundary value problem with boundary values in the local manifolds is rigorously solved by a contraction mapping argument on a ball centered at the numerical solution, yielding the existence of a so-called long connecting orbit. In both cases our argument yields transversality of the corresponding intersection of the manifolds. The method is applied to the Lorenz equations, where a study of a pitchfork bifurcation with saddle-to-saddle stability is done and where several proofs of existence of short and long connections are obtained

Projected impacts of climate and land use changes on the habitat of Atlantic Forest plants in Brazil

Aim: To provide novel evidence on the average impact of climate and land use changes on habitat suitability for tropical plants and to test previous conclusions on the relative importance of these two drivers in shaping future availability of habitat for tropical plant species. Location: Brazil’s Atlantic Forest domain. Time period: Plant occurrences recorded between 1960 and 2014. Baseline climate from 1960 to 2000 and land use from 2015. Projected scenarios of climate for 2041–2060 and land use for 2050. Major taxa studied: Angiosperms. Methods: We modelled the habitat suitability of 2,232 species of angiosperms from the Atlantic Forest domain, endemic to Brazil, and estimated how future climate and land use may affect species-level habitat suitability under a moderate and a business-as-usual scenario for the year 2050. Results: Our results suggest that climate change alone will, surprisingly, have only a modest negative impact on the mean habitat suitability, decreasing it by 2% (median = −5 to −7%, variation associated with scenarios). Land use change alone had a more consistent negative impact on habitat suitability, causing mean and median reductions of 4 to 6%. When the effects of climate and land use are combined, the mean habitat suitability was reduced by 4% (median = −9 to −11%). Main conclusions: The combined impacts of climate and land use changes were substantial, although smaller than expected. Habitat suitability decreased for most species, but it increased substantially for some species, suggesting that the distribution of impacts across species is markedly right skewed. The impacts were typically detrimental to small-ranged species and neutral or beneficial to widespread species. Land use change rather than climate change will likely cause more losses to the habitat of Atlantic Forest plant species within the next several decades

Wargames as Data: Addressing the Wargamer's Trilemma

Policymakers often want the very best data with which to make decisions--particularly when concerned with questions of national and international security. But what happens when this data is not available? In those instances, analysts have come to rely on synthetic data-generating processes--turning to modeling and simulation tools and survey experiments among other methods. In the cyber domain, where empirical data at the strategic level are limited, this is no different--cyber wargames are quickly becoming a principal method for both exploring and analyzing the security challenges posed by state and non-state actors in cyberspace. In this chapter, we examine the design decisions associated with this method.Comment: 3 figure

Did Uranus' regular moons form via a rocky giant impactor?

The formation of Uranus' regular moons has been suggested to be linked to the origin of its enormous spin axial tilt (~98^o). A giant impact between proto-Uranus and a 2-3 M_Earth impactor could lead to a large tilt and to the formation of an impact generated disc, where prograde and circular satellites are accreted. The most intriguing features of the current regular Uranian satellite system is that it possesses a positive trend in the mass-distance distribution and likely also in the bulk density, implying that viscous spreading of the disc after the giant impact plays a crucial role in shaping the architecture of the final system. In this paper, we investigate the formation of Uranus' satellites by combining results of SPH simulations for the giant impact, a 1D semi-analytic disc model for viscous spreading of the post-impact disc, and N-body simulations for the assembly of satellites from a disc of moonlets. Assuming the condensed rock (i.e., silicate) remains small and available to stick onto the relatively rapid growing condensed water-ice, we find that the best case in reproducing the observed mass and bulk composition of Uranus' satellite system is a pure-rocky impactor with 3 M_Earth colliding with the young Uranus with an impact parameter b = 0.75. Such an oblique collision could also naturally explain Uranus' large tilt and possibly, its low internal heat flux. The giant impact scenario can naturally explain the key features of Uranus and its regular moons. We therefore suggest that the Uranian satellite system formed as a result of an impact rather than from a circumplanetary disc.Comment: Accepted for publication in Icaru

Diverse migration tactics of fishes within the large tropical Mekong River system

Fish often migrate to feed, reproduce and seek refuge from predators and prevailing environmental conditions. As a result, migration tactics often vary among species based on a diversity of life history needs, although variation within species is increasingly being recognised as important to population resilience. In this study, within- and among-species diversity in life history migratory tactics of six Mekong fish genera was examined using otolith microchemistry to explore diadromous and potamodromous traits. Two species were catadromous and one species was an estuarine resident, while the remaining three species were facultative in their migration strategies, with up to four tactics within a single species. Migrant and resident contingents co-existed within the same species. Management, conservation and mitigation strategies that maintain connectivity in large tropical rivers, such as effective fishway design, should consider a diversity of migration tactics at the individual level for improved outcomes

Dihydropyrimidine Accumulation Is Required for the Epithelial-Mesenchymal Transition

It is increasingly appreciated that oncogenic transformation alters cellular metabolism to facilitate cell proliferation, but less is known about the metabolic changes that promote cancer cell aggressiveness. Here, we analyzed metabolic gene expression in cancer cell lines and found that a set of high-grade carcinoma lines expressing mesenchymal markers share a unique 44 gene signature, designated the “mesenchymal metabolic signature” (MMS). A FACS-based shRNA screen identified several MMS genes as essential for the epithelial-mesenchymal transition (EMT), but not for cell proliferation. Dihydropyrimidine dehydrogenase (DPYD), a pyrimidine-degrading enzyme, was highly expressed upon EMT induction and was necessary for cells to acquire mesenchymal characteristics in vitro and for tumorigenic cells to extravasate into the mouse lung. This role of DPYD was mediated through its catalytic activity and enzymatic products, the dihydropyrimidines. Thus, we identify metabolic processes essential for the EMT, a program associated with the acquisition of metastatic and aggressive cancer cell traits.United States. National Institutes of Health (RO1 CA103866)United States. National Institutes of Health (AI047389)United States. National Institutes of Health (K99 CA168940)American Cancer Society (PF-12-099-01-TGB)American Cancer Society (PF-13-356-01-TBE)United States. Department of Defense (BC123066)United States. National Institutes of Health (CA112967)United States. National Institutes of Health (ES015339

Changing asset endowments and smallholder participation in higher value markets: Evidence from certified coffee producers in Nicaragua

This paper examines the capacities of smallholders in Nicaragua to exploit new linkages to certified coffee markets following the coffee crisis. Data on livelihood assets were collected from 292 households, which were clustered to test how differences in outcomes (asset building) reflect variations in initial asset endowments. The results suggest that most households built particular elements of their asset base and increased their resilience to future shocks. However, households struggled to make effective use of the gains for intensifying their livelihoods. Of the least-endowed households, few made investments in the scale or productivity of coffee, and most continued to depend heavily on subsistence production and seasonal off-farm income for survival. In conclusion, improved market access alone, even under relatively favorable market conditions and with considerable external support, will have uncertain impacts on rural poverty if the underlying constraints on household assets and investments are not addressed concurrently