Contribution of Lianas to Plant Area Index and Canopy Structure in A Panamanian Forest

Lianas are an important component of tropical forests, where they reduce tree growth, fecundity, and survival. Competition for light from lianas may be intense; however, the amount of light that lianas intercept is poorly understood. We used a large-scale liana-removal experiment to quantify light interception by lianas in a Panamanian secondary forest. We measured the change in plant area index (PAI) and forest structure before and after cutting lianas (for 4 yr) in eight 80 m × 80 m plots and eight control plots (16 plots total). We used ground-based LiDAR to measure the 3-dimensional canopy structure before cutting lianas, and then annually for 2 yr afterwards. Six weeks after cutting lianas, mean plot PAI was 20% higher in control vs. liana removal plots. One yr after cutting lianas, mean plot PAI was ~17% higher in control plots. The differences between treatments diminished significantly 2 yr after liana cutting and, after 4 yr, trees had fully compensated for liana removal. Ground-based LiDAR revealed that lianas attenuated light in the upper- and middle-forest canopy layers, and not only in the upper canopy as was previously suspected. Thus, lianas compete with trees by intercepting light in the upper- and mid-canopy of this forest

New Eunicellin-Type Diterpenes from the Panamanian Octocoral Briareum Asbestinum

Gorgonian octocorals are considered a prolific source of secondary metabolites with a wide range of biological activities, including anti-inflammatory activity. In particular, the genus Briareum is known for producing a wealth of diterpenes with complex chemical structures. The chemical study of the methanolic extract of Briareum asbestinum collected in Bocas del Toro, on the Caribbean side of Panama, led to the isolation of three new eunicellin-type diterpenes: briarellin T (1), asbestinin 27 (2), asbestinin 28 (3) and the previously described asbestinin 17 (4). The structures of the new compounds were determined by extensive NMR analyses and HRMS. Anti-inflammatory activity assays showed a significant reduction of the pro-inflammatory cytokines TNF-α, IL-6, IL-1β and IL-8 as well as a downregulation of COX-2 expression in LPS-stimulated THP-1 macrophages. These findings support the potential use of these marine compounds as therapeutic agents in the treatment of inflammatory diseases

The transmission of US shocks to Latin America

I study whether and how US shocks are transmitted to eight Latin American countries. US shocks are identified using sign restrictions and treated as exogenous with respect to Latin American economies. Posterior estimates for individual and average effects are constructed. US monetary shocks produce significant fluctuations in Latin America, but real demand and supply shocks do not. Floaters and currency boarders display similar output but different inflation and interest rate responses. The financial channel plays a crucial role in the transmission. US disturbances explain important portions of the variability of Latin American macrovariables, producing continental cyclical fluctuations and, in two episodes, destabilizing nominal exchange rate effects. Policy implications are discussed.Shocks, inflation

Comparing MapReduce and pipeline implementations for counting triangles

A generalized method to define the Divide & Conquer paradigm in order to have processors acting on its own data and scheduled in a parallel fashion. MapReduce is a programming model that follows this paradigm, and allows for the definition of efficient solutions by both decomposing a problem into steps on subsets of the input data and combining the results of each step to produce final results. Albeit used for the implementation of a wide variety of computational problems, MapReduce performance can be negatively affected whenever the replication factor grows or the size of the input is larger than the resources available at each processor. In this paper we show an alternative approach to implement the Divide & Conquer paradigm, named pipeline. The main features of pipeline are illustrated on a parallel implementation of the well-known problem of counting triangles in a graph. This problem is especially interesting either when the input graph does not fit in memory or is dynamically generated. To evaluate the properties of pipeline, a dynamic pipeline of processes and an ad-hoc version of MapReduce are implemented in the language Go, exploiting its ability to deal with channels and spawned processes. An empirical evaluation is conducted on graphs of different sizes and densities. Observed results suggest that pipeline allows for the implementation of an efficient solution of the problem of counting triangles in a graph, particularly, in dense and large graphs, drastically reducing the execution time with respect to the MapReduce implementation.Peer ReviewedPostprint (published version

Comparing MapReduce and pipeline implementations for counting triangles

A common method to define a parallel solution for a computational problem consists in finding a way to use the Divide and Conquer paradigm in order to have processors acting on its own data and scheduled in a parallel fashion. MapReduce is a programming model that follows this paradigm, and allows for the definition of efficient solutions by both decomposing a problem into steps on subsets of the input data and combining the results of each step to produce final results. Albeit used for the implementation of a wide variety of computational problems, MapReduce performance can be negatively affected whenever the replication factor grows or the size of the input is larger than the resources available at each processor. In this paper we show an alternative approach to implement the Divide and Conquer paradigm, named dynamic pipeline. The main features of dynamic pipelines are illustrated on a parallel implementation of the well-known problem of counting triangles in a graph. This problem is especially interesting either when the input graph does not fit in memory or is dynamically generated. To evaluate the properties of pipeline, a dynamic pipeline of processes and an ad-hoc version of MapReduce are implemented in the language Go, exploiting its ability to deal with channels and spawned processes. An empirical evaluation is conducted on graphs of different topologies, sizes, and densities. Observed results suggest that dynamic pipelines allows for an efficient implementation of the problem of counting triangles in a graph, particularly, in dense and large graphs, drastically reducing the execution time with respect to the MapReduce implementation.Peer ReviewedPostprint (published version

Letter and Recollections of Alexander Agassiz: The 1891 Albatross Expedition

Presented here is another in the list of historic accounts of iconic research cruises of the USFC Steamer Albatross, this a reminiscence of the renowned scientist Alexander Agassiz edited by his son G. R. Agassiz, a chapter from the volume “Letters and Recollections of Alexander Agassiz,” published in 1913. Agassiz made three major cruises in the Albatross in 1891, 1899–1900, and 1904–05, adding greatly to the world’s store of specimens and knowledge of thalasography, his favored term for oceangraphy, and specifically of the Pacific Ocean. Having made important cruises and studies with the Blake in the Caribbean, he sought to do comparable research in the Pacific. His opportunity came in 1890, and with the consent of President Benjamin Harrison, he took charge of this Albatross research cruise, paying much of the expense himself. In contrast with the other ships he had been on, he found the laboratories, equipment, and furnishings to be comparatively luxurious and extremely well appointed for his work. Further, the Albatross was then captained by Lieutenant Commander Zera Luther Tanner who seemed to take as much interest in the oceanographic research as did the scientists, and Agassiz appreciated working with him, too. Little of the original text has been altered, and readers are cautioned that some of the views expressed may reflect unfortunate prejudices of that era toward individuals, nationalities, etc

New militarism, the media and the manufacture of warfare 1982-1991: the implications for peace journalism theory and practice

This article highlights the emergence of a distinctly new kind of militarism in the 1980s - in which the mainstream media played a crucial role

Biodiversity shapes tree species aggregations in tropical forests

Spatial patterns of conspecific trees are considered as the consequences of biological interactions and environmental influences. They also reflect species interactions in plant communities. However, biological attributes are often neglected while deliberating the factors shaping species distributions. As rising attentions are paid to spatial patterns of tropical forest trees, we noticed that seven Center of Tropical Forest Sites and four Forest Dynamic Plots in Asia and America have presented analogously high proportions of species with aggregated conspecific individuals coincidently. This phenomenon is distinctive and repudiates fundamental ecology hypotheses which suggested dispersed distributions of conspecific tropical trees due to intensive density and natural enemy pressures in tropical forests. We believe that similar aggregation patterns shared by these tropical forests implies the existence of structuring forces in biogeographical scale instead of habitat heterogeneity in local community scales as scientists have considered. To approach the factors contributing to this cross-continent spatial pattern of trees, we obtained and reviewed ecosystem attributes, including topography, temperature, precipitation, biodiversity, density, and biomass, of these forests. Here we show that the proportions of aggregated species are actually constants independent of any ecosystem attributes regardless the nature of these tropical forests. However, local biodiversity are the major factor determining the number of aggregated species and the aggregation of large individuals of these forests. Aggregation of large trees declines along rising biodiversity, while the numbers of aggregated species increase permanently along lifting biodiversity. We propose a possible equilibrium and saturated status of the tropical forests in accommodating aggregated species. Furthermore, the tight correlations of biodiversity and species aggregation strongly imply the importance of overlooked biological interactions in shaping the spatial patterns in the tropical forests

Remembering an Invasion: The Panama Intervention in America’s Political Memory

In December of 1989, the United States launched Operation Just Cause, a military invasion of the country of Panama, capturing Manuel Noriega and overthrowing his government. This research project examines how Colin Powell, Richard Cheney, James Baker, and George H.W. Bush presented Operation Just Cause in their memoirs. It attempts to determine how these senior leaders’ depictions of this invasion incorporated it into the Bush administration’s overall foreign-policy strategy. The research finds that their general approach was to present the Panama intervention as an isolated incident which had no intentional link to other major events at the time, was not made for strategic or political gain, and was driven entirely or almost entirely by idealist reasons. These former leaders accomplished this by neglecting to connect the Panama intervention with the decline of Soviet power, painting the media as an antagonistic force which hindered the invasion rather than helped the administration’s standing, connecting the intervention to the Gulf War in incidental or only minor ways, frequently holding each other responsible for the decision to invade instead of taking responsibility themselves, and justifying it by appealing to democracy and self-defense

Latin American clubs: uncovering patterns of convergence

This paper explores the dynamics of convergence in Latin American countries and asks whether there are tendencies for converging to different clubs. The analysis shows clear differences between two groups: a large group of low-to-middle income countries and a small group of rich ountries. The club of low-to-middle income countries showed a tendency of spreading out until the mid 1990s and slight convergence afterwards. At the same time, the distance between the rich countries and the low-to-middle income countries faded away over time,particularly during the 1980s. However, during most of the 1990s, when convergence was occurring in the group of low-to-middle income countries, the rich countries started to pull away clearly distancing themselves again as a different club. The study of club behavior is important because the presence of clubs might suggest that there are common factors among groups of countries leading them to develop (and converge) in similar fashion. Identifying such common factors (if they exist) might improve our understanding of why some countries in the region grow faster than others. This is not possible to analyze with traditional growth regressions that employ a single catching up parameter or with a dispersion statistics like the sigma-convergence. Since these methods cannot detect club behavior much less they can analyze the reasons behind their formation.Convergence clubs, polarization, stratification