Lianas Suppress Seedling Growth and Survival of 14 Tree Species in a Panamanian Tropical Forest

Lianas are a common plant growth form in tropical forests, where they compete intensely with trees, decreasing tree recruitment, growth, and survival. If the detrimental effects of lianas vary significantly with tree species identity, as is often assumed, then lianas may influence tree species diversity and community composition. Furthermore, recent studies have shown that liana abundance and biomass are increasing relative to trees in neotropical forests, which will likely magnify the detrimental effects of lianas and may ultimately alter tree species diversity, relative abundances, and community composition. Few studies, however, have tested the responses of multiple tree species to the presence of lianas in robust, well‐replicated experiments. We tested the hypotheses that lianas reduce tree seedling growth and survival, and that the effect of lianas varies with tree species identity. We used a large‐scale liana removal experiment in Central Panama in which we planted 14 replicate seedlings of 14 different tree species that varied in shade tolerance in each of 16 80 × 80 m plots (eight liana‐removal and eight unmanipulated controls; 3136 total seedlings). Over a nearly two‐yr period, we found that tree seedlings survived 75% more, grew 300% taller, and had twice the aboveground biomass in liana‐removal plots than seedlings in control plots, consistent with strong competition between lianas and tree seedlings. There were no significant differences in the response of tree species to liana competition (i.e., there was no species by treatment interaction), indicating that lianas had a similar negative effect on all 14 tree species. Furthermore, the effect of lianas did not vary with tree species shade tolerance classification, suggesting that the liana effect was not solely based on light. Based on these findings, recently observed increases in liana abundance in neotropical forests will substantially reduce tree regeneration, but will not significantly alter tropical tree species diversity, relative abundance, or community composition

FDI and Domestic Investment: An Industry-Level View

Previous empirical work on the link between domestic and foreign investment provides mixed results which partly depend on the level of aggregation of the data. We argue that the aggregated home country implications of foreign direct investment (FDI) cannot be gauged using firm-level data. Aggregated data, in turn, miss channels through which domestic and foreign activities interact. Instead, industry-level data provide useful information on the link between domestic and foreign investment. We theoretically show that the effects of FDI on the domestic capital stock depend on the structure of industries and the relative importance of domestic and multinational firms. Our model allows distinguishing intra-sector competition from inter-sector linkage effects. We test the model using data on German FDI. Using panel cointegration methods, we find evidence for a positive long-run impact of FDI on the domestic capital stock and on the stock of inward FDI. Effects of FDI on the domestic capital stock are driven mainly by intrasector effects. For inward FDI, inter-sector linkages matter as well

Financial Constraints and the Margins of FDI

Recent literature on multinational firms has stressed the importance of low productivity as a barrier to the cross-border expansion of firms. But firms may also need external finance to shoulder the costs of entering foreign markets. We develop a model of multinational firms facing real and financial barriers to foreign direct investment (FDI), and we analyze their im-pact on the FDI decision (the extensive margin) and foreign affiliate sales (the intensive margin). We provide empirical evidence based on a detailed dataset of German multinationals which contains information on parent-level and affiliate-level financial constraints as well as on the location the foreign affiliates. We find that financial factors constrain firms’ foreign investment decisions, an effect felt in particular by large firms. Financial constraints at the parent level matter for the extensive, but less so for the intensive margin. For the intensive margin, financial constraints at the affiliate level are relatively more important

FDI and Domestic Investment: An Industry-Level View

Previous empirical work on the link between domestic and foreign investment provides mixed results which partly depend on the level of aggregation of the data. We argue that the aggregated home country implications of foreign direct investment (FDI) cannot be gauged using firm-level data. Aggregated data, in turn, miss channels through which domestic and foreign activities interact. Instead, industry-level data provide useful information on the link between domestic and foreign investment. We theoretically show that the effects of FDI on the domestic capital stock depend on the structure of industries and the relative importance of domestic and multinational firms. Our model allows distinguishing intra-sector competition from inter-sector linkage effects. We test the model using data on German FDI. Using panel cointegration methods, we find evidence for a positive long-run impact of FDI on the domestic capital stock and on the stock of inward FDI. Effects of FDI on the domestic capital stock are driven mainly by intrasector effects. For inward FDI, inter-sector linkages matter as well.foreign direct investment; domestic capital stock

Model for the unidirectional motion of a dynein molecule

Cytoplasmic dyneins transport cellular organelles by moving on a microtubule filament. It has been found recently that depending on the applied force and the concentration of the adenosine triphosphate (ATP) molecules, dynein's step size varies. Based on these studies, we propose a simple model for dynein's unidirectional motion taking into account the variations in its step size. We study how the average velocity and the relative dispersion in the displacement vary with the applied load. The model is amenable to further extensions by inclusion of details associated with the structure and the processivity of the molecule.Comment: 10 pages, 5 figure

Exports Versus FDI Revisited: Does Finance Matter?

This paper explores the impact of financial constraints on the internationalization strategies of firms. It contributes to the literature by focusing on three aspects: First, the paper studies the impact of financial constraints on exporting relative to FDI. Consistent with theory, the empirical results confirm that the impact of financial constraints is stronger for FDI than for exporting. Second, the paper analyzes the extensive and the intensive margins and finds that financial frictions matter for both. Third, the paper explores the impact on manufacturing as compared to service industries and shows that firms in service industries are affected more than firms in manufacturing. The paper also identifies a threshold effect: Financial constraints do not matter for small firms whose productivity seems to be too low to consider international expansions

Exports versus FDI revisited: does finance matter?

The crisis on international financial markets that started in 2007 has shown the potential links between the financial sector and the real economy. Exports and foreign direct investment (FDI) have declined, presumably not only because of a lack of demand, but also because of restricted access of firms to external finance. In this paper, we explore the impact of access to external finance on firms' choices to export or to engage in FDI. We simultaneously model a firm's decision to engage in FDI and in exports, and we assess the importance of financial factors for this choice (the extensive margin) as well as for the volume of activities (the intensive margin). We find that financial frictions matter, in particular for the decision to engage internationally. --Multinational firms,exports versus FDI,financial constraints,heterogeneity,productivity

Higgs-regularized three-loop four-gluon amplitude in N=4 SYM: exponentiation and Regge limits

We compute the three-loop contribution to the N=4 supersymmetric Yang-Mills planar four-gluon amplitude using the recently-proposed Higgs IR regulator of Alday, Henn, Plefka, and Schuster. In particular, we test the proposed exponential ansatz for the four-gluon amplitude that is the analog of the BDS ansatz in dimensional regularization. By evaluating our results at a number of kinematic points, and also in several kinematic limits, we establish the validity of this ansatz at the three-loop level. We also examine the Regge limit of the planar four-gluon amplitude using several different IR regulators: dimensional regularization, Higgs regularization, and a cutoff regularization. In the latter two schemes, it is shown that the leading logarithmic (LL) behavior of the amplitudes, and therefore the lowest-order approximation to the gluon Regge trajectory, can be correctly obtained from the ladder approximation of the sum of diagrams. In dimensional regularization, on the other hand, there is no single dominant set of diagrams in the LL approximation. We also compute the NLL and NNLL behavior of the L-loop ladder diagram using Higgs regularization.Comment: 45 pages, 9 figures; v3: major revision (more stringent tests, discussion of order of limits in the Regge regime

Financial constraints and the margins of FDI

Recent literature on multinational firms has stressed the importance of low productivity as a barrier to the cross-border expansion of firms. But firms may also need external finance to shoulder the costs of entering foreign markets. We develop a model of multinational firms facing real and financial barriers to foreign direct investment (FDI), and we analyze their impact on the FDI decision (the extensive margin) and foreign affiliate sales (the intensive margin). We provide empirical evidence based on a detailed dataset of German multinationals which contains information on parent-level and affiliate-level financial constraints as well as about the location the foreign affiliates. We find that financial factors constrain firms’ foreign investment decisions, an effect felt in particular by large firms. Financial constraints at the parent level matter for the extensive, but less so for the intensive margin. For the intensive margin, financial constraints at the affiliate level are relatively more important. --Multinational firms,heterogeneity,productivity,financial constraints

Slender-body theory for plasmonic resonance

We develop a slender-body theory for plasmonic resonance of slender metallic nanoparticles, focusing on a general class of axisymmetric geometries with locally paraboloidal tips. We adopt a modal approach where one first solves the plasmonic eigenvalue problem, a geometric spectral problem which governs the surface-plasmon modes of the particle; then, the latter modes are used, in conjunction with spectral-decomposition, to analyse localized-surface-plasmon resonance in the quasi-static limit. We show that the permittivity eigenvalues of the axisymmetric modes are strongly singular in the slenderness parameter, implying widely tunable, high-quality-factor, resonances in the near-infrared regime. For that family of modes, we use matched asymptotics to derive an effective eigenvalue problem, a singular non-local Sturm–Liouville problem, where the lumped one-dimensional eigenfunctions represent axial voltage profiles (or charge line densities). We solve the effective eigenvalue problem in closed form for a prolate spheroid and numerically, by expanding the eigenfunctions in Legendre polynomials, for arbitrarily shaped particles. We apply the theory to plane-wave illumination in order to elucidate the excitation of multiple resonances in the case of non-spheroidal particles