Well-defined homopolypeptides, copolypeptides, and hybrids of Poly(l-proline)

l-Proline is the only, out of 20 essential, amino acid that contains a cyclized substituted α-amino group (is formally an imino acid), which restricts its conformational shape. The synthesis of well-defined homo- and copolymers of l-proline has been plagued either by the low purity of the monomer or the inability of most initiating species to polymerize the corresponding N-carboxy anhydride (NCA) because they require a hydrogen on the 3-N position of the five-member ring of the NCA, which is missing. Herein, highly pure l-proline NCA was synthesized by using the Boc-protected, rather than the free amino acid. The protection of the amine group as well as the efficient purification method utilized resulted in the synthesis of highly pure l-proline NCA. The high purity of the monomer and the use of an amino initiator, which does not require the presence of the 3-N hydrogen, led for the first time to well-defined poly(l-proline) (PLP) homopolymers, poly(ethylene oxide)-b-poly(l-proline), and poly(l-proline)-b-poly(ethylene oxide)-b-poly(l-proline) hybrids, along with poly(γ-benzyl-l-glutamate)-b-poly(l-proline) and poly(Boc-l-lysine)-b-poly(l-proline) copolypeptides. The combined characterization (NMR, FTIR, and MS) that results for the l-proline NCA revealed its high purity. In addition, all synthesized polymers exhibit high molecular and compositional homogeneity

Corporate financial leverage and M&As choices: evidence from the shipping industry

High capital intensity and reliance on debt financing are among the most prominent characteristics of the shipping industry. The corporate finance literature has documented that beyond a certain threshold, leverage can hamper a firm’s ability to raise capital, and as a result, have a bearing on its corporate investment policy. The new, more restrictive, financing landscape in the shipping sector has put the management of capital structure on the spotlight as a key driver of investment policy, financial health, and thus, firm success. In this paper, we examine for the first time the link between the financing policy of shipping companies and their corporate investment decisions. We focus on the impact of deviations from target capital structure on mergers and acquisitions (M&A); an increasingly important corporate growth vehicle for shipping companies, with directly measurable outcomes. Deviations from optimal leverage display a strong association with the likelihood to consummate acquisitions, deal size, the financing method as well as the M&A outcome. Higher debt levels are shown to have a negative effect on acquisitiveness and a positive effect on the quality of corporate investment; a pattern with direct policy implications for shipping companies, their management teams, and shareholders

Individual-based simulation of the spatial and temporal dynamics of macroinvertebrate functional groups provides insights into benthic community assembly mechanisms

The complexity and scales of the processes that shape communities of marine benthic macroinvertebrates has limited our understanding of their assembly mechanisms and the potential to make projections of their spatial and temporal dynamics. Individual-based models can shed light on community assembly mechanisms, by allowing observed spatiotemporal patterns to emerge from first principles about the modeled organisms. Previous work in the Rance estuary (Brittany, France) revealed the principal functional components of its benthic macroinvertebrate communities and derived a set of functional relationships between them. These elements were combined here for the development of a dynamic and spatially explicit model that operates at two spatial scales. At the fine scale, modeling each individual’s life cycle allowed the representation of recruitment, inter- and intra-group competition, biogenic habitat modification and predation mortality. Larval dispersal and environmental filtering due to the tidal characteristics of the Rance estuary were represented at the coarse scale. The two scales were dynamically linked and the model was parameterized on the basis of theoretical expectations and expert knowledge. The model was able to reproduce some patterns of α- and β-diversity that were observed in the Rance estuary in 1995. Model analysis demonstrated the role of local and regional processes, particularly early post-settlement mortality and spatially restricted dispersal, in shaping marine benthos. It also indicated biogenic habitat modification as a promising area for future research. The combination of this mechanism with different substrate types, along with the representation of physical disturbances and more trophic categories, could increase the model’s realism. The precise parameterization and validation of the model is expected to extend its scope from the exploration of community assembly mechanisms to the formulation of predictions about the responses of community structure and functioning to environmental change

Equity premium prediction: The role of information from the options market

This paper examines the role of information from the options market in forecasting the equity premium. We provide empirical evidence that the equity premium is predictable out-of-sample using a set of CBOE strategy benchmark indices as predictors. We use a range of econometric approaches to generate point, quantile and density forecasts of the equity premium, and we find that models based on option variables consistently outperform the historical average benchmark. In addition to statistical gains, using option predictors results in substantial economic benefits for a mean-variance investor, delivering up to a fivefold increase in certainty equivalent returns over the benchmark during the 1996-2021 sample period

The Antiangiogenic Properties of Adipose-Derived Mesenchymal Stem/Stromal Cells in Corneal Neovascularization in a Rabbit Model

The purpose was to study the anti-angiogenic effect of adipose-derived mesenchymal stem/stromal cells (ADMSCs) on experimentally induced corneal injuries. Corneal neovascularization (NV) was induced by incising and subsequently suturing the corneal surface in 32 New Zealand rabbits. Following suturing, the rabbits were randomly allocated into 2 groups, and received either phosphate-buffered saline (PBS) (control) or ADMSCs, both administered via three different routes. Digital images of the cornea were obtained two weeks post-incision to measure the area of neovascularized cornea. Tumor necrosis factor (TNF) was immunohistochemically assessed in the both groups. The corneal tissue was evaluated for vascular endothelial growth factor (VEGF). The extent of corneal NV in all eyes was assessed photographically by an independent observer. Fourteen days after the incisions, the degree of corneal NV was substantially decreased in the ADMSC-treated group (1.87 ± 0.9 mm2, 1.4 % ± 0.67 % of corneal surface) compared to the control and PBS-treated group (4.66 ± 1.74 mm2, 3.51 % ± 1.31 %, p < 0.001). ADMSCs significantly decreased injury-induced corneal NV in New Zealand rabbits two weeks post-treatment. This strategy has potential for use in the control of corneal NV in vivo.Â

The Antiangiogenic Properties of Adipose-Derived Mesenchymal Stem/Stromal Cells in Corneal Neovascularization in a Rabbit Model

The purpose was to study the anti-angiogenic effect of adipose-derived mesenchymal stem/stromal cells (ADMSCs) on experimentally induced corneal injuries. Corneal neovascularization (NV) was induced by incising and subsequently suturing the corneal surface in 32 New Zealand rabbits. Following suturing, the rabbits were randomly allocated into 2 groups, and received either phosphate-buffered saline (PBS) (control) or ADMSCs, both administered via three different routes. Digital images of the cornea were obtained two weeks post-incision to measure the area of neovascularized cornea. Tumor necrosis factor (TNF) was immunohistochemically assessed in the both groups. The corneal tissue was evaluated for vascular endothelial growth factor (VEGF). The extent of corneal NV in all eyes was assessed photographically by an independent observer. Fourteen days after the incisions, the degree of corneal NV was substantially decreased in the ADMSC-treated group (1.87 ± 0.9 mm2, 1.4 % ± 0.67 % of corneal surface) compared to the control and PBS-treated group (4.66 ± 1.74 mm2, 3.51 % ± 1.31 %, p < 0.001). ADMSCs significantly decreased injury-induced corneal NV in New Zealand rabbits two weeks post-treatment. This strategy has potential for use in the control of corneal NV in vivo.

Climate change and ecological intensification of agriculture in sub-Saharan Africa-A systems approach to predict maize yield under push-pull technology

Assessing effects of climate change on agricultural systems and the potential for ecological intensification to increase food security in developing countries is essential to guide management, policy-making and future research. 'Push-pull' technology (PPT) is a poly-cropping design developed in eastern Africa that utilizes plant chemicals to mediate plant-insect interactions. PPT application yields significant increases in crop productivity, by reducing pest load and damage caused by arthropods and parasitic weeds, while also bolstering soil fertility. As climate change effects may be species-and/or context-specific, there is need to elucidate how, in interaction with biotic factors, projected climate conditions are likely to influence future functioning of PPT. Here, we first reviewed how changes in temperature, precipitation and atmospheric CO2 concentration can influence PPT components (i.e., land use, soils, crops, weeds, diseases, pests and their natural enemies) across sub-Saharan Africa (SSA). We then imposed these anticipated responses on a landscape-scale qualitative mathematical model of maize production under PPT in eastern Africa, to predict cumulative, structure-mediated impacts of climate change on maize yield. Our review suggests variable impacts of climate change on PPT components in SSA by the end of the 21st century, including reduced soil fertility, increased weed and arthropod pest pressure and increased prevalence of crop diseases, but also increased biological control by pests' natural enemies. Extrapolating empirical evidence of climate effects to predict responses to projected climate conditions is mainly limited by a lack of mechanistic understanding regarding single and interactive effects of climate variables on PPT components. Model predictions of maize yield responses to anticipated impacts of climate change in eastern Africa suggest predominantly negative future trends. Nevertheless, maize yields can be sustained or increased by favourable changes in system components with less certain future behaviour, including higher PPT adoption, preservation of field edge density and agricultural diversification beyond cereal crops

Models of natural pest control : Towards predictions across agricultural landscapes

Natural control of invertebrate crop pests has the potential to complement or replace conventional insecticide based practices, but its mainstream application is hampered by predictive unreliability across agroecosystems. Inconsistent responses of natural pest control to changes in landscape characteristics have been attributed to ecological complexity and system-specific conditions. Here, we review agroecological models and their potential to provide predictions of natural pest control across agricultural landscapes. Existing models have used a multitude of techniques to represent specific crop-pest-enemy systems at various spatiotemporal scales, but less wealthy regions of the world are underrepresented. A realistic representation of natural pest control across systems appears to be hindered by a practical trade-off between generality and realism. Nonetheless, observations of context-sensitive, trait-mediated responses of natural pest control to land-use gradients indicate the potential of ecological models that explicitly represent the underlying mechanisms. We conclude that modelling natural pest control across agroecosystems should exploit existing mechanistic techniques towards a framework of contextually bound generalizations. Observed similarities in causal relationships can inform the functional grouping of diverse agroecosystems worldwide and the development of the respective models based on general, but context-sensitive, ecological mechanisms. The combined use of qualitative and quantitative techniques should allow the flexible integration of empirical evidence and ecological theory for robust predictions of natural pest control across a wide range of agroecological contexts and levels of knowledge availability. We highlight challenges and promising directions towards developing such a general modelling framework.Peer reviewe

Modélisations des mécanismes généraux d'assemblage des communautés pour simuler la dynamique spatio-temporelle de la biodiversité benthique

Benthic macroinvertebrates are part of a complex network of interactions. The spatial and temporal scales of the processes that form the basis for these interactions have traditionally restricted their empirical investigation. The first chapter of the manuscript attempts a review of the modelling tools that have been employed for the study of the marine benthos.The implementation of a mechanistic modelling framework seems fitting, but it requires the derivation of a few model entities with a clear functional role. The second chapter of the manuscript employs the emergent group hypothesis to do that in a way that is objective and testable. The resulting grouping is tested against theoretical expectations and the results support its ability to represent functional diversity in the Rance estuary.The lack of knowledge for the attribution of relationships among functional components is still important. The third chapter of the manuscript addresses this issue based on ecological theories that predict the existence of functional trade-offs operating at both large and small spatial scales. In a first inception of the system, these elements are incorporated in the form of general rules of interaction into qualitative models of the functional groups.In spite of the interest in developing and analysing qualitative models, the goal of studying the dynamic and spatially explicit behaviour of benthic biodiversity can only be reached by a model with the same characteristics. The fourth chapter of the manuscript presents the architecture of an individual-based model, primarily transferring the rules of interaction from the qualitative models to a dynamic and spatially explicit framework.Les macroinvertébrés benthiques entretiennent un ensemble complexe d’interactions. Les échelles spatiales et temporelles des processus formant la base de ces interactions ont traditionnellement limité leur étude empirique. Le premier chapitre du manuscrit tente une revue des outils de modélisation utilisés dans l’étude du benthos marin.Même si l’implémentation d’un modèle mécaniste semble s’ajuster aux communautés benthiques, son utilisation nécessite la création d’un nombre limité d’entités avec un rôle fonctionnel clair. Le second chapitre du manuscrit utilise l’hypothèse des groupes émergents, afin de faire cela via une procédure objective et testable. Le groupement est testé face aux postulats théoriques et les résultats supportent sa capacité à reproduire la diversité fonctionnelle dans l’estuaire de la Rance.Le manque de connaissances dans l’attribution des relations entre les composantes fonctionnelles reste important. Le troisième chapitre du manuscrit s’inscrit dans ce besoin, basé sur des théories écologiques qui prévoient l’existence de trade-offs fonctionnels opérant à grande et petite échelle. Dans un premier temps, ces éléments sont incorporés dans des modèles qualitatifs des groupes fonctionnels.Malgré l’intérêt du développement et de l’analyse de modèles qualitatifs, le but d’étudier la dynamique et le comportement spatialement explicite de la biodiversité ne peut être atteint que par un modèle avec ces mêmes caractéristiques. Le quatrième chapitre du manuscrit présente l’architecture d’un modèle individu-centré, en mettant l’accent sur le transfert des règles d’interactions des modèles qualitatifs vers un cadre dynamique et spatialement explicite