Optimized design and performance of a shared pump single clad 2 µm TDFA

International audienceWe report the design, experimental performance, and simulation of a single stage, co-and counter-pumped Tm-doped fiber amplifier (TDFA) in the 2 μm signal wavelength band with an optimized 1567 nm shared pump source. We investigate the dependence of output power, gain, and efficiency on pump coupling ratio and signal wavelength. Small signal gains of >50 dB, an output power of 2 W, and small signal noise figures of <3.5 dB are demonstrated. Simulations of TDFA performance agree well with the experimental data. We also discuss performance tradeoffs with respect to amplifier topology for this simple and efficient TDFA

Cultivation of trees as a way to achieve diversification for smallholdings in Nicaragua

This study was carried out in the two villages of Buena Vista and Santa Teresa, department of Jinotega in north central Nicaragua. The purpose of the study was to investigate farmers' attitudes toward timber trees and forests, and to investigate the occurrence of tree species with high timber value in the area. The study shows that people consider the forest to be important for both biological reasons and as an area for extraction of different products, among those timber is one. Today there are only a few farmers who are selling timber, and when it is done it is to some one in the neighbourhood. The study also shows that there is a lack of those tree species with the most valuable timber. On the other hand less popular tree species with good timber properties are abundant. There is a possibility to expand the use of the well-known valuable species: however, the risk is higher and the establishment more difficult than using species that exist today and regenerate in an easy way, for example the laurel, Cordia alliodora. It is possible to extend the cultivation of trees in the areas where coffee today is grown, but it is also possible to establish areas primary used for the cultivation of trees. The way that the forest act is written today makes it hard for small farmers to use their forest resource in a legal way.Este estudio es un estudio experimental hecho para conseguir información de la posibilidad de la cultivación de árboles como modo de diversificación para pequeños propietarios en Nicaragua. El trabajo en el terreno en el estudio se centró en dos puntos principales: las actitudes de los productores sobre árboles y bosques, y la existencia de árboles con las buenas características en el área. Siete productores en Buena Vista y Santa Teresa en Cuá-Bocay han entrevistado con varias veces, y los recursos de los árboles de sus fincas eran estudiados. El estudio demostró que los campesinos tienen buenos conocimientos de bosque y árboles, y también de su manejo. Saben como manejar árboles de sombra en los cafetales, aunque esta actividad no tiene como meta primaria la producción de madera. Con condiciones diferentes, que permitirían una arboricultura comercial, estos conocimientos podrían ser dirigidos a una producción de mayor escala. Los inventarios de campo mostraron una falta de especias de alta valor reconicida (caoba, cedro, granadillo y nogal), pero una presencia de especios de buena calidad pero de menor demanda (comenegro, ceiba, laurel, madero negro, maria y roble encino). Particularmente, en cafetales y bosque secundario existe una potencialidad tanto de árboles como plantas de especies atractivas, como laurel y madero negro. Una posible arboricultura futura debe ser concentrada a cafetales, rastrojos etc., y no a los residuos de bosque primario, los cuales tienen su importancia como fuente de varios productos y para la protección del agua potable. Existe una opción para los finqueros a diversificar su economía por el cultivo de árboles maderables. Hay dos alternativos: plantación de especies demanda reconocida (como caoba), ó el desarrollo de recursos de árboles y plantas ya existentes (como laurel). El primer alternativo corre un riesgo economico en caso de un fracaso de las plantaciones, mientras que el segundo ofrece ingresos más seguros por su regeneración natural. Particularmente deseo proponer una atención a las posibilidades del laurel, con su madera bella y resistente, su regeneración fácil y presencia natural en mucho de las tierras relevantes. El cultivo del laurel podría formar un componente valeroso en los sistemas agroforestales ya existentes y en la transformación de bosque secundario y de pastos de baja calidad. La solución óptima es diferente en cada finca, según los tipos de tierra y su uso corriente. En algunas zonas la población ya sufre, ó sufrirán en un futuro próximo, de una falta tanto de leña como de madera para construcción. En tales fincas la regeneración del recurso arbóreo debe ser desarrollada hacía las necesidades domésticas. Pero en otras fincas será posible cultivar y vender madera para la comunidad vecina ó, en caso del desarrollo de mecanismos de mercado, a compradores fuera del vecindad. En ambos casos, además del laurel, el madero negro representa una potencial por su capacidad de mejorar los suelos, su uso como alimento de animales, y como madera. Madera negro es común como cercas vivas en el área

Environmental identification of arbuscular mycorrhizal fungi using the LSU rDNA gene region: an expanded database and improved pipeline

Arbuscular mycorrhizal fungi (AMF; Glomeromycota) are difficult to culture; therefore, establishing a robust amplicon-based approach to taxa identification is imperative to describe AMF diversity. Further, due to low and biased sampling of AMF taxa, molecular databases do not represent the breadth of AMF diversity, making database matching approaches suboptimal. Therefore, a full description of AMF diversity requires a tool to determine sequence-based placement in the Glomeromycota clade. Nonetheless, commonly used gene regions, including the SSU and ITS, do not enable reliable phylogenetic placement. Here, we present an improved database and pipeline for the phylogenetic determination of AMF using amplicons from the large subunit (LSU) rRNA gene. We improve our database and backbone tree by including additional outgroup sequences. We also improve an existing bioinformatics pipeline by aligning forward and reverse reads separately, using a universal alignment for all tree building, and implementing a BLAST screening prior to tree building to remove non-homologous sequences. Finally, we present a script to extract AMF belonging to 11 major families as well as an amplicon sequencing variant (ASV) version of our pipeline. We test the utility of the pipeline by testing the placement of known AMF, known non-AMF, and Acaulospora sp. spore sequences. This work represents the most comprehensive database and pipeline for phylogenetic placement of AMF LSU amplicon sequences within the Glomeromycota clade

The electronic properties of a homoleptic bisphosphine Cu(I) complex: a joint theoretical and experimental insight

The origin of the optical properties of the firstly reported stable luminescent [Cu(PP)_2]^+ complex [Cu(dppb)_2]+ [dppb = 1,2-bis(diphenylphosphino) benzene] is investigated using the exchange-correlation functional PBE0. The choice of the basis set used is discussed and a comparison with the results obtained by other functionals is performed. The role played by the bisphosphine ligands within the complex is elucidated by considering the electronic properties of the ligand alone to evidence how both the geometrical changes and the electronic interactions, induced by the inclusion of the metal cation, affect the electronic behavior of the whole system. The NBO analysis shows how the aryl groups of the ligands act as a reservoir of electrons within the complex. The electronic excitations of both the complex and of the ligand, calculated by including the solvation effects, allow to assign the lowest energy absorption broad band, recorded in CH_2Cl_2 solution. The peculiar contribution of the phosphorus atoms to the description of the high occupied MOs and the participation of the copper cation to the description of the lowest singlet excited state, is pointed out. The origin of the observed phosphorescence of the complex is attributed to a triplet state, whose SOMO is characterized by the contributions of the valence 4s and of the Rydberg 5s AOs of the metal cation, along with the lone pair orbitals of the P atoms.Si sono studiate le proprieta` ottiche del primo complesso stabile e luminescente di tipo [Cu(PP}]^+ [[Cu(dppb)$_2]^+$ [dppb = 1,2-bis(difenilfosfino) benzene], riportato in letteratura utilizzando il metodo PBE0. Si e` discussa la scelta della base orbitale utilizzata nello studio e si e` effettuato un confronto con altri metodi DFT. Si e` illustrato il ruolo dei leganti bisfosfinici nel complesso esaminando come cambia la loro geometria e configurazione elettronica con l\u27inclusione del metallo per formare il complesso. Sono state studiate le eccitazioni elettroniche del complessso e del legante includendo gli effetti di solvatazione. per assegnare la prima banda di assorbimento osservata negli spettri con i campioni in soluzioni di diclorometano. Sono stati evidenziati i contributi dell\u27atomo di fosforo alla descrizione degli orbitali occupati ad alta energia del complesso e del Cu^+ a quelli virtuali a piu` bassa energia. L\u27origine della fosforescenza del complesso e` attribuita ad uno stato di tripletto il cui SOMO e` caratterizzato dagli orbitali atomici di valenza di tipo 4s e da un orbitale di Rydberg 5s di Cu^+ e dagli orbitali atomici singolarmente occupati del fosforo

Root pathogen diversity and composition varies with climate in undisturbed grasslands, but less so in anthropogenically disturbed grasslands

Soil-borne pathogens structure plant communities, shaping their diversity, and through these effects may mediate plant responses to climate change and disturbance. Little is known, however, about the environmental determinants of plant pathogen communities. Therefore, we explored the impact of climate gradients and anthropogenic disturbance on root-associated pathogens in grasslands. We examined the community structure of two pathogenic groups—fungal pathogens and oomycetes—in undisturbed and anthropogenically disturbed grasslands across a natural precipitation and temperature gradient in the Midwestern USA. In undisturbed grasslands, precipitation and temperature gradients were important predictors of pathogen community richness and composition. Oomycete richness increased with precipitation, while fungal pathogen richness depended on an interaction of precipitation and temperature, with precipitation increasing richness most with higher temperatures. Disturbance altered plant pathogen composition and precipitation and temperature had a reduced effect on pathogen richness and composition in disturbed grasslands. Because pathogens can mediate plant community diversity and structure, the sensitivity of pathogens to disturbance and climate suggests that degradation of the pathogen community may mediate loss, or limit restoration of, native plant diversity in disturbed grasslands, and may modify plant community response to climate change

Preface to the Special Issue on short pulse fiber lasers

[No abstract available

Nitrogen-fixing symbiotic bacteria act as a global filter for plant establishment on islands

Island biogeography has classically focused on abiotic drivers of species distributions. However, recent work has highlighted the importance of mutualistic biotic interactions in structuring island floras. The limited occurrence of specialist pollinators and mycorrhizal fungi have been found to restrict plant colonization on oceanic islands. Another important mutualistic association occurs between nearly 15,000 plant species and nitrogen-fixing (N-fixing) bacteria. Here, we look for evidence that N-fixing bacteria limit establishment of plants that associate with them. Globally, we find that plants associating with N-fixing bacteria are disproportionately underrepresented on islands, with a 22% decline. Further, the probability of N-fixing plants occurring on islands decreases with island isolation and, where present, the proportion of N-fixing plant species decreases with distance for large, but not small islands. These findings suggest that N-fixing bacteria serve as a filter to plant establishment on islands, altering global plant biogeography, with implications for ecosystem development and introduction risks

Conjugated Porphyrin Dimers: Cooperative Effects and Electronic Communication in Supramolecular Ensembles with C60

Two new conjugated porphyrin-based systems (dimers 3 and 4) endowed with suitable crown ethers have been synthesized as receptors for a fullerene-ammonium salt derivative (1). Association constants in solution have been determined by UVvis titration experiments in CH2Cl2 at room temperature. The designed hosts are able to associate up to two fullerene-based guest molecules and present association constants as high as 5 × 108 M‒1 . Calculation of the allosteric cooperative factor for supramolecular complexes [3·12] and [4·12] showed a negative cooperative effect in both cases. The interactions accounting for the formation of the associates are based, firstly, on the complementary ammonium-crown ether interaction and, secondly, on the π−π interactions between the porphyrin rings and the C60 moieties. Theoretical calculations have evidenced a significant decrease of the electron density in the porphyrin dimers 3 and 4 upon complexation of the first C60 molecule, in good agreement with the negative cooperativity found in these systems. This negative effect is partially compensated by the stabilizing C60-C60 interactions that take place in the more stable syn-disposition of [4·12]

Native diversity buffers against severity of non-native tree invasions

Determining the drivers of non-native plant invasions is critical for managing native ecosystems and limiting the spread of invasive species1,2. Tree invasions in particular have been relatively overlooked, even though they have the potential to transform ecosystems and economies3,4. Here, leveraging global tree databases5,6,7, we explore how the phylogenetic and functional diversity of native tree communities, human pressure and the environment influence the establishment of non-native tree species and the subsequent invasion severity. We find that anthropogenic factors are key to predicting whether a location is invaded, but that invasion severity is underpinned by native diversity, with higher diversity predicting lower invasion severity. Temperature and precipitation emerge as strong predictors of invasion strategy, with non-native species invading successfully when they are similar to the native community in cold or dry extremes. Yet, despite the influence of these ecological forces in determining invasion strategy, we find evidence that these patterns can be obscured by human activity, with lower ecological signal in areas with higher proximity to shipping ports. Our global perspective of non-native tree invasion highlights that human drivers influence non-native tree presence, and that native phylogenetic and functional diversity have a critical role in the establishment and spread of subsequent invasions.EEA Santa CruzFil: Delavaux, Camille S. Swiss Federal Institute of Technology. Institute of Integrative Biology; SuizaFil: Crowther, Thomas W. Swiss Federal Institute of Technology. Institute of Integrative Biology; SuizaFil: Zohner, Constantin M. Swiss Federal Institute of Technology. Institute of Integrative Biology; SuizaFil: Robmann, Niamh M. Swiss Federal Institute of Technology. Institute of Integrative Biology; SuizaFil: Lauber, Thomas. Swiss Federal Institute of Technology. Institute of Integrative Biology; SuizaFil: van den Hoogen, Johan. Swiss Federal Institute of Technology. Institute of Integrative Biology; SuizaFil: Kuebbing, Sara. Yale University. The Forest School at The Yale School of the Environment; Estados UnidosFil: Liang, Jingjing. Purdue University. Department of Forestry and Natural Resources; Estados UnidosFil: de-Miguel, Sergio. University of Lleida. Department of Crop and Forest Sciences; EspañaFil: de-Miguel, Sergio. Joint Research Unit CTFC–AGROTECNIO–CERCA; EspañaFil: Nabuurs, Gert-Jan. Wageningen University and Research; Países BajosFil: Peri, Pablo Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Santa Cruz; Argentina.Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina.Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Maynard, Daniel S. Swiss Federal Institute of Technology. Institute of Integrative Biology; SuizaFil: Maynard, Daniel S. University College London. Department of Genetics, Evolution, and Environment; Reino Unid