Polar optical phonons in core-shell semiconductor nanowires

We obtain the the long-wavelength polar optical vibrational modes of semiconductor core-shell nanowires by means of a phenomenological continuum model. A basis for the space of solutions is derived, and by applying the appropriate boundary conditions, the transcendental equations for the coupled and uncoupled modes are attained. Our results are applied to the study of the GaAs-GaP core-shell nanowire, for which we calculate numerically the polar optical modes, analyzing the role of strain in the vibrational properties of this nanosystem

Identification, geo-hydromorphological assessment and the state of degradation of the southernmost blanket bogs in Europe

Blanket bogs are a globally rare type of ombrotrophic peatland internationally recognised for long-term terrestrial carbon storage, the potential to serve as carbon sinks and habitat provision. The majority of recognised areas of this habitat in Europe are found in the United Kingdom and Ireland, but the rarer examples found in Spain represent the southernmost continental edge-of-range. However, gaps in the peatland inventory suggest that a number of blanket bogs in the Cantabrian Mountains (northern Spain) are not recognised and are at increased threat of loss. This study identifies and provides geo-hydromorphological classification for 14 unrecorded blanket bogs and one protected blanket bog located between the administrative regions of Cantabria and Castilla y León. Peat depth surveys and carbon analysis of peat cores were used to determine the amount of carbon stored within the newly identified blanket bogs and the current rate, and drivers, of peatland degradation were examined using remote sensing techniques. A total extent of blanket bog covering 44.45 ha (>40 cm peat depth) containing more than 500,000 m3 of peat and an estimated 44.88 ± 3.31 kt C was mapped. Approximately 30.8% of the surface of blanket bogs examined was exposed peat, and even in the protected site, exposed peat surfaces are losing a minimum of 1.7 t C m-2 yr-1. The presence of livestock in unprotected sites is increasing the rate of erosion by over five times, and without protection exposed peat surfaces are releasing as much as 3.84 t C m-2 yr-1. The peatlands identified in this research extend the known limit of blanket bogs in Europe farther south than previously recorded and represent 10.5% of blanket bog currently recognised and protected in Spain. The range of anthropogenic pressures currently acting on peatlands in the Cantabrian Mountains, specifically livestock and windfarms, indicates that without protection these important landforms and stored carbon may be lost. An urgent update of European peatland inventories is thus required to preserve these valuable carbon stores and potential carbon sinks

The potential of geospatial technology for monitoring peatland environments

There have been significant advances in the spectral and spatial resolution of data collected from spaceborne, airborne and terrestrial based geospatial technologies over the past 20 years. In sensitive peatland ecosystems, the non-intrusive application of these technologies offers great potential to improve vegetation monitoring and topographical mapping. This paper discusses the potential of geospatial technologies for monitoring vegetation, mapping natural erosion features and assessing artificial drainage with reference to two peatland sites in England. Earth Observation (EO) data can now provide colour imagery with spatial resolution comparable to conventional aerial photography. Enhanced spectral resolution of spaceborne sensors has also increased the accuracy of automated image classification for bog vegetation and EO data may challenge the relevance of conventional aerial photography in landscape-scale assessment. Ultra-high resolution data achievable from Unmanned Aerial Vehicle (UAV) and Terrestrial Laser Scanner (TLS) technologies are providing unprecedented levels of detail from remote sensing. UAV imagery now provides the possibility of identifying individual plants which greatly increases a researcher’s ability to map vegetation from aerial imagery. UAV derived elevation data, combined with the capability of TLS, provide enhanced resolution of gully and artificial drain morphology compared to airborne LiDAR and allow a new approach for quantifying erosion. These technologies provide opportunities to extend traditional surveys over far larger areas than was previously possible and can assist both in targeting areas for future restoration and in monitoring of subsequent change. Traditional survey methods will however maintain an important role in assessing many aspects of peatlands, as they not only provide information to verify remotely sensed data, but are currently the only method that can ‘see’ underneath peatland vegetation

Heating Strategies in Cellulose Pyrolysis as an Alternative For Targeting Energy Efficient Product Distribution

Energy generation and platform chemicals production from biomass are a potential route towards an oil-free economy. Pyrolysis is one of the key technologies for transforming biomass into both fuels and chemicals. However, pyrolysis is a complex and energy-intensive process, and optimizing the operation for reducing its energy requirements is critical for the design of competitive biorefineries. This work presents a model to describe cellulose pyrolysis based on mass, energy and momentum conservation of solid and gaseous species. Lumped and detailed kinetic models are used to investigate how heating conditions impact pyrolysis product distribution. The resulting complex system was solved using gPROMS. Results suggest that pyrolysis mainly occurs in the boundary of the modelled particles. The developed model presents flexibility to use lumped and detailed kinetic models and provided both a general perspective of the pyrolysis process and detailed information on product distribution. Using this model, the results show that an initial high heating rate, followed by a lower heating rate, could reduce energy requirements by 10 % without changing the product distribution. There is also a trade-off between the yield of high added-value products, such as levoglucosan, and the overall energy requirement

Coleópteros hipogeos protegidos o que requieren medidas de conservación en Cataluña

Coleòpters hipogeus protegits o que requereixen mesures de conservació a Catalunya La fauna hipogea es caracteritza per una estreta adaptació a les condicions adverses del domini subterrani. Tal grau d’especialització, però, fa que esdevingui especialment vulnerable a l’alteració del seu hàbitat. En l’àmbit de Catalunya hi ha diferents normes legislatives per a la conservació d’invertebrats amenaçats. De fet, bona part de les espècies de coleòpters incloses en el Decret 328/1992, del Pla d’Espais d’Interès Natural, (PEIN) o en el futur Catàleg de la Fauna Amenaçada de Catalunya (CFAC) estan associades al domini subterrani. El present treball recopila la normativa aplicable i altres documents relatius a la protecció de la fauna de coleòpters hipogeus de Catalunya. S’hi aporten dades faunístiques i biogeogràfiques actualitzades, així com la informació disponible sobre l’estat de conservació de les espècies considerades, la majoria endemismes circumscrits a una àrea reduïda. Finalment, es comenten breument els resultats del seguiment d’algunes d’aquestes espècies portat a terme durant els últims anys pel Departament d’Artròpodes del Museu de Ciències Naturals de Barcelona, en col·laboració amb l’Associació Catalana de Biospeleologia.Species of hypogean beetles that are protected or that require conservation measures  in Catalonia Hypogean species are characterized by their good  adaptation  to the adverse conditions of their subterranean habitats. Such specialization, however, makes them particularly vulnerable to alterations in their habitat. In the Autonomous Community of Catalonia, several legislative tools have been developed to  protect  threatened invertebrates and most  beetle species included in Decree 328/1992 protecting Areas of Natural Interest in Catalonia (PEIN) or considered in the future decree on the protection of Catalan invertebrates (CFAC) are linked to subterranean habitats. In the present revision we compile regulations and other documents relating to the protection of beetle hypogean fauna in Catalonia.  We provide updated faunistic and biogeographic data as well as information on the conservation status of the species, most of which are endemisms confined to a small area. Some of these species have been monitored in recent years by the Arthropod Department of the Natural Sciences Museum of Barcelona (in collaboration with the Catalan Biospeleology Association) and the results of these studies are briefly discussed.La fauna hipogea se caracteriza por una estrecha adaptación a las condiciones adversas del dominio subterráneo. Tal grado de especialización, sin embargo, hace que resulte especialmente vulnerable a las alteraciones de su hábitat. En el ámbito de Cataluña existen diferentes normas legislativas para la conservación de invertebrados amenazados. De hecho, gran parte de las especies de coleópteros contempladas en el Decreto 328/1992, del Plan de Espacios de Interés Natural (PEIN), o en el futuro Catálogo de la Fauna Amenazada de Cataluña (CFAC) están asociadas al dominio subterráneo. El presente trabajo recopila la normativa aplicable y otros documentos relativos a la protección de la fauna de coleópteros hipogeos de Cataluña. Se aportan datos faunísticos y biogeográficos actualizados, así como la información disponible sobre el estado de conservación de las especies consideradas, la mayoría endemismos circunscritos a un área reducida. Por último, se comentan brevemente los resultados del seguimiento de algunas de estas especies realizado durante los últimos años por el Departamento de Artrópodos del Museo de Ciencias Naturales de Barcelona, en colaboración con la Asociación Catalana de Biospeleología

Conductance of carbon nanotubes with disorder: A numerical study

We study the conductance of carbon nanotube wires in the presence of disorder, in the limit of phase coherent transport. For this purpose, we have developed a simple numerical procedure to compute transmission through carbon nanotubes and related structures. Two models of disorder are considered, weak uniform disorder and isolated strong scatterers. In the case of weak uniform disorder, our simulations show that the conductance is not significantly affected by disorder when the Fermi energy is close to the band center. Further, the transmission around the band center depends on the diameter of these zero bandgap wires. We also find that the calculated small bias conductance as a function of the Fermi energy exhibits a dip when the Fermi energy is close to the second subband minima. In the presence of strong isolated disorder, our calculations show a transmission gap at the band center, and the corresponding conductance is very small