Extinction calculations of multi-sphere polycrystalline graphitic clusters - A comparison with the 2175 AA peak and between a rigorous solution and discrete-dipole approximations

Certain dust particles in space are expected to appear as clusters of individual grains. The morphology of these clusters could be fractal or compact. In this paper we study the light scattering by compact and fractal polycrystalline graphitic clusters consisting of touching identical spheres. We compare three general methods for computing the extinction of the clusters in the wavelength range 0.1 - 100 micron, namely, a rigorous solution (Gerardy & Ausloos 1982) and two different discrete-dipole approximation methods -- MarCODES (Markel 1998) and DDSCAT (Draine & Flatau 1994). We consider clusters of N = 4, 7, 8, 27,32, 49, 108 and 343 particles of radii either 10 nm or 50 nm, arranged in three different geometries: open fractal (dimension D = 1.77), simple cubic and face-centred cubic. The rigorous solution shows that the extinction of the fractal clusters, with N < 50 and particle radii 10 nm, displays a peak within 2% of the location of the observed interstellar extinction peak at ~4.6 inverse micron; the smaller the cluster, the closer its peak gets to this value. By contrast, the peak in the extinction of the more compact clusters lie more than 4% from 4.6 inverse micron. At short wavelengths (0.1 - 0.5 micron), all the methods show that fractal clusters have markedly different extinction from those of non-fractal clusters. At wavelengths > 5 micron, the rigorous solution indicates that the extinction from fractal and compact clusters are of the same order of magnitude. It was only possible to compute fully converged results of the rigorous solution for the smaller clusters, due to computational limitations, however, we find that both discrete-dipole approximation methods overestimate the computed extinction of the smaller fractal clusters.Comment: Corrections added in accordance with suggestions by the referee. 12 pages, 12 figures. Accepted for publication in Astronomy & Astrophysic

Relation between TMAOase activity and content of formaldehyde in fillet minces and bellyflap minces from gadoid fishes

Minced fish is a significant component of a number of frozen fishery products like fish fingers, cakes and patties. Predominately minced fish is produced from gadoid species (Alaska pollack, cod, saithe, hake and others) possessing the enzyme trimethylamine oxide demethylase (TMAOase, E.C. 4.1.2.32) (Rehbein and Schreiber 1984). TMAOase catalyses the degradation of trimethylamine oxide (TMAO) to formaldehyde (FA) and dimethylamine (DMA), preferentially during frozen storage of products (Hultin 1992). In most gadoid species light muscle contains only low activity of TMAOase, the activity of red muscle and bellyflaps being somewhat higher. In contrast, the TMAOase activity in blood, kidney and other tissues, residues of which may contaminate minced fish flesh, may be higher for several orders of magnitude (Rehbein and Schreiber 1984)

Axon micro-dissection and transcriptome profiling reveals the in vivo RNA content of fully differentiated myelinated motor axons

Axonal protein synthesis has been shown to play a role in developmental and regenerative growth, as well as in the maintenance of the axoplasm in steady state. Recent studies have begun to identify the mRNAs localized in axons, which could be translated locally under different conditions. Despite that now hundreds or thousands of mRNAs have been shown to be localized into the axonal compartment of cultured neurons in vitro, knowledge of which mRNAs are localized in mature myelinated axons is quite limited. With the purpose of characterizing the transcriptome of mature myelinated motor axons of peripheral nervous system, we modified the axon micro-dissection method devised by Koenig, enabling the isolation of the axoplasm RNA to perform RNA-seq analysis. The transcriptome analysis indicates that the number of RNAs detected in mature axons is lower in comparison with in vitro data, is depleted of glial markers and enriched in neuronal markers. The mature myelinated axons are enriched for mRNAs related to cytoskeleton, translation and oxidative phosphorylation. Moreover, it was possible to define core genes present in axons when comparing our data with transcriptomic data of axons grown in different conditions. This work provides evidence that axon micro-dissection is a valuable method to obtain data at genome-wide levels of mature and myelinated axons of the peripheral nervous system, and could be especially useful for the study of axonal involvement in neurodegenerative pathologies of motor neurons such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophies (SMA). Faria

Spittlebugs: Bioecology, Host Plant Resistance and Advances in IPM

Several species and genera of spittlebugs (Homoptera: Cercopidae) are economic pests of grasses in tropical America. These insects compete with grazing animals by reducing forage availability and quality. They may cause serious losses on millions of hectares of improved pastures based on cultivars of several species of Brachiaria (signal grasses). Except for the cultivar Marandu, most of the available commercial cultivars of Brachiaria are susceptible to spittlebugs. In spite of their economic importance, much research need to be done yet. Such insect-plant system encompasses a diverse group of spittlebug species, a diverse group of forage grass species, which are under different management systems, in a broad range of ecological zones. Control efforts have been directed to host plant resistance, alternative that has been recognized as being of easy adoption and of low cost to farmers. It is probably the best control measure for controlling insect pests in low value crops, like pastures, widely established over vast areas. Screening for spittlebug resistance has been conducted both at CIAT and Embrapa-Beef Cattle Center, and promising accessions have been found. It is important however, that additional biological and behavioral studies of these insects, together with evaluations of other control techniques, like biological control and cultural practices, are also performed. Promising control measures and future research needs are discussed

Modification of titania films by chemical vapour deposition for enhanced photocatalysis

Titanium dioxide (TiO2) is the leading material for self-cleaning applications due to its intrinsic properties, such as chemical inertness, mechanical robustness, high photocatalytic activity and durability to extend photocatalytic cycling. However, its relatively wide bandgap limits its outdoor applications. There has been a strenuous effort to try and improve the photocatalytic efficiency of TiO2, in particular by modifying its electronic structure to enhance its function under solar illumination. The most commonly studied approaches for achieving this have been to incorporate anionic and/or cationic species into the TiO2 structure and the design of TiO2-based heterojunction systems. The addition of nitrogen, phosphorus and sulfur species into the matrix of TiO2 was investigated. Films were grown using atmospheric-pressure chemical vapour deposition (APCVD). The nitrogen-doped system has been investigated most prominently to enhance and extend the photocatalytic response of TiO2 materials into the visible region of the electromagnetic spectrum. Nitrogen can either replace oxygen sites (Ns, substitutional doping) or sit within the TiO2 structure (Ni, interstitial doping) and form N-O groups with lattice oxygen. Interestingly, these NOx groups, as well as NHx surface species present similar binding energies, ca. 400 eV, hindering the identification of the nitrogen species and their role in the photocatalytic response of the material. Various synthesis conditions were experimented using different nitrogen precursors (tert-butylamine, benzylamine and ammonia), which were used to establish a correlation between surface and bulk nitrogen species and the photocatalytic behaviour of the N-TiO2 films. A loss of the Ni environment (as observed by X-ray photoelectron spectroscopy), as well as a decrease in photoactivity over time was observed, suggesting a direct participation of the nitrogen species in photocatalytic iv processes. In addition to traditional CVD methods, a pulse precursor approach was used for the first time, to the best of our knowledge, to synthesise stratified N-doped TiO2 thin films, by adding nitrogen into specific regions of the N-TiO2 film. Physical and functional comparison of stratified and non-stratified N-TiO2 films with similar structural and morphological features allowed us to evaluate the benefits of this synthetic approach, which not only resulted in an increase in the photocatalytic efficiency of the stratified N-TiO2 films but also did not affect the overall crystallinity of the films. The addition of phosphorus and sulfur was investigated as the most promising alternative to the use of nitrogen doping, as both could be added to the lattice of TiO2 either as cations or anions. Through functional testing, it was found that both dopant species were beneficial from a photocatalytic point of view. Interestingly, the use of APCVD techniques to deposit P-TiO2 thin films resulted in the addition for the first time, to the best of our knowledge, of P3- species, as well as P5+, to the TiO2 structure with the relative proportion being determined by the synthesis conditions. Through Hall effect probe, photocatalytic testing and transient absorption spectroscopy (TAS) analyses, it was found that the incorporation of P3- species was detrimental from an electrical conduction and photocatalytic point of view; however, the presence of solely P5+ species resulted in P-TiO2 films with enhanced self-cleaning and TCO properties. These results provide important insights on the influence of dopant nature and its location within a semiconductor’s structure. Heterojunction semiconductor materials are used in a wide range of applications including catalysis, electronic devices, sensors and solar-to-chemical energy conversion. These materials benefit from effective electron transfer processes, electron tunnelling, surface passivation and other synergistic effects to enhance their performance beyond the individual components. By using CVD methods, two different v heterojunction systems, rutile/ anatase TiO2 and WO3/TiO2, were grown. The interposition of an amorphous TiO2-based interlayer allowed direct vapour deposition of anatase on a rutile substrate, which is otherwise hindered by templating. The subsequent crystallisation of the amorphous interlayer after annealing, allowed us to investigate the impact of an efficient interface between the two rutile-anatase phases in the photodegradation of an organic model pollutant, stearic acid. Clear evidence on the synergy between the two polymorphs and more importantly, on the charge flow across the interface, which is against much conventional understanding, was evaluated through the photoreduction of silver particles. This charge flow involves electron transfer from rutile to anatase. Likewise, a conformal coating of WO3 nanorods with TiO2 was performed using APCVD techniques. The resulting WO3/TiO2 heterojunction films showed an electron transfer phenomenon, where electrons moved from WO3 into TiO2, against widely reported observation. State-of-the-art hybrid density functional theory (DFT) and hard X-ray photoelectron spectroscopy (HAXPES) were employed to elucidate the electronic interaction at the heterojunction of the WO3 and TiO2 crystalline phases. This vectorial charge separation reduces electron-hole recombination and most likely extends the lifetime and relative population of photogenerated charges. These results provide important insights on the influence of vectorial charge separation in heterojunctions. These phenomena had a dramatic impact on the photocatalytic efficiency of the heterojunction films, which are among the very highest ever reported by a thin film

An Implemented of a Real-Time Experimental Setup for Robotic Teleoperation System

The development of this work presents the implementation of an experimental platform, which will permit to investigate on a methodology for the design and analysis of a teleoperated system, considering the delay in the communication channel. The project has been developed in partnership with the laboratory of Automatic and Robotics of the Universidad Politécnica de Madrid and the Laboratory at the Centro de Tecnologías Avanzadas de Manufactura at the Pontificia Universidad Católica del Perú. The mechanical structure of the arm that is located in the remote side has been built and the electric servomechanism has been mounted to control their movement. The experimental test of the Teleoperation system has been developed. The PC104 card commands the power interface and sensors of the DC motor of each articulation of the arm. Has developed the drives for the management of the operations of the master and the slave: send/reception of position, speed, acceleration and current data through a CAN network. The programs for the interconnection through a LAN network, between the Windows Operating System and the Real-time Operating System (QNX), has been developed. The utility of the developed platform (hardware and software) has been demonstrated

Effect of Ce substitution on the magnetoresistivity and flux pinning energy of the Bi2Sr2Ca1-x CexCu2O8+δ superconductors

In this study, the effect of Ce doping on the properties of Bi 2Sr2Ca1-x Ce x Cu2O 8+δ ceramic superconductors, with x=0.0, 0.01, 0.05, 0.1, and 0.25, has been investigated. Samples' precursors were prepared using the conventional solid state method and subsequently textured using the Laser Floating Zone technique. The magnetoresistance measurements were studied under various applied magnetic fields. The activation energies, irreversibility fields (H irr ), upper critical fields (H c2) and coherence lengths at 0 K (ξ(0)) were calculated from the resistivity versus temperature (ρ-T) curves, under DC magnetic fields up to 5 T. The thermally activated flux flow model has been applied in order to calculate the flux pinning energies. The results indicated that H c2(0) varied from 416.19 to 115 T and the flux pinning energies varied from 1.46 to 0.042 eV at 0 T. © 2013 Springer Science+Business Media New York.This work is supported by the Research Fund of Çukurova University, Adana, Turkey, under grant contracts No: FEF2011YL27 and FEF2013BAP11. A. Sotelo and M.A. Madre wish to thank the Gobierno de Aragón (Research Group T12), for financial support. M.A. Madre also acknowledges the MINECO-FEDER (Project MAT2011-22719) for funding.Peer Reviewe

Effect of Yb substitution in Bi-2212 ceramics prepared by laser floating zone technique

In the present work, the influence of Yb substitution for Bi on the structural, electrical and magnetic properties of textured Bi-2212 ceramics has been investigated. X-ray diffraction studies indicated that the major peaks correspond to the Bi-2212 phase. The SEM images clearly show that there is an increase in the number of secondary phases with raising Yb content while all samples maintain similar grain morphology. Magnetic analysis of all samples has been done by magnetic hysteresis measurements, indicating that an enhancement in the M-H loops is obtained by a low Yb doping. The critical current density of samples was calculated from the M-H curves by using Bean’s critical state model, indicating that sample with 0.05 Yb substitution possesses the highest Jc values.The authors wish to thank the Gobierno de Aragón and Fondo Social Europeo (Grupos de Investigacion Consolidados T12 and T87) and MINECO-FEDER (MAT2013-46505-C3-1-R) for financial support.Peer Reviewe

A multiple-species participatory domestication programme in the Peruvian Amazon: experiences and results to date

In 1995, the World Agroforestry Centre (ICRAF) and partners initiated a participatory agroforestry domestication programme in the Aguaytía Watershed and Alto Amazonas province of the Peruvian Amazon. The programme, aimed primarily at conservation-through-use of genetic diversity, began with formal, participatory prioritization, leading to selection of four species: bolaina blanca (Guazuma crinita Martius: Sterculiaceae),capirona (Calycophyllum spruceanum (Bentham) Hooker f. Ex Schumann)), guaba (Inga edulis C. Martius: Leguminosae (Mimosoideae)), peach palm (Bactris gasipaes Kunth: Palmae). Open-pollinated seed of each was collected from farmer-selected mother trees, and used in the establishment of a series of seedling seed orchards / progeny tests, the individual blocks of which were dispersed on lands of individual collaborating farmers. Almost ten years later these trials are beginning to produce seed, the Aguaytían famers have organized themselves into a wood and seed producers’ cooperative, the technology developed is being adopted more widely, and genetic results are becoming available. We describe the programme and its results in detail, with special emphasis on its innovative features. Subsequently, we evaluate success to date in relation both to initial objectives and the programme’s response to the evolving local forestry and development environment. Finally, we consider future priorities