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Two new species of Canthidium Erichson, 1847 (Coleoptera: Scarabaeidae: Scarabaeinae) from Mexico are described: Canthidium nebularum Moctezuma, Sánchez-Huerta, and Halffter, new species; and C. chimalapense Moctezuma and Halffter, new species. An updated key for the North American species is included, with a brief discussion on taxonomic and biogeographic relevance of the new taxa.
Endemic insular species are particularly vulnerable to anthropogenic threats. The fish-eating bat Myotis vivesi is restricted mainly to the islands of the Gulf of California in Mexico and although several aspects of its biology have been studied there are no recent accounts of its current distribution. We conducted several expeditions during 2001–2016 to verify the current geographical distribution of this bat, and to record the presence of introduced predators. We identified the localities in which maternity colonies occur, estimated the size of the bat population on Partida Norte Island in 2003, and monitored bat presence on this island during 2004–2016. We found fish-eating bats on 36 islands and maternity colonies on 19 islands. Introduced rats Rattus rattus or cats Felis catus were captured on seven islands where the bats were present, and on five islands where they were absent. We estimated a population of c. 30,000 fish-eating bats in May 2003 and we confirmed the species’ presence on Partida Norte Island during 2004–2016. Based on the information compiled from our surveys and previous studies, we discuss the adequacy of the species’ current categorization as Vulnerable on the IUCN Red List, and its conservation status conferred by Mexican conservation authorities.
This paper is focused on explaining the radiation test in temperature performed on the Engineering and Qualification Model of the Medium Gain Antenna Radiofrequency (MGA-RFA) Assembly of ESA's BepiColombo mission. The goal of this program is to observe and study Mercury and its surroundings in a very demanding environment in terms of temperature and radiation. The MGA is an X-band two-axis steerable horn, which provides bidirectional communications between spacecraft and Earth as backup of the High Gain Antenna and also operates as primary communication link at several mission stages or conditions. The paper presents the measurement set-up for the qualification campaign of the antenna, where it was necessary to characterize the antenna in a representative thermal environment, and the results obtained from this test. Results of test up to 150°C show how gain and radiation pattern shapes are slightly affected by thermal stress, but without jeopardizing mission requirements. In addition, by analyzing correlation of this test with RF analysis in the same thermal conditions, it becomes possible to accurately extrapolate the MGA-RFA behavior up to temperatures of more than 500°C. This fact allowed the successful space qualification of this model.
In this paper, we propose a new family of premium calculation principles based on the use of prior information from different sources. Under this framework and based on the use of Ordered Weighted Averaging operators, we provide alternative collective and Bayes premiums and describe some approaches to efficiently compute them. Several examples are detailed to illustrate the performance of the new methods.
We study the second-order invariants of a Lorentzian surface in ℝ2,2, and the curvature hyperbolas associated with its second fundamental form. Besides the four natural invariants, new invariants appear in some degenerate situations. We then introduce the Gauss map of a Lorentzian surface and give an extrinsic proof of the vanishing of the total Gauss and normal curvatures of a compact Lorentzian surface. The Gauss map and the second-order invariants are then used to study the asymptotic directions of a Lorentzian surface and discuss their causal character. We also consider the relation of the asymptotic lines with the mean directionally curved lines. We finally introduce and describe the quasi-umbilic surfaces, and the surfaces whose four classical invariants vanish identically.
A micro heteregenous reprocessed fuel spiked with thorium in a PWR fuel element considering (TRU-Th) cycle was simulated using three different configurations and different fissile materials that varied from 6.0% to 7.0%. The reprocessed fuels were obtained using the ORIGEN 2.1 code from a burned PWR standard fuel (33,000 MWd/tHM burned), with 3.1% of initial enrichment, which was remained in the cooling pool for five years and then reprocessed using UREX+ technique. The keff and plutonium generation during the burnup were evaluated and compared with the standard fuel. This study was performed using the SCALE 6.0.
ZnO thin films were deposited using the DC pulsed magnetron sputtering technique to study how composition and structure influences their magnetic properties. Low sputtering powers and high substrate temperatures were used to increase adatom mobility during deposition, resulting in increased crystallite size and reduced residual stress in the films. Another set of ZnO films were Mn-doped using a second magnetron gun and the amount of doping was changed by controlling the RF sputtering power. For these films, the crystallite size increased with the amount of Mn. The magnetic properties of these materials were counterintuitive; not intentionally doped ZnO showed the highest magnetization and magnetization decreased with increasing Mn concentration.
Dynamic mechanical properties of polypropylene (PP) and grafted polypropylene (PP-g-MA) composites reinforced with acetylated wheat straw fibers (WSF) is reported in this work. The materials were prepared with different fiber particle sizes (40, 80 and 140 U.S. mesh) and at different fiber contents (5, 10 and 15 wt.%). The PP and PP-g-MA composites, where anhydride maleic (MA) was used as coupling agent, were obtained using a twin-screw extruder; whereas an injection-molding machine molded the composite pellets into testing specimens. To observe the morphology of the composites, micrographs were taken with an optical microscope. The Dynamic mechanical properties were analyzed using a torsional rheometer. The morphological analysis showed a high porous structure somehow similar to foamed materials. The storage modulus (G′) increased by increasing the fiber content, and decreased with fiber particle sizes for the PP composites. Meanwhile, the use of the coupling agent additive promoted a modulus increase due to higher fiber-polymer interaction, from better adhesion and chemical bonds formation between the fibers-coupling agent-PP.
This paper presents a systematic approach to compute the angularity and the axiality indices for a Schönflies parallel manipulator. Angularity index may be considered as a measure of the sensitivity of the mobile platform to changes in rotation, while axiality index can be used to measure the sensitivity of the OP of the mobile platform to changes in translation. Since both indices were inspired by very fundamental concepts of classical kinematics (angular velocity vector and helicoidal velocity field), they offer a clear and simple physical meaning, which may be useful to the designer of parallel manipulators. Moreover, both dexterity indices do not require obtaining a dimensionally homogeneous Jacobian matrix, nor do they depend on having similar types of actuators in each manipulator's leg. Detailed numerical examples are given in order to illustrate the computation of the dexterity indices.
Currently, the research team is systematically studying the oxide compounds present in the ternary system In2O3-TiO2-MgO in order to analyze its thermoluminescent (TL) response. The oxide Mg1.5InTi0.5O4 present in this system was synthesized by a solid state reaction at 1350 °C in air. The X-ray powder diffraction pattern showed a spinel-type structure for this compound. In this work, this spinel, as well as its TL properties when exposed to beta particles, are being reported for the first time. The glow curve is simple and wide with a TL maximum located at 203 °C at 21.33 Gy. The peak shows a shift to lower temperatures and it increases its intensity, as the irradiation dose increases. The lineal behavior was observed between 10.66 to 341 Gy, and no saturation signs were observed. The relative sensitivity variation was 2.7% and standard deviation after ten consecutive irradiation - TL readout cycles was 1 %. The minimum detectable dose was 5.65 Gy for this spinel-type oxide . These results suggest the possible application of Mg1.5InTi0.5O4 in dosimetry.
Recently, the research team synthesized some scandium- and titanium-based oxide compounds, in order to analyze their thermoluminescent (TL) response [1-2]. The oxides mixture Sc2TiO5:Eu2Ti2O7:Sc2O3 was synthesized in equilibrium phase by solid state reaction at 1100 °C / 48 h. The structural characterization was performed by XRD and SEM. The TL properties of this oxide mixture were examined after exposing it to gamma radiation from a 60Co source. The glow curve showed two main glow peaks at 151 °C and 260 °C, yet the curve shape looks quite complex, revealing that it is composed by overlapped individual TL peaks, which was confirmed with the Tstop preheat method performed . The linear dose-response between 150 to 600 Gy was obtained, followed by a slow saturation stage. The intensity of the glow curves increases as the radiation dose increases, and their maxima remain at the same temperature values, which indicates that the TL phenomenon follows first-order kinetics . After ten irradiation-TL readout cycles at 500 Gy, good stability (SD 2.02 %) between TL integrated response and the exposure dose was found. It is concluded that Sc2TiO5:Eu2Ti2O7:Sc2O3 is a promising material to use as high-dose dosimeter.
An alternative approach for reduction of interface traps density at 4H-SiC/SiO2 interface is proposed. Silicon nitride / silicon oxide stack was deposited on p-type 4H-SiC (0001) epilayers and subsequently over-oxidized. The electrical characterization of the interface was done by employing metal-oxide semiconductor (MOS) devices, inversion-channel MOS devices and lateral MOS field effect transistors (MOSFETs).
Several studies have shown that qualitative (binary) ant-plant networks are highly nested in tropical environments, in which specialist species (with fewer interactions) are connected with generalists (with the most interactions) in cohesive subgroups. Interactions occur in both qualitative and quantitative networks, however, how their frequency may structure the nestedness in ecological networks involving these organisms is, we believe, unknown. Based on this perspective, we used nestedness analysis to address the effect of interaction frequency on ant-plant networks (n = 14 networks). Unlike binary networks, quantitative networks are often significantly non-nested. In addition, species with a higher interaction frequency have a higher number of links, indicating that these species are possibly more abundant and/or competitive. Moreover, different biological parameters can change the nature of ant-plant interactions, as a plant can be a good resource for one ant and a ‘bad’ resource for another. Thus, this suggests a new perspective for the study of interaction networks in the tropics, since species with lower interaction frequency are not necessarily subsets of species with higher frequency, and consequently generate the non-nested pattern in quantitative networks.
In this paper, an experimental study aimed at achieving better control of the deposition patterns of carbon nanotubes (CNTs) is presented. CNTs were grown on a long of reactor by the catalytic chemical vapor deposition (CVD) of a benzene/ferrocene solution at 1073 K. The deposition patterns on the substrate were controlled for process times and carrier gas flow rates. In order to investigate the reaction mechanism and production rate for the growth of CNTs in catalyst CVD, computational fluid dynamics (CFD) model was developed in this study. Then the computational model was integrated with the dynamic model to optimize the process parameters formulating a correlation between turbulence, deposition rate for the growth of carbon nanotubes and parameters as process time and carrier gas flow rate. Scanning electron microscopes (SEM) are used to characterize carbon nanotubes products.
We analysed the effect of a hurricane on a plant–ant network and on vegetation cover. Plant cover was sampled using linear sampling in several vegetation types: deciduous forest, a dry forest, sand dune pioneers, sand dune scrub, ecotone of freshwater marsh, deciduous forest and dune scrub, and mangrove forest. We sampled ant–plant interactions and vegetation cover before and after Hurricane Karl hitting (September 2010) the central coast of the state of Veracruz, Mexico. The pre-hurricane network consisted of 16 plant and 25 ant species in 52 associations. The post-hurricane network consisted of 17 plant and 20 ant species in 56 associations. We found a significant decrease in the total linear cover of EFN-bearing plants between October 2009 (646 m, no hurricane effect) and October 2010 (393 m, after hurricane Karl) (total sample length 2025 m). Both networks were significantly nested (0.999 and 0.973, P < 0.001), suggesting that network topology remained similar. Our results show changes in several network characteristics and species proportions. The number of plant species that contributed to nestedness vs. idiosyncratic species did not differ significantly in the pre-hurricane network, while the number of plant species that contributed to nestedness vs. idiosyncratic species did differ significantly in the post-hurricane network. The number of ant species that contributed to nestedness vs. idiosyncratic species differed significantly in the pre-hurricane network, and also in the post-hurricane network. Differences in nestedness contributions of species before and after the hurricane reflect an alteration from a generalized, highly nested, more stable pre-disturbance network, to a more low-degree or specialized network (i.e. fewer interactions among generalist species, those species with the most associations). The maintenance of important core components of the network after a huge disturbance, suggests a short-term resilience typical of mutualistic networks.
Lead is an engineering material used mainly in the manufacturing of lead-acid batteries for the automotive industry. Lead recovery from exhausted batteries is carried out by the pyrometallurgical route by injecting sulfur the powder reagent through a lance into the lead bath. In this work a mathematical simulation was carried out on the copper drossing process with the software COMSOL 3.4. A kinetic study of the injection process of the lance-kettle system was carried out. The copper concentration profiles were obtained according with the injection rate of the particles. The best conditions for the copper drossing process were an injection rate of 3.31 m/s at 380°C. The modeling results were validated with experimental results obtaining good agreement.
Aluminum films were deposited from a high purity aluminum source by the self-ion assisted technique onto oxidized silicon wafers with TiN sub-layers. The ions were accelerated toward the substrate by potentials of 0, 3 and 6 kV. The films were patterned into strips 670 μm long and 8 μm wide using photo-lithographic procedures and wet etching. Average drift velocities were measured in the films tested under electromigration conditions. Electromigration activation energy was obtained for the films. It was found that electromigration activation energy increased with the acceleration potential. The strength of the (111) fiber texture, however, decreased with the acceleration potential. Therefore, the weaker textures resulted in higher electromigration activation energies. These results can be explained in terms of grain boundary structure, which controls electromigration behavior. By using orientation imaging microscopy to characterize the structures, it was shown that the weaker textured specimens contained a high fraction of low angle and low diffusivity grain boundaries.
We have prepared organic-inorganic hybrid materials (OIHM), incorporating an organic phase in the inorganic precursor sol, using high power ultrasound for assistance with agitation. A sono-ormosil results after gelation. Colloidal silica particles have been added to these hybrids to enable network porous volume and pore radius to be tailored to specific requirements. Finally, in vitro bioactivity of this material has been promoted by adding calcium to the initial sol. The structure and bioactivity of these materials have been subjected to preliminary study, including their mechanical behaviour. These materials have a very fine structure especially after colloidal silica particles have been included. When immersed in a solution simulating blood plasma, they are bioactive, and the sample with colloid particles presents a better behaviour in vitro
The covalent immobilization of crude lipases within silica-based macroporous frameworks have been performed by combining sol-gel process, concentrated direct emulsion, lyotropic mesophase and post-synthesis functionalizations. The as-synthesized open cell hybrid monoliths exhibit high macroscopic porosity, around 90 %, providing interconnected scaffold while reducing the diffusion low kinetic issue. The entrapment of enzymes in such foams deals with a high stability over esterification and transesterification batch process catalysis.
Magnetic entropy change and refrigerant capacity have been determined for a field change of 20 kOe around the second-order magnetic transition of austenite in as-quenched Ni51.1Mn31.2In17.7 alloy ribbons produced by melt spinning technique. Samples crystallize in a single-phase austenite with the highly ordered L21-type crystal structure and a Curie temperature of 275 K. The material shows a maximum magnetic entropy change of ΔSMmax= - 1.7 Jkg-1K-1, an useful working temperature range of 78 K (δTFWHM) and a refrigerant capacity of RC=132 Jkg-1 (RC= │ΔSMmax│ x δTFWHM). The considerable RC value obtained together with the fabrication via a single-step process make austenitic Ni-Mn-In ribbons of potential interest as magnetic refrigerants for room temperature magnetic refrigeration.