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The photodissociation rate of H2 molecules by UV photons from PN central stars is generally several orders of magnitude larger than the rate produced by the average interstellar field (Sternberg 1988, Escalante et al. 1991). Thus, in neutral envelopes of PN's, H2 molecules are destroyed quickly, and a photodissociation region forms around ionization bounded nebulae. Observations of H2 in PN's reveal that not all the hydrogen is photodissociated, and it has been suggested that this is due to the existence of dense disks around the ionized region (Zuckerman and Gatley 1988).
In cattle, reduced reproductive efficiency of beef and milk production systems is attributed to nutritional factors, health, climate changes and ultimately to genetic characteristics of animals. However, under warm humid tropics genetic variations between breeds could reduce age first calving, calving interval and increase the life of cows. Sanmartinero and Casanareño creole breeds can improve cattle production due to the contribution of genetic variants that emerged in the process of adaptation to the harsh conditions of the Colombian Orinoqia. Currently, genes with known biological function are used as molecular markers to estimate livestock genetic diversity parameters, facilitating the identification and location of genetic loci within the genome that encode or regulate the expression of traits of economic interest. In Colombia Romosinuano cattle candidate genes of the Growth hormone / Insulin growth factor axis have been identified and are positively associated with age at first calving, calving interval, longevity and protection of the embryo growth to heat stress. However, native Colombian bovine breeds such as Casanareño and Sanmartinero, which are empirically recognized by having those characteristic, have not been subjected to those genetic analysis for candidate genes that may allow to promote added value to animals. The aim of this review is to document some reproductive and genetic parameters of Sanmartinero and Casanareño bovine brees that may give support the need to conduct molecular studies and justify their use in beef and milk production systems in the Colombian Orinoquia.
Chondrichthyans are usually caught incidentally in fisheries for species of high commercial value and then discarded on board or landed as by-products. On the coast of Chubut province and adjacent waters (43°00′S–44°56′S) a bottom trawl fishery has developed targeted at the Patagonian shrimp (Pleoticus muelleri) and common hake (Merluccius hubbsi). Since 2005, this fishery has been monitored by the On-board Observers Program of Chubut province (POBCh). With the aim of advancing towards an ecosystem approach, POBCh not only collects information about target species but also about all the species caught by the trawl nets of the province fisheries. From the information collected by this programme it was possible to identify and record the chondrichthyan species vulnerable to the fishing gear used by the coastal fleet that operates from Puerto Rawson. The composition of the fleet catch was characterized according to the target species during the 2005–2014 period. In the analysis of 3786 hauls, 23 species of chondrichthyans (seven species of sharks, 15 species of batoids and a single species of Holocephali) were identified. Seven species showed a frequency of occurrence greater than 10% (Callorhinchus callorynchus, Discopyge tschudii, Mustelus schmitti, Sympterygia bonapartii, Psammobatis normani, Squalus acanthias and Zearaja chilensis). Species spatial distribution was evaluated and five areas of species assemblages were established. Besides the aspects related to bycatch, these analyses have contributed to the knowledge of the chondrichthyan biodiversity in the provincial coast where the fleet operates, a region with incomplete and mostly dispersed and outdated information.
The optical and structural properties of co-doped HfO2 thin films with rare earth trivalent ions prepared by ultrasonic spray pyrolysis technique, are reported. An arrangement of multi-layer (Si-SiO2-HfO2:Eu3+-HfO2:Tb3+-HfO2:Tm3+-SiO2) were deposited on silicon substrates at temperatures from 400 to 550°C, using acetyl acetonates as precursory reagents. A refractive index value of 2.1 was determined by spectral ellipsometry. The surface morphology was obtained by AFM measurements. For 50 to 550 nm thickness films, an average roughness value of ∼56.8 Å was obtained for different substrate temperatures and grown deposition times. EDS measurements showed the presence of hafnium, and rare earths dopants as elemental composition. XPS measurements demonstrated that hafnium and rare earths oxidation species are formed at hafnium dioxide thin films. Photoluminescence emission spectra of multi-layer structures present characteristic emission peaks associated with Tb+3, Eu3+, and Tm3+ dopants. The results presented above motivate us to consider that these multilayer structures could be appropriate to be used as a rare earth host to improve optical emission.
The catalytic activity of disordered binary alloy metal surfaces is investigated for the oxygen reduction reaction (ORR) by generating free energy diagrams and performing calculations on d-band centers of alloys. The disorder was simulated using virtual crystal approximation; then, based on periodic, self-consistent density functional theory (DFT) methods, we calculated adsorption energies of reaction intermediates. Alternative pathway for ORR mechanism, involving proton/electron transfer to adsorbed oxygen and hydroxyl, is considered. The methodology was applied to (111) surface of PdxCu1-x disordered binary alloys, with different values of x concentration. This study found that at the ORR equilibrium potential of 1.23 V, the reactivity of all surfaces is shown to be limited by the rate of OH removal from the surface. Among the surfaces studied, the surface of Pd0.80Cu0.20 shows the highest reactivity and is more active than other non-Pt alloys. These results are in excellent agreement with earlier experimental and theoretical work.
A study of the ferroelectric and magnetic properties and of the magnetoelectric coupling effects of Pb(Fe0.5Nb0.5)O3 (PFN) thin films, grown on SrRuO3/Si [(100) or (111)] substrates by the rf-magnetron sputtering technique, is presented. Structural, morphological, and compositional characterization was realized using the XRD, AFM, XPS, and TEM techniques. Highly textured single phase films with different thickness (from 45 to 270 nm) were successfully grown without Fe2+ presence. A vertically  oriented grainy structure was observed. Polarization vs. electric field (P-E) hysteresis loops exhibit excellent and almost constant values of the maximum (∼ 60 μC/cm2) and remanent (∼ 22 μC/cm2) polarizations in the temperature range from 4 K to room temperature; small values of the coercive field, characteristic of soft ferroelectric materials, are observed in these samples. Measurements of the zero-field cooled (ZFC) and field cooled (FC) magnetization behavior and magnetic (M-H) hysteresis loops were realized at different temperatures between 5 and 300 K. Proof of the existence of ferromagnetic order in the low temperature region (below to 50 K) is discussed and reported for the first time. Values of the maximum (∼ 3 emu/g) and remanent (∼ 1.5 emu/g) magnetizations were obtained. dc magnetic field dependence of the ferroelectric hysteresis loops are shown as evidence of the magnetoelectric coupling.
The objective of this study was to investigate the genetic diversity of methicillin-resistant Staphylococcus aureus (MRSA) clonal complex (CC) 398 using pulsed-field gel electrophoresis (PFGE). Dust and pigs at five age groups were sampled in six Danish MRSA-positive pig farms. MRSA CC398 was isolated from 284 of the 391 samples tested, including 230 (74%) animal and 54 (68%) environmental samples. PFGE analysis of a subset of 48 isolates, including the six strains previously isolated from farm workers, revealed the existence of farm-specific pulsotypes. With a single exception, human, environmental and porcine isolates originating from the same farm clustered together in the PFGE cluster analysis, indicating that spread of MRSA CC398 in Danish pig farms is mainly due to clonal dissemination of farm-specific lineages that can be discriminated by PFGE. This finding has important implications for planning future epidemiological studies investigating the spread of CC398 in pig farming.
Sagging of suspended or laminated structures is a common problem in the processing of Low Temperature Co-Fired Ceramics (LTCC). These glass-ceramic composites are susceptible to plastic deformation upon lamination, or under the stress of body forces once the glass transition temperature of the glass binder is reached during processing. We have designed and fabricated, using the conventional methods of LTCC fabrication, meso-scale structures (ranging in size from 100 mm to 1 cm) to quantify and seek control strategies for this problem. We have implemented bridge structures and membranes to emulate most of the conventional structures encountered during packaging or sensor (actuator) device fabrication.
We have observed that when an LTCC tape with holes larger than 400 µm in diameter is laminated, the tapes above and below deform into the cavity. For smaller diameters, deformation is negligible. Bridging structures can be compensated for the potential effect of body forces by screen-printing a thick film over-layer which exert internal tensile stresses on sintering. This can often yield straight bridges. The use of fugitive phase materials, which disappear or flow during firing, is another way of supporting bridging structures. Several of these strategies have been explored, and results are presented.
In this work we report about the design and construction of a simple and cheap calorimeter for phase transitions monitoring using Peltier elements and based in the well known inverse (front) photopyroelectric method for thermophysical characterization of materials. We describe its application for the detection of phase transitions in chocolate samples, as an alternative, for example, to the most widely used and more expensive Differential Scanning Calorimetry technique. The manufacture of chocolate requires an understanding of the chemistry and the physical properties of the product. Thus the involved problems during the confection process are those of the so-called materials science. Among them, those related with tempering are of particular importance. Because the fats in cocoa butter experience the so-called polymorphous crystallization, the primary purpose of tempering is to assure that only the best form is present in the final product. One way to characterize this is by measurement of the temperature dependence of the thermal properties of the chocolate and the monitoring of the temperature at which phase transitions take place. We show that the photopyroelectric method, aided with Peltier cells temperature control, can be a useful choice for this purpose.
People detection and tracking are essential capabilities in order to achieve a natural human–robot interaction. A great portion of the research in that area has been focused on monocular techniques. However, the use of stereo vision for these purposes concentrates a great interest nowadays. This paper presents a multi-agent system that implements a basic set of perceptual-motor skills providing mobile robots with primitive interaction capabilities. The skills designed use stereo and ultrasound information to enable mobile robots to (i) detect an interested user who desires to interact with the robot, (ii) keep track of the user while they move in the environment without confusing them with other people, and (iii) follow the user along the environment avoiding obstacles in the way. The system presented has been evaluated in several real-life experiments achieving good results and real-time performance on modest computers.
It is now a familiar theme in the literature on the emergence and development of the state in the Western world to refer to war and war preparation—in short, war making—as an important contributing factor to the development of the modern state. As Charles Tilly succinctly put it, “War made the state, and the state made war.” We know, however, little about the relation between war making and the development of the state in the contemporary Middle East. This is rather surprising considering the importance of war and war preparation in the history of many states in the region and the current wave of academic interest in the study of state formation in the Middle East. A review of the literature would show that war is usually integrated as a contingent factor, but not as a systematic process that can influence state development. For instance, accounts of state development in Egypt mention the impact ofthe 1956 and 1967 wars on the capacity of the state to intervene in the economy and society; yet until recently no one had systematically studied the impact of war preparation on state formation in Egypt.
A. Vexliard indiquait récemment qu'il n'existe pas de définition tout à fait exhaustive du vagabondage. Le vagabondage est un phénomène qui présente des formes très diverses suivant les structures historiques dominantes, sans parler du vagabondage élémentaire, simple répercussion de catastrophes naturelles ou humaines. Le caractère qui paraît essentiel dans ce mode de vie est moins le déplacement en soi que l'irrégularité, le retreatism au sens défini par R. Merton, la déviation face aux finalités et institutions sociales. Il existe un vagabondage agressif, qui tend à coïncider avec le banditisme, et il en existe un autre, pacifique, proche de la mendicité. Mais, au fond, le vagabondage ne s'identifie jamais pleinement avec ces formes fixes et comme institutionnalisées elles aussi. Dans son âge d'or, au Moyen Age, le vagabondage fut en relation avec des phénomènes culturels aussi importants que les pèlerinages, les croisades, le métier de jongleur.
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