1,316 research outputs found
Parrondian Games in Discrete Dynamic Systems
An interesting problem in nonlinear dynamics is the stabilization of chaotic trajectories, assuming that such chaotic behavior is undesirable. The method described in this chapter is based on the Parrondo’s paradox, where two losing games can be alternated, yielding a winning game. The idea of alternating parameter values has been used in chemical systems, but for these systems, the undesirable behavior is not chaotic. In contrast, ecological relevant map in one and two dimensions, most of the time, can sustain chaotic trajectories, which we consider as undesirable behaviors. Therefore, we analyze several of such ecological relevant maps by constructing bifurcation diagrams and finding intervals in parameter space that satisfy the conditions to yield a desirable behavior by alternating two undesirable behaviors. The relevance of the work relies on the apparent generality of method that establishes a dynamic pattern of behavior that allows us to state a simple conjecture for two-dimensional maps. Our results are applicable to models of seasonality for 2-D ecological maps, and it can also be used as a stabilization method to control chaotic dynamics
Molecules with a peptide link in protostellar shocks: a comprehensive study of L1157
Interstellar molecules with a peptide link -NH-C(=O)-, like formamide
(NHCHO), acetamide (NHCOCH) and isocyanic acid (HNCO) are
particularly interesting for their potential role in pre-biotic chemistry. We
have studied their emission in the protostellar shock regions L1157-B1 and
L1157-B2, with the IRAM 30m telescope, as part of the ASAI Large Program.
Analysis of the line profiles shows that the emission arises from the outflow
cavities associated with B1 and B2. Molecular abundance of
and are derived for
formamide and isocyanic acid, respectively, from a simple rotational diagram
analysis. Conversely, NHCOCH was not detected down to a relative
abundance of a few . B1 and B2 appear to be among the richest
Galactic sources of HNCO and NHCHO molecules. A tight linear correlation
between their abundances is observed, suggesting that the two species are
chemically related. Comparison with astrochemical models favours molecule
formation on ice grain mantles, with NHCHO generated from hydrogenation of
HNCO.Comment: 11 pages, 9 figures. Accepted for publication in MNRAS Main Journal.
Accepted 2014 August 19, in original form 2014 July
How good are the Garvey-Kelson predictions of nuclear masses?
The Garvey-Kelson relations are used in an iterative process to predict
nuclear masses in the neighborhood of nuclei with measured masses. Average
errors in the predicted masses for the first three iteration shells are smaller
than those obtained with the best nuclear mass models. Their quality is
comparable with the Audi-Wapstra extrapolations, offering a simple and
reproducible procedure for short range mass predictions. A systematic study of
the way the error grows as a function of the iteration and the distance to the
known masses region, shows that a correlation exists between the error and the
residual neutron-proton interaction, produced mainly by the implicit assumption
that varies smoothly along the nuclear landscape.Comment: 10 pages, 18 figure
Degradation of AlInGap red LEDs under drive current and temperature accelerated life tests
AlInGaP LEDs are widely used in illumination applications as automotive and signalization due their low consumption and high durability. In order to verify the high durability data it is necessary to consider not only catastrophic failures but also degradation. In this work LEDs degradation at different temperature and drive current accelerated tests have been analyzed. In all the tests we have carried out an exponential degradation trend have been observed. Temperature and drive current influence in degradation rate and reliability have been evaluated
Shedding light on the formation of the pre-biotic molecule formamide with ASAI
Formamide (NH2CHO) has been proposed as a pre-biotic precursor with a key
role in the emergence of life on Earth. While this molecule has been observed
in space, most of its detections correspond to high-mass star-forming regions.
Motivated by this lack of investigation in the low-mass regime, we searched for
formamide, as well as isocyanic acid (HNCO), in 10 low- and intermediate-mass
pre-stellar and protostellar objects. The present work is part of the IRAM
Large Programme ASAI (Astrochemical Surveys At IRAM), which makes use of
unbiased broadband spectral surveys at millimetre wavelengths. We detected HNCO
in all the sources and NH2CHO in five of them. We derived their abundances and
analysed them together with those reported in the literature for high-mass
sources. For those sources with formamide detection, we found a tight and
almost linear correlation between HNCO and NH2CHO abundances, with their ratio
being roughly constant -between 3 and 10- across 6 orders of magnitude in
luminosity. This suggests the two species are chemically related. The sources
without formamide detection, which are also the coldest and devoid of hot
corinos, fall well off the correlation, displaying a much larger amount of HNCO
relative to NH2CHO. Our results suggest that, while HNCO can be formed in the
gas phase during the cold stages of star formation, NH2CHO forms most
efficiently on the mantles of dust grains at these temperatures, where it
remains frozen until the temperature rises enough to sublimate the icy grain
mantles. We propose hydrogenation of HNCO as a likely formation route leading
to NH2CHO.Comment: 26 pages, 9 figures. Accepted by Monthly Notices of the Royal
Astronomical Societ
Effectiveness of 3 COVID-19 vaccines in preventing SARS-CoV-2 infections, January–May 2021, Aragon, Spain
Reducing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission is a worldwide challenge; widespread vaccination could be one strategy for control. We conducted a prospective, population-based cohort study of 964, 258 residents of Aragon, Spain, during December 2020–May 2021. We used the Cox proportional-hazards model with vaccination status as the exposure condition to estimate the effectiveness of 3 coronavirus disease vaccines in preventing SARS-CoV-2 infection. Pfizer-BioNTech had 20.8% (95% CI 11.6%–29.0%) vaccine effectiveness (VE) against infection after 1 dose and 70.0% (95% CI 65.3%–74.1%) after 2 doses, Moderna had 52.8% (95% CI 30.7%–67.8%) VE after 1 dose and 70.3% (95% CI 52.2%–81.5%) after 2 doses, and Oxford-AstraZeneca had 40.3% (95% CI 31.8%–47.7%) VE after 1 dose. All estimates were lower than those from previous studies. Results imply that, although high vaccination coverage remains critical to protect people from disease, it will be difficult to effectively minimize transmission opportunities
The Mating System of the Wild-to-Domesticated Complex of Gossypium hirsutum L. Is Mixed
The domestication syndrome of many plants includes changes in their mating systems. The evolution of the latter is shaped by ecological and genetic factors that are particular to an area. Thus, the reproductive biology of wild relatives must be studied in their natural distribution to understand the mating system of a crop species as a whole. Gossypium hirsutum (upland cotton) includes both domesticated varieties and wild populations of the same species. Most studies on mating systems describe cultivated cotton as self-pollinated, while studies on pollen dispersal report outcrossing; however, the mating system of upland cotton has not been described as mixed and little is known about its wild relatives. In this study we selected two wild metapopulations for comparison with domesticated plants and one metapopulation with evidence of recent gene flow between wild relatives and the crop to evaluate the mating system of cotton’s wild-to-domesticated complex. Using classic reproductive biology methods, our data demonstrate that upland cotton presents a mixed mating system throughout the complex. Given cotton’s capacity for outcrossing, differences caused by the domestication process in cultivated individuals can have consequences for its wild relatives. This characterization of the diversity of the wild relatives in their natural distribution, as well as their interactions with the crop, will be useful to design and implement adequate strategies for conservation and biosecurity
El dibujo de aproximación en Oporto: construyendo la imagen de la ciudad
[EN] Porto is a city located in a privileged enclave. The observer is able to see its construction, both spatially and temporally, in a simple way. Collecting the concepts stated by several authors regarding the sensory experience that cities offer for their recognition and legibility, we move towards a reflection regarding the creation of the image of the city. On a more practical level applied to the specific case of the city of Porto, we will conclude with a detailed analysis, through the approximation drawing, which follows the story of K. Lynch, about fundamental elements in the recognition and identification of the urban image: borders, neighbourhoods, paths, nodes, landmarks, and the original relief itself.[ES] Oporto es una ciudad ubicada en un enclave privilegiado y que exhibe al observador, de una manera sencilla, su construcción, tanto a nivel espacial como temporal. Recogiendo los conceptos enunciados por varios autores en cuanto a la experiencia sensorial que ofrecen las ciudades para su reconocimiento y su legibilidad, se avanza hacia una reflexión en cuanto a la creación de la imagen de la ciudad. Finalmente, y ya en un plano práctico más aplicado al caso concreto de la ciudad de Oporto, se concluirá con un análisis pormenorizado, a través del dibujo de aproximación, y siguiendo el relato de K. Lynch, de los elementos fundamentales en el reconocimiento e identificación de la imagen urbana: bordes, barrios, sendas, nodos, hitos, y el propio relieve primigenio.Úbeda Blanco, M.; Mendoza RodrÃguez, I.; López Bragado, D.; Lafuente Sánchez, VA. (2020). The approximation drawing in Porto: building the image of the city. EGA Expresión Gráfica Arquitectónica. 25(40):216-229. https://doi.org/10.4995/ega.2020.14570OJS216229254
Surface shape resonances in lamellar metallic gratings
The specular reflectivity of lamellar gratings of gold with grooves 0.5
microns wide separated by a distance of 3.5 microns was measured on the 2000
cm - 7000 cm spectral range for p-polarized light. For the first
time, experimental evidence of the excitation of electromagnetic surface shape
resonances for optical frequencies is given. In these resonances the electric
field is highly localized inside the grooves and is almost zero in all other
regions. For grooves of depth equal to 0.6 microns, we have analyzed one of
these modes whose wavelength (3.3 microns) is much greater than the lateral
dimension of the grooves.Comment: 4 pages (LaTex), 5 postscript figures, to be published in Physical
Review Letter
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