11,039 research outputs found
Common connections: on the uses of autonomous videogame networks in Havana and the snet case
Este artÃculo sistematiza un grupo de investigaciones coordinadas por el autor y otros
colaboradores sobre las comunidades de redes inalámbricas autónomas en la ciudad
de La Habana durante los años 2015 y 2018. En estas redes acontecen trasformaciones
en las formas de decir, articular y definir relaciones cooperativas, de lo social-no
institucional, lo público y lo común, poco regulares en el contexto cubano.This article systematizes a group of investigations coordinated by the author and other
collaborators on communities of autonomous networks of videogames in the city of Havana,
during the years 2015 and 2018. In these networks, transformations take place in the ways
of saying, articulating and defining cooperative relations, of the non-institutional social, the
public and the common, which are not regular in the Cuban context
Organic Molecules in the Galactic Center. Hot Core Chemistry without Hot Cores
We study the origin of large abundances of complex organic molecules in the
Galactic center (GC). We carried out a systematic study of the complex organic
molecules CH3OH, C2H5OH, (CH3)2O, HCOOCH3, HCOOH, CH3COOH, H2CO, and CS toward
40 GC molecular clouds. Using the LTE approximation, we derived the physical
properties of GC molecular clouds and the abundances of the complex
molecules.The CH3OH abundance between clouds varies by nearly two orders of
magnitude from 2.4x10^{-8} to 1.1x10^{-6}. The abundance of the other complex
organic molecules relative to that of CH3OH is basically independent of the
CH3OH abundance, with variations of only a factor 4-8. The abundances of
complex organic molecules in the GC are compared with those measured in hot
cores and hot corinos, in which these complex molecules are also abundant. We
find that both the abundance and the abundance ratios of the complex molecules
relative to CH3OH in hot cores are similar to those found in the GC clouds.
However, hot corinos show different abundance ratios than observed in hot cores
and in GC clouds. The rather constant abundance of all the complex molecules
relative to CH3OH suggests that all complex molecules are ejected from grain
mantles by shocks. Frequent (similar 10^{5}years) shocks with velocities >6km/s
are required to explain the high abundances in gas phase of complex organic
molecules in the GC molecular clouds. The rather uniform abundance ratios in
the GC clouds and in Galactic hot cores indicate a similar average composition
of grain mantles in both kinds of regions. The Sickle and the Thermal Radio
Arches, affected by UV radiation, show different relative abundances in the
complex organic molecules due to the differentially photodissociation of these
molecules.Comment: 18 pages, 10 Postscript figures, uses aa.cls, aa.bst, 10pt.rtx,
natbib.sty, revsymb.sty revtex4.cls, aps.rtx and aalongtabl.sty. Accepted in
A&A 2006. version 2. relocated figures and tables. Language editor
suggestions. added reference
Interaction of oxygen with TiN (001): N↔O exchange and oxidation process
This work presents a detailed experimental and theoretical study of the oxidation of TiN(001) using a combination of synchrotron-based photoemission and density functional theory (DFT). Experimentally, the adsorption of O2 on TiN(001) was investigated at temperatures between 250 and 450K. At the lowest temperature, there was chemisorption of oxygen (O2,gas→2Oads) without significant surface oxidation. In contrast, at 450K the amount of O2 adsorbed increased continuously, there was no evidence for an oxygen saturation coverage, a clear signal in the Ti 2p core level spectra denoted the presence of TiOx species, and desorption of both N2 and NO was detected. The DFT calculations show that the adsorption/dissociation of O2 is highly exothermic on a TiN(001) substrate and is carried out mainly by the Ti centers. A high oxygen coverage (larger than 0.5 ML) may induce some structural reconstructions of the surface. The exchange of a surface N atom by an O adatom is a highly endothermic process (ΔE=2.84eV). However, the overall oxidation of the surface layer is thermodynamically favored due to the energy released by the dissociative adsorption of O2 and the formation of N2 or NO. Both experimental and theoretical results lead to conclude that a TiN+mO2→TiOx+NO reaction is an important exit channel for nitrogen in the oxidation process.Ministerio de Educación y Ciencia de España, MEC. MAT2005-01872Junta de AndalucÃa. FQM-132División de Ciencias QuÃmicas del Departamento de EnergÃa de EE. UU. DE-AC02-98CH10086Fundación japonesa para la Ciencia de los Materiale
A theoretical insight into the catalytic effect of a mixed-metal oxide at the nanometer level: The case of the highly active metal/CeOx/TiO2(110) catalysts
The structural and electronic properties of CeOx species supported on the rutile TiO2 110 surface
have been examined by means of periodic density-functional calculations that use a generalized
gradient approximation functional including a Hubbard-like type correction. Deposition of Ce atoms
leads in a first step to Ce3+ ions bound to the surface through bridge and in-plane oxygen atoms, the
released electrons occupying the Ti 3d empty orbitals. Further addition of Ce and molecular oxygen
gives place to Ce2O3 dimers diagonally arranged on the surface, in agreement with the spots
observed in the scanning tunnel microscope images. The formation process of CeOx nanoparticles
NPs on the TiO2 surface is highly exothermic and our calculations show that the redox properties
of the Ce III-Ce IV couple are significantly altered when it is supported on TiO2. In particular the
reactivity against CO/O2 indicates that on the surface the presence of Ce III is favored over Ce IV
species. Our results also indicate that the CeOx /TiO2 interface should be seen like a real
mixed-metal oxide rather than a supported NP of ceria. Finally, in the context of the high catalytic
activity of the M /CeOx /TiO2 M =Au,Cu,Pt systems in the water-gas shift reaction, we
have examined the dissociation of water on the CeOx /TiO2 surface and estimated a barrier as
small as 0.04 eV, i.e. 8 times smaller than that computed for a TiO2 oxygen vacancy. This result
agrees with the experimental superior catalytic activity of the M /CeOx /TiO2 systems over
M /TiO2.Gobierno de España. Ministerio Ciencia e Innovación (MICINN) MAT2005-01872 y CSD2008-0023Junta de AndalucÃa FQM-132Departamento de EnergÃa de EE. UU. División de Subvención de Ciencias QuÃmicas DE-AC02-98CH1088
Diavideos: a Diabetes Health Video Portal
Diavideos1 is a web platform that collects trustworthy
diabetes health videos from YouTube and offers them in a easy
way. YouTube is a big repository of health videos, but good
content is sometimes mixed with misleading and harmful
videos such as promoting anorexia [1].Diavideos is a web
portal that provides easy access to a repository of trustworthy
diabetes videos. This poster describes Diavideos and explains
the crawling method used to retrieve these videos from trusted
channels
ISO observations of the Galactic center Interstellar Medium: neutral gas and dust
The 500 central pc of the Galaxy (hereafter GC) exhibit a widespread gas
component with a kinetic temperature of 100-200 K. The bulk of this gas is not
associated to the well-known thermal radio continuum or far infrared sources
like Sgr A or Sgr B. How this gas is heated has been a longstanding problem.
With the aim of studying the thermal balance of the neutral gas and dust in the
GC, we have observed 18 molecular clouds located at projected distances far
from thermal continuum sources with the Infrared Space Observatory (ISO). In
this paper we present observations of several fine structure lines and the full
continuum spectra of the dust between 40 and 190 microns. A warm dust component
with a temperature between 27 and 42 K is needed to fit the spectra. We have
compared the gas and the dust emission with the predictions from J-type and
C-type shocks and photodissociation region (PDRs) models. We conclude that the
dust and the fine structure lines observations are best explained by a PDR with
a density of 10 cm^-3 and an incident far-ultraviolet field 10 times
higher than the local interstellar radiation field. PDRs can naturally explain
the discrepancy between the gas and the dust temperatures. However, these PDRs
can only account for 10-30% of the total H2 column density with a temperature
of ~ 150 K. We discuss other possible heating mechanisms (short version).Comment: Accepted for publication by A&
Modeling the secular evolution of migrating planet pairs
The subject of this paper is the secular behaviour of a pair of planets
evolving under dissipative forces. In particular, we investigate the case when
dissipative forces affect the planetary semi-major axes and the planets move
inward/outward the central star, in a process known as planet migration. To
perform this investigation, we introduce fundamental concepts of conservative
and dissipative dynamics of the three-body problem. Based on these concepts, we
develop a qualitative model of the secular evolution of the migrating planetary
pair. Our approach is based on analysis of the energy and the orbital angular
momentum exchange between the two-planet system and an external medium; thus no
specific kind of dissipative forces is invoked. We show that, under assumption
that dissipation is weak and slow, the evolutionary routes of the migrating
planets are traced by the Mode I and Mode II stationary solutions of the
conservative secular problem. The ultimate convergence and the evolution of the
system along one of these secular modes of motion is determined uniquely by the
condition that the dissipation rate is sufficiently smaller than the proper
secular frequency of the system. We show that it is possible to reassemble the
starting configurations and migration history of the systems on the basis of
their final states and consequently to constrain the parameters of the physical
processes involved.Comment: 20 pages, 17 figures. Accepted for publication in MNRA
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