2,292 research outputs found
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
El valle medio del Guadalquivir: De Montoro a Alcalá del Río
Consideración de los aspectos más relevantes del tramo medio del río Guadalquivir. Se consideran no sólo los aspectos hidrológicos, sino igualmente aquellos otros que se refieren a los paisajes por los que el gran río de Andalucía va discurriendo. En este orden de cosas, además de identificar claramente el escenario, se consideran los aspectos climáticos, la dinámica y la morfología fluvial (terrazas, meandros, etc…) y ¿cómo no? Los resultados de la intervención antrópica. En este último aspecto tienen tratamiento la relación de las vías de comunicación con el río, la intervención para la regulación de la cuenca, la agricultura irrigada y los efectos del proceso urbanizador
Le centre historique de Cordoue et le premier plan de la ville: Le «Plan des Français», de 1811
Durante la guerra de Independencia, el gobierno de los afrancesados
elaboró en 1811 el llamado Plano de los Franceses, el primer plano
urbano de Córdoba realizado de manera científica. Por ello, ha resultado
ser un documento imprescindible para analizar el pasado y el presente
urbano de la ciudad. Con ocasión de su bicentenario, intentamos
una lectura contemporánea de la información que en él se contiene,
haciendo una valoración de sus autores y de su papel en los procesos de
reinvención de una ciudad históricaPendant la Guerre d’Espagne, le gouvernement
des occupants réalisa en 1811 le premier plan urbain de la ville
basé sur procédés scientifiques, le « Plan des Français », ce qui lui valut
devenir un document incontournable pour l’analyse du passé et du présent
de la ville. À l’occasion du bicentenaire du plan, nous essayons
une lecture contemporaine de son contenu, en faisant une évaluation
des auteurs et de son rôle dans les processus de réinvention d’une ville
historiqueIn 1811, during the Peninsular War, the
Napoleonic government executed the Cordoba first town map made
with a scientific procedure, subsequently known as the “Map of the
French”, which became an essential document to understand the urban
past and present. On the occasion of its bicentenary, we try to make a
modern interpretation of its content, as well as an evaluation both of
the authorship and the role the map played in the historic city centre
reinventio
Interrelación entre ciencia y enseñanza a principios del siglo XX: Juan Carandell Pericay
En estos momentos (primer tercio del siglo XXI), etapa en que de una forma tan tajante se están modificando muchos de los que fueran axiomas pedagógicos en todas las disciplinas, partiendo de los contenidos mismos que se enseñan y continuando con las formas mismas de enseñar, se plantea la conveniencia de una mirada hacia atrás para intentar recordar cómo eran y se hacían las cosas a principios del s. XX.
Y para ello se plantea el análisis de la trayectoria –científica y pedagógica- de un catedrático de Bachillerato, D. Juan Carandell Pericay, en el que se aúnan de modo inseparable la pasión por el conocimiento científico, el afán ferviente de enseñarlo y, además, de enseñarlo correctamente
Abundant Z-cyanomethanimine in the interstellar medium: paving the way to the synthesis of adenine
We report the first detection in the interstellar medium of the Z-isomer of
cyanomethanimine (HNCHCN), an HCN dimer proposed as precursor of adenine. We
identified six transitions of Z-cyanomethanimine, along with five transitions
of E-cyanomethanimine, using IRAM 30m observations towards the Galactic Center
quiescent molecular cloud G+0.693. The Z-isomer has a column density of
(2.00.6)10 cm and an abundance of
1.510. The relative abundance ratio between the isomers is
[Z/E]6. This value cannot be explained by the two chemical formation
routes previously proposed (gas-phase and grain surface), which predicts
abundances ratios between 0.9 and 1.5. The observed [Z/E] ratio is in good
agreement with thermodynamic equilibrium at the gas kinetic temperature
(130210 K). Since isomerization is not possible in the ISM, the two species
may be formed at high temperature. New chemical models, including surface
chemistry on dust grains and gas-phase reactions, should be explored to explain
our findings. Whatever the formation mechanism, the high abundance of Z-HNCHCN
shows that precursors of adenine are efficiently formed in the ISM.Comment: Accepted in Monthly Notices of the Royal Astronomical Society Letter
Complex organic molecules in the Galactic Centre: the N-bearing family
We present an unbiased spectral line survey toward the Galactic Centre (GC)
quiescent giant molecular cloud (QGMC), G+0.693 using the GBT and IRAM 30
telescopes. Our study highlights an extremely rich organic inventory of
abundant amounts of nitrogen (N)-bearing species in a source without signatures
of star formation. We report the detection of 17 N-bearing species in this
source, of which 8 are complex organic molecules (COMs). A comparison of the
derived abundances relative to H is made across various galactic and
extragalactic environments. We conclude that the unique chemistry in this
source is likely to be dominated by low-velocity shocks with X-rays/cosmic rays
also playing an important role in the chemistry. Like previous findings
obtained for O-bearing molecules, our results for N-bearing species suggest a
more efficient hydrogenation of these species on dust grains in G+0.693 than in
hot cores in the Galactic disk, as a consequence of the low dust temperatures
coupled with energetic processing by X-ray/cosmic ray radiation in the GC.Comment: 24 pages, 23 figures, 7 tables, accepted for publication in MNRA
3 mm spectral line survey of two lines of sight toward two typical cloud complexes in the Galactic Center
We present the results of two Mopra 3-mm spectral line surveys of the Lines
of Sight (LOS) toward the Galactic Center (GC) molecular complexes Sgr B2
(LOS+0.693) and Sgr A (LOS-0.11). The spectra covered the frequency ranges of
~77-93 GHz and ~105-113 GHz. We have detected 38 molecular species and 25
isotopologues. The isotopic ratios derived from column density ratios are
consistent with the canonical values, indicating that chemical isotopic
fractionation and/or selective photodissociation can be considered negligible
(<10%) for the GC physical conditions. The derived abundance and rotational
temperatures are very similar for both LOSs, indicating very similar chemical
and excitation conditions for the molecular gas in the GC. The excitation
conditions are also very similar to those found for the nucleus of the
starburst galaxy NGC 253. We report for the first time the detection of HCO and
HOC+ emission in LOS+0.693. Our comparison of the abundance ratios between CS,
HCO, HOC+ and HCO+ found in the two LOSs with those in typical Galactic
photodissociation regions (PDRs) and starbursts galaxies does not show any
clear trend to distinguish between UV and X-ray induced chemistries. We propose
that the CS/HOC+ ratio could be used as a tracer of the PDR components in the
molecular clouds in the nuclei of galaxies
Cartographic and geohistoric resources for the inventory of temporary wetlands and mediterranean desections
El presente artículo recopila y examina, desde una vertiente metodológica y geográfica, las fuentes o recursos cartográficos que se han analizado y utilizado para la realización del in-ventario de humedales temporales en el Medio Guadalquivir, y en el seno de nuestro proyecto de investigación.
Estudiaremos fundamentalmente las fuentes cartográficas disponibles para el área citada, aunque en gran medida puedan ser extrapolables a la mayor parte de España.
Se lleva a cabo una exposición de las líneas de trabajo y de los autores más representativos para el inventario de humedales temporales o desecados, mediante la investigación de la historia de los Archivos, de las Bibliotecas, de los Museos y de los Centros de Documentación convencionales y digitales actuales. En un segundo momento se aborda una propuesta metodológica para la investigación de esta faceta particular, acompañada por un nutrido apéndice en el que se recopilan las fuentes más significativas que venimos utilizando en nuestra investigación.This paper compiles and examines, from a methodological and geographical perspective, the sources or cartographic resources that have been analyzed and used for the realization of the inventory of temporary wetlands in the Middle Guadalquivir, and within our research project.
We will study fundamentally the cartographic sources available for the mentioned area, although to a large extent they can be extrapolated to the greater part of Spain.
An exposition of the lines of work and of the most representative authors for the inventory of temporary or dried wetlands is carried out, through the investigation of the History of Archives, of Libraries, of Museums and of Conventional Documentation Centers And digital technologies. In a second moment, a methodological proposal for the investigation of this particular facet is approached, accompanied by several appendices in which are collected the most significant sources that we have been using in our investigatio
Fabrication of zinc oxide and nanostructured porous silicon composite micropatterns on silicon
The luminescent properties of zinc oxide (ZnO) and nanostructured porous silicon (PSi)
make these materials very appealing for photoemission applications. The current study reports on
the fabrication of a composite of ZnO and nanostructured porous silicon micropatterns (ZnO + PSi
micropatterns) onto heavily-doped silicon surfaces. The proposed composite micropattern is devoted
to the future development of light-emitting diodes. The fabrication of the ZnO + PSi micropatterns
was carried out in a two–step process. (1) A regular hexagonal micropattern of a photoresist/ZnO
stack was fabricated by UV lithography on crystalline silicon substrates. (2) Before being lifted off
the photoresist, nanostructured PSi micropatterns were fabricated by electrochemically etching the
exposed areas of the silicon substrate. Subsequently, wet etching of the photoresist was carried out
for the final development of the composite ZnO and PSi micropatterns. Further, thin films of ZnO
and nanostructured PSi layers were characterized. In particular, their photoluminescent properties
were analyzed, as well as their morphology and composition. The experimental PL results show
that the ZnO layers have emission broadbands centered at (2.63 eV, blue), while the PSi layers show
a band centered at (1.71 eV, red). Further, the emission peaks from the PSi layers can be tuned by
changing their fabrication conditions. It was observed that the properties of the ZnO thin films are
not influenced by either the surface morphology of PSi or by its PL emissions. Therefore, the PL
properties of the composite ZnO + PSi micropatterns are equivalent to those featuring the addition of
PSi layers and ZnO thin films. Accordingly, broadband optical emissions are expected to arise from
a combination between the ZnO layer (blue band) and PSi (red band). Furthermore, the electrical
losses associated with the PSi areas can be greatly reduced since ZnO is in contact with the Si surface.
As a result, the proposed composite micropatterns might be attractive for many solid-state lighting
applications, such as light-emitting diodesThis research was partially funded by Universidad Autónoma de Madrid, FPI-UAM grant (2019) and by the Egyptian Ministry of Higher Education, Missions Section under Egyptian Joint Supervision Grant, call 015/01
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