125 research outputs found
Palynological study of the Galapagos endemic genus Darwiniothamnus (Asteraceae)
XV lnternational A.P.L.E. Symposium of Palynolog
Ultra High Resolution Transmission Electron Microscopy of Matrix Mineral Grains in CM Chondrites: Preaccretionary or Parent Body Aqueous Processing?
CM chondrites are highly hydrated
meteorites associated with a parent asteroid that has
experienced significant aqueous processing. The meteoritic
evidence indicates that these non-differentiated
asteroids are formed by fine-grained minerals embedded
in a nanometric matrix that preserves chemical
clues of the forming environment. So far there are two
hypothesis to explain the presence of hydrated minerals
in the content of CM chondrites: one is based on textural
features in chondrule-rim boundaries [1-3], and
the other ‘preaccretionary’ hypothesis proposes the
incorporation of hydrated phases from the protoplanetary
disk [4-6]. The highly porous structure of these
chondrites is inherited from the diverse materials present
in the protoplanetary disk environment. These
bodies were presumably formed by low relative velocity
encounters that led to the accretion of silicate-rich
chondrules, refractory Ca- and Al-rich inclusions
(CAIs), metal grains, and the fine-grained materials
forming the matrix. Owing to the presence of significant
terrestrial water in meteorite finds [7], here we
have focused on two CM chondrite falls with minimal
terrestrial processing: Murchison and Cold Bokkeveld.
Anhydrous carbonaceous chondrite matrices are usually
represented by highly chemically unequilibrated
samples that contain distinguishable stellar grains.
Other chondrites have experienced hydration and
chemical homogeneization that reveal parent body
processes. We have studied CM chondrites because
these meteorites have experienced variable hydration
levels [8-10]. It is important to study the textural effects
of aqueous alteration in the main minerals to
decipher which steps and environments promote bulk
chemistry changes, and create the distinctive alteration
products. It is thought that aqueous alteration has particularly
played a key role in modifying primordial
bulk chemistry, and homogenizing the isotopic content
of fine-grained matrix materials [7, 11, 12]. Fortunately,
the mineralogy produced by parent-body and terrestrial
aqueous alteration processes is distinctive [5, 11]
Insect pollinators of Jasminocereus thouarsii, an endemic cactus of the Galapagos Islands
Jasminocereus is a columnar cactus endemic to the Galapagos Islands, and is distributed mainly in the lowland arid zones. Its only species, J. thouarsii, has several varieties on different islands. Observations of the variety J. thouarsii var. delicatus on Santa Cruz Island suggested limited recruitment. We therefore studied its floral biology, pollination requirements and seed germination to determine whether recruitment might be limited by seed production or seed quality. Flowers opened in the early morning, from 5h00 to 10h00. No seed was produced by flowers isolated in pollination bags. Pollination was allogamous, mostly brought about by the endemic Xylocopa darwini (Hymenoptera: Apidae), followed by the introduced Acrosticta apicalis (Diptera) and endemic Camponotus planus (Hymenoptera: Formicidae). Seeds germinated well, with the highest germination rate obtained from seeds that were soaked before planting
Ultra High Resolution Transmission Electron Microscopy of Matrix Mineral Grains in CM Chondrites: Preaccretionary or Parent Body Aqueous Processing?
CM chondrites are highly hydrated
meteorites associated with a parent asteroid that has
experienced significant aqueous processing. The meteoritic
evidence indicates that these non-differentiated
asteroids are formed by fine-grained minerals embedded
in a nanometric matrix that preserves chemical
clues of the forming environment. So far there are two
hypothesis to explain the presence of hydrated minerals
in the content of CM chondrites: one is based on textural
features in chondrule-rim boundaries [1-3], and
the other ‘preaccretionary’ hypothesis proposes the
incorporation of hydrated phases from the protoplanetary
disk [4-6]. The highly porous structure of these
chondrites is inherited from the diverse materials present
in the protoplanetary disk environment. These
bodies were presumably formed by low relative velocity
encounters that led to the accretion of silicate-rich
chondrules, refractory Ca- and Al-rich inclusions
(CAIs), metal grains, and the fine-grained materials
forming the matrix. Owing to the presence of significant
terrestrial water in meteorite finds [7], here we
have focused on two CM chondrite falls with minimal
terrestrial processing: Murchison and Cold Bokkeveld.
Anhydrous carbonaceous chondrite matrices are usually
represented by highly chemically unequilibrated
samples that contain distinguishable stellar grains.
Other chondrites have experienced hydration and
chemical homogeneization that reveal parent body
processes. We have studied CM chondrites because
these meteorites have experienced variable hydration
levels [8-10]. It is important to study the textural effects
of aqueous alteration in the main minerals to
decipher which steps and environments promote bulk
chemistry changes, and create the distinctive alteration
products. It is thought that aqueous alteration has particularly
played a key role in modifying primordial
bulk chemistry, and homogenizing the isotopic content
of fine-grained matrix materials [7, 11, 12]. Fortunately,
the mineralogy produced by parent-body and terrestrial
aqueous alteration processes is distinctive [5, 11]
Dos años de estudios aerobiológicos en Vélez-Málaga (sur de España): periodo Febrero-Junio
XV lnternational A.P.L.E. Symposium of Palynolog
Simulation in Information Systems: Potential of the vulnerability theory
Systems simulation has been widely used in the last decades in order to analyze the impact of different scenarios in several areas, and its application to information systems in no exception. Analyzing information systems through simulation models is simultaneously much more affordable; it is required a smaller amount of resources and it is less disruptive with the real system. Since information systems are becoming a cornerstone for our society, a failure in these systems can have a huge impact. The theory of vulnerability identifies failures in which small damage can have disproportionate impact consequences in terms of the functionality of the whole system. This paper discusses the use of the theory of vulnerability in information system simulation
Análisis y tendencias del polen de Chenopodiáceas-Amarantáceas en la atmósfera de cuatro ciudades del sur de España
XV lnternational A.P.L.E. Symposium of Palynolog
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