1,044 research outputs found
Uppermost Miocene Lamniform Selachians (Pisces) from the Alvalade basin (Portugal)
This paper deals with Lamniform teeth collected in deposits from the Esbarrondadoiro Formation, Alvalade Basin in Southern Portugal. The following genera were recognized: Carcharias, Pseudocarcharias, Alopias, Isurus and Carcharocles. The species
Carcharias acutissima is by far the most predominant, all other taxa being rare or very rare. This situation points to neritic, tropical to subtropical, rather shallow waters not far away from the coast. This is corroborated by the rarity of the associated, mainly pelagic, taxa.
The ratio between C. acutissima and the remaining Lamniforms as a whole is markedly uneven between Esbarrondadoiro and
the localities of Santa Margarida and Vale de Zebro. This suggests quite different environmental conditions, a matter that will
require a more thorough examination taking into account all palaeontologic and geologic data
Stellar Populations Found in the Central kpc of Four Luminous Compact Blue Galaxies at Intermediate Redshift
We investigate the star formation history of the central regions of four
Luminous Compact Blue Galaxies (LCBGs). LCBGs are blue (B-V<0.6), compact
(MU_B<21.5 mag arcsec^-2) galaxies with absolute magnitudes M_B brighter than
-17.5. The LCBGs analyzed here are located at 0.436<z<0.525. They are among the
most luminous (M_B < -20.5), blue (B-V < 0.4) and high surface brightness (MU_B
< 19.0 mag arcsec^-2) of this population. The observational data used were
obtained with the HST/STIS spectrograph, the HST/WF/PC-2 camera and the
HST/NICMOS first camera. We find evidence for multiple stellar populations. One
of them is identified as the ionizing population, and the other one corresponds
to the underlying stellar generation.
The estimated masses of the inferred populations are compatible with the
dynamical masses, which are typically 2--10x 10^9 M_sun. Our models also
indicate that the first episodes of star formation the presented LCBGs
underwent happened between 5 and 7 Gyr ago.
We compare the stellar populations found in LCBGs with the stellar
populations present in bright, local HII galaxies, nearby spheroidal systems
and Blue Compact Dwarf Galaxies. It turns out that the underlying stellar
populations of LCBGs are similar yet bluer to those of local HII galaxies. It
is also the case that the passive color evolution of the LCBGs could convert
them into local Spheroidal galaxies if no further episode of star formation
takes place. Our results help to impose constraints on evolutionary scenarios
for the population of LCBGs found commonly at intermediate redshifts.Comment: 35 pages, 10 Figures. Accepted for publication in AJ. Compile with
pdflatex. Contains png figure
Os tubarões hybodontiformes (Chondrichthyes: Euselachii) do Jurássico Superior de Torres Vedras, Portugal
ABSTRACT: In this work, the description and classification of a set of fossil shark tooth specimens, from the upper Kimmeridgian-lower Tithonian (Upper Jurassic) of Torres Vedras, was developed. The material, currently
housed in the paleontological collection of Sociedade de História Natural, was collected on the surface of the marine deposits at the top of the Praia Azul Member, Lourinhã Formation, Lusitanian Basin. The attribution of
the specimens to Hybodus cf. reticulatus, was based on the presence of the following most striking characteristics: a reticulated, spongy root, perpendicular to the crown; a completely to almost completely straight main cusp; several straight, well-defined, and parallel ridges that run from the base of the crown to about half of the height of the main cusp; and flat, well-defined cutting edges.RESUMO: No presente trabalho, fez-se a descrição e a classificação de um conjunto de espécimes de dentes fósseis de tubarão, do Kimmeridgiano superior-Tithoniano inferior (Jurássico Superior) de Torres Vedras. O
material, atualmente sediado na coleção paleontológica da Sociedade de História Natural, foi colhido à superfície nos depósitos marinhos do topo do Membro da Praia Azul, Formação da Lourinhã, Bacia Lusitaniana. A atribuição dos espécimes a Hybodus cf. reticulatus, baseou-se na presença das seguintes características mais marcantes: raiz reticulada, esponjosa e perpendicular à coroa; cúspide principal totalmente ou quase totalmente estreita; várias pregas estreitas, bem definidas e paralelas entre si, que
surgem desde a base da coroa até aproximadamente metade da altura da cúspide principal; e bordo cortante liso e bem definido.info:eu-repo/semantics/publishedVersio
BIODIESEL FROM MICROALGAE: THE EFFECT OF FUEL PROPERTIES ON POLLUTANT EMISSIONS
Recently, biofuels have been presented as a viable alternative for the main challenges of the energy industry: the depleting supplies of petroleum and the global warming due to greenhouse effect. Biofuels may be produced from several different feedstocks, such as sugarcane, animal fat, oil crops or even microalgae. Replacing conventional petroleum sourced fuels with biofuels may significantly reduce global greenhouse effect gases emission when considering the life cycle of such fuels. Even with this advantage, biofuels present new challenges concerning the engine adaptation and the pollutant emissions. In this context, this paper aims to clarify the relation between fuel properties of microalgae biodiesel and pollutant emissions, studying which properties are desirable in these new fuels to guarantee engine operation without degradation of performance in comparison to conventional diesel
The Cristo Rei section (Lower Miocene). Distal fluviatile environments in a marine series, plants, vertebrates and other evidence, age
The section at Cristo Rei shows sandy beds with intercalated clayey lenses (IVb division from the Lisbon Miocene series)
that correspond to a major regression event dated from between ca. 17.6 and 17 Ma. They also correspond to a distal position
(relatively to the typical fluviatile facies in Lisbon), nearer the basin's axis. Geologic data and paleontological analysis (plant fossils, fishes, crocodilians, land mammals) allow the reconstruction of environments that were represented in the concerned area: estuary with channels and ox-bows; upstream, areas occupied by brackish waters where Gryphaea griphoides banks developped; still farther upstream, freshwaters sided by humid forests and low mountain subtropical forests under warm temperate and rainy conditions, as well as not far away, seasonally dry environments (low density tree or shrub cover, or steppe)
Out-of-phase oscillation between superfluid and thermal components for a trapped Bose condensate under oscillatory excitation
The vortex nucleation and the emergence of quantum turbulence induced by
oscillating magnetic fields, introduced by Henn E A L, et al. 2009 (Phys. Rev.
A 79, 043619) and Henn E A L, et al. 2009 (Phys. Rev. Lett. 103, 045301), left
a few open questions concerning the basic mechanisms causing those interesting
phenomena. Here, we report the experimental observation of the slosh dynamics
of a magnetically trapped Rb Bose-Einstein condensate (BEC) under the
influence of a time-varying magnetic field. We observed a clear relative
displacement in between the condensed and the thermal fraction center-of-mass.
We have identified this relative counter move as an out-of-phase oscillation
mode, which is able to produce ripples on the condensed/thermal fractions
interface. The out-of-phase mode can be included as a possible mechanism
involved in the vortex nucleation and further evolution when excited by time
dependent magnetic fields.Comment: 5 pages, 5 figures, 25 reference
Emission-Line Galaxy Surveys as Probes of the Spatial Distribution of Dwarf Galaxies. I. The University of Michigan Survey
Objective-prism surveys which select galaxies on the basis of line-emission
are extremely effective at detecting low-luminosity galaxies and constitute
some of the deepest available samples of dwarfs. In this study, we confirm that
emission-line galaxies (ELGs) in the University of Michigan (UM)
objective-prism survey (MacAlpine et al. 1977-1981) are reliable tracers of
large-scale structure, and utilize the depth of the samples to examine the
spatial distribution of low-luminosity (M -18.0) dwarfs relative to
higher luminosity giant galaxies (M -18.0) in the Updated Zwicky
Catalogue (Falco et al. 1999). New spectroscopic data are presented for 26 UM
survey objects. We analyze the relative clustering properties of the overall
starbursting ELG and normal galaxy populations, using nearest neighbor and
correlation function statistics. This allows us to determine whether the
activity in ELGs is primarily caused by gravitational interactions. We conclude
that galaxy-galaxy encounters are not the sole cause of activity in ELGs since
ELGs tend to be more isolated and are more often found in the voids when
compared to their normal galaxy counterparts. Furthermore, statistical analyses
performed on low-luminosity dwarf ELGs show that the dwarfs are less clustered
when compared to their non-active giant neighbors. The UM dwarf samples have
greater percentages of nearest neighbor separations at large values and lower
correlation function amplitudes relative to the UZC giant galaxy samples. These
results are consistent with the expectations of galaxy biasing.Comment: 17 pages, 4 tables, 10 figures. Accepted for publication in the Ap
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