361 research outputs found
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
Development and characterization of new microsatellites for Eugenia dysenterica DC (Myrtaceae).
Microsatellite markers were developed for population genetic analyses of the Neotropical tree Eugenia dysenterica DC (Myrtaceae), after construction of a shotgun genomic library for microsatellite discovery. Nine primers were designed, of which 5 yielded amplified product. These primers were polymorphic for 97 individuals collected in 3 distinct localities. The number of alleles per locus (primer) ranged from 3 to 11 and expected heterozygosities varied from 0.309 to 0.884. The probability of locus identity was ~1.88 x 10-4 and the probability of paternity exclusion was ~0.9367. The 5 microsatellite primer pairs may be suitable for population genetic studies such as parentage and fine-scale genetic analyses of this species
An imaging and spectroscopic study of the very metal-deficient blue compact dwarf galaxy Tol 1214--277
We present a spectrophotometric study based on VLT/FORS I observations of one
of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol
1214-277 (Z ~ Zsun/25). The data show that roughly half of the total luminosity
of the BCD originates from a bright and compact starburst region located at the
northeastern tip of a faint dwarf galaxy with cometary appearance. The
starburst has ignited less than 4 Myr ago and its emission is powered by
several thousands O7V stars and ~ 170 late-type nitrogen Wolf-Rayet stars
located within a compact region with < 500 pc in diameter. For the first time
in a BCD, a relatively strong [Fe V] 4227 emission line is seen which together
with intense He II 4686 emission indicates the presence of a very hard
radiation field in Tol 1214-277. We argue that this extraordinarily hard
radiation originates from both Wolf--Rayet stars and radiative shocks in the
starburst region. The structural properties of the low-surface-brightness (LSB)
component underlying the starburst have been investigated by means of surface
photometry down to 28 B mag/sq.arcsec. We find that, for a surface brightness
level fainter than ~ 24.5 B mag/sq.arcsec, an exponential fitting law provides
an adequate approximation to its radial intensity distribution. The broad-band
colors in the outskirts of the LSB component of Tol 1214-277 are nearly
constant and are consistent with an age below one Gyr. This conclusion is
supported by the comparison of the observed spectral energy distribution (SED)
of the LSB host with theoretical SEDs.Comment: 17 pages, 11 Postscript figures, uses emulateapj.sty, to appear in
Astronomical Journa
Ultracompact Blue Dwarf Galaxies: Hubble Space Telescope Imaging and Stellar Population Analysis
We present deep Hubble Space Telescope Advanced Camera for Surveys / High
Resolution Channel U, narrow-V, and I images of nine "ultracompact" blue dwarf
galaxies (UCBDs) selected from the Sloan Digital Sky Survey. We define UCBDs as
local (z < 0.01) star-forming galaxies having angular diameters < 6" and
physical sizes < 1 kpc. They are also among the most metal-poor galaxies known,
and are found to reside within voids. Both the HST images and the objects'
optical spectra reveal that they are composites of young (~1 Myr) populations
that dominate their light, and older (~10 Gyr) populations that dominate their
stellar masses, which we estimate to be ~10^7 - 10^8 Msol. An intermediate-age
population is also indicated in most cases. The objects are not as dynamically
disturbed as the prototype UCBD, POX 186, but the structure of several of them
suggests that their current starbursts have been triggered by the
collisions/mergers of smaller clumps of stars. In one case, HS 0822+3542, the
ACS/HRC images resolve the object into two small (~100 pc) components which
appear to have recently collided, supporting this interpretation. In six of the
objects much of their star formation is concentrated in Young Massive Star
clusters. The evidence that the galaxies consist mainly of ~10 Gyr old stars
establishes that they are not protogalaxies; their low metallicities are more
likely to be the result of the escape of supernova ejecta, as opposed to youth.
These results are consistent with recent galaxy formation simulations which
predict that cosmic re-ionization at z ~ 6 significantly limited the subsequent
star formation of dwarf galaxies in voids due to the photo-evaporation of
baryons from their cold dark matter halos (Abridged).Comment: 43 pages, 6 figures, accepted for publication in ApJ; figures
available at ftp://ftp.nofs.navy.mil/pub/outgoing/mcorbin
Optimizing sampling efforts for ex situ conservation of genetic variability of Dipteryx alata Vogel
Teletandem and telepresence: Rethinking the cultural component in language teaching and language teacher education
HS 2134+0400 - new very metal-poor galaxy, a representative of void population?
We present the SAO 6m telescope spectroscopy of a blue compact galaxy (BCG)
HS 2134+0400 discovered in frame of the dedicated Hamburg/SAO survey for Low
Metallicity BCGs (HSS-LM). Its very low abundance of oxygen (12+log(O/H) =
7.44), as well as other heavy elements (S, N, Ne, Ar), assigns this dwarf
galaxy to the group of BCGs with the lowest metal content. There are only eight
that low metallicity among several thousand known BCGs in the nearby Universe.
The abundance ratios for the heavy elements (S/O, Ne/O, N/O, and Ar/O) are well
consistent with the typical values of other very metal-poor BCGs. The global
environment of HS 2134+0400 is atypical of the majority of BCGs. The object
falls within the Pegasus void, the large volume with the very low density of
galaxies with the normal (M_B* = -19.6) or high luminosity. Since we found in
voids a dozen more the very metal-poor galaxies, we discuss the hypothesis that
such objects can be representative of a substantial fraction of the void dwarf
galaxy population.Comment: 6 pages, including 2 tables and 2 postscript figures. Submitted to
Astronomy Letter
Large atom number dual-species magneto-optical trap for fermionic 6Li and 40K atoms
We present the design, implementation and characterization of a dual-species
magneto-optical trap (MOT) for fermionic 6Li and 40K atoms with large atom
numbers. The MOT simultaneously contains 5.2x10^9 6Li-atoms and 8.0x10^9
40K-atoms, which are continuously loaded by a Zeeman slower for 6Li and a
2D-MOT for 40K. The atom sources induce capture rates of 1.2x10^9 6Li-atoms/s
and 1.4x10^9 40K-atoms/s. Trap losses due to light-induced interspecies
collisions of ~65% were observed and could be minimized to ~10% by using low
magnetic field gradients and low light powers in the repumping light of both
atomic species. The described system represents the starting point for the
production of a large-atom number quantum degenerate Fermi-Fermi mixture
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