605 research outputs found
Algal Biofuels: Challenges and Opportunities
Biodiesel production using microalgae is attractive in a number of respects. Here a number of pros and cons to using microalgae for biofuels production are reviewed. Algal cultivation can be carried out using non-arable land and non-potable water with simple nutrient supply. In addition, algal biomass productivities are much higher than those of vascular plants and the extractable content of lipids that can be usefully converted to biodiesel, triacylglycerols (TAGs) can be much higher than that of the oil seeds now used for first generation biodiesel. On the other hand, practical, cost-effective production of biofuels from microalgae requires that a number of obstacles be overcome. These include the development of low-cost, effective growth systems, efficient and energy saving harvesting techniques, and methods for oil extraction and conversion that are environmentally benign and cost-effective. Promising recent advances in these areas are highlighted
Exploring the Diversity of Physiology for Applications in Wastewater Treatment and Biofuels Production
A recently established strain collection of freshwater microalgae native to Quebec was examined for physiological diversity. The 100 strains appeared very heterogeneous in terms of growth when they were cultured at 10±2 °C or 22±2 °C on the secondary effluent from a municipal wastewater treatment plant (WW) and defined BBM medium. Scatterplots were used to examine the diversity in physiology that might be present in the collection. These showed a number of interesting results. There was a fair amount of dispersion in growth rates by media type independent of temperature. Surprisingly considering that all the isolates had been initially enriched on BBM, the distribution was quite symmetrical around the iso-growth line, suggesting that enrichment on BBM did not seem to bias the cells for growth on this medium versus WW. As well, considering that all the isolates had been initially enriched at 22 °C, it is quite surprising that the distribution of specific growth rates was quite symmetrical around the iso-growth line with roughly equal numbers of isolates found on either side. Thus enrichment at 22 °C does not seem to bias the cells for growth at this temperature versus 10°C. The scatterplots obtained when the percentage lipid of cultures grown on BBM were compared with cultures grown on WW at either 10 °C or 22 °C made it apparent that lipid production was favored by growth on WW at either temperature and that lipid production does not seem to be particularly favored by one temperature over the other. When the collection was queried for differences with respect to sampling location, statistical analysis showed that roughly the same degree of physiological diversity was found with samples from the two different aggregate locations.This research was supported by a grant from FQRNT (Le Fonds Québécois de la recherche sur la nature et les technologies), programme de recherche en partenariat contribuant à la séquestration des gaz à effet de serre (2011-GZ-141307) to P.C.H
Utilization of biodiesel-derived glycerol or xylose for increased growth and lipid production by indigenous microalgae
The use of industrial wastes rich in mineral nutrients and carbon sources to increase the final microalgal biomass and lipid yield at a low cost is an important strategy to make algal biofuel technology viable. Using strains from the microalgal collection of the Université de Montréal, this report shows for the first time that microalgal strains can be grown on xylose, the major carbon source found in wastewater streams from pulp and paper industries, with an increase in growth rate of 2.8 fold in comparison to photoautotrophic growth, reaching up to µ=1.1/day. On glycerol, growth rates reached as high as µ=1.52/day. Lipid productivity increased up to 370% on glycerol and 180% on xylose for the strain LB1H10, showing the suitability of this strain for further development for biofuels production through mixotrophic cultivation.This research was supported by a Grant from FQRNT (Le Fonds Québécois de la recherche sur la nature et les technologies), programme de recherche en partenariat contribuant à la séquestration des gaz à effet de serre (2011-GZ-141307) to P.C.H
Traffic Forecasting for Pavement Design
The need for improved traffic estimation procedures has been emphasized by several studies that demonstrated that previously available data were not adequate. Some data were not considered representative of actual traffic conditions because of overloaded trucks avoiding weighing scales and insufficient traffic sampling programs. In addition, previous forecasting procedures did not reflect the increases in legal load limits, the significant increase in the number of heavy trucks, or the shift toward larger vehicle types that has occurred in recent years.
Improved estimates of current traffic loadings based on larger samples of much higher quality data would allow development of procedures for making improved estimates of historical traffic loadings and better forecasts of traffic loadings during the design period. The emergence of automatic vehicle classification equipment, permanent and portable weigh-in-motion (WIM) systems, and the application of microprocessors and microcomputers to these data acquisition functions now offer tools that may be used effectively in meeting these needs.
Representatives from four States (Florida, Kentucky, Oregon, and Washington) met on several occasions to discuss the subject of traffic forecasting for pavement design. Information was compiled on all aspects of the traffic forecasting process, options were presented for each step of the process, and recommendations were developed to assist highway agencies in improving current practices and procedures
Grain growth in the inner regions of Herbig Ae/Be star disks
We present new mid-infrared spectroscopy of
the emission from warm circumstellar dust grains
in Herbig Ae/Be stars. Our survey significantly
extends the sample that was studied by Bouwman et
al. (2001). We find a correlation between the
strength of the silicate feature and its shape.
We interpret this as evidence for the removal of
small (0.1 mu m) grains from the disk surface
while large (1-2 mu m) grains persist. If the
evolution of the grain size distribution is
dominated by gravitational settling, large grains
are expected to disappear first, on a timescale
which is much shorter than the typical age of our
programme stars. Our observations thus suggest a
continuous replenishment of micron sized grains
at the disk surface. If the grain replenishment
is due to the dredge-up of dust from the disk
interior, the mineralogy we observe is
representative of the bulk composition of dust in
these stars. Based on observations obtained at
the European Southern Observatory (ESO), La
Silla, and on observations with ISO, an ESA
project with instruments funded by ESA Member
States (especially the PI countries: France,
Germany, The Netherlands and the UK) and with the
participation of ISAS and NASA
C2D Spitzer-IRS spectra of disks around T Tauri stars V. Spectral decomposition
(Abridged) Dust particles evolve in size and lattice structure in
protoplanetary disks, due to coagulation, fragmentation and crystallization,
and are radially and vertically mixed in disks. This paper aims at determining
the mineralogical composition and size distribution of the dust grains in disks
around 58 T Tauri stars observed with Spitzer/IRS. We present a spectral
decomposition model that reproduces the IRS spectra over the full spectral
range. The model assumes two dust populations: a warm component responsible for
the 10\mu m emission arising from the disk inner regions and a colder component
responsible for the 20-30\mu m emission, arising from more distant regions. We
show evidence for a significant size distribution flattening compared to the
typical MRN distribution, providing an explanation for the usual boxy 10\mu m
feature profile generally observed. We reexamine the crystallinity paradox,
observationally identified by Olofsson et al. (2009), and we find a
simultaneous enrichment of the crystallinity in both the warm and cold regions,
while grain sizes in both components are uncorrelated. Our modeling results do
not show evidence for any correlations between the crystallinity and either the
star spectral type, or the X-ray luminosity (for a subset of the sample). The
size distribution flattening may suggests that grain coagulation is a slightly
more effective process than fragmentation in disk atmospheres, and that this
imbalance may last over most of the T Tauri phase. This result may also point
toward small grain depletion via strong stellar winds or radiation pressure in
the upper layers of disk. The non negligible cold crystallinity fractions
suggests efficient radial mixing processes in order to distribute crystalline
grains at large distances from the central object, along with possible nebular
shocks in outer regions of disks that can thermally anneal amorphous grains
Discrimination of low missing energy look-alikes at the LHC
The problem of discriminating possible scenarios of TeV scale new physics
with large missing energy signature at the Large Hadron Collider (LHC) has
received some attention in the recent past. We consider the complementary, and
yet unexplored, case of theories predicting much softer missing energy spectra.
As there is enough scope for such models to fake each other by having similar
final states at the LHC, we have outlined a systematic method based on a
combination of different kinematic features which can be used to distinguish
among different possibilities. These features often trace back to the
underlying mass spectrum and the spins of the new particles present in these
models. As examples of "low missing energy look-alikes", we consider
Supersymmetry with R-parity violation, Universal Extra Dimensions with both
KK-parity conserved and KK-parity violated and the Littlest Higgs model with
T-parity violated by the Wess-Zumino-Witten anomaly term. Through detailed
Monte Carlo analysis of the four and higher lepton final states predicted by
these models, we show that the models in their minimal forms may be
distinguished at the LHC, while non-minimal variations can always leave scope
for further confusion. We find that, for strongly interacting new particle
mass-scale ~600 GeV (1 TeV), the simplest versions of the different theories
can be discriminated at the LHC running at sqrt{s}=14 TeV within an integrated
luminosity of 5 (30) fb^{-1}.Comment: 40 pages, 10 figures; v2: Further discussions, analysis and one
figure added, ordering of certain sections changed, minor modifications in
the abstract, version as published in JHE
Left-right symmetry at LHC and precise 1-loop low energy data
Despite many tests, even the Minimal Manifest Left-Right Symmetric Model
(MLRSM) has never been ultimately confirmed or falsified. LHC gives a new
possibility to test directly the most conservative version of left-right
symmetric models at so far not reachable energy scales. If we take into account
precise limits on the model which come from low energy processes, like the muon
decay, possible LHC signals are strongly limited through the correlations of
parameters among heavy neutrinos, heavy gauge bosons and heavy Higgs particles.
To illustrate the situation in the context of LHC, we consider the "golden"
process . For instance, in a case of degenerate heavy neutrinos
and heavy Higgs masses at 15 TeV (in agreement with FCNC bounds) we get
fb at TeV which is consistent with muon
decay data for a very limited masses in the range (3008 GeV, 3040 GeV).
Without restrictions coming from the muon data, masses would be in the
range (1.0 TeV, 3.5 TeV). Influence of heavy Higgs particles themselves on the
considered LHC process is negligible (the same is true for the light, SM
neutral Higgs scalar analog). In the paper decay modes of the right-handed
heavy gauge bosons and heavy neutrinos are also discussed. Both scenarios with
typical see-saw light-heavy neutrino mixings and the mixings which are
independent of heavy neutrino masses are considered. In the second case heavy
neutrino decays to the heavy charged gauge bosons not necessarily dominate over
decay modes which include only light, SM-like particles.Comment: 16 pages, 10 figs, KL-KS and new ATLAS limits taken into accoun
Crystalline silicate dust around evolved stars III. A correlations study of crystalline silicate features
We have carried out a quantitative trend analysis of the crystalline
silicates observed in the ISO spectra of a sample of 14 stars with different
evolutionary backgrounds. We have modeled the spectra using a simple dust
radiative transfer model and have correlated the results with other known
parameters. We confirm the abundance difference of the crystalline silicates in
disk and in outflow sources, as found by Molster et al. (1999, Nature 401,
563). We found some indication that the enstatite over forsterite abundance
ratio differs, it is slightly higher in the outflow sources with respect to the
disk sources. It is clear that more data is required to fully test this
hypothesis. We show that the 69.0 micron feature, attributed to forsterite, may
be a very suitable temperature indicator. We found that the enstatite is more
abundant than forsterite in almost all sources. The temperature of the
enstatite grains is about equal to that of the forsterite grains in the disk
sources but slightly lower in the outflow sources. Crystalline silicates are on
average colder than amorphous silicates. This may be due to the difference in
Fe content of both materials. Finally we find an indication that the ratio of
ortho to clino enstatite, which is about 1:1 in disk sources, shifts towards
ortho enstatite in the high luminosity (outflow) sources.Comment: 16 pages, 20 figures, accepted by A&A, this paper and others (in this
series) can also be found at http://zon.wins.uva.nl/~frankm/papers.htm
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