13,646 research outputs found
Improved mass cultivation of the marine diatom Chaetoceros calcitrans for shellfish hatcheries : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Biotechnology at Massey University, Palmerston North, New Zealand
A medium for the optimal growth of Chaetoceros calcitrans in batch and continuous culture systems was developed. A method was developed for continuous culture of C. calcitrans that was free from detrimental infection by bacteria. The concentration of tested nutrients in the developed medium were sodium nitrate, 160 mg/L; sodium dihydrogen orthophosphate, 40 mg/L; and the molar Si:N ratio was 0.25 (99.9 mg/L sodium metasilicate). Isolated bacterial strains were shown to be detrimental to the growth of C. calcitrans in batch and continuous culture. Electrolytically treated water was suitable for the growth of C. calcitrans, but a subsequent flourish of bacterial growth at the late exponential phase reduced the quality of the algal cells and made the culture unsuitable for feeding to shellfish larvae. Heat treated water (95°C for ten and a half minutes) gave stable growth for the continuous culture of C. calcitrans in 38 L plastic bioreactor bags for at least 38 days. The superficial gas velocity in the culture bags was 0.09 L/min. Higher superficial gas velocities (e.g. 0.40 L/min were detrimental to C. calcitrans
A Backward-traversal-based Approach for Symbolic Model Checking of Uniform Strategies for Constrained Reachability
Since the introduction of Alternating-time Temporal Logic (ATL), many logics
have been proposed to reason about different strategic capabilities of the
agents of a system. In particular, some logics have been designed to reason
about the uniform memoryless strategies of such agents. These strategies are
the ones the agents can effectively play by only looking at what they observe
from the current state. ATL_ir can be seen as the core logic to reason about
such uniform strategies. Nevertheless, its model-checking problem is difficult
(it requires a polynomial number of calls to an NP oracle), and practical
algorithms to solve it appeared only recently.
This paper proposes a technique for model checking uniform memoryless
strategies. Existing techniques build the strategies from the states of
interest, such as the initial states, through a forward traversal of the
system. On the other hand, the proposed approach builds the winning strategies
from the target states through a backward traversal, making sure that only
uniform strategies are explored. Nevertheless, building the strategies from the
ground up limits its applicability to constrained reachability objectives only.
This paper describes the approach in details and compares it experimentally
with existing approaches implemented into a BDD-based framework. These
experiments show that the technique is competitive on the cases it can handle.Comment: In Proceedings GandALF 2017, arXiv:1709.0176
Tip streaming from drops flowing in a spiral microchannel
This fluid dynamics video shows drops of water being transported by a mean
flow of oil, in a microchannel shaped as a logarithmic spiral. The channel
shape means that the drops are submitted to an increasing shear and elongation
as they flow nearer to the center of the spiral. A critical point is reached at
which a long singular tail is observed behind the drops, indicating that the
drops are accelerating. This is called "Tip streaming".Comment: Abstract accompanying movie to the Gallery of Fluid Motion: APS-DFD
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Scattering of a cross-polarized linear wave by a soliton at an optical event horizon in a birefringent nanophotonic waveguide
The scattering of a linear wave on an optical event horizon, induced by a
cross polarized soliton, is experimentally and numerically investigated in
integrated structures. The experiments are performed in a dispersion-engineered
birefringent silicon nanophotonic waveguide. In stark contrast with
co-polarized waves, the large difference between the group velocity of the two
cross-polarized waves enables a frequency conversion almost independent on the
soliton wavelength. It is shown that the generated idler is only shifted by 10
nm around 1550 nm over a pump tuning range of 350 nm. Simulations using two
coupled full vectorial nonlinear Schr\"odinger equations fully support the
experimental results
Generation of ultra broadband coherent supercontinuum in tapered and dispersion managed silicon nanophotonic waveguides
Tapered and dispersion managed (DM) silicon nanophotonic waveguides are
investigated for the generation of optimal ultra broadband supercontinuum (SC).
DM waveguides are structures showing a longitudinally dependent group velocity
dispersion that results from the variation of the waveguide width with the
propagation distance. For the generation of optimal SC, a genetic algorithm has
been used to find the best dispersion map. This allows for the generation of
highly coherent supercontinuums that span over 1.14 octaves from 1300 nm to
2860 nm and 1.25 octaves from 1200 nm to 2870 nm at -20 dB level for the
tapered and DM waveguides respectively, for a 2 m, 200 fs and 6.4 pJ input
pulse. The comparison of these two structures with the usually considered
optimal fixed width waveguide shows that the SC is broader and flatter in the
more elaborated DM waveguide, while the high coherence is ensured by the
varying dispersion.Comment: arXiv admin note: substantial text overlap with arXiv:1610.0566
Food Price Changes and Consumer Welfare in Ghana in the 1990s
In this paper, we analyse the effect of food price changes on household consumption in Ghana during the 1990s and assess the extent to which changes can be explained by trade and agricultural policy reforms. The measurement of the total household welfare effect, one that jointly considers (static) first order effects as well as (dynamic) consumption responses, is the object of this study. Food consumption behaviour in Ghana is analyzed by estimating a complete food demand system using the linear approximate version of the AIDS model with household survey data for 1991/92 and 1998/99. The estimated price elasticities are then utilized to evaluate the distributional impacts of the relative food price changes in terms of compensating variation. The results indicate that the distributional burden of higher food prices fell mainly on the urban poor. While it is difficult to attribute the price changes and by implication the welfare losses, to any particular policy per se, a simulation analysis indicates that trade liberalisation may not have been responsible for the welfare losses. Our simulation exercise suggests that further tariff liberalisation would tend to offset the welfare losses for all households although it is the poor and rural consumers who stand to gain the most.Food prices, Demand analysis, Consumer behaviour, Welfare, Ghana
Hadronic Production of Thermal Photons
We study the thermal emission of photons from hot and dense strongly
interacting hadronic matter at temperatures close to the expected phase
transition to the Quark-Gluon Plasma (QGP). Earlier calculations of photon
radiation from ensembles of interacting mesons are re-examined with additional
constraints, including new production channels as well as an assessment of
hadronic form factor effects. Whereas strangeness-induced photon yields turn
out to be moderate, the hitherto not considered t-channel exchange of omega
mesons is found to contribute appreciably for photon energies above ~1.5 GeV.
The role of baryonic effects is assessed using existing many-body calculations
of lepton pair production. We argue that our combined results constitute a
rather realistic emission rate, appropriate for applications in relativistic
heavy-ion collisions. Supplemented with recent evaluations of QGP emission, and
an estimate for primordial (hard) production, we compute photon spectra at SPS,
RHIC and LHC energies.Comment: 19 pages, 13 figures, 1 appendix. Discussion added, improved
parameterisation
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