11,127 research outputs found
Experiment MA-028 crystal growth
A crystal growth experiment is reported on orbital space flights. The experiment was performed during the Apollo-Soyuz Test Project. The Crystal Growth Experiment assessed a novel process for growing single crystals of insoluble substances by allowing two or more reactant solutions to diffuse toward each other through a region of pure solvent in zero gravity. The experiment was entirely successful and yielded crystals of about the expected size, quality, and number
Follow up on the crystal growth experiments of the LDEF
The results of the 4 solution growth experiments on the LDEF have been published elsewhere. Both the crystals of CaCO3, which were large and well shaped, and the much smaller TTF-TCNQ crystals showed unusual morphological behavior. The follow up on these experiments was begun in 1981, when ESA initiated a 'Concept Definition Study' on a large, 150 kg, Solution Growth Facility (SGF) to be included in the payload of EURECA-1, the European Retrievable Carrier. This carrier was a continuation of the European Spacelab and at that time planned for launch in 1987. The long delay of the LDEF retrieval and of subsequent missions brought about reflections both on the concept of crystal growth in space and on the choice of crystallization materials that had been made for the LDEF. Already before the LDEF retrieval, research on TTF-TCNQ had been stopped, and a planned growth experiment with TTF-TCNQ on the SGF/EURECA had been cancelled. The target of the SGF investigation is now more fundamental in nature. None of the crystals to be grown here are, like TTF-TCNQ, in particular demand by science or industry, and the crystals only serve the purpose of model crystals. The real purpose of the investigation is to study the growth behavior. One of the experiments, the Soret Coefficient Measurement experiment is not growing crystals at all, but has it as its sole purpose to obtain accurate information on thermal diffusion, a process of importance in crystal growth from solution
Diurnal periodicity of activity in the spawning perch P. fluviatilis L. [Translation from: Kalamies 1972(7) 3, 1972]
Diurnal periodicity of spawning in the perch so far are rather meagre and found to be partly contrary to experiences of perch anglers. Therefore a study was made on the spawning during a 5-day period in the spring of 1971 in the Kuusamo area. Observations were made during the main spawning season, between 4- 9 June 1971. The perch were often measured, weighed and then released back into the water. The differences between spawning and non-spawning perch were studied as well as the time of roe discharge in a 24 hour period. Activity and environmental factors such as light intensity were also taken into consideration
Model of mobile agents for sexual interactions networks
We present a novel model to simulate real social networks of complex
interactions, based in a granular system of colliding particles (agents). The
network is build by keeping track of the collisions and evolves in time with
correlations which emerge due to the mobility of the agents. Therefore,
statistical features are a consequence only of local collisions among its
individual agents. Agent dynamics is realized by an event-driven algorithm of
collisions where energy is gained as opposed to granular systems which have
dissipation. The model reproduces empirical data from networks of sexual
interactions, not previously obtained with other approaches.Comment: 6 pages, 8 figure
Searching for optimal variables in real multivariate stochastic data
By implementing a recent technique for the determination of stochastic
eigendirections of two coupled stochastic variables, we investigate the
evolution of fluctuations of NO2 concentrations at two monitoring stations in
the city of Lisbon, Portugal. We analyze the stochastic part of the
measurements recorded at the monitoring stations by means of a method where the
two concentrations are considered as stochastic variables evolving according to
a system of coupled stochastic differential equations. Analysis of their
structure allows for transforming the set of measured variables to a set of
derived variables, one of them with reduced stochasticity. For the specific
case of NO2 concentration measures, the set of derived variables are well
approximated by a global rotation of the original set of measured variables. We
conclude that the stochastic sources at each station are independent from each
other and typically have amplitudes of the order of the deterministic
contributions. Such findings show significant limitations when predicting such
quantities. Still, we briefly discuss how predictive power can be increased in
general in the light of our methods
Observational signatures of lithium depletion in the metal-poor globular cluster NGC6397
The "stellar" solution to the cosmological lithium problem proposes that
surface depletion of lithium in low-mass, metal-poor stars can reconcile the
lower abundances found for Galactic halo stars with the primordial prediction.
Globular clusters are ideal environments for studies of the surface evolution
of lithium, with large number statistics possible to obtain for main sequence
stars as well as giants. We discuss the Li abundances measured for >450 stars
in the globular cluster NGC6397, focusing on the evidence for lithium depletion
and especially highlighting how the inferred abundances and interpretations are
affected by early cluster self-enrichment and systematic uncertainties in the
effective temperature determination.Comment: 6 pages, 2 figures, conference proceedings for IAU symposium 26
Transition from endemic behavior to eradication of malaria due to combined drug therapies: an agent-model approach
We introduce an agent-based model describing a
susceptible-infectious-susceptible (SIS) system of humans and mosquitoes to
predict malaria epidemiological scenarios in realistic biological conditions.
Emphasis is given to the transition from endemic behavior to eradication of
malaria transmission induced by combined drug therapies acting on both the
gametocytemia reduction and on the selective mosquito mortality during parasite
development in the mosquito. Our mathematical framework enables to uncover the
critical values of the parameters characterizing the effect of each drug
therapy. Moreover, our results provide quantitative evidence of what is
empirically known: interventions combining gametocytemia reduction through the
use of gametocidal drugs, with the selective action of ivermectin during
parasite development in the mosquito, may actively promote disease eradication
in the long run. In the agent model, the main properties of human-mosquito
interactions are implemented as parameters and the model is validated by
comparing simulations with real data of malaria incidence collected in the
endemic malaria region of Chimoio in Mozambique. Finally, we discuss our
findings in light of current drug administration strategies for malaria
prevention, that may interfere with human-to-mosquito transmission process.Comment: 12 pages, 6 figure
- …