1,934 research outputs found
The size of two-body weakly bound objects : short versus long range potentials
The variation of the size of two-body objects is investigated, as the
separation energy approaches zero, with both long range potentials and short
range potentials having a repulsive core. It is shown that long range
potentials can also give rise to very extended systems. The asymptotic laws
derived for states with angular momentum l=1,2 differ from the ones obtained
with short range potentials. The sensitivity of the asymptotic laws on the
shape and length of short range potentials defined by two and three parameters
is studied. These ideas as well as the transition from the short to the long
range regime for the l=0 case are illustrated using the Kratzer potential.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Fungi Associated with Decay in Treated Southern Pine Utility Poles in the Eastern United States
Approximately 1,320 fungi were isolated and studied from 246 creosote- or pentachlorophenol-treated southern pine poles in service in the eastern United States. The fungi identified were Basidiomycete decayers, soft rotters, and microfungi. White rot fungi predominated in the 262 Basidiomycete decayers isolated from 180 poles. The major Basidiomycetes isolated by radial position from poles of varying service ages appeared to develop initially in the outer treated zones and were often associated with seasoning checks. Some decay origins, however, appeared to be cases of preinvasion and escapes of preservative treatment. Five species of soft rot fungi comprised nearly 85% of 211 isolates obtained from 131 poles. They were isolated primarily from creosote-treated poles in outer treated zones at the groundline. Dissection analysis of 92 poles indicated that six developmental decay patterns and certain fungi were associated commonly with a pattern. The pole mycoflora isolated was relatively uniform in distribution in the eastern United States. The soft rotters and white rot group of Basidiomycete decayers appear to be a more important component of the treated southern pine pole mycoflora than has been recognized previously
Piecewise constant potentials and discrete ambiguities
This work is devoted to the study of discrete ambiguities. For parametrized
potentials, they arise when the parameters are fitted to a finite number of
phase-shifts. It generates phase equivalent potentials. Such equivalence was
suggested to be due to the modulo uncertainty inherent to phase
determinations. We show that a different class of phase-equivalent potentials
exists. To this aim, use is made of piecewise constant potentials, the
intervals of which are defined by the zeros of their regular solutions of the
Schr\"odinger equation. We give a classification of the ambiguities in terms of
indices which include the difference between exact phase modulo and the
numbering of the wave function zeros.Comment: 26 pages Subject: Mathematical Physics math-p
Differential clearance rates of microbial phylotypes by four appendicularian species
Appendicularians are abundant planktonic filter feeders that play a significant role in the pelagic food web due to their high clearance rates. Their diet and feeding rates have typically been measured as bulk chlorophyll or cell removal, with some attention given to prey size but no differentiation between the microbial phylotypes. Using a combination ofin situand laboratory incubations with flow cytometry and next-generation sequencing, we found species-specific differences in clearance rates and diet compositions of 4 common species:Oikopleura albicans,O. fusiformis,O. longicauda, andO. dioica. WhileO. albicansmost efficiently removed nano-eukaryotic algae, the other smaller species preferentially removed micron-sized pico-eukaryotic algae. Pico- and nano-eukaryotic cells constituted the major food source of the studied appendicularians despite their occurrence in oligotrophic water dominated by prokaryotic cells. Across species, pico- and nano-planktonic microalgae biomass comprised 45 to 75% of the appendicularian diets. Although non-photosynthetic bacteria were removed at lower rates than all other prey groups, their total contribution to the appendicularian diet was not trivial, representing 5 to 19% of the planktonic carbon in the appendicularian diet; pico-cyanobacteria contributed an additional 9 to 18%. Removal rates and efficiencies of pico-eukaryotes were higher than those of prokaryotes of similar size. Strikingly different clearance rates were observed for different prokaryotic phylotypes, indicating that factors other than size are involved in determining the capturability of the cells. Collectively, our findings provide additional evidence for differential retention of microbial prey among mucous-mesh grazers and its substantial effect on the upper-ocean microbial community.</jats:p
Trois mélanoblastomes de siÚge inaccoutumé chez les bovidés
Lombard Charles, Puget E., Rogé F., Rossignol A. Trois mélanoblastomes de siÚge inaccoutumé chez les bovidés. In: Bulletin de l'Académie Vétérinaire de France tome 116 n°4, 1963. pp. 171-174
Effect of type and concentration of ballasting particles on sinking rate of marine snow produced by the Appendicularian Oikopleura dioica
Ballast material (organic, opal, calcite, lithogenic) is suggested to affect sinking speed of aggregates in the ocean. Here, we tested this hypothesis by incubating appendicularians in suspensions of different algae or Saharan dust, and observing the sinking speed of the marine snow formed by their discarded houses. We show that calcite increases the sinking speeds of aggregates by ~100% and lithogenic material by ~150% while opal only has a minor effect. Furthermore the effect of ballast particle concentration was causing a 33 m d(-1) increase in sinking speed for a 5Ă10(5) ”m(3) ml(-1) increase in particle concentration, near independent on ballast type. We finally compare our observations to the literature and stress the need to generate aggregates similar to those in nature in order to get realistic estimates of the impact of ballast particles on sinking speeds
Designing multiplayer games to facilitate emergent social behaviours online
This paper discusses an exploratory case study of the design of games that facilitate spontaneous social interaction and group behaviours among distributed individuals, based largely on symbolic presence 'state' changes. We present the principles guiding the design of our game environment: presence as a symbolic phenomenon, the importance of good visualization and the potential for spontaneous self-organization among groups of people. Our game environment, comprising a family of multiplayer 'bumper-car' style games, is described, followed by a discussion of lessons learned from observing users of the environment. Finally, we reconsider and extend our design principles in light of our observations
Testing the reconstruction of modelled particulate organic carbon from surface ecosystem components using PlankTOM12 and machine learning
Understanding the relationship between surface marine ecosystems
and the export of carbon to depth by sinking organic particles is key to
representing the effect of ecosystem dynamics and diversity, and their
evolution under multiple stressors, on the carbon cycle and climate in
models. Recent observational technologies have greatly increased the amount
of data available, both for the abundance of diverse plankton groups and for
the concentration and properties of particulate organic carbon in the ocean
interior. Here we use synthetic model data to test the potential of using
machine learning (ML) to reproduce concentrations of particulate organic
carbon within the ocean interior based on surface ecosystem and
environmental data. We test two machine learning methods that differ in
their approaches to data-fitting, the random forest and XGBoost methods. The
synthetic data are sampled from the PlankTOM12 global biogeochemical model
using the time and coordinates of existing observations. We test 27
different combinations of possible drivers to reconstruct small (POCS)
and large (POCL) particulate organic carbon concentrations. We show
that ML can successfully be used to reproduce modelled particulate organic
carbon over most of the ocean based on ecosystem and modelled environmental
drivers. XGBoost showed better results compared to random forest thanks to
its gradient boosting trees' architecture. The inclusion of plankton
functional types (PFTs) in driver sets improved the accuracy of the model
reconstruction by 58â% on average for POCS and by 22â% for
POCL. Results were less robust over the equatorial Pacific and some
parts of the high latitudes. For POCS reconstruction, the most
important drivers were the depth level, temperature, microzooplankton and
PO4, while for POCL it was the depth level, temperature,
mixed-layer depth, microzooplankton, phaeocystis, PO4 and chlorophyll a averaged over the mixed-layer depth. These results suggest that it will be
possible to identify linkages between surface environmental and ecosystem
structure and particulate organic carbon distribution within the ocean
interior using real observations and to use this knowledge to improve both
our understanding of ecosystem dynamics and of their functional
representation within models.</p
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