142 research outputs found
Decay of Classical Chaotic Systems - the Case of the Bunimovich Stadium
The escape of an ensemble of particles from the Bunimovich stadium via a
small hole has been studied numerically. The decay probability starts out
exponentially but has an algebraic tail. The weight of the algebraic decay
tends to zero for vanishing hole size. This behaviour is explained by the slow
transport of the particles close to the marginally stable bouncing ball orbits.
It is contrasted with the decay function of the corresponding quantum system.Comment: 16 pages, RevTex, 3 figures are available upon request from
[email protected], to be published in Phys.Rev.
Quasi-equilibria in one-dimensional self-gravitating many body systems
The microscopic dynamics of one-dimensional self-gravitating many-body
systems is studied. We examine two courses of the evolution which has the
isothermal and stationary water-bag distribution as initial conditions. We
investigate the evolution of the systems toward thermal equilibrium. It is
found that when the number of degrees of freedom of the system is increased,
the water-bag distribution becomes a quasi-equilibrium, and also the
stochasticity of the system reduces. This results suggest that the phase space
of the system is effectively not ergodic and the system with large degreees of
freedom approaches to the near-integrable one.Comment: 21pages + 7 figures (available upon request), revtex, submitted to
Physical Review
Slow relaxation in weakly open vertex-splitting rational polygons
The problem of splitting effects by vertex angles is discussed for
nonintegrable rational polygonal billiards. A statistical analysis of the decay
dynamics in weakly open polygons is given through the orbit survival
probability. Two distinct channels for the late-time relaxation of type
1/t^delta are established. The primary channel, associated with the universal
relaxation of ''regular'' orbits, with delta = 1, is common for both the closed
and open, chaotic and nonchaotic billiards. The secondary relaxation channel,
with delta > 1, is originated from ''irregular'' orbits and is due to the
rationality of vertices.Comment: Key words: Dynamics of systems of particles, control of chaos,
channels of relaxation. 21 pages, 4 figure
Food effects on statolith composition of the common cuttlefish (Sepia officinalis)
The concentration of trace elements within cephalopod statoliths can provide a record of the environmental characteristics at the time of calcification. To reconstruct accurately the environmental characteristics at the time of calcification, it is important to understand the influence of as many factors as possible. To test the hypothesis that the elemental composition of cuttlefish statoliths could be influenced by diet, juvenile Sepia officinalis were fed either shrimp Crangon sp. or fish Clupea harengus under equal temperature and salinity regimes in laboratory experiments. Element concentrations in different regions of the statoliths (core–lateral dome–rostrum) were determined using laser ablation inductively coupled plasma mass spectrometry (LA- ICPMS). The ratios of Sr/Ca, Ba/Ca, Mn/Ca and Y/Ca in the statolith’s lateral dome of shrimp-fed cuttlefish were significantly higher than in the statolith’s lateral dome of fish-fed cuttlefish. Moreover, significant differences between statolith regions were found for all analysed elements. The fact that diet adds a considerable variation especially to Sr/Ca and Ba/Ca must be taken into account in future micro-chemical statolith studies targeting cephalopod’s life history
Functional Analysis of the Leading Malaria Vaccine Candidate AMA-1 Reveals an Essential Role for the Cytoplasmic Domain in the Invasion Process
A key process in the lifecycle of the malaria parasite Plasmodium falciparum is the fast invasion of human erythrocytes. Entry into the host cell requires the apical membrane antigen 1 (AMA-1), a type I transmembrane protein located in the micronemes of the merozoite. Although AMA-1 is evolving into the leading blood-stage malaria vaccine candidate, its precise role in invasion is still unclear. We investigate AMA-1 function using live video microscopy in the absence and presence of an AMA-1 inhibitory peptide. This data reveals a crucial function of AMA-1 during the primary contact period upstream of the entry process at around the time of moving junction formation. We generate a Plasmodium falciparum cell line that expresses a functional GFP-tagged AMA-1. This allows the visualization of the dynamics of AMA-1 in live parasites. We functionally validate the ectopically expressed AMA-1 by establishing a complementation assay based on strain-specific inhibition. This method provides the basis for the functional analysis of essential genes that are refractory to any genetic manipulation. Using the complementation assay, we show that the cytoplasmic domain of AMA-1 is not required for correct trafficking and surface translocation but is essential for AMA-1 function. Although this function can be mimicked by the highly conserved cytoplasmic domains of P. vivax and P. berghei, the exchange with the heterologous domain of the microneme protein EBA-175 or the rhoptry protein Rh2b leads to a loss of function. We identify several residues in the cytoplasmic tail that are essential for AMA-1 function. We validate this data using additional transgenic parasite lines expressing AMA-1 mutants with TY1 epitopes. We show that the cytoplasmic domain of AMA-1 is phosphorylated. Mutational analysis suggests an important role for the phosphorylation in the invasion process, which might translate into novel therapeutic strategies
Otolith geochemistry does not reflect dispersal history of clownfish larvae
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Coral Reefs 29 (2010): 883-891, doi:10.1007/s00338-010-0652-z.Natural geochemical signatures in calcified structures are commonly employed to retrospectively estimate dispersal pathways of larval fish and invertebrates. However, the accuracy of the approach is generally untested due to the absence of individuals with known dispersal histories. We used genetic parentage analysis (genotyping) to divide 110 new recruits of the orange clownfish, Amphiprion percula, from Kimbe Island, Papua New Guinea, into two groups: “self-recruiters” spawned by parents on Kimbe Island and “immigrants” that had dispersed from distant reefs (>10km away). Analysis of daily increments in sagittal otoliths found no significant difference in PLDs or otolith growth rates between self-recruiting and immigrant larvae. We also quantified otolith Sr/Ca and Ba/Ca ratios during the larval phase using laser ablation inductively coupled plasma mass spectrometry. Again, we found no significant differences in larval profiles of either element between self-recruits and immigrants. Our results highlight the need for caution when interpreting otolith dispersal histories based on natural geochemical tags in the absence of water chemistry data or known-origin larvae with which to test the discriminatory ability of natural tags.Research was supported by the Australian Research Council, the Coral Reef Initiatives for the Pacific (CRISP), the Global Environmental Facility CRTR Connectivity Working Group, the Total Foundation, a National Science Foundation grant (#0424688) to SRT, and a National Science Foundation Graduate Research Fellowship to MLB
Trace element fingerprinting of cockle (Cerastoderma edule) shells can reveal harvesting location in adjacent areas
Determining seafood geographic origin is critical for controlling its quality and safeguarding
the interest of consumers. Here, we use trace element fingerprinting (TEF) of bivalve shells to
discriminate the geographic origin of specimens. Barium (Ba), manganese (Mn), magnesium (Mg),
strontium (Sr) and lead (Pb) were quantified in cockle shells (Cerastoderma edule) captured with
two fishing methods (by hand and by hand-raking) and from five adjacent fishing locations within
an estuarine system (Ria de Aveiro, Portugal). Results suggest no differences in TEF of cockle shells
captured by hand or by hand-raking, thus confirming that metal rakes do not act as a potential
source of metal contamination that could somehow bias TEF results. In contrast, significant
differences were recorded among locations for all trace elements analysed. A Canonical Analysis
of Principal Coordinates (CAP) revealed that 92% of the samples could be successfully classified
according to their fishing location using TEF. We show that TEF can be an accurate, fast and reliable
method to determine the geographic origin of bivalves, even among locations separated less
than 1 km apart within the same estuarine system. Nonetheless, follow up studies are needed to
determine if TEF can reliably discriminate between bivalves originating from different ecosystems
Thermal tolerance of Strongylocentrotus purpuratus early life history stages: mortality, stress-induced gene expression and biogeographic patterns
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