1,128 research outputs found
Hindcasting cyanobacterial communities in Lake Okaro with germination experiments and genetic analyses
Cyanobacterial blooms are becoming increasingly prevalent worldwide. Sparse historic phytoplankton records often result in uncertainty as to whether bloom-forming species have always been present and are proliferating in response to eutrophication or climate change, or if there has been a succession of new arrivals through recent history. This study evaluated the relative efficacies of germination experiments and automated rRNA intergenic spacer analysis (ARISA) assays in identifying cyanobacteria in a sediment core and thus reconstructing the historical composition of cyanobacterial communities. A core (360 mm in depth) was taken in the central, undisturbed basin of Lake Okaro, New Zealand, a lake with a rapid advance of eutrophication and increasing cyanobacteria populations. The core incorporated a tephra from an 1886 volcanic eruption that served to delineate recent sediment deposition. ARISA and germination experiments successfully detected akinete-forming nostocaleans in sediment dating 120 bp and showed little change in Nostocales species structure over this time scale. Species that had not previously been documented in the lake were identified including Aphanizomenon issatschenkoi, a potent anatoxin-a producer. The historic composition of Chrococcales and Oscillatoriales was more difficult to reconstruct, potentially due to the relatively rapid degradation of vegetative cells within sediment
Deformation, seismicity, and fluids: Results of the 2004/2005 water injection experiment at the KTB/Germany
Unexpected mutual regulation underlies paralogue functional diversification and promotes epithelial tissue maturation in Tribolium
Insect Hox3/zen genes represent an evolutionary hotspot for changes in function and copy number. Single orthologues are required either for early specification or late morphogenesis of the extraembryonic tissues, which protect the embryo. The tandemly duplicated zen paralogues of the beetle Tribolium castaneum present a unique opportunity to investigate both functions in a single species. We dissect the paralogues' expression dynamics (transcript and protein) and transcriptional targets (RNA-seq after RNAi) throughout embryogenesis. We identify an unexpected role of Tc-Zen2 in repression of Tc-zen1, generating a negative feedback loop that promotes developmental progression. Tc-Zen2 regulation is dynamic, including within co-expressed multigene loci. We also show that extraembryonic development is the major event within the transcriptional landscape of late embryogenesis and provide a global molecular characterization of the extraembryonic serosal tissue. Altogether, we propose that paralogue mutual regulation arose through multiple instances of zen subfunctionalization, leading to their complementary extant roles
Towards a conflict account of déjà vu : the role of memory errors and memory expectation conflict in the experience of déjà vu
This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) [grant number BB/M010996/1].DĂ©jĂ vu can be defined as conflict between a subjective evaluation of familiarity and a concurrent evaluation of novelty. Accounts of the dĂ©jĂ vu experience have not explicitly referred to a âconflict account of dĂ©jĂ vuâ despite the acceptance of conflict-based definitions of dĂ©jĂ vu and relatively recent neuroimaging work that has implicated brain areas associated with conflict as underpinning the experience. Conflict monitoring functioning follows a similar age-related trajectory to dĂ©jĂ vu with a peak in young adulthood and a subsequent age-related decline. In this narrative review of the literature to date, we consider how dĂ©jĂ vu is defined and how this has influenced the understanding of dĂ©jĂ vu. We also review how dĂ©jĂ vu can be understood within theories of recognition memory and cognitive control. Finally, we summarise the conflict account of dĂ©jĂ vu and propose that this account of the experience may provide a coherent explanation as to why dĂ©jĂ vu experiences tend to decrease with age in the non-clinical population.Publisher PDFPeer reviewe
On the noise-induced passage through an unstable periodic orbit II: General case
Consider a dynamical system given by a planar differential equation, which
exhibits an unstable periodic orbit surrounding a stable periodic orbit. It is
known that under random perturbations, the distribution of locations where the
system's first exit from the interior of the unstable orbit occurs, typically
displays the phenomenon of cycling: The distribution of first-exit locations is
translated along the unstable periodic orbit proportionally to the logarithm of
the noise intensity as the noise intensity goes to zero. We show that for a
large class of such systems, the cycling profile is given, up to a
model-dependent change of coordinates, by a universal function given by a
periodicised Gumbel distribution. Our techniques combine action-functional or
large-deviation results with properties of random Poincar\'e maps described by
continuous-space discrete-time Markov chains.Comment: 44 pages, 4 figure
Social control in civil wars
The primacy of territorial control in theories of civil war has advanced our understanding of war dynamics, most notably lethal violence, but has hindered our understanding of the distinct ways in which armed groups seek control over people. We propose to complement territorial control by separately conceptualising social control, which we define as the extent to which armed groups have access to people and their resources. Access to people requires different tactics compared to access to territory, because people are mobile. We develop a framework in which state and non-state armed groups choose whether to prioritise territorial or social control first in order to gain sovereignty, which requires both territorial and social control. Alternatively, armed groups choose to pursue territorial control or social control only, resulting in corridors or social networks, respectively. We illustrate the advantages of the framework by showing how it allows us to analyse armed groupsâ tactics to control access to people, to connect research agendas on armed group violence, governance, and civilian displacement, and to better conceptualise armed group power and strength.Institutions, Decisions and Collective Behaviou
Mixed-mode oscillations and interspike interval statistics in the stochastic FitzHugh-Nagumo model
We study the stochastic FitzHugh-Nagumo equations, modelling the dynamics of
neuronal action potentials, in parameter regimes characterised by mixed-mode
oscillations. The interspike time interval is related to the random number of
small-amplitude oscillations separating consecutive spikes. We prove that this
number has an asymptotically geometric distribution, whose parameter is related
to the principal eigenvalue of a substochastic Markov chain. We provide
rigorous bounds on this eigenvalue in the small-noise regime, and derive an
approximation of its dependence on the system's parameters for a large range of
noise intensities. This yields a precise description of the probability
distribution of observed mixed-mode patterns and interspike intervals.Comment: 36 page
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