451 research outputs found
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Artificial evolution of the morphology and kinematics in a flapping-wing mini-UA
Open-Ended Evolutionary Robotics: an Information Theoretic Approach
This paper is concerned with designing self-driven fitness functions for
Embedded Evolutionary Robotics. The proposed approach considers the entropy of
the sensori-motor stream generated by the robot controller. This entropy is
computed using unsupervised learning; its maximization, achieved by an on-board
evolutionary algorithm, implements a "curiosity instinct", favouring
controllers visiting many diverse sensori-motor states (sms). Further, the set
of sms discovered by an individual can be transmitted to its offspring, making
a cultural evolution mode possible. Cumulative entropy (computed from ancestors
and current individual visits to the sms) defines another self-driven fitness;
its optimization implements a "discovery instinct", as it favours controllers
visiting new or rare sensori-motor states. Empirical results on the benchmark
problems proposed by Lehman and Stanley (2008) comparatively demonstrate the
merits of the approach
Low expression of bcl-2 in Brca1-associated breast cancers
Little data are available concerning the molecular mechanisms of action of Brca1 and Brca2 in breast oncogenesis. Recent experimental results suggest that Brca1 plays a role in the regulation of apoptosis. In order to determine whether the analysis of human tumours would provide data supporting this hypothesis, we have assessed the expression of the antiapoptotic bcl-2 and of the proapoptotic p53 genes in Brca1- and Brca2-associated breast carcinomas. The levels of expression of these genes were compared to those observed in controls and to the mitotic and the apoptotic indexes. Our series were composed of 16 cases of breast carcinoma in women with a germline Brca1 gene mutation, and of four cases with Brca2 mutation. A group of 39 patients aged under 36 years and for whom the search for Brca1 gene mutations was negative, and a group of 36 cases of sporadic cancers without data on their Brca status were used as controls. Immunohistochemistry was used to detect p53 and bcl-2 gene products. Mitotic and apoptotic indexes were higher in Brca1-associated tumours than in controls. No significant difference in p53 immunostaining was observed between the four groups of patients. In contrast, the rate of bcl-2-positive tumours was lower (31%) in Brca1-carcinomas than in carcinomas without Brca1 mutation (90%) (P< 10â3). A strong Bcl-2 expression was found in the four cases of Brca2-associated carcinomas. No significant correlation was observed between p53 and Bcl-2 immunostainings, either in cases or in controls. The association between Brca1 status and Bcl-2 expression remained significant after adjustment for the oestrogen receptor status. Our study shows that a low expression of bcl-2 characterises most Brca1-associated breast carcinomas, a biological trait which seems not to be shared by Brca2-associated tumours nor to be related to oestrogen receptor and/or p53 status.bcl-2 might thus be one of the target genes involved in the oncogenesis related to Brca1 and its down-regulation may account for the increased apoptosis and the high proliferative rate observed in Brca1-associated carcinomas. © 2000 Cancer Research Campaig
Two dimensional mapping of iron release in marine sediments at submillimetre scale
Coastal and shelf sediments are considered as an important source of dissolved iron to the ocean. Here, we present a new numerical approach to estimate geochemical fluxes and production rates in an estuarine sediment at sub-millimetre resolution. This approach is based on application of SavitskyâGolay filter (SGF) procedure to two-dimensional concentration distributions of dissolved iron. We verified the procedure by applying it to artificial data of known production rates, and analysed the resulting uncertainty on production rates and fluxes across the waterâsediment interface. This SGF procedure was applied to data from an intertidal mudflat that is densely inhabited by macrofauna (e.g. 630 ind mâ 2 of Hediste diversicolor, I. MĂ©tais, pers.com.). Our analysis reveals an apparent recycling rate of 3780 ± 1399 Όmol mâ 2 dâ 1 and a mean residence time of iron in the dissolved phase of 2.3 days. Visual identification of burrows permitted to calculate separately the diffusive flux across the sedimentâwater interface (104 ± 20 Όmol mâ 2 dâ 1) and the bio-irrigational flux (410 ± 213 Όmol mâ 2 dâ 1). Reactive iron particles will undergo on average 7.4 cycles of dissolution/precipitation before being released to the water column. These results show that estuarine sediments support intensive iron recycling that has probably a large impact on terrigeneous particles before being released into the ocean
Local adaptations of Mediterranean sheep and goats through an integrative approach
Small ruminants are suited to a wide variety of habitats and thus represent promising study models for identifying genes underlying adaptations. Here, we considered local Mediterranean breeds of goats (n = 17) and sheep (n = 25) from Italy, France and Spain. Based on historical archives, we selected the breeds potentially most linked to a territory and defined their original cradle (i.e., the geographical area in which the breed has emerged), including transhumant pastoral areas. We then used the programs PCAdapt and LFMM to identify signatures of artificial and environmental selection. Considering cradles instead of current GPS coordinates resulted in a greater number of signatures identified by the LFMM analysis. The results, combined with a systematic literature review, revealed a set of genes with potentially key adaptive roles in relation to the gradient of aridity and altitude. Some of these genes have been previously implicated in lipid metabolism (SUCLG2, BMP2), hypoxia stress/lung function (BMPR2), seasonal patterns (SOX2, DPH6) or neuronal function (TRPC4, TRPC6). Selection signatures involving the PCDH9 and KLH1 genes, as well as NBEA/NBEAL1, were identified in both species and thus could play an important adaptive role
Neurogenesis Drives Stimulus Decorrelation in a Model of the Olfactory Bulb
The reshaping and decorrelation of similar activity patterns by neuronal
networks can enhance their discriminability, storage, and retrieval. How can
such networks learn to decorrelate new complex patterns, as they arise in the
olfactory system? Using a computational network model for the dominant neural
populations of the olfactory bulb we show that fundamental aspects of the adult
neurogenesis observed in the olfactory bulb -- the persistent addition of new
inhibitory granule cells to the network, their activity-dependent survival, and
the reciprocal character of their synapses with the principal mitral cells --
are sufficient to restructure the network and to alter its encoding of odor
stimuli adaptively so as to reduce the correlations between the bulbar
representations of similar stimuli. The decorrelation is quite robust with
respect to various types of perturbations of the reciprocity. The model
parsimoniously captures the experimentally observed role of neurogenesis in
perceptual learning and the enhanced response of young granule cells to novel
stimuli. Moreover, it makes specific predictions for the type of odor
enrichment that should be effective in enhancing the ability of animals to
discriminate similar odor mixtures
Specific local induction of DNA strand breaks by infrared multi-photon absorption
Highly confined DNA damage by femtosecond laser irradiation currently arises as a powerful tool to understand DNA repair in live cells as a function of space and time. However, the specificity with respect to damage type is limited. Here, we present an irradiation procedure based on a widely tunable Er/Yb : fiber femtosecond laser source that favors the formation of DNA strand breaks over that of UV photoproducts by more than one order of magnitude. We explain this selectivity with the different power dependence of the reactions generating strand breaks, mainly involving reactive radical intermediates, and the direct photochemical process leading to UV-photoproducts. Thus, localized multi-photon excitation with a wavelength longer than 1 ”m allows for the selective production of DNA strand breaks at sub-micrometer spatial resolution in the absence of photosensitizers
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SEIS: Insight's Seismic Experiment for Internal Structure of Mars.
By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars' surface the SEIS (Seismic Experiment for Internal Structure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking's Mars seismic monitoring by a factor of ⌠2500 at 1 Hz and ⌠200 000 at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars' surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of M w ⌠3 at 40 â epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution.Electronic supplementary materialThe online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users
Coupled calcium and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite
Shell chemistry of foraminiferal carbonate proves to be
useful in reconstructing past ocean conditions. A new addition to the proxy
toolbox is the ratio of sulfur (S) to calcium (Ca) in foraminiferal shells,
reflecting the ratio of SO42- to CO32- in seawater. When
comparing species, the amount of SO42- incorporated, and therefore
the SâCa of the shell, increases with increasing magnesium (Mg) content. The
uptake of SO42- in foraminiferal calcite is likely connected to
carbon uptake, while the incorporation of Mg is more likely related to Ca
uptake since this element substitutes for Ca in the crystal lattice. The
relation between S and Mg incorporation in foraminiferal calcite therefore
offers the opportunity to investigate the timing of processes involved in Ca
and carbon uptake. To understand how foraminiferal SâCa is related to MgâCa,
we analyzed the concentration and within-shell distribution of SâCa of three
benthic species with different shell chemistry: Ammonia tepida, Bulimina marginata and Amphistegina lessonii. Furthermore, we
investigated the link between MgâCa and SâCa across species and the
potential influence of temperature on foraminiferal SâCa. We observed that
SâCa is positively correlated with MgâCa on a microscale within specimens, as
well as between and within species. In contrast, when shell MgâCa increases
with temperature, foraminiferal SâCa values remain similar. We evaluate our
findings in the light of previously proposed biomineralization models and
abiological processes involved during calcite precipitation. Although all
kinds of processes, including crystal lattice distortion and element
speciation at the site of calcification, may contribute to changes in either
the amount of S or Mg that is ultimately incorporated in foraminiferal
calcite, these processes do not explain the covariation between MgâCa and
SâCa values within specimens and between species. We observe that groups of
foraminifera with different calcification pathways, e.g., hyaline versus
porcelaneous species, show characteristic values for SâCa and MgâCa, which
might be linked to a different calcium and carbon uptake mechanism in
porcelaneous and hyaline foraminifera. Whereas Mg incorporation might be
controlled by Ca dilution at the site of calcification due to Ca pumping, S
is linked to carbonate ion concentration via proton pumping. The fact that
we observe a covariation of S and Mg within specimens and between species
suggests that proton pumping and Ca pumping are intrinsically coupled across
multiple scales.</p
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