4,097 research outputs found
Poppet valve tester
Tester investigates fundamental factors affecting cyclic life and sealing performance of valve seats and poppets. Tester provides for varying impact loading of poppet against seat and rate of cycling, and controls amount and type of relative motion between sealing faces of seat and poppet. Relative motion between seat and poppet can be varied in three modes
Coalescence 2.0: a multiple branching of recent theoretical developments and their applications
Population genetics theory has laid the foundations for genomics analyses
including the recent burst in genome scans for selection and statistical
inference of past demographic events in many prokaryote, animal and plant
species. Identifying SNPs under natural selection and underpinning species
adaptation relies on disentangling the respective contribution of random
processes (mutation, drift, migration) from that of selection on nucleotide
variability. Most theory and statistical tests have been developed using the
Kingman coalescent theory based on the Wright-Fisher population model. However,
these theoretical models rely on biological and life-history assumptions which
may be violated in many prokaryote, fungal, animal or plant species. Recent
theoretical developments of the so called multiple merger coalescent models are
reviewed here ({\Lambda}-coalescent, beta-coalescent, Bolthausen-Snitzman,
{\Xi}-coalescent). We explicit how these new models take into account various
pervasive ecological and biological characteristics, life history traits or
life cycles which were not accounted in previous theories such as 1) the skew
in offspring production typical of marine species, 2) fast adapting
microparasites (virus, bacteria and fungi) exhibiting large variation in
population sizes during epidemics, 3) the peculiar life cycles of fungi and
bacteria alternating sexual and asexual cycles, and 4) the high rates of
extinction-recolonization in spatially structured populations. We finally
discuss the relevance of multiple merger models for the detection of SNPs under
selection in these species, for population genomics of very large sample size
and advocate to potentially examine the conclusion of previous population
genetics studies.Comment: 3 Figure
The Development of Language Learning Aptitude and Metalinguistic Awareness in Primary-School Children: A Classroom Study
In the typical foreign language classroom, many learners all over the world find themselves in a minimal-input environment. Existing research suggests that in such a setting, adolescents typically outperform younger children. The greater cognitive maturity of older learners manifests itself in greater language learning aptitude, greater metalinguistic awareness, and enhanced capacity for explicit learning. We examined whether the teaching and learning of either Esperanto or French would facilitate the development of language learning aptitude and metalinguistic awareness in 8-9-year-old children (N=28), thus setting the scene for enhanced explicit learning even at a young age. Following instruction in either Esperanto or French over a school year, children made significant gains on measures of aptitude, metalinguistic awareness, and L2 proficiency. Effect sizes in the Esperanto group were larger throughout, however, with greater homogeneity of performance in evidence and a closer association between aptitude, metalinguistic awareness, and L2 proficiency at the end of the treatment. Moreover, Esperanto proved significantly easier to learn than French, with larger gains in L2 proficiency achieved by the Esperanto group compared with the French group. Finally, we found that language-analytic ability emerged as a significant predictor of L2 achievement in the sample as a whole
Effective Spoken Language Labeling with Deep Recurrent Neural Networks
Understanding spoken language is a highly complex problem, which can be
decomposed into several simpler tasks. In this paper, we focus on Spoken
Language Understanding (SLU), the module of spoken dialog systems responsible
for extracting a semantic interpretation from the user utterance. The task is
treated as a labeling problem. In the past, SLU has been performed with a wide
variety of probabilistic models. The rise of neural networks, in the last
couple of years, has opened new interesting research directions in this domain.
Recurrent Neural Networks (RNNs) in particular are able not only to represent
several pieces of information as embeddings but also, thanks to their recurrent
architecture, to encode as embeddings relatively long contexts. Such long
contexts are in general out of reach for models previously used for SLU. In
this paper we propose novel RNNs architectures for SLU which outperform
previous ones. Starting from a published idea as base block, we design new deep
RNNs achieving state-of-the-art results on two widely used corpora for SLU:
ATIS (Air Traveling Information System), in English, and MEDIA (Hotel
information and reservation in France), in French.Comment: 8 pages. Rejected from IJCAI 2017, good remarks overall, but slightly
off-topic as from global meta-reviews. Recommendations: 8, 6, 6, 4. arXiv
admin note: text overlap with arXiv:1706.0174
Fisher-Wright model with deterministic seed bank and selection
Seed banks are a common characteristics to many plant species, which allow
storage of genetic diversity in the soil as dormant seeds for various periods
of time. We investigate an above-ground population following a Fisher-Wright
model with selection coupled with a deterministic seed bank assuming the length
of the seed bank is kept constant and the number of seeds is large. To assess
the combined impact of seed banks and selection on genetic diversity, we derive
a general diffusion model. The applied techniques outline a path of
approximating a stochastic delay differential equation by an appropriately
rescaled stochastic differential equation, which is a common issue in
statistical physics. We compute the equilibrium solution of the site-frequency
spectrum and derive the times to fixation of an allele with and without
selection. Finally, it is demonstrated that seed banks enhance the effect of
selection onto the site-frequency spectrum while slowing down the time until
the mutation-selection equilibrium is reached
Various Types of Learning with Types
International audienceThis paper suggests another look on already known grammatical inference approaches based on specialization strategies
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