141 research outputs found
Metallurgy of soft spheres with hard core: from BCC to Frank-Kasper phases
Understanding how soft particles can fill the space is still an open
question. Structures far from classical FCC or BCC phases are now commonly
experimentally observed in many different systems. Models based on pair
interaction between soft particle are at present much studied in 2D. Pair
interaction with two different lengths have been shown to lead to
quasicrystalline architectures. It is also the case for a hard core with a
square repulsive shoulder potential. In 3D, global approaches have been
proposed for instance by minimizing the interface area between the deformed
objects in the case of foams or micellar systems or using self-consistent mean
field theory in copolymer melts. In this paper we propose to compare a strong
van der Waals attraction between spherical hard cores and an elastic energy
associated to the deformation of the soft corona. This deformation is measured
as the shift between the deformed shell compared to a corona with a perfect
spherical symmetry. The two main parameters in this model are: the hard core
volume fraction and the weight of the elastic energy compared to the van der
Waals one. The elastic energy clearly favours the BCC structure but large van
der Waals forces favors Frank and Kasper phases. This result opens a route
towards controlling the building of nanoparticle superlattices with complex
structures and thus original physical properties.Comment: To appear in EPJ
A Good Idea Gone Bad in the Service of Cultural Globalization: The Impact Factor in the Psychological Disciplines
Symbolic approach and induction in the Heisenberg group
We associate a homomorphism in the Heisenberg group to each hyperbolic
unimodular automorphism of the free group on two generators. We show that the
first return-time of some flows in "good" sections, are conjugate to
niltranslations, which have the property of being self-induced.Comment: 18 page
The intrinsic hypoelliptic Laplacian and its heat kernel on unimodular Lie groups
We present an invariant definition of the hypoelliptic Laplacian on sub-Riemannian structures with constant
growth vector, using the Popp\u2019s volume form introduced by Montgomery. This definition generalizes
the one of the Laplace-Beltrami operator in Riemannian geometry. In the case of left-invariant problems
on unimodular Lie groups we prove that it coincides with the usual sum of squares.
We then extend a method (first used by Hulanicki on the Heisenberg group) to compute explicitly
the kernel of the hypoelliptic heat equation on any unimodular Lie group of type I. The main tool is the
noncommutative Fourier transform. We then study some relevant cases: SU(2), SO(3), SL(2) (with the
metrics inherited by the Killing form), and the group SE(2) of rototranslations of the plane.
Our study is motivated by some recent results about the cut and conjugate loci on these sub-Riemannian
manifolds. The perspective is to understand how singularities of the sub-Riemannian distance reflect on
the kernel of the corresponding hypoelliptic heat equation
Global data on earthworm abundance, biomass, diversity and corresponding environmental properties
Publisher Copyright: © 2021, The Author(s).Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provided directly by authors, were collated with information on site locations, including coordinates, habitat cover, and soil properties. Datasets were required, at a minimum, to include abundance or biomass of earthworms at a site. Where possible, site-level species lists were included, as well as the abundance and biomass of individual species and ecological groups. This global dataset contains 10,840 sites, with 184 species, from 60 countries and all continents except Antarctica. The data were obtained from 182 published articles, published between 1973 and 2017, and 17 unpublished datasets. Amalgamating data into a single global database will assist researchers in investigating and answering a wide variety of pressing questions, for example, jointly assessing aboveground and belowground biodiversity distributions and drivers of biodiversity change.Peer reviewe
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Global data on earthworm abundance, biomass, diversity and corresponding environmental properties
Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provided directly by authors, were collated with information on site locations, including coordinates, habitat cover, and soil properties. Datasets were required, at a minimum, to include abundance or biomass of earthworms at a site. Where possible, site-level species lists were included, as well as the abundance and biomass of individual species and ecological groups. This global dataset contains 10,840 sites, with 184 species, from 60 countries and all continents except Antarctica. The data were obtained from 182 published articles, published between 1973 and 2017, and 17 unpublished datasets. Amalgamating data into a single global database will assist researchers in investigating and answering a wide variety of pressing questions, for example, jointly assessing aboveground and belowground biodiversity distributions and drivers of biodiversity change
Weathering of Rhyolites and Soil Formation in an Atlantic Forest Fragment in Northeastern Brazil
COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study
Background:
The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms.
Methods:
International, prospective observational study of 60â109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms.
Results:
âTypicalâ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (â€â18 years: 69, 48, 23; 85%), older adults (â„â70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each Pâ<â0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country.
Interpretation:
This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men
Juger de la valeur sociale des personnes : les pratiques sociales dâĂ©valuation
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