150 research outputs found
Symbolic Formulae for Linear Mixed Models
A statistical model is a mathematical representation of an often simplified
or idealised data-generating process. In this paper, we focus on a particular
type of statistical model, called linear mixed models (LMMs), that is widely
used in many disciplines e.g.~agriculture, ecology, econometrics, psychology.
Mixed models, also commonly known as multi-level, nested, hierarchical or panel
data models, incorporate a combination of fixed and random effects, with LMMs
being a special case. The inclusion of random effects in particular gives LMMs
considerable flexibility in accounting for many types of complex correlated
structures often found in data. This flexibility, however, has given rise to a
number of ways by which an end-user can specify the precise form of the LMM
that they wish to fit in statistical software. In this paper, we review the
software design for specification of the LMM (and its special case, the linear
model), focusing in particular on the use of high-level symbolic model formulae
and two popular but contrasting R-packages in lme4 and asreml
Biogeographic historical legacies in the net primary productivity of Northern Hemisphere forests
Older fathers' children have lower evolutionary fitness across four centuries and in four populations
Peer reviewe
Profile and width of rough interfaces
In the context of Landau theory and its field theoretical refinements,
interfaces between coexisting phases are described by intrinsic profiles. These
intrinsic interface profiles, however, are neither directly accessible by
experiment nor by computer simulation as they are broadened by long-wavelength
capillary waves. In this paper we study the separation of the small scale
intrinsic structure from the large scale capillary wave fluctuations in the
Monte Carlo simulated three-dimensional Ising model. To this purpose, a
blocking procedure is applied, using the block size as a variable cutoff, and a
translationally invariant method to determine the interface position of
strongly fluctuating profiles on small length scales is introduced. While the
capillary wave picture is confirmed on large length scales and its limit of
validity is estimated, an intrinsic regime is, contrary to expectations, not
observed.Comment: 18 pages, 4 Postscript figures, LaTeX2e, formulation of sec.3.2
improved, 1 reference adde
Relaxed selection and mutation accumulation are best studied empirically : reply to Woodley of Menie et al.
Correction to: replay to Woodley of Menie et al. 10.1098/rspb.2018.1427.Peer reviewe
Computing the Roughening Transition of Ising and Solid-On-Solid Models by BCSOS Model Matching
We study the roughening transition of the dual of the 2D XY model, of the
Discrete Gaussian model, of the Absolute Value Solid-On-Solid model and of the
interface in an Ising model on a 3D simple cubic lattice. The investigation
relies on a renormalization group finite size scaling method that was proposed
and successfully tested a few years ago. The basic idea is to match the
renormalization group flow of the interface observables with that of the
exactly solvable BCSOS model. Our estimates for the critical couplings are
, and for
the XY-model, the Discrete Gaussian model and the Absolute Value Solid-On-Solid
model, respectively. For the inverse roughening temperature of the Ising
interface we find . To the best of our knowledge,
these are the most precise estimates for these parameters published so far.Comment: 25 pages, LaTeX file, no figure
Monte Carlo Methods for Estimating Interfacial Free Energies and Line Tensions
Excess contributions to the free energy due to interfaces occur for many
problems encountered in the statistical physics of condensed matter when
coexistence between different phases is possible (e.g. wetting phenomena,
nucleation, crystal growth, etc.). This article reviews two methods to estimate
both interfacial free energies and line tensions by Monte Carlo simulations of
simple models, (e.g. the Ising model, a symmetrical binary Lennard-Jones fluid
exhibiting a miscibility gap, and a simple Lennard-Jones fluid). One method is
based on thermodynamic integration. This method is useful to study flat and
inclined interfaces for Ising lattices, allowing also the estimation of line
tensions of three-phase contact lines, when the interfaces meet walls (where
"surface fields" may act). A generalization to off-lattice systems is described
as well.
The second method is based on the sampling of the order parameter
distribution of the system throughout the two-phase coexistence region of the
model. Both the interface free energies of flat interfaces and of (spherical or
cylindrical) droplets (or bubbles) can be estimated, including also systems
with walls, where sphere-cap shaped wall-attached droplets occur. The
curvature-dependence of the interfacial free energy is discussed, and estimates
for the line tensions are compared to results from the thermodynamic
integration method. Basic limitations of all these methods are critically
discussed, and an outlook on other approaches is given
Within-individual phenotypic plasticity in flowers fosters pollination niche shift
Authors thank Raquel Sánchez, Angel Caravante, Isabel Sánchez Almazo, Tatiana López
Pérez, Samuel Cantarero, María José Jorquera and Germán Fernández for helping us during
several phases of the study and Iván Rodríguez Arós for drawing the insect silhouettes. This
research is supported by grants from the Spanish Ministry of Science, Innovation and
Universities (CGL2015-71634-P, CGL2015-63827-P, CGL2017-86626-C2-1-P, CGL2017-
86626-C2-2-P, UNGR15-CE-3315, including EU FEDER funds), Junta de Andalucía (P18-
FR-3641), Xunta de Galicia (CITACA), BBVA Foundation (PR17_ECO_0021), and a
contract grant to C.A. from the former Spanish Ministry of Economy and Competitiveness
(RYC-2012-12277). This is a contribution to the Research Unit Modeling Nature, funded by
the Consejería de Economía, Conocimiento, Empresas y Universidad, and European
Regional Development Fund (ERDF), reference SOMM17/6109/UGR.Phenotypic plasticity, the ability of a genotype of producing different phenotypes when exposed to different environments, may impact ecological interactions. We study here how within-individual plasticity in Moricandia arvensis flowers modifies its pollination niche. During spring, this plant produces large, cross-shaped, UV-reflecting lilac flowers attracting mostly long-tongued large bees. However, unlike most co-occurring species, M. arvensis keeps flowering during the hot, dry summer due to its plasticity in key vegetative traits. Changes in temperature and photoperiod in summer trigger changes in gene expression and the production of small, rounded, UV-absorbing white flowers that attract a different assemblage of generalist pollinators. This shift in pollination niche potentially allows successful reproduction in harsh conditions, facilitating M. arvensis to face anthropogenic perturbations and climate change. Floral phenotypes impact interactions between plants and pollinators. Here, the authors show that Moricandia arvensis displays discrete seasonal plasticity in floral phenotype, with large, lilac flowers attracting long-tongued bees in spring and small, rounded, white flowers attracting generalist pollinators in summer.Spanish Ministry of Science, Innovation and Universities (EU FEDER funds)
CGL2015-71634-P
CGL2015-63827-P
CGL2017-86626-C2-1-P
CGL2017-86626-C2-2-P
UNGR15-CE-3315Junta de Andalucia
P18-FR-3641Xunta de GaliciaBBVA Foundation
PR17_ECO_0021Spanish Ministry of Economy and Competitiveness
RYC-2012-12277Consejeria de Economia, Conocimiento, Empresas y Universidad
SOMM17/6109/UGREuropean Union (EU)
SOMM17/6109/UG
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