1,328 research outputs found
Application of computer techniques to some problems in linear viscoelasticity
Computer solutions in terms of molecular theories of linear viscoelasticit
Attraction between Neutral Dielectrics Mediated by Multivalent Ions in an Asymmetric Ionic Fluid
We study the interaction between two neutral plane-parallel dielectric bodies
in the presence of a highly asymmetric ionic fluid, containing multivalent as
well as monovalent (salt) ions. Image charge interactions, due to dielectric
discontinuities at the boundaries, as well as effects from ion confinement in
the slit region between the surfaces are taken fully into account, leading to
image-generated depletion attraction, ion correlation attraction and
steric-like repulsive interactions. We investigate these effects by employing a
combination of methods including explicit-ion and implicit-ion Monte-Carlo
simulations, as well as an effective interaction potential analytical theory.
The latter incorporates strong ion-image charge correlations, which develop in
the presence of high valency ions in the mixture. We show that the implicit-ion
simulations and the proposed analytical theory can describe the explicit
simulation results on a qualitative level, while excellent quantitative
agreement can be obtained for sufficiently large monovalent salt
concentrations. The resultant attractive interaction between the neutral
surfaces is shown to be significant, as compared with the usual van der Waals
interactions between semi-infinite dielectrics, and can thus play a significant
role at the nano scale.Comment: 9 pages, 4 figure
Rare coral under the genomic microscope: timing and relationships among Hawaiian Montipora
Background
Evolutionary patterns of scleractinian (stony) corals are difficult to infer given the existence of few diagnostic characters and pervasive phenotypic plasticity. A previous study of Hawaiian Montipora (Scleractinia: Acroporidae) based on five partial mitochondrial and two nuclear genes revealed the existence of a species complex, grouping one of the rarest known species (M. dilatata, which is listed as Endangered by the International Union for Conservation of Nature - IUCN) with widespread corals of very different colony growth forms (M. flabellata and M. cf. turgescens). These previous results could result from a lack of resolution due to a limited number of markers, compositional heterogeneity or reflect biological processes such as incomplete lineage sorting (ILS) or introgression.
Results
All 13 mitochondrial protein-coding genes from 55 scleractinians (14 lineages from this study) were used to evaluate if a recent origin of the M. dilatata species complex or rate heterogeneity could be compromising phylogenetic inference. Rate heterogeneity detected in the mitochondrial data set seems to have no significant impacts on the phylogenies but clearly affects age estimates. Dating analyses show different estimations for the speciation of M. dilatata species complex depending on whether taking compositional heterogeneity into account (0.8 [0.05–2.6] Myr) or assuming rate homogeneity (0.4 [0.14–0.75] Myr). Genomic data also provided evidence of introgression among all analysed samples of the complex. RADseq data indicated that M. capitata colour morphs may have a genetic basis.
Conclusions
Despite the volume of data (over 60,000 SNPs), phylogenetic relationships within the M. dilatata species complex remain unresolved most likely due to a recent origin and ongoing introgression. Species delimitation with genomic data is not concordant with the current taxonomy, which does not reflect the true diversity of this group. Nominal species within the complex are either undergoing a speciation process or represent ecomorphs exhibiting phenotypic polymorphisms.info:eu-repo/semantics/publishedVersio
Exploring the association between welfare state and mental wellbeing in Europe: does age matter?
Previous research reports show mixed results regarding the age gradient in population mental wellbeing, which may be linked to the role that welfare states play. In this study, we investigate whether an age gradient exists in relation to the association between welfare state and mental wellbeing within the adult population in Europe. We combine individual level data from Round 6 of the European Social Survey and country level data on welfare state and use multilevel regression analyses to explore population mental wellbeing. Subjective and psychological wellbeing dimensions were analyzed, and different approaches to measuring welfare state were explored, including a regime typology and composite welfare state measures constructed on the basis of a set of eight individual indicators. We found the age gradient for mental wellbeing to differ between welfare states, with the positive impact of the welfare state increasing with age. A universal and generous welfare state seems to be particularly important for older adults, who are also more likely to be in higher need of transfers and services provided by the welfare state
Diversity and Relatedness Enhance Survival in Colour Polymorphic Grasshoppers
Evolutionary theory predicts that different resource utilization and behaviour by alternative phenotypes may reduce competition and enhance productivity and individual performance in polymorphic, as compared with monomorphic, groups of individuals. However, firm evidence that members of more heterogeneous groups benefit from enhanced survival has been scarce or lacking. Furthermore, benefits associated with phenotypic diversity may be counterbalanced by costs mediated by reduced relatedness, since closely related individuals typically are more similar. Pygmy grasshoppers (Tetrix subulata) are characterized by extensive polymorphism in colour pattern, morphology, behaviour and physiology. We studied experimental groups founded by different numbers of mothers and found that survival was higher in low than in high density, that survival peaked at intermediate colour morph diversity in high density, and that survival was independent of diversity in low density where competition was less intense. We further demonstrate that survival was enhanced by relatedness, as expected if antagonistic and competitive interactions are discriminately directed towards non-siblings. We therefore also performed behavioural observations and staged encounters which confirmed that individuals recognized and responded differently to siblings than to non-siblings. We conclude that negative effects associated with competition are less manifest in diverse groups, that there is conflicting selection for and against genetic diversity occurring simultaneously, and that diversity and relatedness may facilitate the productivity and ecological success of groups of interacting individuals
Classical Density Functional Study on Interfacial Structure and Differential Capacitance of Ionic Liquids near Charged Surfaces
We have implemented a generic coarse-grained model for the aromatic ionic liquid [CnMIM+][Tf2N-]. Various lengths for the alkyl chain on the cation define a homologous series, whose electric properties are expected to vary in a systematic way. Within the framework of a classical density functional theory, the interfacial structures of members of this series are compared over a range of surface charge densities, alkyl chain lengths, and surface geometries. The differential capacitance of the electric double layer, formed by ionic liquids against a charged electrode, is calculated as a function of the surface electric potential. A comparison of planar, cylindrical, and spherical surfaces confirms that the differential capacitance increases and varies less with surface potential as the surface curvature increases. Our results are in qualitative agreement with recent atomistic simulations
Fragility of the Dirac Cone Splitting in Topological Crystalline Insulator Heterostructures
The 'double Dirac cone' 2D topological interface states found on the (001)
faces of topological crystalline insulators such as PbSnSe
feature degeneracies located away from time reversal invariant momenta, and are
a manifestation of both mirror symmetry protection and valley interactions.
Similar shifted degeneracies in 1D interface states have been highlighted as a
potential basis for a topological transistor, but realizing such a device will
require a detailed understanding of the intervalley physics involved. In
addition, the operation of this or similar devices outside of ultra-high vacuum
will require encapsulation, and the consequences of this for the topological
interface state must be understood. Here we address both topics for the case of
2D surface states using angle-resolved photoemission spectroscopy. We examine
bulk PbSnSe(001) crystals overgrown with PbSe, realizing
trivial/topological heterostructures. We demonstrate that the valley
interaction that splits the two Dirac cones at each is extremely
sensitive to atomic-scale details of the surface, exhibiting non-monotonic
changes as PbSe deposition proceeds. This includes an apparent total collapse
of the splitting for sub-monolayer coverage, eliminating the Lifshitz
transition. For a large overlayer thickness we observe quantized PbSe states,
possibly reflecting a symmetry confinement mechanism at the buried topological
interface
Low Frequency Vibration Approach for Assessing Performance of Wood Floor Systems1
The primary means of inspecting buildings and other structures is to evaluate each structure member individually. This is a time-consuming and expensive process, particularly if sheathing or other covering materials must be removed to access the structural members. The objective of this study was to determine if a low frequency vibration method could be used to effectively assess the structural performance of wood floors as component systems. Twelve wood floors were constructed with solid sawn wood joists in the laboratory and tested with both vibration and static load methods. The results indicated that the forced vibration method was capable of measuring the fundamental natural frequency (bending mode) of the wood floors investigated. An analytical model derived from the flexural beam theory was found to fit the physics of the floor structures and can be used to correlate natural frequency to section modulus (EI product) of the floor systems
Density and conformation with relaxed substrate, bulk, and interface electrophoretic deposition of polymer chains
Characteristics of relaxed density profile and conformation of polymer chains
are studied by a Monte Carlo simulation on a discrete lattice in three
dimensions using different segmental (kink-jump , crank-shaft , reptation
) dynamics. Three distinct density regimes, substrate, bulk, and interface,
are identified. With the segmental dynamics we find that the substrate
coverage grows with a power-law, with a field
dependent nonuniversal exponent . The bulk volume
fraction and the substrate polymer density () increases
exponentially with the field (, ) in
the low field regime. The interface polymer density increases with the
molecular weight. With the segmental dynamics, bulk and substrate density
decreases linearly with the temperature at high temperatures. The bulk volume
fraction is found to decay with the molecular weight, . The radius of gyration remains Gaussian in all density regions.Comment: Changed double to single spacin
- …