3,378 research outputs found
Molecular Dynamics Simulations of a Pressure-induced Glass Transition
We simulate the compression of a two-component Lennard-Jones liquid at a
variety of constant temperatures using a molecular dynamics algorithm in an
isobaric-isothermal ensemble. The viscosity of the liquid increases with
pressure, undergoing a broadened transition into a structurally arrested,
amorphous state. This transition, like the more familiar one induced by
cooling, is correlated with a significant increase in icosahedral ordering. In
fact, the structure of the final state, as measured by an analysis of the
bonding, is essentially the same in the glassy, frozen state whether produced
by squeezing or by cooling under pressure. We have computed an effective
hard-sphere packing fraction at the transition, defining the transition
pressure or temperature by a cutoff in the diffusion constant, analogous to the
traditional laboratory definition of the glass transition by an arbitrary, low
cutoff in viscosity. The packing fraction at this transition point is not
constant, but is consistently higher for runs compressed at higher temperature.
We show that this is because the transition point defined by a constant cutoff
in the diffusion constant is not the same as the point of structural arrest, at
which further changes in pressure induce no further structural changes, but
that the two alternate descriptions may be reconciled by using a thermally
activated cutoff for the diffusion constant. This enables estimation of the
characteristic activation energy for diffusion at the point of structural
arrest.Comment: Latex using Revtex macro
Are current ecological restoration practices capturing natural levels of genetic diversity? A New Zealand case study using AFLP and ISSR data from mahoe (Melicytus ramiflorus)
Sourcing plant species of local provenance (eco-sourcing) has become standard practice in plant community restoration projects. Along with established ecological restoration practices, knowledge of genetic variation in existing and restored forest fragments is important for ensuring the maintenance of natural levels of genetic variation and connectivity (gene flow) among populations. The application of restoration genetics often employs anonymous ‘fingerprinting’ markers in combination with limited sample sizes due to financial constraints. Here, we used two such marker systems, AFLPs and ISSRs, to estimate population-level genetic variation of a frequently used species in restoration projects in New Zealand, māhoe (Melicytus ramiflorus, Violaceae). We examined two rural and two urban forest fragments, as potential local source populations, to determine whether the māhoe population at the recently (re)constructed ecosystem at Waiwhakareke Natural Heritage Park (WNHP), Hamilton, New Zealand reflects the genetic variation observed in these four potential source populations. Both marker systems produced similar results and indicated, even with small population sizes, that levels of genetic variation at WNHP were comparable to in situ populations. However, the AFLPs did provide finer resolution of the population genetic structure than ISSRs. ISSRs, which are less expensive and technically less demanding to generate than AFLPs, may be sufficient for restoration projects where only a broad level of genotypic resolution is required. We recommend the use of AFLPs when species with a high conservation status are being used due to the greater resolution of this technique
DNA and pacific commensal models : applications, construction, limitations, and future prospects
Components of the Pacific transported landscape have been used as proxies to trace the prehistoric movement of humans across the Pacific for almost two decades. Analyses of archaeological remains and DNA sequences of plants, animals, and microorganisms moved by or with humans have contributed to understanding prehistoric migration, trade, exchange, and sometimes revealed the geographic origins of particular plants and animals. This paper presents the basic elements of a DNA-based commensal model and discusses the phylogenetic and population genetic approaches these models employ. A clear delineation of the underlying assumptions of these models and the background information required to construct them have yet to appear in the literature. This not only provides a framework with which to construct a commensal model but also highlights gaps in current knowledge. The ways in which commensal models have enriched archaeological reconstructions will be highlighted, as will their current limitations. With these limitations in mind, options will be outlined for augmenting commensal models through the application of established techniques and new technologies in order to provide the best tools for reconstructing ancient human mobility and behavior in the Pacific and beyond
Ethnobiology : the missing link in ecology and evolution
Evolutionary biologists and ecologists increasingly appreciate the value of local knowledge of human communities for research into the past, present, and future of biodiversity. However, there are often significant problems accessing and interpreting this knowledge. Here, we argue that closer interaction with ethnobiologists, who study the relation between humans and the natural world, will enable local knowledge to be better applied in ecological and evolutionary biological research. This will provide more comprehensive answers to the scientific questions being asked, and will result in improved engagement with both academic and non-academic communities
Recommendations for aging beef (1993)
The main reason for aging beef is to improve tenderness and flavor of the meat so that if properly cooked it will be more satisfying to the consumer. Proper aging of beef results in a combination of changes that many people appreciate
Coordinated assembly and release of adhesions builds apical junctional belts during de novo polarisation of an epithelial tube
Using the zebrafish neural tube as a model, we uncover the in vivo
mechanisms allowing the generation of two opposing apical epithelial
surfaces within the centre of an initially unpolarised, solid organ.
We show that Mpp5a and Rab11a play a dual role in
coordinating the generation of ipsilateral junctional belts whilst
simultaneously releasing contralateral adhesions across the centre
of the tissue. We show that Mpp5a and Rab11a-mediated resolution of
cell-cell adhesions are both necessary for midline lumen opening and
contribute to later maintenance of epithelial organisation.We propose
that these roles for both Mpp5a and Rab11a operate through the
transmembrane protein Crumbs. In light of a recent conflicting
publication, we also clarify that the junction-remodelling role of Mpp5a is
not specific to dividing cells
Exploring multiple factors affecting participation outcomes for children with communication aids
Many factors affect how much communication aids support and promote children’s participation in everyday settings. However, little research has explored which combinations of environmental, child and communication aid factors appear most influential.
This paper will present preliminary findings from a pilot study of outcomes of communication aid provision to children. The main aims were to: (1) develop a self-report questionnaire for the parents and carers; (2) conduct a descriptive analysis of parents’ and carers’ perspectives.
It is hoped that this presentation will stimulate discussion on issues such as identifying key influential factors in the take-up and use of communication aids and measuring children’s participation
A holistic approach to fragile X syndrome integrated guidance for person-centred care
Background: The Fragile X community has expressed a desire for centralised, national guidelines in the form of integrated guidance for Fragile X Syndrome (FXS).
Methods: This article draws on existing literature reviews, primary research and clinical trials on FXS, a Fragile X Society conference workshop and first-hand experience of clinicians who have worked with those living with FXS over many years.
Results: The article scopes proposed integrated guidance over the life course, including appendices of symptoms, comorbidities and referral options for FXS and Fragile X Premutation Associated Conditions.
Conclusion: Integrated guidance would provide an authoritative source for doctors, health professionals, therapists, care workers, social workers, educators, employers, families and those living with FXS, so that a holistic, person-centred approach can be taken across the United Kingdom to garner the best outcomes for those with FXS
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Contrasting arbuscular mycorrhizal communities colonizing different host plants show a similar response to a soil phosphorus concentration gradient
High soil phosphorus (P) concentration is frequently shown to reduce root colonization by arbuscular mycorrhizal (AM) fungi, but the influence of P on the diversity of colonizing AM fungi is uncertain.
We used terminal restriction fragment length polymorphism (T-RFLP) of 18S rDNA and cloning to assess diversity of AM fungi colonizing maize (Zea mays), soybean (Glycene max) and field violet (Viola arvensis) at three time points in one season along a P gradient of 10–280 mg l−1 in the field.
Percentage AM colonization changed between sampling time points but was not reduced by high soil P except in maize. There was no significant difference in AM diversity between sampling time points. Diversity was reduced at concentrations of P > 25 mg l−1, particularly in maize and soybean. Both cloning and T-RFLP indicated differences between AM communities in the different host species. Host species was more important than soil P in determining the AM community, except at the highest P concentration.
Our results show that the impact of soil P on the diversity of AM fungi colonizing plants was broadly similar, despite the fact that different plants contained different communities. However, subtle differences in the response of the AM community in each host were evident
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