289 research outputs found
Negative Linear Compressibility
While all materials reduce their intrinsic volume under hydrostatic (uniform)
compression, a select few actually \emph{expand} along one or more directions
during this process of densification. As rare as it is counterintuitive, such
"negative compressibility" behaviour has application in the design of pressure
sensors, artificial muscles and actuators. The recent discovery of surprisingly
strong and persistent negative compressibility effects in a variety of new
families of materials has ignited the field. Here we review the phenomenology
of negative compressibility in this context of materials diversity, placing
particular emphasis on the common structural motifs that recur amongst known
examples. Our goal is to present a mechanistic understanding of negative
compressibility that will help inform a clear strategy for future materials
design.Comment: Submitted to PCC
Design of crystal-like aperiodic solids with selective disorder--phonon coupling
Functional materials design normally focuses on structurally-ordered systems
because disorder is considered detrimental to many important physical
properties. Here we challenge this paradigm by showing that particular types of
strongly-correlated disorder can give rise to useful characteristics that are
inaccessible to ordered states. A judicious combination of low-symmetry
building unit and high-symmetry topological template leads to aperiodic
"procrystalline" solids that harbour this type of topological disorder. We
identify key classes of procrystalline states together with their
characteristic diffraction behaviour, and establish a variety of mappings onto
known and target materials. Crucially, the strongly-correlated disorder we
consider is associated with specific sets of modulation periodicities
distributed throughout the Brillouin zone. Lattice dynamical calculations
reveal selective disorder-phonon coupling to lattice vibrations characterised
by these same periodicities. The principal effect on the phonon spectrum is to
bring about dispersion in energy rather than wave-vector, as in the
poorly-understood "waterfall" effect observed in relaxor ferroelectrics. This
property of procrystalline solids suggests a mechanism by which
strongly-correlated topological disorder might allow new and useful
functionalities, including independently-optimised thermal and electronic
transport behaviour as required for high-performance thermoelectrics.Comment: 4 figure
Fructan synthesis, accumulation, and polymer traits I:Festulolium chromosome substitution lines
The fructans found as storage carbohydrates in temperate forage grasses have a physiological role in regrowth and stress tolerance. They are also important for the nutritional value of fresh and preserved livestock feeds, and are potentially useful as feedstocks for biorefining. Seasonal variation in fructan content and the capacity for de novo fructan synthesis have been examined in a Festulolium monosomic substitution line family to investigate variation in the polymers produced by grasses in the ryegrass-fescue complex. There were significant differences between ryegrass and fescue. Fescue had low polymeric fructan content and a high oligomer/polymer ratio; synthesis of polymers longer than degree of polymerisation 6 (DP6) from oligomers was slow. However, extension of polymer length from DP10/DP20 upwards appeared to occur relatively freely, and, unlike ryegrass, fescue had a relatively even spread of polymer chain lengths above DP20. This included the presence of some very large polymers. Additionally fescue retained high concentrations of fructan, both polymeric and oligomeric, during conditions of low source/high sink demand. There were indications that major genes involved in the control of some of these traits might be located on fescue chromosome 3 opening the possibility to develop grasses optimised for specific applications
Fructan synthesis, accumulation and polymer traits II:Fructan pools in populations of perennial ryegrass (Lolium perenne L.) with variation for water-soluble carbohydrate and candidate genes were not correlated with biosynthetic activity and demonstrated constraints to polymer chain extension
Differences have been shown between ryegrass and fescue within the Festulolium subline introgression family for fructan synthesis, metabolism and polymer-size traits. It is well-established that there is considerable variation for water-soluble carbohydrate and fructan content within perennial ryegrass. However there is much still to be discovered about the fructan polymer pool in this species, especially in regard to its composition and regulation. It is postulated that similar considerable variation for polymer traits may exist, providing useful polymers for biorefining applications. Seasonal effects on fructan content together with fructan synthesis and polymer-size traits have been examined in diverse perennial ryegrass material comprising contrasting plants from a perennial ryegrass F2 mapping family and from populations produced by three rounds of phenotypic selection. Relationships with copy number variation in candidate genes have been investigated. There was little evidence of any variation in fructan metabolism across this diverse germplasm under these conditions that resulted in substantial differences in the complement of fructan polymers present in leaf tissue at high water-soluble carbohydrate concentrations. The importance of fructan synthesis during fructan accumulation was unclear as fructan content and polymer characteristics in intact plants during the growing season did not reflect the capacity for de novo synthesis. However, the retention of fructan in environmental conditions favouring high sink / low source demand may be an important component of the high sugar trait and the roles of breakdown and turnover are discussed
Individuals with higher metabolic rates have lower levels of reactive oxygen species in vivo
There is increasing interest in the effect of energy metabolism on oxidative stress, but much ambiguity over the relationship between the rate of oxygen consumption and the generation of reactive oxygen species (ROS). Production of ROS (such as hydrogen peroxide, H2O2) in the mitochondria is primarily inferred indirectly from measurements in vitro, which may not reflect actual ROS production in living animals. Here, we measured in vivo H2O2 content using the recently developed MitoB probe that becomes concentrated in the mitochondria of living organisms, where it is converted by H2O2 into an alternative form termed MitoP; the ratio of MitoP/MitoB indicates the level of mitochondrial H2O2 in vivo. Using the brown trout Salmo trutta, we tested whether this measurement of in vivo H2O2 content over a 24 h-period was related to interindividual variation in standard metabolic rate (SMR). We showed that the H2O2 content varied up to 26-fold among fish of the same age and under identical environmental conditions and nutritional states. Interindividual variation in H2O2 content was unrelated to mitochondrial density but was significantly associated with SMR: fish with a higher mass-independent SMR had a lower level of H2O2. The mechanism underlying this observed relationship between SMR and in vivo H2O2 content requires further investigation, but may implicate mitochondrial uncoupling which can simultaneously increase SMR but reduce ROS production. To our knowledge, this is the first study in living organisms to show that individuals with higher oxygen consumption rates can actually have lower levels of H2O2
The jellification of north temperate lakes.
Calcium (Ca) concentrations are decreasing in softwater lakes across eastern North America and western Europe. Using long-term contemporary and palaeo-environmental field data, we show that this is precipitating a dramatic change in Canadian lakes: the replacement of previously dominant pelagic herbivores (Ca-rich Daphnia species) by Holopedium glacialis, a jelly-clad, Ca-poor competitor. In some lakes, this transformation is being facilitated by increases in macro-invertebrate predation, both from native (Chaoborus spp.) and introduced (Bythotrephes longimanus) zooplanktivores, to which Holopedium, with its jelly coat, is relatively invulnerable. Greater representation by Holopedium within cladoceran zooplankton communities will reduce nutrient transfer through food webs, given their lower phosphorus content relative to daphniids, and greater absolute abundances may pose long-term problems to water users. The dominance of jelly-clad zooplankton will likely persist while lakewater Ca levels remain low.This work was primarily supported by grants from the Natural Sciences and Engineering
Research Council of Canada and funding from the Ontario Ministry of the Environment.This is the accepted manuscript. The final version is available at http://rspb.royalsocietypublishing.org/content/282/1798/20142449
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