Soft and stiff normal modes in floppy colloidal square lattices

Floppy microscale spring networks are widely studied in theory and simulations, but no well-controlled experimental system currently exists. Here, we show that square lattices consisting of colloid-supported lipid bilayers functionalized with DNA linkers act as microscale floppy spring networks. We extract their normal modes by inverting the particle displacement correlation matrix, showing the emergence of a spectrum of soft modes with low effective stiffness in addition to stiff modes that derive from linker interactions. Evaluation of the softest mode, a uniform shear mode, reveals that shear stiffness decreases with lattice size. Experiments match well with Brownian particle simulations and we develop a theoretical description based on mapping interactions onto linear response to describe the modes. Our results reveal the importance of entropic steric effects, and can be used for developing reconfigurable materials at the colloidal length scale

Proteomic analysis revealed that the oomyceticide phosphite exhibits multi-modal action in an oomycete pathosystem

Phytopathogenic oomycetes constitute some of the most devastating plant pathogens and cause significant crop and horticultural yield and economic losses. The phytopathogen Phytophthora cinnamomi causes dieback disease in native vegetation and several crops. The most commonly used chemical to control P. cinnamomi is the oomyceticide phosphite. Despite its widespread use, the mode of action of phosphite is not well understood and it is unclear whether it targets the pathogen, the host, or both. Resistance to phosphite is emerging in P. cinnamomi isolates and other oomycete phytopathogens. The mode of action of phosphite on phosphite-sensitive and resistant isolates of the pathogen and through a model host was investigated using label-free quantitative proteomics. In vitro treatment of sensitive P. cinnamomi isolates with phosphite hinders growth by interfering with metabolism, signalling and gene expression; traits that are not observed in the resistant isolate. When the model host Lupinus angustifolius was treated with phosphite, proteins associated with photosynthesis, carbon fixation and lipid metabolism in the host were enriched. Increased production of defence-related proteins was also observed in the plant. We hypothesise the multi-modal action of phosphite and present two models constructed using comparative proteomics that demonstrate mechanisms of pathogen and host responses to phosphite. Significance: Phytophthora cinnamomi is a significant phytopathogenic oomycete that causes root rot (dieback) in a number of horticultural crops and a vast range of native vegetation. Historically, areas infected with phosphite have been treated with the oomyceticide phosphite despite its unknown mode of action. Additionally, overuse of phosphite has driven the emergence of phosphite-resistant isolates of the pathogen. We conducted a comparative proteomic study of a sensitive and resistant isolate of P. cinnamomi in response to treatment with phosphite, and the response of a model host, Lupinus angustifolius, to phosphite and its implications on infection. The present study has allowed for a deeper understanding of the bimodal action of phosphite, suggested potential biochemical factors contributing to chemical resistance in P. cinnamomi, and unveiled possible drivers of phosphite-induced host plant immunity to the pathogen

Escitalopram restores reversal learning impairments in rats with lesions of orbital frontal cortex

This study was funded by H. Lundbeck A/S.The term ‘cognitive structures’ is used to describe the fact that mental models underlie thinking, reasoning and representing. Cognitive structures generally improve the efficiency of information processing by providing a situational framework within which there are parameters governing the nature and timing of information and appropriate responses can be anticipated. Unanticipated events that violate the parameters of the cognitive structure require the cognitive model to be updated, but this comes at an efficiency cost. In reversal learning a response that had been reinforced is no longer reinforced, while an alternative is now reinforced, having previously not been (A+/B− becomes A−/B+). Unanticipated changes of contingencies require that cognitive structures are updated. In this study, we examined the effect of lesions of the orbital frontal cortex (OFC) and the effects of the selective serotonin reuptake inhibitor (SSRI), escitalopram, on discrimination and reversal learning. Escitalopram was without effect in intact rats. Rats with OFC lesions had selective impairment of reversal learning, which was ameliorated by escitalopram. We conclude that reversal learning in OFC-lesioned rats is an easily administered and sensitive test that can detect effects of serotonergic modulation on cognitive structures that are involved in behavioural flexibility.Publisher PD

Trans-Planckian physics and signature change events in Bose gas hydrodynamics

We present an example of emergent spacetime as the hydrodynamic limit of a more fundamental microscopic theory. The low-energy, long-wavelength limit in our model is dominated by collective variables that generate an effective Lorentzian metric. This system naturally exhibits a microscopic mechanism allowing us to perform controlled signature change between Lorentzian and Riemannian geometries. We calculate the number of particles produced from a finite-duration Euclidean-signature event, where we take the position that to a good approximation the dynamics is dominated by the evolution of the linearized perturbations, as suggested by Calzetta and Hu [Phys. Rev. A 68 (2003) 043625]. We adapt the ideas presented by Dray et al. [Gen. Rel. Grav. 23 (1991) 967], such that the field and its canonical momentum are continuous at the signature-change event. We investigate the interplay between the underlying microscopic structure and the emergent gravitational field, focussing on its impact on particle production in the ultraviolet regime. In general, this can be thought of as the combination of trans-Planckian physics and signature-change physics. Further we investigate the possibility of using the proposed signature change event as an amplifier for analogue "cosmological particle production" in condensed matter experiments.Comment: 18 pages, revtex

Chemical Kinetic Modeling of Combustion of Automotive Fuels

The objectives of this report are to: (1) Develop detailed chemical kinetic reaction models for components of fuels, including olefins and cycloalkanes used in diesel, spark-ignition and HCCI engines; (2) Develop surrogate mixtures of hydrocarbon components to represent real fuels and lead to efficient reduced combustion models; and (3) Characterize the role of fuel composition on production of emissions from practical automotive engines

The innate immune signaling system as a regulator of disease resistance and induced systemic resistance activity against Verticillium dahliae

In the last decades, the plant innate immune responses against pathogens have been extensively studied, while biocontrol interactions between soilborne fungal pathogens and their hosts have received much less attention. Treatment of Arabidopsis thaliana with the nonpathogenic bacterium Paenibacillus alvei K165 was shown previously to protect against Verticillium dahliae by triggering induced systemic resistance (ISR). In the present study, we evaluated the involvement of the innate immune response in the K165-mediated protection of Arabidopsis against V. dahliae. Tests with Arabidopsis mutants impaired in several regulators of the early steps of the innate immune responses, including fls2, efr-1, bak1-4, mpk3, mpk6, wrky22, and wrky29 showed that FLS2 and WRKY22 have a central role in the K165-triggered ISR, while EFR1, MPK3, and MPK6 are possible susceptibility factors for V. dahliae and bak1 shows a tolerance phenomenon. The resistance induced by strain K165 is dependent on both salicylate and jasmonate-dependent defense pathways, as evidenced by an increased transient accumulation of PR1 and PDF1.2 transcripts in the aerial parts of infected plants treated with strain K165

Phytoplankton and microbial plankton of the Northeast Atlantic Shelf

The Northeast Atlantic Shelf region includes the sites from all coastal waters of Ireland, the Irish Sea, and western Scottish and Norwegian Sea waters. The region was defined by WGPME to include locations on the northern margin of Europe that were outside the North Sea/English Channel influence. The character of sites in the region are shallow, coastal-water sites ranging from sheltered bays on the south coast of Ireland and fjordic sea lochs of Scotland to fully exposed locations on the west coasts of Ireland and Scotland. Bathymetry of the region ranges from shallow embayments to regions of shallow, exposed continental-shelf waters. The topography of the shelf drops rapidly to 80–100 m within 20 km of the coast, where it extends to the shelf edge as a relatively flat plateau. Time-series of phytoplankton data from the Atlantic Shelf exhibit a typical seasonal pattern of temperate waters, with considerable geographical and temporal variation. The well-mixed winter conditions lead to a region-wide strong spring bloom observed at all sites. The ensuing decrease in nutrient levels lead to a variable summer period characterized by stratified conditions in coastal areas and periodic blooms of mixed or occasionally monospecific diatom and dinoflagellate composition. The growth period tails off in autumn, when a secondary bloom may occur in response to increased mixing and breakdown of the summer thermocline. The seasonal cycle returns to a quiescent winter phase, with generally mixed conditions, light limitation, and increased nutrients return. Seasonal stabilization and destabilization of the water column in this region accounts for most of the natural variation in both phytoplankton species composition and biomass

The use of immunoassay technology in the monitoring of algal biotoxins in farmed shellfish

The use of immunoassay technology as an adjunct method for monitoring biotoxins in shellfish was investigated at aquaculture sites in Killary Harbour, Ireland, during summer 2009. Sub-samples of mussels (Mytilus edulis) were taken from batches collected as part of the Irish National Phytoplankton and Biotoxin Monitoring Programme (NMP). Samples were analysed for Diarrhetic Shellfish Poisoning (DSP) toxins using a commercially available ELISA immunoassay kit. The results were compared with those obtained by chemical (liquid chromatography with mass spectrometry, LC-MS) and biological (mouse bioassay, MBA) methods from the monitoring programme. DSP levels increased in late June 2009 over the European Union maximum permitted level of 0.16 μg g-1 and positive MBA results led to harvest closures. This event was reflected in both the chemical and immunoassay results, where a positive relationship between them was found.This work is a contribution to project WATER and part-funded through Northern Periphery Programme

The occurrence of DSP toxicity in Ireland

The geographical and temporal variations in the occurrence of DSP in Ireland are presented and the implications of the resulting closures on aquaculture operations and fisheries are discussed. Prior to 1992 DSP toxicity had been confined to the southwest and south coasts but in 1992 a protracted occurrence of DSP was recorded in Killary Harbour on the west coast