220 research outputs found
Radiological Risks of Neutron Interrogation of Food
In recent years there has been growing interest in the use of neutron scanning techniques for security. Neutron techniques with a range of energy spectra including thermal, white and fast neutrons have been shown to work in different
scenarios. As international interest in neutron scanning increases the risk of activating cargo, especially foodstuffs must be considered.
There has been a limited amount of research into the activation of foods by neutron beams and we have sought to improve the amount of information available. In this paper we show that for three important metrics; Activity, Ingestion
Dose and Time to Background there is a strong dependence on the food being irradiated and a weak dependence on the energy of irradiation.
Previous studies into activation used results based on irradiation of pharmaceuticals as the basis for research into activation of food. The earlier work reports that 24Na production is the dominant threat which motivated the search for 23(n;\gamma)24Na in highly salted foods. We show that 42K can be more significant than 24Na in low
salt foods such as Bananas and Potatoes
Mechanical properties of the superficial biofilm layer determine the architecture of biofilms
© 2016 The Royal Society of Chemistry. Cells in biofilms sense and interact with their environment through the extracellular matrix. The physicochemical properties of the matrix, particularly at the biofilm-environment interface, determine how cells respond to changing conditions. In this study we describe the application of atomic force microscopy and confocal imaging to probe in situ the mechanical properties of these interfacial regions and to elucidate how key matrix components can contribute to the physical sensing by the cells. We describe how the Young's modulus of microcolonies differs according to the size and morphology of microcolonies, as well as the flow rate. The Young's modulus increased as a function of microcolony diameter, which was correlated with the production of the polysaccharide Psl at later stages of maturation for hemispherical or mushroom shaped microcolonies. The Young's modulus of the periphery of the biofilm colony was however independent of the hydrodynamic shear. The morphology of the microcolonies also influenced interfacial or peripheral stiffness. Microcolonies with a diffuse morphology had a lower Young's modulus than isolated, circular ones and this phenomenon was due to a deficiency of Psl. In this way, changes in the specific polysaccharide components imbue the biofilm with distinct physical properties that may modulate the way in which bacteria perceive or respond to their environment. Further, the physical properties of the polysaccharides are closely linked to the specific architectures formed by the developing biofilm
Exploring Mechanisms for ModelâDependency of the Stratospheric Response to Arctic Warming
The Arctic is estimated to have warmed up to four times faster than the rest of the globe since the 1980s. There is significant interest in understanding the mechanisms by which such warming may impact weather and climate at lower latitudes. One such mechanism is the âstratospheric pathwayâ; Arctic warming is proposed to induce a waveâdriven weakening of the stratospheric polar vortex, which may subsequently impact largeâscale tropospheric circulation. However, recent comprehensive model studies have found systematic differences in both the magnitude and sign of the stratospheric response to Arctic warming. Using a series of idealized model simulations, we show that this response is sensitive to characteristics of the warming and mean polar vortex strength. In all simulations, imposed polar warming amplifies upward wave propagation from the troposphere, consistent with comprehensive models. However, as polar warming strength and depth increases, the region through which waves can propagate is narrowed, inducing wave breaking and deceleration of the flow in the lower stratosphere. Thus, the midâstratosphere is less affected, with reduced sudden stratospheric warming frequency for stronger and deeper warming compared to weaker and shallower warming. We also find that the sign of the stratospheric response depends on the mean strength of the vortex, and that the stratospheric response in turn plays a role in the magnitude of the tropospheric jet response. Our results help explain the spread across multimodel ensembles of comprehensive climate models
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Thorium Energy Futures
The potential for thorium as an alternative or supplement to uranium in fission power generation has long been recognised, and several reactors, of various types, have already operated using thorium-based fuels. Accelerator Driven Subcritical (ADS) systems have benefits and drawbacks when compared to conventional critical thorium reactors, for both solid and molten salt fuels. None of the four options â liquid or solid, with or without an accelerator â can yet be rated as better or worse than the other three, given today's knowledge. We outline the research that will be necessary to lead to an informed choice
Pamela: development of the RF system for a non-relativistic non-scaling FFAG
The PAMELA project(Particle Accelerator For MEdical
Applications) currently consists of the design of a particle
therapy facility. The project, which is in the design phase,
contains Non-Scaling FFAG, particle accelerator capable
of rapid beam acceleration, giving a pulse repetition rate of
1kHz, far beyond that of a conventional synchrotron. To
realise the repetition rate, a key component of the accelerator
is the rf accelerating system. The combination of a high
energy gain per turn and a high repetition rate is a significant
challenge. In this paper, options for the rf system of
the proton ring and the status of development are presented
Anomalous transport in normal-superconducting and ferromagnetic-superconducting nanostructures
We have calculated the temperature dependence of the conductance variation
() of mesoscopic superconductor normal metal(S/N) structures, in
the diffusive regime, analysing both weak and strong proximity effects. We show
that in the case of a weak proximity effect there are two peaks in the
dependence of on temperature. One of them (known from previous
studies) corresponds to a temperature of order of the Thouless energy
(), and another, newly predicted maximum, occurs at a
temperature where the energy gap in the superconductor is
of order . In the limit the temperature is
determined by ( is the phase breaking length),
and not . We have also calculated the voltage dependence for a S/F structure (F is a ferromagnet) and predict non-monotonic
behaviour at voltages of order the Zeeman splitting.Comment: 6 figures. Submitted to PRB Rapid com
Wave Energy Amplification in a Metamaterial based Traveling Wave Structure
We consider the interaction between a particle beam and a propagating
electromagnetic wave in the presence of a metamaterial. We show that the
introduction of a metamaterial gives rise to a novel dispersion curve which
determines a unique wave particle relationship, via the frequency dependence of
the metamaterial and the novel ability of metamaterials to exhibit simultaneous
negative permittivity and permeability. Using a modified form of Madey's
theorem we find that the novel dispersion of the metamaterial leads to a
amplification of the EM wave power
Influence of Supercurrents on Low-Temperature Thermopower in Mesoscopic N/S Structures
The thermopower of mesoscopic normal metal/superconductor structures has been
measured at low temperatures. Effect of supercurrent present in normal part of
the structure was studied in two cases: when it was created by applied external
magnetic field and when it was applied directly using extra superconducting
electrodes. Temperature and magnetic field dependencies of thermopower are
compared to the numerical simulations based on the quasiclassical theory of the
superconducting proximity effect.Comment: 21 pages, 12 figures. To be published in the proceedings of the ULTI
conference organized in Lammi, Finland (2006
An Explanation for the Metric Dependence of the Midlatitude JetâWaviness Change in Response to Polar Warming
The biofilm matrix scaffold of Pseudomonas aeruginosa contains G-quadruplex extracellular DNA structures.
Extracellular DNA, or eDNA, is recognised as a critical biofilm component; however, it is not understood how it forms networked matrix structures. Here, we isolate eDNA from static-culture Pseudomonas aeruginosa biofilms using ionic liquids to preserve its biophysical signatures of fluid viscoelasticity and the temperature dependency of DNA transitions. We describe a loss of eDNA network structure as resulting from a change in nucleic acid conformation, and propose that its ability to form viscoelastic structures is key to its role in building biofilm matrices. Solid-state analysis of isolated eDNA, as a proxy for eDNA structure in biofilms, reveals non-canonical Hoogsteen base pairs, triads or tetrads involving thymine or uracil, and guanine, suggesting that the eDNA forms G-quadruplex structures. These are less abundant in chromosomal DNA and disappear when eDNA undergoes conformation transition. We verify the occurrence of G-quadruplex structures in the extracellular matrix of intact static and flow-cell biofilms of P. aeruginosa, as displayed by the matrix to G-quadruplex-specific antibody binding, and validate the loss of G-quadruplex structures in vivo to occur coincident with the disappearance of eDNA fibres. Given their stability, understanding how extracellular G-quadruplex structures form will elucidate how P. aeruginosa eDNA builds viscoelastic networks, which are a foundational biofilm property
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