Tracer studies on the solid state

A study of self-diffusion in anthracene single crystals has been carried out using a radioactive tracer technique. A method was developed for the growth of large single crystals of anthracene from the melt, starting from the Bridgman technique. On to one surface of the crystals was evaporated a deposit of anthracene - 9 - carbon-14, prepared by a seven stage synthesis from barium 14-carbonate, and the crystals and their deposits were heated at constant temperatures in the range 150 -190 G for periods up to 230 hours. The crystals were then sectioned parallel to the initial active face, using a calibrated, hand operated, lathe. The quantity of radioactive material which had diffused into each section was determined by quantitative combustion of the sections to carbon dioxide in an "Empty Tube" rapid combustion apparatus, followed by the determination of the disintegration rate of this gas in a gas counting tube, using carbon disulphide as charge transfer agent. Penetration was found up to a depth of 4 x 10(^-2) cms. It was found that two concurrent diffusion processes were occurring in the crystal. One of these involved only a small proportion of the total diffusing activity and may represent diffusion along intersecting dislocations in the crystal. The second process involved most of the diffusing activity and was thought to represent bulk diffusion in the crystal The temperature dependance of the diffusion coefficient for the second process is given lay the equation. D = (1.31 ± 1.13) x l0(^ll)e (^–(42,400 ± 1,200)/RT) cm. (^2) per second. The pre-exponential factor and activation energy for this process are unusually high. This leads to the conclusion that a co-operative diffusion phenomenon is occurring in the crystal, in which diffusion occurs by way of vacant lattice sites, and that the loosening or premelting of from four to six molecules occurs in the neighbourhood of the vacancy during diffusion. This is one of the few studies of self-diffusion in molecular crystals

Escherichia coli, Salmonella, and Mycobacterium avium subsp. paratuberculosis in Wild European Starlings at a Kansas Cattle Feedlot

The prevalence of Escherichia coli, Salmonella spp., and Mycobacterium avium subsp.paratuberculosis isolated from the feces of wild European starlings (Sturnus vulgaris) humanely trapped at a feedlot in central Kansas was assessed. All E. coli and Salmonellaisolates recovered were tested for antimicrobial susceptibility using National Antimicrobial Resistance Monitoring System panels and the E. coli isolates were classified as to their content of genes associated with pathogenic E. coli of birds and cattle, including cvaC, iroN2, ompTp, hlyF2, eitC, iss, iutA, ireA, papC, stxI, stxII, sta, K99, F41, and eae.Escherichia coli O157:H7 and Mycobacterium avium subsp. paratuberculosis were not detected and Salmonella was isolated from only three samples, two of which displayed antimicrobial resistance. Approximately half of the E. coli isolates were resistant to antimicrobial agents with 96% showing resistance to tetracycline. Only one isolate was positive for a single gene associated with bovine pathogenic E. coli. An interesting finding of this study was that 5% of the E. coli isolates tested met the criteria established for identification as avian pathogenic E. coli (APEC). Thus these findings suggest that starlings are not a significant source of Salmonella spp., Mycobacterium avium subsp.paratuberculosis, E. coli O157, or other shiga toxin–producing E. coli in this feedlot. However, they may have the potential to spread APEC, an important pathogen of poultry and a potential pathogen to human beings

INSPIRE: Interplanetary NanoSpacecraft Pathfinder in Relevant Environment

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106507/1/AIAA2013-5323.pd

Lime stabilisation for earthworks: a UK perspective

Lime stabilisation is a versatile technique applied during earthworks operations. Modern soil recycling units are much more efficient at pulverising fill material and intermixing the added binder/water than machinery available 20 years ago. While supplier innovation adds flexibility to the site working method, specifications have not been sufficiently updated to permit optimal application. This review paper details the physico-chemical changes instigated through the lime-clay soil reaction, updating previous reviews. It aims to assist scientific debate, current practitioners and future specification changes. For example, the application of the minimum 24 h mellowing periods (mandatory to UK specifications) with high reactivity, quicklime powders is concluded to cause increased air voids in the compacted fill. Increased air voids are associated with reduced long-term strength and potential volume change from water ingress, which is of particular concern for sulfate swelling. Shorter mellowing periods and/or use of hydrated lime may lesson this issue; however, a 'one size fits all' approach is discouraged in preference to site-specific methodologies refined to suit the fill material and project requirements. The discussion also summarises working methods which may lower the risk of sulfate swell and defines areas requiring further practical research

A Secure DHT via the Pigeonhole Principle

The standard Byzantine attack model assumes no more than some fixed fraction of the participants are faulty. This assumption does not accurately apply to peer-to-peer settings, where Sybil attacks and botnets are realistic threats. We propose an attack model that permits an arbitrary number of malicious nodes under the assumption that each node can be classified based on some of its attributes, such as autonomous system number or operating system, and that the number of classes with malicious nodes is bounded (e.g., an attacker may exploit at most a few operating systems at a time). In this model, we present a secure DHT, evilTwin, which replaces a single, large DHT with sufficiently many smaller instances such that it is impossible for an adversary to corrupt every instance. Our system ensures high availability and low-latency lookups, is easy to implement, does not require a complex Byzantine agreement protocol, and its proof of security is a straightforward application of the pigeonhole principle. The cost of security comes in the form of increased storage and bandwidth overhead; we show how to reduce these costs by replicating data and adaptively querying participants who historically perform well. We use implementation and simulation to show that evilTwin imposes a relatively small additional cost compared to conventional DHTs

Effect of roughness formulation on the performance of a coupled wave, hydrodynamic, and sediment transport model

This paper is not subject to U.S. copyright. The definitive version was published in Ocean Modelling 33 (2010): 299-313, doi:10.1016/j.ocemod.2010.03.003.A variety of algorithms are available for parameterizing the hydrodynamic bottom roughness associated with grain size, saltation, bedforms, and wave–current interaction in coastal ocean models. These parameterizations give rise to spatially and temporally variable bottom-drag coefficients that ostensibly provide better representations of physical processes than uniform and constant coefficients. However, few studies have been performed to determine whether improved representation of these variable bottom roughness components translates into measurable improvements in model skill. We test the hypothesis that improved representation of variable bottom roughness improves performance with respect to near-bed circulation, bottom stresses, or turbulence dissipation. The inner shelf south of Martha’s Vineyard, Massachusetts, is the site of sorted grain-size features which exhibit sharp alongshore variations in grain size and ripple geometry over gentle bathymetric relief; this area provides a suitable testing ground for roughness parameterizations. We first establish the skill of a nested regional model for currents, waves, stresses, and turbulent quantities using a uniform and constant roughness; we then gauge model skill with various parameterization of roughness, which account for the influence of the wave-boundary layer, grain size, saltation, and rippled bedforms. We find that commonly used representations of ripple-induced roughness, when combined with a wave–current interaction routine, do not significantly improve skill for circulation, and significantly decrease skill with respect to stresses and turbulence dissipation. Ripple orientation with respect to dominant currents and ripple shape may be responsible for complicating a straightforward estimate of the roughness contribution from ripples. In addition, sediment-induced stratification may be responsible for lower stresses than predicted by the wave–current interaction model.Funding was provided through the Office of Naval Research Ripples DRI and U.S. Geological Survey Coastal and Marine Geology Program

Technical tip: high-resolution isolation of nanoparticle–protein corona complexes from physiological fluids

Nanoparticles (NPs) in contact with biological fluids are generally coated with environmental proteins, forming a stronger layer of proteins around the NP surface called the hard corona. Protein corona complexes provide the biological identity of the NPs and their isolation and characterization are essential to understand their in vitro and in vivo behaviour. Here we present a one-step methodology to recover NPs from complex biological media in a stable non-aggregated form without affecting the structure or composition of the corona. This method allows NPs to be separated from complex fluids containing biological particulates and in a form suitable for use in further experiments. The study has been performed systematically comparing the new proposed methodology to standard approaches for a wide panel of NPs. NPs were first incubated in the biological fluid and successively recovered by sucrose gradient ultracentrifugation in order to separate the NPs and their protein corona from the loosely bound proteins. The isolated NP–protein complexes were characterized by size and protein composition through Dynamic Light Scattering, Nanoparticle Tracking Analysis, SDS-PAGE and LC-MS. The protocol described is versatile and can be applied to diverse nanomaterials and complex fluids. It is shown to have higher resolution in separating the multiple protein corona complexes from a biological environment with a much lower impact on their in situ structure compared to conventional centrifugal approaches

Methylation and Loss of Secreted Frizzled-Related Protein 3 Enhances Melanoma Cell Migration and Invasion

Wnt signaling is important in development and can also contribute to the initiation and progression of cancer. The Secreted Frizzled Related Proteins (SFRPs) constitute a family of Wnt modulators, crucial for controlling Wnt signaling. Here we investigate the expression and role of SFRP3 in melanoma