Synergistic efficacy of 405 nm light and chlorinated disinfectants for the enhanced decontamination of Clostridium difficile spores

The ability of Clostridium difficile to form highly resilient spores which can survive in the environment for prolonged periods causes major contamination problems. Antimicrobial 405 nm light is being developed for environmental decontamination within hospitals, however further information relating to its sporicidal efficacy is required. This study aims to establish the efficacy of 405 nm light for inactivation of C. difficile vegetative cells and spores, and to establish whether spore susceptibility can be enhanced by the combined use of 405 nm light with low concentration chlorinated disinfectants. Vegetative cells and spore suspensions were exposed to increasing doses of 405 nm light (at 70–225 mW/cm2) to establish sensitivity. A 99.9% reduction in vegetative cell population was demonstrated with a dose of 252 J/cm2, however spores demonstrated higher resilience, with a 10-fold increase in required dose. Exposures were repeated with spores suspended in the hospital disinfectants sodium hypochlorite, Actichlor and Tristel at non-lethal concentrations (0.1%, 0.001% and 0.0001%, respectively). Enhanced sporicidal activity was achieved when spores were exposed to 405 nm light in the presence of the disinfectants, with a 99.9% reduction achieved following exposure to 33% less light dose than required when exposed to 405 nm light alone. In conclusion, C. difficile vegetative cells and spores can be successfully inactivated using 405 nm light, the sporicidal efficacy can be significantly enhanced when exposed in the presence of low concentration chlorinated disinfectants. Further research may lead to the potential use of 405 nm light decontamination in combination with selected hospital disinfectants to enhance C. difficile cleaning and infection control procedures

Enhanced decontamination of C. difficile spores on surfaces via the synergistic action of 405nm light and disinfectants

The ability of C. difficile to form spores which can survive for prolonged periods causes significant environmental contamination problems. 405nm light has wide antimicrobial activity against vegetative bacteria, and is being developed for environmental decontamination within hospitals. As expected, spores are more resilient to inactivation. This study aims to establish whether spore susceptibility can be enhanced by combining 405nm light with low concentration chlorinated disinfectants: sodium hypochlorite, Actichlor and Tristel. Spore suspensions were seeded onto surfaces including PVC, stainless steel and vinyl flooring. Disinfectant was added to the surface, and the samples were then exposed to 405nm light at irradiances of ~0.2-225 mWcm-2. Control samples were exposed to 405nm light alone, and disinfectants alone, to establish the sporicidal activity of each agent, and to demonstrate the synergistic effect when combined. Results demonstrated increased sporicidal activity of 405nm light and low-concentration sodium hypochlorite and Actichlor against C. difficile seeded on vinyl flooring and PVC surfaces, with approximately 3-log10 reductions achieved with up to 66% lower doses than achieved with light alone. Tristel demonstrated limited synergy on vinyl and PVC, whilst all three disinfectants demonstrated minimal synergy on stainless steel. Results are also reported for lower intensity light, as used in the clinical environment. In conclusion, the sporicidal efficacy of 405nm light is enhanced when used alongside chlorinated disinfectants. Further research could potentially lead to the use of lower strength chlorinated disinfectants in combination with 405nm light to provide enhanced decontamination of C. difficile spores in the clinical environment

Decontamination of the hospital environment : new technologies for infection control

Environmental contamination is being increasingly recognized as a significant source of healthcare-associated infection (HAI). Cross-contamination of the patient from the environment can result from the direct transfer of organisms from the air and surfaces, or indirectly from the hospital environment via contact with healthcare workers or equipment. Traditional methods of environmental decontamination, including cleaning with disinfectants, and the standard infection control procedures implemented by modern Health Services, are critical to controlling the spread of potentially pathogenic microbial contaminants from environmental sources to the patient; however there is constant pressure to maintain, and indeed, improve on the standards that are in place to ensure optimal patient care. To address this issue, much research has been directed towards the development and testing of novel ‘whole-room’ environmental decontamination methods which could be used to enhance hospital hygiene, and consequently reduce the risk of HAI-acquisition from environmental sources. Gaseous methods such as the use of hydrogen peroxide, chlorine dioxide, ozone and steam, as well as ultraviolet and violet-blue visible light methods have all been laboratory tested, and to varying extents, clinically evaluated to assess their efficacy for environmental decontamination. This review article considers these different decontamination technologies, discussing their mechanism of action, antimicrobial efficacy, and advantages and limitations, with a view to providing the reader with a comprehensive overview of the technological advances being developed to reduce the levels of environmental contamination around patient areas, thus aiding in the fight against healthcare-associated infection

Recent Corrections to Meteoroid Environment Models

The dynamical and physical characteristics of a meteoroid affects its behavior in the atmosphere and the damage it does to spacecraft surfaces. Accurate environment models must therefore correctly describe the speed, size, density, and direction of meteoroids. However, the measurement of dynamical characteristics such as speed is subject to observational biases, and physical properties such as size and density cannot be directly measured. De-biasing techniques and proxies are needed to overcome these challenges. In this presentation, we discuss several recent improvements to the derivation of the meteoroid velocity, directionality, and bulk density distributions. We derive our speed distribution from observations made by the Canadian Meteor Orbit Radar. These observations are de-biased using modern descriptions of the ionization efficiency and sharpened to remove the effects of measurement uncertainty, and the result is a meteoroid speed distribution that is skewed slower than in previous analyses. We also adopt a higher fidelity density distribution than that used by many older models. In our distribution, meteoroids with T(sub J) less than 2 are assigned to a low-density population, while those with T(sub J) greater than 2 have higher densities. This division and the distributions themselves are derived from the densities reported by Kikwaya et al. (2009, 2011). These changes have implications for the environment. For instance, helion and antihelion meteors have lower speeds and higher densities than apex and toroidal meteors. A slower speed distribution therefore corresponds to a sporadic environment that is more completely dominated by the helion and antihelion sources than in previous models. Finally, assigning these meteors high densities further increases their significance from a spacecraft damage perspective

The Velocity and Density Distribution of Earth-Intersecting Meteoroids: Implications for Environment Models

Meteoroids are known to damage spacecraft: they can crater or puncture components, disturb a spacecraft's attitude, and potentially create secondary electrical effects. Because the damage done depends on the speed, size, density, and direction of the impactor, accurate environment models are critical for mitigating meteoroid-related risks. Yet because meteoroid properties are derived from indirect observations such as meteors and impact craters, many characteristics of the meteoroid environment are uncertain. In this work, we present recent improvements to the meteoroid speed and density distributions. Our speed distribution is derived from observations made by the Canadian Meteor Orbit Radar. These observations are de-biased using modern descriptions of the ionization efficiency. Our approach yields a slower meteoroid population than previous analyses (see Fig. 1 for an example) and we compute the uncertainties associated with our derived distribution. We adopt a higher fidelity density distribution than that used by many older models. In our distribution, meteoroids with TJ less than 2 are assigned to a low-density population, while those with TJ greater than 2 have higher densities (see Fig. 2). This division and the distributions themselves are derived from the densities reported by Kikwaya et al. These changes have implications for the environment: for instance, the helion/antihelion sporadic sources have lower speeds than the apex and toroidal sources and originate from high-T(sub J) parent bodies. Our on-average slower and denser distributions thus imply that the helion and antihelion sources dominate the meteoroid environment even more completely than previously thought. Finally, for a given near-Earth meteoroid cratering rate, a slower meteoroid population produces a comparatively higher rate of satellite attitude disturbances

Gravitational Couplings of Intrinsic Spin

The gravitational couplings of intrinsic spin are briefly reviewed. A consequence of the Dirac equation in the exterior gravitational field of a rotating mass is considered in detail, namely, the difference in the energy of a spin-1/2 particle polarized vertically up and down near the surface of a rotating body is $\hbar\Omega\sin\theta$. Here $\theta$ is the latitude and $\Omega = 2GJ/(c^2 R^3)$, where $J$ and $R$ are, respectively, the angular momentum and radius of the body. It seems that this relativistic quantum gravitational effect could be measurable in the foreseeable future.Comment: LaTeX file, no figures, 16 page

The distribution of transit durations for Kepler planet candidates and implications for their orbital eccentricities

‘In these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.’ Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyDoppler planet searches have discovered that giant planets follow orbits with a wide range of orbital eccentricities, revolutionizing theories of planet formation. The discovery of hundreds of exoplanet candidates by NASA's Kepler mission enables astronomers to characterize the eccentricity distribution of small exoplanets. Measuring the eccentricity of individual planets is only practical in favorable cases that are amenable to complementary techniques (e.g., radial velocities, transit timing variations, occultation photometry). Yet even in the absence of individual eccentricities, it is possible to study the distribution of eccentricities based on the distribution of transit durations (relative to the maximum transit duration for a circular orbit). We analyze the transit duration distribution of Kepler planet candidates. We find that for host stars with T > 5100 K we cannot invert this to infer the eccentricity distribution at this time due to uncertainties and possible systematics in the host star densities. With this limitation in mind, we compare the observed transit duration distribution with models to rule out extreme distributions. If we assume a Rayleigh eccentricity distribution for Kepler planet candidates, then we find best fits with a mean eccentricity of 0.1-0.25 for host stars with T ≤ 5100 K. We compare the transit duration distribution for different subsets of Kepler planet candidates and discuss tentative trends with planetary radius and multiplicity. High-precision spectroscopic follow-up observations for a large sample of host stars will be required to confirm which trends are real and which are the results of systematic errors in stellar radii. Finally, we identify planet candidates that must be eccentric or have a significantly underestimated stellar radius.Peer reviewedFinal Accepted Versio

Formation of the Flatreef deposit, northern Bushveld, by hydrodynamic and hydromagmatic processes

New lithological and whole rock compositional data show that the main platinum-group element (PGE) horizons of the Flatreef succession show strong compositional similarities to the Merensky and Bastard reefs of the western Bushveld Complex (WBC), notably in terms of many immobile and incompatible minor and trace elements such as TiO2, Zr, Y, and REE. However, Al2O3, CaO, and Na2O contents are markedly lower in the Flatreef, whereas MgO contents are higher. In view of broadly similar silicate mineral compositions in the Flatreef and the WBC reefs, we suggest that the major element compositional differences between the rocks are largely due to higher modal proportions of orthopyroxene and olivine and lower proportions of plagioclase in the Flatreef. The thickness of the mineralised interval is much greater in the Flatreef than in the WBC (several 10 s of m vs ~ 1 m) and the abundance of sulfides in the Flatreef is typically somewhat higher (on average ~ 1.5% vs ~ 1%). These data, complemented by textural observations, are interpreted to reflect enhanced hydrodynamic crystal sorting accompanied by percolation of sulfide melt through incompletely solidified cumulates. Further genetic constraints are provided by metal data: The concentration of Ni (~ 3000 ppm) in the Flatreef is broadly similar to that in the Merensky Reef of the WBC, but Cu contents are markedly higher (average ~ 1500 ppm vs 700 ppm in the WBC). The concentrations of most PGE are slightly lower (Flatreef ~ 1.5–2 ppm Pt, ~ 100–150 ppb Rh; WBC MR 3.7 ppm Pt, 240 ppb Rh), but Pd has broadly similar contents (Flatreef ~ 1.2–2 ppm; WBC MR 1.54 ppm). The relatively high Cu content of the Flatreef is interpreted as a result of assimilation of Cu sulfides from the sedimentary floor rocks. The reason for the enrichment of Pd relative to Pt, especially in the basal rocks, remains unclear. It could reflect mobilisation of Pd via a fluid phase from the country rocks or the interior of the intrusion, relatively enhanced partitioning of Pd into the sulfides, or relative Pt depletion of the earliest magma pulses in response to Pt alloy fractionation triggered by contamination with reducing country rocks