Determining whether estimated spore release rates for Aspergillus fumigatus are compatible with their measured growth rates in composting systems

The composting process like other waste management activities has the potential to generate large concentrations of bioaerosols which can be widely dispersed into the surrounding environment. There has been considerable interest in the literature of the effect of bioaerosols and in particular Aspergillus fumigatus on the health of plant operators and those living in close proximity to composting plants (Olver, 1994; Fischer et al., 1999; Fischer et al., 2000; Bunger et al., 200). Although bioaerosols can be generated through a range of operational procedures it has also been suggested that large numbers of Aspergillus fumigatus spores can be emitted from static compost piles through the action of natural air movements across the surface of the biodegrading material. Through the use of a portable wind tunnel apparatus researchers have determined the rate of emission of Aspergillus fumigatus spores as a result of air movement across the surface of the material (Taha et al., 2004; 2005; 2006 & 2007). The aim of this work was to use controlled laboratory experiments using compost samples and Aspergillus fumigatus spores to determine the sporulation rate of Aspergillus fumigatus. Using this data it would then be possible to verify whether bioaerosol emission rates from static compost windrows calculated and quoted in the literature can in fact be maintained over longer time periods. A series of experiments were carried out using Aspergillus fumigatus spores on agar plates and small samples of green waste compost to determine the number of spores that could be generated by each existing spore over a seven day period. From the experiments the sporulation rate determined from the agar plates varied with averages of either 4.48x104 or 2.83 spores/day depending upon the date set used and from the compost experiments it was 1.33 spores/day. Using this data and making a number of assumptions for moisture content (50%), bulk density (650 kg/m3) and the wind penetration depth (10-25mm) the potential release rates were calculated. The data from the agar experiments yielded a potential release rate at 10mm up to 5 orders of magnitude in excess of that quoted by Taha et al. (2004 & 2005. Using the trimmed data set the agar release figures are between 6.17 x 103 and 1.23 x 104 cfu/m2/s depending upon the wind penetration depth used and are comparable to those quoted in the literature. The release rate calculated using the compost experiments was slightly lower than the agar 2 data and consequently the release rates even at a wind penetration depth of 25mm are just outside the range quoted by Taha et al. (2004 & 2005). Although the data presented in this paper were determined from controlled laboratory experiments they show that it is possible for Aspergillus fumigatus to generate spores at a sufficient rate to allow the release of significant numbers of spores. The calculated sporulation rates would allow spores to be released at the rates quoted in the literature and suggest that the fugitive release rates quoted in the literature would be able to be maintained over long periods of time. However it is recognised that the data is affected greatly by the assumptions one makes, in particular the existing concentration of Aspergillus fumigatus. Despite the limitations the original intention of the work was to attempt to establish the long term applicability of the fugitive release rates for Aspergillus fumigatus from green waste compost quoted in the literature and it has achieved this objective

Determining whether estimated spore release rates for Aspergillus fumigatus are compatible with their measured growth rates in composting systems

The composting process like other waste management activities has the potential to generate large concentrations of bioaerosols which can be widely dispersed into the surrounding environment. There has been considerable interest in the literature of the effect of bioaerosols and in particular Aspergillus fumigatus on the health of plant operators and those living in close proximity to composting plants (Olver, 1994; Fischer et al., 1999; Fischer et al., 2000; Bunger et al., 200). Although bioaerosols can be generated through a range of operational procedures it has also been suggested that large numbers of Aspergillus fumigatus spores can be emitted from static compost piles through the action of natural air movements across the surface of the biodegrading material. Through the use of a portable wind tunnel apparatus researchers have determined the rate of emission of Aspergillus fumigatus spores as a result of air movement across the surface of the material (Taha et al., 2004; 2005; 2006 & 2007). The aim of this work was to use controlled laboratory experiments using compost samples and Aspergillus fumigatus spores to determine the sporulation rate of Aspergillus fumigatus. Using this data it would then be possible to verify whether bioaerosol emission rates from static compost windrows calculated and quoted in the literature can in fact be maintained over longer time periods. A series of experiments were carried out using Aspergillus fumigatus spores on agar plates and small samples of green waste compost to determine the number of spores that could be generated by each existing spore over a seven day period. From the experiments the sporulation rate determined from the agar plates varied with averages of either 4.48x104 or 2.83 spores/day depending upon the date set used and from the compost experiments it was 1.33 spores/day. Using this data and making a number of assumptions for moisture content (50%), bulk density (650 kg/m3) and the wind penetration depth (10-25mm) the potential release rates were calculated. The data from the agar experiments yielded a potential release rate at 10mm up to 5 orders of magnitude in excess of that quoted by Taha et al. (2004 & 2005. Using the trimmed data set the agar release figures are between 6.17 x 103 and 1.23 x 104 cfu/m2/s depending upon the wind penetration depth used and are comparable to those quoted in the literature. The release rate calculated using the compost experiments was slightly lower than the agar 2 data and consequently the release rates even at a wind penetration depth of 25mm are just outside the range quoted by Taha et al. (2004 & 2005). Although the data presented in this paper were determined from controlled laboratory experiments they show that it is possible for Aspergillus fumigatus to generate spores at a sufficient rate to allow the release of significant numbers of spores. The calculated sporulation rates would allow spores to be released at the rates quoted in the literature and suggest that the fugitive release rates quoted in the literature would be able to be maintained over long periods of time. However it is recognised that the data is affected greatly by the assumptions one makes, in particular the existing concentration of Aspergillus fumigatus. Despite the limitations the original intention of the work was to attempt to establish the long term applicability of the fugitive release rates for Aspergillus fumigatus from green waste compost quoted in the literature and it has achieved this objective

A broadly tunable ultrafast diode-pumped Ti:sapphire laser

We report a diode-pumped ultrafast Ti:sapphire laser tunable over a 50 nm range. Sub-100 fs pulses are generated at a pulse repetition rate of 139 MHz with a maximum average output power of 430 mW

A look at the consumption behaviours along Ghana’s slave routes.

This study examines the consumption behaviours of four types of visitors to sites associated with the Transatlantic Slave Trade in Ghana. A questionnaire was used to elicit information regarding sites they intended or actually visited, perceived differences regarding site experiences and impressions of the heritage product itself. The results show that visitors were highly selective in their consumption patterns, although the sites in the country’s south were the major attractions and generators for all purposes. There is evidence that trip motive and connection to slavery influence consumption behaviour, as some visitors are willing to invest effort, expense and time to consume truly unique learning experiences. The findings were interpreted as evidence that site managers may need to design strategies using visitor profile and consumption patterns to deliver a coordinated and integrated appeal to the target visitor group

Magnetic Field Generation in Stars

Enormous progress has been made on observing stellar magnetism in stars from the main sequence through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence,in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Thus we maybe at the dawn of a new era of exciting discoveries in compact star magnetism driven by the opening of a new, non-electromagnetic observational window. We also review recent advances in the theory and computation of magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo theory. These advances offer insight into the action of stellar dynamos as well as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field generation in stars to appear in Space Science Reviews, Springe

Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory

Data from the Pierre Auger Observatory are analyzed to search for anisotropies near the direction of the Galactic Centre at EeV energies. The exposure of the surface array in this part of the sky is already significantly larger than that of the fore-runner experiments. Our results do not support previous findings of localized excesses in the AGASA and SUGAR data. We set an upper bound on a point-like flux of cosmic rays arriving from the Galactic Centre which excludes several scenarios predicting sources of EeV neutrons from Sagittarius $A$. Also the events detected simultaneously by the surface and fluorescence detectors (the `hybrid' data set), which have better pointing accuracy but are less numerous than those of the surface array alone, do not show any significant localized excess from this direction.Comment: Matches published versio

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic

The exposure of the hybrid detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays. It consists of a surface array to measure secondary particles at ground level and a fluorescence detector to measure the development of air showers in the atmosphere above the array. The "hybrid" detection mode combines the information from the two subsystems. We describe the determination of the hybrid exposure for events observed by the fluorescence telescopes in coincidence with at least one water-Cherenkov detector of the surface array. A detailed knowledge of the time dependence of the detection operations is crucial for an accurate evaluation of the exposure. We discuss the relevance of monitoring data collected during operations, such as the status of the fluorescence detector, background light and atmospheric conditions, that are used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic

Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum

We report a first measurement for ultra-high energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the `ankle' at $\lg(E/{\rm eV})=18.5-19.0$ differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass $A > 4$. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavoured as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth.Comment: Published version. Added journal reference and DOI. Added Report Numbe