Recycling concrete: An undiscovered source of ultrafine particles

While concrete recycling is practiced worldwide, there are many unanswered questions in relation to ultrafine particle (UFP; Dp<100nm) emissions and exposure around recycling sites. In particular: (i) Does recycling produce UFPs and in what quantities? (ii) How do they disperse around the source? (iii) What impact does recycling have on ambient particle number concentrations (PNCs) and exposure? (iv) How effective are commonly used dust respirators to limit exposure? We measured size-resolved particles in the 5-560 nm range at five distances from a simulated concrete recycling source and found that: (i) the size distributions were multimodal, with up to ~93% of total PNC in the UFP size range; and (ii) dilution was a key particle transformation mechanism. UFPs showed a much slower decay rate, requiring ~62% more distance to reach 10% of their initial concentration compared with their larger counterparts. Compared with typical urban exposure during car journeys, exposure decay profiles showed up to ~5 times higher respiratory deposition within 10 m of the source. Dust respirators were found to remove half of total PNC; however the removal factor for UFPs was only ~57% of that observed in the 100-560 nm size range. These findings highlight a need for developing an understanding of the nature of the particles as well as for better control measures to limit UFP exposure.

Measuring the biases in self-reported disability status : Evidence from aggregate data

Self-reported health status measures are generally used to analyse Social Security Disability Insurance's (SSDI) application and award decisions as well as the relationship between its generosity and labour force participation. Due to endogeneity and measurement error, the use of self-reported health and disability indicators as explanatory variables in economic models is problematic. We employ county-level aggregate data, instrumental variables and spatial econometric techniques to analyse the determinants of variation in SSDI rates and explicitly account for the endogeneity and measurement error of the self-reported disability measure. Two surprising results are found. First, it is shown that measurement error is the dominating source of the bias and that the main source of measurement error is sampling error. Second, results suggest that there may be synergies for applying for SSDI when the disabled population is larger. © 2011 Taylor & Francis.

Self-organized carbon connections between catalyst particles on a silicon surface exposed to atmospheric-pressure Ar + CH4 microplasmas

Ag nanoparticles and Fe-coated Si micrograins were separately deposited onto Si(1 0 0) surfaces and then exposed to an Ar + CH4 microplasma at atmospheric pressure. For the Ag nanoparticles, self-organized carbon nanowires, up to 400 nm in length were produced, whereas for the Fe-coated Si micrograins carbon connections with the length up to 100 μm were synthesized on the plasma-exposed surface area of about 0.5 mm2. The experiment has revealed that long carbon connections and short nanowires demonstrate quite similar behavior and structure. While most connections/nanowires tended to link the nearest particles, some wires were found to 'dissolve' into the substrate without terminating at the second particle. Both connections and nanowires are mostly linear, but long carbon connections can form kinks which were not observed in the carbon nanowire networks. A growth scenario explaining the carbon structure nucleation and growth is proposed. Multiscale numerical simulations reveal that the electric field pattern around the growing connections/nanowires strongly affects the surface diffusion of carbon adatoms, the main driving force for the observed self-organization in the system. The results suggest that the microplasma-generated surface charges can be used as effective controls for the self-organized formation of complex carbon-based nano-networks for integrated nanodevices.

Delivery of therapeutic molecules using electrosprayed polymeric particles for applications in tissue engineering

This thesis has developed an innovative technology, electrospraying, that allows biodegradable microparticles to deliver pharmaceuticals that aid bone regeneration. The establishment, characterisation and optimisation of the technique are a step forward in developing an affordable and safe alternative to the products used currently in the clinical setting for the treatment of musculoskeletal disorders. The researcher has also investigated electrospraying as a coating technique on biodegradable structures that are used to replace damaged tissues, in order to provide localised and efficient drug delivery in the site of the defect to help tissue reconstruction.

Charged particles produced by corona emission from an overhead high voltage powerline

High voltage powerlines may give rise to corona breakdown, resulting in the release of large concentrations of charged ions into the surrounding environment. These ions quickly attach to aerosols and the resulting charged particles are carried by prevalent winds. This paper describes a study carried out at a site near an overhead double circuit ac transmission voltage powerline to investigate factors that control the rate at which charged particles are produced, and to determine the total particle number concentrations, total particle charge concentrations and vertical dc electric fields in the proximity of the line. Measured mean values of these three parameters at a perpendicular distance of 50m from the line were 1.8 x 103 particle cm-3, 518 ions cm3 and 520 V m-1 respectively. The net electric charge was positive and the electric field was directed downwards. These parameters were correlated with each other and monitored at four different distances from the line. Effects of meteorological parameters such as wind speed and wind direction were also investigated.

Aggregate Icons/Combat Drag

A series of large-scale photographic collages and videoworks installed in the 2010 The Beauty Of Distance: Songs of Survival in a Precarious Age, Sydney Biennale Cockatoo Island, Sydney (cat.)The work addresses her ongoing interest in feminist strategies for negotiating individual and collective identities, equality,and social activism.

Size dependent photodegradation of CdS particles deposited onto TiO2 mesoporous films by SILAR method

The properties of CdS nanoparticles incorporated onto mesoporous TiO2 films by a successive ionic layer adsorption and reaction (SILAR) method were investigated by Raman spectroscopy, UV-visible spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). High resolution TEM indicated that the synthesized CdS particles were hexagonal phase and the particle sizes were less than 5 nm when SILAR cycles were fewer than 9. Quantum size effect was found with the CdS sensitized TiO2 films prepared with up to 9 SILAR cycles. The band gap of CdS nanoparticles decreased from 2.65 eV to 2.37 eV with the increase of the SILAR cycles from 1 to 11. The investigation of the stability of the CdS/TiO2 films in air under illumination (440.6 µW/cm2) showed that the photodegradation rate was up to 85% per day for the sample prepared with 3 SILAR cycles. XPS analysis indicated that the photodegradation was due to the oxidation of CdS, leading to the transformation from sulphide to sulphate (CdSO4). Furthermore, the degradation rate was strongly dependent upon the particle size of CdS. Smaller particles showed faster degradation rate. The size-dependent photo-induced oxidization was rationalized with the variation of size-dependent distribution of surface atoms of CdS particles. Molecular Dynamics (MD) simulation has indicated that the surface sulphide anion of a large CdS particle such as CdS made with 11 cycles (CdS11, particle size = 5.6 nm) accounts for 9.6% of the material whereas this value is increased to 19.2% for (CdS3) based smaller particles (particle size: 2.7 nm). Nevertheless, CdS nanoparticles coated with ZnS material showed a significantly enhanced stability under illumination in air. A nearly 100% protection of CdS from photon induced oxidation with a ZnS coating layer prepared using four SILAR cycles, suggesting the formation of a nearly complete coating layer on the CdS nanoparticles.

Including nonequilibrium interface kinetics in a continuum model for melting nanoscaled particles

The melting temperature of a nanoscaled particle is known to decrease as the curvature of the solid-melt interface increases. This relationship is most often modelled by a Gibbs--Thomson law, with the decrease in melting temperature proposed to be a product of the curvature of the solid-melt interface and the surface tension. Such a law must break down for sufficiently small particles, since the curvature becomes singular in the limit that the particle radius vanishes. Furthermore, the use of this law as a boundary condition for a Stefan-type continuum model is problematic because it leads to a physically unrealistic form of mathematical blow-up at a finite particle radius. By numerical simulation, we show that the inclusion of nonequilibrium interface kinetics in the Gibbs--Thomson law regularises the continuum model, so that the mathematical blow up is suppressed. As a result, the solution continues until complete melting, and the corresponding melting temperature remains finite for all time. The results of the adjusted model are consistent with experimental findings of abrupt melting of nanoscaled particles. This small-particle regime appears to be closely related to the problem of melting a superheated particle.

Polymer-mediated synthesis of γ-Fe2O3 nano-particles

Nano-particles of γ-Fe2O3 were synthesized by reacting polyethylene oxide–FeCl3 complex with NH4OH. These were characterized by X-ray diffraction (XRD), scanning electron miscroscopy (SEM), selected area electron diffraction (SAED) and transmision electron microscopy (TEM). The average particle size was found to be 10 nm, as determined from the line broadening of the main XRD peak. The crystalline phase was a spinel-type tetragonal structure, which was confirmed from the electron diffraction pattern. The zero field cooled magnetization of samples with varying γ-Fe2O3 content as a function of temperature was measured using a vibrating sample magnetometer. The magnetization curves show a peak at low temperature (15 K) corresponding to the blocking temperature TB. The value of TB was found to decrease with decreasing particle size. The magnetization measurements with respect to field at 5 and 170 K confirmed the transition from superparamagnetic to spin-glass state at TB, as evidenced from the remanence and hysteresis. These results can be explained on the basis of Néel's theory of superparamagnetism as applied to nano-particles.