Intense Source of Slow Positrons

We describe a novel design for an intense source of slow positrons based on pair production with a beam of electrons from a 10 MeV accelerator hitting a thin target at a low incidence angle. The positrons are collected with a set of coils adapted to the large production angle. The collection system is designed to inject the positrons in a Greaves-Surko trap [1]. Such a source could be the basis for a series of experiments in fundamental and applied research and would also be a prototype source for industrial applications which concern the field of defect characterization in the nanometer scale.Comment: submitted to N.I.M.

Commercial vehicle tour data collection using passive GPS technology: Issues and potential applications

In mid-2006 a GPS survey of commercial vehicles was piloted in Melbourne, Australia to support a major update of freight data and modelling capabilities in the metropolitan region. This survey marked the first of its kind in Australia, and to the best of the authors’ knowledge, one of the first world-wide. This paper presents the issues surrounding the collection and use of GPS data as a method to provide information on commercial vehicle tours within an urban setting. The paper focuses on passive GPS methods where the truck driver’s involvement in the data collection effort is minimal. We address (a) implementation issues with the data collection, (b) the algorithms used to process the raw GPS data into meaningful trip tour information, (c) pilot survey data tour results, and (d) potential uses and limitations of passive GPS technology in urban freight modelling and planning. Despite processing challenges, GPS provides an appealing method to enrich commercial vehicle data collection and enhance our understanding of on-road behaviour. As increasing numbers of commercial vehicles become equipped with GPS receivers, we argue only privacy concerns remain as a major barrier to gathering and using such data on a wide-spread basis in the future

Collecting longitudinal data from freight operators: survey design and implementation

Freight transport research has generally been limited by a lack of data of the breadth and quality available for passenger transport, particularly in terms of behavioural data. Although there are a number of reasons for this lack of data, the challenges of collecting freight data including the expense, participant burden and confidentiality issues are amongst the most significant. Although some improvements in technology and survey design have allowed for the collection of more behavioural freight data more improvements would be beneficial. This paper discusses the survey design and implementation of a survey intended to collect longitudinal behavioural data on the responses of freight transport firms to the introduction of environmental policies. The design of the survey is centred around a hypothetical scenario where respondents are asked how they would complete a given freight task within common constraints including time windows and delivery requirements. One of the key components of the survey design is a dynamic component that is intended to simulate the changing business environment to which firms are required to adapt. This paper also looks at the participant burden involved in completing the survey and compares how this differs depending on how respondents completed the survey

Structure and superconductivity in (Bi(0.35)Cu(0.65))Sr2YCu2O7 and related materials

The recently reported (Bi/Cu)Sr2YCu2O7 phase has been studied by time of flight powder neutron diffraction. The proposed 1212 structure has been confirmed and refinements have shown the oxygen in the (Bi/Cu)O layer is displaced by 0.78 A from the ideal (1/2,1/2,0) site (P4/mmm space group) along /100/. Bond Valence Sum calculations have suggested oxidation states of Bi(5+) and Cu(2+) for the cations in the (Bi/Cu)O layers. The material is non-superconducting and all attempts to induce superconductivity have been unsuccessful. Work on the related material (Ce/Cu)Sr2YCu2O7 has shown the ideal Ce content to be 0.5 Ce per formula unit. The introduction of Ba (10%) onto the Sr site dramatically increases phase stability and also induces superconductivity (62 K)

Linkage mapping of the gpdA gene of Aspergillus nidulans

In the last few years many genes of several Aspergillus species have been cloned and sequenced. For many of these genes mutant alleles and genetic linkage data are also available. However, for those genes for which no mutant alleles have been isolated, genetic mapping was not possible. Here we report linkage mapping of the glyceraldehyde-3- phosphate dehydrogenase gene (gpdA) of A. nidulans for which no mutant alleles have been isolated. The method used is applicable to all other cloned genes

Matrix controlled channel diffusion of sodium in amorphous silica

To find the origin of the diffusion channels observed in sodium-silicate glasses, we have performed classical molecular dynamics simulations of Na$_2$O--4SiO$_2$ during which the mass of the Si and O atoms has been multiplied by a tuning coefficient. We observe that the channels disappear and that the diffusive motion of the sodium atoms vanishes if this coefficient is larger than a threshold value. Above this threshold the vibrational states of the matrix are not compatible with those of the sodium ions. We interpret hence the decrease of the diffusion by the absence of resonance conditions.Comment: 5 pages, 4 figure

Sputtering yields exceeding 1000 by 80keV Xe irradiation of Au nanorods

Using experiments and computer simulations, we find that 80 keV Xe ion irradiation of Au nanorods can produce sputtering yields exceeding 1000, which to our knowledge are the highest yields reported for sputtering by single ions in the nuclear collision regime. This value is enhanced by more than an order of magnitude compared to the same irradiation of flat Au surfaces. Using MD simulations, we show that the very high yield can be understood as a combination of enhanced yields due to low incoming angles at the sides of the nanowire, as well as the high surface-to-volume ratio causing enhanced explosive sputtering from heat spikes. We also find, both in experiments and simulations, that channeling has a strong effect on the sputtering yield: if the incoming beam happens to be aligned with a crystal axis of the nanorod, the yield can decrease to about 100