34,212 research outputs found
Cautionary considerations for positive dingo management: a response to the Johnson and Ritchie critique of Fleming et al. (2012)
No full textJohnson and Ritchie (2012) have provided a criticism of our opinion piece (Fleming et al. 2012). There is some common ground, but we remain unconvinced by their view that our reasoning was unsound or beside the point. In this response, we discuss where Johnson and Ritchie have provided unconvincing evidence to refute our seven considerations, and reiterate and demonstrate why these considerations remain important. The mesopredator release or suppression hypothesis in Australian ecosystems must be objectively evaluated before positive management of dingoes and other free-ranging dogs is recommended or implemented. Adaptive comanagement of free-ranging dogs can be used for both biodiversity conservation and the mitigation of livestock predation but caution must be exercised when considering using free-ranging dogs as a conservation tool
Honour and Plenary Lectures presented at the 11th International Conference on Fracture (ICF11), held in Turin, Italy, on March 20-25, 2005 – Special Issue of the International Journal of Fracture
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Architected cellular materials: a review on their mechanical properties towards fatigue-tolerant design and fabrication
No full textAdditive manufacturing of industrially-relevant high-performance parts and products is today a reality, especially for metal additive manufacturing technologies. The design complexity that is now possible makes it particularly useful to improve product performance in a variety of applications. Metal additive manufacturing is especially well matured and is being used for production of end-use mission-critical parts. The next level of this development includes the use of intentionally designed porous metals - architected cellular or lattice structures. Cellular structures can be designed or tailored for specific mechanical or other performance characteristics and have numerous advantages due to their large surface area, low mass, regular repeated structure and open interconnected pore spaces. This is considered particularly useful for medical implants and for lightweight automotive and aerospace components, which are the main industry drivers at present. Architected cellular structures behave similar to open cell foams, which have found many other industrial applications to date, such as sandwich panels for impact absorption, radiators for thermal management, filters or catalyst materials, sound insulation, amongst others. The advantage of additively manufactured cellular structures is the precise control of the micro-architecture which becomes possible. The huge potential of these porous architected cellular materials manufactured by additive manufacturing is currently limited by concerns over their structural integrity. This is a valid concern, when considering the complexity of the manufacturing process, and the only recent maturation of metal additive manufacturing technologies. Many potential manufacturing errors can occur, which have so far resulted in a widely disparate set of results in the literature for these types of structures, with especially poor fatigue properties often found. These have improved over the years, matching the maturation and improvement of the metal additive manufacturing processes. As the causes of errors and effects of these on mechanical properties are now better understood, many of the underlying issues can be removed or mitigated. This makes additively manufactured cellular structures a highly valid option for disruptive new and improved industrial products. This review paper discusses the progress to date in the improvement of the fatigue performance of cellular structures manufactured by additive manufacturing, especially metal-based, providing insights and a glimpse to the future for fatigue-tolerant additively manufactured architected cellular materials. © 2021 The Author(s
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Solid-state photonic interfaces using semiconductor quantum dots
No full textNew technologies based on the properties of quantum mechanics promise
to revolutionise the way information is processed by outperforming what is
possible using classical devices. Examples include massively parallel processing
using quantum computers, verifiably secure communication using quantum
cryptography, and measurement with sensitivity beyond classical limitation
with quantum metrology. Realising the full potential of these technologies
necessitates the ability to communicate quantum information over large
distances, a key requirement for future quantum networks. However, developing
practical implementations of long-distance quantum communication
is challenging as it necessitates three major ingredients: light-matter interfaces,
elementary quantum operations, and quantum memories. This thesis
describes work that has been undertaken to address these requirements using
semiconductor nanotechnology.
We have first demonstrated that single InAs quantum dots embedded inside
conventional diode structures constitute high-fidelity controllable interfaces
between optical qubits and solid-state qubits. Indeed, the polarisation
state of a photon was transferred into the spin state of an electron-hole pair
and eventually restored through radiative recombination of the electron and
the hole with a fidelity up to 95%. Moreover, spins were manipulated using
subnanosecond modulation of a vertical electric field applied to the quantum
dots. By controlling this electrical modulation, we demonstrated elementary
phase-shift and spin-flip gate operations with near-unity fidelities.
An electron-hole pair confi ned in a single quantum dot has a short radiative
lifetime limiting therefore its use as an excitonic quantum memory.
The solution we proposed was to use a quantum dot molecule to control the
spatial separation of the electron and the hole and therefore prevent their
recombination. Comprehensive studies of electric field eff ects upon the photoluminescence
of quantum dot molecules lead to a clear understanding and
a good control over their physical properties. Single photons were stored in
individual quantum dot molecules up to 1μs and read out on a subnanosecond time scale. Moreover, the circular polarisation of individual photons was
transferred into the spin state of electron-hole pairs with a fidelity above
90%, which does not degrade for storage times up to the 12.5 ns repetition
period of the experiment.
Our work on single quantum dots could be extended in the near future to
allow for two-qubits quantum operations by con fining a second electron-hole
pair to be electrically manipulated. Storage of a superposition of spin states
in a quantum dot molecule should also be possible if the spin states are made
degenerate, which is feasible using the electric fi eld dependence of the energy
splitting between the spin states discussed in this thesis. We believe that
combining both approaches will lead to the development of a controllable
multi-qubit quantum memory for polarised light, a building block for long distance
quantum communication based on semiconductor nanotechnology
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Scaling of strength and ductility in bioinspired brick and mortar composites
No full textThis paper provides scaling relationships between constituent properties and the uniaxial tensile response of synthetic “brick and mortar” composite materials inspired by nacre. The macroscopic strength and ductility (work of fracture) are predicted in terms of the brick properties (size, strength, and layout) and interface cohesive properties (e.g., maximum shear and normal stresses and separations). The results illustrate the trade-off between increasing strength and decreasing ductility with the increasing aspect ratio of the bricks. The models can be used to identify optimum mortar properties that maximize toughness for a given brick strength
Empowerment evaluation of Te Taiwhenua o Heretaunga Family Start: Improving service delivery
No full textThis thesis explores child maltreatment in New Zealand by considering service delivery of the Family Start programme at Te Taiwhenua o Heretaunga through an empowerment evaluation. The purpose of this research is to evaluate the service delivery process of the Family Start programme at this site to inform the organization and other Family Start key agents of possible improvements to service delivery so that the Family Start programme is best able to reduce the risk factors that are known to influence child maltreatment in New Zealand. The best possible service delivery by kaupapa providers supports sustainability and the continuity of service with Māori through continual funding. The two objectives of this research are to look at how well the Family Start programme is implemented at Te Taiwhenua o Heretaunga and to consider the cultural appropriateness of service delivery. Community psychology is the paradigm within which I position myself. I respect the values of community psychology that aim to improve the position of disadvantaged people through their participation in social change and community development. Te Taiwhenua o Heretaunga is a kaupapa Māori provider and I see an empowerment evaluation as a tool for internal evaluation to assist organizations who value self determination in their own practice. Both quantitative and qualitative data were collected and analyzed. There are two objectives to consider service delivery; firstly process aspects of service delivery are looked at and secondly the cultural relevance of service delivery to the population receiving the Family Start programme at this site. These are described as nine points about service delivery. The aim is to provide an empowerment evaluation for Te Taiwhenua o Heretaunga to inform, assist and improve service delivery of the Family Start programme in a culturally appropriate manner. The findings suggest better understanding is needed by Te Taiwhenua o Heretaunga Family Start staff, about the programme intentions, the use of tools such as Born to Learn/Ahuru Mōwai, individual family plans, service delivery levels, maintaining health records and ways to encourage collaboration between agencies. Te Taiwhenua o Heretaunga are shown in this research to be reaching the intended population for the Family Start programme, and service delivery appears to be culturally relevant to the clients on the programme at this time. The findings are limited by the fact that access to some information was restricted by Te Taiwhenua o Heretaunga Family Start management. Consequently, this research looked only at service delivery, and not the benefits of or barriers to the actual programme. The effectiveness of the programme in reducing child maltreatment is important but could not be measured in this research. Reducing child maltreatment is the main aim of the Family Start programme and would be measured through client outcomes. This research considered service delivery to see if the Family Start programme is offered optimally to assist the aim of reducing child maltreatment
Time Dependent Debonding of Aluminum/Alumina Interfaces under Cyclic and Static Loading J. J. Kruzic, J. M. McNaney, R. M. Cannon, and R. O. Ritchie
No full textThe structural integrity of oxide/metal interfaces is important in many applications. While most attention has focused on the debonding of oxide/metal interfaces by conducting strength and fracture toughness tests, very few investigations have looked at time dependant failure of interfaces under cyclic or static loading. Tests have been conducted on sandwich specimens consisting of 5 - 100 micron thick aluminum layers bonded between either polycrystalline or single crystal Al 2 O 3 to determine cyclic fatigue-crack growth, as well as static loaded moistureassisted crack-growth, properties of Al/Al 2 O 3 interfaces. Under cyclic loading, crack growth was observed to occur predominantly by interfacial debonding, but was also observed to make excursions into the Al 2 O 3 . Static loading in a moist environment also caused interfacial cracks to deviate into the Al 2 O 3 or alternatively to arrest. Due to the poor crack growth resistance of the Al 2 O 3 , cracks leaving the interface grew at faster rates than those at the interface. Trends in crack trajectories and crack growth rates are explained in terms of the degree of plastic constraint in the aluminum layer, the modulus mismatch, and the effects of environmental mechanisms
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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