3,518 research outputs found
An experimental investigation of the hypergolic ignition of some polymeric fuels with oxygen
Hypergolic ignition of polymeric fuels with oxyge
Increased surface flashover voltage in microfabricated devices
With the demand for improved performance in microfabricated devices, the
necessity to apply greater electric fields and voltages becomes evident. When
operating in vacuum, the voltage is typically limited by surface flashover
forming along the surface of a dielectric. By modifying the fabrication process
we have discovered it is possible to more than double the flashover voltage.
Our finding has significant impact on the realization of next-generation micro-
and nano-fabricated devices and for the fabrication of on-chip ion trap arrays
for the realization of scalable ion quantum technology
Towards operational measures of computer security
Ideally, a measure of the security of a system should capture quantitatively the intuitive notion of ‘the ability of the system to resist attack’. That is, it should be operational, reflecting the degree to which the system can be expected to remain free of security breaches under particular conditions of operation (including attack). Instead, current security levels at best merely reflect the extensiveness of safeguards introduced during the design and development of a system. Whilst we might expect a system developed to a higher level than another to exhibit ‘more secure behaviour’ in operation, this cannot be guaranteed; more particularly, we cannot infer what the actual security behaviour will be from knowledge of such a level. In the paper we discuss similarities between reliability and security with the intention of working towards measures of ‘operational security’ similar to those that we have for reliability of systems. Very informally, these measures could involve expressions such as the rate of occurrence of security breaches (cf rate of occurrence of failures in reliability), or the probability that a specified ‘mission’ can be accomplished without a security breach (cf reliability function). This new approach is based on the analogy between system failure and security breach. A number of other analogies to support this view are introduced. We examine this duality critically, and have identified a number of important open questions that need to be answered before this quantitative approach can be taken further. The work described here is therefore somewhat tentative, and one of our major intentions is to invite discussion about the plausibility and feasibility of this new approach
Dissipation due to tunneling two-level systems in gold nanomechanical resonators
We present measurements of the dissipation and frequency shift in
nanomechanical gold resonators at temperatures down to 10 mK. The resonators
were fabricated as doubly-clamped beams above a GaAs substrate and actuated
magnetomotively. Measurements on beams with frequencies 7.95 MHz and 3.87 MHz
revealed that from 30 mK to 500 mK the dissipation increases with temperature
as , with saturation occurring at higher temperatures. The relative
frequency shift of the resonators increases logarithmically with temperature up
to at least 400 mK. Similarities with the behavior of bulk amorphous solids
suggest that the dissipation in our resonators is dominated by two-level
systems
The Healthy Migrant Families Initiative: Development of a culturally competent obesity prevention intervention for African migrants Disease epidemiology - Chronic
Background: Although obesity among immigrants remains an important area of study given the increasing migrant population in Australia and other developed countries, research on factors amenable to intervention is sparse. The aim of the study was to develop a culturally-competent obesity prevention program for sub-Saharan African (SSA) families with children aged 12-17 years using a community-partnered participatory approach. Methods: A community-partnered participatory approach that allowed the intervention to be developed in collaborative partnership with communities was used. Three pilot studies were carried out in 2008 and 2009 which included focus groups, interviews, and workshops with SSA parents, teenagers and health professionals, and emerging themes were used to inform the intervention content. A cultural competence framework containing 10 strategies was developed to inform the development of the program. Using findings from our scoping research, together with community consultations through the African Review Panel, a draft program outline (skeleton) was developed and presented in two separate community forums with SSA community members and health professionals working with SSA communities in Melbourne. Results: The \u27Healthy Migrant Families Initiative (HMFI): Challenges and Choices\u27 program was developed and designed to assist African families in their transition to life in a new country. The program consists of nine sessions, each approximately 1 1/2 hours in length, which are divided into two modules based on the topic. The first module \u27Healthy lifestyles in a new culture\u27 (5 sessions) focuses on healthy eating, active living and healthy body weight. The second module \u27Healthy families in a new culture\u27 (4 sessions) focuses on parenting, communication and problem solving. The sessions are designed for a group setting (6-12 people per group), as many of the program activities are discussion-based, supported by session materials and program resources. Conclusion: Strong partnerships and participation by SSA migrant communities enabled the design of a culturally competent and evidence-based intervention that addresses obesity prevention through a focus on healthy lifestyles and healthy families. Program implementation and evaluation will further inform obesity prevention interventions for ethnic minorities and disadvantaged communities
Concepts of animal well-being and predicting the impact of procedures on experimental animals
1. We argue that:
• in their application to non-human animals, \u27welfare\u27 and \u27well-being\u27 are interchangeable words; and that
• good welfare/well-being is the state of being manifest in an animal when its nutritional, environmental, health, behavioural and mental needs are met.
2. These latter are essentially the \u27five freedoms\u27 formulated by the Farm Animal Welfare Council of the United Kingdom.
3. Using the five freedoms as a basis, we have developed a system for assessing the impact of a proposed animal experiment or usage. The freedoms are now transformed into \u27domains of potential compromise\u27 and are redefined better to emphasise the extent of welfare compromise rather than the ideal of absence of compromise. Domain 1 is Thirst/hunger/malnutrition, 2 is Environmental challenge, 3 is Disease/injury/functional impairment, 4 is Behavioural/interactive restriction, and domain 5 is Anxiety/fear/pain/distress. A proposal would be examined systematically in all domains, and the degree of compromise in each rated on a 5-step non-numerical scale - O, A, B, C, X. Anxiety/fear/pain/distress arising from compromise in domains 1-4 would be cumulated into domain 5. The overall rating would commonly be that given to domain 5, but if this were low or unknown, it would be given to the highest rating in the other domains.
4. The proposer would be required to present to the institutional Animal Ethics Committee his/her assessment of the impact of a proposed experiment on the animals involved, together with an appropriate justification for the work and a cost-benefit analysis.
5. The extent of the justification required for a proposal would be directly related to the severity of compromise expected, being low for grade O and very high for grade X.
6. The cost-benefit decision would be based on the balance between the expected severity of welfare compromise and the expected benefits set out in the justification.
7. The major advantage of this system for assessing the impact on welfare is that it encourages systematic consideration of all sources of possible compromise. Such wider consideration would allow more accurate assessment of the severity of impact and thereby would improve the validity and efficiency of cost-benefit analyses.
8. The philosophical background to our approach is outlined, graded examples of welfare compromise are given and ethical and practical implications of using the system are discussed.
9. We also set out what we consider to be the ethical and practical responsibilities of the researcher to the animals, and to his/her assistants. The conscientiousness and comprehensiveness of the assessments of welfare compromise and the actions taken to minimise it are measures of the researcher\u27s acceptance of ethical responsibility for all features of each experiment which affect the animals adversely
Nonlinear modal coupling in a high-stress doubly-clamped nanomechanical resonator
We present results from a study of the nonlinear intermodal coupling between
different flexural vibrational modes of a single high-stress, doubly-clamped
silicon nitride nanomechanical beam. The measurements were carried out at 100
mK and the beam was actuated using the magnetomotive technique. We observed the
nonlinear behavior of the modes individually and also measured the coupling
between them by driving the beam at multiple frequencies. We demonstrate that
the different modes of the resonator are coupled to each other by the
displacement induced tension in the beam, which also leads to the well known
Duffing nonlinearity in doubly-clamped beams.Comment: 15 pages, 7 figure
Resistance Noise Scaling in a Dilute Two-Dimensional Hole System in GaAs
We have measured the resistance noise of a two-dimensional (2D)hole system in
a high mobility GaAs quantum well, around the 2D metal-insulator transition
(MIT) at zero magnetic field. The normalized noise power increases
strongly when the hole density p_s is decreased, increases slightly with
temperature (T) at the largest densities, and decreases strongly with T at low
p_s. The noise scales with the resistance, , as for a
second order phase transition such as a percolation transition. The p_s
dependence of the conductivity is consistent with a critical behavior for such
a transition, near a density p* which is lower than the observed MIT critical
density p_c.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
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