Microscopic Investigation of Vortex Breakdown in a Dividing T-Junction Flow

3D-printed microfluidic devices offer new ways to study fluid dynamics. We present the first clear visualization of vortex breakdown in a dividing T-junction flow. By individual control of the inflow and two outflows, we decouple the effects of swirl and rate of vorticity decay. We show that even slight outflow imbalances can greatly alter the structure of vortex breakdown, by creating a net pressure difference across the junction. Our results are summarized in a dimensionless phase diagram, which will guide the use of vortex breakdown in T-junctions to achieve specific flow manipulation.Comment: 5 pages, 5 figure

A slip model for micro/nano gas flows induced by body forces

A slip model for gas flows in micro/nano-channels induced by external body forces is derived based on Maxwell's collision theory between gas molecules and the wall. The model modifies the relationship between slip velocity and velocity gradient at the walls by introducing a new parameter in addition to the classic Tangential Momentum Accommodation Coefficient. Three-dimensional Molecular Dynamics simulations of helium gas flows under uniform body force field between copper flat walls with different channel height are used to validate the model and to determine this new parameter

Stakeholder values and attitudes towards water markets across northern Australia<br />

SummaryThis report is the second of three reports and part of a two year project entitled Establishing water markets in northern Australia: a study to assess feasibility and consequences of market-based mechanisms of water delivery undertaken through the Australian National University&rsquo;s Crawford School of Economics and Government. The Tropical Rivers and Coastal Knowledge (TRaCK) hub funded this project under Theme 6.1 &ldquo;Sustainable Enterprises&rdquo;. This research is also being done in collaboration with the North Australian Indigenous Land and Sea Management Alliance (NAILSMA). This second report provides analysis of stakeholder attitudes and values and their implications for the design of water markets across tropical Queensland, Northern Territory and Western Australia, (with focus on the Gulf, Timor and North East drainage divisions). The study utilised a mixed qualitative and quantitative approach, employing a survey with closed ended (5 point Likert scales and multiple choice) and open ended measures.In Task 2 we surveyed 120 people from government, Indigenous, industry and recreational user groups and present a range of values and attitudes related to markets and we discuss the general implications for market design in the north. Analysing data from open ended measures involved coding and grouping data into categories, then identifying patterns and themes. While statistical analysis involved ordered probit models, using robust standard errors and also controlling for lack of independence within each group using cluster. Preliminary findings were sent out to respondents for their feedback and where appropriate changes made. From this the final report was produced.Our findings highlight that sustainability; environmental protection; social justice and equity; and economic development were important values to respondents in relation to water markets. Respondents emphasised the importance of robust water planning frameworks that support ecological values and irrigator and Indigenous livelihoods, and respondents overwhelmingly disagreed with the trade of environmental and cultural flows. There was also significant support for the preservation of certain catchments and aquifers for their unique values (particularly among Indigenous respondents). Social justice and equity were important to respondents, with a sentiment to include Indigenous people in water reform and in water markets. Indigenous respondents felt that current arrangements were not equitable. As well, respondents from government, Indigenous and recreational groups felt that consultation and water policy fail to adequately address the needs and interests&nbsp; of Indigenous Australians. Indigenous respondents showed support for water markets, the development of water based enterprise (such as agriculture and horticulture) and believe strongly that the benefits of water trading will be significant. These views were tempered by some concerns that&nbsp; Indigenous people may be alienated from markets and that the ecological impacts from markets could be significant.Respondents felt that water management was sustainable in their region, but at the same time they did not believe water management to be efficient. This may be related to perceptions that certain systems are not over-allocated to consumptive users. A little over half of respondents agreed that water markets help sustainable water management and that water should be a tradable commodity, and respondents that were male and had a higher education were more likely to agree to these statements. Support for separating land and water title (unbundling) was mixed, with Indigenous respondents less likely to agree to a separation. There is a level of understanding of water management in their jurisdictions were more likely to agree to water transfers. There was unanimous support for government involvement in water markets, with overwhelming support for government as regulator.Literature highlights that importance of integrating values and attitudes in resource management frameworks. We identify four general implications for the design of water markets from our findings. The first is that Indigenous involvement in water markets and reform is important as one way to address Indigenous disadvantage and to support Indigenous livelihoods. This involvement could range from water management and planning, to the recognition of customary and commercial rights. Second, respondents thought that the general community should have greater involvement in water management and planning. This would require education programs to improve awareness of reform and increased support for stakeholder input into reform, particularly where language barriers and cultural differences exist. Third, given the importance of sustainability and environmental protection, it is recommended that markets develop within a planning framework, with robust but simple trading rules to protect ecological and customary values. Fourth it was emphasised by some respondents that there should be minimal red tape and costs associated with markets given the marginal operating conditions for producers across the north.Further research could build on this exploratory work to improve understanding of how to involve Indigenous interests in water markets, and examine the attitudes and values of a broader range of stakeholders across the north (such as examining women&rsquo;s attitudes and values to water markets across the north)

Relay selection for efficient HARQ-IR protocols in relay-assisted multisource multicast networks

This paper investigates relay selection for reliable data transmission in relay-assisted multisource multicast networks (RMMNs) where multiple source nodes distribute information to a set of destination nodes with the assistance of multiple relay nodes. Hybrid automatic repeat request with incremental redundancy (HARQ-IR) is used and supported by either a physical-layer network coding (PNC) or an analog network coding (ANC) technique employed at the relays. By deriving efficiency metrics of the HARQ-IR protocols, we propose relay selection schemes for RMMNs to minimize the transmission delay and energy consumption. Simulation results are provided to analyse each relay selection scheme

Electron transport and band structure in phosphorus-doped polycrystalline silicon films

We study transport mechanisms, effective mass, and band structure by measuring the resistivity, Hall, and Seebeck and Nernst coefficients in heavily phosphorus-doped polycrystalline silicon films made by thermal crystallization of amorphous silicon. We observe a change in transport mechanism which results in an increase in electron mobility from 10% to 80% of the single-crystal silicon mobility as the carrier concentration increases from 1019 to 1020 cm-3. Our measurements of effective mass at the Fermi level indicate that as the carrier concentration increases, there is a shift from impurity-band transport to conduction-band transport, and that the electron effective mass is lower in the impurity band than in the conduction band of Si. The shift to conduction-band transport improves electron mobility with carrier density by improving intragrain carrier mean free path lengths and relaxation times. © 2009 American Institute of Physics.published_or_final_versio

3D-printed glass microfluidics for fluid dynamics and rheology

Microfluidics provides a versatile platform for handling small volumes of fluids at small length scales. From a fluid dynamics perspective, microfluidics gives access to a regime of very high deformation rates at moderate to negligible Reynolds numbers Re. For viscoelastic fluid flows, the resulting high Weissenberg numbers Wi = tau, where tau is the fluid characteristic time, means the flow occurs at high elasticity number El = Wi/Re. Consequently, microfluidics supports a burgeoning interest in the experimental study of purely elastic flow instabilities and elastic turbulence. However, for rheological studies, typical microfluidic fabrications by soft lithography in poly (dimethyl siloxane) suffer from a number of limitations arising from the low elastic modulus and poor optical properties of the material. In this review, we summarise a few recent studies from our group in which we have experimented with microdevice fabrications using the subtractive three-dimensional (3D)-printing technique of selective laser-induced etching (SLE). SLE can be used to fabricate arbitrary 3D geometries with micron precision in fused silica: a high modulus, highly transparent material, which is robust and resistant to organic solvents. Apart from high elasticity number flows, we have found that SLE fabricated devices can sustain very high deformation rates without device failure, providing new access to little-explored inertio-elastic regimes in extremely dilute polymer solutions. Furthermore, it is possible to visualize flows from multiple planes of observation, allowing the quantitative study of 3D flow instabilities and vortex dynamics in both Newtonian and non-Newtonian fluids. SLE fabrication offers many new opportunities to those involved in fluid dynamics and rheology research at the microscale, and we highlight what we perceive as potentially fruitful ideas for future studies using this technique

Coupling of vortex breakdown and stability in a swirling flow

Swirling flows are ubiquitous over a large range of length scales and applications including micron-scale microfluidic devices up to geophysical flows such as tornadoes. As the viscous dissipation, shear, and centrifugal stresses interact, such flows can often exhibit unexpected fluid dynamics. Here, we use microfluidic experiments and numerical simulations to study the flow in a vortex T-mixer: a T-shaped channel with staggered, offset inlets. The vortex T-mixer flow is characterized by a single dominant vortex, the stability of which is closely coupled to the appearance of vortex breakdown. Specifically, at a Reynolds number of Re≈90, a first vortex breakdown region appears in the steady-state solution, rendering the vortex pulsatively unstable. A second vortex breakdown region appears at Re≈120, which restabilizes the vortex. Finally, a third vortex breakdown region appears at Re≈180, which renders the vortex helically unstable. Thus, a counterintuitive flow regime exists for the vortex T-mixer in which increasing the Reynolds number has a stabilizing effect on the steady-state flow. The pulsatively unstable vortex evolves into a periodically pulsating state with a Strouhal number of St≈0.5, and the helically unstable vortex evolves into a helically oscillating state with St≈1.75. These transitions can be explained within the framework of linear hydrodynamic stability. In addition, the vortex T-mixer flow exhibits multistability; multiple flow states are stable over various ranges of Re, including a narrow range of tristability for 160≤Re≤170, in which the steady state, the pulsatile oscillation, and the helical oscillation are all stable. This study provides experimental and numerical evidence of the close coupling between vortex breakdown and flow stability, including the restabilization of the flow with increasing Reynolds number due to the appearance of a vortex breakdown region, which will provide new insights into how vortex breakdown can affect the stability of a swirling flow

Unconventional anomalous Hall effect in 3d/5d multilayers mediated by the nonlocal spin-conductivity

We evidenced unconventionnal Anomalous Hall Effects (AHE) in 3d/5d (Co0.2nm/Ni0.6nm)N multilayers grown on a thin Pt layer or thin Au:W alloy. The inversion observed on AHE originates from the opposite sign of the spin-orbit coupling of Pt compared to Ni. Via advanced simulations methods for the description of the spin-current profiles based on the spin-dependent Boltzmann formalism, we extracted the spin Hall angle (SHA) of Pt and (Co/Ni) as well as the relevant transport parameters. The extracted SHA for Pt, +20%, is opposite to the one of (Co/Ni), giving rise to an effective AHE inversion for thin (Co/Ni) multilayers (N < 17). The spin Hall angle in Pt is found to be larger than the one previously measured in combined spin-pumping inverse spin-Hall effect experiments in a geometry of current perpendicular to plane. Whereas magnetic proximity effects cannot explain the effect, spin-current leakage and anisotropic electron scattering at Pt/(Co,Ni) interfaces fit the experiments.Comment: 7 pages, 2 figure

Highly phosphorescent platinum(II) emitters: photophysics, materials and biological applications

published_or_final_versio

Microscopic investigation of vortex breakdown in a dividing T-junction flow

Three-dimensional (3D)-printed microfluidic devices offer new ways to study fluid dynamics. We present a clear visualization of vortex breakdown in a dividing T-junction flow. By individual control of the inflow and two outflows, we decouple the effects of swirl and rate of vorticity decay. We show that even slight outflow imbalances can greatly alter the structure of vortex breakdown, by creating a net pressure difference across the junction. Our results are summarized in a dimensionless phase diagram, which will guide the use of vortex breakdown in T-junctions to achieve specific flow manipulation