22,991 research outputs found
Dental erosion: In vitro model of wine assessor's erosion
The document attached has been archived with permission from the Australian Dental Association. An external link to the publisher’s copy is included.Background: Wine makers and assessors frequently experience severe dental erosion. The objectives of this study were to develop an in vitro model of dental erosion caused by frequent wine contact with teeth, and to use this model to assess the effectiveness of a variety of methods which might protect against this form of erosion. Methods: An initial pilot study found that riesling style wine was more erosive than champagne style, and both more than claret. Wine tasting was simulated by subjecting exposed windows of enamel and root surfaces on 50 intact, extracted human teeth to 1400 one minute exposures to white wine (pH 3.2). A variety of dental materials were applied to the exposed windows on groups of teeth prior to erosive challenge, to assess their protective ability. Results: Protective resin coatings and fluoride varnishes protected both enamel and roots against wine induced erosion. A high degree of protection was provided by APF gel, with less by NaF gel. Conclusions: It was concluded that dentists may be able to help minimise erosion resulting from frequent wine-tasting in their patients by the clinical application of one or a combination of these agents at times prior to prolonged assessment periods.Tong Bee Mok, J McIntyre and D Hun
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Viscous coupling of shear-free turbulence across nearly flat fluid interfaces
The interactions between shear-free turbulence in two regions (denoted as + and − on either side of a nearly flat horizontal interface are shown here to be controlled by several mechanisms, which depend on the magnitudes of the ratios of the densities, ρ+/ρ−, and kinematic viscosities of the fluids, μ+/μ−, and the root mean square (r.m.s.) velocities of the turbulence, u0+/u0−, above and below the interface. This study focuses on gas–liquid interfaces so that ρ+/ρ− ≪ 1 and also on where turbulence is generated either above or below the interface so that u0+/u0− is either very large or very small. It is assumed that vertical buoyancy forces across the interface are much larger than internal forces so that the interface is nearly flat, and coupling between turbulence on either side of the interface is determined by viscous stresses. A formal linearized rapid-distortion analysis with viscous effects is developed by extending the previous study by Hunt & Graham (J. Fluid Mech., vol. 84, 1978, pp. 209–235) of shear-free turbulence near rigid plane boundaries. The physical processes accounted for in our model include both the blocking effect of the interface on normal components of the turbulence and the viscous coupling of the horizontal field across thin interfacial viscous boundary layers. The horizontal divergence in the perturbation velocity field in the viscous layer drives weak inviscid irrotational velocity fluctuations outside the viscous boundary layers in a mechanism analogous to Ekman pumping. The analysis shows the following. (i) The blocking effects are similar to those near rigid boundaries on each side of the interface, but through the action of the thin viscous layers above and below the interface, the horizontal and vertical velocity components differ from those near a rigid surface and are correlated or anti-correlated respectively. (ii) Because of the growth of the viscous layers on either side of the interface, the ratio uI/u0, where uI is the r.m.s. of the interfacial velocity fluctuations and u0 the r.m.s. of the homogeneous turbulence far from the interface, does not vary with time. If the turbulence is driven in the lower layer with ρ+/ρ− ≪ 1 and u0+/u0− ≪ 1, then uI/u0− ~ 1 when Re (=u0−L−/ν−) ≫ 1 and R = (ρ−/ρ+)(v−/v+)1/2 ≫ 1. If the turbulence is driven in the upper layer with ρ+/ρ− ≪ 1 and u0+/u0− ≫ 1, then uI/u0+ ~ 1/(1 + R). (iii) Nonlinear effects become significant over periods greater than Lagrangian time scales. When turbulence is generated in the lower layer, and the Reynolds number is high enough, motions in the upper viscous layer are turbulent. The horizontal vorticity tends to decrease, and the vertical vorticity of the eddies dominates their asymptotic structure. When turbulence is generated in the upper layer, and the Reynolds number is less than about 106–107, the fluctuations in the viscous layer do not become turbulent. Nonlinear processes at the interface increase the ratio uI/u0+ for sheared or shear-free turbulence in the gas above its linear value of uI/u0+ ~ 1/(1 + R) to (ρ+/ρ−)1/2 ~ 1/30 for air–water interfaces. This estimate agrees with the direct numerical simulation results from Lombardi, De Angelis & Bannerjee (Phys. Fluids, vol. 8, no. 6, 1996, pp. 1643–1665). Because the linear viscous–inertial coupling mechanism is still significant, the eddy motions on either side of the interface have a similar horizontal structure, although their vertical structure differs
Material Flow Analysis: Outcome Focus (MFA:OF) for Elucidating the Role of Infrastructure in the Development of a Liveable City
Engineered infrastructures (i.e., utilities, transport & digital) underpin modern society. Delivering services via these
is especially challenging in cities where differing infrastructures form a web of interdependencies. There must be a
step change in how infrastructures deliver services to cities, if those cities are to be liveable in the future (i.e., provide
for citizen wellbeing, produce less CO2 & ensure the security of the resources they use). Material Flow Analysis
(MFA) is a useful methodology for understanding how infrastructures transfer resources to, within and from cities
and contribute to the city’s metabolism. Liveable Cities, a five-year research programme was established to identify
& test radical engineering interventions leading to liveable cities of the future. In this paper, the authors propose an
outcome-focussed variation on the MFA methodology (MFA: OF), evidenced through work on the resource flows of
Birmingham, UK. These flows include water, energy, food & carbon-intensive materials (e.g., steel, paper, glass), as
well as their associated waste. The contribution MFA: OF makes to elucidating the interactions & interdependencies
between the flows is highlighted and suggestions are made for how it can contribute to the (radical) rethinking of the
engineered infrastructure associated with such flow
Hypersonic structures: An aerodynamicist's perspective, or one man's dream is another man's nightmare
The relationship between hypersonic aerodynamic and structural design is reviewed. The evolution of the hypersonic vehicle design is presented. Propulsion systems, structural materials, and fuels are emphasized
An acoustic charge transport imager for high definition television applications
In this report we present the progress during the second six month period of the project. This includes both experimental and theoretical work on the acoustic charge transport (ACT) portion of the chip, the theoretical program modelling of both the avalanche photodiode (APD) and the charge transfer and overflow transistor and the materials growth and fabrication part of the program
Solar silicon via the Dow Corning process
Carbon, as a reductant for quartz, must be made available so as to have suitable reactivity in conjunction with high purity, especially with respect to boron and phosphorus. A detailed experimental plan was developed to do this. Different sources of carbon were selected to be subjected to various purification methods and reactivity-enhancement processes. A developmental scale arc furnace was installed to perform quartz-carbon reactivity testing
Hypersonic Airbreathing Missile
A hypersonic airbreathing missile using dual mode scramjet engines for propulsion is described. The fuselage is constructed of a material with a high heat sink capacity and is covered with a thermal protective shield and lined with an internal insulating blanket. The engine airframe integration uses the flat lower portion of the lower fuselage to precompress the air entering the scramjet engines. The precompression of air entering the scramjet inlets increases as the angles of attack. This feature results in a highly maneuverable missile which can accelerate as it banks into a turn
Taking stock of SLSN and LGRB host galaxy comparison using a complete sample of LGRBs
Long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe) are both
explosive transients with very massive progenitor stars. Clues about the nature
of the progenitors can be found by investigating environments in which such
transients occur. While studies of LGRB host galaxies have a long history,
dedicated observational campaigns have only recently resulted in a high enough
number of photometrically and spectroscopically observed SLSN hosts to allow
statistically significant analysis of their properties. In this paper we make a
comparison of the host galaxies of hydrogen-poor (H-poor) SLSNe and the
Swift/BAT6 sample of LGRBs. In contrast to previous studies we use a complete
sample of LGRBs and we address a special attention to the comparison
methodology and the selection of SLSN sample whose data have been compiled from
the available literature. At intermediate redshifts (0.3 < z < 0.7) the two
classes of transients select galaxies whose properties (stellar mass,
luminosity, star-formation rate, specific star-formation rate and metallicity)
do not differ on average significantly. Moreover, the host galaxies of both
classes of objects follow the fundamental metallicity relation and the
fundamental plane of metallicity. In contrast to previous studies we show that
at intermediate redshifts the emission line equivalent widths of the two
populations are essentially the same and that the previous claims regarding the
higher fraction of SLSN hosts among the extreme emission line galaxies with
respect to LGRBs are mostly due to a larger fraction of strong-line emitters
among SLSN hosts at z < 0.3, where samples of LGRB hosts are small and poorly
defined.Comment: 7 pages, 4 figures, accepted to Astronomy & Astrophysic
Stellar Motion around Spiral Arms: Gaia Mock Data
We compare the stellar motion around a spiral arm created in two different
scenarios, transient/co-rotating spiral arms and density-wave-like spiral arms.
We generate Gaia mock data from snapshots of the simulations following these
two scenarios using our stellar population code, SNAPDRAGONS, which takes into
account dust extinction and the expected Gaia errors. We compare the observed
rotation velocity around a spiral arm similar in position to the Perseus arm,
and find that there is a clear difference in the velocity features around the
spiral arm between the co-rotating spiral arm and the density-wave-like spiral
arm. Our result demonstrates that the volume and accuracy of the Gaia data are
sufficient to clearly distinguish these two scenarios of the spiral arms.Comment: 5 pages, 1 figure, to appear in the proceedings of "The Milky Way
Unravelled by Gaia: GREAT Science from the Gaia Data Releases", Barcelona,
1-5 December 2014, eds. N. Walton, F. Figueras, C. Soubira
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