9,079 research outputs found
Computation of turbulent high speed mixing layers using a two-equation turbulence model
A two-equation turbulence model was extended to be applicable for compressible flows. A compressibility correction based on modelling the dilational terms in the Reynolds stress equations were included in the model. The model is used in conjunction with the SPARK code for the computation of high speed mixing layers. The observed trend of decreasing growth rate with increasing convective Mach number in compressible mixing layers is well predicted by the model. The predictions agree well with the experimental data and the results from a compressible Reynolds stress model. The present model appears to be well suited for the study of compressible free shear flows. Preliminary results obtained for the reacting mixing layers are included
Biodegradable and compostable alternatives to conventional plastics
This article is available open access through the publisherâs website at the link below. Copyright @ 2009 The Royal Society.Packaging waste forms a significant part of municipal solid waste and has caused increasing environmental concerns, resulting in a strengthening of various regulations aimed at reducing the amounts generated. Among other materials, a wide range of oil-based polymers is currently used in packaging applications. These are virtually all non-biodegradable, and some are difficult to recycle or reuse due to being complex composites having varying levels of contamination. Recently, significant progress has been made in the development of biodegradable plastics, largely from renewable natural resources, to produce biodegradable materials with similar functionality to that of oil-based polymers. The expansion in these bio-based materials has several potential benefits for greenhouse gas balances and other environmental impacts over whole life cycles and in the use of renewable, rather than finite resources. It is intended that use of biodegradable materials will contribute to sustainability and reduction in the environmental impact associated with disposal of oil-based polymers.
The diversity of biodegradable materials and their varying properties makes it difficult to make simple, generic assessments such as biodegradable products are all âgoodâ or petrochemical-based products are all âbadâ. This paper discusses the potential impacts of biodegradable packaging materials and their waste management, particularly via composting. It presents the key issues that inform judgements of the benefits these materials have in relation to conventional, petrochemical-based counterparts. Specific examples are given from new research on biodegradability in simulated âhomeâ composting systems. It is the view of the authors that biodegradable packaging materials are most suitable for single-use disposable applications where the post-consumer waste can be locally composted.EPSR
Small-Scale Variations of HI Spectra from Interstellar Scintillatio
I suggest that radio-wave scattering by the interstellar plasma, in
combination with subsonic gradients in the Doppler velocity of interstellar HI,
is responsible for the observed small-scale variation in HI absorption spectra
of pulsars. Velocity gradients on the order of 0.05 to 0.3 km/s across 1 AU can
produce the observed variations. I suggest observational tests to distinguish
between this model and the traditional picture of small-scale opacity
variations from cloudlets.Comment: 24 pages, 2 figures, Latex, uses AASTe
One pion events by atmospheric neutrinos: A three flavor analysis
We study the one-pion events produced via neutral current (NC) and charged
current (CC) interactions by the atmospheric neutrinos. We analyze the ratios
of these events in the framework of oscillations between three neutrino
flavors. The ratios of the CC events induced by to that of the NC
events and a similar ratio defined with help us in distinguishing the
different regions of the neutrino parameter space.Comment: 14 pages, 4 figures (separate postscript files
An analytic relation for the thickness of accretion flows
We take the vertical distribution of the radial and azimuthal velocity into
account in spherical coordinates, and find that the analytic relation
c_{s0}/(v_K \Theta) = [(\gamma -1)/(2\gamma)]^{1/2} is valid for both
geometrically thin and thick accretion flows, where c_{s0} is the sound speed
on the equatorial plane, v_K is the Keplerian velocity, \Theta is the
half-opening angle of the flow, and \gamma is the adiabatic index.Comment: 4 pages, 2 figures, accepted by Science in China Series
- âŠ