1,654 research outputs found
The Effects of Foreign Price Uncertainty on Australian Production and Trade
This paper provides a framework for the empirical analysis of the role of uncertain international prices for the Australian economyâs production sector and its international trade. We model the movement of traded goods prices via a bivariate GARCH model and embed this within an expected utility maximizing model of the production sector. We find that the empirical results are consistent with expected utility maximization and that the hypothesis of risk neutrality is soundly rejected. Estimates of the effects of changes in expected prices and volatility of traded goods prices upon production decisions and the return to capital are presented and discussed, as are the impacts of changes in output growth of Australiaâs major trading partners. The overall conclusion is that price uncertainty matters for the Australian production sector.Price uncertainty, production under risk, expected utility maximization, international trade
Timely Updates over an Erasure Channel
Using an age of information (AoI) metric, we examine the transmission of
coded updates through a binary erasure channel to a monitor/receiver. We start
by deriving the average status update age of an infinite incremental redundancy
(IIR) system in which the transmission of a k-symbol update continuesuntil k
symbols are received. This system is then compared to a fixed redundancy (FR)
system in which each update is transmitted as an n symbol packet and the packet
is successfully received if and only if at least k symbols are received. If
fewer than k symbols are received, the update is discarded. Unlike the IIR
system, the FR system requires no feedback from the receiver. For a single
monitor system, we show that tuning the redundancy to the symbol erasure rate
enables the FR system to perform as well as the IIR system. As the number of
monitors is increased, the FR system outperforms the IIR system that guarantees
delivery of all updates to all monitors
Life cycle assessment of Swiss organic farming systems
The impacts of organic and integrated farming systems in Switzerland on the environment have been assessed in a comprehensive study by the life cycle assessment method. This paper reports a comparison of the treatments of the DOC experiment. Organic farming showed clear ecological advantages particularly for eco- and human toxicity, resource use and biodiversity. These ecological advantages only partly apply to nutrient losses and are not always found for single products. Per kg of organic product, higher impacts were often found for global warming potential, ozone formation, eutrophication and acidification compared to integrated production. In the same crop rotation with the same amount of organic fertilisers there were no systematic differences in soil quality of organic compared with integrated production. Further improvement of the environmental performance of organic farming should focus on achieving higher yields of good quality â especially in potatoes and cereals - by using inputs more efficiently and minimising nitrogen losses
Self-Similarity and Energy Dissipation in Stepped Polymer Films
The surface of a thin liquid film with nonconstant curvature is unstable, as
the Laplace pressure drives a flow mediated by viscosity. We present the
results of experiments on one of the simplest variable curvature surfaces: a
stepped polymer film. Height profiles are measured as a function of time for a
variety of molecular weights. The evolution of the profiles is shown to be
self-similar. This self-similarity offers a precise measurement of the
capillary velocity by comparison with numerical solutions of the thin film
equation. We also derive a master expression for the time dependence of the
excess free energy as a function of the material properties and film geometry.
The experiment and theory are in excellent agreement and indicate the
effectiveness of stepped polymer films to elucidate nanoscale rheological
properties.Comment: 5 pages, 4 figures, article accepted for publication in Physical
Review Letter
Capillary leveling of stepped films with inhomogeneous molecular mobility
A homogeneous thin polymer film with a stepped height profile levels due to
the presence of Laplace pressure gradients. Here we report on studies of
polymeric samples with precisely controlled, spatially inhomogeneous molecular
weight distributions. The viscosity of a polymer melt strongly depends on the
chain length distribution; thus, we learn about thin-film hydrodynamics with
viscosity gradients. These gradients are achieved by stacking two films with
different molecular weights atop one another. After a sufficient time these
samples can be well described as having one dimensional viscosity gradients in
the plane of the film, with a uniform viscosity normal to the film. We develop
a hydrodynamic model that accurately predicts the shape of the experimentally
observed self-similar profiles. The model allows for the extraction of a
capillary velocity, the ratio of the surface tension and the viscosity, in the
system. The results are in excellent agreement with capillary velocity
measurements of uniform mono- and bi-disperse stepped films and are consistent
with bulk polymer rheology.Comment: Accepted for publication in Soft Matter, Themed Issue on "The
Geometry and Topology of Soft Materials
Liquid droplets act as "compass needles" for the stresses in a deformable membrane
We examine the shape of droplets atop deformable thin elastomeric films
prepared with an anisotropic tension. As the droplets generate a deformation in
the taut film through capillary forces, they assume a shape that is elongated
along the high tension direction. By measuring the contact line profile, the
tension in the membrane can be completely determined. Minimal theoretical
arguments lead to predictions for the droplet shape and membrane deformation
that are in excellent agreement with the data. On the whole, the results
demonstrate that droplets can be used as probes to map out the stress field in
a membrane
Interplay of internal stresses, electric stresses and surface diffusion in polymer films
We investigate two destabilization mechanisms for elastic polymer films and
put them into a general framework: first, instabilities due to in-plane stress
and second due to an externally applied electric field normal to the film's
free surface. As shown recently, polymer films are often stressed due to
out-of-equilibrium fabrication processes as e.g. spin coating. Via an
Asaro-Tiller-Grinfeld mechanism as known from solids, the system can decrease
its energy by undulating its surface by surface diffusion of polymers and
thereby relaxing stresses. On the other hand, application of an electric field
is widely used experimentally to structure thin films: when the electric
Maxwell surface stress overcomes surface tension and elastic restoring forces,
the system undulates with a wavelength determined by the film thickness. We
develop a theory taking into account both mechanisms simultaneously and discuss
their interplay and the effects of the boundary conditions both at the
substrate and the free surface.Comment: 14 pages, 7 figures, 1 tabl
Intelligent Feature Engineering for Cybersecurity
Feature engineering and selection is a critical step in the implementation of any machine learning system. In application areas such as intrusion detection for cybersecurity, this task is made more complicated by the diverse data types and ranges presented in both raw data packets and derived data fields. Additionally, the time and context specific nature of the data requires domain expertise to properly engineer the features while minimizing any potential information loss. Many previous efforts in this area naively apply techniques for feature engineering that are successful in image recognition applications. In this work, we use network packet dataflows from the Defense Research and Engineering Network (DREN) and the Engineer Research and Development Center\u27s (ERDC) high performance computing systems to experimentally analyze various methods of feature engineering. The results of this research provide insight on the suitability of the features for machine learning based cybersecurity applications
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