27,944 research outputs found
Computing the Scaling Exponents in Fluid Turbulence from First Principles: Demonstration of Multi-scaling
This manuscript is a draft of work in progress, meant for network
distribution only. It will be updated to a formal preprint when the numerical
calculations will be accomplished. In this draft we develop a consistent
closure procedure for the calculation of the scaling exponents of the
th order correlation functions in fully developed hydrodynamic turbulence,
starting from first principles. The closure procedure is constructed to respect
the fundamental rescaling symmetry of the Euler equation. The starting point of
the procedure is an infinite hierarchy of coupled equations that are obeyed
identically with respect to scaling for any set of scaling exponents .
This hierarchy was discussed in detail in a recent publication [V.S. L'vov and
I. Procaccia, Phys. Rev. E, submitted, chao-dyn/9707015]. The scaling exponents
in this set of equations cannot be found from power counting. In this draft we
discuss in detail low order non-trivial closures of this infinite set of
equations, and prove that these closures lead to the determination of the
scaling exponents from solvability conditions. The equations under
consideration after this closure are nonlinear integro-differential equations,
reflecting the nonlinearity of the original Navier-Stokes equations.
Nevertheless they have a very special structure such that the determination of
the scaling exponents requires a procedure that is very similar to the solution
of linear homogeneous equations, in which amplitudes are determined by fitting
to the boundary conditions in the space of scales. The re-normalization scale
that i necessary for any anomalous scaling appears at this point. The Holder
inequalities on the scaling exponents select the renormalizaiton scale as the
outer scale of turbulence .Comment: 10 pages, 5 figs. to be submitted PR
A Covert Channel Using Named Resources
A network covert channel is created that uses resource names such as
addresses to convey information, and that approximates typical user behavior in
order to blend in with its environment. The channel correlates available
resource names with a user defined code-space, and transmits its covert message
by selectively accessing resources associated with the message codes. In this
paper we focus on an implementation of the channel using the Hypertext Transfer
Protocol (HTTP) with Uniform Resource Locators (URLs) as the message names,
though the system can be used in conjunction with a variety of protocols. The
covert channel does not modify expected protocol structure as might be detected
by simple inspection, and our HTTP implementation emulates transaction level
web user behavior in order to avoid detection by statistical or behavioral
analysis.Comment: 9 page
Relationship between sensory attributes, hidden attributes and price in influencing consumer perception of organic foods
This report was presented at the UK Organic Research 2002 Conference. Consumer attitudes to foods are mainly influenced by quality attributes. Ethical factors are important in some cases, but they may be overstated. The relationships between consumers' awareness of organic food, price and perceived quality of food were investigated by tests involving series of consumer panels and sensory evaluation. Sensory responses were also matched to instrumental analysis data. Results indicated that overall there was no relation between panellist’s views about organic foods and their sensory perceptions. Eighty percent of the panellists felt that organic products were too expensive, but would buy them if they were cheaper. However the study showed that most of the people would not be likely to change their preference once they had made a product choice based upon sensory attributes. This has important implications, indicating that not only price, but also sensory quality of organic food must be considered in order to maintain repeated purchases by most consumers
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