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Conducting market research using the internet: The case of Xenon laboratories
The way market research is conducted has changed dramatically over the past 30 years, as a result of both the development of the prevailing view of best practice and the state of technology available to researchers. While it is clear that the World Wide Web (WWW) will increasingly be used as a medium for conducting market research, the full implications of this new channel are not yet fully understood. This paper examines the potential for an Internet-based financial services firm (Xenon Laboratories) to analyse conduct market research using the WWW. The case demonstrates that, by employing a novel approach to market research, Xenon Laboratories is in a unique position to understand the charging structures in its market, the market for international payments using credit or charge cards. In doing so, the paper highlights the opportunity to unobtrusively gather market information from an international group of customers by providing Internet-based value-added services
Identifying Deficiencies of Standard Accretion Disk Theory: Lessons from a Mean-Field Approach
Turbulent viscosity is frequently used in accretion disk theory to replace
the microphysical viscosity in order to accomodate the observational need for
in- stabilities in disks that lead to enhanced transport. However, simply
replacing the microphysical transport coefficient by a single turbulent
transport coeffi- cient hides the fact that the procedure should formally arise
as part of a closure in which the hydrodynamic or magnetohydrodynamic equations
are averaged, and correlations of turbulent fluctuations are replaced by
transport coefficients. Here we show how a mean field approach leads quite
naturally two transport coefficients, not one, that govern mass and angular
momentum transport. In particular, we highlight that the conventional approach
suffers from a seemingly inconsistent neglect of turbulent diffusion in the
surface density equation. We constrain these new transport coefficients for
specific cases of inward, outward, and zero net mass transport. In addition, we
find that one of the new transport terms can lead to oscillations in the mean
surface density which then requires a constant or small inverse Rossby number
for disks to maintain a monotonic power-law surface density.Comment: 11 page
Reprocessed emission line profiles from dense clouds in geometrically thick accretion engines
The central engines of active galactic nuclei (AGN) contain cold, dense
material as well as hot X-ray emitting gas. The standard paradigm for the
engine geometry is a cold thin disc sandwiched between hot X-ray coronae.
Strong support for this geometry in Seyferts comes from the study of
fluorescent iron line profiles, although the evidence is not ubiquitously air
tight. The thin disc model of line profiles in AGN and in X-ray binaries should
be bench marked against other plausible possibilities. One proposed alternative
is an engine consisting of dense clouds embedded in an optically thin,
geometrically thick X-ray emitting engine. This model is further motivated by
studies of geometrically thick engines such as advection dominated accretion
flows (ADAFs). Here we compute the reprocessed iron line profiles from dense
clouds embedded in geometrically thick, optically thin X-ray emitting discs
near a Schwarzchild black hole. We consider a range of cloud distributions and
disc solutions, including ADAFs, pure radial infall, and bipolar outflows. We
find that such models can reproduce line profiles similar to those from
geometrically thin, optically thick discs and might help alleviate some of the
problems encountered from the latter.Comment: 9 Pages LaTex, + Figs, submitted to MNRA
Reprocessed emission from warped accretion discs with application to X-ray iron line profiles
Flourescent iron line profiles currently provide the best diagnostic for
active galactic nuclei (AGN) engine geometries. Here we construct a method for
calculating the relativistic iron line profile from an arbitrarily warped
accretion disc, illuminated from above and below by hard X-ray sources. This
substantially generalises previous calculations of reprocessing by accretion
discs by including non-axisymmetric effects. We include a relativistic
treatment of shadowing by ray-tracing photon paths along Schwarzchild
geodesics. We apply this method to two classes of warped discs, and generate a
selection of resulting line profiles. New profile features include the
possibility of sharper red, and softer blue fall-offs, a time varying line
profile if the warp precesses about the disc, and some differences between
`twisted' and `twist-free' warps. We discuss some qualitative implications of
the line profiles in the context of Type I and II Seyfert AGN.Comment: 15 pages, LaTeX + eps files + 6 separate gif files, Submitted to
MNRA
Iron line profiles from black hole accretion discs with spiral velocity structure
We calculate the iron line profiles from accretion discs with spiral velocity
structures around Schwarzschild black holes. We find that quasi-periodic bumps
appear in the the profiles, thereby providing a test for spiral wave patterns.
This study is motivated by recent work showing that spiral density waves can
result from MHD instabilities even in non-self-gravitating discs, and by
improved spectral resolution of forthcoming X-ray missions.Comment: 4 pages LaTeX with 3 of the figures separate, submitted to MNRA
Does Eco-Certification Have Environmental Benefits? Organic Coffee in Costa Rica
Eco-certification of coffee, timber and other high-value agricultural commodities is increasingly widespread. In principle, it can improve commodity producers’ environmental performance, even in countries where state regulation is weak. However, evidence needed to evaluate this hypothesis is virtually nonexistent. To help fill this gap, we use detailed farm-level data to analyze the environmental impacts of organic coffee certification in central Costa Rica. We use propensity score matching to control for self-selection bias. We find that organic certification improves coffee growers’ environmental performance. It significantly reduces chemical input use and increases adoption of some environmentally friendly management practices.certification, coffee, Costa Rica, propensity score matching
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