4,448 research outputs found
Phase coherence length and quantum interference patterns at step edges
The accepted approximation used to describe quantum interference patterns at
steps is shown to be incorrect. As a result, electron lifetimes determined
using it are in error by a factor 2.Comment: 3 pages, 1 figur
Consumption Externalities and Diffusion in Pharmaceutical Markets: Antiulcer Drugs
We examine the role of consumption externalities in the demand for pharmaceuticals at both the brand level and over a therapeutic class of drugs. These effects emerge when use of a drug by others affects its value, and/or conveys information abut efficacy and safety to patients and physicians. This can affect that rate of market diffusion for a new entrant, and can lead to herb behavior whereby a particular drug can dominate the market despite the availability of close substitutes. We use data for H2-antagonist antiulcer drugs to estimate a dynamic demand model and quantify these effects. The model has three components: an hedonic price equation that measures how the aggregate usage of a drug, as well as conventional attributes, affect brand valuation; equations relating equilibrium market shares to quality-adjusted prices and marketing levels; and diffusion equations describing the dynamic adjustment process. We find that consumption externalities influence both valuations and rates of diffusion, but that they operate at the brand and not the therapeutic class level.
Theoretical analysis of STM-derived lifetimes of excitations in the Shockley surface state band of Ag(111)
We present a quantitative many-body analysis using the GW approximation of
the decay rate due to electron-electron scattering of excitations in
the Shockley surface state band of Ag(111), as measured using the scanning
tunnelling microscope (STM). The calculations include the perturbing influence
of the STM, which causes a Stark-shift of the surface state energy and
concomitant increase in . We find varies more rapidly with
than recently found for image potential states, where the STM has been shown to
significantly affect measured lifetimes. For the Shockley states, the
Stark-shifts that occur under normal tunnelling conditions are relatively small
and previous STM-derived lifetimes need not be corrected.Comment: 4 pages, 3 figure
q-Newton binomial: from Euler to Gauss
A counter-intuitive result of Gauss (formulae (1.6), (1.7) below) is made
less mysterious by virtue of being generalized through the introduction of an
additional parameter
Decoherence and Entropy Production in Relativistic Nuclear Collisions
Short thermalization times of less than 1 fm/c for quark and gluon matter
have been suggested by recent experiments at the Relativistic Heavy Ion
Collider (RHIC). It has been difficult to justify this rapid thermalization in
first-principle calculations based on perturbation theory or the color glass
condensate picture. Here, we address the related question of the decoherence of
the gluon field, which is a necessary component of thermalization. We present a
simplified leading-order computation of the decoherence time of a gluon
ensemble subject to an incoming flux of Weizsacker-Williams gluons. We also
discuss the entropy produced during the decoherence process and its relation to
the entropy in the final state which has been measured experimentally.Comment: 8 pages, 3 figure
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