19,986 research outputs found
The role of search engine optimization in search marketing
This paper examines the impact of search engine optimization (SEO) on the competition between advertisers for organic and sponsored search results. The results show that a positive level of search engine optimization may improve the search engine's ranking quality and thus the satisfaction of its visitors. In the absence of sponsored links, the organic ranking is improved by SEO if and only if the quality provided by a website is sufficiently positively correlated with its valuation for consumers. In the presence of sponsored links, the results are accentuated and hold regardless of the correlation. When sponsored links serve as a second chance to acquire clicks from the search engine, low-quality websites have a reduced incentive to invest in SEO, giving an advantage to their high-quality counterparts. As a result of the high expected quality on the organic side, consumers begin their search with an organic click. Although SEO can improve consumer welfare and the payoff of high-quality sites, we find that the search engine's revenues are typically lower when advertisers spend more on SEO and thus less on sponsored links. Modeling the impact of the minimum bid set by the search engine reveals an inverse U-shaped relationship between the minimum bid and search engine profits, suggesting an optimal minimum bid that is decreasing in the level of SEO activity. © 2013 INFORMS
Matter wave interference using two-level atoms and resonant optical fields
A theory of matter wave interference is developed in which resonant optical
fields interact with two-level atoms. When recoil effects are included, spatial
modulation of the atomic density can occur for times that are greater than or
comparable with the inverse recoil frequency. In this regime, the atoms exhibit
matter-wave interference. Two specific atom field geometries are considered. In
the first, atoms characterized by a homogeneous velocity distribution are
subjected to a single radiation pulse. The pulse excites the atoms which then
decay back to the lower state. The spatial modulation of the total atomic
density is calculated as a function of , where is the time following the
pulse. In contrast to the normal Talbot effect, the spatially modulated density
is not a periodic function of owing to spontaneous emission; however,
after a sufficiently long time, the contribution from spontaneous processes no
longer plays a role and the Talbot periodicity is restored. In the second
atom-field geometry, there are two pulses separated by an interval . The
atomic velocity distribution in this case is assumed to be inhomogeneously
broadened. In contrast to the normal Talbot-Lau effect, the spatially modulated
density is not a periodic function of , owing to spontaneous emission;
however, for sufficiently long time, the contribution from spontaneous
processes no longer plays a role and the Talbot periodicity is restored. The
structure of the spatially modulated density is studied, and is found to mirror
the atomic density following the first pulse. The spatially modulated atomic
density serves as an indirect probe of the distribution of spontaneously
emitted radiation.Comment: 14 pages, 3 figure
Atomic entanglement generation with reduced decoherence via four-wave mixing
In most proposals for the generation of entanglement in large ensembles of
atoms via projective measurements, the interaction with the vacuum is
responsible for both the generation of the signal that is detected and the spin
depolarization or decoherence. In consequence, one has to usually work in a
regime where the information aquisition via detection is sufficiently slow
(weak measurement regime) such as not to strongly disturb the system. We
propose here a four-wave mixing scheme where, owing to the pumping of the
atomic system into a dark state, the polarization of the ensemble is not
critically affected by spontaneous emission, thus allowing one to work in a
strong measurement regime
Entropy of the Universe
After a discussion on several limiting cases where General Relativity turns
into less sophisticated theories, we find that in the correct thermodynamical
and cosmological weak field limit of Einstein's field equations the entropy of
the Universe is R^(3/2) -- dependent, where R stands for the radius of the
causally related Universe. Thus, entropy grows in the Universe, contrary to
Standard Cosmology prediction.Comment: To be published by International Journal of Theoretical Physic
Influence of qubit displacements on quantum logic operations in a silicon-based quantum computer with constant interaction
The errors caused by qubit displacements from their prescribed locations in
an ensemble of spin chains are estimated analytically and calculated
numerically for a quantum computer based on phosphorus donors in silicon. We
show that it is possible to polarize (initialize) the nuclear spins even with
displaced qubits by using Controlled NOT gates between the electron and nuclear
spins of the same phosphorus atom. However, a Controlled NOT gate between the
displaced electron spins is implemented with large error because of the
exponential dependence of exchange interaction constant on the distance between
the qubits. If quantum computation is implemented on an ensemble of many spin
chains, the errors can be small if the number of chains with displaced qubits
is small
Effects of environmental exposures on silicon solar cells
Effect of environmental tests on mechanical and electrical properties of silicon solar cell
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