8,004 research outputs found
A dynamic policy model to manage temporal performance amongst contracting firms in a competitive situation
Studies have been conducted to measure competitiveness in the construction industry. Such research has focused on all levels from the national picture to individual projects. While useful, the results are limited in that they present a snapshot picture at one point in time. Moreover, they do not suggest how under-performance might be improved. The research reported here is part of a large collaborative study to evaluate sustained competitiveness in the UK construction industry. It enhances previous research in that a system dynamics model of contracting firms operating in competition is used to not only measure each firm’s temporal performance by means of a dynamic competitive index, but it can also suggest high leverage policies which mitigate against under-performance. The model structure is described and simulated scenario runs presented. Besides the contribution to strategic policy making at the level of the contracting firm, the exemplar shows that the system dynamics methodology could have significant utility in the field of construction management
Is a Higgs Vacuum Instability Fatal for High-Scale Inflation?
We study the inflationary evolution of a scalar field with an unstable
potential for the case where the Hubble parameter during inflation is
larger than the instability scale of the potential. Quantum
fluctuations in the field of size imply that
the unstable part of the potential is sampled during inflation. We investigate
the evolution of these fluctuations to the unstable regime, and in particular
whether they generate cosmological defects or even terminate inflation. We
apply the results of a toy scalar model to the case of the Standard Model (SM)
Higgs boson, whose quartic evolves to negative values at high scales, and
extend previous analyses of Higgs dynamics during inflation utilizing
statistical methods to a perturbative and fully gauge-invariant formulation. We
show that the dynamics are controlled by the renormalization group-improved
quartic coupling evaluated at a scale , such that Higgs
fluctuations are enhanced by the instability if . Even if , the instability in the SM Higgs potential does not end inflation;
instead the universe slowly sloughs off crunching patches of space that never
come to dominate the evolution. As inflation proceeds past 50 -folds, a
significant proportion of patches exit inflation in the unstable vacuum, and as
much as 1% of the spacetime can rapidly evolve to a defect. Depending on the
nature of these defects, however, the resulting universe could still be
compatible with ours.Comment: 31 pages, 3 figures; v2: references added, journal versio
Probable or Improbable Universe? Correlating Electroweak Vacuum Instability with the Scale of Inflation
Measurements of the Higgs boson and top quark masses indicate that the
Standard Model Higgs potential becomes unstable around
GeV. This instability is cosmologically relevant since quantum fluctuations
during inflation can easily destabilize the electroweak vacuum if the Hubble
parameter during inflation is larger than (as preferred by the
recent BICEP2 measurement). We perform a careful study of the evolution of the
Higgs field during inflation, obtaining different results from those currently
in the literature. We consider both tunneling via a Coleman-de Luccia or
Hawking-Moss instanton, valid when the scale of inflation is below the
instability scale, as well as a statistical treatment via the Fokker-Planck
equation appropriate in the opposite regime. We show that a better
understanding of the post-inflation evolution of the unstable AdS vacuum
regions is crucial for determining the eventual fate of the universe. If these
AdS regions devour all of space, a universe like ours is indeed extremely
unlikely without new physics to stabilize the Higgs potential; however, if
these regions crunch, our universe survives, but inflation must last a few
e-folds longer to compensate for the lost AdS regions. Lastly, we examine the
effects of generic Planck-suppressed corrections to the Higgs potential, which
can be sufficient to stabilize the electroweak vacuum during inflation.Comment: 26 pages, 7 figures. Clarifications added. Matches published version
in JHE
A learning design for student-generated digital storytelling
The literature on digital video in education emphasises the use of prefabricated, instructional-style video assets. Learning designs for supporting the use of these expert-generated video products have been developed. However, there has been a paucity of pedagogical frameworks for facilitating specific genres of learner-generated video projects. Informed by two studies, this article describes the development of a learning design for a popular genre: learner-generated digital storytelling. A particular learning design representation is used to present a structured description of an approach to digital storytelling, and issues are raised relating to future iterations of the design. © 2011 Taylor & Francis
One-Dimensional Directed Sandpile Models and the Area under a Brownian Curve
We derive the steady state properties of a general directed ``sandpile''
model in one dimension. Using a central limit theorem for dependent random
variables we find the precise conditions for the model to belong to the
universality class of the Totally Asymmetric Oslo model, thereby identifying a
large universality class of directed sandpiles. We map the avalanche size to
the area under a Brownian curve with an absorbing boundary at the origin,
motivating us to solve this Brownian curve problem. Thus, we are able to
determine the moment generating function for the avalanche-size probability in
this universality class, explicitly calculating amplitudes of the leading order
terms.Comment: 24 pages, 5 figure
Towards a learning design for student-generated digital storytelling
The literature on digital video in education often emphasises the use of pre-fabricated, instructional style video assets. Learning designs for supporting the use of these expert-generated video products have been developed (e.g. Burden & Atkinson, 2008). However, there has been a paucity of pedagogical frameworks for facilitating learner-generated video projects. This paper outlines an emerging learning design for a popular genre: learner-generated digital storytelling
Long- and short-time asymptotics of the first-passage time of the Ornstein-Uhlenbeck and other mean-reverting processes
The first-passage problem of the Ornstein-Uhlenbeck process to a boundary is
a long-standing problem with no known closed-form solution except in specific
cases. Taking this as a starting-point, and extending to a general
mean-reverting process, we investigate the long- and short-time asymptotics
using a combination of Hopf-Cole and Laplace transform techniques. As a result
we are able to give a single formula that is correct in both limits, as well as
being exact in certain special cases. We demonstrate the results using a
variety of other models
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