103 research outputs found
De Sitter space and perpetuum mobile
We give general arguments that any interacting non--conformal {\it classical}
field theory in de Sitter space leads to the possibility of constructing a
perpetuum mobile. The arguments are based on the observation that massive free
falling particles can radiate other massive particles on the classical level as
seen by the free falling observer. The intensity of the radiation process is
non-zero even for particles with any finite mass, i.e. with a wavelength which
is within the causal domain. Hence, we conclude that either de Sitter space can
not exist eternally or that one can build a perpetuum mobile.Comment: 11 pages revtex, no figures. Added discussion to strengthen
conclusio
A thermal instability for positive brane cosmological constant in the Randall-Sundrum cosmologies
We describe a novel dynamical mechanism to radiate away a positive four
dimensional cosmological constant, in the Randall-Sundrum cosmological
scenario. We show that there are modes of the bulk gravitational field for
which the brane is effectively a mirror. This will generally give rise to an
emission of thermal radiation from the brane into the bulk. The temperature
turns out to be nonvanishing only if the effective four dimensional
cosmological constant is positive. In any theory where the four dimensional
vacuum energy is a function of physical degrees of freedom, there is then a
mechanism that radiates away any positive four dimensional cosmological
constant.Comment: 14 pages. The discussion on the relation between temperature and
effective 4d cosmological constant is changed. References are adde
The Schwinger Mechanism, the Unruh Effect and the Production of Accelerated Black Holes
We compute the corrections to the transition amplitudes of an accelerated
Unruh ``box'' that arise when the accelerated box is replaced by a ``two level
ion'' immersed in a constant electric field and treated in second quantization.
There are two kinds of corrections, those due to recoil effects induced by the
momentum transfers and those due to pair creation. Taken together, these
corrections show that there is a direct relationship between pair creation
amplitudes described by the Heisenberg-Euler-Schwinger mechanism and the Unruh
effect, i.e. the thermalisation of accelerated systems at temperature where is the acceleration. In particular, there is a thermodynamical
consistency between both effects whose origin is that the euclidean action
governing pair creation rates acts as an entropy in delivering the Unruh
temperature. Upon considering pair creation of charged black holes in an
electric field, these relationships explain why black holes are created from
vacuum in thermal equilibrium, i.e. with their Hawking temperature equal to
their Unruh temperature.Comment: Revised version: expanded introduction and discussion of pair
creation of black holes, 2figures added, 22 pages, Late
Aspects of Quantum Gravity in de Sitter Spaces
In these lectures we give a review of recent attempts to understand quantum
gravity on de Sitter spaces. In particular, we discuss the holographic
correspondence between de Sitter gravity and conformal field theories proposed
by Hull and by Strominger, and how this may be reconciled with the
finite-dimensional Hilbert space proposal by Banks and Fischler. Furthermore we
review the no-go theorems that forbid an embedding of de Sitter spaces in
string theory, and discuss how they can be circumvented. Finally, some curious
issues concerning the thermal nature of de Sitter space are elucidated.Comment: 36+1 pages, 5 Postscript figures, introduction and section 6
extended, further references, final version to appear in JCA
Marginalization of end-use technologies in energy innovation for climate protection
Mitigating climate change requires directed innovation efforts to develop and deploy energy technologies. Innovation activities are directed towards the outcome of climate protection by public institutions, policies and resources that in turn shape market behaviour. We analyse diverse indicators of activity throughout the innovation system to assess these efforts. We find efficient end-use technologies contribute large potential emission reductions and provide higher social returns on investment than energy-supply technologies. Yet public institutions, policies and financial resources pervasively privilege energy-supply technologies. Directed innovation efforts are strikingly misaligned with the needs of an emissions-constrained world. Significantly greater effort is needed to develop the full potential of efficient end-use technologies
A study of patent thickets
Report analysing whether entry of UK enterprises into patenting in a technology area is affected by patent thickets in the technology area
Analysis of the FGF gene family provides insights into aquatic adaptation in cetaceans
Cetacean body structure and physiology exhibit dramatic adaptations to their aquatic environment. Fibroblast growth factors (FGFs) are a family of essential factors that regulate animal development and physiology; however, their role in cetacean evolution is not clearly understood. Here, we sequenced the fin whale genome and analysed FGFs from 8 cetaceans. FGF22, a hair follicle-enriched gene, exhibited pseudogenization, indicating that the function of this gene is no longer necessary in cetaceans that have lost most of their body hair. An evolutionary analysis revealed signatures of positive selection for FGF3 and FGF11, genes related to ear and tooth development and hypoxia, respectively. We found a D203G substitution in cetacean FGF9, which was predicted to affect FGF9 homodimerization, suggesting that this gene plays a role in the acquisition of rigid flippers for efficient manoeuvring. Cetaceans utilize low bone density as a buoyancy control mechanism, but the underlying genes are not known. We found that the expression of FGF23, a gene associated with reduced bone density, is greatly increased in the cetacean liver under hypoxic conditions, thus implicating FGF23 in low bone density in cetaceans. Altogether, our results provide novel insights into the roles of FGFs in cetacean adaptation to the aquatic environment.ope
The Effect of Gravitational Tidal Forces on Renormalized Quantum Fields
The effect of gravitational tidal forces on renormalized quantum fields
propagating in curved spacetime is investigated and a generalisation of the
optical theorem to curved spacetime is proved. In the case of QED, the
interaction of tidal forces with the vacuum polarization cloud of virtual e^+
e^- pairs dressing the renormalized photon has been shown to produce several
novel phenomena. In particular, the photon field amplitude can locally increase
as well as decrease, corresponding to a negative imaginary part of the
refractive index, in apparent violation of unitarity and the optical theorem.
Below threshold decays into e^+ e^- pairs may also occur. In this paper, these
issues are studied from the point of view of a non-equilibrium initial-value
problem, with the field evolution from an initial null surface being calculated
for physically distinct initial conditions and for both scalar field theories
and QED. It is shown how a generalised version of the optical theorem, valid in
curved spacetime, allows a local increase in amplitude while maintaining
consistency with unitarity. The picture emerges of the field being dressed and
undressed as it propagates through curved spacetime, with the local
gravitational tidal forces determining the degree of dressing and hence the
amplitude of the renormalized quantum field. These effects are illustrated with
many examples, including a description of the undressing of a photon in the
vicinity of a black hole singularity.Comment: 76 pages, jheppub.sty, 10 figures, small corrections. arXiv admin
note: text overlap with arXiv:1006.014
A gaming simulation approach to understanding blue ocean strategy development as a transition from traditional competitive strategy
Blue Ocean Strategy (BOS) has attracted a resurgence of interest following various market discontinuities, including digital disruption, the growth of the sharing economy and the development of ecosystems. BOS is a combination of value innovation and new markets, driving sustained higher performance through specific marketing activities, but it is difficult to conceive and implement.
We outline five cases that use various transition paths to BOS through white spaces - with product extensions in the existing market. An important part of this transition are âblue ocean dropletsâ which drive profitable growth through the transition and then onto a successful deployment of a blue ocean strategy. Blue ocean droplets drive profitable growth - simultaneously increasing volume sales, maintaining/increasing prices and maintaining/decreasing costs.
We then use an inductive qualitative approach in a multi-team gaming simulation to examine drivers of firm performance. Higher than average performance is driven by repositioning in white spaces and execution of the three blue ocean droplets.
Finally, we discuss implications for firms: execute a number of real options to follow one of several transition paths to a full BOS. This approach involves less downside risk than a full BOS approach, but can still be sustainably profitable, while also breaking the traditional value/cost trade-off
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