27 research outputs found
On the Perturbative Stability of Quantum Field Theories in de Sitter Space
We use a field theoretic generalization of the Wigner-Weisskopf method to
study the stability of the Bunch-Davies vacuum state for a massless,
conformally coupled interacting test field in de Sitter space. We find that in
theory the vacuum does {\em not} decay, while in
non-conformally invariant models, the vacuum decays as a consequence of a
vacuum wave function renormalization that depends \emph{singularly} on
(conformal) time and is proportional to the spatial volume. In a particular
regularization scheme the vacuum wave function renormalization is the same as
in Minkowski spacetime, but in terms of the \emph{physical volume}, which leads
to an interpretation of the decay. A simple example of the impact of vacuum
decay upon a non-gaussian correlation is discussed. Single particle excitations
also decay into two particle states, leading to particle production that
hastens the exiting of modes from the de Sitter horizon resulting in the
production of \emph{entangled superhorizon pairs} with a population consistent
with unitary evolution. We find a non-perturbative, self-consistent "screening"
mechanism that shuts off vacuum decay asymptotically, leading to a stationary
vacuum state in a manner not unlike the approach to a fixed point in the space
of states.Comment: 36 pages, 4 figures. Version to appear in JHEP, more explanation
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
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
Characterization and Generation of Male Courtship Song in Cotesia congregata (Hymenoptera: Braconidae)
Background
Male parasitic wasps attract females with a courtship song produced by rapid wing fanning. Songs have been described for several parasitic wasp species; however, beyond association with wing fanning, the mechanism of sound generation has not been examined. We characterized the male courtship song of Cotesia congregata (Hymenoptera: Braconidae) and investigated the biomechanics of sound production. Methods and Principal Findings
Courtship songs were recorded using high-speed videography (2,000 fps) and audio recordings. The song consists of a long duration amplitude-modulated “buzz” followed by a series of pulsatile higher amplitude “boings,” each decaying into a terminal buzz followed by a short inter-boing pause while wings are stationary. Boings have higher amplitude and lower frequency than buzz components. The lower frequency of the boing sound is due to greater wing displacement. The power spectrum is a harmonic series dominated by wing repetition rate ~220 Hz, but the sound waveform indicates a higher frequency resonance ~5 kHz. Sound is not generated by the wings contacting each other, the substrate, or the abdomen. The abdomen is elevated during the first several wing cycles of the boing, but its position is unrelated to sound amplitude. Unlike most sounds generated by volume velocity, the boing is generated at the termination of the wing down stroke when displacement is maximal and wing velocity is zero. Calculation indicates a low Reynolds number of ~1000. Conclusions and Significance
Acoustic pressure is proportional to velocity for typical sound sources. Our finding that the boing sound was generated at maximal wing displacement coincident with cessation of wing motion indicates that it is caused by acceleration of the wing tips, consistent with a dipole source. The low Reynolds number requires a high wing flap rate for flight and predisposes wings of small insects for sound production
Migrant birds and mammals live faster than residents
Billions of vertebrates migrate to and from their breeding grounds annually, exhibiting
astonishing feats of endurance. Many such movements are energetically costly yet there is
little consensus on whether or how such costs might influence schedules of survival and
reproduction in migratory animals. Here we provide a global analysis of associations between
migratory behaviour and vertebrate life histories. After controlling for latitudinal and evolutionary
patterns, we find that migratory birds and mammals have faster paces of life than
their non-migratory relatives. Among swimming and walking species, migrants tend to have
larger body size, while among flying species, migrants are smaller. We discuss whether pace
of life is a determinant, consequence, or adaptive outcome, of migration. Our findings have
important implications for the understanding of the migratory phenomenon and will help
predict the responses of bird and mammal species to environmental changeinfo:eu-repo/semantics/publishedVersio
DNA Nanotechnology
Cite this entry as: Yaradoddi J.S. et al. (2019) DNA Nanotechnology. In: MartĂnez L., Kharissova O., Kharisov B. (eds) Handbook of Ecomaterials. Springer, Cham DOI: https://doi.org/10.1007/978-3-319-68255-6_191 First Online: 14 February 2019 Online ISBN: 978-3-319-68255-6 Print ISBN: 978-3-319-68254-9Since from the past few decades DNA appeared as an excellent molecular building block for the synthesis of nanostructures because of its probable encoded and confirmation intra- and intermolecular base pairing, various case strategies and consistent assembly techniques have been established to manipulate DNA nanostructures to at higher complexity. The capability to develop DNA construction with precise special control has permitted scientists to discover novel applications in many ways, such as scaffold development, sensing applications, nanodevices, computational applications, nanorobotics, nanoelectronics, biomolecular catalysis, disease diagnosis, and drug delivery. The present chapter emphasizes to brief the opportunities, challenges, and future prospective on DNA nanotechnology and its advancements.Peer reviewe