186 research outputs found
Numerical approach to the dynamical Casimir effect
The dynamical Casimir effect for a massless scalar field in 1+1-dimensions is
studied numerically by solving a system of coupled first-order differential
equations. The number of scalar particles created from vacuum is given by the
solutions to this system which can be found by means of standard numerics. The
formalism already used in a former work is derived in detail and is applied to
resonant as well as off-resonant cavity oscillations.Comment: 15 pages, 4 figures, accepted for publication in J. Phys. A (special
issue: Proceedings of QFEXT05, Barcelona, Sept. 5-9, 2005
Dynamical Casimir effect for gravitons in bouncing braneworlds
We consider a two-brane system in a five-dimensional anti-de Sitter
spacetime. We study particle creation due to the motion of the physical brane
which first approaches the second static brane (contraction) and then recedes
from it(expansion). The spectrum and the energy density of the generated
gravitons are calculated. We show that the massless gravitons have a blue
spectrum and that their energy density satisfies the nucleosynthesis bound with
very mild constraints on the parameters. We also show that the Kaluza-Klein
modes cannot provide the dark matter in an anti-de-Sitter braneworld. However,
for natural choices of parameters, backreaction from the Kaluza-Klein gravitons
may well become important. The main findings of this work have been published
in the form of a Letter [R. Durrer and M. Ruser, Phys. Rev. Lett. 99, 071601
(2007), arXiv:0704.0756].Comment: 40 pages, 34 figures, improved and extended version, matches
published versio
Development of a Method for the Fast and Complete Assessment of Quality Characteristics in Undried Grass Silages by Means of an NIR-Diode Array Spectrometer
Traditionally, the determination of grass silage is very time consuming and needs a lot of manpower and chemicals. The advantages of conventional laboratory NIRS instruments are well known but their disadvantage lies in their lacking suitability for on-farm use. A new type of spectrometer based on diode arrays may be used for this purpose. However, these new instruments still need to be calibrated for an accurate estimate of the fermentative and nutritive value of wet and unchopped grass silage
Dynamical Casimir Effect for a Swinging Cavity
The resonant scalar particle generation for a swinging cavity resonator in
the Casimir vacuum is examined. It is shown that the number of particles grows
exponentially when the cavity rotates at some specific external frequency.Comment: to appear in J. Phys. A: Math. Theo
Exact closed form analytical solutions for vibrating cavities
For one-dimensional vibrating cavity systems appearing in the standard
illustration of the dynamical Casimir effect, we propose an approach to the
construction of exact closed-form solutions. As new results, we obtain
solutions that are given for arbitrary frequencies, amplitudes and time
regions. In a broad range of parameters, a vibrating cavity model exhibits the
general property of exponential instability. Marginal behavior of the system
manifests in a power-like growth of radiated energy.Comment: 17 pages, 7 figure
Graviton production in anti-de Sitter braneworld cosmology: A fully consistent treatment of the boundary condition
In recent work by two of us, [Durrer & Ruser, PRL 99, 071601 (2007); Ruser &
Durrer PRD 76, 104014 (2007)], graviton production due to a moving spacetime
boundary (braneworld) in a five dimensional bulk has been considered. In the
same way as the presence of a conducting plate modifies the electromagnetic
vacuum, the presence of a brane modifies the graviton vacuum. As the brane
moves, the time dependence of the vacuum leads to particle creation via the so
called 'dynamical Casimir effect'. In our previous work a term in the boundary
condition which is linear in the brane velocity has been neglected. In this
work we develop a new approach which overcomes this approximation. We show that
the previous results are not modified if the brane velocity is low.Comment: 13 pages, 6 figures, added a clarifying paragraph about the setup,
the brane motion adapted w.r.t the version published in PR
Vibrating Cavities - A numerical approach
We present a general formalism allowing for efficient numerical calculation
of the production of massless scalar particles from vacuum in a one-dimensional
dynamical cavity, i.e. the dynamical Casimir effect. By introducing a
particular parametrization for the time evolution of the field modes inside the
cavity we derive a coupled system of first-order linear differential equations.
The solutions to this system determine the number of created particles and can
be found by means of numerical methods for arbitrary motions of the walls of
the cavity. To demonstrate the method which accounts for the intermode coupling
we investigate the creation of massless scalar particles in a one-dimensional
vibrating cavity by means of three particular cavity motions. We compare the
numerical results with analytical predictions as well as a different numerical
approach.Comment: 28 pages, 19 figures, accepted for publication in J. Opt. B: Quantum
Semiclass. Op
In-Air Evoked Potential Audiometry of Grey Seals (Halichoerus grypus) from the North and Baltic Seas
In-air anthropogenic sound has the potential to affect grey seal (Halichoerus grypus) behaviour and interfere with acoustic communication. In this study, a new method was used to deliver acoustic signals to grey seals as part of an in-air hearing assessment. Using in-ear headphones with adapted ear inserts allowed for the measurement of auditory brainstem responses (ABR) on sedated grey seals exposed to 5-cycle (2-1-2) tone pips. Thresholds were measured at 10 frequencies between 1–20 kHz. Measurements were made using subcutaneous electrodes on wild seals from the Baltic and North Seas. Thresholds were determined by both visual and statistical approaches (single point F-test) and good agreement was obtained between the results using both methods. The mean auditory thresholds were ≤40 dB re 20 µPa peak equivalent sound pressure level (peSPL) between 4–20 kHz and showed similar patterns to in-air behavioural hearing tests of other phocid seals between 3 and 20 kHz. Below 3 kHz, a steep reduction in hearing sensitivity was observed, which differed from the rate of decline in sensitivity obtained in behavioural studies on other phocids. Differences in the rate of decline may reflect influence of the ear inserts on the ability to reliably transmit lower frequencies or interference from the structure of the distal end of the ear canal
Dynamical Casimir Effect for Two Oscillating Mirrors in 3-D
The generation of photons in a three dimensional rectangular cavity with two
moving boundaries is studied by using the Multiple Scale Analysis (MSA). It is
shown that number of photons are enhanced for the cavity whose walls oscillate
symmetrically with respect to the center of the cavity. The non-stationary
Casimir effect is also discussed for the cavity which oscillates as a whole.Comment: 11 pqge
Assessing auditory evoked potentials of wild harbor porpoises (Phocoena phocoena)
© 2016 Acoustical Society of America. Testing the hearing abilities of marine mammals under water is a challenging task. Sample sizes are usually low, thus limiting the ability to generalize findings of susceptibility towards noise influences. A method to measure harbor porpoise hearing thresholds in situ in outdoor conditions using auditory steady state responses of the brainstem was developed and tested. The method was used on 15 live-stranded animals from the North Sea during rehabilitation, shortly before release into the wild, and on 12 wild animals incidentally caught in pound nets in Denmark (inner Danish waters). Results indicated that although the variability between individuals is wide, the shape of the hearing curve is generally similar to previously published results from behavioral trials. Using 10-kHz frequency intervals between 10 and 160 kHz, best hearing was found between 120 and 130 kHz. Additional testing using one-third octave frequency intervals (from 16 to 160 kHz) allowed for a much faster hearing assessment, but eliminated the fine scale threshold characteristics. For further investigations, the method will be used to better understand the factors influencing sensitivity differences across individuals and to establish population-level parameters describing hearing abilities of harbor porpoises
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