2,046 research outputs found
An exact solution for the Hawking effect in a dispersive fluid
We consider the wave equation for sound in a moving fluid with a fourth-order
anomalous dispersion relation. The velocity of the fluid is a linear function
of position, giving two points in the flow where the fluid velocity matches the
group velocity of low-frequency waves. We find the exact solution for wave
propagation in the flow. The scattering shows amplification of classical waves,
leading to spontaneous emission when the waves are quantized. In the
dispersionless limit the system corresponds to a 1+1-dimensional black-hole or
white-hole binary and there is a thermal spectrum of Hawking radiation from
each horizon. Dispersion changes the scattering coefficients so that the
quantum emission is no longer thermal. The scattering coefficients were
previously obtained by Busch and Parentani in a study of dispersive fields in
de Sitter space [Phys. Rev. D 86, 104033 (2012)]. Our results give further
details of the wave propagation in this exactly solvable case, where our focus
is on laboratory systems.Comment: 18 pages, minor change
Electromagnetic energy-momentum in dispersive media
The standard derivations of electromagnetic energy and momentum in media take
Maxwell's equations as the starting point. It is well known that for dispersive
media this approach does not directly yield exact expressions for the energy
and momentum densities. Although Maxwell's equations fully describe
electromagnetic fields, the general approach to conserved quantities in field
theory is not based on the field equations, but rather on the action. Here an
action principle for macroscopic electromagnetism in dispersive, lossless media
is used to derive the exact conserved energy-momentum tensor. The time-averaged
energy density reduces to Brillouin's simple formula when the fields are
monochromatic. The momentum density is not given by the familiar Minkowski
expression , even for time-averaged monochromatic
fields. The results are unaffected by the debate over momentum balance in
light-matter interactions.Comment: 7 pages. Incorporates the Erratum to the published versio
All-frequency reflectionlessness
We derive planar permittivity profiles that do not reflect perpendicularly
exiting radiation of any frequency. The materials obey the Kramers-Kronig
relations and have no regions of gain. Reduction of the Casimir force by means
of such materials is also discussed.Comment: 7 page
No quantum friction between uniformly moving plates
The Casimir forces between two plates moving parallel to each other are found
by calculating the vacuum electromagnetic stress tensor. The perpendicular
force between the plates is modified by the motion but there is no lateral
force on the plates. Electromagnetic vacuum fluctuations do not therefore give
rise to "quantum friction" in this case, contrary to previous assertions. The
result shows that the Casimir-Polder force on a particle moving at constant
speed parallel to a plate also has no lateral component.Comment: 17 pages. Final, published versio
Critical Analysis and Evaluation of the Technology Pathways for Carbon Capture and Utilization
Carbon capture and utilization (CCU) is the process of capturing unwanted carbon dioxide (CO2) and utilizing for further use. CCU offers significant potential as part of a sustainable circular economy solution to help mitigate the impact of climate change resulting from the burning of hydrocarbons and alongside adoption of other renewable energy technologies. However, implementation of CCU technologies faces a number of challenges, including identifying optimal pathways, technology maturity, economic viability, environmental considerations as well as regulatory and public perception issues. Consequently, this research study provides a critical analysis and evaluation of the technology pathways for CCU in order to explore the potential from a circular economy perspective of this emerging area of clean technology. This includes a bibliographic study on CCU, evaluation of carbon utilization processes, trend estimation of CO2 usage as well as evaluation of methane and methanol production. A value chain analysis is provided to support the development of CCU technologies. The research study aims to inform policy-makers engaged in developing strategies to mitigate climate change through reduced carbon dioxide emission levels and improve our understanding of the circular economy considerations of CCU in regard to production of alternative products. The study will also be of use to researchers concerned with pursuing empirical investigations of this important area of sustainability
Thermal energies of classical and quantum damped oscillators coupled to reservoirs
We consider the global thermal state of classical and quantum harmonic
oscillators that interact with a reservoir. Ohmic damping of the oscillator can
be exactly treated with a 1D scalar field reservoir, whereas general non-Ohmic
damping is conveniently treated with a continuum reservoir of harmonic
oscillators. Using the diagonalized Hamiltonian of the total system, we
calculate a number of thermodynamic quantities for the damped oscillator: the
mean force internal energy, mean force free energy, and another internal energy
based on the free-oscillator Hamiltonian. The classical mean force energy is
equal to that of a free oscillator, for both Ohmic and non-Ohmic damping and no
matter how strong the coupling to the reservoir. In contrast, the quantum mean
force energy depends on the details of the damping and diverges for strictly
Ohmic damping. These results give additional insight into the steady-state
thermodynamics of open systems with arbitrarily strong coupling to a reservoir,
complementing results for energies derived within dynamical approaches (e.g.
master equations) in the weak-coupling regime.Comment: 13 page
Managing complex technology projects
This article explores some of the issues associated with the management of complex technology projects, specifically through the use of systems methodologies. As part of this assessment, the results from an industry survey are reported, which was designed to identify the key features in the use of systems approaches in technology and engineering management. The paper also describes a new conceptual framework, called the four-frames systems view, which has been developed as a tool for the management of complex projects. This innovative framework brings together different systems-related methodologies and tools, in order to reduce risk in the design, implementation and management of complex technology projects. The framework is based on a view that different systems methodologies are needed in order to accommodate different levels of complexity. The paper provides an initial application of the framework to the development of a UAV (unmanned aerial vehicle) system for the civil sector
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