274 research outputs found
An investigation of aerodynamic effects of body morphing for passenger cars in close-proximity
The potential energy-saving benefit for vehicles when travelling in a ‘platoon’ formation results from the reduction in total aerodynamic drag which may result from the interaction of bluff bodies in close-proximity. Early investigations of platooning, prompted by problems of congestion, had shown the potential for drag reduction but was not pursued. More recently, technologies developed for connected-autonomous vehicle control have provided a renewed interest in platooning particularly within the commercial vehicle industry. To date, most aerodynamics-based considerations of platooning have been conducted to assess the sensitivity of drag-saving to vehicle spacing and were based on formations of identically shaped constituents. In this study, the interest was the sensitivity of drag-saving to the shape of the individual platoon constituents. A new reference car, the Resnick model, was specially designed to include front and rear-end add-on sections to make distinct changes in profile form and simulate large-scale body morphing. The results of wind tunnel tests on small-scale models suggested that current trends in low-drag styling may not provide the ideal shape for platoon constituent members and that optimised forms are likely to be dependent upon position in the platoon
Nonlinear surface waves in left-handed materials
We study both linear and nonlinear surface waves localized at the interface
separating a left-handed medium (i.e. the medium with both negative dielectric
permittivity and negative magnetic permeability) and a conventional (or
right-handed) dielectric medium. We demonstrate that the interface can support
both TE- and TM-polarized surface waves - surface polaritons, and we study
their properties. We describe the intensity-dependent properties of nonlinear
surface waves in three different cases, i.e. when both the LH and RH media are
nonlinear and when either of the media is nonlinear. In the case when both
media are nonlinear, we find two types of nonlinear surface waves, one with the
maximum amplitude at the interface, and the other one with two humps. In the
case when one medium is nonlinear, only one type of surface wave exists, which
has the maximum electric field at the interface, unlike waves in right-handed
materials where the surface-wave maximum is usually shifted into a
self-focussing nonlinear medium. We discus the possibility of tuning the wave
group velocity in both the linear and nonlinear cases, and show that
group-velocity dispersion, which leads to pulse broadening, can be balanced by
the nonlinearity of the media, so resulting in soliton propagation.Comment: 9 pages, 10 figure
Spectral sequence operations converge to Araki-Kudo operations
Previously we constructed operations in the mod 2 homology spectral sequence
associated to a cosimplicial E-infinity space X. The correct target for this
spectral sequence is the homology of Tot X. Noting that in this setting Tot X
is an E-infinity space, we show that our operations agree with the usual
Araki-Kudo operations in the target. We also prove that the multiplication in
the spectral sequence agrees with the multiplication in H_*(Tot X).Comment: Final versio
Non-resonant terahertz field enhancement in periodically arranged nanoslits
We analyze ultra strong non-resonant field enhancement of THz field in periodic arrays of nanoslits cut in ultrathin metal films. The main feature of our approach is that the slit size and metal film thickness are several orders of magnitude smaller than the wavelength k of the impinging radiation.
Two regimes of operation are found. First, when the grating period, frequency-independent enhancement is observed, accompanied by a very high transmission approaching unity. With high accuracy, this enhancement equals the ratio of P to the slit width w. Second, when the grating
period approaches the THz wavelength but before entering the Raleigh-Wood anomaly, the field enhancement in nanoslit stays close to that in a single isolated slit, i.e., the well-known inversefrequency
dependence. Both regimes are non-resonant and thus extremely broadband. The results are obtained by the microscopic Drude-Lorentz model taking into account retardation processes in the metal film and validated by the finite difference frequency domain method. We expect sensor and modulation applications of the predicted giant broadband field enhancement
Multi-component optical solitary waves
We discuss several novel types of multi-component (temporal and spatial)
envelope solitary waves that appear in fiber and waveguide nonlinear optics. In
particular, we describe multi-channel solitary waves in bit-parallel-wavelength
fiber transmission systems for high performance computer networks, multi-colour
parametric spatial solitary waves due to cascaded nonlinearities of quadratic
materials, and quasiperiodic envelope solitons due to quasi-phase-matching in
Fibonacci optical superlattices.Comment: 12 pages, 11 figures; To be published in: Proceedings of the Dynamics
Days Asia-Pacific: First International Conference on Nonlinear Science
(Hong-Kong, 13-16 July, 1999), Editor: Bambi Hu (Elsevier Publishers, 2000
Mobile crowdsensing for road sustainability: exploitability of publicly-sourced data
ABSTRACTThis paper examines the opportunities and the economic benefits of exploiting publicly-sourced datasets of road surface quality. Crowdsourcing and crowdsensing initiatives channel the parti..
Chemical evolution of local post-starburst galaxies: Implications for the mass-metallicity relation
We use the stellar fossil record to constrain the stellar metallicity
evolution and star-formation histories of the post-starburst regions within 45
local post-starburst galaxies from the MaNGA survey. The direct measurement of
the regions' stellar metallicity evolution is achieved by a new two-step
metallicity model that allows for stellar metallicity to change at the peak of
the starburst. We also employ a Gaussian process noise model that accounts for
correlated errors introduced by the observational data reduction or
inaccuracies in the models. We find that a majority of post-starburst regions
(69% at significance) increased in stellar metallicity during the
recent starburst, with an average increase of 0.8 dex and a standard deviation
of 0.4 dex. A much smaller fraction of PSBs are found to have remained constant
(22%) or declined in metallicity (9%, average decrease 0.4 dex, standard
deviation 0.3 dex). The pre-burst metallicities of the post-starburst galaxies
are in good agreement with the mass-metallicity relation of local star-forming
galaxies. These results are consistent with hydrodynamic simulations, which
suggest that mergers between gas-rich galaxies are the primary formation
mechanism of local PSBs, and rapid metal recycling during the starburst
outweighs the impact of dilution by any gas inflows. The final mass-weighted
metallicities of the post-starburst galaxies are consistent with the
mass-metallicity relation of local passive galaxies. Our results suggest that
rapid quenching following a merger-driven starburst is entirely consistent with
the observed gap between the stellar mass-metallicity relations of local
star-forming and passive galaxies.Comment: 18+4 pages, 8+2 figures, submitted to MNRA
Chemical evolution of local post-starburst galaxies : implications for the mass-metallicity relation
We use the stellar fossil record to constrain the stellar metallicity evolution and star-formation histories of the post-starburst (PSB) regions within 45 local PSB galaxies from the MaNGA survey. The direct measurement of the regions’ stellar metallicity evolution is achieved by a new two-step metallicity model that allows for stellar metallicity to change at the peak of the starburst. We also employ a Gaussian process noise model that accounts for correlated errors introduced by the observational data reduction or inaccuracies in the models. We find that a majority of PSB regions (69 per cent at >1σ significance) increased in stellar metallicity during the recent starburst, with an average increase of 0.8 dex and a standard deviation of 0.4 dex. A much smaller fraction of PSBs are found to have remained constant (22 per cent) or declined in metallicity (9 per cent, average decrease 0.4 dex, standard deviation 0.3 dex). The pre-burst metallicities of the PSB galaxies are in good agreement with the mass–metallicity (MZ) relation of local star-forming galaxies. These results are consistent with hydrodynamic simulations, which suggest that mergers between gas-rich galaxies are the primary formation mechanism of local PSBs, and rapid metal recycling during the starburst outweighs the impact of dilution by any gas inflows. The final mass-weighted metallicities of the PSB galaxies are consistent with the MZ relation of local passive galaxies. Our results suggest that rapid quenching following a merger-driven starburst is entirely consistent with the observed gap between the stellar mass–metallicity relations of local star-forming and passive galaxies.Peer reviewe
Operations in the homology spectral sequence of a cosimplicial infinite loop space
Consider the mod 2 homology spectral sequence associated to a cosimplicial
space X. We construct external operations whose target is the spectral sequence
associated to E\Sigma_2 \times_{\Sigma_2} (X\times X). If X is a cosimplicial
E_\infty-space, we couple these external operations with the structure map
E\Sigma_2 \times_{\Sigma_2} (X\times X) \to X to produce internal operations in
the spectral sequence. In the sequel we show that they agree with the usual
Araki-Kudo operations on the abutment H_*(Tot X).Comment: final versio
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