1,210 research outputs found
Internal Kinematics of Distant Field Galaxies: I. Emission Line Widths for a Complete Sample of Faint Blue Galaxies at <z>=0.25
We present measurements of the OII(3727) emission line width for a complete
sample of 24 blue field galaxies (21.25=0.25, obtained
with the AUTOFIB fibre spectrograph on the Anglo-Australian Telescope. Most
emission lines are spectrally resolved, yet all have dispersions sigma<100km/s.
Five of the 24 sample members have OII doublet line flux ratios which imply gas
densities in excess of 100 cm^-3. The line emission in these galaxies may be
dominated by an active nucleus and the galaxies have been eliminated from the
subsequent analysis. The remaining 19 linewidths are too large by a factor of
two (7sigma significance) to be attributed to turbulent motions within an
individual star forming region, and therefore most likely reflect the orbital
motion of ionized gas in the galaxy. We use Fabry--Perot observations of nearby
galaxies to construct simulated datasets that mimic our observational setup at
z=0.25; these allow us to compute the expected distribution of (observable)
linewidths sigma_v for a galaxy of a given ``true'' (optical) rotation speed
v_c. These simulations include the effects of random viewing angles, clumpy
line emission, finite fibre aperture, and internal dust extinction on the
emission line profile. We assume a linewidth--luminosity--colour relation: ln[
v_c(M_B,B-R) ] = ln[v_c(-19,1)] - eta*(M_B+10) + zeta*[(B-R)-1] and determine
the range of parameters consistent with our data. We find a mean rotation speed
of v_c(-19,1)=66+-8km/s (68% confidence limits) for the distant galaxies with
M_B=-19 and B-R=1, with a magnitude dependence for v_c of eta=0.07+-0.08, and a
colour dependence of zeta =0.28+-0.25. Through comparison with several local
samples we show that this value of v_c(-19,1) is significantly lower than the
optical rotation speed of present-day galaxies with the same absolute magnitudeComment: TeX Text and Tables, no Figures. Compressed and uuencoded PS file of
the complete paper (43 pages including 9 figures) available at
http://zwicky.as.arizona.edu/~rix/; submitted to MNRA
Self-consistent triaxial de Zeeuw-Carollo Models
We use the usual method of Schwarzschild to construct self-consistent
solutions for the triaxial de Zeeuw & Carollo (1996) models with central
density cusps. ZC96 models are triaxial generalisations of spherical
-models of Dehnen whose densities vary as near the center
and at large radii and hence, possess a central density core for
and cusps for . We consider four triaxial models from
ZC96, two prolate triaxials: with and
1.5, and two oblate triaxials: with and
1.5. We compute 4500 orbits in each model for time periods of .
We find that a large fraction of the orbits in each model are stochastic by
means of their nonzero Liapunov exponents. The stochastic orbits in each model
can sustain regular shapes for or longer, which suggests
that they diffuse slowly through their allowed phase-space. Except for the
oblate triaxial models with , our attempts to construct
self-consistent solutions employing only the regular orbits fail for the
remaining three models. However, the self-consistent solutions are found to
exist for all models when the stochastic and regular orbits are treated in the
same way because the mixing-time, , is shorter than the
integration time, . Moreover, the ``fully-mixed'' solutions can
also be constructed for all models when the stochastic orbits are fully mixed
at 15 lowest energy shells. Thus, we conclude that the self-consistent
solutions exist for our selected prolate and oblate triaxial models with
and 1.5.Comment: 6 Pages, 3 Figures, 2 Tables. Accepted for Publication in A&
Automated topology optimisation of hybrid electric vehicle powertrains
Ing, A. H., & McPhee, J. (2015). Automated topology optimisation of hybrid electric vehicle powertrains. International Journal of Electric and Hybrid Vehicles, 7(4), 342. Final version published by Inderscience Publishers, and available at: https://doi.org/10.1504/IJEHV.2015.074671Gasoline and electric powertrain components can be connected in numerous configurations to create hybrid powertrains. Owing to the exponential increase of permutations as the number of components increases, a framework to determine the best possible powertrain configuration that minimises fuel consumption was developed. This framework uses enumeration to discover all powertrains, the Graph-Theoretic Method to generate system equations, dynamic programming to evaluate fuel consumption and generate an objective score, and Pattern Search to optimise the sizing of each component. A multi-stage screening process was used to reduce computation time. Parallel and powersplit-like topologies with additional discrete gearboxes were found to be the most efficient. The best performing topology is a powersplit hybrid type: a discrete gearbox connected to the final drive, with the output gear of the planetary carrier and electric motor in parallel.The project is funded by Toyota, Maplesoft, and NSERC
Bloch-Redfield equations for modeling light-harvesting complexes
We challenge the misconception that Bloch-Redfield equations are a less
powerful tool than phenomenological Lindblad equations for modeling exciton
transport in photosynthetic complexes. This view predominantly originates from
an indiscriminate use of the secular approximation. We provide a detailed
description of how to model both coherent oscillations and several types of
noise, giving explicit examples. All issues with non-positivity are overcome by
a consistent straightforward physical noise model. Herein also lies the
strength of the Bloch-Redfield approach because it facilitates the analysis of
noise-effects by linking them back to physical parameters of the noise
environment. This includes temporal and spatial correlations and the strength
and type of interaction between the noise and the system of interest. Finally
we analyze a prototypical dimer system as well as a 7-site Fenna-Matthews-Olson
(FMO) complex in regards to spatial correlation length of the noise, noise
strength, temperature and their connection to the transfer time and transfer
Dynamical Effects from Asteroid Belts for Planetary Systems
The orbital evolution and stability of planetary systems with interaction
from the belts is studied using the standard phase-plane analysis. In addition
to the fixed point which corresponds to the Keplerian orbit, there are other
fixed points around the inner and outer edges of the belt. Our results show
that for the planets, the probability to move stably around the inner edge is
larger than the one to move around the outer edge. It is also interesting that
there is a limit cycle of semi-attractor for a particular case. Applying our
results to the Solar System, we find that our results could provide a natural
mechanism to do the orbit rearrangement for the larger Kuiper Belt Objects and
thus successfully explain the absence of these objects beyond 50 AU.Comment: accepted by International Journal of Bifurcation and Chaos in Aug.
2003, AAS Latex, 27 pages with 6 color figure
Automated Topology Synthesis and Optimization of Hybrid Electric Vehicle Powertrains
This thesis presents a framework to automate the process of designing Hybrid Electric Vehicle (HEV) powertrain architectures. An algorithm was developed to assemble and compare all possible configurations of powertrain components. Combinatorics was used to discover all possible combinations of: an internal combustion engine, high-torque low-speed electric motor, low-torque high-speed electric motor, planetary gearset, and five-speed discrete gearbox. The Graph Theoretic Method was used to generate the powertrain models.
The powertrain models were comprised of steady-state equations in symbolic form. An optimal control strategy is required to fairly compare the different topologies because a powertrain control strategy is dependant on the configuration. Dynamic Programming was used to determine the control law that minimizes the energy consumption for a given drivecycle. Evaluating every possible topology would take an extremely long time, so topologies were evaluated using a multi-stage screening process.
The first stage examined the structure of the powertrain and used heuristics to eliminate infeasible topologies; 512 topologies were feasible.
The second stage eliminated topologies that could not meet basic driving performance; 193 topologies were feasible. Basic driving performance was tested using a section of the US06 drivecycle. The sizes of three components were optimized to ensure the topology is feasible independent of the size of the components.
The third stage eliminated topologies which could not achieve driving performance design goals; 159 could achieve the performance requirements, but only 119 were reasonably fuel efficient. The driving performance goals were implemented with a drivecycle based on the Partnership for a New Generation of Vehicles (PNGV) goals. The sizes for five components were optimized at this stage.
The 20 most fuel efficient powertrains were selected for further evaluation. Additionally, 4 common powertrains were evaluated for reference. The size of the components were optimized for a combination of the PNGV drivecycle and the HWFET drivecycle.
The most fuel efficient topology was found to be a Powersplit hybrid which has a discrete gearbox between the final drive and the powersplit device. The electric motor, planetary carrier gear, and gearbox were connected in parallel. It was found that Parallel-like, Powersplit-like, and Complex-like topologies were were the most efficient powertrain configurations. Powertrains containing two gearboxes were more efficient because the geartrain models ignored mechanical inefficiencies
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