102 research outputs found
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Measuring motion with kinematically redundant accelerometer arrays: theory, simulation and implementation
This work presents two schemes of measuring the linear and angular kinematics of a rigid body using a kinematically redundant array of triple-axis accelerometers with potential applications in biomechanics. A novel angular velocity estimation algorithm is proposed and evaluated that can compensate for angular velocity errors using measurements of the direction of gravity. Analysis and discussion of optimal sensor array characteristics are provided. A damped 2 axis pendulum was used to excite all 6 DoF of the a suspended accelerometer array through determined complex motion and is the basis of both simulation and experimental studies. The relationship between accuracy and sensor redundancy is investigated for arrays of up to 100 triple axis (300 accelerometer axes) accelerometers in simulation and 10 equivalent sensors (30 accelerometer axes) in the laboratory test rig. The paper also reports on the sensor calibration techniques and hardware implementation
Adaptation of an Commercially Available Stabilised R/C Helicopter to a Fully Autonomous Surveillance UAV
ABSTRACT This paper presents the development of an autonomous surveillance UAV that competed in the Ministry of Defence Grand Challenge 2008. In order to focus on higher-level mission control, the UAV is built upon an existing commercially available stabilised R/C helicopter platform. The hardware architecture is developed to allow for non-invasion integration with the existing stabilised platform, and to enable to the distributed processing of closed loop control and mission goals. The resulting control system proved highly successful and was capable of flying within 40knott gusts. The software and safety architectures were key to the success of the research and also hold the potential for use in the development of more complex system comprising of multiple UAVs. BIOGRAPHY Sebastian Madgwick is an MEng Cybernetics undergraduate student currently in his final year. His research interests include: robotics, embedded systems, control systems, and Human Machine Interfaces. For his third year project he developed an autonomous UAV. For his final year research project he is developing accelerometer sensory systems; for human motion capture. After graduating he plans to stay in research, possibly by doing a PhD. Chris Turner is an MEng Cybernetics undergraduate student currently in his final year. For his third year project he researched Autonomous UAV control, and for his final year project he is developing hands-free UAV control techniques using head and eye tracking technologies. Post graduation he intends to go into the control engineering industry. Professor William Harwin is head of the interactive systems research group at the University of Reading with a keen interest in novel human-system information exchanges. He is a leading researcher in the field of robotic mediated neuro-rehabilitation having previously lead research in rehabilitation and assistive robotics. He also maintains a strong research interest in haptic interfaces as these form the basis for much of his research and provide interesting opportunities for innovative solutions to difficult problems in human-machine interaction
Clustering properties of a type-selected volume-limited sample of galaxies in the CFHTLS
(abridged) We present an investigation of the clustering of i'AB<24.5
galaxies in the redshift interval 0.2<z<1.2. Using 100,000 precise photometric
redshifts in the four ultra-deep fields of the Canada-France Legacy Survey, we
construct a set of volume-limited galaxy catalogues. We study the dependence of
the amplitude and slope of the galaxy correlation function on absolute B-band
rest-frame luminosity, redshift and best-fitting spectral type. We find: 1. The
comoving correlation length for all galaxies decreases steadily from z~0.3 to
z~1. 2. At all redshifts and luminosities, galaxies with redder rest-frame
colours have clustering amplitudes between two and three times higher than
bluer ones. 3. For bright red and blue galaxies, the clustering amplitude is
invariant with redshift. 4. At z~0.5, less luminous galaxies have higher
clustering amplitudes of around 6 h-1 Mpc. 5. The relative bias between
galaxies with red and blue rest-frame colours increases gradually towards
fainter absolute magnitudes. One of the principal implications of these results
is that although the full galaxy population traces the underlying dark matter
distribution quite well (and is therefore quite weakly biased), redder, older
galaxies have clustering lengths which are almost invariant with redshift, and
by z~1 are quite strongly biased.Comment: 16 pages, 18 figures, accepted for publication in Astronomy and
Astrophysic
The SWIRE-VVDS-CFHTLS surveys: stellar mass assembly over the last 10 Gyears. Evidence for a major build up of the red sequence between z=2 and z=1
(abridged abstract) We present an analysis of the stellar mass growth over
the last 10 Gyrs using a large 3.6 selected sample. We split our sample
into active (blue) and quiescent (red) galaxies. Our measurements of the K-LFs
and LD evolution support the idea that a large fraction of galaxies is already
assembled at . Based on the analysis of the evolution of the stellar
mass-to-light ratio (in K-band) for the spectroscopic sub-sample, we derive the
stellar mass density for the entire sample. We find that the global evolution
of the stellar mass density is well reproduced by the star formation rate
derived from UV dust corrected measurements. Over the last 8Gyrs, we observe
that the stellar mass density of the active population remains approximately
constant while it gradually increases for the quiescent population over the
same timescale. As a consequence, the growth of the stellar mass in the
quiescent population must be due to the shutoff of star formation in active
galaxies that migrate into the quiescent population. From to , we
observe a major build-up of the quiescent population with an increase by a
factor of 10 in stellar mass, suggesting that we are observing the epoch when
an increasing fraction of galaxies are ending their star formation activity and
start to build up the red sequence.Comment: Accepted to A&A with major changes. 1 table and 13 figure
The Vimos VLT Deep Survey: Global properties of 20000 galaxies in the I_AB<=22.5 WIDE survey
The VVDS-Wide survey has been designed with the general aim of tracing the
large-scale distribution of galaxies at z~1 on comoving scales reaching
~100Mpc/h, while providing a good control of cosmic variance over areas as
large as a few square degrees. This is achieved by measuring redshifts with
VIMOS at the ESO VLT to a limiting magnitude I_AB=22.5, targeting four
independent fields with size up to 4 sq.deg. each. The whole survey covers 8.6
sq.deg., here we present the general properties of the current redshift sample.
This includes 32734 spectra in the four regions (19977 galaxies, 304 type I
AGNs, and 9913 stars), covering a total area of 6.1 sq.deg, with a sampling
rate of 22 to 24%. The redshift success rate is above 90% independently of
magnitude. It is the currently largest area coverage among redshift surveys
reaching z~1. We give the mean N(z) distribution averaged over 6.1 sq.deg.
Comparing galaxy densities from the four fields shows that in a redshift bin
Deltaz=0.1 at z~1 one still has factor-of-two variations over areas as large as
~0.25 sq.deg. This level of cosmic variance agrees with that obtained by
integrating the galaxy two-point correlation function estimated from the F22
field alone, and is also in fairly good statistical agreement with that
predicted by the Millennium mocks. The variance estimated over the survey
fields shows explicitly how clustering results from deep surveys of even ~1
sq.deg. size should be interpreted with caution. This paper accompanies the
public release of the first 18143 redshifts of the VVDS-Wide survey from the 4
sq.deg. contiguous area of the F22 field at RA=22h, publicly available at
http://cencosw.oamp.frComment: Accepted for publication on Astronomy & Astrophysic
The VIMOS VLT Deep Survey - Evolution of the luminosity functions by galaxy type up to z=1.5 from first epoch data
From the first epoch observations of the VVDS up to z=1.5 we have derived
luminosity functions (LF) of different spectral type galaxies. The VVDS data,
covering ~70% of the life of the Universe, allow for the first time to study
from the same sample and with good statistical accuracy the evolution of the
LFs by galaxy type in several rest frame bands from a purely magnitude selected
sample. The magnitude limit of the VVDS allows the determination of the faint
end slope of the LF with unprecedented accuracy. Galaxies have been classified
in four spectral classes, using their colours and redshift, and LFs have been
derived in the U, B, V, R and I rest frame bands from z=0.05 to z=1.5. We find
a significant steepening of the LF going from early to late types. The M*
parameter is significantly fainter for late type galaxies and this difference
increases in the redder bands. Within each of the galaxy spectral types we find
a brightening of M* with increasing redshift, ranging from =< 0.5 mag for early
type galaxies to ~1 mag for the latest type galaxies, while the slope of the LF
of each spectral type is consistent with being constant with redshift. The LF
of early type galaxies is consistent with passive evolution up to z~1.1, while
the number of bright early type galaxies has decreased by ~40% from z~0.3 to
z~1.1. We also find a strong evolution in the normalization of the LF of latest
type galaxies, with an increase of more than a factor 2 from z~0.3 to z~1.3:
the density of bright late type galaxies in the same redshift range increases
of a factor ~6.6. These results indicate a strong type-dependent evolution and
identifies the latest spectral types as responsible for most of the evolution
of the UV-optical luminosity function out to z=1.5.Comment: 18 pages with encapsulated figures, revised version after referee's
comments, accepted for publication in A&
The VIMOS VLT Deep Survey: Evolution of the non-linear galaxy bias up to z=1.5
We present the first measurements of the Probability Distribution Function
(PDF) of galaxy fluctuations in the VIMOS-VLT Deep Survey (VVDS) cone, covering
0.4x0.4 deg between 0.4<z<1.5. The second moment of the PDF, i.e. the rms
fluctuations of the galaxy density field, is with good approximation constant
over the full redshift baseline investigated: we find that, in redshift space,
sigma_8 for galaxies brighter than M=-20+5log h has a mean value of 0.94\pm0.07
in the redshift interval 0.7<z<1.5. The third moment, i.e. the skewness,
increases with cosmic time: we find that the probability of having underdense
regions is greater at z~0.7 than it was at z~1.5. By comparing the PDF of
galaxy density contrasts with the theoretically predicted PDF of mass
fluctuations we infer the redshift-, density-, and scale-dependence of the
biasing function b(z, \delta, R) between galaxy and matter overdensities up to
redshift z=1.5. Our results can be summarized as follows: i) the galaxy bias is
an increasing function of redshift: evolution is marginal up to z~0.8 and more
pronounced for z>0.8; ii) the formation of bright galaxies is inhibited below a
characteristic mass-overdensity threshold whose amplitude increases with
redshift and luminosity; iii) the biasing function is non linear in all the
redshift bins investigated with non-linear effects of the order of a few to 10%
on scales >5Mpc.Comment: 30 pages, 17 figs, Accepted by A&
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
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