567 research outputs found
Learning by observation through system identification
In our previous works, we present a new method
to program mobile robots —“code identification by
demonstration”— based on algorithmically transferring
human behaviours to robot control code using
transparent mathematical functions. Our approach
has three stages: i) first extracting the trajectory of the
desired behaviour by observing the human, ii) making
the robot follow the human trajectory blindly to
log the robot’s own perception perceived along that
trajectory, and finally iii) linking the robot’s perception
to the desired behaviour to obtain a generalised,
sensor-based model.
So far we used an external, camera based motion
tracking system to log the trajectory of the human
demonstrator during his initial demonstration of the
desired motion. Because such tracking systems are
complicated to set up and expensive, we propose an alternative method to obtain trajectory information, using the robot’s own sensor perception.
In this method, we train a mathematical polynomial using the NARMAX system identification methodology which maps the position of the “red jacket” worn by the demonstrator in the image captured by the robot’s camera, to the relative position of the demonstrator in the real world according to the robot.
We demonstrate the viability of this approach by teaching a Scitos G5 mobile robot to achieve door traversal behaviour
Robot programming by demonstration through system identification
Increasingly, personalised robots — robots especially
designed and programmed for an individual’s needs
and preferences — are being used to support humans in
their daily lives, most notably in the area of service robotics. Arguably, the closer the robot is programmed to the individual’s needs, the more useful it is, and we believe that giving people the opportunity to program their own robots, rather than programming robots for them, will push robotics research one step further in the personalised robotics field. However, traditional robot programming techniques require specialised technical skills from different disciplines and it is not reasonable to expect end-users to have these skills. In this paper, we therefore present a new method of obtaining robot control code — programming by demonstration through system identification which algorithmically and automatically transfers human behaviours into robot control code, using transparent, analysable mathematical functions. Besides providing a simple means of generating perception-action mappings, they have the additional advantage that can also be used to form hypotheses and theoretical analysis of robot behaviour. We demonstrate the viability of this approach by teaching a Scitos G5 mobile robot to achieve wall following and corridor passing behaviours
Realtime calibration of the A4 electromagnetic lead fluoride calorimeter
Sufficient energy resolution is the key issue for the calorimetry in particle
and nuclear physics. The calorimeter of the A4 parity violation experiment at
MAMI is a segmented calorimeter where the energy of an event is determined by
summing the signals of neighbouring channels. In this case the precise matching
of the individual modules is crucial to obtain a good energy resolution. We
have developped a calibration procedure for our total absorbing electromagnetic
calorimeter which consists of 1022 lead fluoride (PbF_2) crystals. This
procedure reconstructs the the single-module contributions to the events by
solving a linear system of equations, involving the inversion of a 1022 x
1022-matrix. The system has shown its functionality at beam energies between
300 and 1500 MeV and represents a new and fast method to keep the calorimeter
permanently in a well-calibrated state
Comparison of breast and bowel cancer screening uptake patterns in a common cohort of South Asian women in England
Background: Inequalities in uptake of cancer screening by ethnic minority populations are well documented in a
number of international studies. However, most studies to date have explored screening uptake for a single cancer
only. This paper compares breast and bowel cancer screening uptake for a cohort of South Asian women invited to
undertake both, and similarly investigates these women's breast cancer screening behaviour over a period of fifteen
years.
Methods: Screening data for rounds 1, 2 and 5 (1989-2004) of the NHS breast cancer screening programme and for
round 1 of the NHS bowel screening pilot (2000-2002) were obtained for women aged 50-69 resident in the English
bowel screening pilot site, Coventry and Warwickshire, who had been invited to undertake breast and bowel cancer
screening in the period 2000-2002. Breast and bowel cancer screening uptake levels were calculated and compared
using the chi-squared test.
Results: 72,566 women were invited to breast and bowel cancer screening after exclusions. Of these, 3,539 were South
Asian and 69,027 non-Asian; 18,730 had been invited to mammography over the previous fifteen years (rounds 1 to 5).
South Asian women were significantly less likely to undertake both breast and bowel cancer screening; 29.9% (n =
1,057) compared to 59.4% (n = 40,969) for non-Asians (p < 0.001). Women in both groups who consistently chose to
undertake breast cancer screening in rounds 1, 2 and 5 were more likely to complete round 1 bowel cancer screening.
However, the likelihood of completion of bowel cancer screening was still significantly lower for South Asians; 49.5% vs.
82.3% for non-Asians, p < 0.001. South Asian women who undertook breast cancer screening in only one round were
no more likely to complete bowel cancer screening than those who decided against breast cancer screening in all
three rounds. In contrast, similar women in the non-Asian population had an increased likelihood of completing the
new bowel cancer screening test. The likelihood of continued uptake of mammography after undertaking screening in
round 1 differed between South Asian religio-linguistic groups. Noticeably, women in the Muslim population were less
likely to continue to participate in mammography than those in other South Asian groups.
Conclusions: Culturally appropriate targeted interventions are required to reduce observed disparities in cancer
screening uptakes
Improving mitochondrial function significantly reduces metabolic, visual, motor and cognitive decline in aged Drosophila melanogaster
Mitochondria play a major role in aging. Over time, mutations accumulate in mitochondrial DNA leading to reduced adenosine triphosphate (ATP) production and increased production of damaging reactive oxygen species. If cells fail to cope, they die. Reduced ATP will result in declining cellular membrane potentials leading to reduced central nervous system function. However, aged mitochondrial function is improved by long wavelength light (670 nm) absorbed by cytochrome c oxidase in mitochondrial respiration. In Drosophila, lifelong 670-nm exposure extends lifespan and improves aged mobility. Here, we ask if improved mitochondrial metabolism can reduce functional senescence in metabolism, sensory, locomotor, and cognitive abilities in old flies exposed to 670 nm daily for 1 week. Exposure significantly increased cytochrome c oxidase activity, whole body energy storage, ATP and mitochondrial DNA content, and reduced reactive oxygen species. Retinal function and memory were also significantly improved to levels found in 2-week-old flies. Mobility improved by 60%. The mode of action is likely related to improved energy homeostasis increasing ATP availability for ionic ATPases critical for maintenance of neuronal membrane potentials. 670-nm light exposure may be a simple route for resolving problems of aging
A luminosity monitor for the A4 parity violation experiment at MAMI
A water Cherenkov luminosity monitor system with associated electronics has
been developed for the A4 parity violation experiment at MAMI. The detector
system measures the luminosity of the hydrogen target hit by the MAMI electron
beam and monitors the stability of the liquid hydrogen target. Both is required
for the precise study of the count rate asymmetries in the scattering of
longitudinally polarized electrons on unpolarized protons. Any helicity
correlated fluctuation of the target density leads to false asymmetries. The
performance of the luminosity monitor, investigated in about 2000 hours with
electron beam, and the results of its application in the A4 experiment are
presented.Comment: 22 pages, 12 figures, submitted to NIM
Evolution in random fitness landscapes: the infinite sites model
We consider the evolution of an asexually reproducing population in an
uncorrelated random fitness landscape in the limit of infinite genome size,
which implies that each mutation generates a new fitness value drawn from a
probability distribution . This is the finite population version of
Kingman's house of cards model [J.F.C. Kingman, \textit{J. Appl. Probab.}
\textbf{15}, 1 (1978)]. In contrast to Kingman's work, the focus here is on
unbounded distributions which lead to an indefinite growth of the
population fitness. The model is solved analytically in the limit of infinite
population size and simulated numerically for finite . When
the genome-wide mutation probability is small, the long time behavior of
the model reduces to a point process of fixation events, which is referred to
as a \textit{diluted record process} (DRP). The DRP is similar to the standard
record process except that a new record candidate (a number that exceeds all
previous entries in the sequence) is accepted only with a certain probability
that depends on the values of the current record and the candidate. We develop
a systematic analytic approximation scheme for the DRP. At finite the
fitness frequency distribution of the population decomposes into a stationary
part due to mutations and a traveling wave component due to selection, which is
shown to imply a reduction of the mean fitness by a factor of compared to
the limit.Comment: Dedicated to Thomas Nattermann on the occasion of his 60th birthday.
Submitted to JSTAT. Error in Section 3.2 was correcte
Measurement of the Transverse Beam Spin Asymmetry in Elastic Electron Proton Scattering and the Inelastic Contribution to the Imaginary Part of the Two-Photon Exchange Amplitude
We report on a measurement of the asymmetry in the scattering of transversely
polarized electrons off unpolarized protons, A, at two Q values of
\qsquaredaveragedlow (GeV/c) and \qsquaredaveragedhighII (GeV/c) and a
scattering angle of . The measured transverse
asymmetries are A(Q = \qsquaredaveragedlow (GeV/c)) =
(\experimentalasymmetry alulowcorr \statisticalerrorlow
\combinedsyspolerrorlowalucor) 10 and
A(Q = \qsquaredaveragedhighII (GeV/c)) = (\experimentalasymme
tryaluhighcorr \statisticalerrorhigh
\combinedsyspolerrorhighalucor) 10. The first
errors denotes the statistical error and the second the systematic
uncertainties. A arises from the imaginary part of the two-photon
exchange amplitude and is zero in the one-photon exchange approximation. From
comparison with theoretical estimates of A we conclude that
N-intermediate states give a substantial contribution to the imaginary
part of the two-photon amplitude. The contribution from the ground state proton
to the imaginary part of the two-photon exchange can be neglected. There is no
obvious reason why this should be different for the real part of the two-photon
amplitude, which enters into the radiative corrections for the Rosenbluth
separation measurements of the electric form factor of the proton.Comment: 4 figures, submitted to PRL on Oct.
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