1,566 research outputs found
A Comparison of Inverse Simulation-Based Fault Detection in a Simple Robotic Rover with a Traditional Model-Based Method
Robotic rovers which are designed to work in extra-terrestrial environments present a unique challenge in terms of the reliability and availability of systems throughout the mission. Should some fault occur, with the nearest human potentially millions of kilometres away, detection and identification of the fault must be performed solely by the robot and its subsystems. Faults in the system sensors are relatively straightforward to detect, through the residuals produced by comparison of the system output with that of a simple model. However, faults in the input, that is, the actuators of the system, are harder to detect. A step change in the input signal, caused potentially by the loss of an actuator, can propagate through the system, resulting in complex residuals in multiple outputs. These residuals can be difficult to isolate or distinguish from residuals caused by environmental disturbances. While a more complex fault detection method or additional sensors could be used to solve these issues, an alternative is presented here. Using inverse simulation (InvSim), the inputs and outputs of the mathematical model of the rover system are reversed. Thus, for a desired trajectory, the corresponding actuator inputs are obtained. A step fault near the input then manifests itself as a step change in the residual between the system inputs and the input trajectory obtained through inverse simulation. This approach avoids the need for additional hardware on a mass- and power-critical system such as the rover. The InvSim fault detection method is applied to a simple four-wheeled rover in simulation. Additive system faults and an external disturbance force and are applied to the vehicle in turn, such that the dynamic response and sensor output of the rover are impacted. Basic model-based fault detection is then employed to provide output residuals which may be analysed to provide information on the fault/disturbance. InvSim-based fault detection is then employed, similarly providing \textit{input} residuals which provide further information on the fault/disturbance. The input residuals are shown to provide clearer information on the location and magnitude of an input fault than the output residuals. Additionally, they can allow faults to be more clearly discriminated from environmental disturbances
Inverse Simulation as a Tool for Fault Detection and Isolation in Planetary Rovers
With manned expeditions to planetary bodies beyond our own and the Moon currently intractable, the onus falls upon robotic systems to explore and analyse extraterrestrial environments such as Mars. These systems typically take the form of wheeled rovers, designed to navigate the difficult terrain of other worlds. Rovers have been used in this role since Lunokhod 1 landed on the Moon in 1970. While early rovers were remote controlled, communication latency with bodies beyond the Moon and the desire to improve mission effectiveness have resulted in increasing autonomy in planetary rovers. With an increase in autonomy, however, comes an increase in complexity. This can have a negative impact on the reliability of the rover system. With a fault-free system an unlikely prospect and human assistance millions of miles away, the rover must have a robust fault detection, isolation and recovery (FDIR) system. The need for comprehensive FDIR is demonstrated by the recent Chinese lunar rover, Yutu (or âJade Rabbitâ). Yutu was rendered immobile 42 days after landing and remained so for the duration of its operational life: 31 months. While its lifespan far exceeded its expected value, Yutu's inability to move severely impaired its ability to perform its mission. This clearly highlights the need for robust FDIR. A common approach to FDIR is through the generation and analysis of residuals. Output residuals may be obtained by comparing the outputs of the system with predictions of those outputs, obtained from a mathematical model of the system which is supplied with the system inputs. Output residuals allow simple detection and isolation of faults at the output of the system. Faults in earlier stages of the system, however, propagate through the system dynamics and can disperse amongst several of the outputs. This problem is exemplified by faults at the input, which can potentially excite every system state and thus manifest in every output residual. Methods exist for decoupling and analysing output residuals such that input faults may be isolated, however, these methods are complex and require comprehensive development and testing. A conceptually simpler approach is presented in this paper. Inverse simulation (InvSim) is a numerical method by which the inputs of a system are obtained for a desired output. It does so by using a Newton-Raphson algorithm to solve a non-linear model of the system for the input. When supplied with the outputs of a fault-afflicted system, InvSim produces the input required to drive a fault-free system to this output. The fault therefore manifests itself in this generated input signal. The InvSim-generated input may then be compared to the true system input to generate input residuals. Just as a fault at an output manifests itself in the residual for that output alone, a fault at an input similarly manifests itself only in the residual for that input. InvSim may also be used to generate residuals at other locations in the system, by considering distinct subsystems with their own inputs and outputs. This ability is tested comprehensively in this paper. Faults are applied to a simulated rover at a variety of locations within the system structure and residuals generated using both InvSim and conventional forward simulation. Residuals generated using InvSim are shown to facilitate detection and isolation of faults in several locations using simple analyses. By contrast, forward simulation requires the use of complex analytical methods such as structured residuals or adaptive thresholds
The significance of seniority for women managersâ interpretations of organizational restructuring
This paper examines the impact of restructuring within the transport and logistics sector on women managers working at senior and less senior (middle/junior management) levels of the organization. The majority of women experienced increased performance pressures and heavier workloads as well as an increase in working hours. At the same time, there were pressures to work at home (i.e. week-ends and evenings) and reduced opportunities to work from home (i.e. during normal office hours). Management level emerged as an important factor in how these changes were interpreted. Senior managers perceived more positive outcomes in terms of increased motivation and loyalty. Despite a longer working week, they were less likely to report low morale as an outcome from long hours. In fact, irrespective of management level, women working shorter hours were more likely to report low morale as an outcome. Results are discussed in relation to literature on restructuring and careers, in terms of perceptual framing and in relation to different levels of investment in the organization
Continuing a Chandra Survey of Quasar Radio Jets
We are conducting an X-ray survey of flat spectrum radio quasars (FSRQs) with
extended radio structures. We summarize our results from the first stage of our
survey, then we present findings from its continuation.
We have discovered jet X-ray emission from 12 of our first 20 Chandra
targets, establishing that strong 0.5-7.0 keV emission is a common feature of
FSRQ jets. The X-ray morphology is varied, but in general closely matches the
radio structure until the first sharp radio bend. In the sources with optical
data as well as X-ray detections we rule out simple synchrotron models for
X-ray emission, suggesting these systems may instead be dominated by inverse
Compton (IC) scattering. Fitting models of IC scattering of cosmic microwave
background photons suggests that these jets are aligned within a few degrees of
our line of sight, with bulk Lorentz factors of a few to ten and magnetic
fields a bit stronger than G.
In the weeks prior to this meeting, we have discovered two new X-ray jets at
. One (PKS B1055+201) has a dramatic, -long jet. The other (PKS
B1421-490) appears unremarkable at radio frequencies, but at higher frequencies
the jet is uniquely powerful: its optically-dominated, with jet/core flux
ratios of 3.7 at 1 keV and 380 at 480 nm.Comment: 4 pages, 8 figures. To appear in `X-Ray and Radio Connections', ed.
L.O. Sjouwerman and K.K. Dyer (published electronicly at
http://www.aoc.nrao.edu/events/xraydio/). Additional material and higher
resolution figures may be found at http://space.mit.edu/home/jonathan/jets
A Multi-Wavelength Study of the Jet, Lobes and Core of the Quasar PKS 2101-490
We present a detailed study of the X-ray, optical and radio emission from the
jet, lobes and core of the quasar PKS 2101-490 as revealed by new Chandra, HST
and ATCA images. We extract the radio to X-ray spectral energy distributions
from seven regions of the 13 arcsecond jet, and model the jet X-ray emission in
terms of Doppler beamed inverse Compton scattering of the cosmic microwave
background (IC/CMB) for a jet in a state of equipartition between particle and
magnetic field energy densities. This model implies that the jet remains highly
relativistic hundreds of kpc from the nucleus, with a bulk Lorentz factor Gamma
~ 6 and magnetic field of order 30 microGauss. We detect an apparent radiative
cooling break in the synchrotron spectrum of one of the jet knots, and are able
to interpret this in terms of a standard one-zone continuous injection model,
based on jet parameters derived from the IC/CMB model. However, we note
apparent substructure in the bright optical knot in one of the HST bands. We
confront the IC/CMB model with independent estimates of the jet power, and find
that the IC/CMB model jet power is consistent with the independent estimates,
provided that the minimum electron Lorentz factor gamma_min > 50, and the knots
are significantly longer than the jet width, as implied by de-projection of the
observed knot lengths.Comment: 16 pages, 10 figures, 6 table
Discovery of an X-ray Jet and Extended Jet Structure in the Quasar PKS 1055+201
This letter reports rich X-ray jet structures found in the Chandra
observation of PKS 1055+201. In addition to an X-ray jet coincident with the
radio jet we detect a region of extended X-ray emission surrounding the jet as
far from the core as the radio hotspot to the North, and a similar extended
X-ray region along the presumed path of the unseen counterjet to the Southern
radio lobe. Both X-ray regions show a similar curvature to the west, relative
to the quasar. We interpret this as the first example where we separately
detect the X-ray emission from a narrow jet and extended, residual jet plasma
over the entire length of a powerful FRII jet.Comment: Accepted for publication in Ap. J. Letters. 4 pages, 3 figure
Economic evaluation protocol of a short, all-oral bedaquiline-containing regimen for the treatment of rifampicin-resistant tuberculosis from the STREAM trial
Introduction: A December 2019 WHO rapid communication recommended the use of 9-month all-oral regimens for treating multidrug-resistant tuberculosis (MDR-TB). Besides the clinical benefits, they are thought to be less costly than the injectable-containing regimens, for both the patient and the health system. STREAM is the first randomised controlled trial with an economical evaluation to compare all-oral and injectable-containing 9â11-month MDR-TB treatment regimens.
Methods and analysis: Health system costs of delivering a 9-month injectable-containing regimen and a 9-month all-oral bedaquiline-containing regimen will be collected in Ethiopia, India, Moldova and Uganda, using âbottom-upâ and âtop-downâ costing approaches. Patient costs will be collected using questionnaires that have been developed based on the STOP-TB questionnaire. The primary objective of the study is to estimate the cost utility of the two regimens, from a health system perspective. Secondary objectives: include estimating the cost utility from a societal perspective as well as evaluating the cost-effectiveness of the regimens, using both health system and societal perspectives. The effect measure for the costâutility analysis will be the quality-adjusted life years (QALY), while the effect measure for the cost-effectiveness analysis will be the efficacy outcome from the clinical trial.
Ethics and dissemination: The study has been evaluated and approved by the Ethics Advisory Group of the International Union Against Tuberculosis and Lung Disease and also approved by ethics committees in all participating countries. All participants have provided written informed consent. The results of the economic evaluation will be published in a peer-reviewed journal
A Chandra Survey of Quasar Jets: First Results
We present results from Chandra X-ray imaging and spectroscopy of a
flux-limited sample of flat spectrum radio-emitting quasars with jet-like
extended structure. Twelve of twenty quasar jets are detected in 5 ks ACIS-S
exposures. The quasars without X-ray jets are not significantly different from
those in the sample with detected jets except that the extended radio emission
is generally fainter. New radio maps are combined with the X-ray images in
order to elucidate the relation between radio and X-ray emission in spatially
resolved structures. We find a variety of morphologies, including long straight
jets and bends up to 90 degrees. All X-ray jets are one-sided although the
radio images used for source selection often show lobes opposite the X-ray
jets. The FR II X-ray jets can all be interpreted as inverse Compton scattering
of cosmic microwave background photons by electrons in large-scale relativistic
jets although deeper observations are required to test this interpretation in
detail. Applying this interpretation to the jets as a population, we find that
the jets would be aligned to within 30 degrees of the line of sight generally,
assuming that the bulk Lorentz factor of the jets is 10.Comment: 25 pages with 5 pages of color figures; accepted for publication in
the Astrophysical Journal Supplements; higher resolution jpeg images are
available at http://space.mit.edu/home/jonathan/jets
Adherence with NICE guidance on lifestyle advice for people with schizophrenia: a survey
Background
Substantial weight gain is common in people taking antipsychotics. NICE recommends these patients
are offered physical health screening and intervention. The STEPWISE trial is currently evaluating a
lifestyle education programme in addition to usual care. However, it is difficult to define what
constitutes âusual careâ.
Aims
To define âusual careâ for lifestyle management in people with schizophrenia, schizoaffective
disorder and first episode psychosis in STEPWISE study sites.
Method
Ten NHS Mental Health Trusts participated in a bespoke survey based on NICE guidance.
Results
Eight trusts reported offering lifestyle education programmes. Nine Trusts reported offering smoking
cessation support. Reported recording of biomedical measures varied.
Conclusions
No consistent lifestyle education programme is currently offered across UK NHS Mental Health
Trusts. The survey benchmarks âusual careâ for the STEPWISE study on which changes can be
measured
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