34,035 research outputs found
Viability of commercial depth sensors for the REX medical exoskeleton : a thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in Mechatronics at Massey University, Albany, New Zealand
Closing the feedback loop of machine control has been a known method for gaining stability.
Medical exoskeletons are no exception to this phenomenon. It is proposed that through machine
vision, their stability control can be enhanced in a commercially viable manner. Using machines
to enhance human’s capabilities has been a concept tried since the 19th century, with a range of
successful demonstrations since then such as the REX platform. In parallel, machine vision has
progressed similarly, and while applications that could be considered to be synonymous have been
researched, using computer vision for traversability analysis in medical exoskeletons still leaves a
lot of questions unanswered. These works attempt to understand better this field, in particular,
the commercial viability of machine vision system’s ability to enhance medical exoskeletons.
The key method to determine this will be through implementation. A system is designed that
considers the constraints of working with a commercial product, demonstrating integration into
an existing system without significant alterations. It shows using a stereo vision system to gather
depth information from the surroundings and amalgamate these. The amalgamation process
relies on tracking movement to provide accurate transforms between time-frames in the threedimensional
world. Visual odometry and ground plane detection is employed to achieve this,
enabling the creation of digital elevation maps, to efficiently capture and present information
about the surroundings. Further simplification of this information is accomplished by creating
traversability maps; that directly relate the terrain to whether the REX device can safely navigate
that location. Ultimately a link is formed between the REX device and these maps, and that
enables user movement commands to be intercepted. Once intercepted, a binary decision is
computed whether that movement will traverse safe terrain. If however the command is deemed
unsafe (for example stepping backwards off a ledge), this will not be permitted, hence increasing
patient safety. Results suggest that this end-to-end demonstration is capable of improving patient
safety; however, plenty of future work and considerations are discussed. The underlying data
quality provided by the stereo sensor is questioned, and the limitations of macro vs. micro
applicability to the REX are identified. That is; the works presented are capable of working on a
macro level, but in their current state lack the finer detail to improve patient safety when operating
a REX medical exoskeleton considerably
Set Theory or Higher Order Logic to Represent Auction Concepts in Isabelle?
When faced with the question of how to represent properties in a formal proof
system any user has to make design decisions. We have proved three of the
theorems from Maskin's 2004 survey article on Auction Theory using the
Isabelle/HOL system, and we have produced verified code for combinatorial
Vickrey auctions. A fundamental question in this was how to represent some
basic concepts: since set theory is available inside Isabelle/HOL, when
introducing new definitions there is often the issue of balancing the amount of
set-theoretical objects and of objects expressed using entities which are more
typical of higher order logic such as functions or lists. Likewise, a user has
often to answer the question whether to use a constructive or a
non-constructive definition. Such decisions have consequences for the proof
development and the usability of the formalization. For instance, sets are
usually closer to the representation that economists would use and recognize,
while the other objects are closer to the extraction of computational content.
In this paper we give examples of the advantages and disadvantages for these
approaches and their relationships. In addition, we present the corresponding
Isabelle library of definitions and theorems, most prominently those dealing
with relations and quotients.Comment: Preprint of a paper accepted for the forthcoming CICM 2014 conference
(cicm-conference.org/2014): S.M. Watt et al. (Eds.): CICM 2014, LNAI 8543,
Springer International Publishing Switzerland 2014. 16 pages, 1 figur
Planck pre-launch status: HFI ground calibration
Context. The Planck satellite was successfully launched on May 14th 2009. We have completed the pre-launch calibration measurements of the High Frequency Instrument (HFI) on board Planck and their processing.
Aims. We present the results of the pre-launch calibration of HFI in which we have multiple objectives. First, we determine instrumental parameters that cannot be measured in-flight and predict parameters that can. Second, we take the opportunity to operate and understand the instrument under a wide range of anticipated operating conditions. Finally, we estimate the performance of the instrument built.
Methods. We obtained our pre-launch calibration results by characterising the component and subsystems, then by calibrating the focal plane at IAS (Orsay) in the Saturne simulator, and later from the tests at the satellite level carried out in the CSL (Liège) cryogenic vacuum chamber. We developed models to estimate the instrument pre-launch parameters when no measurement could be performed.
Results. We reliably measure the Planck-HFI instrument characteristics and behaviour, and determine the flight nominal setting of all parameters. The expected in-flight performance exceeds the requirements and is close or superior to the goal specifications
Microstructural changes in Beta-silicon nitride grains upon crystallizing the grain-boundary glass
Crystallizing the grain boundary glass of a liquid phase sintered Si3N4 ceramic for 2 h or less at 1500 C led to formation of gamma Y2Si2O7. After 5 h at 1500 C, the gamma Y2Si2O7 had transformed to beta Y2Si2O7 with a concurrent dramatic increase in dislocation density within beta Si3N4 grains. Reasons for the increased dislocation density is discussed. Annealing for 20 h at 1500 C reduced dislocation densities to the levels found in as-sintered materials
Using particle shape to induce tilted and bistable liquid crystal anchoring
We use Monte Carlo simulations of hard Gaussian overlap (HGO) particles symmetrically confined in slab geometry to investigate the role of particle-substrate interactions on liquid crystalline
anchoring. Despite the restriction here to purely steric interactions and smooth substrates, a range of behaviours are captured, including tilted anchoring and homeotropic-planar bistability. These macroscopic behaviours are all achieved through appropriate tuning of the microscopics of the HGO-substrate interaction, based upon non-additive descriptions for the HGO-substrate shape parameter.</p
Real closed exponential fields
In an extended abstract Ressayre considered real closed exponential fields
and integer parts that respect the exponential function. He outlined a proof
that every real closed exponential field has an exponential integer part. In
the present paper, we give a detailed account of Ressayre's construction, which
becomes canonical once we fix the real closed exponential field, a residue
field section, and a well ordering of the field. The procedure is constructible
over these objects; each step looks effective, but may require many steps. We
produce an example of an exponential field with a residue field and a
well ordering such that is low and and are ,
and Ressayre's construction cannot be completed in .Comment: 24 page
Optical characteristics of Nd:YAG optics and distortions at high power
The intensity profile and beam caustics of a fiber coupled high power Nd:YAG laser beam through a lens system are studied. The thermal lensing effect and its influence on the beam profile and focal position are discussed. Asymmetry of the intensity profile in planes above and below the focal plane is demonstrated. Also the influence of small pollutions on the protective window is explained. Three different methods are used to measure the occurrence\ud
of thermal lensing and quantify these effects
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