1,598 research outputs found
When the goal is to generate a series of activities: A self-organized simulated robot arm
Behavior is characterized by sequences of goal-oriented conducts, such as
food uptake, socializing and resting. Classically, one would define for each
task a corresponding satisfaction level, with the agent engaging, at a given
time, in the activity having the lowest satisfaction level. Alternatively, one
may consider that the agent follows the overarching objective to generate
sequences of distinct activities. To achieve a balanced distribution of
activities would then be the primary goal, and not to master a specific task.
In this setting, the agent would show two types of behaviors, task-oriented,
and task-searching phases, with the latter interseeding the former.
We study the emergence of autonomous task switching for the case of a
simulated robot arm. Grasping one of several moving objects corresponds in this
setting to a specific activity. Overall, the arm should follow a given object
temporarily and then move away, in order to search for a new target and
reengage. We show that this behavior can be generated robustly when modeling
the arm as an adaptive dynamical system. The dissipation function is in this
approach time dependent. The arm is in a dissipative state when searching for a
nearby object, dissipating energy on approach. Once close, the dissipation
function starts to increase, with the eventual sign change implying that the
arm will take up energy and wander off. The resulting explorative state ends
when the dissipation function becomes again negative and the arm selects a new
target. We believe that our approach may be generalized to generate
self-organized sequences of activities in general.Comment: 10 pages, 7 figure
A Novel Decomposition for Control of DC Circuits and Grid Models with Heterogeneous Energy Sources
The way in which electric power depends on the topology of circuits with
mixed voltage and current sources is examined. The power flowing in any
steady-state DC circuit is shown to depend on a minimal set of key variables
called fundamental node voltages and fundamental edge currents. Every
steady-state DC circuit can be decomposed into a voltage controlled subcircuit
and a current controlled subcircuit. In terms of such a decomposition, the I^2R
losses of a mixed source circuit are always the sum of losses on the voltage
controlled subcircuit and the current controlled subcircuit. The paper
concludes by showing that the total power flowing in a mixed source circuit can
be found as critical points of the power expressed in terms of the key voltage
and current variables mentioned above. The possible relationship to topology
control of electric grid operations is discussed
VĂ©lomobility - A critical analysis of planning and space
The purpose of this doctoral study is to bring a spatial dimension into the research on urban mobilities and connect the spatial dimension to the marginalisation of cyclists in urban space. This is been done by exploring the role of urban bicycling and transport planning. The theoretical frame of space, mobilities and power is used for analysing that role through case studies in two Scandinavian cities, Copenhagen and Stockholm. Urban bicycling is a good example of showing the relation between space and mobilities, since cyclists often suffer from marginalised space in cities around the world. The philosophical foundation of the thesis is in critical realism and critical theory. For background data, observations and document studies have been conducted in Stockholm and Copenhagen. The main data collection for this thesis was done both qualitatively, in the form of interviews with planners and politicians, and quantitatively, in the form of survey studies among the citizens of Copenhagen and Stockholm. The data is analysed with the help of the theoretical framework that builds on mobility studies, spatial theory by Lefebvre, and Harvey and power theories deriving mainly from Lukes’ three dimensions of power. The materialisation of power relations is analysed with the example of modern planning in Sweden and Denmark. Overall this thesis manages to show how cycling as a mode of transport is marginalised in urban space, and that urban space wars between cyclists and car drivers and among cyclists are fought in Copenhagen as well as in Stockholm. The conclusion is that different factors, such as the economic situations in Denmark and Sweden, have affected urban and transport planning and thus have created two very different transport systems, where cycling plays a large role (Copenhagen) and a smaller role (Stockholm). Nevertheless, this thesis shows that even in cities that are very good for cycling, like Copenhagen, the motorised modes of transport create many problems and are still dominating urban space
Kick control: using the attracting states arising within the sensorimotor loop of self-organized robots as motor primitives
Self-organized robots may develop attracting states within the sensorimotor
loop, that is within the phase space of neural activity, body, and
environmental variables. Fixpoints, limit cycles, and chaotic attractors
correspond in this setting to a non-moving robot, to directed, and to irregular
locomotion respectively. Short higher-order control commands may hence be used
to kick the system from one self-organized attractor robustly into the basin of
attraction of a different attractor, a concept termed here as kick control. The
individual sensorimotor states serve in this context as highly compliant motor
primitives.
We study different implementations of kick control for the case of simulated
and real-world wheeled robots, for which the dynamics of the distinct wheels is
generated independently by local feedback loops. The feedback loops are
mediated by rate-encoding neurons disposing exclusively of propriosensoric
inputs in terms of projections of the actual rotational angle of the wheel. The
changes of the neural activity are then transmitted into a rotational motion by
a simulated transmission rod akin to the transmission rods used for steam
locomotives.
We find that the self-organized attractor landscape may be morphed both by
higher-level control signals, in the spirit of kick control, and by interacting
with the environment. Bumping against a wall destroys the limit cycle
corresponding to forward motion, with the consequence that the dynamical
variables are then attracted in phase space by the limit cycle corresponding to
backward moving. The robot, which does not dispose of any distance or contact
sensors, hence reverses direction autonomously.Comment: 17 pages, 9 figure
In-flight PSF calibration of the NuSTAR hard X-ray optics
We present results of the point spread function (PSF) calibration of the hard
X-ray optics of the Nuclear Spectroscopic Telescope Array (NuSTAR). Immediately
post-launch, NuSTAR has observed bright point sources such as Cyg X-1, Vela
X-1, and Her X-1 for the PSF calibration. We use the point source observations
taken at several off-axis angles together with a ray-trace model to
characterize the in-orbit angular response, and find that the ray-trace model
alone does not fit the observed event distributions and applying empirical
corrections to the ray-trace model improves the fit significantly. We describe
the corrections applied to the ray-trace model and show that the uncertainties
in the enclosed energy fraction (EEF) of the new PSF model is < 3% for
extraction apertures of R > 60" with no significant energy dependence. We also
show that the PSF of the NuSTAR optics has been stable over a period of ~300
days during its in-orbit operation.Comment: 10 pages, 6 figures. Presented at the SPIE conference Astronomical
Telescopes + Instrumentation 201
Shopping Centres, Cycling Accessibility and Planning–The Case of Nova Lund in Sweden
This paper evaluates the history and cycling accessibility of Nova, a shopping centre established in Lund, Sweden, in 2002. The current situation was also analysed through observation and a literature review. Moreover, the study conducted a closer analysis of the history and role of the municipality based on further literature study and interviews with officials. The conclusion of the analysis indicates poor and unsafe bikeways caused by conflicts of interest between politicians, officials, landowners and the general public. It also depicts a situation in which the municipality’s master plan has been ignored, and, in contrast to the local goals, cycling accessibility at Nova has seen no significant improvement since the shopping centre was first established. The reasons for this, arguably, are a relatively low budget for bikeway improvements in the municipality, as well as a situation in which decision-makers have stopped approaching the subject, as a result of the long and often boisterous conflicts it has created in the past. Lastly, it must be noted that it is easy to regard the whole process of Nova, from its establishment to the current situation, as being symptomatic of the power structures between drivers and cyclists that still affect decision-makers at all levels
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