1,020 research outputs found
Neural control on multiple time scales: Insights from human stick balancing
The time-delayed feedback control mechanisms of the nervous system are continuously subjected to the
effects of uncontrolled random perturbations (herein referred to as noise). In this setting the statistical properties
of the fluctuations in the controlled variable(s) can provide non-invasive insights into the nature of the
underlying control mechanisms. We illustrate this concept through a study of stick balancing at the fingertip
using high speed motion capture techniques. Experimental observations together with numerical studies of a
stochastic delay differential equation demonstrate that on time scales short compared to the neural time delay
(“fast control”), parametric noise provides a non-predictive mechanism that transiently stabilizes the upright
position of the balanced stick. Moreover, numerical simulations of a delayed random walker with a repulsive
origin indicate that even an unstable fixed point can be transiently stabilized by the interplay between noise
and time delay. In contrast, on time scales comparable to the neural time delay (“slow control”), feedback and
feedforward control mechanisms become more important. The relative contribution of the fast and slow control
mechanisms to stick balancing is dynamic and, for example, depends on the context in which stick balancing
is performed and the expertise of the balancer
Effect of a Domain Wall on the Conductance Quantization in a Ferromagnetic Nanowire
The effect of the domain wall (DW) on the conductance in a ballistic
ferromagnetic nanowire (FMNW) is revisited by exploiting a specific
perturbation theory which is effective for a thin DW; the thinness is often the
case in currently interested conductance measurements on FMNWs. Including the
Hund coupling between carrier spins and local spins in a DW, the conductance of
a FMNW in the presence of a very thin DW is calculated within the
Landauer-B\"{u}ttiker formalism. It is revealed that the conductance plateaus
are modified significantly, and the switching of the quantization unit from
to ``about '' is produced in a FMNW by the introduction of a
thin DW. This accounts well for recent observations in a FMNW.Comment: 5 pages, 2 figures, Corrected typos and added reference
Results of the 2004 Spanish Experimental Fishing in NAFO Subarea 1
An experimental fishing was carried out with three bottom trawlers commercial Spanish vessels from July to December
of the year 2004 in the Subarea 1. The main objective of the experimental fishing was to search for cephalopods species
concentrations inside the territorial waters of Greenland. During the experimental fishing a scientific observer stayed on
board each vessel to collect effort data, catches and yields by haul and Division. The observers carried out length
distribution samplings of the following species: Reinhardtius hippoglossoides, Pandalus borealis, Gadus morhua,
Sebastes spp., Hippoglossoides platessoides and Macrourus berglax. Biological samplings of R. hippoglossoides, P.
borealis, H. platessoides, G. morhua and M. berglax were also carried out. Otoliths of Greenland halibut (1 356) and
Atlantic cod (739) were collected for age determination. Greenland halibut was the main species caught and the
cephalopods, target species, have not been found in the experimental fishing
Modelling the photo-Fenton oxidation of the pharmaceutical paracetamol in water including the effect of photon absorption (VRPA)
A new model is proposed for the photo-Fenton oxidation of water contaminants including the effect of photon absorption (volumetric rate of photon absorption, VRPA), the effect of the geometry of the reactor and the illuminated volume to total volume ratio (Ri) in the reaction system. Fe(III) was found to be the main species in the aqueous solution responsible for photon absorption provided that hydrogen peroxide was not totally consumed. Paracetamol was used as model pollutant at a concentration of 1 mM to validate the model. The illuminated part of the raceway reactor configuration (total length of 80 cm) was operated at two liquid depths (5.0 and 2.5 cm) equivalent to two irradiated reactor volumes (2 and 1 L) and using Ri ratios in the range 0.30–0.65, which changed the dark reactor volume. These values are commonly found in photo-Fenton pilot plants for water treatment and purification. The model successfully fitted the temporal evolution of the dissolved oxygen (O2) and the hydrogen peroxide (H2O2) concentrations and the evolution of the total organic carbon (TOC) in solution in both reactor geometries and for different illuminated volume to total volume ratios. The model can be easily extended to model other water contaminants and provides a robust method for process design, process control and optimization
Development of a prototype test system for certification of curved fuselage panels
Volume 1024, Issue 1
Article number 012081A prototype test system with capacity to reproduce combined loads representative of real loading cases of a curved fuselage panel has been developed. This prototype test system allows the structural validation of curved fuselage panels to be accomplished. The developed system is able to apply combined mechanical and pressurization loading states under quasi-static and dynamic loading conditions. It has been designed using CAD models and calculated with the aid of Finite Element models to ensure its integrity. A data acquisition system synchronized with a control system enables real time monitoring of test parameters.Horizonte 2020 (Unión Europea) CS2-AIR-GAM-2014-2015-0
Vegetative growth response of beets and lettuce to stored human urine
ArticleIn this work, we present the experimental results of the effect of stored human urine (SHU) on the growth of beets (Beta vulgaris L) and lettuce (Lactuca sativaL). We apply different amounts of SHU according to the recommended dose of nitrogen, considering soil from farmland and vermiculite as substrates. The last allows us to determine with high precision the isolated effect of SHU over the vegetative development of beet plants, without considering other nutrients present in common soils. Experimental results demonstrate that the application of SHU has no significant effects on lettuce vegetative growth under our soil conditions. In contrast, SHU can be used successfully as a fertilizer of beets. The optimum dose was found at 120kgN ha-1and resulted in average dry weight of 125g. However, if the dose exceeds the optimum levels, the growth of the plant is inhibited. Beets fertilized with SHU does not pose any hygienic risk for human consumption. Our findings represent a promising alternative to propose expanding the use of SHU as fertilizer in medium-sized greenhouses and to provide benefits to families in rural areas, with little or no available water supplies
Dynamics of Simple Balancing Models with State Dependent Switching Control
Time-delayed control in a balancing problem may be a nonsmooth function for a
variety of reasons. In this paper we study a simple model of the control of an
inverted pendulum by either a connected movable cart or an applied torque for
which the control is turned off when the pendulum is located within certain
regions of phase space. Without applying a small angle approximation for
deviations about the vertical position, we see structurally stable periodic
orbits which may be attracting or repelling. Due to the nonsmooth nature of the
control, these periodic orbits are born in various discontinuity-induced
bifurcations. Also we show that a coincidence of switching events can produce
complicated periodic and aperiodic solutions.Comment: 36 pages, 12 figure
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