scholarly journals The Concurrent Control of Motion and Contact Force in the Presence of Predictable Disturbances

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Davide Piovesan ◽  
Maxim Kolesnikov ◽  
Kevin Lynch ◽  
Ferdinando A. Mussa-Ivaldi
Keyword(s):  
Contact Force ◽  
Position Control ◽  
Low Frequency ◽  
Major Axis ◽  
Steady Increase ◽  
Contact Impedance ◽  
Concurrent Control ◽  
Simultaneous Control ◽  
The Central Nervous System ◽  
Endpoint Stiffness

Abstract The simultaneous control of force and motion is important in everyday activities when humans interact with objects. While many studies have analyzed the control of movement within a perturbing force field, few have investigated its dual aspects of controlling a contact force in nonisometric conditions. The mechanism by which the central nervous system controls forces during movements is still unclear, and it can be elucidated by estimating the mechanical properties of the arm during tasks with concurrent motion and contact force goals. We investigate how arm mechanics change when a force control task is accomplished during low-frequency positional perturbations of the arm. Contrary to many force regulation algorithms implemented in robotics, where contact impedance is decreased to reduce force fluctuations in response to position disturbances, we observed a steady increase of arm endpoint stiffness as the task progressed. Based on this evidence, we propose a theoretical framework suggesting that an internal model of the perturbing trajectory is formed. We observed that force regulation in the presence of predictable positional disturbances is implemented using a position control strategy together with the modulation of the endpoint stiffness magnitude, where the direction of the endpoint stiffness ellipse's major axis is oriented toward the desired force.

scholarly journals Neural Network Based Contact Force Control Algorithm for Walking Robots

Sensors ◽  
2021 ◽  
Vol 21 (1) ◽  
pp. 287
Author(s):  
Byeongjin Kim ◽  
Soohyun Kim
Keyword(s):  
Neural Network ◽  
Contact Force ◽  
Force Control ◽  
Control Algorithm ◽  
Position Control ◽  
Linear Quadratic Regulator ◽  
Walking Robots ◽  
Test Model ◽  
Linear Quadratic ◽  
Contact Force Control

Walking algorithms using push-off improve moving efficiency and disturbance rejection performance. However, the algorithm based on classical contact force control requires an exact model or a Force/Torque sensor. This paper proposes a novel contact force control algorithm based on neural networks. The proposed model is adapted to a linear quadratic regulator for position control and balance. The results demonstrate that this neural network-based model can accurately generate force and effectively reduce errors without requiring a sensor. The effectiveness of the algorithm is assessed with the realistic test model. Compared to the Jacobian-based calculation, our algorithm significantly improves the accuracy of the force control. One step simulation was used to analyze the robustness of the algorithm. In summary, this walking control algorithm generates a push-off force with precision and enables it to reject disturbance rapidly.

The 795CT polymorphism in osteopontin gene is not associated with multiple sclerosis in a Spanish population

2007 ◽  
Vol 13 (2) ◽  
pp. 250-252 ◽  
Author(s):  
A Mas ◽  
A Martínez ◽  
V De Las Heras ◽  
M Bartolomé ◽  
Eg De La Concha ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Low Frequency ◽  
Interleukin 10 ◽  
Interleukin 12 ◽  
Italian Population ◽  
Cytokine Network ◽  
Activated T Cells ◽  
Negative Finding ◽  
The Central Nervous System ◽  
Ms Pathogenesis

Multiple sclerosis (MS) is an inflammatory disease affecting the central nervous system. The dysregulation of the cytokine network is an important component of its pathogenesis. One of the cytokines produced by activated T-cells is osteopontin (OPN). OPN enhances the production of the pro-inflammatory cytokines, interleukin-12 and interferon-gamma, while reducing interleukin-10 levels. Therefore, OPN is considered a pro-inflammatory cytokine, and could play a key role in MS pathogenesis. The OPN gene contains several common polymorphisms, distributed in two main haplotypes, which may modulate its production or activity. A total of 326 MS patients and 484 healthy controls were typed for 795CT OPN polymorphism. In order to perform a familial study, 51 progenitor pairs were also included. No difference was found in the case-control or family study. This negative finding is inconsistent with a previous haplotype study in an Italian population, where the haplotype associated carried the low-frequency allele in position 795. In a Japanese population, a similar study yielded no association with this polymorphism. In conclusion, our data suggest that the 795 polymorphism does not play an etiological role per se and the haplotype structure may differ from one population to another. Multiple Sclerosis 2007; 13: 250–252. http://msj.sagepub.com

scholarly journals Dispersive changes in magnetic background noise polarization at 0.1 to 6Hz during sunset and sunrise at L=1.3

2004 ◽  
Vol 22 (6) ◽  
pp. 1989-2000 ◽  
Author(s):  
T. Bösinger ◽  
S. L. Shalimov
Keyword(s):  
Background Noise ◽  
Azimuthal Angle ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Major Axis ◽  
Resonance Structure ◽  
Frequency Range ◽  
Ionosphere Model ◽  
F Region ◽  
E Region

Abstract. Polarization properties of the magnetic background noise (MBN) and the spectral resonance structure (SRS) of the ionospheric Alfvén resonator (IAR) below the first Schumann resonance but above 0.1 Hz are measured by a sensitive pulsation magnetometer at the island of Crete (L=1.3) and analyzed using the existing SRS theory by Belyaev et al. (1989b). The focus of the paper is on the systematic changes in the MBN and SRS properties associated with the transition from a sunlit to a dark ionosphere (sunset) and vice versa (sunrise). We are able to pinpoint in observations an E-region and F-region terminator effect and to simulate it by means of a simple ionosphere model, implying the formalism given by Belyaev et al. (1989b). The E-region terminator effect is associated with an apparent control for the SRS presence or absence with no clear frequency dispersion in polarization properties, whereas the F-region terminator effect exhibits strong frequency dispersion, especially in the low frequency range. This yields a change in the ellipticity of MBN, starting as early as 2 to 3h ahead of the "zero-line" of the terminator. In a 24h presentation of the ellipticity versus frequency and time, the sunrise/sunset effect produces a sharp, dispersive boundary between night and day (day and night). Only inside this boundary, during the night hours, is SRS observed, at times accompanied by a large quasi-periodic long period modulation in the azimuthal angle of the major axis of the polarization ellipse. Attention is also paid to peculiarities in the low frequency range (~0.1Hz), where especially large changes in the polarization properties occur in association with the passage of the terminator. The F-region effect is very distinct and well reproduced by our simple model. Changes in the azimuth associated with the E-region terminator effect are of the order of 20&deg.

scholarly journals Effect of magnetic fields on cryptochrome-dependent responses in Arabidopsis thaliana

2009 ◽  
Vol 6 (41) ◽  
pp. 1193-1205 ◽  
Author(s):  
Sue-Re Harris ◽  
Kevin B. Henbest ◽  
Kiminori Maeda ◽  
John R. Pannell ◽  
Christiane R. Timmel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Arabidopsis Thaliana ◽  
Magnetic Fields ◽  
Low Frequency ◽  
Zero Field ◽  
Experimental Conditions ◽  
Replication Studies ◽  
Weak Magnetic Fields ◽  
Simultaneous Control ◽  
Independent Replication

The scientific literature describing the effects of weak magnetic fields on living systems contains a plethora of contradictory reports, few successful independent replication studies and a dearth of plausible biophysical interaction mechanisms. Most such investigations have been unsystematic, devoid of testable theoretical predictions and, ultimately, unconvincing. A recent study, of magnetic responses in the model plant Arabidopsis thaliana , however, stands out; it has a clear hypothesis—that seedling growth is magnetically sensitive as a result of photoinduced radical-pair reactions in cryptochrome photoreceptors—tested by measuring several cryptochrome-dependent responses, all of which proved to be enhanced in a magnetic field of intensity 500 μT. The potential importance of this study in the debate on putative effects of extremely low-frequency electromagnetic fields on human health prompted us to subject it to the ‘gold standard’ of independent replication. With experimental conditions chosen to match those of the original study, we have measured hypocotyl lengths and anthocyanin accumulation for Arabidopsis seedlings grown in a 500 μT magnetic field, with simultaneous control experiments at 50 μT. Additionally, we have determined hypocotyl lengths of plants grown in 50 μT, 1 mT and approximately 100 mT magnetic fields (with zero-field controls), measured gene ( CHS , HY5 and GST ) expression levels, investigated blue-light intensity effects and explored the influence of sucrose in the growth medium. In no case were consistent, statistically significant magnetic field responses detected.

scholarly journals Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system

2014 ◽  
Author(s):  
Lorenzo Iorio
Keyword(s):  
Gravitational Wave ◽  
Extrasolar Planets ◽  
A Priori ◽  
Low Frequency ◽  
Major Axis ◽  
Characteristic Size ◽  
Body System ◽  
Semi Major Axis ◽  
Plane Gravitational Wave

We analytically compute the long-term orbital variations of a test particle orbiting a central body acted upon by an incident monochromatic plane gravitational wave. We assume that the characteristic size of the perturbed two-body system is much smaller than the wavelength of the wave. Moreover, we also suppose that the wave's frequency νg is much smaller than the particle's orbital one nb. We make neither a priori assumptions about the direction of the wavevector k nor on the orbital configuration of the particle. While the semi-major axis a is left unaffected, the eccentricity e, the inclination I, the longitude of the ascending node Ω, the longitude of pericenter ϖ and the mean anomaly ℳ undergo non-vanishing long-term changes of the form dΨ/dt=F(Kij;e,I,Ω,ω),Ψ=e,I,Ω,ϖ,M, where Kij, i,j=1,2,3 are the coefficients of the tidal matrix K. Thus, in addition to the variations of its orientation in space, the shape of the orbit would be altered as well. Strictly speaking, such effects are not secular trends because of the slow modulation introduced by K and by the orbital elements themselves: they exhibit peculiar long-term temporal patterns which would be potentially of help for their detection in multidecadal analyses of extended data records of planetary observations of various kinds. In particular, they could be useful in performing independent tests of the inflation-driven ultra-low gravitational waves whose imprint may have been indirectly detected in the Cosmic Microwave Background by the Earth-based experiment BICEP2. Our calculation holds, in general, for any gravitationally bound two-body system whose orbital frequency nb is much larger than the frequency νg of the external wave, like, e.g., extrasolar planets and the stars orbiting the Galactic black hole. It is also valid for a generic perturbation of tidal type with constant coefficients over timescales of the order of the orbital period of the perturbed particle.

scholarly journals Orbital effects of a monochromatic plane gravitational wave with ultra-low frequency incident on a gravitationally bound two-body system

2014 ◽  
Author(s):  
Lorenzo Iorio
Keyword(s):  
Gravitational Wave ◽  
Extrasolar Planets ◽  
A Priori ◽  
Low Frequency ◽  
Major Axis ◽  
Characteristic Size ◽  
Body System ◽  
Semi Major Axis ◽  
Plane Gravitational Wave

We analytically compute the long-term orbital variations of a test particle orbiting a central body acted upon by an incident monochromatic plane gravitational wave. We assume that the characteristic size of the perturbed two-body system is much smaller than the wavelength of the wave. Moreover, we also suppose that the wave's frequency νg is much smaller than the particle's orbital one nb. We make neither a priori assumptions about the direction of the wavevector k nor on the orbital configuration of the particle. While the semi-major axis a is left unaffected, the eccentricity e, the inclination I, the longitude of the ascending node Ω, the longitude of pericenter ϖ and the mean anomaly ℳ undergo non-vanishing long-term changes of the form dΨ/dt=F(Kij;e,I,Ω,ω),Ψ=e,I,Ω,ϖ,M, where Kij, i,j=1,2,3 are the coefficients of the tidal matrix K. Thus, in addition to the variations of its orientation in space, the shape of the orbit would be altered as well. Strictly speaking, such effects are not secular trends because of the slow modulation introduced by K and by the orbital elements themselves: they exhibit peculiar long-term temporal patterns which would be potentially of help for their detection in multidecadal analyses of extended data records of planetary observations of various kinds. In particular, they could be useful in performing independent tests of the inflation-driven ultra-low gravitational waves whose imprint may have been indirectly detected in the Cosmic Microwave Background by the Earth-based experiment BICEP2. Our calculation holds, in general, for any gravitationally bound two-body system whose orbital frequency nb is much larger than the frequency νg of the external wave, like, e.g., extrasolar planets and the stars orbiting the Galactic black hole. It is also valid for a generic perturbation of tidal type with constant coefficients over timescales of the order of the orbital period of the perturbed particle.

Research on Normal Motion of Specimen of Ultrasonic Feeding

2012 ◽  
Vol 433-440 ◽  
pp. 3826-3830
Author(s):  
Liang Li ◽  
Mian Zheng
Keyword(s):  
Contact Force ◽  
Structural Model ◽  
Contact Process ◽  
Low Frequency ◽  
Normal Velocity ◽  
Normal Contact ◽  
Nonlinear Dynamical ◽  
Normal Contact Force ◽  
Theoretical Results ◽  
Good Agreement

In this paper, a micro structural model is applied to study the normal contact process of the specimen of the ultrasonic feeding. Firstly, the normal velocity of the specimen with the actuation of the oscillator is calculated by solving the nonlinear dynamical equation of the specimen. The theoretical results of the normal velocity are in good agreement with the experimental results under the same conditions. The theoretical results indicate that for the low frequency of the oscillator, at most time, the normal contact force is zero, whereas for the high frequency the normal contact force is periodical. In addition, the theoretical results also indicate the contact time between specimen and the oscillator in a period decreases with the increasing amplitude of the oscillator.

scholarly journals Mapping the Distributions of Exoplanet Populations with NICI and GPI

2015 ◽  
Vol 10 (S314) ◽  
pp. 220-225
Author(s):  
Eric L. Nielsen ◽  
Michael C. Liu ◽  
Zahed Wahhaj ◽  
Beth A. Biller ◽  
Thomas L. Hayward ◽  
...  
Keyword(s):  
Low Frequency ◽  
Major Axis ◽  
Giant Planets ◽  
Direct Imaging ◽  
Semi Major Axis ◽  
Solar Systems ◽  
Test Models ◽  
Nearby Stars ◽  
Formation And Evolution ◽  
Band Contrast

AbstractWhile more and more long-period giant planets are discovered by direct imaging, the distribution of planets at these separations (≳5 AU) has remained largely uncertain, especially compared to planets in the inner regions of solar systems probed by RV and transit techniques. The low frequency, the detection challenges, and heterogeneous samples make determining the mass and orbit distributions of directly imaged planets at the end of a survey difficult. By utilizing Monte Carlo methods that incorporate the age, distance, and spectral type of each target, we can use all stars in the survey, not just those with detected planets, to learn about the underlying population. We have produced upper limits and direct measurements of the frequency of these planets with the most recent generation of direct imaging surveys. The Gemini NICI Planet-Finding Campaign observed 220 young, nearby stars at a median H-band contrast of 14.5 magnitudes at 1”, representing the largest, deepest search for exoplanets by the completion of the survey. The Gemini Planet Imager Exoplanet Survey is in the process of surveying 600 stars, pushing these contrasts to a few tenths of an arcsecond from the star. With the advent of large surveys (many hundreds of stars) using advanced planet-imagers we gain the ability to move beyond measuring the frequency of wide-separation giant planets and to simultaneously determine the distribution as a function of planet mass, semi-major axis, and stellar mass, and so directly test models of planet formation and evolution.

scholarly journals Determination of soluble ICAM-1 and TNFalphaR in the cerebrospinal fluid and serum levels in a population of Brazilian patients with relapsing-remitting multiple sclerosis

2001 ◽  
Vol 59 (1) ◽  
pp. 18-22 ◽  
Author(s):  
Soniza Vieira Alves-Leon ◽  
Elizabeth Batista ◽  
Regina Papais-Alvarenga ◽  
Thereza Quírico-Santos
Keyword(s):  
Multiple Sclerosis ◽  
Clinical Signs ◽  
Serum Levels ◽  
Chronic Inflammatory Disease ◽  
Herniated Disc ◽  
Intercellular Adhesion Molecule ◽  
Steady Increase ◽  
Acute Relapse ◽  
Significant Difference ◽  
The Central Nervous System

Cytokines and adhesion molecules have been implicated in the pathogenesis of multiple sclerosis (MS), a chronic inflammatory disease of the central nervous system. In this study we analyzed intrathecal (CSF) and serum levels of soluble intercellular adhesion molecule (ICAM-1) and TNFalphaR (60kD) from 20 patients with clinically definite MS during acute relapse or stable disease. Comparing to control groups of healthy individuals and patients with intervertebral herniated disc, MS patients showed increased levels (p< 0.001) of sICAM-1 and TNFalphaR in both serum and CSF samples. Regardless stage of disease there was no significant difference in the levels of sICAM-1 during acute relapse (657±124.9 ng/ml) or remission (627±36.2 ng/ml). A steady increase of TNFalphaR (60kD) in both serum and CSF, indicate the existence of a continuous inflammatory process within the brain tissue of MS patients despite absence of clinical signs of disease activity.

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