14,112 research outputs found
INDUSTRIALIZATION OF AGRICULTURE OR A REALIGNMENT OF THE FOOD AND AGRICULTURAL SYSTEM?
Agribusiness,
Feedback control of unsupported standing in paraplegia. Part II: experimental results
For pt. I see ibid., vol. 5, no. 4, p. 331-40 (1997). This is the second of a pair of papers which describe an investigation into the feasibility of providing artificial balance to paraplegics using electrical stimulation of the paralyzed muscles. By bracing the body above the shanks, only stimulation of the plantar flexors is necessary. This arrangement prevents any influence from the intact neuromuscular system above the spinal cord lesion. Here, the authors present experimental results from intact and paraplegic subjects
Optimal control of ankle joint moment: Toward unsupported standing in paraplegia
This paper considers part of the problem of how to provide unsupported standing for paraplegics by feedback control. In this work our overall objective is to stabilize the subject by stimulation only of his ankle joints while the other joints are braced, Here, we investigate the problem of ankle joint moment control. The ankle plantarflexion muscles are first identified with pseudorandom binary sequence (PRBS) signals, periodic sinusoidal signals, and twitches. The muscle is modeled in Hammerstein form as a static recruitment nonlinearity followed by a linear transfer function. A linear-quadratic-Gaussian (LQG)-optimal controller design procedure for ankle joint moment was proposed based on the polynomial equation formulation, The approach was verified by experiments in the special Wobbler apparatus with a neurologically intact subject, and these experimental results are reported. The controller structure is formulated in such a way that there are only two scalar design parameters, each of which has a clear physical interpretation. This facilitates fast controller synthesis and tuning in the laboratory environment. Experimental results show the effects of the controller tuning parameters: the control weighting and the observer response time, which determine closed-loop properties. Using these two parameters the tradeoff between disturbance rejection and measurement noise sensitivity can be straightforwardly balanced while maintaining a desired speed of tracking. The experimentally measured reference tracking, disturbance rejection, and noise sensitivity are good and agree with theoretical expectations
Standard and exotic interpretations of the atmospheric neutrino data
The present status of some theoretical interpretations of the atmospheric
neutrino deficit is briefly discussed. Specifically, we show the results for
the FC mechanism and for the standard oscillation hypothesis, both in the
active and in the sterile channels. All these mechanisms are able to fit the
present data to a good statistical level. Among them, the nu_mu --> nu_tau
oscillation is certainly the best explanation to the atmospheric neutrino
deficit, providing a remarkably good agreement with the data.Comment: 3 pages, 2 figures, talk delivered at the 6th International Workshop
on Topics in Astroparticle and Underground Physics (TAUP 99), September 1999,
Paris, (to appear in the Conference Proceedings, Nucl. Phys. B (Proc.
Suppl.), eds. M. Froissart, J. Dumarchez and D. Vignaud
Imperfect Church, Perfect God
Jesusâ death on the cross demonstrates the most radical act of love. So when the church, which is biblically supposed to reflect Jesusâ love, causes pain and disagreements, there is no doubt as to why people choose to leave, completely stay away from the church, or lose their faith altogether. Despite this, the solution remains in Jesus. Through His ministry represented in scripture, one can see the way in which the church is called to care for the world. Despite this, the church has come short of Jesusâ example, often skewing peopleâs perspective on Christ. When on Earth, Jesus defied religion again and again. He healed on the sabbath, sat at a table of tax collectors, and touched lepers. Despite Jesusâ example, many Christians, similar to the Pharisees, are caught up in religious acts focusing on the rituals, laws, and rules of a religion. Jesus did not come to Earth to see people have religion or be hurt. He came for relationships and freedom. While Jesus designed the church to reflect His love, Satan has belittled aspects of the church to a list of rules and regulations which has pushed many away from the church, and even their belief in Christ altogether
The cluster environments of radio loud quasars
We have carried out multi-colour imaging of the fields of a statistically
complete sample of low-frequency selected radio loud quasars at 0.6<z<1.1, in
order to determine the characteristics of their environments. The largest radio
sources are located in the field, and smaller steep-spectrum sources are more
likely to be found in richer environments, from compact groups through to
clusters. This radio-based selection (including source size) of high redshift
groups and clusters is a highly efficient method of detecting rich environments
at these redshifts. Although our single filter clustering measures agree with
those of other workers, we show that these statistics cannot be used reliably
on fields individually, colour information is required for this.Comment: 5 pages, 3 figures, contribution to "Tracing Cosmic Evolution with
Galaxy Clusters" (Sesto 2001), ASP Conference Serie
Tunable-filter imaging of quasar fields at z ~ 1. II. The star-forming galaxy environments of radio-loud quasars
We have scanned the fields of six radio-loud quasars using the Taurus Tunable
Filter to detect redshifted [OII] 3727 line-emitting galaxies at redshifts 0.8
< z < 1.3. Forty-seven new emission-line galaxy (ELG) candidates are found.
This number corresponds to an average space density about 100 times that found
locally and, at L([OII]) < 10^{42} erg s^{-1} cm^{-2}, is 2 - 5 times greater
than the field ELG density at similar redshifts, implying that radio-loud
quasars inhabit sites of above-average star formation activity. The implied
star-formation rates are consistent with surveys of field galaxies at z ~ 1.
However, the variation in candidate density between fields is large and
indicative of a range of environments, from the field to rich clusters. The ELG
candidates also cluster -- both spatially and in terms of velocity -- about the
radio sources. In fields known to contain rich galaxy clusters, the ELGs lie at
the edges and outside the concentrated cores of red, evolved galaxies,
consistent with the morphology-density relation seen in low-redshift clusters.
This work, combined with other studies, suggests that the ELG environments of
powerful AGN look very much the same from moderate to high redshifts, i.e. 0.8
< z < 4.Comment: 18 pages, 18 figures, uses emulateapj.cls. Accepted for publication
in A
Simple supersymmetric solution to the strong CP problem
It is shown that the minimal supersymmetric left-right model can provide a
natural solution to the strong {\it CP} problem without the need for an axion,
nor any additional symmetries beyond supersymmetry and parity.Comment: Plain Latex. 10 pages, including two figures which are part of the
Latex file. Shortened version, to appear in Phys. Rev. Lett. 7
A Simple Grand Unified Relation between Neutrino Mixing and Quark Mixing
It is proposed that all flavor mixing is caused by the mixing of the three
quark and lepton families with vectorlike fermions in 5 + 5-bar multiplets of
SU(5). This simple assumption implies that both V_{CKM} and U_{MNS} are
generated by a single matrix. The entire 3-by-3 complex mass matrix of the
neutrinos M_{nu} is then found to have a simple expression in terms of two
complex parameters and an overall scale. Thus, all the presently unknown
neutrino parameters are predicted. The best fits are for theta_{atm} less than
or approximately 40 degrees. The leptonic Dirac CP phase is found to be
somewhat greater than pi radians.Comment: 10 pages, 4 figures, one table. Typos correcte
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