17,478 research outputs found
Design, fabrication and test of a flueric servovalve
Design and performance of pneumatic-input fluidic servovalv
Design, fabrication and test of a flueric servovalve Quarterly report, 28 Sep. - 28 Dec. 1965
Breadboard model of pneumatic-input flueric servovalve test
Development in a biologically inspired spinal neural network for movement control
In two phases, we develop neural network models of spinal circuitry which self-organises into networks with opponent channels for the control of an antagonistic muscle pair. The self-organisation is enabled by spontaneous activity present in the spinal cord. We show that after the process of self-organisation, the networks have developed the possibility to independently control the length and tension of the innerated muscles. This allows the specification of joint angle independent from the specification of joint stiffness. The first network comprises only motorneurons and inhibitory interneurons through which the two channels interact. The inhibitory interneurons prevent saturation of the motorneuron pools, which is a necessary condition for independent control. In the second network, however, the neurons in the motorneuron pools obey the size-principle, which is a threat to the desired invariance of joint angle for varying joint stiffness, because of the different amplification of inputs in the case these inputs are not equal. To restore the desired invariance the second network ha.s been expanded with Renshaw cells. The manner in which they are included in the circuitry corrects the problem caused by the addition of the size-principle. The results obtained from the two models compare favourably with the FLETE-model for spinal circuitry (Bullock & Grossberg, 1991; Bullock et al., HJ93; Bullock & Contreras-Vidal, 1993) which has been successful in explaining several phenomena related to motor control.Fulbright Scholarship; Office of Naval Research (N00014-92-J-1309, N00014-95-1-0409
Limits on Lorentz violation in neutral-Kaon decay
The KLOE collaboration recently reported bounds on the directional dependence
of the lifetime of the short-lived neutral kaon K_S with respect to the cosmic
microwave background dipole anisotropy. We interpret their results in a general
framework developed to probe Lorentz violation in the weak interaction. In this
approach a Lorentz-violating tensor \chi_{\mu\nu} is added to the standard
propagator of the W boson. We derive the K_S decay rate in a naive tree-level
model and calculate the asymmetry for the lifetime. By using the KLOE data the
real vector part of \chi_{\mu\nu} is found to be smaller than 10^-2. We briefly
discuss the theoretical challenges concerning nonleptonic decays.Comment: Presented at the Sixth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 17-21, 2013
Equilibrium of a Brownian particle with coordinate dependent diffusivity and damping: Generalized Boltzmann distribution
Fick's law for coordinate dependent diffusivity is derived. Corresponding
diffusion current in the presence of coordinate dependent diffusivity is
consistent with the form as given by Kramers-Moyal expansion. We have obtained
the equilibrium solution of the corresponding Smoluchowski equation. The
equilibrium distribution is a generalization of the Boltzmann distribution.
This generalized Boltzmann distribution involves an effective potential which
is a function of coordinate dependent diffusivity. We discuss various
implications of the existence of this generalized Boltzmann distribution for
equilibrium of systems with coordinate dependent diffusivity and damping.Comment: 11 pages, 1 figur
Testing Lorentz invariance in orbital electron capture
Searches for Lorentz violation were recently extended to the weak sector, in
particular neutron and nuclear decay [1]. From experiments on forbidden
-decay transitions strong limits in the range of -
were obtained on Lorentz-violating components of the -boson propagator [2].
In order to improve on these limits strong sources have to be considered. In
this Brief Report we study isotopes that undergo orbital electron capture and
allow experiments at high decay rates and low dose. We derive the expressions
for the Lorentz-violating differential decay rate and discuss the options for
competitive experiments and their required precision.Comment: accepted for publication as a Brief Report in Physical Review
Symmetry violations in nuclear and neutron decay
The role of decay as a low-energy probe of physics beyond the
Standard Model is reviewed. Traditional searches for deviations from the
Standard Model structure of the weak interaction in decay are discussed
in the light of constraints from the LHC and the neutrino mass. Limits on the
violation of time-reversal symmetry in decay are compared to the strong
constraints from electric dipole moments. Novel searches for Lorentz symmetry
breaking in the weak interaction in decay are also included, where we
discuss the unique sensitivity of decay to test Lorentz invariance. We
end with a roadmap for future -decay experiments.Comment: Accepted for publication in Rev. Mod. Phys. 86 pages, 13 figure
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