Zero Cross Research Articles

Application of Artificial Neural Network Model in Estimation of Wave Spectra

Estimation of a wave spectrum from specified values of significant wave heights and average zero cross periods is traditionally made through empirical equations like those of Pierson — Moskowitz and Jonswap. This technical note discusses an alternative scheme based on artificial neural network. Wave spectral distribution over various wave frequencies was obtained for given values of significant wave height and period using feedforward back-propagation network. The rider buoy data at a site off the United States coast monitored by the National Data Buoy Center was used as a basis for network development. Qualitative as well as quantitative comparisons of the network-yielded spectra with target spectra indicated that the developed network could model the wave spectral shapes in a better way than commonly used theoretical spectra.

Minimization of Dissipated Energy in Position Control System Considering the Friction of Gears

This paper discusses on optimal current and velocity functions which minimize the dissipated energy of a servo system with a reduction gear train. Coulomb friction of the gears is represented by the efficiency of the gears and assumed to be proportional to the absolute value of the current of a motor. The optimal functions can be obtained from an optimal control theory by introducing a zero cross time tc, when the current is changed from positive to negative. As the dissipated energy can be given as a function of tc, the optimal zero cross time tc* minimizing the energy can be represented by a simple function of the efficiency of the gears. This method is expanded into the case including the viscous friction in addition to the Coulomb friction. The influence of the viscous frictional coefficient upon the optimal zero cross time tc* is examined by simulations. The expression of the Coulomb and the viscous frictions is verified by experiments using planetary gears with a DC motor.

Upper facial muscle activity and survival after hypoxic insult in rats

Spontaneous cerebral biopotentials were monitored during and after hypoxic insults in 30 ketamine-anesthetized rats. Upper facial electromyographic (EMG, mean integrated amplitude) and electroencephalographic (mean zero cross frequency (ZXF) and mean integrated amplitude (MIA] data were recorded within 30 min after reoxygenation and cardiopulmonary resuscitation. The animals were separated into 2 groups based on 24 h survival. EMG in Survivors (n = 16) recovered regularly to pre-insult levels by 30 min after resuscitation. At this time, EMG activity was consistently low in Non-survivors. In contrast, ZXF and MIA, albeit sensitive hypoxia detectors, did not totally discriminate between Survivors and Non-survivors. Absent EMG in Non-survivors may have reflected irreversible hypoxic damage at the brainstem level.

A Generalized Analysis of Zero Cross over Timing Systems for Semiconductor Detectors

A generalized analysis of zero cross-over timing systems is developed and applied to the case of germanium planar detectors to determine operating parameters which give smallest timing dispersion under the constraints of available charge-sensitive preamplifier risetimes. Charts are given using normalized values to indicate these parameters. The conclusions are verified by experimental results published elsewhere.

Optically Detected Spin Locking of Zero Field Electronic Triplet States and Cross Relaxation in the Rotating Frame

The spin locking method known from NMR is shown to be useful also in ESR for investigating spin lattice relaxation problems and “slow” motions, e. g. questions of energy transfer by triplet states in organic molecular crystals, and probing of nuclear quadrupolar splittings even smaller than the ESR line width at zero magnetic field. Optically detected ESR spin locking experiments for isolated triplet states in zero field are demonstrated. It is shown how the complication of incoming and decaying triplet states and relaxation between all three triplet sublevels has to be handled during spin locking. An application, the study of the cross-relaxation between electronic triplet spin states and deuteron or proton spins is presented. These experiments are possible in spite of the first order quenching of the hyperfine coupling in zero magnetic field. Another application is briefly mentioned, in which the adiabatically demagnetized state in the rotating frame is used to probe the electronic triplet state transfer and nuclear spin lattice relaxation.