Noise spectra of the drain current of ion selective field effect transistors in equilibrium were measured. The spectra differ from one type of ISFET to the other. The ionic activity in solution does not modify perceptibly the noise level for any of the various types of ISFET's. Computer assisted modeling is used to fit experimental data and to assign an equivalent electrical circuit to the electrochemical system. The overall response time of the system is shown to depend on the input capacitance of the electrometer.

Type of publicationArticle (peer-reviewed) Adiabatic techniques using multilevel systems have recently been generalized from the optical case to settings in atom optics, solid state physics, and even classical electrodynamics. The most well known example of these is the so-called stimulated Raman adiabatic passage (STIRAP) process, which allows transfer of a particle between different states with large fidelity. Here we generalize and examine this process for an atomic center-of-mass state with a nontrivial phase distribution and show that even though dark state dynamics can be achieved for the atomic density, the phase dynamics will still have to be considered as a dynamical process. In particular we show that the combination of adiabatic and nonadiabatic behavior can be used to engineer phase superposition states.

Probability density distributions of the interval spacings between zero-crossings of band-limited Nyquist and 1/f noise signals are examined using an interval-to-pulseheight converter and a multichannel pulse-height analyzer. The Nyquist noise distributions follow a simple exponential law, as expected. In the case of 1/f noise, the distributions are approximately proportional to the inverse square of the spacing interval. The probability density is statistically stationary, that is, independent of sample length and independent of the sample selected. For signals in a 1 Hz to 5 kHz band the most probable spacing interval is 1.2×10−4 sec, which occurs with a maximum probability density of 2.2×103 sec−1. The most probable value is inversely proportional to the highest signal frequency present and the peak probability density is proportional to this frequency.

A correlator-amplifier system based on a Hall multiplier improves the sensitivity of low level amplifiers by two to three orders of magnitude. The system is assembled largely from commercial instruments, with the exception of the Hall element itself. Over the frequency interval from 10 cps to 10 kc, the equivalent input noise level ranges from 5×10−15 to 10−19 V2/cycle. The system is capable of detecting correlated signals presented to both inputs in the presence of uncorrelated noise two to three orders of magnitude greater.

Critical-point polarization fluctuations in ferroelectric triglycene sulfate have been observed at the Curie temperature by measuring the random noise voltages appearing between electrodes applied to the crystal. These noise voltages are interpreted in terms of the Nyquist noise associated with the crystal conductance and therefore can be used to determine the true crystal impedance at and near the transition temperature where the crystal is highly nonlinear. The polarization noise density at the Curie point has a simple relaxation spectrum with a time constant of 5.3X10" 3 sec, which furthermore is relatively independent of temperature near the Curie temperature. A thermal Barkhausen noise observed in barium titanate as the crystal is passed slowly through the transition temperature appears to be associated with the inherent domain structure of the sample.