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The dynamic Faraday cup is an electrostatic device used to measure the charge and velocity of a moving charged particle. In this paper, the interaction between a charged particle and a dynamic Faraday cup is described analytically, including the difficult case where the particle is close to but not in the cup. A summation method is used to extract information from the slowly converging series that results from the approximation that we use, and we are able to determine the charge distribution and mutual capacitance of the system. An example of the calculated and measured responses of a typical Faraday cup is provided. The agreement between the calculated and measured response of the cup, given in terms of the standard deviation, is from 4.5 × 10−3 to 9.4 × 10−3 for the inside of the cup and from 3.3 × 10−2 to 3.6 × 10−2 for the outside of the cup.

The human retina consists of an electrically-charged nerve membrane. This potential is a constant value for a given adaptation without stimulation; it is the retinal resting potential. The retinal resting potential causes an electric field around the eyeball, centered on the optical axis, which can be measured by placing electrodes near to the eye. As a result, the motion of the eye causes a measurable change of DC voltage between the surface electrodes. The same vector coordinate system employed in the modern computer mouse may be adapted for use with our electro-ocular interface. Such a device would provide a relative position of gaze and have application in both hands-busy and assistive research. The theory behind our device, hardware design, the experimental results, and efficacy of the system are presented.

This paper presents an experimental study of time-resolved gain in H(2)O, H(2)O-He, and H(2)O-H(2) mixtures as a function of gas composition and excitation current. Utilizing the fast rising (~70 nsec) pulse from H(2)O-He laser as a probe, the amplifier gain was measured with a time resolution of about 100 nsec. The gain was observed to follow the excitation current pulse rather closely indicating that population inversion was established in times less than 100 nsec. This suggested that excitation was most likely by means of rapid cascading from higher levels and/or by direct electron impact. The gain was found to be describable by a two-level rate equation model containing one dominant relaxation rate and assuming immediate excitation of the levels involved by inelastic collisions with electrons. With pure H(2)O, the relaxation rate was proportional to pressure to within 10%, indicating that the upper level was de-excited primarily by c llisions with other H(2)O molecules. At a pressure of 1 Torr the relaxation rate in pure H(2)O was 0.35 +/- 0.05 for the 28-microm transition. The addition of small amounts of foreign gases was observed to increase this relaxation rate, consistent with the measured decrease in the amplifier gain. By subsequently increasing the water vapor pressure it was found possible to optimize the gain at an enhanced level over the pure H(2)O case. The peak gain obtained in water vapor at 1000 A was 0.34 m(-1). Under foreign gas addition this increased to 0.68 m(-l) for the same peak current. In this case the relaxation rate, as a function of the foreign gas (He or H(2)) pressure, remained constant to within 10%, suggesting that these gases at higher concentrations may enhance the system gain by altering the discharge conditions without appreciably collisionally de-exciting the upper laser level.

ordinal scales, grading scales, equivalent scales, arithmetic mean or average, grade or mark conversion, decision-making,