PubMed · 7390532
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R W Barnes. 1980. Conversion errors in 4-bit flash analog-to-digital converters.. https://doi.org/10.1109/tbme.1980.326743
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In the development of suitable standards and calibration materials for fluorescence measurement, it becomes necessary to make accurate fluorescence measurements of these materials on flow cytometers. The results of such measurements may be affected by numerous sources of error, prominent among which are deviations of logarithmic amplifiers (log amps) from ideal response. To minimize the deleterious effects of log amps and multicolor fluorescence compensation circuitry on measurements, we built a flow cytometer with electronics incorporating high-precision peak detectors usable over a range from below 2 mV to 10 V, and we developed data acquisition software that transfers held peak values to a commercial 16-bit data acquisition system mounted in a personal computer running Windows 95. Fluorescence compensation is done in software, and transformation of the compensated data from a 16-bit linear to an 8-bit, 4-decade logarithmic scale is accomplished using a look-up table. Although dynamic range may be restricted by noise in the data acquisition system, high sensitivity can be achieved by photomultiplier tube gain adjustment, and it is likely that the use of a lower noise data acquisition system and/or digital processing of pulse information will enable operation over the full 4-decade dynamic range. Even at its current performance level, our instrument provides substantially better linearity over most of the scale than can be obtained using conventional electronics incorporating log amps; we believe this characteristic is critical for use in standards development.
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This study compared the fine control of forces generated by the tongue, lips and fingers in middle-aged adults. The aims were to determine whether (1) the articulatory organs (tongue, lips) and fingers differed in the manner of motor control, (2) force control of the various articulatory organs was similar, and (3) control of forces generated by males was different from that of forces generated by females. The relation among several variables of the ramp-and-hold force contraction and target force level was quantified for the articulatory organs and the fingers in 14 normal individuals (7 males and 7 females). Using visual feedback, participants produced ramp-and-hold compression forces as rapidly and accurately as possible to targets ranging from 0.25 to 2 N. The results showed differences in the profiles of forces generated by the articulatory organs and fingers. In particular, the forefingers were characterized by a greater accuracy of force control and precision of movement, a greater stability of the hold phase, but by slower velocities than the articulatory organs. Motor control of the lower lip differed from that of the upper lip and tongue. Mostly, the lower lip was characterized by a greater precision of contraction, faster development of the force, and greater stability of the hold phase than the upper lip and tongue. Gender was a distinguishing factor in the force task; males were able to produce forces with higher velocities and greater precision than females.