PubMed · 6169051
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G F Tyers. 1981. T wave sensing with a programmable pacemaker.. https://doi.org/10.1111/j.1540-8159.1981.tb06236.x
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The use of a poly(methylmethacrylate) capillary electrophoresis chip, provided with a high sample load capacity separation system (a 8500 nL separation channel coupled to a 500 nL sample injection channel) and a pair of on-chip conductivity detectors, for zone electrophoresis (ZE) determination of oxalate in urine was studied. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the separations performed on the chip. A low pH of the carrier electrolyte (4.0) provided an adequate selectivity in the separation of oxalate from anionic urine constituents and, at the same time, also a sufficient sensitivity in its conductivity detection. Under our working conditions, this anion could be detected at a 8 x 10(-8) mol/L concentration also in samples containing chloride (a major anionic constituent of urine) at 3.5 x 10(-3) mol/L concentrations. Such a favorable analyte/matrix concentration ratio (in part, attributable to a transient isotachophoresis stacking in the initial phase of the separation) made possible accurate and reproducible (typically, 2-5% relative standard deviation (RSD) values of the peak areas of the analyte in dependence on its concentration in the sample) determination of oxalate in 500 nL volumes of 20-100-fold diluted urine samples. Short analysis times (about 280 s), no sample pretreatment (not considering urine dilution) and reproducible migration times of this analyte (0.5-1.0% RSD values) were characteristic for ZE on the chip. This work indicates general potentialities of the present chip design in rapid ZE analysis of samples containing the analyte(s) at high ionic matrix/analyte concentration ratios.
Humans effortlessly interpret speech and music, whose patterns can contain sound durations up to thousands of milliseconds. How nervous systems measure such long durations is unclear. We show here that model neurons containing physiological slow conductances are 'naturally' sensitive to duration, replicate known duration-sensitive neurons and can be 'tuned' to respond to a wide range of specific durations. In addition, these models reproduce several other properties of duration-sensitive neurons not selected for in model construction. These data, and the widespread presence of slow conductances in nervous systems, suggest that slow conductances might play a major role in duration measurement.
The purpose of this study was to quantify the distortion of electrical fields by skull foramina using an in vitro model. Extracranial voltage generated by current dipoles located inside a human calva immersed in saline were measured when a 4-mm hole was open and when it was blocked with paraffin wax. Dipoles were located either along the internal surface of the bone (superficial dipoles) or at increasing distances from the bone (deep dipoles). With the hole open, extracranial signals had a substantially greater amplitude than with the hole blocked. The locations of the largest voltage values recorded outside the skull depended on the distance of the recording electrode from the hole rather than on the location of the internal dipole. For superficial dipoles, voltage values with the hole open were as much as 116 times greater than when the hole was blocked. Furthermore, when the hole was open, the largest extracranial signals were seen at the hole even when the dipole was 5 to 6 cm away from the hole. The effects of skull holes were less prominent for deep dipoles than for superficial dipoles. Skull discontinuities can be major determinants for the distribution of extracranial EEG signals. These results have implications for EEG interpretation and for source localization.