Ep Data Research Articles

Signal to noise ratio and response variability measurements in single trial evoked potentials

Techniques were developed for measurement of signal to noise ratio and response variability in single trial evoked potentials. These techniques were extended and verified using a digital computer simulation of signal plus noise trials. When applied to real data the measures appear to have high reliability and to demonstrate that human evoked potentials are more variable than would be expected from background noise variation alone. Empirical equations are presented which can be applied to existing single trial EP data to estimate both signal-to-noise ratio and its expected variance.

Simple parametrizations of parton distributions with Q2dependence given by asymptotic freedom

We show that the Q 2dependence of parton distributions as given by asymptotically free gauge theories can be represented by simple analytic expressions. In particular the sea distributions can be read directly from the first two moments. We compare our results with the SLAC ep data and with the recent Fermilab μp data. The agreement is good.

Asymptotic freedom beyond the leading order

We make a quantitative analysis of the full g 2 interaction corrections to the leading Q 2 dependence of νW 2 at x ⩾ 0.4, as given by an asymptotically free gauge theory. It turns out that due to partial cancellations between various contributions the g 2 corrections are small. The best fit with the SLAC ep data after including the g 2 corrections is almost identical to that without these corrections, the only effect being a change in Λ, the one free parameter, which sets the scale of the theory. On the other hand the effect of including target mass corrections is to improve the agreement of the prediction for νW 2 ep with data for large values of x. We study the implications of g 2 and target mass corrections for R = σ L/ σ L and conclude, in agreement with other authors, that although both types of corrections are vital they do not account for values of R for x ⩾ 0.5 as measured at SLAC.

The spectral sensitivities of isolated human color mechanisms determined from contrast evoked potential measurements

Previous attempts to measure human spectral sensitivity curves by physiological methods have not yielded results with the precision and over a sufficiently wide intensity range to enable useful predictions to be made about the fine details of color vision. In the present experiment we have used a contrast evoked response technique to measure a set of spectral sensitivities whose quality is comparable to that of psychophysically obtained data. For this purpose a visual stimulus was prepared that would presumably be seen as a pattern by only one color mechanism. The EP data obtained from one rod-monochromat correspond well with the CIE 1951 scotopic relative luminous efficiency function, whereas the data from normal and dichromatic subjects resemble several of Stiles' πμ mechanisms. At the long wavelength end of the visible spectrum the relative peak sensitivities and the shapes of the spectral sensitivity functions closely agree with Stiles' π4 and π5 mechanisms. The spectral sensitivity of the short wavelength mechanism had the form of either the π1 or π3 mechanism. The dichromat results can be fitted by the same mechanisms. The long wavelength mechanism of a protanope resembled π4 and that of a deuteranope π5.

A Critical Appraisal of Some Popular Laboratory Electrochemical Tests for Predicting the Localized Corrosion Resistance of Stainless Alloys in Sea Water

Abstract Evidence is presented to demonstrate that although the critical pitting potential is qualitatively related to the resistance of a material to passivity breakdown by pit initiation, it is of questionable value in predicting the corrosion performance off a structure containing crevices. Experiments conducted on a 30Cr-3Mo-Fe alloy indicated total immunity to passivity breakdown by pit initiation during anodic polarization in 1M NaCl and under freely corroding conditions in acidified 10% FeCl3. However, on specimens containing an artificial crevice, passivity breakdown by crevice corrosion initiation was observed in the same two media. The long term implications of these data were confirmed by 16 month immersion tests in sea water, where severe crevice attack was noted equal in extent to that observed on A9SS Types 304 and 316 stainless steels whose pit initiation properties were considerably inferior to those of the 30Cr-3Mo-Fe alloy. The results of cyclic potentiodynamic anodic polarization experiments conducted on A8S1 Type 430 stainless steel are presented to demonstrate that the so called protection potential, Ep, is not a unique material parameter. It is shown that Ep varies in a semi logarithmic manner with the amount of localized attack induced by polarization; that is, with the chemistry changes in the growing pit caused by hydrolysis of corrosion products and chloride ion buildup in the pit cavities. On this basis, it is concluded that Ep data (however determined) cannot be used alone as a criteria for protection against the propagation of pre-existing pits or crevices in an engineering structure. Based on cyclic polarization procedures, a method of assessing the susceptibility and resistance of an alloy to crevice corrosion is suggested. It is shown that, for alloys which initiate pits during anodic polarization, the magnitude of the “difference potential” (Ec-Ep) is related to the crevice corrosion weight loss. For alloys that have no critical pitting potential, the presence of hysteresis during cyclic polarization with an artificial crevice indicates susceptibility to crevice corrosion.

Deep inelastic eN scattering and the structure of the nucleon

Structure functions νW 2 and 2 MW 1 were constructed from a 3-quark-boson Ylon model with local interaction assumption. With the co ntribution from n ϱ + channel (15%) obtained by T.D. Lee, excellent simultaneous fits to νW 2 and 2 MW 1 ep data were obtained.