Secondary electron emission from oxide-coated cathodes

The secondary electron emission from alkaline-earth oxide-coated cathodes has been investigated under both continuous and pulsed bombardment. Various factors affecting the yield, such as dependence upon primary voltage, collecting voltage, temperature, time, and angle of incidence, are noted, and the present state of the theory is discussed.Experiments have been performed with three types of apparatus. Yield vs. Energy data reveal values of δ of 4–7 at room temperature, with a more or less flat maximum at approximately 1,000 volts primary energy.The yield increases with temperature in an exponential manner, and plots of log Δδ (i.e. δ_K° ? δ_300°K) vs. 1/T give straight lines. Values of Q₁ between 0.9 – 1.5 eV. are generally indicated, and from extrapolation of these curves, yields exceeding 100 at 850° C. are deduced. The secondary emission depends upon the degree of activation, and increases with enhancement of the thermionic emission characteristics. Short-time effects such as growth or decay of secondary current after the onset of primary bombardment or persistence after the cessation of bombardment have not been observed, and values of yield obtained by pulsed methods are in accord with those obtained under D.C. conditions. Tail phenomena reported by J. B. Johnson and interpreted as “enhanced thermionic emission” from oxidecoated cathodes become manifest only under experimental conditions characterized by certain space-charge effects, and have been effectively simulated by bombarding a tantalum target adjacent to an electron-emitting tungsten filament. Various measurements of the energy distribution of secondary electrons as a function of primary voltage and temperature have been obtained. It was observed that the average energy of the secondary electrons decreases with temperature at a rate which more than compensates for the increase in the number of secondaries emitted per incident primary. The mechanism of the observed dependence of yield upon temperature is not well understood. Various alternative explanations are discussed and, in the light of the present state of our knowledge, regarded as untenable.     

Effects of race and social class on preschool performance on the developmental test of visual-motor integration

The visual-motor integration of preschool children who varied in terms of race, sex, and socioeconomic status was assessed using the Beery-Buktenica Test of Visual-Motor Integration (VMI). An analysis of covariance revealed that there were significant main effects for race, sex, and socioeconomic status. Since, at the three- and four-year level, the VMI was normed only on white suburban children, the results of this study seemed to indicate the need for norms for black children at the preschool level. Thus, the second part of this paper reports normative data for black preschool children on the VMI.     

Sociological and Political Concerns about School Effectiveness Research: Time for a New Research Agenda

In recent years school effectiveness research (SER) has become increasingly criticised for being a socially and politically decontextualised body of literature which provides support for inequitable educational reforms. This article demonstrates that SER proponents have not responded much to these criticisms and suggests that this is primarily because they do not share the same epistemological commitments as their critics. Nevertheless it is argued that the concerns of critics should be taken seriously by SER proponents because they speak powerfully to a number of key problem areas within the SER field. Three such areas are discussed: the overclaiming of SER; the continued undertheorising of SER, and the inability of SER to control the political use of its findings. The article concludes by noting that some SER researchers are attempting to connect more with the sociological and political concerns of their critics and argues that this has to be the key SER agenda for the future.     

The Florida teletraining project: Military training via two‐way compressed video

Abstract

The Florida Teletraining Project tested the feasibility of using community colleges as providers of various types of military training to personnel in the Reserve Components (RC). Training was delivered via the Army's TNET system, which employs two‐way interactive video. Five courses were produced, delivered, and evaluated during the project. Results showed that effective military course reconfiguration can be accomplished by civilian institutions, that the delivery system was technically reliable, that students performed well using specially reconfigured courseware, and that students rated the video teletraining approach as effective. The project demonstrated the potential of two‐way video teletraining for a variety of military training applications for several different levels of military personnel.