Teachers' perspectives on the challenges of teaching physical education in urban schools: the student emotional filter

The purpose of this study was to analyze how the challenges of urban schools influence physical education teachers' emotional understanding and connections with their students and the implications on their teaching. Sixty-one elementary physical educators from an urban school district in the midwestern U.S. were interviewed multiple times (N = 136) over 3 years using interpretive methodology. Teachers reported five unique challenges that significantly shaped their thinking about students and their careers, along with strategies they used to overcome or manage those challenges. The challenges were: (a) insufficient instructional resources, (b) implementing culturally relevant pedagogy, (c) dealing with community violence, (d) integrating more games in curricula, and (e) teaching in a culture of basketball. Implications centered on the guilt-inducing nature of urban teaching, developing an informed and realistic vision of urban physical education, and the role of teacher preparation and professional development.     

Climate control through ionization

This paper summarizes some of the experimental evidence of the apparent biological effects produced by atmospheric ionization. Thermionic ion sources are discussed and the results of experimental determinations of their characteristics are presented.     

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.     

Emission of electrons from cold metal surfaces

The results of Del Rosario on cold emission are shown to result from the fact that, through the attainment of specially good vacuum conditions and freedom from contamination, the cold electron current from the wire was suppressed up to field strengths greater than those at which measurable current was obtained in the work of previous observers. It was in fact suppressed beyond the point at which discharge started from points on the welding of the support. The results of Del Rosario are thus probably characteristic of conditions other than those pertaining to the wire, a conclusion which accounts for his current voltage curves. The formula of Fowler and Nordheim is found to apply in the measurable regions in form directly and in magnitude only if irregularities of the surface are such as to raise the field at the surface to a sufficiently high value. Breakdowns after intense heat treatment are studied and found to be caused by immeasurably small currents of electrons knocking ions from the anode. The erratic original curves obtained by previous investigators are found to be caused by successive breakdowns similar to those found after intense heating.