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.     

Arts education partnerships: sources of harmony and dissonance with cultural institutions’ collaborative efforts

ABSTRACT

Due to budget constraints, schools in the United States have increasingly turned to community arts organizations for support. School-community arts partnership stakeholders collaborate because of shared missions to provide students with valuable arts learning experiences. Investigations of these initiatives indicate that these partnerships improve arts learning opportunities and increase public support and resources for arts education. However, not much is known about the experiences and perspectives of the arts organizations that participate in these partnerships. Coordinating collective efforts with a multitude of institutions and interests poses challenges. In this study, we examine survey data collected from arts organization administrators who participated in a large-scale school-community arts partnership initiative. We find that these organizations are generally positive about their impacts on students’ educational outcomes, but there is substantial variation in these views. We also find that organizations differ in their levels of support for these collective efforts. Sources of this variation appear to be attributable to organizations’ preexisting resources and extent to which they are established. While this difference in levels of support is potentially inevitable, we find evidence that the operations handled by the “backbone” organization, i.e. the initiative’s facilitators and overseers, can significantly influence organizations’ levels of support for these efforts. Organizations are more likely to support these collaborative efforts when they believe the backbone organization ensures transparency with initiative operations, provides regular, effective communication, and effectively resolves competing priorities.     

Technical analysis of a Central Asian wall painting detached from a Buddhist cave temple on the northern Silk Road

A great number of Central Asian wall paintings, archeological materials, architectural fragments, and textiles, as well as painting fragments on silk and paper, make up the so called Turfan Collection at the Asian Art Museum in Berlin. The largest part of the collection comes from the Kucha region, a very important cultural center in the third to ninth centuries. Between 1902 and 1914, four German expeditions traveled along the northern Silk Road. During these expeditions, wall paintings were detached from their original settings in Buddhist cave complexes. This paper reports a technical study of a wall painting, existing in eight fragments, from the Buddhist cave no. 40 (Ritterhöhle). Its original painted surface is soot blackened and largely illegible. Grünwedel, leader of the first and third expeditions, described the almost complete destruction of the rediscovered temple complex and evidence of fire damage. The aim of this case study is to identify the materials used for the wall paintings. Furthermore, soot deposits as well as materials from conservation interventions were of interest. Non-invasive analyses were preferred but a limited number of samples were taken to provide more precise information on the painting technique. By employing optical and scanning electron microscopy, energy dispersive X-ray spectroscopy, micro X-ray fluorescence spectroscopy, X-ray diffraction analysis, and Raman spectroscopy, a layer sequence of earthen render, a ground layer made of gypsum, and a paint layer containing a variety of inorganic pigments were identified.     

The Combined Effects of Instructor Communicative Behaviors,Instructor Credibility,and Student Personality Traits on Incivility in the College Classroom

This study investigated the combined role of instructor communication variables (nonverbal immediacy and self-disclosure), instructor credibility (competence, caring, and trustworthiness), and student personality traits (extraversion, neuroticism, agreeableness, conscientiousness, and openness) in predicting students’ uncivil behaviors in class. A total of 406 students completed online questionnaires regarding the instructor of the class they attended prior to the one in which the study was administered. Personality and instructor behavior variables contributed approximately equally to explaining variance in student incivility. Students’ conscientiousness and agreeableness had direct negative relationships with incivility, whereas instructors’ amount and negativity of self-disclosure had direct positive relationships with incivility.     

Intrinsic Versus Extrinsic Motivation: An Approach/Avoidance Reformulation

The main purpose of this article is to advance an alternative perspective on the relationship between intrinsic and extrinsic motivation, and in particular to examine critically the assertion that these processes are antagonistic such that the will to learn for its own sake is inhibited by the presence of extrinsic, tangible rewards and incentives such as school grades. The presumption of an antagonistic relationship largely depends on the theoretical perspective adopted. An alternative interpretation based on need achievement theory leads to distinctly different conclusions. Exploring this new perspective allows one to identify both the conditions under which intrinsic motives may coexist with extrinsic motives as well as to consider some of the means by which intrinsic motives and caring about learning can be stimulated in their own right in school settings.