Initial conditioned solutions of a second-order nonlinear conservative differential equation with a periodically varying coefficient

The exact solution of the equation

$\text{d}{}^2\text{x}\text{dt}{}^2\text{+dx+d′f(wt)x}{}^3\text{=0,}$

where d, d' and w are positive constants, and ?(wt) is a rectangular periodic function of time is discussed. The equation describes approximately the transversal movement of a particle in an alternating gradient accelerator. The exact solution is obtained in the form of a composite recurrent relation containing five particular solutions. Each of these solutions corresponds to a specific well-defined area of the phase plane of the initial conditions. The dynamical behaviour and the stability of the movement are examined analytically.     

The lack of representation of educational psychology and school psychology in introductory psychology textbooks

The first goal of this study was to look at the representation of educational and school psychology in introductory psychology textbooks. Research into the representation of other sub‐fields of psychology has been conducted but no research has looked specifically at educational or school psychology. The second goal was to compare the representation of educational and school psychology in introductory psychology textbooks to see if one or the other is receiving more coverage. Third, the textbooks with the most coverage were listed in order to aid educational and school psychologists teaching introductory psychology courses in selecting textbooks that adequately cover material from their sub‐fields. A total of 57 introductory psychology textbooks were content analyzed: 65% of the introductory psychology textbooks had educational psychology material and 65% had school psychology material. However, in the textbooks containing this material the educational and school psychology material made up only .29% and .19% of the textbooks’ total content.     

Assessing emergent literacy in preschool classrooms

Recent research on the literacy development of children during the preschool years has emphasized the notion of “emergent literacy,” according to authors Kontos (1986) and Teale and Sulzby (1986). According to this view, preschool children learn about reading and writing as they participate in a literate culture. Early social interactions involving print are crucial to children's reading and writing development, according to the Early Childhood and Literacy Development Committee (1986).     

The impact of body image and Afrocentric appearance on sexual refusal self-efficacy in early adolescent African American girls

Research examining the association between body image and sexual risk-taking has been mostly limited to clinical and/or White female samples. It is unclear whether body image plays a role in sexual risk-taking among African American early adolescent females. Moreover, research has neglected to consider body image within a cultural and ethnic framework. A positive sense of Afrocentric appearance may influence, either positively or negatively, sexual attitudes and behaviors among African American early adolescent girls. The purpose of this study, conducted with 156 urban African American early adolescent females, was to examine the relationships among body image, Afrocentric appearance, and sexual refusal self-efficacy. Results found no significant association between body image and sexual refusal self-efficacy. However, structural equation modeling found that a positive sense of Afrocentric appearance significantly predicted increased sexual refusal self-efficacy. Implications of this study in regard to culturally-based teenage pregnancy prevention and education initiatives are discussed.     

Telecommunications (non-broadcasting)

Martin C.J. Elton, William A. Lucas, and David W. Conrath, eds. Evaluating New Telecommunications Services (New York: Plenum Press, 1978—$59.50)

Harold Issadore Sharlin, Lord Kelvin: The Dynamic Victorian (University Park: Pennsylvania State University Press, 1979 —$16.00)     

Energy expenditure in professional flat jockeys using doubly labelled water during the racing season: Implications for body weight management

To formulate individualized dietary strategies for jockeys, it is vital that energy requirements are quantified. We measured total energy expenditure (TEE) over two separate weeks in spring and summer using doubly labelled water in a group of male flat jockeys (n?=?8, 36.9?±?5.7 years, 164?±?8?cm, 54.6?±?2.5?kg). Total energy intake (TEI) was self-recorded, as were all riding and structured exercise activity. Mean daily TEE was 10.83 (±2.3) and 10.66 (±1.76) MJ, (p?=?.61) respectively. Self-reported TEI were 6.03 (±1.7) and 5.37 (±1.1) MJ (p?=?.40), respectively, and were significantly lower than TEE (p?=?.01). Mean race rides were 17 (±6) and 13 (±3; p?=?0.37) and horses ridden at morning exercise were 8 (±6) and 7 (±4; p?=?.77) respectively. Additional structured exercise was 76.25 (±95.1) and 52.5 (±80.9) min per week (p?=?.35), respectively. At the individual level, TEE was related to body mass and the level of non-racing physical activity, but not riding. Physical activity levels for TEE were 1.76 (±0.37) and 1.69 (±0.27; p?=?.59) and appear modest when compared with other athletes, and similar to age-matched non-athletes, suggesting that conventional sport-specific nutritional recommendations do not appear applicable. The large discrepancy between TEE and TEI suggests significant under reporting of dietary intake. These data now provide an appropriate framework from which to formulate jockey nutritional guidelines to promote the ability to achieve the daily weight target and improve athlete welfare.     

Parasympathetic activity delayed after self-paced exercise

The main purpose of this study was to compare the effect of the constant load and self-paced exercise with similar total work on autonomic control after endurance exercise. Ten physically active men were submitted to (i) a maximal incremental exercise test, (ii) a 4-km cycling time trial (4-km TT), and (iii) a constant workload test with identical total external work performed at 4-km TT. Gas exchange was measured throughout the tests, while blood lactate, heart rate, and heart rate variability (HRV) were measured during the passive recovery. Power output measured at the last lap (i.e. 3600–4000?m) of 4-km TT (316?±?89?W) was statistically higher than power output measured at the end of the constant workload exercise (211?±?42?W). The 4-km TT produced higher values of blood lactate concentration (8.8?±?2.1?mmol?L^?1) than the constant workload test (7.8?±?2.1?mmol?L^?1). The heart rate recovery measured at 60?s (constant workload: 37?±?7?bpm; 4-km TT: 30?±?6) and 120?s (constant workload: 57?±?9?bpm; 4-km TT: 51?±?9?bpm) were higher in the constant workload than in the self-paced exercise. The HRV (i.e. RMSSD30s) was statistically higher in the constant load exercise measured at 120, 420, 450, 480, 540, and 570?s than the self-paced exercise. These findings suggest that the autonomic control responses were dependent of the endurance exercise modalities, with parasympathetic activity being delayed after self-paced exercise, as evidenced by post-exercise heart rate indices.     

Career adaptability and associations with personality traits and pathological traits utilizing network analysis

This study investigated relationships between career adaptability and personality and pathological traits using the network analysis approach. We administered CAAS, BFI-2-S, and IDCP-2 to 630 working adults. We observed positive associations between personality and career adaptability and negative associations between pathological traits and career adaptability. This paper contributes to the understanding of the associations between career adaptability and Big Five personality traits and pathological traits. We found stronger associations between career adaptability and personality traits as compared to pathological traits. Our findings suggest that Neuroticism and Conscientiousness contribute more to adaptation to professional development tasks than do pathological traits.