Conceptual Problems in the Foundations of Mechanics

There has been much research on principles and fundamental concepts of mechanics. Problems concerning the law of inertia, the concepts of force, fictitious force, weight, mass and the distinction between inertial and gravitational mass are addressed in the first part of the present paper. It is argued in the second that the law of inertia is the source of these problems. Consequences drawn from the law explain the metaphysical concept of force, the problematic concept of fictitious force, the nominal definition of weight and the difficulty with defining mass operationally. The core of this connection between the law and these consequences lies in the fact that acceleration is a sufficient condition for force. The experimental basis of the law in the course of its history shows, however, that the law presupposes acceleration necessarily whereas acceleration does not presuppose the law. Therefore, there is no inconvenience in taking acceleration independently of the law. This is enough to bypass those problems. Taking into account how force is measured by force meters and how mass is basically determined, by comparison with the standard mass, a minimal meaning for both concepts of force and mass is established. All this converges with several solutions proposed in the course of history and increases the communicability of mechanics, as outlined in the final part of this paper.     

A cross-age study of junior high school students' conceptions of basic astronomy concepts

Junior high school students' astronomy conceptions were analysed by means of a written questionnaire presented to them during the beginning of the first semester. The main findings were as follows: almost half of the students indicated that the cause of the day-night cycle is the Earth spinning on its axis; most students chose as their best account for changes in the Moon's phases the Moon moving around the Earth. Despite that, most students thought that the Moon must be in its Full phase for there to be a total solar eclipse; most students underestimated the distances in the Universe and overestimated the Earth's diameter. A great proportion of students indicated that the reason for the different seasons is the tilt of the Earth's axis relative to the plane of its orbit as it revolves around the Sun. But almost the same number of students chose the varying distance between Sun and Earth or between the Earth, Moon and Sun, as a reason for the seasons. Only a third of the students answered correctly that in Israel's latitude, north of the Tropic of Cancer, the Sun is never directly overhead at noon; most students chose the correct estimate of a month for the Moon revolving around the Earth and a year for the Moon going around the Sun; about a third of the students chose the correct answer that when it is noon in Haifa, it would be about sunset in Beijing (90° east of Haifa). Few students indicated that the fact that we always see the same side of the Moon from the Earth implies that the Moon rotates on its axis once a month.     

La conducta autopunitiva en el autismo: un nuevo enfoque conductual de tratamiento

Resumen

En este trabajo se investigan dos procedimientos de reducción de las conductas autopunitivas que frecuentemente presentan los niños autistas. El primer procedimiento consiste en el reforzamiento de respuestas incompatibles con estas conductas, lográndose así una franca disminución en su frecuencia. El segundo procedimiento parte del supuesto (comprobado en el análisis conductual) que las autopuniciones representan una respuesta de escape ante la ansiedad generada por determinadas situaciones; de este modo, el procedimiento va encaminado a la reducción, o eliminación, de esta ansiedad situacional mediante la técnica de la desensibilización sistemática «in vivo», dando como resultado la eliminación total de las conductas autopunitivas ante estas situaciones, y a más largo plazo, su erradicación del repertorio conductual del sujeto.     

Nature and profiles of racial prejudice: analyses and educational implications in Secondary School students / Naturaleza y perfiles del prejuicio racial: análisis e implicaciones educativas en alumnos de Educación Secundaria

Abstract

The reduction of racial prejudice is an important challenge of intercultural education. Thus, the aim of this study was to analyze racial prejudice, as well as the different profiles and the possible educational implications in secondary school students. A total of 327 third form students completed the scales of blatant and subtle prejudice and also a scale of emotions towards North Africans. The results showed significant levels of subtle prejudice and four profiles of racial prejudice, with a low number of students showing equalitarian tendencies. A multivariate analysis showed significant differences in prejudice depending on social distance as well as the academic level of the participants’ families. Finally, we discuss the results from the perspective of intercultural education and we suggest some lines of intervention in order to promote the integration of students from different cultures.     

Tiny noise,big mistakes: adversarial perturbations induce errors in brain–computer interface spellers

An electroencephalogram (EEG)-based brain–computer interface (BCI) speller allows a user to input text to a computer by thought. It is particularly useful to severely disabled individuals, e.g. amyotrophic lateral sclerosis patients, who have no other effective means of communication with another person or a computer. Most studies so far focused on making EEG-based BCI spellers faster and more reliable; however, few have considered their security. This study, for the first time, shows that P300 and steady-state visual evoked potential BCI spellers are very vulnerable, i.e. they can be severely attacked by adversarial perturbations, which are too tiny to be noticed when added to EEG signals, but can mislead the spellers to spell anything the attacker wants. The consequence could range from merely user frustration to severe misdiagnosis in clinical applications. We hope our research can attract more attention to the security of EEG-based BCI spellers, and more broadly, EEG-based BCIs, which has received little attention before.     

The role of executive functions in the relation between socioeconomic level and the development of reading and maths skills / El rol de las funciones ejecutivas en la relación entre el nivel socioeconómico y el desarrollo de habilidades lectoras y matemáticas

Executive functions (EF) are a set of processes that allow individuals to plan, monitor and organize tasks and thus play a key role in the development of reading and maths skills. Environmental factors such as socioeconomic level (SEL) influence reading and maths skills as well as EFs. The aim of this study is to explore the extent to which executive functions play a mediating role between SEL and reading and maths performance. To this end, we assessed 286 Chilean primary education students: 86 with a high SEL and 200 with a low level. The results show that the high-SEL group obtained consistently higher scores than their peers with low SEL levels in both reading and maths tasks as well as in EF measurements. This suggests that SEL could influence the development of these variables. The results also showed that EFs partially mediate the relation between SEL and reading and maths skills in primary school students through the specific function of inhibition. The results are discussed in light of the effect of SEL on the development of EFs and school learning.     

A Longitudinal Study of Physics Students' Conceptions on Energy in Pre-Service Training for High School Teachers

Journal of Science Education and Technology - How physics students teachers' understanding of energy develops during their pre-service high school teacher university program? How do their...     

Antecedents and consequents of student satisfaction in higher technical-vocational education: evidence from Brazil

International Journal for Educational and Vocational Guidance - This article proposes a model of antecedents and consequences of student satisfaction in Higher Technical-Vocational Education (HTVE)...     

Beyond Rock and Roll: The Economic Impact of the Grateful Dead on a Local Economy

For-profit popular music concerts, a seldom studied event, may create sizeable economic impacts in a local economy. Using information from a survey of more than 1,000 concert goers to a Grateful Dead performance in Las Vegas and RIMS II multipliers, we estimate income and employment impacts. We conclude that the potential large spill-overs effects of such an event should not be ignored. This revised version was published online in August 2006 with corrections to the Cover Date.     

Impact sports and bone fractures among adolescents

The objective of the present study was to investigate the effects of different sports on stress fractures among adolescents during a 9-month follow-up period. The sample was composed of 184 adolescents divided into three groups (impact sports [n = 102]; swimming [n = 35]; non-sports [n = 47]). The occurrence of stress fracture was reported by participants and coaches. As potential confounders we considered age, sex, resistance training, body composition variables and age at peak of height velocity. There were 13 adolescents who reported fractures during the 9-month period. Bone mineral density values were higher in adolescents engaged in impact sports (P-value = 0.002). Independently of confounders, the risk of stress fracture was lower in adolescents engaged in impact sports than in non-active adolescents (hazard ratio [HR] = 0.23 [95% confidence interval (CI) = 0.05 to 0.98]), while swimming practice was not associated to lower risk of fracture (HR = 0.49 [95% CI = 0.09 to 2.55]). In conclusion, the findings from this study indicate the importance of sports participation among adolescents in the reduction of stress fracture risk, especially with impact sports. More importantly, these results could be relevant for recognising adolescents in danger of not reaching their potential for peak bone mass and later an increased risk of fractures.