146 research outputs found
A Longitudinal Analysis of Adolescent Substance Use and School Motivation Among African American Youth
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72421/1/1532-7795.1302003.pd
Examining transactional influences between reading achievement and antisocially-behaving friends
The association between poorer academic outcomes and having antisocial friends is reliably demonstrated yet not well understood. Genetically sensitive designs uniquely allow for measuring genetic vulnerabilities and/or environmental risk in the association of antisocial friend behavior and poor school achievement, allowing for a better understanding of the nature of the association. This study included 233 pairs of twins from the Florida Twin Project on Reading. First, the role of antisocial friends as an environmental moderator of reading comprehension was examined. Antisocial friends significantly moderated the nonshared environmental variance in reading comprehension, with increased variation at lower levels of association with antisocial friends, with niche-picking indicated. Second, the role of reading comprehension as an environmental moderator of antisocial friends was examined. Reading comprehension significantly moderated the nonshared environmental variance in associating with antisocial friends, with increased variance at lower levels of reading comprehension and indication that common genetic influences contributed to higher reading achievement and better-behaved friends. In total, these results suggested reciprocal influences between reading achievement and antisocially-behaving friends. The impact of antisocial friends appeared to be limited in the extent to which they can undermine reading achievement, and high reading achievement appeared to support less association with antisocial friends
Self-oscillation
Physicists are very familiar with forced and parametric resonance, but
usually not with self-oscillation, a property of certain dynamical systems that
gives rise to a great variety of vibrations, both useful and destructive. In a
self-oscillator, the driving force is controlled by the oscillation itself so
that it acts in phase with the velocity, causing a negative damping that feeds
energy into the vibration: no external rate needs to be adjusted to the
resonant frequency. The famous collapse of the Tacoma Narrows bridge in 1940,
often attributed by introductory physics texts to forced resonance, was
actually a self-oscillation, as was the swaying of the London Millennium
Footbridge in 2000. Clocks are self-oscillators, as are bowed and wind musical
instruments. The heart is a "relaxation oscillator," i.e., a non-sinusoidal
self-oscillator whose period is determined by sudden, nonlinear switching at
thresholds. We review the general criterion that determines whether a linear
system can self-oscillate. We then describe the limiting cycles of the simplest
nonlinear self-oscillators, as well as the ability of two or more coupled
self-oscillators to become spontaneously synchronized ("entrained"). We
characterize the operation of motors as self-oscillation and prove a theorem
about their limit efficiency, of which Carnot's theorem for heat engines
appears as a special case. We briefly discuss how self-oscillation applies to
servomechanisms, Cepheid variable stars, lasers, and the macroeconomic business
cycle, among other applications. Our emphasis throughout is on the energetics
of self-oscillation, often neglected by the literature on nonlinear dynamical
systems.Comment: 68 pages, 33 figures. v4: Typos fixed and other minor adjustments. To
appear in Physics Report
Whole Brain Size and General Mental Ability: A Review
We review the literature on the relation between whole brain size and general mental ability (GMA) both within and between species. Among humans, in 28 samples using brain imaging techniques, the mean brain size/GMA correlation is 0.40 (N = 1,389; p < 10−10); in 59 samples using external head size measures it is 0.20 (N = 63,405; p < 10−10). In 6 samples using the method of correlated vectors to distill g, the general factor of mental ability, the mean r is 0.63. We also describe the brain size/GMA correlations with age, socioeconomic position, sex, and ancestral population groups, which also provide information about brain–behavior relationships. Finally, we examine brain size and mental ability from an evolutionary and behavior genetic perspective
On the Winning Virtuous Strategies for Ultra High Frequency Electronic Trading in Foreign Currencies Exchange Markets
Proprioceptive gating of inhibitory pathways to hindleg flexor motoneurons in the locust
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