Data tables for Ar/Ar geochronology and paleomagnetic analyses for Rajahmundry basalt samples. <br>
Any review of adolescent lifestyles in our society will reveal more than a dozen forces converging to push sleep/arousal balance away from sleep and toward ever-higher arousal. harm could there be in trying to push back a little toward valuing The potential benefits, according to Dr. Dahl, seem enormous. ADOLESCENTS often get with relatively little sleep, but it may be far less than they need. The observations of many parents, educators, and clinicians are in close agreement with a wealth of scientific data about growing frequency of this worrisome pattern of behavior. As discussed in other articles in this special section, there has been recent progress in understanding many of factors that contribute to adolescent sleep loss, including role of early school starting times and role of various biological and social influences on adolescents' self-selected bedtimes. The increasing evidence that teenagers seem to be getting less sleep leads inevitably to pragmatic question How much sleep do adolescents really need? Unfortunately, medical/scientific answer to this question seems tautological. Sufficient sleep is defined as the amount necessary to permit optimal daytime functioning. As impractical as that answer may appear, there are two important reasons for such a definition. First, sleep requirements can be remarkably different across individuals. Second, at a physiological level, sleep and waking states are closely intertwined aspects of a larger system of arousal regulation. (Sleep researchers often use Chinese symbol of yin/yang to designate interrelationship of sleep/wake states.) At center of this discussion is a critical and pragmatic point: any evaluation of sleep habits of adolescents must include a careful consideration of waking consequences of sleep loss. The question becomes, in essence, What are daytime signs of diminished functioning that indicate insufficient sleep? While there is a shortage of well-controlled research studies that seek to answer this question, this article focuses on convergence of evidence suggesting that changes in mood and motivation are among most important effects of sleep loss. Thus an important place to begin looking for evidence of insufficient sleep among adolescents is in area of emotional or behavioral difficulties. There is no shortage of epidemiological and clinical studies documenting recent increases in rates of many psychiatric disorders among adolescents. Certainly many complex factors are likely to have contributed to emotional and behavioral problems of teenagers, but possible link to adolescent sleep patterns bears some scrutiny. There is clear evidence that sleep loss can lead to development or exacerbation of behavioral and emotional problems.1 The key question is How great is contribution of sleep deprivation to these problems? The magnitude of this link remains an open question that can only be answered through careful empirical research. In meantime, these issues have enormous ramifications for fields of medicine and education with regard both to physical and mental health of adolescents and to detriments to effective learning and social development. Many policy decisions will be influenced by our understanding and interpretation of importance of sleep in these areas. In this article I provide an overview of current scientific and clinical information regarding consequences of insufficient sleep in adolescents. I pay particular attention to links between sleep and emotional regulation. The following is a brief outline of main points to be presented: 1. Sleepiness. This is most direct consequence of adolescent sleep loss, and it manifests itself most significantly in difficulty getting up on time for school and in falling asleep in school. …
Zeolites have been used successfully for over 30 years to separate small molecules of almost identical physical and chemical properties, relying on shape differences such as normal from branched paraffins. Many zeolites have approximately circular windows and these are the only ones used in current applications. As of today, the structures of 176 zeolites are available; many of them have windows that may be described as elliptic or irregular, presenting many opportunities for shape selective catalysis or adsorption. A molecule approaching a window may take a number of orientations, and it is difficult to visualize the three-dimensional shape and the best fit to the window. Search engines are needed to accelerate the discovery of one or more zeolite windows that can separate a given pair of molecules. A great deal of progress has already been made to construct such search engines, and innovative industrial processes may follow in the future.
Abstract YSZ‐Membran‐Elektroden (durch 9% Y 2 O 3 stabilisiertes ZrO 2 ) zeigen als pH ‐ Sensoren gute Stabilität (bes.
On page 1287, E. A. Zimmermann and R. O. Ritchie discuss how human cortical bone's hierarchical structure resists deformation and crack growth through physics-based mechanisms at small and large length-scales, which are essential to resist fracture. Using synchrotron micro-computed tomography, the three-dimensional structure of human cortical bone, with its vascular canals at the center of each osteon (in green), can be observed resisting the propagation of a crack (in yellow) through crack-tip shielding mechanisms, such as uncracked ligament bridging.