{"id":25426,"date":"2014-08-21T11:01:36","date_gmt":"2014-08-21T09:01:36","guid":{"rendered":"https:\/\/ocasapiens-dweb.blogautore.repubblica.it\/?p=25426"},"modified":"2021-10-10T15:02:28","modified_gmt":"2021-10-10T13:02:28","slug":"velocita-di-flusso","status":"publish","type":"post","link":"https:\/\/archivio.ocasapiens.org\/index.php\/2014\/08\/21\/velocita-di-flusso\/","title":{"rendered":"Velocit\u00e0 di flusso"},"content":{"rendered":"

Per uscire sui PNAS<\/em> \u00a0– il settimanale dell’Accademia americana delle scienze, not hay – si pu\u00f2 essere presentati da un accademico che provvede all’editing, al posto della peer review. \u00a0Per Patricia Yang, Jonathan Pham, Jerome Choo, David Hu, del Politecnico della Georgia, la procedura sembra aver accelerato la pubblicazione di:<\/p>\n

Duration of urination does not change with body size<\/b><\/em>.<\/em><\/a><\/p>\n

Many urological studies rely on models of animals, such as rats and pigs, but their relation to the human urinary system is poorly understood. Here, we elucidate the hydrodynamics of urination across five orders of magnitude in body mass. Using high-speed videography and flow-rate measurement obtained at Zoo Atlanta, we discover that all mammals above 3 kg in weight empty their bladders over nearly constant duration of 21 \u00b1 13 s. This feat is possible, because larger animals have longer urethras and thus, higher gravitational force and higher flow speed. Smaller mammals are challenged during urination by high viscous and capillary forces that limit their urine to single drops. Our findings reveal that the urethra is a flow-enhancing device, enabling the urinary system to be scaled up by a factor of 3,600 in volume without compromising its function. This study may help to diagnose urinary problems in animals as well as inspire the design of scalable hydrodynamic systems based on those in nature<\/em><\/p>\n

Anche la “significanza” merita di essere citata per esteso<\/p>\n

Animals eject fluids for waste elimination, communication, and defense from predators. These diverse systems all rely on the fundamental principles of fluid mechanics, which we use to predict urination duration across a wide range of mammals. In this study, we report a mathematical model that clarifies misconceptions in urology and unifies the results from 41 independent urological and anatomical studies. The theoretical framework presented may be extended to study fluid ejection from animals, a universal phenomenon that has received little attention.<\/em><\/p>\n

(h\/t Stefano Z.)<\/p>\n

***<\/p>\n

Quanto sopra \u00e8 dedicato ai matematici, biologi, fisici, chimici e altri giullari che l’hanno fatta fuori dal vaso, stando a un chimico per il quale in termodinamica il tempo non esiste e per questo motivo \u00e8 corretto affermare insieme ai creazionisti che in base alla II legge della termodinamica<\/p>\n

Tra qualche altro milione di anni<\/strong>, <\/a>le Dolomiti saranno completamente franate\u2026<\/em><\/p>\n

\u00a0***<\/p>\n

In open access, un paper interessante su Scientific Reports<\/a>, Kaicun Wang della Normale di Pechino ha confrontato i modelli che rappresentavano bene il dimming – dovuto agli aerosol e quindi alle nubi – negli anni 60-70, per vedere se erano altrettanto capaci di prevedere il dimming \u00a0e relativa variazione della radiazione solare negli anni ’90:<\/p>\n