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boira13 bisSpider's dew La rosada de l'aranya
Why spider webs glisten with dew
Two driving forces acting on wet spider silk help it to capture water.
Janet Fang
spiderweb
The spider's web captures a string of dewy pearls.Janet Fang
Researchers have puzzled out how spider silk is able to catch the morning dew. Their findings may lead to the development of new materials that are able to capture water from the air.
The study, published today in Nature1, examines the silk of the hackled orbweaver spider Uloborus walckenaerius. "Bright, pearl-like water drops hang on thin spider silk in the morning after fogging," says study author Lei Jiang from the Beijing National Laboratory for Molecular Sciences. "It is unexpected and interesting. Human hair can't do that."
Dry spider silk forms a necklace-like structure. Two main fibres support a series of separate rounded 'puffs', each made up of tiny, randomly intertwined nanofibrils. When water vapour condenses onto these puffs, they shrink into densely packed knots, shaped like spindles (or two cones with their bases stuck together). Thinner connecting stretches of nanofibrils, separating the knots, become more apparent; these areas are called 'joints'.
The researchers studied the webs under both electron and light microscopes. They noticed that as water condenses on the web, droplets move towards the nearest spindle-knot, where they coalesce to form larger drops.
The spindle-knots have a rough surface, because the fibrils within them are randomly interweaved. But the joints between the knots have a smooth texture, because their constituent fibrils run parallel to each other. It is this difference in roughness that helps water drops to slide towards the spindle-knots, sticking when they arrive.
The cone shape of the spindle-knots also drives droplets towards their centre. Once they hit the edge of a cone, drops are propelled towards its base, the least curved region, because of the pressure difference caused by surface tension.
Mimicking nature
Guided by their findings, the team made their own artificial spider silk using nylon fibres dipped in a polymer solution that, when dried, formed spindle-knots similar to those in natural spider silk. They anticipate that their studies of these fibres could lead to new materials for collecting water from the air.
"It is impressive that they were able to produce an analogue of wetted [spider] thread that duplicated the properties that they observed," says spider silk expert Brent Opell of Virginia Tech in Blacksburg.
But it doesn't seem likely that natural selection has directed the evolution of this particular spider's silk for water collection, he adds. The spider's thread seems to have evolved to work best when it is dr
La rosada s'observa de matinada, amb nits serenes i encalmades, tot i que no és estrany veure-la tot just després del crepuscle. És més freqüent en llocs baixos i plans que en els cims de les muntanyes. La major part dels dies, quan surt el sol, el terra s'escalfa i les gotes d'aigua desapareixen ràpidament en evaporar-se. Quan l'observador disposa d'instrumental de mesura homologat i en bon estat de funcionament, pot constatar com un augment de la humitat absoluta i/o un descens de la temperatura en la capa d'aire més propera a terra són condicions necessàries per a la formació de la rosada. Cal insistir que la rosada no és un tipus de precipitació des d'un núvol. La rosada va associada a humitats relatives altes, habitualment superiors al 80%.[1]
Degut a la seva dependència del balanç de radiació, les quantitat de radiació poden arribar a un màxim teòric de 0,8 mm per nit, tanmateix, rarament excedeixen de 0,5 mm. i de 40 a 50 mm per any.[2] A la majoria dels climes del món la quantitat de rosada és massa petita per competir amb la pluja. En regions amb estació seca considerable plantes adaptades com els líquens o les plànules de pins es beneficien de la rosada. A gran escala regar sense pluja a llocs com el desert d'Atacama o el Namib es fan capturant la boira no pas la rosada.
Un aparell clàssic de mesurar la rosada és el drosòmetre encara que només proporciona el potencial de formació de rosades. Per a mesurar la quantitat real de rosada es fan servir petits lisímetres o altres mètodes.
boira13 bisSpider's dew La rosada de l'aranya
Why spider webs glisten with dew
Two driving forces acting on wet spider silk help it to capture water.
Janet Fang
spiderweb
The spider's web captures a string of dewy pearls.Janet Fang
Researchers have puzzled out how spider silk is able to catch the morning dew. Their findings may lead to the development of new materials that are able to capture water from the air.
The study, published today in Nature1, examines the silk of the hackled orbweaver spider Uloborus walckenaerius. "Bright, pearl-like water drops hang on thin spider silk in the morning after fogging," says study author Lei Jiang from the Beijing National Laboratory for Molecular Sciences. "It is unexpected and interesting. Human hair can't do that."
Dry spider silk forms a necklace-like structure. Two main fibres support a series of separate rounded 'puffs', each made up of tiny, randomly intertwined nanofibrils. When water vapour condenses onto these puffs, they shrink into densely packed knots, shaped like spindles (or two cones with their bases stuck together). Thinner connecting stretches of nanofibrils, separating the knots, become more apparent; these areas are called 'joints'.
The researchers studied the webs under both electron and light microscopes. They noticed that as water condenses on the web, droplets move towards the nearest spindle-knot, where they coalesce to form larger drops.
The spindle-knots have a rough surface, because the fibrils within them are randomly interweaved. But the joints between the knots have a smooth texture, because their constituent fibrils run parallel to each other. It is this difference in roughness that helps water drops to slide towards the spindle-knots, sticking when they arrive.
The cone shape of the spindle-knots also drives droplets towards their centre. Once they hit the edge of a cone, drops are propelled towards its base, the least curved region, because of the pressure difference caused by surface tension.
Mimicking nature
Guided by their findings, the team made their own artificial spider silk using nylon fibres dipped in a polymer solution that, when dried, formed spindle-knots similar to those in natural spider silk. They anticipate that their studies of these fibres could lead to new materials for collecting water from the air.
"It is impressive that they were able to produce an analogue of wetted [spider] thread that duplicated the properties that they observed," says spider silk expert Brent Opell of Virginia Tech in Blacksburg.
But it doesn't seem likely that natural selection has directed the evolution of this particular spider's silk for water collection, he adds. The spider's thread seems to have evolved to work best when it is dr
La rosada s'observa de matinada, amb nits serenes i encalmades, tot i que no és estrany veure-la tot just després del crepuscle. És més freqüent en llocs baixos i plans que en els cims de les muntanyes. La major part dels dies, quan surt el sol, el terra s'escalfa i les gotes d'aigua desapareixen ràpidament en evaporar-se. Quan l'observador disposa d'instrumental de mesura homologat i en bon estat de funcionament, pot constatar com un augment de la humitat absoluta i/o un descens de la temperatura en la capa d'aire més propera a terra són condicions necessàries per a la formació de la rosada. Cal insistir que la rosada no és un tipus de precipitació des d'un núvol. La rosada va associada a humitats relatives altes, habitualment superiors al 80%.[1]
Degut a la seva dependència del balanç de radiació, les quantitat de radiació poden arribar a un màxim teòric de 0,8 mm per nit, tanmateix, rarament excedeixen de 0,5 mm. i de 40 a 50 mm per any.[2] A la majoria dels climes del món la quantitat de rosada és massa petita per competir amb la pluja. En regions amb estació seca considerable plantes adaptades com els líquens o les plànules de pins es beneficien de la rosada. A gran escala regar sense pluja a llocs com el desert d'Atacama o el Namib es fan capturant la boira no pas la rosada.
Un aparell clàssic de mesurar la rosada és el drosòmetre encara que només proporciona el potencial de formació de rosades. Per a mesurar la quantitat real de rosada es fan servir petits lisímetres o altres mètodes.