Trustmyscience : Comment fonctionne un moteur à explosion ? Et quelle est son origine ? - (Science & Technologie - Mécanique) 1/6

En 1860, le premier moteur à allumage commandé opérationnel par bougie d’allumage est créé : il s’agit d’un moteur à deux temps utilisant du gaz de houille comme carburant. Ce dernier a été inventé par Étienne Lenoir (un inventeur belge, de son nom complet Jean-Joseph Étienne Lenoir) et est l’ancêtre des moteurs que nous utilisons (notamment) aujourd’hui dans nos véhicules. Dans cet article, nous mettons en lumière les origines du moteur à explosion.

En réalité, il faut savoir qu’un tel mécanisme avait déjà été mis au point, dès 1690, par le physicien Denis Rapin, qui a utilisé la vapeur au sein d’une chaudière extérieure au moteur. Malheureusement, ce système était instable et donc inutilisable. Par la suite, il a été indispensable de décomposer le moteur en plusieurs éléments séparés, mais cela entraînait une perte de chaleur, et donc, une diminution du rendement…

Le fonctionnement du moteur à simple effet et à deux temps, surnommé « moteur dilaté par la combustion du gaz de l’éclairage enflammé par l’électricité » par Étienne Lenoir, lorsqu’il déposa son brevet pour sa création, le 24 janvier 1860, peut se résumer ainsi :

Dans un premier temps, le piston s’éloigne du fond du cylindre, aspire le mélange de gaz d’éclairage (à l’origine, il désigne le gaz de houille, car il était destiné à l’éclairage : le terme gaz d’éclairage renvoie à la technique permettant d’éclairer à partir d’un gaz) et d’air ; vers le milieu de sa course, l’ouverture d’aspiration est fermée, une étincelle éclate au fond du cylindre et produit l’explosion ; la fin de la course est motrice du fait de la détente des gaz brûlés. Puis, dans un second temps, le piston, en revenant en arrière par l’effet d’une bielle (soit une pièce dotée de deux articulations, une à chaque extrémité, dans le but de transmettre une forme, un mouvement, ou une position), chasse dehors les gaz de combustion par une soupape d’échappement commandée mécaniquement par le moteur.

Il faut savoir que ce moteur est littéralement l’ancêtre de ceux qui se trouvent aujourd’hui dans la plupart des véhicules que nous utilisons.

(à suivre)

Martha Schaefer, Brad Schaefer, Jim Stamm; Music & License : Picture Rocks Sun Dagger (Science & Technology - Astronomy picture of the day)

2020 August 5
Picture Rocks Sun Dagger
Video Credit & Copyright: Martha Schaefer, Brad Schaefer, Jim Stamm; Music & License: Awakening (Wojciech Usarewicz), Lone Tree Music

Explanation: Ancient sun daggers will not hurt you, but they may tell you the time.  A sun dagger is a dagger-shaped gap in a shadow created by sunlight streaming through a crevice in a nearby rock. Starting over a thousand year ago, native people of the American southwest carved spiral petroglyphs into rocks that became illuminated by sun daggers in different ways as the Sun shifts in the sky. A type of sundial, where the end of the sundagger points in the spiral at high noon (for example) indicates a time of year, possibly illuminating a solstice or equinox.  Sun daggers are thought to have been used by Sun Priests during lone vigils with prayers and offerings.  Of the few known, the featured video discusses the historic Picture Rocks Sun Dagger near Tucson, Arizona, USA, likely created by a Hohokam Sun Priest around 1000 AD. 

Robert Gendler & Roberto Colombari : NGC 2442: Galaxy in Volans (Science & Technology - Astronomy picture of the day)

2020 August 4

NGC 2442: Galaxy in Volans
Image Credit & Copyright: Processing: Robert Gendler & Roberto Colombari
Data: Hubble Legacy Archive, European Southern Observatory

Explanation: Distorted galaxy NGC 2442 can be found in the southern constellation of the flying fish, (Piscis) Volans. Located about 50 million light-years away, the galaxy's two spiral arms extending from a pronounced central bar have a hook-like appearance in wide-field images. But this mosaicked close-up, constructed from Hubble Space Telescope and European Southern Observatory data, follows the galaxy's structure in amazing detail. Obscuring dust lanes, young blue star clusters and reddish star forming regions surround a core of yellowish light from an older population of stars. The sharp image data also reveal more distant background galaxies seen right through NGC 2442's star clusters and nebulae. The image spans about 75,000 light-years at the estimated distance of NGC 2442.

Leonard Cohen : "Anthem" - Music - Live - Video

Damia Bouic : Two Worlds, One Sun - Science & Technology - Astronomy picture of the day

2020 August 2
Two Worlds, One Sun
Left Image Credit & Copyright: Damia Bouic;
Right Image Credit: NASA, JPL-Caltech, MSSS; Digital processing: Damia Bouic

Explanation: How different does sunset appear from Mars than from Earth? For comparison, two images of our common star were taken at sunset, one from Earth and one from Mars. These images were scaled to have same angular width and featured here side-by-side. A quick inspection will reveal that the Sun appears slightly smaller from Mars than from Earth. This makes sense since Mars is 50% further from the Sun than Earth. More striking, perhaps, is that the Martian sunset is noticeably bluer near the Sun than the typically orange colors near the setting Sun from Earth. The reason for the blue hues from Mars is not fully understood, but thought to be related to forward scattering properties of Martian dust. The terrestrial sunset was taken in 2012 March from Marseille, France, while the Martian sunset was captured in 2015 by NASA's robotic Curiosity rover from Gale crater on Mars. Last week a new rover and a helicopter -- onboard Mars 2020 -- launched for Mars.

Chad Leader : The Elephant's Trunk Nebula in Cepheus - Science & Technology - Astronomy picture of the day

2020 August 1
The Elephant's Trunk Nebula in Cepheus
Image Credit & Copyright: Chad Leader

Explanation: Like an illustration in a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission nebula and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Also known as vdB 142, the cosmic elephant's trunk is over 20 light-years long. This detailed close-up view was recorded through narrow band filters that transmit the light from ionized hydrogen and oxygen atoms in the region. The resulting composite highlights the bright swept-back ridges that outline pockets of cool interstellar dust and gas. Such embedded, dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees. This dramatic scene spans a 1 degree wide field of view though, about the size of 2 Full Moons.

Jean-Luc Dauvergne : The Giants of Summer - (Science & Technologie - Astronomy picture of the day)

2020 July 30
The Giants of Summer
Image Credit & Copyright: Jean-Luc Dauvergne

Explanation: As Comet NEOWISE sweeps through northern summer skies, Jupiter and Saturn are shining brightly, near opposition. With Jupiter opposite the Sun on July 14 and Saturn on July 21, the giant planets are still near their closest to planet Earth in 2020. Sharing the constellation Sagittarius they are up all night, and offer their best and brightest views at the telescope. Both captured on July 22 from a balcony in Paris these two sharp telescopic images don't disappoint, showing off what the giant planets are famous for, Saturn's bright rings and Jupiter's Great Red Spot. These giants of the Solar System are worth following during 2020. On December 21, skygazers can watch the once-in-20-year great conjunction of Jupiter and Saturn.

Observador - Portugal : Vacina contre Covid-19 ja està a ser testada nos Estados Unidos (Ciência & Tecnologia - Saude/Medecina)

A vacina desenvolvida pela Moderna, empresa de biotecnologia de Massachussetts, em parceria com o National Institutes of Health, a agência norte-americana de investigação médica, já está a ser testada com a colaboração de 30 mil voluntários, em 87 locais nos Estados Unidos.

Na primeira fase do estudo, os testes mostraram que todos os voluntários apresentaram respostas imunes. O resultado preliminar foi publicado há duas semanas no New England Journal of Medicine e, apesar de desencadear efeitos secundários leves — fadiga, calafrios, dor de cabeça, dor muscular, dor no local da injeção — a resposta imunológica foi positiva.

Nessa altura, os testes foram feitos a apenas 45 adultos saudáveis, com idades entre 18 e 55 anos, que receberam duas vacinas com 28 dias de intervalo. Agora é diferente, com a fase final de testes a envolver 30 mil participantes, incluindo pessoas que estão em grupos de risco — metade recebendo a vacina, de facto, e a outra metade um placebo.

Anthony S. Fauci, o especialista em doenças infecciosas que integra o grupo de trabalhado criado por Donald Trump para lidar com a pandemia, disse em conferência de imprensa, citada pelo Washington Post, que este é “o lançamento de um evento verdadeiramente histórico na história da vacinologia”. Fauci prevê que em nos últimos meses do ano já seja possível saber se a vacina é ou não eficaz.

Em breve deverão começar também outros 30 mil testes em 120 locais por todo o mundo, feitos pela farmacêutica Pfizer, de acordo com o Washigton Post.

Ariel L. Cappelletti : NGC 6188: The Dragons of Ara (Astronomy picture of the day - Science & Technology)

2020 July 28
NGC 6188: The Dragons of Ara
Image Credit & Copyright: Ariel L. Cappelletti

Explanation: Dark shapes with bright edges winging their way through dusty NGC 6188 are tens of light-years long. The emission nebula is found near the edge of an otherwise dark and large molecular cloud in the southern constellation Ara, about 4,000 light-years away. Born in that region only a few million years ago, the massive young stars of the embedded Ara OB1 association sculpt the fantastic shapes and power the nebular glow with stellar winds and intense ultraviolet radiation. The recent star formation itself was likely triggered by winds and supernova explosions, from previous generations of massive stars, that swept up and compressed the molecular gas. The featured image accumulated over 10 hours through a backyard telescope in Córdoba, Argentina and was false-colored using the Hubble palette highlighting emission from sulfur, hydrogen, and oxygen atoms in red, green, and blue hues. The field of view spans about four full Moons, corresponding to about 150 light years at the estimated distance of NGC 6188.

Jeff Dai (TWAN) : Tianwen-1 Mission to Mars (Science & Technology - Astronomy picture of the day)

2020 July 26
Tianwen-1 Mission to Mars
Image Credit & Copyright: Jeff Dai (TWAN)

Explanation: On July 23, this Long March 5 heavy-lift rocket rose into a blue morning sky from China's Hainan Island Wenchang Satellite Launch Center. The rocket carried an orbiter, lander, and rover to ask Heavenly Questions on the ambitious Tianwen-1 mission to Mars. In fact Tianwen-1 was the second of three missions scheduled for a July departure to the Red Planet. The United Arab Emirates launched its Amal (Hope) Mars probe on July 19. NASA's launch of its Mars Perseverance Rover from Cape Canaveral Air Force Station, USA is scheduled for July 30. That is the last planned Mars launch for 2020 though. The minimum-energy launch window for an expedition to Mars is coming to a close in 2020 and will reopen in 2022.