Joined in 2023 
82 
63 About this deal
One of the most important, yet underappreciated, features of the Arctic sea ice is the ability of its blindingly white surfaces to reflect sunlight. For at least as long as our species has existed, the frozen seas at the top of our world have acted as a massive parasol that helps keep the planet cool and its climate stable.
Terry ground the mirror against the convex disc using ever finer pastes of water mixed with sand, from coarse, gritty grades right down to ground pumice stone as smooth as flour. He then polished it to a high shine on a bed of slightly softened set pitch, or tar, with polishing powder. This is exactly what earlier astronomers did: William Herschel ground his speculum metal mirrors with coarse emery and water; Newton polished his on a bed of pitch while John Hadley similarly used pitch-soaked silk. Left: The coarsest sand used for grinding the mirror. Sand sold in pet shops to line birdcages proved particularly effective! Right: The bed of pitch, also known as the pitch-lap or polishing-lap, on which the mirror was finally polished. Credit: Matthew Howles. Kovalev VA, Eichinger WE (2004) Elastic Lidar: theory, practice, and analysis methods. Wiley-Interscience They said: "From the first statement, we know that Albert is sure that Bernard doesn't know the birthday, so May and June should be ruled out (day 19 only appears in May and day 18 only appears in June). In other words, if Albert had May or June, then he cannot be sure that Bernard doesn’t know, since Bernard could have had 18 or 19.The work underlines that the AM metal mirror fabrication can have an important progress by combining the geometrical design with new high performance MMC materials. However, the integration with the secondary finishing operation and the deformation induced by the assembly are of primary importance to assure the functionality. Hey JV (2014) Design, implementation, and characterization of a novel lidar ceilometer. Springer Cham, London. https://doi.org/10.1007/978-3-319-12613-5 Hilpert E, Hartung J, Risse S, Eberhardt R, Tünnermann A (2018) Precision manufacturing of a lightweight mirror body made by selective laser melting. Precis Eng 53:310–317. https://doi.org/10.1016/j.precisioneng.2018.04.013 The dynamic analysis showed smaller displacements than the case the mirror is assembled via tightening the screws;
Astronomers experimented with different recipes for speculum metal over the centuries, but the two main ingredients were copper and tin. Newton added small amounts of arsenic to his, arguing that it made the metal whiter and more reflective. He did at least take some basic precautionary measures when melting this poisonous substance to make his alloy, ‘bewaring in the mean time, not to draw in breath near the pernicious fumes’ ( Philosophical Transactions of the Royal Society, vol. 7 (1672)). It may sound straightforward enough, but grinding and polishing a speculum metal mirror is not for the faint-hearted. Caroline Herschel, sister of William and herself an accomplished astronomer who went on to discover eight comets, wrote of her ‘attendance on my Brother when polishing, that by way of keeping him alife I was even obliged to feed him by putting the Vitals by bits into his mouth – this was once the case when at the finishing of a 7 foot mirror, he had not left his hands from it for 16 hours together’ (Michael Hoskin (ed.), Caroline Herschel’s Autobiographies (Cambridge, 2003) p. 55). Atkins C, Brzozowski W, Dobson N et al (2019) Lightweighting design optimisation for additively manufactured mirrors. Proceedings Volume 11116, Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems II. https://doi.org/10.1117/12.2528105 The selected configuration allowed a 25% total mass reduction of static balanced mirror (from 415 to 311.8 g), compared with traditional technology (surface with ribs) mirror with geometry optimized for lightness; Dong P, Chen Q (2017) LiDAR remote sensing and applications. CRC Press. https://doi.org/10.4324/9781351233354AlMangour B (2019) Additive manufacturing of emerging materials. Springer Nature, Cham, Switzerland. In the question, you're given 10 dates across four months - May 15, 16, and 19, June 17 and 19, July 14 and 16, and August 14, 15, and 17. Then, you're given a couple of cryptic quotes from Albert, who only knows the month Cheryl was born, and Bernard, who only knows the date. A tweet with almost 7,000 likes said: "How is a zombie virus get buried in a frozen lake? And why did they dig it up? That doesn't even make sense". Zhang K, Qu H, Guan H et al (2021) Design and fabrication technology of metal mirrors based on additive manufacturing: a review. Appl Sci 11(22):10630. https://doi.org/10.3390/app112210630
Great Deal 
New Comment