Joined in 2023 
82 
63 About this deal
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. Many functionalities are demanded to this subsystem. Since it is under rotation, the mechanical balancing must be assured through an adequate stabilization to take care of the deformation which may affect the reflective surface. Modern LIDAR systems for aerospace applications require complex optical elements whose performance and lighter weight must be improved to meet growing application requirements. Metallic optics are a good choice to achieve the desired performance. Bottini L (2021) Study of selective laser melting process parameters to improve the obtainable roughness of AlSi10Mg parts. Selected Topics in Manufacturing. pp 121–139. Springer, Cham. https://doi.org/10.1007/978-3-030-57729-2_9 Scientists agree that the beads are well-intentioned, but worry about their potential effects on the Arctic ecosystem. If they float around there indefinitely, “it’s just going to clog up the ocean and mess with the ecosystem,” says Cecilia Bitz, an atmospheric scientist at the University of Washington who specialises in Arctic sea ice. https://www.elementum3d.com/wp-content/uploads/2021/11/A2024-RAM10-Data-Sheets-2021-04-02-FINAL.pdf
The tensile test confirmed the expected mechanical properties of the SLMed MMC, namely a ultimate strength of more than 500 MPa and a Young Modulus of 96 GPa; Nuechterlein J, Iten J (2016) Reactive additive manufacturing. Patent Application Publication No. US2016/0271878A1 Sep.22,2016 Kovalev VA, Eichinger WE (2004) Elastic Lidar: theory, practice, and analysis methods. Wiley-InterscienceField doesn’t want to carpet the Arctic in glass. Instead, she plans on distributing it strategically to protect some particularly fast-melting, vulnerable areas, like the Fram Strait, a thin passage between Greenland and Svalbard. According to results of a climate model she presented last December at the annual meeting of the American Geophysical Union, treating the Fram Strait could lead to large-scale ice regrowth across parts of the Arctic. As well as some beautiful refracting telescopes in this gallery, we currently have one of the very earliest reflecting telescopes on display, generously lent by the Royal Society. It was made in the early 1670s by none other than Sir Isaac Newton and used mirrors to gather light, rather than lenses as found in refracting telescopes. In fact, Newton is often credited with inventing the reflecting telescope – but it’s worth remembering that contemporaries like James Gregory were experimenting with similar designs at this time. Speculum metal might look light and fluid when it’s molten, but it’s actually very heavy: our resulting mirror disc – a modest 6 inches in diameter – weighed about 4kg! Still, that’s peanuts compared to the 6-foot speculum metal mirror from the Great Rosse Telescope in our collection, which weighs in at over 4 tonnes… Casting the molten speculum metal into its mould at Coles Castings Foundry, Dorset. Credit: Matthew Howles.
Newton’s reflecting telescope mirrors were made from an alloy called speculum metal. Essentially a type of bronze, speculum metal has an unusually high tin content – typically about 30% – to give mirrors a suitably silvery, reflective surface. This peculiarity allows the use of precursor materials with a preferred size and shape for a good powder flow. RAM technology utilizes exothermic chemical reactions to synthesize product materials during the additive process to improve printability and properties. The RAM process enables formation of advanced MMCs that combine a metal matrix and high strength reinforcing ceramic or intermetallic phases [ 23]. AlMangour B (2019) Additive manufacturing of emerging materials. Springer Nature, Cham, Switzerland.This would result in a much colder climate for the UK while accelerating warmth in the tropics. Some scientists predict this could happen next century. James Gray, Chair of the polar research sub-committee, said: "For too long the effects of a changing Arctic have been out of sight, out of mind. Before melting glaciers and ice sheets contribute to widespread flooding and irreversible weather patterns in the UK, we must throw our full toolbox at understanding changes in the Arctic better." Cheryl's birthday is July 16. The geniuses at Singapore's Study Room worked out the answer to provide the solution, and said it has to be July 16 as there's no other solution that would allow both Albert and Bernard to know the answer without conferring with each other. It took Terry over 20 hours of grinding and polishing to produce our mirror – and no, thankfully, he didn’t do it non-stop! Left: Detail from a portrait of William Herschel published in 1835. He holds a diagram of Uranus labelled ‘The Georgian Planet’, the name which he originally chose in honour of his patron King George III. Credit: Science Museum Group Collection. Right: Reflecting telescope made by William Herschel, 1783-5. Credit: Science Museum Group Collection. There has been some discussion about whether infection changes human behaviour or not, possibly making some infected humans more likely to take risks, but it's certainly not a dramatic behavioural change like we see with zombies.
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. Rometsch PA, Zhu Y, Wu X, Huang A (2022) Review of high-strength aluminium alloys for additive manufacturing by laser powder bed fusion. Mater Des 219:110779. https://doi.org/10.1016/j.matdes.2022.110779 Due to climate warming, irreversibly thawing permafrost is releasing organic matter frozen for up to a million years, most of which decomposes into carbon dioxide and methane, further enhancing the greenhouse effect. I see that we have assisted you in the past multiple times, Goodwill is not guaranteed and very limited at this time.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)). 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
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).This measurement principle is usually referred to as time of flight (ToF). ToF can be obtained by sending through a laser a pulsed signal, and by measuring the phase and frequency of the reflected light signal with respect to a reference.
Great Deal 
New Comment