The secret origins of the Moon

posted by @ulaulaman about #Moon formation #astronomy #Earth with Italo Calvino quotes

Our satellite, the Moon, is really fascinating, not only for artists and poets, but also for scientists. For example the first, precise description of the Moon was made by Galileo Galilei in the Sidereus Nuncius:

One of the problems that the astronomy try to resolve about the Moon is its origins: for example in the beginning of the Twentieth Century it was developed the Earth-Moon Theory, that was reviewed by LeRoy Hughbanks⁽⁸⁾:

"The moon," says Prof. Percival Lowell, "did not originate as a separate body, but had its birth in a rib of earth." Doctor Lowell is an ardent sup- porter of "the earth-moon theory," and his views and deductions are frankly stated in his two last scientific works, "Mars as the Abode of Life" and "Evolution of Worlds," both of which are publications of the Macmillan Company, New York.

In the discussion has a really great importance George Darwin with his works about the tidal friction⁽⁶⁾ and the viscous spheroids⁽⁵⁾:

Following Sir George Darwin, the Moon would have been detached from the Earth because to a solar tide. The attraction of the Sun acted on the covering of lighter rock (granite) as on a fluid, lifting one hand and tearing it to our planet. The waters that covering the entire Earth were largely sucked down by the abyss that had opened by the escape of the Moon (i.e. the Pacific Ocean), leaving uncovered the remaining granite, which fragmented and wrinckled itself into the continents. Without the Moon, the evolution of the life on the Earth, although it had been, would have been very different.⁽²⁾

Another good description of the earth-moon theory was given by Andrew Patterson:

In brief, the theory is that when the earth had cooled, from its molten condition sufficiently to have a crust of solidified matter something like thirty miles thick over its entire surface, it was revolving so rapidly that gravitational attraction and centrifugal force practically balanced each other. For some reason, perhaps some vast and sudden cataclysm, a large portion of this crust was thrown off the earth, and by tidal action was forced gradually outward in a spiral path. In order to form the moon, a mass of this crust about thirty miles thick and of area nearly equal to the combined areas of the present oceans on the earth must have been thrown off. It is supposed that this immense amount of crust was largely taken from the present basin of the Pacific, and that the remaining parts of the earth's crust, while it still floated on a liquid interior, split along an irregular line into two pieces which floated apart, and the gap between these two parts was later filled with the waters of the Atlantic.⁽⁷⁾

But following Gerstenkorn⁽¹¹⁾ we could arrive to a variation of this picture:

Following H. Gerstenkorn's calculations⁽¹¹⁾, developed by H. Alfven^{(9, 10)}, Earth's continents would be fragments of the Moon fell on our planet. The Moon in origin would also be a planet gravitating around the Sun, until such time as the proximity to the Earth derailed her from its orbit. Captured by Earth's gravity, the Moon came up more and more, tightening its orbit around us. At one point, the mutual attraction began to deform the surface of the two celestial bodies, raising high waves which were detached fragments whirling in space between Earth and Moon, especially fragments of lunar matter that fell on Earth. Later, under the influence of our tides, the Moon was pushed away to reach its present orbit. But part of the lunar mass, perhaps half, was left on Earth, forming the continents.⁽³⁾

Impact from kin via Jane Grant

The practical value of science

I have endeavored to state the higher and more abstract arguments by which the study of physical science may be shown to be indislensable to the complete training of the human mind, but I do not wish it to be supposed that because I may be devoted to more or less abstract and unpractical pursuits I am insensible to the weight which ought to be attached to that which has been said to be the English conception of Paradise - namely, ' gettinig on'. Now the value of a knowledge of physical scienice as a means of getting on, is indubitable. There are hardly any of our trades, except the merely hukcstering ones, in which some knowledge of science may not be directly profitable to the pursuer of that occupation. An Industry attains higher stages of its development as its processes become more complicated and refined, and the sciences are dragged in, one by one, to take their share in the fray.

Thomas Huxley, Science vol.1 n.1 (1880)

The network of scientific journals

At the beginning of 2012, Science published a briefly paper about the coercitive action of the editors in most of the scientific journals in world:

We find that coercion is uncomfortably common and appears to be practiced opportunistically⁽¹⁾

One of the most coercitive practice is to say to the authors to cite in their paper more source from the journal where the work is submitted (the practice of coercive self-citation is common in the business disciplines, for example). Now a new research try to describe the interaction between scientific journals with a really particular network:

In the network, an arrow from journal A to journal B represents a “resubmission link,” that is, an article that was submitted to and published by journal B after submission to journal A. This network can be used to learn more about publication strategies and perceived journal importance than is available in citation networks alone⁽²⁾

The idea is: you submit to a journal with an high impact factor, your paper was rejected for example because is too specialistic, and you resubmit to another journal, and in this case your paper is accepted. And, incredible:

Resubmissions were significantly more cited than first-intents published the same year in the same journal⁽²⁾

Keith Bowers, commenting the results of the paper, write on the same issue of Science:

Journal editors could increase the quality of papers published in their own journals by exacting more rigorous standards for revision without rejecting them. Providing authors more opportunities to revise and resubmit manuscripts following peer review, while being clear to authors that substantial improvement must be made before a final decision is reached, would increase the citation impact of an editor's own journal.⁽³⁾

As is he right?

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(1) Wilhite A.W. & Fong E.A. (2012). Coercive Citation in Academic Publishing, Science, 335 (6068) 542-543. DOI: 10.1126/science.1212540
(2) Calcagno V., Demoinet E., Gollner K., Guidi L., Ruths D. & de Mazancourt C. (2012). Flows of Research Manuscripts Among Scientific Journals Reveal Hidden Submission Patterns, Science, 338 (6110) 1065-1069. DOI: 10.1126/science.1227833
(3) Bowers E.K. (2012). Journals: Increase Revisions, Not Rejections, Science, 338 (6110) 1029-1029. DOI: 10.1126/science.338.6110.1029-a

Mathematics Research Communities

The #AMS invites mathematicians to become part of #Mathematics Research Communities

Mathematics Research Communities | click to enlarge
via Notices of the American Mathematical Society

Proofs without words: Ptolemy's theorem and cosine's law

Ptolemy's theorem

Derrick W. & Hirstein J. (2012). Proof Without Words: Ptolemy’s Theorem, The College Mathematics Journal, 43 (5) 386-386. DOI: 10.4169/college.math.j.43.5.386 (via Cut the Knot)

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Law of cosines

Kung S.H. (1990). Proof without Words: The Law of Cosines, Mathematics Magazine, 63 (5) 342. DOI: 10.2307/2690911 (pdf)

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Law of cosines via Ptolemy's theorem

Kung S.H. (1992). Proof without Words: The Law of Cosines via Ptolemy's Theorem, Mathematics Magazine, 65 (2) 103. DOI: 10.2307/2690488 (pdf)

A is for atom

#video posted by @ulaulaman about #nuclearenergy

A is for atom is a promotional animation written by True Boardman and directed by Carl Urbino with music by Eugene Poddany. It was commisioned by General Electric to John Sutherland and distributed by the Sutherland Production in 1953.
You can download the original video, that it is in public domain, from archive.org.

via boingboing

Looking through an opaque material

posted by @ulaulaman about #JacopoBertolotti #physics #optics #opaque #matter

I am proud to publish a feature article about the research word of a Wikipedia's friend like Jacopo Bertolotti. The work was finally published on "Nature", that decided also to honor the paper with the cover.
I admit to have received the paper a couple of weeks ago, so I hope to have made ​​a good service to Jacopo and all of his colleagues.

Recently one of my students asked me why glass is transparent while other materials are not. Its transparency is substantially due to the interaction between the electrons of the glass and the incident light, and so from the interaction between the photons (or electromagnetic radiation) and matter. A photon, when it interacts with matter, can be absorbed, reflected or continue on its way without change. These different behaviors are due to the energy levels occupied by the electrons of the atoms that constitute matter, in particular by the energy difference between these levels. We know, thanks to the photoelectric effect and the explanation given to it by Einstein, that the electrons are excited by the incident photons only if the energy of these photons is equal to (or greater than) the energy required to jump to another level. This means that if the light does not excite the electrons of the material, this is transparent to its passage, just as occurs in the glass: the visible light, in fact, has not enough energy to excite the electrons of the glass, which is therefore transparent to its passage, despite the rays of light are reflected.
Now, if we take a sheet of glass and do hit by light from one of its ends, a part of the rays will be reflected and then detected by a device (such as our eyes) placed for example at the opposite end. Not all reflected rays, however, follow an equal path and therefore not all the rays reach the eyes at the same time.

Something similar also occurs when light passes through the glass of our windows: the light rays don't travel all at the same speed.

In order to enable to all the rays of light to reach the detection point at the same time one can construct a structure which gradually tapering as it approaches the ends, i.e. it builds a lens.

One of the ways to use a lens is for example for the magnification of objects, but not all magnifications can be made using the lenses that take advantage of the visible light. If, for example, we have some objects that are at a scale of less than 200 nm, the usual optical lenses are not able to resolve their details. Unless you build a HIRES(1) (High Resolution Enhancement by Scattering Index) lens.
This lens, developed by the group of van Putten and Bertolotti (our Jacopo!) consists of:

(...) of a homogeneous slab of high-index material on top of a strongly disordered scattering layer. The disordered layer breaks the translational invariance of the interface, which enables incident light to be coupled to all propagating angles inside the highrefractive-index material as shown in figure.

Yet multiple scattering also scrambles the wavefront creating a speckle-like pattern on the object plane that itself cannot be used for imaging. Therefore we manipulate the incident wavefront in order to force constructive interference of the scattered light at a position in the object plane of our HIRES-lens.⁽¹⁾