Presentation on theme: "The Rope and The Snake Unanswered Scientific Questions and Unquestioned Scientific Answers H.Aourag University of Tlemcen, Algeria."— Presentation transcript:
The Rope and The Snake Unanswered Scientific Questions and Unquestioned Scientific Answers H.Aourag University of Tlemcen, Algeria
H.Aourag2 §Supposez que dans la pénombre, alors que vous marchiez sur le chemin, vous aperceviez un gros morceau de corde roulé par terre et que vous le preniez pour un serpent. §Ce serpent n'a pas d'existence réelle en tant que serpent, il n'est qu'une apparence fausse assumée à vos yeux par une corde. Mais il a une réalité d'ordre phénoménal et pragmatique; subjectivement vous le trouvez vrai. Et cela au point qu'il vous fait reculer d'effroi, que votre coeur se met à battre plus rapidement et que, si vous avez des troubles cardiaques, vous pouvez même en mourir. §Et malgré cela c'est toujours une corde inoffensive; il suffit que vous voyiez sa nature réelle, que vous perdiez à son sujet l'illusion qui existe uniquement dans votre esprit, pour qu'à vos yeux le serpent disparaisse à jamais, ce serpent qui en réalité n'a jamais existé. §Mais en fait vous ne pouvez jamais voir à la fois la corde et le serpent : la vision de l'un exclut forcément la vision de l'autre. Et c'est en étudiant le serpent qu'on arrivera à le faire disparaître et à voir la corde.
H.Aourag3 The Attractive Universe - Gravity and the Shape of Space by E.G. Valens
H.Aourag4 §New Phase must form from an old phase by a process of nucleation A discontinuous process In a metastable starting With the involvement of Sharp interfaces New phase could form By a continuous process In unstable starting phase Theory of Diffuse Interface that gradually thickens as the unstable Parent phase decomposes continuously into regions of diverging compostions Unquestionned Answer Dogma Nucleation
H.Aourag5 That a compound must have a unique well defined molecular Weight and Melting temperature Dogma Organic Chemist Delayed the progress of Polymer by at least 20 years form 1910 to 1930
H.Aourag6 P. Duwez wanted to find a way of enhancing efective quenching rates of alloys, with a view of examining metastable phase Dogma Spalt Quenching Surprise: that quenching from the melt was more effective than quenching a solid sheet or wire New State of Matter Metallic Glasses
H.Aourag7 How the atoms pack themselve in metallic glass has been a mystery Mystery Metallic Glass In conventional metals, atoms crystallize into uniform three-dimensional patterns known as lattices Surprise : metallic glass atoms do not arrange themselves in a completely random way. Instead, groups of seven to 15 atoms tend to arrange themselves around a central atom, forming three-dimensional shapes called Kasper polyhedra.
H.Aourag8 Conviction that sintered ceramics must always be opaque because of unavoidable residual pores Dogma Sintered Ceramics Surprise: Pore-free ceramic could be manufactured Lamp Envelopes
H.Aourag9 Conviction that sintered ceramics must always be opaque because of unavoidable residual pores Dogma Photoceram Surprise: Pore-free ceramic could be manufactured Lamp Envelopes
H.Aourag10 Aluminum -- one of nature’s best conductors of electricity -- may behave like a ceramic or a semiconductor in certain situations Mystery Aluminium Surprise: aluminum may endure mechanical stress more than 30 percent better than copper, which is normally considered to be the stiffer metal. Directional Bond: Ceramic solve a long-standing mystery of so-called abnormal intrinsic stacking fault energy in aluminum. Metallurgists have long known that this abnormality has profound consequences for the mechanical behavior of aluminum, because it controls the structure of an important class of material defects called dislocations.
H.Aourag11 hese heat-resistant, lightweight compounds have stumped scientists for decades. Why do so many break so easily? Mystery Intermetallic Surprise: materials with complex crystal structures, such as Laves phases, the atomic arrangement around these defects, and how these defects move, are not well understood a concept called “synchroshear” was proposed to explain how this defect moved in many complex structures. Under that theory, this movement is accomplished by coordinated shifting of atoms in two adjacent atomic layers. This synchronized movement is necessary to prevent atoms in one layer from colliding with atoms in the neighboring layer It has long been known that a dislocation, or crystal defect, moves when force is applied to a material. The easier it is to move this defect, the less brittle the material will be.
H.Aourag12 for material scientists the phrase "ductile intermetallic compounds" has long been considered an oxymoron Dogma Ductile Intermetallic Compounds Discovered Surprise: yttrium-silver (YAg), yttrium-copper (YCu), and dysprosium-copper (DyCu) There are particular planes (within the B2 structure) that tend to slip most easily Why these materials deform while other intermetallics shatter isn't quite clear, but show that the ductile materials possess much lower unstable stacking-fault energies. Because these energies are lower in the ductile materials, it is easier for them to plastically deform instead of fracturing at the grain boundaries..
H.Aourag13 It is hard to imagine that graphite, the soft "lead" of pencils, can be transformed into a form that competes in strength with its molecular cousin diamond. Dogma Can Graphic cracks Diamond Surprise: Using a diamond anvil to produce extreme pressures and the ultra- brilliant X-ray beams at the Advanced Photon Source in Illinois, scientists with the High-Pressure Collaborative Access Team (HPCAT)* have surmounted experimental obstacles to probe the changes that graphite undergoes to produce this unique, super- hard substance. Graphite and diamond are both made of carbon. The geometric arrangement and spacing of the carbon atoms is what makes the materials differ in appearance and strength. The atoms in graphite are arranged in layers that are widely spaced. The atoms in diamond, on the other hand, are tightly linked producing a strongly bonded structure.
H.Aourag14 It is hard to imagine that graphite, the soft "lead" of pencils, can be transformed into a form that competes in strength with its molecular cousin diamond. Dogma Can Graphic cracks Diamond Surprise: Using a diamond anvil to produce extreme pressures and the ultra- brilliant X-ray beams at the Advanced Photon Source in Illinois, scientists with the High-Pressure Collaborative Access Team (HPCAT)* have surmounted experimental obstacles to probe the changes that graphite undergoes to produce this unique, super- hard substance. Graphite and diamond are both made of carbon. The geometric arrangement and spacing of the carbon atoms is what makes the materials differ in appearance and strength. The atoms in graphite are arranged in layers that are widely spaced. The atoms in diamond, on the other hand, are tightly linked producing a strongly bonded structure.
H.Aourag15 §to senior author Ainissa G. Ramirez, assistant professor of mechanical engineering, the Yale team monitored real-time images taken at two-second intervals while they heated crystallizing samples of nickel-titanium within a transmission Although there are theoretical models that predict grain size and ways to monitor the growth of individual crystals, this new method makes it possible to estimate grain size and therefore the properties of materials that are dependant on microstructure. §Researchers in many fields including materials science, geology, physical chemistry and biochemistry will now be able to tailor material properties that are sensitive to microstructure. §According electron microscope. §They directly determined the rate of crystal assembly (nucleation), and the rate that the crystals grew, by measuring the number of crystals and their change in size with time. Their results agree with the conventional Johnson-Mehl-Avrami-Kolmogorov method which only gives an overall crystallization rate, with the nucleation and growth rates coupled. §The novel contribution of this work is that the nucleation and growth rates are measured independently during crystallization and can be used to infer the grain size after crystallization is complete. §"We used the mathematics of crystallization in a new way," said Ramirez. "We found that our measured grain sizes and the mathematical predictions agreed over a broad range of temperatures. This method allows researchers to now explore the connection between structure and properties of different materials."
H.Aourag16 Every high school student is taught that opposite charges attract. Even in the complex world inside living cells, simple rules of thumb like this one usually continue to hold, and go a long way to explaining how the machinery of life all holds together. Dogma When Opposites Don't Attract Surprise: may have implications for the development of new materials for sophisticated sensors and optical devices In complex systems, such as multi-component materials or living cells, opposite charges don't necessarily attract