Presentation on theme: "“Application”- “ Textbooks”- “Application” Tan Lei （谭 磊） July, 2012 广州 湛江 Institute of Theoretical Physics, Lanzhou University 2012 年高等学校热力学与统计物理学教学及学术研讨会."— Presentation transcript:
“Application”- “ Textbooks”- “Application” Tan Lei （谭 磊） July, 2012 广州 湛江 Institute of Theoretical Physics, Lanzhou University 2012 年高等学校热力学与统计物理学教学及学术研讨会
Introduction Motivation So interesting-So many-So what ? 60% (graduate):40% (work): More is different Interest model Principle Authoritative Advanced Colorful
outline Why Is Ice Slippery –Physics today 58, 50
Why Is Ice Slippery ?? Can we skate over the glasses??
!! Explanation: pressure melting –in the textbooks for a very long time The pressure exerted along the blade lowers the melting temperature of the top layer of ice, the ice melts and the blade glides on a thin layer of water that refreezes to ice as soon as the blade passes. Textbooks are full of it Correct Absolutely !! This means that ice under pressure melts at a lower temperature or that we can melt ice by applying pressure.
Pressure Melting: ice skates We can do a simple calculation to estimate the pressure exerted by the blades of a skate. Remember that we already learnt this on the first lecture: Pressure is force per unit area. P=F/A. e.g.a150kG person and a typical blade edge, which is not razor sharp, is about one-eighth of an inch wide and about 12 inches long, yielding a surface area of 1.5 square inches each or 3 square inches for two blades That amount of pressure lowers the meltingtemperature only a small amount, from 32 degrees to degrees. Yet ice skaters can easily slip and fall at temperatures much colder. For a flat-bottom shoes, a smaller amount temperature. Explanation: Fails !! New idea are expected! phenomilogically
Frictional melting ?? Beyond the textbooks the rubbing of a skate blade or a shoe bottom over ice, heats the ice and melts it, creating a slippery layer. Many of you might ask about the slipperiness of ice, that you can feel standing on ice without skates of skies. Pressure and friction do not explain it! A liquid layer of water on the surface of ice ?? ----Beyond the textbooks there are no molecules above them to help hold them in place, and they thus remain an unfrozen liquid even at temperatures far below freezing. Michael Faraday
1. Pressure decreases the melting temperature of ice. 2. However pressure is not the main reason why ice is so slippery. 3. Pressure melting is only important down to -0.5 C. 4. Frictional melting also contributes to the slipperiness of ice. At very low T's in order to gain speed it is necessary to ski faster! 5. Independently of pressure or friction, there is always a liquid layer at the surface of ice. This layer is what makes ice slippery even without skies or skates. 6. We can not skate over the glasses! Conclusions: slippery when wet It's amazing,“. "We're in 2012, and we're still talking about this thing." The story is not completed yet. continue to debate yet !! The story is still far away from its end… where will we go?
The thin liquid layer From Red Cells to Snowboarding: A New Concept for a Train Track, Phys. Rev. Lett., Red Cells move quickly in the Vascular. Train runs on the Feather ….. Far away from the textbook Beyond the textbooks So What ?? People flies on the grass ??
outline photons in an optical microcavity –Nuture 468, 545 –Nature Photonics XXXX
Photons the electromagnetic field wave the quantized harmonic oscillator Particle (bosonic) BosonsFermions Laser cooling !!! (Blackbody radiation) (Bose-Einstein distribution) Very lower temperatures are needed. How to get there? BECBCS Wave-particle duality
Laser cooling Doppler cooling Ramam cooling VSCPT cooling Cavity cooling Limit temperature Main processes Spontaneous emission spontaneous emission Photon Escape atom certain atomic species Atom the ensemble of atoms Molecules The order of nK temperatures can be achieved! Laser cooling mechanism Science 321, 232 (2008) Nat. Phys. 1, 122 (2005) ----Beyond the textbooks
Photons --?? Why not BEC The reason is that the photon number is not constant when their temperature is changed, as the photons can be absorbed by atoms in the surrounding apparatus. In BECs comprised of cold atoms, the atoms reach thermal equilibrium by exchanging energy in collisions with other atoms. This is not possible with mass-less photons as they interact too weakly with each other. Ultracold atomic gases Mimicking condensed matter physics and beyond Perfect models for a fundamental understanding of quantum many-body system So What ??
Photons –Photons BEC: impossible or possible? which way on earth will be taken? where is the way? An optical cavity formed between two curved mirrors was used to confine the photons, and a dye was placed in between the mirrors to fill the cavity. The large number of dye molecules acted as a heat sink and allowed the photon energy to rapidly reach thermal equilibrium with the dye. This process reduced the range of energy states the photons were in, until they all occupied the lowest state possible, and thereby producing a BEC. Nuture 468, Beyond the textbooks
Photons BEC So What ?? The applications of photon BECs are perhaps still some way off, but it is thought that they could be used as a novel light source, or for steps towards improving the efficiency of a laser. Nevertheless, the production of a BEC from photons is still an important experiment for our understanding of fundamental physical systems, and further blurs the distinctions we had previously made between atoms and light. ----Beyond the textbooks
To the end? No Photons -- wave-particle Fifty years of conscious thought still does not make me closer to the answer of light quantum. Maybe, we just begin now or we are still on the way … ----Beyond the textbooks
A quantum drum has become the first visible object to be put into a superposition of quantum states. Nature 464, 697 Optomechanical system Physics 2, 40 Largest ever object put into quantum state. Which played a vital role in the conceptual exploration of the boundaries between classical and quantum mechanical systems the surf is up Milestones Nature and Science
Macroscopic quantum phenomena -BEC or BCS ? Or both not ! Geckos can easily walk on surfaces with any roughness, climb vertical walls, and even cling to the ceilings Nature 448, 338 Spider-Man water striders So What ?? Who is the greatest “man” in qunatum world?? Maybe, there is a long way to go…
Brownian Particle Modle: Langevin equation, … Phenomena: Coastline, Zebra, Biological populations… Picture Quantum Brownian Particle --- the Second Law ?? ----decoherence?? ?? the instantaneous velocity of a Brownian particle -----can we? How can ? Still going on… What we konw Average speed, Fluctuation, Einstein relation….
Textbook …. Question Think deeply------Application Conclusion The knowledge in the textbook is the key to the Avenue of life and research ! The textbook is not only the textbook! Correct: condition The knowledge is limited! Application
Conclusion Acta Phys. Sin. 61, (2012) arXiv: (2009) Acta Phys. Sin. 60, (2011) Mod. Phys. Lett. B 23, 1499 (2009) Chin. Phys. Lett. 25, 48(2008) Journal of Lanzhou University (Natural Sciences) 46, 119(2010) Journal of Lanzhou University (Natural Sciences) 44, 131(2008) Harvard University, Penn State University …… Paper University