180317 Flat Optical Components with Meta-Optics

Title:
Flat Optical Components with Meta-Optics

Speaker:
吳品頡 (Pin Chieh Wu)

Time:
03/17 (Sat.) 3 pm PDT, 4 pm MDT, 5 pm CDT, 6 pm EDT
03/18 (Sun.) 6 am Taiwan

Abstract:
Optical/plasmonic metamaterials composed of artificial structures have attracted a huge number of interests due to their extraordinary optical properties, such as negative refractive index, optical invisibility, etc. Their single layer configuration, optical metasurfaces, enable abrupt changes to the properties of electromagnetic wave like phase, amplitude as well as polarization within a subwavelength spatial region, which is promising for the development of flat optics systems. In this presentation, I will talk about the intriguing light control through flat optical metasurfaces, which enables feasible applications of versatile polarization generations, high efficiency metalens with multi-functionality, and achromatic metasurface devices. By incorporating metasurfaces with active materials/systems, one can dynamically control the optical properties of metasurface devices on demand like beam steering, and tunable polarization conversion.

180310 Flux reconstruction/correction procedure via correction in computational fluid dynamics

Title:
Flux reconstruction/correction procedure via correction in computational fluid dynamics

Speaker:
莊璧躍 (Pi-Yueh Chuang)

Time:
03/10 (Sat.) 6 pm PDT, 7 pm MDT, 8 pm CDT, 9 pm EDT
03/11 (Sun.) 10 am Taiwan

Abstract:
In this talk, I will give an introduction to a recently proposed high-order numerical methods -- flux reconstruction (FR), also known as correction procedure via reconstruction (CPR). Discussion of FR in the context of computational incompressible flow will also be addressed.

In CFD (computational fluid dynamics) area, high-order methods are considered to be computationally cheaper than low-order ones (such as finite difference/volume/element). Traditional high-order methods, however, pose many problems, such as numerical stability, ill-conditioned systems, difficult implementations, and challenging adaption to HPC (high-performance computing) systems. Therefore nowadays, in production CFD codes and practical uses, the use of high-order methods is still limited. The FR method may become a game changer to this situation. FR has been proved to be numerically stable and computationally efficient on modern heterogeneous HPC systems. While FR is initially designed for hyperbolic conservation laws and compressible flow, applying FR to incompressible flow is still a challenge and leaves us many open questions. In this talk, I will try to bring these questions out after the introduction to FR.

180303 Topological quantum phase transitions in Haldane spin chains

Title:
Topological quantum phase transitions in Haldane spin chains

Speaker:
曾郁欽 (Yu-Chin Tzeng)

Time:
03/03 (Sat.) 11 am PDT, 12 pm MDT, 1 pm CDT, 2 pm EDT
03/04 (Sun.) 2 am Taiwan

Abstract:
I will give some introductions to the 2016 Nobel price in physics, particular in the Topological phases and Topological quantum phase transitions in one-dimensional quantum spin chains. In quantum mechanics, the volume of the spin can only be half-odd-integer (S=1/2, 3/2, 5/2,...) or integer. (S=1,2,3,...) When the spins are aligned into a 1D array, by their spin-spin interactions, the behaviors are very different between half-odd-integer spin chain and integer spin chain. This is the so-called "Haldane conjecture" which was made by D.Haldane in 1980's. Nowadays we further know the odd-integer (S=1,3,5,...) spin chains belong to the Symmetry-Protected-Topological phase, and the even-integer (S=2,4,6,...) spin chains are connected with trivial phases. Haldane won the Nobel price in 2016 for his contributions to ​the ​ theoretical discoveries of topological phase transitions and topological phases of matter.