2018 Spring Graduate Colloquium Series: Kai Yang/Jingyi Yang

DateMarch 23, 2018Time3:35 - 5:00 pm
LocationBaylor Sciences Building, Room E.125
Description
Kai Yang

Experimental Study of Ordering of Hard Cubes by Shearing

The compaction dynamics of an ensemble of cubic particles submitted to a novel type of excitation are analyzed experimentally. Instead of the standard tapping procedure used in granular materials, alternative twists are applied to the cylindrical container. Under this agitation, the development of shear forces among the different layers of cubes leads to particle alignment. As a result, the packing fraction grows monotonically with the number of twists. If the intensity of the excitations is sufficiently large, an ordered final state is reached where the volume fraction is the densest possible compatible with the boundary condition. This ordered final state resembles the tetratic or cubatic phases observed in colloids.

Asencio K, Acevedo M, Zuriguel I, et al. Experimental Study of Ordering of Hard Cubes by Shearing[J]. Phys.rev.lett,2017, 119(22).
Jaeger H M, Nagel S R, Behringer R P. Granular solids, liquids, and gases[C]// MOD. PHYS. 1996:187.
Nasuno S, Kudrolli A, Bak A, et al. Time-Resolved Studies of Stick-Slip Friction in Sheared Granular Layers[J]. Physical Review E Statistical Physics Plasmas Fluids & Related Interdisciplinary Topics, 1998, 58(2):2161-2171.
Liu A J. Jamming is not just cool any more[J]. Nature, 1998, 21(6706):21-22.

Jingyi Yang

Broadband Achromatic Metalens in the Visible

Conventional refractive optical lens specifically relies on a polished surface profile on transparent material to attain the gradual phase change. It is bulky and time-consuming to manufacture with high precision. With the ability of high-resolution nanofabrication, metasurface consists of metallic elements with thickness on the order of subwavelength (i.e., tens of nanometer) can interact with the incoming light and shape the wave front. By producing a hyperbolical phase profile, designed metasurfaces can work as lens (referred to as metalens), which has convergent effect for incident light beams with considerable efficiency. In this talk, I will give an introduction of two designs of achromatic metalens in the visible from the recent reports. This proof-of-concept demonstration show that flat achromatic metalens could allow practical applications in focusing and full color imaging.

[1] Wang S, et al. Nature Nanotechnology (13), 227 232 (2018).
[2] Chen W T, et al. Nature Nanotechnology (13), 220 226 (2018).

For more information contact: Dr. Howard Lee, 254-710-2277
PublisherDepartment of Physics
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