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SUMMARY:Phononics: Structural dynamics of materials and implications to fl
 uid dynamics\, heat transfer\, and beyond - Prof Mahmoud I. Hussein\, Alva
 h and Harriet Hovlid Professor of Aerospace Engineering Sciences\, Univers
 ity of Colorado Boulder
DTSTART:20230203T140000Z
DTEND:20230203T150000Z
UID:TALK194881@talks.cam.ac.uk
CONTACT:Hilde Hambro
DESCRIPTION:Phononics is an emerging field that seeks to elucidate the nat
 ure of intrinsic mechanical motion in both conventional and artificially s
 tructured materials\, and uses this knowledge to extend the boundaries of 
 physical response at either the material or structural/device level or bot
 h. The field bridges multiple disciplines across applied physics and engin
 eering\, and spans multiple scales reaching the atomic scale where a rigor
 ous definition of phonons originates–quanta of lattice vibrations. In th
 is talk\, I will present two distinct contributions of phononics\, one to 
 the classical field of fluid dynamics and the other to the emerging field 
 of nanoscale heat transfer. In both cases\, intervention that causes criti
 cal changes in fundamental physical behaviour is demonstrated.\n\nIn fluid
  dynamics\, I will show that phonon motion underneath a surface interactin
 g with a flow may be engineered to cause the flow to stabilize\, or destab
 ilize\, as desired [Hussein et al.\, Proc. R. Soc. A\, 2015]. The underlyi
 ng control mechanism utilizes the principle of destructive or constructive
  interferences and the notion of symmetry breaking\, core concepts in phon
 onics. This is realized by installing a “phononic subsurface” (PSub)\,
  which is an architectured periodic structure placed in the subsurface reg
 ion and configured to extend all the way such that its edge is exposed to 
 the flow\, forming an elastic fluid-structure interface. I will present re
 sults showcasing perfectly synchronized\, passive\, and responsive\, phase
 d response and energy exchange between the elastic domain of a PSub and th
 e perturbation (instability) field within an interfacing flow. One outcome
  of this state of response is delay of laminar-to-turbulent transition.\n\
 nIn heat transfer\, I will present the concept of a locally resonant nanop
 hononic metamaterial (NPM) [Davis and Hussein\, Phys. Rev. Lett.\, 2014]\,
  of which one realization is a freestanding silicon membrane (thin film) w
 ith a periodic array of nanoscale pillars extruding out of one or both fre
 e surfaces. Heat is transported along the membrane portion of this nanostr
 uctured material as a succession of wavenumber-dependent propagating vibra
 tional waves\, phonons. The atoms making up the minuscule pillars\, on the
 ir part\, generate wavenumber-independent resonant vibrational waves\, whi
 ch we describe as vibrons. These two types of waves interact causing a mod
 e coupling for each pair leading to (1) the generation of new modes locali
 zed in the nanopillar portion(s) and (2) the reduction of the base membran
 e phonon group velocities around the coupling regions. These effects take 
 place across the full spectrum and bring rise to a unique form of heat con
 duction\, namely\, resonant thermal transport. The outcome is an inherent 
 reduction in the in-plane thermal conductivity of the base membrane materi
 al. \n\nPSubs provide a new paradigm of flow control for drag reduction in
  air\, sea\, and land vehicles\, and NPMs offer a new route for high-effic
 iency solid-state thermoelectric energy conversion. \n\n------------------
 ---------------------\n\nBio: Mahmoud I. Hussein is the Alvah and Harriet 
 Hovlid Professor at the Smead Department of Aerospace Engineering Sciences
  at the University of Colorado Boulder. He holds a courtesy faculty appoin
 tment in the Department of Physics and an affiliate faculty appointment in
  the Department of Applied Mathematics\, and he has formally served as the
  Engineering Faculty Director of the Pre-Engineering Program and the Progr
 am of Exploratory Studies. He received a BS degree from the American Unive
 rsity in Cairo (1994) and MS degrees from Imperial College London (1995) a
 nd the University of Michigan‒Ann Arbor (1999\, 2002). In 2004\, he rece
 ived a PhD degree from the University of Michigan‒Ann Arbor\, after whic
 h he spent two years at the University of Cambridge as a postdoctoral rese
 arch associate.\n\nDr. Hussein’s research focuses on the dynamics of mat
 erials and structures\, especially phononic crystals and metamaterials\, a
 t both the continuum and atomistic scales. His research considers areas th
 at range from vibrations and acoustics of engineering materials and struct
 ures and passive flow control to lattice dynamics and thermal transport in
  semiconductor-based nanostructured materials. His studies are concerned w
 ith physical phenomena governing these systems\, associated theoretical an
 d computational treatments\, and analysis of relevant mechanisms such as d
 ispersion\, resonance\, dissipation\, and nonlinearity. His team also cond
 ucts experiments to support some aspects of the theoretical work. \n\nDr. 
 Hussein received a DARPA Young Faculty Award in 2011\, an NSF CAREER award
  in 2013\, and in 2017 was honored with a Provost’s Faculty Achievement 
 Award for Tenured Faculty at CU Boulder. He has co-edited a book titled Dy
 namics of Lattice Materials published by Wiley. He is a Fellow of ASME and
  has served as an associate editor for the ASME Journal of Vibration and A
 coustics. In addition\, he is the founding vice president of the Internati
 onal Phononics Society and has co-established the Phononics 20xx conferenc
 e series which is widely viewed as the world’s premier event in the emer
 ging field of phononics.\n
LOCATION:Department of Engineering - LR4
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