Bao Yang

Bio: Bao Yang is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Thermoelectric cooling & Thermal conductivity. The author has an hindex of 44, co-authored 141 publications receiving 7219 citations. Previous affiliations of Bao Yang include Massachusetts Institute of Technology & University of California, Los Angeles.

Thermal Conductivity Equations Based on Brownian Motion in Suspensions of Nanoparticles (Nanofluids)

Abstract: Thermal conductivity equations for the suspension of nanoparticles (nanofluids) have been derived from the kinetic theory of particles under relaxation time approximations. These equations, which take into account the microconvection caused by the particle Brownian motion, can be used to evaluate the contribution of particle Brownian motion to thermal transport in nanofluids. The relaxation time of the particle Brownian motion is found to be significantly affected by the long-time tail in Brownian motion, which indicates a surprising persistence of particle velocity. The long-time tail in Brownian motion could play a significant role in the enhanced thermal conductivity in nanofluids, as suggested by the comparison between the theoretical results and the experimental data for the Al 2 O 3 -in-water nanofluids.

Synthesis of Metal Oxide Nanoparticles by Rapid, High-Temperature 3D Microwave Heating

Abstract: Microwave-assisted fabrication has propelled the recent synthesis and processing approaches of various nanomaterials. However, in most previous studies, the synthesis temperature is limited to below 1100 K, which restricts its application. Here, a rapid, in situ 3D heating method to manufacture well-dispersed metal oxide nanoparticles on a 3D carbonized wood (denoted as C-wood) host using microwaves as the driving power is reported. The moderate electronic conductivity of C-wood contributes to the local Joule heating and the good thermal conductivity guarantees the rapid 3D heating of the overall material. The temperature of the C-wood increases from room temperature to ≈2200 K in 4 s (≈550 K s−1), stabilizing to 1400 K, and then cooling back down to room temperature within 2 s. The preloaded precursor salts rapidly decompose and form ultrafine (≈11 nm) metal oxide nanoparticles on the surface of the C-wood during the rapid quenching. The process takes place in air, which helps prevent the metal oxides from being reduced by the carbon. The 3D heating method offers an effective route to the rapid and scalable synthesis of metal oxide nanoparticles.

Experimental studies of the size effect affected microscale plastic deformation in micro upsetting process

Abstract: Microforming is one of the promising approaches to fabricating microparts for its high productivity, low production cost and good mechanical properties The material deformation behavior in microforming, however, is different from the one in macroforming The macroforming knowledge is not applicable to the design and development of microparts It is thus necessary to investigate the size effect on deformation behaviors and the physics behind in the microforming In this research, the micro upsetting of cold-drawn and annealed pure copper with different billet sizes from macro- to micro-scale is conducted to investigate the size effect on material flow behavior, surface roughness evolution, flow stress and the hardening behavior It is found that the compressive instability takes place for the cold-drawn specimens, resulting in the occurrence of double barreling In addition, the inhomogeneous material flow occurs, surface roughness increases, flow stress decreases and the scattering range of the measured material properties increases with the decrease of workpiece size and the increase of grain size To quantify the size effect, the ratio of the internal grain boundary surface area to the total grain boundary surface area of the workpiece is introduced Based on the hardening behavior and the flow stress, the proposed modeling methodology for describing the size effect phenomena is verified The reported experimental results and the modeling methodology thus provide an in-depth understanding of the size effect in microscale plastic deformation

La0.5Sr0.5CoO3/Pb(Nb0.04Zr0.28Ti0.68)O3/La0.5Sr0.5CoO3 thin film heterostructures on Si using TiN/Pt conducting barrier

Abstract: A high density ferroelectric memory process flow requires the integration of conducting barrier layers to connect the drain of the pass-gate transistor to the bottom electrode of the ferroelectric stack. We are studying the effect of crystallinity of the TiN/Pt barrier layer with Si wafers on the ferroelectric properties of La0.5Sr0.5CoO3/Pb(Nb0.04Zr0.28Ti0.68)O3/La0.5Sr0.5CoO3 (LSCO/PNZT/LSCO) capacitors. Structural studies indicate complete phase purity (i.e., fully perovskite) in both epitaxial and polycrystalline materials. The polycrystalline capacitors show lower remnant polarization and coercive voltages. However, the retention, fatigue, and imprint characteristics are similar, indicating minimal influence of crystalline quality on the ferroelectric properties.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Toward Safe Lithium Metal Anode in Rechargeable Batteries: A Review.

Abstract: The lithium metal battery is strongly considered to be one of the most promising candidates for high-energy-density energy storage devices in our modern and technology-based society. However, uncontrollable lithium dendrite growth induces poor cycling efficiency and severe safety concerns, dragging lithium metal batteries out of practical applications. This review presents a comprehensive overview of the lithium metal anode and its dendritic lithium growth. First, the working principles and technical challenges of a lithium metal anode are underscored. Specific attention is paid to the mechanistic understandings and quantitative models for solid electrolyte interphase (SEI) formation, lithium dendrite nucleation, and growth. On the basis of previous theoretical understanding and analysis, recently proposed strategies to suppress dendrite growth of lithium metal anode and some other metal anodes are reviewed. A section dedicated to the potential of full-cell lithium metal batteries for practical applicatio...

Physics of thin-film ferroelectric oxides

Abstract: This review covers important advances in recent years in the physics of thin-film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin-film form. The authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this the review covers the enormous progress that has been made in the first-principles computational approach to understanding ferroelectrics. The authors then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, this review ends with a look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in nonconventional nanoscale geometries.

Bulk nanostructured thermoelectric materials: current research and future prospects

Abstract: Thermoelectrics have long been recognized as a potentially transformative energy conversion technology due to their ability to convert heat directly into electricity. Despite this potential, thermoelectric devices are not in common use because of their low efficiency, and today they are only used in niche markets where reliability and simplicity are more important than performance. However, the ability to create nanostructured thermoelectric materials has led to remarkable progress in enhancing thermoelectric properties, making it plausible that thermoelectrics could start being used in new settings in the near future. Of the various types of nanostructured materials, bulk nanostructured materials have shown the most promise for commercial use because, unlike many other nanostructured materials, they can be fabricated in large quantities and in a form that is compatible with existing thermoelectric device configurations. The first generation of these materials is currently being developed for commercialization, but creating the second generation will require a fundamental understanding of carrier transport in these complex materials which is presently lacking. In this review we introduce the principles and present status of bulk nanostructured materials, then describe some of the unanswered questions about carrier transport and how current research is addressing these questions. Finally, we discuss several research directions which could lead to the next generation of bulk nanostructured materials.

Engineered doping of organic semiconductors for enhanced thermoelectric efficiency

Abstract: The conversion efficiency of heat to electricity in thermoelectric materials depends on both their thermopower and electrical conductivity. It is now reported that, unlike their inorganic counterparts, organic thermoelectric materials show an improvement in both these parameters when the volume of dopant elements is minimized; furthermore, a high conversion efficiency is achieved in PEDOT:PSS blends.