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.

The Deformation Measurement and Analysis on Meso-Structure of Aluminum Foams During SHPB Test

Abstract: The split Hopkinson pressure bar (SHPB) is most widely used to measure the dynamic mechanical properties of materials. Such a testing methodology implies the assumption of uniform deformation during an impact test. However, the experimental verification of this assumption for aluminum foams has, as yet, been unreported. In this paper, a test system combining the SHPB with a high-speed digital camera was designed and constructed to study the problem. In the system, the synchronization between SHPB and the high-speed digital camera, the lighting, and the surface treatment of specimen are established. The deformation of meso-structure of aluminum foams during the SHPB impact was observed successfully; furthermore, the localized strains along the specimens were measured quantitatively. Experimental results show that the deformation is non-uniform; that means the assumption of uniform deformation for aluminum foam is not well satisfied. Therefore, a need exists for some modifications to characterize the dynamic mechanical properties of aluminum foams by SHPB.

Lead based ferroelectric capacitors for low voltage non-volatile memory applications

Abstract: We report on novel, low voltage properties of ferroelectric lanthanum doped lead zirconate titanate (PLZT) capacitors. These PLZT ferroelectric films sandwiched between lanthanum strontium cobaltite, (La0.5Sr0.5)CoO3(LSCO) electrodes were epitaxially grown on yttria stabilized zirconia (YSZ) buffered Si, using a bismuth titanate template. These epitaxial capacitors exhibit much lower switching voltages (∼0.5 V) compared to what has been reported on other PZT systems. Ferroelectric testing shows excellent fatigue, retention and imprint properties. Pulse width dependent measurements show that the low voltage performance is possible at widths less than 1 μsec. The dramatic change in the switching behavior is tentatively attributed to the reduction in the c-axis lattice parameter (due to La substitution) and the consequent absence of 90° domain walls.

Highly Sensitive and Durable Structured Fibre Sensors for Low-Pressure Measurement in Smart Skin.

Abstract: Precise measurements of low pressure are highly necessary for many applications. This study developed novel structured fibre sensors embedded in silicone, forming smart skin with high sensitivity, high durability, and good immunity to crosstalk for precise measurement of pressure below 10 kPa. The transduction principle is that an applied pressure leads to bending and stretching of silicone and optical fibre over a purposely made groove and induces the axial strain in the gratings. The fabricated sensor showed high pressure sensitivity up to 26.8 pm/kPa and experienced over 1,000,000 cycles compression without obvious variation. A theoretical model of the sensor was presented and verified to have excellent agreement with experimental results. The prototype of smart leg mannequin and wrist pulse measurements indicated that such optical sensors can precisely measure low-pressure and can easily be integrated for smart skins for mapping low pressure on three-dimensional surfaces.

Development of a polarized electron source for the MIT-Bates Linear Accelerator Center

Abstract: The polarized electron source at MIT-Bates has been developed to provide beams for nuclear physics experiments with a very diverse set of requirements. The source has combined operation at high peak and average current with high polarization. Developments have included the pioneering of several techniques used in parity violating experiments to remove helicity correlations from beam properties. This paper describes the design of the source and its performance during beam operations.

Equilibrium Thermodynamic Properties of Aqueous Solutions of Ionic Liquid 1-Ethyl-3-Methylimidazolium Methanesulfonate [EMIM][MeSO 3 ]

Abstract: The ionic liquid 1-ethyl-3-methylimidazolium methanesulfonate ([EMIM][MeSO3]) has been considered as a promising alternative desiccant to triethylene glycol and lithium bromide commonly used in the industry. In this paper, the water activity coefficient of this binary system was measured from 303 K to 363 K with water concentration from 18% to 92%. The interaction energies between the ionic liquid molecules ($${g}_{22}$$) and between the ionic liquid and water molecules ($${g}_{12}$$) for the [EMIM][MeSO3]/water binary system were determined from the water activity coefficient data using the Non-Random Two-Liquid (NRTL) model. The magnitude of the interaction energy between the [EMIM][MeSO3] and water molecules ($${g}_{12}$$) was found to be in the range of 45~49 kJ/mol, which was about 20% larger than that between the water molecules ($${g}_{11}$$) in the [EMIM][MeSO3]/water system. The large ($${g}_{12}$$) can explain many observed macroscopic thermodynamic properties such as strong hygroscopicity in the ionic liquid [EMIM][MeSO3]. These interaction energies were used to determine the heat of desorption of the [EMIM][MeSO3]/water system, and the obtained heat of desorption was in good agreement with that calculated from the conventional Clausius-Clapeyron Equation.

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.