Engineering Commons^™

Thermal Activation In Atomic Friction: Revisiting The Theoretical Analysis, Yalin Dong, Danny Perez, Hongyu Gao, Ashlie Martini

Dr. Yalin Dong

The effect of thermal activation on atomic-scale friction is often described in the framework of the Prandtl–Tomlinson model. Accurate use of this model relies on parameters that describe the shape of the corrugation potential β and the transition attempt frequency f0. We show that the commonly used form of β for a sinusoidal corrugation potential can lead to underestimation of friction, and that the attempt frequency is not, as is usually assumed, a constant value, but rather varies as the energy landscape evolves. We partially resolve these issues by demonstrating that numerical results can be captured by a model with …

Thermally Cross-Linked Oligo(Poly(Ethylene Glycol) Fumarate) Hydrogels Support Osteogenic Differentiation Of Encapsulated Marrow Stromal Cells In Vitro, Johnna Temenoff, Hansoo Park, Esmaiel Jabbari, Daniel Conway, Tiffany Sheffield, Catherine Ambrose, Antonios Mikos

Esmaiel Jabbari

No abstract provided.

Quantitative Analysis Of Structure And Bandgap Changes In Graphene Oxide Nanoribbons During Thermal Annealing, Yu Zhu, Xianyu Li, Qinjia Cai, Zhengzong Sun, Gilberto Casillas, Miguel Jose-Yacaman, Rafael Verduzco, James Tour

Yu Zhu

Graphene oxide nanoribbons (GONRs) are wide bandgap semiconductors that can be reduced to metallic graphene nanoribbons. The transformation of GONRs from their semiconductive to the metallic state by annealing has attracted significant interest due to its simplicity. However, the detailed process by which GONRs transform from widebandgap semiconductors to semimetals with a near zero bandgap is unclear. As a result, precise control of the bandgap between these two states is not currently achievable. Here, we quantitatively examine the removal of oxygen-containing groups and changes in the bandgap during thermal annealing of GONRs. X-ray photoelectron spectroscopy measurements show the progressive removal …

Carbon Nanotube-Reduced Graphene Oxide Composites For Thermal Energy Harvesting Applications, Mark S. Romano, Na Li, Dennis Antiohos, Joselito M. Razal, Andrew Nattestad, Stephen Beirne, Shaoli Fang, Yongsheng Chen, Rouhollah Jalili, Gordon G. Wallace, Ray Baughman, Jun Chen

Gordon Wallace

By controlling the SWNT-rGO electrode composition and thickness to attain the appropriate porosity and tortuosity, the electroactive surface area is maximized while rapid diffusion of the electrolyte through the electrode is maintained. This leads to an increase in exchange current density between the electrode and electrolyte which results in enhanced thermocell performance.

Superlattice Ultrasonic Generation, Thomas E. Wilson, M. Oehme, E. Kasper, H-J. L. Gossmann

Thomas E. Wilson

We report the first experimental evidence for the resonant excitation of coherent high-frequency acoustic phonons in semiconducting doping superstructures by far-infrared laser radiation. After a grating-coupled delta-doped silicon doping superlattice is illuminated with ~1 kW/mm2 nanosecond-pulsed 246 GHz laser radiation, a delayed nanosecond pulse is detected by a superconducting bolometer at a time corresponding to the appropriate time-of-flight for ballistic longitudinal acoustic phonons across the (100) silicon substrate. The absorbed phonon power density in the microbolometer is observed to be ~10 μW/mm2, in agreement with theory. The phonon pulse duration also matches the laser pulse duration. The absence of any …

The Sun Also Rises: Prospects For Solar District Heating In The United States, Adam L. Reed, John S. Mccartney

Kevin L Doran

Renewable thermal energy remains a largely untapped resource in the United States, despite its low costs and growing popularity in many other countries and the pressing need to rapidly deploy and scale carbon-free energy sources in order to mitigate anthropogenic climate change. In this article, an energy attorney and a civil engineer collaborate to examine the prospects in the United States for solar district heating (SDH), a thermal technology that leverages economies of scale to provide zero-carbon, round-the-clock space and water heating (on average, the two largest components of building energy demand) to neighborhoods and commercial zones at costs competitive …

The Ocean Thermal Energy Conversion Strategies And Analysis Of Current Challenges, Lasantha Meegahapola, Lanka Udawatta, Sanjeeva Witharana

Dr Lasantha G Meegahapola

This paper presents different roots of Ocean Thermal Energy Conversion (OTEC) strategies and challenges faced in terms of efficiency and economy of OTEC plants. The conversion strategies primarily focus on open cycle, closed cycle and hybrid plants. The efficiency studies mainly skew towards the effect of plant distance and thermal gradient towards plant efficiency. The economic analysis is based upon the effect of per unit cost for OTEC plant together with other important considerations such as Plant Factor (PF) and offshore distance, which determine the cost of power generation. Some illustrative examples are also provided using the derived equations under …

Optical Solitary Waves In Thermal Media With Non-Symmetric Boundary Conditions, Simon Louis, Timothy R. Marchant, Noel F. Smyth

Tim Marchant

Optical spatial solitary waves are considered in a nonlocal thermal focusing medium with non-symmetric boundary conditions. The governing equations consist of a nonlinear Schrödinger equation for the light beam and a Poisson equation for the temperature of the medium. Three numerical methods are investigated for calculating the ground and excited solitary wave solutions of the coupled system. It is found that the Newton conjugate gradient method is the most computationally efficient and versatile numerical technique. The solutions show that by varying the ambient temperature, the solitary wave is deflected towards the warmer boundary. Solitary wave stability is also examined both …

Structure, Magnetic, And Thermal Properties Of Nd1-Xlaxcro3 (0 ≤ X ≤ 1.0), Yi Du, Zhenxiang Cheng, Xiaolin Wang, S X. Dou

Shi Xue Dou

Perovskite-type Nd1−xLaxCrO3(0 ≤ x ≤1.0) polycrystalline samples were synthesized using solid state reaction. Structural studies indicate that the lattice parameters, metal–oxygen bond lengths, and angles of Nd1−xLaxCrO3 strongly depend on the La content. Two magnetic transition temperatures, Cr3+ antiferromagnetic ordering temperature (TN) and the spin reorientation phase transition temperature (TSRPT), have been observed in the M-T curves. The increase in TN and decrease in TSRPT with increasing x value can be explained by the change in the magnetic interactions due to La doping. The heat capacity of Nd1−xLaxCrO3 measured from 2 to 300 K reveals that the lattice, electronic, and …

Crystal Structure And Electronic And Thermal Properties Of Tbfeaso0.85, N Kaurav, Y.T Chung, Y.K Kuo, R S Liu, T S Chan, J.M Chen, J.F Lee, H.S Sheu, Xiaolin Wang, S X. Dou, Sung-Ik Lee, Y.G Shi, A.A Belik, K Yamaura, E Takayama-Muromachi

Shi Xue Dou

The crystal structure and the electronic and thermal properties of a high-quality polycrystalline TbFeAsO0.85 sample made by a high-pressure technique are investigated. The crystal structure, as determined by synchrotron X-ray powder diffraction, possesses a tetragonal unit cell (space group: P4/nmm) with lattice parameters of a=b=3.8851 Å and c =8.3630 Å. In order to elucidate the electronic structure and oxidation states of corresponding elements, X-ray absorption near-edge structure (XANES) spectra are presented. The XANES spectra confirm that the oxidation states of Fe, As, and Tb in the TbFeAsO0.85 sample are ~Fe2+, ~As3−, and ~Tb3+, respectively, which are consistent with the previously …

Thermal-Strain-Induced Enhancement Of Electromagnetic Properties Of Sic-Mgb2 Composites, Rong Zeng, S X. Dou, Lin Lu, Wenxian Li, Jung Ho Kim, Paul G. Munroe, Rongkun Zheng, S P. Ringer

Shi Xue Dou

The effect of thermal strain caused by the different thermal expansion coefficients (α) of the MgB2 and SiC phases on the electromagnetic properties was studied for SiC–MgB2 composite, which was made by premixing SiC and B, followed by Mg diffusion and reaction. Thermal strain in the MgB2 phase was demonstrated with x-ray diffraction, Raman spectroscopy, and transmission electron microscopy. In contrast to the common practice of improving the critical current density Jc and the upper critical field Hc2 of MgB2 through chemical substitution, by taking advantage of residual thermal strains, we are able to design a composite showing only a …

On The Atomic Anisotropy Of Thermal Expansion In Bulk Metallic Glass, Dongdong Qu, Klaus-Dieter Liss, Kun Yan, Mark Reid, Jonathan Almer, Yanbo Wang, Xiaozhou Liao, Jun Shen

Dr Jun Shen

Glass transition temperature and plastic yield strength are known to be correlated in metallic glasses. We have observed by in situ synchrotron high energy X-ray diffraction anisotropy of the thermal expansion behavior in the nearest neighbor and second nearest neighbor atomic distances in the building blocks of Zr-Cu-Ni-Al based bulk metallic glass, leading inevitably to shear. Mechanical yielding of the latter on the atomic scale leads to the glass transition and the increase of the free volume. These experimental results uncover the mechanism, how glass transition and yield strength are linked.

Thermal Degradation Of Segmented Polyurethanes, William Macknight, Zoran S. Petrovic, Zoltan Zavargo, Joseph H. Flynn

William MacKnight

Thermal, Dielectric, And Mechanical Relaxation In Poly(Benzimidazole)/Poly(Etherimide) Blends, William Macknight, Kuiming Liang, Gyorgy Banhegyi, F. E. Karasz

William MacKnight

Thermal And Rheological Properties Of A Liquid-Crystalline Polyurethane, William Macknight, Peter J. Stenhouse, Enrique M. Valles, Simon W. Kantor

William MacKnight

Thermal And Mechanical Properties Of Linear Segmented Polyurethanes With Butadiene Soft Segments, William Macknight, C. M. Brunette, S. L. Hsu, M. Rossman, N. S. Schneider

William MacKnight

No abstract provided.

Mechanical And Thermal Properties Of Aromatic Copolyesters Containing Rigid Binaphthyl Units, William Macknight, J. Manusz, R. W. Lenz

William MacKnight

No abstract provided.

Thermal, Dynamic Mechanical, And Dielectric Properties Of Hydrogenated, Sulfonated Polypentenamers, William Macknight, D. Rahrig

William MacKnight

No abstract provided.

Thermal And Dynamic Mechanical Properties Of Sulfonated Polypentenamers, William Macknight, D. Rahrig

William MacKnight

No abstract provided.

Properties Of Polyethylene Modified With Phosphonate Side Groups. I. Thermal And Mechanical Properties.Pdf, William Macknight, R. A. Weiss, R. W. Lenz

William MacKnight

No abstract provided.

The Hydrogenation Of A Polypentenamer And Thermal Properties Of The Resulting Products, William Macknight, K. Sanui, R. W. Lenz

William MacKnight

No abstract provided.

Mechanical And Thermal Properties Of Phosphorylated Polyethylene, William Macknight, P. J. Phillips

William MacKnight

No abstract provided.