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Full-Text Articles in Aerospace Engineering
Finite-Size Effects On Molecular Dynamics Interfacial Thermal-Resistance Predictions, Zhi Liang, Pawel Keblinski
Finite-Size Effects On Molecular Dynamics Interfacial Thermal-Resistance Predictions, Zhi Liang, Pawel Keblinski
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Using Molecular Dynamics Simulations, We Study the Role of Finite Size Effects on the Determination of Interfacial Thermal Resistance between Two Solids Characterized by High Phonon Mean Free Paths. in Particular, We Will Show that a Direct, Heat Source-Sink Method Leads to Strong Size Effect, Associated with Ballistic Phonon Transport to and From, and Specular Reflections at the Simulation Domain Boundary. Lack of Proper Account for These Effects Can Lead to Incorrect Predictions About the Role of Interfacial Bonding and Structure on Interfacial Thermal Resistance. We Also Show that the Finite Size Effect Can Be Dramatically Reduced by Introduction of …
Thermal Transport Across A Substrate-Thin-Film Interface: Effects Of Film Thickness And Surface Roughness, Zhi Liang, Kiran Sasikumar, Pawel Keblinski
Thermal Transport Across A Substrate-Thin-Film Interface: Effects Of Film Thickness And Surface Roughness, Zhi Liang, Kiran Sasikumar, Pawel Keblinski
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Using Molecular Dynamics Simulations and a Model AlN-GaN Interface, We Demonstrate that the Interfacial Thermal Resistance RK (Kapitza Resistance) between a Substrate and Thin Film Depends on the Thickness of the Film and the Film Surface Roughness When the Phonon Mean Free Path is Larger Than Film Thickness. in Particular, When the Film (External) Surface is Atomistically Smooth, Phonons Transmitted from the Substrate Can Travel Ballistically in the Thin Film, Be Scattered Specularly at the Surface, and Return to the Substrate Without Energy Transfer. If the External Surface Scatters Phonons Diffusely, Which is Characteristic of Rough Surfaces, RK is Independent …
Thermal Resistance At An Interface Between A Crystal And Its Melt, Zhi Liang, William J. Evans, Pawel Keblinski
Thermal Resistance At An Interface Between A Crystal And Its Melt, Zhi Liang, William J. Evans, Pawel Keblinski
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Non-Equilibrium Molecular Dynamics Simulations Are Used to Determine Interfacial Thermal Resistance (Kapitza Resistance) between a Crystal and its Melt for Three Materials Including Ar, H2O, and C8H 18 (Octane). the Simulation Results Show that the Kapitza Resistance at a Crystal-Melt Interface is Very Small and Thus Has a Negligible Effect on Thermal Transport Across the Crystal-Melt Interface. the Underlying Origins of This Behavior Are the Very Good Vibrational Property Match between the Two Materials Forming the Interface and Good Interfacial Bonding. the Result Also Indicates that the Commonly-Used Assumption that Temperature Profile is Continuous at the Crystal-Melt Interface is Valid …
Curvature Induced Phase Stability Of An Intensely Heated Liquid, Kiran Sasikumar, Zhi Liang, David G. Cahill, Pawel Keblinski
Curvature Induced Phase Stability Of An Intensely Heated Liquid, Kiran Sasikumar, Zhi Liang, David G. Cahill, Pawel Keblinski
Mechanical and Aerospace Engineering Faculty Research & Creative Works
We Use Non-Equilibrium Molecular Dynamics Simulations to Study the Heat Transfer Around Intensely Heated Solid Nanoparticles Immersed in a Model Lennard-Jones Fluid. We Focus Our Studies on the Role of the Nanoparticle Curvature on the Liquid Phase Stability under Steady-State Heating. for Small Nanoparticles We Observe a Stable Liquid Phase Near the Nanoparticle Surface, Which Can Be at a Temperature Well above the Boiling Point. Furthermore, for Particles with Radius Smaller Than a Critical Radius of 2 Nm We Do Not Observe Formation of Vapor Even above the Critical Temperature. Instead, We Report the Existence of a Stable Fluid Region …
Femtosecond And Nanosecond Dual-Laser Optical Emission Spectroscopy Of Gas Mixtures, Cheng Hsiang Lin, Zhi Liang, Jun Zhou, Hai-Lung Tsai
Femtosecond And Nanosecond Dual-Laser Optical Emission Spectroscopy Of Gas Mixtures, Cheng Hsiang Lin, Zhi Liang, Jun Zhou, Hai-Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
A Method Employing an Integrated Femtosecond (Fs) and Nanosecond (Ns) Dual-Laser System Was Developed to Generate Plasma with Desired Radical Species from Gas Mixtures Via a Fs Laser Pulse and Then to Excite Selected Radical Species to Higher Electronic States using a Wavelength-Tunable Ns Laser Pulse. an Optical Spectrometer Was Used to Measure the Emission Spectra and Identify the Transition from the Excited Electronic State to the Ground State. the Proposed Technique Has Been Demonstrated for an N2-CO2 Mixture with Various Time Delays between the Two Fs and Ns Pulses. the Results Have Indicated that the Population of Selected Radical …
Radical Species Generation And Their Lifetime Extension By A Femtosecond And Nanosecond Dual-Laser System, Cheng Hsiang Lin, Zhi Liang, Jun Zhou, Hai-Lung Tsai
Radical Species Generation And Their Lifetime Extension By A Femtosecond And Nanosecond Dual-Laser System, Cheng Hsiang Lin, Zhi Liang, Jun Zhou, Hai-Lung Tsai
Mechanical and Aerospace Engineering Faculty Research & Creative Works
For Many Material Processes, Desired Radical Species at Excited States Are Produced Which Interact with a Given Substrate for a Certain Period of Time Allowing Chemical Reactions between Them to Occur and Complete. Hence, It is Important to Maintain the Population of the Excited Radical Species for an Extended Period of Time, I.e., their Lifetime, Which is Defined as the Time for Emission Intensity to Decay to 1/e of the Initial Intensity. in This Study, a Femtosecond-Nanosecond (Fs-Ns) Dual-Laser System Was Employed to Generate Desired Radical Species Via the Fs Laser And, Then, to Extend the Lifetime of the Radical …
Nonlinear Development And Secondary Instability Of Traveling Crossflow Vortices, Fei Li, Meelan M. Choudhari, Lian Duan, Chau-Lyan Chang
Nonlinear Development And Secondary Instability Of Traveling Crossflow Vortices, Fei Li, Meelan M. Choudhari, Lian Duan, Chau-Lyan Chang
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Building upon the prior research targeting the laminar breakdown mechanisms associated with stationary crossflow instability over a swept-wing configuration, this paper investigates the secondary instability of traveling crossflow modes as an alternate scenario for transition. For the parameter range investigated herein, this alternate scenario is shown to be viable unless the initial amplitudes of the traveling crossflow instability are lower than those of the stationary modes by considerably more than one order of magnitude. The linear growth predictions based on the secondary instability theory are found to agree well with both parabolized stability equations and direct numerical simulation, and the …
Crystallization In Nano-Confinement Seeded By A Nanocrystal -- A Molecular Dynamics Study, Heng Pan, Costas Grigoropoulos
Crystallization In Nano-Confinement Seeded By A Nanocrystal -- A Molecular Dynamics Study, Heng Pan, Costas Grigoropoulos
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Seeded crystallization and solidification in nanoscale confinement volumes have become an important and complex topic. Due to the complexity and limitations in observing nanoscale crystallization, computer simulation can provide valuable details for supporting and interpreting experimental observations. In this article, seeded crystallization from nano-confined liquid, as represented by the crystallization of a suspended gold nano-droplet seeded by a pre-existing gold nanocrystal seed, was investigated using molecular dynamics simulations in canonical (NVT) ensemble. We found that the crystallization temperature depends on nano-confinement volume, crystal orientation, and seed size as explained by classical two-sphere model and Gibbs-Thomson effect.
Parametric Studies Of The Thermal And Momentum Accommodation Of Monoatomic And Diatomic Gases On Solid Surfaces, Zhi Liang, Pawel Keblinski
Parametric Studies Of The Thermal And Momentum Accommodation Of Monoatomic And Diatomic Gases On Solid Surfaces, Zhi Liang, Pawel Keblinski
Mechanical and Aerospace Engineering Faculty Research & Creative Works
The Thermal Accommodation Coefficient (TAC) and the Momentum Accommodation Coefficient (MAC) Are the Two Fundamental Parameters Quantifying the Solid-Gas Energy and Momentum Exchange Efficiencies. We Use Molecular Dynamics (MD) Simulations to Study the Effect of Individual Interfacial Parameters Including, (I) Solid-Gas Interaction Strength, (Ii) Gas-Solid Atomic Mass Ratio, (Iii) Solid Elastic Stiffness, and (Iv) Temperature, on TAC and MAC at Solid Surfaces in Contact with Monoatomic and Diatomic Gases. in Addition to Offering a Fundamental Understanding on How These Individual Parameters Affect the Nature of Gas-Solid Collisions, We Provide an Extensive Database for the TAC and MAC. We Also Study …
Association Between Vitamin D Receptor Gene Polymorphisms (Fok1 And Bsm1) And Osteoporosis: A Systematic Review, Zahra Mohammadi, Fateme Fayyazbakhsh, Mehdi Ebrahimi, Mahsa M. Amoli, Patricia Khashayar, Mahboubeh Dini, Reza Nezam Zadeh, Abbasali Keshtkar, Hamid Reza Barikani
Association Between Vitamin D Receptor Gene Polymorphisms (Fok1 And Bsm1) And Osteoporosis: A Systematic Review, Zahra Mohammadi, Fateme Fayyazbakhsh, Mehdi Ebrahimi, Mahsa M. Amoli, Patricia Khashayar, Mahboubeh Dini, Reza Nezam Zadeh, Abbasali Keshtkar, Hamid Reza Barikani
Mechanical and Aerospace Engineering Faculty Research & Creative Works
Osteoporosis is a Health Concern Characterized by Reduced Bone Mineral Density (BMD) and Increased Risk of Fragility Fractures. Many Studies Have Investigated the Association between Genetic Variants and Osteoporosis. Polymorphism and Allelic Variations in the Vitamin D Receptor Gene (VDR) Have Been Found to Be Associated with Bone Mineral Density. However, Many Studies Have Not Been Able to Find This Association. Literature Review Was Conducted in Several Databases, Including MEDLINE/Pubmed, Scopus, EMBASE, Ebsco, Science Citation Index Expanded, Ovid, Google Scholar, Iran Medex, Magiran and Scientific Information Database (SID) for Papers Published between 2000 and 2013 Describing the Association between Fok1 …