Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 30 for “"mean free paths"”.
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Studying phonon mean free paths at the nanoscale : modeling and experiments
… from phonons with different frequencies and mean free paths (MFPs). Knowing the phonon MFP distribution allows us to gain insight into the fundamental microscopic transport physics and has important implications for many energy applications. The key metric that quantifies the relative …
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Heat transport by phonons in crystalline materials and nanostructures
… emphasizes advancing understanding of the mean-free-paths (i.e., the distance phonons propagate without being scattered) of acoustic phonons, which are the dominant heat carriers in most crystalline semiconductor nanostructures. Two primary tools for the studies presented in this …
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Proximity effect in superconductors: Experimental and theoretical determination of the transition temperature
… Werthamer; this theory is valid only when the mean free paths in the two metals are small compared to the respective coherence lengths, (ii) an extension, under certain restrictive assumptions, of the above theory to all values of the mean free paths. The experimental work consists of …
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Thermal conductivity of superconducting tin films in a magnetic field
… temperatures from 0.3 to 10 K. They had electron mean free paths which were from 18% to 85% of the bulk coherence 1ength Eo. The Landau-Ginzburg parameter x o was sufficiently enhanced by the effect of the.short mean free paths that in our thicker films we were able to observe the surface. sheath …
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A moment-preserving single-event Monte Carlo model of electron and positron energy-loss straggling
… energy-losses and extremely small collision mean free paths. The resulting transport process is dominated by very frequent small energy transfer collisions but a significant contribution to the overall energy-loss distribution comes from the infrequent high energy-losses. Sufficient …
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Study of phonon-dislocation interaction in LiF and KCl crystals
… Yet, some fraction of phonons still have long mean-free-paths. Numerical calculations for the mean-free-paths assuming dynamic scattering processes and including phonon focusing effects are in fair agreement with experiments made at low temperatures. Our thermal conductivity measurements on KCl …
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Niobium-Tantalum Superlattices Grown by Molecular Beam Epitaxy: Structure, Transport, and Superconducting Properties
… (MBE) techniques. For the first time, electronic mean free paths and crystal domain sizes were much larger than the imposed wavelength in metallic superlattices. X-ray structure factor determinations of superlattices grown in four different crystal orientations found that interfacial alloying was …
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Ab initio study of electron transport in lead telluride
… Next, we study the screening effect of free carriers on electron transport by modulating the polar scattering. These considerations enabled us to report parameter-free first-principles calculation of electron and phonon transport in PbTe, including mode-by-mode electron-phonon …
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Pseudospin transfer torques and the effect of disorder in semiconductor electron bilayers
… semiconductor bilayers requires materials with mean-free paths larger than the spatial extent of the system.
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Carbon nanotubes as interconnect for next generation network on chip
… current carrying capacity and large electron mean free paths. This work suggests using Single Wall Carbon Nanotubes (SWCNT) as interconnects for Networks-on-Chip as they consume less energy and gives more throughput and bandwidth when compared with traditional Copper wires.
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Molecular dynamics analysis of spectral characteristics of phonon heat conduction in silicon
… some lingering questions surrounding the phonon mean free path and importance of different polarizations. This research investigates phonon transport in bulk crystalline silicon using molecular dynamics and lattice dynamics. The interactions are modeled with the environment dependent interatomic …
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Computational investigation of the thermal conductivities and phonon properties of strontium cobalt oxides
… heat capacities, group velocities, lifetimes and mean free paths have been calculated, and the key roles of local atomic environment and crystal symmetry in determining the thermal conductivities have been identified. We have also analyzed the impact of interfaces, isotropic strains and defects on …
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The thermal conductivity of double nitrate crystals below 1 K
… independent of frequency. The phonon mean free paths, calculated in the usual way from the thermal conductivities of the individual samples, were appreciably greater than the smallest dimensions of the respective samples. A depression observed in the thermal conductivity of samples …
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Theoretical and experimental investigation of Hall thruster miniaturization
… plasma density required to maintain collisional mean free paths. Although the thrust efficiency was significantly lower than predicted by scaling laws, the MHT-9 is the best performing subcentimeter diameter Hall thruster built to date. A dimensionless performance analysis has shown that while …
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Effects of vacancies and electron temperature on the electron phonon coupling in cubic silicon carbide and their connection to the inelastic thermal spike
… on the presence of vacancies. Electron-phonon mean free paths were calculated to explore the possibility of extending those calculations to lower vacancy concentrations using a rule-of-mixtures approach. </p><p>The electron-temperature-dependent couplings were implemented in the Two-Temperature …
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Architecture and CAD for carbon nanomaterial integrated circuits
… high current densities, and micron-scale mean free paths. Carbon nanomaterial transistors offer many opportunities for circuits and systems, but also present a number of challenges in terms of fabrication, architecture design, and CAD integration. In order to be useful to the semiconductor …
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Energy conversion using thermal transpiration : optimization of a Knudsen compressor
… on the order of, or smaller than, the molecular mean free path, then the gas flows from cold to hot regions. The nanoscale nature of this phenomenon lends itself to use in nanoscale devices where moving parts are difficult to manufacture. Additional applications include low pressure environments, …
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semiconducting carbon nanotube transistors: electron and spin transport properties
… and technologically due to their long mean free paths and high carrier velocities at room temperature, and possibly very long spin-scattering lengths. This thesis will describe experiments to probe the charge-and spin-transport properties of long, clean individual SWNTs prepared by …
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Optical transient grating measurements of micro/nanoscale thermal transport and mechanical properties
… First-principles calculations of the phonon mean free paths in Si and GaAs were compared with experimental results and showed good agreement. Preliminary measurements on promising thermoelectric materials such as PbTe and Bi2Te3 are presented showing evidence of non-diffusive transport at …
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Studies of non-hydrodynamic processes in ICF implosions on OMEGA and the National Ignition Facility
… are expected to modify plasma dynamics when ion mean-free-paths and collision times become comparable to the scale sizes of the plasma. Such conditions arise during the shock convergence phase of inertial confinement fusion (ICF) implosions, when they may modify the compression and ignition of …
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