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Ultrafast Non-Equilibrium Electron Dynamics in Metal Nanoparticles
Published in Kong-Thon Tsen, and Nanostructures, 2018
The electron gas is collectively described by its temperature Te, and the electron gas kinetics by the Te time evolution, when a Fermi-Dirac distribution fFD is established. This is not the case for short times (i.e., a few hundred femtoseconds), for which the distribution is athermal and the non-Fermi-Dirac time-dependent f must be used. An important collective parameter here is the transient excess energy of the electron gas Δue, that is, its energy at time t minus the one before excitation: Δue(t)=2me3/2π2ℏ3∫E3/2Δf(E,t)dE=a[Te2(t)−T02]
Diagnostics and prediction of geomechanical objects state based on back analysis
Published in Vladimir Litvinenko, Geomechanics and Geodynamics of Rock Masses: Selected Papers from the 2018 European Rock Mechanics Symposium, 2018
Pre-mine degassing is an inherent element of coal mining. It allows mitigation of induced accidents in mines (coal and gas outbursts, rock bursts) (Seidle, 2011) and also furnishes an alternative and ecology-friendly energy source-methane (Nambo, 2001). Choosing an optimized pattern of degassing boreholes, as well as estimating degassing time and amount of gas recovered requires data on gas-kinetics indices of coal beds out of which the key parameter is a gas content S. The existent methods of in situ estimation of S are based on the lab experiments with coal samples, or borehole pressure measurements (Diamond & Schatzel, 1998, Seidle, 2011). The results are interpreted, as a rule, using integral approaches and simple models while useful information on the properties of coal and country rocks gets “lost.”
Diagnostics and prediction of geomechanical objects state based on back analysis
Published in Vladimir Litvinenko, EUROCK2018: Geomechanics and Geodynamics of Rock Masses, 2018
Pre-mine degassing is an inherent element of coal mining. It allows mitigation of induced accidents in mines (coal and gas outbursts, rock bursts) (Seidle, 2011) and also furnishes an alternative and ecology-friendly energy source-methane (Nambo, 2001). Choosing an optimized pattern of degassing boreholes, as well as estimating degassing time and amount of gas recovered requires data on gas-kinetics indices of coal beds out of which the key parameter is a gas content S. The existent methods of in situ estimation of S are based on the lab experiments with coal samples, or borehole pressure measurements (Diamond & Schatzel, 1998, Seidle, 2011). The results are interpreted, as a rule, using integral approaches and simple models while useful information on the properties of coal and country rocks gets “lost.”
Tuning phonon transport spectrum for better thermoelectric materials
Published in Science and Technology of Advanced Materials, 2019
While it is clear from above that impedance of phonon transport is stronger for smaller grains, an important question now is; what is the limit to suppression of phonon relaxation or mean free path? A widely accepted reference so far is the minimum thermal conductivity scenario, i.e. mean free path of phonon becomes equal to half its wavelength. Aiming to gain further insight into this aspect, measurements have been performed for nanocrystal grains with diameters of 3, 5, and 40 nm [182]. The samples are epitaxial silicon nanocrystalline (SiNC) structures composed of grains separated by ultrathin silicon-oxide films. The ultrathin silicon-oxide films have nanowindows that connect the nanograins preserving the crystal orientation, and thus, allowing electrons to travel with coherent wavefunctions. Thermal conductivities of SiNC structures are significantly below the values of bulk amorphous Si and SiO2. To identify the mechanism of the low thermal conductivity, its temperature dependence was measured. Figure 7(a) summarizes the temperature dependence of the thermal conductivity of SiNC structures compared with those of amorphous Si and amorphous SiO2 [183–185]. The temperature dependence was successfully reproduced by a phonon gas kinetics model with intrinsic (bulk) transport properties obtained by first-principle-based anharmonic lattice and phonon transmittance across silicon-oxide films obtained by atomistic Green’s function. Consequently, as shown in Figure 7(b), the analysis revealed that relaxation time of acoustic phonons in the case of 3-nm SiNC structures are suppressed below the minimum thermal conductivity scenario.