The complete and accurate thermodynamic and kinetic description of any systemis crucialfor understanding and predicting its properties. A particular interest is in systemsthat are used for some practical applications and have to be constantly improved usingmodification of their composition and structure. This task can be quite accuratelysolved at a fundamental level by density functional theory methods. Thesemethods areapplied to two practically important systems Fe-Cr and TiC-ZrC.The elastic properties of pure iron and substitutionally disordered Fe-Cr alloy are investigatedas a function of temperature and concentration using first-principles electronicstructurecalculations by the exact muffin-tin orbitals method. The temperature effectson the elastic properties are included via the electronic, magnetic, and lattice expansioncontributions. It is shown that the degree of magnetic order in both pure iron andFe90Cr10 alloy mainly determines the dramatic change of the elastic anisotropy of thesematerials at elevated temperatures. A peculiarity in the concentration dependence ofthe elastic constants in Fe-rich alloys is demonstrated and related to a change in theFermi surface topology.A thermodynamic model for the magnetic alloys is developed from first principles andapplied to the calculation of bcc Fe-Cr phase diagram. Various contributions to the freeenergy (magnetic, electronic, and phonon) are estimated and included in the model. Inparticular, it is found that magnetic short range order effects are important just abovethe Curie temperature. The model is applied for calculating phase equilibria in disorderedbcc Fe-Cr alloys. Model calculations reproduce a feature known as a Nishizawahorn for the Fe-rich high-temperature part of the phase diagram.The investigation of the TiC-ZrC system includes a detailed study of the defect formationenergies and migration barriers of point defects and defect complexes involvedin the diffusion process. It is found, using ab initio atomistic simulations of vacancymediateddiffusion processes in TiC and ZrC, that a special self-diffusion mechanism isoperative for metal atom diffusion in sub-stoichiometric carbides. It involves a noveltype of a stable point defect, a metal vacancy ”dressed” in a shell of carbon vacancies.It is shown that this vacancy cluster is strongly bound and can propagate through thelattice without dissociating. / <p>QC 20120604</p> / HERO-M

Interrogating metals with ultrasonic waves can be used to evaluate their microstructural and mechanical properties. These techniques analyze ultrasonic wave features in order to make inferences on the medium of interest. Current research is being conducted to determine higher order elastic properties and characterize material degradation of 7075-T651 aluminum with ultrasonics. This thesis topic will use acoustoelasticity, the stress dependency of acoustic velocity, to accomplish these goals. Acoustoelasticity is a manifestation of the inherent nonlinearity in the interatomic binding energy, which appears mathematically as higher order elastic terms in the stress strain constitutive relation. The acoustoelasticity will be determined for longitudinal and shear waves propagating through a sample under uni-axial stress. Experimentally, specific techniques and tooling will be designed to insure accurate measurements of acoustic wave velocity as a function of stress. Using acoustoelasticity the third order elastic constants of 7075-T651 aluminum will be determined. Further, Al samples will be fatigue damaged and acoustoelasticity and third order elastic constants will be mapped versus damage. Literature will be used to verify measured values of acoustoelasticity as well as provide theoretical models for acoustoelastic dependence on damage.

This study investigates wave propagation in an elastic half-space with quadratic nonlinearity due to a line load on the surface. The consideration of this problem is one of the well known Lamb problems. Even since Lamb's original solution, numerous investigators have obtained solutions to many different variants of the Lamb problem. However, most of the solutions existing in the current literature are limited to wave propagation in a linear elastic half-space. In this work, the Lamb problem in an elastic half-space with quadratic nonlinearity is considered. For this, the problem is first formulated as a hyperbolic system of conservation laws, which is then solved numerically using a semi-discrete central scheme. The numerical method is implemented using the package CentPack. The accuracy of the numerical method is first studied by comparing the numerical solution with the analytical solution for a half-space with linear response (the original Lamb's problem). The numerical results for the half-space with quadratic nonlinearity are than studied using signal-processing tools such as the fast Fourier transform (FFT) in order to analyze and interpret any nonlinear effects. This in particular gives the possibility to evaluate the excitation of higher order harmonics whose amplitude is used to infer material properties. To quantify and compare the nonlinearity of different materials, two parameters are introduced; these parameters are similar to the acoustical nonlinearity parameter for plane waves.

Optical properties of Tl4In3GaSe8, Tl4InGa3Se8, Tl4In3GaS8, Tl2InGaS4 and Tl4InGa3S8 chain and layered crystals were studied by means of photoluminescence (PL) and transmission-reflection experiments. Several emission bands were observed in the PL spectra within the 475-800 nm wavelength region. The results of the temperature- and excitation intensity-dependent PL measurements in 15-300 K and 0.13&times / 10-3-110.34 W cm-2 ranges, respectively, suggested that the observed bands were originated from the recombination of electrons with the holes by realization of donor-acceptor or free-to-bound type transitions. Transmission-reflection measurements in the wavelength range of 400-1100 nm revealed the values of indirect and direct band gap energies of the crystals studied. By the temperature-dependent transmission measurements in 10-300 K range, the rates of change of the indirect band gap of the samples with temperature were found to be negative. The oscillator and dispersion energies, and zero-frequency refractive indices were determined by the analysis of the refractive index dispersion data using the Wemple&ndash / DiDomenico single-effective-oscillator model. Furthermore, the structural parameters of all crystals were defined by the analysis of X-ray powder diffraction data. The determination of the compositional parameters of the studied crystals was done by energy dispersive spectral analysis experiments.

Trapping centres in as-grown TlInS2 layered single crystals have been studied by using a thermally stimulated current (TSC) technique. TSC measurements have been performed in the temperature range of 10-300 K with various heating rates. Experimental evidence has been found for the presence of five trapping centres with activation energies 12, 14, 400, 570 and 650 meV. Their capture cross-sections and concentrations were also determined. It is concluded that in these centres retrapping is negligible as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. An exponential distribution of traps was revealed from the analysis of the TSC data obtained at different light excitation temperatures. The transmission and reflection spectra of TlInS2 crystals were measured over the spectral region of 400-1100 nm to determine the absorption coefficient and refractive index. The analysis of the room temperature absorption data revealed the coexistence of the indirect and direct transitions. The absorption edge was observed to shift toward the lower energy values as temperature increases from 10 to 300 K. The oscillator and the dispersion energies, and the zero-frequency refractive index were also reported. Furthermore, the chemical composition of TlInS2 crystals was determined from energy dispersive spectroscopic analysis. The parameters of monoclinic unit cell were found by studying the x-ray powder diffraction.

名古屋大学博士学位論文 学位の種類:博士(工学) 学位授与年月日:平成19年9月28日

Particles originating from bacteria, fungi (including mold spores, mildew, yeast), pollen, dust mites, and viruses can induce immune responses that trigger allergies and asthma. Carpeting is believed to act as a "sink" where bioparticulates are trapped via adhesive interactions and then are released by foot traffic or cleaning. This scenario can result in an accumulation of contaminants at higher levels than would be found outdoors or in a carpet-less environment. Numerous organizations (school districts, hospitals) have taken steps to remove carpeting, even though this hypothesis remains unproven. While statistical studies exist both in support and denial of the accumulation hypothesis, there is little fundamental understanding of the microscopic-level interactions between carpet and bioparticles. A fundamental understanding of particle affinities with polymers utilized in carpet would help to develop accurate models and address real problems in a rational and productive manner. In addition, a solution to the bioparticulate accumulation problem would have a profound impact on US health, resulting in significant economic savings. More than 20 million people suffer from asthma in the U.S., with children being the most vulnerable. In 2000 there were 9.3 million physician office visits and 1.8 million emergency room visits due to asthma alone, resulting in an estimated $9.4 billion in medical costs and $4.6 billion in lost productivity annually. In this thesis, two measurement techniques were developed to quantify the adhesive interactions between biological particulates and polymeric carpeting materials. Atomic force microscopy (AFM) was used to measure the adhesive interactions of relevant biological particulates (in this case the E. coli bacteria and A. artemisiifolia ragweed pollen grains) with Nylon-6 and Nylon-6,6, polyamide-12 and polystyrene. The adhesion force measurements were modeled using several adhesion theories. We found that the Hamaker models were sufficient for explaining the data, indicating the prominence of van der Waals forces in controlling bioparticle interactions with polyamides. In addition, the geometry of the pollen played a significant role: adhesion forces were approximately a multiple of the number of contact points the grain has with the surface. Forces for E. coli and polyamides were about the same magnitude as polyamide-polyamide surface self-interactions.

An investigation of the high spectral resolution signatures and radiative forcing of tropospheric aerosol in the thermal infrared was conducted. To do so and to support advanced modeling of optical properties, a high spectral resolution library of atmospheric aerosol optical constants was developed. This library includes new optical constants of sulfate-nitrate-ammonium aqueous solutions and the collection of a broad range of existing optical constants for aerosol components, particularly mineral optical constants. The mineral optical constants were used to model and study infrared dust optical signatures as a function of composition, size, shape and mixing state. In particular, spherical and non-spherical optical models of dust particles were examined and compared to high spectral resolution laboratory extinction measurements. Then the performance of some of the most common effective medium approximations for internal mixtures was examined by modeling the optical constants of the newly determined sulfate-nitrate-ammonium mixtures. The optical signature analysis was applied to airborne and satellite high spectral resolution thermal infrared radiance data impacted by Saharan dust events. A new technique to retrieve dust microphysical properties from the dust spectral signature was developed and compared to a standard technique. The microphysics retrieved from this new technique and from a standard technique were then used to investigate the effects of dust on radiative forcing and cooling rates in the thermal IR.

Η παρούσα διατριβή εντάσσεται ερευνητικά στην περιοχή της μη γραμμικής ανάλυσης και ειδικότερα στην εύρεση βέλτιστων σταθερών για ανισότητες Sobolev στο χώρο Rn με ανώτερης τάξης δεκαδικές παραγώγους. Επίσης, δίνονται οι αντίστοιχες βέλτιστες σταθερές αυτών των ανισοτήτων πάνω στη σφαίρα Sn με τη χρησιμοποίηση ως βασικού εργαλείου την στερεογραφική προβολή. Τέλος, σαν μια εφαρμογή των ευρεθέντων ανισοτήτων έχουμε ένα θεώρημα σχετικό με αυτό των Rellich-Kondrashov και το οποίο είναι εξαιρετικής σημασίας, ιδιαίτερα στο λογισμό των μεταβολών.

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