Doctor of Philosophy

dissertationIn this thesis, I examine the impact of the mandatory adoption of International Financial Reporting Standards (IFRS) on accounting comparability and representational faithfulness. The motivation for the study is to provide further evidence on whether mandatory IFRS adoption improves accounting comparability, and whether this improvement comes at the cost of reduced representational faithfulness. The faithful representation of the underlying economic phenomena of the reporting entity and accounting comparability are both desirable qualitative characteristics of financial information. Nevertheless, the conceptual framework considers comparability to be of secondary importance relative to representational faithfulness. That is, greater comparability is preferable, provided the accounting information is faithfully representative of the underlying economic phenomena. I document empirically that both cross-country and within-country accounting comparability increase while representational faithfulness decreases with mandatory IFRS adoption. Inconsistent with my prediction, I find that the impact of IFRS adoption on within-country comparability is not conditional on the flexibility of the local accounting standards relative to IFRS. Moreover, the results suggest that while all firms experience decreases in representational faithfulness, firms with higher quality local accounting standards than IFRS experience fewer decreases in representational faithfulness than firms with lower quality local accounting standards than IFRS. Overall, my results provide evidence of a trade-off between improved cross-country accounting comparability and reduced representational faithfulness among all adopters of IFRS. The empirical evidence from this study shall be of interest to policy and accounting standard setters

Structure and properties of (1-x)Pb(Mg1/2W1/2)O3–xPb(Zr0.5Ti0.5)O3 solid solution ceramics

The widely used piezoelectric Pb(Zr1−x Ti x )O3 ceramics have been known to have Zr4+ and Ti4+ randomly distributed on the B-site lattice in the ABO3 perovskite structure. In this study, we attempted to develop long range 1:1 B-site cation order by forming the solid solution of (1 − x)Pb(Mg1/2W1/2)O3 − xPb(Zr0.5Ti0.5)O3 (x ≥ 0.60). High temperature X-ray diffraction tests indicate that the cation order is embedded in the structural order. The solid solution ceramics appear to have a non-cubic paraelectric phase above their Curie temperatures. The competition between the antiferroelectric order in Pb(Mg1/2W1/2)O3 and the ferroelectric order in Pb(Zr0.5Ti0.5)O3 leads to the relaxor ferroelectric behavior in the solid solution. Since the temperature at dielectric maximum, T m, is significantly above room temperature, regular polarization versus electric field hysteresis loops are recorded in these compositions at room temperature. In addition, these ceramics show very good piezoelectric properties

A critical review of research on strategies in learning Chinese as both a second and foreign language

This article critically reviews strategy research on learning Chinese both as a second and foreign language. Through a careful examination of major data bases in both the Chinese and English languages, the article summarizes research in the field and the principal research methods used in the studies reviewed. Moreover, key limitations in research designs, inconsistencies in reported findings, inappropriate use of research methods, and weaknesses in both Chinese- and English-language publications are discussed. The article concludes by calling for future research paying more attention to current language learning strategy theories and practices

Rare case of magnetic Ag3+^{3+} ion: double perovskite Cs2_{2}KAgF6_{6}

Normally $4d$ or $5d$ transition metals are in a low-spin state. Here using first-principles calculations, we report on a rare case of a high-spin $S$=1 magnetic state for the Ag$^{3+}$ ion in the double perovskite Cs$_{2}$KAgF$_{6}$. We also explored a possibility of a conventional low-spin $S$=0 ground state and find an associated tetragonal distortion to be 0.29 {\AA}. However, the lattice elastic energy cost and the Hund exchange loss exceed the e$_{g}$ crystal-field energy gain, thus making the low-spin tetragonal structure less favorable than the high-spin cubic structure. We conclude that the compact perovskite structure of Cs$_{2}$KAgF$_{6}$ is an important factor in stabilizing the unusual high-spin ground state of Ag$^{3+}$.Comment: 6 pages, 6 figures, accepted for publication in PR

A continuum model for the dynamics of the phase transition from slow-wave sleep to REM sleep

Previous studies have shown that activated cortical states (awake and rapid eye-movement (REM) sleep), are associated with increased cholinergic input into the cerebral cortex. However, the mechanisms that underlie the detailed dynamics of the cortical transition from slow-wave to REM sleep have not been quantitatively modeled. How does the sequence of abrupt changes in the cortical dynamics (as detected in the electrocorticogram) result from the more gradual change in subcortical cholinergic input? We compare the output from a continuum model of cortical neuronal dynamics with experimentally-derived rat electrocorticogram data. The output from the computer model was consistent with experimental observations. In slow-wave sleep, 0.5–2-Hz oscillations arise from the cortex jumping between “up” and “down” states on the stationary-state manifold. As cholinergic input increases, the upper state undergoes a bifurcation to an 8-Hz oscillation. The coexistence of both oscillations is similar to that found in the intermediate stage of sleep of the rat. Further cholinergic input moves the trajectory to a point where the lower part of the manifold in not available, and thus the slow oscillation abruptly ceases (REM sleep). The model provides a natural basis to explain neuromodulator-induced changes in cortical activity, and indicates that a cortical phase change, rather than a brainstem “flip-flop”, may describe the transition from slow-wave sleep to REM

Structural Relationship between Negative Thermal Expansion and Quartic Anharmonicity of Cubic ScF_3

Cubic scandium trifluoride (ScF_3) has a large negative thermal expansion over a wide range of temperatures. Inelastic neutron scattering experiments were performed to study the temperature dependence of the lattice dynamics of ScF3 from 7 to 750 K. The measured phonon densities of states show a large anharmonic contribution with a thermal stiffening of modes around 25 meV. Phonon calculations with first-principles methods identified the individual modes in the densities of states, and frozen phonon calculations showed that some of the modes with motions of F atoms transverse to their bond direction behave as quantum quartic oscillators. The quartic potential originates from harmonic interatomic forces in the DO_9 structure of ScF_3, and accounts for phonon stiffening with the temperature and a significant part of the negative thermal expansion

Design of a Direct-Detection Wind and Aerosol Lidar for Mars Orbit

The present knowledge of the Mars atmosphere is greatly limited by a lack of global measurements of winds and aerosols. Hence, measurements of height-resolved wind and aerosol profiles are a priority for new Mars orbiting missions. We have designed a direct-detection lidar (MARLI) to provide global measurements of dust, winds and water ice profiles from Mars orbit. From a 400-km polar orbit, the instrument is designed to provide wind and backscatter measurements with a vertical resolution of 2 km and with resolution of 2 in latitude along track. The instrument uses a single-frequency, seeded Nd:YAG laser that emits 4 mJ pulses at 1064 nm at a 250 Hz pulse rate. The receiver utilizes a 50-cm diameter telescope and a double edge Fabry-Prot etalon as a frequency discriminator to measure the Doppler shift of the aerosol-backscatter profiles. The receiver also includes a polarization-sensitive channel to detect the cross-polarized backscatter profiles from water ice. The receiver uses a sensitive 4 4 pixel HgCdTe avalanche photodiode array as a detector for all signals. Here we describe the measurement concept, instrument design, and calculate its performance for several cases of Mars atmospheric conditions. The calculations show that under a range of atmospheric conditions MARLI is capable of measuring wind speed profiles with random error of 24 m/s within the first three scale heights, enabling vertically resolved mapping of transport processes in this important region of the atmosphere

Synergistically activated dual-locked fluorescent probes to monitor H₂S-induced DNA damage

Naphthalimide-based fluorescent probes (NAN0-N3 and NAN6-N3) were developed with dual locked fluorescence. Here, ≥1.9 × 10−2 mM of H2S and ≥2.2 × 10−2 μg mL−1 of DNA could unlock a highly sensitive off-on fluorescence response through synergistic changes of the molecular structure and conformation. As such, the probes could monitor DNA damage induced by the overexpression of H2S, and were able to evaluate the degree of apoptosis of living cells mediated by H2S-induced mtDNA or nDNA damage.</p

HgCdTe Avalanche Photodiode Array Detectors with Single Photon Sensitivity and Integrated Detector Cooler Assemblies for Space Lidar Applications

A HgCdTe avalanche photodiode (APD) focal plane array assembly with linear mode photon-counting capability has been developed for space lidar applications. An integrated detector cooler assembly (IDCA) has been built using a miniature Stirling cooler. A microlens array has been included to improve the fill factor. The HgCdTe APD has a spectral response from 0.9- to 4.3-m wavelengths, a photon detection efficiency as high as 70%, and a dark count rate of <250 kHz at 110 K. The mass of the IDCA is 0.8 kg and the total electrical power consumption is about 7 W. The HgCdTe APD arrays have been characterized at NASA Goddard Space Flight Center. A series of environmental tests have been conducted for the IDCAs, including vibration, thermal cycling, and thermal vacuum tests. A description of the device and the test results at NASA are given in this paper