Rare-earth transition-metal intermetallics: structure-bonding-property relationships

The purpose of this thesis is to explore novel rare-earth, transition metal compounds and to investigate their structure and bonding and how these influence their properties. We have focused on the synthesis, characterization and electronic structure investigations, as well as physical properties of ternary rare-earth Fe-rich intermetallics, e.g., LaFe13-xSi x, and RE2-xFe4Si14-y, etc;The LaFe13-xSix, (1.0 ≤ x ≤ 5.0) compounds with structures related to the cubic NaZn13type are an important series of compounds to study for possible efficient magnetic refrigeration. A systematic structural study of the compositional variation in LaFe 13-xSix exhibits a structural transformation from the cubic NaZn13-structure type to a tetragonal derivative due to preferential ordering of Fe and Si atoms. Temperature-dependent single crystal X-ray diffraction at various temperatures and electronic structure calculations (both Extended Huckel and TB-LMTO) was performed on the cubic phases to examine the origin of the large magnetic entropy change. The giant magnetocaloric effect of cubic LaFe13-xSix alloys results from coupling between magnetic ordering and structural transformation;In light of the potential superstructures that could be observed for RE2-xFe4Si14-y as well as possible modifications of semiconducting beta-FeSi2, we report herein a thorough examination of the chemical composition and structure of RE2-xFe 4Si14-y (RE = Y, Gd-Lu) using a combination of electron microscopy and X-ray diffraction, and demonstrate a new superstructure for this class of compound. The structures are built up of rare-earth silicide planes with approximate compositions RE1.2Si1.9 alternating with beta-FeSi2-derived (hkl)-type slabs. Investigation by transition electron microscopy (TEM) reveals a superstructure in the crystallographic ab-plane. Fe Mossbauer spectra confirm two different iron environments in superstructure. Magnetic susceptibilities suggest weak magnetic coupling between rare-earth elements, and resistance measurements indicate poor metallic behavior with a large residual resistivity at low temperatures, which is consistent with disorder. Electronic structure calculations on model structures identify a pseudogap in the densities of states for specific valence electron counts that helps to provide a useful electron counting scheme for this class of rare-earth/transition metal/main group compound

Dynamics of Information Packaging in Korean

This paper discusses deletion and movement operations in Korean from the perspective of information packaging, and claims that each operation is a systematic process of information packaging to generate the most optimized information structure. This paper argues that there is neither free word order nor free deletion in Korean. This paper explicitly illustrates that old arguments cannot stand still in information structure, but must undergo some kind of structural changes or deletion. This paper proposes a constraint on information packaging that covers both operations and gives an explanation of underlying motivation for them. It is also suggested to decompose each component of information structure into a feature complex. 1

Computational models for coupled electronic-vibrational energy transfer in biological photosynthetic complexes

The specialized pigment-protein complexes involved in the first process of photosynthesis are light-harvesting structures that are composed of networks of chromophores in protein scaffolds. Though light-harvesting complexes vary in chromophore composition and protein structure, they are capable of transferring the absorbed energy as molecular excitation energy from chromophore to chromophore with maximal efficiency. Thus, numerous interdisciplinary studies focus on elucidating energy transfer mechanisms in these biological complexes and how the same principles can be applied to artificial photosynthetic and photovoltaic machines. From advanced spectroscopic measurements and theoretical models, the interaction between the excited electronic states and the nuclear vibrational degrees of freedom is now established to be crucial for efficient energy transfer. In light-harvesting complexes of plants and bacteria, it is now understood that the classical-like vibrational modes of the protein and solvent environment drive energy transfer between the energetically close electronic states of the chromophores. On the other hand, recent spectroscopic measurements on algae light-harvesting complexes discovered signatures of quantized, high frequency vibrational modes of the chromophore. Unfortunately, a deterministic interpretation of the data and the underlying Hamiltonian is hindered due to significant inhomogeneous spectral line-broadening. Though numerous model Hamiltonians have been proposed from theoretical work, various computational approximations employed in these studies necessitate empirical parameter tuning in order to obtain agreement with benchmark linear optical spectra. Thus in this work, we present a simple, but improved, computational prescription to compute the ensemble of Hamiltonians for four closely-related algae light-harvesting complexes. We verify the reliability of our proposed models by comparing simulated optical spectra with experimental measurements. We show that static disorder and inhomogeneous broadening are significant for phycobiliproteins due to large site energy fluctuations. We also show that the nuclear environment plays an important role in defining the trapping state, or the final energy acceptor. Finally, our work for the first time suggests that EET dynamics can be tuned by varying the titration states of the chromophores

Joseon mummies before mummy studies began in Korea

Mummy studies in Korea are instrumental in reconstructing the health and disease status of pre-modern Joseon peoples using firm scientific evidence. However, this scientific approach to such investigations in Korea is a relatively new discipline which began only within the last decade. Previous studies on Joseon tombs and their contents were performed exclusively by dress historians because most of the artefacts recoverable from Joseon tombs were textiles. In this report, we examine some of the excavation records left by dress historians in order to elucidate the approximate number and preservation status of Korean mummies discovered prior to the advent of their scientific investigation

Work-Related Perceptions, Injuries, and Musculoskeletal Symptoms: Comparison Between U.S.-Educated and Foreign-Educated Nurses.

Immigrants account for a significant proportion of the nursing workforce in the United States (U.S.). Although different cultural backgrounds may affect immigrant nurses' perceptions of work and occupational health risks, little research has been conducted. Defining immigrant nurses as those who received initial nursing education in foreign countries, this study examined the differences in work-related perceptions and experiences of musculoskeletal (MS) symptoms and injuries between U.S.-educated and foreign-educated nurses. We analyzed data from a cross-sectional study using a statewide random sample of 419 California registered nurses. Foreign-educated nurses reported a more positive safety climate (p = .017) and perceived their jobs as less demanding (p = .008) than did U.S.-educated nurses. The prevalence of work-related MS symptoms was significantly lower in foreign-educated nurses than in U.S.-educated nurses (p = .044), but the difference was not significant in the multivariable analyses. Positive safety climate was significantly associated with a decreased risk of work-related MS symptoms and injuries, and this relationship was greater among U.S.-educated nurses than among foreign-educated nurses. Our findings suggest that immigrant nurses may have different perceptions about safety climate and job demand, which may modify their occupational health risks

Genome-wide analysis to predict protein sequence variations that change phosphorylation sites or their corresponding kinases

We define phosphovariants as genetic variations that change phosphorylation sites or their interacting kinases. Considering the essential role of phosphorylation in protein functions, it is highly likely that phosphovariants change protein functions and may constitute a proportion of the mechanisms by which genetic variations cause individual differences or diseases. We categorized phosphovariants into three subtypes and developed a system that predicts them. Our method can be used to screen important polymorphisms and help to identify the mechanisms of genetic diseases