Experimental and theoretical investigations in rare earth-triel-tetrel polar intermetallic systems: composition-structure-properties relationships

This dissertation consists of eight chapters, which include experimental and theoretical studies of novel polar intermetallics and Zintl phases to understand the interrelationships among stoichiometry, structure and properties. Chapter 1 shows general introduction and motivation including a preview of projects. The main part of my doctoral research starts from Chapter 2, and four subsequent chapters are about the investigations of RE(M1-xM’x)2 systems, where RE is rare-earth metals, and M and M’ are Group 12–14 elements. To gain insights into driving forces determining their crystal structures at the given compositions, I exploited two controllable factors one at a time which were the atomic size and the valence electron counts. In Chapter 2: ‘Planar versus Puckered Nets in the Polar Intermetallic Series EuGaTt (Tt = Si, Ge, Sn)’, only the atomic size was changed by substituting tetrels to see the impact of atomic size to the crystal and electronic structures. On the other hand, in Chapter 3 and 4: ‘To What Extent Does the Zintl-Klemm Formalism Work? The Eu(Zn1—xGex) (0 ≤ x ≤ 1) Series’ and ‘Theoretical Interpretation of the Structural Transition along the Eu(Zn1—xGex) (0 ≤ x ≤ 1) Series’, I attempted to reduce the atomic size factor and to focus on valence electron count for the series only by altering atomic compositions. In Chapter 5: ‘Structure-Composition Sensitivities in “Metallic” Zintl Phase: A study of Eu(Ga1—xTtx) (Tt = Si, Ge; 0 ≤ x ≤ 1) Series’, I exploited two controllable factors, which are atomic size and valence electron counts, simultaneously, and compared the results with two previously investigated systems. Other parts of my research are composed of Chapter 6 and 7, which are respectively, ‘On the “Coloring Problem” in YMgZn and Related Phase’ and ‘Phase Width and Site Preference in the EuMgxGa4—x Series’:. In these two chapters, I tried to understand the observed phase widths of certain structural types from the perspective of particular chemical bondings. General conclusion of my overall doctoral research is shown in Chapter 8

Diytterbium(II) lithium indium(III) digermanide, Yb2LiInGe2

The title compound, Yb2LiInGe2, a new ordered quaternary inter­metallic phase, crystallizes with the ortho­rhom­bic Ca2LiInGe2 type (Pearson code oP24). The crystal structure contains six crystallographically unique sites in the asymmetric unit, all in special positions with site symmetry .m.. The structure is complex and based on [InGe4] tetra­hedra, which share corners in two directions, forming layers parallel to (001). Yb atoms fill square-pyramidal (Yb1) and octa­hedral (Yb2) inter­stices between the [InGe4/2] layers, while the small Li+ atoms fill tetra­hedral sites

Theoretical Interpretation of the Structural Variations along the Eu(Zn1−xGex)2 (0 ≤ x ≤ 1) Series

The electronic structures of EuZn2, Eu(Zn0.75Ge0.25)2, Eu(Zn0.5Ge0.5)2, Eu(Zn0.25Ge0.75)2, and EuGe2 have been investigated using tight-binding, linear muffin-tin orbital (TB-LMTO) and pseudopotential methods to understand the structural preferences influenced by valence electron counts and to explain the observed homogeneity range of the AlB2-type phases as reported in the companion article. A crystal orbital Hamilton population (COHP) analysis for Zn−Zn contacts in EuZn2 suggests a possible homogeneity width for the KHg2-type phase, which is indicated from analysis of X-ray powder diffraction patterns. Total electronic energy comparisons, as well as density of states (DOS) and COHP analysis for a hypothetical Zn-rich compound, Eu(Zn0.75Ge0.25)2, indicate that two distinct phases, KHg2-type EuZn2 and AlB2-type Eu(Zn1−xGex)2 (0.5 ≤ x ≤ 0.70), are more favorable than a single Zn-rich composition adopting the AlB2-type phase. Among 10 structural models of Eu(Zn0.5Ge0.5)2, the one with heteroatomic Zn−Ge interactions both within and perpendicular to the 63 nets is energetically the most favorable structure. The experimentally observed Zn−Ge bond distance is attributed to the contribution of both σ- and π-bond interactions. Zn−Ge, Eu−Zn, and Eu−Ge COHP curves of the minimum energy form of Eu(Zn0.5Ge0.5)2 show bonding character above the Fermi level and explain the observed wide homogeneity width of the AlB2-type phase. In the Ge-rich case, Eu(Zn0.25Ge0.75)2, the planar hexagonal nets are not energetically favorable due to the significant antibonding character of Ge−Ge bonding at the Fermi level. Structural relaxation using pseudopotentials also revealed that the hexagonal nets tend to pucker rather than being planar, in agreement with the observed incommensurately modulated superstructure. An electron localization function analysis for Eu(Zn0.5Ge0.5)2 reveals that there exists no two-center, two-electron bond or multicentered interactions between interlayer Zn···Ge contacts

Vagus Nerve Stimulation in Intractable Childhood Epilepsy: a Korean Multicenter Experience

We evaluated the long-term outcome of vagus nerve stimulation (VNS) in 28 children with refractory epilepsy. Of these 28 children, 15 (53.6%) showed a >50% reduction in seizure frequency and 9 (32.1%) had a >75% reduction. When we compared seizure reduction rates according to seizure types (generalized vs. partial) and etiologies (symptomatic vs. cryptogenic), we found no significant differences. In addition, there was no correlation between the length of the stimulation period and treatment effect. The seizure reduction rate, however, tended to be inversely related to the seizure duration before VNS implantation and age at the time of VNS therapy. VNS also improved quality of life in this group of patients, including improved memory in 9 (32.1%), improved mood in 12 (42.9%), improved behavior in 11 (39.3%), improved altertness in 12 (42.9%), improved achievement in 6 (21.4%), and improved verbal skills in 8 (28.6%). Adverse events included hoarseness in 7 patients, dyspnea at sleep in 2 patients, and wound infection in 1 patient, but all were transient and successfully managed by careful follow-up and adjustment of parameters. These results indicate that VNS is a safe and effective alternative therapy for pediatric refractory epilepsy, without significant adverse events

Inflammatory Polyarthritis in a Patient with Psoriasis: Is It Psoriatic Arthritis or Rheumatoid Arthrirtis?

Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis. There are no generally accepted diagnostic criteria for PsA. Indeed, the diagnosis of this inflammatory arthritis is made by exclusion of other possible diseases and based upon immunologic, radiologic, and clinical features which are consistent with the diagnosis. Inflammatory arthritis in a patient with psoriasis can be an important clue for the diagnosis of PsA, but the possibility for diagnosis of other inflammatory arthritides ever remains. Herein we report a case of a female patient who was not diagnosed with PsA, but with rheumatoid arthritis, even though she had psoriasis

Weekly Paclitaxel and Trastuzumab as a First-Line Therapy in Patients with HER2-Overexpressing Metastatic Breast Cancer: Magnitude of HER2/neu Amplification as a Predictive Factor for Efficacy

We evaluated the efficacy and safety of weekly paclitaxel plus trastuzumab as firs-tline chemotherapy in women with HER2-overexpressing metastatic breast cancer (MBC), and we investigated the prognostic factors including magnitude of HER2/neu amplification in this population. We analyzed 54 patients with HER2-overexpressing MBC that were treated with weekly paclitaxel plus trastuzumab as first-line chemotherapy from February 2004 to December 2006. At a median follow-up of 28 months, median time to progression (TTP) was 16.6 months (95% CI, 9.4 to 23.7 months) and median overall survival was 25.6 months (95% CI, 21.8 to 27.3 months). Therapy was generally well tolerated, although three patients (5.5%) experienced reversible, symptomatic heart failure. Of the 27 patients evaluable for the HER2 FISH, patients with a HER2/CEP17 ratio of ≤4.0 had significantly shorter TTP than those with a HER2/CEP17 ratio of >4.0 (10.8 vs. 23.2 months, P=0.034). A HER2/CEP17 ratio of >4.0 was identified as significant predictive factor of TTP by multivariate analysis (P=0.032). The combination of weekly paclitaxel plus trastuzumab as first-line chemotherapy is an effective regimen in patients with HER2-FISH-positive MBC. Furthermore, the magnitude of HER2 amplification is an independent predictive factor of TTP

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements