Direct observation and temperature control of the surface Dirac gap in a topological crystalline insulator.

Since the advent of topological insulators hosting Dirac surface states, efforts have been made to gap these states in a controllable way. A new route to accomplish this was opened up by the discovery of topological crystalline insulators where the topological states are protected by crystal symmetries and thus prone to gap formation by structural changes of the lattice. Here we show a temperature-driven gap opening in Dirac surface states within the topological crystalline insulator phase in (Pb,Sn)Se. By using angle-resolved photoelectron spectroscopy, the gap formation and mass acquisition is studied as a function of composition and temperature. The resulting observations lead to the addition of a temperature- and composition-dependent boundary between massless and massive Dirac states in the topological phase diagram for (Pb,Sn)Se (001). Overall, our results experimentally establish the possibility to tune between massless and massive topological states on the surface of a topological system.

DFT calculations of magnetic anisotropy energy of Ge(1-x)Mn(x)Te ferromagnetic semiconductor.

Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted ferromagnetic semiconductor Ge(1-x)Mn(x)Te were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magnetic anisotropy energy is presented. Analysis of microscopic mechanism of magnetic anisotropy is provided, in particular the role of spin-orbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magnetic anisotropy in rhombohedral Ge(1-x)Mn(x)Te (1 1 1) thin layers.

Utilizing topology to generate and test theories of change.

Statistical and methodological innovations in the study of change are advancing rapidly, and visual tools have become an important component in model building and testing. Graphical representations such as path diagrams are necessary, but may be insufficient in the case of complex theories and models. Topology is a visual tool that connects theory and testable equations believed to capture the theorized patterns of change. Although some prior work has made use of topologies, these representations have often been generated as a result of the tested models. This article argues that utilizing topology a priori, when developing a theory, and applying analogous statistical models is a prudent method to conduct research. This article reviews topology by demonstrating how to build a topological representation of a theory and recover the implied equations, ultimately facilitating the transition from complex theory to testable model. Finally, topologies can guide researchers as they adjust or expand their theories in light of recent model testing.

Topological crystalline insulator states in Pb(1-x)Sn(x)Se.

Topological insulators are a class of quantum materials in which time-reversal symmetry, relativistic effects and an inverted band structure result in the occurrence of electronic metallic states on the surfaces of insulating bulk crystals. These helical states exhibit a Dirac-like energy dispersion across the bulk bandgap, and they are topologically protected. Recent theoretical results have suggested the existence of topological crystalline insulators (TCIs), a class of topological insulators in which crystalline symmetry replaces the role of time-reversal symmetry in ensuring topological protection. In this study we show that the narrow-gap semiconductor Pb(1-x)Sn(x)Se is a TCI for x = 0.23. Temperature-dependent angle-resolved photoelectron spectroscopy demonstrates that the material undergoes a temperature-driven topological phase transition from a trivial insulator to a TCI. These experimental findings add a new class to the family of topological insulators, and we anticipate that they will lead to a considerable body of further research as well as detailed studies of topological phase transitions.

Fractals, Vigilance, and Adolescent Diabetes Management: A Case for When Regulation May Be Difficult to Measure With the Current Medical Standards.

Temporal patterning in blood glucose (BG) consistent with fractals-how BG follows a repetitive pattern through resolutions of time-was used to examine 2 different samples of adolescents with Type 1 diabetes (10-14 years). Sample 1 contained 10 adolescents with longtime series for accurate estimations of long-term dependencies associated with fractals. The second contained 94 adolescents measured multiple times daily over a 2-week period corresponding to psychosocial measures. In both samples, temporal dependencies in BG showed patterns consistent with fractals. In the second sample, temporal dependencies were associated with indicators of vigilant regulation including adolescents' higher anxiety, mothers' higher monitoring, and intrusive support. The existence of temporal dependencies in BG moderated the relationship between glycosylated hemoglobin (HbA1c) and indicators of low BG risk but not the relationship between HbA1c and high BG risk. These results show how a biomedical indicator may be susceptible to metric issues associated with fractals.

The influence of microscopic disorder on electron paramagnetic resonance spectra of Eu(2+) ions in Pb(1-x)Ge(x)Te.

In mixed crystals, because of the different ionic radii of cations or anions and the randomness in the placement of ions of different kinds, the crystal lattice is locally deformed. Such local deformations have significant influence on the ground state splitting of magnetic ions. Because this ground state splitting is responsible for the position of the electron paramagnetic resonance (EPR) lines, microscopic disorder is one of the factors which lead to the broadening of the lines, and eventually to their disappearance. This paper is devoted to semi-quantitative analysis of the influence of microscopic disorder on EPR spectra. The theory is compared against measurements performed on mono-crystalline Pb(1-x)Ge(x)Te epitaxial layers containing Eu(2+) ions for different germanium and europium contents. With increasing germanium content we observe gradual disappearance of the EPR lines, although macroscopically, on the basis of x-ray diffraction analysis, each layer might have been considered as a perfect crystal.

Age, marital satisfaction, and optimism as predictors of positive sentiment override in middle-aged and older married couples.

This study examined whether positive sentiment override (greater positive appraisal of spouse's affiliative behavior than is warranted by observed behavior) occurred more frequently in older compared with middle-aged married couples and whether age differences were mediated by older adults' greater marital satisfaction when controlling for optimism. Participants included 270 middle-aged (40-50 years old) and older (60-70 years old) couples who discussed a marital disagreement and completed an errand task. Couples provided appraisals of their spouse's affiliation, and the authors coded affiliative interactions using the structural analysis of social behavior. Hierarchical multivariate linear modeling indicated that older husbands and wives viewed their spouse's behavior as more positive during disagreement interactions than did independent observers; in the errand task, only older wives demonstrated positive sentiment override. Age differences in positive sentiment override were mediated by marital satisfaction, even when controlling for optimism. The results are consistent with theories of emotion regulation, such as socioemotional selectivity theory, that suggest that older adults are biased toward the positive aspects of close relationships.

Treatment of acquired cognitive-communicative deficits in young children.

This article argues that pediatric cognitive rehabilitation is different from rehabilitation for adults; that available theoretical perspectives (Piaget, information processing theory, Luria, and learning theory), are both necessary for and seriously underutilized in planning and conducting pediatric therapy; and that the recognition of such theoretical perspectives would significantly alter clinical pediatric practice. This article then suggests an approach to a theory-based clinical pediatric practice and provides examples.