Spin-conserving and reversing photoemission from the surface states of Bi2_2Se3_3 and Au (111)

We present a theory based on first-principles calculations explaining (i) why the tunability of spin polarizations of photoelectrons from Bi$_2$Se$_3$ (111) depends on the band index and Bloch wavevector of the surface state and (ii) why such tunability is absent in the case of isosymmetric Au (111). The results provide not only an explanation for the recent, puzzling experimental observations but also a guide toward making highly-tunable spin-polarized electron sources from topological insulators.Comment: 5 pages, 6 figures; Supplemental Material (2 pages) added, typos correcte

Breakdown of the Chiral Anomaly in Weyl Semimetals in a Strong Magnetic Field

The low-energy quasiparticles of Weyl semimetals are a condensed-matter realization of the Weyl fermions introduced in relativistic field theory. Chiral anomaly, the nonconservation of the chiral charge under parallel electric and magnetic fields, is arguably the most important phenomenon of Weyl semimetals and has been explained as an imbalance between the occupancies of the gapless, zeroth Landau levels with opposite chiralities. This widely accepted picture has served as the basis for subsequent studies. Here we report the breakdown of the chiral anomaly in Weyl semimetals in a strong magnetic field based on ab initio calculations. A sizable energy gap that depends sensitively on the direction of the magnetic field may open up due to the mixing of the zeroth Landau levels associated with the opposite-chirality Weyl points that are away from each other in the Brillouin zone. Our study provides a theoretical framework for understanding a wide range of phenomena closely related to the chiral anomaly in topological semimetals, such as magnetotransport, thermoelectric responses, and plasmons, to name a few.Comment: 6+7 pages, 5+6 figures; published versio

Momentum-dependent spin selection rule in photoemission with glide symmetry

We present a comprehensive theory on the spin- and angle-resolved photoemission spectroscopy (SARPES) of materials with glide-mirror symmetry, focusing on the role of glide symmetry on the spin selection rule. In the glide-symmetric SARPES configuration, where the surface of a material, the incoming light and the outgoing photoelectrons are invariant under a glide reflection, the spin polarization of photoelectrons is determined by the glide eigenvalue of the initial state, which makes SARPES a powerful tool for studying topological phases protected by glide symmetry. We also show that, due to the nonsymmorphic character of glide symmetry, the spin polarization of a photoelectron whose momentum is in the second surface Brillouin zone is the opposite of the spin polarization of a photoelectron which is ejected from the same initial Bloch state but whose momentum is in the first zone. This momentum dependence of spin selection rule clearly distinguishes glide symmetry from mirror symmetry and is particularly important if the Bloch wavevector of the initial state is close to the first surface Brillouin zone boundary. As a proof of principle, we simulate the SARPES from the surface states of KHgSb (010) and investigate how the spin selection rule imposed by the glide symmetry manifests itself in a real material.Comment: 8 pages, 5 figure

Financial Development, Fiscal Policy and Macroeconomic Volatility

This thesis examines empirically the effect of financial frictions and public debt on economic variables and seeks for an appropriate fiscal consolidation strategy. First, the thesis explores the determinants of output volatility, especially the roles of financial development and government debt. The analysis, based on a panel of 127 countries over four decades, employs system GMM dynamic panel regression. According to the regression results financial development is estimated to have a non-linear effect on output volatility. Increased government debt levels are statistically associated with increased macroeconomic volatility. However, we need to interpret the results carefully due to endogeneity problems. The effect of the interactions between the two is insignificant. Second, it analyses the role of financial frictions on economic fluctuations. When the three models are compared with the U.S. data along the second moments, the firm friction model helps in fitting some macroeconomic variables and outperforms the other models. In the impulse response functions, we find that financial frictions greatly amplify and propagate the effects of the exogenous shocks on economic variables. Specially, the firm friction model shows more persistent response than the bank friction model. In addition, the size of the response depends on the leverage in the model with financial frictions. Third, the thesis considers how the effects of fiscal policy consolidation differ depending on alternative strategies. To do this, we develop an open economy DSGE model with an endogenous risk premium mechanism. The government consumption cut has larger negative effects on output than the government investment cut because of a complementarity with private consumption. The response of the tax hike is smaller than the expenditue cut because the tax hikes reduce more debts and the lower risk premium crowds in consumption and investment. Among three fiscal rules, the expenditure adjusted rule is the most effective for both preventing the economic downturn and reducing government debt

Finding pathway regulators: gene set approach using peak identification algorithms

Recently, a number of different approaches have been used to examine variation in gene expression and to identify genes whose level of transcript differed greatly among unrelated individuals. Previous studies have commonly focused on identifying determinants that regulate gene expressions by targeting individual genes. However, it is difficult to detect true differences in the level of gene expression among genotypes from noise due to issues such as multiple testing and limited sample size. To increase the statistical power for detecting this difference, we consider a 'gene set' approach by focusing on subtle but coordinated changes in gene expression across multiple genes rather than individual genes. We defined a 'gene set' as a set of genes in the same biological pathway and focused on identifying common regulators based on an assumption that the genes within the same pathway are controlled by common regulators. We applied the gene set approach to the expression data of mRNA in Centre d'Etude du Polymorphisme Humain lymphoblast cells to identify regulators controlling the genes in a biological pathway. Our gene set approach successfully identified potent regulators controlling gene expression in an inflammatory response pathway

BIM-Based Construction Information Management Framework for Site Information Management

Projects in the construction industry are becoming increasingly large and complex, with construction technologies, methods, and the like developing rapidly. Various different types of information are generated by construction projects. Especially, a construction phase requires the input of many resources and generates a diverse set of information. While a variety of IT techniques are being deployed for information management during the construction phase, measures to create databases of such information and to link these various different types of information together are still insufficient. As such, this study aims to suggest a construction information database system based on BIM technology to enable the comprehensive management of site information generated during the construction phase. This study analyzed the information generated from construction sites and proposed a categorization system for structuring the generated information, along with a database model for storing such structured information. Through such efforts, it was confirmed that such a database system can be used for accumulating and using construction information; it is believed that, in the future, the continual accumulation and management of construction information will allow for corporate-level accumulation of knowledge as opposed to the individual accumulation of know-how