E(lementary) Strings in Six-Dimensional Heterotic F-Theory

Using E-strings, we can analyze not only six-dimensional superconformal field theories but also probe vacua of non-perturabative heterotic string. We study strings made of D3-branes wrapped on various two-cycles in the global F-theory setup. We claim that E-strings are elementary in the sense that various combinations of E-strings can form M-strings as well as heterotic strings and new kind of strings, called G-strings. Using them, we show that emissions and combinations of heterotic small instantons generate most of known six-dimensional superconformal theories, their affinizations and little string theories. Taking account of global structure of compact internal geometry, we also show that special combinations of E-strings play an important role in constructing six-dimensional theories of $D$- and $E$-types. We check global consistency conditions from anomaly cancellation conditions, both from five-branes and strings, and show that they are given in terms of elementary E-string combinations.Comment: 58 pages, 16 figures; v2. version to appear in JHE

Josephson current in carbon nanotubes with spin-orbit interaction

We demonstrate that curvature-induced spin-orbit (SO) coupling induces a $0-\pi$ transition in the Josephson current through a carbon nanotube quantum dot coupled to superconducting leads. In the non-interacting regime, the transition can be tuned by applying parallel magnetic field near the critical field where orbital states become degenerate. Moreover, the interplay between charging and SO effects in the Coulomb Blockade and cotunneling regimes leads to a rich phase diagram with well-defined (analytical) boundaries in parameter space. Finally, the 0 phase always prevails in the Kondo regime. Our calculations are relevant in view of recent experimental advances in transport through ultra-clean carbon nanotubes.Comment: 4 (main text) + 10 (appendices) pages, 3 figure

Estimation Method to Achieve a Noise Reduction Effect of Airfoil with a Serrated Trailing Edge for Wind Turbine Rotor

This chapter describes a wind tunnel experiment that was undertaken to investigate the changes in the aerodynamic performance of a wind turbine due to the inclusion of a 2-Dimension (2D) airfoil with a serrated trailing edge designed to reduce the noise caused by a wind turbine rotor blade. The restrictive condition for the serrated trailing edge equipped with the use of a 2D airfoil was examined through the use of a wind tunnel experiment after studying existing restrictive condition and analyzing prior research on serrated trailing edges. The study was conducted according to Howe’s theory, which is a cornerstone of the study of noise reduction effects produced by a serrated trailing edge. For the serrated trailing edge equipped on a 2D airfoil, the wake distribution and the relation to noise were analyzed in order to determine the restrictive condition in accordance with Howe’s theory. The results indicated that an empirical formula or a theoretical approach should consider changes in the boundary layer thickness of a 2D airfoil, so an empirical noise prediction formula is suggested for the serrated trailing edge. Also, a comparison and an analysis of the prediction and the experimental results for the noise produced by the NACA0012 or the baseline airfoil equipped with a serrated trailing edge suggested a novel formula for a 2D airfoil. Finally, the 2D airfoil noise data are compared with wind tunnel test data by using an empirical formula estimation method

Statistical Analysis of the Metropolitan Seoul Subway System: Network Structure and Passenger Flows

The Metropolitan Seoul Subway system, consisting of 380 stations, provides the major transportation mode in the metropolitan Seoul area. Focusing on the network structure, we analyze statistical properties and topological consequences of the subway system. We further study the passenger flows on the system, and find that the flow weight distribution exhibits a power-law behavior. In addition, the degree distribution of the spanning tree of the flows also follows a power law.Comment: 10 pages, 4 figure

Thin-Film PZT Scanning Micro-actuators for Vertical Cross-sectional Imaging in Endomicroscopy

The advancement of optics and the development of microelectromechanical systems (MEMS) based scanners has enabled powerful optical imaging techniques that can perform optical sectioning with high resolution and contrast, large field of view, and long working distance to be realized in endoscope-compatible form factors. Optical endomicroscopes based on these imaging techniques can be used to obtain in vivo vertical cross-sectional images of dysplastic tissues in the hollow organs before they progress to mucosal diseases such as colorectal cancer. However, existing endomicroscopic systems that use imaging modalities compatible with the use of fluorescent biomarkers are not capable of deep vertical sectioning in real time. This work proposes a unique MEMS-based scanning mechanism to be incorporated into endoscopic microscopes for real-time in vivo deep into-tissue scanning for early cancer detection. For this task, a class of novel multi-axis micro-scanners based on thin-film lead-zirconate-titanate (PZT) has been developed. Leveraging the large piezoelectric strain coefficient of PZT, the prototypes have demonstrated more than 400 μm of out-of-plane displacement with bandwidths on the order of 100-200 Hz in only a 3.2 mm-by-3.2 mm footprint, which meets the requirements for this application. The scanners have a central rectangular-shaped reflector, whose corners are supported by four symmetric PZT bending legs that generate vertical translation. This design gives the reflector a three-axis motion. The challenges to fabricate high performance piezoelectric actuators are discussed with device failure mechanisms observed during the fabrication of the 1st generation scanners. Improved fabrication steps are presented that solve the issues with the 1st generation devices and enhance the robustness of the scanners for instrument integration. Remaining non-ideal fabrication outcomes cause MEMS devices to produce unwanted motions, which can degrade imaging quality. To overcome this problem, a method to drive MEMS actuators having multiple vibration modes with close frequencies to produce a desired motion pattern with a single input is presented, and was used to generate a pure vertical motion for imaging. Two-photon based vertical cross-sectional images of mouse colon was obtained in real time for the first time using a thin-film piezoelectric microscanner. To understand the effects of fabrication non-idealities on the device behavior and produce more robust scanner performance, analytical models that describes large vertical and rotational motions including multi-axis coupling were developed. A static model that was initially developed for design optimization was calibrated, along with a transient model, using experimental data to incorporate the effects of dimensional variations and residual stress. This models can be used with future integrated sensors and feedback controllers for more precise and robust motion of the scanner. This calibration technique can be useful in developing analytic models for MEMS devices subject to fabrication uncertainty. In addition, nonlinear dynamic behavior due to large vertical stroke in the presence of fabrication non-idealities is captured by linearizing an expanded dynamic model about different static positions obtained by numerically solving the expanded nonlinear model.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137124/1/jongs_1.pd