Corner Junction as a Probe of Helical Edge States

We propose and analyze inter-edge tunneling in a quantum spin Hall corner junction as a means to probe the helical nature of the edge states. We show that electron-electron interactions in the one-dimensional helical edge states result in Luttinger parameters for spin and charge that are intertwined, and thus rather different than those for a quantum wire with spin rotation invariance. Consequently, we find that the four-terminal conductance in a corner junction has a distinctive form that could be used as evidence for the helical nature of the edge states.Comment: 4+ pages, 3 figure

Adaptive computer‐generated forces for simulator‐based training, Expert Systems with Applications

Simulator-based training is in constant pursuit of increasing level of realism. The transition from doctrine-driven computer-generated forces (CGF) to adaptive CGF represents one such effort. The use of doctrine-driven CGF is fraught with challenges such as modeling of complex expert knowledge and adapting to the trainees’ progress in real time. Therefore, this paper reports on how the use of adaptive CGF can overcome these challenges. Using a self-organizing neural network to implement the adaptive CGF, air combat maneuvering strategies are learned incrementally and generalized in real time. The state space and action space are extracted from the same hierarchical doctrine used by the rule-based CGF. In addition, this hierarchical doctrine is used to bootstrap the self-organizing neural network to improve learning efficiency and reduce model complexity. Two case studies are conducted. The first case study shows how adaptive CGF can converge to the effective air combat maneuvers against rule-based CGF. The subsequent case study replaces the rule-based CGF with human pilots as the opponent to the adaptive CGF. The results from these two case studies show how positive outcome from learning against rule-based CGF can differ markedly from learning against human subjects for the same tasks. With a better understanding of the existing constraints, an adaptive CGF that performs well against rule-based CGF and human subjects can be designed

Robust human activity recognition using lesser number of wearable sensors

In recent years, research on the recognition of human physical activities solely using wearable sensors has received more and more attention. Compared to other types of sensory devices such as surveillance cameras, wearable sensors are preferred in most activity recognition applications mainly due to their non-intrusiveness and pervasiveness. However, many existing activity recognition applications or experiments using wearable sensors were conducted in the confined laboratory settings using specifically developed gadgets. These gadgets may be useful for a small group of people in certain specific scenarios, but probably will not gain their popularity because they introduce additional costs and they are unusual in everyday life. Alternatively, commercial devices such as smart phones and smart watches can be better utilized for robust activity recognitions. However, only few prior studies focused on activity recognitions using multiple commercial devices. In this paper, we present our feature extraction strategy and compare the performance of our feature set against other feature sets using the same classifiers. We conduct various experiments on a subset of a public dataset named PAMAP2. Specifically, we only select two sensors out of the thirteen used in PAMAP2. Experimental results show that our feature extraction strategy performs better than the others. This paper provides the necessary foundation towards robust activity recognition using only the commercial wearable devices.NRF (Natl Research Foundation, S’pore)Accepted versio

Effect of drawing stress on mesophase structure formation of poly(ethylene 2,6-naphthalene dicarboxylate) fiber just after the neck-drawing point

The structural development of poly(ethylene 2,6-naphthalene dicarboxylate) (PEN) fibers was analyzed by in situ X-ray diffraction and fiber temperature measurements. The PEN fiber was drawn continuously under three drawing stresses, where the neck-drawing point was fixed accurately by CO2 laser irradiation heating. The developed crystal structures of the drawn fibers depended on the drawing stresses, that is, only the alpha-crystal was obtained under a drawing stress of 148 MPa, an alpha-rich mixed crystal was obtained for 54 MPa, and a beta-rich mixed crystal was obtained under 23 MPa stress. Fiber containing over 70% beta-crystal was obtained in the third case. Orientation-induced crystallization rates (K) and crystallization induction times (t(0)) were estimated for the three drawing stresses: K = 2210 s(-1) and t(0) = 0.5 ms for 148 MPa, K = 940 s(-1) and t(0) = 1.0 ms for 54 MPa, and K= 655 s(-1) and t(0) = 4.0 ms for 23 MPa. In addition, the drawing stress acted as a definitive influence not only on the resulting crystal form but also on the chain conformation of the mesophase structure. The d-spacing of the (001') diffraction increased with drawing stress, and the longer (001') spacing generated the alpha-crystal while the comparatively shorter (001') spacing yielded the beta-crystal. The d-spacings of 1.27 and 1.23 nm for the drawing stresses of 148 and 23 MPa, respectively, were somewhat shorter than the c-axis lengths of the alpha- and beta-crystals of 1.32 and 1.27 nm, respectively.ArticlePOLYMER. 53(19):4272-4279 (2012)journal articl

In-situ analysis of fiber structure development for isotactic polypropylene

Structural development of isotactic polypropylene (iPP) fibers was analyzed in real time through in-situ WAXD/SAXS and fiber temperature measurements during CO(2) laser-heated drawing because the CO(2) laser irradiation can nearly fix the necking position on the running fiber. The in-situ WAXD/SAXS measurements were carried out with a high time-resolution of 0.4 ms. The as-spun iPP fibers of two different initial structures were laser-heat-drawn to a draw ratio of 6.5. For the drawing of PP fiber containing mesophase structure, diffraction from the oriented mesophase remained until an elapsed time of 1.0 ms, when oriented alpha-phase crystal started to form. Meanwhile, for the drawing of PP fiber containing both an alpha-phase and a mesophase structure, fragmented microcrystals were reorganized by orientation-induced crystallization before an elapsed time of 1.0 ms. The long period increased drastically with fragmentation, and decreased with reorganization. The long period was about 16 nm for both drawn fibers.ArticlePOLYMER. 52(9):2044-2050 (2011)journal articl

Development of a fiber structure in poly(vinylidene fluoride) by a CO(2) laser-heated drawing process

Rapid and uniform heating by CO(2) laser radiation can fix the position where necking occurs. Therefore, this study investigated the development of a fiber structure in poly(vinylidene fluoride) in continuous drawing by in situ measurement using synchrotron X-ray radiation with a time resolution of several hundred microseconds. Two neck-deformation behaviors were observed in the laser drawing: a moderate neck deformation under low drawing stress and a steep neck deformation under high drawing stress. The low drawing stress resulted in a mixture of alpha- and beta-crystals in which the beta-crystal was formed within 1ms after the necking, earlier than the alpha-crystal. The development of the fiber structure under high drawing stress was almost complete in less than 1 ms, and the developed structure contained only beta-crystals. Small-angle X-ray scattering images showed meridional streaks at low drawing stress, whereas a four-pointed pattern occurred under high drawing stress. Low drawing stress generated a long periodic structure that was defective in the periodic regularity of crystalline and amorphous regions, although the molecular chains were nearly oriented along the fiber axis. The high drawing stress resulted in a well-packed structure of adjacent fibrils with alternating amorphous and crystalline regions. Polymer Journal (2010) 42, 657-662; doi: 10.1038/pj.2010.53; published online 23 June 2010ArticlePOLYMER JOURNAL. 42(8):657-662 (2010)journal articl

Gait Characterization in Duchenne Muscular Dystrophy (DMD) Using a Single-Sensor Accelerometer: Classical Machine Learning and Deep Learning Approaches

Differences in gait patterns of children with Duchenne muscular dystrophy (DMD) and typically-developing (TD) peers are visible to the eye, but quantifications of those differences outside of the gait laboratory have been elusive. In this work, we measured vertical, mediolateral, and anteroposterior acceleration using a waist-worn iPhone accelerometer during ambulation across a typical range of velocities. Fifteen TD and fifteen DMD children from 3-16 years of age underwent eight walking/running activities, including five 25 meters walk/run speed-calibration tests at a slow walk to running speeds (SC-L1 to SC-L5), a 6-minute walk test (6MWT), a 100 meters fast-walk/jog/run (100MRW), and a free walk (FW). For clinical anchoring purposes, participants completed a Northstar Ambulatory Assessment (NSAA). We extracted temporospatial gait clinical features (CFs) and applied multiple machine learning (ML) approaches to differentiate between DMD and TD children using extracted temporospatial gait CFs and raw data. Extracted temporospatial gait CFs showed reduced step length and a greater mediolateral component of total power (TP) consistent with shorter strides and Trendelenberg-like gait commonly observed in DMD. ML approaches using temporospatial gait CFs and raw data varied in effectiveness at differentiating between DMD and TD controls at different speeds, with an accuracy of up to 100%. We demonstrate that by using ML with accelerometer data from a consumer-grade smartphone, we can capture DMD-associated gait characteristics in toddlers to teens

Fractional quantum Hall effect in a quantum point contact at filling fraction 5/2

Recent theories suggest that the excitations of certain quantum Hall states may have exotic braiding statistics which could be used to build topological quantum gates. This has prompted an experimental push to study such states using confined geometries where the statistics can be tested. We study the transport properties of quantum point contacts (QPCs) fabricated on a GaAs/AlGaAs two dimensional electron gas that exhibits well-developed fractional quantum Hall effect, including at bulk filling fraction 5/2. We find that a plateau at effective QPC filling factor 5/2 is identifiable in point contacts with lithographic widths of 1.2 microns and 0.8 microns, but not 0.5 microns. We study the temperature and dc-current-bias dependence of the 5/2 plateau in the QPC, as well as neighboring fractional and integer plateaus in the QPC while keeping the bulk at filling factor 3. Transport near QPC filling factor 5/2 is consistent with a picture of chiral Luttinger liquid edge-states with inter-edge tunneling, suggesting that an incompressible state at 5/2 forms in this confined geometry

A framework for integrating sustainability estimation with concepts of rules of building measurement

BIM promises improvement in project delivery efficiencies such as reduction in costs and errors and timely completion. Benefits are also expected in sustainable construction aspect with research efforts being extended to sustainable design and assessment. These efforts are still been explored for the purposes of unifying quantification methodologies, the standardisation of system boundaries, terms of references and sustainability measures. Embodied energy and CO2 are two common measures that have been widely used in the construction sector. Although a number calculation system exists, they are not useful to the iterations that occur at the early stages of the project life cycle. At the procurement stage, professionals often rely on schedules and bill of quantities with no reference to sustainability credentials. It is therefore important to integrate sustainability measure with concepts in standard measurement methods. As such, we propose a framework to integrate sustainability credential with the concepts in rule of building measurement. We conclude that this framework can be applicable to any rule of building measurement and it is implementable in a computer programmable environment