Image and Volume Segmentation by Water Flow

A general framework for image segmentation is presented in this paper, based on the paradigm of water flow. The major water flow attributes like water pressure, surface tension and capillary force are defined in the context of force field generation and make the model adaptable to topological and geometrical changes. A flow-stopping image functional combining edge- and region-based forces is introduced to produce capability for both range and accuracy. The method is assessed qualitatively and quantitatively on synthetic and natural images. It is shown that the new approach can segment objects with complex shapes or weak-contrasted boundaries, and has good immunity to noise. The operator is also extended to 3-D, and is successfully applied to medical volume segmentation

Conductance of Quantum Impurity Models from Quantum Monte Carlo

The conductance of two Anderson impurity models, one with two-fold and another with four-fold degeneracy, representing two types of quantum dots, is calculated using a world-line quantum Monte Carlo (QMC) method. Extrapolation of the imaginary time QMC data to zero frequency yields the linear conductance, which is then compared to numerical renormalization group results in order to assess its accuracy. We find that the method gives excellent results at low temperature (T<Tk) throughout the mixed valence and Kondo regimes, but it is unreliable for higher temperature.Comment: 5 pages, 7 figure

Quantum Phase Transition and Dynamically Enhanced Symmetry in Quadruple Quantum Dot System

We propose a system of four quantum dots designed to study the competition between three types of interactions: Heisenberg, Kondo and Ising. We find a rich phase diagram containing two sharp features: a quantum phase transition (QPT) between charge-ordered and charge-liquid phases, and a dramatic resonance in the charge liquid visible in the conductance. The QPT is of the Kosterlitz-Thouless type with a discontinuous jump in the conductance at the transition. We connect the resonance phenomenon with the degeneracy of three levels in the isolated quadruple dot and argue that this leads to a Kondo-like dynamical enhancement of symmetry from U(1) x Z_2 to U(1) x U(1).Comment: 4 pages main text + 4 pages supplementary materia

Cooperative Relative Positioning of Mobile Users by Fusing IMU Inertial and UWB Ranging Information

Relative positioning between multiple mobile users is essential for many applications, such as search and rescue in disaster areas or human social interaction. Inertial-measurement unit (IMU) is promising to determine the change of position over short periods of time, but it is very sensitive to error accumulation over long term run. By equipping the mobile users with ranging unit, e.g. ultra-wideband (UWB), it is possible to achieve accurate relative positioning by trilateration-based approaches. As compared to vision or laser-based sensors, the UWB does not need to be with in line-of-sight and provides accurate distance estimation. However, UWB does not provide any bearing information and the communication range is limited, thus UWB alone cannot determine the user location without any ambiguity. In this paper, we propose an approach to combine IMU inertial and UWB ranging measurement for relative positioning between multiple mobile users without the knowledge of the infrastructure. We incorporate the UWB and the IMU measurement into a probabilistic-based framework, which allows to cooperatively position a group of mobile users and recover from positioning failures. We have conducted extensive experiments to demonstrate the benefits of incorporating IMU inertial and UWB ranging measurements.Comment: accepted by ICRA 201

Time-Dependent Transport Through Molecular Junctions

We investigate transport properties of molecular junctions under two types of bias--a short time pulse or an AC bias--by combining a solution for the Green functions in the time domain with electronic structure information coming from ab initio density functional calculations. We find that the short time response depends on lead structure, bias voltage, and barrier heights both at the molecule-lead contacts and within molecules. Under a low frequency AC bias, the electron flow either tracks or leads the bias signal (capacitive or resistive response) depending on whether the junction is perfectly conducting or not. For high frequency, the current lags the bias signal due to the kinetic inductance. The transition frequency is an intrinsic property of the junctions.Comment: 5 pages, 9 figure

Influence of semicon shields on the dielectric loss of XLPE cables

Dielectric response measurement techniques in both time and frequency domains are studied in order to measure the dielectric loss of XLPE cables, which have very low losses. A high sensitivity transformer ratio bridge system, which can measure loss tangents as low as 10-5, has been developed with the ability to measure these cables. A tuned amplifier was designed to help to extend the frequency range from 200Hz to 20kHz. Different model cables from Borealis AB with different semiconducting materials have been measured in the temperature range 15⁰C to 120⁰C. It is found that the semiconducting layers dominate the dielectric loss in the insulation system of the XLPE cables, when the outer semicon is treated as measuring electrode. In this case, steadily increasing dielectric loss has been measured at higher frequencies. The resistivity of the semiconducting materials was measured, which confirmed that the increasing slope is due to the semiconducting layers. After using conductive tapes to wrap the cable samples, monotonically decreasing losses were measured, corresponding to the actual dielectric frequency response of the XLPE cables. It is concluded that the axial resistance of semiconducting shields have a substantial influence on the dielectric loss of XLPE cables, especially for dielectric response in high frequency range. A device on measuring the loss of such cables is presented