75,192 research outputs found
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
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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
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