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ABSTRACT: Data races hamper parallel programming and threaten the reliability of future software. This paper proposes the data race
prevention scheme View-Oriented Data race Prevention (VODAP), which can prevent data races in the View-Oriented Parallel Programming
(VOPP) model. VOPP is a novel shared-memory data-centric parallel programming model, which uses views to bundle mutual exclusion
with data access. We have implemented the data race prevention scheme with a memory protection mechanism. Experimental results
show that the extra overhead of memory protection is trivial in our applications. The performance is evaluated and compared
with modern programming models such as OpenMP and Cilk.
VOPP-View oriented parallel programming-Concurrent programming-SPMD-Data race free-Data-centric programming-Cilk-Multicore-Shared-memory
The Journal of Supercomputing 04/2012; 51(3):258-278. · 0.58 Impact Factor
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ABSTRACT: High-voltage transmission lines are responsible for transmission of electric power. Their sag and electric current are important parameters for transmission-line monitoring. In this paper, a simple and promising method based on magnetoresistive sensors is proposed for transmission-line monitoring. This is a noncontact method and its installation is simple without the need for power cut. The method involves measuring emanated magnetic field from a line conductor at the ground level and, then, calculating the source position and current inversely. A proof-of-concept laboratory setup was constructed and a series of experiments were carried out for demonstration. This method can handle complicated transmission-line configuration by integrating the stochastic optimization approach into the inverse electromagnetic calculation. It was tested with the computational simulation of a 500 kV transmission-line configuration. The result shows the feasibility of using this transmission-line monitoring method in reality.
IEEE Transactions on Magnetics 11/2011; · 1.36 Impact Factor
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ABSTRACT: Research so far on adaptive bilateral control of master-slave teleoperation systems considers dynamic uncertainties but stops short of considering kinematic uncertainties. However, when picking up objects of unknown lengths, orientations and gripping points, the overall kinematics of a robot in the teleoperation system becomes uncertain. Therefore, new controllers are required that can guarantee the stability and motion tracking performance of the system in the presence of both dynamic and kinematic uncertainties in the master and the slave robots. In this paper, first the uncertain dynamics of the human operator and the environment are incorporated into the dynamics of the master and the slave, respectively. Then, for a teleoperation system with uncertain dynamics and kinematics, nonlinear adaptive controllers are designed for both the master and the slave. The controllers do not need exact knowledge of the dynamics of the master, the slave, the operator, or the environment, or of the kinematics of the master or the slave. The stability and position tracking convergence of the entire teleoperation system are studied. The validity of the theoretical results is verified by simulations.
Intelligent Robots and Systems (IROS), 2010 IEEE/RSJ International Conference on; 11/2010
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ABSTRACT: This paper addresses complexity issues at algorithmic and architectural level of digital baseband receiver ASIC design for GSM/GPRS/EDGE, in order to reduce power and die area as desired for cellular applications. A 2.5G multi-mode architecture is implemented in 0.13 μm CMOS technology occupying 1.0 mm<sup>2</sup> and dissipating only 1.3 mW in fastest EDGE data transmission mode.
VLSI System on Chip Conference (VLSI-SoC), 2010 18th IEEE/IFIP; 10/2010
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ABSTRACT: In the present paper, we study the effect of trap depth for shallow traps on the surface flashover performance in vacuum; that is on deepening the trap depth, the flashover performance is firstly enhanced and then weakened, only when the trap depth changes in the certain range, the best surface flashover performance in vacuum is exhibited. Further to a previous study, we extensively study wide range of trap depths by changing the aggregation structure of semi-crystalline cross-linked polyethylene (XLPE). In the present study, we firstly annealed the XLPE at 135 °C for 10 minutes then cooled it at different conditions to get samples with different trap depths. We found that the trap depth deepened on increasing the grain size. Furthermore, we found that the flashover performances of the samples (Cooled at a rate of 0.5 °C /min) were enhanced by 76% and 19%, respectively under dc and impulse voltage. These results demonstrate heat-treatment as an effective way
IEEE Transactions on Dielectrics and Electrical Insulation 07/2010; · 1.09 Impact Factor
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ABSTRACT: This paper proposes a data race prevention scheme, which can prevent data races in the View-Oriented Parallel Programming (VOPP) model. VOPP is a novel shared-memory data-centric parallel programming model, which uses views to bundle mutual exclusion with data access. We have implemented the data race prevention scheme with a memory protection mechanism. Experimental results show that the extra overhead of memory protection is trivial in our applications. We also present a new VOPP implementation-Maotai 2.0, which has advanced features such as deadlock avoidance, producer/consumer view and system queues, in addition to the data race prevention scheme. The performance of Maotai 2.0 is evaluated and compared with modern programming models such as OpenMP and Cilk.
Parallel and Distributed Computing, Applications and Technologies, 2009 International Conference on; 01/2010
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ABSTRACT: For organic solar cells, effective absorption over a wide wavelength range is important. A simple donor-acceptor pair is usually not sufficient to reach this goal. Thus, it would be desirable to utilize multiple photoactive materials in a single cell. In this work, two hole conducting materials, pentacene and zinc phthalocyanine (ZnPc), and electron conducting C <sub>60</sub> are chosen to construct three-component heterojunctions aiming at improved effective photon harvesting in organic solar cells. It is found that in pentacene / ZnPc / C <sub>60</sub> multiple heterojunctions, part of the excitons in pentacene reach the ZnPc / C <sub>60</sub> interface, where efficient exciton separation occurs and contributes to the photocurrent (PC). Triplet excitons are confirmed to be the major origin of PC by transient PC response measurements, suggesting that triplet-to-triplet energy transfer from pentacene to ZnPc is responsible for the improved PC of pentacene / ZnPc / C <sub>60</sub> multiheterojunctions. Furthermore, exothermic energy transfer from ZnPc to the lower lying triplet levels of pentacene is employed for extending the absorption range and enlarging the absorption intensity. To realize such a structure, an ultrathin ZnPc layer is embedded in the pentacene film in pentacene / C <sub>60</sub> single heterojunctions, leading to an enhanced quantum efficiency in the long wavelength range compared to the reference cell. These findings pave a way to efficient photovoltaic cells with a wide photoresponse ranging from near UV through the visible to the near infrared.
Journal of Applied Physics 10/2009; · 2.17 Impact Factor
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ABSTRACT: An accelerated iterative method for a self-consistent solution of the coupled Poisson-Schrodinger equations is presented by virtue of the Anderson mixing scheme. In this proposed method, the number of iterations is remarkably reduced at the cost of slightly longer computational time at each iteration. An example of a two-dimensional double-gate MOSFET is included, in which simulations with different device profiles and transport models are accelerated.
Micro & Nano Letters 07/2009; · 0.94 Impact Factor
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ABSTRACT: We investigated whether flapping flight has an inherent stability by analyzing the inertial and aerodynamic effects of flapping wings on body dynamics. Based on wing and body kinematics of free flying fruit flies during rapid maneuvers, we found a passive counter torque due to body rotation. It is identified both in simulation through quasi-steady state aerodynamic model and through experiments on a dynamically scaled robotic wing. An analytical form is derived correspondingly. In the turning yaw axis, the estimated damping coefficient of flapping wings is significantly higher than body frictional damping; this indicates a passive deceleration during turning. By simulating insect to rotate about each principal axis of inertial and body frames, we calculated the corresponding damping coefficients, and further analyzed the attitude stability. The result reveals that, passive damping of flapping flight, while does not necessarily lead to a stable full body dynamics, provides a considerable passive restoring torque that could be critical for flight stabilization and control in the design of micro aerial vehicles. Preliminary analysis on the scaling parameters of passive damping was also performed.
Robotics and Automation, 2009. ICRA '09. IEEE International Conference on; 06/2009
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ABSTRACT: Design of a nonlinear optimal and robust controller for a lightweight all-electric vehicle is presented. An electric vehicle driven by a DC motor is modelled. A controller is designed with differential-geometric approach and linear quadratic regulator techniques, to guarantee optimal performance. Then the uncertainties of the system are considered. A nonlinear robust controller that can tolerate multi-parametric uncertainties is designed. The model and controllers are implemented in Simulinkw environment and numerical simulations are performed. To compare the performance of the controllers, two regular PID controllers are designed. The performance of the designed controllers are compared with that of PID controllers and a driving cycle test is performed to test the control performance and energy consumption. The controller designed here demonstrates much better performance than that of regular PID controller under tests.
IET Control Theory and Applications 05/2009; · 0.99 Impact Factor
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ABSTRACT: The vapor pressure of MgB<sub>2</sub>, corresponding to the reaction, 2MgB<sub>2</sub>(cr)→MgB<sub>4</sub>(cr)+Mg(g), has been measured by Knudsen effusion vacuum thermogravimetry. The vapor pressure over the range 600°C-850°C can be expressed as: logp<sub>mg</sub>(Pa)=-1.129141(10000/T)+7.328161, where T is the temperature in Kelvin. By extrapolation, the 0.1 MPa decomposition temperature of MgB<sub>2</sub> is estimated to be 1268°C. In a separate calorimetric investigation on the same material, using the isoperibol solution method, we measured the enthalpy of formation of MgB<sub>2</sub>, Δ<sub>f</sub>H<sub>MgB2</sub>°(298.15), to be -(155.9±14.2)kJ·mol<sup>-1</sup>. By combining the vapor pressure data and the enthalpy data, the Mg-rich part of the Mg-B phase diagram can be calculated. The measured vapor pressures are approximately an order of magnitude higher than those derived from published thermodynamic data. The lower limit of Mg pressures for the deposition of high-purity MgB<sub>2</sub> thin films at any given temperature may therefore be at a higher value than previously thought.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
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ABSTRACT: The transport behaviour of Fe-doped Pr0.75Sr0.25MnO3 (PSMFO, Fe = 0.05) is studied by zero-field conductivity probing and Raman spectroscopy. It is revealed that the conductivity of PSMFO above Tm, the metal-insulator transition point, shows variable-range-hopping behaviour instead of the small-polaron mode. The B2g Raman line at 630 cm-1 arising from the Mn-O bending and stretching modes undergoes anomalous softening as the temperature is lowered from ambient temperature, indicating a magnetic ordering sequence above Tm. It is demonstrated that the electronic conduction of PSMFO above Tm is governed by magnetic polarons embedded in a matrix of paramagnetic insulating phase.
Journal of Physics Condensed Matter 01/2002; 14(6):L141. · 2.55 Impact Factor
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ABSTRACT: We have performed magnetic and transport measurements on a series of Nd0.67Sr0.33Mn1−xFexO3 polycrystalline compounds with x=0.0, 0.05, 0.10, and 0.15. For the Fe-undoped Nd0.67Sr0.33MnO3 (NSMO) materials, a magnetoresistance (MR) as high as ∼33% was observed at the metal–insulator transition temperature, Tp=273 K, in a magnetic field of 10 kOe. Fe substitution in Mn sites leads to a reduction in Tp and an increase in the overall MR. A 10% Fe contribution increases the MR up to about 65% and lowers Tp to 88 K. The calculated magnetic moment at 5 K and an applied field at 9 T for the parent NSMO is 4.21 μB and decreases continuously with an increasing amount of iron added. It was found that with the same amount of Fe doping, the Curie temperature, TC, decreases much faster in the Nd-based system than in the corresponding La-based system. The enhanced colossal magnetoresistance and the suppression of ferromagnetism observed in this compound can be interpreted as due to the weakening of the double exchange mechanism by Fe3+ ions, which causes the localization of the hopping electrons. © 2002 American Institute of Physics.
Journal of Applied Physics 01/2002; 91(2):789-793. · 2.17 Impact Factor
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ABSTRACT: Amorphous/crystalline mixed La0.5Sr0.5MnO3 (LSMO) thin films on quartz wafers are prepared at different depositing temperatures using laser ablation and their low-field
magnetoresistive property is investigated. It is argued that the insulating amorphous layers separating the magnetic microcrystalline
grains may act as the barriers for electron tunneling. The rapid decay of magnetoresistance with increasing temperature is
explained by the spin-polarized inter-grain tunneling. Given the spin-polarized inter-grain tunneling as the probable mechanism,
it is believed that the spin flip during inter-grain tunneling reaches a minimum at the optimized depositing temperature of
600°C and consequently the maximal low-field magnetoresistance is obtained.
Applied Physics A 10/2001; 73(5):625-630. · 1.63 Impact Factor
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ABSTRACT: The La <sub> 0.67 </sub> Sr <sub> 0.33 </sub> MnO <sub>3</sub>/ BaFe <sub> 11.3 </sub> (ZnSn) <sub> 0.7 </sub> O <sub> 19 </sub> (LSMO/BaM) composites have been prepared by cosintering the LSMO and the BaM powders. The microstructural, magnetic, and magnetoresistive (MR) properties of those systems were systematically studied. Due to the magnetic coupling between the LSMO (a soft magnet metal) and BaM (a hard magnet insulator) grains, the low-field MR sensitivity was reduced and the high-field MR slope was enhanced for the composites. In addition, an abnormal MR hysteresis (resistance reaches its maximum before field reversal) was identified for the composite when the field is applied vertical to the sample plane. Its origin was attributed to a coplay of the LSMO/BaM spin coupling and the demagnetization effect. Finally, an anisotropic magnetoresistance (AMR) effect was observed in the composites. The AMR value decreased with increasing the BaM content, which can be explained by the changes of the local effective field on the grain boundaries. © 2001 American Institute of Physics.
Journal of Applied Physics 10/2001; · 2.17 Impact Factor
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ABSTRACT: In this article, we report our investigations on the doping effect metallic Ag on the intergrain magnetoresistance phenomenon. La <sub> 2/3 </sub> Sr <sub> 1/3 </sub> MnO <sub> 3 </sub> (LSMO) thin films with Ag doping were prepared on (001) LaAlO <sub> 3 </sub> at different substrate temperatures (T<sub>s</sub>) by the dual-beam pulsed-laser deposition technique. Grown at T<sub>s</sub>=750 ° C , the films are perfectly epitaxial with their c axis perpendicular to the film surface. Ag dopant cannot substitute into the LSMO lattice, thus showing no obvious effect on the magnetotransport properties of the film, though it did impair the film in-plane epitaxy and improve the intergrain diffusion of the lattice atoms. However, grown at lower T<sub>s</sub>(400 ° C ), the films are granular with c-axis texture. The Ag dopant exists at GBs and helps to increase the local Mn spin disorder at GBs and the phase interfaces, thus enhancing the eMR value by a factor of 2 compared with the undoped film. Experiment data also suggest that the transport mechanism underlying the Ag-doping enhanced eMR is spin-dependent scattering. © 2001 American Institute of Physics.
Journal of Applied Physics 07/2001; · 2.17 Impact Factor
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ABSTRACT: Polycrystalline La0.7Sr0.3Mn1−xFexO3 thin films, with x=0–0.12, have been prepared on (001)-Si substrates using pulsed laser deposition. The films consist of fine grains with an average size of 60–80 nm. For those films, the metal–insulator transition temperature, Tp, is much lower than the Curie temperature, TC. The high field magnetoresistance, HFMR, is nearly temperature independent for x<0.08, whereas the extrapolated low field magnetoresistance at zero field, LFMR∗, decreases rapidly with increasing temperature. Moreover, Fe doping significantly decreases LFMR∗ and enhances HFMR at low temperatures. We propose that for the Fe-doped films, both the reduced spin polarization of conduction electrons and the increased spin-flip scattering are responsible for the decrease of LFMR∗, while the weakened ferromagnetic spin interaction at the grain boundaries is responsible for the enhanced HFMR. © 2001 American Institute of Physics.
Journal of Applied Physics 05/2001; 89(11):7410-7412. · 2.17 Impact Factor
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ABSTRACT: Nanosized La <sub> 0.7 </sub> Sr <sub> 0.3 </sub> MnO <sub> 3 </sub> /Pr <sub> 0.5 </sub> Sr <sub> 0.5 </sub> MnO <sub> 3 </sub> (LSMO <sub>1-x</sub> PSMO <sub>x</sub>) ceramic composites are prepared using solid-sate sintering. Their microstructural, electro- and magnetotransport properties are characterized by means of various techniques. It is found that the antiferromagnetic/ferromagnetic coupling between PSMO/LSMO at low temperature and the weak ferromagnetic order of PSMO at high temperature results in enhanced low-field magnetoresistance (LFMR) of the composites. With increasing temperature up to 250 K the observed LFMR decays more slowly than that for pure LSMO and this behavior may be explained by the spin coupling near boundaries between LSMO and PSMO grains. © 2001 American Institute of Physics.
Applied Physics Letters 03/2001; · 3.84 Impact Factor
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ABSTRACT: La0.5Sr0.5MnO3 thin films deposited on (001) SrTiO3 substrates at different temperatures are prepared using pulsed laser deposition, and their electro- and magnetotransport properties are experimentally evaluated. The structure analysis reveals that the thin films show amorphous, mixed amorphous/nanocrystalline as well as epitaxial microstructures, respectively, depending on the deposition temperature. While the amorphous thin film exhibits variable range hopping conduction, the epitaxial sample is metal like and ferromagnetic. Enhanced low-field magnetoresistance at low temperature for the microstructure in which the nanocrystalline phase and amorphous phase coexist is demonstrated. It is argued that the amorphous layer separating the neighboring nanocrystals behaves as barrier for the spin-dependent tunneling, resulting in enhanced magnetoresistance at low magnetic field. The modified two-channel model where the insulating conduction channel and the spin-ordered and metallic conduction channel coexist in parallel is employed to explain the magnetotransport phenomena. © 2000 American Institute of Physics.
Journal of Applied Physics 08/2000; 88(5):2791-2798. · 2.17 Impact Factor
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ABSTRACT: We report magnetization measurements in the Ln ( Mn <sub>1-x</sub> Co <sub>x</sub>) O <sub>3+λ</sub> ( Ln=Eu, Nd ; 0≤x≪1) and Y ( Mn <sub>1-x</sub> Co <sub>x</sub>) O <sub> 3 </sub> (0.35≤x≤0.5) perovskites as a function of temperature and magnetic field. Compositions in the range of 0.35≤x≤0.8 ( Ln=Eu ), 0.4≤x≤0.6 ( Ln=Nd ), and 0.35≤x≤0.45 ( Ln=Y ) exhibit metamagnetic behavior associated with a transformation of the magnetic structure from ferrimagnetic, where the magnetic moments of Co <sup> 2+ </sup> and Mn <sup> 4+ </sup> ions are antiparallel, to ferromagnetic where they are parallel. A ferromagnetic state is observed for the 0.1≤x≤0.15 ( Ln=Nd ) and 0.45≪x≤0.5 ( Ln=Y ) compositions. Doping and H-T phase diagrams are presented, and these diagrams resemble those of Ln <sub>1-x</sub> Ca <sub>x</sub> MnO <sub> 3 </sub> charge-ordered manganites. Neutron diffraction studies indicate site ordering of the Co and Mn ions in the Y(Co <sub> 0.5 </sub> Mn <sub> 0.5 </sub> )O <sub> 3 </sub> system, which is presumably responsible for its ferromagnetic behavior. © 2000 American Institute of P-
hysics.
Journal of Applied Physics 08/2000; · 2.17 Impact Factor
