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Now showing items 145 - 160 of 1639

  • Interfacial studies on the O3 modified carbon fiber-reinforced polyamide 6 composites

    J. Li  

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  • A study of the surface chemistry, morphology and wear of silicon based MEMS

    J. Li   Z. Cui   M. A. Baker  

    Polysilicon microelectromechanical systems (MEMS) are the subject of intense research activity. This paper reports on the surface chemistry, topography and nanowear properties of a MEMS test structure fabricated at Sandia National Laboratories, studied using XPS and atomic force microscopy (AFM). XPS C 1s and Si 2p spectra from the polysilicon components, silicon nitride substrate and a reference Si wafer are compared. The results confirm the presence of a self-assembled monolayer (SAM) on the MEMS surface. An island-like morphology is found on both polysilicon and silicon nitride surfaces of the MEMS. The islands take the form of caps, being up to 0.5 mum in diameter and 20 nm in height. It is concluded that a dual columnar and equiaxed microstructure develops during growth of these low pressure chemical vapour deposition (LPCVD) layers and the islands are caps to the columnar structures. A 35 muN load applied to the AFM diamond tip leads to a wear depth of 1.4 plusmn 0.13 nm and 2.1 plusmn 0.06 nm on the polysilicon and silicon nitride MEMS equiaxed surfaces, respectively. Under the same load, greater wear of the columnar caps on both surfaces is observed. The results suggest that the morphology present on the polysilicon surface will be worn flat during operation and will not adversely affect the wear properties of the polysilicon components
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  • CCR5 blockade in combination with rapamycin prolongs cardiac allograft survival in mice

    J. Li   K. Zhang   P. Ye   S. Wang   J. Xia  

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  • Mechanical properties of a polyamide 6-reinforced PTFE composite

    J. Li  

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  • Is growth hormone helpful in poor ovarian responders?

    J. Li   H. Xu   T. Xia   W. Yu   M. Liu  

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  • Phase-sensitive X-ray imaging of synovial joints

    J. Li   Z. Zhong   D. Connor   J. Mollenhauer   C. Muehleman  

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  • Proper-time resolution function in – mixing search at Belle

    J. Li   L.M. Zhang   Z.P. Zhang   Z.P. Zheng   C.C. Zhang  

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  • Experimental Rocket Motor Applied in Evaluate the Ablation Performance of Ablation Resistance Materials

    G. He   J. Li   P. Liu   and W. Wang   Northwestern Polytechnical University   Xi''an  

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  • The Analysis on the Rising Section of Experimental Pressure in Variable Thrust Pintle Solid Rocket Motor

    G. He   J. Li   and Z. Zhou   Northwestern Polytechnical University   Xi''an  

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  • Buoyancy-driven motion of bubbles in square channels

    J. Li   V. Bulusu   N.R. Gupta  

    The motion of air bubbles in square capillaries moving under the influence of gravity is studied over a range of Reynolds numbers. The steady shapes and velocities of the bubbles as a function of the bubble size are determined experimentally at moderate Bond and capillary numbers. Bubbles are nearly spherical at lower bubble volumes and become prolate losing their fore and aft symmetry at larger bubble volumes. At higher Weber numbers, a reentrant cavity develops at the rear of bubble. The critical Weber number at which this shape transition occurs lies between 0.89 and 1.38. At small Weber numbers, the terminal velocity of bubbles increases monotonically with bubble volume and eventually reaches a plateau value, which is independent of the bubble size. At higher Weber numbers, a maxima develops in the velocity–volume curve at moderate bubble sizes which grows in magnitude as the Weber number increases. Even at small bubble volumes with nearly spherical shape, the terminal velocity of the bubbles is less than the Hadamard–Rybczynski velocity due to the wall drag. The speed and the maximum bubble width for air bubbles rising in a square channel is higher than that of an air bubble rising in a circular channel with the same hydraulic diameter. The experimental data compares well with predicted trends in the viscous and inertial limits for long bubbles.
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  • Implementation of Unmanned Ground Vehicle navigation in Wireless Sensor and Actuator Networks

    J. Li   R. R. Selmic  

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  • Influence of gas inertia and edge effect on squeeze film in near field acoustic levitation

    J. Li   W. Cao   P. Liu   H. Ding  

    Detailed analysis showed that the existing theoretical models for near field acoustic levitation are not good enough to interpret the experimental data. The best existing models can only work in a small range of the squeeze numbers even with a fitting parameter. We report here a comprehensive nonlinear model, which takes into account the nonuniform surface vibration profile, gas inertia as well as entrance pressure drop at the film edge. Our model has no empirical parameters and the predicted results agree exceptionally well with our experimental measurements over a wide range of squeeze numbers.
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  • Studying Digital Imagery of Ancient Paintings by Mixtures of Stochastic Models

    J. Li   J. Wang  

    The paper addresses learning-based characterization of fine art painting styles. The research has the potential to provide a powerful tool to art historians for studying connections among artists or periods in the history of art. Depending on specific applications, paintings can be categorized in different ways. We focus on comparing the painting styles of artists. To profile the style of an artist, a mixture of stochastic models is estimated using training images. The two-dimensional (2D) multiresolution hidden Markov model (MHMM) is used in the experiment. These models form an artist's distinct digital signature. For certain types of paintings, only strokes provide reliable information to distinguish artists. Chinese ink paintings are a prime example of the above phenomenon; they do not have colors or even tones. The 2D MHMM analyzes relatively large regions in an image, which in turn makes it more likely to capture properties of the painting strokes. The mixtures of 2D MHMMs established for artists can be further used to classify paintings and compare paintings or artists. We implemented and tested the system using high-resolution digital photographs of some of China's most renowned artists. Experiments have demonstrated good potential of our approach in automatic analysis of paintings. Our work can be applied to other domains
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  • A tunable optical Kerr switch based on a nanomechanical resonator coupled to a quantum dot

    J. Li   K. Zhu  

    We have theoretically demonstrated the large enhancement of the optical Kerr effect in a scheme of a nanomechanical resonator coupled to a quantum dot and shown that this phenomenon can be used to realize a fast optical Kerr switch by turning the control field on or off. Due to the vibration of the nanoresonator, as we pump on the strong control beam, the optical spectrum shows that the magnitude of this optical Kerr effect is proportional to the intensity of the control field. In this case, a fast and tunable optical Kerr switch can be implemented easily by an intensity-adjustable laser. Based on this tunable optical Kerr switch, we also provide a detection method to measure the frequency of the nanomechanical resonator in this coupled system.
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  • INTEGRAL and Swift/XRT observations of IGR J18179?1621

    J. Li   S. Zhang   D. F. Torres   A. Papitto   Y. P. Chen   J. M. Wang  

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  • Calculation and usage of containment monitor radiation readings during PWR accidents

    J. Li   Y. Ye   Z. Shi   J. Wang  

    A computer code named CALCON for calculation of containment monitor radiation readings is introduced. The validity of the code was verified by comparison with data given in IAEA technical documents. The contribution of isotopes to containment readings under conditions of core melt, gap release and normal coolant release were investigated. The conclusions were that the radiation reading in containment is mainly from iodine and noble gases when sprays are off, and the radiation reading is mainly from noble gases when sprays are on, and during the beginning hours when radionuclides are released into containment, the monitor readings will decrease rapidly. Curves of containment radiation readings versus shutdown time for DAYA BAY nuclear power plant were calculated using CALCON.
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