170 research outputs found

    Statistical Self-Similar Properties of Complex Networks

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    It has been shown that many complex networks shared distinctive features, which differ in many ways from the random and the regular networks. Although these features capture important characteristics of complex networks, their applicability depends on the type of networks. To unravel ubiquitous characteristics that complex networks may have in common, we adopt the clustering coefficient as the probability measure, and present a systematic analysis of various types of complex networks from the perspective of statistical self-similarity. We find that the probability distribution of the clustering coefficient is best characterized by the multifractal; moreover, the support of the measure had a fractal dimension. These two features enable us to describe complex networks in a unified way; at the same time, offer unforeseen possibilities to comprehend complex networks.Comment: 11 pages, 4 figure

    Interaction of particles with a cavitation bubble near a solid wall

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    Hard particle erosion and cavitation damage are two main wear problems that can affect the internal components of hydraulic machinery such as hydraulic turbines or pumps. If both problems synergistically act together, the damage can be more severe and result in high maintenance costs. In this work, a study of the interaction of hard particles and cavitation bubbles is developed to understand their interactive behavior. Experimental tests and numerical simulations using computational fluid dynamics (CFD) were performed. Experimentally, a cavitation bubble was generated with an electric spark near a solid surface, and its interaction with hard particles of different sizes and materials was observed using a high-speed camera. A simplified analytical approach was developed to model the behavior of the particles near the bubble interface during its collapse. Computationally, we simulated an air bubble that grew and collapsed near a solid wall while interacting with one particle near the bubble interface. Several simulations with different conditions were made and validated with the experimental data. The experimental data obtained from particles above the bubble were consistent with the numerical results and analytical study. The particle size, density and position of the particle with respect to the bubble interface strongly affected the maximum velocity of the particles

    Growing crack analyses using nodal release technique

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    Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1995.Includes bibliographical references (leaves 78-80).by Sunghwan Jung.M.S

    Experiments and theory of selective assembly using topography and ultrasonically-induced fluid forces

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaves 127-129).A site-selective self-assembly technique called templated assembly by selective removal (TASR) is introduced and demonstrated. A theory is created to describe its operation, and its correspondence with experiments is shown. In the experiments, the topography of the template is modified to match the shapes of micron-sized microsphere components at the locations where the components are intended to assemble; then the components and template are coated with a hydrophobic layer. The substrate and components are then placed in a fluid environment for the assembly process, and megahertz frequency ultrasound is applied to the fluidic bath to selectively remove components from undesired sites. Experiments successfully demonstrated highly selective assembly of the microcomponents with the diameters in the range from 1.6[mu]m to 0.4[mu]m into the shapematched holes in the template. Based on the understanding of hydrophobic interfacial energy and the flow fields created by ultrasound, a theory was proposed to describe the mechanism of component removal and was carefully verified with additional experiments. In the present work, scalability and repeatability of the present approach were also addressed and experimentally investigated. Additionally, component circulation was qualitatively assessed in association with near-boundary acoustic streaming flow, and its contribution to the present assembly process is discussed.by Sunghwan Jung.Ph.D

    Surface Waves on a Semi-toroidal Water Ring

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    We study the dynamics of surface waves on a semi-toroidal ring of water that is excited by vertical vibration. We create this specific fluid volume by patterning a glass plate with a hydrophobic coating, which confines the fluid to a precise geometric region. To excite the system, the supporting plate is vibrated up and down, thus accelerating and decelerating the fluid ring along its toroidal axis. When the driving acceleration is sufficiently high, the surface develops a standing wave, and at yet larger accelerations, a traveling wave emerges. We also explore frequency dependencies and other geometric shapes of confinement
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