1,722,007 research outputs found
Communication-Flow oriented Organizational Redesign Methodology by Analyzing Unstructured Business Process Executions
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Mechanics of indentation of plastically graded materials - I: Analysis
No full textThe introduction of controlled gradients in plastic properties is known to influence the resistance to damage and cracking at contact surfaces in many tribological applications. In order to assess potentially beneficial effects of plastic property gradients in tribological applications, it is essential first to develop a comprehensive and quantitative understanding of the effects of yield strength and strain hardening exponent on contact deformation under the most fundamental contact condition: normal indentation. To date, however, systematic and quantitative studies of plasticity gradient effects on indentation response have not been completed. A comprehensive parametric study of the mechanics of normal indentation of plastically graded materials was therefore undertaken in this work by recourse to finite element method (FEM) computations. On the basis of a large number of computational simulations, a general methodology for assessing instrumented indentation response of plastically graded materials is formulated so that quantitative interpretations of depth-sensing indentation experiments could be performed. The specific case of linear variation in yield strength with depth below the indented surface is explored in detail. Universal dimensionless functions are extracted from FEM simulations so as to predict the indentation load versus depth of penetration curves for a wide variety of plastically graded engineering metals and alloys for interpretation of, and comparisons with, experimental results. Furthermore, the effect of plasticity gradient on the residual indentation pile-up profile is systematically studied. The computations reveal that pile-up of the graded alloy around the indenter, for indentation with increasing yield strength beneath the surface, is noticeably higher than that for the two homogeneous reference materials that constitute the bounding conditions for the graded material. Pile-up is also found to be an increasing function of yield strength gradient and a decreasing function of frictional coefficient. The stress and plastic strain distributions under the indenter tip with and without plasticity gradient are also examined to rationalize the predicted trends. In Part 11 of this paper, we compare the predictions of depth-sensing indentation and pile-up response with experiments on a specially made, graded model Ni-W alloy with controlled gradients in nanocrystalline grain size. (c) 2007 Elsevier Ltd. All rights reserved.N
펄스형 광펌핑을 이용한 루비듐 원자시계 개발 연구
No full text학위논문(박사) - 한국과학기술원 : 물리학과, 2010.08, [ ix, 61 p. ]The atomic clock using a vapor cell is appropriate for many applications because it has simple, compact, and stable characteristics. The atomic clock is realized by the use of the atomic transitions between the ground state hyperfine levels. The two approaches have been used to implement a vapor cell atomic clock. One is the microwave-optical double resonance (MODR) technique and the other is the coherent population trapping (CPT) technique. We propose a pulsed optically pumped Rb atomic clock using a laser absorption in MODR technique and a carrier mode suppression of a phase modulated beam using an optical cavity in CPT technique.
We report an optical detection approach instead of the detection of a microwave decay method in a Rb vapor cell atomic clock for its compact setup. We present the data processing method which transfors the optical transmission signal into the clock transition signal in the optical detection approach. We obtained the FWHM of the clock transition signal which is 293 Hz by this data processing method when the microwave interrogation time is 3 ms and microwave power is -4 dBm. The line broadening of the clock transition signal versus the microwave interrogation time for the respective microwave optimum power was measured. In order to estimate the tolerance of the temperature variation of the temperature stabilization servo, we measured the fractional frequency stability versus temperature variation which is 6.6\times10^{-10} / \degC. The measured frequency stability of our 2 \times10^{-11}\tau_{\frac{-1}{2}}$ and the short-term stability could be improved by employing the more stable laser system and the more precise data processing method. And to enhance the long-term stability, the temperature variations of the laser diode and the components of the electronic systems should be greatly reduced.
We adopted an electro-optic modulator (EOM) approach to produce a phas...한국과학기술원 : 물리학과
광결정 광섬유의 모드 특성 연구
No full text학위논문(석사) - 한국과학기술원 : 물리학과, 2006.2, [ vii, 33 p. ]Photonic crystal fibers (PCFs) are a special class of pure-silica optical fibers. They consist of a silica core, surrounded by a periodic array of air-holes running along the entire length of the fiber. These air-holes permit guidance of light through total internal reflection in the case of index-guiding microstructured fibers (IGMF). And a periodic air-silica cladding exhibits a band gap for photons in the radial direction in photonic band gap fibers (PBGF). Diameter, spacing of the air-holes and geometric air-holes distribution determine the optical properties of the fiber, therefore allowing for tailoring of the fiber according to the intended application.
In this thesis, we numerically investigate the propagation modes and dispersion proper-ties of light in several types of PCFs such as regular index-guiding microstructured fibers, photonic band gap fibers and irregularly structured low- and high-birefringent PCFs. Effects of fiber birefringence, effective index of cladding and the number of guided modes are studied in designing two modes birefringent PCFs. Birefringence of the fiber is realized by adjusting the size and geometry of the air holes around the core regions. We present a design for a birefringent two modes IGMF which can be applied to interferometers and optical sensors.한국과학기술원 : 물리학과
effects of hold time on low-cycle fatigue life with or without high pressure hydrogen gas
No full text학위논문(박사) - 한국과학기술원 : 재료공학과, 1984.8, [ iv, 87 p. ]한국과학기술원 : 재료공학과
Electromigration-induced via failure assisted by neighboring clusters
No full textWith different locations of a cluster, stress evolutions at a via are simulated. Via fails fastest at a specific location of a cluster, which is named fastest stress enhancing polygranular cluster position (FaSEPP). Suggested model and simulated results show that FaSEPP decreases with increasing current density but does not vary with temperature. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.N
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
An epifluidic electronic patch with spiking sweat clearance for event-driven perspiration monitoring
No full textSensory neurons generate spike patterns upon receiving external stimuli and encode key information to the spike patterns, enabling energy-efficient external information processing. Herein, we report an epifluidic electronic patch with spiking sweat clearance using a sensor containing a vertical sweat-collecting channel for event-driven, energy-efficient, long-term wireless monitoring of epidermal perspiration dynamics. Our sweat sensor contains nanomesh electrodes on its inner wall of the channel and unique sweat-clearing structures. During perspiration, repeated filling and abrupt emptying of the vertical sweat-collecting channel generate electrical spike patterns with the sweat rate and ionic conductivity proportional to the spike frequency and amplitude over a wide dynamic range and long time (> 8 h). With such ‘spiking’ sweat clearance and corresponding electronic spike patterns, the epifluidic wireless patch successfully decodes epidermal perspiration dynamics in an event-driven manner at different skin locations during exercise, consuming less than 0.6% of the energy required for continuous data transmission. Our patch could integrate various on-skin sensors and emerging edge computing technologies for energy-efficient, intelligent digital healthcare
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