1,721,296 research outputs found
A hybrid approach for program understanding based on graph parsing and expectation-driven analysis
No full textProgram understanding is an important part of the domain expertise required for programming language tutoring systems. However, the understanding of student programs by a computer is extremely difficult because of the tremendous scope of variability in student solutions for nontrivial tasks. This article aims to handle such variability and improve understanding performance by a hybrid approach based on two complementary methods of graph parsing and expectation-driven analysis. The graph parsing method by Wills is utilized to recognize the programming plans in the code. At the same time, a new expectation-driven analysis is devised to generate expectations about the program design using such knowledge as the programming goals, plans, and information about the problem task. The analysis guides the plan recognition process through confirming, amending, or rejecting the expectations by checking them against the given code. Expectation-driven analysis can recognize the function and implementation level variations and errors. Unknown goal-implementing plans ale also detected. These advantages are demonstrated in an experiment of a set of student programs
The optimum design of a pick-up actuator for a minimum seek time
No full textIn this paper, we proposed a pick-up actuator that has a small size, mass, and high resonant frequencies. In order to reduce the mass of the moving part, the proposed actuator has only a pair of permanent magnets. The high resonant frequencies of the actuator are confirmed by FEM analysis. Also, we investigated an optimum design method to minimize the seek times of the actuator. This method uses the time optimal technique to minimize the seek time, with the characteristic values of 2-axis actuators as the constraints. Simulation results show that this method can reduce the seek time to less than that of the conventional method which maximizes the acceleration of the actuator. (C) 2001 Elsevier Science Ltd. All rights reserved
Structural-acoustic coupling in a partially opened plate-cavity system: Experimental observation by using nearfield acoustic holography
No full textIn order to understand the cause and effect relation between a structure and a fluid, many studies on structural-acoustic coupling have been done. However, the studies were restricted to the interaction between only a structure and a fluid located on one or the other side of the structure. It is our aim to understand the coupling mechanism of a generally coupled system that has direct interaction between a finite interior fluid and a semi-infinite exterior one. We believe that this configuration allows the structure to interact with the fluid of the finite volume and that of the infinite one, thus providing a more general structure-fluid coupling (or structural-acoustic coupling) mechanism. For this purpose, we selected a partially opened plate-cavity system which has two different modally reacting boundary conditions: a plate and a hole. In order to understand the physical coupling phenomena of the selected system, visualization of the sound fields was performed experimentally. We used near field acoustic holography to estimate sound field variables, such as pressures and intensities. Examining the acoustic variables, we found that there are two types of coupling mechanisms depending on frequency and associated wavelength. One is where the plate and the cavity are so strongly coupled that the plate can be considered as a source. In this case, the system radiates acoustic energy effectively through the plate. The other is where the coupling interaction behavior decreases the radiation efficiency. The frequencies that determine whether the plate is a good ol bad radiator are found to be around the natural frequencies of the plate. (C) 2001 Acoustical Society of America. [DOI: 10.1121/1.1320476]
Solution of coupled acoustic problems: A partially opened cavity coupled with a membrane and a semi-infinite exterior field
No full textThere have been many attempts to understand the coupling phenomena between a solid structure and the surrounding fluid. However, the studies were restricted to interaction only between a structure and a finite cavity or a structure and acoustic field of infinite size. The system that we have studied has a structure that faces both a cavity of finite size and an external field of semi-infinite size. We also allow a hole, which can directly interact with the cavity as well as the external field. This configuration, therefore, provides two different interactions, or communication means. One is the finite structure and the other is the hole of finite size. This paper studies as to how these two components interact with the other two systems: the finite cavity covered by the structure and the hole, and the semi-infinite fluid. For simplicity, a two-dimensional and partially opened cavity coupled with a membrane and an exterior field was selected. The solution has to be found by solving a boundary value problem, but this case has to do with the boundaries that have two different conditions: one is the membrane and the other is the hole. The solution has been found in terms of the modal functions that satisfy the boundary conditions of finite cavity, membrane and hole. Non-dimensional coupling coefficients are obtained from the solution. The results exhibit that the coupling effect gives additional peaks and troughs in the averaged pressure of the cavity. These peaks and troughs are symmetrically arranged with respect to Helmholtz frequency of the cavity. The strong coupling occurs at the trough frequencies where the membrane interacts actively with the cavity and the exterior field. (C) 2002 Elsevier Science Ltd. All rights reserved
The efficient clock-extraction methods of NRZ signal for chromatic dispersion monitoring
No full textClock-frequency component (CFC) is widely used to monitor chromatic dispersion. However, the CFCs extracted by different clock-extraction (CE) methods show different characteristics about dispersion. We compare the CE methods of nonreturn-to-zero signal for chromatic dispersion monitoring. We also compare the ability of the CE methods to detect the optimum amount of dispersion compensation when optical nonlinearity exists. As a result, we find out the efficient CE methods to monitor the optimum amount of dispersion compensation in the real high-speed transmission systems.This
work was supported by the National Research Laboratory (NRL) Program of
the Ministry of Science and Technology (MOST)
Modelling and optimum design of a fine actuator for optical heads
No full textIn this paper, a new modelling of a fine actuator for optical pick-up has been proposed and multiobjective optimization of it has been performed. The fine actuator is constituted of the bobbin supported by wire suspension, the coils wound around the bobbin, and the magnets which cause the magnetic flux. If current flows in the coils, magnetic force is produced to position the bobbin. The magnetic force is not only balanced with spring force of wire, but also with the inertial and viscous force. In this model the transfer function from input voltage to output displacement of bobbin has been obtained so that we can describe this integrated system which have both electromagnetic and mechanical parts. Wire suspension is regarded as a continuous Euler beam, damper as distributed viscous damping, and bobbin as a rigid body which can make vertical motion only. According to the modelling, the high frequency dynamic characteristics of the fine actuator can be known and the effect of damping can be investigated while the conventional modelling cannot. In optimization, two objective function has been chosen to maximize the fundamental frequency and the sensitivity with respect to input voltage. These objective functions will satisfy the trends which will enhance the access speed and the actuator gain in the optical pick-up technology of next generation. (C) 1997 Published by Elsevier Science Ltd
A microcalcification detection using adaptive contrast enhancement on wavelet transform and neural network
No full textMicrocalcification detection is an important part of early breast cancer detection. In this paper, we propose a microcalcification detection algorithm using adaptive contrast enhancement in a mammography CAD (computer-aided diagnosis) system. The proposed microcalcification detection algorithm includes two parts. One is adaptive contrast enhancement in which the enhancement filtering parameters are determined based on noise characteristics of the mammogram. The other is a multi-stage microcalcification detection. The results show that the proposed microcalcification detection algorithm is much more robust against fluctuating noisy environments.This paper is supported by the development of digital CAD system project (02-PJ3-PG6-EV06-0002) of Ministry of Health and Welfare in The Republic of Korea
Secrecy Multiuser Diversity for Distributed Antenna Systems from the Perspective of User--Scaling Law
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