• School Mathematics
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• v.8 no.4
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• pp.397-415
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• 2006

This paper is to find out the reason why students often make mistakes with 0 during computation and to get some instructional implication. For this, history of 0 is reviewed and mathematics textbook and workbook are analyzed. History of 0 tells us that the ancients had almost the same problem with 0 as we have. So we can guess children's problems with 0 have a kind of epistemological obstacles. And textbook analysis tells us that there are some instructional problems with 0 in textbooks: method and time of introducing 0, method of introducing computational algorithms, implicit teaching of the number facts with 0, ignoring the problems which can give rise to errors with 0. Finally, As a reult of analysis of Japanese and German textbooks, three instructional implications are induced:(i) emphasis of role of 0 as a place holder in decimal numeration system (ii) explicit and systematic teaching of the process and product of calculation with 0 (iii) giving practice of problems which can give rise to errors with 0 for prevention of systematical errors with 0.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.4
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• pp.720-740
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• 2011

Wi-Fi-enabled portable devices have recently been introduced into the consumer electronics market. These devices download or upload content, from or to a host machine, such as a personal computer, a laptop, a home gateway, or a media server. This paper investigates the fairness among multiple Wi-Fi-enabled portable devices in a home network when they are simultaneously communicated with the host machine. First, we present that, a simple IEEE 802.11-based home network suffers from unfairness, and the fairness is exaggerated by the wireless link errors. This unfairness is due to the asymmetric response of the TCP to data-packet loss and to acknowledgment-packet loss, and the wireless link errors that occur in the proximity of any node; the errors affect other wireless devices through the interaction at the interface queue of the home gateway. We propose a QoS-provisioning framework in order to achieve per-device fairness and service differentiation. For this purpose, we introduce the medium access price, which denotes an aggregate value of network-wide traffic load, per-device link usage, and per-device link error rate. We implemented the proposed framework in the ns-2 simulator, and carried out a simulation study to evaluate its performance with respect to fairness, service differentiation, loss and delay. The simulation results indicate that the proposed method enforces the per-device fairness, regardless of the number of devices present and regardless of the level of wireless link errors; furthermore it achieves high link utilization with only a small amount of frame losses.

• Speech Sciences
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• v.15 no.3
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• pp.203-217
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• 2008

The number of Asian women immigrants in Korea is getting bigger and it's important to note that their communication problem in Korean causes not only the difficulty of adapting to Korean society but their children's speech-language disorder. To date there is little research on their acoustics characters and articulatory errors. Therefore, this study focuses on acoustic characters and articulatory error patterns of the women immigrants from Japan and Philippine based on the theory of "contrastive analysis". The subjects were 16 Japanese women immigrants(age: 42.5$\pm$4.4) and 14 Philippine women immigrants(age: 31.64$\pm$6.7) and control group consisted of 10 Korean women(age: 28.3$\pm$1.2). Speech and hearing of all subjects and control group were within normal limits. Speech samples were analyzed in a computer using CSL and data analysis was done on FFT widow for F1, F2, F3 of vowels and on wideband spectrogram for VOT of plosives and africatives. The results of this study were like this; For Japanese women immigrants, they had different articulatory patterns of /e/, /a/, /u/, /o/, /$\varepsilon$/, /m/ from those of Koreans and showed articulatory errors on the fortis and aspirated sounds. The reason is Japanese has only two distinctive characters for plosives and affricates; voicing and voiceless. The Philippine women immigrants also showed the same error patterns as the Japanese women immigrants. Especially the errors on aspirated sounds were prominent because their mother tongue has no distinctive characters about aspirated sounds. For vowels, they showed errors of /a/, /o/, /c/.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.4
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• pp.177-183
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• 2015

Incremental sheet metal forming is a manufacturing process to produce thin parts using sheet metals by a series of small incremental deformation. The process rarely needs dedicated dies and molds, thus, preparation time for the process is relatively short as to be compared to conventional metal forming. Spring back in sheet metal working is very common, which causes critical errors in dimensions. Incremental sheet metal forming is not fully investigated yet. Hence, incremental sheet metal forming frequently produces inaccurate parts. This paper proposes a method to minimize dimensional errors to improve shape accuracy of products manufactured by incremental forming. This study conducts experiments using an exclusive incremental forming machine and the material for these experiments are sheets of aluminum AL1015. This research defines a process parameter and selects a few factors for the experiments. The parameters employed in this paper are tool feed rate, tool diameter, step depth, material thickness, forming method, dies applied, and tool path method. In addition, their levels for each factor are determined. The plan of the experiments is designed using orthogonal array $L_8$ ($2^7$) which requires minimum number of experiments. Based on the measurements, dimensional errors are collected both on the tool contacted surfaces and on the non-contacted surfaces. The distances between the formed surfaces and the CAD models are scanned and recorded using a commercial software product. These collected data are statistically analyzed and ANOVAs (analysis of variances) are drawn up. From the ANOVAs, this paper concludes that the process parameters of tool diameter, forming depth, and forming method are the significant factors to reduce the errors on the tool contacted surface. On the other hand, the experimental factors of forming method and dies applied are the significant factors on the non-contacted surface. However, the negative forming method always produces better accuracy than the positive forming method.

• Journal of Korean Association for Spatial Structures
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• v.3 no.2 s.8
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• pp.85-90
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• 2003

If we use a third order approximation for the displacement function of beam element in finite element methods, finite element solutions of beams yield nodal displacement values matching to beam theory results to have no connection with the number increasing of elements of beams. It is assumed that, as the member displacement value at beam nodes are correct, the calculation procedure of beam element stiffness matrix have no numerical errors. A the member forces are calculated by the equations of $\frac{-M}{EI}=\frac{{d^2}{\omega}}{dx^2}\;and\;\frac{dM}{dx}=V$, the member forces at nodes of beams have errors in a moment and a shear magnitudes in the case of smaller number of element. The nodal displacement value of plate subject to the lateral load converge to the exact values according to the increase of the number of the element. So it is assumed that the procedures of plate element stiffness matrix calculations has a error in the fundamental assumptions. The beam methods for the high accuracy ratio solution Is also applied to the plate analysis. The method of reducing a error ratio of member forces and element stiffness matrix in the finite element methods is studied. Results of study were as follows. 1. The matrixes of EI[B] and [K] in the equations of M(x)=EI[B]{q} and M(x) = [K]{q}+{Q} of beams are same. 2. The equations of $\frac{-M}{EI}=\frac{{d^2}{\omega}}{dx^2}\;and\;\frac{dM}{dx}=V$ for the member forces have a error ratio in a finite element method of uniformly loaded structures, so equilibrium node loads {Q} must be substituted in the equation of member forces as the numerical examples of this paper revealed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.12 s.115
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• pp.1249-1258
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• 2006

Two-dimensional(2-D) radar images, namely, ISAR images from a maneuvering target include unwanted phase errors due to the target's motion. These phase errors make ISAR images to be blurred. The ISAR autofocus technique is required in order to remove these unwanted phase errors. Unless those unwanted phase errors produced by the target's motion are removed prior to target identification, we cannot expect a reliable target identification performance. In this paper, we use the entropy-based ISAR autofocus technique which consists of two steps: range alignment and phase adjustment. We analyze a relationship between the number of sampling point and a image quality in a range alignment algorithm and also analyze a technique for reducing computation time of the SSA(Stage-by-Stage Approachng) algorithm in a phase adjustment.

• Journal of the Korean Society of Safety
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• v.21 no.5 s.77
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• pp.103-111
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• 2006

The purpose of this study was to analyse the relationships between cognitive abilities and driving characteristics of elderly drivers. Driving characteristics of elderly and younger drivers who were driving a fixed base driving simulator vehicle were examined. Participants consisted of 12 drivers over age 65 (the 'older' group) and 12 drivers between the ages of 25 and 55 (the "younger" group). As indices of cognitive ability, critical flicker fusion frequency (CFF) tests and cognitive reaction tests were given before the driving task. CFF was also tested after the simulated driving task for both groups. Cognitive reaction tests, which were composed of speed estimation tests, multiple choice reaction tests and obstacle avoidance tests, were developed by the Korean Road Traffic Safety Authority in 2003. CFF values between the two groups exhibited significant differences both before and after the task, with a p-value less than 0.01 and a t-value of -3.01 before the test and a p-value less than 0.031 and a t-value of -2.35 after the test. Older drivers' CFF values were lower than those of the younger. However, there was no difference in older or younger driver CFF values before and after the task within the same group. Except for the multiple choice reaction test, there was no difference in cognitive reaction test results between the two groups. The elderly drivers made more errors though they did not differ from the younger drivers in reaction times. At the simulated driving task the reaction time of the elderly driver was longer than that of the younger; however, the driving speed of the elderly was lower and the number of collisions greater. There was a positive correlation (r=.496) between the number of errors in the multiple choice reaction test and the number of collisions in the driving task. Therefore, it was identified that critical attributes contributing to automobile crashes involving elderly drivers included cognitive difficulty in judging and responding to complex situations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.483-491
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• 2019

The aim of this study is to shed light on factors that influence securing of university research grants. For this purpose, this study emphasizes the role of management capability of industry-university cooperation foundation in securing research grants. We analyze whether the potential capabilities influence research grants using panel data from 194 universities during 2016 to 2018. The results obtained from the Driscoll & Kraay standard errors (DKSE) indicate that a number of variables including the portion of industry-university collaboration professors, academic performance of professors, and the number of paid researchers are positively associated with the amount of external research grant approved. However, the percentage of employees employed for less than two years is negatively related with securing external research grants. Once the dependent variable is measured by the total university research grants, the negative coefficient of employees with short-term career disappears. Instead, the percentage of employees who are in charge of research planning and management and the total number of employees involved in industry-university collaboration foundations are negatively related with the total university research grant amounts.

• Journal of Radiation Protection and Research
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• v.45 no.4
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• pp.171-177
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• 2020

Background: This study aims to determine the effective atomic number (Zeff) from dual-energy image sets obtained using a conventional computed tomography (CT) simulator. The estimated Zeff can be used for deriving the stopping power and material decomposition of CT images, thereby improving dose calculations in radiation therapy. Materials and Methods: An electron-density phantom was scanned using Philips Brilliance CT Big Bore at 80 and 140 kVp. The estimated Zeff values were compared with those obtained using the calibration phantom by applying the Rutherford, Schneider, and Joshi methods. The fitting parameters were optimized using the nonlinear least squares regression algorithm. The fitting curve and mass attenuation data were obtained from the National Institute of Standards and Technology. The fitting parameters obtained from stopping power and material decomposition of CT images, were validated by estimating the residual errors between the reference and calculated Zeff values. Next, the calculation accuracy of Zeff was evaluated by comparing the calculated values with the reference Zeff values of insert plugs. The exposure levels of patients under additional CT scanning at 80, 120, and 140 kVp were evaluated by measuring the weighted CT dose index (CTDIw). Results and Discussion: The residual errors of the fitting parameters were lower than 2%. The best and worst Zeff values were obtained using the Schneider and Joshi methods, respectively. The maximum differences between the reference and calculated values were 11.3% (for lung during inhalation), 4.7% (for adipose tissue), and 9.8% (for lung during inhalation) when applying the Rutherford, Schneider, and Joshi methods, respectively. Under dual-energy scanning (80 and 140 kVp), the patient exposure level was approximately twice that in general single-energy scanning (120 kVp). Conclusion: Zeff was calculated from two image sets scanned by conventional single-energy CT simulator. The results obtained using three different methods were compared. The Zeff calculation based on single-energy exhibited appropriate feasibility.

• Journal of IKEEE
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• v.28 no.1
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• pp.65-71
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• 2024

This paper proposes a neural network that can reduce the number of parameters while reducing matching errors in occluded regions to increase the accuracy of depth maps in stereo matching. Stereo matching-based object recognition is utilized in many fields to more accurately recognize situations using images. When there are many objects in a complex image, an occluded area is generated due to overlap between objects and occlusion by background, thereby lowering the accuracy of the depth map. To solve this problem, existing research methods that create context information and combine it with the cost volume or RoIselect in the occluded area increase the complexity of neural networks, making it difficult to learn and expensive to implement. In this paper, we create a depthwise seperable neural network that enhances regional feature extraction before cost volume generation, reducing the number of parameters and proposing a neural network that is robust to occlusion errors. Compared to PSMNet, the proposed neural network reduced the number of parameters by 30%, improving 5.3% in color error and 3.6% in test loss.