• Journal of Navigation and Port Research
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• 제31권1호
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• pp.21-27
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• 2007

The wave load and its influence on the response of offshore structure have been well investigated through the statistical approach based on the linear theory. The linear approach has a limitation to apply the extreme condition such as extreme wave, which corresponds to extreme value of wave spectrum. The main topic of present study is to develop an efficient numerical method to predict wave load induced by extreme wave. As a numerical method, finite element method based on variational principle is adopted. The frequency-focusing method is applied to generate the extreme wave in the numerical wave tank. The wave load on the bottom mounted vertical cylinder is investigated. The hydroelastic response of the vertical cylinder is also investigated so as to compare the wave loads with the rigid body case in the extreme wave condition.

• The Journal of the Acoustical Society of Korea
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• 제41권5호
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• pp.525-533
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• 2022

We propose an effective method for suppressing both side and grating lobes by applying 2-dimensional Fourier Transform to the received channel data during the receive focusing process of an ultrasound imaging system. When the signal from the image point is focused, the channel signals have the same DC value across the channels. However, even after echoes from outside an imaging point are focused, they are manifested as having different spatial frequencies depending on their incident angles. Therefore, after the receive focusing delay time is applied, 2-D Fourier Transform is performed on the time-channel data to separate the DC component and other frequency components in the spectral domain, and the weighting value is defined using the ratio of the two values. The side lobe and grating lobe were suppressed by multiplying the ultrasound image by a weighting value. Ultrasound images with a frequency of 5 MHz were simulated in a 64-channel linear array. The grating lobe appearing in the ultrasound image was completely removed by applying the proposed method. In addition, the side lobe was reduced and the lateral resolution was greatly increased. Results of computer simulation on a human organ mimicking image show that the proposed method can aid in better lesion diagnosis by increasing the image contrast.

• The Journal of the Acoustical Society of Korea
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• 제30권4호
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• pp.215-222
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• 2011

In order to obtain high resolution images, a focusing ultrasonic transducer operated in very high frequency (VHF) range was fabricated and its characteristics were evaluated. A 9-${\mu}m$ thick PVDF film with only one metalized surface for electric ground was adhered to a CCP (Copper-clad polyimide) film by using epoxy. It was pressed by a metal ball to form a concave surface and its rear side was filled with the epoxy. The radius of curvature and the f-number of the fabricated transducer are 7.5 mm and 1.7, respectively. The pulse-echo measurement results from a target located at the focal point showed that the frequency bandwidth was 35.0 MHz and the insertion loss near the peak frequency of approximately 40 MHz was about 60 dB. Those values agreed well with the simulation results by the KLM equivalent circuit analysis including the effect of the epoxy bonding layer. When the image of thin copper lines by the 35 MHz transducer of the UBM (Ultrasonic Backscattering Microscope) system was compared with the image by the transducer fabricated in this study, the fabricated transducer was observed that the axial resolution was improved although the lateral resolution was degraded.

• Physical Therapy Rehabilitation Science
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• 제10권2호
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• pp.212-216
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• 2021

Objective: Mirror therapy is one of the promising methods suggested for the upper limb rehabilitation of stroke patients. While mirror therapy was presented to be effective in improving motor function of stroke patients, problems were raised as preceding studies had various methods in applying mirror therapy. Some studies even reported no effect in mirror therapy. Our supposition for the reason of such problems was a decrease of attention on the illusive image during mirror therapy of stroke patients, and we aimed to observe this. Design: A cross-sectional preliminary study. Methods: Three hemiplegic acute patients were recruited for the traditional mirror therapy. It lasted for 30 minutes, and 12 different tasks were asked to perform. All procedures were video-recorded, and Observer XT was used to analyse mirror-gazing time, gaze-distracted time, preparation time, frequency of mirror gazing, frequency of distraction, frequency of preparation for treatment. Results: Subjects spent an average of 4-5 minutes having instructions about the mirror therapy intervention (preparation duration), an average of 11 minutes watching the mirror during therapy (mirror-gazing duration), and the rest of 14-15 minutes looking around the environment (gaze-distracted duration). During the mirror therapy, the number of distracted moments (frequency of distraction) was eight times more than focusing on the mirror (frequency of mirror gazing). Conclusions: Once the patient looks at the mirror, it only lasts about 5 seconds on average. Thus, we confirmed that patients could not concentrate on the illusion during the session and therefore it may have affected the effectiveness of the therapy.

• MALSORI
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• 제37호
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• pp.73-85
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• 1999

The prosodic characteristics of Korean particles in read speech were examined in this paper based on K-ToBI labeling system in order to see whether they are prosodically weak form like functions words in English. Acoustic measurements and statistical analysis were done focusing on the distribution of particles over a variety of prosodic positions, prosodic positional effects on the phonetic realization of particles, and acoustic strength of particles compared to those of their surrounding syllables. The panicles were distributed rather equally over all 4 prosodic positions with the highest frequency at IP-medial/AP-final position and the lowest at IP-medial/AP-medial position except that topic marker 'Un/nUn' showed preference for IP-final/AP-final position. There was a significant prosodic positional effect on the duration and F0 of the particles. Duration was the longest at IP-final/AP-final position and interestingly, at IP-medial/AP-medial position while F0 was the highest at IP-final/AP-medial Position as expected. The comparison of the acoustic properties of the particles with those of neighbor syllables showed that duration was generally significantly longer and energy also showed larger values, if not significant, in particles suggesting that the particles in Korean are not prosodically weaker like function words in English.

• Journal of the Optical Society of Korea
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• 제17권3호
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• pp.262-268
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• 2013

We study the focusing properties of a two-dimensional square-lattice photonic crystal (PC) comprising silica and germanium partitioned cylinders in air background. The finite difference time domain (FDTD) method with periodic boundary condition is utilized to calculate the dispersion band diagram and the FDTD method incorporating the perfectly matched layer boundary condition is employed to simulate the image formation. In contrast to the common square PCs in which the negative refraction effect occurs in the first photonic band without negative phase propagation, in our suggested model system, the frequency with negative refraction exists in the second band and in near-infrared region. In this case, the wave propagates with a negative phase velocity and the evanescent waves can be supported. We also discuss the dependency of the image resolution and its location on surface termination, source location, and slab thickness. According to the simulation results, spatial resolution of the proposed PC lens is below the radiation wavelength.

• The Research Journal of the Costume Culture
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• 제9권6호
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• pp.818-829
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• 2001

The purposes of this study were to segment the men in twenties and thirties according to clothing benefits sought, and to develop a profile of each segment concerning shopping orientation, self·image, and importance of store attributes. The questionnaire was administered to men in twenties and thirties living in Seoul and data were analyzed by frequency, percentage, factor analysis, cluster analysis, and MANOVA(multivarite analysis of variance). By cluster analysis of clothing benefits sought, three groups were identified and labeled as: (1) the group of focusing the influence of other people and comfort clothing(31.7%): (2) the group of pursuing the fashion trend (48.1%); the group of pursuing the individuality(20.1%). Three groups were then compared through MANOVA on shopping orientation, importance of store attributes, and self-image. Significant differences were found among three groups on three variables. In general, the group of focusing the influence of other people and comfort clothing tended to be ostentatious and tended to wear comfortable clothing. The group of pursuing the fashion trend didn't show specific shopping orientation and just liked to follow the current fashion trend. The group of pursuing the individuality enjoyed the shopping and liked to buy the clothing which enhances the personal character.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제25권5호
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• pp.741-749
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• 2001

An inhomogeneous hyperbolic electric field is established among two-dimensional quadrupole electrodes to which an ac voltage is applied. Conditions under which charged particles are focused into a narrow axis region of the plug laminar flow are discussed. The aerodynamic forces influence the behavior of the charged particles in the quadrupole electric field. We derived the dimensionless equations of motion of a charged particle in the alternating quadrupole electric field, and discussed particle trajectories and focusing performance in terms of two dimensionless parameters, which are functions of particle size, operating pressure, and the amplitude and frequency of applied AC voltage, with the results of numerical simulations and experiments.

• 정보저장시스템학회:학술대회논문집
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• 정보저장시스템학회 2005년도 추계학술대회 논문집
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• pp.190-194
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• 2005

There is a great demand of micro-actuators for mobile information devices such as SFF optical drives and mobile camera phones. However, conventional magnetic coils of electromagnetic motors are a major obstacle for miniaturization because of their complicated structures and large power consumption. In this paper, a linear ultrasonic motor to actuate focusing lens of mobile devices is proposed. The new actuator uses a ring type bimorph piezoelectric material, and $d_{31}$ mode is adopted for applying linear motion. The interaction between inertia force and friction force makes linear motion by high-frequency saw signal input. The saw signal gives steady forces on the one direction by asymmetric inclination property of the signal itself on time domain. A commercial FEM (ANSYS) was used in this investigation for simulating structural analysis, identification of dynamic property, such as resultant displacement and coupled analysis with piezoelectric material. To evaluate the performance of the new design, a prototype was manufactured and experiments were carried out. Experimental results show the actuator motion of 1.52 mm/s at 10 kHz input signal in 5 V.

• Transactions of the Society of Information Storage Systems
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• 제2권4호
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• pp.251-256
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• 2006

There is a great demand of micro-actuators for mobile information devices such as SFF optical drives and mobile phone cameras. However, the magnetic coils used in conventional electromagnetic motors are a major obstacle for the miniaturization because of their complicated structures and large power consumption. In this paper, a linear ultrasonic motor to actuate focusing lens of mobile devices is proposed. The new actuator uses a ring type bimorph piezoelectric material, and $d_{31}$ mode is adopted for applying linear motion. The interaction between inertia force and friction force makes linear motion by high-frequency saw signal input. The saw signal gives steady forces on the one direction by asymmetric inclination property of the signal itself on time domain. A commercial FEM(ANSYS) was used in this investigation for simulating structural analysis, identification of dynamic property, such as resultant displacement and coupled analysis with piezoelectric material. To evaluate the performance of the new design, a prototype was manufactured and experiments were carried out. Experimental results show the actuator motion of 5.4 mm/s at 10V saw signal of 41 kHz.