• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.1
• /
• pp.1-12
• /
• 1990

The study is concerned with the analysis of combined forging of non-axisymmetric shapes with inclined protrusions by UBET technique. Work hardening is considered for the given range of strain rate during the forging process. A complex shape with inclined cavities is analyzed by subdividing the workpiece into finite UBET elements for which simple velocity fields are applicable. An experimental set-up was designed and manufactured for the experiment, and experiments are carried out with lead billets. The devised set-up can be used for closed-die forging of complex shapes with protrusions in which the dies can be separated automatically for easy removal of the forged products. Based on the derived kinematically admissible velocity fields for corresponding UBET elements, general computer programs have been developed. Since the energy dissipation rate for each elemental region is provided by subprograms (Subroutine or Function), the developed program can be applied to the forging problems of various shapes. The present study has shown that the method developed can be effectively applied to forging of non-axisymmetric shapes with complicated protrusions.

• The Transactions of the Korea Information Processing Society
• /
• v.3 no.1
• /
• pp.118-126
• /
• 1996

Memory hierarchy is a useful mechanism for improving the memory access speed and making the program space larger by layering the memories and separating program spaces from memory spaces. However, it needs at least two memory accesses for each data reference : a TLB(Translation Lookaside Buffer) access for the address translation and a data cache access for the desired data. If the cache size increases to the multiplication of page size and the cache associativity, it is difficult to access the TLB with the cache in parallel, thereby making longer the critical timing path in the processor. To achieve such parallel accesses, we present the hybrid mapped TLB which combines a direct mapped TLB with a very small fully-associative mapped TLB. The former can reduce the TLB access time. while the latter removes the conflict misses from the former. The trace-driven simulation shows that under given workloads the proposed TLB is effective even when a fully-associative mapped TLB with only four entries is added because the effects of its increased misses are offset by its speed benefits.

• Korean Journal of Community Nutrition
• /
• v.15 no.2
• /
• pp.275-283
• /
• 2010

There are few studies reporting optimal waist circumference that can be utilized to prevent the incidence of cardiovascular disease (CVD). We evaluated the association of waist circumference and waist and hip circumference ratio (WHR) with incident cases of CVD developed over 6 years in a population-based prospective study including Korean adults. Analyses for receiver-operating characteristic (ROC) curve were performed with data for 1,733 men and 1,579 women who were aged 40 to 69 years and were free of a physician-diagnosis of CVD at baseline. Information on the diagnosis of CVD was periodically reported using interviewer-administered questionnaires and anthropometric measures were obtained by biennial health examinations. We newly identified 77 cases of CVD during a follow-up period between 2003 and 2008. On the basis of measures of diagnostic accuracy including minimum distance to ROC curve and Youden index, waist circumference of 85 cm for men, in particular for male nonsmokers, and of 80 cm for women and WHR of 0.88 to 0.90 for men and of 0.83 for women were found to be optimal cutoff points to identify individuals at CVD risks. The study also found that the use of the suggested optimal values for waist circumference show higher sensitivity and lower specificity compared with 90 cm for men and 85 cm for women, which are waist cutoff points given by the Korean Society for the Study of Obesity to define abdominal obesity for Korean adults. Although lower cutoff points of waist circumference (83 cm) and WHR (0.87) were observed to be optimal for male smokers compared with male nonsmokers, whether suggesting waist cutoff points specific to smokers is needed warrants further studies. After taking into account other cardiovascular risk factors including smoking, men with waist circumference of 85 cm or greater and women with 80 cm or greater were at an increased risk of CVD. Thus, these cutoff points of waist circumference may be able to capture more individuals at CVD risks contributing to the prevention of future development of CVD.

• Journal of Internet Computing and Services
• /
• v.5 no.5
• /
• pp.17-26
• /
• 2004

Mobile multicast schemes are classified into remote subscription and bi-directional tunneling. While the former scheme has much overhead in the maintenances of multicast tree, the latter suffers from inefficient routing. In this paper, we propose dynamic mobile multicast routing (DMMR) scheme, which is operated on the basis of cost functions related with forwarding cost and tree reconstruction cost, Basically DMMR intends to find lower cost between forwarding cost and tree reconstruction cost. Forwarding cost is the cost of tunneling multicast packets from home agent, and tree reconstruction cost is the joining cost of foreign agent to multicast group. In the case that a mobile host moves to the other area, its foreign agent calculates cost functions related with forwarding cost and tree reconstruction cost. If forwarding cost is higher than tree reconstruction cost, foreign agent joins to multicast group and reconstructs the multicast tree. Accordingly, foreign agent can dynamically adapt remote subscription or bi-directional tunneling, Our scheme provides more stable multicast service to the mobile hosts regardless of the movements of mobile host and the number of mobile group members.

• Tunnel and Underground Space
• /
• v.12 no.4
• /
• pp.277-283
• /
• 2002

This experimental study concerns the characteristics of a helical flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. The pressure losses and skin friction coefficients have been measured for the fully developed flow of Non-Newtonian fluid, aqueous solution of sodium carbomethyl cellulose (CMC) and bentonite with inner cylinder rotational speed of 0~400 prm. Also, the visualization of helical flows has been performed to observe the unstable waves. The results of present study reveal the relation of the Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The pressure losses increase as the rotational speed increases, but the gradient of pressure losses decreases as the Reynolds number increases in the regime of transition and turbulence. And the increase of flow disturbance by Taylor vortex in a concentric annulus with rotating inner cylinder results in the decrease of the critical Reynolds number with the increase of skin friction coefficient.

• Journal of the Korean Ceramic Society
• /
• v.33 no.3
• /
• pp.339-347
• /
• 1996

Mechanical properties(flexural strength hardness fracture toughness) of alumina ceramics were evaluated. Alumina products of four companies were selected and three of those were made in Korea and one of those was made in Japan. The large differences according to manufacturing companies had resulted from flexural strength and weibull modulus which had a wide ranges of 300 to 400 MPa and 5 to 15 respectively. Critical indenstation load which could be neglected the effect of elastic recovery was about 9.8N and Vickers' hardness were about 15 GPa. Fracture toughnesses were evaluated by IF and ISB method. It was more preferable to the average at one indentation load that fracture toughness were obtained from the slope of the relationship between indentation load and crack length in IF method and between indentation load and fracture load in ISB method and fracture toughness was about 4 MPa·m1/2.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.41 no.7
• /
• pp.53-61
• /
• 2004

In this paper, we proposed a new architecture of MAC(Multiplier-Accumulator) to operate high-speed multiplication-accumulation. We used the MBA(Modified radix-4 Booth Algorithm) which is based on the 1's complement number system, and CSA(Carry Save Adder) for addition of the partial products. During the addition of the partial product, the signed numbers with the 1's complement type after Booth encoding are converted in the 2's complement signed number in the CSA tree. Since 2-bit CLA(Carry Look-ahead Adder) was used in adding the lower bits of the partial product, the input bit width of the final adder and whole delay of the critical path were reduced. The proposed MAC was applied into the DWT(Discrete Wavelet Transform) filtering operation for JPEG2000, and it showed the possibility for the practical application. Finally we identified the improved performance according to the comparison with the previous architecture in the aspect of hardware resource and delay.

• Journal of IKEEE
• /
• v.19 no.3
• /
• pp.342-348
• /
• 2015

High speed implementation of digital filters is required in high data rate applications such as hard-wired wide band modem and high resolution video codec. Since the critical path of the digital filter is the MAC (multiplication and accumulation) circuit, the filter coefficient with sparse non-zero bits enables high speed implementation with adders of low hardware cost. Compressive sensing has been reported to be very successful in sparse representation and sparse signal recovery. In this paper a filter design method for digital FIR filters with CSD (canonic signed digit) coefficients using compressive sensing technique is proposed. The sparse non-zero signed bits are selected in the greedy fashion while pruning the mistakenly selected digits. A few design examples show that the proposed method can be utilized for designing sparse CSD coefficient digital FIR filters approximating the desired frequency response.

• Journal of the Korean Institute of Telematics and Electronics C
• /
• v.35C no.11
• /
• pp.1-10
• /
• 1998

The advent of deep submicron technologies in the age of portable electronic systems creates a moving target for CAB algorithms, which now need to reduce power as well as delay and area in the existing design methodology. This paper presents a resynthesis algorithm for logic decomposition on mapped circuits. The existing algorithm uses a Huffman encoding, but does not consider glitches and effects on logic depth. The proposed algorithm is to generalize the Huffman encoding algorithm to minimize the switching activity of non-critical subcircuits and to preserve a given logic depth. We show how to obtain a transition-optimum binary tree decomposition for AND tree with zero gate delay. The algorithm is tested using SIS (logic synthesizer) and Level-Map (LUT-based FPGA lower power technology mapper) and shows 58%, 8% reductions on power consumptions, respectively.

• Journal of Advanced Navigation Technology
• /
• v.22 no.5
• /
• pp.415-419
• /
• 2018

This paper predicts and measures the C/N ratio of a beacon signal transmitted from geostationary orbit satellite KorSat 5A ($113^{\circ}E$) at a ground station located in Kimpo. Based on the ground stations, we compared the rain attenuation of the zone K of ITU-R and the rain attenuation which analyzed the domestic weather information. In ITU-R, the Korean rainfall characteristics are classified into zone K, but forecasting the rainfall intensity and attenuation of three adjacent cities based on the cumulative rainfall data per minute from 2013 to 2017. The calculation of rainfall path and attenuation is based on ITU-R recommendations. The change of the C/N according to the rainfall amount was confirmed through the 2 week satellite beacon signal C/N measurement. The predicted critical C/N was decreased to 12 dB at $A_{0.3}$. During the experiment, it was confirmed that it decreased up to 8 dB according to the concentrated rainfall.