• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2524-2527
• /
• 2007

Solid propellant gas generators (SPGG) play a role as a turbopump starter in liquid propellant propulsion systems by supplying pressurized gas to power turbines for engine start. For such a purpose, the propellants should burn with a relative low flame temperature and the combustion gas should not contain corrosive constituents such as chlorine compounds. In accordance with these requirements, stabilized AN-based propellants have been usually used as the most appropriate oxidizer for propellant compositions. However, the burning area of the propellant intends to increase to satisfy the required mass flux because of its low burning rate. Consequently the burning area incensement brings on the SPGG size augmentation. A flow restriction such as filters is applied to decrease the SPGG size by rising up the combustion pressure resulting in increasing the burning rate. The feasibility of the size reduction of SPGG by the employment of filters have been studied. The preliminary results of this study show that the considerable reduction of SPGG size would be achievable just by installing a filter with relatively high pressure loss coefficient.

• Journal of the Korean Ceramic Society
• /
• v.50 no.1
• /
• pp.31-36
• /
• 2013

${\beta}$-SiC powders were synthesized by a carbothermal reduction process using $SiO_2$-C precursors fabricated by a sol-gel process using phenol resin and TEOS as starting materials for carbon and Si sources, respectively. The C/Si molar ratio was selected as an important parameter for synthesizing SiC powders using a sol-gel process, and the effects of the C/Si molar ratio (1.4-3.0) on the particle size, particle size distribution, and yield of the synthesized ${\beta}$-SiC powders were investigated. It was found that (1) the particle size of the synthesized ${\beta}$-SiC powders decreased with an increase in the C/Si molar ratio in the $SiO_2$-C hybrid precursors, (2) the particle size distribution widened with an increase in the C/Si molar ratio, and (3) the yield of the ${\beta}$-SiC powder production increased with an increase in the C/Si molar ratio.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.6 no.2
• /
• pp.126-137
• /
• 2007

In this paper, a new method to reduce the size of ROM in the direct digital frequency synthesizer(DDFS) is proposed. And we design the phase-to-sine converter using the phase accumulator of parallel type for generating the high frequency. The new ROM compression method can reduce the ROM size by using the two ROM. The quantized value of sine is saved by the quantized-ROM(Q-ROM) and the differential ROM(D-ROM). So the total size of the ROM in the proposed DDFS is significantly reduced compared to the original ROM. The ROM compression ratio of 67.5% is achieved by this method. Also, the power consumption is decreased according to the ROM size reduction.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.17 no.9 s.112
• /
• pp.845-851
• /
• 2006

Folded lines are applied to design a compact microstrip ring hybrid. Using the proposed structure we achieve both significant size reduction and good harmonic suppression with the same results of conventional ring hybrid at 2.41 GHz. Including the third harmonic frequency, up to 11 GHz band harmonics are suppressed to -20 dB. The size of the proposed ring-hybrid is reduced to one forth of the conventional ring hybrid. The measured frequency responses agree well with simulated ones.

• Molecular & Cellular Toxicology
• /
• v.4 no.1
• /
• pp.52-60
• /
• 2008

In order to investigate whether the particles reduced to almost nano grade might affect the chemical and physical properties of organic materials, whole Korean Black-Red Ginseng was pulverized into almost nano size and then ginsenosides, minerals, carbohydrates, lipids and proteins in the ultrafine particles were compared with those in the regular particles as control. The mean size of the ultrafine particles was in the 350 nm range, while that of the regular particles was $127{\mu}m$. More ginsenosides, minerals, carbohydrates, lipids and proteins were detected in the ultrafine particles than in the regular particles. Interestingly, more lipids from the ultrafine particles dissolved in the water than those from the regular particles in the ethanol. Absorption and transport of carbohydrate, lipid or antioxidant activity across the intestinal wall using everted intestine sacks of mice was also enhanced by particle size reduction at the almost nano scale. More cytotoxic effect against hepatoma cell growth by ultrafine particles was also found. These results could be used as the basic data for the understanding and evaluation of the effects of organic nanomaterials on the human health.

• Journal of Institute of Control, Robotics and Systems
• /
• v.6 no.8
• /
• pp.623-628
• /
• 2000

Video-on-demand system in which users can request any video through the network at any time is made possible by rapid increase in network bandwidth and capacity of the media server. However true video-on-demand system cannot support all requests since bandwidth requirement is still too demanding. Therefore efficient bandwidth reduction algorithm is necessary. both the piggybacking method and the batching method are novel solutions that can provide more logical number of streams than the physical system can support. Of course each of them has its pros and cons. hence piggybacking with batching-by-size can take advantage of both the schemes. Some parameters such as the size of batch and the size of the catch-up window should be adjusted and order to maximize the bandwidth reduction for piggybacking with batching-by-size method. One of the most important parameters is decided optimally in this paper. Simulation shows that the optimized parameter can achieve considerable reductionand consequently remarkable enhancement in performance.

• Journal of Korea Multimedia Society
• /
• v.14 no.1
• /
• pp.94-102
• /
• 2011

To alleviate the size and bandwidth requirement in JPEG2000 system, a new Embedded Compression(EC) algorithm with minor image quality drop is proposed. For both random accessibility and low latency, very simple and efficient hadamard transform based compression algorithm is devised. We reduced LL intermediate memory and code-block memory to about half size and achieved significant memory bandwidth reductions(about 52~73%) through proposed multi-mode algorithms, without requiring any modification in JPEG2000 standard algorithm.

• Journal of Powder Materials
• /
• v.9 no.5
• /
• pp.315-321
• /
• 2002

Pure tantalum powder has been produced by combining Na as a reducing agent, $K_2TaF_{7}$ as feed material, KCl and KF as a diluent in a stainless steel(SUS) bomb, using the method of metallothermic reduction. The present study investigated the effect of the amount of the diluent and reaction temperature on the characteristics of tantalum powder in the production process. The temperature applied in this study $850^{\circ}C$ and the amount of the additional reductant from +5% of the theoretical amount used for the reduction of the entire $K_2TaF_{7}$. The results showed that as the amount of the diluent increased, the reaction temperature became lower because the diluent prevented a temperature rise. Also, according to the mixture ratio of the feed materials and the diluent changed from 1 : 0.25 to 1 : 2, the particle size decreased from $5\mutextrm{m}$ to $1\mutextrm{m}$ and a particle size distribution which is below 325 mesh in fined powder increases from 71% to 83%. The average size of Tantalum powder, $2-4\mutextrm{m}$, was close to that of the commercial powders($2-5\mutextrm{m}$). Also under this condition, impurities contained in the powder were within the range allowed for the commercial Ta powders.

• Journal of Advanced Navigation Technology
• /
• v.16 no.1
• /
• pp.35-40
• /
• 2012

In this paper, we present the size reduction method of HF whip antenna for ship communication. To reduce the size of the HF whip, the end part of linear whip is modified to helical type. We designed the whip antenna with 60% size of the commercial whip antenna and carried out communication experiments using the commercial and the designed whip antennas. From the experimental results, we found that the proposed whip antenna can replace the commercial whip antenna for ship communication.

• Macromolecular Research
• /
• v.16 no.7
• /
• pp.626-630
• /
• 2008

Poly(vinyl pyrrolidone) was used successfully to control the size and distribution of silver nanoparticles generated on inorganic silica nanofibers. The inorganic nanofibers were electro spun using sol-gel chemistry of silicates, and the diameter of the prepared nanofibers was unaffected by adding up to 7% of poly(vinyl pyrrolidone). The silver ions, in the form of silver nitrate, were introduced into the silica nanofibers and reduced to metallic silver by ultraviolet irradiation with a subsequent thermal treatment. The size of the generated silver particles was decreased dramatically by adding poly(vinyl pyrrolidone). The size of the silver nanoparticles was 73 nm when no poly(vinyl pyrrolidone) was added but 23 nm with the addition of only 1% of poly(vinyl pyrrolidone). The extent of reduction could be checked by determining the concentration of silver ions leached into water from the silica nanofibers. After thermal treatment of the silica nanofibers, more than 99% of the silver remained in the nanofibers, indicating almost complete reduction of the silver ions to silver metal.