• 한국세라믹학회지
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• 제28권1호
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• pp.29-36
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• 1991

Microporous glasses in the system TiO2-SiO2-Al2O3-B2O3-CaO-Na2O were prepared by the phase-separation technique. Morphology and distribution of pore and specific surface area of glasses heated and leached out at various conditions were investigated by SEM and Porosimeter. Crystallization of glasses heated above transition temperature was also inspected by X-ray diffraction method. When the heating temperature and time increased, the pore size and volume increased, but the specific surface area decreased above the critical temperature. The phase-separation, specific surface area and pore size showed more sensitive change on the variation of heating temperature than of heating time. The specific surface area and micropore volume of porous glasses prepared in this study were about 120-330$m^2$/g and 0.001-0.01cc/g, respectively. Mean pore size of porous glasses were about 20-90$\AA$. Anatase phases was deposited when the parent glass was heat-treated at 75$0^{\circ}C$ for 6hrs.

• 한국주조공학회지
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• 제23권4호
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• pp.187-194
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• 2003

The effect of rare earth elements (R.E)(from 0.0 to 0.04%) on the microstructure formation and mechanical properties of thin-wall ductile iron castings were investigated. Tensile strength and hardness were decreased with an addition of up to 0.03% rare-earth elements. After addition of more than 0.03%, those were increased. Graphite nodule sizes were the finest, nodule count was the highst regardless of thickness and volume fraction of ferrite was the largest when that was 0.02%. However, the nodule count was decreased with increasing R.E. Futhermore. nodule size increased with increasing thickness and the volume fraction of ferrite decreased as that was increased. Nodularity was increased regardless of the thickness as that was increased. The castings of minium thickness up to 3 mm was possible without the formation of chill.

• 한국연소학회지
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• 제5권2호
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• pp.63-68
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• 2000

Combustion phenomenon in scale-downed combustor is investigated. As the combustor scale decreases surface to volume ratio increases and chamber size approaches quenching distance. As the combustor scales down surface to volume ratio increases resulting increased heat loss. And this heat loss can affect quenching and instability of the flame. To investigate this effect plastic mini combustor is made. Stoichiometricaly premixed Hydrogen / air gas is used as fuel. Initial chamber pressure and chamber size are varied and the effects are evaluated. Peak pressure decreased with the decrease in chamber height. As initial chamber pressure decreases peak pressure decreases and this change is more important than scale down effect till the chamber height of 1mm. With this result and further information following the experiments design parameter for micro engine can be established.

• 한국세라믹학회지
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• 제32권11호
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• pp.1227-1232
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• 1995

Effect of heating rate on the microstructure of the silicon nitride ceramics has been investigated. The specimens with composition of 92Si3N4-6Y2O3-2Al2O3 (in wt%) were sintered at 176$0^{\circ}C$ under 127 kPa for 3h in N2 atmosphere at various heating rates from 1 to 10$0^{\circ}C$/min. The grain size of larger than 2${\mu}{\textrm}{m}$ and less than 1${\mu}{\textrm}{m}$ were measured and compared for the specimens. Regardless of heating rate, grain size of all the specimens showed bimodal distributions and the fracture toughness remained in the range of 5.53~5.72 MPa.m1/2. However, the aspect ratio of the grains of diameter above 2${\mu}{\textrm}{m}$ increased with the heating rate while their grain size and volume fraction decreased.

• Journal of Medicine and Life Science
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• 제20권1호
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• pp.21-31
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• 2023

We aimed (a) to investigate the associations between age, body mass index (BMI), and breast size with mammographic density based on the breast imaging reporting and data system (BI-RADS) and volumetric breast density measurement (VBDM) with Volpara, (b) to evaluate the associations of age, BMI, and breast size with fibroglandular tissue volume (FGV), and (c) to demonstrate the association of mammographic density grade with FGV. From April 2012 to May 2012, 1,203 women consecutively underwent mammography, and their breast density was calculated using the density grade and volume determined by Volpara. In total, 427 women were included in this study. The BMI and breast size of the 427 women were determined. The associations between mammographic density and age, BMI, and bra cup size were assessed. In addition, the associations between FGV and age, BMI, bra cup size, and mammographic density were assessed. The mean age of the women was 51 years (range, 27-83). Age was associated with mammographic density based on BI-RADS (P<0.0001), and both age and BMI were associated with mammographic density based on Volpara (P<0.0001). The mean FGV significantly decreased as age increased (P<0.0001) and increased as BMI and bra cup size increased (P<0.0001 and P=0.0007, respectively). Age was associated with mammographic density, according to both the BI-RADS and VBDM; however, BMI was only associated with mammographic density based on the VBDM. Larger FGV was associated with younger age, higher BMI, larger bra cup size, and higher mammographic density

• 한국세라믹학회지
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• 제35권9호
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• pp.988-994
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• 1998

In the manufacturing of vitreous bonded CBN tool the porosity change associated with various processing conditions, I. e. the sintering temperature and the size and the amount of abrasive grits was observed. In the case of sintering of vitreous bond material only the specimen density reached the maximum at 950$^{\circ}C$ and then the total porosity was increased slightly with the temperature above 950$^{\circ}C$. In the sintering of a-brasive grits and the vitreous bond material together a marked increase in the total porosity was found with the temperature above 950$^{\circ}C$ Reducing the grit size at the constant volume fraction of abrasive grits showed an increase in the total porosity at whole sintering temperature. On the contrary. it was observed that increasing the volume fraction of abrasive grits with a same size showed the increased open porosity simultaneously with decreased closed porosity at whole sintering temperature.

• 한국가시화정보학회지
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• 제9권1호
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• pp.42-48
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• 2011

Six different size of torch-ignition device were applied in a constant volume combustion chamber for evaluating the effects of torch-ignition on combustion. The torch-ignition device was designed for six different volumes and same orifice size. The combustion pressures were measured to calculate the mass burn fraction and combustion enhancement rate. In addition, the flame propagations were visualized by shadowgraph method for the qualitative comparison. The result showed that the combustion pressure and mass burn fraction were increased when using the torch ignition device. And the combustion duration were decreased. The combustion enhancement rates of torch-ignition cases were improved in comparison with conventional spark ignition. Finally, the visualization results showed that the torch-ignition induced faster burn than conventional spark ignition due to the earlier transition to turbulent flame and larger flame surface, during the initial stage. Finally, the initial flame propagation was affected by torch-ignition volume.

• Clinical and Experimental Reproductive Medicine
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• 제18권1호
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• pp.107-111
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• 1991

The testicular volume measured by a Prader orchidometer was compared with sperm count in semen, the levels of serum FSH, LH, testosterone, prolactin, estradiol and progesterone in 59 nonobstructive infertile men. 1. The causes of infertility were primary hypogonadisms in 50 patients (35 unknown, 9 Klinefelter syndromes, 6 varicocels) and secondary hypogonadism in 9 (5 isolated FSH deficiencies, 1 hyperprolactinerriia, 3 pituitary hypogonadisms). 2. Decreased levels of serum FSH (less than 4 mIU/ml) did not correlate with testis volume but increased level of serum FSH (more than 20 mIU/ml) were mostly noted in the testis less than 10ml. 3. Decreased level of serum testosterone (less than 3 ng/ml) were distinguishably noted in the atrophied testis less than 5 ml. 4. There was no correlation between the testicular volume and the levels of serum prolactin, estradiol, and progesterone. Coclusively, testicular volume less than 11 ml suggests poor spermatogenesis, but normal testicular volume dose not nessarily rule out poor spermatogenesis. Function of Leydig cell is relatively well preserved in atrophied testis of 5 to 10 ml comparing with that of seminiferous tubule.

• Environmental Engineering Research
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• 제14권4호
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• pp.262-269
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• 2009

This study examined the separation characteristics of particles in the rainfall runoff from paved roads using a ${\varphi}7.5$ cm hydrocyclone. The volume fraction and total suspended solids concentrations in the overflow and underflow from the hydrocyclone, as well as the separation efficiency were determined. The results indicated that the overflow volume increased with increasing operational pressure, but decreased with decreasing ratio of underflow outlet to inlet sizes ($D_u/D_i$), while the underflow to overflow volumes showed contrary behavior. The total suspended solid (TSS) concentration ratio between the overflow and inflow ($TSS_{over/in}$) decreased as a function of the operational pressure, while the corresponding ratio of underflow to inflow ($TSS_{under/in}$) increased. There was no visible difference in the $TSS_{over/in}$ with increasing $D_u/D_i$ ratio, but the $TSS_{under/in}$ decreased sharply. The particle removal efficiency was mainly affected by the particle size.

• 한국세라믹학회지
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• 제33권8호
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• pp.855-862
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• 1996

The nucleation and the crystal growth rates of Ge-Se-Te chalcogenide glass by two step heat-treatment and its effect on the mechanical optical properties and water-resistance were determined. The maximum nuclea-tion and crystal growth rate were 2.1$\times$103/mm3 .min at 28$0^{\circ}C$ and 0.4${\mu}{\textrm}{m}$/min at 33$0^{\circ}C$ respectively. When the crystal volume fraction with crystal size $1.5mutextrm{m}$ was about 4% the (hardness and fracture toughness were about 117kg/mm2 and 6.0 MPa.mm1/2)respectively. The weight loss of crystallized glass in water was lower than parent glass($25^{\circ}C$ for 32 hrs : 0.03% 8$0^{\circ}C$ for 16 hrs : 0.1%) as 0.01% at $25^{\circ}C$, 0.03% at 8$0^{\circ}C$ for 16 hrs : 0.1%) at $25^{\circ}C$ 0.03% at 8$0^{\circ}C$ respectively. The IR-transmittance decreased with increasing crystal size and crystal volume fraction. The IR-transmittance of crystallized glass with the crystal size of $1.5mutextrm{m}$ (crystal volume fraction : 4%) presented 56% which was about 4% lower than that of parent glass.