• International Journal of Fluid Machinery and Systems
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• v.7 no.4
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• pp.160-173
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• 2014

Surge phenomena in multi-stage axial flow compressors were studied with attention to the frequency behaviors. A new parameter "volume-modified reduced surge frequency" was introduced, which took into consideration the essential surge process, i.e., emptying and filling of the working gas in the delivery plenum. The behaviors of the relative surge frequencies at the stall stagnation boundaries, compared with the corresponding duct resonance frequencies, have demonstrated the existence of two types of surges; i.e., a near-resonant surge and a subharmonic surge. The former, which has fundamentally a near-resonance frequency, occurs predominantly at the stall stagnation boundary for the short -and-fat plenum delivery flow-path and the long-and-narrow delivery duct flow-path, and possibly in the intermediate conditions. The latter, which has a subharmonic frequency of the fundamental near-resonant one and occurs mainly in the intermediate zone, is considered to be caused by the reduced frequency restricted to a limited range. In relation with those dimensionless frequencies at the stall stagnation boundary, the surge frequency behaviors in more general situations away from the boundaries could be estimated, though very roughly.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.1057-1063
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• 1994

An instantaneous frequency analysis is a technique to examine a signature for the rotating machinery if the signal has several transitions within a cycle. This paper discusses the conditions of existing negative frequency components in the instantaneous frequency. By using a signal consisted of two frequency components, the instantaneous frequency analysis is conducted while the amplitude ratio between two frequency components has been changed. The analysis shows that, depending on the amplitude ratio, the instantaneous frequencies have averaged, zero-valued, or negative components. It turns out that the negative-valued instantaneous frequencies, which have been regarded as the noise effect, are the consequence of the calculation process for the multisignal components. The criteria of existing the negative values in instantaneous frequencies is given in terms of the relative amplitude ratio and the frequency difference. Especially when the amplitude ratio approaches to 1, the instantaneous frequency fluctuates ${\pm}\infty$ in theory, which implies that instantaneous frequency has unstable region around the amplitude ratio, 1.Also, as the frequency difference between major signal components is increased, the region of existing negative instantaneous becomes broader. In an instantaneous frequency analysis, therefore, a narrow band analysis is suggested, with extreme care if the amplitude ratio approaches to 1. In this paper, a vibration signal monitored from a rotating machinery is also examined as an application example in order to show the existence of negative instantaneous frequencies components.

• Journal of Biomedical Engineering Research
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• v.16 no.2
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• pp.231-238
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• 1995

Tc-99m-MIBI (Sestamibi) myocardial SPECT along with TI-201 tomographic Imaging has demonstrated wide application and high image quality sufficient for the diagnosis of myocardial perfusion defect, which consequently reflects regional myocardial blood flow. The qualitative values of myocardial SPECT with Tc-99m-MIBI as well ds the quantitative cases depend in some degree on the reconstruction techniques of multiple projections. Filtered backprojection (FBP) Is the common standard method for reconstruction rather than the complicated and time-consuming arithmetic methods. In FBP it is known that the distribution of radioactivity in reconstructed transverse slices varies with the selected litter parameters such as cutoff frequencies and order (Butterworth case) The cutoff frequencies used in clinicAl practice partially remove and decrease the true radioactive distribution and alter the pixel counts, which lead to underestimation of true counts in specific myocardial regions. In this study, we have investigated the effect of cutoff frequencies of reconstruction filter on the artifactually induced perfusion defects, which are often demonstrated near inferior and/or inferoseptal cardiac walls due to the intense hepatic uptake of Tc-99m-MIBI. A computerized method for Identifying the relative degree of artifactual perfusion defect and for comparing those degrees along with the relative amount of hepatic uptake to myocardium was developed and patient images were studied to observe the quantitative degree of underestimation of myocardial perfusion, and to propose some reasonable threshold of cutoff frequency in the diagnosis of perfusion defect quantitatively. We concluded that from the quantitative viewpoint cutoff frequencies may be used as high as possible with the sacrifice of homogeneity of image quality, and those frequencies lower than the common 0.3 Wyquist frequency would reveal severe degradation of radioactive distribution near inferior and/or inferoseptal myocardium when applying Butterworth or low pass filter.

• Korean Journal of Veterinary Research
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• v.38 no.2
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• pp.232-238
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• 1998

The distributions and relative frequencies of bovine chromogranin(BCG)-, serotonin-, and bovine pancreatic polypeptide(BPP)-immunoreactive cells in the pancreas of the duck(Anas plaryrhynchos plaryrhyncos, Linne) were studied immunohistochemically on 23 days of incubation, at hatching, 1 week, 2 weeks, 3 weeks, 5 weeks, 6 weeks, 7 weeks, 9 weeks, 10 weeks, and 32 weeks after hatching. In the exocrine portions, the relative frequencies of BCG- and serotonin-immunoreactive cells tend to decrease according to ages. BPP-immunoreactive cells first appeared 1 week after hatching, and thereafter decreased. These cells were mainly observed in the exocrine pancreas and marginal region of the pancreatic islets. In the endocrine portions, BCG-, serotonin- and BPP-immunoreacteve cells disappeared 2 weeks, 9 weeks and 5 weeks after hatching, respectively.

• Korean Journal of Veterinary Research
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• v.39 no.3
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• pp.417-424
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• 1999

Ontogeny, distributions and relative frequencies of somatostatin-immunoreactive cells were investigated in the proventriculus of the chicken embryos with incubation periods. Samples were taken from 10 groups(10 days of incubation to hatching) and studied by immunohistochemical methods. The findings were as follows. Somatostatin-immunoreactive cells were observed from 12 days of incubation in the proventricular glands and after that increased with incubation periods. The first observation time of these cells in the epithelium were at 15 days of incubation in the basal portion but in 16 and 17 days of incubation, no immunoreactive cells were observed in the epithelium but after that a few immunoreactive cells were observed in the basal portion and gastric gland regions. The shapes of these cells were spherical to spindle in the proventricular glands and spherical to round in the epithelium and gastric gland.

• Animal cells and systems
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• v.4 no.1
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• pp.95-100
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• 2000

The regional distribution and relative frequencies of endocrine cells were studied immunogistochemically (PAP methods) in the alimentary tract of the tree frog, Hyla areorea japonica, using specific antisera against serotonin, somatostatin, bovine Sp-1/chromogranin (BCG), cholecystokinin (CCK)-8, vasoactive intestinal polypeptide (VIP), gastrin, bombesin, secretin and pancreatic polypeptide (PP). Six kinds of endocrine cells were identified in this study, These immunoreactive cells were located in the gastric glands of stomach regions and in the basal portion of the epithelium of the intestinal tract or esophagus with variable frequencies. They were spherical or spindle-shaped. Serotonin-immunoreactive cells were observed in the whole alimentary tract including the esophagus. Somatostatin-immunoreactive cells were also detected throughout the alimentary tract except the rectum. CCK-8-immunoreactive cells were observed from the pylorus to ileum. Vip-immunoreactive cells were restricted to the rectum. Bombesin-immunoreactive cells were restricted to the fundic gastric regions and gastrin-immunoreactive cells were restricted to the pylorus. However, no BCG-, secretin and PP-immunoreactive cells were demonstrated in this study. In conclusion, the regional distribution and relative frequency of the endocrine cells in the alimentary tract of the tree frog were similar to other anuran species, but some differences which may be caused by feeding habits and species specification were also observed.

• Journal of Veterinary Clinics
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• v.19 no.3
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• pp.290-294
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• 2002

The frequencies of gamma-ray-induced micronuclei (MN) in cytokinesis-blocked (CB) lymphocytes at several doses were measured in three donors of Korean native cattle and Korean native goat. Measurements performed after irradiation showed a dose-related increases in MN frequency in each of the donors studied. When analysed by linear-quadratic model the line of best fit was cattle : y : 0.1016D +$0.0118D^2$+0.0147, goat : y = 0.1353D +$0.0043D^2$+0.0087 (y : number of MN/CB cells and D = irradiation dose in Gy). The relative sensitivity of goat lymphocytes compared with cattle lymphocytes was estimated by best fitting linear-quadratic model based on the radiation-induced MN data over the range from 0 Gy to 4 Gy. In the case of MN frequency with 0.05, 0.1, 0.2, 0.4 and 0.8, the relative sensitivities of goat lymphocytes were 1.106. 1.166. 1.140, 1.069 and 0.976 respectively. Our in vitro radiobiological study confirmed that the cytogenetic response obtained in blood from cattle and goat can be utilized for application in environmental studies.

• Journal of The Korean Society of Grassland and Forage Science
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• v.10 no.3
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• pp.147-151
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• 1990

The purpose of this study is to clarify the relation of survival rates of seedling plants under grown orchardgrass populations and control by the difference cutting frequency. The orchardgrass populations investigated in this study have passed for 10 years after establishment. Cutting frequencies were 3, 4 and 5 times in a year. This experiment was conducted from April to October, 1989 at the experimental field of Institute of Agricultural Development, Yonsei University. The results are summarized as follows: 1. The survival rates of seedling plants decreased by the days after sowing. The final survival rates of seedling plants were 7.8%, 38.9% and 33.8% in 3, 4 and 5 cuttings, respectively. 2. Relative light intensity indicated highly possitive correlation with relative survival rates of seedling plants and negative correlation with plant length of orchardgrass populations in 4 and 5 cuttings. 3. The frequency distribution of survival seedling plants at 177 days after sowing were showed high values in seeding spots near the adjacent plants of 3 cutings, but in the middle of seeding spots between adjacent plants of 4 .and 5 cuttings, respectively. 4. The plant length of seedling became longer towards the seeding spots near the adjacent plants but the number of tillers increased slightly up to the middle of seeding spots between adjacent plants in all cutting frequencies.

• Preventive Nutrition and Food Science
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• v.2 no.2
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• pp.162-166
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• 1997

This study investigated the antigenotoxic effects of Synurus deltoides extract on the mutagenesis induced by benzo[a]pyene(B[a]P). About 80% and 90% antimutagenic effects were observed in the presence of over 200$\mu\textrm{g}$/plate of methanol extract of Synurus deltoides against Salmonella typhimurium TA98 and TA100 induced by B[a]P, respectively. The methanol extract itself did not induce an increased frequency of micronucleated polychromatic erythrocytes(MNPCE) irrespective of the sampling time(up to 72h), while the treatment with benzo[a]pyrene(B[a]P) at 150mg/kg significantly increased (p<0.05) the incidence of MNPCE. The strongest relative frequency of MNPCE was observed at 36h after injection of B[a]P and the most significant reduction (p<0.05) in the frequencies of MNPCE was occurred at the feeding of the methanol extract to mice 12 h before injection of B[a]P. The most significant reduction (p<0.05) with 48% was observed in the frequencies of MNPCE when 50 mg/kg of the methanol extract was given to the mice 12h before injection of B[a]P, while the strongest relative frequency inhibition was 54% at the multiple feeding of 5mg/kg of the methanol extract e time every day for 5 days on th frequencies of MNPCE induced by 150 mg/kg of B[a]P. These results indicate that the methanol extract of Synurus deltoides have a strong modulatory effect on benzo[a]pyrene induced MNPCE.

• Structural Engineering and Mechanics
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• v.13 no.4
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• pp.355-368
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• 2002

In this paper, we address the numerical investigation on the effect of liquid compressibility onto the natural frequency of liquid-filled containers. Traditionally the liquid motion has been treated as an ideal fluid motion. However, from the numerical experiments for the axisymmetrical free-vibration of cylindrical liquid-storage tanks, we found that the relative difference in natural frequencies between ideal and compressible motions becomes remarkable, as the slenderness of tank or the relative liquid-fill height becomes larger. Therefore, in such cases of dynamic systems, the liquid compressibility becomes an important parameter, for the accurate vibration analysis. For the free-vibration analysis of compressible liquid-structure interaction we employed the coupled finite element formulation expressed in terms of the acoustic wave pressure and the structure deformation.