• Journal of the Optical Society of Korea
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• v.4 no.1
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• pp.14-18
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• 2000

We have investigated gain flattening of EDFA systems with or without a gain equalizer for WDM long-haul transmission using a re-circulating EDFA loop. Without a gain equalizer, gain variation as small as 2.9 dB was achieved over the 10-nm band of a 100 cascaded EDFA system by the inversion principle. With a gain equalizer based on all-fiber acousto-optic tunable filters, two different config-urations of EDFAs were tested. For a single-stage EDFA scheme, the 21-nm band has shown 3.8 dB of gain variation at 17.4 ∼ 20.3 dB of OSNRs after the 100the stage of EDFAs. For a dual-stage EDFA scheme, a wider bandwidth of 34 nm has shown 3.6-dB variation after 40 cascaded EDFAs.

• Journal of the Optical Society of Korea
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• v.7 no.2
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• pp.64-66
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• 2003

The optical gain and noise figure improved double-pass two-stage EDFA using a mirror, circulator, and gain-flattening filters is proposed. By double passing the pump light and removing the ASE propagating into the input part, the signal gain of 5 ㏈ and noise figure of 2.1 ㏈ are improved compared to the conventional single- and double-pass EDFA With gain-fattening filters in the second stage of EDFA, we obtain an improved flat gain with a gain flatness less than 1 ㏈ over 33-nm wavelength range at the 980-nm pump power of 86 ㎽.

• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.81-84
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• 1989

EHZP is a kind of holographic optical element, which is generated by the interference of two divergent spherical waves from point sources on the same axis. It has the spherical aberration that the focal power increases as the radial distance r increases. By using this property, optimal design of EHZP was performed for f-$\theta$ lens. As the result of optimization, the f-$\theta$ condition and the field flattening condition were well satisfied when EHZP has f0=0.803f, faR=4.076f, 1=0.406f. It was assumed for calculation of field flattening condition that the incident wave was a plane wave with the diameter of 1mm.

• Proceedings of the Zoological Society Korea Conference
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• 2000.04a
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• pp.78.1-78
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• 2000

No Abstract, See Full Text

• 대한방사선치료학회:학술대회논문집
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• 2000.04a
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• pp.12-13
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• 2000

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.21 no.2
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• pp.341-351
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• 1991

The purpose of this study was to aid in the evaluation of prognosis of temporomandibular joint after open reduction of fractured mandible. The author studied the bony changes (remodelling) of 116 temporomandibular joints and facial asymmetry in 58 patients. Subjects were divided into 4 Groups according to the follow up periods after open reduction of fractured mandible. The bony changes and facial asymmetry were observed on lateral tomograms and cephalometric posteroanterior skull radiograms. The results were as follows: 1. The bony changes of condyles were observed in 56 cases (38 flattening, 14 osteophyte, 3 erosion, 1 sclerosis). Flattening was observed in 32.8% (Group Ⅰ 27.8%, Group Ⅱ 37.5%, Group Ⅲ 35.7%, Group Ⅳ 32.1%). Osteophyte was observed in 12.1% (Group Ⅰ 11.1%, Group Ⅱ 8.3%, Group Ⅲ 7.1%, Group Ⅳ 21.4%). Erosion and sclerosis were observed in 2.6%, 0.9%, respectively. 2. The bony changes of articular fossa were observed in 18 cases (15.5%). Flattening was observed in 12.1% (Group Ⅰ 2.8%, Group Ⅱ 4.2%, Group Ⅲ 10.7%, Group Ⅳ 17.9%). Sclerosis was observed in 3.4% (Group Ⅰ 5.6%, Group Ⅲ 3.6%, Group Ⅳ 3.6%). 3. The amount of facial asymmetry was 2.81±2.20㎜ (Group Ⅰ 3.06±1.93㎜, Group Ⅱ 2.38±2.44㎜, Group Ⅲ 2.74±1.19㎜, Group Ⅳ 2.93±2.93㎜). There was no significant difference between all groups according to bony changes of temporomandibular joints after open reduction of fractured mandibles (x²-Test, P>0.05).

• Journal of the Korean Society of Radiology
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• v.10 no.2
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• pp.125-131
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• 2016

Radiation therapy is usually using linear accelerator and used X-ray energy is also getting higher. Recently linear accelerators has been developed 3F mode and tracking jaw technology and that was applied for patient therapy. This study aims at measuring photoneutrons depending on the use of 3F and tracking jaw system when radiation is irradiated using a linear accelerator. The generation of photoneutrons of 3F system was 70% smaller than 2F system and that of tracking jaw system was 83% higher than static jaw system. Photoneutron value is relatively low. However, it must be minimized for Photoneutron exposure during radiation therapy.

• Journal of Radiation Protection and Research
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• v.43 no.3
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• pp.107-113
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• 2018

Background: The purpose of our study was to compare the dosimetric advantages of Flattening filter free (FFF) beams for trigeminal neuralgia patients using 4 mm conical collimators over previously treated patients with 6 MV SRS beam. Materials and Methods: A retrospective study was conducted for 5 TN patients who had been previously treated at our institution using frame-based, LINAC-based stereotactic radiosurgery (SRS) on Novalis Tx using 6 MV SRS beam were replanned on 6X FFF beams on Edge Linear accelerator with same beam angles and dose constraints using 4 mm conical collimator. The total number of monitor units along with the beam on time was compared for both Edge and Novalis Tx by redelivering the plans in QA mode of LINAC to compare the delivery efficiency. Plan quality was evaluated by homogeneity index (HI) and Paddick gradient index (GI) for each plan. We also analyzed the doses to brainstem and organ at risks (OARs). Results and Discussion: A 28% beam-on time reduction was achieved using 6X FFF when compared with 6X SRS beam of Novalis Tx. A sharp dose fall off with gradient index value of $3.4{\pm}0.27$ for 4 mm Varian conical collimator while $4.17{\pm}0.20$ with BrainLab cone. Among the 5 patients treated with a 4 mm cone, average maximum brainstem dose was 10.24 Gy for Edge using 6X FFF and 14.28 Gy for Novalis Tx using 6X SRS beam. Conclusion: The use of FFF beams improves delivery efficiency and conical collimator reduces dose to OAR's for TN radiosurgery. Further investigation is warranted with larger sample patient data.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.1
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• pp.79-86
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• 2012

In most patients with severe crowding or lip protrusion, orthodontic treatment with tooth extraction is done. In these patients, even though space is closed after orthodontic treatment, gingival invagination is observed on the extracted site. Since there are possibilities of space recurrence and regional periodontic problems occurrence, periodontic treatment is necessary on the gingival invagination region. This case was a 16 year old female with a chief complaint of crooked teeth. Since her maxillary premolars were already extracted a few years ago at a local dental clinic, orthodontic treatment was done by extracting mandibular premolars. Unlike maxillary premolar regions, gingival invagination occurred in mandibular premolar regions and gingival flattening was done by excising the gingival invaginated region. Gingival flattening was done once on the left side, twice on the right side and showed stable results. This is a case report of a patient that was prone to gingival invagination after orthodontic treatment with extraction and was treated with gingival flattening.

• Radiation Oncology Journal
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• v.10 no.1
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• pp.85-93
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• 1992

We have studied the dosimetric properties of electron beam using Lyon intraoperative device for intraoperative radiation therapy. The dosimetry data had compiled in such a way that a quick and correct decision regarding the cone shape, energy, and accurate calculations could be made. Using 3 dimensional water phantom, we have got the following data: cone output ratios, surface dose, $d_{max}$, $d_{90}$, flatness, symmetry, beam profiles, isodose curve, and SSD correction factors. The cone output ratios were measured with straight and bevelled cone, respectively. As the cone size and the energy were reduced, the cone output ratios decreased rapidly. With the flattening filter, the surface dose increased by electron beam to $85.3\%$, $89.2\%$, and $93.4\%$, for 6 MeV, 9 MeV, and 12 MeV, respectively. It is important to increase the surface dose to $90\%$ or more. Inspite of diminishing dose rate and beam penetration, this flattening filter increases the treatment volume significantly. With the combination of the three levels collimation and the flattening filter, we achieved good homogeneity of the beam and better flatness and the diameter of the 90$\%$ isodose curve was increased. It is important to increase the area that is included in the $90\%$ isodose level. The value of measured and calculated SSD correction factors did not agree over the clinically important range from 100 cm to 110 cm.