-
[show abstract]
[hide abstract]
ABSTRACT: To report a series of patients who presented with an atypical retinal traction band, which was developed after an intravitreal injection of bevacizumab for stage 3 retinopathy of prematurity (ROP).
We retrospectively reviewed the medical record of three patients (five eyes) who had been referred to a tertiary care centre for the management of fibrous retinal traction band, which occurred after a bevacizumab injection for stage 3 ROP with plus disease. Clinical features and courses of these eyes were described based on the medical record and RetCam fundus photography.
All three patients had taken an intravitreal injection of bevacizumab with or without concomitant laser photocoagulation as an initial treatment option for the active stage 3 ROP. With close follow-ups, regression of extraretinal fibrovascular proliferation and plus disease was noted invariably. After the regression of ROP, atypical fibrous traction membrane had arisen along the major vascular arcades with 2.5 to 4 months of latency, which progressed into tractional retinal detachment (TRD) in three out of five eyes.
In active stage 3 ROP, fibrous tractional membrane and subsequent TRD along the major vascular arcades were developed unpredictably after the regression of neovascular activity following bevacizumab injection as an initial treatment. Therefore, ROP patients who received bevacizumab treatment without previous retinal photocoagulation should be closely followed for more than 4 months after the treatments even if the disease seems to have regressed.
Eye (London, England) 06/2012; 26(7):903-9; quiz 910. · 1.97 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: It is our endeavor to develop switching technology for the breakdown reliability and reproducibility at extremely high voltages above 1 MV. One of the key objectives of the endeavor is to derive precise breakdown criteria for use in high-voltage applications. We have developed empirical criteria by which the breakdown field strength of a high-pressure SF_6-filled spark gap can be computed. The validity of the computed result has been verified with several experimental data from different investigators. The computed result has shown good agreement in an extended range of pd (pressure times gap distance) and field enhancement factor of the spark gap geometry. Furthermore, a spark gap has been designed and constructed with particular intention of generating a high-pulsed-power source in Pohang Accelerator Laboratory. In parallel, field modeling has been performed to verify the appropriate shape of the highly stressed insulator and electrode design in the spark gap and to evaluate their field enhancements. A series of breakdown voltage tests has demonstrated the function of the spark gap switch as intended up to 9 bars of SF_6. Aside from this, the limitation of the switching behavior has been examined with an aim of operating the designed spark gap to its maximum capability.
IEEE Transactions on Plasma Science 11/2010; · 1.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: It is difficult to predict or measure the breakdown strength of SF<sub>6</sub> gas in the high pressure range. Therefore, it is hard to find reference data of the high pressure SF<sub>6</sub> gas breakdown strength. This paper attempts to provide empirically a novel criterion for the estimation of SF<sub>6</sub> gas breakdown strength in a spark gap switch. For this purpose, J.C. Martin's breakdown field strength of non-uniform gap in air and Kuffel et al's breakdown field strength by exploiting streamer criterion of uniform field in SF<sub>6</sub> gas are adopted. The research is made for the empirical method of predicting the high pressure SF<sub>6</sub> breakdown strength and compared results have been ascertained with several experimental data from different investigators in a wide range of pd (pressure times distance) and field enhancement factor (FEF). For further confirmation of the empirical approach, we have designed and developed a high pressure spark gap switch to be closely coupled to a high voltage PFN-Marx system. The designed spark gap switch operates above 1 MV. Our tests have verified the prediction of the breakdown strength of the SF<sub>6</sub> filled spark gap switch in a pd range of 0.27-1.62 MPa . cm (2.7 to 16.2 bar.cm).
IEEE Transactions on Dielectrics and Electrical Insulation 09/2009; · 1.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: It is difficult to predict or measure breakdown strength of SF<sub>6</sub> gas, especially in high pressure range. It is even hard to find reference data of the high pressure SF<sub>6</sub> breakdown strength. We tried analytically to compute the breakdown strength of SF<sub>6</sub> gas above 3 bar-cm range in a spark gap switch. The computed result is compared with several published experimental data and showed good agreement for different geometries with a wide range of pd (pressure time gap distance) and field enhancement factor (FEF) to a great extent. For the computation, J.C. Martin's modified field formula as well as Kuffel et al's formula for breakdown in SF<sub>6</sub> gas is adopted. We will discuss the analytical prediction method of the high pressure SF<sub>6</sub> breakdown strength and the compared result with experimental data.
IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008; 07/2008
-
H. Heo,
S.S. Park,
S.C. Kim,
J.H. Seo,
S.H. Kim,
O.R. Choi,
S.H. Nam,
D.W. Choi,
J.H. Kim,
W.S. Lee,
J.H. So,
W. Jang
[show abstract]
[hide abstract]
ABSTRACT: We designed a Marx generator for repetitive applications. The Marx generator has 25 stages. Each stage was constructed 4 door knob ceramic capacitors and a ball spark gap switch. We used the inductor charging method for higher repetitive operation. The designed maximum output voltage of the Marx generator is 1 MV at open circuit condition. The overall size of the Marx generator is 150 cm in length and 60 cm in diameter. We tested the Marx generator at different load conditions. We present the results of the test and characterize the Marx generator.
IEEE International Power Modulators and High Voltage Conference, Proceedings of the 2008; 07/2008
-
[show abstract]
[hide abstract]
ABSTRACT: It is beneficial to use a resonant pulse transformer charging circuit for designing of a high voltage generator. A high voltage triple resonant generator is designed. A high voltage air core transformer is used in the circuit. Triple resonant charging circuit with the transformer is used to step up the primary voltage. The voltage step-up ratio is designed as about eleven at the charging stage. A distributed pulse forming network (PFN) is used to form a square output waveform. The output has an over-volted spark-gap switch that transfers energy to a matched resistive load with a distributed PFN. The generator is positioned in a cylindrical transformer oil tank. Height and diameter of the tank are respectively 1.06 m and 1.28 m. A dummy water load and a beam stick are used to test the generator. Design procedures and preliminary test results are discussed.
Pulsed Power Conference, 2007 16th IEEE International; 07/2007
-
H. Heo,
S. S. Park,
S.C. Kim,
J. H. Seo,
S. H. Kim,
O.R. Choi,
S. H. Nam,
D. W. Choi,
J. Y. Kim,
W. S. Lee,
J. H. So,
W. Jang
[show abstract]
[hide abstract]
ABSTRACT: We designed a compact repetitive Marx generator. The Marx generator contains 25 stages consisted with capacitor banks and spark gap switches. We used door knob ceramic capacitors. The capacitors are charged through inductors by a capacitor charging power supply. The length and the diameter of the Marx generator are about 150 cm and 60 cm, respectively. We conducted a preliminary test at the condition of low charging voltage using nitrogen gas. We present the characteristic of the Marx generator and discuss the design issues such as high voltage insulation.
Pulsed Power Conference, 2007 16th IEEE International; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: A multi-gap multi-channel (MGMC) switch of 500 kV has been developed at Pohang Accelerator Laboratory (PAL). It consists of ten of gaps to increase self-discharge voltage by filling up the gas. A structure of a multi-gap switch can increase its inductances. Thus, in order to solve those problems its structure made by multi-channels had been designed to decrease the inductance effects. The fabricated switch tested using marx generator of 500 kV. The design concept and its characteristics will be discussed.
Pulsed Power Conference, 2005 IEEE; 07/2005
-
[show abstract]
[hide abstract]
ABSTRACT: We designed a fuse opening switch for the purpose of generation of high voltage pulses. The fuse opening switch was made with copper foil. The fuse opening switch was tested at a capacitor powered circuit discharged by a high current triggered vacuum switch. The experimental results were compared with simple numerical calculations. We measured several electrical parameters for a circuit composed of the fuse opening switch, a pulse transformer, and a peaking switch.
Pulsed Power Conference, 2005 IEEE; 07/2005
-
[show abstract]
[hide abstract]
ABSTRACT: Cylindrical type air core pulse transformers capable of passing high voltage and energy pulse waveforms with high efficiency and low distortion require a much more delicate design balance of physical dimensions and electrical parameters than iron or ferrite core units. The structure of an air core high voltage pulse transformer is relatively simple, but considerable attention is needed to prevent breakdown between transformer windings. Since the thickness of the windings in spiral type is on the order of sub-millimeter, field enhancement at the edge of the windings is very high. It is, therefore, important to find proper electrical insulation parameter to make the system compact. Several shapes of the winding are considered for air core pulse transformer development. Requirements of the transformer are 170 nH inductance at primary side, 500 kV. In this paper, we will describe a design procedure, parameters, measurement and experiment results of air core type 500 kV HV pulse transformer.
Pulsed Power Conference, 2005 IEEE; 07/2005
-
[show abstract]
[hide abstract]
ABSTRACT: We propose a new family of two-dimensional wavelength-hopping/time-spreading code for optical code-division multiple-access systems with balanced detection, and we numerically analyze the characteristics of the proposed system. By using the proposed decoding scheme, the undesired interference is efficiently eliminated. The proposed scheme has enhanced performance and allows for a large number of simultaneous users compared with the three-dimensional and other balanced codes for differential detection.
IEEE Photonics Technology Letters 10/2004; 16(9):2189-2191. · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We developed sealed-off type pseudospark switches for high current applications over 100 kA, with long pulse duration of several ms. We investigated the characteristics of sealed-off pseudospark switches, such as trigger delay times, hold-off voltages, peak currents, and effective charge transfer energy losses, recovery times. Effects of the electrode material and structure, power level of the switch reservoir, and vacuum conditioning of virgin electrodes as a method of electrode pretreatment are considered in this investigation. We also discuss the fabrication process of the high current sealed-off type pesudospark switches at the Pohang Accelerator Laboratory (PAL).
Power Modulator Symposium, 2004 and 2004 High-Voltage Workshop. Conference Record of the Twenty-Sixth International; 06/2004
-
[show abstract]
[hide abstract]
ABSTRACT: We designed, fabricated, and tested sealed-off triggered vacuum switches (TVSs) used as an ETC-gun switch. To fabricate the sealed-off TVS, we developed processes of the fabrication such as part machining, chemical cleaning, ceramic to metal and metal to metal brazing, metal welding, baking, getter processing and test procedures. The fabricated switches were tested with capacitor banks of 100 kJ and 300 kJ. The prototype switches were successfully tested up to 20 kV peak charging voltage, 109 kA peak current, 1.5 ms pulse-width, and 75-coulomb integrated charge transfer at 300 kJ capacitor bank. Compared to other reported similar switches, the tested switch showed high quality electrical characteristics in high operating voltage, high charge transfer, and long pulse operation.
Power Modulator Symposium, 2004 and 2004 High-Voltage Workshop. Conference Record of the Twenty-Sixth International; 06/2004
-
[show abstract]
[hide abstract]
ABSTRACT: Radial multichannel pseudospark switches for extremely high-charge transfer were designed, constructed, and tested. The characteristics of the switches were measured for different electrode geometries and materials in hydrogen and helium as function of gas pressure. The switches were operated in a 100 kJ capacitor bank and conducted an effective charge up to 31 C. A sealed-off radial multichannel pseudospark switch was also manufactured and tested with a 300 kJ capacitor bank. The switch was successfully tested up to 105 kA peak current and 78 C charge transfer. The experimental results demonstrated that a radial multichannel pseudospark switch with SiC electrodes and triggered by a high dielectric trigger has the capability of extremely high charge transfer under pulsed operation.
IEEE Transactions on Plasma Science 03/2004; · 1.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We investigated a radial multi-channel pseudospark switch with a high dielectric trigger for applications of long pulse high currents. Optimum pressure condition of the switch was investigated by using optical and electrical measurements of the discharges. We compared the erosion of a SiC anode electrode with stainless steel anode electrode after high current tests in order to investigate the SiC effect on the reducing strong arc erosions. We reported preliminary results of the switch tested on 20 kJ, and 100 kJ capacitor banks.
Pulsed Power Conference, 2003. Digest of Technical Papers. PPC-2003. 14th IEEE International; 07/2003
-
-1:3108.
