• Korean Journal of Optics and Photonics
• /
• 제17권6호
• /
• pp.544-547
• /
• 2006

A time-domain modeling approach is used to study characteristics of a widely tunable coupled-ring reflector (CRR) laser diode(LD). The CRR consists of a bus waveguide and two coupled ring resonators coupled to the bus without resorting to distributed Bragg grating structure. The tuning range can be a few tens of nanometers with a side mode suppression ratio exceeding 35dB through the adjustment of currents into the phase control sections in the rings. The CRR laser diode has long effective cavity length compared to conventional laser diodes. Accordingly, a broad additional resonance peak in the amplitude modulation characteristics is observed between 20 to 30 GHz, implying the extension of amplitude modulation bandwidth.

• Korean Journal of Optics and Photonics
• /
• 제17권3호
• /
• pp.216-222
• /
• 2006

We propose the use of the Gaussian-curve fitting algorithm for the improvement of measurement accuracy in wavelengthscanned Fabry-Perot filter based demodulation systems. The peak locations of FBG sensors were calculated from the fitted curves rather than from distorted PD profiles, resulting in much better measurement accuracy than that of the highest-peak search algorithm. Also, the algorithm was proved to minimize measurement uncertainty of spectrally-distorted grating sensors. From our experimental results, a temperature resolution as small as ${\sim}0.3^{\circ}C$ was readily achieved by use of the Gaussian-curve fitting algorithm whereas the highest-peak search algorithm gave a temperature resolution larger than ${\sim}4^{\circ}C$.

• Progress in Medical Physics
• /
• 제21권4호
• /
• pp.311-322
• /
• 2010

In proton therapy, the analysis of secondary particles is important due to delivered dose outside the target volume and thus increased potential risk for the development of secondary cancer. The purpose of this study is to analyze the influence of secondary particles from proton beams on fluence and energy deposition in the presence of inhomogeneous material by using Geant4 simulation toolkit. The inhomogeneity was modeled with the condition that the adipose tissue, bone and lung equivalent slab with thickness of 2 cm were inserted at 30% (Plateau region) and 80% (Bragg peak region) dose points of maximum dose in Bragg curve. The energy of proton was varied with 100, 130, 160 and 190 MeV for energy dependency. The results for secondary particles were presented for the fluence and deposited energy of secondary particles at inhomogeneous condition. Our study demonstrates that the fluence of secondary particles is neither influenced insertion of inhomogeneties nor the energy of initial proton, while there is a little effect by material density. The deposited energy of secondary particles has a difference in the position placed inhomogeneous materials. In the Plateau region, deposited energy of secondary particles mostly depends on the density of inserted materials. Deposited energy in the Bragg region, in otherwise, is influenced by both density of inserted material and initial energy of proton beams. Our results suggest a possibility of prediction about the distribution of secondary particles within complex heterogeneity.

• Journal of radiological science and technology
• /
• 제36권2호
• /
• pp.165-173
• /
• 2013

This study was the estimation of the dose distribution for proton, prompt gamma rays and proton induced neutron particles, in case of exposing the proton beam to polymer gel dosimeter and water phantom. The polymer gel dosimeter was compositeness material of Gelatin, Methacrylic acid, Hydroquinone, Tetrakis and Distilled water. The density of gel dosimeter was $1.04g/cm^3$ which was similar to water. The 72, 116 and 140 MeV proton beams were used in the simulation. Proton beam interacted with the nuclei of the phantom and the nuclei in excited states emitted prompt gamma rays and proton induced neutron particles during the process of de-excitation. The proton particles, prompt gamma rays, proton induced neutron particles were detected by polymer gel dosimeter and water phantom, respectively. The gap of the axis for gel was 2 mm. The Bragg-peak for proton particles in gel dosimeter was similar to water phantom. The dose distribution for proton and prompt gamma rays in gel dosimeter and water phantom was approximately identical in case of 72, 116 and 140 MeV for proton beam. However, in case of proton induced neutron particles for 72, 116 and 140 MeV proton beam, particles were not detected in gel dosimeter, while the Water phantom absorbed neutron particles. Considering the resulting data, gel dosimeter which was developed in the normoxic state attentively detected the dose distribution for proton beam exposure except proton induced neutron particles.

• Applied Microscopy
• /
• 제47권3호
• /
• pp.208-213
• /
• 2017

The microstructural changes in Co nanoparticles and an Au-10at.%Pd thin film have been investigated using an in situ heating holder with a micro-electro-mechanical system (MEMS). In Co nanoparticles, two phases (face-centered cubic and hexagonal close-packed crystal structures) were found to coexist at room temperature and microstructures at temperatures, higher than $1,000^{\circ}C$, were observed with a quick response time and significant stability. The actual temperature of each specimen was directly estimated from the changes in the lattice spacing (Bragg-peak separation). For the Au-10at.%Pd thin film, at a set temperature of $680^{\circ}C$, the actual temperature of the sample was estimated to be $1,020^{\circ}C{\pm}123^{\circ}C$. Note that the specimen temperature should be carefully evaluated because of the undesired effects, i.e., the temperature non-uniformity due to the sample design of the MEMS chip, and distortion due to thermal expansion.

• Korean Journal of Materials Research
• /
• 제11권11호
• /
• pp.997-1000
• /
• 2001

Conducting perovskite oxide, $(Ba,Sr)RuO_3(BSR)$, which has many advantages for $(Ba,Sr)TiO_3(BST)$ due to their similarity in crystal structure, lattice constant and chemical composition, was prepared on n-type Si (100) by liquid delivery metalorganic chemical vapor deposition(LDMOCVD). The deposition characteristics of BSR were controlled by gas-phase mass-transfer in the experiment. The BSR films deposited at 50$0^{\circ}C$ and oxygen flow rate of 100 sccm(standard cc/min) showed an average roughness of 22 $\AA$and resistivity of 810 $\mu$$\Omega$-cm. The roughness of BSR films with oxygen flow rate showed a close relationship with the resistivity of films. BSR (110) peak shifted toward lower Bragg angle with increase of x in the$(Ba_x,Sr_{1-x})TiO_3$. The resistivity of BSR films increased from 810 to 924 $\mu$$\Omega$-cm with increase of Ba content(x).

• Progress in Medical Physics
• /
• 제15권3호
• /
• pp.140-148
• /
• 2004

The absorbed dose for proton beam in water was calculated using the PTRAN code system. The proton interactions with water and the description on absorbed dose calculations are discussed, and the file structure and an execution example of the PTRAN codes are described. For 60, 100, 150, 200, and 250 MeV proton beams it is demonstrated that the absorbed dose is determined from the sum of Coulomb interactions and nuclear reactions, and that the Bragg peak feature depends On the energy straggling and multiple scattering. The PTRAN code was useful for studying the fundamental mechanism of the absorbed dose to water for clinical proton beams.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
• /
• pp.675-678
• /
• 2003

We studied the electrical characteristics of pentacene-based organic field-effect transistors (FETs) with polymethyl methacrylate (PMMA) or poly-4-vinylphenol (PVP) as the gate insulator. PMMA or PVP was spin-coated on the indium tin oxide glass substrate that serves as gate electrodes. The source-drain current dependence on the gate voltage shows the FET characteristics of the hole accumulation type. The transistor with PVP shows a higher field-effect mobility of 0.14 $cm^{2}/Vs$ compared with 0.045 $cm^{2}/Vs$ for the transistor with PMMA. The atomic force microscope (AFM) images indicate that the grain size of the pentacene on PVP is larger than that on PMMA. X-ray diffraction (XRD) patterns for the pentacene deposited on PVP exhibit a new Bragg reflection at $19.5{\pm}0.2^{\circ}$, which is absent for the pentacene on PMMA. This peak corresponds to the flat-lying pentacene molecules with less intermolecular spacing.

• Proceedings of the Korean Society of Medical Physics Conference
• /
• 한국의학물리학회 2002년도 Proceedings
• /
• pp.199-201
• /
• 2002

Cancer therapy using high-energy $^{12}$ C ions is successfully under way at HIMAC, Japan. An alternative beam to $^{12}$ C is $^{11}$ C ions. The merit of $^{11}$ C over $^{12}$ C is its capability for monitoring spatial distribution of the irradiated $^{11}$ C by observing the $\beta$$^{+}$ decay with a good position resolution. One of the several problems to be solved before its use for therapy is the amount of nuclear interaction that deteriorates the dose concentration owing to the Bragg curve. Utilizing the dedicated secondary beam course for R&D studies at HIMAC, we measured the total energy loss of $^{11}$ C ions in a scintillator block that simulates the soft tissue in human bodies. In addition to the total absorption $^{11}$ C peak, non-negligible bump-shaped contribution is observed in the energy spectrum. The origin of the bump contribution can be nuclear interaction of the incident $^{11}$ C ions with hydrogen and carbon atoms. Further studies to reduce the ambiguity in dose distribution are mentioned.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 한국건축시공학회 2016년도 추계 학술논문 발표대회
• /
• pp.94-95
• /
• 2016

Calcium Silicate Hydrate (C-S-H), which takes up most of the hydration products of Portland Cement (PC), has the greatest impact on the mechanical behavior and strength development of concrete. The exact mechanism of its deformation, however, has not yet been elucidated. The present study aims to demonstrate the mechanism of nano-deformation behavior of C-S-H in tricalcium silicate paste under compressive loading, unloading and reloading by interpreting atomic pair distribution function (PDF) based on synchrotron X-ray scattering. The strain of the tricalcium silicate paste for a short-range of 0 ~ 20 Å under compressive load exhibited two stages, I) nano-packing of interlayer of C-S-H and II) micro-packing of C-S-H globules, whereas the deformation for a long-range order of 20 ~ 40 Å was similar to that of a calcium hydroxide phase measured by Bragg peak shift. Moreover, the residual strains due to the plastic deformation of C-S-H was clearly observed.