Novel control of plasma expansion direction aimed at very low pressure laser-induced plasma spectroscopy.

Choi, Soo-Jin,Choi, Jae-Jun,Yoh, Jack J Optical Society of America 2015 Optics express Vol.23 No.5

<P>A plasma confinement approach has been applied to enhance the signal intensity of laser-induced plasma in low pressure conditions down to 10(-2) torr. Detection of plasma emission spectrum is a daunting task at low pressure due to the low electron density and the short persistence time of plasma that undergoes a rapid expansion. Here we devised a spatial confinement setup that increases the electron density at various range of low pressures. A confining window is placed above the sample surface to control the direction of the expanding plasma aimed at optimizing the efficiency of the low pressure detection. More ions, atoms, and molecules can reach the detector by a direction-controlled confinement of an otherwise freely expanding plasma. The spectral intensities of neutral atoms increased up to 4 times with a single laser pulse by the proposed confining method at 1 torr. The signal of doubly ionized carbon atom which was detectable only at low pressure is also enhanced 4 times. The results of this study provide an important guideline for strengthening the otherwise weak signals at low pressure by controlling the plasma expansion direction.</P>

Phonation Threshold Flow and Phonation Threshold Pressure in Patients with Adductor Spasmodic Dysphonia

Choi Seong Hee,Jiang Jack J.,Yun Bo Ram,Lee JiYeoun,Lim Sung-Eun,Choi Hong-Shik 한국음성학회 2010 말소리와 음성과학 Vol.2 No.3

This study investigated the characteristics of two aerodynamic indices, PTP (Phonation threshold pressure) and PTF (Phonation threshold flow) in patients with ADSD (adductor spasmodic dysphonia) and to see if two new aerodynamic indices can differentiate between normal and ADSD group. Additionally, PTP and PTF values were compared in terms of overall severity of ADSD in the patient group. The severity of ADSD was rated on a 7-point rating scale by two experienced speech language pathologists. The Kay Elemetrics Phonatory Aerodynamic System (PAS) (Kay Elemetrics Corp., Lincoln Park, NJ) was used to collect PTP and PTF measurements from 16 female normal subjects, 31 female patients with ADSD. Significantly lower PTF values (P< 0.05) were observed in ADSD when compared to those of normal control. Also, significantly lower PTF values in severe ADSD patients (P<.001). However, PTP could not distinguish patients with ADSD from control groups (P=0.119) and among the ADSD groups according to the severity (P=0.177). Consequently, PTF was more sensitive than PTP which might differentiate between normal speakers and ADSD and among different levels of severity within ADSD, suggesting that PTF could be a useful diagnostic parameter to measure the aerodynamic function of ADSD and provide the neurolaryngeal dysfunction in patients with ADSD.

Standoff Detection of Geological Samples of Metal, Rock, and Soil at Low Pressures Using Laser-Induced Breakdown Spectroscopy

Choi, Jae-Jun,Choi, Soo-Jin,Yoh, Jack J. SAGE Publications 2016 APPLIED SPECTROSCOPY Vol.70 No.9

<P>Categorized certified reference materials simulating metal, rock, soils, or dusts are used to demonstrate the standoff detection capability of laser-induced breakdown spectroscopy (LIBS) at severely low pressure conditions. A Q-switched Nd:YAG laser operating at 1064nm with 17.2-50mJ energy per pulse was used to obtain sample signals from a distance of 5.5m; the detection sensitivity at pressures down to 0.01 torr was also analyzed. The signal intensity response to pressure changes is explained by the ionization energy and electronegativity of elements, and from the estimated full width half-maximum (FWHM) and electron density, the decrease in both background noise and line broadening makes it suitable for low pressure detection using the current standoff LIBS configuration. The univariate analyses further showed high correlation coefficients for geological samples. Therefore, the present work has extended the current state-of-the-art of standoff LIBS aimed at harsh environment detection.</P>

Development of Bio-ballistic Device for Laser Ablation-induced Drug Delivery

Choi, Ji-Hee,Gojani, Ardian B.,Lee, Hyun-Hee,Jeung, In-Seuk,Yoh, Jack J. Korean Society for Precision Engineering 2008 International Journal of Precision Engineering and Vol.9 No.3

Transdermal and topical drug delivery with minimal tissue damage has been an area of vigorous research for a number of years. Our research team has initiated the development of an effective method for delivering drug particles across the skin (transdermal) for systemic circulation, and to localized (topical) areas. The device consists of a micro particle acceleration system based on laser ablation that can be integrated with endoscopic surgical techniques. A layer of micro particles is deposited on the surface of a thin metal foil. The rear side of the foil is irradiated with a laser beam, which generates a shockwave that travels through the foil. When the shockwave reaches the end of the foil, it is reflected as an expansion wave and causes instantaneous deformation of the foil in the opposite direction. Due to this sudden deformation, the microparticles are ejected from the foil at very high speeds, and therefore have sufficient momentum to penetrate soft body tissues. We have demonstrated this by successfully delivering cobalt particles $3\;{\mu}m$ in diameter into gelatin models that represent soft tissue with remarkable penetration depth.

Acoustic Analysis with Moving Window in Normal and Pathologic Voices

Choi Seong Hee,Lee JiYeoun Jiang,J. Jack 한국음성학회 2010 말소리와 음성과학 Vol.2 No.3

In this study, the most stable portion was identified using 5% moving window during /a/ sustained phonation in normal and pathologic voice signals and the perturbation values were compared between normal and pathologic voices at the mid-point and at the most stable portion using moving window, respectively. The results revealed that some severe pathologic voice signals can be eligible for perturbation analysis by identifying the most stable portion with Err less than 10. In addition, the perturbation acoustic parameters did not differentiate the pathologic voice signals from the normal voice signals when the mid-point was selected to measure the perturbation analysis(p>0.05). However, significantly higher %shimmer and lower SNR values were observed in pathologic voices (p<0.05) when the most stable portion was selected by moving window. In conclusion, moving window could identify the most stable portion objectively which can allow toget the minimum perturbation values (%jitter, %shimmer) and maximum SNR values. Thus, moving window technique can be applicable for more reliable and accurate perturbation acoustic analysis.

Precessing Jet and Large Dust Grains in the V380 Ori NE Star-forming Region

Choi, Minho,Kang, Miju,Lee, Jeong-Eun,Tatematsu, Ken’ichi,Kang, Sung-Ju,Sayers, Jack,Evans II, Neal J.,Cho, Jungyeon,Kwon, Jungmi,Park, Geumsook,Ohashi, Satoshi,Yoo, Hyunju,Lee, Youngung American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.232 No.2

<P>The V380 Ori NE bipolar outflow was imaged in the SiO and CO J = 1 -> 0lines, and dense cores in L1641 were observed in the 2.0-0.89 mm continuum. The highly collimated SiO jet shows point-symmetric oscillation patterns in both position and velocity, which suggests that the jet axis is precessing and the driving source may belong to a non-coplanar binary system. By considering the position and velocity variabilities together, accurate jet parameters were derived. The protostellar system is viewed nearly edge-on, and the jet has a flow speed of similar to 35 km s(-1) and a precession period of similar to 1600 years. The CO outflow length gives a dynamical timescale of similar to 6300 years, and the protostar must be extremely young. The inferred binary separation of 6-70 au implies that this protobinary system may have been formed through the disk instability process. The continuum spectra of L1641 dense cores indicate that the emission comes from dust, and the fits with modified blackbody functions give emissivity power indices of beta= 0.3-2.2. The emissivity index shows a positive correlation with the molecular line width, but no strong correlation with bolometric luminosity or temperature. V380 Ori NE has a particularly low value of beta= 0.3, which tentatively suggests the presence of millimeter-sized dust grains. Because the dust growth takes millions of years, much longer than the protostellar age, this core may have produced large grains in the starless core stage. HH 34 MMS and HH 147 MMS also have low emissivity indices.</P>

Effective Laser-Induced Breakdown Spectroscopy (LIBS) Detection Using Double Pulse at Optimum Configuration

Choi, Soo Jin,Yoh, Jack J. SAGE Publications 2011 APPLIED SPECTROSCOPY Vol.65 No.8

Thrust enhancement via gel-type liquid confinement of laser ablation of solid metal propellant

Choi, Soojin,Han, Tae-hee,Gojani, Ardian B.,Yoh, Jack J. Springer-Verlag 2010 APPLIED PHYSICS A MATERIALS SCIENCE AND PROCESSING Vol.98 No.1

Accuracy Enhancement of Raman Spectroscopy Using Complementary Laser-Induced Breakdown Spectroscopy (LIBS) with Geologically Mixed Samples

Choi, Soojin,Kim, Dongyoung,Yang, Junho,Yoh, Jack J. Society for Applied Spectroscopy 2017 Applied spectroscopy Vol.71 No.4

<P>Quantitative Raman analysis was carried out with geologically mixed samples that have various matrices. In order to compensate the matrix effect in Raman shift, laser-induced breakdown spectroscopy (LIBS) analysis was performed. Raman spectroscopy revealed the geological materials contained in the mixed samples. However, the analysis of a mixture containing different matrices was inaccurate due to the weak signal of the Raman shift, interference, and the strong matrix effect. On the other hand, the LIBS quantitative analysis of atomic carbon and calcium in mixed samples showed high accuracy. In the case of the calcite and gypsum mixture, the coefficient of determination of atomic carbon using LIBS was 0.99, while the signal using Raman was less than 0.9. Therefore, the geological composition of the mixed samples is first obtained using Raman and the LIBS-based quantitative analysis is then applied to the Raman outcome in order to construct highly accurate univariate calibration curves. The study also focuses on a method to overcome matrix effects through the two complementary spectroscopic techniques of Raman spectroscopy and LIBS.</P>

Synthesis of a series of cis-diamminaedichloro-platinum (II) Complexes Linked to Uracil and Uridine as Candidate An-titumor Agents.

Kim, Jack-C.,Kim, Mi-Hyang,Kim, Seon-Hee,Choi, Soon-Kyu The Pharmaceutical Society of Korea 1995 Archives of Pharmacal Research Vol.18 No.6

The search for patinum (II)-based compounds with improved therapeutic properties was prompted to design and synthesize a new family of water-soluble, third generation cis-diamminedichlorplatinum (II) complexes linked to uracil and uridine. Six heretofore undescribed uracil and uridine-platinum (II) complexes are ; [N-(2-aminoethyl)uracil-5-carboxamide]dichloroplatinum (II)(3a), [N-2(2-aminoethyl)uracil-6-carboxmide]dichloroplatinum (II) (3b),[5-(2-aminorthyl)carbamoyl-2',3',5',-tri-O-acetyluridine] dichloroplatinum (II) (6b), [5-(2-aminoethyl)-carbamoyl]-2',3',5',-tri-O-acetyluridine] dichloroplatinum (II) (6b), [5-(2-aminoethyl)carbamoylu-ridine]dihloroplatinum (II) (7a), [6-(2-aminoethyl)carbamoyluridine]dichloroplatinum (II) (7b). These analogues were prepared from the key starting materials, 5-carboxyuracil (1a) and 6-carboxyuracil (1b) which were reacted with ethylenediamine to afford the respective N-(2-aminoethyl)uracil-5-carboxmide (2a) land N-(2-aminoethyl)uracil-6-carboxamide (2b). The cisplatin complexes 3a and 3b were obtained through the reaction of the respective 2a and 2b ficiently introduced on the .betha.-D-ribose ring via a Vorbruggen-type nucleoside coupling procedure with hexamethyldisilazane, trimethylchlorosilane and stannicchloride under anhydrous acetonitfile to yield the sterospecific .betha.-anomeric 5-carboxy-2',3',5'-tri-O-acetyluridine (4a) and 6-carboxy-2',3',5'-tri-O-acetyluridine (4b), respective 5-(2-aminoethyl)carbamoyl-2',3',5'-tri-O-acetyluridine (5a) and 6-(2-aminoethyl)carbamoyl-2',3',5'-tri-O-acetyluridine (5b). The diamino-uridines 5a and 5b were reacted with potassium tetrachloroplatinate (II) to give the novel nucleoside complexes, 6a and 6b respectively which were deacetylated into the free nucleosides, 7a and 7b by the treatment with CH/sub 3/ONa. The antitumor activities were evaluated against three cell lines (K-562, FM-3A and P-388).