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HJ Shin

Publications and source records attributed to HJ Shin.

16 recordsLinked to original sources
PubMed2000

Soft-x-ray emission from small-sized Ne clusters heated by intense, femtosecond laser pulses

Soft-x-ray emission from a cryogenically cooled Ne jet irradiated by intense, 25-fs laser pulses was measured. The Ne spectrum started to drastically change in emitting ions from Ne5+ to Ne7+ below the preexpansion temperature of -120 degrees C. The significant change in the spectrum is attributed to the collisional heating of small-sized Ne clusters formed in the cooled jet. The increase of the laser pulse length from 25 fs to 100 fs resulted in further increase of x-ray emission from Ne7+ states.

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PubMed1999

Guided waves by axisymmetric and non-axisymmetric surface loading on hollow cylinders

Guided waves generated by axisymmetric and non-axisymmetric surface loading on a hollow cylinder are studied. For the theoretical analysis of the superposed guided waves, a normal mode concept is employed. The amplitude factors of individual guided wave modes are studied with respect to varying surface pressure loading profiles. Both theoretical and experimental focus is given to the guided waves generated by both axisymmetric and non-axisymmetric excitation. For the experiments, a comb transducer and high power tone burst function generator system are used on a sample Inconel tube. Surface loading conditions, such as circumferential loading angles and axial loading lengths, are used with the frequency and phase velocity to control the axisymmetric and non-axisymmetric mode excitations. The experimental study demonstrates the use of a practical non-axisymmetric partial loading technique in generating axisymmetric modes, particularly useful in the inspection of tubing and piping with limited circumferential access. From both theoretical and experimental studies, it also could be said that the amount of flexural modes reflected from a defect contains information on the reflector's circumferential angle, as well as potentially other classification and sizing feature information. The axisymmetric and non-axisymmetric guided wave modes should both be carefully considered for improvement of the overall analysis of guided waves generated in hollow cylinders.

Journal Article↗
PubMed1999

Prenylagaramides A and B, new cyclic peptides from two strains of oscillatoria agardhii

Prenylagaramides A (1) and B (2), two new cyclic peptides, were isolated from the cultured cyanobacteria Oscillatoria agardhii (NIES-205) and O. agardhii (NIES-596), respectively. The structures of 1 and 2, which both contain a rare O-prenyltyrosine (Ptyr) unit, were established as cyclo(-Ptyr1-Gly2-Thr3-Gly4-Glu5-Phe6-Phe7-Asn8-Pro9-) and cyclo(-Ptyr1-Leu2-Tyr3-Pro4-Ile5-Asn6-Pro7-), respectively, by spectroscopic analysis and chemical degradation.

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