• Journal of the Korean Vacuum Society
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• v.12 no.1
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• pp.51-54
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• 2003

The spontaneous oscillations in the optogalvanic signals are observed in negative glow region of Ar hollow cathode discharge. The spontaneous oscillations in the optogalvanic signals are observed at low discharge currents less than about 3 mA. Based on the simultaneous measurements of both the density variation of metastable atoms and emission intensities of the 1s-2p transitions, one of the possible mechanisms for the spontaneous oscillation is considered to be related to the stepwise ionization of the metastable atoms due to collisions with slow electrons in the discharge.

• Biomolecules & Therapeutics
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• v.6 no.3
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• pp.232-241
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• 1998

This study was done to investigate whether cholic acid derivatives have anti-stress activity in various stress models. Two cholic acid derivatives, ursodeoxycholic acid (UDCA) and tauroursodeoxycholic acid (WDCA), were used. physical, psychological, chemical and environmental stress models were performed. Adrenal weight, serum glucose levels and ALP activity were elevated in restraint stress model, but this elevation was prevented by UDCA treatment. Moreover, UDCA and TUDCA inhibited exploratory and spontaneous movements in oscillation stress model. In alcohol-induced stress model, TUDCA improved rotarod performance. UDCA and TUDCA significantly reduced the involution of lymphoid organs and the increment of WBC counts in cold stress model. These findings suggest that choric acid derivatives have antistress effects in various stress models.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.68-73
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• 2022

Thermoacoustic oscillations (TAOs) are spontaneous pressure oscillations frequently seen in hydrogen or helium cryogenic systems. Half-open tubes connected to cryogenic fluid with a closed room temperature end have a high potential for oscillation generation. Thermoacoustic oscillations will result in significant pressure fluctuations and additional heat load, endangering the security and stability of the cryogenic system. The goal of this paper is to investigate TAOs in superfluid helium using both theoretical and experimental methods. Five half-open tubes with varied typical inner diameters inserted into superfluid helium were installed in a test cryostat. The onset characteristics of thermoacoustic oscillations were presented and studied. The effect of temperature profile was discussed. Finally, a simple eliminating method was introduced.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.4
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• pp.671-682
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• 1998

Electrophysiological phenomena of pyramidal cells in the CA1 area of the dorsal hippocampus were recorded from and filled with neurobiotin in anesthetized rats. The electropharmacological properties of membrane as well as the cellular-synaptic generation of rhythmic slow activity (theta) were examined. The intracellular response characteristics of these pyramidal cells were distinctly different from responses of interneurons. Pyramidal cells had a high resting membrane potential, a low input resistance, and a large amplitude action potential. A afterhyperpolarization was followed a single action potential. Most of pyramidal cells did not display a spontaneous firing. Pyramidal cells displayed weak inward rectification and anodal break excitation. The slope of the frequency-current relation was 53.4 Hz/nA for the first interspike interval and 15.9 Hz/nA for the last intervals, suggesting the presence of spike frequency adaptation. Neurobiotin-filled neurons showed pyramidal morphology. Cells were generally bipolar dendritc processes ramifying in stratum lacunosum-moleculare, radiatum, and oriens. Commissural stimulation discharged pyramidal cells, followed by excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs). The frequency of theta-related membrane potential oscillation was voltage-independent in pyramidal neurons. At strong depolarization levels (less than 30 mV) pyramidal cells emitted sodium spike oscillation, phase-locked to theta. The observations provide direct evidence that theta-related rhythmic hyperpolarization of principal cells is brought by the rhythmically discharging interneurons. Furthermore, the findings in which interneurons were also paced by rhythmic inhibitory postsynaptic potentials during theta suggest that they were periodically hyperpolarized by their GABAergic septal afferents.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.2
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• pp.197-202
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• 2010

A combustion chamber with a branch tube was built to investigate the characteristics of a spontaneous oscillating laminar premixed Bunsen flame. The flame behavior was observed, and the relation between the flame surface area and heat release rate was inspected. The equivalence ratio and mean velocity were fixed at 1.1 and 1.75 m/s, respectively. The amplitude of the pressure fluctuation in the combustion chamber was changed and the flame behavior was affected when the length ratio between the branch tube and combustion chamber (L:R) was varied. The $OH^*$, $CH^*$, and flame chemiluminescence had similar behavior qualitatively. There was linearity between the flame surface area and heat release rate.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.4
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• pp.193-198
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• 2006

Many gastrointestinal muscles show electrical oscillation, so-called 'slow wave', originated from interstitial cells of Cajal (ICCs). Thus, a technique to freshly isolate the cells is indispensable to explore the electrophysiological properties of the ICCs. To apply an enzyme solution on the serosal surface for cell isolation, the intestine was inverted and 0.02% trypsin solution and 0.04% collagenase solution were applied to serosal cavity. After the enzyme treatment, mucosal layer was removed and longitudinal muscle layer was gently separated from the rest of tissue. The thin layer was stretched in the recording chamber and mounted on an inverted microscope. Using ${\beta}-escine$, perforated whole cell patch clamp technique was used. Under a microscope, the tissue showed smooth muscle cells and interstitial cells around the myenteric plexus. Under voltage clamp condition, three types of membrane potential were recorded. One group of interstitial cells, which were positive to methylene blue and CD34, showed spontaneous outward current. These cells had bipolar shape and were considered as fibroblast-like cells because of their peculiar shape and arrangement. Another group, positive to c-kit and methylene blue, showed spontaneous inward current. These cells had more rounded shape and processes and were considered as ICCs. The third, positive to c-kit and had granules containing methylene blue, showed quiet membrane potentials under the voltage-clamp mode. These cells appeared to be resident macrophages. Therefore, in the freshly isolated thin tissue preparation, methylene blue could easily identify three types of cells rather than morphological properties. Using this method, we were able to study electrical properties of fibroblast and residential macrophage as well as myenteric ICCs.

• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.162-168
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• 1999

A new design of four-pass dye laser amplifier affording a narrow-bandwidth pulsed output is demonstrated to suppress the amplified spontaneous emission(ASE) carried by the amplifier output and reduce the possibility of parasitic oscillation in the amplifier. By the direct pulsed amplification of a cw 100 mW dye laser under a Q-switched doubled Nd:YAG laser pumping with energy of 5.6 mJ/pulse, high-peak-power pulsed output with 1.5-mJ energy in 130-MHz bandwidth is obtained corresponding to a power gain greater than $2{\times}10^6$ and an energy efficiency of 27%. The ASE ratio in the four-pass amplifier output is dramatically reduced by using a diffraction grating in the amplifier. Compared with the results obtained from the normal operation of the amplifier with no frequency-selective device, the ASE ratio is reduced by a factor in excess of 10 to remain under 1.5% of the amplifier output whereas the total output energy is slightly increased by ~4%.

• Korean Journal of Materials Research
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• v.18 no.2
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• pp.103-106
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• 2008

The magneto-transport properties of an individual single crystalline Bi nanowire grown by a spontaneous growth method are reported. A four-terminal device based on an individual 400-nm-diameter nanowire was successfully fabricated using a plasma etching technique that removed an oxide layer that had formed on the surface of the nanowire. Large transverse ordinary magnetoresistance (1401%) and negative longitudinal ordinary magnetoresistance (-38%) were measured at 2 K. It was observed that the period of Shubnikov-de Haas oscillations in transverse geometry was $0.074^{T-1}$, $0.16^{T-1}$ and $0.77^{T-1}$, which is in good agreement with those of bulk Bi. However, it was found that the period of SdH oscillation in longitudinal geometry is $0.24^{T-1}$, which is larger than the value of $0.16^{T-1}$ reported for bulk Bi. The deviation is attributable to the spatial confinement arising from scattering at the nanowire surface boundary.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.340-346
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• 2002

To understand the characteristics of the passively Q-switched Nd:YAG laser output energy with $Cr^{4+}$:YAG saturable absorbers, the transmissions of $Cr^{4+}$:YAG and the inversion population densities of Nd:YAG at the onset of Q-switch were experimentally analysed. The measured transmissions at the onset of Q-switch were 0.70$\pm$0.02 and 0.62$\pm$0.02 for the 0.48 and 0.38 of initial transmission, respectively. It means that the initial transmission loss of $Cr^{4+}$:YAG absorber is reduced in a low Q-state due to the initial absorbing effect of $Cr^{4+}$:YAG. In pumping stage, $Cr^{4+}$:YAG has absorbing processes due to the fluorescence and amplified spontaneous emissions of the Nd:YAG even if there is no laser oscillation. The minimum population inversion densities for Qswitch were approximately 3.7${\times}{10^{17}}$ and 4.0${\times}{10^{17}}$ $cm^{-3}$, respectively. At the beginning of Q-switch, the number density of $Cr^{4+}$ions in the ground state of $Cr^{4+}$:YAG was approximately 1.4${\times}{10^{17}}$ $cm^{-3}$ and the ratio of the ground to the excited state of absorbing $Cr^{4+}$ions was 0.44 both. The modified theoretical output energies with the initial absorbing effect were 18 and 18.5 mJ. The measured output energies were 17$\pm$1 and 18$\pm$1.5 mJ, respectively. The quantum extraction efficiencies of Q-switch were 0.32 both. The theoretical Q-switched output results with the initial absorbing effect of the saturable absorber are a good agreement with the experimental results.