Joon Hyong Cho

Percutaneous Radiofrequency Lumbar Facet Rhizotomy in Mechanical Low Back Pain Syndrome

During the period from March 1992 to June 1996, we performed percutaneous radiofrequency (RF) facet rhizotomy in 324 patients with low back pain. Employing the lesion generator, we coagulated branches of the zygapophyseal nerve to treat low back pain. The follow-up period was 6-51 months (average: 22.5 months). There were no complications during the procedure and the follow-up period and no poor results were observed. Two-hundred and thirty-one patients (103 females and 128 males) had mechanical low back pain syndrome and showed marked improvement of pain after the procedure, including 29 cases with previous spinal surgery. We concluded that percutaneous RF facet rhizotomy is a safe and effective procedure for low back pain patients, especially for those with mechanical low back pain syndrome.

Radio-frequency characteristics of graphene oxide

We confirm graphene oxide, a two-dimensional carbon structure at the nanoscale level can be a strong candidate for high-efficient interconnector in radio-frequency range. In this paper, we investigate high frequency characteristics of graphene oxide in range of 0.5–40 GHz. Radio-frequency transmission properties were extracted as S-parameters to determine the intrinsic ac transmission of graphene sheets, such as the impedance variation dependence on frequency. The impedance and resistance of graphene sheets drastically decrease as frequency increases. This result confirms graphene oxide has high potential for transmitting signals at gigahertz ranges.

Nonlinear characteristics in radio frequency nanoelectromechanical resonators

The nonlinear oscillations of nanoelectromechanical resonators have previously been studied both experimentally and analytically. Nanoresonators have achieved superior sensitivity and high quality factors in many applications. However, the linear operating range of nanoresonators is significantly limited because of the small dimensions and thus the linear regime of nanoresonators may be required to expand performance in various conditions. In order to increase the linear operating range, we proposed that proper adjustments of simultaneous application of drive and electrothermal power can be used to optimize the resonance performance, providing a wider linear range as well as to tune the resonance frequency. For a nanoresonator operated by simultaneous drive and electrothermal power, experimental data are theoretically supported using nonlinear damping and spring terms. In the transition between linearity and nonlinearity by proper combinations of ac drive and dc electrothermal power, the experimental data can be better fitted, by theoretical study, with newly derived nonlinear damping terms. We believe that better understanding of these effects with different ac/dc combinations on radio frequency oscillation is crucial for utilizing nanoresonators for various applications such as sensors, oscillators and filters.

Observation of terahertz-radiation-induced ionization in a single nano island

Terahertz (THz) electromagnetic wave has been widely used as a spectroscopic probe to detect the collective vibrational mode in vast molecular systems and investigate dielectric properties of various materials. Recent technological advances in generating intense THz radiation and the emergence of THz plasmonics operating with nanoscale structures have opened up new pathways toward THz applications. Here, we present a new opportunity in engineering the state of matter at the atomic scale using THz wave and a metallic nanostructure. We show that a medium strength THz radiation of 22 kV/cm can induce ionization of ambient carbon atoms through interaction with a metallic nanostructure. The prepared structure, made of a nano slot antenna and a nano island located at the center, acts as a nanogap capacitor and enhances the local electric field by two orders of magnitudes thereby causing the ionization of ambient carbon atoms. Ionization and accumulation of carbon atoms are also observed through the change of the resonant condition of the nano slot antenna and the shift of the characteristic mode in the spectrum of the transmitted THz waves.

Resonance Properties of 3C-SiC Nanoelectromechanical Resonator in Room-Temperature Magnetomotive Transduction

We demonstrate the effect of nanoresonator geometry on the resonance property using a magnetomotive transduction technique for SiC nanoresonators in moderate conditions of pressure, temperature, and magnetic intensity. These trials were performed in conditions similar to those useful for practical applications to assist in the deployment of SiC-based nanoelectromechanical system prototype devices. This letter confirms that the resonant properties of a nanoscaled electromechanical resonator in moderate conditions are similar to those found during tests in ideal conditions. The resonance characteristics were analyzed based on the geometrical changes of the nanoresonator. The radio-frequency performance parameters such as the critical amplitude and dynamic range, which are crucial in the determination of linear operation range of nanoresonators, were maintained at a level comparable to those found under laboratory conditions. This letter brings this technology closer to practical applications in sensors, filters, and the oscillation of nanoscaled electromechanical devices.

Microwave transmission in graphene oxide.

We investigated the radio-frequency transmission properties of reduced graphene oxide (GO) sheets including contact effects with the metal electrodes. GO sheets were prepared by dielectrophoresis and their structural characteristics were analyzed by x-ray photoelectron spectroscopy and Raman spectroscopy. The contact resistance was much higher than the intrinsic resistance over the entire frequency range, thus the contact resistance was considered as a dominant component of impedance in the radio-frequency regime. In the radio-frequency regime, GO sheets showed a drastic decrease in impedance based on a consistent decrease in the intrinsic and contact resistance. These results support the potential of GO as a radio-frequency interconnector with a solution-based fabrication method.

Long-Term Follow-Up Results of Stereotactic Adrenal Medullary Transplantation in Parkinson's Disease

Stereotactic adrenal medullary transplantation into the striatum was performed in 5 patients with severe Parkinsons disease. Four patients had previously been treated with thalamotomies and all were on L-dopa therapy with significant side effects. All 5 patients had shown marked disability before the procedure. Autologous adrenal medullary tissue was sliced into 20-30 fragments and transplanted into two sites of the caudate nucleus, one at the ventricular surface and the other in the head of the nucleus. The cases were followed for 4-5 years (mean 4.5 years), except for 1 patient who died of unrelated causes 22 months after the procedure. Initial bilateral symptom improvement was observed in all cases for 9-21 months (mean 15.2 months) after transplantation without L-dopa therapy. Later, these improvements progressively deteriorated. L-dopa therapy had to be resumed for all. MRI on the long-term follow-up showed the transplanted tissue as a low signal intensity area surrounded by high intensity spots in T1- and T2-weighted images. Compared to previous MR studies, the transplanted tissue was shrunken and presumed nonviable.

Nonlinearity Control of Nanoelectromechanical Resonators

To achieve high performance of nanoelectromechanical resonators in room-temperature and low-vacuum conditions, the precise control of electrothermal power is critical in not only frequency tuning but also regulating nonlinearity in the radio-frequency range. This study presents theoretical analysis and experimental results for controlling nonlinearity of nanoelectromechanical resonators using nonlinear damping and stiffness terms. Experiments show that, with increasing electrothermal power, critical amplitude increases up to where the resonators display linear harmonic oscillation. As a result, the linearity of the resonator that has been driven into the nonlinear regime can be reclaimed.

Graphene based NO 2 gas sensor

Graphene is a two-dimensional monolayer comprised of carbon atoms. By its unique intrinsic properties, graphene has many advantages for gas sensing. In this paper, we find results of the gas sensing performance using uniform single crystal structure graphene by mechanical exfoliation method measured under room temperature, atmospheric pressure. Also, we discuss the effects of various thermal treatments on the graphene at atmospheric pressure. The sensitivity increases and recovery time decreases as measurement temperature increases.

Mechanical Properties Changes During Electrothermal RF Tuning in a Nanoelectromechanical Resonator

This paper demonstrates the electrothermal tuning of a nanoelectromechanical resonator correlated with the mechanical properties of an Al/SiC bilayer beam structure at radio frequencies under the moderate conditions. This study confirms a relatively low change in the quality factor (Q-factor) over a wide range of frequency tuning (Δfr = 2.4 MHz). The effective stress of the beam plays an important role in the resonance frequency modulation and is critical to the Q-factor during electrothermal tuning. The Q-factor was decreased with the stress variation. However, the resonant frequency is linearly tuned on the basis of varied effective beam stresses and no major scarification of the Q-factor was observed.