Suyoun Lee

Attenuated pain responses in mice lacking Ca(V)3.2 T-type channels.

Although T‐type Ca2+ channels are implicated in nociception, the function of specific subtypes has not been well defined. Here, we compared pain susceptibility in mice lacking CaV3.2 subtype of T‐type Ca2+ channels (CaV3.2−/−) with wild‐type littermates in various behavioral models of pain to explore the roles of CaV3.2 in the processing of noxious stimuli in vivo. In acute mechanical, thermal and chemical pain tests, CaV3.2−/− mice showed decreased pain responses compared to wild‐type mice. CaV3.2−/− mice also displayed attenuated pain responses to tonic noxious stimuli such as intraperitoneal injections of irritant agents and intradermal injections of formalin. In spinal nerve ligation‐induced neuropathic pain, however, behavioral responses of CaV3.2−/− mice were not different from those of wild‐type mice. The present study reveals that the CaV3.2 subtype of T‐type Ca2+ channels are important in the peripheral processing of noxious signals, regardless of modality, duration or affected tissue type.

Detection of microorganisms using terahertz metamaterials

Microorganisms such as fungi and bacteria cause many human diseases and therefore rapid and accurate identification of these substances is essential for effective treatment and prevention of further infections. In particular, contemporary microbial detection technique is limited by the low detection speed which usually extends over a couple of days. Here we demonstrate that metamaterials operating in the terahertz frequency range shows promising potential for use in fabricating the highly sensitive and selective microbial sensors that are capable of high-speed on-site detection of microorganisms in both ambient and aqueous environments. We were able to detect extremely small amounts of the microorganisms, because their sizes are on the same scale as the micro-gaps of the terahertz metamaterials. The resonant frequency shift of the metamaterials was investigated in terms of the number density and the dielectric constants of the microorganisms, which was successfully interpreted by the change in the effective dielectric constant of a gap area.

Deficits in social behavior and sensorimotor gating in mice lacking phospholipase Cβ1

Abnormal phospholipid metabolism has been implicated in the pathogenesis of schizophrenia, and it was reported that phospholipase C (PLC) β1 is reduced in specific brain areas of patients with schizophrenia. However, the causal relationship of the PLCβ1 gene with behavioral symptoms of schizophrenia remains unclear. To address this issue, we have examined the mutant mice lacking PLCβ1 for schizophrenia‐related phenotypes by performing various behavioral tests, including general locomotor activity, sensorimotor gating, social behaviors, and learning and memory. Phospholipase C β1 knockout mice showed hyperactivities in an open field. They showed impaired prepulse inhibition of acoustic startle response, which was ameliorated by a systemic administration of an antipsychotic D2‐receptor antagonist, haloperidol. In addition, they showed abnormal social behaviors, such as lack of barbering behavior, socially recessive trait and lack of nesting behavior. Furthermore, they showed impaired performance in the delayed‐non‐match‐to‐sample T‐maze test. The present results show that the PLCβ1 mutant mice share some of the behavioral abnormalities that have been reported in patients with schizophrenia. Thus, the PLCβ1‐linked signaling pathways may be involved in the neural system whose function is disrupted in the pathogenesis of schizophrenia.

Ge2Sb2Te5 Confined Structures and Integration of 64 Mb Phase-Change Random Access Memory

Phase-change random access memory is considered a potential challenger for conventional memories, such as dynamic random access memory and flash memory due to its numerous advantages. Nevertheless, high reset current is the ultimate problem in developing high-density phase-change random access memory (PRAM). We focus on the adoption of Ge2Sb2Te5 confined structures to achieve lower reset currents. By changing from a normal to a GST confined structure, the reset current drops to as low as 0.8 mA. Eventually, our integrated 64 Mb PRAM based on 0.18 µm CMOS technology offers a large sensing margin: Rreset ~200 kΩ and Rset ~2 kΩ, as well as reasonable reliability: an endurance of 1.0×109 cycles and a retention time of 2 years at 85°C.

Effect of Be doping on the properties of GaMnAs ferromagnetic semiconductors

We have studied two series of molecular beam epitaxy grown Ga1−xMnxAs epilayers with several different Be doping levels. Two Mn concentrations x were chosen for this study: 0.03 and 0.05, and these values were maintained constant in each series. These samples were characterized by using SQUID and magnetotransport measurements. A systematic increase of the Curie temperature TC was observed in SQUID measurements on the series of Ga1−xMnxAs with x=0.03. The resistivity measured at zero magnetic field shows a local maximum near the Curie temperature, reflecting the effects of critical scattering near TC. The observed increase of TC in Ga1−xMnxAs for this low range of x can be explained by the increase of the free carrier concentrations in the system arising from Be doping. However, in the series of Ga1−xMnxAs with the higher concentration of Mn (x=0.05), the measurements reveal that the TC systematically decreases with increasing Be doping level. We discuss this effect in terms of a fundamental limitation of ...

Highly Reliable Ring-Type Contact for High-Density Phase Change Memory

An advanced bottom electrode contact (BEC) was successfully developed for reliable high-density 256 Mb phase-change random access memory (PRAM) using a ring-type contact scheme. This advanced ring-type BEC was prepared by depositing very thin TiN films inside a contact hole, after which core dielectrics were uniformly filled into the TiN-deposited contact hole. Using this novel contact scheme, it was possible to reduce reset current while maintaining a low set resistance and a uniform cell distribution. Thus, it has been clearly demonstrated that the use of the ring-type contact technology is very feasible for high-density PRAM beyond 256 Mb.

Pollutants in Rainwater Runoff in Korea: Their Impacts on Rainwater Utilization

Frequent urban floods and insufficient water supply have led to developing technologies for rainwater utilization in order to buffer extreme runoff situations in the watercourses and to provide an ongoing water supply for non-potable use. However, little information is available on the water qualities and runoff properties of collected rainwater in connection with efficient design and maintenance strategies of rainwater utilization systems. In this work, the characteristics of rainwater were investigated in a full-scale rainwater utilization facility in Korea. Samples of runoff rainwater from various catchment surfaces were analyzed for physico-chemical and microbial determinants including metals, nutrients, pH, turbidity, conductivity, and microorganisms. The pollutant concentrations in rainwater storage tank were also monitored to elucidate the impact of input rainwater quality on stored water property. It is likely that particles and total coliforms are major issues in operating rainwater utilization system. However, further studies will be necessary to address the health effect of rainwater in terms of microbial and ecotoxicological measures.

A Study on the Failure Mechanism of a Phase-Change Memory in Write/Erase Cycling

Using a phase-change memory (PCM) device composed of Ge2Sb2e5 (GST), we studied the mechanism of the SET-stuck failure (SSF), a constantly low-resistance state during write/erase (W/E) cycling. The SSF state was characterized with increased RESET current and decreased threshold voltage, which were thought to be due to depletion of Ge and enrichment of Sb inside the active volume of GST. Moreover, we found that device characteristics of an SSF-PCM could be recovered by reversing bias polarity and the repaired device could endure many W/E cycles, implying that field-induced ion migration was the major cause of the SSF of a PCM.

Threshold resistive and capacitive switching behavior in binary amorphous GeSe

A threshold switching (TS) event in a binary amorphous GeSe film placed between Pt top and bottom electrodes was examined. This GeSe film exhibits fast (<40 ns) TS behavior. The observed TS of the resistance was found to be accompanied with the TS of the capacitance. A mechanism for the TS of the GeSe film was suggested by revisiting the previous controversy about the thermal versus non-thermal electronic mechanism. The non-thermal electronic mechanism envisaging the double-injection of electronic carriers can qualitatively account for the measured threshold resistive and capacitive switching, whereas the TS behavior simulated using the thermal mechanism is inconsistent with the experimental observation.

Non-Volatile Control of 2DEG Conductivity at Oxide Interfaces

The functionalization of two-dimensional electron gas (2DEG) at oxide interfaces can be realized integrating 2DEG with multifunctional oxide overlayers by epitaxial growth. Using a ferroelectric Pb(Zr0.2 Ti0.8 )O3 overlayer on 2DEG (LaAlO3 /SrTiO3 ), we demonstrate a model system of the functionalized 2DEG, where electrical conductivity of 2DEG can be reversibly controlled with a large on/off ratio (>1000) in a non-volatile way by ferroelectric polarization switching.