Hyung-Ki Park

Electrical impedance properties of bulk carbon nanotube composites for chemical sensors and biosensors

Electrical impedance properties of bulk carbon nanotube (CNT) composite electrodes have been studied to develop chemical and biosensors. The CNTs embedded in composite electrodes were fabricated by means of traditional film casting and electrospun nanoweb. The morphology of the bulk CNT electrode was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Under the various amounts of buffer solution, electrical impedance of the composite electrodes was measured by means of LCR meter. It is generally known that electrical impedance measurement provides rapid and simple sensing mechanism. In this study, we found out that CNT bulk composite electrodes showed good sensing properties for chemical and bio sensors.

Effect of Asymmetric Hot Rolling on the Texture Evolution of Fe–3%Si Steel

In Fe–3%Si steel, the hot rolling process affects not only the hot rolling texture but also the primary recrystallization texture. Here, the effect of asymmetric hot rolling was studied by comparing the difference in the texture evolved between asymmetric and symmetric hot rolling. The effect of asymmetric hot rolling on the texture of primary recrystallized Fe–3%Si steel was also studied. The symmetric hot rolling of Fe–3%Si steel produces a rotated cube texture at the center but Goss and copper textures near the surface. Asymmetric hot rolling tends to produce Goss and copper textures even at the center like the texture near the surface. After primary recrystallization, the dominant texture at the center changes from {001} <210> to {111} <112> and the new texture has a higher fraction of the grains which make the low energy boundary with Goss grains than that of symmetric hot rolling.

Calcium pyrophosphate dihydrate deposition disease in the temporomandibular joint: diagnosis and treatment

BackgroundCalcium pyrophosphate dihydrate deposition disease (CPDD) is a rare disease in the temporomandibular joint (TMJ) space. It forms a calcified crystal mass and induces a limitation of joint movement.Case presentationThe calcified mass in our case was occupied in the left TMJ area and extended to the infratemporal and middle cranial fossa. For a complete excision of this mass, we performed a vertical ramus osteotomy and resected the mass around the mandibular condyle. The calcified mass in the infratemporal fossa was carefully excised, and the segmented mandible was anatomically repositioned. Scanning electronic microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS) microanalysis was performed to evaluate the calcified mass. The result of SEM/EDS showed that the crystal mass was completely composed of calcium pyrophosphate dihydrate. This result strongly suggested that the calcified mass was CPDD in the TMJ area.ConclusionsCPDD in the TMJ is a rare disease and is difficult to differentially diagnose from other neoplasms. A histological examination and quantitative microanalysis are required to confirm the diagnosis. In our patient, CPDD in the TMJ was successfully removed via the extracorporeal approach. SEM/EDS microanalysis was used for the differential diagnosis.

Improvement of mechanical properties of cast pure titanium by repeated heat treatment

ABSTRACT Pure titanium components fabricated by casting have a coarse grain microstructure. To improve the mechanical strength of pure titanium components by refining the grain size, the cast samples were repeatedly heat-treated. During the heat treatment, the titanium samples were repeatedly heated above the alpha-to-beta (α–β) transition temperature and cooled to room temperature to undergo phase transformation. The heating cycle was performed 1, 3, 5, and 7 times. As the number of heating cycles increased, the grain size decreased. The tensile strength was 267.9 MPa in the as-cast sample and improved to 343.4 MPa after 7 heat-treatment cycles owing to the grain size refinement, while the elongation was maintained during the heat treatment. This paper is part of a thematic issue on Titanium.

Development of Novel Impact Paint Sensor by Using Graphene based Smart Nano Composite

This paper presents a novel impact sensor which can be fabricated with smart paint made of grapheme. This smart nano paint can be easily installed on structures using a spray-on technique and that can make the sensor low cost and practical. The graphene effectively improves the piezoresistivity of the smart paint and that is available to achieve sensitive impact sensor with high gauge factor. The nano smart-paint can detect sufficient impact to cover the damaged energy range of the composite around 1~3J. The voltage outputs from the sprayed paints show fairly linear responses after signal processing. The impact makes deformation of the structure and it brings change of piezoresistivity of the paint and those converts into voltage output consequently by means of a simple signal processing system. The nano smart paint is lightweight and easily applied to the structural surface, and there is no stress concentration. The nano smart paint is expected to be a cost effective and sensitive multi-functional sensor for composites and other damage monitoring applications in the field of structural health monitoring.