Seung-Hoon Nahm

Biomedical applications of holographic microspectroscopy [invited].

The identification and quantification of specific molecules are crucial for studying the pathophysiology of cells, tissues, and organs as well as diagnosis and treatment of diseases. Recent advances in holographic microspectroscopy, based on quantitative phase imaging or optical coherence tomography techniques, show promise for label-free noninvasive optical detection and quantification of specific molecules in living cells and tissues (e.g., hemoglobin protein). To provide important insight into the potential employment of holographic spectroscopy techniques in biological research and for related practical applications, we review the principles of holographic microspectroscopy techniques and highlight recent studies.

Investigations on indentation size effects using a pile-up corrected hardness

Indentation size effects (ISEs) become severe in the nanoindentation regime because various influencing factors become active in a very shallow indentation regime. Additionally, the general analysis on the nanoindentation curve yields hardness overestimation because it cannot take into account material pile-up around contacts. Thus we tried to investigate intrinsic ISEs in monolithic materials by proposing a new hardness measurement method; the load-supporting contact boundary was approximated as the peak trajectory around an impression and analysed by a radial differentiation of the remnant indent morphology. Dependence of the new load-off hardness on the indentation depth was investigated for (1 0 0) tungsten single crystal and fused quartz. The contribution of the material pile-up to the new hardness was clearly modified but more significant hardness increase appeared at a very shallow indentation regime due to severe elastic recovery. These phenomena are discussed with the strain-gradient plasticity model.

A nondestructive method for estimation of the fracture toughness of CrMoV rotor steels based on ultrasonic nonlinearity

The objective of this paper is to develop a nondestructive method for estimating the fracture toughness (K(IC)) of CrMoV steels used as the rotor material of steam turbines in power plants. To achieve this objective, a number of CrMoV steel samples were heat-treated, and the fracture appearance transition temperature (FATT) was determined as a function of aging time. Nonlinear ultrasonics was employed as the theoretical basis to explain the harmonic generation in a damaged material, and the nonlinearity parameter of the second harmonic wave was the experimental measure used to be correlated to the fracture toughness of the rotor steel. The nondestructive procedure for estimating the K(IC) consists of two steps. First, the correlations between the nonlinearity parameter and the FATT are sought. The FATT values are then used to estimate K(IC) using the K(IC) versus excess temperature (i.e., T-FATT) correlation that is available in the literature for CrMoV rotor steel.

A new non-destructive method for estimating the remanent life of a turbine rotor steel by reversible magnetic permeability

Abstract We present a new magnetic and non-destructive procedure to evaluate the remanent life of 1Cr–1Mo–0.25V steel using the value of reversible magnetic permeability. The method is based on the existence of reversible magnetic permeability in the differential magnetization around the coercive force. The measurement principle is based on the foundation harmonics voltage induced in a coil using a lock-in amplifier tuned to a frequency of the exciting one. Results obtained for reversible magnetic permeability and Vickers hardness on the aged sample show that the peak interval of reversible magnetic permeability (PIRMP) and Vickers hardness decreases as aging time increases. A softening curve is obtained from the correlation between Vickers hardness and the PIRMP. This curve can be used as a non-destructive method to evaluate the remanent life of 1Cr–1Mo–0.25V steel.

Crystal structure and spontaneous polarization of Bi4−xNdxTi3O12 studied by using neutron powder diffraction data

Crystal structural parameters of Bi4−xNdxTi3O12 (BNT, x = 0.25, 0.5, 0.75 and 1.0) were determined by means of neutron powder diffraction and Rietveld analysis based on the monoclinic space group of B1a1. The a-axis has been found to shrink monotonically from 5.4475(8) to 5.4100(1) A with x increasing from 0 to 0.75. The orthorhombicity defined as 2(a − b)/(a + b) decreased with increasing x because the b-axis lattice parameter remained almost constant. The c-axis increases monotonically up to x = 0.75. The spontaneous polarization, which is oriented along the a-axis (Ps//a), decreased from 35.4 to 28.3, 24.8 and 22.2 µ Cc m −2 with x increasing from 0 to 0.25, 0.5 and 0.75, respectively as calculated by using the refined structural parameters. Thus, the substitution of Nd for Bi has been found to cause a considerable structural relaxation. Bi3Nd1Ti3O12 showed a considerably small a-lattice parameter of 5.4004 (1) A and a very small Ps value of only 7.5 µ Cc m −2 indicating that its structure is orthorhombic or close to tetragonal.

In-situ Resistance Measurements during Tensile Test of Carbon Nanotube using Nano-manipulator

A variety of outstanding experimental results on mechanical properties of carbon nanotube (CNT) are fast appearing. Nevertheless, mechanical properties of CNT have been rarely understood because of measurement difficulties. The response of multi walled carbon nanotube (MWNT) to mechanical strain applied with a nano-manipulator was investigated inside scanning electron microscope (SEM). MWNTs were produced by arc-discharge method and the protruded sample for tensile test was selected among the MWNTs fragment which has rectilinearity and purity above 40%. The average diameter of MWNT was approximately 15 nm. In order to measure the resistance of a MWNT during tensile test, an individual MWNT was attached at the tungsten (W) tip using electron beam induced deposition. We confirmed that the contact resistance between a MWNT and the W tip decrease during the exposure of electron beam. And then the W tip were manipulated and controlled by nano-manipulator and personal computer. We observed that resistance of sample was significantly changed until the MWNT fracture

Degradation Evaluation of Mechanical Property for Modified 9Cr-1Mo Steel by Reversible Permeability

The present work studies a nondestructive evaluation of the degradation of modified 9Cr-1Mo steel using a magnetic method based on the existence of the peaks of reversible permeability (RP) in the differential magnetization around the coercive force. The apparatus is based on detection of the voltage induced in a coil using a lock-in amplifier tuned to the frequency of the AC perturbing field. Results obtained for the reversible permeability and Vickers hardness on the aged samples showed the peak interval of reversible permeability (PIRP) and Vickers hardness decrease as aging time increased. The correlation between Vickes hardness and the PIRP could be used to evaluate degradation of modified 9Cr-1Mo steel.

Crystal structure of Bi4−xCexTi3O12(x = 0, 0.25, 0.5 and 0.75) studied by Raman spectroscopy and neutron powder diffraction

Structural refinement using both neutron powder diffraction data and Raman spectroscopy were carried out to determine the site preference of Ce atoms and structural changes in Bi4−xCexTi3O12 (x = 0, 0.25, 0.5 and 0.75) compounds. In the Raman spectroscopic study, the peak at 65 cm−1 of Bi4Ti3O12 (BTO), assigned to the Bi–O bonds in the Bi2O2 layers, did not shift or shifted to 63 cm−1 after Ce incorporation. However, the peaks of BTO at 119 and 148 cm−1, assigned to the Bi–O bonds in the perovskite units, became diffusive and moved to higher frequencies of (121 and 150 cm−1), (123 and 152 cm−1) and (125 and 157 cm−1) when x was 0.25, 0.5 and 0.75, respectively. From the Raman spectroscopic study, the substitution sites of the Ce atoms were determined to be only the Bi sites in the perovskite units. The peaks originated from the TiO6 octahedrons moved to higher frequencies and merged with the neighbouring peaks, indicating relaxation of distortion of TiO6 octahedrons with increase in x. Structural refinement results showed that the a-axis lattice parameters decreased with increase in x, while the b-axis lattice parameters did not exhibit significant changes and the c-axis lattice parameters decreased. Decrease in orthorhombicity with increasing x showed the relaxation of structural distortion of TiO6 octahedrons. Spontaneous polarization was calculated based on the refinement results, which decreased from 35.4 to 30.4, 27.5 and 16.5 µC cm−2 when x is 0, 0.25, 0.5 and 0.75, respectively.

Software and Hardware Development of Micro-indenter for Material Property Evaluation of Hyper-Elastic Rubber

In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are examined via finite element (FE) analyses. An optimal location for data analysis is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions, which map an indentation load vs. deflection curve into a strain energy density vs. first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/com-pression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress-strain curve with an average error less than 3%.

Simultaneous reception of solar power and visible light communication using a solar cell

Abstract. Solar cells are widely used in various applications. However, they are only used to harvest solar power. We propose and demonstrate a technique to use a solar cell as a simultaneous receiver of solar power and visible light communication (VLC) signals. First, we investigate the optic-to-electric conversion efficiency and the frequency response of a solar cell. Then, we demonstrate that a solar cell receiver can receive both solar power and VLC signals simultaneously. We also investigate the effect of solar power interference on the VLC performance. The results show that the VLC operation is successful even when the solar power is the maximum.