Representative traditional Korean pigments (oyster shell white hobun, massicot miltaseung, indigo jjok, azurite seokcheong, malachite seokrok, and red lead yeondan) have been studied with terahertz ...time-domain spectroscopy (THz-TDS) and Fourier-transform infrared spectroscopy (FTIRS) over the spectral region of 0.1–7.5 THz. Both the refractive index
n
and the extinction coefficient
k
were simultaneously and independently determined in the terahertz region without a Kramers-Kronig analysis while the absoprtion coefficient spectra were acquired in the infrared region. All pigments studied in the present work exhibited a set of characteristic absorption peaks unique to the pigment species in addition to a background that increased with increasing frequency. Our study demonstrates that terahertz and infrared techniques can be useful identification and diagnostic tools for the traditional Korean pigments used in heritage buildings and artworks.
The self-assembly behaviors of flow-enhanced CdSe nanoparticle (NP) colloidal systems were investigated, which were systemically prepared by adding ethylene glycol (EG) or acetic acid (AA) to NP ...suspensions with deionized water (DI water) base. The additive solvents, which had higher boiling points and lower surface tensions than those of the DI water, modified the internal flow of the NP colloidal system, consequently affecting the morphologies of the generated NP superstructures after the full evaporation of their droplets. In flow-enhanced systems, NPs were formed into highly elongated dendrites that stretched from the center region to the edges along the direction of convective flow inside the droplet, while NPs in random drift system were easily aggregated to form cluster-shaped thick dendritic structures. When the volume fraction of EG was increased, the dominant superstructures were changed from dendrites to clusters, which can be mainly attributed to the changes in the dielectric properties of the NP droplets as evaporation proceeded because of the large discrepancy in the vapor pressures of EG and DI water. The balance between the interparticle potentials of electrostatic repulsion and van der Waals attraction was continuously altered, resulting in the formation of clusters with increasing EG ratio. Contrastively, the transition of superstructures could not be observed in the case of colloidal system prepared by mixing DI water and AA, which can be ascribed to the similar vapor pressures of the two solvents; the dielectric properties of the solution mixture was barely changed throughout the steady evaporation process, which resulted in the formation of uniformly distributed highly elongated dendrites. Polarization-dependent imaging experiments and photoluminescence measurements revealed that the stretched dendrites formed under the flow-enhanced conditions showed higher crystallinity than that of the clusters.
We have developed a terahertz time-domain spectroscopy (THz-TDS) system for transmission and reflection measurements of metallic thin films. Using our THz-TDS system, we studied the conventional ...superconductor niobium (Nb) in the normal state in the spectral range from 5 to $50cm^{-1}$. Both the real and imaginary parts of the conductivity are acquired without Kramers-Kronig analysis. Nb exhibits a nearly frequency independent real conductivity spectrum in the terahertz range, with a very small imaginary part.
The development of textile-based stretchable displays has faced challenges related to the deterioration of image quality due to mechanical stretching. In this study, we introduce a novel approach to ...address this issue by implementing negatively strain-resistive switch-type conductive fibers based on pre-designed crack localizing technologies. The fabricated switch exhibited an extremely-high negative gauge factor (resistance change ratio \approx 10 ^{9} ohms) that can dramatically convert its insulating properties into conducting ones. The integration of this fiber-based on/off switch into the stretchable displays enables the activation of hidden-pixel structures to maintain image resolution and luminance under tensile strain conditions. This cutting-edge solution paves the way for the next generation of stretchable display technologies for various wearable applications.
Manipulation involves a broad spectrum of skills, e.g., polishing, peeling, flipping, screwing, etc., requiring complex and delicate control over both force and position. This paper aims at designing ...an optimal haptic interface for providing a robot with direct demonstrations of human's innate intelligence in performing a wide range of force-based bimanual manipulation tasks. Based on the proprioceptive actuation mechanism, kinodynamic design parameters of the (dual) 7-DOF haptic arm are optimized so as to maximize the force transparency perceived by the operator over the full real-scale workspace of human arm while also ensuring other important constraints including robot-to-operator collision and singularity avoidance, payload, controlled stiffness, etc. 2.65 kg of average reflective mass and 1500 N/m of controlled stiffness is achieved over the entire workspace. We show the efficacy of our haptic interface by demonstrating various force-based manipulation tasks with a light-weight anthropomorphic bimanual manipulator, LIMS2-AMBIDEX 1.
Relatively narrow molecular weight distribution polyaniline/poly(4-styrene sulfonate) were synthesized by aqueous chemical oxidation polymerization using a dialysis membrane as the key to controlling ...the diffusion speed of the initiator. The optical, electrochemical, and electrical properties of the resulting polyaniline/poly(4-styrene sulfonate) were estimated by ultraviolet-visible-near infrared spectroscopy, cyclic voltammetry, and four-point probe. Compared to a bulk polyaniline/poly(4-styrene sulfonate), the resulting polyaniline/poly(4-styrene sulfonate) showed relatively high crystallinity according to X-ray diffraction, and their polydispersity indices ranged from 1.6 to 2.0 as a function of the reaction time. The electrical conductivities of the resulting polyaniline/poly(4-styrene sulfonates) were also enhanced gradually with increasing reaction time.
Terahertz study of reduced graphene oxide Kyujin Choi; Juhwan Lim; Taeyoon Hong ...
2012 37th International Conference on Infrared, Millimeter, and Terahertz Waves,
2012-Sept.
Conference Proceeding
We report on our terahertz study of the reduction effect on graphene oxide films grown on fused silica substrates by spin-coating. The optical characteristics before and after thermal reduction were ...studied by terahertz time-domain spectroscopy.
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