Microwave Metamaterial Applications using Complementary Split Ring Resonators and High Gain Rectifying Reflectarray for Wireless Power Transmission

In the past decade, artificial materials have attracted considerable attention as potential solutions to meet the demands of modern microwave technology for simultaneously achieving component minimization and higher performance in mobile communications, medical, and optoelectronics applications. To realize this potential, more research on metamaterials is needed. In this dissertation, new bandpass filter and diplexer as microwave metamaterial applications have been developed. Unlike the conventional complementary split ring (CSRR) filters, coupled lines are used to provide larger coupling capacitance, resulting in better bandpass characteristics with two CSRRs only. The modified bandpass filters are used to deisgn a compact diplexer. A new CSRR antenna fed by coplanar waveguide has also been developed as another metamaterial application. The rectangular shape CSRRs antenna achieves dual band frequency properties without any special matching network. The higher resonant frequency is dominantly determined by the outer slot ring, while the lower resonant frequency is generated by the coupling between two CSRRs. The proposed antenna achieves about 35 percent size reduction, compared with the conventional slot antennas at the low resonant frequencies. As a future alternative energy solution, space solar power transmission and wireless power transmission have received much attention. The design of efficient rectifying antennas called rectennas is very critical in the wireless power transmission system. The conventional method to obtain long distance range and high output power is to use a large antenna array in rectenna design. However, the use of array antennas has several problems: the relatively high loss of the array feed networks, difficultiy in feeding network design, and antenna radiator coupling that degrades rectenna array performance. In this dissertation, to overcome the above problems, a reflectarray is used to build a rectenna system. The spatial feeding method of the reflectarray eliminates the energy loss and design complexity of a feeding network. A high gain rectifying antenna has been developed and located at the focal point of the reflectarray to receive the reflected RF singals and genterate DC power. The technologies are very useful for high power wireless power transmission applications

The Limits of Reductionism in Medicine: Could Systems Biology Offer an Alternative?

In the first of a two part series, Ahn and colleagues discuss the reductionist approach pervading medicine and explain how a systems approach (as advocated by systems biology) may complement reductionism

Multiple Subcutaneous Nodules, Persistent High Fever and Lymphadenopathy Case - SNUCH CPC-33 -

This 15-year-old boy was admitted for the second time to Seoul National University Children's Hospital (SNUCH) on February 28, 1988, because of intermittent high fever and lymph node swelling. His illness started in 1985 as repeated sore throat and high fever, for which he was brought to Korea University Hospital. There he underwent an oropharyngeal biopsy that was read as acute necrotizing inflammation. In August 1987, neck lymph node swelling and splenomegaly were noted in addition to the intermittent fever. On February 29, 1988, he was admitted to SNUCH to receive a lymph node biopsy, which revealed necrotizing and granulomatous inflammation with heavy eosinophi-lia. He was born via normal full term spontaneous delivery, and his immediate postnatal course was uneventful. Although no specific disease could be recalled by the parents,intermittent high fever, otitis, and sore throat were recurrent symptoms and si-gns through his infancy and early childhood

Experimental Field Tests and Finite Element Analyses for Rock Cracking Using the Expansion of Vermiculite Materials

In the previous research, laboratory tests were performed in order to measure the expansion of vermiculite upon heating and to convert it into expansion pressure. Based on these test results, this study mainly focuses on experimental field tests conducted to verify that expansion pressure obtained by heating vermiculite materials is enough to break massive and hard granite rock with an intention to excavate the tunnel. Hexahedral granite specimens with a circular hole perforated in the center were constructed for the experimental tests. The circular holes were filled with vermiculite plus thermal conduction and then heated using the cartridge heater. As a result, all of hexahedral granite specimens had cracks in the surface after 700-second thermal heating and were finally spilt into two pieces completely. The specimen of larger size only requires more heating time and expansion pressure. The material properties of granite rocks, which were obtained from the experimental tests, were utilized to produce finite element models used for numerical analyses. The analysis results show good agreement with the experimental results in terms of initial cracking, propagation direction, and expansion pressure

Resonant Scattering and Ly-alpha Radiation Emergent from Neutral Hydrogen Halos

With a state-of-the-art numerical method for solving the integral-differential equation of radiative transfer, we investigate the flux of the Ly$\alpha$ photon $\nu_0$ emergent from an optically thick halo containing a central light source. Our focus is on the time-dependent effects of the resonant scattering. We first show that the frequency distribution of photons in the halo are quickly approaching to a locally thermalized state around the resonant frequency, even when the mean intensity of the radiation is highly time-dependent. Since initial conditions are forgotten during the thermalization, some features of the flux, such as the two peak structure of its profile, actually are independent of the intrinsic width and time behavior of the central source, if the emergent photons are mainly from photons in the thermalized state. In this case, the difference $|\nu_{\pm}-\nu_0|$, where $\nu_{\pm}$ are the frequencies of the two peaks of the flux, cannot be less than $2$ times of Doppler broadening. We then study the radiative transfer in the case where the light emitted from the central source is a flash. We calculate the light curves of the flux from the halo. It shows that the flux is still a flash. The time duration of the flash for the flux, however, is independent of the original time duration of the light source but depends on the optical depth of the halo. Therefore, the spatial transfer of resonant photons is a diffusion process, even though it is not a purely Brownian diffusion. This property enables an optically thick halo to trap and store thermalized photons around $\nu_0$ for a long time after the cease of the central source emission. The photons trapped in the halo can yield delayed emission, of which the profile also shows typical two peak structure as that from locally thermalized photons. Possible applications of these results are addressed.Comment: 25 pages, 10 figures, accepted for publication in Ap

Enhancement of service life of polymer electrolyte fuel cells through application of nanodispersed ionomer

Copyright © 2020 The Authors, some rights reserved.In polymer electrolyte fuel cells (PEFCs), protons from the anode are transferred to the cathode through the ionomer membrane. By impregnating the ionomer into the electrodes, proton pathways are extended and high proton transfer efficiency can be achieved. Because the impregnated ionomer mechanically binds the catalysts within the electrode, the ionomer is also called a binder. To yield good electrochemical performance, the binder should be homogeneously dispersed in the electrode and maintain stable interfaces with other catalyst components and the membrane. However, conventional binder materials do not have good dispersion properties. In this study, a facile approach based on using a supercritical fluid is introduced to prepare a homogeneous nanoscale dispersion of the binder material in aqueous alcohol. The prepared binder exhibited high dispersion characteristics, crystallinity, and proton conductivity. High performance and durability were confirmed when the binder material was applied to a PEFC cathode electrode11sciescopu

Brownian dynamics of colloidal microspheres with tunable elastic properties from soft to hard

We study the Brownian thermal motion of a colloidal model system made by emulsifying hot liquid α-eicosene wax into an aqueous surfactant solution of sodium dodecyl sulfate (SDS). When this waxy oil-in-water emulsion is cooled below α- eicosene's melting point of Tc ≃ 25 °C, the microscale emulsion droplets solidify, effectively yielding a dispersed particulate system. So, the interiors of these wax droplets can be tuned from a viscous liquid to an elastic solid through very modest changes in absolute temperature. Using the multiple light scattering technique of diffusing wave spectroscopy (DWS), which is very sensitive to small-scale motion and shape fluctuations of dispersed colloidal objects, we show that the thermal fluctuations of the interfaces of these liquid droplets at higher temperature, seen in the DWS intensity–intensity correlation function at early times, effectively disappear when these droplets solidify at lower temperature. Thus, we show that the early-time behavior of this DWS correlation function can be used to probe mechanical properties of viscoelastic soft materials dispersed as droplets