Effect of Ba(Cu1/3Nb2/3)O3 content on multiferroic properties in BiFeO3 ceramics

The crystal structure, microstructural evolution, and ferroelectric and magnetic properties of BiFeO₃ (BFO) ceramic materials, widely known as room temperature multiferroic materials, were investigated with various contents of Ba(Cu_1/3Nb_2/3)O₃ (BCN). The ceramics were synthesized through the solid state reaction and pressureless sintering in air. By adding tetragonal structured BCN phase to the rhombohedral structured BFO phase, a solid solution was formed. The rhombohedral crystal structure and lattice parameter, densification behavior, and microstructure of BFO were noticeably changed upon the addition of BCB. The electrical properties of BFO were slightly enhanced by the addition of BCN. However, the magnetic properties of BFO which is the most critical issue in BFO multiferroics were drastically changed and the 20 mol% BCN added BFO ceramics showed extremely enhanced magnetization characteristics compared to the other BFO–BCN ceramics. It is expected that BFO–BCN ceramics with this composition could be one of the most promising multiferroic materials for future multiferroic applications.     

Switchable induced polarization in LaAlO3/SrTiO3 heterostructures

Demonstration of a tunable conductivity of the LaAlO(3)/SrTiO(3) interfaces drew significant attention to the development of oxide electronic structures where electronic confinement can be reduced to the nanometer range. While the mechanisms for the conductivity modulation are quite different and include metal-insulator phase transition and surface charge writing, generally it is implied that this effect is a result of electrical modification of the LaAlO(3) surface (either due to electrochemical dissociation of surface adsorbates or free charge deposition) leading to the change in the two-dimensional electron gas (2DEG) density at the LaAlO(3)/SrTiO(3) (LAO/STO) interface. In this paper, using piezoresponse force microscopy we demonstrate a switchable electromechanical response of the LAO overlayer, which we attribute to the motion of oxygen vacancies through the LAO layer thickness. These electrically induced reversible changes in bulk stoichiometry of the LAO layer are a signature of a possible additional mechanism for nanoscale oxide 2DEG control on LAO/STO interfaces.     

Synthesis and characterization of vertically aligned carbon nanotube forest for solid state fiber spinning

Continuous carbon nanotubes (CNT) fibers were directly spun from a vertically aligned CNT forest grown by a plasma-enhanced chemical vapor deposition (PECVD) process. The correlation of the CNT structure with Fe catalyst coarsening, reaction time, and the CNTs bundling phenomenon was investigated. We controlled the diameters and walls of the CNTs and minimized the amorphous carbon deposition on the CNTs for favorable bundling and spinning of the CNT fibers. The CNT fibers were fabricated with an as-grown vertically aligned CNT forest by a PECVD process using nanocatalyst an Al2O3 buffer layer, followed by a dry spinning process. Well-aligned CNT fibers were successfully manufactured using a dry spinning process and a surface tension-based densification process by ethanol. The mechanical properties were characterized for the CNT fibers spun from different lengths of a vertically aligned CNT forest. Highly oriented CNT fibers from the dry spinning process were characterized with high strength, high modulus, and high electrical as well as thermal conductivities for possible application as ultralight, highly strong structural materials. Examples of structural materials include space elevator cables, artificial muscle, and armor material, while multifunctional materials include E-textile, touch panels, biosensors, and super capacitors.     

The application of the cryogenic system on the HTS power cable circuit in actual grid

The 22.9 kV/50 MVA AC HTS power cable system consisted of power cable with 410 m length and cryogenic system has been manufactured by LS Cable & System and installed in Icheon substation of KEPCO grid in the end of 2010. High temperature superconductor only appears the superconductivity at the constant temperate range. So in order to maintain the superconductivity, the cryogenic system is needed. The cryogenic system, the open-loop type, is consisted of the Pressure Control System (PCS), Gas/liquid separator, Circulation Pump, Decompression unit, Filter and so on. Decompression unit is a device that keeps the sub-cooled nitrogen by way of the latent heat of evaporation and includes the heat exchanger. The effectiveness-NTU method is used for the design of the heat exchanger. After installation of the cryogenic system on the site, the test of the cooling capacity of the cryogenic system and commissioning tests were performed. During the grid operation of the HTS power cable system, no major problems have been encountered to this point. The cryogenic system has been operated sufficiently to maintain a stable of the HTS power cable system. This paper will summarize the design of the cryogenic system and the results of the grid operation.     

Yellow lighting upconversion from Yb3+/Ho3+ co-doped CaMoO4

Yellow upconversion (UC) luminescence is observed in Ho³⁺/Yb³⁺ co-doped CaMoO₄ synthesized by complex citrate-gel method. Under 980 nm excitation, Ho³⁺/Yb³⁺ co-doped CaMoO₄ exhibited yellow emission based on green emission near 543 nm generated by ⁴F₄, ⁵S₂ → ⁵I8 transition and strong red emission around 656 nm generated by ⁵F₅ → ⁵I₈ transition, which are assigned to the intra 4f transitions of Ho³⁺ ions. The optimum doping concentration of Ho³⁺ and Yb³⁺ was investigated for highest upconversion luminescence. Based on pump power dependence, upconversion mechanism of Ho³⁺/Yb³⁺ co-doped CaMoO₄ was studied in detail.     

Preparation and absorption properties of ZnO nanostructures for cleanup of H2S contained gas

A nano-size zinc oxide sorbents was formulated for the effective removal of sulfur compounds (H₂S) at a very low concentration (under 50 ppmv) in a gasified fuel gas. They were prepared by a matrix-assisted method in this study. An active carbon was used as a matrix and zinc acetate (Zn(C₂H₃O₂)₂ 2H₂O) was selected as a precursor. About 10–40 wt% of zinc was doped over the activated carbon in the preparation of the sorbents. Content of the zinc doped over the activated carbon had an influence on the morphology of zinc oxide nanostructure. The reactivity tests of the ZnO nanostructures having various morphologies were performed in a fixed bed reactor. Their reactivity increased as their sizes became smaller and their surface areas made larger. Most prepared nanosize zinc oxides showed an excellent performance for the removal of H₂S at a very low concentration.     

Optimum design of 6-DOF parallel manipulator with translational/rotational workspaces for haptic device application

This paper proposes an optimum design method that satisfies the desired orientation workspace at the boundary of the translation workspace while maximizing the mechanism isotropy for parallel manipulators. A simple genetic algorithm is used to obtain the optimal linkage parameters of a six-degree-of-freedom parallel manipulator that can be used as a haptic device. The objective function is composed of a desired spherical shape translation workspace and a desired orientation workspace located on the boundaries of the desired translation workspace, along with a global conditioning index based on a homogeneous Jacobian matrix. The objective function was optimized to satisfy the desired orientation workspace at the boundary positions as translated from a neutral position of the increased-entropy mechanism. An optimization result with desired translation and orientation workspaces for a haptic device was obtained to show the effectiveness of the suggested scheme, and the kinematic performances of the proposed model were compared with those of a preexisting base model.     

Baseband stage for WCDMA direct conversion receiver with high dynamic range and accurate temperature compensation

A highly integrated baseband stage, which adopts a new configuration for the wideband code-division multiple access (WCDMA) direct conversion receiver (DCR), is described. The baseband stage satisfies all requirements of the WCDMA DCR and consists of opamp-RC channel select filters and variable gain amplifiers with linear-in-dB gain control. It achieves a high dynamic range of 85 dB with /spl plusmn/1.5 dB accuracy over a temperature variation from -25 to 85/spl deg/C, 16.5 nV//spl radic/Hz input-referred noise, +20 dBV out-of-band IIP3 and +70 dBV out of band IIP2. The baseband stage is fabricated using a 0.35 /spl mu/m SiGe BiCMOS process and consumes a total current of 11 mA/CH from a 2.7 V supply.     

Mussel‐Inspired Polydopamine Coating as a Universal Route to Hydroxyapatite Crystallization

Bone tissue is a complex biocomposite material with a variety of organic (e.g., proteins, cells) and inorganic (e.g., hydroxyapatite crystals) components hierarchically organized with nano/microscale precision. Based on the understanding of such hierarchical organization of bone tissue and its unique mechanical properties, efforts are being made to mimic these organic–inorganic hybrid biocomposites. A key factor for the successful designing of complex, hybrid biomaterials is the facilitation and control of adhesion at the interfaces, as many current synthetic biomaterials are inert, lacking interfacial bioactivity. In this regard, researchers have focused on controlling the interface by surface modifications, but the development of a simple, unified way to biofunctionalize diverse organic and inorganic materials remains a critical challenge. Here, a universal biomineralization route, called polydopamine‐assisted hydroxyapatite formation (pHAF), that can be applied to virtually any type and morphology of scaffold materials is demonstrated. Inspired by the adhesion mechanism of mussels, the pHAF method can readily integrate hydroxyapatites on ceramics, noble metals, semiconductors, and synthetic polymers, irrespective of their size and morphology (e.g., porosity and shape). Surface‐anchored catecholamine moieties in polydopamine enriches the interface with calcium ions, facilitating the formation of hydroxyapatite crystals that are aligned to the c‐axes, parallel to the polydopamine layer as observed in natural hydroxyapatites in mineralized tissues. This universal surface biomineralization can be an innovative foundation for future tissue engineering.     

Microstructural Observations in Barium Calcium Magnesium Niobate

Microstructural studies on (1 − x )Ba(Mg_1/3Nb_2/3)O₃– x Ca(Mg_1/3Nb_2/3)O₃ (BCMN) complex perovskite compounds, which are mixtures of Ba(Mg_1/3Nb_2/3)O₃ (BMN) and Ca(Mg_1/3Nb_2/3)O₃ (CMN), were conducted using scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. Pure BMN and CMN both have a 1:2 ordered structure, via the chemical ordering of B-site cations; however, the tilting of oxygen octahedra is involved in pure CMN, whose structure has a 1:2 ordered monoclinic unit cell that is characterized by (±1/6,±1/6,±1/6)-type superlattice reflections in electron diffraction patterns along the [110] zone axis that is based on a simple cubic perovskite. Studies of the morphologic differences have indicated two types of inhomogeneities in a mixture of the BCMN system: (i) a rather large-scale segregation (i.e., grain sizes of several micrometers), where the grains are separated compositionally as being barium-rich or calcium-rich, and (ii) fine-scale lamellar-type segregations 20 nm wide and 200 nm long. The segregation that is caused by Ba and Ca ions can be identified by the difference of superlattice modulations from high-resolution transmission electron microscopy lattice images.