Effects of WO3 addition on the structure and electrical properties of Pb3O4 modified PZT–PFW–PMN piezoelectric ceramics

The ceramics were prepared successfully by Pb₃O₄ and WO₃ additions to 0.90Pb(Zr,Ti)O₃–0.03Pb(Fe_2/3W_1/3)O₃–0.07Pb(Mn_1/3Nb_2/3)O₃ (0.90PZT–0.03PFW–0.07PMN). Effects of the additions on the structure, bulk density and electrical properties of ceramics were investigated. The results revealed that the proper additions of WO₃ with 2.0 wt.% Pb₃O₄ excess could form liquid phase that promoted the densification of the ceramics. The fracture mode changed from transgranular to intergranular as increasing WO₃ with 2.0 wt.% Pb₃O₄ excess. The piezoelectric and dielectric properties were also promoted by excess of Pb₃O₄ and WO₃ additions. The optimized electrical properties were obtained at excess of 2.0 wt.% Pb₃O₄ and 0.15 wt.% WO₃. The parameters were as follows: d₃₃ = 351 pC/N, K_p = 0.64, Q_m = 1882, ɛ_r = 1798, tan δ = 0.0052, P_r = 19.94 μC/cm² and E_c = 11.98 kV/cm, which shows high K_p, Q_m, d₃₃ and low tan δ can be obtained simultaneously by adding WO₃ addition to Pb₃O₄ modified PZT–PFW–PMN system.     

Design,fabrication, and initial testing of a miniature PEM fuel cell with micro-scale pyrolyzed carbon fluidic plates

Carbonization of machined polymers is a method of creating carbon structures with small feature sizes without having to directly machine carbon (a difficult and expensive process). Pyrolyzed carbon fluidic plates with feature sizes less than 1 mm are used to create a miniature fuel cell. Epoxy is used to seal the fuel cell and water is directly applied to exposed Nafion^® to hydrate the membrane. The use of miniature carbon fluidic plates will allow for fabrication of 3D (non-planar) proton exchange membrane fuel cells utilizing carbon bipolar plates. Initial test results of the fuel cell are given.     

Linear-Time Algorithms for Finding the Shadow Volumes from a Convex Area Light Source

An area light source in three-dimensional space shines past a scene polygon to generate two types of shadow volumes for each scene polygon, i.e., one with partial occlusion and the other with complete occlusion. These are called penumbra and umbra, respectively. In this paper we propose linear-time algorithms for computing the penumbra and the umbra of a scene polygon from an area light source, respectively. Received June 27, 1995; revised May 20, 1996.     

Partial Discharge Signal Detection by Piezoelectric Ceramic Sensor and The Signal Processing

Partial discharge (PD) in an insulator or on surface of defective conductor emits acoustic wave transmitting through an air or an insulator. The acoustic wave between 20 kHz and several hundred of kHz can be detected by piezoelectric ceramic sensor that converts the acoustic wave into an electrical signal. Piezoelectric ceramic sensor has either the wide resonant band or the local resonant band depending on the ceramic material or the various combinations of each different component in the manufacturing process. This paper presents the piezoelectric ceramic sensor with 0.95 PZT–0.05 PMNS that yields the piezoelectric properties of high k_p, high Q_m. It has the frequency characteristics of local resonant band, such that it can be applied to PD detection. We have demonstrated the properties of the proposed piezoelectric ceramic sensor by comparing with the conventional electrical PD detector. Quantitative analysis is accomplished by comparing the -q_max from a PD detector and the -v_max from the proposed sensor while -n distributions are the same for both the conventional phase-resolved PD analysis method and the proposed one.     

Design and Performance of Miniaturized Piezoelectric Step-Down Transformer

Piezoelectric transformers are expected to be small, thin and highly efficient, and which are attractive as a transformer with high power density for step down voltage. For these reasons, we have attempted to develop a step-down piezoelectric transformer for the miniaturized adaptor. we propose a piezoelectric transformer, operating in thickness extensional vibration mode for step-down voltage. This transformer consists of a multi-layered construction in the thickness direction. In order to develop the step-down piezoelectric transformers of 10 W class and turn ratio of 0.1 with high efficiency and miniaturization, the piezoelectric ceramics and piezoelectric transformer designs are estimated with a variety of characteristics. The basic composition of piezoelectric ceramics consists of ternary yPb(Zr_xTi_{1 – x})O₃–(1–y)Pb(Mn_1/3Nb_1/3Sb_1/3)O₃. In the piezoelectric characteristics evaluations, at y = 0.95 and x = 0.505, the electromechanical coupling factor(k_p) is 58%, piezoelectric strain constant (d₃₃) is 270 pC/N, mechanical quality factor(Q_m) is 1520, permittivity ( ₃₃^T/₀) is 1500, and Curie temperature is 350C. At y = 0.90 and x = 0.500, k_p is 56%, d₃₃ is 250 pC/N, Q_m is 1820, ₃₃^T/₀ is 1120, and Curie temperature is 290C. It shows the excellent properties at morphotropic phase boundary regions. PZT-PMNS ceramic may be available for high power piezoelectric devices such as piezoelectric transformers. The design of step-down piezoelectric transformers for adaptor proposes a multi-layer structure to overcome some structural defects of conventional piezoelectric transformers. In order to design piezoelectric transformers and analyze their performances, the finite element analysis and equivalent circuit analysis method are applied. The maximum peak of gain G as a first mode for thickness extensional vibration occurs near 0.85 MHz at load resistance of 10 . The peak of second mode at 1.7 MHz is 0.12 and the efficiency is 92%.     

An investigation on photopolymer solidification considering laser irradiation energy in micro-stereolithography

Micro-stereolithography technology has made it possible to fabricate freeform three-dimensional microstructures. This technology is based on conventional stereolithography, in which a UV laser beam irradiates the free surface of a UV-curable liquid photopolymer, causing it to solidify. In micro-stereolithography, a laser beam that is a few m in diameter is used to solidify a very small area of the photopolymer. Photopolymer solidification phenomena in response to variations in the scanning pitch of a focused laser beam were investigated experimentally in this study according to the irradiation energy. The effect of the layer thickness on the solidification width and depth was also examined. The study was conducted using both a relatively low laser power and high scanning speed (low irradiation energy method), and a relatively high laser power and low scanning speed (high irradiation energy method). The experimental results were compared with those obtained using a photopolymer solidification model. Based on these results, a new laser-scanning scheme is proposed according to the three-dimensional microstructure shape desired. Samples were successfully fabricated using both methods.This research was supported by the Center for Nanoscale Mechatronics and Manufacturing (CNMM; http://www.nanomecca.re.kr), which performs some of the 21st Centurys frontier R&D projects, and sponsored by the Korean Ministry of Science and Technology under the contract project code M102KN010001–02K1401–00211.     

Simulations of Supersonic Astrophysical Jets and Their Environments Using Level Set Methods

Computational fluid dynamics simulations using the WENO method and level set method are applied to high Mach number nonrelativistic astrophysical jets, including the effects of radiative cooling. WENO methods introduced in Liu et al. (J. Comput. Phys., 115:200–212, 1994) have allowed us to simulate HH 1-2 astrophysical jets at Mach number much higher than Mach 80 (Ha et al. in J. Sci. Comput. 24:29–44, 2005). Simulations at high Mach numbers and with radiative cooling are essential for achieving detailed agreement with the astrophysical images. Simulations of interaction between astrophysical jet and environment using level set methods are considered in this paper.     

Revisiting reorder buffer architecture for next generation high performance computing

Modern microprocessors achieve high application performance at an acceptable level of power dissipation. Reorder buffer is used for out-of-order instructions to be committed in-order. The reorder buffer plays a key role in modern microprocessors because performance improvement techniques highly rely on aggressive speculation to feed wider issue, out-of-order, and deep pipelines. In terms of power to performance trade-off, reorder buffer is particularly important. This is because enlarging the reorder buffer size achieves high performance but naive scaling of the conventional reorder buffer architecture can severely increase the complexity and power consumption. In this paper, we propose low-power reorder buffer techniques for contemporary microprocessors. First, the separated reorder buffer reduces power dissipation by deferred allocation and early release. The deferred allocation delays the SROB allocation of instructions until all their data dependencies are resolved. Then, the instructions are executed in program order and they are released faster from the SROB. The result of the instruction is written into rename buffers immediately after the execution completes. Then, the result values in the rename buffer are written into the architectural register file at the commit state. The proposed approaches in this paper provide higher resource utilization and low power consumption.     

Oxidation and reduction effects of propane–oxygen on Pd–chlorine/alumina catalysts

Pd–chloride precursor salt was used to prepare Pd/Al₂O₃ catalysts. TPSR measurements showed three distinct reactions for the oxidation of propane on palladium surface under excess of hydrocarbon: complete oxidation, steam reforming and propane hydrogenolysis. Propane oxidation on palladium catalysts was related to the Pd²⁺ sites observed on Pd/Al₂O₃ through infrared of adsorbed carbon monoxide. In fresh catalysts reduced by H₂, the IR spectra showed the linear and bridge adsorbed CO species on the Pd⁰ surface. After propane reaction, a new band at 2130 cm^-1 related to CO adsorption on Pd²⁺ species was noted. Carbon monoxide species adsorbed on Pd⁰ were also observed in all samples after reaction. Our results suggest surface ratios of Pd⁰/PdO during the propane oxidation. On the other hand, time on stream conversions of the complete oxidation of propane were affected by either the water generated during the reaction or added as a reactant at 10 vol%. The water generated by the reaction helped to eliminate chlorine residues in the form of oxychloride species leading to an increasing of the activity. However, the presence of water into the reaction mixture caused a strong decreasing of the activity. The inhibition mechanism of propane oxidation in the presence of water consisted in the dissociative adsorption of water on palladium sites with the possible formation of palladium hydroxide (Pd–OH) at the surface, diminishing the number of active surface sites. Dynamic fluctuations into the reaction conditions supported the idea that a pseudo‐equilibrium adsorption–desorption of water was reached. After water removal or increasing in the reaction temperature the equilibrium was shifted to the direction of OH–Pd decomposition. This behavior suggests that the inhibitory effect of water is a reversible phenomenon, being a function of the amount of water and the reaction temperature. This revised version was published online in July 2006 with corrections to the Cover Date.