Showing papers by "National Tsing Hua University published in 2005"

Microstructure characterization of AlxCoCrCuFeNi high-entropy alloy system with multiprincipal elements

Abstract: A new approach for the design of alloy systems with multiprincipal elements is presented in this research. The Al x CoCrCuFeNi alloys with different aluminum contents (i.e., x values in molar ratio, x=0 to 3.0) were synthesized using a well-developed arc-melting and casting method. These alloys possessed simple fcc/bcc structures, and their phase diagram was predicted by microstructure characterization and differential thermal analyses. With little aluminum addition, the alloys were composed of a simple fcc solid-solution structure. As the aluminum content reached x=0.8, a bcc structure appeared and constructed with mixed fcc and bcc eutectic phases. Spinodal decomposition occurred further on when the aluminum contents were higher than x=1.0, leading to the formation of modulated plate structures. A single ordered bcc structure was obtained for aluminum contents larger than x=2.8. The effects of high mixing entropy and sluggish cooperative diffusion enhance the formation of simple solid-solution phases and submicronic structures with nanoprecipitates in the alloys with multiprincipal elements rather than intermetallic compounds.

Mechanical performance of the AlxCoCrCuFeNi high-entropy alloy system with multiprincipal elements

Abstract: The AlxCoCrCuFeNi alloys with multiprincipal elements (x=the aluminum content in molar ratio, from 0 to 3.0) were synthesized using a well-developed arc-melting and casting method, and their mechanical properties were investigated. These alloys exhibited promising mechanical properties, including excellent elevated-temperature strength and good wear resistance. With the addition of aluminum from x=0 to 3.0, the hardness of the alloys increased from HV 133 to 655, mainly attributed to the increased portion of strong bcc phase to ductile fcc phase, both of which were strengthened by the solid solution of aluminum atoms and the precipitation of nanophases. The alloys exhibited superior high-temperature strengths up to 800 °C, among which the Al0.5CoCrCuFeNi alloy, especially, had enhanced plasticity and a large strain-hardening capacity. Moreover, the wear resistance of these alloys was similar to that of ferrous alloys at the same hardness level, while the alloys with lower hardness exhibited relatively higher resistance because of their large strain-hardening capacity.

Inkjet printing of nanosized silver colloids

Abstract: A water-based conducting ink, composed of well dispersed nano-silver particles, has been successfully inkjet printed using an ordinary commercial printer. The silver colloids with diameter around 50 nm were dispersed in a water and diethylene glycol cosolvent system. The 25 wt% silver ink had a viscosity of about 7.4 cP and surface tension of 33.5 dyn cm(-1) at 20 degrees C, which is appropriate for printing jobs. Continuous and smooth lines of 130 microm width could be printed on ordinary glass substrates using an Epson R210 printer. After baking at 260 degrees C for 3 min, these lines exhibited a resistivity of 1.6 x 10(-5) Omega cm, which could serve as conducting lines for electronic applications.

Charge transport properties of tris(8-hydroxyquinolinato)aluminum(III): why it is an electron transporter.

Abstract: The charge transport properties of mer-tris(8-hydroxyquinolinato)aluminum(III) (mer-Alq), which is the most widely used electron transport material in OLED, were investigated by quantum chemistry calculations within the framework of the charge hopping model and Marcus electron transfer theory. Internal reorganization energies of 0.276 and 0.242 eV were calculated by the DFT-B3LYP method employing a 6-31 G* basis set for the electrons λi(e) and holes λi(h), respectively. The relative distances and orientations of Alq molecules in amorphous film were simulated by those in the β-phase. The intermolecular charge-transfer integrals, Hda(h) and Hda(e), along all 14 hopping pathways were then calculated by the Koopmans Theorem in conjunction with the Hartree−Fock method employing a 6-31 G* basis set as well as by the direct coupling method. The results showed that there were some Hda(e) that were 1 order of magnitude larger than any Hda(h), because hopping pathways with effective overlaps of LUMOs can occur and,...

Robust H/sub /spl infin// filtering for nonlinear stochastic systems

Abstract: This paper describes the robust H/sub /spl infin// filtering analysis and synthesis of nonlinear stochastic systems with state and exogenous disturbance-dependent noise. We assume that the state and measurement are corrupted by stochastic uncertain exogenous disturbance and that the system dynamic is modeled by Ito/spl circ/-type stochastic differential equations. For general nonlinear stochastic systems, the H/sub /spl infin// filter can be obtained by solving second-order nonlinear Hamilton-Jacobi inequalities. When the worst-case disturbance is considered in the design procedure, a mixed H/sub 2//H/sub /spl infin// filtering problem is also solved by minimizing the total estimation error energy. It is found that for a class of special nonlinear stochastic systems, the H/sub /spl infin// filtering design can be given via solving several linear matrix inequalities instead of Hamilton-Jacobi inequalities. A few examples show that the proposed methods are effective.

Hydrothermal synthesis of ZnO microspheres and hexagonal microrods with sheetlike and platelike nanostructures.

Abstract: Unusual ZnO microspheres constructed of interconnected sheetlike nanostructures were prepared by the hydrothermal synthesis approach. These microspheres possess high surface areas (28.9 m2/g) and are amorphous. Trisodium citrate plays a key role in directing the formation of these microstructures. By increasing the reaction time, these microspheres gradually dissolved to form short hexagonal microrods with stacked nanoplate or nanosheet structure. The microrods were also formed under the influence of trisodium citrate. They are crystalline and show a strong (002) X-ray diffraction peak of wurtzite ZnO structure. Both microsphere and microrod samples show near-band-edge emission at ∼385 nm, but only the microrod sample exhibits yellow luminescence at ∼560 nm. Due to their high surface areas, these ZnO microstructures were examined for their ability to photodecompose phenol. The as-prepared samples did not display photocatalytic activity due to possible surface adsorption of solution species. However, micro...

Low-complexity selected mapping schemes for peak-to-average power ratio reduction in OFDM systems

Abstract: Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitter's output signal. The selected mapping (SLM) approach provides good performance for PAPR reduction, but it requires a bank of inverse fast Fourier transforms (IFFTs) to generate a set of candidate transmission signals, and this requirement usually results in high computational complexity. In this paper, we propose a kind of low-complexity conversions to replace the IFFT blocks in the conventional SLM method. Based on the proposed conversions, we develop two novel SLM schemes with much lower complexity than the conventional one; the first method uses only one IFFT block to generate the set of candidate signals, while the second one uses two IFFT blocks. Computer simulation results show that, as compared to the conventional SLM scheme, the first proposed approach has slightly worse PAPR reduction performance and the second proposed one reaches almost the same PAPR reduction performance.

Performance analysis of software reliability growth models with testing-effort and change-point

Abstract: In this paper, a scheme for constructing software reliability growth model based on Non-Homogeneous Poisson Process is proposed. The main focus is to provide a method for software reliability modeling, which considers both testing-effort and change-point. In the vast literature, most researchers assume a constant detection rate per fault in deriving their software reliability models. They suppose that all faults have equal probability of being detected during the software testing process, and the rate remains constant over the intervals between fault occurrences. In reality, the fault detection rate strongly depends on the skill of test teams, program size, and software testability. Therefore, it may not be smooth and can be changed. On the other hand, sometimes we have to detect more additional faults in order to reach the desired reliability objective during testing. It is advisable for project managers to purchase new automated test tool, technology or additional manpower. These approaches can provide a conspicuous improvement in software testing and productivity. In this case, the fault detection rate will be changed during the software development process. Therefore, here we incorporate both generalized logistic testing-effort function and change-point parameter into software reliability modeling. New theorems are proposed and software testing data collected from real application are utilized to illustrate the proposed model. Experimental results show that the proposed framework to incorporate both testing-effort and change-point for SRGM has a fairly accurate prediction capability.

Effects of Web-based Concordancing Instruction on EFL Students' Learning of Verb – Noun Collocations

Abstract: This study investigates the influence of using five web-based practice units on English verb-noun collocations with the design of a web-based Chinese-English bilingual concordancer (keyword retrieval program) on collocation learning. Thirty-two college EFL students participated by taking a pre-test and two post-tests, and responding to a background questionnaire and an evaluation questionnaire. Results indicated that learners made significant collocation improvement immediately after the online practice but regressed later. Yet, the final performance was still better than students' entry level. Different verb-noun collocation types and learners with different prior collocation knowledge were found to be not equally receptive to the practice effects. Both the online instructional units and the concordancer were acceptable to most participants.

Crystalline Forms and Emission Behavior of Poly(9,9-di-n-octyl-2,7-fluorene)

Abstract: By means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) we demonstrate the presence of a previously unspecified modification (α‘) of the crystalline (α) phase in poly(9,9-di-...

Heteroleptic Cyclometalated Iridium(III) Complexes Displaying Blue Phosphorescence in Solution and Solid State at Room Temperature

Abstract: A series of heteroleptic Ir(III) metal complexes 1−3 bearing two N-phenyl-substituted pyrazoles and one 2-pyridyl pyrazole (or triazole) ligands were synthesized and characterized to attain highly efficient, room-temperature blue phosphorescence. The N-phenylpyrazole ligands, dfpzH = 1-(2,4-difluorophenyl)pyrazole, fpzH = 1-(4-fluorophenyl)pyrazole, dfmpzH = 1-(2,4-difluorophenyl)-3,5-dimethylpyrazole, and fmpzH = 1-(4-fluorophenyl)-3,5-dimethylpyrazole, show a similar reaction pattern with respect to the typical cyclometalated (C∧N) chelate, which utilizes its ortho-substituted phenyl segment to link with the central Ir(III) atom, while the second 2-pyridylpyrazole (or triazole) ligand, namely, fppzH = 3-(trifluoromethyl)-5-(2-pyridyl)pyrazole, fptzH = 3-(trifluoromethyl)-5-(2-pyridyl)triazole, and hptzH = 3-(heptafluoropropyl)-5-(2-pyridyl)triazole, undergoes typical anionic (N∧N) chelation to complete the octahedral framework. X-ray structural analyses on complexes [(dfpz)2Ir(fppz)] (1a) and [(fmpz)2Ir...

Computerized tomography and C-Scan for measuring delamination in the drilling of composite materials using various drills

Abstract: Whilst drilling is the most frequently employed operation of secondary machining for structure joining, delamination is a very serious defect during drilling of fiber-reinforced composite materials,. The evaluation of the delamination damage in the material is important but rather difficult, particularly for carbon fiber-based composites, because their colour makes visual inspection difficult. A special technique using medical equipment for computerized tomography is presented in this paper. It is compared to techniques using ultrasonic and is demonstrated as a feasible and an effective tool for the evaluation of drilling-induced delamination.

Synthesis of Branched Gold Nanocrystals by a Seeding Growth Approach

Abstract: Synthesis of branched gold nanocrystals by a seeding growth approach is described. In this process, HAuCl4 aqueous solution was supplied stepwise to grow the gold seeds (∼2.5 nm) into larger nanoparticles with a highly faceted particle structure (∼15−20 nm in diameter). Sodium dodecyl sulfate (SDS) served as a capping agent to facilitate the formation of highly faceted nanoparticles, and ascorbic acid was used as a weak reducing agent. The highly faceted nanoparticles then transformed into branched nanocrystals (∼40 nm in length) by further addition of the SDS−HAuCl4 solution and ascorbic acid for particle growth. The branched nanocrystals show bipod, tripod, tetrapod, and pentapod structures and are composed of mainly (111) lattice planes. These multipods appear to grow along the twin boundaries of the initially formed highly faceted gold nanoparticles, as the twin boundaries on the pods originate from the centers of the branched nanocrystals. The concentration of ascorbate ions in the solution was found...

A linear maximum torque per ampere control for IPMSM drives over full-speed range

Abstract: In this paper, a linear torque control strategy is first proposed for interior permanent magnet synchronous motor drives to fully utilize the reluctance torque and simplify the controller design. The proposed linear torque control strategy also extends the existing maximum torque per ampere control in the constant torque limit region up to the entire field-weakening region. It is found that in an intermediate speed region, called partial field-weakening region, the existing maximum torque per ampere control can still be applied under lighter load condition. In addition, the proposed control can also achieve the objective of minimum copper loss (i.e., maximum torque per ampere) for the entire speed range. Sound theoretical basis is given in the context. Moreover, an adaptive limiter is proposed for efficiently implementing the proposed control strategy over the entire speed range. Finally, a prototype is also constructed by using a fixed-point DSP TMS320F240 and some experimental results are given to verify the validity of the proposed control strategy.

Thin film plate phase change RAM circuit and manufacturing method

Abstract: A memory device comprising a access circuits, an electrode layer over the access circuits, an array of phase change memory bridges over the electrode layer, and a plurality of bit lines over the array of phase change memory bridges. The electrode layer includes electrode pairs. Electrode pairs include a first electrode having a top side, a second electrode having a top side and an insulating member between the first electrode and the second electrode. A bridge of memory material crosses the insulating member, and defines an inter-electrode path between the first and second electrodes across the insulating member.