Integrated approach for assembly tolerance analysis

In mechanical design, tolerance assignment is a critical but complex task since the designer will not only have to consider the associated cost to achieve a certain tolerance level, but also the cost due to failure in assembling task. These associated tolerance costs as well as the failure rate are fuzzy in nature. This paper presents an integrated approach to incorporate manufacturing costs of certain tolerance specifications into design stages for automatic tolerance assignment and design. Tolerance design is interdisciplinary in nature and is characterized by a highly uncertain environment. In recent years, fuzzy logic has appeared as a credible alternative for tolerance design. A fuzzy based tolerance representation scheme is presented to model three dimensional (3D) tolerances. With this representation, relative assembly tolerance constraints can be expressed. A fuzzy tolerance generation and assignment process for assembly is discussed. Fuzzy tolerance equations are generated for 3D assembly considerations. Manufacturing process information, along with uncertain cost information modelled in fuzzy terms, is added to the system to arrive at a cost-optimal tolerance assignment.     

Accurate calculation of the pressure and temperature of water, steam, and ice: Formulation for CFD

An accurate approach is proposed for calculating the thermodynamic properties of water in three states: liquid, steam and ice, and the transitional states among them. The formulation is expressed in terms of quantities that are naturally used in Computational Fluid Dynamics (CFD), namely the specific volume (v) and specific internal energy (u), through the use of Gibbs free energy. The Gibbs free energy formula proposed by IAPWS, formulated as a function of pressure and temperature, is used as a basis in our calculations. The Jacobian matrix resulting from the transformation between sets of variables (p, T) and (v, u) are derived for each phase; the Newton-Raphson method is used to iteratively solve the nonlinear equations. Numerical calculations have been carried out for the entire phase diagram covering all three phases. The numerical results are compared with the original data of IAPWS and the associated errors are analyzed. It is confirmed that the pressure and temperature are accurately calculated, with largest relative error on the order of 10⁻⁷ in the ice phase. Hence, other thermodynamic properties are also obtained within the same level of accuracy. The method proposed in this paper for calculating pressure and temperature, variables needed in CFD, is reliable and can be applied to the numerical simulation of multiphase flows, including phase changes.     

Effects of modified-process on the microstructure,internal bias field,and activation energy in CuO-doped NKN ceramics

In this study, (Na_0.5K_0.5)NbO₃ + xCuO (NKNCx, where x = 0–1 mol%) were separately prepared using the two-step calcination process (BO method) and a conventional mixed oxide method (MO method). The microstructure of NKNCx ceramics prepared using the MO method exhibited obviously inhomogeneous microstructure. In contrast, the BO method improved the compositional homogeneity as well as the electrical properties. A high Q_m value of 2100 was obtained for NKNCx ceramics prepared using the BO method. The ceramics prepared using the BO method exhibited the formation of more oxygen vacancies, resulting in an increase in the internal bias field. The value for the activation energy of the samples supports the presence of oxygen vacancies. The bulk density, dielectric loss, k_p, Q_m, d₃₃ and ?₃₃^T/?₀ of the NKNCx ceramics prepared using the BO method were 4.488 g/cm³, 0.15%, 41.5%, 2100, 95 pC/N and 280, respectively.     

Modeling Government Subsidies and Project Risk for Financially Non-Viable Build-Operate-Transfer (BOT) Projects

Abstract:

Governments encourage private sector participation in building infrastructure through Build-Operate-Transfer (BOT) agreements. Large projects may be financially non-viable despite their net economic benefits for the host society. Host governments might subsidize initial private investments to create financial feasibility. Small-scale subsidies might not sufficiently reduce project risks to attract private investment; however, large percentage subsidies might result in loose profit structures, discouraging the pursuit of efficiency. This article applies Monte Carlo techniques to data from the Taiwanese West Corridor High-Speed Rail Project to assess the subsidy-risk trade-off relationship. The results provide guidance for public-private negotiations.     

Integration-based approach to evaluate the sub-threshold slope of MOSFETs

We propose the use of simple integration-based methods to extract the sub-threshold current slope factor of MOSFETs as an alternative to traditional extraction processes based on differentiating the sub-threshold transfer characteristics. The purpose is to lessen the effects of error and noise often present in the measurement of very small currents, which are aggravated by the differentiation processes. The effectiveness of the proposed methods is compared to the traditional Transconductance-to-Current Ratio method using the measured transfer characteristics of two experimental devices as application examples.     

A COMPUTATION FOR THE BOUNDARY VALUE PROBLEM OF A DOUBLE-TUBE HEAT EXCHANGER

The boundary value problems of u low Piélet number flow in a double-tube heat exchanger for an arbitrary velocity profile are analyzed by linear operator methods. The induced eigen equation, of which the eigenvalues are combined in the final boundary condition, is solved by an approximation method. A computational algorithm is then proposed for computing the eigenvalues and expansion coefficients of the solution by an efficient recursive formula. The correctness of the proposed algorithm is verified by Par-srvol's relation and demonstrated by three examples.     

Fuel sensor-less control of a liquid feed fuel cell under dynamic loading conditions for portable power sources (I)

This work presents a novel fuel sensor-less control scheme for a liquid feed fuel cell system that operates under dynamic loading conditions and is suitable for portable power sources. The proposed technique utilizes the operating characteristics of a fuel cell, such as voltage, current and power, to control the supply of liquid fuel and regulate its concentration. As verified by systematic experiments, this scheme controls effectively the supply of fuel under dynamic loading conditions and pushes the system toward higher power output. The primary features and advantages of sensor-less fuel control are as follows. When the fuel concentration sensor is excluded, the cost of a liquid feed fuel cell system is decreased and system volume and weight are reduced, thereby increasing specific energy density and design simplicity, and shortening system response time. Notably, temperature compensation for measurement data is unnecessary. With a decreased number of components, the control scheme improves durability and reliability of liquid feed fuel cells. These advantages will help commercialization of liquid feed fuel cells as portable power sources.     

Kinetics investigation of antioxidant capacity and total phenols of low‐temperature steeping Bi Luo Chun green tea

Traditionally, tea is steeped in boiled water in Taiwan. In this study, Bi Luo Chun (250 μg mL^?1) steeped at 4, 22, 30, 40 and 50 °C reached the saturation of 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging capacity at the time of 15, 8, 2, 0.17 (10 s) and 0.17 min (10 s), respectively. The result indicated that tea steeped in cold water (under 22 °C) still can reach a saturation of antioxidant capacity in 15 min. However, the initial scavenging rate (% min^?1) was quick and decreased with time at all steeping temperatures (r: ?0.98 to ?1.00). Total phenols and the DPPH scavenging capacity of Bi Luo Chun showed excellent correlation with time. However, the plot of DPPH scavenging capacity vs. total phenols was not always correlated. The result indicated that polyphenol infusion at different times may have a different DPPH scavenging capacity.