Fabrication and characterization of porous Ti–7.5Mo alloy scaffolds for biomedical applications

Porous titanium and titanium alloys are promising scaffolds for bone tissue engineering, since they have the potential to provide new bone tissue ingrowth abilities and low elastic modulus to match that of natural bone. In the present study, porous Ti–7.5Mo alloy scaffolds with various porosities from 30 to 75 % were successfully prepared through a space-holder sintering method. The yield strength and elastic modulus of a Ti–7.5Mo scaffold with a porosity of 50 % are 127 MPa and 4.2 GPa, respectively, being relatively comparable to the reported mechanical properties of natural bone. In addition, the porous Ti–7.5Mo alloy exhibited improved apatite-forming abilities after pretreatment (with NaOH or NaOH + water) and subsequent immersion in simulated body fluid (SBF) at 37 °C. After soaking in an SBF solution for 21 days, a dense apatite layer covered the inner and outer surfaces of the pretreated porous Ti–7.5Mo substrates, thereby providing favorable bioactive conditions for bone bonding and growth. The preliminary cell culturing result revealed that the porous Ti–7.5Mo alloy supported cell attachment.     

Influence of oxygen partial pressure on structural, electrical, and optical properties of Al-doped ZnO film prepared by the ion beam co-sputtering method

Aluminum doped zinc oxide (AZO) films were prepared at room temperature by ion beam co-sputtering system under various oxygen partial pressures. The structural, electrical, and optical properties of the films were studied by XRD, XPS, Hall measurement, and spectrometer. The AZO film with low resistivity, 7.8 × 10^?4 Ω cm, and high transparency, ~80 %, was obtained at the optimum oxygen partial pressure of 1.3 × 10^?4 Torr and the intense (002) diffraction peak was observed simultaneously. Different optical band gaps observed in the films prepared under various oxygen partial pressures are closely related to the carrier concentrations in the films. Three O_1s components were applied to fit the XPS O_1s spectra. They consist of adsorbed oxygen species, oxygen in O-Zn bonds surrounded by oxygen vacancies, and oxygen in the O-Zn bonds. Two components, Zn in Zn–O bonds and Zn with higher than +2 oxidation states, were used to fit Zn_2p3/2 spectra. It was found that the increase of film’s resistivity which may result from the drops in the oxygen vacancy, Zn interstitial, carrier concentration, and grain size. No apparent transmission change of the film in the visible light region as a function of oxygen partial pressure was detected.     

Supply chain management practices as a mediator of the relationship between operations capability and firm performance

The current study uses mediated regression analysis and structural equation modelling to test the proposition that supply chain management practices mediate the relationship between operations capability and firm performance. Operations capability is defined in terms of a firm's new product design and development, total quality management and just-in-time capabilities. Results support the research model and also suggest the existence of a direct relationship between operations capability and performance.     

Transport of ions through a cylindrical membrane: Effect of radius

Abstract

The performance of a cylindrical ion‐selective membrane of arbitrary radius is investigated theoretically. In particular, the effect of the radius of the membrane on its current efficiency is examined without assuming local electroneutrality and Donnan equilibrium. Two types of fixed charge distribution are considered, namely, linear and sinusoidal. The results of numerical simulation reveal that the boundary condition at the axis of a membrane should be assumed appropriately. We show that if the inner radius of a membrane is smaller than its thickness, assuming bulk conditions at the membrane axis is inadequate. Also, the potential drop across a membrane will change its sign, which is disadvantageous to the transport of ions.     

Modeling and fabrication of a piezoelectric vibration‐induced micro power generator

Abstract

In this paper, theoretical and experimental study on a piezoelectric vibration‐induced micro power generator that can convert mechanical vibration energy into electrical energy is presented. The mechanical‐electrical energy conversion mechanism is a voltage between two capacitors, which belong to the mechanical and the piezoelectric equivalent circuits, respectively. To verify the theoretical analysis, two clusters of transducer structures are fabricated. Piezoelectric lead zirconate titanate (PZT) material is chosen to make the energy conversion transducer. The desired shape of the piezoelectric generator with its resonance frequency in accordance with the ambient vibration source is designed by finite element analysis (FEA).

Experimental results show that the maximum output voltages are generated at the first mode resonance frequencies of the structure. The overall conversion efficiency is measured to be 33%. The experimental results coincide with the theoretical analysis.     

Input Estimation Method in the Use of Electronic Device Temperature Prediction and Heat Flux Inverse Estimation

The input estimation method (IEM) is proposed in this research to estimate the real-time time-variant core heat flux of electronic components. The IEM is an on-line real-time estimation method, which combines the Kalman filter mechanism and recursive least-square estimation (RLSE). On the premise that there exists both system processing error and measurement error, using temperature measurements measured from the exterior of the device package, the core time-variant heat flux of the device can be precisely estimated inversely.     

A 2-D INVERSE METHOD FOR SIMULTANEOUS ESTIMATION OF THE INLET TEMPERATURE AND WALL HEAT FLUX IN A LAMINAR CIRCULAR DUCT FLOW

A two-dimensional inverse analysis is presented for the estimation of the inlet temperature of the fluid flow and wall heat flux in a thermally developing hydrodynamically developed laminar flow in a duct. The inverse analysis is based on the temperature reading located at a stream inside the duct at several different points. At the beginning of the study, finite difference methods are employed to discretize the problem, and then a linear inverse model is constructed to identify the unknown conditions. The present approach is to rearrange the matrix forms of the differential governing equation and estimate the inlet temperature of the fluid and unknown surface conditions of the duct. The linear least squares method is adopted to find the solution. The advantage of applying this method in inverse analysis is that no prior information is needed on the functional form of the unknown quantities, no initial guess is required, and the number of iterations in the calculation process is limited to one. The effects of sensor position, magnitude of measurement error, and number of measurements on the accuracy of estimates are examined. The results show that the preferred position of the sensor is closer to the inlet region and only few measuring points are sufficient to estimate the wall heat flux and inlet temperatures of the fluid when the measurement errors are neglected. When the measurement errors an considered, more measuring points are needed in order to increase the congruence of the estimated results to exact solutions.     

Effect of Aluminum Content on Microstructure and Mechanical Properties of Al x CoCrFeMo0.5Ni High-Entropy Alloys

High-entropy alloys Al _x CoCrFeMo_0.5Ni with varied Al contents (x = 0, 0.5, 1.0, 1.5, and 2.0) have been designed based on the Al _x CoCrCuFeNi system to improve mechanical properties for room and elevated temperatures. They have been investigated for microstructure and mechanical properties. As the aluminum content increases, the as-cast structure evolves from face-centered cubic dendrite + minor σ-phase interdendrite at x = 0 to B2 dendrite with body-centered cubic (bcc) precipitates + bcc interdendrite with B2 precipitates at x = 2.0. This confirms the strong bcc-forming tendency of Al. The room-temperature Vickers hardness starts from the lowest, HV 220, at x = 0, attains to the maximum, HV 720, at x = 1.0, and then decreases to HV 615 at x = 2.0. Compared with the base alloy system, the current alloy system has a superior combination of hardness and fracture toughness. In addition, Al _x CoCrFeMo_0.5Ni alloys except x = 0 display a higher hot hardness level than those of Ni-based superalloys, including In 718 and In 718 H, up to 1273 K and show great potential in high-temperature applications.     

Phase Diagrams of High-Entropy Alloy System Al-Co-Cr-Fe-Mo-Ni

The high-entropy alloy system Al-Co-Cr-Fe-Mo-Ni has been previously designed based on the Al _x CoCrCuFeNi system and was demonstrated to have great improvements in toughness at high hardness level and in softening resistance at elevated temperatures. For this promising system, it is important to have phase diagrams for further efficient alloy design and research. The current study combines the results from scanning electron microscopy, transmission electron microscopy, room-temperature and high-temperature x-ray diffractometry, and differential thermal analysis to construct approximate phase diagrams by varying the content of each composing element. Thermodynamic calculation in considering both mixing enthalpy and entropy was also used to justify the simple phase fields in these phase diagrams.     

ESCSD – expert system for control system design

Abstract

The purpose of this paper is to design an expert system for control system design. The architecture of ESCSD is designed and implemented using CLIPS, which is an expert system building tool. The achievements of ESCSD are extracting the heuristics of design approaches, building design methods into knowledge‐bases, partitioning of knowledge‐bases, and providing explanation facilities. The user interface of ESCSD is icon‐based with pop‐up menus for user selections. We have demonstrated in this paper that this kind of user interface is better than previous similar systems, where complex dialogues are required. Also, due to the flexible partitions of the knowledge‐bases, ESCSD can be implemented successfully on the IBM PC with a limited 640K‐byte MSDOS environment. It is further explained that, regardless of the computer size, the knowledge‐bases must be partitioned into the smallest entities to allow future expansion. Several design examples are fully illustrated to clarify the advantages of using the expert system to design control systems.