Interfacial reactions of Sn–58Bi and Sn–0.7Cu lead-free solders with Alloy 42 substrate

Eutectic Sn–58 wt%Bi (SB) and Sn–0.7 wt%Cu (SC) lead-free solders reacting with Alloy 42 substrates were investigated at 240, 270, 300, and 330 °C for various reaction times. The FeSn₂ phase was the only phase formed at the solder/Alloy 42 interface for all couples. However, this FeSn₂ phase had two different microstructures. The intermetallic compound (IMC) morphology near the solder/Alloy 42 interface was dense with a tiny microstructure after reflowing at 240 °C. Massive spalling FeSn₂ phases with large and platy grain were observed in the solder matrix. When the reflow temperature was increased the IMC morphology assumed bulk or cylindrical shape with no spalling IMCs observed at the solder/Alloy 42 interface. The IMC thickness increased with increasing reaction temperature and time. Both SB/Alloy 42 and SC/Alloy 42 couples presented a diffusion controlled growth mechanism in. The activation energies for SB/Alloy 42 and SC/Alloy 42 couples were 86.2 and 103.4 kJ/mol, respectively.     

Networking with cooperative communications: holistic design and realistic evaluation - [Accepted from open call]

Cooperative communications fundamentally changes the abstraction of a wireless link and offers significant potential advantages for wireless networks. However, such technologies are evaluated with idealized scenarios where many control costs are assumed to be negligible. Moreover, even if these costs appear small in simple network scenarios, they increase significantly with the size and traffic level of the network, requiring careful evaluation, or even innovative design, of cooperative protocols to ensure their usefulness in realistic networks. This article describes a realistic evaluation of cooperative communications in a networking context. Insights obtained from this evaluation help guide work on cooperative communications toward practical and potentially beneficial protocols.     

Analysis of composite finite wedges under anti-plane shear

Problems of composite finite wedges under anti-plane shear applied on a circular arc are analyzed in this study. The considered conditions of radial edges are free–free, free–fixed, and fixed–fixed. A procedure that uses the finite Mellin transform and the Laplace transform is developed to solve these problems. Explicit solutions for displacement and stress fields are derived. Stress intensity factors (SIFs) of composite circular shafts with an interfacial edge crack are extracted from the derived stress fields, and the distributions for various loading angles are presented and discussed. It was found that if the loading angles are the same, free–free and fixed–fixed edge problems can be degenerated into single material problems. Uniform stresses were found along the interface in free–free and fixed–fixed edge problems. Solutions of a general loading case deduced from the derived results compare well with those obtained from finite element (FE) analyses.     

A tunable S-band erbium-doped fiber ring laser

In this paper, we experimentally investigate and demonstrate an S-band erbium-doped fiber (EDF) ring laser based on an erbium-doped silica fiber and 980-nm pumping laser. Widely tunable range from 1480 to 1522 nm, and the sidemode suppression ratio (SMSR) of >30 dB/0.1 nm and the output power of >-2 dBm in the operating range from 1482 nm to 1517 nm have been achieved for this ring laser. Under the constant power control, the output power variation less than /spl plusmn/0.05 dB can also be accomplished over the tuning range from 1482 to 1517 nm. This S-band EDF ring laser is promising for the future S-band applications.     

Querying time indexed information in mobile Ad hoc networks

Time indexed information refers to information whose instance producing time is used as the search key for its access. One common scenario of querying time indexed information is to discover the information instance whose producing time is the closest to a given queried time. However, in the context of mobile ad hoc networks (MANETs), lack of infrastructure support, node mobility, and potential packet loss in wireless communications make querying time indexed information a challenging task. This paper describes a Self-Organizing Mechanism for querying Time indexed Information in MANETs, termed SOMTI. Using SOMTI, each instance producer h discovers routes to a set of instance producers whose instance producing times are the closest to a set of computed time points both before and after h’s instance producing time. These routes form a web of search indices, which allow queries received by any instance producer to be forwarded in the manner of n-ary search for the instance producer whose instance producing time is the closest to the queried time. Both mathematical analysis and simulation study show that SOMTI is scalable with the number of nodes and the query producing rate. In addition, simulations results demonstrate that the goodness, in terms of the closeness to the queried time, of the discovered instance is always better than competing approaches under various node mobility speeds, query generation rates, and the number of nodes in the network, which demonstrates the effectiveness of SOMTI.     

Computer-aided process planning for NC tool path generation of complex shoe molds

This paper presents a computer aided process planning (CAPP) system for numerical control tool path generation of complex shoe molds. This CAPP system includes both the automation of auxiliary boundary curve generation and machining strategies. The automation of auxiliary boundary curve generation and machining strategies make tool path generation more accurately and efficiently. Traditional shoe mold making is a very tedious process. Even with the utilization of computer-aided design and computer-aided manufacturing (CAD/CAM), the CAM process requires long hours of tool path programming and debugging. It would also take a long time to calculate (sometimes several hours) the tool path for complex athletic footwear. In order to reduce the tool path editing and programming time, this paper proposes the use of CAPP to reduce processing time and increase efficiency. It is difficult, if not impossible, to develop a generic CAPP system that can generate a process plan to solve general production problems. However, it is quite possible to capture the domain knowledge of a certain production process and embed that knowledge into a CAPP system. We prove, by using such a system, that a very complicated process planning problem can be overcome by a knowledge-based CAPP approach. With such an approach, the traditional manufacturing process of shoe molds can be converted to an automatic manufacturing process with the CAPP system. In fact, shoe molds for real production have been created using the developed CAPP system, demonstrating the effectiveness of this approach. In this paper, we show that several complex and different shoe molds and their machining strategies were automatically planned by the proposed CAPP system. The result of a comparison between the CAPP system with the traditional approach is presented and discussed.     

Nanomechanics of streptavidin hubs for molecular materials

A new strategy is reported for creating protein-based nanomaterials by genetically fusing large polypeptides to monomeric streptavidin and exploiting the propensity of streptavidin monomers(SM) to self-assemble into stable tetramers. We have characterized the mechanical properties of streptavidin-linked structures and measured, for the first time, the mechanical strength of streptavidin tetramers themselves. Using streptavidin tetramers as molecular hubs offers a unique opportunity to create a variety of well-defined, self-assembled protein-based (nano)materials with unusual mechanical properties.     

Metal deposition on flexible membrane through the combination of localized electrochemical deposition and electroless plating

In this paper, we combined localized electrochemical deposition and electroless plating process for fabricating the metal pattern with the large area on flexible membrane. The pattern of the anode plate can rapidly transfer to the cathode membrane by localized electrochemical deposition. The thickness of the pattern can be increased by electroless plating process. The width of the mask pattern was close to the width of the final pattern. The anode plate can be used over fifty times for this process until the pattern was electrolyzed completely. This method provides a possible low cost approach to fabricate high metal structures on the flexible substrate with large area. It may have the potential to be applied in the fabrication of e-paper, flexible printed circuit and eventually adapted to roll-to-roll process.     

Vancomycin–chitosan composite deposited on post porous hydroxyapatite coated Ti6Al4V implant for drug controlled release

Through the hydrogen bonds and the deprotonation, the vancomycin–chitosan composite has been originally deposited on Ti4Al4V by electrochemical technology. However, the rapid destruction of the hydrogen bonding between them by polar water molecules during immersion tests revealed 80% drug burst in a few hours. In this study, the post porous hydroxyapatite (HA) coated Ti4Al4V is prepared for the subsequent electrolytic deposition of vancomycin–chitosan composite to control the drug release. As expected, the initial burst is reduced to 55%, followed by a steady release about 20% from day 1 to day 5 and a slower release of the retained 25% after day 6, resulting in bacterial inhibition zone diameter of 30 mm which can last for more than a month in antibacterial tests, compared with the coated specimen without HA gradually loosing inhibition zone after 21 days. Besides, the cell culture indicates that the vancomycin–chitosan/HA composite coated has enhanced the proliferation, the differentiation and the mineralization of the osteoblast-like cell. In general, it is helpful for the osteointegration on permanent implants. Consistently, it effectively provides the prophylaxis and therapy of osteomyelitis according to the results of the rabbit infection animal model.