Mathematical investigation of interfacial property in fiber reinforced model composites

In the current paper, we have investigated the dependence of the effective elastic properties of a composite material on the fiber/matrix interface elastic property. The model composite consists of a single cylindrical fiber embedded in a concentric cylindrical matrix material. A three dimensional mathematical method has been developed connecting the interface properties with the effective axial Young’s modulus of the composite structure. Special effort has been devoted to decode information about the quality of the interface by exploiting the information provided by the elastic effective parameters. In particular, the effective modulus vs. stiffness coefficient curves have been generated for Ti/SiC composites. The aforementioned curves reveal the characteristics of the transition from the regime of perfect interface to the realm of complete debonding.     

Chemisorption,physisorption and hysteresis during hydrogen storage in carbon nanotubes

The question of chemisorption versus physisorption during hydrogen storage in carbon nanotubes (CNTs) is addressed experimentally. We utilize a powerful measurement technique based on a magnetic suspension balance coupled with a residual gas analyzer, and report new data for hydrogen sorption at pressures of up to 100 bar at 25 °C. The measured sorption capacity is less than 0.2 wt.%, and there is hysteresis in the sorption isotherms when multi-walled CNTs are exposed to hydrogen after pretreatment at elevated temperatures. The cause of the hysteresis is then studied, and is shown to be due to a combination of weak sorption – physisorption – and strong sorption – chemisorption – in the CNTs. Analysis of the experimental data enables us to calculate separately the individual hydrogen physisorption and chemisorption isotherms in CNTs that, to our knowledge, are reported for the first time here. The maximum measured hydrogen physisorption and chemisorption are 0.13 wt.% and 0.058 wt.%, respectively.     

Architecture Takes Time

Though condensed between the stages of design and completion, the conventional process of designing a building is time consuming, involving various stakeholders, planning processes and a wide team of consultants and contractors. What happens, though, if the time period of an architect's involvement is expanded? How might a more process-orientated approach shift the role of the architect? Tobias Armborst, Daniel D'Oca and Georgeen Theodore , principals of Interboro Partners in New York, describe how they have developed projects that have sought opportunities in expanding the timescale and remit of traditional practice.     

Innovation in Homebuilding and the Future of Housing

Problem: The future of housing depends in part on innovation by homebuilders. Planners should know how to influence innovation in homebuilding in order to promote innovative practices that conserve the environment, improve quality, and reduce costs.

Purpose: This article explains challenges involved in innovation in home building, as well as providing planners with strategies to influence innovation in the industry.

Methods: I review the literature and identify sources of resistance to or acceptance of innovation in home building. I also report the results of two national surveys of innovation adoption and use regression analysis to test variables likely to inhibit or promote innovation.

Results and conclusions: Small builders receptive to innovation are likely to be led by a technology champion and to build custom homes for a relatively affluent and informed clientele. These firms provide a likely audience for technology innovations that require more upfront investment, as with some green building products, but can be marketed as highly innovative to homebuyers interested in higher performance in energy efficiency, sustainability or durability. In order to impact a larger portion of the housing market, large production builders should be the target for innovations that contribute to affordability in entry-level homes or to energy efficiency, sustainability and durability in higher priced houses.

Takeaway for practice: Planners aiming to encourage innovation in homebuilding should craft strategies that recognize the opportunities, the structure of the industry, and the factors influencing innovation adoption. Local builders with owners who champion innovation are good targets for demonstration programs that involve custom homes. Larger production builders will want strategies that can be replicated in multiple market areas, and are likely to avoid localities whose codes and regulations would require them to change their production models.

Research support: This research was partially funded by the U. S. Department of Housing and Urban Development under the Partnership to Advance Technology in Housing (PATH) program.     

Directional neighbor discovery in mmWave wireless networks

The directional neighbor discovery problem, i.e., spatial rendezvous, is a fundamental problem in millimeter wave (mmWave) wireless networks, where directional transmissions are used to overcome the high attenuation. The challenge is how to let the transmitter and the receiver beams meet in space under deafness caused by directional transmission and reception, where no control channel, prior information, and coordination are available. In this paper, we present a Hunting-based Directional Neighbor Discovery (HDND) scheme for ad hoc mmWave networks, where a node follows a unique sequence to determine its transmission or reception mode, and continuously rotates its directional beam to scan the neighborhood for other mmWave nodes. Through a rigorous analysis, we derive the conditions for ensured neighbor discovery, as well as a bound for the worst-case discovery time and the impact of sidelobes. We validate the analysis with extensive simulations and demonstrate the superior performance of the proposed scheme over several baseline schemes.