Materials Sliding Wear Model Based on Energy Dissipation

A mathematical model is developed to correlate the volumetric wear of materials with the dissipation energy in sliding contacts. In the analysis, the wear of contacting materials originating from the energy loss due to friction process in the contact is studied. Two mechanisms responsible for energy loss at contact are considered. The first is the amount of energy spent to import plastic deformation and the second is the elastic energy of the particulate. The energy loss due to elastic and plastic deformation is calculated. The statistical loss of energy is calculated for two rough surfaces by the assumption that there is negligible change in the statistical parameters of the surface during wear. The model can be useful to predict the service lifetime of components and eventually structures. The results showed that the amount of dissipated energy and the volumetric loss increased with increasing normal load. Also, changing the normal load changed the rate of energy dissipation per unit sliding distance.     

iFrag: interference-aware frame fragmentation scheme for wireless sensor networks

Reliable data transmission is a fundamental challenge in resource-constrained wireless sensor networks. In current implementations, a single bit error requires retransmitting the entire frame. This incurs extra processing overhead and power consumption, especially for large frames. Frame fragmentation into small blocks with individual error detection codes can reduce the unnecessary retransmission of the correctly received blocks. The optimal block size, however, varies based on the wireless channel conditions. In this paper, we propose an interference-aware frame fragmentation scheme called iFrag. iFrag dynamically adjusts the number of blocks inside a frame based on current channel conditions, and effectively addresses all challenges associated with such dynamic partitioning. Through analytical and experimental results, we show that iFrag achieves up to \(3\times\) improvement in goodput when the channel is noisy, while reducing the delay by 12 % compared to other static fragmentation approaches. On average, it shows a 13 % gain in goodput across all channel conditions used in our experiments. Our testbed results also show that iFrag lowers the energy consumed per useful bit by 60 %, as improved data transmission reliability reduces the number of frame retransmissions which increases the motes energy efficiency.     

In-vitro anticancer and antimicrobial activities of PLGA/silver nanofiber composites prepared by electrospinning

In the present work, a series of 0, 1 and 7 wt% silver nano-particles (Ag NPs) incorporated poly lactic-co-glycolic acid (PLGA) nano-fibers were synthesized by the electrospinning process. The PLGA/Ag nano-fibers sheets were characterized using SEM, TEM and DSC analyses. The three synthesized PLGA/silver nano-fiber composites were screened for anticancer activity against liver cancer cell line using MTT and LDH assays. The anticancer activity of PLGA nano-fibers showed a remarkable improvement due to increasing the concentration of the Ag NPs. In addition to the given result, PLGA nano-fibers did not show any cytotoxic effect. However, PLGA nano-fibers that contain 1 % nano silver showed anticancer activity of 8.8 %, through increasing the concentration of the nano silver to 7 % onto PLGA nano-fibers, the anticancer activity was enhanced to a 67.6 %. Furthermore, the antibacterial activities of these three nano-fibers, against the five bacteria strains namely; E.coli o157:H7 ATCC 51659, Staphylococcus aureus ATCC 13565, Bacillus cereus EMCC 1080, Listeria monocytogenes EMCC 1875 and Salmonella typhimurium ATCC25566 using the disc diffusion method, were evaluated. Sample with an enhanced inhibitory effect was PLGA/Ag NPs (7 %) which inhibited all strains (inhibition zone diameter 10 mm); PLGA/Ag NPs (1 %) sample inhibited only one strain (B. cereus) with zone diameter 8 mm. The PLGA nano-fiber sample has not shown any antimicrobial activity. Based on the anticancer as well as the antimicrobial results in this study, it can be postulated that: PLGA nanofibers containing 7 % nano silver are suitable as anticancer- and antibiotic-drug delivery systems, as they will increase the anticancer as well as the antibiotic drug potency without cytotoxicity effect on the normal cells. These findings also suggest that Ag NPs, of the size (5–10 nm) evaluated in the present study, are appropriate for therapeutic application from a safety standpoint.     

Modeling of the mechanical behavior of polyethylene/polypropylene blends using artificial neural networks

Polymers possess good thermal and electrical insulation properties, low density, and high resistance to chemicals, thus they have been widely used in industrial applications. Nevertheless, they are mechanically weaker and exhibit lower strength and stiffness than metals. However, their mechanical behavior can be enhanced through different techniques such as blending. Accurate estimation of the mechanical behavior is essential in structural design. Since the process of experimental measurements of a blend’s properties can be costly and time consuming, this paper explores the potential use of artificial neural networks (ANNs) in the field of polymer characterization. It addresses the use of ANNs in modeling the tensile curves and mechanical properties of two commonly utilized polymers (polyethylene PE and polypropylene PP) and their blends. Blends of different proportions have been considered. The experimentally acquired data is used to train and test the neural network’s performance. The key system inputs for the ANN modeler are blend ratio and percent strain, and the system output is the stress. The ANN-predicted outputs were compared and verified against the experimental date. The study indicates that a multilayered ANN can simulate the effect of the blending ratio on the mechanical behavior and properties to a high degree of accuracy. It also demonstrates that ANN approach is an effective tool that can be adopted to reduce cost and time of the experimental work. Moreover, the results show that ANNs demonstrate promising potential in the area of polymer characterization.     

FAST TCP over optical burst switched networks: Modeling and stability analysis

FAST TCP is important for promoting data-intensive applications since it can cleverly react to both packet loss and delay for detecting network congestion. This paper provides a continuous time model and extensive stability analysis of FAST TCP congestion-control mechanism in bufferless Optical Burst Switched Networks (OBS). The paper first shows that random burst contentions are essential to stabilize the network, but cause throughput degradation in FAST TCP flows when a burst with all the packets from a single round is dropped. Second, it shows that FAST TCP is vulnerable to burst delay and fails to detect network congestion due to the little variation of round-trip time, thus unstable. Finally it shows that introducing extra delays by implementing burst retransmission stabilizes FAST TCP over OBS. The paper proves that FAST TCP is not stable over barebone OBS. However, it is locally, exponentially, and asymptotically stable over OBS with burst retransmission.     

Microstructural development in cast and aged Ni–Al–Cr-based alloys derived from the B2 type β-NiAl structure

The formation of intermetallic compounds consisting of nickel-rich B2-type NiAl (-phase) ductilized by two-phase A1 ()/L12 () regions provides the possibility of combining ductility and high-temperature performance. Similar microstructures can also form the basis of high-temperature shape memory alloys, due to martensitic transformation of the -phase to an L10-type product. One route by which –/ microstructures can be produced involves the use of chromium as a -stabilizer. However, microstructural development in such a case is complicated by the formation of -Cr precipitates.This paper examines microstructural development and stability in cast Ni-25 at % Al-14 at % Cr, Ni-29 at % Al-22 at % Cr and Ni-27 at % Al-8 at % Cr alloys, together with a more complex material, namely, Ni-20 at % Al-13 at % Co-9 at % Cr-4 at % Ti-1 at % Mo-1 at % V. Both the as-cast condition and samples aged at 850 and 1100 °C for 140 h are examined using transmission electron microscopy. The paper discusses the formation of L10 martensite, intradendritic ', interdendritic /' and -Cr precipitation.