Effects of heat treatment on mechanical properties and microstructure of tungsten fi ber reinforced grey cast iron matrix composites

In this study, grey cast iron matrix composites reinforced by different volume fractions of tungsten fibers (Vr = 0.95 %, 1.90 %, 2.85 %, 3.80 %) were investigated in as-cast and under the heat treatment temperatures of 1,000℃ and 1,100℃. The microstructure and mechanical properties of the composites were analyzed and tested by means of SEM, micro-hardness tester and three-point bend testing. The results show that with increasing of the volume fraction of tungsten fibers, the composites reinforced by the tungsten fiber have higher fl exural strength and modulus than that of cast iron without reinforcement, and the fl exural strength increases with the increasing of heat treatment temperatures. Due to diffusion reaction between matrix and reinforcing phases, the process of heat treatment, the number of graphite fl akes in the matrix seemingly becomes lower; and some hard carbide particles are formed around the residual tungsten fi bers. Not only does the hardness of both matrix and reinforcement change tremendously, but also the region of reinforcement is also extended from the original 0.11 mm to 0.19 mm in radius

Online Ridesharing with Meeting Points [Technical Report]

Nowadays, ridesharing becomes a popular commuting mode. Dynamically arriving riders post their origins and destinations, then the platform assigns drivers to serve them. In ridesharing, different groups of riders can be served by one driver if their trips can share common routes. Recently, many ridesharing companies (e.g., Didi and Uber) further propose a new mode, namely "ridesharing with meeting points". Specifically, with a short walking distance but less payment, riders can be picked up and dropped off around their origins and destinations, respectively. In addition, meeting points enables more flexible routing for drivers, which can potentially improve the global profit of the system. In this paper, we first formally define the Meeting-Point-based Online Ridesharing Problem (MORP). We prove that MORP is NP-hard and there is no polynomial-time deterministic algorithm with a constant competitive ratio for it. We notice that a structure of vertex set, $k$-skip cover, fits well to the MORP. $k$-skip cover tends to find the vertices (meeting points) that are convenient for riders and drivers to come and go. With meeting points, MORP tends to serve more riders with these convenient vertices. Based on the idea, we introduce a convenience-based meeting point candidates selection algorithm. We further propose a hierarchical meeting-point oriented graph (HMPO graph), which ranks vertices for assignment effectiveness and constructs $k$-skip cover to accelerate the whole assignment process. Finally, we utilize the merits of $k$-skip cover points for ridesharing and propose a novel algorithm, namely SMDB, to solve MORP. Extensive experiments on real and synthetic datasets validate the effectiveness and efficiency of our algorithms.Comment: 18 page

Application of CCG Sensors to a High-Temperature Structure Subjected to Thermo-Mechanical Load

This paper presents a simple methodology to perform a high temperature coupled thermo-mechanical test using ultra-high temperature ceramic material specimens (UHTCs), which are equipped with chemical composition gratings sensors (CCGs). The methodology also considers the presence of coupled loading within the response provided by the CCG sensors. The theoretical strain of the UHTCs specimens calculated with this technique shows a maximum relative error of 2.15% between the analytical and experimental data. To further verify the validity of the results from the tests, a Finite Element (FE) model has been developed to simulate the temperature, stress and strain fields within the UHTC structure equipped with the CCG. The results show that the compressive stress exceeds the material strength at the bonding area, and this originates a failure by fracture of the supporting structure in the hot environment. The results related to the strain fields show that the relative error with the experimental data decrease with an increase of temperature. The relative error is less than 15% when the temperature is higher than 200 °C, and only 6.71% at 695 °C

Kuijia: Traffic Rescaling in Software-Defined Data Center WANs

Network faults like link or switch failures can cause heavy congestion and packet loss. Traffic engineering systems need a lot of time to detect and react to such faults, which results in significant recovery times. Recent work either preinstalls a lot of backup paths in the switches to ensure fast rerouting or proactively prereserves bandwidth to achieve fault resiliency. Our idea agilely reacts to failures in the data plane while eliminating the preinstallation of backup paths. We propose Kuijia, a robust traffic engineering system for data center WANs, which relies on a novel failover mechanism in the data plane called rate rescaling. The victim flows on failed tunnels are rescaled to the remaining tunnels and enter lower priority queues to avoid performance impairment of aboriginal flows. Real system experiments show that Kuijia is effective in handling network faults and significantly outperforms the conventional rescaling method

Measurement of high-temperature strains in superalloy and carbon/carbon composites using chemical composition gratings

This is a text file associated with Ref. [11] from R. Siew, "Practical automated glass selection and the design of apochromats with large field of view," App. Opt. 55, pp. 9232 - 9236 (2016). It lists the lens prescription for the Zemax lens file of Ref. [10] in the above manuscript.  This lens represents a re-optimized state of the prior lens "AUTO GLASS FINISHED.zmx".  The design form is based on the design by A. Yang, X. Gao, and M. Li, "Design of apochromatic lens with large field and high definition for machine vision," App. Opt. 55, 5977 - 5985 (2016)