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The moving k nearest neighbor query computes one’s k nearest neighbor set and maintains it while at move. This query is gaining importance due to the prevalent use of smart mobile devices and location-based services. Safe region is a popular technique for processing the query. It is a region where the movement of the query object does not cause the query answer to change. Processing a moving k nearest neighbor query is a continuing process of validating the safe region and recomputing it if invalidated. The size of the safe region largely decides the recomputation frequency and hence query efficiency. Existing algorithms lack efficiency due to either computing too small safe regions frequently or computing larger but expensive safe regions. We propose to replace safe regions in metric space (e.g., Euclidean space and spatial networks) with safe guarding objects which have low cost to compute.We prove that, the k nearest neighbors stay valid as long as they are closer to the query object than the safe guarding objects are. We hence avoid the high cost of safe region recomputation. We also prove that, the region defined by the safe guarding objects is the largest possible safe region. Thus, the recomputation frequency of the proposed method is also minimized. We conduct extensive experiments comparing the proposed method with the state-of-the-art methods on both real and synthetic data. The results confirm the superiority of the proposed method.

In this paper, a much compact structure of configurable optical pulse synthesizer is proposed based on the signal processing theory. The desired optical pulse waveform is described by coherently overlapping the initial input pulse and its first-order, second-order differential signals, which are obtained by microring resonator (MR) working on the critical coupling condition. By optimizing the relative amplitudes and phases, output optical pulse can be tuned dynamically and several typical waveforms (e.g. flat-top, asymmetric triangular) are achieved. In addition, our results demonstrate that the proposed synthesizer can be applied for a variety of input sources (e.g. Gaussian or Sech-shape input pulses) with a certain range of temporal duration (FWHM = 5ps–20ps).

Using solar energy to produce syngas via the endothermic reforming of methane has been extensively investigated at the laboratory- and pilot plant-scales as a promising method of storing solar energy. One of the challenges to scaling up this process in a tubular reformer is to improve the reactor's performance, which is limited by mass and heat transfer issues. High thermal conductivity Cu foam was therefore used as a substrate to improve the catalyst's thermal conductivity during solar reforming. We also developed a method to coat the foam with the catalytically active component NiMg 3 AlO x . The Cu foam-based NiMg 3 AlO x performs better than catalysts supported on SiSiC foam, which is currently used as a substrate for solar-reforming catalysts, at high gas hourly space velocity (≥400,000 mL/(g·h)) or at low reaction temperatures (≤ 720 °C). The presence of a γ-Al 2 O 3 intermediate layer improves the adhesion between the catalyst and substrate as well as the catalytic activity.

The purpose of this paper is to investigate heat dissipation performance of porous copper with long cylindrical pores fabricated by a unidirectional solidification method. Three samples with porosity of 29.87%, 34.47% and 50.98% were chosen and cut into size of 60 mm (length) × 26 mm (width) × 2 mm (thickness) along the vertical direction of pore axis. Their heat dissipation performance was evaluated by a nonsteady method in air and compared to those of not only bulk copper but also bored coppers with porosity of 30.61% and 32.20%. It is found that the porous copper dissipated heat faster by a forced air convection than that by natural convection from 80 °C to room temperature and both porosity and pore size play an important role in the performance for the porous copper. Furthermore, the heat dissipation rate is higher when the forced air was circulated along the specimens than that perpendicular to the specimens for the porous copper. It is revealed that porous copper with bigger porosity and a proper pore size possesses a higher heat dissipation rate. It is concluded that the porous copper with elongated cylindrical pores has larger heat dissipation performance than both the bulk copper and the bored copper, which is attributed to its higher specific surface area. Application of the porous copper for heat dissipation is promising.

A visible k nearest neighbor (Vk NN) query retrieves k objects that are visible and nearest to the query object, where “visible” means that there is no obstacle between an object and the query object. Existing studies on the Vk NN query have focused on static data objects. In this paper we investigate how to process the query on moving objects continuously. We propose an effective filtering-and-refinement framework for evaluating this type of queries. We exploit spatial proximity and visibility properties between the query object and data objects to prune search space under this framework. A detailed cost analysis and a comprehensive experimental study are conducted on the proposed framework. The results validate the effectiveness of the pruning techniques and verify the efficiency of the proposed framework. The proposed framework outperforms a straightforward solution by an order of magnitude in terms of both communication and computation costs.

Porous copper with elongated cylindrical pores aligned either axially or radially was fabricated under a high pressure of mixture gas of hydrogen and argon. Structure characterization indicated that pore size increased, pore density decreased, pore size distribution became wider with an increase in porosity for the porous copper. The dependence of oil retaining capability and sliding friction coefficient on porosity and pore size of the porous copper were investigated. It was found that the oil content of the porous copper depended mainly on the porosity, and reached 27.6% on the specimen with a porosity of 47.1%. On the other hand, the oil efficiency was not satisfactory, and became worse when the porosity increased, which was attributed to the increase in pore size and the wider pore size distribution for the porous copper. It was proven that the impregnated oil in the pores played an important role in improving the sliding friction behaviour of the porous copper. (C) 2012 Elsevier B.V. All rights reserved.

Porous copper with elongated pores was fabricated by a radial solidification method. The process was carried out in a combined crystallizer under high pressure of a mixture of hydrogen and argon. Pore size, pore length, pore density and porosity of the porous copper were characterized. Furthermore, the oil retaining capacity including oil content and oil efficiency was also evaluated. It is found that porous copper solidified with water-circulated chiller through a thick graphite jacket possesses a gradient structure with increasing pore size, and thus pore density decreases. Also pore length and pore aspect ratio decrease from lateral inwardly, while its porosity is almost uniform. The results show that the porous copper with radial pores has a good oil retaining capacity. (C) 2010 Elsevier B.V. All rights reserved.

The TiAl(3)-Al composite coating on orthorhombic Ti(2)AlNb based alloy was prepared by cold spray. Oxidation in air at 950 degrees C indicated that the bare alloy exhibited poor oxidation resistance due to the formation of TiO(2)/AlNbO(4) mixture and intended to scale off at the TiO(2) rich zone. A nitride layer about 2 mu m was formed under the oxide layer. The oxygen invaded deeply into the alloy and caused severe microhardness enhancement in the near Surface region. The TiAl(3)-Al composite coating exhibited Parabolic oxidation kinetics and showed no sign of degradation after oxidized up to 1098 h at 950 degrees C in air under quasi-isothermal condition. No scaling of the coating was observed after oxidized at 950 degrees C up to the tested 150 cycles. The major oxide in the oxidized coating was Al(2)O(3). The AlTi(2)N, TiAl and small amount of TiO(2) were also observed in the oxidized coating. The EPMA and microhardness tests showed that inward oxygen diffusion was prevented by the interlayer, which was formed between the composite coating and the substrate during heat-treatment. Microstructure analyses demonstrated that the interlayer play a major role in protecting the substrate alloy from high temperature oxidation and interstitial embrittlement. (C) 2009 Elsevier B.V. All rights reserved.