With the development of lightweight aerospace equipment, magnesium alloys are receiving increasing attention. Wire-arc directed energy deposition (Wire-arc DED) is a highly promising manufacturing method for magnesium alloy parts, but its development has been severely restricted by the problems of coarse grain size and low mechanical properties. To address these issues, a hammer-forging assisted Wire-arc DED technology for magnesium alloy AZ91 is proposed. The effects of interlayer hammer-forging and synchronous hammer-forging on macrostructure, microstructure and mechanical properties of the Wire-arc DED samples are compared, and the microstructure evolution and performance enhancement mechanism are discussed. The results show that the maximum plastic deformation caused by hammer forging reaches 11.7%. Hammer forging can significantly refine grains, and the average grain size decreases from 27.7 μm to 13.5 μm. Synchronous hammer-forging is better than interlayer hammer-forging in terms of performance enhancement, the UTS reaches 301.8 MPa, an increase of 10.9%, which is comparable to that of traditional forged parts, mainly attributed to the grain refinement and increased dislocation density.
We consider a facility location scenario that is common in public transit or logistics system planning where the service area and demand area have been laid out and another set of facilities need to be set up to connect these two kinds of area. Given a network G=(V, A), we model this kind problem as a Gravitational Facility Location Problem (GFLP) with consideration of service accessibility and the feature of demand. We firstly formulate a GFLP with budget constraint to maximize total accessibility of selected demand and service area measured by Newton's law of universal gravitation. Secondly, GFLP is reduced to Gravitational Prize-Collecting Salesman Problem (GPCSP) according to the properties of needs in demand area. Even the reduced problem GPCSP is a generalization of Prize- Collecting Traveling Salesman Problem (PCTSP) which belongs to the hard core of NP-hard problems. Thirdly, we develop a merger-cluster based grafting heuristic algorithms for GPCSP, comparing with an adapted heuristics from an O(log 2 (min (R, n)) -approximation algorithm proposed by Awerbuch et al. The numerical examples show that our algorithm is more effective on a set of instances tailored from on line database for PCST instances and three cities street network.
In this research, we demonstrated that defect states in sol–gel-derived SrTa2O6 (STA) thin films can be detected by a thermal simulated current (TSC) technique. We also tentatively explained leakage current properties using these defect states. Similar defect states were found in STA thin films that were annealed at 700 and 800 °C by the TSC technique. Defects that caused the TSC peak at measurement temperatures of 130–150 °C showed higher trap densities in the 800 °C-annealed STA thin film. These defects were likely to be caused by diffused Ti, which mainly contributed to the larger leakage current in the 800 °C-annealed STA thin film. Oxygen-vacancy-related defect states were also clearly observed with the change in measurement atmosphere from air to vacuum.
The internal control has stepped into the developing stage of risk management as the main stream.It is necessary for petroleum enterprises with the industrial feature of resource consumption to attach an importance to the prevention and control of risks.Its purpose is to adapt themselves to the compulsory normalization orientation of state economic management policy.Based on the review of research history about the internal control of petroleum enterprises,the paper analyzes the value of internal control in petroleum enterprises with the orientation of the risk management,and then puts forward the concept structure of internal control in oil enterprises that carry out the risk management.
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