3D hydrodynamics simulations of a 3 M⊙M_{\odot} core-helium burning star

The inner structure of core-helium burning (CHeB) stars remains uncertain due to the yet unknown nature of mixing at the boundary of their cores. Large convective cores beyond a bare Schwarzschild model are favoured both from theoretical arguments and from asteroseismological constraints. However, the exact nature of this extra mixing, and in particular the possible presence of semiconvective layers, is still debated. In this work, we approach this problem through a new avenue by performing the first full-sphere 3D hydrodynamics simulations of the interiors of CHeB stars. We use the PPMstar explicit gas dynamics code to simulate the inner 0.45 $M_{\odot}$ of a 3 $M_{\odot}$ CHeB star. Simulations are performed using different Cartesian grid resolutions (768$^3$, 1152$^3$ and 1728$^3$) and heating rates. We use two different initial states, one based on MESA's predictive mixing scheme (which yields a large overshoot region) and one based on the convective premixing approach (which exhibits a semiconvective interface). The general behaviour of the flow in the convective core and in the stable envelope (where internal gravity waves are observed) is consistent with our recent simulations of core convection in massive main-sequence stars, and so are the various scaling relations. The semiconvective layers are dominated by strong internal gravity waves that do not produce measurable species mixing, but overshooting motions from the convective core gradually homogenize the semiconvective interface. This process can possibly completely erase the semiconvective layers, which would imply that CHeB stars do not harbour a semiconvection zone.Comment: Submitted to MNRAS. Movies available at https://www.ppmstar.or

3D hydrodynamics simulations of core convection in supermassive main-sequence stars

Supermassive stars are Population III stars with masses exceeding $10^4\,M_{\odot}$ that could be the progenitors of the first supermassive black holes. Their interiors are in a regime where radiation pressure dominates the equation of state. In this work, we use the explicit gas dynamics code PPMstar to simulate the hydrogen-burning core of a $10^4\,M_{\odot}$ supermassive main-sequence star. These are the first 3D hydrodynamics simulations of core convection in supermassive stars. We perform a series of ten simulations at different heating rates and on Cartesian grids with resolutions of $768^3$, $1152^3$ and $1728^3$. We examine different properties of the convective flow, including its large-scale morphology, its velocity spectrum and its mixing properties. We conclude that the radiation pressure-dominated nature of the interior does not noticeably affect the behaviour of convection compared to the case of core convection in a massive main-sequence star where gas pressure dominates. Our simulations also offer support for the use of mixing-length theory in 1D models of supermassive stars.Comment: 9 pages, 9 figures, movies at https://www.ppmstar.org/, accepted for publication in MNRA

Optimization Analysis of Tennis Players’ Physical Fitness Index Based on Data Mining and Mobile Computing

Tennis is a very explosive, continuous, and intense sport, including many continuous short-term explosive actions. It has the characteristics of short-term, high-intensity, high-density training, and it belongs to the category of purely competitive skills. In the competition, athletes must maintain good physical condition, physical fitness, and long-term endurance in order to demonstrate outstanding technical and tactical skills. Therefore, this paper proposes a mobile processor performance data mining framework MobilePerfMiner, which uses hardware counters and iteratively uses the XGBoost algorithm to build a performance model, ranks the importance of the microarchitecture events of the big data task, and reduces the performance big data dimension, so as to optimize the big data algorithm according to the performance characteristics described. Undoubtedly, the comprehensive monitoring of the sports training process is complex system engineering. The main monitoring includes three aspects: physical condition, technical and tactical skills, and intelligence. Sports technology is reflected in the ultimate load. According to the convenience and actual needs of the research, this article will discuss the methods of evaluating tennis training load and the actual technical and tactical parameter characteristics that can be obtained by studying the characteristics of tennis, namely, kinematics. Parameters for noncontact testing, the next step is to discuss the appropriateness and necessity of the load, as well as the technical and routine monitoring of tennis training ability. The final experimental results show that it can improve the physical energy of tennis players by more than 17%

Train Schedule Adjustment Strategies for Train Dispatch

Train schedule adjustment is the identity of key components of Train Dispatch System. Manually arranging the time table is a time-consuming and error-prone process. In this work, we mainly discuss three strategies of train schedule adjustment in train dispatch. First, we propose a new algorithm to calculate the maximum traffic capacity of freight-train in Beijing-Shanghai railway. We use a VMM (Vacancy Maximum Matching) grid to find the vacancy time table of freight-train base on the passenger train schedule, and solve the possible time sequence of freight-train by searching the bottleneck of freight-train traffic capacity. Second, we study the special circumstances in China when the spring transport or the Golden Week comes. It is necessary to put on extra passenger trains, and in order to arrange the extra passenger trains, we set up a double objective model, and the experiment shows that all the extra passenger trains arrive at the terminus within 20 hours. Finally, for the speed raising adjustment or train reschedule, we propose the SIA (Schedule inherited adjustment) algorithm to reschedule the freight-train time table. We compare the results of the SIA algorithm with that of the regular method, and find that the SIA leads to better results. DOI: http://dx.doi.org/10.11591/telkomnika.v11i5.248

Study and Practices of IT Specialists Cultivation Mode: A Chinese Independent College Perspective

International audienc

Decentralized Blind Spectrum Selection in Cognitive Radio Networks Considering Handoff Cost

Due to the spectrum varying nature of cognitive radio networks, secondary users are required to perform spectrum handoffs when the spectrum is occupied by primary users, which will lead to a handoff delay. In this paper, based on the multi-armed bandit framework of medium access in decentralized cognitive radio networks, we investigate blind spectrum selection problem of secondary users whose sensing ability of cognitive radio is limited and the channel statistics are a priori unknown, taking the handoff delay as a fixed handoff cost into consideration. In this scenario, secondary users have to make the choice of either staying foregoing spectrum with low availability or handing off to another spectrum with higher availability. We model the problem and investigate the performance of three representative policies, i.e., ρPRE, SL(K), kth-UCB1. The simulation results show that, despite the inclusion of the fixed handoff cost, these policies achieve the same asymptotic performance as that without handoff cost. Moreover, through comparison of these policies, we found the kth-UCB1 policy has better overall performance

Effect of geometrical structure of embedded phase change material on the power generation of thermoelectric module

The effect of geometrical structure of embedded phase change material (PCM) on the power generation of the thermoelectric module (TEM) was studied in this work. Paraffin wax with different geometrical structure was embedded in a polymer container which is adhered to the hot junction of the fabricated TEM. Since the PCM can used as the heat source and provide latent heat when the heat source stops providing heat, applying the PCM in the TEM is an efficiency method to enhance the power generation of the TEM. Our experimental results show that the energy harvesting time becomes 60 seconds longer in comparison with the case without the PCM when 4.3 g weight of paraffin wax is applied. At the same time, the power generation of the TEM increases by magnitude of 25%. Moreover, the output voltage and electrical energy generation of TEM with PCM increase with increasing both cross-area and height of the applied PCM