46,848 research outputs found
Distributed Flow Scheduling in an Unknown Environment
Flow scheduling tends to be one of the oldest and most stubborn problems in
networking. It becomes more crucial in the next generation network, due to fast
changing link states and tremendous cost to explore the global structure. In
such situation, distributed algorithms often dominate. In this paper, we design
a distributed virtual game to solve the flow scheduling problem and then
generalize it to situations of unknown environment, where online learning
schemes are utilized. In the virtual game, we use incentives to stimulate
selfish users to reach a Nash Equilibrium Point which is valid based on the
analysis of the `Price of Anarchy'. In the unknown-environment generalization,
our ultimate goal is the minimization of cost in the long run. In order to
achieve balance between exploration of routing cost and exploitation based on
limited information, we model this problem based on Multi-armed Bandit Scenario
and combined newly proposed DSEE with the virtual game design. Armed with these
powerful tools, we find a totally distributed algorithm to ensure the
logarithmic growing of regret with time, which is optimum in classic
Multi-armed Bandit Problem. Theoretical proof and simulation results both
affirm this claim. To our knowledge, this is the first research to combine
multi-armed bandit with distributed flow scheduling.Comment: 10 pages, 3 figures, conferenc
Dryland maize yields and water use efficiency in response to tillage and nutrient management practices in China
Rainfed crop production in northern China is constrained by low and variable rainfall. This study explored the effects of tillage and nutrient management practices on maize (Zea mays L.) yield and water use efficiency (WUE), at Shouyang Dryland Farming Experimental Station in northern China during 2003-2008. The experiment was set-up using a split-plot design with 3 tillage methods as main treatments: conventional, reduced (till with crop residue incoperated in fall but no-till in spring), and no-till. Sub-treatments were 3 NP fertilizer rates: 105-46, 179-78 and 210-92 kg N and P ha. -1 Maize grain yields were greatly influenced by the amount of growing season rainfall, and by soil water contents at sowing. Mean grain yields over the 6-year period in response to tillage treatments were 5604, 5347 and 5185 kg ha, under reduced, no-till and conventional tillage, respectively. Mean WUE was 13.7, 13.6 and 12.6 kg ha mm under reduced, no-till, and conventional tillage, respectively. Mean soil water contents at sowing and at harvest were significantly influenced by tillage treatments. At harvest time, the no-till treatment had ~8-12% more water in the soil than the conventional and reduced tillage treatments. Under conventional tillage, grain yields increased with NP fertilizer application rates. However, under reduced tillage, grain yields were highest with lowest NP fertilizer application rate. In conclusion, grain yields and WUE were highest under reduced tillage at modest NP fertilizer application rates of 105 kg N and 46 kg P per ha. No-till increased soil water storage by 8-12% and improved WUE compared to conventional tillage
Tracers of chromospheric structure. I. CaII HK emission distribution of 13000 F, G and K stars in SDSS DR7 spectroscopic sample
We present chromospheric activity index measurements for over
13,000 F, G and K disk stars with high signal-to-noise ratio ( 60) spectra
in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) spectroscopic
sample. A parameter S is defined as the difference between
and a `zero' emission line fitted by several of the most inactive stars. The
indices of subgiant stars tend to be much lower than dwarfs, which
provide a way to distinguish dwarfs and giants with relatively low resolution
spectra. Cooler stars are generally more active and display a larger scatter
than hotter stars. Stars associated with the thick disk are in general less
active than those of the thin disk. The fraction of K dwarfs that are active
drops with vertical distance from the Galactic plane. Metallicity affects
measurements differently among F, G and K dwarfs in this sample.
Using the open clusters NGC 2420, M67 and NGC6791 as calibrations, ages of most
field stars in this SDSS sample range from 3-8 Gyr.Comment: 9 pages, 11 figures, AJ, 2013, 145, 14
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