Online Meta-learning by Parallel Algorithm Competition

The efficiency of reinforcement learning algorithms depends critically on a few meta-parameters that modulates the learning updates and the trade-off between exploration and exploitation. The adaptation of the meta-parameters is an open question in reinforcement learning, which arguably has become more of an issue recently with the success of deep reinforcement learning in high-dimensional state spaces. The long learning times in domains such as Atari 2600 video games makes it not feasible to perform comprehensive searches of appropriate meta-parameter values. We propose the Online Meta-learning by Parallel Algorithm Competition (OMPAC) method. In the OMPAC method, several instances of a reinforcement learning algorithm are run in parallel with small differences in the initial values of the meta-parameters. After a fixed number of episodes, the instances are selected based on their performance in the task at hand. Before continuing the learning, Gaussian noise is added to the meta-parameters with a predefined probability. We validate the OMPAC method by improving the state-of-the-art results in stochastic SZ-Tetris and in standard Tetris with a smaller, 10$\times$10, board, by 31% and 84%, respectively, and by improving the results for deep Sarsa($\lambda$) agents in three Atari 2600 games by 62% or more. The experiments also show the ability of the OMPAC method to adapt the meta-parameters according to the learning progress in different tasks.Comment: 15 pages, 10 figures. arXiv admin note: text overlap with arXiv:1702.0311

A pragmatic approach to the problem of the self-adjoint extension of Hamilton operators with the Aharonov-Bohm potential

We consider the problem of self-adjoint extension of Hamilton operators for charged quantum particles in the pure Aharonov-Bohm potential (infinitely thin solenoid). We present a pragmatic approach to the problem based on the orthogonalization of the radial solutions for different quantum numbers. Then we discuss a model of a scalar particle with a magnetic moment which allows to explain why the self-adjoint extension contains arbitrary parameters and give a physical interpretation.Comment: 8 pages, LaTeX, to appear in J. Phys.

Tobacco control policies and respiratory conditions among children presenting in primary care

Tobacco control policies can protect child health. We hypothesised that the parallel introduction in 2008 of smoke-free restaurants and bars in the Netherlands, a tobacco tax increase and mass media campaign, would be associated with decreases in childhood wheezing/asthma, respiratory tract infections (RTIs), and otitis media with effusion (OME) presenting in primary care. We conducted an interrupted time series study using electronic medical records from the Dutch Integrated Primary Care Information database (2000-2016). We estimated step and slope changes in the incidence of each outcome with negative binomial regression analyses, adjusting for underlying time-trends, seasonality, age, sex, electronic medical record system, urbanisation, and social deprivation. Analysing 1,295,124 person-years among children aged 0-12 years, we found positive step changes immediately after the policies (incidence rate ratio (IRR): 1.07, 95% CI: 1.01-1.14 for wheezing/asthma; IRR: 1.16, 95% CI: 1.13-1.19 for RTIs; and IRR: 1.24, 95% CI: 1.14-1.36 for OME). These were followed by slope decreases for wheezing/asthma (IRR: 0.95/year, 95% CI: 0.93-0.97) and RTIs (IRR: 0.97/year, 95% CI: 0.96-0.98), but a slope increase in OME (IRR: 1.05/year, 95% CI: 1.01-1.09). We found no clear evidence of benefit of changes in tobacco control policies in the Netherlands for the outcomes of interest. Our findings need to be interpreted with caution due to substantial uncertainty in the pre-legislation outcome trends.</p

Tobacco control policies and respiratory conditions among children presenting in primary care

Tobacco control policies can protect child health. We hypothesised that the parallel introduction in 2008 of smoke-free restaurants and bars in the Netherlands, a tobacco tax increase and mass media campaign, would be associated with decreases in childhood wheezing/asthma, respiratory tract infections (RTIs), and otitis media with effusion (OME) presenting in primary care. We conducted an interrupted time series study using electronic medical records from the Dutch Integrated Primary Care Information database (2000-2016). We estimated step and slope changes in the incidence of each outcome with negative binomial regression analyses, adjusting for underlying time-trends, seasonality, age, sex, electronic medical record system, urbanisation, and social deprivation. Analysing 1,295,124 person-years among children aged 0-12 years, we found positive step changes immediately after the policies (incidence rate ratio (IRR): 1.07, 95% CI: 1.01-1.14 for wheezing/asthma; IRR: 1.16, 95% CI: 1.13-1.19 for RTIs; and IRR: 1.24, 95% CI: 1.14-1.36 for OME). These were followed by slope decreases for wheezing/asthma (IRR: 0.95/year, 95% CI: 0.93-0.97) and RTIs (IRR: 0.97/year, 95% CI: 0.96-0.98), but a slope increase in OME (IRR: 1.05/year, 95% CI: 1.01-1.09). We found no clear evidence of benefit of changes in tobacco control policies in the Netherlands for the outcomes of interest. Our findings need to be interpreted with caution due to substantial uncertainty in the pre-legislation outcome trends.</p

Efeito de herbicidas sobre a taxa de transporte de elétrons e o acúmulo de matéria seca em tomateiro.

Objetivou-se com este trabalho avaliar o efeito dos herbicidas metribuzin e carfentrazone sobre a taxa de transporte de elétrons (ETR) do fotossistema II (FSII) e o acúmulo de matéria seca em tomateiro.CD-ROM. Suplemento. Trabalho apresentado no 51. Congresso Brasileiro de Olericultura, Viçosa, MG

Electron transport, penetration depth and upper critical magnetic field of ZrB12 and MgB2

We report on the synthesis and measurements of the temperature dependence of resistivity, R(T), the penetration depth, l(T), and upper critical magnetic field, Hc2(T), for polycrystalline samples of dodecaboride ZrB12 and diboride MgB2. We conclude that ZrB12 as well as MgB2 behave like simple metals in the normal state with usual Bloch-Gruneisen temperature dependence of resistivity and with rather low resistive Debye temperature, TR=280 K, for ZrB12 (as compared to MgB2 with TR=900 K). The R(T) and l(T) dependencies of ZrB12 reveal a superconducting transition at Tc=6.0 K. Although a clear exponential l(T)dependence in MgB2 thin films and ceramic pellets was observed at low temperatures, this dependence was almost linear for ZrB12 below Tc/2. These features indicate s-wave pairing state in MgB2, whereas a d-wave pairing state is possible in ZrB12. A fit to the data gives a reduced energy gap 2D(0)/kTc=1.6 for MgB2 films and pellets, in good agreement with published data for 3D \pi - sheets of the Fermi surface. Contrary to conventional theories we found a linear temperature dependence of Hc2(T) for ZrB12 (Hc2(0)=0.15 T).Comment: 8 pages, 10 figures, submitted to JET

Groundwater springs formed during glacial retreat are a large source of methane in the high Arctic

Permafrost and glaciers in the high Arctic form an impermeable ‘cryospheric cap’ that traps a large reservoir of subsurface methane, preventing it from reaching the atmosphere. Cryospheric vulnerability to climate warming is making releases of this methane possible. On Svalbard, where air temperatures are rising more than two times faster than the average for the Arctic, glaciers are retreating and leaving behind exposed forefields that enable rapid methane escape. Here we document how methane-rich groundwater springs have formed in recently revealed forefields of 78 land-terminating glaciers across central Svalbard, bringing deep-seated methane gas to the surface. Waters collected from these springs during February–May of 2021 and 2022 are supersaturated with methane up to 600,000 times greater than atmospheric equilibration. Spatial sampling reveals a geological dependency on the extent of methane supersaturation, with isotopic evidence of a thermogenic source. We estimate annual methane emissions from proglacial groundwaters to be up to 2.31 kt across the Svalbard archipelago. Further investigations into marine-terminating glaciers indicate future methane emission sources as these glaciers transition into fully land-based systems. Our findings reveal that climate-driven glacial retreat facilitates widespread release of methane, a positive feedback loop that is probably prevalent across other regions of the rapidly warming Arcti