Further Studies of the Impact of Waste Heat Release on Simulated Global Climate: Part I

The general circulation model (GCM) of the United Kingdom Meteorological Office (UKMO) has been used to investigate the impact of an input of waste heat (1.5 x 10e14 watts) into the atmosphere in a small area in the mid-latitude eastern Atlantic Ocean. The results of this experiment have been compared with those of two earlier experiments in which the waste heat was input from two energy parks, one in the Atlantic and one in the Pacific Ocean. The energy park produced significant responses in the surface pressure field, the temperature in the lowest layer of the model, and in the total precipitation distribution. The changes are of the same order of magnitude as the changes found in two earlier energy park experiments, and there are some similarities between changes in this experiment and EX01, especially over the area immediately downstream of the energy park. The results of all three energy park experiments have been investigated using zonal harmonic analysis, and the influence of the energy parks on the positions and amplitudes of waves in the temperature and wind fields are discussed

Impact of Waste Heat on Simulated Climate: A Megalopolis Scenario

The general circulation model (GCM) of the Meteorological Office (NO), U.K., was used to investigate the impact of waste heat on simulated global climate. These experiments are a further set in a series of experiments made to investigate the behavior of the simulated circulation with different scenarios and energy releases. In contrast to the previous experiments, the heat is distributed only over continental areas, where large energy and/or population densities can be expected in the future. The results suggest that the atmosphere responds very sensitively to the distribution of the heat input. Although the total hemispheric changes are smaller than in some of the previous experiments, there are still considerable areas where the difference between the perturbed model run and the control cases is large compared with the inherent variability of the model

Universality of the Gunn effect: self-sustained oscillations mediated by solitary waves

The Gunn effect consists of time-periodic oscillations of the current flowing through an external purely resistive circuit mediated by solitary wave dynamics of the electric field on an attached appropriate semiconductor. By means of a new asymptotic analysis, it is argued that Gunn-like behavior occurs in specific classes of model equations. As an illustration, an example related to the constrained Cahn-Allen equation is analyzed.Comment: 4 pages,3 Post-Script figure

Hierarchical relative entropy policy search

Many reinforcement learning (RL) tasks, especially in robotics, consist of multiple sub-tasks that are strongly structured. Such task structures can be exploited by incorporating hierarchical policies that consist of gating networks and sub-policies. However, this concept has only been partially explored for real world settings and complete methods, derived from first principles, are needed. Real world settings are challenging due to large and continuous state-action spaces that are prohibitive for exhaustive sampling methods. We define the problem of learning sub-policies in continuous state action spaces as finding a hierarchical policy that is composed of a high-level gating policy to select the low-level sub-policies for execution by the agent. In order to efficiently share experience with all sub-policies, also called inter-policy learning, we treat these sub-policies as latent variables which allows for distribution of the update information between the sub-policies. We present three different variants of our algorithm, designed to be suitable for a wide variety of real world robot learning tasks and evaluate our algorithms in two real robot learning scenarios as well as several simulations and comparisons

Learning sequential motor tasks

Many real robot applications require the sequential use of multiple distinct motor primitives. This requirement implies the need to learn the individual primitives as well as a strategy to select the primitives sequentially. Such hierarchical learning problems are commonly either treated as one complex monolithic problem which is hard to learn, or as separate tasks learned in isolation. However, there exists a strong link between the robots strategy and its motor primitives. Consequently, a consistent framework is needed that can learn jointly on the level of the individual primitives and the robots strategy. We present a hierarchical learning method which improves individual motor primitives and, simultaneously, learns how to combine these motor primitives sequentially to solve complex motor tasks. We evaluate our method on the game of robot hockey, which is both difficult to learn in terms of the required motor primitives as well as its strategic elements

Learning to predict phases of manipulation tasks as hidden states

Phase transitions in manipulation tasks often occur when contacts between objects are made or broken. A switch of the phase can result in the robot’s actions suddenly influencing different aspects of its environment. Therefore, the boundaries between phases often correspond to constraints or subgoals of the manipulation task. In this paper, we investigate how the phases of manipulation tasks can be learned from data. The task is modeled as an autoregressive hidden Markov model, wherein the hidden phase transitions depend on the observed states. The model is learned from data using the expectation-maximization algorithm. We demonstrate the proposed method on both a pushing task and a pepper mill turning task. The proposed approach was compared to a standard autoregressive hidden Markov model. The experiments show that the learned models can accurately predict the transitions in phases during the manipulation tasks

Axisymmetric pulse recycling and motion in bulk semiconductors

The Kroemer model for the Gunn effect in a circular geometry (Corbino disks) has been numerically solved. The results have been interpreted by means of asymptotic calculations. Above a certain onset dc voltage bias, axisymmetric pulses of the electric field are periodically shed by an inner circular cathode. These pulses decay as they move towards the outer anode, which they may not reach. As a pulse advances, the external current increases continuously until a new pulse is generated. Then the current abruptly decreases, in agreement with existing experimental results. Depending on the bias, more complex patterns with multiple pulse shedding are possible.Comment: 8 pages, 15 figure

Two-electron atoms, ions and molecules

The quantum mechanics of two-electron systems is reviewed, starting with the ground state of the helium atom and helium-like ions, with central charge $Z\ge 2$. For Z=1, demonstrating the stability of the negative hydrogen ion, H$^-$, cannot be achieved using a mere product of individual electron wave functions, and requires instead an explicit account for the anticorrelation among the two electrons. The wave function proposed by Chandrasekhar is revisited, where the permutation symmetry is first broken and then restored by a counter-term. More delicate problems can be studied using the same strategy: the stability of hydrogen-like ions $(M^+,m^-,m^-)$ for any value of the proton-to-electron mass ratio $M/m$; the energy of the lowest spin-triplet state of helium and helium-like ions; the stability of the doubly-excited hydrogen ion with unnatural parity. The positronium molecule $(e^+,e^+,e^-,e^-)$, which has been predicted years ago and discovered recently, can also be shown to be stable against spontaneous dissociation, though the calculation is a little more involved. Emphasis is put on symmetry breaking which can either spoil or improve the stability of systems.Comment: 16 pages, 2 figure