A renormalisation-group treatment of two-body scattering

Nonrelativistic two-body scattering by a short-ranged potential is studied using the renormalisation group. Two fixed points are identified: a trivial one and one describing systems with a bound state at zero energy. The eigenvalues of the linearised renormalisation group are used to assign a systematic power-counting to terms in the potential near each of these fixed points. The expansion around the nontrivial fixed point is shown to be equivalent to the effective-range expansion.Comment: 6 pages (RevTeX), 1 figure (epsf); picture of RG flow and more discussion of momentum dependence adde

Accelerating Reinforcement Learning through the Discovery of Useful Subgoals

An ability to adjust to changing environments and unforeseen circumstances is likely to be an important component of a successful autonomous space robot. This paper shows how to augment reinforcement learning algorithms with a method for automatically discovering certain types of subgoals online. By creating useful new subgoals while learning, the agent is able to accelerate learning on a current task and to transfer its expertise to related tasks through the reuse of its ability to attain subgoals. Subgoals are created based on commonalities across multiple paths to a solution. We cast the task of finding these commonalities as a multiple-instance learning problem and use the concept of diverse density to find solutions. We introduced this approach in [10] and here we present additional results for a simulated mobile robot task

Automatic Discovery of Subgoals in Reinforcement Learning using Diverse Density

This paper presents a method by which a reinforcement learning agent can automatically discover certain types of subgoals online. By creating useful new subgoals while learning, the agent is able to accelerate learning on the current task and to transfer its expertise to other, related tasks through the reuse of its ability to attain subgoals. The agent discovers subgoals based on commonalities across multiple paths to a solution. We cast the task of finding these commonalities as a multiple-instance learning problem and use the concept of diverse density to find solutions. We illustrate this approach using several gridworld tasks

East-West Asymmetry in Coastal Temperatures of Hudson Bay as a Proxy for Sea Ice

Hudson Bay experiences a complete cryogenic cycle, which has been well documented since 1971. We developed a temperature proxy method to extend the sea ice record back to 1944, using mean temperatures for Churchill and Inukjuak and the difference between these means at two different seasonal periods. This method proved to reproduce the 1971 to 2011 ice-free season length record with an error just over eight days (6%). This relationship was used to hindcast ice-free season length to 1944. This hindcast was subsequently appended to the existing 1971–2011 record to form a 68-year sea ice record. This extended record shows that the recent statistically significant increase in length of the ice-free season was not the result of a natural oscillation of less than 68 years and is consistent with a net warming due to increasing greenhouse gases.La baie d’Hudson connaît un cycle cryogénique complet, et celui-ci est bien répertorié depuis 1971. Nous avons élaboré une méthode d’obtention de données indirectes des températures afin d’étendre les données des températures jusqu’à 1944, en nous servant des températures moyennes pour Churchill et Inukjuak et de la différence entre ces moyennes à deux périodes saisonnières différentes. Cette méthode avait pour but de reproduire le registre des durées de saisons sans glace de 1971 à 2011, avec une marge d’erreur d’un peu plus de huit jours (6 %). Cette méthode a permis de faire la simulation rétrospective de la durée des saisons sans glace jusqu’en 1944. Par la suite, la simulation rétrospective a été appliquée au registre actuel de 1971–2011, ce qui a donné lieu à un registre sur la glace de mer réparti sur 68 années. Ce registre prolongé a permis de démontrer que la récente augmentation statistiquement différente en matière de durée de la saison sans glace ne découlerait pas d’une oscillation naturelle de moins de 68 ans, et qu’elle correspond à un réchauffement net attribuable à l’augmentation des gaz à effet de serre

The use of embedded sensors for the monitoring of adhesive joints in marine environments

A copolymer incorporating polyaniline was used as a sensing medium in the construction of a resistance based humidity sensor. Aniline monomer was polymerised in the presence of poly (butyl acrylate / vinyl acetate) and a copolymer containing polyaniline emeraldine salt was obtained. The sensing medium was then developed by redissolving 1-2 w/w% of the resulting polymer residue in dichloromethane to produce a processable polymer blend solution. Some of this polymer residue was also de-doped in a solution of ammonia, and then washed with distilled water until the waste water had a neutral pH. This residue was then redissolved at 1-2 w/w% in dichloromethane to produce a second processable polymer blend this time containing polyaniline emeraldine base. The final sensor design utilised 125μm polyester insulated platinum wire as conducting electrodes that were dip coated in the emeraldine salt copolymer solution and allowed to dry in a desiccator. The sensor was then dip-coated in a protective barrier layer of the emeraldine base copolymer to prevent over-oxidation and/or de-protonation of the emeraldine salt sensing medium under this coating. The sensors had an overall final thickness of less than 150μm and showed high sensitivity to humidity, low resistance, and good reversibility without hysteresis. Sensors were monitored for 2-probe resistance changes when in contact with water. Calibration curves for each sensor were produced to convert the resistance reading to mass uptake of water. Individual sensors were embedded within Aluminium 5083 / Araldite 2015 adhesive joints to monitor mass uptake of water when exposed to marine environments. Correlations between mass uptake of water and joint strength were made. There are various advantages of such a sensor design. Polymer based thin film humidity sensors have the advantage that the high processability of the material allows for simple fabrication of a range of geometries including smaller sensor designs. The ease of processing gives a low cost sensor, whilst the small size and good mechanical properties gives a robust sensor which has the flexibility to be able to be used in applications where dynamic stresses and strains are encountered. Such sensors may find uses in a number of areas including electronic textiles, food/ electronics packaging and corrosion detection

The use of an iPad as a classroom tool

The Apple i line has been steadily increasing in popularity and many educators believe these devices offer great potential as instructional adjuncts. Many schools (including colleges) have begun issuing iPads to students with the assumption that they would enhance the students\u27 educational experience. Little experimental evidence has been produced supporting this claim. This study was an attempt to experimentally evaluate the effectiveness of iPads on learning educational material. Participant\u27s interest and enjoyment while using the iPad versus traditional material presentation (paper images or physical models) were also examined. Participants were randomly assigned to learn 24 anatomical brain structures using one of three conditions; 1) control color paper images, 2) plastic anatomical model, and 3) iPad application 3-D Brain , produced by Dolan DNA Learning Center. Participants were given 10-minutes with their assigned material and were then immediately tested on the material. The results demonstrated that learning & memory performance using the iPad was significantly better than the plastic model, and no different from paper pictures. Compared to the plastic model, participants also reported that they enjoyed the task more, felt more prepared, felt their performance was better, and would be more likely to take a class using the iPad. A gender difference was also discovered, suggesting that females might benefit more from the use of the iPad than males. The limitations and implications of these findings are discussed

Renormalisation and power counting in effective field theories for nucleon-nucleon scattering

The renormalisation of NN scattering in theories with zero-range interactions is examined using a cut-off regularisation and taking the cut-off to infinity. Inclusion of contact interactions that depend on energy as well as momentum allows the effective range to be fitted to experiment with any desired sign or magnitude. However, power counting breaks down: terms of different orders in the potential can contribute to the scattering amplitude at the same order.Comment: 4 pages (RevTeX