Internal Simulation of an Agent\u2019s Intentions

We present the Associative Self-Organizing Map (A-SOM) and propose that it could be used to predict an agent's intentions by internally simulating the behaviour likely to follow initial movements. The A-SOM is a neural network that develops a representation of its input space without supervision, while simultaneously learning to associate its activity with an arbitrary number of additional (possibly delayed) inputs. We argue that the A-SOM would be suitable for the prediction of the likely continuation of the perceived behaviour of an agent by learning to associate activity patterns over time, and thus a way to read its intentions

Influence of massive material injection on avalanche runaway generation during tokamak disruptions

In high-current tokamak devices such as ITER, a runaway avalanche can cause a large amplification of a seed electron population. We show that disruption mitigation by impurity injection may significantly increase the runaway avalanche growth rate in such devices. This effect originates from the increased number of target electrons available for the avalanche process in weakly ionized plasmas, which is only partially compensated by the increased friction force on fast electrons. We derive an expression for the avalanche growth rate in partially ionized plasmas and investigate the effects of impurity injection on the avalanche multiplication factor and on the final runaway current for ITER-like parameters. For impurity densities relevant for disruption mitigation, the maximum amplification of a runaway seed can be increased by tens of orders of magnitude compared to previous predictions. This motivates careful studies to determine the required densities and impurity species to obtain tolerable current quench parameters, as well as more detailed modeling of the runaway dynamics including transport effects.Comment: 6 pages, 2 figure

Kinetic modeling of runaway-electron dynamics in partially ionized plasmas

An essential result of kinetic plasma physics is the runaway phenomenon, whereby a fraction of an electron population can be accelerated to relativistic energies. Such runaway electrons are formed in astrophysical settings, but are also of great practical relevance to fusion research. In the most developed fusion device, known as the tokamak, runaway electrons have the potential to cause severe damage to the first wall. Runaway-electron mitigation is therefore one of the critical issues in the design of a fusion power plant. In many situations, runaway electrons interact with partially ionized atoms. In particular, the currently envisaged mitigation method for tokamaks is to inject heavy atoms which collisionally dissipate the runaway beam before it can collide with the wall, or prevent it from forming at all. When the atoms are partially ionized, their bound electrons screen out a fraction of the atomic charge, which directly affects the collisional scattering rates. However, accurate expressions for these collisional scattering rates between energetic electrons and partially ionized atoms have not been available previously. In this thesis, we explore kinetic aspects of runaway dynamics in partially ionized plasmas. We derive collisional scattering rates using a quantum-mechanical treatment, and study the interaction between fast electrons and partially ionized atoms. We then apply these results to calculate the threshold field for runaway generation, as well as the production rate of runaway electrons via the avalanche and Dreicer mechanisms. We find that even if material injection increases the dissipation rates, it also enhances avalanche generation which could potentially aggravate the runaway problem. These results contribute to more accurate runaway-electron modeling and can lead to more effective mitigation schemes in the longer term

The current status of the simulation theory of cognition

It is proposed that thinking is simulated interaction with the environment. Three assumptions underlie this ‘simulation’ theory of cognitive function. Firstly, behaviour can be simulated in the sense that we can activate motor structures, as during a normal overt action, but suppress its execution. Secondly, perception can be simulated by internal activation of sensory cortex in a way that resembles its normal activation during perception of external stimuli. The third assumption (‘anticipation’) is that both overt and simulated actions can elicit perceptual simulation of their most probable consequences. A large body of evidence, mainly from neuroimaging studies, that supports these assumptions, is reviewed briefly. The theory is ontologically parsimonious and does not rely on standard cognitivist constructs such as internal models or representations. It is argued that the simulation approach can explain the relations between motor, sensory and cognitive functions and the appearance of an inner world. It also unifies and explains important features of a wide variety of cognitive phenomena such as memory and cognitive maps. Novel findings from recent developments in memory research on the similarity of imaging and memory and on the role of both prefrontal cortex and sensory cortex in declarative memory and working memory are predicted by the theory and provide striking support for it

Dynamics of positrons during relativistic electron runaway

Sufficiently strong electric fields in plasmas can accelerate charged particles to relativistic energies. In this paper we describe the dynamics of positrons accelerated in such electric fields, and calculate the fraction of created positrons that become runaway accelerated, along with the amount of radiation that they emit. We derive an analytical formula that shows the relative importance of the different positron production processes, and show that above a certain threshold electric field the pair production by photons is lower than that by collisions. We furthermore present analytical and numerical solutions to the positron kinetic equation; these are applied to calculate the fraction of positrons that become accelerated or thermalized, which enters into rate equations that describe the evolution of the density of the slow and fast positron populations. Finally, to indicate operational parameters required for positron detection during runaway in tokamak discharges, we give expressions for the parameter dependencies of detected annihilation radiation compared to bremsstrahlung detected at an angle perpendicular to the direction of runaway acceleration. Using the full leading order pair production cross section, we demonstrate that previous related work has overestimated the collisional pair production by at least a factor of four

Time Course of Classically Conditioned Purkinje Cell Response is Determined by Initial Part of Conditioned Stimulus

Classical conditioning of a motor response such as eyeblink is associated with the development of a pause in cerebellar Purkinje cell firing that is probably an important driver of the overt response. This conditioned Purkinje cell response is adaptively timed and has a specific temporal profile that probably explains the time course of the overt behavior. It is generally assumed that the temporal properties of the conditioned Purkinje cell response are determined by the temporal pattern of the parallel fiber impulses generated by the conditioned stimulus at the time of the conditioned response. We show here in the decerebrate ferret preparation that a very brief conditioned stimulus, consisting of only one or two impulses in the mossy fibers, can be sufficient to elicit a full conditioned Purkinje cell response with normal time course. The finding suggests that parallel fiber input to the Purkinje cell influences the firing rate several hundred milliseconds later. It poses a serious challenge to the standard view of the role of parallel fiber impulses in response timing

Effect of partially-screened nuclei on fast-electron dynamics

We analyze the dynamics of fast electrons in plasmas containing partially ionized impurity atoms, where the screening effect of bound electrons must be included. We derive analytical expressions for the deflection and slowing-down frequencies, and show that they are increased significantly compared to the results obtained with complete screening, already at sub-relativistic electron energies. Furthermore, we show that the modifications to the deflection and slowing down frequencies are of equal importance in describing the runaway current evolution. Our results greatly affect fast-electron dynamics and have important implications, e.g. for the efficacy of mitigation strategies for runaway electrons in tokamak devices, and energy loss during relativistic breakdown in atmospheric discharges.Comment: 6 pages, 3 figures, fixed minor typo

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I artikeln beskrivs med hjälp av Ivaničs (2004) diskursanalytiska ramverk för skrivundervisning hur två läroböcker i svenska erbjuder elever olika möjligheter att utveckla genrekompetens inom recensionsskrivande, i artikeln benämnt recensionskompetens. Utgångspunkt för studien är att nuvarande kursplaner för svenskämnet tydligare än föregående betonar förmåga att skriva olika texttyper. Resultatet visar att läroböckerna ingår i olika skrivpedagogiska diskurser. Avslutningsvis diskuteras vilka konsekvenser detta kan få för elevers möjligheter att utveckla recensionskompetens samt för lärare i val av lärobok