21 research outputs found
Topical Issues for Particle Acceleration Mechanisms in Astrophysical Shocks
Particle acceleration at plasma shocks appears to be ubiquitous in the
universe, spanning systems in the heliosphere, supernova remnants, and
relativistic jets in distant active galaxies and gamma-ray bursts. This review
addresses some of the key issues for shock acceleration theory that require
resolution in order to propel our understanding of particle energization in
astrophysical environments. These include magnetic field amplification in shock
ramps, the non-linear hydrodynamic interplay between thermal ions and their
extremely energetic counterparts possessing ultrarelativistic energies, and the
ability to inject and accelerate electrons in both non-relativistic and
relativistic shocks. Recent observational developments that impact these issues
are summarized. While these topics are currently being probed by
astrophysicists using numerical simulations, they are also ripe for
investigation in laboratory experiments, which potentially can provide valuable
insights into the physics of cosmic shocks.Comment: 13 pages, no figures. Invited review, accepted for publication in
Astrophysics and Space Science, as part of the HEDLA 2006 conference
proceeding
The Origin, Early Evolution and Predictability of Solar Eruptions
Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt
The effects of illuminating the roost entrance on the emergence behaviour of Pipistrellus pygmaeus
In an attempt to increase the accuracy of roost emergence counts for a monitoring programme, the exits of two Pipistrellus pygmaeus roosts were illuminated with light of different colours and intensities. Light intensityaffected bat emergence more than light colour. At one roost there was no significant difference in the bat emergence pattern between when the roost exit received no illumination and when it was illuminated with red light. The use of the latter is proposed to increase the accuracy of bat roost emergence counts
Subthalamic nucleus stimulation influences expression and suppression of impulsive behavior in Parkinson's disease
Subthalamic nucleus stimulation influences expression and suppression of impulsive behavior in Parkinson's disease
Past studies show beneficial as well as detrimental effects of subthalamic nucleus deep-brain stimulation on impulsive behaviour. We address this paradox by investigating individuals with Parkinson’s disease treated with subthalamic nucleus stimulation (n = 17) and healthy controls without Parkinson’s disease (n = 17) on performance in a Simon task. In this reaction time task, conflict between premature response impulses and goal-directed action selection is manipulated. We applied distributional analytic methods to separate the strength of the initial response impulse from the proficiency of inhibitory control engaged subsequently to suppress the impulse. Patients with Parkinson’s disease were tested when stimulation was either turned on or off. Mean conflict interference effects did not differ between controls and patients, or within patients when stimulation was on versus off. In contrast, distributional analyses revealed two dissociable effects of subthalamic nucleus stimulation. Fast response errors indicated that stimulation increased impulsive, premature responding in high conflict situations. Later in the reaction process, however, stimulation improved the proficiency with which inhibitory control was engaged to suppress these impulses selectively, thereby facilitating selection of the correct action. This temporal dissociation supports a conceptual framework for resolving past paradoxical findings and further highlights that dynamic aspects of impulse and inhibitory control underlying goal-directed behaviour rely in part on neural circuitry inclusive of the subthalamic nucleus
Bat Activity and Community Composition in the Northern Boreal Forest of South-Central Labrador, Canada
Morfologia de sementes e do desenvolvimento pós-seminal de espécies de Bromeliaceae Seed and post-seminal development morphology on Bromeliaceae species
O estudo teve como objetivos caracterizar as sementes, fornecendo informações sobre o tipo e o tempo mĂ©dio de germinação e de formação de plântulas, alĂ©m de descrever a morfologia do desenvolvimento pĂłs-seminal de seis espĂ©cies de Bromeliaceae. Os resultados mostram germinação do tipo epĂgea e plântulas criptocotiledonares para todas as espĂ©cies. As porcentagens máximas de germinação obtidas, acima de 80%, indicam alta qualidade fisiolĂłgica das sementes. O tempo mĂ©dio de germinação e de formação de plântulas foi de 4-15 e 8-18 dias, respectivamente. As sementes sĂŁo filiformes a elĂpticas, lisas ou com apĂŞndices plumosos. Os caracteres morfolĂłgicos mais relevantes para a diferenciação entre gĂŞneros e subfamĂlias de Bromeliaceae referem-se Ă forma e ao tipo de apĂŞndices das sementes, e na forma e tamanho da bainha cotiledonar, hipocĂłtilo e raiz primária das plântulas, subsidiando estudos taxonĂ´micos, ecolĂłgicos e na área de tecnologia de sementes.<br>The aim of this study was to characterize the seeds, providing information about germination type and seedling rate, in addition to describe the post-seminal development morphology of the six species of Bromeliaceae. The results showed that the germination is epigeal with cryptocotylar seedlings. Maximum germination percentage was over 80%, for all species, indicating high physiological quality of the seeds. Germination and seedling rate was 4-15 and 8-18 days, respectively. Seeds are filiform to elliptical, smooth or with flight apparatus. The most relevant morphological characters for distinguishing among genera and subfamilies are shape and appendices of the seeds, form and size of the cotyledonal sheath, hypocotyl and primary root, providing information on taxonomic, ecological and seed technology studies