1,025 research outputs found
Neural mechanisms of affective instability and cognitive control in substance use
Objective: We explored the impact of affect on cognitive control as this relates to individual differences in affective instability and substance use. Toward this end, we examined how different dimensions of affective instability interact to predict substance misuse and the effect of this on two event-related potential components, the reward positivity and the late positive potential, which are said to reflect the neural mechanisms of reward and emotion processing, respectively.
Methods: We recorded the ongoing electroencephalogram from undergraduate students as they navigated two T-maze tasks in search of rewards. One of the tasks included neutral, pleasant, and unpleasant pictures from the International Affective Picture System. Participants also completed several questionnaires pertaining to substance use and personality.
Results: A principal components analysis revealed a factor related to affective instability, which we named reactivity. This factor significantly predicted increased substance use. Individuals reporting higher levels of affective reactivity also displayed a larger reward positivity following stimuli with emotional content.
Conclusion: The current study uncovered a group of high-risk substance users who were characterized by greater levels of affective reactivity and context-specific increased sensitivity to rewards.
Significance: These results help to elucidate the complex factors underlying substance use and may facilitate the creation of individually-tailored treatment programs for those struggling with substance use disorders
Liquid Scintillator Time Projection Chamber Concept
Results are presented from a small-scale experiment to investigate the use of
room temperature organic liquid scintillators as the active medium for a time
projection chamber (TPC). The optical properties of liquid scintillators have
long been known, but their ability to transport charge has remained, until now,
largely untested. The idea of using room temperature liquids as an active
medium for an ionisation chamber was first presented in \cite{EnglerTMS}. Since
then the range of liquid scintillators available has been greatly developed. We
present successful transport of ionization charges in a selection of both, pure
organic liquid solvents and liquid scintillator cocktails over 20mm using a
variety of electric drift field strengths. The target of this research is to
offer a cost effective alternative to liquid noble gas detectors in neutrino
physics.Comment: 6 pages, 5 figures, submitted to Proceedings 12th Pisa Meeting on
Advanced Detectors, La Biodola, Isola d'Elba, Ital
Developing a Print on Demand Service in the Canadian Hydrographic Service
Recent events found the Canadian Hydrographic Service at a crossroads. A number of concurrent pressures seriously challenged the organisation's ability to produce, print, correct and distribute nautical charts, both from a financial perspective as well as a human resource perspective. While facing some difficult decisions, it became apparent that a number of relatively recent technologies could be combined to allow many of these challenges to be met. This paper describes the events that transpired, how the challenges were addressed using new technologies, and what the future may hold, as opportunities to refine and augment the application of new technologies are identified
Adventures in Interactive Compilation
Interactive compilation was proven to be a practical tool in the production of Chart 2011 and Chart 2048. The successful completion of these two charts has shown that applying computer-assisted techniques as an integral part of the construction of nautical charts is an effective alternative to traditional chart compilation. The advent of fast colour graphics devices and the increasing availability of digital hydrographic data requires innovative solutions to manage and use these data effectively
Bootstrap Percolation on Complex Networks
We consider bootstrap percolation on uncorrelated complex networks. We obtain
the phase diagram for this process with respect to two parameters: , the
fraction of vertices initially activated, and , the fraction of undamaged
vertices in the graph. We observe two transitions: the giant active component
appears continuously at a first threshold. There may also be a second,
discontinuous, hybrid transition at a higher threshold. Avalanches of
activations increase in size as this second critical point is approached,
finally diverging at this threshold. We describe the existence of a special
critical point at which this second transition first appears. In networks with
degree distributions whose second moment diverges (but whose first moment does
not), we find a qualitatively different behavior. In this case the giant active
component appears for any and , and the discontinuous transition is
absent. This means that the giant active component is robust to damage, and
also is very easily activated. We also formulate a generalized bootstrap
process in which each vertex can have an arbitrary threshold.Comment: 9 pages, 3 figure
Developmental changes in the reward positivity : an electrophysiological trajectory of reward processing
Children and adolescents learn to regulate their behavior by utilizing feedback from the environment but exactly how this ability develops remains unclear. To investigate this question, we recorded the event-related brain potential (ERP) from children (8-13 years), adolescents (14-17 years) and young adults (18-23 years) while they navigated a "virtual maze" in pursuit of monetary rewards. The amplitude of the reward positivity, an ERP component elicited by feedback stimuli, was evaluated for each age group. A current theory suggests the reward positivity is produced by the impact of reinforcement learning signals carried by the midbrain dopamine system on anterior cingulate cortex, which utilizes the signals to learn and execute extended behaviors. We found that the three groups produced a reward positivity of comparable size despite relatively longer ERP component latencies for the children, suggesting that the reward processing system reaches maturity early in development. We propose that early development of the midbrain dopamine system facilitates the development of extended goal-directed behaviors in anterior cingulate cortex. 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
Linear quadratic regulation control for falling liquid films
We propose and analyse a new methodology based on linear-quadratic regulation
(LQR) for stabilising falling liquid films via blowing and suction at the base.
LQR methods enable rapidly responding feedback control by precomputing a gain
matrix, but are only suitable for systems of linear ordinary differential
equations (ODEs). By contrast, the Navier-Stokes equations that describe the
dynamics of a thin liquid film flowing down an inclined plane are too complex
to stabilise with standard control-theoretical techniques. To bridge this gap
we use reduced-order models - the Benney equation and a weighted-residual
integral boundary layer model - obtained via asymptotic analysis to derive a
multi-level control framework. This framework consists of an LQR feedback
control designed for a linearised and discretised system of ODEs approximating
the reduced-order system, which is then applied to the full Navier-Stokes
system. The control scheme is tested via direct numerical simulation (DNS), and
compared to analytical predictions of linear stability thresholds and minimum
required actuator numbers. Comparing the strategy between the two reduced-order
models we show that in both cases we can successfully stabilise towards a
uniform flat film across their respective ranges of valid parameters, with the
more accurate weighted-residual model outperforming the Benney-derived
controls. The weighted-residual controls are also found to work successfully
far beyond their anticipated range of applicability. The proposed methodology
increases the feasibility of transferring robust control techniques towards
real-world systems, and is also generalisable to other forms of actuation.Comment: 21 pages, 9 figures, 1 tabl
Sensitivity of electrophysiological activity from medial frontal cortex to utilitarian and performance feedback.
A recent study has reported the observation in humans of an event-related brain potential component that is sensitive to the value of outcomes in a gambling task. This component, labeled medial frontal negativity (MFN), was most pronounced following monetary losses as opposed to monetary gains. In this study, we investigate the relationship between the MFN and the error-related negativity (ERN), a component elicited by feedback indicating incorrect choice performance. We argue that the two components can be understood in terms of a recently proposed theory that predicts the occurrence of such scalp negativities following stimuli that indicate that ongoing events are worse than expected. The results from two experiments using a gambling task demonstrate that the sensitivity of the MFN/ERN to the utilitarian and performance aspect of the feedback depends on which aspect is most salient. The results are consistent with the view that the two components are manifestations of the same underlying cognitive and neural process
Heterogeneous-k-core versus Bootstrap Percolation on Complex Networks
We introduce the heterogeneous--core, which generalizes the -core, and
contrast it with bootstrap percolation. Vertices have a threshold which
may be different at each vertex. If a vertex has less than neighbors it
is pruned from the network. The heterogeneous--core is the sub-graph
remaining after no further vertices can be pruned. If the thresholds are
with probability or with probability , the process
forms one branch of an activation-pruning process which demonstrates
hysteresis. The other branch is formed by ordinary bootstrap percolation. We
show that there are two types of transitions in this heterogeneous--core
process: the giant heterogeneous--core may appear with a continuous
transition and there may be a second, discontinuous, hybrid transition. We
compare critical phenomena, critical clusters and avalanches at the
heterogeneous--core and bootstrap percolation transitions. We also show that
network structure has a crucial effect on these processes, with the giant
heterogeneous--core appearing immediately at a finite value for any
when the degree distribution tends to a power law with
.Comment: 10 pages, 4 figure
Pre-exposure embrittlement of sensitized alumimium-magnesium alloy, 5083-H116
Environment-sensitive fracture of aluminum-magnesium alloys containing above ~3 wt% magnesium historically has been considered under anodic-dissolution control. Information from more recent studies, however, suggests a hydrogen-related process is also often involved. Further evidence supporting the involvement of a hydrogen-related process of during Intergranular stress corrosion cracking (IGSCC) will be presented using information gleaned from smooth and pre-cracked test specimens, previously sensitized over a range of temperatures in both ‘dry’ and ‘wet’ conditions and then subjected to rising-load testing in a range of environments. A detailed evaluation of the IGSCC using X-ray computed tomography to provide 3-D images and ultra-high-resolution electron microscopy to characterize selected regions within intergranular stress corrosion cracks enables mechanistic insights
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