95 research outputs found
The influence of the Al stabilizer layer thickness on the normal zone propagation velocity in high current superconductors
The stability of high-current superconductors is challenging in the design of
superconducting magnets. When the stability requirements are fulfilled, the
protection against a quench must still be considered. A main factor in the
design of quench protection systems is the resistance growth rate in the magnet
following a quench. The usual method for determining the resistance growth in
impregnated coils is to calculate the longitudinal velocity with which the
normal zone propagates in the conductor along the coil windings.
Here, we present a 2D numerical model for predicting the normal zone
propagation velocity in Al stabilized Rutherford NbTi cables with large cross
section. By solving two coupled differential equations under adiabatic
conditions, the model takes into account the thermal diffusion and the current
redistribution process following a quench. Both the temperature and magnetic
field dependencies of the superconductor and the metal cladding materials
properties are included. Unlike common normal zone propagation analyses, we
study the influence of the thickness of the cladding on the propagation
velocity for varying operating current and magnetic field.
To assist in the comprehension of the numerical results, we also introduce an
analytical formula for the longitudinal normal zone propagation. The analysis
distinguishes between low-current and high-current regimes of normal zone
propagation, depending on the ratio between the characteristic times of thermal
and magnetic diffusion. We show that above a certain thickness, the cladding
acts as a heat sink with a limited contribution to the acceleration of the
propagation velocity with respect to the cladding geometry. Both numerical and
analytical results show good agreement with experimental data.Comment: To be published in Physics Procedia (ICEC 25 conference special
issue
Preschool children's vision screening in New Zealand: a retrospective evaluation of referral accuracy
Langeslag-Smith MA, Vandal AC, Briane V, et al. Preschool children's vision screening in New Zealand: a retrospective evaluation of referral accuracy. BMJ Open 2015;5:e009207. doi: 10.1136/bmjopen-2015-009207Objectives To assess the accuracy of preschool vision screening in a large, ethnically diverse, urban population in South Auckland, New Zealand. Design Retrospective longitudinal study. Methods B4 School Check vision screening records (n=5572) were compared with hospital eye department data for children referred from screening due to impaired acuity in one or both eyes who attended a referral appointment (n=556). False positive screens were identified by comparing screening data from the eyes that failed screening with hospital data. Estimation of false negative screening rates relied on data from eyes that passed screening. Data were analysed using logistic regression modelling accounting for the high correlation between results for the two eyes of each child. Primary outcome measure Positive predictive value of the preschool vision screening programme. Results Screening produced high numbers of false positive referrals, resulting in poor positive predictive value (PPV=31%, 95% CI 26% to 38%). High estimated negative predictive value (NPV=92%, 95% CI 88% to 95%) suggested most children with a vision disorder were identified at screening. Relaxing the referral criteria for acuity from worse than 6/9 to worse than 6/12 improved PPV without adversely affecting NPV. Conclusions The B4 School Check generated numerous false positive referrals and consequently had a low PPV. There is scope for reducing costs by altering the visual acuity criterion for referral.This work was supported by the Arthur D Bronlund Trust, CCRep and University of Auckland Faculty Research Development Fund Grants (3704420)
A study of asymmetric tensile properties of large area GEM foil
Gas Electron Multiplier (GEM) technology is being used in various applications, particularly in high energy physics experiments. The GEM is known as a reliable detector in high radiation environment which can maintain high temporal and position resolution. GEM foil is the basic part of the detector which consists of a composite material (polyimide and copper). Large size GEM foil has complex mechanical structure and asymmetries which mainly arises due to formation of the HV sectors in the foil. These asymmetries become very relevant when large size foils are stretched to build a detector. In this article asymmetry affects are presented that define the tensile properties of a large size segmented GEM foil
Mind Perception: Real but Not Artificial Faces Sustain Neural Activity beyond the N170/VPP
Faces are visual objects that hold special significance as the icons of other minds. Previous researchers using event-related potentials (ERPs) have found that faces are uniquely associated with an increased N170/vertex positive potential (VPP) and a more sustained frontal positivity. Here, we examined the processing of faces as objects vs. faces as cues to minds by contrasting images of faces possessing minds (human faces), faces lacking minds (doll faces), and non-face objects (i.e., clocks). Although both doll and human faces were associated with an increased N170/VPP from 175–200 ms following stimulus onset, only human faces were associated with a sustained positivity beyond 400 ms. Our data suggest that the N170/VPP reflects the object-based processing of faces, whether of dolls or humans; on the other hand, the later positivity appears to uniquely index the processing of human faces—which are more salient and convey information about identity and the presence of other minds
Verbal instructions override the meaning of facial expressions
Psychological research has long acknowledged that facial expressions can implicitly trigger affective
psychophysiological responses. However, whether verbal information can alter the meaning of facial
emotions and corresponding response patterns has not been tested. This study examined emotional
facial expressions as cues for instructed threat-of-shock or safety, with a focus on defensive responding.
In addition, reversal instructions were introduced to test the impact of explicit safety instructions on
fear extinction. Forty participants were instructed that they would receive unpleasant electric shocks,
for instance, when viewing happy but not angry faces. In a second block, instructions were reversed
(e.g., now angry faces cued shock). Happy, neutral, and angry faces were repeatedly presented, and
auditory startle probes were delivered in half of the trials. The defensive startle reflex was potentiated
for threat compared to safety cues. Importantly, this effect occurred regardless of whether threat
was cued by happy or angry expressions. Although the typical pattern of response habituation was
observed, defense activation to newly instructed threat cues remained significantly enhanced in the
second part of the experiment, and it was more pronounced in more socially anxious participants.
Thus, anxious individuals did not exhibit more pronounced defense activation compared to less anxious
participants, but their defense activation was more persistent
Brain Structural Networks Associated with Intelligence and Visuomotor Ability
Increasing evidence indicates that multiple structures in the brain are associated with intelligence
and cognitive function at the network level. The association between the grey matter (GM) structural
network and intelligence and cognition is not well understood. We applied a multivariate approach
to identify the pattern of GM and link the structural network to intelligence and cognitive functions.
Structural magnetic resonance imaging was acquired from 92 healthy individuals. Source-based
morphometry analysis was applied to the imaging data to extract GM structural covariance. We
assessed the intelligence, verbal fluency, processing speed, and executive functioning of the
participants and further investigated the correlations of the GM structural networks with intelligence
and cognitive functions. Six GM structural networks were identified. The cerebello-parietal component
and the frontal component were significantly associated with intelligence. The parietal and frontal
regions were each distinctively associated with intelligence by maintaining structural networks with
the cerebellum and the temporal region, respectively. The cerebellar component was associated
with visuomotor ability. Our results support the parieto-frontal integration theory of intelligence by
demonstrating how each core region for intelligence works in concert with other regions. In addition,
we revealed how the cerebellum is associated with intelligence and cognitive functions
The alpha-kinase family: an exceptional branch on the protein kinase tree
The alpha-kinase family represents a class of atypical protein kinases that display little sequence similarity to conventional protein kinases. Early studies on myosin heavy chain kinases in Dictyostelium discoideum revealed their unusual propensity to phosphorylate serine and threonine residues in the context of an alpha-helix. Although recent studies show that some members of this family can also phosphorylate residues in non-helical regions, the name alpha-kinase has remained. During evolution, the alpha-kinase domains combined with many different functional subdomains such as von Willebrand factor-like motifs (vWKa) and even cation channels (TRPM6 and TRPM7). As a result, these kinases are implicated in a large variety of cellular processes such as protein translation, Mg2+ homeostasis, intracellular transport, cell migration, adhesion, and proliferation. Here, we review the current state of knowledge on different members of this kinase family and discuss the potential use of alpha-kinases as drug targets in diseases such as cancer
A Genome-wide Drosophila Screen for Heat Nociception Identifies α2δ3 as an Evolutionarily Conserved Pain Gene
Worldwide, acute and chronic pain affects 20% of the adult population and represents an enormous financial and emotional burden. Using genome-wide neuronal-specific RNAi knock-down in Drosophila, we report a global screen for an innate behavior and identify hundreds of novel genes implicated in heat nociception, including the α2δ-family calcium channel subunit straightjacket (stj). Mice mutant for the stj ortholog CACNA2D3 (α2δ3) also exhibit impaired behavioral heat pain sensitivity. In addition, in humans, α2δ3 SNP variants associate with reduced sensitivity to acute noxious heat and chronic back pain. Functional imaging in α2δ3 mutant mice revealed impaired transmission of thermal pain evoked signals from the thalamus to higher order pain centers. Intriguingly, in α2δ3 mutant mice thermal pain and tactile stimulation triggered strong cross-activation or synesthesia of brain regions involved in vision, olfaction, and hearing
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