Identifying the Driver of Pulsating Aurora Nishimura, Y; Bortnik, J; Li, W ...
Science (American Association for the Advancement of Science),
10/2010, Letnik:
330, Številka:
6000
Journal Article
Recenzirano
Pulsating aurora, a spectacular emission that appears as blinking of the upper atmosphere in the polar regions, is known to be excited by modulated, downward-streaming electrons. Despite its ...distinctive feature, identifying the driver of the electron precipitation has been a long-standing problem. Using coordinated satellite and ground-based all-sky imager observations from the THEMIS mission, we provide direct evidence that a naturally occurring electromagnetic wave, lower-band chorus, can drive pulsating aurora. Because the waves at a given equatorial location in space correlate with a single pulsating auroral patch in the upper atmosphere, our findings can also be used to constrain magnetic field models with much higher accuracy than has previously been possible.
The exact physiological role for the monoamine serotonin (5‐HT) in modulation of insulin secretion is yet to be fully understood. Although the presence of this monoamine in islets of Langerhans is ...well established, it is only with recent advances that the complex signalling network in islets involving 5‐HT is being unravelled. With more than fourteen different 5‐HT receptors expressed in human islets and receptor‐independent mechanisms in insulin‐producing β‐cells, our understanding of 5‐HT's regulation of insulin secretion is increasing. It is now widely accepted that failure of the pancreatic β‐cell to release sufficient amounts of insulin is the main cause of type 2 diabetes (T2D), an ongoing global epidemic. In this context, 5‐HT signalling may be of importance. In fact, 5‐HT may serve an essential role in regulating the release of insulin and glucagon, the two main hormones that control glucose and lipid homoeostasis. In this review, we will discuss past and current understanding of 5‐HT's role in the endocrine pancreas.
The majority of short gamma-ray bursts (SGRBs) are thought to originate from the merger of compact binary systems collapsing directly to form a black hole. However, it has been proposed that both ...SGRBs and long gamma-ray bursts (LGRBs) may, on rare occasions, form an unstable millisecond pulsar (magnetar) prior to final collapse. GRB 090515, detected by the Swift satellite was extremely short, with a T90 of 0.036 ± 0.016 s, and had a very low fluence of 2 × 10−8 erg cm−2 and faint optical afterglow. Despite this, the 0.3–10 keV flux in the first 200 s was the highest observed for an SGRB by the Swift X-ray Telescope (XRT). The X-ray light curve showed an unusual plateau and steep decay, becoming undetectable after ∼500 s. This behaviour is similar to that observed in some long bursts proposed to have magnetars contributing to their emission. In this paper, we present the Swift observations of GRB 090515 and compare it to other gamma-ray bursts (GRBs) in the Swift sample. Additionally, we present optical observations from Gemini, which detected an afterglow of magnitude 26.4 ± 0.1 at T+ 1.7 h after the burst. We discuss potential causes of the unusual 0.3–10 keV emission and suggest it might be energy injection from an unstable millisecond pulsar. Using the duration and flux of the plateau of GRB 090515, we place constraints on the millisecond pulsar spin period and magnetic field.
We have used all‐sky imaging to relate different types of auroral oval disturbances to large‐scale traveling ionospheric disturbances (LSTIDs). We selected eight nights with good all‐sky imaging and ...Global Positioning System total electron content coverage, including five non–storm time periods with isolated initiations of geomagnetic activity and three storm main phase periods with continuous activity. Periods with LSTIDs generally started and stopped with initiation and cessation of activity. We found evidence that individual LSTIDs often show 1‐1 correspondence with identifiable auroral disturbances, disturbances either being related to a substorm onset or to auroral streamers without a substorm. Since substorm ground magnetic depressions are directly related to the electric fields and electron precipitation of auroral streamers, we hypothesize that streamers may be the primary drivers of individual nightside LSTIDs with or without a substorm. Additionally, we found evidence that (1) LSTIDs detection is more likely near the longitude range of the initiating disturbance than further away, (2) the orientation of LSTID phase fronts depends on location relative to disturbance longitude, and (3) disturbance ionospheric current and magnetic latitude may influence whether a given disturbance leads to a detectable LSTID. Numerous LSTIDs (10 to 12 over 7‐ to 8‐hr periods) were detected during southward interplanetary magnetic field periods of coronal mass ejection storm main phases, the vast majority reflecting streamers in the absence of substorms. Less LSTIDs were seen during the one examined high‐speed‐stream storm. We have also found evidence that omega band disturbances may drive interesting TIDs that are distinct from the LSTIDs driven by the substorm and streamer disturbances.
Key Points
All‐sky imaging was used to relate auroral oval disturbances to large‐scale traveling ionospheric disturbances (LSTIDs)
Streamers may be the primary drivers of individual nightside LSTIDs, with or without a substorm
Possible LSTID longitude, orientation, and strength connections suggested
Long-duration gamma-ray bursts (GRBs) are thought to be produced by the core-collapse of a rapidly rotating massive star. This event generates a highly relativistic jet and prompt gamma-ray and X-ray ...emission arises from internal shocks in the jet or magnetized outflows. If the stellar core does not immediately collapse to a black hole, it may form an unstable, highly magnetized millisecond pulsar or magnetar. As it spins down, the magnetar would inject energy into the jet causing a distinctive bump in the GRB light curve where the emission becomes fairly constant followed by a steep decay when the magnetar collapses. We assume that the collapse of a massive star to a magnetar can launch the initial jet. By automatically fitting the X-ray light curves of all GRBs observed by the Swift satellite, we identified a subset of bursts which have a feature in their light curves which we call an internal plateau – unusually constant emission followed by a steep decay – which may be powered by a magnetar. We use the duration and luminosity of this internal plateau to place limits on the magnetar spin period and magnetic field strength, and find that they are consistent with the most extreme predicted values for magnetars.
Recent ionospheric measurements suggest polar cap flow channels often trigger nightside auroral brightening. However, measurements were limited to the ionosphere, and it was not understood if such ...flow channels can exist in the lobe and can trigger magnetotail reconnection in a localized cross‐tail extent. We examined if localized flow channels can form self‐consistently in a global MHD regime, and if so, how such flow channels originate and relate to localized magnetotail reconnection. We show that lobe convection became nonuniform with azimuthally narrow flow channels (enhanced dawn‐dusk electric fields) of ~3 RE cross‐tail width. The flow channels propagated from the dayside toward the plasma sheet as an interplanetary magnetic field (IMF) discontinuity swept tailward. The plasma sheet around the lobe flow channels became thinner with a similar cross‐tail extent and then localized reconnection occurred. These results suggest that localized flow channels can propagate tailward across the lobe and drive localized magnetotail reconnection, that the cross‐tail width of reconnection and resulting plasma sheet flow channels and dipolarization fronts are related to the width of inflow from the lobe, and that IMF discontinuities drive lobe flow channels.
Key Points
Lobe convection became nonuniform with azimuthally narrow flow channels
Lobe flow channels propagate tailward and drive localized magnetotail reconnection
The cross‐tail width of reconnection and BBFs is related to the width of inflow from the lobe
Auroral substorms are often associated with optical ray or bead structures during initial brightening (substorm auroral onset waves). Occurrence probabilities and properties of substorm onset waves ...have been characterized using 112 substorm events identified in Time History of Events and Macroscale Interactions during Substorms (THEMIS) all‐sky imager data and compared to Rice Convection Model–Equilibrium (RCM‐E) and kinetic instability properties. All substorm onsets were found to be associated with optical waves, and thus, optical waves are a common feature of substorm onset. Eastward propagating wave events are more frequent than westward propagating wave events and tend to occur during lower‐latitude substorms (stronger solar wind driving). The wave propagation directions are organized by orientation of initial brightening arcs. We also identified notable differences in wave propagation speed, wavelength (wave number), period, and duration between westward and eastward propagating waves. In contrast, the wave growth rate does not depend on the propagation direction or substorm strength but is inversely proportional to the wave duration. This suggests that the waves evolve to poleward expansion at a certain intensity threshold and that the wave properties do not directly relate to substorm strengths. However, waves are still important for mediating the transition between the substorm growth phase and poleward expansion. The relation to arc orientation can be explained by magnetotail structures in the RCM‐E, indicating that substorm onset location relative to the pressure peak determines the wave propagation direction. The measured wave properties agree well with kinetic ballooning interchange instability, while cross‐field current instability and electromagnetic ion cyclotron instability give much larger propagation speed and smaller wave period.
Key Points
Occurrence probability and property of different types of auroral onset waves are determined
Wave property does not relate to substorm strength but to plasma sheet configuration
Wave properties are most consistent with kinetic ballooning interchange instability
We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface ...albedo. The net effect of all agents was to increase radiative forcing during the first year (34 ± 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (-2.3 ± 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming.
Abstract
Background
Ketamine is growing in popularity for procedural sedation in the paediatric population, yet safety concerns remain. We performed a retrospective review of practice and outcomes of ...paediatric ketamine sedation using the World SIVA International Sedation Task Force reporting tool.
Methods
A retrospective inspection of the dedicated emergency department electronic sedation database and subsequent note and sedation chart review was performed for all paediatric sedations throughout a 7 yr period from September 2006. All adverse events were stratified.
Results
During the study period, procedural sedation was provided for a total of 243 children, of whom 215 were sedated with ketamine, most commonly for wound management (
n
=131). The median patient age was 4 yr (14 months to 15 yr), and 63.7% were male. Of the total, 76.7% were discharged home either directly (
n
=101) or after brief observation (
n
=64). One patient required subsequent general anaesthesia after a failed sedation with paradoxical agitation. Of the total, 9.8% of patients had an adverse event, the most severe risk stratification being ‘minor risk’. All interventions were ‘minimal risk’. There were no ‘sentinel risk’ outcomes.
Conclusions
These data support the ongoing use of ketamine for paediatric procedural sedation in the emergency department by emergency physicians. Relatively high resource requirements mean that ensuring adequate numbers of procedures may prove challenging.
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