ABSTRACT Since 2012 August Voyager 1 has been observing the local interstellar energy spectra of Galactic cosmic-ray nuclei down to 3 MeV nuc−1 and electrons down to 2.7 MeV. The H and He spectra ...have the same energy dependence between 3 and 346 MeV nuc−1, with a broad maximum in the 10-50 MeV nuc−1 range and a H/He ratio of 12.2 0.9. The peak H intensity is ∼15 times that observed at 1 AU, and the observed local interstellar gradient of 3-346 MeV H is −0.009 0.055% AU−1, consistent with models having no local interstellar gradient. The energy spectrum of electrons (e− + e+) with 2.7-74 MeV is consistent with E−1.30 0.05 and exceeds the H intensity at energies below ∼50 MeV. Propagation model fits to the observed spectra indicate that the energy density of cosmic-ray nuclei with >3 MeV nuc−1 and electrons with >3 MeV is 0.83-1.02 eV cm−3 and the ionization rate of atomic H is in the range of 1.51-1.64 × 10−17 s−1. This rate is a factor >10 lower than the ionization rate in diffuse interstellar clouds, suggesting significant spatial inhomogeneity in low-energy cosmic rays or the presence of a suprathermal tail on the energy spectrum at much lower energies. The propagation model fits also provide improved estimates of the elemental abundances in the source of Galactic cosmic rays.
We previously reported that pan-cortical effects occur when cognitive tasks end afterdischarges. For this report, we analyzed wavelet cross-coherence changes during cognitive tasks used to terminate ...afterdischarges studying multiple time segments and multiple groups of inter-electrode-con distances. We studied 12 patients with intractable epilepsy, with 970 implanted electrode contacts, and 39,871 electrode contact combinations. When cognitive tasks ended afterdischarges, coherence varied similarly across the cortex throughout the tasks, but there were gradations with time, distance, and frequency: (1) They tended to progressively decrease relative to baseline with time and then to increase toward baseline when afterdischarges ended. (2) During most time segments, decreases from baseline were largest for the closest inter-contact distances, moderate for intermediate inter-contact distances, and smallest for the greatest inter-contact distances. With respect to our patients' intractable epilepsy, the changes found suggest that future therapies might treat regions beyond those closest to regions of seizure onset and treat later in a seizure's evolution. Similar considerations might apply to other disorders. Our findings also suggest that cognitive tasks can result in pan-cortical coherence changes that participate in underlying attention, perhaps complementing the better-known regional mechanisms.
On 25 August 2012, Voyager 1 was at 122 astronomical units when the steady intensity of low-energy ions it had observed for the previous 6 years suddenly dropped for a third time and soon completely ...disappeared as the ions streamed away into interstellar space. Although the magnetic field observations indicate that Voyager 1 remained inside the heliosphere, the intensity of cosmic ray nuclei from outside the heliosphere abruptly increased. We report the spectra of galactic cosmic rays down to ~3 × 10⁶ electron volts per nucleon, revealing H and He energy spectra with broad peaks from 10 × 10⁶ to 40 × 10⁶ electron volts per nucleon and an increasing galactic cosmic-ray electron intensity down to ~10 × 10⁶ electron volts.
Voyager 1 crossed the termination shock of the supersonic flow of the solar wind on 16 December 2004 at a distance of 94.01 astronomical units from the Sun, becoming the first spacecraft to begin ...exploring the heliosheath, the outermost layer of the heliosphere. The shock is a steady source of low-energy protons with an energy spectrum$\sim E^{-1.41 \pm 0.15}$from$0.5 to \sim 3.5 megaelectron volts$, consistent with a weak termination shock having a solar wind velocity jump ratio$r = 2.6_{-0.2}^{+0.4}$. However, in contradiction to many predictions, the intensity of anomalous cosmic ray (ACR) helium did not peak at the shock, indicating that the ACR source is not in the shock region local to Voyager 1. The intensities of ~10-megaelectron volt electrons, ACRs, and galactic cosmic rays have steadily increased since late 2004 as the effects of solar modulation have decreased.
The glaciers within the Amundsen Sea Embayment (ASE), West Antarctica, are amongst the most rapidly retreating in Antarctica. Meteorological reanalysis products are widely used to help understand and ...simulate the processes causing this retreat. Here we provide an evaluation against observations of four of the latest global reanalysis products within the ASE region—the European Centre for Medium‐Range Weather Forecasts Interim Reanalysis (ERA‐I), Japanese 55‐year Reanalysis (JRA‐55), Climate Forecast System Reanalysis (CFSR), and Modern Era Retrospective‐Analysis for Research and Applications (MERRA). The observations comprise data from four automatic weather stations (AWSs), three research vessel cruises, and a new set of 38 radiosondes all within the period 2009–2014. All four reanalyses produce 2 m temperature fields that are colder than AWS observations, with the biases varying from approximately −1.8°C (ERA‐I) to −6.8°C (MERRA). Over the Amundsen Sea, spatially averaged summertime biases are between −0.4°C (JRA‐55) and −2.1°C (MERRA) with notably larger cold biases close to the continent (up to −6°C) in all reanalyses. All four reanalyses underestimate near‐surface wind speed at high wind speeds (>15 m s−1) and exhibit dry biases and relatively large root‐mean‐square errors (RMSE) in specific humidity. A comparison to the radiosonde soundings shows that the cold, dry bias at the surface extends into the lower troposphere; here ERA‐I and CFSR reanalyses provide the most accurate profiles. The reanalyses generally contain larger temperature and humidity biases, (and RMSE) when a temperature inversion is observed, and contain larger wind speed biases (~2 to 3 m s−1), when a low‐level jet is observed.
Key Points
There are significant discrepancies in reanalyses surface wind, humidity, and temperature in the Amundsen Sea area
Temperature biases are greatest over and closer to the Antarctic continent and near the surface
Validation data include 38 radiosondes withheld from the reanalyses
•Cognitive tasks (attention to task instructions, then task performance) can end afterdischarges caused by cortical stimulation.•Electrocorticographic coherence decreases progressively with these ...tasks, returning towards baseline when afterdischarges end.•These decreases may be due to emergent properties of the brain as a whole which might help modify seizures and other disorders.
We previously studied efficacy of cognitive tasks on afterdischarge termination in patients undergoing cortical stimulation and found that diffuse wavelet cross-coherence changes on electrocorticography were associated with termination efficacy. We now report wavelet cross-coherence findings during different time segments of trials during which afterdischarges ended.
For 12 patients with implanted subdural electrodes, we compared wavelet cross-coherence findings among several 1-second portions of cognitive tasks, reflecting task presentation, patient replies, and afterdischarge termination.
Coherence decreased significantly and progressively over time for 16.89, 22.53, and 30.03 Hz frequency ranges, but increased with afterdischarge termination. Coherence first increased, and then decreased for the 7.13 Hz frequency range.
The findings suggest that cumulative but non-specific factors, likely related primarily to attention, influence the coherence results throughout the task, with a separate effect due to resolution of the afterdischarges at the end.
Task performance is well known to localize to specific brain regions and to be restricted in timing. In contrast, attention and overall mental activation might be due to emergent properties of brain as a whole and that are less circumscribed in space or time. Cognitive tasks might modify seizures and other neurological disorders.
At the Voyager 1 (V1) spacecraft in the outer heliosphere, the intensities of both anomalous cosmic rays and galactic cosmic rays (GCRs) changed suddenly and decisively on 25 August (121.7 AU from ...the Sun). Within a matter of a few days, the intensity of 1.9–2.7 MeV protons and helium nuclei had decreased to less than 0.1 of their previous value, and eventually the intensities decreased by factors of at least 300–500. Also, on 25 August, the GCR protons, helium, and electrons increased suddenly in just 2 or 3 days by a factor of up to 2. The intensities of the GCR nuclei of all energies from 2 to 400 MeV then remained essentially constant with intensity levels and spectra that may represent the local GCR. The suddenness of these intensity changes indicates that V1 has crossed a well‐defined boundary for energetic particles at this time possibly related to the heliopause.
Key Points
Boundary of heliosphere is very sudden
Local galactic cosmic ray spectra have peak at 60 MeV
Particle layers observed near heliospheric boundary
•When cognitive effort ends afterdischarges, there are widespread changes in coherence.•These coherence changes are similar throughout the cortex, regardless of the distance between recorded ...sites.•This similarity suggests a pan-cortical effect that may complement the activity of regional and multiregional networks.
It is well known that activity in, or coordination among, brain regions, can underlie movement, sensation, language, and cognition but there are observations that tasks unrelated to specific brain regions can nonetheless alter activity in those regions. These tasks might invoke activity in multiregional networks, but it also is possible that they are associated with changes beyond these networks. We therefore evaluated the possibility that more widespread, or even whole-cortical, mechanisms might complement or alter focal or multifocal cortical activity.
We assessed the extent of electroencephalographic changes occurring outside areas with epileptiform activity, but that were associated with termination of the epileptiform activity. To do this, we measured the distribution of wavelet cross-coherence changes based on electrocorticography from 15 patients who showed regional afterdischarges in response to electrical brain stimulation prior to epilepsy surgery and in whom cognitive tasks were used in attempts to end the afterdischarges. There were 1276 electrodes implanted in these patients, and we analyzed a total of 55,494 electrode combinations. We compared recordings when cognitive effort was versus when it was not successful in ending afterdischarges.
We found that when afterdischarges were suppressed there were changes in electrocorticographic coherence that were similar throughout cortex, regardless of the distance between sites.
The similarity implies coordination of the changes, and the similarity regardless of distance or location implies a pan-cortical effect.
Our results provide physical support for hypotheses that pan-cortical processes complement the well-known regional and multiregional networks. These processes may participate in, be recruited by, modify, or underlie the conative experiences of waking life.
Abstract Subdural electrodes are frequently used to aid in the neurophysiological assessment of patients with intractable seizures. We review the indications for these, their uses for localizing ...epileptogenic regions and for localizing cortical regions supporting movement, sensation, and language.
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