scholarly journals A combined radio and optical study of flare stars. The long-duration events

1979 ◽  
Vol 187 (3) ◽  
pp. 405-419 ◽  
Author(s):  
G. J. Nelson ◽  
R. D. Robinson ◽  
O. B. Slee ◽  
G. Fielding ◽  
A. A. Page ◽  
...  
Keyword(s):  
Optical Study ◽  
Long Duration ◽  
Flare Stars

scholarly journals Two-colour observations of spikes and flares by high time resolution

1990 ◽  
Vol 137 ◽  
pp. 33-34
Author(s):  
V.P. Zalinian ◽  
A.A. Karapetian ◽  
H.M. Tovmassian
Keyword(s):  
Time Resolution ◽  
High Time ◽  
High Time Resolution ◽  
Long Duration ◽  
Flare Stars ◽  
Ev Lac

Observations of flare stars with high time resolution permit to register spiky type flares and also to study in detail bright curves of flares. In Byurakan observatory observations of EV Lac have been made with 0.1 s time resolution simultaneouslyin two filters “U” and “B” [1-3]. These observations permited to detect flares of a burst type (Fig.1) and also to reveil multipeak structure of long duration flares. It is necessary to stress that simultaneous observations in two colours increas appresiably the thrustworthiness of the registered spiky flares.

scholarly journals Flare stars at radio wavelengths

1990 ◽  
Vol 137 ◽  
pp. 125-138
Author(s):  
Kenneth R. Lang
Keyword(s):  
Active Regions ◽  
Plasma Radiation ◽  
Radio Radiation ◽  
Very Large Array ◽  
Brightness Temperatures ◽  
Stellar Flares ◽  
Long Duration ◽  
Electron Cyclotron Masers ◽  
Flare Stars ◽  
Radiation Processes

The radio emission from dMe flare stars is discussed using Very Large Array and Arecibo observations as examples. Active flare stars emit weak, unpolarized, quiescent radio radiation that may be always present. Although thermal bremsstrahlung and/or thermal gyroresonance radiation account for the slowly-varying, quiescent radio radiation of solar active regions, these processes cannot account for the long-wavelength quiescent radiation observed from nearby dMe flare stars. It has been attributed to nonthermal gyrosynchrotron radiation, but some as yet unexplained mechanism must be continually producing the energetic electrons. Long-duration (hours), narrow-band (Δv/v < 0.1) radiation is also emitted from some nearby dMe stars at 20 cm wavelength. Such radiation may be attributed to coherent plasma radiation or to coherent electron-cyclotron masers. Impulsive stellar flares exhibit rapid variations (< 100 msec) that require radio sources that are smaller than the star in size, and high brightness temperatures TB > 1015 K that are also explained by coherent radiation processes. Quasi-periodic temporal fluctuations suggest pulsations during some radio flares. Evidence for frequency structure and positive or negative frequency drifts during radio flares from dMe stars is also presented.

scholarly journals Rosat Observations of Stellar Flares

1994 ◽  
Vol 142 ◽  
pp. 735-742
Author(s):  
J. H. M. M. Schmitt
Keyword(s):  
Time Variability ◽  
X Rays ◽  
Late Type ◽  
X Ray ◽  
Stellar Flares ◽  
Long Duration ◽  
Sky Survey ◽  
Pointed Observation ◽  
Flare Stars ◽  
First Time

AbstractX-ray observations of stellar flares obtained during the ROSAT all-sky survey as well as in the ROSAT pointing program are discussed. The ROSAT all-sky survey allowed—for the first time—an unbiased search for stellar flares among all types of stars. A fundamentally new result obtained is that flares can occur on all types of late-type stars, thus supporting the view that the X-ray emission from these stars is controlled by magnetic processes. Long-duration flares can be studied with the all-sky survey data particularly well, and an especially well-observed long-duration flare event on the flare star EV Lacertae is presented and discussed in detail. Finally, the issue of time variability on the shortest detectable timescales and the question of microflaring is discussed using ROSAT data from a pointed observation of UV Ceti.Subject headings: stars: coronae — stars: flare — stars: late-type — X-rays: stars

The LDE-Type Flare Occurrence (1969-1993)

1994 ◽  
Vol 144 ◽  
pp. 279-282
Author(s):  
A. Antalová
Keyword(s):  
Time Series ◽  
Fourier Analysis ◽  
Sunspot Cycle ◽  
List Type ◽  
Type Number ◽  
Solar Cycles ◽  
Type Iv ◽  
Long Duration ◽  
Cycle Maximum ◽  
Flare Index

AbstractThe occurrence of LDE-type flares in the last three cycles has been investigated. The Fourier analysis spectrum was calculated for the time series of the LDE-type flare occurrence during the 20-th, the 21-st and the rising part of the 22-nd cycle. LDE-type flares (Long Duration Events in SXR) are associated with the interplanetary protons (SEP and STIP as well), energized coronal archs and radio type IV emission. Generally, in all the cycles considered, LDE-type flares mainly originated during a 6-year interval of the respective cycle (2 years before and 4 years after the sunspot cycle maximum). The following significant periodicities were found:• in the 20-th cycle: 1.4, 2.1, 2.9, 4.0, 10.7 and 54.2 of month,• in the 21-st cycle: 1.2, 1.6, 2.8, 4.9, 7.8 and 44.5 of month,• in the 22-nd cycle, till March 1992: 1.4, 1.8, 2.4, 7.2, 8.7, 11.8 and 29.1 of month,• in all interval (1969-1992):a)the longer periodicities: 232.1, 121.1 (the dominant at 10.1 of year), 80.7, 61.9 and 25.6 of month,b)the shorter periodicities: 4.7, 5.0, 6.8, 7.9, 9.1, 15.8 and 20.4 of month.Fourier analysis of the LDE-type flare index (FI) yields significant peaks at 2.3 - 2.9 months and 4.2 - 4.9 months. These short periodicities correspond remarkably in the all three last solar cycles. The larger periodicities are different in respective cycles.

Electron Optical Study of Surface Morphologies of Crystals

1980 ◽  
Vol 38 ◽  
pp. 376-377
Author(s):  
Sumio Iijima ◽  
Tung Hsu
Keyword(s):  
Thin Film ◽  
Optical Study ◽  
Regular Array ◽  
Surface Steps ◽  
Diffracted Waves ◽  
Image Position ◽  
Surface Morphologies

Suppose the thickness of a thin film of a crystal varies periodically like a regular array of surface steps, kinematical intensities of diffracted waves from this crystal are modulated by a shape transform,

Relation Between Level of Prefrontal Activity and Subject's Performance

1999 ◽  
Vol 13 (2) ◽  
pp. 117-125 ◽  
Author(s):  
Laurence Casini ◽  
Françoise Macar ◽  
Marie-Hélène Giard
Keyword(s):  
Brain Activity ◽  
Sensory Information ◽  
Practice Phase ◽  
Trained Subjects ◽  
Anagram Task ◽  
Economic Information ◽  
Long Duration ◽  
Level Of Activity ◽  
The Brain ◽  
Processing Mechanism

Abstract The experiment reported here was aimed at determining whether the level of brain activity can be related to performance in trained subjects. Two tasks were compared: a temporal and a linguistic task. An array of four letters appeared on a screen. In the temporal task, subjects had to decide whether the letters remained on the screen for a short or a long duration as learned in a practice phase. In the linguistic task, they had to determine whether the four letters could form a word or not (anagram task). These tasks allowed us to compare the level of brain activity obtained in correct and incorrect responses. The current density measures recorded over prefrontal areas showed a relationship between the performance and the level of activity in the temporal task only. The level of activity obtained with correct responses was lower than that obtained with incorrect responses. This suggests that a good temporal performance could be the result of an efficacious, but economic, information-processing mechanism in the brain. In addition, the absence of this relation in the anagram task results in the question of whether this relation is specific to the processing of sensory information only.

Effects of Fatigue on Cognitive Performance in Long-Duration Simulated Flight Missions

2020 ◽  
Vol 10 (2) ◽  
pp. 82-93
Author(s):  
Eduardo Rosa ◽  
Ola Eiken ◽  
Mikael Grönkvist ◽  
Roger Kölegård ◽  
Nicklas Dahlström ◽  
...  
Keyword(s):  
Executive Functions ◽  
Task Performance ◽  
Cognitive Performance ◽  
Cognitive Tasks ◽  
Fatigue Index ◽  
Fighter Aircraft ◽  
Long Duration ◽  
Metacognitive Accuracy

Abstract. Fighter pilots may be exposed to extended flight missions. Consequently, there is increasing concern about fatigue. We investigated the effects of fatigue and cognitive performance in a simulated 11-hr mission in the 39 Gripen fighter aircraft. Five cognitive tasks were used to assess cognitive performance. Fatigue was measured with the Samn–Perelli Fatigue Index. Results showed that performance in the non-executive task degraded after approximately 7 hr. Fatigue ratings showed a matching trend to the performance in this task. Performance in tasks taxing executive functions did not decline. We interpreted that fatigue can be overridden by increased attentional effort for executive tasks but not for non-executive components of cognition. Participants underestimated their performance and metacognitive accuracy was not influenced by fatigue.

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