scholarly journals A test of the efficacy of sand saltation for silt production: Implications for the interpretation of loess

Geology ◽  
2020 ◽  
Vol 48 (11) ◽  
pp. 1105-1109 ◽  
Author(s):  
Steven M. Adams ◽  
Gerilyn S. Soreghan
Keyword(s):  
Long Duration ◽  
Wind Velocities ◽  
Loess Deposits ◽  
Paleoclimatic Significance ◽  
Control Samples

Abstract Production of the silt that forms loess is attributed to processes operating in both glacial systems (glacial grinding) and sandy deserts (saltation-induced fracturing). However, the efficacy of saltation for significant silt production is controversial. Understanding the potential for silt production in deserts is essential for determining the paleoclimatic significance of loess. To better assess the significance of eolian abrasion for silt production, experimental abrasion was conducted in a device designed to simulate sand saltation at sustained storm-wind velocities (∼25 m/s). The design differs from previous work in (1) maintaining strong measured velocities for long duration, (2) removing preexisting silt and utilizing control samples, (3) and scaling results to estimate potential for loess accumulation. Scaling experimental rates of production to geologic proportions indicates that eolian abrasion of sand produces insufficient silt to create geologically significant loess deposits.

scholarly journals Ionospheric total electron content responses to HILDCAA intervals

2020 ◽  
Vol 38 (1) ◽  
pp. 27-34
Author(s):  
Regia Pereira da Silva ◽  
Clezio Marcos Denardini ◽  
Manilo Soares Marques ◽  
Laysa Cristina Araujo Resende ◽  
Juliano Moro ◽  
...  
Keyword(s):  
Solar Wind ◽  
Total Electron Content ◽  
High Speed ◽  
Electron Content ◽  
Direct Relation ◽  
Total Electron ◽  
Ionospheric Total Electron Content ◽  
Long Duration ◽  
Wind Velocities ◽  
Hourly Distribution

Abstract. The High-Intensity Long-Duration and Continuous AE Activities (HILDCAA) intervals are capable of causing a global disturbance in the terrestrial ionosphere. However, the ionospheric storms' behavior due to these intervals is still not widely understood. In the current study, we seek to comprise the HILDCAA disturbance time effects in the total electron content (TEC) values with respect to the quiet days' pattern by analyzing local time and seasonal dependences, and the influences of the solar wind velocity on a sample of 10 intervals that occurred in the years 2015 and 2016. The main results showed that the hourly distribution of the disturbance TEC may vary substantially between one HILDCAA interval and another. An equinoctial anomaly was found since the equinoxes represent more ionospheric TEC responses than the solstices. Regarding the solar wind velocities, although HILDCAA intervals are associated with high-speed streams, this association does not present a direct relation to TEC disturbance magnitudes at low and equatorial latitudes.

scholarly journals Ionospheric Total Electron Content responses to HILDCAAs intervals

2019 ◽  
Author(s):  
Regia Pereira Silva ◽  
Clezio Marcos Denardini ◽  
Manilo Soares Marques ◽  
Laysa Cristina Araújo Resende ◽  
Juliano Moro ◽  
...  
Keyword(s):  
Solar Wind ◽  
Total Electron Content ◽  
High Speed ◽  
Geomagnetic Storms ◽  
Electron Content ◽  
Total Electron ◽  
Ionospheric Total Electron Content ◽  
Long Duration ◽  
Wind Velocities ◽  
Hourly Distribution

Abstract. The High-Intensity Long-Duration and Continuous AE Activities (HILDCAA) intervals are capable of causing a global disturbance in the terrestrial ionosphere. However, the ionospheric storms' behavior due to these geomagnetic activity forms is still not widely understood. In this study, we seek to comprise the HILDCAAs disturbance time effects in the Total Electron Content (TEC) values with respect to the quiet days' pattern analyzing local time and seasonal dependences, and the influences of the solar wind velocity to a sample of ten intervals occurred in 2015 and 2016 years. The main results showed that the hourly distribution of the disturbance TEC may vary substantially between one interval and another. Doing a comparative to geomagnetic storms, while the positive ionospheric storms are more pronounced in the winter, this season presents less geoeffectiveness or almost none to HILDCAA intervals. It was find an equinoctial anomaly, since the equinoxes represent more ionospheric TEC responses during HILDCAA intervals than the solstices. Regarding to the solar wind velocities, although HILDCAA intervals are associated to High Speed Streams, this association does not present a direct relation regards to TEC disturbances in low and equatorial latitudes.

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.

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.

An Evaluation of the Long Duration use of an Head Mounted Display

2008 ◽  
Author(s):  
Harry Litaker ◽  
Shelby Thompson ◽  
Ronald Archer
Keyword(s):  
Head Mounted Display ◽  
Long Duration
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