scholarly journals A Very Rapid Extreme Scattering Event in the IDV Source 0954+658

2002 ◽  
Vol 19 (1) ◽  
pp. 10-13 ◽  
Author(s):  
Giuseppe Cimò ◽  
T. Beckert ◽  
T. P. Krichbaum ◽  
L. Fuhrmann ◽  
A. Kraus ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Light Curve ◽  
Frequency Dependence ◽  
Flux Density ◽  
Time Scales ◽  
Time Scale ◽  
Variable Light ◽  
Ray Path ◽  
Intraday Variability ◽  
Scattering Events

AbstractExtreme scattering events (ESEs) are dramatic variations of the flux density at gigahertz frequencies caused by ray path distortions within an isolated inhomogeneity (‘plasma lens’) in the interstellar medium. These events are characterised by a deep flux density minimum in the light curve with, in some cases, surrounding maxima. The variability time scales range from weeks to months. These phenomena show a strong frequency dependence, in which the variability amplitudes increase with wavelength. During an intraday variability (IDV) monitoring project (March 2000), a feature resembling an ESE-like event appeared in the variable light curve of 0954+658, however with a time scale of less than two days. We will discuss this effect and its implications for a better description of the interstellar medium.

scholarly journals Radio light-curve for WR 146 (HM19-3, WC6+O8.5), a colliding wind binary

1999 ◽  
Vol 193 ◽  
pp. 390-391
Author(s):  
Diah Y.A. Setia Gunawan ◽  
A. Ger de Bruyn ◽  
Karel A. van der Hucht ◽  
Peredur M. Williams
Keyword(s):  
Light Curve ◽  
Flux Density ◽  
Radio Telescope ◽  
Time Scale ◽  
Preliminary Results ◽  
Average Flux

We report preliminary results of monitoring the flux from the Wolf-Rayet object WR 146 with the Westerbork Synthesis Radio Telescope at 21 cm since 1989. We find the average flux density slowly rising in the period 1989–1997, with evidence of shorter time-scale variability.

scholarly journals Long-term Monitoring of Molonglo Calibrators

2000 ◽  
Vol 17 (1) ◽  
pp. 72-82 ◽  
Author(s):  
B. M. Gaensler ◽  
R. W. Hunstead
Keyword(s):  
Interstellar Medium ◽  
Light Curve ◽  
Time Scales ◽  
Galactic Plane ◽  
Line Of Sight ◽  
Radio Sources ◽  
Before And After ◽  
Long Term Monitoring ◽  
Term Monitoring

AbstractBefore and after every 12 hour synthesis observation, the Molonglo Observatory Synthesis Telescope (MOST) measures the flux densities of ∼5 compact extragalactic radio sources, chosen from a list of 55 calibrators. From 1984 to 1996, the MOST made some 58,000 such measurements. We have developed an algorithm to process this dataset to produce a light curve for each source spanning this thirteen-year period. We find that 18 of the 55 calibrators are variable, on time scales between one and ten years. There is the tendency for sources closer to the Galactic Plane to be more likely to vary, which suggests that the variability is a result of refractive scintillation in the Galactic interstellar medium. The sources with the flattest radio spectra show the highest levels of variability, an effect possibly resulting from differing orientations of the radio axes to the line of sight.

scholarly journals X-Ray Variability in Active Galactic Nuclei: Two Things That Everybody Should Know

1998 ◽  
Vol 11 (2) ◽  
pp. 804-807
Author(s):  
Karen M. Leighly
Keyword(s):  
Light Curve ◽  
Active Galactic Nuclei ◽  
Time Scales ◽  
Time Scale ◽  
Galactic Nuclei ◽  
X Rays ◽  
X Ray ◽  
Central Engine ◽  
Distinguishing Property

X-ray variability is a distinguishing property of Active Galactic Nuclei (AGN), and the energetics and time scales of the emission dictate that the X-rays must originate very close to the central engine. In this review I discuss two basic topics from AGN variability research. The first is the correlation of the variability time scale with the X-ray luminosity, and the second is the structure of the X-ray light curve. In each case, I first review the old results that have been known for approximately the last 10 years and then I discuss very new results which may force us to modify our ideas about the origin of AGN X-ray variability. Note that I am discussing the variability of non-blazar type AGN.

scholarly journals High-Precision NBPP Timing Measurements at Nançay

2000 ◽  
Vol 177 ◽  
pp. 55-56
Author(s):  
I. Cognard ◽  
J.-F. Lestrade ◽  
D.C. Backer ◽  
P.S. Ray ◽  
R.S. Foster ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Real Time ◽  
Flux Density ◽  
Electron Density ◽  
San Francisco ◽  
High Precision ◽  
Line Of Sight ◽  
Radio Sources ◽  
Search Data ◽  
Scattering Events

The Nançay radiotelescope in France is a large collecting area (7000m2) with receivers around 1.4, 1.7 and 3.5GHz. At this observatory, we are conducting frequent high-precision timing observations of 5 millisecond pulsars (PSR B1937+21, B1821-24 since 1988; J1643-1224, J1713+0747 and B1620-26 since 1996) with a swept frequency oscilllator based on a DDS as a dedisperser.The most interesting result from these dense series of observations is the detection of several Extreme Scattering Events in direction of B1937+21 and possibly in direction of B1821-24 (Cognard, 1993,Nature,366, 320; Cognard & Lestrade, 1996, in ASP Conf. Ser. Vol 105, Pulsars: Problems and Progress (San Francisco: ASP), 469; Lestrade, Rickett & Cognard 1998, A&A,334, 1068). The flux density variations and TOA fluctuations observed have been used to estimate the size (several AU) and electron density (a few hundreds electrons cm−3) of the discrete ionised clouds localized in the interstellar medium that are thought to be responsible for this phenomena. The number of events recorded at Nançay in direction of B1937+21 yields the space density 105– 106pc−3for these clouds. This density is very large and is about 100 times higher than the density estimated from Extreme Scattering Events observed in direction of extragalactic radio sources (Fiedler et al., 1994,ApJ,430, 581). This might mean that the line of sight to B1937+21 is peculiar. This is being investigated with additional observations of a larger array of pulsars at Nançay with the Navy-Berkeley-Pulsar Processor (Figure 1) This processor NBPP (Foster et al., in ASP Conf. Ser. Vol 105, Pulsars: Problems and Progress (San Francisco: ASP), 25) has been used to acquire pulsar search data for 2 years at Nancay and we are now using its real-time folding capability.

scholarly journals Extreme Scattering Events

1988 ◽  
Vol 129 ◽  
pp. 301-302
Author(s):  
Ralph Fiedler ◽  
Brian Dennison ◽  
Kenneth Johnston
Keyword(s):  
Interstellar Medium ◽  
Flux Density ◽  
Light Curves ◽  
Small Scale ◽  
Radio Sources ◽  
Density Measurements ◽  
Extragalactic Radio Sources ◽  
Scattering Events

Dally flux density measurements of 36 extragalactic radio sources over a seven year period, obtained by the Green Bank interferometer, reveal several unusual minima in the light curves that do not follow typical source variations (Fiedler et al. 1987). The most significant departure from typical source variability occurred at both frequencies in the quasar 0954+658 between 1980.95 and 1981.3. Refractive focussing by small scale inhomogeneities in an ionized structure in the interstellar medium appears to be the most likely explanation.

scholarly journals GNSS-to-GNSS time offsets: study on the broadcast of a common reference time

GPS Solutions ◽  
2021 ◽  
Vol 25 (2) ◽  
Author(s):  
Ilaria Sesia ◽  
Giovanna Signorile ◽  
Tung Thanh Thai ◽  
Pascale Defraigne ◽  
Patrizia Tavella
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Reference Time ◽  
Single Time ◽  
Common Reference ◽  
Prediction Quality ◽  
Common Time ◽  
Time Offset ◽  
The Impact ◽  
Low Uncertainty

AbstractWe present two different approaches to broadcasting information to retrieve the GNSS-to-GNSS time offsets needed by users of multi-GNSS signals. Both approaches rely on the broadcast of a single time offset of each GNSS time versus one common time scale instead of broadcasting the time offsets between each of the constellation pairs. The first common time scale is the average of the GNSS time scales, and the second time scale is the prediction of UTC already broadcast by the different systems. We show that the average GNSS time scale allows the estimation of the GNSS-to-GNSS time offset at the user level with the very low uncertainty of a few nanoseconds when the receivers at both the provider and user levels are fully calibrated. The use of broadcast UTC prediction as a common time scale has a slightly larger uncertainty, which depends on the broadcast UTC prediction quality, which could be improved in the future. This study focuses on the evaluation of two different common time scales, not considering the impact of receiver calibration, at the user and provider levels, which can nevertheless have an important impact on GNSS-to-GNSS time offset estimation.

Sensor-Based Estimation of Dim Light Melatonin Onset Using Features of Two Time Scales

2021 ◽  
Vol 2 (3) ◽  
pp. 1-15
Author(s):  
Cheng Wan ◽  
Andrew W. Mchill ◽  
Elizabeth B. Klerman ◽  
Akane Sano
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Light Exposure ◽  
Biological Activities ◽  
Second Step ◽  
Sampled Data ◽  
Dim Light Melatonin Onset ◽  
Dim Light ◽  
Using Data ◽  
Mean Square Errors

Circadian rhythms influence multiple essential biological activities, including sleep, performance, and mood. The dim light melatonin onset (DLMO) is the gold standard for measuring human circadian phase (i.e., timing). The collection of DLMO is expensive and time consuming since multiple saliva or blood samples are required overnight in special conditions, and the samples must then be assayed for melatonin. Recently, several computational approaches have been designed for estimating DLMO. These methods collect daily sampled data (e.g., sleep onset/offset times) or frequently sampled data (e.g., light exposure/skin temperature/physical activity collected every minute) to train learning models for estimating DLMO. One limitation of these studies is that they only leverage one time-scale data. We propose a two-step framework for estimating DLMO using data from both time scales. The first step summarizes data from before the current day, whereas the second step combines this summary with frequently sampled data of the current day. We evaluate three moving average models that input sleep timing data as the first step and use recurrent neural network models as the second step. The results using data from 207 undergraduates show that our two-step model with two time-scale features has statistically significantly lower root-mean-square errors than models that use either daily sampled data or frequently sampled data.

scholarly journals Locally and Remotely Forced Subtropical AMOC Variability: A Matter of Time Scales

2020 ◽  
Vol 33 (12) ◽  
pp. 5155-5172
Author(s):  
Quentin Jamet ◽  
William K. Dewar ◽  
Nicolas Wienders ◽  
Bruno Deremble ◽  
Sally Close ◽  
...  
Keyword(s):  
Time Series ◽  
Time Scales ◽  
North Atlantic ◽  
Time Scale ◽  
Low Frequency ◽  
Meridional Overturning Circulation ◽  
Open Boundary ◽  
Overturning Circulation ◽  
Decadal Scale ◽  
Meridional Overturning

AbstractMechanisms driving the North Atlantic meridional overturning circulation (AMOC) variability at low frequency are of central interest for accurate climate predictions. Although the subpolar gyre region has been identified as a preferred place for generating climate time-scale signals, their southward propagation remains under consideration, complicating the interpretation of the observed time series provided by the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array–Western Boundary Time Series (RAPID–MOCHA–WBTS) program. In this study, we aim at disentangling the respective contribution of the local atmospheric forcing from signals of remote origin for the subtropical low-frequency AMOC variability. We analyze for this a set of four ensembles of a regional (20°S–55°N), eddy-resolving (1/12°) North Atlantic oceanic configuration, where surface forcing and open boundary conditions are alternatively permuted from fully varying (realistic) to yearly repeating signals. Their analysis reveals the predominance of local, atmospherically forced signal at interannual time scales (2–10 years), whereas signals imposed by the boundaries are responsible for the decadal (10–30 years) part of the spectrum. Due to this marked time-scale separation, we show that, although the intergyre region exhibits peculiarities, most of the subtropical AMOC variability can be understood as a linear superposition of these two signals. Finally, we find that the decadal-scale, boundary-forced AMOC variability has both northern and southern origins, although the former dominates over the latter, including at the site of the RAPID array (26.5°N).

scholarly journals A EEG-based emotion recognition model with rhythm and time characteristics

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Jianzhuo Yan ◽  
Shangbin Chen ◽  
Sinuo Deng
Keyword(s):  
Emotion Recognition ◽  
Time Scales ◽  
Time Scale ◽  
Short Term Memory ◽  
Recognition Model ◽  
Memory Network ◽  
Long Short Term Memory ◽  
Valence And Arousal ◽  
Memory Characteristics

Abstract As an advanced function of the human brain, emotion has a significant influence on human studies, works, and other aspects of life. Artificial Intelligence has played an important role in recognizing human emotion correctly. EEG-based emotion recognition (ER), one application of Brain Computer Interface (BCI), is becoming more popular in recent years. However, due to the ambiguity of human emotions and the complexity of EEG signals, the EEG-ER system which can recognize emotions with high accuracy is not easy to achieve. Based on the time scale, this paper chooses the recurrent neural network as the breakthrough point of the screening model. According to the rhythmic characteristics and temporal memory characteristics of EEG, this research proposes a Rhythmic Time EEG Emotion Recognition Model (RT-ERM) based on the valence and arousal of Long–Short-Term Memory Network (LSTM). By applying this model, the classification results of different rhythms and time scales are different. The optimal rhythm and time scale of the RT-ERM model are obtained through the results of the classification accuracy of different rhythms and different time scales. Then, the classification of emotional EEG is carried out by the best time scales corresponding to different rhythms. Finally, by comparing with other existing emotional EEG classification methods, it is found that the rhythm and time scale of the model can contribute to the accuracy of RT-ERM.

scholarly journals Fast Comparison of High-Precision Time Scales Using GNSS Receivers

2017 ◽  
Vol 2017 ◽  
pp. 1-4
Author(s):  
Vojtech Vigner ◽  
Jaroslav Roztocil
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
High Performance ◽  
Data Format ◽  
Common View ◽  
Log Files ◽  
Gnss Receivers ◽  
Precision Time ◽  
The Common ◽  
The Difference

Comparison of high-performance time scales generated by atomic clocks in laboratories of time and frequency metrology is usually performed by means of the Common View method. Laboratories are equipped with specialized GNSS receivers which measure the difference between a local time scale and a time scale of the selected satellite. Every receiver generates log files in CGGTTS data format to record measured differences. In order to calculate time differences recorded by two receivers, it is necessary to obtain these logs from both receivers and process them. This paper deals with automation and speeding up of these processes.

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