Journal articles on the topic 'ESF irregularities'
To see the other types of publications on this topic, follow the link: ESF irregularities.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'ESF irregularities.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Tiwari, D., A. K. Patra, C. V. Devasia, R. Sridharan, N. Jyoti, K. S. Viswanathan, and K. S. V. Subbarao. "Radar Observations of 8.3-m scale equatorial spread F irregularities over Trivandrum." Annales Geophysicae 22, no. 3 (March 19, 2004): 911–22. http://dx.doi.org/10.5194/angeo-22-911-2004.
Full textAbstract:
Abstract. In this paper, we present observations of equatorial spread F (ESF) irregularities made using a newly installed 18MHz radar located at Trivandrum. We characterize the morphology and the spectral parameters of the 8.3-m ESF irregularities which are found to be remarkably different from that observed so extensively at the 3-m scale size. We also present statistical results of the irregularities in the form of percentage occurrence of the echoes and spectral parameters (SNR, Doppler velocity, Spectral width). The Doppler spectra are narrower, less structured and less variable in time as compared to those observed for 3-m scale size. We have never observed the ESF irregularity velocities to be supersonic here unlike those at Jicamarca, and the velocities are found to be within ±200ms–1. The spectral widths are found to be less than 150ms–1. Hence, the velocities and spectral width both are smaller than those reported for 3-m scale size. The velocities and spectral widths are further found to be much smaller than those of the American sector. These observations are compared with those reported elsewhere and discussed in the light of present understanding on the ESF irregularities at different wavelengths. Key words. Ionoshphere (equatorial ionosphere, plasma waves and instabilities; ionospheric irregularities)
2
Tiwari, D., B. Engavale, A. Bhattacharyya, C. V. Devasia, T. K. Pant, and R. Sridharan. "Simultaneous radar and spaced receiver VHF scintillation observations of ESF irregularities." Annales Geophysicae 24, no. 5 (July 3, 2006): 1419–27. http://dx.doi.org/10.5194/angeo-24-1419-2006.
Full textAbstract:
Abstract. Simultaneous observations of equatorial spread F (ESF) irregularities made on 10 nights during March-April 1998 and 1999, using an 18-MHz radar at Trivandrum (77° E, 8.5° N, dip 0.5° N) and two spaced receivers recording scintillations on a 251-MHz signal at Tirunelveli (77.8° E, 8.7° N, dip 0.4° N), have been used to study the evolution of Equatorial Spread F (ESF) irregularities. Case studies have been carried out on the day-to-day variability in ESF structure and dynamics, as observed by 18-MHz radar, and with spaced receiver measurements of average zonal drift Vo of the 251-MHz radio wave diffraction pattern on the ground, random velocity Vc, which is a measure of random changes in the characteristics of scintillation-producing irregularities, and maximum cross-correlation CI of the spaced receivers signals. Results show that in the initial phase of plasma bubble development, the greater the maximum height of ESF irregularities responsible for the radar backscatter, the greater the decorrelation is of the spaced receiver scintillation signals, indicating greater turbulence. The relationship of the maximum spectral width derived from the radar observations and CI also supports this result.
3
Chau, J. L., R. F. Woodman, and L. A. Flores. "Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar." Annales Geophysicae 20, no. 8 (August 31, 2002): 1203–12. http://dx.doi.org/10.5194/angeo-20-1203-2002.
Full textAbstract:
Abstract. We present a summary of the statistical characteristics of echoes from ionospheric (E- and F-region) field-aligned irregularities obtained with the Piura VHF radar. This radar is located at ~ 7.0° dip latitude, just outside the equatorial electrojet (EEJ) region. Our results are based on (1) intermittent observations made between 1991 and 1999 just few days a year, and (2) continuous observations made between January 2000 and June 2001. During most of the intermittent observations, simultaneous measurements of EEJ and equatorial spread F (ESF) irregularities were performed with the Jicamarca VHF radar. From the continuous measurements, we have obtained the diurnal and seasonal characteristics of a variety of parameters (percentage of occurrence, signal-to-noise ratio and/or Doppler velocities) from the lower and upper E-region irregularities and also from F-region irregularities over Piura. For example, we have found that (1) the E-region echoes are stronger and occur more frequently during local summer (i.e. between December and March); (2) between May and June, the E-region echoes are weaker and occur less frequently; moreover, during these months, a semidiurnal wave with large amplitudes is observed in the meridional wind (> 100 ms- 1); (3) there is vertical wavelength of about 20 km in the Doppler velocity, particularly after midnight; (4) the lower (upper) E-region Doppler velocities are influenced mainly by meridional winds (equatorial F-region vertical drifts). In addition, we have observed that the seasonal and daily occurrences of Piura F-region irregularities are similar to the occurrence of topside ESF irregularities over Jicamarca. The likelihood of occurrence of F-region irregularities over Piura and, therefore, topside ESF over Jicamarca is greater when there are no E-region irregularities over Piura. On the other hand, there is more probability of observing bottomtype/bottomside ESF irregularities over Jicamarca when E-region irregularities are observed over Piura.Key words. Ionosphere (ionospheric irregularities; equatorial ionosphere; instruments and techniques)
4
Cueva, R. Y. C., E. R. de Paula, and A. E. Kherani. "Statistical analysis of radar observed F region irregularities from three longitudinal sectors." Annales Geophysicae 31, no. 12 (December 3, 2013): 2137–46. http://dx.doi.org/10.5194/angeo-31-2137-2013.
Full textAbstract:
Abstract. Equatorial Spread F (ESF) is a manifestation of ionospheric interchange instabilities in the nighttime equatorial F region. These instabilities generate plasma density irregularities with scale sizes ranging from centimetres to thousands of kilometres. The irregularities can be detected from a variety of instruments such as digisonde, coherent and incoherent scatter radars, in situ space probes, and airglow photometers. In the present study, occurrence statistics of the ESF, based on various parameters are presented using data obtained from the VHF radars located at three longitudinally separated equatorial stations: Christmas Island (2° N, 202.6° E, 2.9° N dip latitude), São Luís (2.59° S, 315.8° E, 0.5° S dip latitude) and Jicamarca (12° S, 283.1° E, 0.6° N dip latitude). The ESF parameters presented here are the onset altitude, onset time (onset refers to first appearance of signal in the radar field of view) of the bottom-type and plume, and the peak altitude of the plume. Recent studies have used these parameters to classify the spread F occurrence characteristics. The present study reveals novel features namely, the dependence of ESF parameters on the seasonal, solar flux, declination angle and longitudinal dependence from the three radar sites. In addition, we also present an empirical model to determine the nature of these ESF parameters as a function of the solar flux which may enable us to forecast (with 30 min to 1 h tolerance) the plume occurrence at any longitude located in between São Luís and Christmas Island.
5
Stolle, C., H. Lühr, and B. G. Fejer. "Relation between the occurrence rate of ESF and the equatorial vertical plasma drift velocity at sunset derived from global observations." Annales Geophysicae 26, no. 12 (December 8, 2008): 3979–88. http://dx.doi.org/10.5194/angeo-26-3979-2008.
Full textAbstract:
Abstract. In this study, we investigate two global climatological data sets; the occurrence rate of Equatorial Spread-F (ESF), associated with equatorial plasma irregularities, at ~400 km altitude obtained from CHAMP observations, and the evening equatorial vertical plasma drift, vz, from ROCSAT-1 measurements. First, as retrieved for a solar flux level of F10.7=150, the longitudinal variation of the two independently derived quantities correlates between 84% and 93% in the seasons December solstice, equinox and June solstice. The highest correlation is found for the solstice seasons when vz is integrated over local time around the prereversal enhancement (PRE) and displaced 6° towards east. The integrated vz is a suitable estimate of the ionospheric height at the time just after the PRE and the 6° displacement is consistent with ESF eastward drift during 2 h which is assumed between creation and detection at satellite altitudes. Second, our analyses reveal a global threshold vz which is required to observe ESF at satellite altitudes. This threshold depends linearly on solar flux with correlations of 97%. Both results bring global evidence on the linear relations between ESF and the vertical plasma drift which have been proven only by local observations so far. This paper includes the first global map of the seasonal/longitudinal variation of the ESF occurrence rate over local time being valid for high solar flux years 2001–2004. The map reveals, e.g. a longitudinal dependence of the persistence of the plasma irregularities indicating that longitude dependent mechanisms other than the PRE determine the ESF lifetime.
6
Sreeja, V., C. V. Devasia, and R. Sridharan. "The persistence of equatorial spread F – an analysis on seasonal, solar activity and geomagnetic activity aspects." Annales Geophysicae 27, no. 2 (February 2, 2009): 503–10. http://dx.doi.org/10.5194/angeo-27-503-2009.
Full textAbstract:
Abstract. The persistence (duration) of Equatorial Spread F (ESF), which has significant impact on communication systems, is addressed. Its behavior during different seasons and geomagnetic activity levels under the solar maximum (2001) and minimum (2006) conditions, is reported using the data from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip 0.5° N) in India. The study reveals that the persistence of the irregularities can be estimated to a reasonable extent by knowing the post sunset F region vertical drift velocity (Vz) and the magnetic activity index Kp. Any sort of advance information on the possible persistence of the ionospheric irregularities responsible for ESF is important for understanding the scintillation morphology, and the results which form the first step in this direction are presented and discussed.
7
Sripathi, S., S. Bose, A. K. Patra, T. K. Pant, B. Kakad, and A. Bhattacharyya. "Simultaneous observations of ESF irregularities over Indian region using radar and GPS." Annales Geophysicae 26, no. 11 (October 21, 2008): 3197–213. http://dx.doi.org/10.5194/angeo-26-3197-2008.
Full textAbstract:
Abstract. In this paper, we present simultaneous observations of temporal and spatial variability of total electron content (TEC) and GPS amplitude scintillations on L1 frequency (1.575 GHz) during the time of equatorial spread F (ESF) while the MST radar (53 MHz) located at Gadanki (13.5° N, 79.2° E, Dip latitude 6.3° N), a low latitude station, made simultaneous observations. In particular, the latitudinal and longitudinal extent of TEC and L-band scintillations was studied in the Indian region for different types of ESF structures observed using the MST radar during the low solar activity period of 2004 and 2005. Simultaneous radar and GPS observations during severe ESF events in the pre-midnight hour reveal that significant GPS L band scintillations, depletions in TEC, and the double derivative of the TEC index (DROTI), which is a measure of fluctuations in TEC, obtained at low latitudes coincide with the appearance of radar echoes at Gadanki. As expected, when the irregularities reach higher altitudes as seen in the radar map during pre-midnight periods, strong scintillations on an L-band signal are observed at higher latitudes. Conversely, when radar echoes are confined to only lower altitudes, weak scintillations are found and their latitudinal extent is small. During magnetically quiet periods, we have recorded plume type radar echoes during a post-midnight period that is devoid of L-band scintillations. Using spectral slopes and cross-correlation index of the VHF scintillation observations, we suggest that these irregularities could be "dead" or "fossil" bubbles which are just drifting in from west. This scenario is consistent with the observations where suppression of pre-reversal enhancement (PRE) in the eastward electric field is indicated by ionosonde observations of the height of equatorial F layer and also occurrence of low spectral width in the radar observations relative to pre-midnight period. However, absence of L-band scintillations during post-midnight event, when radar observed plume like structures and scintillations were recorded on VHF band, raises questions about the process of evolution of the irregularities. A possible explanation is that whereas small scale (~3 m) irregularities are generated through secondary waves that grow on the walls of km scale size irregularities, in this case evolution of the Rayleigh-Taylor instability itself did not extend to irregularities of scale sizes of a few hundred meters that produce scintillation on a L-band signal.
8
Engavale, B., K. Jeeva, K. U. Nair, and A. Bhattacharyya. "Solar flux dependence of coherence scales in scintillation patterns produced by ESF irregularities." Annales Geophysicae 23, no. 10 (November 30, 2005): 3261–66. http://dx.doi.org/10.5194/angeo-23-3261-2005.
Full textAbstract:
Abstract. The coherence scale length, defined as the 50% decorrelation scale length along the magnetic east-west direction, in the ground scintillation pattern obtained at a dip equatorial location, due to scattering of VHF radio waves by equatorial spread F (ESF) irregularities, is calculated, using amplitude scintillation data recorded by two spaced receivers. The average east-west drift of the ground scintillation pattern, during the pre- and post-midnight periods, also calculated from the same observations, shows an almost linear increase with 10.7-cm solar flux. In the present paper the variability of the drift is automatically taken into account in the calculation of the coherence scale length of the ground scintillation pattern. For weak scintillations, the coherence scale depends on the Fresnel scale, which varies with the height of the irregularity layer, and also on the spectral index of the irregularity power spectrum. It is found that for weak scintillations, the coherence scales are much better organized according to the 10.7-cm solar flux, during the pre-midnight period, than during the post-midnight period, with a general trend of coherence scale length increasing with 10.7-cm solar flux except for cases with F 10.7-cm solar flux <100. This indicates that, during the initial phase of ESF irregularity development, the irregularity spectrum does not have much variability while further evolution of the spatial structure in ESF irregularities is controlled by factors other than the solar flux.
9
Sinha, H. S. S., and S. Raizada. "First in situ measurement of electric field fluctuations during strong spread F in the Indian zone." Annales Geophysicae 18, no. 5 (May 31, 2000): 523–31. http://dx.doi.org/10.1007/s00585-000-0523-y.
Full textAbstract:
Abstract. An RH-560 rocket flight was conducted from Sriharikota rocket range (SHAR) (14°N, 80°E, dip 14°N) along with other experiments, as a part of equatorial spread F (ESF) campaign, to study the nature of irregularities in electric field and electron density. The rocket was launched at 2130 local time (LT) and it attained an apogee of 348 km. Results of vertical and horizontal electric field fluctuations are presented here. Scale sizes of electric field fluctuations were measured in the vertical direction only. Strong ESF irregularities were observed in three regions, viz., 160-190 km, 210-257 km and 290-330 km. Some of the valley region vertical electric field irregularities (at 165 km and 168 km), in the intermediate-scale size range, observed during this flight, show spectral peak at kilometer scales and can be interpreted in terms of the image striation theory suggested by Vickrey et al. The irregularities at 176 km do not exhibit any peak at kilometer scales and appear to be of a new type. Scale sizes of vertical electric field fluctuations showed a decrease with increasing altitude. The most prominent scales were of the order of a few kilometers around 170 km and a few hundred meters around 310 km. Spectra of intermediate-scale vertical electric field fluctuations below the base of the F region (210-257 km) showed a tendency to become slightly flatter (spectral index n = -2.1 ± 0.7) as compared to the valley region (n = -3.6 ± 0.8) and the region below the F peak (n = -2.8 ± 0.5). Correlation analysis of the electron density and vertical electric field fluctuations suggests the presence of a sheared flow of current in 160-330 km region.Keywords: Ionosphere (Electric fields and currents; ionospheric irregularities); Radio science (ionospheric physics)
10
Smith, J. M., F. S. Rodrigues, and E. R. de Paula. "Radar and satellite investigations of equatorial evening vertical drifts and spread <i>F</i>." Annales Geophysicae 33, no. 11 (November 11, 2015): 1403–12. http://dx.doi.org/10.5194/angeo-33-1403-2015.
Full textAbstract:
Abstract. We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of São Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) onboard the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18:00–18:30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.
11
Chau, J. L., D. L. Hysell, K. M. Kuyeng, and F. R. Galindo. "Phase calibration approaches for radar interferometry and imaging configurations: equatorial spread F results." Annales Geophysicae 26, no. 8 (August 5, 2008): 2333–43. http://dx.doi.org/10.5194/angeo-26-2333-2008.
Full textAbstract:
Abstract. In recent years, more and more radar systems with multiple-receiver antennas are being used to study the atmospheric and ionospheric irregularities with either interferometric and/or imaging configurations. In such systems, one of the major challenges is to know the phase offsets between the different receiver channels. Such phases are intrinsic to the system and are due to different cable lengths, filters, attenuators, amplifiers, antenna impedance, etc. Moreover, such phases change as function of time, on different time scales, depending on the specific installation. In this work, we present three approaches using natural targets (radio stars, meteor-head and meteor trail echoes) that allow either an absolute or relative phase calibration. In addition, we present the results of using an artificial source (radio beacon) for a continuous calibration that complements the previous approaches. These approaches are robust and good alternatives to other approaches, e.g. self-calibration techniques using known data features, or for multiple-receiver configurations constantly changing their receiving elements. In order to show the good performance of the proposed phase calibration techniques, we present new radar imaging results of equatorial spread F (ESF) irregularities. Finally we introduce a new way to represent range-time intensity (RTI) maps color coded with the Doppler information. Such modified map allows the identification and interpretation of geophysical phenomena, previously hidden in conventional RTI maps, e.g. the time and altitude of occurrence of ESF irregularities pinching off from the bottomside and their respective Doppler velocity.
12
Kakad, B., C. K. Nayak, and A. Bhattacharyya. "Power spectral characteristics of ESF irregularities during magnetically quiet and disturbed days." Journal of Atmospheric and Solar-Terrestrial Physics 81-82 (June 2012): 41–49. http://dx.doi.org/10.1016/j.jastp.2012.04.008.
Full text
13
Hickey, Dustin A., Carlos R. Martinis, Michael Mendillo, Jeffrey Baumgardner, Joei Wroten, and Marco Milla. "Simultaneous 6300 Å airglow and radar observations of ionospheric irregularities and dynamics at the geomagnetic equator." Annales Geophysicae 36, no. 2 (March 22, 2018): 473–87. http://dx.doi.org/10.5194/angeo-36-473-2018.
Full textAbstract:
Abstract. In March 2014 an all-sky imager (ASI) was installed at the Jicamarca Radio Observatory (11.95∘ S, 76.87∘ W; 0.3∘ S MLAT). We present results of equatorial spread F (ESF) characteristics observed at Jicamarca and at low latitudes. Optical 6300 and 7774 Å airglow observations from the Jicamarca ASI are compared with other collocated instruments and with ASIs at El Leoncito, Argentina (31.8∘ S, 69.3∘ W; 19.8∘ S MLAT), and Villa de Leyva, Colombia (5.6∘ N, 73.52∘ W; 16.4∘ N MLAT). We use Jicamarca radar data, in incoherent and coherent modes, to obtain plasma parameters and detect echoes from irregularities. We find that ESF depletions tend to appear in groups with a group-to-group separation around 400–500 km and within-group separation around 50–100 km. We combine data from the three ASIs to investigate the conditions at Jicamarca that could lead to the development of high-altitude, or topside, plumes. We compare zonal winds, obtained from a Fabry–Pérot interferometer, with plasma drifts inferred from the zonal motion of plasma depletions. In addition to the ESF studies we also investigate the midnight temperature maximum and its effects at higher latitudes, visible as a brightness wave at El Leoncito. The ASI at Jicamarca along with collocated and low-latitude instruments provide a clear two-dimensional view of spatial and temporal evolution of ionospheric phenomena at equatorial and low latitudes that helps to explain the dynamics and evolution of equatorial ionospheric/thermospheric processes. Keywords. Ionosphere (equatorial ionosphere; ionospheric irregularities; plasma temperature and density)
14
Tsai, Lung-Chih, Shin-Yi Su, Jun-Xian Lv, Terry Bullett, and Chao-Han Liu. "Multi-Station and Multi-Instrument Observations of F-Region Irregularities in the Taiwan–Philippines Sector." Remote Sensing 14, no. 10 (May 10, 2022): 2293. http://dx.doi.org/10.3390/rs14102293.
Full textAbstract:
In this study, a multi-station and multi-instrument system, organized and proposed for ionospheric scintillation and equatorial spread-F (ESF) specification and their associated motions in the Taiwan–Philippines sector, is outlined. The issues related to the scintillation and ESF event observed on 26 October 2021, at magnetic quiet conditions are presented and discussed. We first indicate the existence of a plasma bubble in the Taiwan–Philippines sector by using the FormoSat-7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (FS7/COSMIC2) GPS/GLONASS radio occultation observations. We verify the latitudinal extent of the tracked plasma bubble using the recorded ionograms from the Vertical Incidence Pulsed Ionospheric Radar located at Hualien, Taiwan. We further discuss the spatial and temporal variabilities of two-dimensional vertical scintillation index VS4 maps based on the simultaneous GPS L1-band signal measurements from 133 ground-based receivers located in Taiwan and the surrounding islands. We also operate two high-sampling, software-defined GPS receivers and characterize the targeted plasma irregularities by carrying out spectrum analyses of the received signal. As a result, the derived plasma irregularities moved eastward and northward. Furthermore, the smaller the irregularity scale, the higher the spectral index and the stronger the scintillation intensity were at lower latitudes on the aimed irregularity feature.
15
Huang, Chao-Song. "Occurrence Characteristics of VHF Scintillation and Equatorial Spread F over Kwajalein during Moderate Solar Activity in 2012." Atmosphere 14, no. 5 (May 19, 2023): 889. http://dx.doi.org/10.3390/atmos14050889.
Full textAbstract:
The occurrence probability of equatorial plasma bubbles and the associated spread F (ESF) irregularities have been derived from ground-based and space-borne measurements. In general, ESF occurrence depends on season and longitude and is high in equinoctial months and low around June solstice. In the West Pacific sector, previous statistical results show that the ESF occurrence probability increases gradually and continuously from March to August. In this study, we use trans-ionospheric VHF data received at Kwajalein Atoll in 2012 to derive the occurrence characteristics of scintillation. It is found that the occurrence probability of strong scintillation had two maxima in June and September and a minimum in July in the evening and midnight sector but only one maximum in June in the post-midnight sector. The monthly variations of scintillation occurrence at Kwajalein are different from almost all previous studies on ESF and scintillation at or near this longitude. To identify the cause for the June peak and the July minimum of scintillation, the ion density and velocity data measured by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite in 2011–2012 are used to derive the ESF occurrence and the post-sunset vertical ion drift near Kwajalein. The ESF occurrence probability and the ion drift measured by the C/NOFS satellite showed two maxima in May/June and August/September and a minimum in July, verifying that the June peak and the July minimum of the VHF scintillation are realistic and caused by the similar variations in the ionospheric ion drift and density.
16
Sreeja, V., C. Vineeth, Tarun Kumar Pant, Sudha Ravindran, and R. Sridharan. "Role of gravity wavelike seed perturbations on the triggering of ESF – a case study from unique dayglow observations." Annales Geophysicae 27, no. 1 (January 19, 2009): 313–18. http://dx.doi.org/10.5194/angeo-27-313-2009.
Full textAbstract:
Abstract. First observational evidence, from the Indian longitudes, for the presence of gravity wavelike perturbations with periods of 20–30 min, acting as probable seeds for Equatorial Spread F (ESF) irregularities is described. The study is based on the daytime optical measurements of the mesopause temperature and the intensity of the thermospheric O(1D) 630.0 nm dayglow emissions using the unique MultiWavelength Dayglow PhotoMeter from Trivandrum (8.5° N; 77° E; dip lat ~0.5° N), a dip equatorial station. Measurements during the equinoctial months of a solar maximum (2001) and a solar minimum year (2006) have been used in this study. It is shown that under identical background ionospheric conditions within a solar epoch, the power of the gravity waves have a deterministic role in the generation of ESF. The mesopause temperature simultaneously observed, indicate that possible source regions for these perturbations lie in the lower atmosphere.
17
Sekar, R., D. Chakrabarty, R. Narayanan, S. Sripathi, A. K. Patra, and K. S. V. Subbarao. "Characterization of VHF radar observations associated with equatorial Spread F by narrow-band optical measurements." Annales Geophysicae 22, no. 9 (September 23, 2004): 3129–36. http://dx.doi.org/10.5194/angeo-22-3129-2004.
Full textAbstract:
Abstract. The VHF radars have been extensively used to investigate the structures and dynamics of equatorial Spread F (ESF) irregularities. However, unambiguous identification of the nature of the structures in terms of plasma depletion or enhancement requires another technique, as the return echo measured by VHF radar is proportional to the square of the electron density fluctuations. In order to address this issue, co-ordinated radar backscatter and thermospheric airglow intensity measurements were carried out during March 2003 from the MST radar site at Gadanki. Temporal variations of 630.0-nm and 777.4-nm emission intensities reveal small-scale ("micro") and large-scale ("macro") variations during the period of observation. The micro variations are absent on non-ESF nights while the macro variations are present on both ESF and non-ESF nights. In addition to the well-known anti-correlation between the base height of the F-region and the nocturnal variation of thermospheric airglow intensities, the variation of the base height of the F-layer, on occasion, is found to manifest as a bottomside wave-like structure, as seen by VHF radar on an ESF night. The micro variations in the airglow intensities are associated with large-scale irregular plasma structures and found to be in correspondence with the "plume" structures obtained by VHF radar. In addition to the commonly observed depletions with upward movement, the observation unequivocally reveals the presence of plasma enhancements which move downwards. The observation of enhancement in 777.4-nm airglow intensity, which is characterized as plasma enhancement, provides an experimental verification of the earlier prediction based on numerical modeling studies.
18
Aveiro, H. C., and J. D. Huba. "Equatorial spread F studies using SAMI3 with two-dimensional and three-dimensional electrostatics." Annales Geophysicae 31, no. 12 (December 5, 2013): 2157–62. http://dx.doi.org/10.5194/angeo-31-2157-2013.
Full textAbstract:
Abstract. This letter presents a study of equatorial F region irregularities using the NRL SAMI3/ESF model, comparing results using a two-dimensional (2-D) and a three-dimensional (3-D) electrostatic potential solution. For the 3-D potential solution, two cases are considered for parallel plasma transport: (1) transport based on the parallel ambipolar field, and (2) transport based on the parallel electric field. The results show that the growth rate of the generalized Rayleigh–Taylor instability is not affected by the choice of the potential solution. However, differences are observed in the structures of the irregularities between the 2-D and 3-D solutions. Additionally, the plasma velocity along the geomagnetic field computed using the full 3-D solution shows complex structures that are not captured by the simplified model. This points out that only the full 3-D model is able to fully capture the complex physics of the equatorial F region.
19
Gurram, P., B. Kakad, A. Bhattacharyya, and T. K. Pant. "Evolution of Freshly Generated Equatorial Spread F (F-ESF) Irregularities on Quiet and Disturbed Days." Journal of Geophysical Research: Space Physics 123, no. 9 (September 2018): 7710–25. http://dx.doi.org/10.1029/2018ja025705.
Full text
20
Nigussie, Melessew, Mark Moldwin, and Endawoke Yizengaw. "Investigating the Role of Gravity Waves on Equatorial Ionospheric Irregularities Using TIMED/SABER and C/NOFS Satellite Observations." Atmosphere 13, no. 9 (September 1, 2022): 1414. http://dx.doi.org/10.3390/atmos13091414.
Full textAbstract:
In this paper, for the first time, simultaneous atmospheric temperature perturbation profiles obtained from the TIMED/SABER satellite and equatorial ion density and vertical plasma drift velocity observations with and without ESF activity obtained from the C/NOFS satellite are used to investigate the effect of gravity waves (GW) on ESF. The horizontal and vertical wavelengths of ionospheric oscillations and GWs are estimated by applying wavelet analysis techniques. In addition, vertically propagating GWs that dissipate energy in the ionosphere-thermosphere system are investigated using the spectral analysis technique. We find that the vertical wavelength of GW, corresponding to dominant wavelet power, ranges from 12 to 31 km regardless of the conditions of the ionosphere; however, GWs with vertical wavelengths between about 1 to 13 km are found every day, saturated between 90 and 110 km at different longitudinal sectors. Filtering out vertical wavelengths above 13 km from temperature perturbations, ranges of zonal wavelengths of GW (i.e., from about 290 to 950 km) are found corresponding to irregular and non-irregular ionosphere. Similarly, corresponding to dominant oscillations, the zonal wavelength of ion density perturbations is found within 16 to 1520 km. Moreover, we find an excellent agreement among the median zonal wavelengths of GW for the cases of irregular and non-irregular ionosphere and ion density perturbations that are 518, 495, and 491 km, respectively. The results imply that seed perturbations due to GW with a vertical wavelength from about 1 to 13 km evolve to ion density irregularity and may be amplified due to post-sunset vertical upward drift velocity.
21
Sekar, R., D. Chakrabarty, S. Sarkhel, A. K. Patra, C. V. Devasia, and M. C. Kelley. "Identification of active fossil bubbles based on coordinated VHF radar and airglow measurements." Annales Geophysicae 25, no. 10 (November 6, 2007): 2099–102. http://dx.doi.org/10.5194/angeo-25-2099-2007.
Full textAbstract:
Abstract. Plasma irregularity structures associated with an Equatorial Spread-F (ESF) event were recorded by the Indian VHF Radar on 26–27 April 2006 near midnight hours. The plasma structures were found to be isolated without having bottomside structure. They moved predominantly downward and the structures were found to be less turbulent than their post-sunset counterparts. However, the structures were characterized by meter-scale size irregularities. These structures are identified for the first time as plasma depletion structures using simultaneous, collocated measurements of OI 630.0 nm airglow intensity variations. The variation of the base height of ionospheric F layer over dip equator is also presented to buttress the result. Further, these plasma structures are shown to be "active fossil bubbles".
22
Abdu, Mangalathayil A., Paulo A. B. Nogueira, Angela M. Santos, Jonas R. de Souza, Inez S. Batista, and Jose H. A. Sobral. "Impact of disturbance electric fields in the evening on prereversal vertical drift and spread F developments in the equatorial ionosphere." Annales Geophysicae 36, no. 2 (April 9, 2018): 609–20. http://dx.doi.org/10.5194/angeo-36-609-2018.
Full textAbstract:
Abstract. Equatorial plasma bubble/spread F irregularity occurrence can present large variability depending upon the intensity of the evening prereversal enhancement in the zonal electric field (PRE), that is, the F region vertical plasma drift, which basically drives the post-sunset irregularity development. Forcing from magnetospheric disturbances is an important source of modification and variability in the PRE vertical drift and of the associated bubble development. Although the roles of magnetospheric disturbance time penetration electric fields in the bubble irregularity development have been studied in the literature, many details regarding the nature of the interaction between the penetration electric fields and the PRE vertical drift still lack our understanding. In this paper we have analyzed data on F layer heights and vertical drifts obtained from digisondes operated in Brazil to investigate the connection between magnetic disturbances occurring during and preceding sunset and the consequent variabilities in the PRE vertical drift and associated equatorial spread F (ESF) development. The impact of the prompt penetration under-shielding eastward electric field and that of the over-shielding, and disturbance dynamo, westward electric field on the evolution of the evening PRE vertical drift and thereby on the ESF development are briefly examined. Keywords. Ionosphere (ionospheric irregularities)
23
DENG Kun, MA Yonghui, LIU Minbo, GUO Zhixiong, and WANG Shu. "Observations of TEC Depletion, Periodic Structure of TEC, ROTI and Scintillation Associated with ESF Irregularities over South China." Chinese Journal of Space Science 40, no. 3 (2020): 331. http://dx.doi.org/10.11728/cjss2020.03.331.
Full text
24
Huang, Chao-Song. "The characteristics and generation mechanism of small-amplitude and large-amplitude ESF irregularities observed by the C/NOFS satellite." Journal of Geophysical Research: Space Physics 122, no. 8 (August 2017): 8959–73. http://dx.doi.org/10.1002/2017ja024041.
Full text
25
Sreekumar, Sreeba, and S. Sripathi. "A seasonal study on the role of h’F/meridional winds in influencing the development of ESF irregularities over Indian sector." Advances in Space Research 60, no. 3 (August 2017): 652–66. http://dx.doi.org/10.1016/j.asr.2017.04.009.
Full text
26
Sreekumar, Sreeba, and S. Sripathi. "The role of LSWS (satellite traces) and low latitude E sb layers in causing the variability of ESF irregularities over Indian sector." Advances in Space Research 62, no. 1 (July 2018): 94–110. http://dx.doi.org/10.1016/j.asr.2018.04.011.
Full text
27
Sripathi, S., B. Kakad, and A. Bhattacharyya. "Study of equinoctial asymmetry in the Equatorial Spread F (ESF) irregularities over Indian region using multi-instrument observations in the descending phase of solar cycle 23." Journal of Geophysical Research: Space Physics 116, A11 (November 2011): n/a. http://dx.doi.org/10.1029/2011ja016625.
Full text
28
Chatterjee, S., and S. K. Chakraborty. "Variability of ionospheric scintillation near the equatorial anomaly crest of the Indian zone." Annales Geophysicae 31, no. 4 (April 19, 2013): 697–711. http://dx.doi.org/10.5194/angeo-31-697-2013.
Full textAbstract:
Abstract. Multistation observations of ionosphere scintillation at VHF (250 MHz) and GNSS L1 frequency from three locations – (i) Bokkhali (BOK) (geographic 21.6° N, 88.2° E, dip 31.48°, (ii) Raja Peary Mohan College Centre (RPMC) (geographic 22.66° N, 88.4° E, dip 33.5°) and (iii) Krishnath College Centre (KNC), Berhampore (geographic 24.1° N, 88.3° E, dip 35.9°) – at ~ 1° latitudinal separations near the northern crest of the equatorial ionization anomaly (EIA) of the Indian longitude sector are investigated in conjunction with total electron content (TEC) data and available ionosonde data near the magnetic equator to study fine structure in spatial and temporal variability patterns of scintillation occurrences. The observations are carried out in the autumnal equinoctial months of a high solar activity year (2011). In spite of smaller latitudinal/spatial separation among the observing stations, conspicuous differences are reflected in the onset time, duration, fade rate and fade depth of VHF scintillations as well as in spectral features. Scintillations are mostly associated with depletion in TEC around the anomaly crest and occurrence of ESF near the magnetic equator at an earlier time. Not only the strength of EIA, but also the locations of observing stations with respect to the post-sunset resurgence peak of EIA seem to play dominant role in dictating the severity of scintillation activity. A secondary enhancement in diurnal TEC in the post-sunset period seems to accentuate the irregularity activities near the anomaly crest, and a threshold value of the same may fruitfully be utilized for the prediction of scintillation around the locations. An idea regarding latitudinal extent of scintillation is developed by considering observations at L1 frequency from the GPS and GLONASS constellation of satellites. A critical value of h'F near the magnetic equator for the occurrence of simultaneous scintillation at the three centres is suggested. The observations are discussed considering electrodynamical aspect of equatorial irregularities.
29
Palmieri, C., H. Fulka, J. Fulka, Jr, P. Loi, G. Ptak, and L. Della Salda. "72 LIMITED REPROGRAMMING OF SOMATIC CELL NUCLEI TRANSFERRED INTO MOUSE IMMATURE OOCYTES." Reproduction, Fertility and Development 19, no. 1 (2007): 153. http://dx.doi.org/10.1071/rdv19n1ab72.
Full textAbstract:
Somatic cell nuclear transfer, an important approach for the analysis of certain functional changes in the genome during differentiation and for many practical applications, is in general a low-efficiency procedure, mainly due to a low effectivity in the re-establishment of the developmental program in the reconstructed embryo. The process of reprogramming is, however, poorly understood and some additional studies are clearly necessary. The aim of this study was the ultrastructural and immunofluorescent (B23-nucleophosmin) evaluation of somatic (cumulus) cell nuclei reprogramming after their transfer into intact immature mouse oocytes, kept at the germinal vesicle (GV) stage (dbcAMP) during the whole culture. Control somatic cells and nuclear transfer-reconstructed embryos (1 and 24 h after fusion induced by polyethyleneglycol) were fixed for transmission electron mcroscopy (TEM) in 2.5% glutaraldehyde, post-fixed in 1% OsO4, dehydrated through an ethanol series, and embedded in epoxy resin. Finally, ultrathin sections were stained with uranyl acetate followed by lead citrate. The above reagents were purchased from Electron Microscopy Sciences (Hatfield, PA, USA). In parallel, we have evaluated immunocytochemically the pattern of B23 labelling in intact and reconstructed cells. The samples were fixed in 4% paraformaldehyde, incubated with an antibody against B23 (Santa Cruz, CA, USA) and then with a biotinylated secondary antibody, and detected by fluorescein isothiocyanate (FITC)-coupled Streptavidin (Jackson ImmunoResearch, Cambridgeshire, UK). Mouse cumulus cells (12/12) contain a reticulated fibrillogranular nucleolus. The cell are also positively labeled with the anti-B23 antibody. One hour after fusion, the introduced nuclei displayed shape modifications and nuclear envelope irregularities, whereas the nucleolus still showed the typical fibrillar pattern (19/19). The volume of transferred nuclei remains unchanged. Interestingly, while the oocyte nucleolus remains negative for B23, the nucleoli in transferred somatic cells were always positively labeled (45 cells). After 24 h, the transferred nuclei increased their volume up to two-three times and displayed an irregular shape with nucleoli still possessing the unchanged reticulated pattern (17/17). As in the previous experimental interval, only the somatic cell nucleus remained labeled with the anti-B23 antibody (52 cells). The GV oocyte nucleoli remained unchanged during the whole culture period, exhibiting the typical dense-fibrillar pattern. Our results showed that the immature oocyte cytoplasm possesses a limited remodelling activity. Interestingly, the evident increase in volume of transferred somatic cells indicated some changes but TEM morphology and B23 labeling pattern remained basically unchanged. We cannot, however, exclude the beneficial effect upon reprogramming if these nuclei were subsequently used for the transfer into definitive cytoplasts. This work was supported by ESF STE/05/E004.
30
Sinha, H. S. S., P. K. Rajesh, R. N. Misra, and N. Dutt. "Multi-wavelength imaging observations of plasma depletions over Kavalur, India." Annales Geophysicae 19, no. 9 (September 30, 2001): 1119–31. http://dx.doi.org/10.5194/angeo-19-1119-2001.
Full textAbstract:
Abstract. Observations of ionospheric plasma depletions were made over Kavalur (12.56° N, 78.8° E, Mag. Lat 4.6° N), India during March–pril 1998 using an all sky optical imaging system operating at 630 nm, 777.4 nm and 557.7 nm. Out of 14 nights of observations, plasma depletions were seen only on 9 nights. Except for 21 March 1998, which was a magnetically disturbed period, all other nights belonged to a magnetically quiet period. Some of the important results obtained from these observations are: (a) After the onset of the equatorial spread F (ESF), plasma depletions take typically about 2 hrs 40 min to come to a fully developed state, (b) There are three distinct types of plasma depletions: type 1 have an east-west (e–w) extent of 250–350 km with an inter-depletion distance (IDD) of 125–300 km; Type 2 have an e–w extent of 100–150 km and IDD of 50–150 km; Type 3 have smallest the e–w extent (40–100 km) and IDD of 20–60 km, (c) Most of the observed plasma depletions (> 82%) had their eastward velocity in the range of 25–125 ms–1. Almost stationary plasma depletions (0–25 ms–1) were observed on one night, which was magnetically disturbed. These very slow moving depletions appear to be the result of a modification of the F-region dynamo field due to direct penetration of the electric field and/or changes in the neutral winds induced by the magnetic disturbance, (d) On the night of 21/22 March 1998, which was a magnetically disturbed period, plasma depletions could be seen simultaneously in all three observing wavelengths, i.e. in 630 nm, 777.4 nm and 557.7 nm. It is believed that this simultaneous occurrence was due to neutral density modifications as a result of enhanced magnetic activity. (e) Well developed brightness patterns were observed for the first time in 777.4 nm images. Earlier, such brightness patterns were observed only in 630 nm and 557.7 nm images. These brightness patterns initially appear as very small regions in the northern part of the image and then in about 90 min time, they attain their peak brightness and encompass the entire field-of-view in about 2 hrs 30 min. In some cases, brightness patterns contain one or two well developed plasma depletions within them. (f) The brightness patterns reported here differ from the earlier observations in that they do not show any differential behaviour in the direction of movement before and after the midnight, and that they are present for extended periods of time as large as 6 hrs.Key words. Atmospheric composition and structure (air-glow and aurora); Ionosphere (equatorial ionosphere; ionospheric irregularities)
31
Das, Satrajit, and James M. Nau. "Seismic Design Aspects of Vertically Irregular Reinforced Concrete Buildings." Earthquake Spectra 19, no. 3 (August 2003): 455–77. http://dx.doi.org/10.1193/1.1595650.
Full textAbstract:
Seismic building codes such as the Uniform Building Code (UBC) do not allow the equivalent lateral force (ELF) procedure to be used for structures with vertical irregularities. The purpose of this study is to investigate the definition of irregular structures for different vertical irregularities: stiffness, strength, mass, and that due to the presence of nonstructural masonry infills. An ensemble of 78 buildings with various interstory stiffness, strength, and mass ratios is considered for a detailed parametric study. The lateral force-resisting systems (LFRS) considered are special moment-resisting frames (SMRF). These LFRS are designed based on the forces obtained from the ELF procedure. The results from linear and nonlinear dynamic analyses of these engineered buildings exhibit that most structures considered in this study performed well when subjected to the design earthquake. Hence, the restrictions on the applicability of the equivalent lateral force procedure are unnecessarily conservative for certain types of vertical irregularities considered.
32
Arslan, Ayla, Esra Balcioğlu, Mehtap Nisari, Betül Yalçin, Menekşe Ülger, Emel Güler, Gökçe Bağcı Uzun, and Niyazi Acer. "Effect of carnosine on ovarian follicle in rats exposed to electromagnetic field." European Journal of Anatomy 26, no. 6 (November 2022): 659–68. http://dx.doi.org/10.52083/tesq7230.
Full textAbstract:
The electromagnetic field (EMF) has an effect on various organs, including the female reproductive system. The purpose of this study was to evaluate the impact of carnosine on ovarian follicle number and diameter in rats exposed to a 900 Megahertz (Mhz) electromagnetic field. In this study, six different groups were used. 40 female rats divided into groups were evaluated. The ovaries of the rats were removed at the end of the study. Routine histological procedures were performed on ovarian tissues. Follicle number and diameter of all groups were calculated and evaluated under the light microscope. When primary follicle number and diameters were compared statistically among the groups, there was a remarkably meaningful difference between the EMF group and the control, 20 mg carnosine and EMF+20 mg carnosine groups (p<0.05). There were significant irregularities in the structure of the oocyte and the granulosa cells surrounding the oocyte, especially in the EMF-treated groups. However, the structure of the oocyte and the granulosa cells surrounding the oocyte in the EMF+20 mg carnosine group showed a more regular structure compared to the EMF group. In this study, it can be concluded that the number and diameter of ovarian follicles decreased in rats exposed to electromagnetic field and 20 mg of carnosine may prevent damage caused by EMF.
33
Dugassa, Teshome, John Bosco Habarulema, and Melessew Nigussie. "Investigation of the relationship between the spatial gradient of total electron content (TEC) between two nearby stations and the occurrence of ionospheric irregularities." Annales Geophysicae 37, no. 6 (December 13, 2019): 1161–80. http://dx.doi.org/10.5194/angeo-37-1161-2019.
Full textAbstract:
Abstract. The relation between the occurrence of ionospheric irregularities and the spatial gradient of total electron content (TEC) derived from two closely located stations (ASAB: 4.34∘ N, 114.39∘ E and DEBK: 3.71∘ N, 109.34∘ E, geomagnetic), located within the equatorial region, over Ethiopia, during the postsunset hours was investigated. In this study, the Global Positioning System (GPS)-derived TEC during the year 2014 obtained from the two stations were employed to investigate the relationship between the gradient of TEC and occurrence of ionospheric irregularities. The spatial gradient of TEC (ΔTEC∕Δlong) and its standard deviation over 15 min, σ(ΔTEC∕Δlong), were used in this study. The rate of change of TEC-derived indices (ROTI, ROTIave) were also utilized. Our results revealed that most of the maximum enhancement and reduction values in ΔTEC∕Δlong are noticeable during the time period between 19:00 and 24:00 LT. In some cases, the peak values in the spatial gradient of TEC are also observed during daytime and postmidnight hours. The intensity level of σ(ΔTEC∕Δlong) observed after postsunset show similar trends with ROTIave, and was stronger (weaker) during equinoctial (solstice) months. The observed enhancement of σ(ΔTEC∕Δlong) in the equinoctial season shows an equinoctial asymmetry where the March equinox was greater than the September equinox. During the postsunset period, the relation between the spatial gradient of TEC obtained from two closely located Global Navigation Satellite System (GNSS) receivers and the equatorial electric field (EEF) was observed. The variation in the gradient of TEC and ROTIave observed during the evening time period show similar trends with EEF with a delay of about 1–2 h between them. The relationship between σ(ΔTEC∕Δlong) and ROTIave correlate linearly with correlation coefficient of C=0.7975 and C=0.7915 over ASAB and DEBK, respectively. The majority of the maximum enhancement and reduction in the spatial gradient of TEC observed during the evening time period may be associated with ionospheric irregularities or equatorial plasma bubbles. In addition to latitudinal gradients, the longitudinal gradient of TEC has contributed significantly to the TEC fluctuations.
34
Nahid-Mobarakeh, Babak, Farid Meibody-Tabar, and Franois-Michel Sargos. "Back EMF Estimation-Based Sensorless Control of PMSM: Robustness With Respect to Measurement Errors and Inverter Irregularities." IEEE Transactions on Industry Applications 43, no. 2 (2007): 485–94. http://dx.doi.org/10.1109/tia.2006.889826.
Full text
35
Güvercin, Sezim Ezgi, Hayrullah Karabulut, A. Özgün Konca, Uğur Doğan, and Semih Ergintav. "Active seismotectonics of the East Anatolian Fault." Geophysical Journal International 230, no. 1 (February 4, 2022): 50–69. http://dx.doi.org/10.1093/gji/ggac045.
Full textAbstract:
SUMMARY The East Anatolian Fault (EAF) is a 700-km-long left-lateral transform fault located between the Anatolian and Arabian plates. The proximity of the Euler Pole to the Arabia–Anatolia Plate boundary leads to rapid changes in plate velocity along the boundary, which is manifested by the decreasing slip rates from east (10 mm yr–1) to west (∼1–4 mm yr–1). The EAF displays heterogeneous seismicity patterns with seismic gaps, localized clusters and broad diffuse zones. In this study, in order to understand the origin of these complexities and quantify the seismic hazard along the EAF, we present an improved seismicity catalogue with more than 26 000 earthquakes and 160 focal mechanisms from regional moment tensor inversion between 2007 and 2020. The focal mechanisms and seismicity show that the EAF dips towards north and forms a well-defined plate boundary in the east between Palu and Çelikhan with almost pure left-lateral motion. Further west, the boundary becomes broader with activity along subparallel faults. Focal mechanisms show heterogeneous stress orientations in consistence with geodetically determined strain rate field. The stress orientations show a transition from strike-slip to extension towards the west of Çelikhan. Amongst all segments of EAF, the Pütürge segment, which holds the near-repeating earthquakes in the vicinity of the nucleation of the 2020 Mw 6.8 earthquake, is distinguished with its steady and high rate of seismicity. Further east, the neighbouring Palu segment is characterized by several distinct moderate earthquakes. We do not observe any change in the seismicity rate on these segments of the EAF following large earthquakes. In order to quantify the seismic hazard along the EAF, we calculate the recurrence time and maximum magnitude for each segment by using an extended seismicity catalogue of 150 yr including the large historical earthquakes and the geodetic strain rate. The results show ∼150 yr recurrence time with Mmax∼6.7–7.0 along the seismically active Palu and Pütürge segments on the east, while relatively silent western segments yield longer recurrence times; 237–772 for Pazarcık and 414–917 for Amanos segments with slightly larger magnitudes (Mmax ∼7–7.4). We infer that the seismicity patterns and strain-rate field along the EAF are shaped by several factors such as strong geometrical irregularities, heterogeneous coupling and complex plate motion leading to rapid change of fault slip rate.
36
Zhang, D. H., Z. Xiao, Y. Q. Hao, A. J. Ridley, and M. Moldwin. "Modeling ionospheric <I>fo</I>F2 by using empirical orthogonal function analysis." Annales Geophysicae 29, no. 8 (August 31, 2011): 1501–15. http://dx.doi.org/10.5194/angeo-29-1501-2011.
Full textAbstract:
Abstract. A similar-parameters interpolation method and an empirical orthogonal function analysis are used to construct empirical models for the ionospheric foF2 by using the observational data from three ground-based ionosonde stations in Japan which are Wakkanai (Geographic 45.4° N, 141.7° E), Kokubunji (Geographic 35.7° N, 140.1° E) and Yamagawa (Geographic 31.2° N, 130.6° E) during the years of 1971–1987. The impact of different drivers towards ionospheric foF2 can be well indicated by choosing appropriate proxies. It is shown that the missing data of original foF2 can be optimal refilled using similar-parameters method. The characteristics of base functions and associated coefficients of EOF model are analyzed. The diurnal variation of base functions can reflect the essential nature of ionospheric foF2 while the coefficients represent the long-term alteration tendency. The 1st order EOF coefficient A1 can reflect the feature of the components with solar cycle variation. A1 also contains an evident semi-annual variation component as well as a relatively weak annual fluctuation component. Both of which are not so obvious as the solar cycle variation. The 2nd order coefficient A2 contains mainly annual variation components. The 3rd order coefficient A3 and 4th order coefficient A4 contain both annual and semi-annual variation components. The seasonal variation, solar rotation oscillation and the small-scale irregularities are also included in the 4th order coefficient A4. The amplitude range and developing tendency of all these coefficients depend on the level of solar activity and geomagnetic activity. The reliability and validity of EOF model are verified by comparison with observational data and with International Reference Ionosphere (IRI). The agreement between observations and EOF model is quite well, indicating that the EOF model can reflect the major changes and the temporal distribution characteristics of the mid-latitude ionosphere of the Sea of Japan region. The error analysis processes imply that there are seasonal anomaly and semi-annual asymmetry phenomena which are consistent with pre-existing ionosphere theory.
37
Spandonidis, Christos C., and Kyriakoula Arvaniti. "Numerical Modeling of the Exposure on Radiofrequency Radiation of Marine Mammal Observers During Their Shift: A Case Study." International Journal of Safety and Security Engineering 10, no. 6 (December 31, 2020): 753–58. http://dx.doi.org/10.18280/ijsse.100605.
Full textAbstract:
Following the standard numerical modeling approach for Electromagnetic Field (EMF) radiation exposure prediction, we intend to provide an analytical framework to Marine Mammal Observers (MMOs) for dynamic risk assessment; enhancing thus occupational health and safety awareness. The analysis is based on power levels and antenna characteristics reported by MMOs for two systems (VHF and UHF) located close to the working environment. Whilst occupational exposure limits apply for MMOs, as for the rest crew (seismic and maritime), evaluation of exposure levels against general public limits is presented as well. At present we have restricted our study to single-source radiation, as well as we did not consider any irregularities due to system malfunction. The worst-case scenario of continuous RF transmission was considered. Risk assessment indicated regions where radiation exposure is higher than the permissible limits. Uncertainty due to the operational environment is inserted in methodology using an uncertainty coefficient. A list of control measures is proposed, to support both MMO’s and Operators’ decision making.
38
Spandonidis, Christos C., and Kyriakoula Arvaniti. "Numerical Modeling of the Exposure on Radiofrequency Radiation of Marine Mammal Observers During Their Shift: A Case Study." International Journal of Safety and Security Engineering 10, no. 6 (December 31, 2020): 753–58. http://dx.doi.org/10.18280/ijsse.100605.
Full textAbstract:
Following the standard numerical modeling approach for Electromagnetic Field (EMF) radiation exposure prediction, we intend to provide an analytical framework to Marine Mammal Observers (MMOs) for dynamic risk assessment; enhancing thus occupational health and safety awareness. The analysis is based on power levels and antenna characteristics reported by MMOs for two systems (VHF and UHF) located close to the working environment. Whilst occupational exposure limits apply for MMOs, as for the rest crew (seismic and maritime), evaluation of exposure levels against general public limits is presented as well. At present we have restricted our study to single-source radiation, as well as we did not consider any irregularities due to system malfunction. The worst-case scenario of continuous RF transmission was considered. Risk assessment indicated regions where radiation exposure is higher than the permissible limits. Uncertainty due to the operational environment is inserted in methodology using an uncertainty coefficient. A list of control measures is proposed, to support both MMO’s and Operators’ decision making.
39
Krutskikh, Vladislav V., Andrey N. Ushkov, Anton I. Chernikov, Denis O. Zavitaev, and Artavazd E. Mirzoyan. "The effect of docking defects on a metal-dielectric shielded waveguide in the EHF frequency range." Physics of Wave Processes and Radio Systems 26, no. 2 (July 1, 2023): 48–57. http://dx.doi.org/10.18469/1810-3189.2023.26.2.48-57.
Full textAbstract:
Background. To improve the accuracy of navigation and radar systems, functional nodes of the EHF wavelength range are used. At the same time, an increase in the operating frequency increases the requirements for the accuracy of manufacturing and docking devices. Analysis of the propagation of electromagnetic waves, subject to the presence of defects in the waveguide paths, will allow determining sufficient manufacturing accuracy and evaluating physical processes in an irregular area. Aim. The aim of this work was to study the effect of sharp irregularities on the characteristics of the digital twin of a broadband shielded dielectric waveguide operating in the frequency range from 90 to 100 GHz. Methods. Using a numerical experiment, two variants of irregularity were investigated. They are presented in the form of displacement of sections of shielded dielectric waveguides in the vertical and horizontal planes. Results. According to the values of the transfer characteristic of the waveguide path, the regularities of the attenuation of the electromagnetic wave energy from the magnitude of the irregularity are revealed and the permissible manufacturing accuracy is proposed. Conclusion. To solve the problems of sewerage of weak signals, the authors recommend using a non-jointed manufacturing technology.
40
Dunietz, Galit, Kerby Shedden, Kara Michels, Ronald Chervin, Xiru Lyu, Joshua Freeman, Ana Baylin, et al. "0305 Irregularities in Sleep Duration and Biomarkers of Cardiovascular Disease across the Menstrual Cycle." Sleep 45, Supplement_1 (May 25, 2022): A137—A138. http://dx.doi.org/10.1093/sleep/zsac079.303.
Full textAbstract:
Abstract Introduction Irregular sleep duration may disrupt circadian rhythms necessary for optimal cardiovascular function. Yet, few studies have examined irregular sleep duration in relation to cardiovascular health, particularly among diverse cohorts of reproductive-age women. This study examined associations between sleep duration irregularities across the menstrual cycle and cardiovascular disease biomarkers in a cohort of healthy, premenopausal women. Methods We utilized the BioCycle micro-longitudinal cohort study of 259 regularly menstruating women aged 18–44 years. This measurement-intense study collected cardiovascular disease biomarkers at key reproductive time-points along the menstrual cycle (approximately days 2,7,12,13,14,18,22,27 of a 28-day cycle) across two cycles. Specifically, we assessed serum high-density lipoprotein (HDL), low-density lipoprotein (LDL), total cholesterol, triglycerides, and C-reactive protein (CRP). Women recorded sleep duration in daily diaries concurrently. We computed a system of four mathematical measures, the L-moments, robust versions of location, dispersion, skewness, and kurtosis for series of recorded sleep durations. Using linear mixed models with random intercepts and inverse probability weighting we estimated associations between irregular sleep duration and cardiovascular disease biomarkers in all women and within a subset of non-white women. Adjusted analysis accounted for baseline characteristics and time-varying hormonal changes across the menstrual cycle. Results Woman-specific mean sleep duration ranged from 4.4 to 10.6 hours. A one-hour increase in dispersion of sleep duration was associated with a lower mean LDL and higher mean HDL for non-white women (-19.4%, 95%CI -30.9,-6.0% and 24.7%, 95%CI 8.2,43.0, respectively). Unbalanced (skewed) sleep duration, frequent short or long hours, was associated with higher mean CRP for all women and non-white women (99.3%, 95%CI 17.2,238.9 and 126.7%, 95%CI 3.1,398.2, respectively), but lower total cholesterol (-10.9%, 95%CI -19.9,-1.0). Finally, irregular sleep durations, extreme short and long sleep bouts (kurtosis), were associated with reduced mean HDL for all women, and non-white women (-17.1%, 95%CI -31.1,-0.2 and -25.4%, 95%CI -39.5,-8.0, respectively). Conclusion This micro-longitudinal study of premenopausal women found associations between irregularities in sleep duration and differences in CRP, LDL, HDL and total cholesterol, but not with triglycerides. These data suggest that even in young and healthy women, irregularities in sleep duration could have a potential impact on cardiometabolic health. Support (If Any) Dr. Dunietz was supported by a Mentored Research Scientist Development Award from the National Heart, Lung, and Blood Institute (K01 HL144914). This work was supported in part by the Intramural Research Program of the NIH, Eunice Kennedy Shriver National Institute of Child Health and Human Development (authors KAM, JRF, EFS, SLM; The BioCycle Study was funded under the following intramural contracts: HHSN275200403394C HHSN275201100002I, and Task 1 HHSN27500001).
41
Lamqadem, Atman Ait, Hafid Saber, and Abdelmejid Rahimi. "Spatiotemporal Changes of Vegetation in the Middle Draa Valley Oasis: A Study Case of M’hamid El Ghizlane Oasis (Morocco)." European Scientific Journal, ESJ 13, no. 24 (August 31, 2017): 115. http://dx.doi.org/10.19044/esj.2017.v13n24p115.
Full textAbstract:
During the last decades, The Middle Draa Valley (Southeast of Morocco) was subjected to various environmental problems which haves caused land degradation especially in the south of the Middle Draa (M’hamid oasis). This study aims to analyze the spatiotemporal changes of vegetation in the M’hamid oasis. Based on the Landsat images belonging to six separate periods during 1984 to 2016 and Geographical Information System (GIS) techniques, the pattern of spatiotemporal changes of vegetation cover in M’hamid oasis was analyzed based to visual interpretation and NDVI (Normalized Difference Vegetation Index) and supervised classified. For easier understanding of the causes and origins of these changes, we exploited statistical data survey from various local administrations (climatological, socio-economic data) and fieldworks. The results show that the total area of the oasis showed an oscillating decrease between 1984-1999 compared to 1999-2013 and a sharp increase after 2003 to 2007 and a moderate decrease from 2003 to 2016, with an area 3 times smaller than the initial date (loss of 22% of oasis area), correlated with a reduction of the habitants (loss of 21% between 1980 and 2016). Mass tourism, construction of the Mansour Eddahbi dam and the irregularities of the rains and the succession of years of drought led to a modification of the oasis ecosystem. Due to these climatic conditions, the oasis population are obliged to emigration thus they leave their fields which are threatened by sand encroachments, therefore accelerating the phenomenon of sand movements and consequently desertification.
42
Liao, Yan-Juan, Jing-Nan Huang, Jia-Yang Guo, and Shao-Ji Jiang. "Realistic FDTD Simulations of Plasmonic Properties on Ag Columnar Thin Films as SERS Biosensor." Nano 11, no. 10 (September 29, 2016): 1650113. http://dx.doi.org/10.1142/s1793292016501137.
Full textAbstract:
Noble metal sculptured thin films are of great interest during last decade as excellent surface-enhanced Raman scattering (SERS) substrates due to remarkable plasmonic properties in the visible and near-infrared range. In this work, Ag columnar thin films (Ag-CTFs) have been prepared by the glancing angle deposition technique. Finite-difference time-domain simulations has been utilized to study plasmonic properties of Ag-CTFs with a more accurate model based on binary scanning electron microscope (SEM) images by taking account of the shape irregularities, size distributions and random arrangement. The calculated absorption spectra based on the model of binarized SEM images show the best agreement with the measured spectra compared with models of periodic array with a regular shape. The near-field plasmonic properties are simulated based on the verified model. The distributions of electric field enhancement and hot spots are confirmed to be spectral and polarization dependent. There are multiple resonance peaks from visible to near-infrared and multiple eigenmodes coexist at the same wavelength and electric field enhancement are mainly excited by the polarized light vertical to the gap orientation. The electric field enhancement is found to distribute unevenly in the films with surface-localized feature. The equations to calculate the simulation SERS enhancement factor (EF) and total number of hot spots (tHN) are modified according to the above discussions. The experimental SERS EFs are on the order of 107–108, which indicates the high sensitivity of the films and the simulation SERS EFs and tHNs show good agreement with the experimental EFs. It is found that the SERS performance of Ag-CTFs is decided by both the cross-section structural characteristics and film thickness, which affect the electric filed enhancement and number of adsorbed molecules, respectively. Our work could be helpful in understanding the SERS mechanism and useful to the optimization of metal sculptured thin films for designing SERS biosensor.
43
Khayrullina, G, R., E. B. Druzhkova, L. S. Fatkullina, F. I. Fatkullin, and Y. V. Budyak. "Efficiency of organ-saving operations conducted about early postpartum uterine bleeding and their influence on the quality of women’s lives." Medical Herald of the South of Russia 11, no. 2 (June 30, 2020): 111–16. http://dx.doi.org/10.21886/2219-8075-2020-11-2-111-116.
Full textAbstract:
Objective: to study the long-term eff ects of massive blood loss in parturition and the early postpartum period on the reproductive function and psychological status of women.Materials and methods: the study included 49 women who were imposed compressive hemostatic sutures in the uterus due to the development of early postpartum hemorrhage. It was carried out a retrospectiveanalysis of medical records, prospective survey - 46 women, tested scales postpartum depression - 46 women and assessment of quality of life using the SF-36 scales - 36 women.Results: the effi ciency of the compression joints method was 98 % (100 % exclusion criteria were coagulopathic obstetric bleeding), in 1 case the application of compression joints was ineff ective, which required uterus extirpation. In 14 women out of 48 (29.1 %), menstrual irregularities were revealed. In 28 (61.5 %) women, postnatal depression was confi rmed. In 30 out of 36 (87 %) women were found to decrease in quality of life. In 8 (16.7 %) women, a recurrent spontaneous pregnancy occurred within 2 years aft er suturing.Conclusion. Compression sutures remain an effective method for stopping postpartum uterine bleeding, allowing women to maintain fertility. However, some factors, including high blood loss, can signifi cantly reduce the quality of women’s lives.
44
Lanoue, Bradley R., Michael D. Gordon, Robin Battye, and J. Roger Jacobs. "Genetic analysis of vein function in the Drosophila embryonic nervous system." Genome 43, no. 3 (June 1, 2000): 564–73. http://dx.doi.org/10.1139/g00-014.
Full textAbstract:
The Drosophila epidermal growth factor receptor (EGFR) may be activated by two ligands expressed in the embryonic nervous system, Spitz and Vein. Previous studies have established Spitz as an essential activator of EGFR signaling in nervous system development. Here, we report the pattern of expression of vein mRNA in the nervous system and characterize the contribution of vein to cell lineage and axonogenesis. The number of midline glia (MG) precursors is reduced in vein mutants before the onset of embryonic apoptosis. In contrast to spitz, mis-expression of vein does not suppress apoptosis in the MG. These data indicate that early midline EGFR signaling, requiring vein and spitz, establishes MG precursor number, whereas later EGFR signals, requiring spitz, suppress apoptosis in the MG. vein mutants show early irregularities during axon tract establishment, which resolve later to variable defasciculation and thinner intersegmental axon tracts. vein and spitz phenotypes act additively in the regulation of MG cell number, but show synergism in a midline neuronal cell number phenotype and in axon tract architecture. vein appears to act downstream of spitz to briefly amplify local EGFR activation.Key words: Drosophila, vein, midline, axonogenesis, EGF receptor, lineage, neuregulin, spitz, CNS.
45
Wakabayashi, M., T. Ono, H. Mori, and P. A. Bernhardt. "Electron density and plasma waves in mid-latitude sporadic-<i>E</i> layer observed during the SEEK-2 campaign." Annales Geophysicae 23, no. 7 (October 13, 2005): 2335–45. http://dx.doi.org/10.5194/angeo-23-2335-2005.
Full textAbstract:
Abstract. The SEEK-2 campaign was carried out over Kyushu Island in Japan on 3 August 2002, by using the two sounding rockets of S310-31 and S310-32. This campaign was planned to elucidate generation mechanisms of Quasi-Periodic Echoes (QPEs) associated with mid-latitude sporadic-E (Es) layers. Electron number densities were successfully measured in the Es layers by using the impedance probe on board two rockets. The plasma waves in the VLF and ELF ranges were also observed on board the S310-32 rocket. Results of electron density measurement showed that there were one or two major peaks in the Es layers along the rockets' trajectories near the altitude of about 10km. There were some smaller peaks associated with the main Es layers in the altitude range from 90 to 120 km. These density peaks were distributed in a very large extent during the SEEK-2 campaign. The Es layer structure is also measured by using the Fixed Bias Probe (FBP), which has a high spatial resolution of several meters (the impedance probe has an altitude resolution of about 400 m). The comparison with the total electron content (TEC) measured by the Dual Band Beacon revealed that the Es layer was also modulated in the horizontal direction with the scale size of 30–40 km. It was shown that the QP echoes observed by the ground-based coherent radar come from the major density peak of the Es layer. The plasma wave instrument detected the enhancement of VLF and ELF plasma waves associated with the operation of the TMA release, and also with the passage of the Es layers. Keywords. Ionosphere (Ionospheric irregularities; Midlatitude ionosphere; Plasma temeperature and density)
46
Tim, Cvetko, and Robek Tinkara. "Deep Learning Analysis for Estimating Sleep Syndrome Detection Utilizing the Twin Convolutional Model FTC2." BOHR International Journal of Internet of things, Artificial Intelligence and Machine Learning 1, no. 1 (2021): 14–19. http://dx.doi.org/10.54646/bijiam.003.
Full textAbstract:
Manual sleep stage scoring is frequently performed by sleep specialists by visually evaluating the patient's neurophysiological signals acquired in sleep laboratories. This is a difficult, time-consuming, laborious process. Because of the limits of human sleep stage scoring, there is a greater need for creating Automatic Sleep Stage Classification (ASSC) systems. Sleep stage categorization is the process of distinguishing the distinct stages of sleep is an important step in assisting physicians in the diagnosis treatment of associated sleep disorders. In this research, we offer a unique method a practical strategy to predicting early onsets of sleep disorders, such as restless leg syndrome insomnia, using the Twin Convolutional Model FTC2, based on an algorithm composed of two modules. To provide localised time-frequency information, 30 second long epochs of EEG recordings are subjected to a Fast Fourier Transform, a deep convolutional LSTM neural network is trained for sleep stage categorization. Automating sleep stages detection from EEG data offers a great potential to tackling sleep irregularities on a daily basis. Thereby, a novel approach for sleep stage classification is pro- posed which combines the best of signal processing statistics. In this study, we used the PhysioNet Sleep European Data Format (EDF) Database. The code evaluation showed impressive results, reaching accuracy of 90.43, precision of 77.76, recall of 93,32, F1-score of 89.12 with the final mean false error loss 0.09. All the source code is availlable at https://github.com/timothy102/eeg.
47
Cvetko, Tim, and Tinkara Robek. "Deep Learning Analysis for Estimating Sleep Syndrome Detection Utilizing the Twin Convolutional Model FTC2." BOHR International Journal of Future Robotics and Artificial Intelligence 1, no. 1 (2021): 11–17. http://dx.doi.org/10.54646/bijfrai.002.
Full textAbstract:
Sleep specialists often conduct manual sleep stage scoring by visually inspecting the patient's neurophysiological signals collected at sleep labs. This is a difficult, tedious and a time-consuming task. The limitations of manual sleep stage scor- ing have escalated the demand for developing Automatic Sleep Stage Classification (ASSC) systems. Sleep stage classification refers to identifying the various stages of sleep and is a critical step in an effort to assist physicians in the diag- nosis and treatment of related sleep disorders. In this paper, we propose a novel method and a practical approach to predicting early onsets of sleep syndromes utilizing the Twin Convolutional Model FTC2, including restless leg syndrome, insomnia, based on an algorithm which is comprised of two modules. A Fast Fourier Transform is applied to 30 seconds long epochs of EEG recordings to provide localized time-frequency information, and a deep convolutional LSTM neural network is trained for sleep stage classification. Automating sleep stages detection from EEG data offers a great potential to tackling sleep irregularities on a daily basis. Thereby, a novel approach for sleep stage classification is pro- posed which combines the best of signal processing and statistics. In this study, we used the PhysioNet Sleep European Data Format (EDF) Database. The code evaluation showed impressive results, reaching accuracy of 90.43, precision of 77.76, recall of 93,32, F1-score of 89.12 with the final mean false error loss 0.09. All the source code is availlable at https://github.com/timothy102/eeg.
48
Cvetko, Tim, and Tinkara Robek. "Deep learning analysis for estimating sleep syndromedetection utilizing the twin convolutional model FTC2." BOHR International Journal of Internet of things, Artificial Intelligence and Machine Learning 1, no. 1 (2022): 15–21. http://dx.doi.org/10.54646/bijiam.2022.03.
Full textAbstract:
Manual sleep stage scoring is frequently performed by sleep specialists by visually evaluating the patient’sneurophysiological signals acquired in sleep laboratories. This is a difficult, time-consuming, and laborious process.Because of the limits of human sleep stage scoring, there is a greater need for creating automatic sleep stageclassification (ASSC) systems. Sleep stage categorization is the process of distinguishing the distinct stagesof sleep and is an important step in assisting physicians in the diagnosis and treatment of associated sleepdisorders. In this research, we offer a unique method and a practical strategy to predict early onset of sleepdisorders, such as restless leg syndrome and insomnia, using the twin convolutional model FTC2, based on analgorithm composed of two modules. To provide localized time-frequency information, 30-second-long epochs ofelectroencephalogram (EEG) recordings are subjected to a fast Fourier transform, and a deep convolutional longshort-term networks neural network is trained for sleep stage categorization. Automating sleep stage detectionfrom EEG data offers a great potential to tackle sleep irregularities on a daily basis. Thereby, a novel approach forsleep stage classification is proposed, which combines the best of signal processing and statistics. In this study,we used the PhysioNet Sleep European Data Format (EDF) database. The code evaluation showed impressiveresults, reaching an accuracy of 90.43, precision of 77.76, recall of 93,32, F1 score of 89.12, and the final meanfalse error loss of 0.09. All the source code is available athttps://github.com/timothy102/eeg..
49
Devasia, C. V., N. Jyoti, K. S. V. Subbarao, Diwakar Tiwari, C. Raghava Reddi, and R. Sridharan. "On the role of vertical electron density gradients in the generation of type II irregularities associated with blanketing ES(ESb) during counter equatorial electrojet events: A case study." Radio Science 39, no. 3 (May 22, 2004): n/a. http://dx.doi.org/10.1029/2002rs002725.
Full text
50
Yang, Chaoyu, and Haibin Ye. "Enhanced Chlorophyll-a in the Coastal Waters near the Eastern Guangdong during the Downwelling Favorable Wind Period." Remote Sensing 14, no. 5 (February 25, 2022): 1138. http://dx.doi.org/10.3390/rs14051138.
Full textAbstract:
Phytoplankton dynamics, which are highly sensitive to the ecosystem condition and change, are different in coastal waters and open ocean. Previous researches mainly focused on the open ocean dynamic in the South China Sea (SCS), but few research on the Eastern Guangdong (EGD), especially during a period of downwelling-favorable winds. In fact, the influence of topographic irregularities, downwelling, continental outflows, and cold, nutrient-rich currents from Fujian-Zhejiang coastal waters (ZFC) of the East China Sea (ECS) on the spatial distribution of Chlorophyll a (Chl a) in EGD coastal waters could be significant. This study utilized ocean color time series and meteorological and hydrographic data jointly from July 2002 to June 2020 to investigate the heterogeneous regional specific distribution pattern of Chl a in EGD and the environmental determinants in different regions subdivided by water depth. Then the temporal and spatial distribution pattern of Chl a in EGD in winter were discussed in detail by applying an Empirical Orthogonal Function (EOF) analysis, GaoFeng-1 (GF-1) satellite data and in situ measured dataset. The sea surface temperature (SST) in February was negatively related with Chl a in shallow coastal waters less than 60 m deep due to the nutrient-rich, cold waters from ZFC. The monthly mean photosynthetically active radiation (PAR) and precipitation showed significant effects on the phytoplankton growth over regions with a depth less than 10 m. An area with higher Chl a concentration in the downwelling zone were detected in winter. By an examining the temporal variability in meridional distribution of the mean Chl a at 22.41°N and 22.21°N, a symmetrical peak was observed. The coastal fronts extended southwestward from the southeastern coast of Guangdong Province to Dangan Island in the SCS. In addition, a cross-shelf filament was detected near the coast of Shanwei, Guangdong, China on 8 January 2020.