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Articles de revues sur le sujet « Spread F »

Auteur : Grafiati
Publié le 6 septembre 2023

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1

MacDougall, J. W., M. A. Abdu, P. T. Jayachandran, J. F. Cecile et I. S. Batista. « Presunrise spread F at Fortaleza ». Journal of Geophysical Research : Space Physics 103, A10 (1 octobre 1998) : 23415–25. http://dx.doi.org/10.1029/98ja01949.

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Carrasco, A. J., I. S. Batista, J. H. A. Sobral et M. A. Abdu. « Spread F modeling over Brazil ». Journal of Atmospheric and Solar-Terrestrial Physics 161 (août 2017) : 98–104. http://dx.doi.org/10.1016/j.jastp.2017.06.015.

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3

From, W. R., et D. H. Meehan. « Mid-latitude spread-F structure ». Journal of Atmospheric and Terrestrial Physics 50, no 7 (juillet 1988) : 629–38. http://dx.doi.org/10.1016/0021-9169(88)90061-x.

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4

Tozer, T. C. « Spread-Spectrum Systems ». IEE Proceedings F Communications, Radar and Signal Processing 133, no 1 (1986) : 128. http://dx.doi.org/10.1049/ip-f-1.1986.0020.

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5

de Boorder, J. « Spread of F gigantica in Tanzania ». Veterinary Record 131, no 8 (22 août 1992) : 180. http://dx.doi.org/10.1136/vr.131.8.180.

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Wright, J. W. « Quantifying spread F by digital ionosondes ». Advances in Space Research 31, no 3 (janvier 2003) : 729–34. http://dx.doi.org/10.1016/s0273-1177(03)00046-2.

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Becker-Guedes, F., Y. Sahai, P. R. Fagundes, W. L. C. Lima, V. G. Pillat, J. R. Abalde et J. A. Bittencourt. « Geomagnetic storm and equatorial spread-F ». Annales Geophysicae 22, no 9 (23 septembre 2004) : 3231–39. http://dx.doi.org/10.5194/angeo-22-3231-2004.

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Abstract. In August 2000, a new ionospheric sounding station was established at Sao Jose dos Campos (23.2° S, 45.9° W; dip latitude 17.6° S), Brazil, by the University of Vale do Paraiba (UNIVAP). Another ionospheric sounding station was established at Palmas (10.2° S, 48.2° W; dip latitude 5.5° S), Brazil, in April 2002, by UNIVAP in collaboration with the Lutheran University Center of Palmas (CEULP), Lutheran University of Brazil (ULBRA). Both the stations are equipped with digital ionosonde of the type known as Canadian Advanced Digital Ionosonde (CADI). In order to study the effects of geomagnetic storms on equatorial spread-F, we present and discuss three case studies, two from the ionospheric sounding observations at Sao Jose dos Campos (September and November 2000) and one from the simultaneous ionospheric sounding observations at Sao Jose dos Campos and Palmas (July 2003). Salient features from these ionospheric observations are presented and discussed in this paper. It has been observed that sometimes (e.g. 4-5 November 2000) the geomagnetic storm acts as an inhibitor (high strong spread-F season), whereas at other times (e.g. 11-12 July 2003) they act as an initiator (low strong spread-F season), possibly due to corresponding changes in the quiet and disturbed drift patterns during different seasons.
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8

Alex, S., P. V. Koparkar et R. G. Rastogi. « Spread-F and ionization anomaly belt ». Journal of Atmospheric and Terrestrial Physics 51, no 5 (mai 1989) : 371–79. http://dx.doi.org/10.1016/0021-9169(89)90119-0.

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Chandra, H., G. D. Vyas, H. S. S. Sinha, S. Prakash et R. N. Misra. « Equatorial spread-F campaign over SHAR ». Journal of Atmospheric and Solar-Terrestrial Physics 59, no 2 (janvier 1997) : 191–205. http://dx.doi.org/10.1016/1364-6826(95)00199-9.

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Jung, Hye-Young, Woo-Joo Lee et Seung Hoe Choi. « Hybrid Fuzzy Regression Analysis Using the F-Transform ». Applied Sciences 10, no 19 (25 septembre 2020) : 6726. http://dx.doi.org/10.3390/app10196726.

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This paper proposes a hybrid estimation algorithm for independently estimating the response function for the center and the response function for the spread in fuzzy regression model. The proposed algorithm combines the least absolute deviations estimation with discriminant analysis. In addition, the F-transform is used to convert spreads of the dependent variable into several groups. Two examples show that our method is superior to the existing methods based on the fuzzy regression model that assumes the same function for spread and center.
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11

Kelly, Priscilla N. « Notch1 promotes cancer spread ». Science 355, no 6331 (23 mars 2017) : 1278.6–1279. http://dx.doi.org/10.1126/science.355.6331.1278-f.

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Seran, Adrianus Marselus, Ali Warsito et Jehunias L. Tanesib. « ANALISIS KEMUNCULAN SPREAD F DI ATAS KUPANG ». Jurnal Fisika : Fisika Sains dan Aplikasinya 4, no 1 (4 août 2019) : 8–16. http://dx.doi.org/10.35508/fisa.v4i1.1430.

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Abstrak Telah dilakukan dilakukan penelitian tentang kemunculan spread F di atas Kupang dengan menggunakan data hasil scalling ionogram pada tahun 2013 hingga 2015. Penelitian ini bertujuan untuk mengetahui kerakteristik kejadian spread F dan variasi tipe kemunculan spread F berdasarkan klimatologi kemunculannya yang berdampak pada perambatan gelombang radio High Frequency (HF;3-30 MHz) dan sistem navigasi berbasis satelit yang dikenal Global Navigation Satelit System (GNSS). Kemunculan spread F mempunyai korelasi dengan kejadian sintilasi yang bersumber dari aktivitas matahari dan gelombang gravitasi yang umunya terjadi pada malam hari (18.00-06.00) LST. Hasil analisis kemunculan Spread F pada periode tahun 2013-2015 menunjukan bahwa kemunculan spead F tertinggi di tahun 2014 dengan tipe spread F frekuensi karena pada periode tahun 2014 masih merupakan puncak siklus matahari ke 24 meskipun dikatakan siklus terlemah atau aktivitas mataharinya sangat minimum namun gangguan aktivitas matahari seperti flare dan CME awal bulan pertengahan bulan tahun 2014 sangat tinggi intensiasnya yang menimbulkan gangguan geomagnet pada lapisan ionosfer sangat besar dimana tipe spread F frekuensi disebabkan oleh gangguan geomagnet. Intensitas kejadian spread F terjadi di pertengahan tahun yakni bulan Juni dibandingkan dengan bulan-bulan awal dan akhir tahun yang tingkat kemunculannya rendah terutama pada fase ekuinoks. Jumlah kemunculan spread F maksimum terjadi pada tengah malam (22.00-03.00) LST dan minimum di awal dan di akhir malam. Analisis dalam domain frekuensi dengan menggunakan metode Fast Fourier Transform (FFT), menunjukan bahwa adanya kemunculan spread F selama 3 tahun (36 bulan) terjadi rentang waktu 200 hingga 600 hari. Frekuensi kemunculan spread F untuk tiap tahunnya adalah 0,1 sampai 0,2 perhari. Informasi ini menunjukan bahwa intensitas kemunculan spread F yang dapat mengganggu perambatang pelombang radio pada lapisan ionosfer di atas wilayah Kupang masih rendah dengan periode kejadian yaitu 365 hari atau 1 tahun selama 3 tahun (2013-2015) dan dapat digunakan sebagai indicator peluang kejadian spread F setiap tahunnya. Kata kunci: Spread F; FFT; Kupang Abstract Research has been conducted on the emergence of the distribution of F above Kupang by using scaling ionogram data from 2013 to 2015. This study aims to study the characteristics of F distribution events and variations in the type of occurrence of F distribution based on their climatology appearance used in High Frequency radio wave moorings (HF ; 3-30 MHz) and a satellite-based navigation system called the Global Navigation Satellite System (GNSS). The appearance of spread F has an interaction with the scintillation event that originates from the activity of the sun and the wave of release that occurs at night (18.00-06.00) LST. The results of the analysis of the emergence of the F spread in the period 2013-2015 indicate that the appearance of the highest F spead in 2014 with the type of spread F frequency in the period of 2014 is still the peak of the 24th solar cycle which is expected to be protected or used by the minimum sun to be used to monitor solar activity such as flares and CME at the beginning of the middle of 2014 is very high, which causes geomagnetic disturbances in the ionospheric layer to be very large where the frequency F type spread is related to geomagnetic interference. The intensity of diffuse F events occurs in the middle of the year in June compared to the initial and end of the year with a low rate of occurrence in the equinox phase. The maximum number of occurrences of the F spread occurs at midnight (10:00 p.m.: 00: 00) LST and minimum at the beginning and end of the night. Analysis in the domain using the Fast Fourier Transform (FFT) method, showed that there were occurrences that spread F for 3 years (36 months) occurring in the range 200 to 600 days. The frequency of occurrence of spread F for each semester is 0.1 to 0.2 per day. This information shows that the intensity of the spread of occurrence of F that can be carried out by radio waves in the ionospheric layer above the Kupang region is still low with an event period of 365 days or 1 year for 3 years (2013-2015) and can be used as an Annual indicator. Keywords: Spread F; FFT; Kupang
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13

Liperovskaya, E. V. « Studying the spread F effect before earthquakes ». Geomagnetism and Aeronomy 48, no 6 (28 novembre 2008) : 807–11. http://dx.doi.org/10.1134/s0016793208060145.

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Mathews, J. D., S. González, M. P. Sulzer, Q. H. Zhou, J. Urbina, E. Kudeki et S. Franke. « Kilometer-scale layered structures inside spread-F ». Geophysical Research Letters 28, no 22 (15 novembre 2001) : 4167–70. http://dx.doi.org/10.1029/2001gl013077.

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Raghavarao, R., R. Suhasini, H. G. Mayr, W. R. Hoegy et L. E. Wharton. « Equatorial spread-F (ESF) and vertical winds ». Journal of Atmospheric and Solar-Terrestrial Physics 61, no 8 (mai 1999) : 607–17. http://dx.doi.org/10.1016/s1364-6826(99)00017-6.

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16

Laxmi, V. N., et V. K. Tripathi. « Radio wave heating and equatorial spread-F ». Journal of Atmospheric and Terrestrial Physics 49, no 11-12 (novembre 1987) : 1071–74. http://dx.doi.org/10.1016/0021-9169(87)90089-4.

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17

Rodrigues, F. S., M. J. Nicolls, M. A. Milla, J. M. Smith, R. H. Varney, A. Strømme, C. Martinis et J. F. Arratia. « AMISR-14 : Observations of equatorial spread F ». Geophysical Research Letters 42, no 13 (7 juillet 2015) : 5100–5108. http://dx.doi.org/10.1002/2015gl064574.

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18

Anderson, David N., et Robert J. Redmon. « Forecasting scintillation activity and equatorial spread F ». Space Weather 15, no 3 (mars 2017) : 495–502. http://dx.doi.org/10.1002/2016sw001554.

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19

Fritts, D. C., S. L. Vadas, D. M. Riggin, M. A. Abdu, I. S. Batista, H. Takahashi, A. Medeiros et al. « Gravity wave and tidal influences on equatorial spread F based on observations during the Spread F Experiment (SpreadFEx) ». Annales Geophysicae 26, no 11 (21 octobre 2008) : 3235–52. http://dx.doi.org/10.5194/angeo-26-3235-2008.

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Abstract. The Spread F Experiment, or SpreadFEx, was performed from September to November 2005 to define the potential role of neutral atmosphere dynamics, primarily gravity waves propagating upward from the lower atmosphere, in seeding equatorial spread F (ESF) and plasma bubbles extending to higher altitudes. A description of the SpreadFEx campaign motivations, goals, instrumentation, and structure, and an overview of the results presented in this special issue, are provided by Fritts et al. (2008a). The various analyses of neutral atmosphere and ionosphere dynamics and structure described in this special issue provide enticing evidence of gravity waves arising from deep convection in plasma bubble seeding at the bottomside F layer. Our purpose here is to employ these results to estimate gravity wave characteristics at the bottomside F layer, and to assess their possible contributions to optimal seeding conditions for ESF and plasma instability growth rates. We also assess expected tidal influences on the environment in which plasma bubble seeding occurs, given their apparent large wind and temperature amplitudes at these altitudes. We conclude 1) that gravity waves can achieve large amplitudes at the bottomside F layer, 2) that tidal winds likely control the orientations of the gravity waves that attain the highest altitudes and have the greatest effects, 3) that the favored gravity wave orientations enhance most or all of the parameters influencing plasma instability growth rates, and 4) that gravity wave and tidal structures acting together have an even greater potential impact on plasma instability growth rates and plasma bubble seeding.
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20

Sugden, Andrew M. « Invasive birds spread native seeds ». Science 364, no 6435 (4 avril 2019) : 38.6–39. http://dx.doi.org/10.1126/science.364.6435.38-f.

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21

Sastri, J. H. « <i>Letter to the Editor</i> ; : Post-midnight onset of spread-F at Kodaikanal during the June solstice of solar minimum ». Annales Geophysicae 17, no 8 (31 août 1999) : 1111–15. http://dx.doi.org/10.1007/s00585-999-1111-4.

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Abstract. At dip equatorial stations in the Indian zone, spread-F conditions are known to develop preferentially around midnight during the June solstice (northern summer) months of low solar activity, in association with a distinct increase in F layer height. It is currently held that this onset of spread-F far away from the sunset terminator is due to the generalised Rayleigh-Taylor instability mechanism, with the gravitational and cross-field instability factors (and hence F layer height) playing important roles. We have studied the quarter-hourly ionograms of Kodaikanal (10.2°N; 77.5°E; dip 4°N) for the northern summer months (May-August) of 1994 and 1995 to ascertain the ambient ionospheric conditions against which the post-midnight onset of spread-F takes place. A data sample of 38 nights with midnight onset of spread-F and 34 nights without spread-F is used for the purpose. It is found that a conspicious increase in F layer height beginning around 2100 LT occurs on nights with spread-F as well as without spread-F. This feature is seen in the nocturnal pattern of F layer height on many individual nights as well as of average F layer height for the two categories of nights. The result strongly suggests that the F layer height does not play a pivotal role in the midnight onset of spread-F during the June solstice of solar minimum. The implications of this finding are discussed.Key words. Ionosphere (equatorial ionosphere; ionospheric irregularities)
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22

Bowman, G. G. « Some aspects of mid-latitude spread-Es, and its relationship with spread-F ». Planetary and Space Science 33, no 9 (septembre 1985) : 1081–89. http://dx.doi.org/10.1016/0032-0633(85)90027-3.

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Hines, P. J. « How infection rate determines virus spread ». Science 345, no 6198 (14 août 2014) : 783. http://dx.doi.org/10.1126/science.345.6198.783-f.

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HUANG CHAO-SONG et M.C.KELLEY. « NUMERICAL SIMULATIONS OF LARGE SCALE EQUATORIAL SPREAD F ». Acta Physica Sinica 45, no 11 (1996) : 1930. http://dx.doi.org/10.7498/aps.45.1930.

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Bakki, P. « On the region of mid-latitude spread-F ». Acta Geodaetica et Geophysica Hungarica 37, no 4 (octobre 2002) : 409–17. http://dx.doi.org/10.1556/ageod.37.2002.4.4.

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Wang, G. J., J. K. Shi, X. Wang et S. P. Shang. « Seasonal variation of spread-F observed in Hainan ». Advances in Space Research 41, no 4 (janvier 2008) : 639–44. http://dx.doi.org/10.1016/j.asr.2007.04.077.

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Amabayo, Emirant Bertillas, Lee-Anne McKinnell et Pierre J. Cilliers. « Statistical characterisation of spread F over South Africa ». Advances in Space Research 48, no 12 (décembre 2011) : 2043–52. http://dx.doi.org/10.1016/j.asr.2011.08.029.

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Lan, Ting, Yuannong Zhang, Chunhua Jiang, Guobin Yang et Zhengyu Zhao. « Automatic identification of Spread F using decision trees ». Journal of Atmospheric and Solar-Terrestrial Physics 179 (novembre 2018) : 389–95. http://dx.doi.org/10.1016/j.jastp.2018.09.007.

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Liperovskaya, E. V., V. A. Liperovsky, A. S. Silina et M. Parrot. « On spread-F in the ionosphere before earthquakes ». Journal of Atmospheric and Solar-Terrestrial Physics 68, no 2 (janvier 2006) : 125–33. http://dx.doi.org/10.1016/j.jastp.2005.10.005.

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Kelley, Michael C., Jonathan J. Makela, Brent M. Ledvina et Paul M. Kintner. « Observations of equatorial spread-F from Haleakala, Hawaii ». Geophysical Research Letters 29, no 20 (octobre 2002) : 64–1. http://dx.doi.org/10.1029/2002gl015509.

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Saksena, R. C. « Occurrence statistics for spread-F over Indian subcontinent ». Advances in Space Research 18, no 6 (janvier 1996) : 99–102. http://dx.doi.org/10.1016/0273-1177(95)00907-8.

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Kelley, M. C. « Equatorial spread-F : recent results and outstanding problems ». Journal of Atmospheric and Terrestrial Physics 47, no 8-10 (août 1985) : 745–52. http://dx.doi.org/10.1016/0021-9169(85)90051-0.

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Bowman, G. G., G. S. Dunne et D. W. Hainsworth. « Mid-latitude spread-F occurrence during daylight hours ». Journal of Atmospheric and Terrestrial Physics 49, no 2 (février 1987) : 165–76. http://dx.doi.org/10.1016/0021-9169(87)90051-1.

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Alimov, V. A., F. I. Vybornov, L. M. Erukhimov, N. A. Mityakov et A. V. Rakhlin. « On the nature of middle-latitude F-spread ». Radiophysics and Quantum Electronics 37, no 11 (novembre 1994) : 936–38. http://dx.doi.org/10.1007/bf01057284.

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Cécile, J. F., P. Vila et E. Blanc. « HF radar observations of equatorial spread-F over West Africa ». Annales Geophysicae 14, no 4 (30 avril 1996) : 411–18. http://dx.doi.org/10.1007/s00585-996-0411-1.

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Abstract. New experimental data depicting equatorial spread-F were taken during an HF radar sounding campaign in Korhogo (Ivory Coast, 9°24N, 5°37W, dip 4°S). Range-time-intensity maps of the radar echoes have been analyzed to identify the signatures of density depletions and bottomside spread-F. Density depletions are well known features of equatorial spread-F, and are believed to emerge after the development of a Rayleigh-Taylor instability on the bottomside F-layer. A simple model is developed and used to simulate the flow of density depletions over the radar field of view. The simulation permits an interpretation of the data that yields the zonal flow velocity as a function of local time. Comparisons with previous measurements are undertaken to assess the consistency of the computational results, and qualitative arguments are presented to identify bottomside spread-F. Using the computational results as reference, a morphological study of ionograms showing spread-F is undertaken which reveals the specific signature of bottomside spread-F on ionograms recorded just after sunset.
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Ikegame, Satoshi, Takao Hashiguchi, Chuan-Tien Hung, Kristina Dobrindt, Kristen J. Brennand, Makoto Takeda et Benhur Lee. « Fitness selection of hyperfusogenic measles virus F proteins associated with neuropathogenic phenotypes ». Proceedings of the National Academy of Sciences 118, no 18 (26 avril 2021) : e2026027118. http://dx.doi.org/10.1073/pnas.2026027118.

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Measles virus (MeV) is resurgent and caused >200,000 deaths in 2019. MeV infection can establish a chronic latent infection of the brain that can recrudesce months to years after recovery from the primary infection. Recrudescent MeV leads to fatal subacute sclerosing panencephalitis (SSPE) or measles inclusion body encephalitis (MIBE) as the virus spreads across multiple brain regions. Most clinical isolates of SSPE/MIBE strains show mutations in the fusion (F) gene that result in a hyperfusogenic phenotype in vitro and allow for efficient spread in primary human neurons. Wild-type MeV receptor-binding protein is indispensable for manifesting these mutant F phenotypes, even though neurons lack canonical MeV receptors (CD150/SLAMF1 or nectin-4). How such hyperfusogenic F mutants are selected and whether they confer a fitness advantage for efficient neuronal spread is unresolved. To better understand the fitness landscape that allows for the selection of such hyperfusogenic F mutants, we conducted a screen of ≥3.1 × 105 MeV-F point mutants in their genomic context. We rescued and amplified our genomic MeV-F mutant libraries in BSR-T7 cells under conditions in which MeV-F-T461I (a known SSPE mutant), but not wild-type MeV, can spread. We recovered known SSPE mutants but also characterized at least 15 hyperfusogenic F mutations with an SSPE phenotype. Structural mapping of these mutants onto the prefusion MeV-F trimer confirm and extend our understanding of the F regulatory domains in MeV-F. Our list of hyperfusogenic F mutants is a valuable resource for future studies into MeV neuropathogenesis and the regulation of paramyxovirus F.
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Rekah, Yael, D. Shtienberg et J. Katan. « Spatial Distribution and Temporal Development of Fusarium Crown and Root Rot of Tomato and Pathogen Dissemination in Field Soil ». Phytopathology® 89, no 9 (septembre 1999) : 831–39. http://dx.doi.org/10.1094/phyto.1999.89.9.831.

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The spatial distribution and temporal development of tomato crown and root rot, caused by Fusarium oxysporum f. sp. radicis-lycopersici, were studied in naturally infested fields in 1996 and 1997. Disease progression fit a logistic model better than a monomolecular one. Geostatistical analyses and semivariogram calculations revealed that the disease spreads from infected plants to a distance of 1.1 to 4.4 m during the growing season. By using a chlorate-resistant nitrate nonutilizing (nit) mutant of F. oxysporum f. sp. radicis-lycopersici as a “tagged” inoculum, the pathogen was found to spread from one plant to the next via infection of the roots. The pathogen spread to up to four plants (2.0 m) on either side of the inoculated focus plant. Root colonization by the nit mutant showed a decreasing gradient from the site of inoculation to both sides of the inoculated plant. Simulation experiments in the greenhouse further established that this soilborne pathogen can spread from root to root during the growing season. These findings suggest a polycyclic nature of F. oxysporum f. sp. radicis-lycopersici, a deviation from the monocyclic nature of many nonzoosporic soilborne pathogens.
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Hajkowicz, L. A. « Morphology of quantified ionospheric range spread-F over a wide range of midlatitudes in the Australian longitudinal sector ». Annales Geophysicae 25, no 5 (4 juin 2007) : 1125–30. http://dx.doi.org/10.5194/angeo-25-1125-2007.

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Abstract. Ionograms from a standard vertical-incidence ionosonde chain (nine stations), obtained over a wide range of southern latitudes (in geom.lat. range: 23°–52° S), were digitally scanned at 5-min intervals at nighttime (18:00–06:00 LT) for 13 months (January 2004–January 2005). An important parameter of the F-region, so-called range spread-F (Sr), was for the first time quantified in km. Maximum in Sr was recorded at a sounding frequency of 1.8 MHz for each night and for each ionosonde station. A distinct pattern in the magnitude (in km) and in the percentage occurrence of the range spread-F was present in southern winter only (the June solstice). The sub-auroral region (geom. lat. ≥52° S) is characterised by consistently high spread-F (average Sr≈100 km) on 80–100 per cent of the observed nights. There is a sharp equatorward boundary in the spread-F activity in a latitudinal range: 52°–48° S followed by a midlatitude region (44°–48° S) which exhibits a peak in Sr (≈50 km) in winter only, observed on half of the nights. The midlatitude activity reaches its minimum at 42°–43° S, with Sr less than 20 km on one third of the nights. The low midlatitudes (23°–36° S) are characterised by a strong peak in Sr again in winter, centred at about 30° S (average Sr≈70 km) on 80 per cent of the nights. The pattern becomes largely absent during other seasons particularly in southern summer (the December solstice) when spread-F activity shifts to sub-auroral latitudes. The pattern in the occurrence of spread-F appears to have a global character as the enhanced spread-F activity is observed in the Japanese sector in local summer (i.e. the June solstice). It appears that the midlatitude spread-F minimum is only apparent but not real. It delineates the boundary between aurorally generated spread-F (due to travelling ionospheric disturbances, TIDs) and low midlatitude spread-F whose origin is not known.
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39

Ganesan, Ghurumuruhan. « Infection Spread in Random Geometric Graphs ». Advances in Applied Probability 47, no 1 (mars 2015) : 164–81. http://dx.doi.org/10.1239/aap/1427814586.

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In this paper we study the speed of infection spread and the survival of the contact process in the random geometric graph G = G(n, rn, f) of n nodes independently distributed in S = [-½, ½]2 according to a certain density f(·). In the first part of the paper we assume that infection spreads from one node to another at unit rate and that infected nodes stay in the same state forever. We provide an explicit lower bound on the speed of infection spread and prove that infection spreads in G with speed at least D1nrn2. In the second part of the paper we consider the contact process ξt on G where infection spreads at rate λ > 0 from one node to another and each node independently recovers at unit rate. We prove that, for every λ > 0, with high probability, the contact process on G survives for an exponentially long time; there exist positive constants c1 and c2 such that, with probability at least 1 - c1 / n4, the contact process starting with all nodes infected survives up to time tn = exp(c2n/logn) for all n.
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Pujiastuti, Dwi, et Badrul Mustafa. « ANALISIS KEJADIAN SPREAD F IONOSFER PADA GEMPA SOLOK 6 MARET 2007 ». JURNAL ILMU FISIKA | UNIVERSITAS ANDALAS 5, no 2 (15 septembre 2013) : 52–64. http://dx.doi.org/10.25077/jif.5.2.52-64.2013.

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Analisis kejadian Spread F menggunakan data ionosonda FMCW di stasiun pengamat dirgantara LAPAN Kototabang telah dilakukan untuk melihat keterkaitan antara kejadian gempa bumi Solok dengan kemunculan Spread F. Dari hasil pengamatan pada tanggal 20 Februari sampai 20 Maret 2007 kemunculan Spread F terjadi pada tanggal 2, 3 dan 5 Maret 2007. Kemunculan Spread F tersebut diprediksi sebagai prekusor gempa bumi Solok yang terjadi pada tanggal 6 Maret 2007 karena pada saat itu aktivitas geomagnet dan matahari dalam kondisi normal. Setelah gempa Solok aktivitas ionosfer kembali menunjukkan kondisi yang normal.
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Lyttek, Erik, Pankaj Lal, Garrett Nieddu, Eric Forgoston et Taylor Wieczerak. « Modeling Agrilus planipennis F. (Coleoptera : Buprestidae) Spread in New Jersey ». Journal of Economic Entomology 112, no 5 (22 mai 2019) : 2482–88. http://dx.doi.org/10.1093/jee/toz122.

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Abstract Pests and disease have become an increasingly common issue as globalized trade brings non-native species into unfamiliar systems. Emerald ash borer (Agrilus planipennis), is an Asiatic species of boring beetle currently devastating the native population of ash (Fraxinus) trees in the northern forests of the United States, with 85 million trees having already succumbed across much of the Midwest. We have developed a reaction-diffusion partial differential equation model to predict the spread of emerald ash borer over a heterogeneous 2-D landscape, with the initial ash tree distribution given by data from the Forest Inventory and Analysis. As expected, the model predictions show that emerald ash borer consumes ash which causes the local ash population to decline, while emerald ash borer spreads outward to other areas. Once the local ash population begins to decline emerald ash borer also declines due to the loss of available habitat. Our model’s strength lies with its focus on the county scale and its linkage between emerald ash borer population growth and ash density. This enables one to make accurate predictions regarding emerald ash borer spread which allows one to consider various methods of control as well as to accurately study the economic effects of emerald ash borer spread.
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Deng, Zhongxin, Rui Wang, Yi Liu, Tong Xu, Zhuangkai Wang, Guanyi Chen, Qiong Tang, Zhengwen Xu et Chen Zhou. « Investigation of Low Latitude Spread-F Triggered by Nighttime Medium-Scale Traveling Ionospheric Disturbance ». Remote Sensing 13, no 5 (3 mars 2021) : 945. http://dx.doi.org/10.3390/rs13050945.

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In the current study, we investigated the mechanism of medium-scale traveling ionospheric disturbance (MSTID) triggering spread-F in the low latitude ionosphere using ionosonde observation and Global Navigation Satellite System-Total Electron Content (GNSS-TEC) measurement. We use a series of morphological processing techniques applied to ionograms to retrieve the O-wave traces automatically. The maximum entropy method (MEM) was also utilized to obtain the propagation parameters of MSTID. Although it is widely acknowledged that MSTID is normally accompanied by polarization electric fields which can trigger Rayleigh–Taylor (RT) instability and consequently excite spread-F, our statistical analysis of 13 months of MSTID and spread-F occurrence showed that there is an inverse seasonal occurrence rate between MSTID and spread-F. Thus, we assert that only MSTID with certain properties can trigger spread-F occurrence. We also note that the MSTID at night has a high possibility to trigger spread-F. We assume that this tendency is consistent with the fact that the polarization electric field caused by MSTID is generally the main source of post-midnight F-layer instability. Moreover, after thorough investigation over the azimuth, phase speed, main frequency, and wave number over the South America region, we found that the spread-F has a tendency to be triggered by nighttime MSTID, which is generally characterized by larger ΔTEC amplitudes.
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43

Foppiano, A. J., et A. S. Rodger. « F-region ionospheric irregularities over King George Island and Argentine Islands – a comparative study ». Antarctic Science 6, no 3 (septembre 1994) : 411–17. http://dx.doi.org/10.1017/s0954102094000623.

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Spread-F is caused by the presence of ionospheric electron concentration irregularities of scale-size of order 5 km at F-region altitudes. Estimates of spread-F in the vicinity of the maximum plasma frequency of the Flayer (foF2) have been determined at 15 min intervals from ionograms recorded over a ten day period (1–10 May 1986) both at Marsh (62.2°S, 58.9°W), King George Island, and Faraday (65.2°S, 64.3°W), Argentine Islands. The interval, at low solar activity, includes periods of quiet and disturbed geomagnetic activity. Spread-F is observed on every night at both stations. It is more frequent, slightly more intense and starts earlier at Argentine Islands than at King George Island. On most nights, spread-F ceases about local sunrise at 120 km altitude at both stations. On the days of highest geomagnetic activity, the onset of spread-F is delayed compared with days of lower activity. Spread-F is usually most intense on the night(s) following largest geomagnetic activity level, as measured by the geomagnetic index, Kp. The growth rate of the plasma instability processes causing the ionospheric irregularities is inversely related to electron concentration (foF22), amongst other parameters. Thus the lower foF2 values over Argentine Islands are consistent with more spread-F being observed by the higher latitude observatory. However, no firm relationship between the absolute value of foF2, the horizontal gradient of foF2 between the two observatories, and the onset of spread-F, is found. Thus it has not been possible to determine uniquely the instability process responsible for the formation of the plasma irregularities.
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44

Ganesan, Ghurumuruhan. « Infection Spread in Random Geometric Graphs ». Advances in Applied Probability 47, no 01 (mars 2015) : 164–81. http://dx.doi.org/10.1017/s0001867800007758.

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In this paper we study the speed of infection spread and the survival of the contact process in the random geometric graph G = G(n, r n , f) of n nodes independently distributed in S = [-½, ½]2 according to a certain density f(·). In the first part of the paper we assume that infection spreads from one node to another at unit rate and that infected nodes stay in the same state forever. We provide an explicit lower bound on the speed of infection spread and prove that infection spreads in G with speed at least D 1 nr n 2. In the second part of the paper we consider the contact process ξ t on G where infection spreads at rate λ &gt; 0 from one node to another and each node independently recovers at unit rate. We prove that, for every λ &gt; 0, with high probability, the contact process on G survives for an exponentially long time; there exist positive constants c 1 and c 2 such that, with probability at least 1 - c 1 / n 4, the contact process starting with all nodes infected survives up to time t n = exp(c 2 n/logn) for all n.
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45

Woodman, R. F. « Spread F – an old equatorial aeronomy problem finally resolved ? » Annales Geophysicae 27, no 5 (4 mai 2009) : 1915–34. http://dx.doi.org/10.5194/angeo-27-1915-2009.

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Abstract. One of the oldest scientific topics in Equatorial Aeronomy is related to Spread-F. It includes all our efforts to understand the physical mechanisms responsible for the existence of ionospheric F-region irregularities, the spread of the traces in a night-time equatorial ionogram – hence its name – and all other manifestations of the same. It was observed for the first time as an abnormal ionogram in Huancayo, about 70 years ago. But only recently are we coming to understand the physical mechanisms responsible for its occurrence and its capricious day to day variability. Several additional techniques have been used to reveal the spatial and temporal characteristics of the F-region irregularities responsible for the phenomenon. Among them we have, in chronological order, radio star scintillations, trans-equatorial radio propagation, satellite scintillations, radar backscatter, satellite and rocket in situ measurements, airglow, total electron content techniques using the propagation of satellite radio signals and, recently, radar imaging techniques. Theoretical efforts are as old as the observations. Nevertheless, 32 years after their discovery, Jicamarca radar observations showed that none of the theories that had been put forward could explain them completely. The observations showed that irregularities were detected at altitudes that were stable according to the mechanisms proposed. A breakthrough came a few years later, again from Jicamarca, by showing that some of the "stable" regions had become unstable by the non-linear propagation of the irregularities from the unstable to the stable region of the ionosphere in the form of bubbles of low density plasma. A problem remained, however; the primary instability mechanism proposed, an extended (generalized) Rayleigh-Taylor instability, was too slow to explain the rapid development seen by the observations. Gravity waves in the neutral background have been proposed as a seeding mechanism to form irregularities from which the instability would grow, but the former are difficult to observe as a controlling parameter. Their actual role still needs to be determined. More recently, radar observations again have shown the existence of horizontal plasma drift velocities counter streaming the neutral wind at the steep bottom of the F-region which produces a fast growing instability from which a generalized Rayleigh-Taylor instability can grow. The mechanisms proposed would explain the rapid development of the large and medium scale irregularities that have been observed, including some seen only by radars. Nevertheless, a proper quantitative theoretical mechanism that would explain how these irregularities break into the very important meter scale ones, responsible for the radar echoes, needs to be developed. This paper makes a selective historical review of the observations and proposed theories since the phenomenon was discovered to our current understanding.
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Fritts, D. C., M. A. Abdu, B. R. Batista, I. S. Batista, P. P. Batista, R. Buriti, B. R. Clemesha et al. « Overview and summary of the Spread F Experiment (SpreadFEx) ». Annales Geophysicae 27, no 5 (11 mai 2009) : 2141–55. http://dx.doi.org/10.5194/angeo-27-2141-2009.

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Abstract. We provide here an overview of, and a summary of results arising from, an extensive experimental campaign (the Spread F Experiment, or SpreadFEx) performed from September to November 2005, with primary measurements in Brazil. The motivation was to define the potential role of neutral atmosphere dynamics, specifically gravity wave motions propagating upward from the lower atmosphere, in seeding Rayleigh-Taylor instability (RTI) and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12, and the GUVI instrument aboard the TIMED satellite. Initial results of our SpreadFEx analyses are described separately by Fritts et al. (2009). Further analyses of these data provide additional evidence of 1) gravity wave (GW) activity near the mesopause apparently linked to deep convection predominantly to the west of our measurement sites, 2) small-scale GWs largely confined to lower altitudes, 3) larger-scale GWs apparently penetrating to much higher altitudes, 4) substantial GW amplitudes implied by digisonde electron densities, and 5) apparent influences of these perturbations in the lower F-region on the formation of equatorial spread F, RTI, and plasma bubbles extending to much higher altitudes. Other efforts with SpreadFEx data have also yielded 6) the occurrence, locations, and scales of deep convection, 7) the spatial and temporal evolutions of plasma bubbles, 8) 2-D (height-resolved) structures in electron density fluctuations and equatorial spread F at lower altitudes and plasma bubbles above, and 9) the occurrence of substantial tidal perturbations to the large-scale wind and temperature fields extending to bottomside F-layer and higher altitudes. Collectively, our various SpreadFEx analyses suggest direct links between deep tropical convection and large GW perturbations at large spatial scales at the bottomside F-layer and their likely contributions to the excitation of RTI and plasma bubbles extending to much higher altitudes.
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Reddi, C. R., M. S. S. R. K. N. Sarma et K. Niranjan. « HF Doppler radar observations of low-latitude spread F ». Radio Science 44, no 3 (9 mai 2009) : n/a. http://dx.doi.org/10.1029/2007rs003777.

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Patra, A. K., P. B. Rao, V. K. Anandan et A. R. Jain. « Radar observations of 2.8 m equatorial spread-F irregularities ». Journal of Atmospheric and Solar-Terrestrial Physics 59, no 13 (septembre 1997) : 1633–41. http://dx.doi.org/10.1016/s1364-6826(96)00162-9.

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Hysell, D. L. « Imaging coherent backscatter radar studies of equatorial spread F ». Journal of Atmospheric and Solar-Terrestrial Physics 61, no 9 (juin 1999) : 701–16. http://dx.doi.org/10.1016/s1364-6826(99)00020-6.

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Soicher, H., F. Gorman, E. E. Tsedilina et O. V. Weitsman. « Spread-F during quiet and disturbed periods at midlatitudes ». Advances in Space Research 20, no 11 (janvier 1997) : 2199–202. http://dx.doi.org/10.1016/s0273-1177(97)00671-6.

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