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Tian, Xiao, Jia-Lun Li, Shuang-Xi Yi, Yu-Peng Yang, Jian-Ping Hu, Yan-Kun Qu et Fa-Yin Wang. « Radio Plateaus in Gamma-Ray Burst Afterglows and Their Application in Cosmology ». Astrophysical Journal 958, no 1 (1 novembre 2023) : 74. http://dx.doi.org/10.3847/1538-4357/acfed8.
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Abstract The plateau phase in radio afterglows has been observed in very few gamma-ray bursts (GRBs), and in this paper, 27 radio light curves with plateau phases were acquired from the published literature. We obtain the related parameters of the radio plateau, such as temporal indexes during the plateau phase (α 1 and α 2), break time (T b,z), and the corresponding radio flux (F b). The two-parameter Dainotti relation between the break time of the plateau and the corresponding break luminosity (L b,z) in the radio band is L b , z ∝ T b , z − 1.20 ± 0.24 . Including the isotropic energy E γ,iso and peak energy E p,i, the three-parameter correlations for the radio plateaus are written as L b , z ∝ T b , z − 1.01 ± 0.24 E γ , iso 0.18 ± 0.09 and L b , z ∝ T b , z − 1.18 ± 0.27 E p , i 0.05 ± 0.28 , respectively. The correlations are less consistent with those of the X-ray and optical plateaus, implying that radio plateaus may have a different physical mechanism. The typical frequencies crossing the observational band may be a reasonable hypothesis that causes the breaks of the radio afterglows. We calibrate the GRB empirical luminosity correlations as a standard candle for constraining cosmological parameters and find that our samples can constrain the flat ΛCDM model well but are not sensitive to the nonflat ΛCDM model. By combining GRBs with other probes, such as supernovae and the CMB, the constraints on the cosmological parameters are Ωm = 0.297 ± 0.006 for the flat ΛCDM model and Ωm = 0.283 ± 0.008, ΩΛ = 0.711 ± 0.006 for the nonflat ΛCDM model.
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Gong, J., et T. S. M. Maclean. « Radio wave propagation over finite size plateau ». IEEE Transactions on Antennas and Propagation 39, no 8 (1991) : 1152–57. http://dx.doi.org/10.1109/8.97350.
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Raupov, D. A. « Study Of Atmospheric Absorption And PWV In The Suffa Plateau (Uzbekistan) ». American Journal of Applied Sciences 03, no 03 (30 mars 2021) : 28–33. http://dx.doi.org/10.37547/tajas/volume03issue03-05.
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Radio Astronomical Observatory of Suffa, and new proposals for radioastroclimatic (seeing) studies for atmospheric radio prediction are described. The paper presents the results of many-year (2015-2020) and seasonal observations of the astroclimate at the construction site of the RT-70 radio telescope on the Suffa plateau (an altitude of 2400 m above sea level). Observations were carried out automatically every 10 minutes throughout the year, starting from November 2014.
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Dainotti, Maria, Delina Levine, Nissim Fraija et Poonam Chandra. « Accounting for Selection Bias and Redshift Evolution in GRB Radio Afterglow Data ». Galaxies 9, no 4 (7 novembre 2021) : 95. http://dx.doi.org/10.3390/galaxies9040095.
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Gamma-ray Bursts (GRBs) are highly energetic events that can be observed at extremely high redshift. However, inherent bias in GRB data due to selection effects and redshift evolution can significantly skew any subsequent analysis. We correct for important variables related to the GRB emission, such as the burst duration, T90*, the prompt isotropic energy, Eiso, the rest-frame end time of the plateau emission, Ta,radio*, and its correspondent luminosity La,radio, for radio afterglow. In particular, we use the Efron–Petrosian method presented in 1992 for the correction of our variables of interest. Specifically, we correct Eiso and T90* for 80 GRBs, and La,radio and Ta,radio* for a subsample of 18 GRBs that present a plateau-like flattening in their light curve. Upon application of this method, we find strong evolution with redshift in most variables, particularly in La,radio, with values similar to those found in past and current literature in radio, X-ray and optical wavelengths, indicating that these variables are susceptible to observational bias. This analysis emphasizes the necessity of correcting observational data for evolutionary effects to obtain the intrinsic behavior of correlations to use them as discriminators among the most plausible theoretical models and as reliable cosmological tools.
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van Oers, Pieter, et Sera Markoff. « GRS1915+105 : a comparison of the plateau state to the canonical hard state ». Proceedings of the International Astronomical Union 6, S275 (septembre 2010) : 294–98. http://dx.doi.org/10.1017/s1743921310016194.
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AbstractGRS 1915+105 is a very peculiar black hole binary that exhibits accretion-related states that are not observed in any other stellar-mass black hole system. One of these states, however – referred to as the plateau state – may be related to the canonical hard state of black hole X-ray binaries. Both the plateau and hard state are associated with steady, relatively lower X-ray emission and flat/inverted radio emission, that is sometimes resolved into compact, self-absorbed jets. To investigate the relationship between the plateau and the hard state, we fit two multi-wavelength observations using a steady-state outflow-dominated model, developed for hard state black hole binaries. The data sets consist of quasi-simultaneous observations in radio, near-infrared and X-ray bands. Interestingly, we find both significant differences between the two plateau states, as well as between the best-fit model parameters and those representative of the hard state. We discuss our interpretation of these results, and the possible implications for GRS 1915+105's relationship to canonical black hole candidates.
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Levine, Delina, Maria Dainotti, Kevin J. Zvonarek, Nissim Fraija, Donald C. Warren, Poonam Chandra et Nicole Lloyd-Ronning. « Examining Two-dimensional Luminosity–Time Correlations for Gamma-Ray Burst Radio Afterglows with VLA and ALMA ». Astrophysical Journal 925, no 1 (1 janvier 2022) : 15. http://dx.doi.org/10.3847/1538-4357/ac4221.
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Abstract Gamma-ray burst (GRB) afterglow emission can be observed from sub-TeV to radio wavelengths, though only 6.6% of observed GRBs present radio afterglows. We examine GRB radio light curves (LCs) to look for the presence of radio plateaus resembling the plateaus observed at X-ray and optical wavelengths. We analyze 404 GRBs from the literature with observed radio afterglow and fit 82 GRBs with at least five data points with a broken power-law model, requiring four parameters. From these, we find 18 GRBs that present a break feature resembling a plateau. We conduct the first multiwavelength study of the Dainotti correlation between the luminosity L a and the rest-frame time of break T a * for those 18 GRBs, concluding that the correlation exists and resembles the corresponding correlation at X-ray and optical wavelengths after correction for evolutionary effects. We compare T a * for the radio sample with T a * values in X-ray and optical data, finding significantly later break times in the radio. We propose that this late break time and the compatibility in slope suggest either a long-lasting plateau or the passage of a spectral break in the radio band. We also correct the distribution of the isotropic energy E iso versus the rest-frame burst duration T * 90 for evolutionary effects and conclude that there is no significant difference between the T*90 distributions for the radio LCs with a break and for those without.
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Macheret, Yu Ya, J. Otero, F. J. Navarro, E. V. Vasilenko, M. I. Corcuera, M. L. Cuadrado et A. F. Glazovsky. « Ice thickness, internal structure and subglacial topography of Bowles Plateau ice cap and the main ice divides of Livingston Island, Antarctica, by ground-based radio-echo sounding ». Annals of Glaciology 50, no 51 (2009) : 49–56. http://dx.doi.org/10.3189/172756409789097478.
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AbstractWe present the results of low-frequency (20 MHz) radio-echo sounding (RES) carried out in December 2000 and December 2006 on the main ice divides of Livingston Island, South Shetland Islands (SSI), Antarctica, and Bowles Plateau, Antarctica, respectively, as well as high-frequency (200 MHz) RES on the latter, aimed at determining the ice thickness, internal structure and subglacial relief. Typical ice thickness along the main ice divides is ~150 m, reaching maxima of ~200 m. On Bowles Plateau the ice is much thicker, with an average of 265 m and maxima of ~500 m. The bed below the main ice divides is above sea level, while part of the outlet glaciers from Bowles Plateau lies significantly below sea level, down to –120 m. The strong scattering of the radio waves in the areas under study constitutes further evidence that the ice in the accumulation area of the ice masses of the SSI is temperate. Typical thickness of the firn layer in Bowles Plateau is 20–35 m, similar to that found in King George ice cap. A strong internal reflector within the firn layer, interpreted as a tephra layer from the 1970 eruption at Deception Island, has allowed a rough estimate of the specific mass balances for Bowles Plateau within 0.20–0.40ma–1w.e., as average values for the period 1970–2006.
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Gong, J., T. S. M. MacLean et Z. Wu. « Radio propagation over trapezoidal plateau with sloping front face ». Electronics Letters 26, no 9 (1990) : 604. http://dx.doi.org/10.1049/el:19900397.
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Motta, S. E., J. J. E. Kajava, M. Giustini, D. R. A. Williams, M. Del Santo, R. Fender, D. A. Green et al. « Observations of a radio-bright, X-ray obscured GRS 1915+105 ». Monthly Notices of the Royal Astronomical Society 503, no 1 (24 février 2021) : 152–61. http://dx.doi.org/10.1093/mnras/stab511.
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ABSTRACT The Galactic black hole transient GRS 1915+105 is famous for its markedly variable X-ray and radio behaviour, and for being the archetypal galactic source of relativistic jets. It entered an X-ray outburst in 1992 and has been active ever since. Since 2018 GRS 1915+105 has declined into an extended low-flux X-ray plateau, occasionally interrupted by multiwavelength flares. Here, we report the radio and X-ray properties of GRS 1915+105 collected in this new phase, and compare the recent data to historic observations. We find that while the X-ray emission remained unprecedentedly low for most of the time following the decline in 2018, the radio emission shows a clear mode change half way through the extended X-ray plateau in 2019 June: from low flux (∼3 mJy) and limited variability, to marked flaring with fluxes two orders of magnitude larger. GRS 1915+105 appears to have entered a low-luminosity canonical hard state, and then transitioned to an unusual accretion phase, characterized by heavy X-ray absorption/obscuration. Hence, we argue that a local absorber hides from the observer the accretion processes feeding the variable jet responsible for the radio flaring. The radio–X-ray correlation suggests that the current low X-ray flux state may be a signature of a super-Eddington state akin to the X-ray binaries SS433 or V404 Cyg.
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Corr, S. A., J. Grierson, G. Arthurs et N. Woodbridge. « A retrospective study of tibial plateau translation following tibial plateau levelling osteotomy stabilisation using three different plate types ». Veterinary and Comparative Orthopaedics and Traumatology 24, no 06 (2011) : 445–49. http://dx.doi.org/10.3415/vcot-10-06-0090.
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SummaryObjective:To retrospectively evaluate mediolateral translation of the proximal tibial segment (tibial plateau) after tibial plateau levelling osteotomy (TPLO), stabilised with three types of plate.Method: Pre- and postoperative radiographs of 79 dogs that had TPLO surgery using three different types of plates were reviewed. Two plate types incorporated non-locking screws: Slocum (22 cases) and Orthomed Delta (33 cases) plates. The third plate type incorporated locking screws: Synthes TPLO Locking Compression Plate (LCP) (24 cases). The radio-graphs were viewed by three Diplomate surgeons who were blinded to the type of implant used. Medial or lateral translation of the proximal tibial plateau relative to the tibial diaphysis was assessed and measured at the lateral tibial cortex at the osteotomy site.Results: Mean lateral translation of the tibial plateau was significantly greater when using the Synthes TPLO LCP with locking screws (+2.1 mm) compared to the non-locking Slocum (+0.4 mm) or Orthomed Delta (0.0 mm) plates.Clinical significance: The use of the Synthes TPLO LCP will maintain a malalignment of the tibial plateau. Accurate alignment of the tibial plateau must be ensured prior to application of the Synthes TPLO LCP.
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Isa, Jibril G., et Mary Ntala Oliver. « An Analysis on the Sources of Developmental Information among the People of Mambilla, Sardauna Local Government Area of Taraba State ». International Journal of Humanities, Education, and Social Sciences 2, no 2 (29 juin 2024) : 204–30. http://dx.doi.org/10.58578/ijhess.v2i2.3279.
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People of the Mambilla Plateau in Taraba State's Sarduana Local Government Area are believed to be cut off from the rest of the state due to a poor road network, a lack of internet connection in some regions, and a lack of active traditional media presence. On light of the above, this study adopted the survey method to explore the sources of development messages on the Mambilla Plateau. Findings of this study revealed the major sources of developmental information among the populace of the Mambilla Plateau in Sardauna Local Governemnt Area of Taraba State include religions institutions such as Mosques and Churches and traditional leaders. Results of this study also revealed that some of the factors militating against access to developmental information among the populace of the Mambilla Plateau in Sardauna Local Government include lack or absence of the conventional media such radio, television and newspaper; poor road network, illiteracy and language barrier. Therefore the study recommended among other things that there is the need for the government and stakeholders to ensure the active presence of the conventional media outfits on the Mambilla Plateau.]
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Adeyeye, Babatunde, Lanre Amodu, Oscar Odiboh, Kehinde Oyesomi, Evaristus Adesina et Darlynton Yartey. « Agricultural Radio Programmes in Indigenous Languages and Agricultural Productivity in North-Central Nigeria ». Sustainability 13, no 7 (1 avril 2021) : 3929. http://dx.doi.org/10.3390/su13073929.
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This study investigated the influence of agricultural radio programmes in indigenous languages on farmers’ productivity and their implications for agricultural productivity in North-Central Nigeria. It specifically explored how farmers’ knowledge of agricultural radio programmes produced in indigenous languages influences their productivity; how farmers’ acceptance of agricultural radio programmes produced in indigenous languages influences productivity; and whether behavioural changes result from agricultural radio programmes aired in indigenous languages affect farmers’ productivity. Data were gathered through a survey of 663 farmers selected through the three states’ multi-stage sampling technique (Benue, Nasarawa, and Plateau). The hypotheses were tested using regression analysis and structural equation modelling. They revealed that the R value was 0.677, suggesting a highly significant relationship between farmers’ knowledge of agricultural radio programmes in indigenous languages and farmers’ productivity. Results also revealed that farmers’ behavioural changes resulting from agricultural radio programmes in indigenous languages greatly influence farmers’ productivity (F value was 558.358 at the 0.000 significant level). The study concludes that farmers’ knowledge, acceptance and behavioural change towards agricultural radio programmes in indigenous languages significantly influence farmers’ productivity in agriculture. Thus, farmers should be encouraged to continue participating in agricultural radio programmes in indigenous languages to be kept abreast of happenings in the field.
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Raupov, Dilshod, S. Ilyasov et G. I. Shanin. « The results of atmospheric parameters measurements in the millimeter wavelength range on the radio astronomy observatory “Suffa Plateau” ». Acta IMEKO 12, no 2 (6 juin 2023) : 1–5. http://dx.doi.org/10.21014/actaimeko.v12i2.1430.
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The results of measurements of atmospheric absorption and the amount of precipitated water on the Suffa Plateau for the period from January, 2015 to November, 2020, are presented. The measurements of atmospheric parameters in the 2 and 3 mm range of the radio waves spectrum were carried out using the MIAP-2 radiometer. The results of more than six years of measurements have show that on the Suffa Plateau, atmospheric parameters in the above range remain fairly stable. The median value of the atmospheric absorption and the amount of precipitated water over the entire observation period were 0.14 and 0.12 Nep and 5.91 and 9.83 mm, respectively, for the ranges of 2 and 3 mm.
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Canobbio, E., et R. Croci. « Space-dependent quasi-linear theory of lower-hybrid waves ». Journal of Plasma Physics 46, no 2 (octobre 1991) : 347–64. http://dx.doi.org/10.1017/s0022377800016160.
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The quasi-linear diffusion coefficients for the inherently space-dependent wave amplitudes in lower-hybrid heating and current-drive experiments are derived and compared with the usual space-independent approximation. The distribution function is derived and the dependence on the radio-frequency field amplitude gradient of the ‘plateau’, which is an essential quantity in thetheoretical description of LH experiments, is stressed.
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Ladu, Adelaide, Luca Schirru, Pierluigi Ortu, Andrea Saba, Mauro Pili, Alessandro Navarrini, Francesco Gaudiomonte, Pasqualino Marongiu et Tonino Pisanu. « Adaptation of an IRAM W-Band SIS Receiver to the INAF Sardinia Radio Telescope : A Feasibility Study and Preliminary Tests ». Sensors 23, no 17 (25 août 2023) : 7414. http://dx.doi.org/10.3390/s23177414.
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Radio telescopes are used by astronomers to observe the naturally occurring radio waves generated by planets, interstellar molecular clouds, galaxies, and other cosmic objects. These telescopes are equipped with radio receivers that cover a portion of the radio frequency (RF) and millimetre-wave spectra. The Sardinia Radio Telescope (SRT) is an Italian instrument designed to operate between 300 MHz and 116 GHz. Currently, the SRT maximum observational frequency is 26.5 GHz. A feasibility study and preliminary tests were performed with the goal of equipping the SRT with a W-band (84–116 GHz) mono-feed radio receiver, whose results are presented in this paper. In particular, we describe the adaptation to the SRT of an 84–116 GHz cryogenic receiver developed by the Institute de Radio Astronomie Millimétrique (IRAM) for the Plateau de Bure Interferometer (PdBI) antennas. The receiver was upgraded by INAF with a new electronic control system for the remote control from the SRT control room, with a new local oscillator (LO), and with a new refrigeration system. Our feasibility study includes the design of new receiver optics. The single side band (SSB) receiver noise temperature measured in the laboratory, Trec ≈ 66 K at 86 GHz, is considered sufficiently low to carry out the characterisation of the SRT active surface and metrology system in the 3 mm band.
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Chen, Weirui, Zheng Wang et Xiaojun Zhou. « An Improved Radio Pointing Model for SHARC II of the Caltech Submillimeter Observatory Telescope ». Publications of the Astronomical Society of the Pacific 134, no 1040 (1 octobre 2022) : 105002. http://dx.doi.org/10.1088/1538-3873/ac94f7.
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Abstract In this research, we develop a new method of upgrading the radio pointing model of an important instrument of the Caltech Submillimeter Observatory (CSO) telescope, i.e., the Submillimeter High Angular Resolution Camera II (SHARC II), by making three types of structural reconstruction of its existing model. First, the axial displacement of the secondary reflector of the telescope is introduced to the radio pointing model for SHARC II. Second, the multi-layer perceptron is applied for better describing higher-order terms in the radio pointing model, which are hard to be mathematically formulated. Third, a receding horizon modeling method is proposed to replace the time-dependent term in the existing model, for better reducing the negative impact of the time drift on the model’s accuracy. Results of numerical experiments and statistical significance analysis based on the real pointing data of SHARC II show that the reconstructed radio pointing model can improve the accuracy of estimating the pointing error, and the proposed method of upgrading the radio pointing model is effective. Considering that the CSO telescope will be moved from the old site at Maunakea, Hawaii to the new site at the Chajnantor Plateau in Chile, the proposed methods of upgrading the radio pointing model are expected to be employed for pointing correction after the telescope is refurbished at the new site.
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Villela, Rubens J. « Radio weather transmissions in the Antarctic ». Polar Record 27, no 161 (avril 1991) : 103–14. http://dx.doi.org/10.1017/s0032247400012225.
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AbstractDuring seven summer Brazilian expeditions to the Antarctic Peninsula area the author used radio weather transmissions to collect data for synoptic analysis and operational weather forecasting. A particularly intensive effort aboard Barão de Teffé in 1989–90 yielded detailed information on frequencies, schedules, procedures and contents, which should be useful to radio-operators, meteorologists, and other Antarctic workers since official publications listing Antarctic radio transmissions are out-dated or incomplete. Radiotelegraph broadcasts particularly valuable to mariners, which may replace or complement facsimile transmissions, are made by Valparaiso, Punta Arenas, and Buenos Aires. Because of unreliable reception of regular fax and teletype broadcasts, synoptic reports were copied directly by monitoring voice and Morse point-to-point circuits, gaining time crucial to operational decisions. Especially useful sources of reports were the Frei, Marambio, and Faraday collections, and the USSR radiotelegraph communications carrying land and ship reports for all sectors of Antarctica and southern hemisphere oceans. Other signals, eg from Chilean lighthouses, ships of opportunity, and aircraft have become useful sources of meteorological information, especially for Drake Passage since Chile has suspended broadcasts, adversely affecting weather forecasting in the area. An insight into weather conditions on the Antarctic Plateau, as well as a sense of history in the making, were gained by monitoring Adventure Network International's radio frequencies.
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Chen, X. L., Y. M. Ma, H. Kelder, Z. Su et K. Yang. « On the behaviour of the tropopause folding events over the Tibetan Plateau ». Atmospheric Chemistry and Physics 11, no 10 (31 mai 2011) : 5113–22. http://dx.doi.org/10.5194/acp-11-5113-2011.
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Abstract. Due to its harsh natural conditions, there had not been any intensive radiosonde observations over the Tibetan Plateau (TP) before the year 2008, when a regional radiosonde observation network was implemented through a Sino-Japan joint cooperation project. This paper reports, on the basis of these observations, on an analysis of the structure of upper troposphere and lower stratosphere (UTLS) and provides observations of stratosphere and troposphere exchange (STE) over the TP. Due to sparseness of high resolution radiosonde data, many previous studies assumed that there was only one thermal tropopause over the TP. Actually, the radiosonde temperature profiles in winter time over the TP often exhibit a multiple tropopause (MT). The MT occurs in winter with a high frequency over the Plateau. MT events during this time are associated with tropopause folds near the subtropical westerly jet. The MT consistently varied with the movement of the jet. The MT becomes a single tropopause with the development of the monsoon. The detailed analyses of MT characteristics are reported in this paper. Earlier analyses of global MT events (with data based on GPS radio occultation, ERA-40 data and Integrated Global Radiosonde Archive database) resulted in a climatic frequency of MT occurrences in the winter season over the Plateau is not more than 40 %. Based on high resolution data of intensive radiosonde observations, our estimations of MT occurrence over the Plateau can be as high as 80 % during certain winters. This reminds us to pay more attention to the MT events above the Plateau. The influence of the coarse vertical resolution and other effects on the estimation of MT occurrence frequency are also discussed. The stratospheric intruding episodes are generally associated with the presence of subtropical jet stream over the Plateau. The complex structure of dynamic tropopause folding over the Plateau have been reflected by the thermal MT events observed by radiosondes. The intrusion of air masses from the stratosphere may contribute to a higher upper tropospheric ozone concentration in winter than in summer above the plateau.
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Crabtree, Robert, et Maurice Hornocker. « Effects of 1988 Fires on Ecology of Coyotes in Yellowstone National Park : Baseline Preceding Possible Wolf Recovery ». UW National Parks Service Research Station Annual Reports 13 (1 janvier 1989) : 174–82. http://dx.doi.org/10.13001/uwnpsrc.1989.2823.
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Fifteen healthy coyotes (Canis latrans) were captured from 25 September through 25 October 1989 in the Lamar Valley and Blacktail Plateau areas of the northern range of Yellowstone National Park. Six males and nine females weighed an average of 14.1 kg. Only three of the 15 captured were six months-old which suggests low population productivity. After six weeks of radio-tracking all 15 were in the general vicinity of capture. Initially, 7-8 appear to be alpha breeding adults. Pack size appears large and initial minimum counts averaged four adults per group. Pilot studies of direct visual observation and fixed-station radio-telemetry appear very promising. Sixty-five miles of scat-survey transects have been laid out and plans to capture 15 more coyotes at carcasses in specific areas are underway.
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Rowlinson, A., R. L. C. Starling, K. Gourdji, G. E. Anderson, S. ter Veen, S. Mandhai, R. A. M. J. Wijers, T. W. Shimwell et A. J. van der Horst. « LOFAR early-time search for coherent radio emission from short GRB 181123B ». Monthly Notices of the Royal Astronomical Society 506, no 4 (21 juillet 2021) : 5268–77. http://dx.doi.org/10.1093/mnras/stab2060.
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ABSTRACT The mergers of two neutron stars are typically accompanied by broad-band electromagnetic emission from either a relativistic jet or a kilonova. It has also been long predicted that coherent radio emission will occur during the merger phase or from a newly formed neutron star remnant; however, this emission has not been seen to date. This paper presents the deepest limits for this emission from a neutron star merger, following triggered LOFAR observations of the short gamma-ray burst 181123B, starting 4.4 min after the GRB occurred. During the X-ray plateau phase, a signature of ongoing energy injection, we detect no radio emission to a 3σ limit of 153 mJy at 144 MHz (image integration time of 136 s), which is significantly fainter than the predicted emission from a standard neutron star. At a redshift of 1.8, this corresponds to a luminosity of 2.5 × 1044 erg s−1. Snapshot images were made of the radio observation on a range of time-scales, targeting short-duration radio flashes similar to fast radio bursts. No emission was detected in the snapshot images at the location of GRB 181123B enabling constraints to be placed on the prompt coherent radio emission model and emission predicted to occur when a neutron star collapses to form a black hole. At the putative host redshift of 1.8 for GRB 181123B, the non-detection of the prompt radio emission is two orders of magnitude lower than expected for magnetic reconnection models for prompt GRB emission and no magnetar emission is expected.
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Enia, Andrea, Margherita Talia, Francesca Pozzi, Andrea Cimatti, Ivan Delvecchio, Gianni Zamorani, Quirino D’Amato et al. « A New Estimate of the Cosmic Star Formation Density from a Radio-selected Sample, and the Contribution of H-dark Galaxies at z ≥ 3 ». Astrophysical Journal 927, no 2 (1 mars 2022) : 204. http://dx.doi.org/10.3847/1538-4357/ac51ca.
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Abstract The star formation rate density (SFRD) history of the universe is well constrained up to redshift z ∼ 2. At earlier cosmic epochs, the picture has been largely inferred from UV-selected galaxies (e.g., Lyman-break galaxies; LBGs). However, the inferred star formation rates of LBGs strongly depend on the assumed dust extinction correction, which is not well constrained at high z, while observations in the radio domain are not affected by this issue. In this work we measure the SFRD from a 1.4 GHz selected sample of ∼600 galaxies in the GOODS-N field up to redshift ∼3.5. We take into account the contribution of active galactic nuclei from the infrared-radio correlation. We measure the radio luminosity function, fitted with a modified Schechter function, and derive the SFRD. The cosmic SFRD shows an increase up to z ∼ 2 and then an almost flat plateau up to z ∼ 3.5. Our SFRD is in agreement with those from other far-IR/radio surveys and a factor 2 higher than those from LBG samples. We also estimate that galaxies lacking a counterpart in the HST/WFC3 H-band (H-dark) make up ∼25% of the ϕ-integrated SFRD relative to the full sample at z ∼ 3.2, and up to 58% relative to LBG samples.
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Yadav, J. S. « Connection between the Accretion Disk and Superluminal Radio Jets and the Role of the Radio Plateau State in GRS 1915+105 ». Astrophysical Journal 646, no 1 (20 juillet 2006) : 385–93. http://dx.doi.org/10.1086/504787.
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Wiens, J. David, Richard T. Reynolds et Barry R. Noon. « Juvenile Movement and Natal Dispersal of Northern Goshawks in Arizona ». Condor 108, no 2 (1 mai 2006) : 253–69. http://dx.doi.org/10.1093/condor/108.2.253.
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Abstract We investigated the departure, transient movement, and local settlement stages of natal dispersal in a population of Northern Goshawks (Accipiter gentilis) on the Kaibab Plateau of northern Arizona. The study included 614 color-banded juveniles produced at 555 nests during 1991–2003, 89 of which were radio-marked during 1998–2001. Radio-marked juveniles initiated dispersal between 71 and 103 days posthatching, and spent between 33 and 66 days in the natal territory after fledging. Our best-fitting proportional hazards models predicted the timing of dispersal as a function of annual differences in the density of primary bird and mammal prey species, weather conditions, and natal brood size. Once dispersal was initiated, most juveniles moved into the more open habitats that surrounded the study area and few eventually returned to breed; first-year fidelity to the local natal population was 28%, and only 69 (11%) color-banded juveniles had entered the territorial population by 2004. Median natal dispersal distance on the Kaibab Plateau was 15.0 km (range = 0.1–58.1 km), a distance equivalent to about four times the diameter of an average breeding territory (3.8 km). Local settlement behavior of Northern Goshawks appeared to be driven by a combination of intraspecific competition for a limited number of breeding opportunities and inbreeding avoidance. However, much of the natal dispersal process operated at broad spatial scales beyond our study population, indicating a potentially high level of demographic connectivity among naturally fragmented breeding populations in the American Southwest.
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Magdziarz, P., et J. Machalski. « Time Scale of Radio Sources Activity from the Statistical Model of Variability ». Symposium - International Astronomical Union 159 (1994) : 398. http://dx.doi.org/10.1017/s0074180900175874.
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The lack of a plateau in the average structure function (hereafter SF) for the complete flux-limited sample of Seielstad et al. (1983) [Fig.1] suggests that the mean time scale of radio sources variability at 10.8 GHz should be longer than the 3.8-yr time base of those observations. A comparison of the variability time scales derived from the SF analysis with those predicted by the statistical model of Magdziarz & Machalski (1993, AA, in print) [Fig.2] confirms consistency of that model. The mean time scale of variability of <τ> = 6±2 yr was found in both cases for v = 10.8 GHz.
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Ristanović, Rade, et Miloš Čorbić. « Yugoslav army in the homeland radio communication system ». Bastina, no 56 (2022) : 371–85. http://dx.doi.org/10.5937/bastina32-35820.
Texte intégralRésumé :
After a short war in April 1941 Kingdom of Yugoslavia was occupied by Axis forces. Soon after, in May 1941 small group of free Yugoslav army soldiers and officers under the leadership of Colonel Dragoljub Mihailović formed a resistance movement on mountain Suvobor, Ravna Gora plateau, in western Serbia. One of the main problems and tasks of the army, especially the resistance group, was establishing a system of internal and external communication. Yugoslav Army in the Homeland came up with the solutions for the organization of its communication system via communication systems of the pre-war Yugoslav army and the Ministry of foreign affairs. By the end of World War One and the creation of Yugoslavia, the country's military created a system of internal communication which development depended on the economic situation in the country and its diplomatic relations with the great forces. The main difficulties for the Yugoslav Army in the Homeland radio-communication system were lack of equipment and materials for radio communication devices and a small number of people on occupied territory capable of using radio devices. Considering that this organization worked during the Axis occupation, counterintelligence operations of enemy armies, primarily German intelligence, made conducting successful operations even more complex for members of the Ravna Gora movement.
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Mae, Shinji, Fumihiko Nishio, Hirokazu Ohmae, Shuhei Takahashi, Masayoshi Nakawo et Kunio Kawada. « The Variation in the Ice Sheet of Mizuho Plateau, East Antarctica (Abstract) ». Annals of Glaciology 11 (1988) : 219. http://dx.doi.org/10.3189/s0260305500006832.
Texte intégralRésumé :
The Japanese Antarctic Research Expedition (JARE) has conducted glaciological studies on Mizuho Plateau since 1981. We have already reported that the ice sheet flowing from Mizuho Plateau into Shirase Glacier is thinning at a rate of about 70 cm/year and that the profile of the distribution of basal shear stress is similar to that of surging glaciers.A 5 year glaciological programme on Mizuho Plateau and in east Queen Maud Land is now being carried out and we have obtained the following new results:(1) The ice sheet in the down-stream region (where ice elevation is lower than about 2400 m) is thinning, based on measurements of horizontal and vertical flow velocity, strain-rate, the slope of the ice surface, the accumulation rate and densification of snow.(2) δ18O analysis of deep ice cores obtained at Mizuho Station (2240 m a.s.l.) and point G2 (1730 m a.s.l.) shows that δ18O increased about 200 years ago at Mizuho Station and about 400 years ago at point G2. If we can assume that the increase in δ18O is caused by the thinning of the ice sheet, then this result means that this thinning propagates to up-stream areas.(3) Radio-echo-sounding measurements on Mizuho Plateau show that the ice base in the down-stream region is wet. This supports the result described in (1), since the basal sliding due to a wet base causes ice-sheet thinning, as proposed in our previous studies.In summary, a possible explanation of ice-sheet variation on Mizuho Plateau is as follows: the thinning of the ice sheet, caused by the basal sliding due to basal ice melting, started at Shirase Glacier and has been propagating up-stream to reach its present position. A simple calculation, using flow velocities, shows that the thinning started at Shirase Glacier about 1500–2000 years ago.
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Mae, Shinji. « The Variation in the Ice Sheet of Mizuho Plateau, East Antarctica (Abstract) ». Annals of Glaciology 11 (1988) : 219. http://dx.doi.org/10.1017/s0260305500006832.
Texte intégralRésumé :
The Japanese Antarctic Research Expedition (JARE) has conducted glaciological studies on Mizuho Plateau since 1981. We have already reported that the ice sheet flowing from Mizuho Plateau into Shirase Glacier is thinning at a rate of about 70 cm/year and that the profile of the distribution of basal shear stress is similar to that of surging glaciers. A 5 year glaciological programme on Mizuho Plateau and in east Queen Maud Land is now being carried out and we have obtained the following new results: (1) The ice sheet in the down-stream region (where ice elevation is lower than about 2400 m) is thinning, based on measurements of horizontal and vertical flow velocity, strain-rate, the slope of the ice surface, the accumulation rate and densification of snow. (2) δ18O analysis of deep ice cores obtained at Mizuho Station (2240 m a.s.l.) and point G2 (1730 m a.s.l.) shows that δ18O increased about 200 years ago at Mizuho Station and about 400 years ago at point G2. If we can assume that the increase in δ18O is caused by the thinning of the ice sheet, then this result means that this thinning propagates to up-stream areas. (3) Radio-echo-sounding measurements on Mizuho Plateau show that the ice base in the down-stream region is wet. This supports the result described in (1), since the basal sliding due to a wet base causes ice-sheet thinning, as proposed in our previous studies. In summary, a possible explanation of ice-sheet variation on Mizuho Plateau is as follows: the thinning of the ice sheet, caused by the basal sliding due to basal ice melting, started at Shirase Glacier and has been propagating up-stream to reach its present position. A simple calculation, using flow velocities, shows that the thinning started at Shirase Glacier about 1500–2000 years ago.
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Chen, X. L., Y. M. Ma, H. Kelder, Z. Su et K. Yang. « On the behaviour of the tropopause folding events over the Tibetan Plateau ». Atmospheric Chemistry and Physics Discussions 10, no 10 (6 octobre 2010) : 22993–3016. http://dx.doi.org/10.5194/acpd-10-22993-2010.
Texte intégralRésumé :
Abstract. Due to its harsh natural conditions, there had not been any intensive radiosonde observations over the Tibetan Plateau (TP) until the year 2008, when a regional radiosonde observation network was implemented through a Sino–Japan joint cooperation project. This paper reports new findings on the structure of upper troposphere and lower stratosphere (UTLS) layer, and provides evidence for stratosphere and troposphere exchange (STE) over the TP. Due to sparseness of high resolution sonde data, many previous studies assumed that there was only one thermal tropopause over the TP. Actually the radiosonde temperature profiles at pre-onset time of the Asian monsoon over the TP often exhibit a multiple tropopause (MT). The MT occurs in winter time with much higher frequency than any previous estimations over the Plateau. The MT during this time period is associated with tropopause folding near the subtropical westerly jet. The MT consistently varied with the movement of the jet. The MT becomes a single tropopause with the development of the monsoon. According to their height distribution, the MT can be divided into tropical and polar characterized tropopauses. Detailed analyses of MT characteristics are reported in this paper. Although some scientists have analyzed global MT events (with data including GPS radio occultation, ERA40 data and Integrated Global Radiosonde Archive database), the frequency of their MT occurrences in winter season over the plateau is largely under-estimated. This significant difference must be caused by the coarse vertical resolution of these data. The stratospheric intruding episodes are generally associated with the presence of subtropical westerly jet stream over the Plateau. The subtropical jet causes dynamic tropopause foldings over the plateau, which have been observed by us as thermal MT events. Intrusions of high latitude stratospheric ozone rich air into the troposphere over the plateau give us a new explanation to why total column ozone in winter is higher than that in summer.
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Perlman, Eric S., Eileen T. Meyer, Q. Daniel Wang, Qiang Yuan, Richard Henriksen, Judith Irwin, Jiangtao Li, Theresa Wiegert, Haochuan Li et Yang Yang. « Light-curve Evolution of the Nearest Tidal Disruption Event : A Late-time, Radio-only Flare ». Astrophysical Journal 925, no 2 (1 février 2022) : 143. http://dx.doi.org/10.3847/1538-4357/ac3bba.
Texte intégralRésumé :
Abstract Tidal disruption events (TDEs) occur when a star passes close enough to a galaxy’s supermassive black hole to be disrupted by tidal forces. We discuss new observations of IGRJ12580+0134, a TDE observed in NGC 4845 (d = 17 Mpc) in 2010 November, with the Karl G. Jansky Very Large Array (VLA 9 9 The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. ). We also discuss a reanalysis of 2010–2011 Swift and XMM-Newton observations, as well as new, late-time Swift observations. Our JVLA observations show a decay of the nuclear radio flux until 2015, when a plateau was seen, and then a significant (factor ∼3) radio flare during 2016. The 2016 radio flare was also accompanied by radio spectral changes, but was not seen in the X-rays. We model the flare as resulting from the interaction of the nuclear jet with a cloud in the interstellar medium. This is distinct from late-time X-ray flares in a few other TDEs where changes in the accretion state and/or a fallback event were suggested, neither of which appears possible in this case. Our reanalysis of the Swift and XMM-Newton data from 2011 shows significant evidence for thermal emission from a disk, as well as a very soft power law. This, in addition to the extreme X-ray flux increase seen in 2010 (a factor of >100) bolsters the identification of IGRJ12580+0134 as a TDE, not an unusual active galactic nucleus variability event.
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Yi, Weimin, P. B. Hall, Zunli Yuan, W. N. Brandt, D. P. Schneider, Zhicheng He, Jin-Ming Bai et Xue-Bing Wu. « Quasar Winds Caught on Acceleration and Deceleration ». Astrophysical Journal Supplement Series 271, no 2 (1 avril 2024) : 61. http://dx.doi.org/10.3847/1538-4365/ad2a42.
Texte intégralRésumé :
Abstract We present an observational study of wind acceleration based on four low-ionization broad absorption line (BAL) quasars (J0136, J1238, J1259, and J1344). J0136 and J1344 (group 1) are radio-quiet and show large BAL-velocity shifts as opposed to stable line-locking associated absorption lines (AALs). Notably, J1344 displays a linear relation between BAL-velocity shift and time interval over three consecutive epochs, characteristic of compelling evidence for BAL acceleration. J1238 and J1259 (group 2) exhibit small BAL-velocity shifts along with steep-spectrum, weak radio emission at 3.0 and 1.4 GHz. All four quasars have spectral energy distributions (SEDs) with a peak at λ rest ∼ 10 μm, suggesting a link between the BAL acceleration and hot dust emission. The group-2 quasars are redder than group-1 quasars and have a steeper rise at 1 μm < λ rest < 3 μm in their SEDs. All but J1238 exhibit a steep rise followed by a plateau-like time evolution in BAL-velocity shift. Our investigations, combined with previous studies of BAL acceleration, indicate that (1) the coupling process between the BALs and the interstellar medium (ISM) is one of the major avenues for the origin of quasar reddening and patchy obscuration, (2) AAL outflows are ubiquitous and likely signify large-scale remnants of BAL winds coupled to the ISM, and (3) wind deceleration that is closely linked to the BAL–ISM coupling process may produce weak radio emission in otherwise radio-quiet quasars.
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Grabiec, Mariusz, Dariusz Puczko, Tomasz Budzik et Grzegorz Gajek. « Snow distribution patterns on Svalbard glaciers derived from radio-echo soundings ». Polish Polar Research 32, no 4 (1 janvier 2011) : 393–421. http://dx.doi.org/10.2478/v10183-011-0026-4.
Texte intégralRésumé :
Snow distribution patterns on Svalbard glaciers derived from radio-echo soundings The spatial distribution of snow thickness on glaciers is driven by a set of climatological, meteorological, topographical and orographic conditions. This work presents results of snow accumulation studies carried out from 2006 to 2009 on glaciers of different types: valley glacier, ice plateau and ice cap. In order to determine snow depth, a shallow radio echo-sounding method was used. Based on the results, the following snow distribution patterns on Svalbard glaciers have been distinguished: precipitation pattern, precipitation-redistribution pattern, redistribution pattern and complex pattern. The precipitation pattern assumes that the snow distribution on glaciers follows the altitudinal gradient. If the accumulation gradient is significantly modified by local factors like wind erosion and redeposition, or local variability of precipitation, the accumulation pattern turns into the precipitation-redistribution pattern. In the redistribution pattern, local factors play a crucial role in the spatial variability of snow depth. The complex pattern, however, demonstrates the co-existence of different snow distribution patterns on a single glacial object (glacier/icecap/ice field).
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Vijayan, Aditi, K. S. Dwarakanath, Biman B. Nath et Ruta Kale. « Radio halo of NGC 4631 : comparing observations and simulations ». Monthly Notices of the Royal Astronomical Society 511, no 3 (29 janvier 2022) : 3150–58. http://dx.doi.org/10.1093/mnras/stac235.
Texte intégralRésumé :
ABSTRACT We present low-frequency observations at 315 and 745 MHz of the edge-on, nearby galaxy NGC 4631 with upgraded Giant Metrewave Radio Telescope. We compare the observed surface brightness profiles along the minor axis of the galaxy with those obtained from hydrodynamical simulations of galactic outflows. These are 3D simulations that replicate star formation in a Milky-Way-sized galaxy and follow magnetized outflows emerging from the disc. We detect a plateau-like feature in the observed emission at a height of 2–3 kpc from the mid-plane of the galaxy, in qualitative agreement with that expected from simulations. This feature is believed to be due to the compression of magnetic fields behind the outer shocks of galactic outflows. We model the observed surface brightness profiles by assuming an exponential as well as a Gaussian fitting model. Using χ2 statistics, we find that the exponential model fits the profiles better and we use it to determine the scale heights. We estimate the scale height for the synchrotron radio emission to be ∼1 kpc. The time-scales for advection due to outflows and diffusion of cosmic ray electrons are ≳5 and ∼160 Myr, respectively. Because advection acts on a time-scale much shorter than diffusion, we conclude that in NGC 4631 advection, rather than diffusion, plays the dominant role in the formation of radio halo. The spectral index image with regions of flatter radio spectral index in the halo appears to indicate possible effects of gas outflow from the plane of the galaxy.
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Smith, Harlan J. « Lunar-Based Astronomy ». International Astronomical Union Colloquium 123 (1990) : 365–75. http://dx.doi.org/10.1017/s0252921100077290.
Texte intégralRésumé :
AbstractThe Moon offers for astronomy a truly impressive array of advantages, many of which are briefly reviewed in this paper. These advantages include especially the vast inertial platform and the expected availability of human and robotic “hands-on” installation, maintenance, and modification. The Earth-orbiting Great Observatories will advance our knowledge to a new plateau, but some of the most fundamental observational questions which we are already asking will require lunar-based instruments, including very large filled-aperture telescopes, interferometers with baselines of tens and ultimately hundreds of kilometers, and the utilization of the radio-quiet backside. It is already time to begin planning the first such installations.
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O’Connor, Brendan, Dheeraj Pasham, Igor Andreoni, Jeremy Hare, Paz Beniamini, Eleonora Troja, Roberto Ricci et al. « Characterization of a Peculiar Einstein Probe Transient EP240408a : An Exotic Gamma-Ray Burst or an Abnormal Jetted Tidal Disruption Event ? » Astrophysical Journal Letters 979, no 2 (27 janvier 2025) : L30. https://doi.org/10.3847/2041-8213/ada7f5.
Texte intégralRésumé :
Abstract We present the results of our multiwavelength (X-ray to radio) follow-up campaign of the Einstein Probe transient EP240408a. The initial 10 s trigger displayed bright soft X-ray (0.5–4 keV) radiation with peak luminosity L X ≳ 1049 (1050) erg s−1 for an assumed redshift z ≳ 0.5 (2.0). The Neil Gehrels Swift Observatory and Neutron star Interior Composition ExploreR discovered a fading X-ray counterpart lasting for ∼5 days (observer frame), which showed a long-lived (∼4 days) plateau-like emission (t −0.5) before a sharp power-law decline (t −7). The plateau emission was in excess of L X ≳ 1046 (1047) erg s−1 at z ≳ 0.5 (2.0). Deep optical and radio observations resulted in nondetections of the transient. Our observations with Gemini South revealed a faint potential host galaxy (r ≈ 24 AB mag) near the edge of the X-ray localization. The faint candidate host, and lack of other potential hosts (r ≳ 26 AB mag; J ≳ 23 AB mag), imply a higher redshift origin (z ≳ 0.5), which produces extreme X-ray properties that are inconsistent with many known extragalactic transient classes. In particular, the lack of a bright gamma-ray counterpart, with the isotropic-equivalent energy (10–10,000 keV) constrained by GECam and Konus-Wind to E γ,iso ≲ 4 × 1050 (6 × 1051) erg at z ≈ 0.5 (2.0), conflicts with known gamma-ray bursts of similar X-ray luminosities. We therefore favor a jetted tidal disruption event as the progenitor of EP240408a at z ≳ 1.0, possibly caused by the disruption of a white dwarf by an intermediate-mass black hole. The alternative is that EP240408a may represent a new, previously unknown class of transient.
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Ильясов, С. П., et Д. А. Раупов. « The results of observations of atmospheric absorption on the Suffa plateau in the period 2015–2020 in the millimeter range ». Научные труды Института астрономии РАН 8, no 3 (30 novembre 2023) : 155–58. http://dx.doi.org/10.51194/inasan.2023.8.3.009.
Texte intégralRésumé :
Представлены результаты измерений атмосферного поглощения в Радиоастрономической обсерватории РТ-70 на пла- то Суффа (Узбекистан, λ = 65 ◦ 26 ′ , φ = 39 ◦ 37 ′ , h = 2500 м). Наблюдения проводились в автоматическом режиме каждые 11 минут в течение года с января 2015 г. по ноябрь 2020 г. с помощью измерительного комплекса МИАП-2. Рассмотрены сезонные изменения атмосферного поглощения и количества осажденной воды в атмосфере, построе- ны статистические диаграммы. Основным результатом работы являются статистические данные, характеризующие астроклимат и позволяющие прогнозировать возможность радиоастрономических наблюдений в окнах прозрачности миллиметрового диапазона длин волн. The results of atmospheric absorption measurements at the RT-70 Radio Astronomy Observatory on the Suffa plateau (Uzbekistan, λ = 65 ◦ 26 ′ , φ = 39 ◦ 37 ′ , h = 2500 m) are presented. The observations were carried out automatically every 11 minutes during one year, from January 2015 to November 2020, using the MIAP-2 measuring complex. Seasonal changes in atmospheric absorption and the amount of precipitated water in the atmosphere are considered, statistical diagrams are constructed. The main result of the work is statistical data characterizing the astroclimate, allowing to predict the possibility of radio astronomical observations in the transparency windows of the millimeter wavelength range.
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Chen, Liang-Jun, Xiang-Gao Wang, Qi Wang, Zi-Min Zhou, WeiKang Zheng, Yuan-Zhuo Chen et En-Wei Liang. « GRB 191221B : The Two-component Jet with Forward and Reverse Shock ». Astrophysical Journal 972, no 2 (1 septembre 2024) : 158. http://dx.doi.org/10.3847/1538-4357/ad6003.
Texte intégralRésumé :
Abstract The afterglows of gamma-ray bursts are believed to have originated from a relativistic jet, which is driven by the merger of compact binary objects or the core collapse of massive stars. Some of their jets may consist of two components: a faster (but narrower) jet and a slower (but wider) jet. The light curves produced by the interaction between the two-component jet and the surrounding medium typically exhibit a chromatic break in multiple bands. For GRB 191221B, the optical light curve of the afterglow exhibits a plateau from 33 to 143 s, followed by a steeper decay that is consistent with the characteristics of reverse shock from an arbitrarily magnetized ejecta. The flattening at ∼10 ks exhibits chromaticity relative to the X-ray afterglow. We propose that the two-component jet scenario can explain this observational result: For the X-ray afterglow, the narrow jet forward shock is dominated until ∼10 ks, and then both the narrow and wide components contribute comparable flux from the forward shock. For the optical afterglow, the first 2 ks is dominated by the narrow jet reverse shock emission (the plateau from 33 to 143 s is due to the jet being magnetized). Between 2 and 10 ks, the forward shock of the narrow jet dominates the optical afterglow, then transitions to wide component forward shock dominance, causing a chromatic plateau. For radio afterglow, the data are only presented after 105 s, which is dominated by the wide jet forward shock emission.
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Decarli, Roberto, Fabrizio Arrigoni-Battaia, Joseph F. Hennawi, Fabian Walter, Jason X. Prochaska et Sebastiano Cantalupo. « A search for dust and molecular gas in enormous Lyα nebulae at z ≈ 2 ». Astronomy & ; Astrophysics 645 (23 décembre 2020) : L3. http://dx.doi.org/10.1051/0004-6361/202039814.
Texte intégralRésumé :
Enormous Lyα nebulae, extending over 300−500 kpc around quasars, represent the pinnacle of galaxy and cluster formation. Here we present IRAM Plateau de Bure Interferometer observations of the enormous Lyα nebulae “Slug” (z = 2.282) and “Jackpot” (z = 2.041). Our data reveal bright, synchrotron emission associated with the two radio-loud active galactic nuclei embedded in the targeted nebulae as well as molecular gas, as traced via the CO(3−2) line, in three galaxies (two sources in Slug, and one in Jackpot). All of the CO emission is associated with galaxies detected in their rest-frame UV stellar emission. The total mass in molecular gas of these three galaxies [∼(3 − 5) × 1010 M⊙] is comparable with the total ionized gas mass responsible for the diffuse nebular emission. Our observations place limits on the molecular gas emission in the nebulae: the molecular gas surface density is ΣH2 < 12 − 25 M⊙ pc−2 for the Slug nebula and ΣH2 < 34 − 68 M⊙ pc−2 for the Jackpot nebula. These are consistent with the expected molecular gas surface densities, as predicted via photoionization models of the rest-frame UV line emission in the nebulae, and via Lyα absorption in the Jackpot nebula. Compared to other radio-loud quasars at z > 1 and high-redshift radio-loud galaxies, we do not find any strong trends relating the molecular gas reservoirs, the radio power, and the Lyα luminosities of these systems. The significant step in sensitivity required to achieve a detection of the molecular gas from the nebulae, if present, will require a substantial time investment with JVLA, NOEMA, or ALMA.
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Horo, K., A. B. Kouassi, B. Z. Tea, L. Assa, V. M. Icthy, A. Folquet, V. C. Godé et al. « Extraction d’un corps étranger intratrachéobronchique radio-opaque chez un enfant dans un contexte de plateau sous-médicalisé ». Revue de Pneumologie Clinique 65, no 2 (avril 2009) : 97–100. http://dx.doi.org/10.1016/j.pneumo.2008.12.003.
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Courdi, Adel, René-Jean Bensadoun, Jeannine Gioanni et Cyril Caldani. « Inherent radio sensitivity and split-dose recovery in plateau-phase cultures of 10 human tumour cell lines ». Radiotherapy and Oncology 24, no 2 (juin 1992) : 102–7. http://dx.doi.org/10.1016/0167-8140(92)90286-4.
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Akiyama, Kazunori, Jens Kauffmann, Lynn D. Matthews, Kotaro Moriyama, Shoko Koyama et Kazuhiro Hada. « Millimeter/Submillimeter VLBI with a Next Generation Large Radio Telescope in the Atacama Desert ». Galaxies 11, no 1 (20 décembre 2022) : 1. http://dx.doi.org/10.3390/galaxies11010001.
Texte intégralRésumé :
The proposed next generation Event Horizon Telescope (ngEHT) concept envisions the imaging of various astronomical sources on scales of microarcseconds in unprecedented detail with at least two orders of magnitude improvement in the image dynamic ranges by extending the Event Horizon Telescope (EHT). A key technical component of ngEHT is the utilization of large aperture telescopes to anchor the entire array, allowing the connection of less sensitive stations through highly sensitive fringe detections to form a dense network across the planet. Here, we introduce two projects for planned next generation large radio telescopes in the 2030s on the Chajnantor Plateau in the Atacama desert in northern Chile, the Large Submillimeter Telescope (LST) and the Atacama Large Aperture Submillimeter Telescope (AtLAST). Both are designed to have a 50-meter diameter and operate at the planned ngEHT frequency bands of 86, 230 and 345 GHz. A large aperture of 50 m that is co-located with two existing EHT stations, the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Pathfinder Experiment (APEX) Telescope in the excellent observing site of the Chajnantor Plateau, will offer excellent capabilities for highly sensitive, multi-frequency, and time-agile millimeter very long baseline interferometry (VLBI) observations with accurate data calibration relevant to key science cases of ngEHT. In addition to ngEHT, its unique location in Chile will substantially improve angular resolutions of the planned Next Generation Very Large Array in North America or any future global millimeter VLBI arrays if combined. LST and AtLAST will be a key element enabling transformative science cases with next-generation millimeter/submillimeter VLBI arrays.
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Metwaly, Radwan G., Zeiad M. Zakaria, Mohamed A. Elgebeily et Hany El Zahlawy. « Solving the enigma of posterolateral tibial plateau fractures, the clue protocol ». Acta Orthopaedica Belgica 87, no 1 (31 mars 2021) : 125–36. http://dx.doi.org/10.52628/87.1.16.
Texte intégralRésumé :
The study aim is to evaluate functional and radio- logical outcomes following a suggested protocol based on the four-column classification for management of posterolateral column tibial plateau fractures. A prospective cohort study was performed in level I academic center on 42 patients with mean age of 36 years (22-59). Eleven patients had isolated posterolateral column fractures whereas 31 patients had associated columns fractures. According to the suggested protocol, all cases of isolated posterolateral column fracture started treatment via arthroscopic evaluation of soft tissue injuries (menisci and liga- ments), arthroscopically assisted reduction and inter- nal fixation by rafting screws followed by ORIF if plating was needed. If associated with other columns fractures, columns were fixed sequentially in an anti-clockwise direction starting from anteromedial column. Average follow up was 26 months. Mean time to union was 16.3 (12-22) weeks. No radiological evidence of loss of coronal or sagittal alignment was detected at final follow up. Five patients had an average depression of 5 millimeters that did not need further intervention at this short-term follow up. Mean KOOS was 81 (72- 88). The average knee range of motion was (0° - 127°). One patient had temporary common peroneal nerve injury, one patient had deep infection and two had superficial wound infection. implementing the suggested protocol gives good to excellent radiological and functional results as regard posterolateral tibial plateau fracture. A larger study group with longer follow up is needed.
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Collaud Coen, M., C. Praz, A. Haefele, D. Ruffieux, P. Kaufmann et B. Calpini. « Determination and climatology of the planetary boundary layer height by in-situ and remote sensing methods as well as the COSMO model above the Swiss plateau ». Atmospheric Chemistry and Physics Discussions 14, no 10 (12 juin 2014) : 15419–62. http://dx.doi.org/10.5194/acpd-14-15419-2014.
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Abstract. The planetary boundary layer (PBL) height is a key parameter in air quality control and pollutant dispersion. The PBL height can however not be directly measured and its estimation relies on the analysis of the vertical profiles of the temperature, the turbulences or the atmospheric composition. An operational PBL height detection including several remote sensing instruments (windprofiler, Raman lidar, microwave radiometer) and several algorithms (Parcel and bulk Richardson number methods, surface-based temperature inversion, aerosol or humidity gradient analysis) were developed and the first year of application allowed validating these various detection methods against radio sounding measurements. The microwave radiometer provides convective boundary layer heights in good agreement with the radio sounding (median bias < 25 m, R2 > 0.70) and allows to fully analyzing the PBL height diurnal cycle due to its smaller time granularity. The Raman lidar also leads to good results whereas the windprofiler yields some more dispersed results. Comparisons with the numerical weather prediction model COSMO-2 were also established and point out a general overestimation by the model. Finally the seasonal cycles of the daytime and nighttime PBL heights are discussed for each instrument and each detection algorithm for two stations on the Swiss plateau.
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Turbide, Olivier, Diane Vincent et Marty Laforest. « Les « X » à Québec : La construction discursive d’un groupe exclusif ». Recherche 49, no 1 (12 juin 2008) : 87–112. http://dx.doi.org/10.7202/018195ar.
Texte intégralRésumé :
De 1996 à 2005, l’émission radiophonique « Le monde parallèle de Jeff Fillion » prend une place prépondérante dans l’univers médiatique de Québec. L’engouement créé par cette radio repose sur un ensemble de constructions discursives qui suscitent un fort sentiment d’appartenance. Dans cet article, nous voulons explorer de façon spécifique la mécanique discursive qui contribue à la définition du groupe des X, les supporters de la station CHOI. Deux mouvements discursifs complémentaires à l’oeuvre dans la construction identitaire des X telle qu’opérée par Fillion seront décrits. Le premier mouvement, positif, consiste à proposer aux auditeurs de CHOI (des X potentiels) un rapport au monde auquel ils vont s’identifier ; le second, négatif, est une construction identitaire « contre » où l’identité des X est suggérée à travers la présentation dépréciative d’individus, de groupes et d’idéologies. De ce double mouvement émerge une représentation des X incarnant la « vraie » ville de Québec, un Québec opposé tant à celui que représente son élite, qu’au Montréal « de la ‘clique’ du Plateau Mont-Royal ». Notre étude repose sur l’analyse de cinq émissions de Fillion diffusées à l’été et à l’automne 2004, moment propice au déploiement de stratégies de polarisation alors que la survie de la station de radio CHOI est menacée et que Fillion lutte pour conserver son poste d’animateur.
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Kotlyakov, V. M., et Yu, Ya Macheret. « Radio Echo-Sounding of Sub-Polar Glaciers in Svalbard : Some Problems and Results of Soviet Studies ». Annals of Glaciology 9 (1987) : 151–59. http://dx.doi.org/10.3189/s0260305500000537.
Texte intégralRésumé :
The paper discusses data analysed from airborne radio echo-sounding of Svalbard glaciers at frequencies of 440 and 620 MHz. Bottom returns from depths greater than 200 m are recorded with fewer gaps if the more powerful 620 MHz radar is used, and if measurements are carried out in the spring before intensive melt on glaciers. For all relatively thin glaciers and some glaciers up to 320–625 in thick, the track with bed returns is still rather common, apparently caused by their colder temperature regime. However, because of severe scattering of radio waves, this procedure still does not solve the problems of the echo-sounding of accumulation areas of many of the larger glaciers, the ice plateau, and heavily crevassed parts of glaciers.For considerable areas of those Spitsbergen glaciers which have a thickness greater than 200 m, internal radar reflections (IRR) were registered as a single isolated layer from depths usually ranging from ¼ to ½ of their thickness. Studies of two deep bore holes on Fridtjovbreen have- demonstrated that such IRR are related to a boundary between cold ice and water-bearing ice near the melting point. These IRR can be interpreted as indicators of a special class of two-layered or transitional glacier, and of the location within them of the ice-melt isotherm.
45
Kontar, Eduard P., Francesco Azzollini et Olena Lyubchyk. « Advection-nonlinear-diffusion Model of Flare Accelerated Electron Transport in Type III Solar Radio Bursts ». Astrophysical Journal 976, no 2 (26 novembre 2024) : 233. http://dx.doi.org/10.3847/1538-4357/ad8560.
Texte intégralRésumé :
Abstract Electrons accelerated by solar flares and observed as type III solar radio bursts are not only a crucial diagnostic tool for understanding electron transport in the inner heliosphere but also a possible early indication of potentially hazardous space weather events. The electron beams traveling in the solar corona and heliosphere along magnetic field lines generate Langmuir waves and quasilinearly relax toward a plateau in velocity space. The relaxation of the electron beam over the short distance in contrast to large beam-travel distances observed is often referred to as Sturrok’s dilemma. Here, we develop a new electron transport model with quasilinear distance/time self-consistently changing in space and time. This model results in a nonlinear advection-diffusion equation for the electron beam density with a nonlinear diffusion term that is inversely proportional to the beam density. The solution predicts slow super-diffusive (ballistic) spatial expansion of a fast-propagating electron beam. This model also provides the evolution of the spectral energy density of Langmuir waves, which determines brightness temperature of plasma radiation in solar bursts. The model solution is consistent with the results of numerical simulation using kinetic equations and can explain some characteristics of type III solar radio bursts.
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Neu, U. « Ein diagnostisches Modell zur Berechnung von Trajektorien über dem Schweizer Mittelland ». Geographica Helvetica 46, no 1 (31 mars 1991) : 42–49. http://dx.doi.org/10.5194/gh-46-42-1991.
Texte intégralRésumé :
Abstract. The aim of the presented model (called WITRA) is to use the data of the automatic wind stations on the Swiss Plateau as a basis for calculating back-trajectories over a complex terrain. WITRA interpolates a three-dimensional windfield out of the measured data and the radio-sonde profile of Payerne. By a mathematical method developed by SASAKI (1958) based on the variational analysis and with regard to its application to the investigated problem by SHERMAN (1978), the windfield is slightly adjusted in a least-square sense in order to get it free of divergence, i. e. mass-consistent. Within the same step the complex terrain and its effects on the wind are taken into account. Trajectories can be calculated by a method mentioned by PETTERSSEN (1956) using a sequence of these windfields.
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Ageta, Y., K. Kamiyama, F. Okuhira, Y. Fujii et O. Watanabe. « Glaciological and Chemical Characteristics of an Antarctic Inland Plateau (Abstract) ». Annals of Glaciology 11 (1988) : 214. http://dx.doi.org/10.3189/s0260305500006765.
Texte intégralRésumé :
A glaciological research project in east Queen Maud Land, Antarctica, has been carried out by the Japanese Antarctic Research Expeditions between 1982 and 1986 (JARE-23 – JARE-27).In this paper, we deal with the area traversed by JARE-25 and JARE-26, a representative inland plateau in Antarctica. In 1984, a team from JARE-25 extended a route from Mizuho Station (MS) to an advanced camp (AC; 74°12′S, 34°59′E; 3200 m a.s.l.) and returned to MS via the Yamato Mountains region. In the following year, 1985, a team from JARE-26 reached the summit (77°22′S, 39°37′Έ; 3810 m a.s.l.) of an ice dome on the plateau behind AC and continued to Asuka camp, north of Sør-Rondane Mountains. Investigations were carried out along the routes as follows:Geomorphological observations: the altitude along the routes was measured, together with the depth of the bedrock, which was obtained by radio echo-sounding. The shape of the dome and the position of ice divides were revealed. Gravity soundings were also carried out along the routes.Depositional and erosional environments of the snow surface: the net accumulation rate was obtained along the routes by the stake method. Sastrugi orientations were recorded in order to gain information on the prevailing wind. At several points, vertical profiles of snow stratigraphy and snow hardness were obtained, together with snow temperatures at 10 m depth. The glaciological characteristics of the plateau are described with reference to these results.Snow chemistry: the values of the electro-conductivity and pH of melted snow along the routes were obtained, and the results show high conductivity and low pH values around the dome region. Quantitative studies on the chemical composition of the samples are continuing.Ice coring: at the dome camp (DC; 77°00′S, 35°00′E; 3760 m a.s.l.), coring was carried out to a depth of 40 m. In the samples, we have been studying the vertical distribution of δ18O and the products of nuclear fission, in order to determine the accumulation rate and the atmospheric environment.On the basis of the results described above, the relationship between meteorological and glaciological conditions in the inland plateau are discussed.
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Ageta, Y., K. Kamiyama, F. Okuhira, Y. Fujii et O. Watanabe. « Glaciological and Chemical Characteristics of an Antarctic Inland Plateau (Abstract) ». Annals of Glaciology 11 (1988) : 214. http://dx.doi.org/10.1017/s0260305500006765.
Texte intégralRésumé :
A glaciological research project in east Queen Maud Land, Antarctica, has been carried out by the Japanese Antarctic Research Expeditions between 1982 and 1986 (JARE-23 – JARE-27). In this paper, we deal with the area traversed by JARE-25 and JARE-26, a representative inland plateau in Antarctica. In 1984, a team from JARE-25 extended a route from Mizuho Station (MS) to an advanced camp (AC; 74°12′S, 34°59′E; 3200 m a.s.l.) and returned to MS via the Yamato Mountains region. In the following year, 1985, a team from JARE-26 reached the summit (77°22′S, 39°37′Έ; 3810 m a.s.l.) of an ice dome on the plateau behind AC and continued to Asuka camp, north of Sør-Rondane Mountains. Investigations were carried out along the routes as follows: Geomorphological observations: the altitude along the routes was measured, together with the depth of the bedrock, which was obtained by radio echo-sounding. The shape of the dome and the position of ice divides were revealed. Gravity soundings were also carried out along the routes. Depositional and erosional environments of the snow surface: the net accumulation rate was obtained along the routes by the stake method. Sastrugi orientations were recorded in order to gain information on the prevailing wind. At several points, vertical profiles of snow stratigraphy and snow hardness were obtained, together with snow temperatures at 10 m depth. The glaciological characteristics of the plateau are described with reference to these results. Snow chemistry: the values of the electro-conductivity and pH of melted snow along the routes were obtained, and the results show high conductivity and low pH values around the dome region. Quantitative studies on the chemical composition of the samples are continuing. Ice coring: at the dome camp (DC; 77°00′S, 35°00′E; 3760 m a.s.l.), coring was carried out to a depth of 40 m. In the samples, we have been studying the vertical distribution of δ18O and the products of nuclear fission, in order to determine the accumulation rate and the atmospheric environment. On the basis of the results described above, the relationship between meteorological and glaciological conditions in the inland plateau are discussed.
49
Collaud Coen, M., C. Praz, A. Haefele, D. Ruffieux, P. Kaufmann et B. Calpini. « Determination and climatology of the planetary boundary layer height above the Swiss plateau by in situ and remote sensing measurements as well as by the COSMO-2 model ». Atmospheric Chemistry and Physics 14, no 23 (11 décembre 2014) : 13205–21. http://dx.doi.org/10.5194/acp-14-13205-2014.
Texte intégralRésumé :
Abstract. The planetary boundary layer (PBL) height is a key parameter in air quality control and pollutant dispersion. The PBL height cannot, however, be directly measured, and its estimation relies on the analysis of the vertical profiles of the temperature, turbulence or the atmospheric composition. An operational PBL height detection method including several remote sensing instruments (wind profiler, Raman lidar, microwave radiometer) and several algorithms (Parcel and bulk Richardson number methods, surface-based temperature inversion, aerosol or humidity gradient analysis) was developed and tested with 1 year of measurements, which allows the methods to be validated against radio sounding measurements. The microwave radiometer provides convective boundary layer heights in good agreement with the radio sounding (RS) (median bias < 25 m, R2 > 0.70) and allows the analysis of the diurnal variation of the PBL height due to its high temporal resolution. The Raman lidar also leads to a good agreement with RS, whereas the wind profiler yields some more dispersed results mostly due to false attribution problems. A comparison with the numerical weather prediction model COSMO-2 has shown a general overestimation of the model PBL height by some hundreds to thousand meters. Finally the seasonal cycles of the daytime and nighttime PBL heights are discussed for each instrument and each detection algorithm for two stations on the Swiss plateau.
50
Kotlyakov, V. M., et Yu, Ya Macheret. « Radio Echo-Sounding of Sub-Polar Glaciers in Svalbard : Some Problems and Results of Soviet Studies ». Annals of Glaciology 9 (1987) : 151–59. http://dx.doi.org/10.1017/s0260305500000537.
Texte intégralRésumé :
The paper discusses data analysed from airborne radio echo-sounding of Svalbard glaciers at frequencies of 440 and 620 MHz. Bottom returns from depths greater than 200 m are recorded with fewer gaps if the more powerful 620 MHz radar is used, and if measurements are carried out in the spring before intensive melt on glaciers. For all relatively thin glaciers and some glaciers up to 320–625 in thick, the track with bed returns is still rather common, apparently caused by their colder temperature regime. However, because of severe scattering of radio waves, this procedure still does not solve the problems of the echo-sounding of accumulation areas of many of the larger glaciers, the ice plateau, and heavily crevassed parts of glaciers. For considerable areas of those Spitsbergen glaciers which have a thickness greater than 200 m, internal radar reflections (IRR) were registered as a single isolated layer from depths usually ranging from ¼ to ½ of their thickness. Studies of two deep bore holes on Fridtjovbreen have- demonstrated that such IRR are related to a boundary between cold ice and water-bearing ice near the melting point. These IRR can be interpreted as indicators of a special class of two-layered or transitional glacier, and of the location within them of the ice-melt isotherm.