Letteratura scientifica selezionata sul tema "Plateau-Radio"

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.

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.

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.

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.

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.

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.

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.

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.

To determine possible causes of declining Rio Grande wild turkey (RGWT; Meleagris gallopavo intermedia) abundance in the southern Edwards Plateau, research was conducted on 4 sites, 2 with stable (S [SA and SB]; Kerr and Real counties) and 2 with declining (D [DA and DB]; Bandera County) RGWT populations. RGWTs were trapped, radio-tagged, and tracked. Ranges were constructed with 95% kernels. Data on brood survival and invertebrate and predator abundances were combined with range characteristics to assess habitat at a landscape scale. Annual range sizes did not differ in year 1, but were larger in S than in D in year 2. Range sizes in S increased from year 1 to year 2 while there was no change in range sizes in D. Range overlap was higher in D than S in both years. Movement distances remained consistent in S for both years, but were larger in D during year 1. During year 1 and year 2, RGWT females exhibited larger reproductive ranges and less range overlap in S. Invertebrate abundance for 4 insect orders was 2.5–15.9 times greater in S than in D while coyote abundance was 2–3 times greater in D than in S. Results were similar in year 3, with the exception of SB, where reproductive ranges and spatial arrangement were smaller than all other sites. My results refute the conventional assumption that larger ranges are indicative of poorer habitat quality. Range overlap suggests that useable space may have been limiting in D in the less productive year 2. In D, multiple broods used the same reproductive range, presumably depleting resources faster than in S. Greater predator abundance in D increased the risk of brood predation. The smaller reproductive spatial arrangement of SB females in year 3 correlates there being >3 times the percentage of females missing in other sites. If SB females moved further in year 3 than the detection distance of the radio telemetry equipment, the results would fit the pattern of greater dispersion distance in SA. RGWT females may attempt to separate themselves from other breeding females, possibly to avoid nest or brood predation and/or potential competition for brood resources.

Cette thèse de recherche-création s’appuie sur le travail de création mené par r∆∆dio c∆∆rgo , collectif de création radiophonique, autour de la notion de plateau-radio, en tant que dispositif de SF dans le sens que lui donne Donna Haraway, à savoir un espace de recherche-création dans lequel s’entremêlent Spéculation Féministe, Faits Scientifiques (Science Fact, Science-Fiction et jeu de ficelle (String Figure en anglais), c’est-à- dire une pratique collective qui produit autant un échange et une circulation de la pensée interdisciplinaire, qu’elle en cartographie son propre processus. La thèse tente de démontrer que le studio radiophonique tel qu’on le connaît aujourd’hui -avec ses micros, ses casques, ses animateur·ices qui reçoivent des invité·es et sa technicité qui canalise la parole et les sons au service d’une production adressée à des auditeur·ices - peut être appréhendé d’autres manières et à d’autres fins. La thèse se construit de manière polyphonique dans deux temporalités qui se superposent. Tout d’abord celle de comptes-rendus d’expériences artistiques réalisées entre 2017 et 2021, dans lesquels des collectifs vivent et expérimentent l’objet d’étude et dont l’écriture autorise une forme de style, celui d’un journal autoreflexif permettant de rendre compte des relations que les participant·es ont entre elles et eux et avec les dispositifs. En parallèle, une partie théorique, reposant elle sur une écriture scientifique, observera l’objet d’étude du plateau-radio avec le recul nécessaire pour produire une pensée théorique. Cette partie théorique propose une approche du plateau-radio en tant que dispositif de recherche-création artistique, scientifique et politique mais aussi en tant qu’espace relationnel de création aurale et émancipatrice. L’écriture polyphonique permet ainsi une friction entre spéculation artistique et écriture scientifique afin de faire émerger, dans l’entre-deux, une méthodologie de recherche-création. Une troisième voix apparaîtra donc peu à peu pour manifester une théorie-pratique à travers la méthodologie. Pour construire cette thèse il a ainsi été nécessaire de tresser au moins trois approches méthodologiques. La recherche débute par le concept de SF de Donna Haraway. Celui-ci découle des travaux d’Isabelle Stengers et Didier Debaise sur les gestes spéculatifs qui s’intéressent à comment la théorie peut-elle passer vers la pratique. Ce glissement de la théorie à la pratique par un arc à plusieurs cordes qu’offre le concept de SF se révèle nécessaire lorsqu’il n’y a pas encore assez de faits scientifiques pour poser une hypothèse et qu’il implique de passer par la pratique pour rendre manifeste un objet d’étude. Les deux autres approches sont mentionnées dans le plan résumé.Cette recherche débute donc avec la spéculation suivante :Et si,le plateau radio était un dispositif sorcier qui permet de tracer le cercle, dans le sens que lui donne Isabelle Stengers, à savoir un espace temporairement clos qui permet [aux sorcières éco-féministes] de récupérer les pouvoirs dont iels ont besoin ?
This creative research thesis is based on the creative work carried out by r∆∆dio c∆∆rgo, a collective of radio creation, around the notion of the radio platform, understood as a science fiction device in the sense given by Donna Haraway, that is, a space of research-creation where Feminist Speculation, Scientific Facts (Science Fact, Science Fiction), and String Figures intertwine. This approach constitutes a collective practice that produces not only an exchange and circulation of interdisciplinary thought but also maps its own process. The thesis aims to demonstrate that the radio studio as we know it today—with its microphones, headsets, hosts who invite guests, and its technical apparatus that channels speech and sounds for the purpose of production aimed at an audience—can be approached in other ways and for other purposes.The thesis is constructed in a polyphonic manner, unfolding in two overlapping temporalities. First, through reports on artistic experiments conducted between 2017 and 2021, in which collectives live and experiment with the object of study, and where the writing adopts a particular style—a self-reflexive journal that reflects on the relationships between the participants and with the devices. In parallel, a theoretical part, written in a scientific style, observes the object of study—the radio platform—with enough distance to produce theoretical thought. This theoretical section proposes an approach to the radio platform as a device for artistic, scientific, and political research-creation, but also as a relational space for aural and emancipatory creation. The polyphonic writing thus allows for friction between artistic speculation and scientific writing, to bring forth, in the in-between, a research-creation methodology. A third voice will gradually emerge to manifest a theory-practice through the methodology. In constructing this thesis, it was necessary to weave together at least three methodological approaches. The research begins with Donna Haraway’s concept of SF (science fiction/speculative fabulation), drawing from the work of Isabelle Stengers and Didier Debaise on speculative gestures, which examine how theory can move into practice. This shift from theory to practice, through the multi-string arc offered by the concept of SF, becomes necessary when there are not yet enough scientific facts to formulate a hypothesis, requiring practice to make the object of study manifest. The other two approaches are outlined in the summarized plan.Thus, this research begins with the following speculation:What if the radio platform was a witch’s device, enabling the drawing of the circle, in the sense given by Isabelle Stengers—namely, a temporarily enclosed space that allows [eco-feminist witches] to reclaim the powers they need ?

La comète C/1995 O1 (Hale-Bopp) a sans doute été l'une des comètes les plus brillantes jamais observées jusqu'à présent. Son extraordinaire activité a permis pour la première fois d'entreprendre des observations en interférométrie millimétrique avec une grande sensibilité. Lors de son passage au périhélie, les transitions J(2-1) et J(1-0) du monoxyde de carbone, ont été observées avec l'interféromètre du Plateau de Bure de l'Institut de Radio Astronomie Millimétrique (IRAM), à 230 GHz et 115 GHz respectivement. L'analyse temporelle des observations faites en parallèle en mode antenne unique a d'abord permis de mettre en évidence la présence d'un jet de CO en rotation dans l'atmosphère de la comète. L'étude des cartes interférométriques a ensuite montré que la coma était spatialement et spectralement anisotrope. Afin d'analyser au mieux ces données, nous avons développé un modèle d'atmosphère cométaire en 3 dimensions, et simulé les observations. Le modèle consiste en une coma isotrope à laquelle on ajoute un jet de forme conique qui spirale dans la coma à cause de la rotation du noyau. La comparaison des simulations aux observations s'est faite sur l'évolution temporelle des décalages spectraux, et sur celle des visibilités, qui sont les quantités physiques qu'un interféromètre mesure et qui représentent la Transformée de Fourier de la distribution de brillance du gaz sur le plan du ciel. Cette étude a confirmé la présence d'un jet spiralant dans la coma. De plus, nous avons pu déterminer les paramètres du jet tels que la position, l'ouverture et l'intensité, qui interprètent au mieux les observations. La question de l'origine de CO dans la coma est également abordée en dernière partie. Nos observations suggèrent que cette molécule proviendrait pour moitié du noyau, et pour moitié d'une source étendue.

This chapter demonstrates how Judson's management empire began to plateau in the 1940s. The Depression had rattled music's funding structures. Technology had spawned greater competition for live musical experiences. Jazz had supplanted classical music on the pages of many newspapers and trade magazines. But particularly relevant for Judson was an emerging concern about the connection between music and big business. The Federal Communications Commission (FCC) first raised this issue in 1938, when it launched an investigation into the chain-broadcasting practices of the NBC, CBS, and mutual radio networks. The commission also became concerned about the possibility of monopolistic behavior, specifically in the practice of networks representing artists and also buying artists for their radio programs.

AbstractBetween October 1945 and March 1946 Radiophysics staff took advantage of the facilities at radar stations located at Collaroy Plateau and Dover Heights in suburban Sydney to follow up the British and New Zealand solar observations mentioned earlier, and this effectively marked the launch of radio astronomy in Australia. The equipment used at these field stations included radar antennas connected to 200 MHz receivers. In 1947 Ruby Payne-Scott (1912–1981) described the Royal Australian Air Force Radar 54 antenna at Collaroy as a

From a remote outpost of global warming, a summons crackles over a two-way radio several times a week: . . . Kathmandu, Tsho Rolpa! Babar Mahal, Tsho Rolpa! Kathmandu, Tsho Rolpa! Babar Mahal, Tsho Rolpa! . . . In a little brick building on the lip of a frigid gray lake fifteen thousand feet above sea level, Ram Bahadur Khadka tries to rouse someone at Nepal’s Department of Hydrology and Meteorology in the Babar Mahal district of Kathmandu far below. When he finally succeeds and a voice crackles back to him, he reads off a series of measurements: lake levels, amounts of precipitation. A father and a farmer, Ram Bahadur is up here at this frigid outpost because the world is getting warmer. He and two colleagues rotate duty; usually two of them live here at any given time, in unkempt bachelor quarters near the roof of the world. Mount Everest is three valleys to the east, only about twenty miles as the crow flies. The Tibetan plateau is just over the mountains to the north. The men stay for four months at a stretch before walking down several days to reach a road and board a bus to go home and visit their families. For the past six years each has received five thousand rupees per month from the government—about $70—for his labors. The cold, murky lake some fifty yards away from the post used to be solid ice. Called Tsho Rolpa, it’s at the bottom of the Trakarding Glacier on the border between Tibet and Nepal. The Trakarding has been receding since at least 1960, leaving the lake at its foot. It’s retreating about 200 feet each year. Tsho Rolpa was once just a pond atop the glacier. Now it’s half a kilometer wide and three and a half kilometers long; upward of a hundred million cubic meters of icy water are trapped behind a heap of rock the glacier deposited as it flowed down and then retreated. The Netherlands helped Nepal carve out a trench through that heap of rock to allow some of the lake’s water to drain into the Rolwaling River.

The paper presents the results of studying the astroclimate at possible locations for the Eurasian Submillimeter Telescopes (ESMT), including the sites of Kurapdag in the Agul district of Dagestan, Khunzundallbak (3676 m) in the Rutul district of Dagestan, Khulugaisha peak (Eastern Sayan), Tashanta checkpoint in the intermountain basin of the Altai Republic, Boguty (3350 m) in the foothills of the Altai Mountains near the border with Mongolia, the Suffa plateau (Aktashtau, 3282 m), and the Ali region in Tibet. The expected radio brightness temperatures of the clear and cloudy atmosphere at wavelengths of 2 and 3 mm and the characteristics of the 3-mm range radiometer for measuring the optical thickness of the atmosphere are presented.