An accretion torus is an important astrophysical phenomenon which is be- lieved to account for various features of mass inflow and release of radiation on diverse scales near stellar-mass as well as supermassive black holes. When the stationary torus is perturbed it starts to oscillate and once some part of the torus overflows the closed equipotential surface, defined by the stationary solution, this material is accreted or ejected. These oscillations reveal both spacetime properties and the intrinsic characteristics of the torus model. We study the oscillation and accretion properties of geometrically thick accretion tori using general relativistic magnetohydrodynamic simulations. Assuming axial symmetry these simulations are restricted to 2-D approximation. We discuss the impact of the presence of the large scale magnetic field and the profile of the specific angular momentum on the oscillation properties and on the accretion flow motion. 1

Stars can be stretched and ripped apart by the super-massive black hole at the core of a galaxy. The remnant gaseous trail gradually circularizes in a ring of mass that spreads by the viscous forces into an accretion disc. In this thesis we have studied the spectral line profle time evolution of radiation refected by the accretion disc located around a super-massive black hole. We assume the central body to be a slowly rotating or non-rotating super-massive black hole with no charge, in the frst approximation represented by the Schwarzschild solution. In a sense of Shakura-Sunyaev standard accretion disc model with the kinematic viscosity parameter α ≈ 1 we allow the accretion disc evolution to be guided by the angular momentum transfer equation with the initial mass ring located at the tidal radius being the product of tidal disruption of a star passing by a super-massive black hole. During the simulations we keep varying the mass of the central body while we keep the mass and the radius of the star constant (M = 1M⊙ and R = 1R⊙), i.e. taking into account the solar-type stars only. We defer the prospects of the full analysis involving spin (and charge) of the central body for the future study as it will be necessary to use the equations for the redshift factor and the accretion disc evolution...

In the present work we study the properties of accretion tori orbiting black hole. Our approach to this problem comes from the solving of general relativistic magnetohydrodynamic equations, which follow from conservation of the energy-momentum tensor, the particle number and from Maxwell's equations. We solve these equations by numerical methods which are described in Chapter 1. The formalism of tori which we consider here is described in Chapter 2. We are interested in tori with constant density of angular momentum and Fishbone-Moncrief tori mainly. We study accretion rates in these tori when the mass of black hole is increased suddenly and so the equilibrium in the torus is corrupted. For tori with constant density of angular momentum we study the influence of the presence of toroidal magnetic field on accretion rates.

Continental slope channels, which serve as the primary conduits for sediment transport into the deep marine, occasionally become sites of sediment deposition with excellent reservoir potential. Increasingly reported in the literature are subsurface channel fills exhibiting shingled seismic reflectors that are interpreted to have formed by lateral channel migration. In lower Isaac Formation channels inclined strata are observed but at a lateral scale that is far below industry-seismic detection. Distinctively these flat-based channels are filled with coarse-grained sandstone that transitions abruptly and obliquely upwards into thin, fine grained turbidites. Like rivers, lateral accretion in Isaac channels is interpreted to be the result of the interaction of inertial and pressure forces, but in highly turbulent, highly density-stratified turbidity currents. This resulted in the formation of two superimposed secondary circulation cells that caused enhanced erosion on the outer bank and preferential deposition of coarse-grained sediment along the inner bank.

The muscle hypertrophy of lambs expressing the Callipyge phenotype is possibly linked to characteristics of their muscle satellite cells. Therefore, characteristics (proliferation, fusion %, and protein accretion) of cultured satellite cells isolated from the longissimus muscle of Callipyge (n = 3) and normal (n = 3) lambs were compared in this study. In the first experiment, we tested whether or not the lll proliferation rates differ for satellite cells isolated from Callipyge or normal sheep when cultured in the presence of different serum types (horse, normal lamb, or Callipyge lamb). The average population doubling time (PDT, h) during log phase growth was calculated for cells from each animal grown in each serum type. Population doubling time was not affected (P > .1) by the interaction of satellite cell type with serum type, or by satellite cell type. Unexpectedly, PDT was longer (P < .05) for satellite cells grown in Callipyge serum (22 h) than for cells grown in normal sheep serum (20 h) or horse serum (18 h). These results suggest that muscle hypertrophy of Callipyge lambs is not linked to intrinsic differences in satellite cell proliferation, although hypertrophy may be associated with a decreased proliferation induced by a factor in Callipyge serum. In the second experiment, we tested whether cell fusion, or protein accretion differ for cultured satellite cells isolated from Callipyge or normal sheep. DNA and protein were determined at 24, 48, 72, and 96 h after satellite cell cultures were induced to differentiate. Fusion percentage was determined in a Giemsa stained plate after 72 h in differentiation medium (Dulbecco's Modified Eagle Medium containing 1.5% of horse serum). Callipyge cultures tended (P = .14) to have higher fusion% than normal cultures exhibited, suggesting that muscle hypertrophy of Callipyge lambs may be linked to an increased tendency of satellite cells to fuse. Protein content (μg/well) and protein:DNA ratio (ng of protein/ng of DNA) were not affected by satellite cell type (P = .80 and P = .79, respectively). Thus, there was no evidence for a link between increased protein accretion and Callipyge hypertrophy.

Over the last century, the construction and management of large dams and stream-flow diversions, and periodic drought have resulted in significant declines in stream flow of the lower Rio Grande in the Big Bend region. Reductions in mean annual flow and peak discharge have resulted in channel narrowing by the formation of vertically accreting inset floodplains. Narrowing has been temporarily interrupted by infrequent large dam releases greater than 1000 m3/s that have temporarily widened the channel; however, after each of these events, narrowing has resumed. Prior to 1942, floods of this magnitude occurred approximately once every 4 years and maintained a wide sandy channel. Since 1942, they have occurred 4 times. The decline in frequency of these large floods has resulted in a channel approximately 50% narrower than in the 1940s. Since the most recent channel widening floods in 1991, the channel has narrowed between 35 and 50%. In two large floodplain trenches, we observed between 2.75 and 3.5 m of vertical accretion during the same period. Additionally, nearly 90% of bare active channel bars have been converted to vegetated floodplains. Since 1991, the cross section channel area at the Johnson Ranch gage has decreased by approximately 30%. The reduction in cross section area and the invasion of non-native vegetation have resulted in higher flood stages, flooding at lower discharges, and continued vertical accretion. Channel narrowing has negatively impacted the native and endemic aquatic ecosystem through the loss of ecologically important habitats such as backwaters, side channels, and low velocity portions of the channel. Reductions in cross section area and resultant increased flood stages have also endangered historic cultural sites within the Big Bend region. Restoration efforts are currently underway within the region without a clear understanding of these historical channel changes and why they occurred. Our reconstruction of historical channel changes shows that the most significant periods of channel narrowing occurred during drought and increased stream-flow management. Management practices also appear to have enabled the invasion of non-native riparian species, which promoted sedimentation, bank stabilization, and additional channel narrowing. In order to restore historical measures of channel width, management options include non-native vegetation removal, common low magnitude dam releases that provide flood disturbance and prevent vegetation establishment, and large dam releases in excess of 1000 m3/s that create and maintain a wide channel. Vegetation management is expensive; and time consuming, and managed dam releases are politically unpopular and expensive, however, without the management of non-native riparian species and reinstatement of portions of the historical flood regime, ecological restoration will be difficult.

Le travail présenté dans cette thèse s’inscrit dans le domaine de l'astrophysique de laboratoire, qui consiste à étudier en laboratoire des processus physiques qui se produisent dans des objets astrophysiques. Les principaux avantages ici sont que les processus peuvent être étudiés de manière contrôlée et que leur dynamique complète peut être étudiée. Présentement, nous avons profité des installations laser à haute intensité pour effectuer nos études.Pour cela, dans ce manuscrit, seront traitées les questions liées à l'astrophysique de laboratoire qui impliquent l'interaction d’un plasma en détente dans le vide en présence d’un champ magnétique ambiant. La présence d'un champ magnétique dans une variété de phénomènes astrophysiques rend l’introduction de cette composante magnétique dans le laboratoire nécessaire afin que ces études soient pertinentes. Pour ce faire, en collaboration avec Laboratoire National des Champs Magnétiques Intenses -LNCMI, une bobine Helmholtz, spécialement conçue pour travailler dans un environnement laser a été développée, permettant d'atteindre une force de champ magnétique jusqu'à 30 T.Les objets astrophysiques sur lesquels cette étude est centrée sont les étoiles jeunes ou « Young Stellar Objects » (YSOs). Plusieurs étapes du processus de formation de ces étoiles seront ici étudiées : (i) la génération de jets collimatés à très grande échelle, (ii) la dynamique d'accrétion impliquant, dans la représentation standard, des flux de matière tombant sur la surface de l’étoile sous forme de colonnes magnétiquement confinées, et (iii) des canaux d'accrétion plus exotiques, comme l'accrétion équatoriale qui implique la propagation du plasma perpendiculairement aux lignes de champ magnétique.Plus précisément, dans un premier chapitre, la dynamique de formation des jets sera discutée. Une première partie est dédiée au mécanisme de formation de jet dans un champ magnétique poloïdal (aligné par rapport à l'axe principal d’expansion du plasma). Une seconde partie traite de la distorsion d'une telle formation de jet par l'interaction du même plasma en expansion avec un champ magnétique désaligné (c'est-à-dire présentant un angle par rapport à l'axe d’expansion du plasma). Enfin, une troisième partie détaille la propagation du plasma dans un champ magnétique perpendiculaire. Cette dernière partie nous permet d'étudier des canaux exotiques d'accumulation de matière sur les étoiles, consistant en une accrétion du disque d’accrétion directement vers l'étoile, c’est-à-dire sur le plan équatorial, impliquant une propagation orthogonale aux lignes de champ magnétiques. Le deuxième chapitre aborde le thème de la dynamique d'accrétion par l'intermédiaire de colonnes de matière magnétiquement confinées, tombant sur la surface stellaire. En utilisant la même configuration expérimentale que dans le premier chapitre, le jet formé (dans le cas du champ magnétique parfaitement aligné) est utilisé pour imiter la colonne d'accrétion et est lancé sur une cible secondaire qui agit comme la surface stellaire. La dynamique de choc à l'emplacement de l'obstacle est soigneusement étudiée et des liens avec les observations de phénomènes d’accrétion astrophysique sont construits. Un cocon de plasma, formé autour de la région d'impact via l'interaction avec le champ magnétique, est observé être similaire à celui trouvé dans les simulations astrophysiques. Ce cocon est un élément important en tant que milieu potentiel d'absorption des émissions X. Ce milieu permettrait en effet d'expliquer les écarts observés entre les émissions UV / optiques et les émissions X provenant des étoiles lors des phases d’accrétion. / The work that is presented here has been performed in the frame of laboratory astrophysics, which consists in studying in the laboratory physical processes occurring in astrophysical objects. The main advantages in doing so are that the processes can be studied in a controlled way and that their full dynamics can be investigated. Here, we have been taking advantage of high-intensity laser facilities to perform our studies.In this manuscript, will be treated issues that include the interaction of a plasma expanding into vacuum with an ambient magnetic field. The presence of a magnetic field in a variety of astrophysical phenomena makes the inclusion of this component in the laboratory of great interest. We have used for our study a split Helmholtz coil, specifically designed in order to work in a laser environment, that allows for reaching a magnetic field strength up to 30 T.The astrophysical objects on which this study is focused are Young Stellar Objects (YSOs). Several steps of the star formation process are here investigated: (i) the generation of very long range, bright jets, (ii) the accretion dynamic involving, in the standard representation, matter falling down on the star in the shape of magnetically confined columns, and (iii) more exotic accretion channels, as the equatorial accretion that implies propagation of plasma perpendicularly to magnetic field lines.More precisely, in a first chapter, the jet formation dynamic will be discussed. A first part is dedicated to the jet formation mechanism in a poloidal magnetic field (aligned with respect to the main plasma expansion axis). A second part is dealing with the distortion of such jet formation via the interaction of the same expanding plasma with a misaligned magnetic field (i.e. presenting an angle with respect to the plasma expansion axis). Finally, a third part details the propagation of the plasma within a perpendicular magnetic field. This last part allows us to investigate exotic channels of matter accretion onto the stars, consisting of equatorial accretion from the disk to the star, through orthogonal magnetic field lines. The second chapter addresses the topic of the standard accretion dynamic via magnetically confined columns of matter, falling down onto the stellar surface. Using the same experimental setup as in the first chapter, the formed jet (in the case of the perfectly aligned magnetic field) is used to mimic the accretion column, and is launched onto a secondary target that acts as the stellar surface. The shock dynamic at the obstacle location is carefully studied and links with astrophysical accretion observations are built. A plasma cocoon, shaped around the impact region via the interaction with the magnetic field, is found to be similar to the one found in astrophysical simulations. This cocoon is an important element as a potential X-ray absorptive medium in order to explain observed discrepancies, between observed UV/Optical and X-ray emissions emitted from accreting stars.

Symbiotic stars are binaries consisting of a cool evolved G-M/S/C I-III star accreting onto a smaller companion---but the accretion disk itself is rarely detected. Accretion signatures like hard X-rays and optical/ultraviolet flickering are usually suppressed or outshone by shell burning on the accreting white dwarf, the luminous giant, and the giant's wind nebula. In Chapters 2 and 3, we present a new way to find symbiotics that is less biased against accreting-only, non-burning symbiotics with directly detectable accretion disks. Our search methodology is based on finding outliers in SkyMapper Southern Sky Survey broad-band and intermediate-band photometry, using a parameter space built from reconstructed u-g u-v snapshot colors and rapid variability between the three exposures of a 20-minute SkyMapper Main Survey filter sequence, from a sample of luminous red objects selected with 2MASS and Gaia. In a pilot survey employing this new search design, we discovered 12 new symbiotics, including four symbiotics with optical accretion disk flickering and at least two with boundary-layer hard X-rays, as well as 10 new symbiotic candidates. We also discovered optical flickering in the known symbiotic V1044 Cen (CD-36 8436). We conclude that at least 20% of the true population of symbiotics exhibits detectable optical flickering from the inner accretion disk, a substantial fraction of which would not meet the usual H-alpha equivalent width detection thresholds typically used to find symbiotics with traditional narrow-band emission line photometry surveys. There is a significant population of optically-flickering symbiotics hidden both within and beyond the known catalogs of symbiotic stars---however, the question of whether the true population of accreting-only symbiotics is larger than the population of burning symbiotics remains unanswered. We also find that our methods probe a completely different region of parameter space than recent work by the Munari et al. (2021) search for accreting-only symbiotics, while being surprisingly in harmony with the Akras et al. (2019) infrared selection criteria. As an intermediate step in our pilot survey, we explored several outlying regions in our SkyMapper parameter space with optical spectroscopy of 234 luminous red objects, which we present in a 248-page spectral atlas. Our results identify a zone of the u-g u-v snapshot color-color diagram in which virtually all objects are symbiotics. When all-sky uvg colors become available through future DRs of SkyMapper and MEPHISTO, between about 51 and 117 symbiotics missed by previous surveys (of which 11 to 17 have been reported in this work) will be discoverable using only this mostly-symbiotic zone of the color-color diagram, with a near-zero contamination rate. Main Survey filter-sequence variability is also a powerful tool for finding hidden, flickering symbiotics both inside and outside of the mostly-symbiotic color-color zone, but variability must still be used in conjunction with color; there must be enough of an accretion disk contribution to the u-band for it to exhibit detectable variability. We show that yellow post-AGB stars with strong Balmer jump absorption (along with the symbiotic Southern Crab) are outliers with large positive u-v, while some S and carbon stars are outliers with large negative u-v. We also show that it is important to correct the results of SkyMapper's catalog pipeline for variability when dealing with samples containing large-amplitude pulsating stars. In Chapters 4 and 5, we present an in-depth study of one of the few optically-flickering symbiotic stars previously known, MWC 560 (V694 Mon). The persistent outflow from MWC 560 is known to manifest as broad absorption lines (BALs), most prominently at the Balmer transitions. In Chapter 4, we report the detection of high-ionization BALs from C IV, Si IV, N V, and He II in International Ultraviolet Explorer spectra obtained on 1990 April 29-30, when an optical outburst temporarily erased the obscuring "iron curtain" of absorption troughs from Fe II and similar ions. The C IV and Si IV BALs reached maximum radial velocities at least 1000 km/s higher than contemporaneous Mg II and He II BALs; the same behaviors occur in the winds of quasars and cataclysmic variables. An iron curtain lifts to unveil high-ionization BALs during the P Cygni phase observed in some novae, suggesting by analogy a temporary switch in MWC 560 from persistent outflow to discrete mass ejection. At least three more symbiotic stars exhibit broad absorption with blue edges faster than 1500 km/s; high-ionization BALs have been reported in AS 304 (V4018 Sgr), while transient Balmer BALs have been reported in Z And and CH Cyg. These BAL-producing fast outflows can have wider opening angles than has been previously supposed. BAL symbiotics are short-timescale laboratories for their giga-scale analogs, broad absorption line quasars (BALQSOs), which display a similarly wide range of ionization states in their winds. In Chapter 5, we investigate how the accretion disc of MWC 560 is affected by its outflow. We performed optical, radio, X-ray, and ultraviolet observations of MWC 560 during its 2016 optical high state. We tracked multi-wavelength changes that signalled an abrupt increase in outflow power at the initiation of a months-long outflow fast state, just as the optical flux peaked: (1) an abrupt doubling of Balmer absorption velocities; (2) the onset of a 20 𝜇Jy/month increase in radio flux; and (3) an order-of-magnitude increase in soft X-ray flux. Juxtaposing to prior X-ray observations and their coeval optical spectra, we infer that both high-velocity and low-velocity optical outflow components must be simultaneously present to yield a large soft X-ray flux, which may originate in shocks where these fast and slow absorbers collide. Our optical and ultraviolet spectra indicate that the broad absorption-line gas was fast, stable, and dense (⪞10⁶.⁵ cm⁻³) throughout the 2016 outflow fast state, steadily feeding a lower-density (⪝10⁵.⁵ cm⁻³) region of radio-emitting gas. Persistent optical and ultraviolet flickering indicate that the accretion disc remained intact. The stability of these properties in 2016 contrasts to their instability during MWC 560's 1990 outburst, even though the disc reached a similar accretion rate. We propose that the self-regulatory effect of a steady fast outflow from the disc in 2016 prevented a catastrophic ejection of the inner disc. This behaviour in a symbiotic binary resembles disc/outflow relationships governing accretion state changes in X-ray binaries.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20912号 / 理博第4364号 / 新制||理||1626(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 井岡 邦仁, 教授 川合 光, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The following is a compilation of field data collected in 2011 and 2012 in Apalachicola, FL as part of a five year study assessing the ecological effects of sea level rise in the northern Gulf of Mexico. Many coastal communities, both natural and developed, will soon be working to mitigate the effects of sea level rise, if they are not already doing so. This thesis investigates the natural patterns of the Apalachicola estuarine system through the collection and analysis of in situ water, sediment, and biomass samples. Additionally, results of the field samples are presented and recommendations for additional sampling are given. The field methods and procedures developed in this study were designed to be repeated in other estuaries to build upon the work that has been conducted in Apalachicola. Water samples were tested for total suspended solids (TSS) and compared against hydrodynamic (tidal circulation and streamflow) and meteorological (wind and precipitation) characteristics. Streamflow was determined to influence a seasonal base level concentration of TSS. Wind strength and direction consistently influenced small TSS concentration fluctuations, an effect amplified by the shallow nature of the estuary. Tidal circulation appeared to have minor influences on TSS concentration fluctuations within the base level concentration range. Precipitation appeared to influence large TSS concentration fluctuations; however, due to limited data collection during storm events, more data is required to conclusively state this. Sediment cores throughout the lower Apalachicola River revealed that coarse particles settled out in upstream areas while fine particles tended to stay in suspension until low energy areas in the lower portions of the river or marsh system were reached. Finally, biomass samples were used to iv develop regression models utilizing remotely sensed data to predict biomass density in marsh areas with unprecedented accuracy. The documented patterns of this system are to be used as inputs and validation points to update an existing hydrodynamic model and to aid in the coupling and development of sediment transport and marsh equilibrium models. The field campaign developed and implemented here provides a foundation for this novel coupled modeling effort of estuarine systems. From the 2011 and 2012 sampling conducted, it is apparent that Apalachicola can be modeled as a closed system with river inflow and sediment influx as boundary conditions. Forcing local conditions should accurately represent the system. Ultimately, these models will be used to simulate future sea level rise scenarios and will provide useful decision making tools to coastal managers. Future work will include replicating water sampling in subsequent wet and dry seasons in Apalachicola, FL to confirm observed trends, in addition to implementing this sampling in Grand Bay, MS and Weeks Bay, AL. Additional biomass samples will be taken to validate the strong correlations found between remotely sensed data and in situ samples. In similar studies, it is recommended that water samples be taken to adequately represent influences from tidal cycles and riverine inflow. It is also recommended that spatially distributed biomass samples be taken to validate regression models.