Determination of Supermassive Black Hole Spins Based on the Standard Shakura–Sunyaev Accretion Disk Model and Polarimetric Observations     

V.?L.?Afanasiev  Yu.N.?GnedinEmail author  M.Yu.?Piotrovich  S.?D.?Buliga  T.?M.?Natsvlishvili 《Astronomy Letters》2018,44(6):362-369

Based on spectropolarimetry for 47 type 1 active galactic nuclei observed with the 6-m BTA telescope, we have estimated the spins of the supermassive black holes at the centers of these galaxies. We have determined the spins based on the standard Shakura–Sunyaev accretion disk model. About 70% of the investigated active galactic nuclei are shown to have Kerr supermassive black holes with a dimensionless spin greater than 0.9.  相似文献   

Critical Latitude in Tidal Dynamics Using the Kara Sea as an Example     

B.?A.?KaganEmail author  E.?V.?Sofina  A.?A.?Timofeev 《Izvestiya Atmospheric and Oceanic Physics》2018,54(2):206-212

It is well known that, within the linear nonviscous equations of tidal dynamics, the amplitudes of oscillations of the barotropic and baroclinic tidal velocity components unlimitedly increase when approaching the critical latitude. It is also known that the linear equations of tidal dynamics with a constant and specified vertical eddy viscosity indicate the occurrence of significant tidal velocity shears in the near-bottom layer, which are responsible for increasing the baroclinic tidal energy dissipation, the turbulent kinetic energy, and the thickness of the bottom boundary layer. The first circumstance—the growth of the amplitudes of oscillations of the barotropic and baroclinic tidal velocity components—is due to the elimination in the original equations of small terms, which are small everywhere except for the critical latitude zone. The second circumstance—the occurrence of significant tidal velocity shears—is due to the fact that internal tidal waves, which induce the dissipation of the baroclinic tidal energy and the diapycnal diffusion, are either not taken into account or described inadequately. It is suggested that diapycnal diffusion can lead to the degeneration (complete or partial) of tidal velocity shears, with all the ensuing consequences. The aforesaid is confirmed by simulation results obtained using the QUODDY-4 high-resolution three-dimensional finite-element hydrostatic model along the 66.25° E section, which passes in the Kara Sea across the critical latitude.  相似文献   

Classifying GRB 170817A/GW170817 in a Fermi duration–hardness plane     

I. Horváth  B. G. Tóth  J. Hakkila  L. V. Tóth  L. G. Balázs  I. I. Rácz  S. Pintér  Z. Bagoly 《Astrophysics and Space Science》2018,363(3):53

GRB 170817A, associated with the LIGO-Virgo GW170817 neutron-star merger event, lacks the short duration and hard spectrum of a Short gamma-ray burst (GRB) expected from long-standing classification models. Correctly identifying the class to which this burst belongs requires comparison with other GRBs detected by the Fermi GBM. The aim of our analysis is to classify Fermi GRBs and to test whether or not GRB 170817A belongs—as suggested—to the Short GRB class. The Fermi GBM catalog provides a large database with many measured variables that can be used to explore gamma-ray burst classification. We use statistical techniques to look for clustering in a sample of 1298 gamma-ray bursts described by duration and spectral hardness. Classification of the detected bursts shows that GRB 170817A most likely belongs to the Intermediate, rather than the Short GRB class. We discuss this result in light of theoretical neutron-star merger models and existing GRB classification schemes. It appears that GRB classification schemes may not yet be linked to appropriate theoretical models, and that theoretical models may not yet adequately account for known GRB class properties. We conclude that GRB 170817A may not fit into a simple phenomenological classification scheme.  相似文献   

Analytical study of ground motion caused by seismic wave propagation across faulted rock masses          下载免费PDF全文

J.C. Li  N.N. Li  S.B. Chai  H.B. Li 《国际地质力学数值与分析法杂志》2018,42(1):95-109

Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Q_p and Q_s. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions.  相似文献   

Geography Deserts: State and Regional Variation in the Formal Opportunity to Learn Geography in the United States, 2005–2015     

Mark C. Jones  Marcos Luna 《The Journal of geography》2019,118(2):88-100

The formal opportunity to learn geography in the United States is unevenly distributed across space, creating possible geography deserts. Data on the number of exams taken in Advanced Placement Human Geography (APHG) and bachelor’s degrees earned in geography are mapped at the state and regional scales. Normalized rates are ranked and grouped into quintiles. For APHG exams, states in the southeastern region of the United States are in the uppermost quintiles while states in the northeastern region are in the lowermost quintiles. The pattern for bachelor’s degrees in geography is somewhat the spatial inverse of that for APHG.  相似文献   

Comprehensive Geological–Geophysical and Botanic Study of the Tectonic Junction Zone between the Katun Ridge and Uimon Depression (Altai Mountains)     

Boyarskikh  I. G.  Agatova  A. R.  Kulikova  A. I.  Bakiyanov  A. I.  Skaptsov  M. V.  Mazeika  J. 《Izvestiya Atmospheric and Oceanic Physics》2018,54(8):805-825

Izvestiya, Atmospheric and Oceanic Physics - Areas with large gradients and anomalous variations in geomagnetic and radiation fields have been revealed and mapped at the northwestern foot of the...  相似文献   

The spawning and early life-history of a New Zealand endemic amphidromous eleotrid,bluegill bully (Gobiomorphus hubbsi)     

Matt G. Jarvis  Hannah A. Harland  Manna L. Warburton  Gerard P. Closs 《新西兰海洋与淡水研究杂志》2018,52(1):55-68

The larval stage of fishes is critical in determining their dispersal, survival and recruitment, but little is known of the larval behaviours and tolerances of amphidromous fishes, particularly in New Zealand. We report the results of a series of observational and experimental studies on bluegill bully (Gobiomorphus hubbsi), including spawning sites and behaviours, larval characteristics at hatch, phototactic responses of larvae, and larval survival at different salinity levels. Spawning primarily occurred in the lower reaches of the river, and larvae from different nests exhibited marked differences in, and trade-offs between, larval characteristics at hatch, potentially affecting larval success. Larvae were positively phototactic to intense light, an unexpected result based on diel drift patterns and international research. Finally, larvae exhibited markedly higher survival rates when reared at intermediate salinities compared to freshwater or seawater, suggesting estuaries may play an important role as nursery grounds for bluegill bully and other amphidromous fish.  相似文献   

On the coplanar eccentric non-restricted co-orbital dynamics     

A. Leleu  P. Robutel  A. C. M. Correia 《Celestial Mechanics and Dynamical Astronomy》2018,130(3):24

We study the phase space of eccentric coplanar co-orbitals in the non-restricted case. Departing from the quasi-circular case, we describe the evolution of the phase space as the eccentricities increase. We find that over a given value of the eccentricity, around 0.5 for equal mass co-orbitals, important topological changes occur in the phase space. These changes lead to the emergence of new co-orbital configurations and open a continuous path between the previously distinct trojan domains near the \(L_4\) and \(L_5\) eccentric Lagrangian equilibria. These topological changes are shown to be linked with the reconnection of families of quasi-periodic orbits of non-maximal dimension.  相似文献   

Estimating average shock pressures recorded by impactite samples based on universal stage investigations of planar deformation features in quartz—Sources of error and recommendations          下载免费PDF全文

S. Holm-Alwmark  L. Ferrière  C. Alwmark  M. H. Poelchau 《Meteoritics & planetary science》2018,53(1):110-130

Planar deformation features (PDFs) in quartz are the most widely used indicator of shock metamorphism in terrestrial rocks. They can also be used for estimating average shock pressures that quartz-bearing rocks have been subjected to. Here we report on a number of observations and problems that we have encountered when performing universal stage measurements and crystallographically indexing of PDF orientations in quartz. These include a comparison between manual and automated methods of indexing PDFs, an evaluation of the new stereographic projection template, and observations regarding the PDF statistics related to the c-axis position and rhombohedral plane symmetry. We further discuss the implications that our findings have for shock barometry studies. Our study shows that the currently used stereographic projection template for indexing PDFs in quartz might induce an overestimation of rhombohedral planes with low Miller–Bravais indices. We suggest, based on a comparison of different shock barometry methods, that a unified method of assigning shock pressures to samples based on PDFs in quartz is necessary to allow comparison of data sets. This method needs to take into account not only the average number of PDF sets/grain but also the number of high Miller–Bravais index planes, both of which are important factors according to our study. Finally, we present a suggestion for such a method (which is valid for nonporous quartz-bearing rock types), which consists of assigning quartz grains into types (A–E) based on the PDF orientation pattern, and then calculation of a mean shock pressure for each sample.  相似文献   

Analysis of the exoplanet containing system Kepler-13     

E.?Budding  M.?D.?RhodesEmail author 《Astrophysics and Space Science》2018,363(3):60

We have applied the close binary system analysis program WinFitter, with its physically detailed fitting function, to an intensive study of the complex multiple system Kepler-13 using photometry data from all 13 short cadence quarters downloaded from the NASA Exoplanet Archive (NEA) (http://exoplanetarchive.ipac.caltech.edu). The data-point error of our normalized, phase-sequenced and binned (380 points per bin: 0.00025 phase interval) flux values, at 14 ppm, allows the model’s specification for the mean reference flux level of the system to a precision better than 1 ppm. Our photometrically derived values for the mass and radius of KOI13.01 are \(6.8\pm0.6~\mbox{M}_{\mathrm{J}}\) and \(1.44\pm0.04~\mbox{R}_{\mathrm{J}}\). The star has a radius of \(1.67\pm0.05~\mbox{R}_{\odot}\). Our modelling sets the mean of the orbital inclination \(i\) at \(94.35\pm0.14^{\circ}\), with the star’s mean precession angle \(\phi_{p}\)—\(49.1\pm5.0^{\circ}\) and obliquity \(\theta_{o}\)\(67.9 \pm 3.0^{\circ}\), though there are known ambiguities about the sense in which such angles are measured.Our findings did not confirm secular variation in the transit modelling parameters greater than their full correlated errors, as argued by previous authors, when each quarter’s data was best-fitted with a determinable parameter set without prejudice. However, if we accept that most of the parameters remain the same for each transit, then we could confirm a small but steady diminution in the cosine of the orbital inclination over the 17 quarter timespan. This is accompanied by a slight increase of the star’s precession angle (less negative), but with no significant change in the obliquity of its spin axis. There are suggestions of a history of strong dynamical interaction with a highly distorted planet rotating in a 3:2 resonance with its revolution, together with a tidal lag of \(\sim30~\mbox{deg}\). The mean precessional period is derived to be about 1000 y, but at the present time the motion of the star’s rotation axis appears to be supporting the gravitational torque, rather than providing the balance against it that would be expected over long periods of time.The planet has a small but detectable backwarming effect on the star, which helps to explain the difference in brightness just after transit and just before occultation eclipses. In assessing these findings it is recognized that sources of uncertainty remain, notably with possible inherent micropulsational effects, variations from other components of the multiple star, stellar activity, differential rotation and the neglect of higher order terms (than \(r_{1}^{5}\)) in the fitting function, where \(r_{1}\) is the ratio of the radius of the star to the mean orbital separation of planet and host star.  相似文献