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Author: Grafiati
Published: 6 September 2023

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1

Ghosh, Shubhrangshu, and Prabir Banik. "Characteristics of transonic spherical symmetric accretion flow in Schwarzschild-de Sitter and Schwarzschild anti-de Sitter backgrounds, in pseudo-general relativistic paradigm." International Journal of Modern Physics D 24, no. 11 (September 6, 2015): 1550084. http://dx.doi.org/10.1142/s0218271815500844.

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In this paper, we present a complete work on steady state spherically symmetric Bondi type accretion flow in the presence of cosmological constant (Λ) in both Schwarzschild-de Sitter (SDS) and Schwarzschild anti-de Sitter (SADS) backgrounds considering an isolated supermassive black hole (SMBH), with the inclusion of a simple radiative transfer scheme, in the pseudo-general relativistic paradigm. We do an extensive analysis on the transonic behavior of the Bondi type accretion flow onto the cosmological BHs including a complete analysis of the global parameter space and the stability of flow, and do a complete study of the global family of solutions for a generic polytropic flow. Bondi type accretion flow in SADS background renders multiplicity in its transonic behavior with inner "saddle" type and outer "center" type sonic points, with the transonic solutions forming closed loops or contours. There is always a limiting value for ∣Λ∣ up to which we obtain valid stationary transonic solutions, which correspond to both SDS and SADS geometries; this limiting value moderately increases with the increasing radiative efficiency of the flow, especially correspond to Bondi type accretion flow in SADS background. Repulsive Λ suppresses the Bondi accretion rate by an order of magnitude for relativistic Bondi type accretion flow for a certain range in temperature, and with a marginal increase in the Bondi accretion rate if the corresponding accretion flow occurs in SADS background. However, for a strongly radiative Bondi type accretion flow with high mass accretion rate, the presence of cosmological constant do not much influence the corresponding Bondi accretion rate of the flow. Our analysis show that the relic cosmological constant has a substantial effect on Bondi type accretion flow onto isolated SMBHs and their transonic solutions beyond length-scale of kiloparsecs, especially if the Bondi type accretion occurs onto the host supergiant ellipticals or central dominant (CD) galaxies directly from ambient intercluster medium (ICM). However, for high mass accretion rate, the influence of cosmological constant on Bondi accretion dynamics, generically, diminishes. As active galactic nuclei (AGN)/ICM feedback can be advertently linked to Bondi type spherical accretion, any proper modeling of AGN feedback or megaparsecs-scale jet dynamics or accretion flow from ICM onto the central regions of host galaxies should take into account the relevant information of repulsive Λ, especially in context to supergiant elliptical galaxies or CD galaxies present in rich galaxy clusters. This could also explore the feasibility to limit the value of Λ, from the kinematics in local galactic-scales.
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2

Lynden-Bell, Donald, and Jiří Bičák. "Pressure in Lemaître–Tolman–Bondi solutions and cosmologies." Classical and Quantum Gravity 33, no. 7 (March 1, 2016): 075001. http://dx.doi.org/10.1088/0264-9381/33/7/075001.

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3

Hernandez, X., L. Nasser, and A. Aguayo-Ortiz. "A New Hydrodynamic Spherical Accretion Exact Solution and Its Quasi-spherical Perturbations." Astrophysical Journal 945, no. 1 (March 1, 2023): 76. http://dx.doi.org/10.3847/1538-4357/acb538.

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Abstract We present an exact γ = 5/3 spherical accretion solution that modifies the Bondi boundary condition of ρ → constant as r → ∞ to ρ → 0 as r → ∞. This change allows for simple power-law solutions on the density and infall velocity fields, ranging from a cold empty freefall condition where pressure tends to zero, to a hot hydrostatic equilibrium limit with no infall velocity. As in the case of the Bondi solution, a maximum accretion rate appears. As in the γ = 5/3 case of the Bondi solution, no sonic radius appears, this time however, because the flow is always characterized by a constant Mach number. This number equals 1 for the case of the maximum accretion rate, diverges toward the cold empty state, and becomes subsonic toward the hydrostatic equilibrium limit. It can be shown that in the limit r → 0, the Bondi solution tends to the new solution presented, extending the validity of the Bondi accretion value to cases where the accretion density profile does not remain at a fixed constant value out to infinity. We then explore small deviations from sphericity and the presence of angular momentum through an analytic perturbative analysis. Such perturbed solutions yield a rich phenomenology through density and velocity fields in terms of Legendre polynomials, which we begin to explore for simple angular velocity boundary conditions having zeros on the plane and pole. The new solution presented provides complementary physical insight into accretion problems in general.
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4

Waters, Tim, Aycin Aykutalp, Daniel Proga, Jarrett Johnson, Hui Li, and Joseph Smidt. "Outflows from inflows: the nature of Bondi-like accretion." Monthly Notices of the Royal Astronomical Society: Letters 491, no. 1 (November 4, 2019): L76—L80. http://dx.doi.org/10.1093/mnrasl/slz168.

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ABSTRACT The classic Bondi solution remains a common starting point both for studying black hole growth across cosmic time in cosmological simulations and for smaller scale simulations of active galactic nuclei (AGN) feedback. In nature, however, there will be inhomogeneous distributions of rotational velocity and density along the outer radius (Ro) marking the sphere of influence of a black hole. While there have been many studies of how the Bondi solution changes with a prescribed angular momentum boundary condition, they have all assumed a constant density at Ro. In this Letter, we show that a non-uniform density at Ro causes a meridional flow and due to conservation of angular momentum, the Bondi solution qualitatively changes into an inflow–outflow solution. Using physical arguments, we analytically identify the critical logarithmic density gradient |$\partial \ln \rho/\partial \theta$| above which this change of the solution occurs. For realistic Ro, this critical gradient is less than 0.01 and tends to 0 as Ro → ∞. We show using numerical simulations that, unlike for solutions with an imposed rotational velocity, the accretion rate for solutions under an inhomogeneous density boundary condition remains constant at nearly the Bondi rate $\dot{M}_\mathrm{ B}$, while the outflow rate can greatly exceed $\dot{M}_\mathrm{ B}$.
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5

Reddy, D. R. K., and P. Innaiah. "Plane symmetric cosmological solutions of the Lyttleton-Bondi Universe." Acta Physica Hungarica 61, no. 3-4 (June 1987): 269–76. http://dx.doi.org/10.1007/bf03158352.

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6

Sussman, Roberto A., and Luisa G. Jaime. "Lemaître–Tolman–Bondi dust solutions in f ( R ) gravity." Classical and Quantum Gravity 34, no. 24 (November 20, 2017): 245004. http://dx.doi.org/10.1088/1361-6382/aa91f5.

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7

Costa, João L., and Filipe C. Mena. "Global solutions to the spherically symmetric Einstein-scalar field system with a positive cosmological constant in Bondi coordinates." Journal of Hyperbolic Differential Equations 18, no. 02 (June 2021): 311–41. http://dx.doi.org/10.1142/s0219891621500107.

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We consider a characteristic initial value problem, with initial data given on a future null cone, for the Einstein (massless) scalar field system with a positive cosmological constant, in Bondi coordinates. We prove that, for small data, this system has a unique global classical solution which is causally geodesically complete to the future and decays polynomially in radius and exponentially in Bondi time, approaching the de Sitter solution.
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8

Herrera, Luis, Alicia Di Prisco, and Justo Ospino. "Hyperbolically Symmetric Versions of Lemaitre–Tolman–Bondi Spacetimes." Entropy 23, no. 9 (September 16, 2021): 1219. http://dx.doi.org/10.3390/e23091219.

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We study fluid distributions endowed with hyperbolic symmetry, which share many common features with Lemaitre–Tolman–Bondi (LTB) solutions (e.g., they are geodesic, shearing, and nonconformally flat, and the energy density is inhomogeneous). As such, they may be considered as hyperbolic symmetric versions of LTB, with spherical symmetry replaced by hyperbolic symmetry. We start by considering pure dust models, and afterwards, we extend our analysis to dissipative models with anisotropic pressure. In the former case, the complexity factor is necessarily nonvanishing, whereas in the latter cases, models with a vanishing complexity factor are found. The remarkable fact is that all solutions satisfying the vanishing complexity factor condition are necessarily nondissipative and satisfy the stiff equation of state.
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9

Chang, Shu-Cheng. "Global existence and convergence of solutions of the Calabi flow on Einstein 4-manifolds." Nagoya Mathematical Journal 163 (September 2001): 193–214. http://dx.doi.org/10.1017/s0027763000007960.

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In this paper, firstly, we show the Bondi-mass type estimate of solutions of Calabi flow on closed 4-manifolds. Secondly, in our applications, we obtain the long time existence on closed 4-manifolds. In particular, we are able to show the asymptotic convergence of a subsequence of solutions of the Calabi flow on closed Einstein 4-manifolds.
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10

Aguayo-Ortiz, Alejandro, Emilio Tejeda, and X. Hernandez. "Choked accretion: from radial infall to bipolar outflows by breaking spherical symmetry." Monthly Notices of the Royal Astronomical Society 490, no. 4 (October 23, 2019): 5078–87. http://dx.doi.org/10.1093/mnras/stz2989.

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ABSTRACT Steady-state, spherically symmetric accretion flows are well understood in terms of the Bondi solution. Spherical symmetry, however, is necessarily an idealized approximation to reality. Here we explore the consequences of deviations away from spherical symmetry, first through a simple analytic model to motivate the physical processes involved, and then through hydrodynamical, numerical simulations of an ideal fluid accreting on to a Newtonian gravitating object. Specifically, we consider axisymmetric, large-scale, small-amplitude deviations in the density field such that the equatorial plane is overdense as compared to the polar regions. We find that the resulting polar density gradient dramatically alters the Bondi result and gives rise to steady-state solutions presenting bipolar outflows. As the density contrast increases, more and more material is ejected from the system, attaining speeds larger than the local escape velocities for even modest density contrasts. Interestingly, interior to the outflow region, the flow tends locally towards the Bondi solution, with a resulting total mass accretion rate through the inner boundary choking at a value very close to the corresponding Bondi one. Thus, the numerical experiments performed suggest the appearance of a maximum achievable accretion rate, with any extra material being ejected, even for very small departures from spherical symmetry.
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11

Bennewitz, Elizabeth R., Cristian Gaidau, Thomas W. Baumgarte, and Stuart L. Shapiro. "Dark matter heating of gas accreting onto Sgr A*." Monthly Notices of the Royal Astronomical Society 490, no. 3 (October 9, 2019): 3414–25. http://dx.doi.org/10.1093/mnras/stz2781.

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ABSTRACT We study effects of heating by dark matter (DM) annihilation on black hole gas accretion. We observe that, for reasonable assumptions about DM densities in spikes around supermassive black holes, as well as DM masses and annihilation cross-sections within the standard WIMP model, heating by DM annihilation may have an appreciable effect on the accretion on to Sgr A* in the Galactic Centre. Motivated by this observation we study the effects of such heating on Bondi accretion, i.e. spherically symmetric, steady-state Newtonian accretion on to a black hole. We consider different adiabatic indices for the gas, and different power-law exponents for the DM density profile. We find that typical transonic solutions with heating have a significantly reduced accretion rate. However, for many plausible parameters, transonic solutions do not exist, suggesting a breakdown of the underlying assumptions of steady-state Bondi accretion. Our findings indicate that heating by DM annihilation may play an important role in the accretion onto supermassive black holes at the centre of galaxies, and may help explain the low accretion rate observed for Sgr A*.
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12

Tadmon, Calvin, and Sophonie Blaise Tchapnda. "On the spherically symmetric Einstein–Yang–Mills–Higgs equations in Bondi coordinates." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 468, no. 2146 (June 15, 2012): 3191–214. http://dx.doi.org/10.1098/rspa.2012.0171.

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We revisit and generalize, to the Einstein–Yang–Mills–Higgs (EYMH) system, previous results of Christodoulou and Chae concerning global solutions for the Einstein-scalar field and the Einstein–Maxwell–Higgs (EMH) equations. The novelty of the present work is twofold. For one thing, the assumption on the self-interaction potential is improved. For another thing, explanation is furnished why the solutions obtained here and those proved by Chae for the EMH system decay more slowly than those established by Christodoulou in the case of self-gravitating scalar fields. Actually, this latter phenomenon stems from the non-vanishing local charge in EMH and EYMH models.
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13

Lyra, Wladimir, Anders Johansen, Manuel H. Cañas, and Chao‐Chin Yang. "An Analytical Theory for the Growth from Planetesimals to Planets by Polydisperse Pebble Accretion." Astrophysical Journal 946, no. 2 (March 30, 2023): 60. http://dx.doi.org/10.3847/1538-4357/acaf5b.

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Abstract Pebble accretion is recognized as a significant accelerator of planet formation. Yet only formulae for single-sized (monodisperse) distribution have been derived in the literature. These can lead to significant underestimates for Bondi accretion, for which the best accreted pebble size may not be the one that dominates the mass distribution. We derive in this paper the polydisperse theory of pebble accretion. We consider a power-law distribution in pebble radius, and we find the resulting surface and volume number density distribution functions. We derive also the exact monodisperse analytical pebble accretion rate for which 3D accretion and 2D accretion are limits. In addition, we find analytical solutions to the polydisperse 2D Hill and 3D Bondi limits. We integrate the polydisperse pebble accretion numerically for the MRN distribution, finding a slight decrease (by an exact factor 3/7) in the Hill regime compared to the monodisperse case. In contrast, in the Bondi regime, we find accretion rates 1–2 orders of magnitude higher compared to monodisperse, also extending the onset of pebble accretion to 1–2 orders of magnitude lower in mass. We find megayear timescales, within the disk lifetime, for Bondi accretion on top of planetary seeds of masses 10−6 to 10−4 M ⊕, over a significant range of the parameter space. This mass range overlaps with the high-mass end of the planetesimal initial mass function, and thus pebble accretion is possible directly following formation by streaming instability. This alleviates the need for mutual planetesimal collisions as a major contribution to planetary growth.
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14

Keto, Eric. "Stability and solution of the time-dependent Bondi–Parker flow." Monthly Notices of the Royal Astronomical Society 493, no. 2 (February 21, 2020): 2834–40. http://dx.doi.org/10.1093/mnras/staa529.

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ABSTRACT Bondi and Parker derived a steady-state solution for Bernoulli’s equation in spherical symmetry around a point mass for two cases, respectively, an inward accretion flow and an outward wind. Left unanswered were the stability of the steady-state solution, the solution itself of time-dependent flows, whether the time-dependent flows would evolve to the steady state, and under what conditions a transonic flow would develop. In a Hamiltonian description, we find that the steady-state solution is equivalent to the Lagrangian implying that time-dependent flows evolve to the steady state. We find that the second variation is definite in sign for isothermal and adiabatic flows, implying at least linear stability. We solve the partial differential equation for the time-dependent flow as an initial-value problem and find that a transonic flow develops under a wide range of realistic initial conditions. We present some examples of time-dependent solutions.
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15

Sharif, Muhammad, and Rubab Manzoor. "Lemaitre–Tolman–Bondi dust cloud collapse in Brans–Dicke gravity." Modern Physics Letters A 29, no. 35 (November 17, 2014): 1450192. http://dx.doi.org/10.1142/s0217732314501922.

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This paper investigates the phenomenon of gravitational collapse of Lemaitre–Tolman–Bondi (LTB) model in the presence of Brans–Dicke (BD) scalar field with nonzero potential field. We find a class of solutions by taking perfect fluid as well as scalar field and check the validity of weak energy conditions. It turns out that two different types of singularities are formed in the presence of scalar field. We conclude that the end state of gravitational collapse turns out to be a black hole (BH) contrary to general relativity (GR).
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16

Van Acoleyen, Karel. "Lemaître–Tolman–Bondi solutions in the Newtonian gauge: from strong to weak fields." Journal of Cosmology and Astroparticle Physics 2008, no. 10 (October 16, 2008): 028. http://dx.doi.org/10.1088/1475-7516/2008/10/028.

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17

Ciotti, Luca, and Silvia Pellegrini. "Fully analytical solutions for Bondi accretion in galaxies with a central Black Hole." Proceedings of the International Astronomical Union 14, S342 (May 2018): 5–8. http://dx.doi.org/10.1017/s1743921318005732.

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AbstractThe fully analytical solution for isothermal Bondi accretion on a black hole (MBH) at the center of JJ two-component Jaffe (1983) galaxy models is presented. In JJ models the stellar and total mass density distributions are described by the Jaffe profile, with different scale-lengths and masses, and to which a central MBH is added; all the relevant stellar dynamical properties can also be derived analytically. In these new accretion solutions the hydrodynamical and stellar dynamical properties are linked by imposing that the gas temperature is proportional to the virial temperature of the stellar component. The formulae that are provided allow to evaluate all flow properties, and are then useful for estimates of the accretion radius and the mass flow rate when modeling accretion on MBHs at the center of galaxies.
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18

Ribeiro, Marcelo B. "A Fortran code for null geodesic solutions in the Lemaı̂tre–Tolman–Bondi spacetime." Computer Physics Communications 148, no. 2 (October 2002): 236–41. http://dx.doi.org/10.1016/s0010-4655(02)00561-1.

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19

Han, Qing, and Lin Zhang. "On the null-timelike boundary for Maxwell and spin-2 fields in asymptotically flat spaces." Journal of Hyperbolic Differential Equations 18, no. 02 (June 2021): 343–95. http://dx.doi.org/10.1142/s0219891621500119.

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We study the Maxwell equation and the spin-2 field equation in Bondi–Sachs coordinates associated with an asymptotically flat Lorentzian metric. We consider the mixed boundary/initial value problem, where the initial data are imposed on a null hypersurface and a boundary value is prescribed on a timelike hypersurface. We establish Sobolev [Formula: see text] space-time estimates for solutions and their asymptotic expansions at the null infinity.
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20

KOZAMEH, CARLOS, EZRA T. NEWMAN, and GILBERTO SILVA-ORTIGOZA. "ON THE PHYSICAL INTERPRETATION OF ASYMPTOTICALLY FLAT GRAVITATIONAL FIELDS." International Journal of Modern Physics D 17, no. 13n14 (December 2008): 2599–606. http://dx.doi.org/10.1142/s0218271808014138.

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A problem in general relativity is how to extract physical information from solutions to the Einstein equations. Most often information is found from special conditions, e.g., special vector fields, symmetries or approximate symmetries. Our concern is with asymptotically flat space–times with approximate symmetry: the BMS group. For these spaces the Bondi four-momentum vector and its evolution, found at infinity, describes the total energy–momentum and the energy–momentum radiated. By generalizing the simple idea of the transformation of (electromagnetic) dipoles under a translation, we define (analogous to center of charge) the center of mass for asymptotically flat Einstein–Maxwell fields. This gives kinematical meaning to the Bondi four-momentum, i.e., the four-momentum and its evolution is described in terms of a center of mass position vector, its velocity and spin-vector. From dynamical arguments, a unique (for our approximation) total angular momentum and evolution equation in the form of a conservation law is found.
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21

BOCHICCHIO, IVANA, MAURO FRANCAVIGLIA, and ETTORE LASERRA. "A REVIEW ON THE GEOMETRIC FORMULATION OF TOLMAN–BONDI EQUATIONS IN GENERAL RELATIVITY." International Journal of Geometric Methods in Modern Physics 06, no. 04 (June 2009): 595–617. http://dx.doi.org/10.1142/s0219887809003709.

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This work is focused on spherically symmetric space-times. More precisely, geometric and structural properties of spatially spherical shells of a dust universe are analyzed in detail considering recent results of our research. Moreover, exact solutions, obtained for constant Ricci principal curvatures, are inferred and qualitatively analyzed through suitable classic analogies.
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22

Larrabee, Glenn J. "Lessons on measuring construct validity: A commentary on Delis, Jacobson, Bondi, Hamilton, and Salmon." Journal of the International Neuropsychological Society 9, no. 6 (August 27, 2003): 947–53. http://dx.doi.org/10.1017/s1355617703960140.

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AbstractThis commentary expands on issues raised by Delis, Jacobson, Bondi, Hamilton, and Salmon, in their paper on the use of shared variance techniques to establish construct validity. Significant discussion is focused on method variance, and how this can distort the results of factor analysis. Solutions are offered for the appropriate use of factor analysis in construct validation. Examples are also provided of construct validation procedures that do not rely on correlational or shared variance techniques. (JINS, 2003, 9, 947–953.)
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23

Mädler, Thomas, and Ewald Müller. "The Bondi–Sachs metric at the vertex of a null cone: axially symmetric vacuum solutions." Classical and Quantum Gravity 30, no. 5 (February 14, 2013): 055019. http://dx.doi.org/10.1088/0264-9381/30/5/055019.

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24

GHOSH, S. G., D. W. DESHKAR, and N. N. SASTE. "FIVE-DIMENSIONAL DUST COLLAPSE WITH COSMOLOGICAL CONSTANT." International Journal of Modern Physics D 16, no. 01 (January 2007): 53–64. http://dx.doi.org/10.1142/s0218271807009309.

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We study the five-dimensional spherical collapse of an inhomogeneous dust in the presence of a positive cosmological constant. The general interior solutions, in the closed form, of the Einstein field equations, i.e. the 5D Tolman–Bondi–de Sitter, is obtained which in turn is matched to the exterior 5D Schwarzschild–de Sitter. It turns out that the collapse proceeds in the same way as in the Minkowski background, i.e. the strong curvature naked singularities form and thus violate the cosmic censorship conjecture. A brief discussion on the causal structure singularities and horizons is also given.
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25

Ciotti, Luca, and Silvia Pellegrini. "Isothermal Bondi Accretion in Jaffe and Hernquist Galaxies with a Central Black Hole: Fully Analytical Solutions." Astrophysical Journal 848, no. 1 (October 9, 2017): 29. http://dx.doi.org/10.3847/1538-4357/aa8d1f.

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26

Raga, A. C., J. Cantó, A. Castellanos-Ramírez, A. Rodríguez-González, and P. R. Rivera-Ortiz. "THE BONDI-HOYLE ACCRETION TAIL OF POINT SOURCES TRAVELLING HYPERSONICALLY THROUGH A DENSE ENVIRONMENT." Revista Mexicana de Astronomía y Astrofísica 58, no. 2 (October 1, 2022): 215–22. http://dx.doi.org/10.22201/ia.01851101p.2022.58.02.04.

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We present a model for the “Bondi-Hoyle tail” left behind by the hypersonic passage of a compact, massive object through a dense, radiative environment. We derive simple equations for the flow velocity and the mass along the tail, and obtain numerical and approximate analytical solutions for the steady state problem. We then study a time-dependent problem in which the source first travels within a dense cloud, and then emerges into a low density environment. This flow results in the production of a trail of dense gas joining the source at the point in which it emerged from the dense cloud. This trail has a linear velocity vs. position profile.
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27

Bhatti, M. Zaeem-ul-Haq, and Z. Yousaf. "Gravitational collapse and dark universe with LTB geometry." International Journal of Modern Physics D 26, no. 06 (October 10, 2016): 1750045. http://dx.doi.org/10.1142/s0218271817500456.

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The objective of this paper is to examine the influence of polynomial [Formula: see text] dark sector cosmic terms on the collapse of electrically charged Lemaître–Tolman–Bondi geometry. We explored a class of solutions for [Formula: see text] field equations in the existence of electromagnetic field and under the constraint of constant curvature scalar. The influence of [Formula: see text] model on the dynamics of collapsing object have been discussed by studying its black hole and cosmological horizons. Also, the effects of these dark sources on the time interval between the corresponding singularities and horizons have been studied. We investigated that the process of collapse slows down due to the higher order curvature invariants of polynomial [Formula: see text] model and electromagnetic field.
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28

Cruz-Osorio, Alejandro, Luciano Rezzolla, Fabio D. Lora-Clavijo, José Antonio Font, Carlos Herdeiro, and Eugen Radu. "Bondi-Hoyle-Lyttleton accretion onto a rotating black hole with ultralight scalar hair." Journal of Cosmology and Astroparticle Physics 2023, no. 08 (August 1, 2023): 057. http://dx.doi.org/10.1088/1475-7516/2023/08/057.

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Abstract We present a numerical study of relativistic Bondi-Hoyle-Lyttleton (BHL) accretion onto an asymptotically flat black hole with synchronized hair. The hair is sourced by an ultralight, complex scalar field, minimally coupled to Einstein's gravity. Our simulations consider a supersonic flow parametrized by the asymptotic values of the fluid quantities and a sample of hairy black holes with different masses, angular momenta, and amount of scalar hair. For all models, steady-state BHL accretion solutions are attained that are characterized by the presence of a shock-cone and a stagnation point downstream. For the models of the sample with the largest component of scalar field, the shock-cone envelops fully the black hole, transitioning into a bow-shock, and the stagnation points move further away downstream. Analytical expressions for the mass accretion rates are obtained after fitting the numerical results, which can be used to analyze black-hole formation scenarios in the presence of ultralight scalar fields. The formation of a shock-cone leads to regions where sound waves can be trapped and resonant oscillations excited. We measure the frequencies of such quasi-periodic oscillations and point out a possible association with quasi-periodic oscillations in the X-ray light curve of Sgr A* and microquasars.
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29

Sussman, Roberto A., and Luis Garc$iacute$a Trujillo. "A new approach to initial value variables for the Lema$icirc$tre$ndash$Tolman$ndash$Bondi dust solutions." Classical and Quantum Gravity 19, no. 11 (May 18, 2002): 2897–925. http://dx.doi.org/10.1088/0264-9381/19/11/310.

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30

Ramírez-Velásquez, J. M., L. Di G. Sigalotti, R. Gabbasov, J. Klapp, and E. Contreras. "Bondi accretion for adiabatic flows onto a massive black hole with an accretion disc." Astronomy & Astrophysics 631 (October 11, 2019): A13. http://dx.doi.org/10.1051/0004-6361/201935917.

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We present the classical Bondi accretion theory for the case of non-isothermal accretion processes onto a supermassive black hole (SMBH), including the effects of X-ray heating and the radiation force due to electron scattering and spectral lines. The radiation field is calculated by considering an optically thick, geometrically thin, standard accretion disc as the emitter of UV photons and a spherical central object as a source of X-ray emission. In our analysis, the UV emission from the accretion disc is assumed to have an angular dependence, and the X-ray radiation from the central object is assumed to be isotropic. This allows us to build streamlines in any angular direction. The influence of both types of radiation is evaluated for different flux fractions of the X-ray and UV emissions with and without the effects of spectral line driving. We find that the radiation emitted near the SMBH interacts with the infalling matter and modifies the accretion dynamics. In the presence of line driving, a transition takes place from pure type 1 and 2 to type 5 solutions, which takes place regardless of whether the UV emission dominates the X-ray emission. We computed the radiative factors at which this transition occurs, and discard type 5 solution from all our models. We also provide estimated values of the accretion radius and accretion rate in terms of the classical Bondi values. The results are useful for constructing proper initial conditions for time-dependent hydrodynamical simulations of accretion flows onto SMBHs at the centre of galaxies.
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31

Saw, Vee-Liem. "Asymptotically simple spacetimes and mass loss due to gravitational waves." International Journal of Modern Physics D 27, no. 01 (December 28, 2017): 1730027. http://dx.doi.org/10.1142/s0218271817300270.

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The cosmological constant [Formula: see text] used to be a freedom in Einstein’s theory of general relativity (GR), where one had a proclivity to set it to zero purely for convenience. The signs of [Formula: see text] or [Formula: see text] being zero would describe universes with different properties. For instance, the conformal structure of spacetime directly depends on [Formula: see text]: null infinity [Formula: see text] is a spacelike, null, or timelike hypersurface, if [Formula: see text], [Formula: see text], or [Formula: see text], respectively. Recent observations of distant supernovae have taught us that our universe expands at an accelerated rate, and this can be accounted for by choosing [Formula: see text] in Einstein’s theory of GR. A quantity that depends on the conformal structure of spacetime, especially on the nature of [Formula: see text], is the Bondi mass which in turn dictates the mass loss of an isolated gravitating system due to energy carried away by gravitational waves. This problem of extending the Bondi mass to a universe with [Formula: see text] has spawned intense research activity over the past several years. Some aspects include a closer inspection on the conformal properties, working with linearization, attempts using a Hamiltonian formulation based on “linearized” asymptotic symmetries, as well as obtaining the general asymptotic solutions of de Sitter-like spacetimes. We consolidate on the progress thus far from the various approaches that have been undertaken, as well as discuss the current open problems and possible directions in this area.
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32

Bishop, Nigel T. "Linearized solutions of the Einstein equations within a Bondi–Sachs framework, and implications for boundary conditions in numerical simulations." Classical and Quantum Gravity 22, no. 12 (May 26, 2005): 2393–406. http://dx.doi.org/10.1088/0264-9381/22/12/006.

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33

Hanski, M. O., P. Teerikorpi, T. Ekholm, G. Theureau, Yu Baryshev, G. Paturel, and P. Lanoix. "Evidence for dark matter on different scales from the KLUN galaxy sample." International Astronomical Union Colloquium 174 (2000): 457–61. http://dx.doi.org/10.1017/s0252921100055457.

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The KLUN (Kinematics of the Local UNiverse) sample of 6600 spiral galaxies is used in studying dark matter on different scales: •The Morphological Type dependence of the zero-point of the Tully-Fisher relation indicates mass to light ratio M/L ≈ 9 − 16 on galactic scales.•Preliminary results from a study of selection effects influencing double galaxies give a larger value M/L ≈ 30 − 50.•Study of the Perseus-Pisces supercluster, using Malmquist bias corrected TF distances and Tolman-Bondi solutions indicates M/L ≈ 200 − 600 for large clusters. Similar results were obtained in our previous work on Virgo galaxies.•Application of a modified version of Sandage-Tammann-Hardy test of the linearity of Hubble law inside the observed hierarchical (fractal) galaxy distribution up to 200 Mpc suggests that either Ω0 is very small (0.01) or the major part of the matter is uniformly distributed dark matter.
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34

Kim, Do Young, Anthony N. Lasenby, and Michael P. Hobson. "An alternative approach to modelling a cosmic void and its effect on the cosmic microwave background." Monthly Notices of the Royal Astronomical Society 488, no. 3 (July 22, 2019): 4081–92. http://dx.doi.org/10.1093/mnras/stz1979.

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ABSTRACT We apply our tetrad-based approach for constructing spherically symmetric solutions in general relativity to modelling a void, and compare it with the standard Lemaître–Tolman–Bondi (LTB) formalism. In particular, we highlight the importance of considering the velocity as well as the density profile in constraining voids. We apply our approach to construct models for the void observed in the direction of Draco in the WISE–2MASS galaxy survey, and a corresponding cosmic microwave background (CMB) temperature decrement in the Planck data in the same direction. We find that the present-day density and velocity profiles of the void are not well constrained by the existing data, so that void models produced from the two approaches can differ substantially while remaining broadly consistent with the observations. We repeat our analysis to construct void models for the CMB Cold Spot, but show that although a single void can account for the WISE–2MASS galaxy survey data, it is not capable of producing a CMB temperature decrement sufficiently deep to be consistent with Planck CMB data.
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35

Bellino, Vito Flavio, and Giampiero Esposito. "Fractional linear maps in general relativity and quantum mechanics." International Journal of Geometric Methods in Modern Physics 18, no. 10 (June 24, 2021): 2150157. http://dx.doi.org/10.1142/s0219887821501577.

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This paper studies the nature of fractional linear transformations in a general relativity context as well as in a quantum theoretical framework. Two features are found to deserve special attention: the first is the possibility of separating the limit-point condition at infinity into loxodromic, hyperbolic, parabolic and elliptic cases. This is useful in a context in which one wants to look for a correspondence between essentially self-adjoint spherically symmetric Hamiltonians of quantum physics and the theory of Bondi–Metzner–Sachs transformations in general relativity. The analogy therefore arising suggests that further investigations might be performed for a theory in which the role of fractional linear maps is viewed as a bridge between the quantum theory and general relativity. The second aspect to point out is the possibility of interpreting the limit-point condition at both ends of the positive real line, for a second-order singular differential operator, which occurs frequently in applied quantum mechanics, as the limiting procedure arising from a very particular Kleinian group which is the hyperbolic cyclic group. In this framework, this work finds that a consistent system of equations can be derived and studied. Hence, one is led to consider the entire transcendental functions, from which it is possible to construct a fundamental system of solutions of a second-order differential equation with singular behavior at both ends of the positive real line, which in turn satisfy the limit-point conditions. Further developments in this direction might also be obtained by constructing a fundamental system of solutions and then deriving the differential equation whose solutions are the independent system first obtained. This guarantees two important properties at the same time: the essential self-adjointness of a second-order differential operator and the existence of a conserved quantity which is an automorphic function for the cyclic group chosen.
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36

Arnau i Córdoba, Josep Vicent, and Màrius Josep Fullana i Alfonso. "Resolution of Initial Value Problems of Ordinary Differential Equations Systems." Mathematics 10, no. 4 (February 14, 2022): 593. http://dx.doi.org/10.3390/math10040593.

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In this work, we present some techniques applicable to Initial Value Problems when solving a System of Ordinary Differential Equations (ODE). Such techniques should be used when applying adaptive step-size numerical methods. In our case, a Runge-Kutta-Fehlberg algorithm (RKF45) has been employed, but the procedure presented here can also be applied to other adaptive methods, such as N-body problems, as AP3M or similar ones. By doing so, catastrophic cancellations were eliminated. A mathematical optimization was carried out by introducing the objective function in the ODE System (ODES). Resizing of local errors was also utilised in order to adress the problem. This resize implies the use of certain variables to adjust the integration step while the other variables are used as parameters to determine the coefficients of the ODE system. This resize was executed by using the asymptotic solution of this system. The change of variables is necessary to guarantee the stability of the integration. Therefore, the linearization of the ODES is possible and can be used as a powerful control test. All these tools are applied to a physical problem. The example we present here is the effective numerical resolution of Lemaitre-Tolman-Bondi space-time solutions of Einstein Equations.
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YOO, JAEWON, and YUKI WATANABE. "THEORETICAL MODELS OF DARK ENERGY." International Journal of Modern Physics D 21, no. 12 (November 2012): 1230002. http://dx.doi.org/10.1142/s0218271812300029.

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Mounting observational data confirm that about 73% of the energy density consists of dark energy which is responsible for the current accelerated expansion of the Universe. We present observational evidences and dark energy projects. We then review various theoretical ideas that have been proposed to explain the origin of dark energy; they contain the cosmological constant, modified matter models, modified gravity models and the inhomogeneous model. The cosmological constant suffers from two major problems: one regarding fine-tuning and the other regarding coincidence. To solve them there arose modified matter models such as quintessence, k-essence, coupled dark energy and unified dark energy. We compare those models by presenting attractive aspects, new rising problems and possible solutions. Furthermore, we review modified gravity models that lead to late-time accelerated expansion without invoking a new form of dark energy; they contain f(R) gravity and the Dvali–Gabadadze–Porrati (DGP) model. We also discuss observational constraints on those models and on future modified gravity theories. Finally we review the inhomogeneous Lemaître–Tolman–Bondi (LTB) model that drops an assumption of the spatial homogeneity of the Universe. We also present basics of cosmology and scalar field theory, which are useful especially for students and novices to understand dark energy models.
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38

Ranjbar, Razieh, and Shahram Abbassi. "Slowly Rotating Accretion Flow Around Supermassive Black Holes in Elliptical Galaxies: Case With Outflow." Astrophysical Journal 954, no. 2 (August 28, 2023): 117. http://dx.doi.org/10.3847/1538-4357/ace163.

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Abstract Observational evidence and many numerical simulations show the existence of winds (i.e., uncollimated outflows) in the accretion systems of elliptical galaxy centers. One of the primary aims of this study is to investigate the solutions of slowly rotating accretion flows around supermassive black holes with outflows. This paper presents two distinct physical regions, supersonic and subsonic, which extend from the outer boundary to the black hole. In our numerical solution, the outer boundary is chosen beyond the Bondi radius. Due to strong gravity, we ignore outflow (i.e., s = 0) in the inner region (within ∼10r s ). The radial velocity of the flow at the outer region is significantly increased due to the presence of the outflow. Compared to previous works, the accretion mode, namely, the slowly rotating case, that corresponds to low accretion rates that have general wind output is carefully described, and the effect of the galaxy potential and feedback by the wind in this mode are taken into account. As the power-law form of the mass accretion rate is mathematically compatible with our equations, we consider a radius-dependent mass accretion rate ( M ̇ in ∝ r s ), where s is a free parameter and shows the intensity of outflow. There is an unknown mechanism for removing the mass, angular momentum, and energy by outflows in this study. The effects of the outflow appear well on the outer edge of the flow.
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39

Ganelin, Aleksandr E. "Early 20th Century Studio and Theatre Innovations of Vs. E. Meyerhold and S. E. Radlov." Vestnik of Saint Petersburg University. Arts 11, no. 3 (2021): 393–409. http://dx.doi.org/10.21638/spbu15.2021.303.

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The experience of the pedagogical work of the Studio Vsevolod Meyerhold on Borodinskaya Street (1914–1917) to a large extent can be considered one of the important sources of the methodological and pedagogical model inherent in the modern Leningrad — Petersburg theatre school. The education principles of the synthetic actor and director, developed within the studio, combined innovations in the work of teachers and their students both at individual stages of the pedagogical process and on the path to creating a “new” theatre, in a broad understanding of this phenomenon of cultural life at the beginning of the XX century. The unique theatre school-studio became an autonomous art structure, independent of the staffing and financial demands of repertoire and private theatres that studios during this period experienced. For Meyerhold and other teachers of the Studio, particularly, Vladimir Solov’ev, a top priority was reviving the stage technique commedia dell’arte. The student plays of the studio fully reflected the undoubted successes and, naturally, the vulnerabilities inherent in such innovative searches. The article analyzes the detailed list of stylistic, mise-en-scenic and decoration production solutions proposed by Meyerhold and Yuri Bondi, the opportunity to improvise in a pre-prepared directorial plan. Sergei Radlov, a participant in the Studio at Borodinskaya, continued his creative search in the approach proposed by Meyerhold for the development of an improvisational synthetic theatre. Radlov’s directorial and pedagogical work in the studios of Kurmascep, “Popular comedy” (Narodnaya Comediya), etc., at the Institute (later Technical School) of stage arts deserves additional consideration in terms of the scientific analysis of the evolution of his innovative views at the beginning of the century and their interconnection with traditional approaches to theater education and stage practice of those years.
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40

Tchuindjo, Leonard. "Closed-form solutions for pricing credit-risky bonds and bond options." Applied Mathematics and Computation 217, no. 13 (March 2011): 6133–43. http://dx.doi.org/10.1016/j.amc.2010.12.092.

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41

Larguinho, Manuela, José Carlos Dias, and Carlos A. Braumann. "Pricing and hedging bond options and sinking-fund bonds under the CIR model." Quantitative Finance and Economics 6, no. 1 (2022): 1–34. http://dx.doi.org/10.3934/qfe.2022001.

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<abstract><p>This article derives simple closed-form solutions for computing Greeks of zero-coupon and coupon-bearing bond options under the CIR interest rate model, which are shown to be accurate, easy to implement, and computationally highly efficient. These novel analytical solutions allow us to extend the literature in two other directions. First, the static hedging portfolio approach is used for pricing and hedging American-style plain-vanilla zero-coupon bond options under the CIR model. Second, we derive analytically the comparative static properties of sinking-fund bonds under the same interest rate modeling setup.</p></abstract>
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42

Korkina, M. P., and E. M. Kopteva. "Generalization of Tolman–Bondi solution." Astronomical School’s Report 8, no. 1 (2012): 31–33. http://dx.doi.org/10.18372/2411-6602.08.1031.

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43

Naoki, Motosuke, and Takuma Seki. "Hydrogen-bond configuration in hydrogen-bond solutions. 1. Alcohol/alcohol solutions." Fluid Phase Equilibria 281, no. 2 (July 2009): 172–85. http://dx.doi.org/10.1016/j.fluid.2009.04.004.

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44

Baksi, Atanu, and Ranjit Biswas. "Dynamical Anomaly of Aqueous Amphiphilic Solutions: Connection to Solution H-Bond Fluctuation Dynamics?" ACS Omega 7, no. 13 (March 28, 2022): 10970–84. http://dx.doi.org/10.1021/acsomega.1c06831.

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45

Kostjukov, V., S. Leontieva, E. Savchenko, K. Rybakova, and D. Voronin. "PHOTOEXCITATION OF NILE BLUE DYE IN AQUEOUS SOLUTION: TD-DFT STUDY." Russian Journal of Biological Physics and Chemisrty 7, no. 2 (November 15, 2022): 209–21. http://dx.doi.org/10.29039/rusjbpc.2022.0505.

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The vibronic absorption spectra of Nile blue (NB) oxazine dye in an aqueous solution using 13 hybrid functionals, the 6-31++G(d,p) basis set, and the IEFPCM solvent model were calculated. It turned out that the O3LYP functional provided the best agreement with the experiment. Various parameters of the NB cation in the ground and excited states (IR spectra, atomic charges, dipole moments, and transition moment) were obtained. Maps of the distribution of electron density and electrostatic potential have been built. The influence of four strong hydrogen bonds of the dye with water molecules on the absorption spectrum was analyzed. It has been shown that two from these bonds were strengthened upon NB excitation and two ones were weakened. It was found that explicit assignment of water molecules strongly bound to the dye leads to a redshift of the spectrum as a whole and worsened its shape.
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46

Berg, T. G. Owe. "BONDS IN WATER AND AQUEOUS SOLUTIONS." Annals of the New York Academy of Sciences 125, no. 2 (December 16, 2006): 298–316. http://dx.doi.org/10.1111/j.1749-6632.1965.tb45399.x.

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47

Matsuda, Takuya, Hiromu Isaka, and Yukimasa Ohsugi. "Bondi–Hoyle–Lyttleton accretion flow revisited: Analytic solution." Progress of Theoretical and Experimental Physics 2015, no. 11 (November 2015): 113E01. http://dx.doi.org/10.1093/ptep/ptv148.

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48

Asmussen, E., and R. L. Bowen. "Effect of Acidic Pretreatment on Adhesion to Dentin Mediated by Gluma." Journal of Dental Research 66, no. 8 (August 1987): 1386–88. http://dx.doi.org/10.1177/00220345870660082001.

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Tensile bond strengths between dentin and a typical restorative resin were measured after the dentin was treated with Gluma. Solutions of phosphoric, pyruvic, nitric, or oxalic acid, also containing various amino acids, were used as pretreatments. Without amino acids in the solutions, the pretreatments conferred bonds of low strength. Use of acidic solutions containing glycine or N-phenylglycine was found to give bonds of high strength to both dentin and enamel.
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49

Liu, Zhang, Huang, Wu, and Ouyang. "Raman Spectroscopy for the Competition of Hydrogen Bonds in Ternary (H2O–THF–DMSO) Aqueous Solutions." Molecules 24, no. 20 (October 11, 2019): 3666. http://dx.doi.org/10.3390/molecules24203666.

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The effects of hydrogen bonds on the molecular structure of water-tetrahydrofuran (H2O–THF), water-dimethyl sulfoxide (H2O–DMSO), and water-tetrahydrofuran-dimethyl sulfoxide (H2O–THF–DMSO) in binary aqueous solutions and ternary aqueous solutions were studied using Raman spectroscopy. The results indicate that in the binary aqueous solution, the addition of THF and DMSO will generate hydrogen bonds with water molecules, resulting in changes in the peak positions of S=O bonds and C–O bonds. Compared with the binary aqueous solutions, the hydrogen bonds between DMSO and THF, and the hydrogen bonds between DMSO and H2O in the ternary aqueous solutions are competitive, and the hydrogen bond competition is susceptible to water content. In addition, the formation of hydrogen bonds will destroy the fully hydrogen-bonded water and make it change to the partially hydrogen-bonded water. By fitting the spectra into the three Gaussian components assigned to water molecules with different hydrogen bonding (HB) environments, these spectral features are interpreted by a mechanism that H2O in different solution systems has equal types of water molecules with similar HB degrees-fully hydrogen-bonded H2O (FHW) and partially hydrogen-bonded H2O (PHW). The ratio of the intensity transition from FHW to PHW is determined based on Gaussian fitting. Therefore, the variation of hydrogen bond competition can be supplemented by the intensity ratio of PHW/FHW ((IC2 + IC3)/IC1). This study provides an experimental basis for enriching the hydrogen bonding theory of multivariate aqueous solution systems.
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50

Kulkarni, Preeti, and Meghna Vandekar. "Bond reliably-difficult areas... Easy solutions !!" APOS Trends in Orthodontics 2, no. 2 (2012): 5. http://dx.doi.org/10.4103/2321-1407.118182.

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