Natural history and propagation of fresh-water mussels

Clark, H. W.; Coker, R. E.; Howard, A. D.; Shira, A. F.

doi:10.5962/bhl.title.33960

Cited by 60 publications

(72 citation statements)

References 3 publications

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“…Furthermore, their total mass-loss rate from the young stars is higher than ours by a factor of 3. If we take these differences into account, our simulation with the smallest capture radius and 40 fixed stars appears to be consistent with the results of Coker & Melia (1997). Finally, the work of Rockefeller et al (2004) did not directly focus on the accretion on to Sgr A * .…”

Section: Fixed Starssupporting

confidence: 76%

“…We find that our derived accretion rate values are about one order of magnitude lower than those of Coker & Melia (1997). The differences, however, are due to a different physical setup rather than to numerics.…”

Section: Fixed Starsmentioning

confidence: 53%

“…The differences, however, are due to a different physical setup rather than to numerics. Coker & Melia (1997) used v w = 700 km s −1 , whereas we used v w = 1000 km s −1 here. This difference in wind velocity alone accounts for a factor of ≈3 difference inṀ BH .…”

Section: Fixed Starsmentioning

confidence: 99%

“…The first 3D numerical simulations of Sgr A * wind accretion were performed by Ruffert & Melia (1994), who studied feeding the black hole from a uniform large-scale gas flow. This work was extended by Coker & Melia (1997), who used discrete gas sources (10 mass-losing stars semi-randomly positioned a few arcseconds away from Sgr A * ) to model the wind emission. Owing to the numerical difficulties inherent to fixed grid codes, the orbital motions of the stars could not be followed, and thus they were fixed in space.…”

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confidence: 99%

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Galactic Centre stellar winds and Sgr A* accretion

Cuadra

Nayakshin

Springel

et al. 2006

Monthly Notices of the Royal Astronomical Society

156

173

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(ABRIDGED) We present in detail our new 3D numerical models for the accretion of stellar winds on to Sgr A*. In our most sophisticated models, we put stars on realistic orbits around Sgr A*, include `slow' winds (300 km/s), and account for radiative cooling. We first model only one phase `fast' stellar winds (1000 km/s). For wind sources fixed in space, the accretion rate is Mdot ~ 1e-5 Msun/yr, fluctuates by < 10%, and is in a good agreement with previous models. In contrast, Mdot decreases by an order of magnitude for stars following circular orbits, and fluctuates by ~ 50%. Then we allow a fraction of stars to produce slow winds. Much of these winds cool radiatively, forming cold clumps immersed into the X-ray emitting gas. We test two orbital configurations for the stars in this scenario, an isotropic distribution and two rotating discs with perpendicular orientation. The morphology of cold gas is quite sensitive to the orbits. In both cases, however, most of the accreted gas is hot, with an almost constant Mdot ~ 3e-6 Msun/yr, consistent with Chandra observations. The cold gas accretes in intermittent, short but powerful episodes which may give rise to large amplitude variability in the luminosity of Sgr A* on time scales of 10s to 100s of years. The circularisation radii for the flows are ~ 1e3 and 1e4 Rsch, for the one and two-phase wind simulations, respectively, never forming the quasi-spherical accretion flows suggested in some previous work. Our work suggests that, averaged over time scales of 100s to 1000s of years, the radiative and mechanical luminosity of Sgr A* may be substantially higher than it is in its current state. Further improvements of the wind accretion modelling of Sgr A* will rely on improved observational constraints for the wind properties and stellar orbits.Comment: 16 pages, 18 colour figures. Accepted by MNRAS. Full resolution paper and movies available at http://www.mpa-garching.mpg.de/~jcuadra/Winds/ . (v2: minor changes

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Section: Fixed Starssupporting

confidence: 76%

Section: Fixed Starsmentioning

confidence: 53%

Section: Fixed Starsmentioning

confidence: 99%

mentioning

confidence: 99%

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Galactic Centre stellar winds and Sgr A* accretion

Cuadra

Nayakshin

Springel

et al. 2006

Monthly Notices of the Royal Astronomical Society

156

173

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“…To this end, several MQC molecular-dynamics ͑MD͒ algorithms for studying condensed-phase nonadiabatic dynamics have been developed over the last 15 years. [1][2][3][4][5][6][7][8][9][10][11] states produce unphysical dynamics for the classical particles, leading to apparent paradoxes such as "Schrödinger's Cat." 12 Thus, in the asymptotic limit, only pure quantum states are consistent with the presence of classical particles.…”

Section: Introductionmentioning

confidence: 99%

Mean-field dynamics with stochastic decoherence (MF-SD): A new algorithm for nonadiabatic mixed quantum/classical molecular-dynamics simulations with nuclear-induced decoherence

Bedard-Hearn¹,

Larsen²,

Schwartz³

2005

The Journal of Chemical Physics

195

212

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The key factors that distinguish algorithms for nonadiabatic mixed quantum/classical ͑MQC͒ simulations from each other are how they incorporate quantum decoherence-the fact that classical nuclei must eventually cause a quantum superposition state to collapse into a pure state-and how they model the effects of decoherence on the quantum and classical subsystems. Most algorithms use distinct mechanisms for modeling nonadiabatic transitions between pure quantum basis states ͑"surface hops"͒ and for calculating the loss of quantum-mechanical phase information ͑e.g., the decay of the off-diagonal elements of the density matrix͒. In our view, however, both processes should be unified in a single description of decoherence. In this paper, we start from the density matrix of the total system and use the frozen Gaussian approximation for the nuclear wave function to derive a nuclear-induced decoherence rate for the electronic degrees of freedom. We then use this decoherence rate as the basis for a new nonadiabatic MQC molecular-dynamics ͑MD͒ algorithm, which we call mean-field dynamics with stochastic decoherence ͑MF-SD͒. MF-SD begins by evolving the quantum subsystem according to the time-dependent Schrödinger equation, leading to mean-field dynamics. MF-SD then uses the nuclear-induced decoherence rate to determine stochastically at each time step whether the system remains in a coherent mixed state or decoheres. Once it is determined that the system should decohere, the quantum subsystem undergoes an instantaneous total wave-function collapse onto one of the adiabatic basis states and the classical velocities are adjusted to conserve energy. Thus, MF-SD combines surface hops and decoherence into a single idea: decoherence in MF-SD does not require the artificial introduction of reference states, auxiliary trajectories, or trajectory swarms, which also makes MF-SD much more computationally efficient than other nonadiabatic MQC MD algorithms. The unified definition of decoherence in MF-SD requires only a single ad hoc parameter, which is not adjustable but instead is determined by the spatial extent of the nonadiabatic coupling. We use MF-SD to solve a series of one-dimensional scattering problems and find that MF-SD is as quantitatively accurate as several existing nonadiabatic MQC MD algorithms and significantly more accurate for some problems.

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Correlation between intramolecular bond distances and stretching vibrations for polar molecules: An ab initio study

Hermansson

Probst

1997

Int. J. Quant. Chem.

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ABSTRACT:The correlation between intramolecular bond length and vibrational Ž . frequency shifts was calculated at the MP4 aug-cc-PVTZ ab initio level for a number of Ž y y . molecules LiH, BH, HF, OH , HDO, BF, CN , and HCl exposed to uniform electric fields in the range from y0.10 to q0.10 au. The '' vs. r '' correlation curves always e consist of two branches, each approximately linear. The slopes for the molecules y1i nvestigated here vary between y2500 and y16600 cm rA. The slopes are well described by an expression containing only the free-molecule second-and third-order force constants and the reduced mass for the stretching mode. Experimental data for polar molecules can be expected to show deviations from a linear '' vs. r '' correlation e Ž .i for molecules where the maximum of the frequency vs. field curve occurs at a positive Ž . field and ii for molecules where the maximum of the frequency vs. field curve falls on Ž . the negative-field side but very close to the zero-field case, and iii in bonding situations when there is much electron overlap. As opposed to uniform-field situations, anharmonicity and electronic overlap have a substantial influence on the ''frequency vs. r '' slopes in molecular environments.

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Natural history and propagation of fresh-water mussels

Cited by 60 publications

References 3 publications

Galactic Centre stellar winds and Sgr A* accretion

Galactic Centre stellar winds and Sgr A* accretion

Mean-field dynamics with stochastic decoherence (MF-SD): A new algorithm for nonadiabatic mixed quantum/classical molecular-dynamics simulations with nuclear-induced decoherence

Correlation between intramolecular bond distances and stretching vibrations for polar molecules: An ab initio study

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