CLOUDY is a large‐scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. Here we describe version 90 (C90) of the code, paying particular attention to changes in the atomic database and numerical methods that have affected predictions since the last publicly available version, C84. The computational methods and uncertainties are outlined together with the direction future development will take. The code is freely available and is widely used in the analysis and interpretation of emission‐line spectra. Web access to the Fortran source for CLOUDY, its documentation Hazy, and an independent electronic form of the atomic database is also described.

https://iopscience.iop.org/article/10.1086/316190/pdf

CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra

羟氨苄青霉素引起大疱性类天疱疮样疹

Advances in atomic physics, such as cooling and trapping of atoms and molecules and developments in frequency metrology, have added orders of magnitude to the precision of atom-based clocks and sensors. Applications extend beyond atomic physics and this article reviews using these new techniques to address important challenges in physics and to look for variations in the fundamental constants, search for interactions beyond the standard model of particle physics, and test the principles of general relativity.

Search for New Physics with Atoms and Molecules

ABSTRACT CLOUDY is a large‐scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. Here we describe version 90 (C90) of the code, paying particular attention to changes in the atomic database and numerical methods that have affected predictions since the last publicly available version, C84. The computational methods and uncertainties are outlined together with the direction future development will take. The code is freely available and is widely used in the analysis and interpretation of emission‐line spectra. Web access to the Fortran source for CLOUDY, its documentation Hazy, and an independent electronic form of the atomic database is also described.

Cloudy: Numerical simulation of plasmas and their spectra

We introduce a new technique for following the formation and evolution of galaxies in cosmological N-body simulations. Dissipationless simulations are used to track the formation and merging of dark matter haloes as a function of redshift. Simple prescriptions, taken directly from semi-analytic models of galaxy formation, are adopted for gas cooling, star formation, supernova feedback and the merging of galaxies within the haloes. This scheme enables us to explore the clustering properties of galaxies, and to investigate how selection by luminosity, colour or type influences the results. In this paper we study the properties of the galaxy distribution at z=0. These include B- and K-band luminosity functions, two-point correlation functions, pairwise peculiar velocities, cluster mass-to-light ratios, B-V colours, and star formation rates. We focus on two variants of a cold dark matter (CDM) cosmology: a high-density (Ω =1) model with shape-parameter Γ =0.21 (τ CDM), and a low-density model with Ω =0.3 and Λ =0.7 (Λ CDM). Both models are normalized to reproduce the I-band Tully--Fisher relation of Giovanelli et al. near a circular velocity of 220 km s-1. Our results depend strongly both on this normalization and on the adopted prescriptions for star formation and feedback. Very different assumptions are required to obtain an acceptable model in the two cases. For τ CDM, efficient feedback is required to suppress the growth of galaxies, particularly in low-mass field haloes. Without it, there are too many galaxies and the correlation function exhibits a strong turnover on scales below 1 Mpc. For Λ CDM, feedback must be weaker, otherwise too few L* galaxies are produced and the correlation function is too steep. Although neither model is perfect, both come close to reproducing most of the data. Given the uncertainties in modelling some of the critical physical processes, we conclude that it is not yet possible to draw firm conclusions about the values of cosmological parameters from studies of this kind. Further observational work on global star formation and feedback effects is required to narrow the range of possibilities.

Clustering of galaxies in a hierarchical universe - I. Methods and results at z=0

The method of complex-coordinate rotation is applied to investigate resonances in positron scattering by helium ions. Here we present results for high-angular-momentum states $(L=2--6).$ Together with the earlier values for the $L=0$ and 1 states, these stabilized complex eigenvalues exhibit a regular pattern. We also calculate some narrow S-wave resonances below the excited positronium $(N=2)$ threshold. Our converged results for the first S state lying above the ${\mathrm{He}}^{+}$ $(n=5)$ threshold differ substantially from the calculation by Igarashi and Shimamura [Phys. Rev. A 56, 4733 (1997)].

High-angular-momentum resonances in positron scattering by a He + ion

S-wave phase shifts for the positron-helium elastic scattering problem are presented in the coupled static approximation ( i.e. the trial function contains the ground states of both the target atom and positronium but no other terms). Various models of the target atom wavefunction are employed, two of which confirm qualitatively the marked effect on the results as reported by Wardle (1973) for these models. While none of the target models used in this approximation appears to lead to an adequate description of the system, as is also the case in positron-hydrogen scattering in the same approximation, a qualitative comparison of the best results presented here and the corresponding approximation in the hydrogen case suggests a manageable calculation with two open channels (i.e. with real positronium formation) could produce meaningful results.

The S-wave elastic scattering of positrons by helium in the coupled static approximation

In this work, we study the quantum entanglement for doubly excited resonance states in helium by using highly correlated Hylleraas type functions to represent such states of the two-electron system. The doubly-excited resonance states are determined by calculation of density of resonance states under the framework of the stabilization method. The spatial (electron–electron orbital) entanglement measures for the low-lying doubly excited 2s
 2, 2s3s, and 2p
 2
 1
 S
 e
 states are carried out. Once a resonance state wave function is obtained, the linear entropy and von Neumann entropy for such a state are quantified using the Schmidt-Slater decomposition method. To check the consistence, linear entropy is also determined by solving analytically the needed four-electron (12-dimensional) integrals.

Quantification of Entanglement Entropies for Doubly Excited States in Helium

The critical nuclear charge ${Z}_{c}$ of the two-electron atoms below which the ground state transforms into a shape resonance and the critical stability of the system around ${Z}_{c}$ have been well established. However, the behavior of the shape resonance below ${Z}_{c}$ is still a mystery. By employing the complex-scaling method using Hylleraas configuration-interaction basis functions, we trace the trajectory of the shape resonance from ${Z}_{c}$ down to a very small nuclear charge. It is shown that at specific values of $Z$ far below ${Z}_{c}$ the resonance crosses over higher-lying one-electron thresholds, and when $Z$ is decreased below 0.316, the shape resonance lies above the three-body breakup threshold. We finally show that the imaginary part of the resonance energy at small nuclear charges can be modeled by the dispersion relation with a high-order Pad\'e approximant correction. 

Bound and resonance states near the critical charge region in two-electron atoms

The effect of Yukawa potentials on the bound states and resonance states for systems with three self-gravitating bosons and fermions has been investigated using highly correlated basis functions. The complex coordinate rotation method is used to extract resonance parameters. We have investigated the Borromean binding for such systems. The ground and excited state energies, resonance energy and width for the lowest two resonances are reported for different screening parameters along with the critical range for Borromean binding.

Bound states and resonant states of three self-gravitating Bose-Einstein condensates

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