Academic literature on the topic 'Plummer Model'

SYNOPSIS The Governmental Accounting Standards Board issued Statement No. 34, creating a new accrual-based financial reporting model. This study examines whether information from this model is associated with the default risk (a proxy for fiscal distress) of municipal governments and whether this information is incremental to that provided by the fund-based, modified-accrual reporting model. Ordered logistic regressions are used to analyze financial data from 2005 for a sample of 409 municipalities that participated in the Government Finance Officers Association award program. This study extends the work of Plummer et al. (2007) to municipal governments. In addition to the financial position indicator variable (total net assets/total revenues) examined by Plummer et al. (2007), this study provides evidence of the relevance of three other financial indicators (change in net assets/total net assets; total liabilities/total assets; and current assets/current liabilities). We also find that these accrual-based indicators provide information incremental to the fund-based model and that one fund-based measure (total fund balances/total fund revenues) also provides information incremental to the accrual indicator. These results are consistent with perceptions of regulators and others who expect accrual accounting to be a better measure of the economic costs of running a government than the traditional fund-based model. Data Availability: Contact the authors.

We investigated how the encounters between galaxies change their mass M and velocity dispersion σ. We carried out a series of direct N-body simulation of encounters of two spherical galaxies. In Figure 1, the relative change of energy ΔE/E are plotted against that of mass ΔM/M for various initial conditions. The filled and open symbols correspond to the cases of Plummer model and relaxed Hernquist model, respectively. Here β ≡ (ΔE/E)/(ΔM/M).

The aim of this work is to find a progenitor for Canes Venatici I (CVn I), under the assumption that it is a dark matter free object that is undergoing tidal disruption. With a simple point mass integrator, we searched for an orbit for this galaxy using its current position, position angle, and radial velocity in the sky as constraints. The orbit that gives the best results has the pair of proper motions μα = −0.099 mas yr−1 and μδ = −0.147 mas yr−1, that is, an apogalactic distance of 242.79 kpc and a perigalactic distance of 20.01 kpc. Using a dark matter free progenitor that undergoes tidal disruption, the best-fitting model matches the final mass, surface brightness, effective radius, and velocity dispersion of CVn I simultaneously. This model has an initial Plummer mass of 2.47 × 107 M⊙ and a Plummer radius of 653 pc, producing a remnant after 10 Gyr with a final mass of 2.45 × 105 M⊙, a central surface brightness of 26.9 mag arcsec−2, an effective radius of 545.7 pc, and a velocity dispersion with the value 7.58 km s−1. Furthermore, it is matching the position angle and ellipticity of the projected object in the sky.

A model of mass distribution, applicable to globular star clusters and proposed earlier, is reconsidered. It is shown that it can be related to the well-known Plummer-Schuster formula, and the equations yielding its dimensionless parameters are given. The corresponding surface density is calculated numerically. It is indicated that in a general case the surface density should not be proportional to the surface brightness and a more adequate formula relating these two quantities is proposed. .

Scholars have defined economic abuse (EA) as tactics used by abusive partners to undermine the self-sufficiency and economic self-efficacy of survivors of intimate partner violence (IPV). However, no measures of EA have been tested in non-IPV-service seeking samples. The current study assesses the psychometric properties of the Scale of Economic Abuse (SEA)-12 (Postmus, Plummer, & Stylianou, 2016) in a nonservice seeking sample of adult females attending community college. A quantitative web-based survey was administered to a simple random sample of female community college students (n = 435). Analyses included confirmatory factor analysis (CFA) and exploratory factor analysis (EFA). CFA indicated a poor fit for the three-factor model of the SEA-12 in this sample. The results of the EFA found a single factor model retaining four items (the Scale of Economic Abuse-Short, or SEAS). Women are experiencing EA outside of IPV service-seeking populations, and that tactics of economic control seem to be central to EA in this sample.

We present calculations of globular cluster evolution performed by a modified Fokker-Planck approach, in which binaries formed by tidal capture are followed explicitly, along with subsequent heating mechanisms. The cluster is simulated by a two component model, using the cross sections of Press and Teukolsky (1977) for tidal capture, those of Hut (1984) for the single-binary encounters and for distant binary-binary encounters, and those of Mikkola (1983) for the strong binary-binary encounters. The initial state of the cluster is a Plummer model with N = 3 × 105 and scale radius ro = 1.13 pc. All stars are identical, with mass M∗ = 0.7M⊙ and R∗ = 0.57R⊙. This gives an initial core radius rc = 0.8 pc, and one-dimensional dispersion σ = 11.6 km s-1. All binaries are assumed to be identical, with separation a = 2.5R∗. There are no binaries in the cluster initially. Additional important effects, such as tidal truncation, tidal shocks, stellar evolution and mass loss, and stellar mergers, are not included.

Simple but flexible dynamical models are useful for many purposes, including serving as the starting point for more complex models or numerical simulations of galaxies, clusters, or dark matter haloes. We present SpheCow, a new light-weight and flexible code that allows one to easily explore the structure and dynamics of any spherical model. Assuming an isotropic or Osipkov-Merritt anisotropic orbital structure, the code can automatically calculate the dynamical properties of any model with either an analytical density profile or an analytical surface density profile as starting point. We have extensively validated SpheCow using a combination of comparisons to analytical and high-precision numerical calculations, as well as the calculation of inverse formulae. SpheCow contains readily usable implementations for many standard models, including the Plummer, Hernquist, NFW, Einasto, Sérsic, and Nuker models. The code is publicly available as a set of C++ routines and as a Python module, and it is designed to be easily extendable, in the sense that new models can be added in a straightforward way. We demonstrate this by adding two new families of models in which either the density slope or the surface density slope is described by an algebraic sigmoid function. We advocate the use of the SpheCow code to investigate the full dynamical structure for models for which the distribution function cannot be expressed analytically and to explore a much wider range of models than is possible using analytical models alone.

An entrainment model for lazy turbulent plumes is proposed, the resulting solutions of the plume conservation equations are developed and the implications for plume behaviour are considered and compared with the available experimental data. Indeed, the applicability of the classic solutions of the conservation equations subject to source conditions that produce lazy plumes, i.e. those with suitably high source Richardson number, contains an essential weakness: the underlying assumption of a constant entrainment coefficient. While entrainment models prescribing the dependence of the entrainment coefficient on the local Richardson number have been proposed for forced plumes, corresponding formulations for lazy plumes have not until now been considered. In the context of saline plumes, the model is applied directly. For hot gaseous plumes, we use a modified definition of buoyancy flux to recover a constant buoyancy flux in a non-stratified environment, despite the specific heat varying with the temperature. After a brief review of existing forced-plume formulations of entrainment, a power-law variation is adopted for the lazy plume. The plume equations are solved for the parameter $0\leqslant \unicode[STIX]{x1D714}<1$, where $\unicode[STIX]{x1D714}$ denotes the exponent of the power law. The cases of pure plumes and lazy plumes are then analysed in more detail; to the best of our knowledge this represents the first modelling of variable entrainment for lazy plumes. Specifically, it is shown that classic plume theory is recovered for $\unicode[STIX]{x1D714}=0$, while for $\unicode[STIX]{x1D714}=1/5$ the plume equations may be solved using usual functions (notably polynomials) only. The results of the models for these cases are very similar, which advocates the idea of selecting systematically $\unicode[STIX]{x1D714}=1/5$, instead of $\unicode[STIX]{x1D714}=0$, for cases where the effect of variation of entrainment is weak, since the new model leads to simple calculations. In the case of very lazy plumes, it is shown that, provided that a relevant value of $\unicode[STIX]{x1D714}$ is chosen, the new model reproduces the available experimental results well.