2D vector field simplification based on robustness

pre-printVector field simplification aims to reduce the complexity of the flow by removing features in order of their relevance and importance, to reveal prominent behavior and obtain a compact representation for interpretation. Most existing simplification techniques based on the topological skeleton successively remove pairs of critical points connected by separatrices, using distance or area-based relevance measures. These methods rely on the stable extraction of the topological skeleton, which can be difficult due to instability in numerical integration, especially when processing highly rotational flows. These geometric metrics do not consider the flow magnitude, an important physical property of the flow. In this paper, we propose a novel simplification scheme derived from the recently introduced topological notion of robustness, which provides a complementary view on flow structure compared to the traditional topological-skeleton-based approaches. Robustness enables the pruning of sets of critical points according to a quantitative measure of their stability, that is, the minimum amount of vector field perturbation required to remove them. This leads to a hierarchical simplification scheme that encodes flow magnitude in its perturbation metric. Our novel simplification algorithm is based on degree theory, has fewer boundary restrictions, and so can handle more general cases. Finally, we provide an implementation under the piecewise-linear setting and apply it to both synthetic and real-world datasets

Simplification of Morse Decompositions using Morse Set Mergers

Abstract. A common problem of vector field topology algorithms is the large number of the resulting topological features. This paper describes a method to simplify Morse decompositions by iteratively merging pairs of Morse sets that are adjacent in the Morse Connection Graph (MCG). When Morse sets A and B are merged, they are replaced by a single Morse set, that can be thought of as the union of A, B and all trajectories connecting A and B. Pairs of Morse sets to be merged can be picked based on a variety of criteria. For example, one can allow only pairs whose merger results in a topologically simple Morse set to be selected, and give preference to mergers leading to small Morse sets.

Simulating the interaction of galaxies and the intergalactic medium

The co-evolution of galaxies and the intergalactic medium as a function of environment is studied using hydrodynamic simulations of the ACDM cosmogony. It is demonstrated with non-radiative calculations that, in the absence of non-gravitational mechanisms, dark matter haloes accrete a near-universal fraction (~ 0.9Ω(_b)/ Ω (_m))of baryons. The absence of a mass or redshift dependence of this fraction augurs well for parameter tests that use X-ray clusters as cosmological probes. Moreover, this result indicates that non- gravitational processes must efficiently regulate the formation of stars in dark matter haloes if the halo mass function is to be reconciled with the observed galaxy luminosity function. Simulations featuring stellar evolution and non-gravitational feedback mechanisms (photo-heating by the ultraviolet background, and thermal and kinetic supemovae feedback) are used to follow the evolution of star formation, and the thermo- and chemo- dynamical evolution of baryons. The observed star formation history of the Universe is reproduced, except at low redshift where it is overestimated by a factor of a few, possibly indicating the need for feedback from active galactic nuclei to quench cooling flows around massive galaxies. The simulations more accurately reproduce the observed abundance of galaxies with late-type morphologies than has been reported elsewhere. The unique initial conditions of these simulations, based on the Millennium Simulation, allow an unprecedented study of the role of large-scale environment to be conducted. The cosmic star formation rate density is found to vary by an order of magnitude across the extremes of environment expected in the local Universe. The mass fraction of baryons in the observationally elusive warm-hot intergalactic medium (WHIM), and the volume filling factor that this gas occupies, is also shown to vary by a factor of a few across such environments. This variation is attributed to differences in the halo mass functions of the environments. Finally, we compare the X-ray properties of haloes from the simulations with the predictions of the White and Frenk (1991) analytic galaxy formation model, and demonstrate that deviations from the analytic prediction arise from the assumptions i) that haloes retain their cosmic share of baryons, and ii) their gas follows an isothermal density profile. The simulations indicate that a significant fraction of gas is ejected from low mass haloes by galactic superwinds, leading to a significant increase in their cooling time profiles and an associated drop in their soft X-ray luminosities, relative to the analytic model. Simulated X-ray luminosities remain greater than present observational upper limits, but it is argued that the observations provide only weak constraints and may suffer from a systematic bias, such that the mass of the halo hosting a given galaxy is overestimated. This bias also follows from the assumption that haloes exhibit isothermal density profiles

Allosteric Functionality In Mechanical And Flow Networks

Functionally optimized networks abound in nature, efficiently and precisely controlling the propagation of inputs to perform specific tasks. The regulation of protein activity via allostery presents one of the most well-studied examples: such proteins utilize specific conformational or dynamical changes upon the binding of ligands to facilitate communication between distant active sites. Venation networks in animals, plants, fungi and slime molds also display a type of allosteric communication, having the ability to precisely distribute oxygen and nutrients from a limited number of inputs to locally support growth and activity. Whether via genetic evolution or dynamic adaptation, many of these networks are able to create and control allosteric functionality by locally tuning interactions between nodes. Taking inspiration from this ability to regulate function, we approach allostery as a problem in metamaterials design, asking whether it is possible to create synthetic mechanical and flow networks with allosteric properties. We show that not only is this possible, but is remarkably easy, only requiring a small percentage of interactions in a network to be tuned. Leveraging the large statistical ensembles of allosteric networks generated in this way, we show that the limits of multifinctionality in both flow and mechanical networks are governed by the same constraint satisfaction phase transition, unifying both systems into a single theoretical framework. Finally, we investigate the underlying mechanisms by which allosteric function is created in flow networks. We show that the relationship between structure and function in flow networks is topological in nature, not depending on local details of the network architecture. The approaches presented in this work for studying allostery in both flow and mechanical networks set the blueprint for understanding and controlling general functional complex networks

Accounting conservatism, earnings components and accounting losses

This study provides evidence on accounting conservatism based on a large sample of publicly-quoted UK companies over the period 1969-2001. The effects of conservation accounting are studied both indirectly and directly by using earnings measures containing varying levels of accruals and by further decomposing earnings into its operating cash flows and distinct accruals components. The analyses are also separated according to the sign of earnings and earnings components, and account for the effects of asset-recognition rules. Even though conservatism is an accruals phenomenon, this is the first study to provide direct empirical evidence on the role of accruals in accounting conservatism. The thesis addresses the following issues. First, under conservative accounting, earnings-decreasing changes in performance measures (reflecting economic losses) that contain more accruals mean-revert more and earnings-increasing changes (reflecting economic gains) are persistent. Working capital accruals and special items are particularly strongly mean-reverting when they are earnings-decreasing. Depreciation accruals are persistent. Second, direct tests by earnings components show that operating cash flows exhibit low timeliness overall and, given that they contain no accruals, no asymmetry in reflecting bad news. Earnings figures with more accruals exhibit more asymmetry in reflecting bad news. Working capital accruals and special items are important in this asymmetry, but depreciation is not. Interestingly, good news results in a small earnings-decreasing charge, consistent with smoothing. Lagged tests on accruals reveal that bad news from as much as three previous periods is reflected in current earnings through special items, inconsistent with conservatism. Evidence indicates that conservatism is increasing through time. The sensitivity to good news has decreased over time. To capture these changes, higher-moments measures are developed. Third, the analysis by the sign of “bottom-line” earnings does not reveal any differences in reflecting good/bad news for the profit/loss firms. Separating earnings observations by sign of cash flow also reveals no differences. In contrast, separating observations by the sign of accruals (other than depreciation) reliably shows that the asymmetric timeliness is significantly higher in the negative-accruals groups, as expected. The accruals components determine this asymmetry, rather than the operating cash flow (or, earnings by itself). Finally, less conservative recognition rules lead to stronger responsiveness of earnings to bad news, as reflected in working capital accruals and special items. Asset-specific measures of conservative recognition rules reinforce these findings. A puzzling result is that operating cash flows reveal a significant asymmetric response to bad news in the group of observations where it is least-likely to be observed (low book to market). A selection of other results by size, industry, extremity of news, methods, accounting year-ends, market-wide returns, yields, method of estimation, etc., not only corroborates, but generally strengthens the results obtained

Auditing Symposium XII: Proceedings of the 1994 Deloitte & Touche/University of Kansas Symposium on Auditing Problems

Discussant\u27s response to The Acme Financial Statement Insurance Company Inc: A case study / Dan A. Simunic; Behavioral-economics approach to auditors\u27 risk assessments / William S. Waller; Discussant\u27s response to A Behavioral-economics approach to auditors\u27 risk assessments / Peter R. Gillett; Auditing for fraud: Perception vs reality / Alan J. Winters, John B. Sullivan; What we can learn from Yogi Berra: Discussant\u27s response to Auditing for fraud: Perception vs reality / Karen V. Pincus; What\u27s really wrong with the accounting profession? / A. A. Sommer; Client acceptance and continuation decisions / Stephen Asare, Karl Hackenbrack, W. Robert Knechel; Discussant\u27s response to Accounting and auditing history: Major developments in England and the United States from ancient roots through the mid-twentieth century / G. William Graham ; Exploratory analysis of the determinants of audit engagement resource allocations / Timothy B. Bell, W. Robert Knechel, John J. Willingham; Discussant\u27s response to An Exploratory analysis of the determinants of audit engagement resource allocations / Jane F. Mutchler; Investigation of adaptability in evidential planning / Janice D. DiPietro, Theodore J. Mock, Arnold Wright; Accounting and auditing history: Major developments in England and the United States from ancient roots through the mid-twentieth century / Howard Stettler; Discussant\u27s response to An Investigation of adaptability in evidential planning / Norman R. Walker; Acme Financial Statement Insurance Company Inc: A case study / Stephen J. Aldersleyhttps://egrove.olemiss.edu/dl_proceedings/1011/thumbnail.jp

1. Ultrasonic studies of binary liquid structure in the critical region. Theory and experiment for the 2,6-lutidine/water system. 2. Hartree-Fock calculations of electric polarizabilities of some simple atoms and molecules, and their practicality. 3. Calculation of vibrational transition probabilities in collinear atom-diatom and diatom-diatom collisions with Lennard-Jones interaction

Part 1. Many interesting visual and mechanical phenomena occur in the critical region of fluids, both for the gas-liquid and liquid-liquid transitions. The precise thermodynamic and transport behavior here has some broad consequences for the molecular theory of liquids. Previous studies in this laboratory on a liquid-liquid critical mixture via ultrasonics supported a basically classical analysis of fluid behavior by M. Fixman (e. g., the free energy is assumed analytic in intensive variables in the thermodynamics)--at least when the fluid is not too close to critical. A breakdown in classical concepts is evidenced close to critical, in some well-defined ways. We have studied herein a liquid-liquid critical system of complementary nature (possessing a lower critical mixing or consolute temperature) to all previous mixtures, to look for new qualitative critical behavior. We did not find such new behavior in the ultrasonic absorption ascribable to the critical fluctuations, but we did find extra absorption due to chemical processes (yet these are related to the mixing behavior generating the lower consolute point). We rederived, corrected, and extended Fixman's analysis to interpret our experimental results in these more complex circumstances. The entire account of theory and experiment is prefaced by an extensive introduction recounting the general status of liquid state theory. The introduction provides a context for our present work, and also points out problems deserving attention. Interest in these problems was stimulated by this work but also by work in Part 3. Part 2. Among variational theories of electronic structure, the Hartree-Fock theory has proved particularly valuable for a practical understanding of such properties as chemical binding, electric multipole moments, and X-ray scattering intensity. It also provides the most tractable method of calculating first-order properties under external or internal one-electron perturbations, either developed explicitly in orders of perturbation theory or in the fully self-consistent method. The accuracy and consistency of first-order properties are poorer than those of zero-order properties, but this is most often due to the use of explicit approximations in solving the perturbed equations, or to inadequacy of the variational basis in size or composition. We have calculated the electric polarizabilities of H2, He, Li, Be, LiH, and N2 by Hartree-Fock theory, using exact perturbation theory or the fully self-consistent method, as dictated by convenience. By careful studies on total basis set composition, we obtained good approximations to limiting Hartree-Fock values of polarizabilities with bases of reasonable size. The values for all species, and for each direction in the molecular cases, are within 8% of experiment, or of best theoretical values in the absence of the former. Our results support the use of unadorned Hartree-Pock theory for static polarizabilities needed in interpreting electron-molecule scattering data, collision-induced light scattering experiments, and other phenomena involving experimentally inaccessible polarizabilities. Part 3. Numerical integration of the close-coupled scattering equations has been carried out to obtain vibrational transition probabilities for some models of the electronically adiabatic H2-H2 collision. All the models use a Lennard-Jones interaction potential between nearest atoms in the collision partners. We have analyzed the results for some insight into the vibrational excitation process in its dependence on the energy of collision, the nature of the vibrational binding potential, and other factors. We conclude also that replacement of earlier, simpler models of the interaction potential by the Lennard-Jones form adds very little realism for all the complication it introduces. A brief introduction precedes the presentation of our work and places it in the context of attempts to understand the collisional activation process in chemical reactions as well as some other chemical dynamics.</p