Theoretical Footing Research Articles

Convergence Diagnostics for Markov Chain Monte Carlo

Markov chain Monte Carlo (MCMC) is one of the most useful approaches to scientific computing because of its flexible construction, ease of use, and generality. Indeed, MCMC is indispensable for performing Bayesian analysis. Two critical questions that MCMC practitioners need to address are where to start and when to stop the simulation. Although a great amount of research has gone into establishing convergence criteria and stopping rules with sound theoretical foundation, in practice, MCMC users often decide convergence by applying empirical diagnostic tools. This review article discusses the most widely used MCMC convergence diagnostic tools. Some recently proposed stopping rules with firm theoretical footing are also presented. The convergence diagnostics and stopping rules are illustrated using three detailed examples.

Theoretical Justification and Error Analysis for Slender Body Theory

AbstractSlender body theory facilitates computational simulations of thin fibers immersed in a viscous fluid by approximating each fiber using only the geometry of the fiber centerline curve and the line force density along it. However, it has been unclear how well slender body theory actually approximates Stokes flow about a thin but truly three‐dimensional fiber, in part due to the fact that simply prescribing data along a 1D curve does not result in a well‐posed boundary value problem for the Stokes equations in ℝ3. Here, we introduce a PDE problem to which slender body theory (SBT) provides an approximation, thereby placing SBT on firm theoretical footing. The slender body PDE is a new type of boundary value problem for Stokes flow where partial Dirichlet and partial Neumann conditions are specified everywhere along the fiber surface. Given only a 1D force density along a closed fiber, we show that the flow field exterior to the thin fiber is uniquely determined by imposing a fiber integrity condition: the surface velocity field on the fiber must be constant along cross sections orthogonal to the fiber centerline. Furthermore, a careful estimation of the residual, together with stability estimates provided by the PDE well‐posedness framework, allows us to establish error estimates between the slender body approximation and the exact solution to the above problem. The error is bounded by an expression proportional to the fiber radius (up to logarithmic corrections) under mild regularity assumptions on the 1D force density and fiber centerline geometry. © 2019 Wiley Periodicals, Inc.

Nonconvex Optimization Meets Low-Rank Matrix Factorization: An Overview

Substantial progress has been made recently on developing provably accurate and efficient algorithms for low-rank matrix factorization via nonconvex optimization. While conventional wisdom often takes a dim view of nonconvex optimization algorithms due to their susceptibility to spurious local minima, simple iterative methods such as gradient descent have been remarkably successful in practice. The theoretical footings, however, had been largely lacking until recently. In this tutorial-style overview, we highlight the important role of statistical models in enabling efficient nonconvex optimization with performance guarantees. We review two contrasting approaches: (1) two-stage algorithms, which consist of a tailored initialization step followed by successive refinement; and (2) global landscape analysis and initialization-free algorithms. Several canonical matrix factorization problems are discussed, including but not limited to matrix sensing, phase retrieval, matrix completion, blind deconvolution, robust principal component analysis, phase synchronization, and joint alignment. Special care is taken to illustrate the key technical insights underlying their analyses. This article serves as a testament that the integrated consideration of optimization and statistics leads to fruitful research findings.

Taming the Stability-Constrained Performance Optimization Challenge of Distributed On-Chip Voltage Regulation

Distributed on-chip voltage regulation is promising for addressing many IC power delivery challenges. However, complex interactions between active regulators and the surrounding parasitic passive RLC network cause stability concern. The recently developed hybrid stability technique provides a unique opportunity for coping with stability of distributed on-chip regulation and enabling efficient localized system design. However, the inherent conservativeness of the hybrid stability theorem (HST) leads to large pessimism in stability evaluation and hence causes overdesign. In this paper, the above challenge is addressed by extending the HST with an optimal frequency-dependent system partitioning technique which can significantly reduce the amount of pessimism in stability analysis. To put the proposed approach on a firm theoretical footing, we prove that the partitioning technique removes the conservativeness without altering the physical system and key theoretical properties of the partitioned blocks are maintained under certain constraints. Upon this, an efficient stability-ensuring power delivery design methodology using an automated design flow is developed to significantly improve power delivery performance. Within a large design space, the proposed approach ensures stability and improves system performance by up to 53%, measured by a figure of merit (FOM), when compared to the classical phase margin design approach, which provides no guarantee of stability. Furthermore, on average our approach boosts the FOM by 113% while consuming 11% less power compared to a reference hybrid stability approach.

‘Rethinking “Disease”: a fresh diagnosis and a new philosophical treatment’

Despite several decades of debate, the concept of disease remains hotly contested. The debate is typically cast as one between naturalism and normativism, with a hybrid view that combines elements...

Self-interactions and spontaneous black hole scalarization

It has recently been shown that nontrivial couplings between a scalar and the Gauss-Bonnet invariant can give rise to black hole spontaneous scalarization. Theories that exhibit this phenomenon are among the leading candidates for testing gravity with upcoming black hole observations. All models considered so far have focused on specific forms for the coupling, neglecting scalar self-interactions. In this work, we take the first steps towards placing this phenomenon on a more robust theoretical footing by considering the leading-order scalar self-interactions as well as the scalar-Gauss-Bonnet coupling. Our approach is consistent with the principles of effective field theory and yields the simplest and most natural model. We find that a mass term for the scalar alters the threshold for the onset of scalarization, and we study the mass range over which scalarized black hole solutions exist. We also demonstrate that the quartic self-coupling is sufficient to produce scalarized solutions that are stable against radial perturbations, without the need to resort to higher-order terms in the Gauss-Bonnet coupling function. Our model therefore represents a canonical model that can be studied further, with the ultimate aim of developing falsifiable tests of black hole scalarization.

A probabilistic model of pre-erythrocytic malaria vaccine combination in mice

Malaria remains one the world’s most deadly infectious diseases, with almost half a million deaths and over 150 million clinical cases each year. An effective vaccine would contribute enormously to malaria control and will almost certainly be required for eventual eradication of the disease. However, the leading malaria vaccine candidate, RTS,S, shows only 30–50% efficacy under field conditions, making it less cost-effective than long-lasting insecticide treated bed nets. Other subunit malaria vaccine candidates, including TRAP-based vaccines, show no better protective efficacy. This has led to increased interest in combining subunit malaria vaccines as a means of enhancing protective efficacy. Mathematical models of the effect of combining such vaccines on protective efficacy can help inform optimal vaccine strategies and decision-making at all stages of the clinical process. So far, however, no such model has been developed for pre-clinical murine studies, the stage at which all candidate antigens and combinations begin evaluation. To address this gap, this paper develops a mathematical model of vaccine combination adapted to murine malaria studies. The model is based on simple probabilistic assumptions which put the model on a firmer theoretical footing than previous clinical models, which rather than deriving a relationship between immune responses and protective efficacy posit the relationship to be either exponential or Hill curves. Data from pre-clinical murine malaria studies are used to derive values for unknowns in the model which in turn allows simulations of vaccine combination efficacy and suggests optimal strategies to pursue. Finally, the ability of the model to shed light on fundamental biological variables of murine malaria such as the blood stage growth rate and sporozoite infectivity is explored.

A comparative study of single-wire and hollow metallic waveguides for terahertz waves

Motivated by numerous applications, active research is being conducted worldwide to explore the terahertz (THz) region of the electromagnetic spectrum. Waveguides are key components for the generation, propagation, and utilization of THz waves. This paper addresses two types of commonly-used waveguides in their simplest implementation: the single-wire and hollow metallic waveguides. Research on these two types of waveguides has appeared rather separately in literature. Yet they are based on a common formalism. This suggests a treatment on the same theoretical footing for an examination of their basic properties in terms of the field behavior, power flow, dispersion relation, and attenuation rate. Here, we present a comparative study on their similarities, differences, and relative merits, along with physical interpretations.

Modelo conceptual del manejo del síntoma: evaluación y crítica

Objetivos: evaluar, analizar y criticar el modelo conceptual del manejo del síntoma a partir de los pasos planteados por Fawcett en 2013, y mostrar la relevancia que tiene este ejercicio académico en el área investigativa, tanto a nivel académico como asistencial en enfermería. Materiales y métodos: se realizó una búsqueda sistemática de piezas de investigación, las cuales fueron sometidas a un proceso de lectura crítica por medio de la aplicación de las siguientes herramientas: Critical Appraisal Skills Programme (CAPS) para las piezas de investigación cualitativas, MacMaster University para la piezas de investigación de tipo cuantitativo, el rigor metodológico y la estructura conceptual teórico-empírica planteada por Fawcett en 2013, con lo cual se garantizó la calidad de las piezas de investigación seleccionadas. Resultados: se logró identificar los planteamientos del Modelo conceptual del manejo del síntoma y de investigaciones donde se utilizó este modelo como marco teórico para realizar una evaluación y crítica de este, en la que se tuvieron en cuenta: sus orígenes, el enfoque único del modelo, su congruencia lógica, la generación de teoría, su credibilidad y las contribuciones para la disciplina de enfermería, que corresponden a los pasos recomendados por Fawcett para la evaluación crítica de modelos conceptuales. Conclusión: a pesar de ser un modelo conceptual nuevo cuenta con fuertes bases teóricas y filosóficas que permiten su aplicación a cualquier fenómeno referente a la experiencia de los síntomas; sin embargo, se debe realizar más investigación donde se haga uso de las dimensiones de “los componentes de estrategias de manejo de los síntomas” y “resultados”, ya que un amplio volumen de investigación realizada hasta el momento ha hecho uso de la dimensión “la experiencia de los síntomas”.

Interlayer Trions in the MoS2/WS2 van der Waals Heterostructure.

Electronic excitations in van der Waals heterostructures can have interlayer or intralayer character depending on the spatial localization of the involved charges (electrons and holes). In the case of neutral electron-hole pairs (excitons), both types of excitations have been explored theoretically and experimentally. In contrast, studies of charged trions have so far been limited to the intralayer type. Here we investigate the complete set of interlayer excitations in a MoS2/WS2 heterostructure using a novel ab initio method, which allows for a consistent treatment of both excitons and trions at the same theoretical footing. Our calculations predict the existence of bound interlayer trions below the neutral interlayer excitons. We obtain binding energies of 18/28 meV for the positive/negative interlayer trions with both electrons/holes located on the same layer. In contrast, a negligible binding energy is found for trions which have the two equally charged particles on different layers. Our results advance the understanding of electronic excitations in doped van der Waals heterostructures and their effect on the optical properties.

Field studies reveal functions of chemical mediators in plant interactions.

Plants are at the trophic base of most ecosystems, embedded in a rich network of ecological interactions in which they evolved. While their limited range and speed of motion precludes animal-typical behavior, plants are accomplished chemists, producing thousands of specialized metabolites which may function to convey information, or even to manipulate the physiology of other organisms. Plants' complex interactions and their underlying mechanisms are typically dissected within the controlled environments of growth chambers and glasshouses, but doing so introduces conditions alien to plants evolved in natural environments, such as being pot-bound, and receiving artificial light with a spectrum very different from sunlight. The mechanistic understanding gained from a reductionist approach provides the tools required to query and manipulate plant interactions in real-world settings. The few tests conducted in natural ecosystems and agricultural fields have highlighted the limitations of studying plant interactions only in artificial environments. Here, we focus on three examples of known or hypothesized chemical mediators of plants' interactions: the volatile phytohormone ethylene (ET), more complex plant volatile blends, and as-yet-unknown mediators transferred by common mycorrhizal networks (CMNs). We highlight how mechanistic knowledge has advanced research in all three areas, and the critical importance of field work if we are to put our understanding of chemical ecology on rigorous experimental and theoretical footing, and demonstrate function.

The History of Misdemeanor Bail

Bail is one of the most consequential decisions in criminal justice. The ability to secure bail often makes the difference between guilt and innocence, retaining employment and family obligations, and keeping a place to live. These implications affect those charged with felonies and this has been the focus for many years, but it affects even more so those charged with misdemeanors. A misdemeanor is theoretically a less serious crime with less serious consequences, but the effects on a defendant’s life are just as serious in the short term. There is a growing body of important empirical work that demonstrates the impact of being denied bail on those charged with misdemeanors. However, there is a lack of theoretical scholarship explaining defendants’ rights when it comes to misdemeanor bail. There is also a lack of historical perspective in determining how we have dealt with misdemeanor crimes. Considering this historical perspective, we learn that misdemeanors have always been plentiful but it is only recently that they have become a serious problem and that their impact has become as serious as felony offenses. This Article strives to a first step toward creating a theoretical footing for misdemeanor bail decisions by considering the historical role of misdemeanors and discussing the importance of creating an analytical framework for making these decisions.

Invited paper: Reconciling SGTE and ab initio enthalpies of the elements

The CALPHAD framework is built on assumption that all phases have a well-defined free energy over all accessible composition, temperature and pressure conditions. Unfortunately, it is common for phases to exhibit mechanical instabilities in at least some range of conditions, thus precluding direct experimental measurements and hindering computational efforts. A pragmatic solution has often been to extrapolate free energies from stable region into the unstable regions, but extrapolations from different systems that share a common phase may not agree and extrapolated free energies can unintentionally lie below the free energy of stable phases. Computational approaches that aim to directly calculate the free energy of unstable phases offer a promising avenue to address these issues. Among them, the recently proposed “inflection detection” scheme lies on a strong theoretical footing. We provide further support for this approach by demonstrating that it yield free energies that agree very well with the widely used SGTE (Scientific Group Thermodata Europe) data for pure elements. This finding suggest that it may be possible to get the best of both worlds: obtain a theoretically justified definition of the free energy of mechanically unstable phases and preserve much of existing empirical standards for the assignments of such free energies.

Determining the Convergence of Synchronous Measurements for Embedded Industrial Applications

One technique which may be employed in certain types of sensing application is the phase-sensitive or lock-in method. Since this method essentially trades off longer measurement time for a greater accuracy, it is sometimes necessary to capture samples over a long time period to ensure sufficient stability in the calculated parameter estimate. This may adversely affect safety-critical systems, and some method of determining the relative stability of the measured parameter is needed to permit this useful approach to be more widely employed. In this paper, we propose and evaluate a novel entropy-based method for ascertaining stability. The contributions of this paper are to first highlight the need for a convergence measure which is reliable, automatic, and easily computed; second, we propose one such measure, and place it on a theoretical footing; finally, we give results both with simulated Gaussian noise having a typical sensor power spectrum, as well as experimental results using the type of optical sensor which would benefit from the proposed method. It is demonstrated that this approach produces a reliable asymptotic figure for convergence, both under simulated noise conditions as well as with real measurements in the field.

Foregrounding Hybridity as a Master Trope in the Globalisation Discourses The Case of the Advertising Space of Lesotho

The paper foregrounds linguistic and cultural hybridity as a master trope in the advertising space of Lesotho. Kraidy and Yazdiha’s postulations of hybridity together with the transformationalists view of globalisation and the Communication Accommodation Theory (CAT) provide the theoretical footing for the study. It is a qualitative study with data drawn from a total of seventeen adverts from the advertising space of Lesotho. A modification of Firth’s three-stage qualitative analysis is adopted for the study. The paper concludes that the hybridized Lesotho’s advertising space is an arena for resolving the inherent tensions in globalisation through adjustments and accommodation.

Soft X-ray spectroscopy of transition metal compounds: a theoretical perspective

To date, X-ray spectroscopy has become a routine tool that can reveal highly local and element-specific information on the electronic structure of atoms in complex environments. Here, we report on the development of an efficient and versatile theoretical methodology for the treatment of soft X-ray spectra of transition metal compounds based on the multi-configurational self-consistent field electronic structure theory. A special focus is put on the L-edge photon-in/photon-out and photon-in/electron-out processes, i.e. X-ray absorption, resonant inelastic scattering, partial fluorescence yield, and photoelectron spectroscopy, all treated on the same theoretical footing. The investigated systems range from small prototypical coordination compounds and catalysts to aggregates of biomolecules.

Especificidades da tradução de histórias em quadrinhos: abordagem inicial

A tradução de histórias em quadrinhos (HQs) constitui um campo dosEstudos da Tradução ainda pouco explorado, de forma que não há um fundamento teórico específico relacionado à prática. A produção mundial recente de quadrinhos – particularmente das chamadas graphics novels ou novelas gráficas –, contudo, promove um status à mídia comparável ao da literatura, o que gera sua maior aceitabilidade como produto cultural relevante e objeto de estudo acadêmico. Dado deste contexto, o artigo almeja construir linhas-guia para entendimento específico da tradução de HQs no que esta difere da tradução de outras mídias. Para isto, propõe cinco especificidades desta modalidade de tradução: (1) ingerência do tradutor reduzida às unidades de material linguístico; (2) indissolubilidade da mancha gráfica; (3) indissolubilidade das quebras verbais; (4) documento de tradução = roteiro para letreirista; (5) o letreirista como cotradutor.

NONUNIVERSAL STAR FORMATION EFFICIENCY IN TURBULENT ISM

ABSTRACT We present a study of a star formation prescription in which star formation efficiency (SFE) depends on local gas density and turbulent velocity dispersion, as suggested by direct simulations of SF in turbulent giant molecular clouds (GMCs). We test the model using a simulation of an isolated Milky-Way-sized galaxy with a self-consistent treatment of turbulence on unresolved scales. We show that this prescription predicts a wide variation of local SFE per free-fall time, ∼ 0.1%–10%, and gas depletion time, ∼ 0.1–10 Gyr. In addition, it predicts an effective density threshold for star formation due to suppression of in warm diffuse gas stabilized by thermal pressure. We show that the model predicts star formation rates (SFRs) in agreement with observations from the scales of individual star-forming regions to the kiloparsec scales. This agreement is nontrivial, as the model was not tuned in any way and the predicted SFRs on all scales are determined by the distribution of the GMC-scale densities and turbulent velocities σ in the cold gas within the galaxy, which is shaped by galactic dynamics. The broad agreement of the star formation prescription calibrated in the GMC-scale simulations with observations both gives credence to such simulations and promises to put star formation modeling in galaxy formation simulations on a much firmer theoretical footing.

Quasi-Periodically Driven Quantum Systems

Abstract Floquet theory provides rigorous foundations for the theory of periodically driven quantum systems. In the case of non-periodic driving, however, the situation is not so well understood. Here, we provide a critical review of the theoretical framework developed for quasi-periodically driven quantum systems. Although the theoretical footing is still under development, we argue that quasi-periodically driven quantum systems can be treated with generalisations of Floquet theory in suitable parameter regimes. Moreover, we provide a generalisation of the Floquet-Magnus expansion and argue that quasi-periodic driving offers a promising route for quantum simulations.

Wiener Urbanitäten: Kulturwissenschaftliche Ansichten einer Stadt ed. by Brigitta Schmidt-Lauber et al.

Reviewed by: Wiener Urbanitäten: Kulturwissenschaftliche Ansichten einer Stadt ed. by Brigitta Schmidt-Lauber et al. Peter Höyng and Hiram Maxim Brigitta Schmidt-Lauber, Klara Löffler, Ana Rogojanu, and Jens Wietschorke, eds., Wiener Urbanitäten: Kulturwissenschaftliche Ansichten einer Stadt. Ethnographie des Alltags 1. Vienna: Böhlau, 2013. 389 pp. The coeditor Brigitta Schmidt-Lauber, in her brief introduction, is persuasive in her conviction that an ethnographically informed approach to analyze various sites in Vienna should neither be united by a single methodology nor be comprehensive or systematic. However, after reading the nineteen essays, the initial welcome for randomness in regard to the range of topics and locations—and for heterogeneity in regards to methodology or style of writing—morphed into a desire for greater rigor in terms of definitions and methodology. To this extent, the four broad categories of “Orte, Szenen, Bewegungen, Eindrücke,” in which the editors thematically grouped the articles seem rather arbitrary as an organizing principle. One is therefore thankful for the excellent bibliographical information that follows each essay, and [End Page 125] in general for the wonderful layout that could have been even more rewarding with additional black and white photographs. One of the more remarkable essays is certainly the opening chapter by Elke Krasny, entitled “Vom Recht auf Erinnerung im Garten der Rosen.” Krasny combines literary sensitivity with scholarly qualities of historical research by balancing her own observations and positioning of the Rosengarten in summer 2012 with her goal to uncover a chapter of feminist activism taking place in 1848. The reader will certainly remember next time she enters the Volksgarten that it was here where women from all classes formed the first “Frauenverein” in order to fight for their democratic rights. One of the editors, Jens Wietschorke, also is able to convincingly juxtapose two seeming opposites, namely how the Staatsoper as a “Sakralbezirk” (Lutz Musner) of highbrow culture constitutes itself by domesticating lowbrow culture. Wietschorke does so by first linking the history of the Volksoper to the Staatsoper, then by contrasting the “opera toilet” in the Opernpassage or “Unterwelt” to the mighty “Oberwelt” for refined aesthetic consumption, before he, in a third step, theoretically reflects on how the unstable dichotomy of “high” and “low” is constantly renegotiated socially, culturally, and spatially. Compared with these two essays that display a high degree of theoretical underpinnings towards their chosen “Orte,” articles by Herbert Nikitsch on the historical context of the Nibelungenviertel in the 15th District or by Anton Tantner on the “Informationsvermittlung im 18. Jahrhundert: Das Wiener Frag-undKundschaftsamt” are, while informative and well researched, both marked by a more traditional historical recount of their respective topic. How one does disservice to the young and hybrid discipline of Kulturwissenschaft is shown in Jochen Bonze’s “Das Gesprächssummen: Freundchaftlichkeit als Erscheinungsform der Fußballbegeisterung auf der Friedhofstribüne des Wiener Sportclub-Platzes.” This cumbersome subtitle unfortunately is indicative of what follows. Despite the attempt to put his “Eindrücke” on a theoretical footing by referring to Bruno Latour’s actor-network theory or concepts of soundscape studies, Bonz’s essay displays a discrepancy between his own claims and rather pedestrian findings. A similar form of incongruity occurs in Ana Rogojanu’s essay, “Auf den Spuren städtischer Atmosphären,” when she first asserts Gernot Böhme’s methodology of “Atmosphäre” and its variant by Jean-Paul Thibaud before she articulates the observations by three acquaintances who walked from the [End Page 126] Gürtel toward Josefstadt. Because these remain so predictable, it seems that the author herself expresses doubts about such a vague “Atmosphärenkonzept” (315) to be at all helpful in seeing and analyzing familiar territory anew. The section “Szenen” holds great promise because of the compelling topics chosen for examination in its five chapters: the closing of the Südbahnhof, the graduation ceremony (“Sponsion”) at the University of Vienna, the omnipresence of pigeons, the European soccer championship of 2008, and amateur Vienna filmmakers. However, with the exception of Anna Stoff regen’s successful analysis of her experience as a volunteer at the European soccer championship in 2008 that very nicely highlights, for example, the signifi-cance of the volunteers’ “Ausweis,” the...