Asymptotic iteration method for eigenvalue problems

An asymptotic interation method for solving second-order homogeneous linear differential equations of the form y'' = lambda(x) y' + s(x) y is introduced, where lambda(x) \neq 0 and s(x) are C-infinity functions. Applications to Schroedinger type problems, including some with highly singular potentials, are presented.Comment: 14 page

An organizational approach to comparative corporate governance: Costs, contingencies, and complementarities

This paper develops an organizational approach to corporate governance and assesses the effectiveness of corporate governance and implications for policy. Most corporate governance research focuses on a universal link between corporate governance practices (e.g. board structure, shareholder activism) and performance outcomes, but neglects how interdependences between the organization and diverse environments lead to variations in the effectiveness of different governance practices. In contrast to such ‘closed systems’ approaches, we propose a framework based on ‘open systems’ approaches to organizations which examines these organizational interdependencies in terms of the costs, contingencies, and complementarities of different corporate governance practices. These three sets of organizational factors are useful in analyzing the effectiveness of corporate governance in diverse organizational environments. We also explore how costs, contingencies, and complementarities impact effectiveness of different governance aspects through the use of stylized cases and discuss the implications for different approaches to policy such as ‘soft-law’ or ‘hard law’

Studying Configurations with QCA: Best Practices in Strategy and Organization Research

Qualitative Comparative Analysis (QCA) is increasingly applied in strategy and organization research. The main purpose of our essay is to support this growing community of QCA scholars by identifying best practices that can help guide researchers through the key stages of a QCA empirical study (model building, sampling, calibration, data analysis, reporting and interpretation of findings) and by providing examples of such practices drawn from strategy and organization studies. Coupled with this main purpose, we respond to Miller’s (2017) essay on configuration research by highlighting our points of agreement regarding his recommendations for configurational research and by addressing some of his concerns regarding QCA. Our article thus contributes to configurational research by articulating how to leverage QCA for enriching configurational theories of strategy and organization

Perturbation expansions for a class of singular potentials

Harrell's modified perturbation theory [Ann. Phys. 105, 379-406 (1977)] is applied and extended to obtain non-power perturbation expansions for a class of singular Hamiltonians H = -D^2 + x^2 + A/x^2 + lambda/x^alpha, (A\geq 0, alpha > 2), known as generalized spiked harmonic oscillators. The perturbation expansions developed here are valid for small values of the coupling lambda > 0, and they extend the results which Harrell obtained for the spiked harmonic oscillator A = 0. Formulas for the the excited-states are also developed.Comment: 23 page

A basis for variational calculations in d dimensions

In this paper we derive expressions for matrix elements (\phi_i,H\phi_j) for the Hamiltonian H=-\Delta+\sum_q a(q)r^q in d > 1 dimensions. The basis functions in each angular momentum subspace are of the form phi_i(r)=r^{i+1+(t-d)/2}e^{-r^p/2}, i >= 0, p > 0, t > 0. The matrix elements are given in terms of the Gamma function for all d. The significance of the parameters t and p and scale s are discussed. Applications to a variety of potentials are presented, including potentials with singular repulsive terms of the form b/r^a, a,b > 0, perturbed Coulomb potentials -D/r + B r + Ar^2, and potentials with weak repulsive terms, such as -g r^2 + r^4, g > 0.Comment: 22 page

Embracing Causal Complexity: The Emergence of a Neo-Configurational Perspective

Causal complexity has long been recognized as a ubiquitous feature underlying organizational phenomena, yet current theories and methodologies in management are for the most part not well suited to its direct study. The introduction of the Qualitative Comparative Analysis (QCA) configurational approach has led to a reinvigoration of configurational theory that embraces causal complexity explicitly. We argue that the burgeoning research using QCA represents more than a novel methodology; it constitutes the emergence of a neo-configurational perspective to the study of management and organizations that enables a fine-grained conceptualization and empirical investigation of causal complexity through the logic of set theory. In this article, we identify four foundational elements that characterize this emerging neoconfigurational perspective: 1) conceptualizing cases as set theoretic configurations; 2) calibrating cases’ memberships into sets; 3) viewing causality in terms of necessity and sufficiency relations between sets; and, 4) conducting counterfactual analysis of unobserved configurations. We then present a comprehensive review of the use of QCA in management studies that aims to capture the evolution of the neo-configurational perspective among management scholars. We close with a discussion of a research agenda that can further this neoconfigurational approach and thereby shift the attention of management research away from a focus on net effects and towards examining causal complexity

Evidence for a direct band gap in the topological insulator Bi2Se3 from theory and experiment

Using angle-resolved photoelectron spectroscopy and ab-initio GW calculations, we unambiguously show that the widely investigated three-dimensional topological insulator Bi2Se3 has a direct band gap at the Gamma point. Experimentally, this is shown by a three-dimensional band mapping in large fractions of the Brillouin zone. Theoretically, we demonstrate that the valence band maximum is located at the Brillouin center only if many-body effects are included in the calculation. Otherwise, it is found in a high-symmetry mirror plane away from the zone center.Comment: 8 pages, 4 figure

Azadirachtin effectivity in embryogenesis inhibition of Aegorhinus superciliosus (Guérin) (Coleoptera: Curculionidae)

Raspberry is cultivated in the southern part of Chile mainly for export. Its fruit is severely affected by the raspberry weevil (RW) Aegorhinus superciliosus (Guérin), a Curculionidae native of Chile. Little is known about the biology RW and control measures. Conventional insecticides have been tried against the adult, however, their use has been hindered in the practice by the coincidence of the presence of the mature insect with flowering and fructification periods. Entomopathogenic fungi are being incorporated lately, but still not massively used. This work aimed to evaluate azadirachtin, using the commercial product Neem as a growth regulator. Six doses of Neem, 0.5, 1, 2, 3, 4, and 5 ml/L of water, were applied under laboratory conditions, maintaining a check with no insecticide. RW adults stayed confined on the foliage of raspberry bushes treated with Neem during five days and in thirty days during egglaying. Number of eggs, number of emerged larva, percentage of born larva, effectiveness; effective half dose (DE50) and ninety effective dose (DE90) were determined. Neem treatments had significantly lower egg-laying amount, lower emergence of larvae and greater effectiveness, compared to the untreated check. The lowest egg-laying number was obtained with 2 ml of Neem, however, 5 ml of Neem resulted in the smallest number and percent of emerged larvae. DE50 and DE90 were found to be 0.0290 and 8.923 ml of Neem for liter of water, respectively. It was concluded that Neem can significantly alter egg-laying and embryogenesis of the RW.La frambuesa es una fruta de exportación, cuyo cultivo en el sur de Chile es afectado seriamente por el curculiónido Aegorhinus superciliosus (Guérin) o cabrito del frambueso (CF), insecto nativo de Chile. La biología del CF es poco conocida y también su control. Se ha intentado reducir al adulto con insecticidas convencionales; sin embargo, en la práctica se dificulta su uso por coincidir la presencia del insecto adulto con periodos de floración y cosecha de fruta. Recientemente se están incorporando hongos entomopatógenos, pero aún no se aplican masivamente. En este trabajo se experimentó con azadirachtina, utilizando el producto comercial Neem como regulador de crecimiento. Bajo condiciones de laboratorio se aplicaron seis dosis de Neem: 1 ml; 2 ml; 3 ml; 4 ml; 5 ml; 6 ml de Neem por litro de agua. Además, de un testigo sin insecticida. Los adultos del CF se mantuvieron confinados con follaje de frambueso tratados con Neem durante cinco días y en postura por treinta días. Durante este periodo se determinó: cantidad de huevos, cantidad de larvas emergidas, porcentaje de larvas nacidas, grado de eficacia, dosis media efectiva (DE50) y dosis noventa efectiva (DE90). Los tratamientos con Neem fueron significativamente diferentes al testigo, presentando menor postura, menor emergencia de larvas y mayor grado de efectividad. Con 2 ml de Neem se obtuvo la menor postura; sin embargo, la dosis de 5 ml de Neem presentó la menor cantidad de larvas emergidas y el menor porcentaje de emergencia de larvas. La DE50 se determinó en 0,0290 ml de Neem y la DE90 en 8,923 ml de Neem por litro de agua. Con los antecedentes expuestos se concluyó que el Neem tiene un efecto que altera la postura y la embriogénesis del CF

Neutron Transfer reactions induced by 8Li on 9Be

Angular distributions for the elastic scattering of 8Li on 9Be and the neutron transfer reactions 9Be(8Li,7Li)10Be and 9Be(8Li,9Li)8Be have been measured with a 27 MeV 8Li radioactive nuclear beam. Spectroscopic factors for 8Li|n=9Li and 7Li|n=8Li bound systems were obtained from the comparison between the experimental differential cross section and finite-range DWBA calculations with the code FRESCO. The spectroscopic factors obtained are compared to shell model calculations and to other experimental values from (d,p) reactions. Using the present values for the spectroscopic factor, cross sections for the direct neutron-capture reactions 7Li(n,g)8Li and 8Li(n,g)9Li were calculated in the framework of a potential model.Comment: 24 pages, 8 Figures, submitted as regular article to PR

On the order of an automorphism of a smooth hypersurface

In this paper we give an effective criterion as to when a positive integer q is the order of an automorphism of a smooth hypersurface of dimension n and degree d, for every d>2, n>1, (n,d)\neq (2,4), and \gcd(q,d)=\gcd(q,d-1)=1. This allows us to give a complete criterion in the case where q=p is a prime number. In particular, we show the following result: If X is a smooth hypersurface of dimension n and degree d admitting an automorphism of prime order p then p(d-1)^n then X is isomorphic to the Klein hypersurface, n=2 or n+2 is prime, and p=\Phi_{n+2}(1-d) where \Phi_{n+2} is the (n+2)-th cyclotomic polynomial. Finally, we provide some applications to intermediate jacobians of Klein hypersurfaces