# Browsing by Subject "DYNAMICS"

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Item Open Access Boom and Bust: The Effect of Entrepreneurial Inertia on Organizational Populations(Advances in Strategic Management, 2006) Ruef, MAlthough recent public attention has focused on boom-and-bust cycles in industries and financial markets, organizational theorists have made only limited contributions to our understanding of this issue. In this chapter, I argue that a distinctive strategic insight into the mechanisms generating boom-and-bust cycles arises from a focus on entrepreneurial inertia - the lag time exhibited by organizational founders or investors entering a market niche. While popular perceptions of boom-and-bust cycles emphasize the deleterious effect of hasty entrants or overvaluation, I suggest instead that slow, methodical entries into an organizational population or market may pose far greater threats to niche stability. This proposition is explored analytically, considering the development of U.S. medical schools since the mid-18th century. © 2006 Elsevier Ltd. All rights reserved.Item Open Access Competing for global capital or local voters? The politics of business location incentives(Public Choice, 2015-09) Jensen, NM; Malesky, EJ; Walsh, M© 2015, Springer Science+Business Media New York. The competition for global capital has led to interjurisdictional competition between countries, states and cities as to who can offer the most attractive incentives to firms. In this study, we examine the domestic politics of this competition by focusing on incentive use in the United States from 1999 to 2012. We define incentives as the targeted tax deductions or exemptions that are used to lure businesses into a locality. Drawing on data from municipal incentive programs, we examine how electoral competition shapes the use and oversight of targeted incentives. We find evidence that cities with elected mayors provide larger incentives than non-elected city managers by taking advantage of exogeneity in the assignment of city government institutions and a database of over 2000 investment incentives from 2010 to 2012. We also find that elected mayors enjoy more lax oversight of incentive projects than their appointed counterparts. Our results have important implications for the study of interjurisdictional competition and the role of electoral institutions in shaping economic policy.Item Open Access Complexity by Subtraction(Evolutionary Biology, 2013) McShea, DW; Hordijk, WThe eye and brain: standard thinking is that these devices are both complex and functional. They are complex in the sense of having many different types of parts, and functional in the sense of having capacities that promote survival and reproduction. Standard thinking says that the evolution of complex functionality proceeds by the addition of new parts, and that this build-up of complexity is driven by selection, by the functional advantages of complex design. The standard thinking could be right, even in general. But alternatives have not been much discussed or investigated, and the possibility remains open that other routes may not only exist but may be the norm. Our purpose here is to introduce a new route to functional complexity, a route in which complexity starts high, rising perhaps on account of the spontaneous tendency for parts to differentiate. Then, driven by selection for effective and efficient function, complexity decreases over time. Eventually, the result is a system that is highly functional and retains considerable residual complexity, enough to impress us. We try to raise this alternative route to the level of plausibility as a general mechanism in evolution by describing two cases, one from a computational model and one from the history of life. © 2013 Springer Science+Business Media New York.Item Open Access Data clustering based on Langevin annealing with a self-consistent potential(Quarterly of Applied Mathematics, 2018-10-11) Lafata, K; Zhou, Z; Liu, JG; Yin, FFItem Open Access Derivation of a continuum model and the energy law for moving contact lines with insoluble surfactants(Physics of Fluids, 2014-06-05) Zhang, Z; Xu, S; Ren, WA continuous model is derived for the dynamics of two immiscible fluids with moving contact lines and insoluble surfactants based on thermodynamic principles. The continuum model consists of the Navier-Stokes equations for the dynamics of the two fluids and a convection-diffusion equation for the evolution of the surfactant on the fluid interface. The interface condition, the boundary condition for the slip velocity, and the condition for the dynamic contact angle are derived from the consideration of energy dissipations. Different types of energy dissipations, including the viscous dissipation, the dissipations on the solid wall and at the contact line, as well as the dissipation due to the diffusion of surfactant, are identified from the analysis. A finite element method is developed for the continuum model. Numerical experiments are performed to demonstrate the influence of surfactant on the contact line dynamics. The different types of energy dissipations are compared numerically. © 2014 AIP Publishing LLC.Item Open Access Distinct contributions of eroding and depositional profiles to land-atmosphere CO 2 exchange in two contrasting forests(Frontiers in Earth Science, 2019-02-26) Billings, SA; Richter, DDB; Ziegler, SE; Prestegaard, K; Wade, AM© 2019 Billings, Richter, Ziegler, Prestegaard and Wade. Lateral movements of soil organic C (SOC) influence Earth's C budgets by transporting organic C across landscapes and by modifying soil-profile fluxes of CO 2 . We extended a previously presented model (Soil Organic C Erosion Replacement and Oxidation, SOrCERO) and present SOrCERODe, a model with which we can project how erosion and subsequent deposition of eroded material can modify biosphere-atmosphere CO 2 fluxes in watersheds. The model permits the user to quantify the degree to which eroding and depositional profiles experience a change in SOC oxidation and production as formerly deep horizons become increasingly shallow, and as depositional profiles are buried. To investigate the relative importance of erosion rate, evolving SOC depth distributions, and mineralization reactivity on modeled soil C fluxes, we examine two forests exhibiting distinct depth distributions of SOC content and reactivity, hydrologic regimes and land use. Model projections suggest that, at decadal to centennial timescales: (1) the quantity of SOC moving across a landscape depends on erosion rate and the degree to which SOC production and oxidation at the eroding profile are modified as deeper horizons become shallower, and determines the degree to which depositional profile SOC fluxes are modified; (2) erosional setting C sink strength increases with erosion rate, with some sink effects reaching more than 40% of original profile SOC content after 100 y of a relatively high erosion rate (i.e., 1 mm y −1 ); (3) even large amounts of deposited SOC may not promote a large depositional profile C sink even with large gains in autochthonous SOC post-deposition if oxidation of buried SOC is not limited; and (4) when modeled depositional settings receive a disproportionately large amount of SOC, simulations of strong C sink scenarios mimic observations of modest preservation of buried SOC and large SOC gains in surficial horizons, suggesting that C sink scenarios have merit in these forests. Our analyses illuminate the importance of cross-landscape linkages between upland and depositional environments for watershed-scale biosphere-atmosphere C fluxes, and emphasize the need for accurate representations and observations of time-varying depth distributions of SOC reactivity across evolving watersheds if we seek accurate projections of ecosystem C balances.Item Open Access Ergodic properties of highly degenerate 2D stochastic Navier-Stokes equations(Comptes Rendus Mathématique. Académie des Sciences. Paris, 2004) Hairer, Martin; Mattingly, Jonathan CThis Note presents the results from "Ergodicity of the degenerate stochastic 2D Navier-Stokes equation"; by M. Hairer and J.C. Mattingly. We study the Navier-Stokes equation on the two-dimensional torus when forced by a finite dimensional Gaussian white noise and give conditions under which the system is ergodic. In particular, our results hold for specific choices of four-dimensional Gaussian white noise. © 2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.Item Open Access Gardner physics in amorphous solids and beyond.(The Journal of chemical physics, 2019-07) Berthier, Ludovic; Biroli, Giulio; Charbonneau, Patrick; Corwin, Eric I; Franz, Silvio; Zamponi, FrancescoOne of the most remarkable predictions to emerge out of the exact infinite-dimensional solution of the glass problem is the Gardner transition. Although this transition was first theoretically proposed a generation ago for certain mean-field spin glass models, its materials relevance was only realized when a systematic effort to relate glass formation and jamming was undertaken. A number of nontrivial physical signatures associated with the Gardner transition have since been considered in various areas, from models of structural glasses to constraint satisfaction problems. This perspective surveys these recent advances and discusses the novel research opportunities that arise from them.Item Open Access Generalized multipolaron expansion for the spin-boson model: Environmental entanglement and the biased two-state system(Physical Review B - Condensed Matter and Materials Physics, 2014-08-07) Bera, S; Nazir, A; Chin, AW; Baranger, HU; Florens, SWe develop a systematic variational coherent-state expansion for the many-body ground state of the spin-boson model, in which a quantum two-level system is coupled to a continuum of harmonic oscillators. Energetic constraints at the heart of this technique are rationalized in terms of polarons (displacements of the bath states in agreement with classical expectations) and antipolarons (counterdisplacements due to quantum tunneling effects). We present a comprehensive study of the ground-state two-level system population and coherence as a function of tunneling amplitude, dissipation strength, and bias (akin to asymmetry of the double-well potential defining the two-state system). The entanglement among the different environmental modes is investigated by looking at spectroscopic signatures of the bipartite entanglement entropy between a given environmental mode and all the other modes. We observe a drastic change in behavior of this entropy for increasing dissipation, indicative of the entangled nature of the environmental states. In addition, the entropy spreads over a large energy range at strong dissipation, a testimony to the wide entanglement window characterizing the underlying Kondo state. Finally, comparisons to accurate numerical renormalization-group calculations and to the exact Bethe ansatz solution of the model demonstrate the rapid convergence of our variationally optimized multipolaron expansion, suggesting that it should also be a useful tool for dissipative models of greater complexity, as relevant for numerous systems of interest in quantum physics and chemistry. © 2014 American Physical Society.Item Open Access Habitat fragmentation and biodiversity conservation: key findings and future challenges(Landscape Ecology, 2016-02-01) Wilson, MC; Chen, XY; Corlett, RT; Didham, RK; Ding, P; Holt, RD; Holyoak, M; Hu, G; Hughes, AC; Jiang, L; Laurance, WF; Liu, J; Pimm, SL; Robinson, SK; Russo, SE; Si, X; Wilcove, DS; Wu, J; Yu, MItem Open Access Particle Production in Ultrastrong-Coupling Waveguide QED(Physical Review A, 2018-10-08) Gheeraert, Nicolas; Zhang, Xin HH; Sépulcre, Théo; Bera, Soumya; Roch, Nicolas; Baranger, Harold U; Florens, SergeUnderstanding large-scale interacting quantum matter requires dealing with the huge number of quanta that are produced by scattering even a few particles against a complex quantum object. Prominent examples are found from high-energy cosmic ray showers, to the optical or electrical driving of degenerate Fermi gases. We tackle this challenge in the context of many-body quantum optics, as motivated by the recent developments of circuit quantum electrodynamics at ultrastrong coupling. The issue of particle production is addressed quantitatively with a simple yet powerful concept rooted in the quantum superposition principle of multimode coherent states. This key idea is illustrated by the study of multiphoton emission from a single two-level artificial atom coupled to a high impedance waveguide, driven by a nearly monochromatic coherent tone. We find surprisingly that the off-resonant inelastic emission line shape is dominated by broadband particle production, due to the large phase space associated with contributions that do not conserve the number of excitations. Such frequency conversion processes produce striking signatures in time correlation measurements, which can be tested experimentally in quantum waveguides. These ideas open new directions for the simulation of a variety of physical systems, from polaron dynamics in solids to complex superconducting quantum architectures.Item Open Access Reinitialization of the Level-Set Function in 3d Simulation of Moving Contact Lines(Communications in Computational Physics, 2016-11-01) Xu, S; Ren, WThe level set method is one of the most successful methods for the simulation of multi-phase flows. To keep the level set function close the signed distance function, the level set function is constantly reinitialized by solving a Hamilton-Jacobi type of equation during the simulation. When the fluid interface intersects with a solid wall, a moving contact line forms and the reinitialization of the level set function requires a boundary condition in certain regions on the wall. In this work, we propose to use the dynamic contact angle, which is extended from the contact line, as the boundary condition for the reinitialization of the level set function. The reinitialization equation and the equation for the normal extension of the dynamic contact angle form a coupled system and are solved simultaneously. The extension equation is solved on the wall and it provides the boundary condition for the reinitialization equation; the level set function provides the directions along which the contact angle is extended from the contact line. The coupled system is solved using the 3rd order TVD Runge-Kutta method and the Godunov scheme. The Godunov scheme automatically identifies the regions where the angle condition needs to be imposed. The numerical method is illustrated by examples in three dimensions.Item Open Access Selective breakdown of phonon quasiparticles across superionic transition in CuCrSe 2(Nature Physics, 2019-01-01) Niedziela, Jennifer; Bansal, Dipanshu; May, Andrew; Ding, Jingxuan; Lanigan-Atkins, Tyson; Ehlers, Georg; Abernathy, Douglas; Said, Ayman; Delaire, Olivier© 2018, The Author(s), under exclusive licence to Springer Nature Limited. Superionic crystals exhibit ionic mobilities comparable to liquids while maintaining a periodic crystalline lattice. The atomic dynamics leading to large ionic mobility have long been debated. A central question is whether phonon quasiparticles—which conduct heat in regular solids—survive in the superionic state, where a large fraction of the system exhibits liquid-like behaviour. Here we present the results of energy- and momentum-resolved scattering studies combined with first-principles calculations and show that in the superionic phase of CuCrSe 2 , long-wavelength acoustic phonons capable of heat conduction remain largely intact, whereas specific phonon quasiparticles dominated by the Cu ions break down as a result of anharmonicity and disorder. The weak bonding and large anharmonicity of the Cu sublattice are present already in the normal ordered state, resulting in low thermal conductivity even below the superionic transition. These results demonstrate that anharmonic phonon dynamics are at the origin of low thermal conductivity and superionicity in this class of materials.Item Open Access Spectral gaps in wasserstein distances and the 2d stochastic navier-stokes equations(Annals of Probability, 2008-11-01) Hairer, Martin; Mattingly, Jonathan CWe develop a general method to prove the existence of spectral gaps for Markov semigroups on Banach spaces. Unlike most previous work, the type of norm we consider for this analysis is neither a weighted supremum norm nor an Ł p-type norm, but involves the derivative of the observable as well and hence can be seen as a type of 1-Wasserstein distance. This turns out to be a suitable approach for infinite-dimensional spaces where the usual Harris or Doeblin conditions, which are geared toward total variation convergence, often fail to hold. In the first part of this paper, we consider semigroups that have uniform behavior which one can view as the analog of Doeblin's condition. We then proceed to study situations where the behavior is not so uniform, but the system has a suitable Lyapunov structure, leading to a type of Harris condition. We finally show that the latter condition is satisfied by the two-dimensional stochastic Navier-Stokes equations, even in situations where the forcing is extremely degenerate. Using the convergence result, we show that the stochastic Navier-Stokes equations' invariant measures depend continuously on the viscosity and the structure of the forcing. © Institute of Mathematical Statistics, 2008.Item Open Access Stabilizing spin coherence through environmental entanglement in strongly dissipative quantum systems(Physical Review B - Condensed Matter and Materials Physics, 2014-03-18) Bera, S; Florens, S; Baranger, HU; Roch, N; Nazir, A; Chin, AWThe key feature of a quantum spin coupled to a harmonic bath - a model dissipative quantum system - is competition between oscillator potential energy and spin tunneling rate. We show that these opposing tendencies cause environmental entanglement through superpositions of adiabatic and antiadiabatic oscillator states, which then stabilizes the spin coherence against strong dissipation. This insight motivates a fast-converging variational coherent-state expansion for the many-body ground state of the spin-boson model, which we substantiate via numerical quantum tomography. © 2014 American Physical Society.Item Open Access Stationary solutions of stochastic differential equations with memory and stochastic partial differential equations(Communications in Contemporary Mathematics, 2005-10-01) Bakhtin, Y; Mattingly, JCWe explore Itô stochastic differential equations where the drift term possibly depends on the infinite past. Assuming the existence of a Lyapunov function, we prove the existence of a stationary solution assuming only minimal continuity of the coefficients. Uniqueness of the stationary solution is proven if the dependence on the past decays sufficiently fast. The results of this paper are then applied to stochastically forced dissipative partial differential equations such as the stochastic Navier-Stokes equation and stochastic Ginsburg-Landau equation. © World Scientific Publishing Company.Item Open Access Stationary state volume fluctuations in a granular medium.(Physical review. E, Statistical, nonlinear, and soft matter physics, 2005-03-30) Schröter, Matthias; Goldman, Daniel I; Swinney, Harry LA statistical description of static granular material requires ergodic sampling of the phase space spanned by the different configurations of the particles. We periodically fluidize a column of glass beads and find that the sequence of volume fractions phi of postfluidized states is history independent and Gaussian distributed about a stationary state. The standard deviation of phi exhibits, as a function of phi, a minimum corresponding to a maximum in the number of statistically independent regions. Measurements of the fluctuations enable us to determine the compactivity X , a temperaturelike state variable introduced in the statistical theory of Edwards and Oakeshott [Physica A 157, 1080 (1989)].Item Open Access The Emergence of Organizational Forms: A Community Ecology Approach(American Journal of Sociology, 2000) Ruef, MThis article introduces a new ecological approach to the study of form emergence based on the notion of an organizational community - a bounded set of forms with related identities. Applying the approach to 48 organizational forms in the health care sector, this study suggests that the development of novel forms is affected by the positioning of their identities with respect to existing form identities in the community, by the aggregate density and size of organizations matching those existing identities, and by the amount of attention directed at identity attributes by sector participants. Findings show that the process of form emergence is subject to population-dependent effects akin to those noted previously for organizational entries within established populations. The aggregate density and size of organizations with similar identities increase the probability of form emergence to a point (cross-form legitimation), but highly saturated regions of the identity space tend to be uninviting to new forms (cross-form competition).