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The Non-BPS Black Hole Attractor Equation

Description: We study the attractor mechanism for extremal non-BPS black holes with an infinite throat near horizon geometry, developing, as we do so, a physical argument as to why such a mechanism does not exist in non-extremal cases. We present a detailed derivation of the non-supersymmetric attractor equation. This equation defines the stabilization of moduli near the black hole horizon: the fixed moduli take values specified by electric and magnetic charges corresponding to the fluxes in a Calabi Yau compactification of string theory. They also define the so-called double-extremal solutions. In some examples, studied previously by Tripathy and Trivedi, we solve the equation and show that the moduli are fixed at values which may also be derived from the critical points of the black hole potential.
Date: February 8, 2006
Creator: Kollosh, R
Partner: UNT Libraries Government Documents Department

Inflation model constraints from the Wilkinson Microwave Anisotropy Probe three-year data

Description: We extract parameters relevant for distinguishing among single-field inflation models from the Wilkinson Microwave Anisotropy Probe (WMAP) three-year data set, and also from WMAP in combination with the Sloan Digital Sky Survey (SDSS) galaxy power spectrum. Our analysis leads to the following conclusions: (1) the Harrison-Zel'dovich model is consistent with both data sets at a 95% confidence level; (2) there is no strong evidence for running of the spectral index of scalar perturbations; (3) Potentials of the form V {infinity} {phi}{sup P} are consistent with the data for p = 2, and are marginally consistent with the WMAP data considered alone for p = 4, but ruled out by WMAP combined with SDSS. We perform a ''Monte Carlo reconstruction'' of the inflationary potential, and find that: (1) there is no evidence to support an observational lower bound on the amplitude of gravitational waves produced during inflation; (2) models such as simple hybrid potentials which evolve toward an inflationary late-time attractor in the space of flow parameters are strongly disfavored by the data, (3) models selected with even a weak slow-roll prior strongly cluster in the region favoring a ''red'' power spectrum and no running of the spectral index, consistent with simple single-field inflation models.
Date: May 1, 2006
Creator: Kinney, William H.; /SUNY, Buffalo; Kolb, Edward W.; /Fermilab /Chicago U., Astron. Astrophys. Ctr.; Melchiorri, Alessandro; /Rome U. /INFN, Rome et al.
Partner: UNT Libraries Government Documents Department

Constraining inverse curvature gravity with supernovae

Description: We show that the current accelerated expansion of the Universe can be explained without resorting to dark energy. Models of generalized modified gravity, with inverse powers of the curvature can have late time accelerating attractors without conflicting with solar system experiments. We have solved the Friedman equations for the full dynamical range of the evolution of the Universe. This allows us to perform a detailed analysis of Supernovae data in the context of such models that results in an excellent fit. Hence, inverse curvature gravity models represent an example of phenomenologically viable models in which the current acceleration of the Universe is driven by curvature instead of dark energy. If we further include constraints on the current expansion rate of the Universe from the Hubble Space Telescope and on the age of the Universe from globular clusters, we obtain that the matter content of the Universe is 0.07 {le} {omega}{sub m} {le} 0.21 (95% Confidence). Hence the inverse curvature gravity models considered can not explain the dynamics of the Universe just with a baryonic matter component.
Date: October 1, 2005
Creator: Mena, Olga; Santiago, Jose & Weller, Jochen
Partner: UNT Libraries Government Documents Department

Dynamics of the Ginzburg-Landau equations of superconductivity

Description: This article is concerned with the dynamical properties of solutions of the time-dependent Ginzburg-Landau (TDGL) equations of superconductivity. It is shown that the TDGL equations define a dynamical process when the applied magnetic field varies with time, and a dynamical system when the applied magnetic field is stationary. The dynamical system describes the large-time asymptotic behavior: Every solution of the TDGL equations is attracted to a set of stationary solutions, which are divergence free. These results are obtained in the {open_quotes}{phi} = -{omega}({gradient}{center_dot}A){close_quotes} gauge, which reduces to the standard {close_quotes}{phi} = -{gradient}{center_dot}A{close_quotes} gauge if {omega} = 1 and to the zero-electric potential gauge if {omega} = 0; the treatment captures both in a unified framework. This gauge forces the London gauge, {gradient}{center_dot}A = 0, for any stationary solution of the TDGL equations.
Date: August 1997
Creator: Fleckinger-Pelle, J.; Kaper, H. G. & Takac, P.
Partner: UNT Libraries Government Documents Department

Simulations of embodied evolving semiosis: Emergent semantics in artificial environments

Description: As we enter this amazing new world of artificial and virtual systems and environments in the context of human communities, we are interested in the development of systems and environments which have the capacity to grow and evolve their own meanings in the context of this community of interaction. In this paper the authors analyze the necessary conditions to achieve systems and environments with these properties: (1) a coupled interaction between a system and its environment; (2) an environment with sufficient initial richness and structure to allow for; (3) embodied emergent classification of that environment system coupling; and (4) which is subject to pragmatic selection.
Date: February 1, 1998
Creator: Rocha, L.M. & Joslyn, C.
Partner: UNT Libraries Government Documents Department

Syntactic autonomy

Description: The study of adapting and evolving autonomous agents should be based on a complex systems-theoretic framework which requires both self-organizing and symbolic dimensions. An inclusive framework based on the notions of semiotics and situated action is advanced to build models capable of representing, as well as evolving in their environments.Such undertaking is pursued by discussing the ways in which symbol and self-organization are irreducibly intertwined in evolutionary systems. With this semiotic view of self-organization and symbols, the authors re-think the notion of autonomy of evolving systems, and show that evolutionary systems are characterized by a particular type of syntactic autonomy. Recent developments in emergent computation in cellular automata are discussed as examples of the emergence of syntactic autonomy in computational environments. New experiments emphasizing this syntactic autonomy in cellular automata are presented.
Date: December 1, 1998
Creator: Rocha, L.M.
Partner: UNT Libraries Government Documents Department

Experimental Synchronization of Chaotic Attractors Using Control

Description: The focus of this thesis is to theoretically and experimentally investigate two new schemes of synchronizing chaotic attractors using chaotically operating diode resonators. The first method, called synchronization using control, is shown for the first time to experimentally synchronize dynamical systems. This method is an economical scheme which can be viably applied to low dimensional dynamical systems. The other, unidirectional coupling, is a straightforward means of synchronization which can be implemented in fast dynamical systems where timing is critical. Techniques developed in this work are of fundamental importance for future problems regarding high dimensional chaotic dynamical systems or arrays of mutually linked chaotically operating elements.
Date: December 1994
Creator: Newell, Timothy C. (Timothy Charles)
Partner: UNT Libraries

Microscopic time-reversibility and macroscopic irreversibility: Still a paradox

Description: Microscopic time reversibility and macroscopic irreversibility are a paradoxical combination. This was first observed by J. Loschmidt in 1876 and was explained, for conservative systems, by L. Boltzmann the following year. Both these features are also present in modern simulations of classic many-body systems in steady nonequilibrium states. We illustrate them here for the simplest possible models, a continuous one-dimensional model of field-driven diffusion, the so-called driven Lorentz gas or Galton Board, and an ergodic time reversible dissipative map.
Date: September 13, 1995
Creator: Posch, H. A.; Dellago, Ch.; Hoover, W. G. & Kum, O.
Partner: UNT Libraries Government Documents Department

Robust Detection of Dynamical Change in Scalp EEG

Description: We present a robust, model-independent technique for measuring changes in the dynamics underlying nonlinear time-serial data. We define indicators of dynamical change by comparing distribution functions on the attractor via L{sub 1}-distance and X{sup 2} statistics. We apply the measures to scalp EEG data with the objective of capturing the transition between non-seizure and epileptic brain activity in a timely, accurate, and non-invasive manner. We find a clear superiority of the new metrics in comparison to traditional nonlinear measures as discriminators of dynamical change.
Date: June 28, 1999
Creator: Gailey, P.C.; Hively, L.M. & Protopopescu, V.A.
Partner: UNT Libraries Government Documents Department

Proceedings of the Agent 2002 Conference on Social Agents : Ecology, Exchange, and Evolution

Description: Welcome to the ''Proceedings'' of the third in a series of agent simulation conferences cosponsored by Argonne National Laboratory and The University of Chicago. The theme of this year's conference, ''Social Agents: Ecology, Exchange and Evolution'', was selected to foster the exchange of ideas on some of the most important social processes addressed by agent simulation models, namely: (1) The translation of ecology and ecological constraints into social dynamics; (2) The role of exchange processes, including the peer dependencies they create; and (3) The dynamics by which, and the attractor states toward which, social processes evolve. As stated in the ''Call for Papers'', throughout the social sciences, the simulation of social agents has emerged as an innovative and powerful research methodology. The promise of this approach, however, is accompanied by many challenges. First, modeling complexity in agents, environments, and interactions is non-trivial, and these representations must be explored and assessed systematically. Second, strategies used to represent complexities are differentially applicable to any particular problem space. Finally, to achieve sufficient generality, the design and experimentation inherent in agent simulation must be coupled with social and behavioral theory. Agent 2002 provides a forum for reviewing the current state of agent simulation scholarship, including research designed to address such outstanding issues. This year's conference introduces an extensive range of domains, models, and issues--from pre-literacy to future projections, from ecology to oligopolistic markets, and from design to validation. Four invited speakers highlighted major themes emerging from social agent simulation.
Date: April 10, 2003
Creator: Macal, C., ed. & Sallach, D., ed.
Partner: UNT Libraries Government Documents Department

Black Hole Entropy and Fourie-Mukai Transform

Description: We propose a microscopic CFT description of magnetically charged black holes in IIA compactifications on elliptic fibrations based on the Fourier-Mukai transform. The physical derivation of this model involves a chain of string duality transformations including the 4D/5D black hole correspondence. We compute the asymptotic behavior of the microstate degeneracy in a certain limit of large charges and show that it agrees with the macroscopic entropy formula. An interesting aspect of this setup is that the attractor points are situated deep in a hybrid phase of the quantum Kaehler moduli space.
Date: December 4, 2006
Creator: Bena, Iosif; /Saclay; Diaconescu, Duiliu-Emanuel; /Rutgers U., Piscataway; Florea, Bogdan & /Stanford U., Phys. Dept. /SLAC
Partner: UNT Libraries Government Documents Department

New Attractors and Area Codes

Description: In this note we give multiple examples of the recently proposed New Attractors describing supersymmetric flux vacua and non-supersymmetric extremal black holes in IIB string theory. Examples of non-supersymmetric extremal black hole attractors arise on a hypersurface in WP{sub 1,1,1,1,2}{sup 4}. For flux vacua on the orientifold of the same hypersurface existence of multiple basins of attraction is established. It is explained that certain fluxes may give rise to multiple supersymmetric flux vacua in a finite region on moduli space, say at the Landau-Ginzburg point and close to conifold point. This suggests the existence of multiple basins for flux vacua and domain walls in the landscape for a fixed flux and at interior points in moduli space.
Date: December 19, 2005
Creator: Giryavets, Alexander & /Stanford U., Phys. Dept. /SLAC
Partner: UNT Libraries Government Documents Department

Attractor states and quantum instabilities in de Sitter space

Description: The asymptotic behavior of the energy-momentum tensor for a free quantized scalar field with mass m and curvature coupling {zeta} in de Sitter space is investigated. It is shown that for an arbitrary, homogeneous and isotropic, fourth order adiabatic state for which the two-point function is infrared finite, <T{sub ab}> approaches the Bunch-Davies de Sitter invariant value at late times if m{sup 2} + {zeta}R > 0. In the case m = {zeta} = 0, the energy-momentum tensor approaches the de Sitter invariant Allen-Folacci value for such a state. For m{sup 2} + {zeta}R = 0, but m and {zeta} not separately zero it is shown that at late times <T{sub ab}> grows linearly in terms of cosmic time leading to an instability of de Sitter space. The asymptotic behavior is again independent of the state of the field. For m{sup 2} + {zeta}R < 0, it is shown that, for most values of m and {zeta}, <T{sub ab}> grows exponentially in terms of cosmic time at late times in a state dependent manner.
Date: January 1, 2001
Creator: Anderson, P. R. (Paul R.); Eaker, W. (Wayne); Habib, S. (Salman); Molina-Paris, Carmen & Mottola, E. (Emil)
Partner: UNT Libraries Government Documents Department

The Velocity Field of the Local Universe From Measurements of Type Ia Supernovae

Description: We present a measurement of the velocity flow of the local universe relative to the CMB rest frame, based on the Jha, Riess & Kirshner (2007) sample of 133 low redshift type Ia supernovae. At a depth of 4500 km s{sup -1} we find a dipole amplitude of 279 {+-} 68 km s{sup -1} in the direction l = 285{sup o} {+-} 18{sup o}, b = -10{sup o} {+-} 15{sup o}, consistent with earlier measurements and with the assumption that the local velocity field is dominated by the Great Attractor region. At a larger depth of 5900 km s{sup -1} we find a shift in the dipole direction towards the Shapley concentration. We also present the first measurement of the quadrupole term in the local velocity flow at these depths. Finally, we have performed detailed studies based on N-body simulations of the expected precision with which the lowest multipoles in the velocity field can be measured out to redshifts of order 0.1. Our mock catalogues are in good agreement with current observations, and demonstrate that our results are robust with respect to assumptions about the influence of local environment on the type Ia supernova rate.
Date: December 8, 2006
Creator: Haugbolle, T.; Hannestad, S.; Thomsen, B.; U., /Aarhus; Fynbo, J.; Inst., /Bohr et al.
Partner: UNT Libraries Government Documents Department

Joint degradation assessment in an extended structure using chaotic attractor property analysis.

Description: Recently, a new approach in vibration-based structural health monitoring has been developed utilizing features extracted from concepts in nonlinear dynamics systems theory . The structure is excited with a low-dimensional chaotic input, and the steady-state structural response attractor is reconstructed using a false nearest neighbors algorithm . Certain features have been computed from the attractor such as average local 'neighborhood' variance, and these features have been shown in previous works to exceed the damage resolving capability of traditional modal-based features in several computational and experimental studies. In this work, we adopt a similar attractor approach, but we present a feature based on nonlinear predictive models of evolving attractor geometry. This feature has an advantage, over previous attractor-based features in that the input excitation need not be monitored. We apply this overall approach to a steel frame model of a multi-story building, where damage is incurred by the loosening of bolted connections between model members .
Date: January 1, 2003
Creator: Todd, M. D. (Michael D.); Wait, J. R. (Jeannette R.); Nichols, J. M. (Jonathan M.) & Trickey, Stephen
Partner: UNT Libraries Government Documents Department

Prediction and characterization of complex systems

Description: Complex systems are difficult to characterize and to simulate. By considering a series of explicit systems, through experiments and analysis, this project has shown that dynamical systems can be used to model complex systems. A complex dynamical system requires an exponential amount of computer work to simulate accurately. Direct methods are not practical and it is only by an hierarchical approach that one can gain control over the exponential behavior. This allows the development of efficient methods to study fluid flow and to simulate biological systems. There are two steps in the hierarchical approach. First, one must characterize the complex system as a collection of large domains or objects that have their own forms of interactions. This is done by considering coherent structures, such as solitons, spirals, and propagating fronts and determining their interactions. Second, one must be able to predict the properties of the resulting low-dimensional dynamical system.This is accomplished by an understanding of the topology of the orbits of the dynamical system. The coherent structure description was carried out in fluid and reaction diffusion systems. It was shown that very simple models from statistical mechanics could characterize a rotating Rayleigh-Benard system and that patters in reaction-diffusion systems are well described by soliton-like solutions. The studies of dynamical systems showed that simple characterizations of the phase space can be used to determine long time bounds. Also, that periodic orbit theory can be used to demonstrate that Monte Carlo simulations will converge to incorrect results.
Date: October 1, 1996
Creator: Mainieri, R.; Baer, M. & Brand, H.
Partner: UNT Libraries Government Documents Department

Matter and symbols of the artificial

Description: The study of complex systems should be based on a systems-theoretic framework which requires both self-organizing and symbolic dimensions. An inclusive framework based on the notion of semiotics is advanced to build models capable of representing, as well as evolving in their environments, with implications for Artificial Life. Such undertaking is pursued by discussing the ways in which symbol and matter are irreducibly intertwined in evolutionary systems. The problem is thus phrased in terms of the semiotic categories of syntax, semantics, and pragmatics. With this semiotic view of matter and symbols the requirements of semiotic closure are expressed in models with both self-organizing and symbolic characteristics. Situated action and recent developments in the evolution of cellular automata rules to solve non-trivial tasks are discussed in this context. Finally, indirect encoding schemes for genetic algorithms are developed which follow the semiotic framework here proposed.
Date: August 1, 1998
Creator: Rocha, L.M.
Partner: UNT Libraries Government Documents Department

Control of nonlinear systems using periodic parametric perturbations with application to a reversed field pinch

Description: In this thesis, the possibility of controlling low- and high-dimensional chaotic systems by periodically driving an accessible system parameter is examined. This method has been carried out on several numerical systems and the MST Reversed Field Pinch. The numerical systems investigated include the logistic equation, the Lorenz equations, the Roessler equations, a coupled lattice of logistic equations, a coupled lattice of Lorenz equations, the Yoshida equations, which model tearing mode fluctuations in a plasma, and a neural net model for magnetic fluctuations on MST. This method was tested on the MST by sinusoidally driving a magnetic flux through the toroidal gap of the device. Numerically, periodic drives were found to be most effective at producing limit cycle behavior or significantly reducing the dimension of the system when the perturbation frequency was near natural frequencies of unstable periodic orbits embedded in the attractor of the unperturbed system. Several different unstable periodic orbits have been stabilized in this way for the low-dimensional numerical systems, sometimes with perturbation amplitudes that were less than 5% of the nominal value of the parameter being perturbed. In high-dimensional systems, limit cycle behavior and significant decreases in the system dimension were also achieved using perturbations with frequencies near the natural unstable periodic orbit frequencies. Results for the MST were not this encouraging, most likely because of an insufficient drive amplitude, the extremely high dimension of the plasma behavior, large amounts of noise, and a lack of stationarity in the transient plasma pulses.
Date: June 1, 1998
Creator: Mirus, K.A.
Partner: UNT Libraries Government Documents Department

Strange Attractors in Drift Wave Turbulence

Description: A multi-grid part-in-cell algorithm for a shearless slab drift wave model with kinetic electrons is presented. The algorithm, which is based on an exact separation of adiabatic and nonadiabatic electron responses, is used to investigate the presence of strange attractors in drift wave turbulence. Although the simulation model has a large number of degrees of freedom, it is found that the strange attractor is low-dimensional and that it is strongly affected by dissipative (collisional) effects.
Date: April 25, 2003
Creator: Lewandowski, J.L.V.
Partner: UNT Libraries Government Documents Department

Studies in Chaotic adiabatic dynamics

Description: Chaotic adiabatic dynamics refers to the study of systems exhibiting chaotic evolution under slowly time-dependent equations of motion. In this dissertation the author restricts his attention to Hamiltonian chaotic adiabatic systems. The results presented are organized around a central theme, namely, that the energies of such systems evolve diffusively. He begins with a general analysis, in which he motivates and derives a Fokker-Planck equation governing this process of energy diffusion. He applies this equation to study the {open_quotes}goodness{close_quotes} of an adiabatic invariant associated with chaotic motion. This formalism is then applied to two specific examples. The first is that of a gas of noninteracting point particles inside a hard container that deforms slowly with time. Both the two- and three-dimensional cases are considered. The results are discussed in the context of the Wall Formula for one-body dissipation in nuclear physics, and it is shown that such a gas approaches, asymptotically with time, an exponential velocity distribution. The second example involves the Fermi mechanism for the acceleration of cosmic rays. Explicit evolution equations are obtained for the distribution of cosmic ray energies within this model, and the steady-state energy distribution that arises when this equation is modified to account for the injection and removal of cosmic rays is discussed. Finally, the author re-examines the multiple-time-scale approach as applied to the study of phase space evolution under a chaotic adiabatic Hamiltonian. This leads to a more rigorous derivation of the above-mentioned Fokker-Planck equation, and also to a new term which has relevance to the problem of chaotic adiabatic reaction forces (the forces acting on slow, heavy degrees of freedom due to their coupling to light, fast chaotic degrees).
Date: January 1, 1994
Creator: Jarzynski, C.
Partner: UNT Libraries Government Documents Department

Black Hole Attractors and Pure Spinors

Description: We construct black hole attractor solutions for a wide class of N = 2 compactifications. The analysis is carried out in ten dimensions and makes crucial use of pure spinor techniques. This formalism can accommodate non-Kaehler manifolds as well as compactifications with flux, in addition to the usual Calabi-Yau case. At the attractor point, the charges fix the moduli according to {Sigma}f{sub k} = Im(C{Phi}), where {Phi} is a pure spinor of odd (even) chirality in IIB (A). For IIB on a Calabi-Yau, {Phi} = {Omega} and the equation reduces to the usual one. Methods in generalized complex geometry can be used to study solutions to the attractor equation.
Date: February 21, 2006
Creator: Hsu, Jonathan P.; Maloney, Alexander & Tomasiello, Alessandro
Partner: UNT Libraries Government Documents Department

Black Hole Entropy, Marginal Stability and Mirror Symmetry

Description: We consider the superconformal quantum mechanics associated to BPS black holes in type IIB Calabi-Yau compactifications. This quantum mechanics describes the dynamics of D-branes in the near-horizon attractor geometry of the black hole. In many cases, the black hole entropy can be found by counting the number of chiral primaries in this quantum mechanics. Both the attractor mechanism and notions of marginal stability play important roles in generating the large number of microstates required to explain this entropy. We compute the microscopic entropy explicitly in a few different cases, where the theory reduces to quantum mechanics on the moduli space of special Lagrangians. Under certain assumptions, the problem may be solved by implementing mirror symmetry as three T-dualities: this is essentially the mirror of a calculation by Gaiotto, Strominger and Yin. In some simple cases, the calculation may be done in greater generality without resorting to conjectures about mirror symmetry. For example, the K3 x T{sub 2} case may be studied precisely using the Fourier-Mukai transform.
Date: October 6, 2006
Creator: Aspinwall, Paul S.; Maloney, Alexander & Simons, Aaron
Partner: UNT Libraries Government Documents Department

Attractor Explosions and Catalyzed Vacuum Decay

Description: We present a mechanism for catalyzed vacuum bubble production obtained by combining moduli stabilization with a generalized attractor phenomenon in which moduli are sourced by compact objects. This leads straightforwardly to a class of examples in which the Hawking decay process for black holes unveils a bubble of a different vacuum from the ambient one, generalizing the new endpoint for Hawking evaporation discovered recently by Horowitz. Catalyzed vacuum bubble production can occur for both charged and uncharged bodies, including Schwarzschild black holes for which massive particles produced in the Hawking process can trigger vacuum decay. We briefly discuss applications of this process to the population and stability of metastable vacua.
Date: May 5, 2006
Creator: Green, Daniel; Silverstein, Eva & Starr, David
Partner: UNT Libraries Government Documents Department