1,433 research outputs found
Numerical Stochastic Perturbation Theory. Convergence and features of the stochastic process. Computations at fixed (Landau) Gauge
Concerning Numerical Stochastic Perturbation Theory, we discuss the
convergence of the stochastic process (idea of the proof, features of the limit
distribution, rate of convergence to equilibrium). Then we also discuss the
expected fluctuations in the observables and give some idea to reduce them. In
the end we show that also computation of quantities at fixed (Landau) Gauge is
now possible.Comment: 3 pages. Contributed to 17th International Symposium on Lattice Field
Theory (LATTICE 99), Pisa, Italy, 29 Jun - 3 Jul 199
The importance of temporal stress variation and dynamic disequilibrium for the initiation of plate tectonics
We use 1-D thermal history models and 3-D numerical experiments to study the impact of dynamic thermal disequilibrium and large temporal variations of normal and shear stresses on the initiation of plate tectonics. Previous models that explored plate tectonics initiation from a steady state, single plate mode of convection concluded that normal stresses govern the initiation of plate tectonics, which based on our 1-D model leads to plate yielding being more likely with increasing interior heat and planet mass for a depth-dependent Byerlee yield stress. Using 3-D spherical shell mantle convection models in an episodic regime allows us to explore larger temporal stress variations than can be addressed by considering plate failure from a steady state stagnant lid configuration. The episodic models show that an increase in convective mantle shear stress at the lithospheric base initiates plate failure, which leads with our 1-D model to plate yielding being less likely with increasing interior heat and planet mass. In this out-of-equilibrium and strongly time-dependent stress scenario, the onset of lithospheric overturn events cannot be explained by boundary layer thickening and normal stresses alone. Our results indicate that in order to understand the initiation of plate tectonics, one should consider the temporal variation of stresses and dynamic disequilibrium
Extreme fluctuations in noisy task-completion landscapes on scale-free networks
We study the statistics and scaling of extreme fluctuations in noisy
task-completion landscapes, such as those emerging in synchronized
distributed-computing networks, or generic causally-constrained queuing
networks, with scale-free topology. In these networks the average size of the
fluctuations becomes finite (synchronized state) and the extreme fluctuations
typically diverge only logarithmically in the large system-size limit ensuring
synchronization in a practical sense. Provided that local fluctuations in the
network are short-tailed, the statistics of the extremes are governed by the
Gumbel distribution. We present large-scale simulation results using the exact
algorithmic rules, supported by mean-field arguments based on a coarse-grained
description.Comment: 16 pages, 6 figures, revte
Two views on neutral money: Wieser and Hayek versus Menger and Mises
Neutral money plays a central role in contemporary macroeconomic theory, and is a live issue in recent monetary policy discussions. We challenge the opinion that Hayek’s writings on neutral money have been influenced by, and are similar to, the work of Menger and Mises. We show, first, the significant alternative influence of Friedrich von Wieser on Hayek’s work on the subject. Second, we rehabilitate a neglected method of monetary theorizing specific to Menger and Mises that rejects money neutrality both as a tool for investigating monetary phenomena and as the standard by which monetary regimes, and the market economy itself, should be evaluated. Examining this chapter in the history of economic thought can aid in a deeper reconsideration of the doctrinal foundations of modern monetary theory and policy
Mobility induces global synchronization of oscillators in periodic extended systems
We study synchronization of locally coupled noisy phase oscillators which
move diffusively in a one-dimensional ring. Together with the disordered and
the globally synchronized states, the system also exhibits several wave-like
states which display local order. We use a statistical description valid for a
large number of oscillators to show that for any finite system there is a
critical spatial diffusion above which all wave-like solutions become unstable.
Through Langevin simulations, we show that the transition to global
synchronization is mediated by the relative size of attractor basins associated
to wave-like states. Spatial diffusion disrupts these states and paves the way
for the system to attain global synchronization
Commensurability and beyond: from Mises and Neurath to the future of the socialist calculation debate
Mises' 'calculation argument' against socialism argues that monetary calculation is indispensable as a commensurable unit for evaluating factors of production. This is not due to his conception of rationality being purely 'algorithmic,' for it accommodates non-monetary, incommensurable values. Commensurability is needed, rather, as an aid in the face of economic complexity. The socialist Neurath's response to Mises is unsatisfactory in rejecting the need to explore possible non-market techniques for achieving a certain degree of commensurability. Yet Neurath's contribution is valuable in emphasizing the need for a balanced, comparative approach to the question of market versus non-market that puts the commensurability question in context. These central issues raised by adversaries in the early socialist calculation debate have continued relevance for the contemporary discussion
Facts, Values and Quanta
Quantum mechanics is a fundamentally probabilistic theory (at least so far as
the empirical predictions are concerned). It follows that, if one wants to
properly understand quantum mechanics, it is essential to clearly understand
the meaning of probability statements. The interpretation of probability has
excited nearly as much philosophical controversy as the interpretation of
quantum mechanics. 20th century physicists have mostly adopted a frequentist
conception. In this paper it is argued that we ought, instead, to adopt a
logical or Bayesian conception. The paper includes a comparison of the orthodox
and Bayesian theories of statistical inference. It concludes with a few remarks
concerning the implications for the concept of physical reality.Comment: 30 pages, AMS Late
High shock release in ultrafast laser irradiated metals: Scenario for material ejection
We present one-dimensional numerical simulations describing the behavior of
solid matter exposed to subpicosecond near infrared pulsed laser radiation. We
point out to the role of strong isochoric heating as a mechanism for producing
highly non-equilibrium thermodynamic states. In the case of metals, the
conditions of material ejection from the surface are discussed in a
hydrodynamic context, allowing correlation of the thermodynamic features with
ablation mechanisms. A convenient synthetic representation of the thermodynamic
processes is presented, emphasizing different competitive pathways of material
ejection. Based on the study of the relaxation and cooling processes which
constrain the system to follow original thermodynamic paths, we establish that
the metal surface can exhibit several kinds of phase evolution which can result
in phase explosion or fragmentation. An estimation of the amount of material
exceeding the specific energy required for melting is reported for copper and
aluminum and a theoretical value of the limit-size of the recast material after
ultrashort laser irradiation is determined. Ablation by mechanical
fragmentation is also analysed and compared to experimental data for aluminum
subjected to high tensile pressures and ultrafast loading rates. Spallation is
expected to occur at the rear surface of the aluminum foils and a comparison
with simulation results can determine a spall strength value related to high
strain rates
Supersymmetric version of a hydrodynamic system in Riemann invariants and its solutions
In this paper, a supersymmetric extension of a system of hydrodynamic type
equations involving Riemann invariants is formulated in terms of a superspace
and superfield formalism. The symmetry properties of both the classical and
supersymmetric versions of this hydrodynamical model are analyzed through the
use of group-theoretical methods applied to partial differential equations
involving both bosonic and fermionic variables. More specifically, we compute
the Lie superalgebras of both models and perform classifications of their
respective subalgebras. A systematic use of the subalgebra structures allow us
to construct several classes of invariant solutions, including travelling
waves, centered waves and solutions involving monomials, exponentials and
radicals.Comment: 30 page
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