Long-range effects on superdiffusive solitons in anharmonic chains

Studies on thermal diffusion of lattice solitons in Fermi-Pasta-Ulam (FPU)-like lattices were recently generalized to the case of dispersive long-range interactions (LRI) of the Kac-Baker form. The position variance of the soliton shows a stronger than linear time-dependence (superdiffusion) as found earlier for lattice solitons on FPU chains with nearest neighbour interactions (NNI). In contrast to the NNI case where the position variance at moderate soliton velocities has a considerable linear time-dependence (normal diffusion), the solitons with LRI are dominated by a superdiffusive mechanism where the position variance mainly depends quadratic and cubic on time. Since the superdiffusion seems to be generic for nontopological solitons, we want to illuminate the role of the soliton shape on the superdiffusive mechanism. Therefore, we concentrate on a FPU-like lattice with a certain class of power-law long-range interactions where the solitons have algebraic tails instead of exponential tails in the case of FPU-type interactions (with or without Kac-Baker LRI). A collective variable (CV) approach in the continuum approximation of the system leads to stochastic integro-differential equations which can be reduced to Langevin-type equations for the CV position and width. We are able to derive an analytical result for the soliton diffusion which agrees well with the simulations of the discrete system. Despite of structurally similar Langevin systems for the two soliton types, the algebraic solitons reach the superdiffusive long-time limit with a characteristic $t^{1.5}$ time-dependence much faster than exponential solitons. The soliton shape determines the diffusion constant in the long-time limit that is approximately a factor of $\pi$ smaller for algebraic solitons.Comment: 7 figure

Population-specific predictions for the finite Kuramoto model and collective synchronization in a system with resonant coupling

Synchronization of coupled simple harmonic oscillators is a well-studied problem in advanced undergraduate mechanics courses and the solution amounts to solving an eigenvalue problem. Synchronization of populations of auto-oscillators is a comparatively new field of study. The first scientists to consider such problems were mathematical biologists, but applied mathematicians and physicists have made significant contributions as well. The chief model of synchronization of distinct auto-oscillators is due to Kuramoto. The most striking feature of the model is the presence of a phase transition from an unsynchronized to a partially synchronized state at a critical value of the inter-oscillator coupling. Also, in spite of being a microscopic model that describes the interactions between individual oscillators, Kuramoto's model can be recast exactly as a mean field model. A great deal of work has focused on predicting the behavior of the mean field. The first part of this dissertation describes my work exploring the Kuramoto model. Most physicists have approached the problem by analyzing the behavior of infinitely sized systems. I focus instead on making precise predictions for specific, finitely sized populations of oscillators. In particular, I demonstrate that the assumption of a constant mean field leads to surprisingly good self-consistent predictions for the mean field, particularly if the frequency of synchronization is made a tunable parameter. However, I find that the discontinuities in the self-consistent predictions do not exhibit critical scaling, in contradiction with the known critical behavior exhibited by the Kuramoto model. The second part of this dissertation describes laboratory work and modeling of a mechanical system that exhibits synchronization. I examine the synchronization of 16 cell-phone vibrators coupled through a resonant plate. In light of the Kuramoto model, the interactions between the motors and the plate give somewhat unexpected results including bistability as well as ranges of frequencies in which the system never synchronize. I show, by starting with a first-principles model of the motors interacting with the plate, that the motors' interaction is similar to Kuramoto's model with two key differences: frequency-dependent coupling and a frequency-dependent phase delay

The Role of Self-Regulation in Corporate Governance

This paper assesses the effectiveness of self-regulation to promote investor interests. TheNetherlands provides an excellent opportunity to gather such evidence for two reasons. First,characteristics of the Dutch corporate governance structure have made it the recent focus ofattention by the European Union, the International Monetary Fund and countries (e.g., Korea)when deliberating issues of corporate governance. Second, during the period 1996-1998, aprivate sector initiative was undertaken to promote change in the balance of power betweenmanagement and investors. Not surprisingly, the United States Securities and ExchangeCommission has closely followed the Dutch "experiment" in self-regulation. We begin byidentifying corporate governance characteristics that are linked to firm value. We thencompare corporate governance characteristics and the relation between firm value and thesecharacteristics before and after the private sector initiative. We find that therecommendations of the private sector initiative had no substantive effect on corporategovernance characteristics or their relationship with firm value. Using event study techniqueswe document the market's skepticism about the successful evolution of corporate governancepractices in the Netherlands through self-regulation. The one exception to this generalconclusion is the market for new listings. Overall, our results confirm the importance ofshareholder voting rights, and who controls these rights, when considering the design of asuccessful self-regulation process.corporate governance;law and economics;financial economics;International economics

The Role of Self-Regulation in Corporate Governance: Evidence from the Netherlands

The purpose of this paper is to gather evidence on the success of market forces in promoting investor interests through self-regulation.Corporate governance is a complex mechanism design problem that is both economic and legal/political based.As such there is great interest in whether (and when) market forces alone are sufficient to prompt change, and whether (and when) additional legal/political actions are required to write and enforce contracts between the owners and managers of capital.The Netherlands provides an excellent opportunity to gather such information.In 1996, a private sector Committee was formed to initiate debate and change in the balance of power between a company's management and investors.In 1997, the Committee issued its recommendations and one year later the Committee initiated a project to assess the impact of the report.We identify the corporate governance variables that are linked to firm value and assess the impact of the committee's recommendations on the identified variables.Finally, we use event study techniques to assess investors reactions to the various events associated with the evolution of corporate governance practices in the Netherlands during this period.international economics;financial economics;law and economics;corporate governance

The charm quark mass with dynamical fermions

We compute the charm quark mass in lattice QCD and compare different formulations of the heavy quark, and quenched data to that with dynamical sea quarks. We take the continuum limit of the quenched data by extrapolating from three different lattice spacings, and compare to data with two flavours of dynamical sea quarks with a mass around the strange at the coarsest lattice spacing. Both the FNAL and ALPHA formalism are used. We find the different heavy quark formulations have the same continuum limit in the quenched approximation, and limited evidence that this approximation overestimates the charm quark mass.Comment: Lattice2004(heavy) 3 pages, 2 figure

Testrun results from prototype fiber detectors for high rate particle tracking

A fiber detector concept has been realized allowing to registrate particles within less than 100 nsec with a space point precision of about 0.1 mm at low occupancy. Three full size prototypes have been build by different producers and tested at a 3 GeV electron beam at DESY. After 3 m of light guides 8-10 photoelectrons were registrated by multichannel photomultipliers providing an efficiency of more than 99%. Using all available data a resolution of 0.086 mm was measured.Comment: 18 pages, 17 figure