Perfect Regular Equilibrium

We propose a revised version of the perfect Bayesian equilibrium in general multi-period games with observed actions. In finite games, perfect Bayesian equilibria are weakly consistent and subgame perfect Nash equilibria. In general games that allow a continuum of types and strategies, however, perfect Bayesian equilibria might not satisfy these criteria of rational solution concepts. To solve this problem, we revise the definition of the perfect Bayesian equilibrium by replacing Bayes' rule with a regular conditional probability. We call this revised solution concept a perfect regular equilibrium. Perfect regular equilibria are always weakly consistent and subgame perfect Nash equilibria in general games. In addition, perfect regular equilibria are equivalent to simplified perfect Bayesian equilibria in finite games. Therefore, the perfect regular equilibrium is an extended and simple version of the perfect Bayesian equilibrium in general multi-period games with observed actions

Perfect Regular Equilibrium

We propose a revised version of the perfect Bayesian equilibrium in general multi-period games with observed actions. In finite games, perfect Bayesian equilibria are weakly consistent and subgame perfect Nash equilibria. In general games that allow a continuum of types and strategies, however, perfect Bayesian equilibria might not satisfy these criteria of rational solution concepts. To solve this problem, we revise the definition of the perfect Bayesian equilibrium by replacing Bayes' rule with a regular conditional probability. We call this revised solution concept a perfect regular equilibrium. Perfect regular equilibria are always weakly consistent and subgame perfect Nash equilibria in general games. In addition, perfect regular equilibria are equivalent to simplified perfect Bayesian equilibria in finite games. Therefore, the perfect regular equilibrium is an extended and simple version of the perfect Bayesian equilibrium in general multi-period games with observed actions.Bayes' rule, general Multi-period game, Perfect Bayesian equilibrium, Perfect regular equilibrium, Regular conditional probability, Solution concept.

Investor Overlap and Diffusion of Disclosure Practices

This paper examines how one firm’s commitment to provide more public disclosure affects other firms’ disclosure practices in subsequent periods. I develop an investor demand-driven explanation for why and when firms adopt the disclosure innovation of a first-mover firm. I test the hypothesis that overlap in institutional ownership between two firms is a mechanism by which one firm’s greater disclosure creates demand pressure for the other firm to follow. Using market risk disclosures as my empirical setting, I find that a firm’s decision to follow a first-mover in providing more quantitative information in its 10-K filing than is required by the SEC is positively associated with the level of, and changes in, institutional investor overlap. I also find that the association is stronger for overlap among investors with greater influence over managers’ disclosure decisions, investors with incentives to demand public disclosure, and for firms whose investors are most likely to demand expanded disclosure. Overall, this evidence provides new insight into patterns of intra-industry disclosure behavior and highlights investor overlap as a source of variation in firms’ information environments that can be used in future research

Reply to Comment on "Dynamical corrections to the DFT-LDA electron conductance in nanoscale systems"

We reply to the comment by Jung, Bokes, and Godby (arXiv:0706.0140) on our paper Phys. Rev. Lett. 94, 186810 (2005). We show that the results in their comment should not be taken as an indication that the viscosity corrections to the conductance of real nanoscale structures are small. A more accurate treatment of the density and current density distribution and of the electronic correlations may yield much larger corrections in realistic systems.Comment: Reply to the comment by Jung et al (arXiv:0706.0140). 1 page, no figures, to appear in PR

Rotational dynamics of a superhelix towed in a Stokes fluid

Motivated by the intriguing motility of spirochetes (helically-shaped bacteria that screw through viscous fluids due to the action of internal periplasmic flagella), we examine the fundamental fluid dynamics of superhelices translating and rotating in a Stokes fluid. A superhelical structure may be thought of as a helix whose axial centerline is not straight, but also a helix. We examine the particular case where these two superimposed helices have different handedness, and employ a combination of experimental, analytic, and computational methods to determine the rotational velocity of superhelical bodies being towed through a very viscous fluid. We find that the direction and rate of the rotation of the body is a result of competition between the two superimposed helices; for small axial helix amplitude, the body dynamics is controlled by the short-pitched helix, while there is a cross-over at larger amplitude to control by the axial helix. We find far better, and excellent, agreement of our experimental results with numerical computations based upon the method of Regularized Stokeslets than upon the predictions of classical resistive force theory

Surface Waves on a Semi-toroidal Water Ring

We study the dynamics of surface waves on a semi-toroidal ring of water that is excited by vertical vibration. We create this specific fluid volume by patterning a glass plate with a hydrophobic coating, which confines the fluid to a precise geometric region. To excite the system, the supporting plate is vibrated up and down, thus accelerating and decelerating the fluid ring along its toroidal axis. When the driving acceleration is sufficiently high, the surface develops a standing wave, and at yet larger accelerations, a traveling wave emerges. We also explore frequency dependencies and other geometric shapes of confinement

Dynamics of a deformable body in a fast flowing soap film

We study the behavior of an elastic loop embedded in a flowing soap film. This deformable loop is wetted into the film and is held fixed at a single point against the oncoming flow. We interpret this system as a two-dimensional flexible body interacting in a two-dimensional flow. This coupled fluid-structure system shows bistability, with both stationary and oscillatory states. In its stationary state, the loop remains essentially motionless and its wake is a von K\'arm\'an vortex street. In its oscillatory state, the loop sheds two vortex dipoles, or more complicated vortical structures, within each oscillation period. We find that the oscillation frequency of the loop is linearly proportional to the flow velocity, and that the measured Strouhal numbers can be separated based on wake structure

Predicting which genes will respond to transcription factor perturbations

The ability to predict which genes will respond to the perturbation of a transcription factor serves as a benchmark for our systems-level understanding of transcriptional regulatory networks. In previous work, machine learning models have been trained to predict static gene expression levels in a biological sample by using data from the same or similar samples, including data on their transcription factor binding locations, histone marks, or DNA sequence. We report on a different challenge-training machine learning models to predict which genes will respond to the perturbation of a transcription factor without using any data from the perturbed cells. We find that existing transcription factor location data (ChIP-seq) from human cells have very little detectable utility for predicting which genes will respond to perturbation of a transcription factor. Features of genes, including their preperturbation expression level and expression variation, are very useful for predicting responses to perturbation of any transcription factor. This shows that some genes are poised to respond to transcription factor perturbations and others are resistant, shedding light on why it has been so difficult to predict responses from binding locations. Certain histone marks, including H3K4me1 and H3K4me3, have some predictive power when located downstream of the transcription start site. However, the predictive power of histone marks is much less than that of gene expression level and expression variation. Sequence-based or epigenetic properties of genes strongly influence their tendency to respond to direct transcription factor perturbations, partially explaining the oft-noted difficulty of predicting responsiveness from transcription factor binding location data. These molecular features are largely reflected in and summarized by the gene\u27s expression level and expression variation. Code is available at https://github.com/BrentLab/TFPertRespExplainer

Hot-Electron Electroluminescence under RF Operation in GaN-HEMTs::A Comparison Among Operational Classes

Electroluminescence microscopy and spectroscopy are used to compare the average hot-electron concentration and temperature under radio frequency (RF) operation class A, class B, and class F modes. From the results obtained, class A results, on average, in the highest hot-electron concentration, while class F is the mode with the lowest concentration due to its “L”-shaped load line. The electron temperature extracted from the electroluminescence spectra is reduced with increasing RF power, reflecting the dominance of electroluminescence from the portion of the load line in the semi-on region. The electroluminescence method is not able to give substantial information on the portion of the load line with high field and low current density which will be responsible for the potentially damaging hottest electrons present in the channel