Chaos at the border of criticality

The present paper points out to a novel scenario for formation of chaotic attractors in a class of models of excitable cell membranes near an Andronov-Hopf bifurcation (AHB). The mechanism underlying chaotic dynamics admits a simple and visual description in terms of the families of one-dimensional first-return maps, which are constructed using the combination of asymptotic and numerical techniques. The bifurcation structure of the continuous system (specifically, the proximity to a degenerate AHB) endows the Poincare map with distinct qualitative features such as unimodality and the presence of the boundary layer, where the map is strongly expanding. This structure of the map in turn explains the bifurcation scenarios in the continuous system including chaotic mixed-mode oscillations near the border between the regions of sub- and supercritical AHB. The proposed mechanism yields the statistical properties of the mixed-mode oscillations in this regime. The statistics predicted by the analysis of the Poincare map and those observed in the numerical experiments of the continuous system show a very good agreement.Comment: Chaos: An Interdisciplinary Journal of Nonlinear Science (tentatively, Sept 2008

The Second Virial Coefficient of Spin-1/2 Interacting Anyon System

Evaluating the propagator by the usual time-sliced manner, we use it to compute the second virial coefficient of an anyon gas interacting through the repulsive potential of the form $g/r^2 (g > 0)$. All the cusps for the unpolarized spin-1/2 as well as spinless cases disappear in the $\omega \to 0$ limit, where $\omega$ is a frequency of harmonic oscillator which is introduced as a regularization method. As $g$ approaches to zero, the result reduces to the noninteracting hard-core limit.Comment: 9 pages, 2 figs include

Augmented Reality and Surgery: Human Factors, Challenges, and Future Steps

Augmented reality (AR) has shown much potential when applied in surgical settings, which can help guide surgeons through complex procedures, train students, and provide heads-up and hands-free spatial information. In this position paper, we discuss some of the current use cases of AR in surgical practice, evaluation measures, challenges and potential directions for future research. The aim of this paper is to start important discussion to improve future research and outcomes for system implementations for surgery

Erratum: Dirichlet Forms and Dirichlet Operators for Infinite Particle Systems: Essential Self-adjointness

We reprove the essential self-adjointness of the Dirichlet operators of Dirchlet forms for infinite particle systems with superstable and sub-exponentially decreasing interactions.Comment: This is an erratum to the work appeared in J. Math. Phys. 39(12), 6509-6536 (1998

Going beyond the Kaiser redshift-space distortion formula: a full general relativistic account of the effects and their detectability in galaxy clustering

Kaiser redshift-space distortion formula describes well the clustering of galaxies in redshift surveys on small scales, but there are numerous additional terms that arise on large scales. Some of these terms can be described using Newtonian dynamics and have been discussed in the literature, while the others require proper general relativistic description that was only recently developed. Accounting for these terms in galaxy clustering is the first step toward tests of general relativity on horizon scales. The effects can be classified as two terms that represent the velocity and the gravitational potential contributions. Their amplitude is determined by effects such as the volume and luminosity distance fluctuation effects and the time evolution of galaxy number density and Hubble parameter. We compare the Newtonian approximation often used in the redshift-space distortion literature to the fully general relativistic equation, and show that Newtonian approximation accounts for most of the terms contributing to velocity effect. We perform a Fisher matrix analysis of detectability of these terms and show that in a single tracer survey they are completely undetectable. To detect these terms one must resort to the recently developed methods to reduce sampling variance and shot noise. We show that in an all-sky galaxy redshift survey at low redshift the velocity term can be measured at a few sigma if one can utilize halos of mass M>10^12 Msun (this can increase to 10-sigma or more in some more optimistic scenarios), while the gravitational potential term itself can only be marginally detected. We also demonstrate that the general relativistic effect is not degenerate with the primordial non-Gaussian signature in galaxy bias, and the ability to detect primordial non-Gaussianity is little compromised.Comment: 13 pages, 5 figures, published in PR

Ytterbium doped nano-crystalline optical fiber for reduced photodarkening

We report suppression of photodarkening in Yb-doped nano-crystalline fibers in silica host. The photodarkening induced loss reduced by 20 times compared to Yb-doped aluminosilicate fibers. The laser efficiency of the nano-crystalline fiber was 79%

The Wires Go to War: The U.S. Experiment with Government Ownership of the Telephone System During World War I

One of the most distinctive characteristics of the U.S. telephone system is that it has always been privately owned, in stark contrast to the pattern of government ownership followed by virtually every other nation. What is not widely known is how close the United States came to falling in line with the rest of the world. For the one-year period following July 31, 1918, the exigencies of World War I led the federal government to take over the U.S. telephone system. A close examination of this episode sheds new light into a number of current policy issues. The history confirms that natural monopoly was not solely responsible for AT&T’s return to dominance and reveals that the Kingsbury Commitment was more effective in deterring monopoly than generally believed. Instead, a significant force driving the re-monopolization of the telephone system was the U.S. Postmaster General, Albert Burleson — not Theodore Vail, President of AT&T. It also demonstrates that universal service was the result of government-imposed emulation of the postal system, not, as some have claimed, a post hoc rationalization for maintaining monopoly. The most remarkable question is, having once obtained control over the telephone system, why did the federal government ever let it go? The dynamics surrounding this decision reveal the inherent limits of relying on war to justify extraordinary actions. More importantly, it shows the difficulties that governments face in overseeing industries that are undergoing dynamic technological change and that require significant capital investments

Lowering Legal Barriers to RPKI Adoption

Across the Internet, mistaken and malicious routing announcements impose significant costs on users and network operators. To make routing announcements more reliable and secure, Internet coordination bodies have encouraged network operators to adopt the Resource Public Key Infrastructure (“RPKI”) framework. Despite this encouragement, RPKI’s adoption rates are low, especially in North America.This report presents the results of a year-long investigation into the hypothesis—widespread within the network operator community—that legal issues pose barriers to RPKI adoption and are one cause of the disparities between North America and other regions of the world. On the basis of interviews and analysis of the legal framework governing RPKI, the report evaluates the issues raised by community members and proposes a number of strategies to reduce or circumvent the barriers that are material. The report also describes substantial action taken this year by the American Registry for Internet Numbers (“ARIN”) and other private organizations in light of public dialogue about RPKI

Complete Treatment of Galaxy Two-Point Statistics: Gravitational Lensing Effects and Redshift-Space Distortions

We present a coherent theoretical framework for computing gravitational lensing effects and redshift-space distortions in an inhomogeneous universe and investigate their impacts on galaxy two-point statistics. Adopting the linearized FRW metric, we derive the gravitational lensing and the generalized Sachs-Wolfe effects that include the weak lensing distortion, magnification, and time delay effects, and the redshift-space distortion, Sachs-Wolfe, and integrated Sachs-Wolfe effects, respectively. Based on this framework, we first compute their effects on observed source fluctuations, separating them as two physically distinct origins: the volume effect that involves the change of volume and is always present in galaxy two-point statistics, and the source effect that depends on the intrinsic properties of source populations. Then we identify several terms that are ignored in the standard method, and we compute the observed galaxy two-point statistics, an ensemble average of all the combinations of the intrinsic source fluctuations and the additional contributions from the gravitational lensing and the generalized Sachs-Wolfe effects. This unified treatment of galaxy two-point statistics clarifies the relation of the gravitational lensing and the generalized Sachs-Wolfe effects to the metric perturbations and the underlying matter fluctuations. For near future dark energy surveys, we compute additional contributions to the observed galaxy two-point statistics and analyze their impact on the anisotropic structure. Thorough theoretical modeling of galaxy two-point statistics would be not only necessary to analyze precision measurements from upcoming dark energy surveys, but also provide further discriminatory power in understanding the underlying physical mechanisms.Comment: 20 pages, 5 figures, Fig.4 corrected, appendix added, accepted for publication in Physical Review