Ab initio yield curve dynamics

We derive an equation of motion for interest-rate yield curves by applying a minimum Fisher information variational approach to the implied probability density. By construction, solutions to the equation of motion recover observed bond prices. More significantly, the form of the resulting equation explains the success of the Nelson Siegel approach to fitting static yield curves and the empirically observed modal structure of yield curves. A practical numerical implementation of this equation of motion is found by using the Karhunen-Loeve expansion and Galerkin's method to formulate a reduced-order model of yield curve dynamics.Comment: 11 LateX pages, 2 figure

Unsolved questions and preferred solution about living will.

Background: Ethical problems about end-of-life medicine include a variety of issues approached in different ways by physicians and, more recently, special emphasis to this kind of ethical issues and possible answers has done by Italian National Ethical Committee in the issue named “Deep and continuous palliative sedation in the imminence of Death” (January, 2016). The debate is very critical in Intensive Care Units and Cancer Wards, where health care professionals face-off with terminally-ill patients is an outright routine; the Authors investigated their medical knowledge and ethical perception about patient critical and terminal condition to discuss the most relevant conclusions. Material: In the Sicilian province of Palermo, physicians working in Intensive Care and Oncology fields were been given a questionnaire that takes inspiration from the Ethicatt Questionnaire-Doctor. The authors reported the results obtained, by selecting and analyzing the most involved questions about living wills. Results: Generally, the respondents showed a great sensibility on this topic. Overall agreement on the living will was observed, as past surveys, but also a new conception. Euthanasia remains not very popular, attitude in line with other countries. Opinions and aptitudes of relatives have minor importance towards patient’s wishes, that are in some cases in first place. Conclusion: Explicit positive answer towards dilemmas about living wills lifts the veil and reveals how these ones would represent a very useful tool for health care professionals in this study. It is also plausible that, if doctors had available an advance directive (living will) document, they would follow it, overcoming any contingent ethical objections

Observing Brownian motion in vibration-fluidized granular matter

At the beginning of last century, Gerlach and Lehrer observed the rotational Brownian motion of a very fine wire immersed in an equilibrium environment, a gas. This simple experiment eventually permitted the full development of one of the most important ideas of equilibrium statistical mechanics: the very complicated many-particle problem of a large number of molecules colliding with the wire, can be represented by two macroscopic parameters only, namely viscosity and the temperature. Can this idea, mathematically developed in the so-called Langevin model and the fluctuation-dissipation theorem be used to describe systems that are far from equilibrium? Here we address the question and reproduce the Gerlach and Lehrer experiment in an archetype non-equilibrium system, by immersing a sensitive torsion oscillator in a granular system of millimetre-size grains, fluidized by strong external vibrations. The vibro-fluidized granular medium is a driven environment, with continuous injection and dissipation of energy, and the immersed oscillator can be seen as analogous to an elastically bound Brownian particle. We show, by measuring the noise and the susceptibility, that the experiment can be treated, in first approximation, with the same formalism as in the equilibrium case, giving experimental access to a ''granular viscosity'' and an ''effective temperature'', however anisotropic and inhomogeneous, and yielding the surprising result that the vibro-fluidized granular matter behaves as a ''thermal'' bath satisfying a fluctuation-dissipation relation

Hall Anomaly and Vortex-Lattice Melting in Superconducting Single Crystal YBa2Cu3O7-d

Sub-nanovolt resolution longitudinal and Hall voltages are measured in an ultra pure YBa2Cu3O7-d single crystal. The Hall anomaly and the first-order vortex-lattice melting transition are observed simultaneously. Changes in the dynamic behavior of the vortex solid and liquid are correlated with features of the Hall conductivity sxy. With the magnetic field oriented at an angle from the twin-boundaries, the Hall conductivity sharply decreases toward large negative values at the vortex-lattice melting transition.Comment: 6 pages, 2 figures included, Postscript, to appear in Phys. Rev. Let

Extreme events driven glassy behaviour in granular media

Motivated by recent experiments on the approach to jamming of a weakly forced granular medium using an immersed torsion oscillator [Nature 413 (2001) 407], we propose a simple model which relates the microscopic dynamics to macroscopic rearrangements and accounts for the following experimental facts: (1) the control parameter is the spatial amplitude of the perturbation and not its reduced peak acceleration; (2) a Vogel-Fulcher-Tammann-like form for the relaxation time. The model draws a parallel between macroscopic rearrangements in the system and extreme events whose probability of occurrence (and thus the typical relaxation time) is estimated using extreme-value statistics. The range of validity of this description in terms of the control parameter is discussed as well as the existence of other regimes.Comment: 7 pages, to appear in Europhys. Let

Enumeration of many-body skeleton diagrams

The many-body dynamics of interacting electrons in condensed matter and quantum chemistry is often studied at the quasiparticle level, where the perturbative diagrammatic series is partially resummed. Based on Hedin's equations for self-energy, polarization, propagator, effective potential, and vertex function in zero dimension of space-time, dressed Feynman (skeleton) diagrams are enumerated. Such diagram counts provide useful basic checks for extensions of the theory for future realistic simulations.Comment: 5 pages including 4 figure