Space Time Defects as a Source of Curvature and Torsion

Space time is described as a continuum four-dimensional medium similar to ordinary elastic continua. Exploiting the analogy internal stress states are considered. The internal ''stress'' is originated by the presence of defects. The defects are described according to the typical Volterra process. The case of a point defect in an otherwise isotropic four-dimensional medium is discussed showing that the resulting metric tensor corresponds to an expanding (or contracting) universe filled up with a non-zero energy-momentum density.Comment: Presentation at the Sixth Friedman seminar in Cargese 28/6-3/7/2004. Submitted for the proceedings of the seminar to appear in the International Journal of Modern Physics

Macroscopic equations for the adiabatic piston

A simplified version of a classical problem in thermodynamics -- the adiabatic piston -- is discussed in the framework of kinetic theory. We consider the limit of gases whose relaxation time is extremely fast so that the gases contained on the left and right chambers of the piston are always in equilibrium (that is the molecules are uniformly distributed and their velocities obey the Maxwell-Boltzmann distribution) after any collision with the piston. Then by using kinetic theory we derive the collision statistics from which we obtain a set of ordinary differential equations for the evolution of the macroscopic observables (namely the piston average velocity and position, the velocity variance and the temperatures of the two compartments). The dynamics of these equations is compared with simulations of an ideal gas and a microscopic model of gas settled to verify the assumptions used in the derivation. We show that the equations predict an evolution for the macroscopic variables which catches the basic features of the problem. The results here presented recover those derived, using a different approach, by Gruber, Pache and Lesne in J. Stat. Phys. 108, 669 (2002) and 112, 1177 (2003).Comment: 13 pages, 7 figures (revTeX4) The paper has been completely rewritten with new derivation and results, supplementary information can be found at http://denali.phys.uniroma1.it/~cencini/Papers/cppv07_supplements.pd

Explaining human multiple object tracking as resource-constrained approximate inference in a dynamic probabilistic model

Multiple object tracking is a task commonly used to investigate the architecture of human visual attention. Human participants show a distinctive pattern of suc- cesses and failures in tracking experiments that is often attributed to limits on an object system, a tracking module, or other specialized cognitive structures. Here we use a computational analysis of the task of object tracking to ask which human failures arise from cognitive limitations and which are consequences of inevitable perceptual uncertainty in the tracking task. We find that many human perfor- mance phenomena, measured through novel behavioral experiments, are naturally produced by the operation of our ideal observer model (a Rao-Blackwelized par- ticle filter). The tradeoff between the speed and number of objects being tracked, however, can only arise from the allocation of a flexible cognitive resource, which can be formalized as either memory or attention.Psycholog

Slaves, Soldiers, Citizens: African American Artifacts of the Civil War Era

Based on the exhibit Slaves, Soldiers, Citizens: African American Artifacts of the Civil War Era, this book provides the full experience of the exhibit, which was on display in Special Collections at Musselman Library November 2012- December 2013. It also includes several student essays based on specific artifacts that were part of the exhibit. Table of Contents: Introduction Angelo Scarlato, Lauren Roedner ’13 & Scott Hancock Slave Collars & Runaways: Punishment for Rebellious Slaves Jordan Cinderich ’14 Chancery Sale Poster & Auctioneer’s Coin: The Lucrative Business of Slavery Tricia Runzel ’13 Isaac J. Winters: An African American Soldier from Pennsylvania Who Fought at Petersburg Avery Lentz ’14 Basil Biggs: A Prominent African American in Gettysburg after the Battle Lauren Roedner ’13 Linton Ingram: A Former Slave Who Became a Notable African American Educator in Georgia Brian Johnson & Lincoln Fitch ’14 Uncle Tom’s Cabin Theatre Poster: Racism in Post-Emancipation Entertainment Michelle Seabrook ’13 Essay Bibliographies Grand Army of the Republic Exhibit Inventory Acknowledgmentshttps://cupola.gettysburg.edu/libexhibits/1001/thumbnail.jp

Correlation function and generalized master equation of arbitrary age

We study a two-state statistical process with a non-Poisson distribution of sojourn times. In accordance with earlier work, we find that this process is characterized by aging and we study three different ways to define the correlation function of arbitrary age of the corresponding dichotomous fluctuation based respectively on the Generalized Master Equation formalism, on a Liouville-like approach and on a trajectory perspective.Comment: 11 pages, 1figur

Angular momentum effects in Michelson-Morley type experiments

The effect of the angular momentum density of a gravitational source on the times of flight of light rays in an interferometer is analyzed. The calculation is made imagining that the interferometer is at the equator of the gravity source and, as long as possible, the metric, provided it is stationary and axisymmetric, is not approximated. Finally, in order to evaluate the size of the effect in the case of the Earth a weak field approximation is introduced. For laboratory scales and non-geodesic paths the correction turns out to be comparable with the sensitivity expected in gravitational waves interferometric detectors, whereas it drops under the threshold of detectability when using free (geodesic) light rays.Comment: 12 pages, LaTeX; more about the detection technique, references added; accepted for publication in GR

A post-Keplerian parameter to test gravito-magnetic effects in binary pulsar systems

We study the pulsar timing, focusing on the time delay induced by the gravitational field of the binary systems. In particular, we study the gravito-magnetic correction to the Shapiro time delay in terms of Keplerian and post-Keplerian parameters, and we introduce a new post-Keplerian parameter which is related to the intrinsic angular momentum of the stars. Furthermore, we evaluate the magnitude of these effects for the binary pulsar systems known so far. The expected magnitude is indeed small, but the effect is important per se.Comment: 6 pages, RevTeX, 1 eps figure, accepted for publication in Physical Review D; references adde

Doppler Effects from Bending of Light Rays in Curved Space-Times

We study Doppler effects in curved space-time, i.e. the frequency shifts induced on electromagnetic signals propagating in the gravitational field. In particular, we focus on the frequency shift due to the bending of light rays in weak gravitational fields. We consider, using the PPN formalism, the gravitational field of an axially symmetric distribution of mass. The zeroth order, i.e. the sphere, is studied then passing to the contribution of the quadrupole moment, and finally to the case of a rotating source. We give numerical estimates for situations of physical interest, and by a very preliminary analysis, we argue that analyzing the Doppler effect could lead, in principle, in the foreseeable future, to the measurement of the quadrupole moment of the giant planets of the Solar System.Comment: 16 pages, 2 EPS figures; to appear in the International Journal of Modern Physics