On the Truncated Pareto Distribution with applications

The Pareto probability distribution is widely applied in different fields such us finance, physics, hydrology, geology and astronomy. This note deals with an application of the Pareto distribution to astrophysics and more precisely to the statistical analysis of mass of stars and of diameters of asteroids. In particular a comparison between the usual Pareto distribution and its truncated version is presented. Finally a possible physical mechanism that produces Pareto tails for the distribution of the masses of stars is suggested.Comment: 10 pages 6 figure

Constraints on ground motion at Yucca Mountain provided by precarious rocks

This report describes the methodology and results of the use of precariously balanced rocks to study seismic hazard at Yucca Mountain, Nevada, the site of a potential geologic repository for high-level radioactive waste. Precarious rocks are effectively strong-motion seismoscopes that have been in for place thousands of years. Numerous precarious rocks exist in and near Solitario Canyon, Nevada, immediately above the site of the potential repository. Estimates of toppling accelerations using computer models, physical models, and field tests indicate these rocks would be toppled by ground acceleration of a few tenths of the acceleration of gravity (g). Rock-surface age dating using rock varnish layering and cosmogenic age dating indicate that the rocks have been in place tens of thousands of years. Thus, the precarious rock methodology indicates that Yucca Mountain ground accelerations have not exceeded about 0.3 g for the last several tens of thousands of years. These results are consistent with paleoseismic studies of the Solitario Canyon fault that demonstrate the last significant surface offset capable of producing 0.3 g at the surface took place 75,000 to 80,000 years ago. This report presents recent results of testing, calibration, and application of the precarious rock methodology both at Yucca Mountain and in southern California. In southern California, the seismicity rate is much higher than at Yucca Mountain. Thus, the comparison of results of the precarious rock methodology with Probabilistic Seismic Hazard Analysis (PSHA) results is easier and more accurate. This lends confidence to the application of the methodology to Yucca Mountain. Preliminary results from these precarious rock studies suggest: (1) Probabilistic Seismic Hazard Analysis using current procedures gives values that are too high at low probabilities (e.g.,10 4 annual probabilities). This is true both for Yucca Mountain and for southern California. This is a result of unverified statistical assumptions in PSHA procedures. (2) Current ground-motion estimates for the footwall of major normal faults gives values that are too high. This tends to make the PSHA ground-motion estimates for Yucca Mountain too high. (3) Current ground motion estimates for trans-tensional strike-slip faults are too high. This tends to make the PSHA ground-motion estimates for Yucca Mountain too high. (4) Recent preliminary surface-exposure age dates for the pedestals of precarious rocks at Yucca Mountain are considerably older than some previous estimates. This result tends to confirm the conclusion in (1) above. Although the conclusions of this report have not been formally verified by rigorous peer review, they collectively lend strong support to the conclusion that the ground-motion estimates resulting from the Yucca Mountain Probabilistic Seismic Hazard Analysis (PSHA) are too large, perhaps excessively so

Self-consistent analytical solution of a problem of charge-carrier injection at a conductor/insulator interface

We present a closed description of the charge carrier injection process from a conductor into an insulator. Common injection models are based on single electron descriptions, being problematic especially once the amount of charge-carriers injected is large. Accordingly, we developed a model, which incorporates space charge effects in the description of the injection process. The challenge of this task is the problem of self-consistency. The amount of charge-carriers injected per unit time strongly depends on the energy barrier emerging at the contact, while at the same time the electrostatic potential generated by the injected charge- carriers modifies the height of this injection barrier itself. In our model, self-consistency is obtained by assuming continuity of the electric displacement and the electrochemical potential all over the conductor/insulator system. The conductor and the insulator are properly taken into account by means of their respective density of state distributions. The electric field distributions are obtained in a closed analytical form and the resulting current-voltage characteristics show that the theory embraces injection-limited as well as bulk-limited charge-carrier transport. Analytical approximations of these limits are given, revealing physical mechanisms responsible for the particular current-voltage behavior. In addition, the model exhibits the crossover between the two limiting cases and determines the validity of respective approximations. The consequences resulting from our exactly solvable model are discussed on the basis of a simplified indium tin oxide/organic semiconductor system.Comment: 23 pages, 6 figures, accepted to Phys.Rev.

Charge carrier injection into insulating media: single-particle versus mean-field approach

Self-consistent, mean-field description of charge injection into a dielectric medium is modified to account for discreteness of charge carriers. The improved scheme includes both the Schottky barrier lowering due to the individual image charge and the barrier change due to the field penetration into the injecting electrode that ensures validity of the model at both high and low injection rates including the barrier dominated and the space-charge dominated regimes. Comparison of the theory with experiment on an unipolar ITO/PPV/Au-device is presented.Comment: 32 pages, 9 figures; revised version accepted to PR

Properties of Foreshocks and Aftershocks of the Non-Conservative SOC Olami-Feder-Christensen Model: Triggered or Critical Earthquakes?

Following Hergarten and Neugebauer [2002] who discovered aftershock and foreshock sequences in the Olami-Feder-Christensen (OFC) discrete block-spring earthquake model, we investigate to what degree the simple toppling mechanism of this model is sufficient to account for the properties of earthquake clustering in time and space. Our main finding is that synthetic catalogs generated by the OFC model share practically all properties of real seismicity at a qualitative level, with however significant quantitative differences. We find that OFC catalogs can be in large part described by the concept of triggered seismicity but the properties of foreshocks depend on the mainshock magnitude, in qualitative agreement with the critical earthquake model and in disagreement with simple models of triggered seismicity such as the Epidemic Type Aftershock Sequence (ETAS) model [Ogata, 1988]. Many other features of OFC catalogs can be reproduced with the ETAS model with a weaker clustering than real seismicity, i.e. for a very small average number of triggered earthquakes of first generation per mother-earthquake.Comment: revtex, 19 pages, 8 eps figure

Quantité et dynamique des contaminants conventionnels et émergents dans les eaux pluviales de bassins versants types

Colloque avec actes et comité de lecture. Internationale.International audienc

Systematic event generator tuning for the LHC

In this article we describe Professor, a new program for tuning model parameters of Monte Carlo event generators to experimental data by parameterising the per-bin generator response to parameter variations and numerically optimising the parameterised behaviour. Simulated experimental analysis data is obtained using the Rivet analysis toolkit. This paper presents the Professor procedure and implementation, illustrated with the application of the method to tunes of the Pythia 6 event generator to data from the LEP/SLD and Tevatron experiments. These tunes are substantial improvements on existing standard choices, and are recommended as base tunes for LHC experiments, to be themselves systematically improved upon when early LHC data is available.Comment: 28 pages. Submitted to European Physical Journal C. Program sources and extra information are available from http://projects.hepforge.org/professor