Knowledge-based modeling of discrete-event simulation systems

Modeling a simulation system requires a great deal of customization. At first sight no system seems to resemble exactly another system and every time a new model has to be designed the modeler has to start from scratch. The present simulation languages provide the modeler with powerful tools that greatly facilitate building models (modules for arrivals or servers, etc.). Yet, also with these tools the modeler constantly has the feeling that he is reinventing the wheel again and again. Maybe the model he is about to design already exists (maybe the modeler has designed it himself some time ago) or maybe a model already exists that sufficiently resembles the model to be designed. In this article an approach is discussed that deploys knowledge-based systems to help selecting a model from a database of existing models. Also, if the model is not present in the database, would it be possible to select a model that in some sense is close to the model that the modeler had in mind

A 3D simulation case study of airport air traffic handling

Modern Windows-based simulation packages bring simulation within reach of decision-makers. The use of graphics enables the manager to observe an animation of the simulated reality, to focus on the essentials of the model without the need to bother about implementation details. In most applications a 2D representation will satisfy the simulation objectives. One field of application in which 3D simulation is highly recommended is air traffic handling on and above an airport. In order to get a real understanding of this kind of process 3D simulation is indispensable. In this article a simulation is described in which 3D animation is essential to base management decisions on

Long Term Evolution of Magnetic Turbulence in Relativistic Collisionless Shocks

We study the long term evolution of magnetic fields generated by an initially unmagnetized collisionless relativistic $e^+e^-$ shock. Our 2D particle-in-cell numerical simulations show that downstream of such a Weibel-mediated shock, particle distributions are approximately isotropic, relativistic Maxwellians, and the magnetic turbulence is highly intermittent spatially, nonpropagating, and decaying. Using linear kinetic theory, we find a simple analytic form for these damping rates. Our theory predicts that overall magnetic energy decays like $(\omega_p t)^{-q}$ with $q \sim 1$, which compares favorably with simulations, but predicts overly rapid damping of short wavelength modes. Magnetic trapping of particles within the magnetic structures may be the origin of this discrepancy. We conclude that initially unmagnetized relativistic shocks in electron-positron plasmas are unable to form persistent downstream magnetic fields. These results put interesting constraints on synchrotron models for the prompt and afterglow emission from GRBs.Comment: 4 pages, 3 figures, contributed talk at the workshop: High Energy Phenomena in Relativistic Outflows (HEPRO), Dublin, 24-28 September 2007; Downsampled version for arXiv. Full resolution version available at http://astro.berkeley.edu/~pchang/proceedings.pd

Arrival processes in port modeling: insights from a case study

This paper investigates the impact of arrival processes on the ship handling process. Two types of arrival processes are considered: controlled and uncontrolled. Simulation results show that uncontrolled arrivals of ships perform worst in terms of both ship delays and required storage capacity. Stock-controlled arrivals perform best with regard to large vessel delays and storage capacity. The combination of stock-controlled arrivals for large vessels and equidistant arrivals for barges also performs better than the uncontrolled process. Careful allocation of ships to the mooring points of a jetty further improves the efficiency.supply chain management;logistics;simulation;transportation;case study

A Knowledge base representing Porter's Five Forces Model

Strategic Analysis and Planning is a field in which expertise and experience are key factors. In order to decide on strategic matters such as the competitive position of a company experts heavily lean on their ability to reason with uncertain or incomplete knowledge, or in other words on their experience and expertise. An important aspect is to assess a company's profit potential in the industry for which Porter's Competitive Forces Model is by far the most widely used framework. This article focuses on the various aspects of designing and developing an expert system representing Porter's Competitive Forces Model

An object-oriented model for strategic analysis

Strategic analysis is a domain in which human expertise and experience are key factors. This is the reason that attempts have been made to automate the strategic analysis by expert systems. This article means to capture the expert knowledge to be used in an expert system with the focus on an object-oriented model of the domain. Based on this OO model an expert system can be developed that is able to analyze a corporate enterprise with several Strategic Business Units each of which carrying more than one product at a time. Such an expert system would be able to analyze the various synergetic aspects

Implementation and results of a prototype expert system on strategic analysis

Expertise and experience are key factors for experts in strategic analysis in order to give advice on strategic matters such as the strength or the competitive position of an enterprise. They are able to reason with uncertain or incomplete knowledge. Expert systems may be able to do the same if this heuristic knowledge can be modeled and processed properly. This article discusses the modeling, implementation and the results of such an expert on strategic analysis. The results are compared to those generated by Business Insight and further improvements are discussed

Thermal Cyclotron Reprocessing of Gammy-Ray Bursts - Theory and Model Spectra

We examine the generation of infrared, optical, and ultraviolet flashes from single, magnetized neutron stars are experiencing of gamma-ray burst. Cyclotron reprocessing of energetic gamma-ray burst photons in the neutron star magnetosphere is assumed to be the underlying mechanism reponsible for the display at longer wavelengths, and thermal equilibrium is assumed in order to calculate electron distribution function. It is shown that thesea good approximations for a wide range of conditions expected in neutron star magnetospheres. The thermal cycoltron model proves capable fo generating ptical outbursts similar to bright historical events. althrough opitcal transients most likely would be much fainter. For a wide range of conditions the model predicts bright, nondelayed flashes, extending in some cases even beyond the ultraviolet. Since the emission at long wavelengths is correlated with the gammar-rays down to time scales small compared with the burst duration, time-averaged spectra are calculated corresponding to the time-averaged gamma-ray burst spectrum. For flashes that do not exhibit a spectral turnover in the optical region, Lopt α Bas with α ~ 3/4, so that optical transients could be used to constrain the magnetic field strength and distance of gamma-ray burst sources. The long-wavelength fluxes for the recently discovered soft repearing source SGR 1806-20 are also estimated

The Double Pulsar Eclipses I: Phenomenology and Multi-frequency Analysis

The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise around conjunction when the radio waves emitted by pulsar A are absorbed as they propagate through the magnetosphere of its companion pulsar B. These eclipses offer a unique opportunity to probe directly the magnetospheric structure and the plasma properties of pulsar B. We have performed a comprehensive analysis of the eclipse phenomenology using multi-frequency radio observations obtained with the Green Bank Telescope. We have characterized the periodic flux modulations previously discovered at 820 MHz by McLaughlin et al., and investigated the radio frequency dependence of the duration and depth of the eclipses. Based on their weak radio frequency evolution, we conclude that the plasma in pulsar B's magnetosphere requires a large multiplicity factor (~ 10^5). We also found that, as expected, flux modulations are present at all radio frequencies in which eclipses can be detected. Their complex behavior is consistent with the confinement of the absorbing plasma in the dipolar magnetic field of pulsar B as suggested by Lyutikov & Thompson and such a geometric connection explains that the observed periodicity is harmonically related to pulsar B's spin frequency. We observe that the eclipses require a sharp transition region beyond which the plasma density drops off abruptly. Such a region defines a plasmasphere which would be well inside the magnetospheric boundary of an undisturbed pulsar. It is also two times smaller than the expected standoff radius calculated using the balance of the wind pressure from pulsar A and the nominally estimated magnetic pressure of pulsar B.Comment: 9 pages, 7 figures, 3 tables, ApJ in pres