Paradoxical Magnetic Cooling in a Structural Transition Model

In contrast to the experimentally widely used isentropic demagnetization process for cooling to ultra-low temperatures we examine a particular classical model system that does not cool, but rather heats up with isentropic demagnetization. This system consists of several magnetite particles in a colloidal suspension, and shows the uncommon behavior of disordering structurally while ordering magnetically in an increasing magnetic field. For a six-particle system, we report an uncommon structural transition from a ring to a chain as a function of magnetic field and temperature.Comment: 3 pages, 2 figures. For recent information on physics of small systems see http://www.smallsystems.d

An Artificial Neural Network Framework for Pedestrian Walking Behavior Modeling and Simulation

Movement behavior models of pedestrian agents form the basis of computational crowd simulations. In contemporary research, a large number of models exist. However, there is still no walking behavior model that can address the various influence factors of movement behavior holistically. Thus, we endorse the use of artificial neural networks to develop walking behavior models because machine learning methods can integrate behavioral factors efficiently, automatically, and data-driven. In this paper, we support this approach by providing a framework that describes how to include artificial neural networks into a pedestrian research context. The framework comprises 5 phases: data, replay, training, simulation, and validation. Furthermore, we describe and discuss a prototype of the framework

MODIS: ein Expertensystem zur Erstellung von Reparaturdiagnosen für den Ottomotor und seine Aggregate

MODIS ("motor-diagnosis-system") is a fully implemented, interactive knowledge-based expert system for diagnosing faults for internal combustion engines and associated aggregates (fuel-, Carburetor-, ignition-, starter-, lubrication-, exhaustion-, and cooling system; electrical installations only as far as the engine is affected). MODIS is based on some 2100 rules, using the meta-level-diagnosis system MEDl as a shell. Following MEDl, generating and checking diagnostic hypotheses proceeds along several levels of abstraction, with each level providing guidance for those taking more detailed views. MODIS has been field-tested with service-personnel of a major manufacturer, demonstrating satisfactory performance w.r.t. correctness, completeness, efficiency, as well as appropriateness in results, performance, and user interaction.MODIS ("Motor-Diagnose-System") ist ein benutzungsfähiges, interaktives, wissensbasiertes Expertensystem zur Diagnostik von Fehlern in Ottomotoren und damit unmittelbar zusammenhängenden Aggregaten (Kraftstoff-, Vergaser-, Zünd-, Start, Schmier-, Auspuff- und Kühlanlage; elektrische Anlage nur soweit für den Motorbetrieb erforderlich): MODIS arbeitet mit über 2100 Regeln, die in das als Metasystem genommene Meta-Ebenen-Diagnostik-System MEDl eingefügt wurden. Erzeugung und Überprüfung von Verdachtsdiagnosen erfolgt über mehrere Abstraktionsebenen, wobei jede Ebene die Kontrollsteuerung für Ebenen mit größerem Detaillierungsgrad unterstützt. MODIS wurde Feldversuchen mit erfahrenen Kfz-Mechanikern einer Werkstatt eines großen Herstellers unterzogen. Dabei erwiesen sich gute Leistungen in der Korrektheit, Vollständigkeit und Effizienz in der Ableitung der Resultate, sowie Adäquatheit im Verhalten gegenüber dem Benutzer

Order-disorder transition in nanoscopic semiconductor quantum rings

Using the path integral Monte Carlo technique we show that semiconductor quantum rings with up to six electrons exhibit a temperature, ring diameter, and particle number dependent transition between spin ordered and disordered Wigner crystals. Due to the small number of particles the transition extends over a broad temperature range and is clearly identifiable from the electron pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small systems see http://www.smallsystems.d

Classification of phase transitions in small systems

We present a classification scheme for phase transitions in finite systems like atomic and molecular clusters based on the Lee-Yang zeros in the complex temperature plane. In the limit of infinite particle numbers the scheme reduces to the Ehrenfest definition of phase transitions and gives the right critical indices. We apply this classification scheme to Bose-Einstein condensates in a harmonic trap as an example of a higher order phase transitions in a finite system and to small Ar clusters.Comment: 12 pages, 4 figures, accepted for publication in Phys. Rev. Let