Molecular dynamics study of the thermopower of Ag, Au, and Pt nanocontacts

Using molecular dynamics simulations of many junction stretching processes we analyze the thermopower of silver (Ag), gold (Au), and platinum (Pt) atomic contacts. In all cases we observe that the thermopower vanishes on average within the standard deviation and that its fluctuations increase for decreasing minimum cross-section of the junctions. However, we find a suppression of the fluctuations of the thermopower for the s-valent metals Ag and Au, when the conductance originates from a single, perfectly transmitting channel. Essential features of the experimental results for Au, Ag, and copper (Cu) of Ludoph and van Ruitenbeek [Phys. Rev. B 59, 12290 (1999)], as yet unaddressed by atomistic studies, can hence be explained by considering the atomic and electronic structure at the disordered narrowest constriction of the contacts. For the multivalent metal Pt our calculations predict the fluctuations of the thermopower to be larger by one order of magnitude as compared to Ag and Au, and suppressions of the fluctuations as a function of the conductance are absent.Comment: 13 pages, 10 figure

Dynamics of aircraft antiskid braking systems

A computer study was performed to assess the accuracy of three brake pressure-torque mathematical models. The investigation utilized one main gear wheel, brake, and tire assembly of a McDonnell Douglas DC-9 series 10 airplane. The investigation indicates that the performance of aircraft antiskid braking systems is strongly influenced by tire characteristics, dynamic response of the antiskid control valve, and pressure-torque response of the brake. The computer study employed an average torque error criterion to assess the accuracy of the models. The results indicate that a variable nonlinear spring with hysteresis memory function models the pressure-torque response of the brake more accurately than currently used models

Acoustically driven ferromagnetic resonance

Surface acoustic waves (SAW) in the GHz frequency range are exploited for the all-elastic excitation and detection of ferromagnetic resonance (FMR) in a ferromagnetic/ferroelectric (nickel/lithium niobate) hybrid device. We measure the SAW magneto-transmission at room temperature as a function of frequency, external magnetic field magnitude, and orientation. Our data are well described by a modified Landau-Lifshitz-Gilbert approach, in which a virtual, strain-induced tickle field drives the magnetization precession. This causes a distinct magnetic field orientation dependence of elastically driven FMR that we observe in both model and experiment.Comment: 4 page

NewOX - extending the online exXam system to provide automated formative evaluation of student text-based assignments

A cheat-resistant and foolproof distributed electronic application for summativeassessment of student learning outcomes has been developed and field tested "OnlineeXam" (OX). Good usability experience and feedback features for the students as wellas the lecturers were design goals of the implementation. The field tests showed therobustness of the system in a heterogenic PC pool environment, the ease of use and agood student learning outcome assessment ability (summative assessment) but a lackof a formative impact on the student learning efforts. The incorporation and adoption(for European needs) of a short essay assessment algorithm with a rich user interfaceis proposed

On new emerging concepts of modeling petroleum digital ecosystems by multidimensional data warehousing and mining approaches

Petroleum system and its ingredients are narrated for each and every oil and gas field in each and everypetroleum-bearing sedimentary basin. A new concept of ecosystem and its digitization are emerging within the generic petroleum system. Significance of this concept is to make connectivity among petroleum systems through attributes of ingredients and their contextualization and specification. Most popularly known ingredients are geological structure, reservoir, source and seal rocks. Other ingredients involved are in the form of process of these ingredients such as maturation (of source rocks) and migration and timing (of formation of structure, reservoir and seal rocks). One can notice the connectivity among primary petroleum system ingredients, through different processes, such as maturation of source rocks and charging capability and migration of hydrocarbons into suitablestructural (structure) entrapment areas of reservoir. Unless the phenomenon of interconnectivity is understood; integration between ingredients and processes in the context of digital representation and visualization, petroleum system existence and its survival cannot be well explained. Its value cannot beadded in terms of petroleum accumulations and volumes, unless these phenomena are explicit. Authors propose ontology based data warehousing and data mining technologies, in which, conceptualization and contextualization of multiple data dimensions (petroleum system?s ingredients and processes), integration (within data warehouse environment) and data mining of interpretable emerging petroleum digital ecosystems are accomplished. Multidimensional data warehousingand mining facilitate an effective interpretation of petroleum systems, minimizing the ambiguities involved during structure and reservoir qualifications and quantifications