A STUDY OF EXPERIMENTAL DESIGN OPTIMALITY FOR WIENER SYSTEMS

In the context of nonlinear dynamic system identification for Hammerstein systems, Rollins et al. (2003a) studied the information efficiency of the following two competing experimental design approaches: statistical design of experiments (SDOE) and pseudo-random sequences design (PRSD). The focus of this study is the Wiener system and evaluates SDOE against PRS under D-optimal efficiency. Three cases are evaluated and the results strongly support SDOE as the better approach.     

Methodology for spectral emissivity measurement by means of single color pyrometer

The application of non-intrusive optical devices, such as infrared pyrometers able to measure the temperature of surfaces, makes possible the evaluation of emissivity curve of the tested materials at different temperature values. In this paper the authors propose a methodology for the spectral emissivity measurement by means of a single color pyrometer providing a semi-empirical formula, obtained experimentally at CIRA’s laboratory. The semi-empirical formula allows to know the actual emissivity value of the sample’s surface for whatever emissivity value set up on the pyrometer. The agreement between the experimental emissivity and the emissivity predicted by semi-empirical formula was verified.     

Water wettability/non-wettability of polymer materials by molecular orbital studies

The water wettability and non-wettability onto various kinds of polymers, which have so far been macroscopically described by the water contact angle, were investigated using the molecular orbital theory. An atomistic model consisting of an H₂O molecule and a selected polymer crystal surface was analyzed in the isolated and the physisorbed states. The degree of interaction between the water molecule and the polymer surface was evaluated by considering the change of Mulliken charge at the oxygen site in the water molecule, and also the work of adhesion during the physisorption process. Such energetic quantities for several polymers were compared with the macroscopic water wettability/non-wettability. We found fairly good agreement between these approaches for the highly non-wettability polymers.     

A new spd tight-binding model of magnetism in transition metals

We present the extension of an efficient spd tight-binding model to the case of spin polarized materials by including electron–electron interactions, in an extended Hubbard–Hartree–Fock formalism. It is applied with success to rhodium and palladium clusters and slabs.     

Probing Aromaticity of Borozene Through Optical and Dielectric Response: A Theoretical Study

In this work, we report electronic structure calculations aimed at computing the linear optical absorption spectrum and static dipole polarizablity of a newly proposed boron-based planar aromatic compound borozene (B ₁₂ H ₆). For the purpose, we use the semiempirical INDO model Hamiltonian, accompanied by large-scale correlation calculations using the multi-reference singles-doubles configuration-interaction (MRSDCI) approach. We present detailed predictions about the energetics, polarization properties, and the nature of many-particle states contributing to various peaks in the linear absorption spectrum. Our results can be used to characterize this material in future optical absorption experiments. We also argue that one can deduce the aromaticity of the cluster from the optical absorption and static polarizability results.     

Structure of point defects in B2 Fe-Al alloys: An atomistic study by semi-empirical simulation

We present the first results of a simulation study of point-defect properties in B2 ordered Fe-Al alloys (34% < x_Al < 52%). After examining the T = 0 K energetics of simple defects, we turn to complexes and discuss the usual hypothesis of independent elementary defects. Almost all complex defects involving an Al vacancy and an Al antisite atom in nearest neighbour position are shown to be unstable, confirming that Al vacancies are rare in these alloys. Small deviations from stoichiometry induce a change in the nature of defects: whereas on the Al-rich side, isolated Al antisite atoms dominate, Fe antisite atoms have a strong trend towards clustering on the Fe-rich side, leading to the formation of local DO₃ order.     

System identification of the human thermoregulatory system using continuous-time block-oriented predictive modeling

This article presents preliminary results of a new research program for identifying predictive models for human thermoregulatory (HT) response using only an individual's attributes and their physical property data to build the model. This program is being developed in phases and this article presents results of the first phase. This initial phase demonstrates that the proposed semi-empirical (i.e., gray-box), continuous-time, block-oriented modeling (BOM) approach [Rollins, et al. 2003. A continuous time nonlinear dynamic predictive modeling method for Hammerstein processes. Industrial and Engineering Chemistry Research 42, 861-872; Bhandari and Rollins, 2003. A continuous-time MIMO Wiener modeling method. Industrial and Engineering Chemistry Research 42, 5583-5595.] is capable of accurately predicting HT response. This ability is demonstrated using real data from literature [Hardy and Stolwijck, 1966. Partitional calorimetric studies of man during exposures to thermal transients. Journal of Applied Physiology 21(6), 1799-1806.] and computer generated data from a HT semi-theoretical model with qualitatively accurate physiological behavior [Wissler, 1963. An analysis of factors affecting temperature levels in the nude human. Temperature—its Measurement and Control in Science and Industry 3(3), 603-612; Wissler, 1964. Mathematical model of the human thermal system. Bulletin of Mathematical Biophysics 26, 147-166.]. A critical strength of the proposed gray-box BOM approach is the use of physically interpretable structures and model coefficients. This article discusses how this strength can be exploited to identify a predictive HT response model for an individual without using environmental chamber data of the individual.     

The electronic configuration and the conductance of silicon nanograins: An application of the scattering approach

The purpose of this study is the assessment of the properties of the electronic structure and of the transport characteristics of silicon nanostructures of a size comparable with the experimental ones. Accordingly, crystalline columnar grains, sandwiched between two adsorbing aluminum contacts, with a size of several hundreds atoms and linear dimensions up to a few nanometers, have been considered. The calculation method elaborates on the scattering approach, as reported in the recent chemical literature, using the extended Hückel theory for the evaluation of either the electronic charge or the transmission function. The calculations show that the binding energy has bulk-like features, i.e. its size dependence has a nearly flat asymptote with a value close to the cohesive energy of the solid. However the effect of the loosely coordinated boundary atoms is perceptible even at the sizes few hundreds atoms and produces an oscillatory behaviour of the binding energy. The comparison between this energy and the conductance indicates that both quantities increase at the same sizes and therefore the orbitals of the loosely bounded atoms are the important conductive channels.     

Efficient model selection for real-time adaptive cold start strategy of a fuel cell system on vehicular applications

The PEMFC maximum power is greatly influenced by subfreezing temperature and degradation phenomena. Therefore, a dependable model is required to estimate the power with respect to the variation of the operating conditions and state of health. Semi-empirical models are potent tools in this regard. Nonetheless, there is not much information about their cold environment reliability. This paper comprehensively compares the performance of some models (already tested in normal ambient temperature) in subfreezing condition to introduce the most reliable one for PEMFC cold start-up application. Firstly, seven models are compared regarding voltage losses and precision. Subsequently, the three most dependable ones are selected and experimentally compared at sub-zero temperature in terms of polarization curve estimation for three PEMFCs with different degradation levels. The results of this study indicate that the model introduced by Amphlett et al. has a superior performance compared to other ones regarding the characteristic's estimation in below-zero temperature.