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Necessary Parameters (necessary + parameter)

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Engineering50%

Selected Abstracts

Refractive Index Drop Observed After Precision Molding of Optical Elements: A Quantitative Understanding Based on the Tool,Narayanaswamy,Moynihan Model

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008
Ulrich Fotheringham
The room-temperature refractive index is measured for three different prior cooling rates (approximately 10, 50, and 250 K/h) for two glasses especially developed for precision molding. The empirical logarithmic relationship between the cooling rate and the refractive index is also reproduced for the comparatively high cooling rate of ca. 250 K/h. The same relationship is found in a simulation of these cooling rates by the semiempirical Tool,Narayanaswamy,Moynihan model for structural relaxation, with the necessary parameters obtained from differential scanning calorimetry and temperature jump experiments. The measured and the simulated refractive indices coincide within the limits of experimental error. The results demonstrate that the index drop, which is observed when these glasses are first cooled at a regular optical cooling rate (e.g., 2 K/h), and then precision molded (typical cooling rate 1000 K/h), can be understood considering the concepts of structural relaxation. [source]

Bayesian calibration of computer models

JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 3 2001
Marc C. Kennedy
We consider prediction and uncertainty analysis for systems which are approximated using complex mathematical models. Such models, implemented as computer codes, are often generic in the sense that by a suitable choice of some of the model's input parameters the code can be used to predict the behaviour of the system in a variety of specific applications. However, in any specific application the values of necessary parameters may be unknown. In this case, physical observations of the system in the specific context are used to learn about the unknown parameters. The process of fitting the model to the observed data by adjusting the parameters is known as calibration. Calibration is typically effected by ad hoc fitting, and after calibration the model is used, with the fitted input values, to predict the future behaviour of the system. We present a Bayesian calibration technique which improves on this traditional approach in two respects. First, the predictions allow for all sources of uncertainty, including the remaining uncertainty over the fitted parameters. Second, they attempt to correct for any inadequacy of the model which is revealed by a discrepancy between the observed data and the model predictions from even the best-fitting parameter values. The method is illustrated by using data from a nuclear radiation release at Tomsk, and from a more complex simulated nuclear accident exercise. [source]

Characterization of optical collectors for concentration photovoltaic applications

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2003
I. Antón
Abstract The design and characterization of the collector of a photovoltaic concentrator system is commonly carried out for a given receiver, the optical parameters of the collector being linked to it. This paper, which has substantial tutorial content, deals with the characterization of collectors for concentrator photovoltaic systems, independently of any receiver, and providing the necessary parameters for the design of a system. This strategy allows the parameters related to the collector and the receiver, which are usually manufactured by different industries, to be totally separated. It also allows the optical collectors coming from non-photovoltaic industries to be evaluated. The information that the mirror and lens manufacturers should provide for a photovoltaic concentrator application can be summarized under three characteristics: overall optical efficiency; light distribution; and acceptance angle. Theory, equipment, and procedures to carry out the optical characterization of the collectors are explained. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Mehraxiales mechanisches Ermüdungsmodell von Ultra-Hochfestem Beton: Experimentelle und analytische Untersuchungen

BETON- UND STAHLBETONBAU, Issue 6 2007
Jürgen Grünberg Prof. Dr.-Ing.
Die besonderen Eigenschaften von ultra-hochfestem Beton (UHPC) gegenüber normalfestem Beton erfordern für numerische Analysen die Entwicklung eines mehraxialen mechanischen Modells. Im Dreiphasenmodell werden sowohl sprödes als auch duktiles Baustoffverhalten durch charakteristische Verläufe der Hauptmeridiane, insbesondere des Druckmeridians der Bruchumhüllenden beschrieben. Die anisotrope Ermüdungsschädigung wird im Hauptspannungsraum durch unterschiedliche Schädigungsraten für den Zug- bzw. Druckmeridian berücksichtigt. In umfangreichen experimentellen Untersuchungen werden zur Kalibrierung des Dreiphasenmodells für UHPC die Modellparameter für die Beschreibung der Hauptmeridianverläufe bestimmt. In dynamischen Untersuchungen werden die Parameter für die anisotrope Schädigung bestimmt. Multiaxial Mechanical Model of Ultra-High-Performance Concrete The special and outstanding characteristics of ultra-high-performance concrete (UHPC) require the development of a multiaxial mechanical model for numerical investigations. With the three phases model it is possible to describe the behaviour of concrete from extremely brittle to more ductile using the characteristic development of the principal meridians, in particular the compressive meridian of the fracture surface. Furthermore, the anisotropic damage due to fatigue is considered in the principal-stressarea by different grades of damage in relation to the tensile and the compressive meridian. In experimental investigations, the necessary parameters are determined to calibrate the three phases model for UHPC by specifying the principal meridians for static loading. In further dynamic investigations the parameters for an anisotropic damage model are determined for fatigue loading. [source]