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71.
There is considerable current interest in the design and constructionof directly executable modelling languages for mathematicalprogramming. The present research extends contemporary modellinglanguages by specifying a type calculus for an extended dimensionalsystem that determines if the model is well formed in the sensethat the objective function and constraints consist of homogeneouscomponents. Each variable, coefficient, constant, function,constraint, input, and output of the model is assigned a typethat consists of its concepts, quantities, and units of measurementwith optional scale factors. In checking the composition offunctions and constraints, the system can do automatic unitconversions and apply user-supplied conversions. The systemallows a hierarchy of concepts that provides inheritance ofquantities and automatic concept conversion. In addition, eachset in a model is typed so the system can check the validityof operations on indices. 相似文献
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OVERSTREET GEORGE A. JR.; BRADLEY EDWIN L. JR.; KEMP ROBERT S. JR. 《IMA Journal of Management Mathematics》1992,4(1):97-109
Received on 1 July 1991. Predicting human behaviour patterns with linear correlationmodels has absorbed researchers for the past five decades. Althoughmost observers generally concede that humans are inferior tosuch models in combining information, linear scoring modelsare unfortunately, plagued by the flat-maximum effect or thecurse of insensitivity. As Lovie & Lovie(1986)observe: The predictive ability of linear models is insensitiveto large variations in the size of regression weights and tothe number of predictors. In essence, seemingly differentscoringmodels tend to produce indistinguishable predictive outcomes. Since its demonstration by Dawes & Corrigan (1974), observershave cast the flat maximum in a decidedly negative light. Incontrast, Lovie & Lovie (1986) present a provocatively contrarianview of the flat maximums positive potential. In thissame vein, we examine the predictive power of a generic credit-scoringmodel versus individual empirically derived systems. If, asWainer (1976) noted in regard to the flat maximum, itdont make no nevermind, generic credit-scoringmodels could provide cheaper alternatives to individual empiricallyderived models. During the period 1984–8, a series of linear credit-scoringmodels were developed for ten Southeastern U.S. credit unions.For each credit union, stepwise multiple regression was employedto select a subset of explanatory variables to be used in adiscriminant analysis. A generic credit-scoring equation wasdeveloped from the resulting discriminant analyses using weightedaverage coefficients from five systems. The predictive powerof the generic model was compared to the predictive power ofholdout sample of the five remaining credit-scoring models. In all cases, the generic model's performance was very closeto that of the empirically derived models. Thus, our findingssupport Lovie & Lovie's (1986) challenge to the conventionalwisdom that the flat maximum casts a pall on the successfulmodelling of judgement processes. Indeed, the flat maximum impliesa positive role for simpler, and hence cheaper, generic models.Although further research is needed, it should be possible todevelop hybrid models with generic cores that perform as wellas empirically derived linear models. 相似文献
75.
J. Kappler N. Barsan U. Weimar A. Dièguez J. L. Alay A. Romano-Rodriguez J. R. Morante W. G?pel 《Fresenius' Journal of Analytical Chemistry》1998,361(2):110-114
Nanocrystalline thick-film SnO2 sensors with different dopants were fabricated by an optimized screen printing process and subsequent annealing. Powders
were used as starting materials which were prepared by a wet chemical process from SnCl4. Microanalysis was performed of both, the precursors and the final sensor materials with their different annealing conditions.
Gas sensing tests with CO, CH4 and NO2 in air with controlled humidity were correlated with results from X-ray photoemission spectroscopy (XPS), Raman spectroscopy
and transmission electron microscopy (TEM). As an interesting result, the distribution of the transition metal dopants Pd
and Pt (as deduced from TEM and XPS data) rules out the existence of metallic clusters or even atoms in the metallic state
at the surface. This finding does not allow to explain the sensor effects on SnO2 based materials as usually done by means of spill-over effects or Fermi energy control.
Received: 8 August 1997 / Revised: 24 October 1997 / Accepted: 31 October 1997 相似文献
76.
INTRODUCTION Before beginning Part 2 of this review, a caveat noted by Deming and Palasota is brought to the reader's attention: [1] “Press et al. [2] have emphasized that data ‘consist of numbers, of course. But these numbers are fed into the computer, not produced by it. These are numbers to be treated with considerable respect, never to be tampered with, nor subjected to a numerical process whose character you do not completely understand. You are well advised to acquire reverence for data that is rather diferent fiom the “sporty” attitude which is sometimes allowable, or even commendable, in other numerical tasks.’ Yet by and large within chemometrics, preprocessing often seems to be carried out with little understanding of its fundamental efect on the structure of the data.” 相似文献
77.
Ibáñez M Zamani R LaLonde A Cadavid D Li W Shavel A Arbiol J Morante JR Gorsse S Snyder GJ Cabot A 《Journal of the American Chemical Society》2012,134(9):4060-4063
A synthetic route for producing Cu(2)ZnGeSe(4) nanocrystals with narrow size distributions and controlled composition is presented. These nanocrystals were used to produce densely packed nanomaterials by hot-pressing. From the characterization of the thermoelectric properties of these nanomaterials, Cu(2)ZnGeSe(4) is demonstrated to show excellent thermoelectric properties. A very preliminary adjustment of the nanocrystal composition has already resulted in a figure of merit of up to 0.55 at 450 °C. 相似文献
78.
E. Alarcn‐Llad J. Ibez R. Cusc L. Artús J. D. Prades S. Estrad J. R. Morante 《Journal of Raman spectroscopy : JRS》2011,42(2):153-159
We use near‐resonance Raman scattering to investigate zinc oxide (ZnO) nanowires grown by chemical vapor deposition on Si substrates. We discuss the role of quasimode mixing on the wavenumber of the longitudinal optical (LO) bands, and we perform Raman measurements with different excitation powers to investigate possible laser heating effects. We find that in the Raman spectra of as‐deposited nanowires grown along the c‐axis of wurtzite, the LO bands are located slightly below the E1(LO) mode of bulk ZnO. We perform a calculation of the expected LO wavenumber in an ensemble of randomly oriented nanowires. Our analysis shows that light refraction, together with the orientation‐dependent cross‐section of the nanowires for the incoming light, counterbalances quasimode mixing effects in the as‐grown product, giving rise to LO bands that are barely redshifted relative to the E1(LO) mode. In the case of ZnO nanowires that have been mechanically removed (scratched) and subsequently deposited onto separate Si substrates, we observe clear laser‐induced heating. Temperature effects account well for the Raman wavenumber shifts displayed by the LO bands in the Raman spectra of the scratched nanowires. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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S. Charvet R. Madelon R. Rizk B. Garrido O. Gonzlez-Varona M. Lpez A. Prez-Rodríguez J. R. Morante 《Journal of luminescence》1998,80(1-4):241-245
Si particles embedded in an SiO2 matrix were obtained by co-sputtering of Si and SiO2 at various deposition temperatures Td (200–700°C) and annealing at different temperatures Ta (900–1100°C). The systems were characterized by X-ray photoelectron, Raman scattering, infrared absorption and photoluminescence spectroscopy techniques. The results show that the photoluminescence efficiency is strongly dependent on the degree of phase separation between the Si nanocrystals and the SiO2 matrix. This is likely connected with the Si/SiO2 interface characteristics, together with the features indicating the involvement of quantum confinement. 相似文献