Search results for "Linear Model"
showing 10 items of 598 documents
Antimicrobial Activity Characterization in a Heterogeneous Group of Compounds
1998
In this work we carry out a study of pattern recognition to detect the microbiological activity in a group of heterogeneous compounds. The structural descriptors utilized are the topological connectivity indexes. The methods followed are stepwise linear discriminant analysis (linear analysis) and artificial neural network (nonlinear analysis). Although both methods are appropriate to differentiate between active and inactive compounds, the artificial neural network is, in this case, more adequate, since it shows in a test set a prediction success of 98%, versus 92% obtained with linear discriminant analysis.
Geographical variation in pharmacological prescription
2009
Promoting rational drug administration in treatments is one of the most important issues in Public Health. Bayesian hierarchical models are a very useful tool for incorporating geographical information into the analysis of pharmacological prescription data. They allow the mapping of spatial components which express the trend of geographical variation. In addition, these models are able to deal with uncertainty in a sequential way through prior distributions on parameters and hyperparameters. Bayes' theorem combines all types of information and provides the posterior distribution which is computed through Markov Chain Monte Carlo (MCMC) simulation methods. Simulated data for pharmacological …
Reference tracking control of hypersonic vehicles using switched linear parameter-varying approach
2013
This paper is concerned with the control problem of the air-breathing hypersonic vehicle using switched linear parameter-varying (LPV) systems approach. By linearizing the nonlinear model of the hypersonic vehicle at trim points and dividing the velocity scope into several partitions, a switched LPV model for the underlying systems is derived. With aid of multiple Lyapunov-like functions technique, the controllers ensuring the tracking of given commands of the closed-loop system are designed under the mode-independent and mode-dependent switching logics, respectively. Simulation results for the hypersonic vehicle show the effectiveness of the proposed method and the advantages of the mode-d…
Desigualdades y mortalidad por cirrosis en varones (Zaragoza, 1996-2003)
2011
ResumenObjetivosAnalizar diferencias geográficas en la mortalidad por cirrosis hepática, en varones, en la provincia de Zaragoza, y su posible asociación con indicadores socioeconómicos, así como identificar la adecuación, en el ámbito rural, del índice de privación del proyecto MEDEA.MétodosLa unidad geográfica de análisis para Zaragoza capital fue la sección censal, y para el resto de la provincia el municipio. Para cada unidad de análisis se calculó la razón de mortalidad estandarizada cruda y suavizada mediante un modelo lineal generalizado mixto bayesiano. Se calculó un índice sintético de privación y se incluyó en el modelo en cuartiles. También se realizó el análisis exploratorio inc…
Unconventional monetary policy reaction functions: evidence from the US
2020
Abstract We specify unconventional monetary policy reaction functions for the Fed using linear and nonlinear econometric frameworks. We find that nonstandard policy measures are largely driven by the dynamics of inflation and the output gap, with the effect being particularly strong during QE rounds. Moreover, we uncover the presence of asymmetry and regime dependence in central bank’s actions since the global financial crisis, especially concerning the response of the term spread and the shadow short rate to the growth rate of central bank reserves. From a policy perspective and given the lack of a systematic response of monetary policy to asset price growth in nonstandard times, our findi…
Analysis of insecticides in honey by liquid chromatography–ion trap-mass spectrometry: Comparison of different extraction procedures
2010
The feasibility of different extraction procedures was tested and compared for the determination of 12 organophosphorus and carbamates insecticides in honey samples. In this sense, once the samples were pre-treated - essentially dissolved in hot water by stirring - and before they could be analyzed by liquid chromatography-ion trap-second stage mass spectrometry (LC-MS(2)), four different approaches were studied for the extraction step: QuEChERS, solid-phase extraction (SPE), pressurized liquid extraction (PLE) and solid-phase microextraction (SPME). The main aim of this work was to maximise the sensitivity of pesticides and to minimise the presence of interfering compounds in the extract. …
Solid-phase microextraction-liquid chromatography-mass spectrometry applied to the analysis of insecticides in honey
2007
An approach based on solid-phase microextraction-liquid chromatography-mass spectrometry (SPME-LC-MS) has been developed for determining 12 insecticides (bromophos ethyl, chlorpyrifos methyl, chlorpyrifos ethyl, diazinon, fenoxycarb, fonofos, phenthoate, phosalone, pirimiphos methyl, profenofos, pyrazophos, and temephos) in honey. The influence of several parameters on the efficiency of the SPME was systematically investigated. Under optimal conditions, the procedure provided excellent linearity (>0.990), detection and quantification limits (between 0.001 and 0.1 microg g(-1) and between 0.005 and 0.5 microg g(-1), respectively), and precision (<19% at the quantification limits and from 6 t…
Substitution–dilution method to correct the matrix effect in multi-element quantitative analysis by X-ray fluorescence
2001
Abstract A mathematical model based on the dilution–addition method (DAM) for multi-elemental analysis using an X-ray fluorescence technique is proposed. The conditions for sample preparation do not require both the unknown and standard samples to be similar in composition and mineralogy, and the unknown sample is replaced quantitatively by the standard sample, hence the denomination substitution–dilution method (SDM). This method makes it possible to correct the matrix effect in multi-elemental quantitative analysis by X-ray fluorescence for each analyte. The proposed model presents hyperbolic behaviour of the experimental data when the X-ray fluorescence intensities are represented versus…
Internal Test Sets Studies in a Group of Antimalarials
2006
Topological indices have been applied to build QSAR models for a set of 20 an- timalarial cyclic peroxy cetals. In order to evalua te the reliability of the proposed linear models leave-n-out and Internal Test Sets (ITS) approaches have b een considered. The pro- posed procedure resulted in a robust and consensued prediction equation and here it is shown why it is superior to the employed standard c ross-validation algorithms involving multilinear regression models.
Linear Regression Analysis
2010
SUMMARY Background: Regression analysis is an important statistical method for the analysis of medical data. It enables the identification and characterization of relationships among multiple factors. It also enables the identification of prognostically relevant risk factors and the calculation of risk scores for individual prognostication. Methods: This article is based on selected textbooks of statistics, a selective review of the literature, and our own experience. Results: After a brief introduction of the uni- and multivariable regression models, illustrative examples are given to explain what the important considerations are before a regression analysis is performed, and how the resul…