Non-linear Correlation (non-linear + correlation)

Distribution by Scientific Domains

Selected Abstracts

Laser-induced breakdown spectroscopy for soil diagnostics

J. Bublitz
Summary Laser-optical measurements and fibre optics are potentially attractive tools for applications in soil science because of their great sensitivity and selectivity and their capabilities for on-line and in situ analysis. We have investigated laser-induced breakdown spectroscopy (LIBS) for the quantitative detection of metal ions on the surface of natural soil samples from two sites (Hohenschulen and Oderbruch, Germany). The LIBS technique allows the spatially resolved investigation of adsorption and desorption effects of ions in soil. A frequency doubled (532 nm) and Q-switched Nd:YAG laser with a pulse duration of 8 ns is focused on the soil surface and induces a plasma. Typical power densities are 150 mJ mm,2. The plasma emission is recorded in time and spectrally resolved by a gateable optical multichannel analyser (OMA). A delay time of about 500 ns between laser pulse and OMA gate was used to resolve single atomic and ionic spectral lines from the intense and spectrally broad light that is emitted by the plasma itself. The dependency of the LIBS signal of a single spectral line on the amount of water in the sample is investigated in detail. The results indicate that quenching of water in the plasma plume reduces the line intensities, while the interaction with aquatic colloids increases the intensity. The two processes compete with each other, and a non-linear correlation between measured line intensities and the amount of water in the sample is obtained. This is verified by a simple computer simulation and has to be taken into account for the quantitative interpretation of LIBS signals, e.g. when absolute concentrations are estimated. In the present investigation natural calcium concentrations <,2 ,g kg,1 were measured with the LIBS technique in the samples for the two test sites. In addition, measurements were made with dry and water-saturated BaCl2 mixed soil samples, and no significant difference in the detection limit for barium was obtained. [source]

Bilayer to micelle transition of DMPC and alcohol ethoxylate surfactants as studied by isoperibol calorimetry

Leticia Barriocanal
Abstract The interaction of dimyristoylphosphatidylcholine (DMPC) with non-ionic surfactants has been studied using isoperibol calorimetry. Phospholipid-surfactant systems were formed in the isoperibol calorimeter with varying amounts of surfactant and the change in enthalpy on formation was measured. Solubilization of the phospholipid lamellae was assessed as a decrease in the enthalpy of reaction of co-films containing DMPC and increasing amounts of three linear alcohol ethoxylate surfactants: C10H21(OCH2CH2)3OH, C10H21(OCH2CH2)5OH, or C12H25(OCH2CH2)7OH. The isoperibol calorimetry data for DMPC/surfactant/water systems were consistent with a theoretical three-stage model for the solubilization of phospholipids by surfactants, whereby phospholipid bilayers are transformed into mixed micelles with increasing amounts of surfactant. The results indicate that: (i) the interaction between phospholipid and surfactants results in a non-linear correlation between the enthalpy of reaction and the surfactant concentration; (ii) the structural stage of the lamellar to micelle transition (mixed bilayers, mixed micelles, or both) can be determined from calorimetric data; (iii) phase boundaries in the solubilization process (bilayer saturation, micelle saturation) can be identified as break points in the enthalpy-concentration curve; and (iv) increasing the hydrophilicity of the surfactant results in a decrease of the surfactant concentration producing the onset of solubilization. 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1747,1755, 2005 [source]

The kinetic power of jets magnetically accelerated from advection-dominated accretion flows in radio galaxies

Shuang-Liang Li
ABSTRACT There is a significant non-linear correlation between the Eddington ratio (Lbol/LEdd) and the Eddington-scaled kinetic power (Lkin/LEdd) of jets in low luminosity active galactic nuclei (AGNs). It is believed that these low luminosity AGNs contain advection-dominated accretion flows (ADAFs). We adopt the ADAF model developed by Li & Cao, in which the global dynamics of ADAFs with magnetically driven outflows is derived numerically, to explore the relation between the bolometric luminosity and the kinetic power of jets. We find that the observed relation, , can be well reproduced by the model calculations with reasonable parameters for ADAFs with magnetically driven outflows. Our model calculations are always consistent with the slope of the correlation independent of the values of the parameters adopted. Compared with the observations, our results show that over 60 per cent of the accreted gas at the outer radius escapes from the accretion disc in a wind before the gas falls into the black holes. The observed correlation between the Eddington-scaled kinetic power and Bondi power can also be qualitatively reproduced by our model calculations. Our results show that the mechanical efficiency varies from 10,2 to10,3, which is roughly consistent with that required in AGN feedback simulations. [source]

Application of artificial neural networks for the estimation of tumour characteristics in biological tissues

Seyed Mohsen Hosseini
Abstract Background Artificial tactile sensing is a method in which the existence of tumours in biological tissues can be detected and computerized inverse analyses used to produce ,forward results'. Methods Three feed-forward neural networks (FFNN) have been developed for the estimation of tumour characteristics. Each network provides one of the three parameters of the tumour, i.e. diameter, depth and tumour:tissue stiffness ratio. A resilient back-propagation (RP) algorithm with a leave-one-out (LOO) cross-validation approach is used for training purposes. Results The proposed inverse approach based on neural networks is a reliable and efficient tool for diagnostic tests in order to accurately estimate the basic parameters of the tumour in the tissue. Conclusion There is a non-linear correlation between the tumour characteristics and their effects on the extracted features. In general, reliable estimation of tumour stiffness is obtained when the depth of tumour is small. Copyright 2007 John Wiley & Sons, Ltd. [source]

Application of PC-ANN to Acidity Constant Prediction of Various Phenols and Benzoic Acids in Water

Abstract Principal component regression (PCR) and principal component-artificial neural network (PC-ANN) models were applied to prediction of the acidity constant for various benzoic acids and phenols (242 compounds) in water at 25 C. A large number of theoretical descriptors were calculated for each molecule. The first fifty principal components (PC) were found to explain more than 95% of variances in the original data matrix. From the pool of these PC's, the eigenvalue ranking method was employed to select the best set of PC for PCR and PC-ANN models. The PC-ANN model with architecture 47-20-1 was generated using 47 principal components as inputs and its output is pKa. For evaluation of the predictive power of the PCR and PC-ANN models, pKa values of 37 compounds in the prediction set were calculated. Mean percentage deviation (MPD) for PCR and PC-ANN models are 18.45 and 0.6448, respectively. These improvements are due to the fact that the pKa of the compounds demonstrate non-linear correlations with the principal components. Comparison of the results obtained by the models reveals superiority of the PC-ANN model relative to the PCR model. [source]