Image feature based automatic correction of low-frequency spatial intensity variations in MR images

An automatic method of compensating for low-frequency variations in magnetic resonance images is presented. Small variations within a tissue type are modelled and a correction function is generated. The methods is based completely on image features and does not need a phantom or user interaction to generate the compensation function. This image correction simplifies digital image analysis and may enhance clinical evaluation. As a result, the correction technique reduces inhomogeneity and improves contrast. Our results show that the radiofrequency response variation of coils can be reduced. The segmentation process, even with a simple threshold method, produces more reliable results when corrected images are used. The presented method is most useful for images acquired in the sagital and coronal planes with circular local coils, or using surface coils, e.g., spine coils.     

Atmospheric chemistry of C3-C6 cycloalkanecarbaldehydes

The rate coefficients for the gas phase reaction of NO3 and OH radicals with a series of cycloalkanecarbaldehydes have been measured in purified air at 298 +/- 2 K and 760 +/- 10 Torr by the relative rate method using a static reactor equipped with long-path Fourier transform infrared (FT-IR) detection. The values obtained for the OH radical reactions (in units of 10(-11) cm3 molecule(-1) s(-1)) were the following: cyclopropanecarbaldehyde, 2.13 +/- 0.05; cyclobutanecarbaldehyde, 2.66 +/- 0.06; cyclopentanecarbaldehyde, 3.27 +/- 0.07; cyclohexanecarbaldehyde, 3.75 +/- 0.05. The values obtained for the NO3 radical reactions (in units of 10(-14) cm3 molecule(-1) s(-1)) were the following: cyclopropanecarbaldehyde, 0.61 +/- 0.04; cyclobutanecarbaldehyde, 1.99 +/- 0.06; cyclopentanecarbaldehyde, 2.55 +/- 0.10; cyclohexanecarbaldehyde, 3.19 +/- 0.12. Furthermore, the reaction products with OH radicals have been investigated using long-path FT-IR spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS). The measured carbon balances were in the range 89-97%, and the identified products cover a wide spectrum of compounds including nitroperoxycarbonyl cycloalkanes, cycloketones, cycloalkyl nitrates, multifunctional compounds containing carbonyl, hydroxy, and nitrooxy functional groups, HCOOH, HCHO, CO, and CO2.     

CoMFA modeling of human catechol O-methyltransferase enzyme kinetics

Three-dimensional QSAR models with different charge calculation methods (MOPAC-AM1-ESP, MOPAC-AM1-Coulson and Gasteiger-Hückel) were developed for predicting all three enzyme kinetic parameters Km, Vmax and Vmax/Km for catecholic substrates of human soluble catechol O-methyltransferase (S-COMT). The empirical parameters of 45 substrates were correlated to the steric and electronic molecular fields of the substrates utilizing Comparative Molecular Field Analysis (CoMFA). Alignment rules for CoMFA were developed based on the catalytic mechanism and crystal structure of S-COMT, and the analysis was optimized using an all-space search technique. Leave-one-out and leave-n-out cross-validation (with 5 and 10 cross-validation groups) was carried out, and all developed models proved to be statistically significant with q2 values up to 0.84. The models based on MOPAC charge calculations predicted the empirical values clearly better than the Gasteiger-Hückel method. The derived CoMFA coefficient contour maps of steric and electrostatic interactions correlated clearly with the S-COMT crystallographic structures.     

Ratio-based RTS determination in weight-restricted DEA models

This paper provides computationally efficient approaches for determining to which returns to scale (RTS) class a unit belongs in weight-restricted Data Envelopment Analysis (DEA) models. A non-traditional computational algorithm is introduced. The suggested approach is based on the calculation of certain ratios within the data set and offers obvious computational advantages over the traditional approaches involving the solution of standard DEA models. Some theorems and algorithms are given. Computational advantages of the provided results are discussed and one of the algorithms is illustrated using real world data.     

Interactive evolutionary multi-objective optimization for quasi-concave preference functions

We present a new hybrid approach to interactive evolutionary multi-objective optimization that uses a partial preference order to act as the fitness function in a customized genetic algorithm. We periodically send solutions to the decision maker (DM) for her evaluation and use the resulting preference information to form preference cones consisting of inferior solutions. The cones allow us to implicitly rank solutions that the DM has not considered. This technique avoids assuming an exact form for the preference function, but does assume that the preference function is quasi-concave. This paper describes the genetic algorithm and demonstrates its performance on the multi-objective knapsack problem.     

Dynamic Hemivariational Inequalities and Their Applications

Dynamic hemivariational inequalities are studied in the present paper. Starting from their solution in the distributional sense, we give certain existence and approximation results by using the Faedo–Galerkin method and certain compactness arguments. Applications from mechanics (viscoelasticity) illustrate the theory.     

CoMFA modeling of enzyme kinetics: K(m) values for sulfation of diverse phenolic substrates by human catecholamine sulfotransferase SULT1A3

Three-dimensional QSAR models were developed for predicting kinetic Michaelis constant (K(m)) values for phenolic substrates of human catecholamine sulfating sulfotransferase (SULT1A3). The K(m) values were correlated to the steric and electronic molecular fields of the substrates utilizing Comparative Molecular Field Analysis (CoMFA). The evaluated SULT1A3 substrate data set consisted of 95 different substituted phenols, catechols, catecholamines, steroids, and related structures for which the K(m) values were available. The data set was divided in three different subgroups in the initial analysis: (1). for the first CoMFA model substrates with only one reacting hydroxyl group were selected (n = 51), (2).the second model was build with structurally rigid substrates (n = 59), and (3). finally all substrates of the data set were included in the analysis (n = 95). Substrate molecules were aligned using the aromatic ring and the reacting hydroxyl group as a template. After the initial analysis different substrate alignment rules based on the existing knowledge of the SULT1A3 active site structure were evaluated. After this optimization a final CoMFA model was built including all 95 substrates of the data set. Cross-validated q(2) values (leave-one-out and leave-n-out) and coefficient contour maps were calculated for all derived CoMFA models. All four CoMFA models were statistically significant with q(2) values up to 0.624. These predictive QSAR models will provide us information about the factors that affect substrate binding at the active site of human catecholamine sulfotransferase SULT1A3.     

Polylactides - degradable polymers for fibres and films

Modification of a poly(L-lactide) (PLLA) base resin, by treatment with peroxides and compounding with plasticisers, yield resins which can be processed by conventional techniques and equipment to thin blown films, fibres and nonwoven fabrics having properties comparable to those of corresponding PP and PE samples. Film samples have tensile strength between 30 and 50 MPa, elongation at break around 250%, and puncture resistance, measured as dart drop values, of 12 g/μm. Fibres can be spun to filaments or directly to nonvowen fabrics by spun-bond techniques. These fabrics have mechanical properties comparable to polypropylene materials. The polymer products are readily degraded in a compost to carbon dioxide, water and biomass.     

Feshbach-resonant interactions in 40K and 6Li degenerate Fermi gases

We theoretically examine a system of Fermi degenerate atoms coupled to bosonic molecules by a Feshbach resonance, focusing on the superfluid transition to a molecular Bose-Einstein condensate dressed by Cooper pairs of atoms. This problem raises interest because it is unclear at present whether bimodal density distributions observed recently in 40K and 6Li are due to a condensate of bosonic molecules or fermionic atom pairs. As opposed to 40K, we find that any measurable fraction of above-threshold bosonic molecules is necessarily absent for the 6Li system in question, which strongly implicates Cooper pairs as the culprit behind its bimodal distributions.