Modeling Lac du Bonnet granite using a discrete element model

A discrete element method code developed by the authors is used to model Lac du Bonnet granite in triaxial compression. The paper first presents the features of the model and the algorithms used to identify the micro deformability and strength parameters. With these identification algorithms, the model was calibrated to match experimental triaxial test data on Lac du Bonnet granite. With the calibrated model, investigation on failure evolution was then performed. The monitored evolution of the number and type of contact failures (micro cracks) reveals that at micro level tensile failures occur first, followed by mobilization of residual friction. Three distinct stages of stress–strain curve can be well identified by the accumulated number of contact failures and the mode of contact failures.     

Phase change problems with free convection: fixed grid numerical simulation

A numerical and experimental study of unsteady natural convection during freezing of water is presented. The mathematical model for the numerical simulations is based on the enthalpy-porosity method in vorticity-velocity formulation, equations are discretised on a fixed grid by means of a finite volume technique. A fully implicit method has been adopted for the mass and momentum equations. Experiments are performed for water in a differentially heated cube surrounded by air. The experimental data for natural convection with freezing in the cavity are collected to create a reference for comparison with numerical results. The method of simultaneous measurement of the flow and temperature fields using liquid crystal tracers is used. It allows us to collect transient data on the interface position, and the temperature and velocity fields. In order to improve the capability of the numerical method to predict experimental results, a conjugate heat transfer problem was solved, with finite thickness and internal heat conductivity of the non-isothermal walls. These results have been compared with the simulations obtained for the idealised case of perfectly adiabatic side walls, and with our experimental findings. Results obtained for the improved numerical model shown a very good agreement with the experimental data only for pure convection and initial time of freezing process. As time passes the discrepancies between numerical predictions and the experiment became more significant, suggesting a necessity for further improvements of the physical model used for freezing water. Received: 30 April 1999 / Accepted: 17 June 1999     

Statistical Analysis of High-Resolution SAR Ground Clutter Data

This paper deals with the problem of modeling high-resolution synthetic aperture radar clutter data from different vegetated areas. We analyzed moving and stationary target recognition (MSTAR) data sets focusing on histograms, moments, and covariance of clutter amplitude, texture, and speckle. The most celebrated statistical models are tested on real data of grass field or wood and trees to validate the goodness of fit of the compound Gaussian model in different scenarios. The results demonstrate that for grass fields, the compound Gaussian model provides a good data fitting. This is not the case for woods images where the speckle is not more Gaussian distributed. Covariance analysis and concluding remarks complete this paper     

Microsomal lipid peroxidation: Effect of vitamin E and its functional interaction with phospholipid hydroperoxide glutathione peroxidase

The role of vitamin E in the protection against iron dependent lipid peroxidation was studied in rat liver microsomes and Triton-dispersed microsomal lipid micelles. In these systems, an antioxidant effect of vitamin E at a physiological ratio to phospholipids could be observed only in the presence of phospholipid hydroperoxide glutathione peroxidase (PHGPX) and glutathione. The rationale of this cooperation is discussed on the basis of the hydroperoxyl radical scavenging capacity of vitamin E and the reduction of membrane hydroperoxides by PHGPX. The scavenging of lipid hydroperoxyl radicals by vitamin E, although inhibiting propagation of the peroxidative chain, produces lipid hydroperoxides from which ferrous iron generates alkoxyl radicals that react with vitamin E almost as fast as with fatty acids. Therefore, only if membrane hydroperoxides are continuously reduced by this specific peroxidase does the scavenging of hydroperoxyl radicals by vitamin E lead to an effective inhibition of lipid peroxidation.     

Perceived orientation of axis rotation in structure-from-motion.

Perceived orientation of axis of rotation and accuracy in discriminating fixed-axis from nonfixed-axis rotations were investigated for orthographic projections of three-dimensional rotating objects. The principal findings were (1) the slant of the axis of rotation was systematically misperceived; (2) in both two-view and multiview displays, the perceived slant of the axis of rotation was well-predicted by the ratio between the deformation (a property of the first-order optic flow) and the component parallel to the image plane of the global velocity vector; (3) if this ratio was kept constant in each frame transition of the stimulus sequence (or it was varied), then the stimuli tended to be judged as fixed-axis rotations (or as nonfixed-axis rotations), regardless of whether they simulated a fixed-axis rotation or not; and (4) the tilt of the axis of rotation was perceived in two-view displays with a very small error. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Polymerization of bicyclic ethers

Summary Structure of copolymers obtained by ring opening cationic polymerization from 7-oxabicyclo[ 2.2.1] heptane and ethylene oxide has been recently reported. This study about the spin lattice relaxation times and Nuclear Overhauser enhancement factor in the carbon-13 NMR spectra was performed and the results interpreted in terms of different internal mobility of the units in the copolymer chain.Previous papers in this series are: G. CECCARELLI, F.ANDRUZZI, Makromol. Chem. 180, 1371(1979); F.ANDRUZZI, G.CECCARELLI, M.PACI Polymer 21, 1180(1980); and ref (M.PACI et al. 1981).     

Mixed micelles containing lipophilic gadolinium complexes as MRA contrast agents

Mixed micelles for MRA are multicomponent systems containing a phospholipid, a biocompatible non-ionic surfactant (e.g. Synporonic^(k) F-108) and a lipophilic gadolinium complex. A variety of lipophilic gadolinium complexes were designed taking into account features such as: (i) nature of ligand (cyclic versus acyclic); (ii) lipophilic moiety; (iii) global charge of the complex; and (iv) nature of bond connecting the complex to the lipophilic moiety. All the lipophilic gadolinium complexes after formulation as mixed micelles show high relaxivities in water and in blood (rat). Mixed micelles containing gadolinium complexes bearing only one aliphatic chain cannot be used as MRA contrast agents because they have a high haemolytic effect. Furthermore, in rats they are quickly eliminated from the blood stream. These drawbacks are completely circumvented using gadolinium complexes bearing two aliphatic chains. Mixed micelles containing such complexes show high relaxivities. no haemolytic effect and long blood permanence. This makes them promising candidates as MRA contrast agents. However, elimination, which occurs exclusively through the liver, is not complete, even after 7 days. Complexes containing labile (e.g. ester) bonds between the lipophilic moieties and the chelate subunit are eliminated through both the liver and the kidneys. However, elimination is stiil not complete after 7 days.     

Mathematical modeling of the hot strip rolling of microalloyed Nb, multiply-alloyed Cr-Mo, and plain C-Mn steels

Industrial mill logs from seven different hot strip mills (HSMs) were analyzed in order to calculate the mean flow stresses (MFSs) developed in each stand. The schedules were typical of the processing of microalloyed Nb, multiply-alloyed Cr-Mo, and plain C-Mn steels. The calculations, based on the Sims analysis, take into account work roll flattening, redundant strain, and the forward slip ratio. The measured stresses are then compared to the predictions of a model based on an improved Misaka MFS equation, in which solute effects, strain accumulation, and the kinetics of static recrystallization (SRX) and metadynamic recrystallization (MDRX) are fully accounted for. Good agreement between the measured and predicted MFSs is obtained over the whole range of rolling temperatures. The evolution of grain size and the fractional softening are also predicted by the model during all stages of strip rolling. Special attention was paid to the Nb steels, in which the occurrence of Nb(C, N) precipitation strongly influences the rolling behavior, preventing softening between passes. The present study leads to the conclusion that Mn addition retards the strain-induced precipitation of Nb; by contrast, Si addition has an accelerating effect. The critical strain for the onset of dynamic recrystallization (DRX) in Nb steels is derived, and it is shown that the critical strain/peak strain ratio decreases with increasing Nb content; furthermore, Mn and Si have marginal but opposite effects. It is demonstrated that DRX followed by MDRX occurs under most conditions of hot strip rolling; during the initial passes, it is due to high strains, low strain rates, and high temperatures, and, in the final passes, it is a consequence of strain accumulation.     

Synthesis and Biological Evaluation of Pyrazoline and Pyrrolidine-2,5-dione Hybrids as Potential Antitumor Agents

In search of novel and effective antitumor agents, pyrazoline-substituted pyrrolidine-2,5-dione hybrids were designed, synthesized and evaluated in silico, in vitro and in vivo for anticancer efficacy. All the compounds exhibited remarkable cytotoxic effects in MCF7 and HT29 cells. The excellent antiproliferative activity toward MCF7 (IC₅₀=0.78±0.01 μM), HT29 (IC₅₀=0.92±0.15 μM) and K562 (IC₅₀=47.25±1.24 μM) cell lines, prompted us to further investigate the antitumor effects of the best compound S2 (1-(2-(3-(4-fluorophenyl)-5-(p-tolyl)-4,5-dihydro-1H-pyrazol-1-yl)-2-oxoethyl)pyrrolidine-2,5-dione). In cell-cycle analysis, S2 was found to disrupt the growth phases with increased cell population in G₁/G₀ phase and decreased cell population in G₂/M phase. The excellent in vitro effects were also supported by inhibition of anti-apoptotic protein Bcl-2. In vivo tumor regression studies of S2 in HT29 xenograft nude mice, exhibited equivalent and promising tumor regression with maximum TGI, 66 % (i. p. route) and 60 % (oral route) at 50 mg kg⁻¹ dose by both the routes, indicating oral bioavailability and antitumor efficacy. These findings advocate that hybridization of pyrazoline and pyrrolidine-2,5-dioes holds promise for the development of more potent and less toxic anticancer agents.