Foods protected by the important biological antioxidant: Uric acid

Uric acid has been proposed as an antioxidant in biological fluids especially in humans. It is shown that uric acid can be used effectively to protect food and model food preparations against oxidation. Precooked cereal flakes and food emulsions were stabilised with varying levels of uric acid.     

Effect of Chitosan Physical Form on Its Antibacterial Activity Against Pathogenic Bacteria

The antibacterial activity of chitosan (CS) nanospheres, in comparison with other physical forms, was investigated against Salmonella enterica serovar Typhimurium and Staphylococcus aureus, which are 2 foodborne harmful pathogens. Results showed that the antibacterial efficacy of CS nanospheres: (1) was superior to that displayed by CS in powder and solution form; (2) was higher against S. aureus than against Salmonella Typhimurium; and (3) was dependent on the temperature and pH of the medium depending on the strain. For S. Typhimurium, a higher activity was displayed at 37 °C, in which 99.9% of the population was eradicated independently of the pH, followed by 20 °C and 7 °C, in which acidic pH conditions favored a higher susceptibility of bacteria to the effect of CS. On the contrary, S. aureus was less susceptible to the pH and temperature conditions of the medium, and no statistical difference in the antibacterial effect was observed for pH 5.8 and 8.0 at 20 °C and 37 °C. However, at 7 °C a slightly higher activity was displayed at pH 5.8 than at 8.0.     

Screening of 23 β-lactams in foodstuffs by LC–MS/MS using an alkaline QuEChERS-like extraction

A fast and robust high performance LC–MS/MS screening method was developed for the analysis of β-lactam antibiotics in foods of animal origin: eggs, raw milk, processed dairy ingredients, infant formula, and meat- and fish-based products including baby foods. QuEChERS extraction with some adaptations enabled 23 drugs to be simultaneously monitored. Screening target concentrations were set at levels adequate to ensure compliance with current European, Chinese, US and Canadian regulations. The method was fully validated according to the European Community Reference Laboratories Residues Guidelines using 93 food samples of different composition. False-negative and false-positive rates were below 5% for all analytes. The method is adequate for use in high-routine laboratories. A 1-year study was additionally conducted to assess the stability of the 23 analytes in the working standard solution.     

Symbolic Test-generation in HOL-TESTGEN/CirTA A Case Study

HOL-TestGen/CirTA is a theorem-prover based test generation environment for speci cations written in Circus, a process-algebraic speci cation language in the tradition of CSP. HOL-TestGen/CirTA is based on a formal embedding of its semantics in Isabelle/HOL, allowing to derive rules over speci cation constructs in a logically safe way. Beyond the derivation of algebraic laws and calculi for process re nement, the originality of HOL-TestGen/ CirTA consists in an entire derived theory for the generation of symbolic test-traces, including optimized rules for test-generation as well as rules for symbolic execution. The deduction process is automated by Isabelle tactics, allowing to protract the state-space explosion resulting from blind enumeration of data. The implementation of test-generation procedures in CirTA is completed by an integrated tool chain that transforms the initial Circus speci cation of a system into a set of equivalence classes (or "symbolic tests"), which were compiled to conventional JUnit test-drivers. This paper describes the novel tool-chain based on prior theoretical work on semantics and test-theory and attempts an evaluation via a medium-sized case study performed on a component of a real-world safety-critical medical monitoring system written in Java. We provide experimental measurements of the kill-capacity of implementation mutants.     

Simplified theory for linear rheology of monodisperse linear polymers

A new version of the tube theory based on the de Gennes–Doi–Edwards reptation concept (reported in Likhtman and McLeish's work published in 2002) is evaluated, modified to allow for simplified computations, and used to study the relationship between zero‐shear viscosity and molecular weight for monodisperse entangled linear homopolymers. The Likhtman–McLeish model combines self‐consistent theories for contour length fluctuations and constraint release with reptation theory for monodisperse linear polymers. Because of the nature of the Rubinstein and Colby approach used for the treatment of constraint release, the related term is probabilistic and requires stochastic simulations for the calculation of the relaxation modulus G(t). This makes the Likhtman–McLeish model computationally difficult to use. In this work we solve this problem by generating an approximate closed‐form solution for the stochastic term. Then analytical integration of the relaxation modulus function G(t) provides an expression for the zero‐shear viscosity (η₀). Results of the computations of the zero‐shear viscosity and of the slope of η₀ versus molecular weight are compared with available experimental data for monodisperse entangled linear polystyrene and polyethylene (hydrogenated polybutadiene). The model is a major improvement over previous theoretical models, even if there is still some disagreement between the predictions and experimental data of the slope of η₀ versus molecular weight. The possibility of inferring monomer chemistry–dependent parameters from the zero‐shear viscosity remains a difficult task because of the introduction of a constraint‐release parameter. Nevertheless, the model is a useful tool for the prediction of linear viscoelasticity data. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 569–586, 2004     

Lipid biosynthesis in cultured arterial smooth muscle cells is related to their phenotype

During the atherogenic processin vivo, arterial smooth muscle cells (SMC) undergo changes in their phenotype. In the present study, rat SMC from primary cultures and from subcultures before 10 and after 200 passages, showing contractile-like, synthetic and transformed phenotypes, respectively, were compared in regard to their lipid content and biosynthesis. The rationale for comparing these phenotypes rests in the similar changes in phenotype of SMC that occur in the formation and progression of atherosclerotic lesions. Phenotype changes were shown to be associated with changes in the phospholipid content of SMC. Phospholipid levels increased, but not as significantly as did cholesterol levels when passing from contractile to synthetic and transformed cells (1.23±0.18, 2.28±0.26 and 3.25±0.23 μg/10⁶ cells, respectively). Cholesterol normalized in respect to cell protein was increased to the same extent. Lipid synthesis as judged by [¹⁴C]acetate incorporation was increased 3- to 12-fold in the synthetic and transformed cells, respectively, compared to contractile cells. After thin-layer chromatography, radioactivity was shown to be markedly increased in most of the lipid fractions, but label in the cholesterol fraction of synthetic and transformed cells was increased by 7- and 21-fold, respectively. Thus, SMCin vitro were shown to drastically increase cholesterol biosynthesis associated with phenotype changes. Such changes are known to occurin vivo and might represent a critical step in the deposition of excess cholesterol within foam cells.     

Rheological modeling of carbon nanotube suspensions with rod–rod interactions

To explain the shear‐thinning behavior of untreated carbon nanotube (CNT) suspensions in a Newtonian matrix, a new set of rheological equations is developed. The CNTs are modeled as rigid rods dispersed in a Newtonian matrix and the evolution of the system is controlled by hydrodynamic and rod–rod interactions. The particle–particle interactions is modeled by a nonlinear lubrication force, function of the relative velocity at the contact point, and weighted by the contact probability. The stress tensor is calculated from the known fourth‐order orientation tensor and a new fourth‐order interaction tensor. The Fokker‐Planck equation is numerically solved for steady simple shear flows using a finite volume method. The model predictions show a good agreement with the steady shear data of CNTs dispersed in a Newtonian epoxy matrix as well as for suspensions of glass fibers in polybutene,¹ demonstrating its ability to describe the behavior of micro‐ and nanoscale particle suspensions. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1476–1487, 2014     

Simulation of QRST integral maps with a membrane-based computer heart model employing parallel processing

The simulation of the propagation of electrical activity in a membrane-based realistic-geometry computer model of the ventricles of the human heart, using the governing monodomain reaction-diffusion equation, is described. Each model point is represented by the phase 1 Luo-Rudy membrane model, modified to represent human action potentials. A separate longer duration action potential was used for the M cells found in the ventricular midwall. Cardiac fiber rotation across the ventricular wall was implemented via an analytic equation, resulting in a spatially varying anisotropic conductivity tensor and, consequently, anisotropic propagation. Since the model comprises approximately 12.5 million points, parallel processing on a multiprocessor computer was used to cut down on simulation time. The simulation of normal activation as well as that of ectopic beats is described. The hypothesis that in situ electrotonic coupling in the myocardium can diminish the gradients of action-potential duration across the ventricular wall was also verified in the model simulations. Finally, the sensitivity of QRST integral maps to local alterations in action-potential duration was investigated.     

Shear and extensional properties of short glass fiber reinforced polypropylene

Shear and extensional properties of a commercial short glass fiber reinforced polypropylene were carefully investigated using commercial rheometers and a novel on‐line rheometer. This on‐line slit rheometer, installed on an injection molding press, has been designed to measure the steady shear viscosity, the first normal stress difference, and the apparent extensional viscosity of polymer melts and composites for high strain rates up to 10⁵ s⁻¹ in shear and 200 s⁻¹ in extension. Our results show that the steady‐state viscosity measurements using the on‐line rheometer are in excellent agreement with those obtained using commercial rheometers. The steady‐state and the complex viscosities of the composites were found to be fairly close to that of the matrix, but the Cox‐Merz rule was not verified for the composites at high rates. The elasticity of the composites was found to be equal to that of the polypropylene matrix. The apparent extensional viscosity was obtained from the pressure drop in the planar converging die of the slit rheometer using the analyses proposed by Cogswell [1] and Binding [2]. The extensional viscosity of the polypropylene was found to be much larger than the shear viscosity at low strain rates with a Trouton ratio of about 40 that decreased rapidly with increasing strain rate down to the value of 4 at 200 s⁻¹. The extensional viscosity of the composites was also found to be close to that of the matrix, with values 35 and 5% larger for the 30 and 10 wt% reinforced polypropylenes, respectively. These results are compared with the predictions of the Goddard model [3], which are shown to overpredict our experimental results. POLYM. COMPOS. 26:247–264, 2005. © 2005 Society of Plastics Engineers.