Nanocomposites of syndiotactic polypropylene: Phase behavior and morphology

Through differential scanning calorimetry, the crystallization kinetics of syndiotactic polypropylene (sPP) nanocomposites with organically modified layered silicates has been investigated in both nonisothermal and isothermal conditions. A strong influence on the thermal behavior is exerted by the compatibilizer agent (low molecular weight isotactic polypropylene‐g‐maleic anydrhyde, iPP‐g‐MA), which increases the crystallization rate of sPP. A further strong increase in the crystallization rate is observed upon increasing the OLS content in the sample. The kinetics data have been analyzed through the Ozawa, Avrami, and Tobin methods, the first of them resulted ineffective in describing our data. Morphological analyses have been performed by polarized optical microscopy and atomic force microscopy. Spherulitic morphology is observed for neat sPP; for the sample containing only the compatibilizer the spherulites grow around the iPP‐g‐MA particles, revealing their nucleating effect on sPP crystallization; for the nanocomposites the spherulitic morphology is lost: the texture appears globular, compact; inside the globules lamellae are present, parallel one to the other. POLYM. ENG. SCI., 46:1433–1442, 2006. © 2006 Society of Plastics Engineers     

Relationship between gelation and morphology of rubber-modified epoxy resins

The addition of both a solid and a liquid rubber to an epoxy resin has been shown to strongly increase the toughness of the material. Moreover, it is well known that toughening depends on the morphology of the system, which, in turn, depends on the cure conditions. In the present work the morphologies of epoxy resins modified with mixtures of solid and liquid rubbers have been studied through transmission electron microscopy. An investigation of the influence of the elastomers and of the gel time on the morphology of the hardened material was carried out. Gel times were evaluated, through rheological measurements, at different cure temperatures.     

Selection and Use of Phytate-Degrading LAB to Improve Cereal-Based Products by Mineral Solubilization During Dough Fermentation

ABSTRACT:  New producers of phytate-degrading enzymes, especially lactic acid bacteria (LAB), were used to improve mineral solubilization during dough fermentation. In all, among strains from different sources by microorganisms (150 lactic acid bacteria, 36 yeasts), 38 (24%) exhibited a clear zone around the colonies by hydrolyzing hexacalcium phytate contained in solid medium. When phytase-positive strains from plate assay were tested for phytase activity in liquid medium, 6 of the strains (37%) exhibited phytate-degrading activity in at least one of the 3 different media used. Of the LAB, the highest phytase values were found for  Enterococcus faecium  A86 (0.74 U/mL) and  Lactobacillus plantarum  H5 (0.71 U/mL). Two different starter cultures obtained by combinations of phytase-positive (phy+:  L. plantarum  H5 and L3,  Leuconostoc gelidum  A16, and  E. faecium  A86) or phytase-negative (phy−:  L. gelidum  LM249,  L. plantarum  H19, and  L. plantarum  L8) selected LAB strains, were used to measure mineral concentrations of iron, zinc, and manganese during dough fermentation. Although the 2 kinds of starter showed similar acidic values, the presence of phytate-degrading LAB strains increased mineral solubilization in comparison to the starter phy−.     

Discovery and preliminary pharmacology of Sch 37370, a dual antagonist of PAF and histamine

From a series of amide analogs of the histamine H₁ antagonist, azatadine, a potent, orally active, dual platelet-activating factor (PAF) and histamine antagonist, Sch 37370, namely 1-acetyl-4-(8-chloro-5,6-dihydro-11H-benzo-[5,6]cyclohepta[1,2-b]pyridin-11-ylidine)piperidine, was discovered. Sch 37370 selectively inhibits PAF-induced aggregation of human plateletsin vitro (IC₅₀=0.6 μM), andin vivo inhibits PAF- and histamine-induced bronchospasm in guinea pigs with ED₅₀ values of 6.0 and 2.4 mg/kg p.o., respectively. Sch 37370 is expected to be more efficacious than single mediator antagonists in allergic diseases, such as asthma. Based on papers presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

An optical method for measuring the near-wall volume fraction in granular dispersions

The volume fraction plays a crucial role in the dynamics of granular flows. This work is devoted to developing a novel cost-effective optical method for determining the near-wall volume fraction. By means of a numerical investigation, performed by Monte Carlo generations of mono-disperse sphere distributions under controlled illumination conditions, the stochastic relationship between the near-wall volume fraction and a measurable quantity, referred to as two-dimensional volume fraction, is figured out. A binarization algorithm is proposed for estimating the two-dimensional volume fraction from gray-scale digital images. The relation is found to be of exponential type, with parameters only depending on the angle of incidence of light. An experimental investigation is designed for implementing the proposed method to a real laboratory context. The laboratory campaign, performed on dispersions of white plastic grains immersed in different ambient fluids, enables us to validate the proposed approach. It is found that the exponential law provides results in sound agreement with experimental data. Sensitivity analyses are also performed to confirm and evaluate the robustness and the accuracy of the proposed method.     

Can Wigner distribution functions with collisions satisfy complete positivity and energy conservation?

To avoid the computational burden of many-body quantum simulation, the interaction of an electron with a photon (phonon) is typically accounted for by disregarding the explicit simulation of the photon (phonon) degree of freedom and just modeling its effect on the electron dynamics. For quantum models developed from the (reduced) density matrix or its Wigner–Weyl transformation, the modeling of collisions may violate complete positivity (precluding the typical probabilistic interpretation). In this paper, we show that such quantum transport models can also strongly violate the energy conservation in the electron–photon (electron–phonon) interactions. After comparing collisions models to exact results for an electron interacting with a photon, we conclude that there is no fundamental restriction that prevents a collision model developed within the (reduced) density matrix or Wigner formalisms to satisfy simultaneously complete positivity and energy conservation. However, at the practical level, the development of such satisfactory collision model seems very complicated. Collision models with an explicit knowledge of the microscopic state ascribed to each electron seems recommendable (Bohmian conditional wavefunction), since they allow to model collisions of each electron individually in a controlled way satisfying both complete positivity and energy conservation.

     

Coloured Petri nets and graphical simulation for the validation of a robotic cell in aircraft industry

This paper proposes a mixed validation approach based on coloured Petri nets and 3D graphic simulation for the design of supervisory systems in manufacturing cells with multiple robots. The coloured Petri net is used to model the cell behaviour at a high level of abstraction. It models the activities of each cell component and its coordination by a supervisory system. The graphical simulation is used to analyse and validate the cell behaviour in a 3D environment, allowing the detection of collisions and the calculation of process times. The motivation for this work comes from the aeronautic industry. The automation of a fuselage assembly process requires the integration of robots with other cell components such as metrological or vision systems. In this cell, the robot trajectories are defined by the supervisory system and results from the coordination of the cell components. The paper presents the application of the approach for an aircraft assembly cell under integration in Brazil. This case study shows the feasibility of the approach and supports the discussion of its main advantages and limits.     

Largest Consistent Set in International Environmental Agreements

We study the formation and the stability of International Environmental Agreements (IEAs) in a pollution abatement model with a quadratic cost function. Countries play a two-stage game: in the first stage each country decides to join or not the coalition while, in the second stage, the quantity of pollution abatement is chosen. To analyze the stability of coalition structures in a multiple coalition game, we use the notion of the Largest Consistent Set (LCS) which allows players to be farsighted. Chwe (1994) developed the concept of farsighted stability: an outcome is stable and it is in the LCS if and only if deviations from it or potential further deviations are not unanimously preferred to the original outcome by the coalition considering the deviations. Applying this notion of stability in the IEA context we assume that, when a country or a sub-coalition contemplate exiting or joining an agreement, it takes into account the reactions of other countries ignited by its own actions. The goal of this paper is to identify the resulting stable structures and the LCS, examining the cooperation among countries with respect to an indicator of countries’ environmental awareness. We show that large coalitions are possible outcomes of the game if the farsightedness is considered. In particular, we obtain general sufficient conditions that assure the farsighted stability of the Grand Coalition. In a computational way, we prove that if the environmental awareness is larger than a threshold value, the number of coalition structures belonging to LCS goes down with respect to the initial coalition structures and coalitions with singleton countries never exist. Moreover, we present a useful Maple algorithm to compare the cost functions and to determine direct dominance.