Submillimeter features on injected acrylonitrile butadiene styrene parts: Visualization of the flow and numerical simulation

Numerical simulation of classical dimension parts with micrometric textures on their surface is still difficult to master. The limit condition of the calculations, and in particular, the implemented values, characteristics of the polymer and thermal exchanges (polymer/mold) strongly impact the results. Starting from a model with a 370 μm wide rib, by means of a numerical simulation, a study was done on the evolution of the material flow front velocities and the flow lengths in both the macroscopic part and the microgroove. This innovative visualization mold design was used to determine the velocities from an experimental perspective and to discuss the calculation conditions. On the one hand, there are significant differences regarding the choice of the no flow temperature (~ 40 K) used in the calculation code, the analytical heat transfer equation as well as the experimental results. On the other hand, according to the no flow temperature, it may be necessary to consider, during the filling phase, a perfect mold/polymer thermal contact in the groove. Depending in particular on the injection velocity and the geometry of the micro textures, a characteristic time can be determined which defines an optimal operating point for the topographic texture of the part.     

Synthesis and Characterization of Ultra-Fine Tin Oxide Fibers Using Electrospinning

Ultrafine tin oxide (SnO₂) fibers having a rutile structure, with diameter ranging from 100 nm to several micrometers, were synthesized using electrospinning and metallorganic decomposition techniques. In this work, we propose a precursor solution that is a mixture of pure SnO₂ sol made from SnCl₄:H₂O:C₃H₇OH:2-C₃H₇OH at a molar ratio of 1:9:9:6, and a viscous solution made from poly(ethylene oxide) (PEO) (molecular weight 900 000) and chloroform (CHCl₃) at a ratio of 200 mg PEO/10 mL CHCl₃. This solution allows to obtain an appropriate viscosity for the electrospinning process. The as-deposited fibers were sintered at 400°, 500°, 600°, 700°, and 800°C in air for 2 h. Scanning electron microscopy, scanning probe microscopy, X-ray diffraction, Raman microspectrometry, and X-ray photoelectron spectroscopy (XPS) were used to characterize the sintered fibers and elucidate the chemical reaction during sintering. The results showed that up to the sintering temperature of 700°C, the synthesized fibers are composed of SnO₂. XPS was found to reflect the complicate chemical changes caused by the sintering process.     

The origin of N2O formation in the selective catalytic reduction of NOx by NH3 in O2 rich atmosphere on Cu-faujasite catalysts

The selective catalytic reduction (SCR) of NO_x (NO + NO₂) by NH₃ in O₂ rich atmosphere has been studied on Cu-FAU catalysts with Cu nominal exchange degree from 25 to 195%. NO₂ promotes the NO conversion at NO/NO₂ = 1 and low Cu content. This is in agreement with next-nearest-neighbor (NNN) Cu ions as the most active sites and with N_xO_y adsorbed species formed between NO and NO₂ as a key intermediate. Special attention was paid to the origin of N₂O formation. CuO aggregates form 40–50% of N₂O at ca. 550 K and become inactive for the SCR above 650 K. NNN Cu ions located within the sodalite cages are active for N₂O formation above 600 K. This formation is greatly enhanced when NO₂ is present in the feed, and originated from the interaction between NO (or NO₂) and NH₃. The introduction of selected co-cations, e.g. Ba, reduces very significantly this N₂O formation.     

Effect of iron compounds (oxide,salt, or complexes) on poly(vinyl chloride) thermal and photochemical stability

The color requirements for vinyl siding have drastically evolved over the last decade and have moved toward medium to dark colors. Therefore, manufacturers are exploring new ways to modify their formulations in order to improve weather-ability of these challenging colors. Examination of some of the PVC additives typically used in these formulations has led to some interesting revelations about the performance of iron-containing pigments, which are extensively used in darker colors. A quick weathering test was designed to evaluate the effect of iron in PVC formulations, and this test clearly demonstrates the correlation between iron content and PVC photodegradation.     

A polyamidoamine dendrimer as a selective colorimetric and ratiometric fluorescent sensor for Li+ cations in alkali media

In a DMF + NaOH medium, a polyamidoamine dendrimer having sixteen 1,8-naphthalimide fragments in its periphery, formed a complex only with Li⁺ ions, detected by a colour change from red to yellow and by a significant increase in fluorescence intensity. The dendrimer can be used as a selective sensor for Li⁺ ions in the presence of other alkali ions such as Na⁺ or K⁺.     

A constructive fixed point theorem for min-max functions

Min-max functions, F :R n R n , arise in modelling the dynamic behaviour of discrete event systems. They form a dense subset of those functions which are homogeneous, F i (x 1 + h, .. . , x n + h) = Fi(x 1 , . . . , x n ) + h, monotonic , x y F(x) F(y), and nonexpansive in the l infinity norm-so-called topical functions-which have appeared recently in the work of several authors. Our main result characterizes those min-max functions which have a (generalized) fixed point, where Fi(x) = x i + h for some h R. We deduce several earlier fixed point results. The proof is inspired by Howard's policy improvement scheme in optimal control and yields an algorithm for finding a fixed point, which appears efficient in an important special case. An extended introduction sets the context for this paper in recent work on the dynamics of topical functions.     

Modeling the short-circuit current density of polymer solar cells based on P3HT:PCBM blend

We have investigated the short-circuit current density of organic solar cells based on poly (3-hexylthiophene)(P3HT)/6,6-phenyl C61-butyric acid methyl ester (PCBM) blend. In order to model charge collection efficiencies with respect to short circuit density in such blends, a full optical modeling of the cell is performed. From the distribution of the electromagnetic field, we compute the rate of exciton generation. This exciton generation rate is used as input in the transport equations of holes and electrons. Charge densities at steady state are obtained as solutions are used for computing short-circuit current densities generated in the cell. The dependence of short-circuit current densities versus the thickness of the blend is analyzed and compared with our experimental data and with data extracted from the literature.     

Did the Stern Review underestimate US and global climate damages?

The Stern Review received widespread attention for its innovative approach to the economics of climate change when it appeared in 2006, and generated controversies that have continued to this day. One key controversy concerns the magnitude of the expected impacts of climate change. Stern's estimates, based on results from the PAGE2002 model, sounded substantially greater than those produced by many other models, leading several critics to suggest that Stern had inflated his damage figures.     

On Reducible Monodromies Realized by Reducible Fuchsian Systems

It is shown that under the conditions of Theorems 1 and 2 in [2], the Fuchsian systems realizing the reducible monodromy are in fact reducible systems. On the other hand, when the reducible monodromy is realized by a Fuchsian system, sufficient conditions on the monodromy matrices under which the final Fuchsian system can be chosen reducible are given.     

Antimicrobial soy protein isolate‐based films: physical characterisation,active agent retention and antifungal properties against Penicillium italicum

Soy protein isolates (SPI) films were evaluated as carriers of citral and limonene, and their physical and antifungal properties were evaluated. The presence of antimicrobials in SPI films resulted in changes on colour without affecting the transparency. Films with citral added were more extensible; however, a reduction in tensile strength and elastic modulus was observed in films with limonene added. Aroma compounds addition in films induced a slight increase in water vapour properties in relation to discontinuity of network proteins evidenced by SEM. Besides, FTIR spectra evidenced a partial alteration of SPI secondary structure. Citral was less retained than limonene. The increase in limonene release with high relative humidity was explained by increase in protein chain mobility. SPI films enriched with limonene exhibited strong antifungal activity against the postharvest decay pathogen Penicillium italicum under storage conditions.