Particle image velocimetry in Rayleigh-Be´rnard convection: Photographs with a high number of exposures

We present here an application of particle image velocimetry (PIV) to the analysis of the Rayleigh-Be´nard convection patterns in small ☐es, in which a low power laser (5 mW He-Ne) has been used and photographs with a high number of exposures have been taken. Parameters which affect the quality of photographs are analyzed and related with the number of exposures.

The data reduction is made by fringe analysis (point-by-point technique) and by spatial filtering (whole-field technique). The fringe analysis is made with a1 − D integration method, which has been fully automated in the way described here.

The velocity field is numerically processed in order to obtain some additional information (like flow rates, vorticity, streamlines, …) which is relevant in fluid mechanics.

Finally, results obtained from an application of the whole process to the study of motion in the mid-plane of a Rayleigh-Be´nard cell are shown.     

The relationship between thermodynamic stabilities of carbenium ions in the gas phase and in aqueous solution: A wide scope study

The thermodynamics of the reaction involving R_ref = tert-butyl and 21 carbenium ion/alcohol systems has been studied at the MP2/6-311+G(3d, 2p)//MP2/6-311+G(d, p) level. The results have been compared to the experimental data for the same systems in solution. The range of structural effects spans 102 kcal mol⁻¹ in the gas phase and is the widest ever examined. A physically meaningful correlation has been found. Phenyl-substituted systems are among the most important exceptions.     

Synthesis of 10-aminophenothiazines and derivatives

In this paper it is shown that 2-nitro-2′-(β-acetyl) hydrazinodiphenyl sulfides cyclize, via a Smiles rearrangement, to 10-acetylaminophenothiazines, which are inert to alkalis and suffer a strong decomposition by acids. 10-Aminophenothiazine has been obtained by ring closure of 2-bromo-2′-hydrazinodiphenyl sulfide via an assumed benzyne intermediate.     

Exponential decay in nonsimple thermoelasticity of type III

This paper deals with the model proposed for nonsimple materials with heat conduction of type III. We analyze first the general system of equations, determine the behavior of its solutions with respect to the time, and show that the semigroup associated with the system is not analytic. Two limiting cases of the model are studied later. Copyright © 2015 John Wiley & Sons, Ltd.     

Impossibility of localization in linear thermoelasticity with voids

In this note we prove the impossibility of the localization in time of the solutions of the linear thermoelasticity with voids. This means that the only solution for this problem that vanishes after a finite time is the null solution. From a thermomechanical point of view, this result says that the combination of the thermal and porous dissipation in the linear theory is not sufficiently strong to guarantee that the thermomechanical deformations will vanish after a finite time. The main idea to prove this result is to show the uniqueness of solutions for the backward in time problem.     

Does the maximum principle hold for anti-plane shear deformations in elastic mixtures?

In this note we consider the equations which govern the anti-plane shear deformations for a mixture of elastic solids. We give the conditions that guarantee the maximum principle for the solutions of this system. When these conditions are not satisfied, we give solutions that do no satisfy this principle.     

Flash DSC crystallization study of blown film grade bimodal high density polyethylene (HDPE) resins. Part 2. Non‐isothermal kinetics

Non‐isothermal ultra‐fast cooling crystallization tests were conducted on three blown film grade bimodal high density polyethylene (HDPE) resins using a fast differential scanning calorimeter, the Flash DSC. Non‐isothermal tests were performed at cooling rates between 50 and 4000°K/s, and the data were analyzed using the modified Avrami model by Jeziorny (Polymer, 1978 , 19, 1142). Non‐isothermal data were used to propose a new method named crystallization–time–temperature–superposition, and the two activation energies were obtained for each of the resins. This is very useful for obtaining theoretical crystallization kinetics data at different cooling rates, allowing its use in ultra‐fast cooling polymer processes such as blown film. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1822–1827     

Polarized emission and absorption cross-section calculation in LiNbO3:Tm3+

Absorption and emission cross-sections are essential spectroscopic parameters that determine the performance of rare-earth solid state lasers and amplifiers. A precise characterization of such parameters is of great interest in order to proceed with the necessary optimization stage which will assure the development of photonic devices with high efficiency. In particular, in order to model Tm³⁺ infrared lasers under 800 nm pumping, the absorption and emission cross-sections associated with optical transitions involving the ³H₄ and ³F₄ manifolds are needed. In this work, the classical McCumber theory is applied to evaluate the polarized absorption and emission cross-sections of Tm³⁺ ions in LiNbO₃.     

Electrofluidized bed of silica nanoparticles

The behavior of a fluidized bed of electroneutral silica nanopowder under the influence of a cross-flow electric field is studied. Nanoparticle agglomerates experience an electrophoretic force as a consequence of being naturally charged, which leads to electrophoretic deposition at static and low frequency fields. In contrast, fluidization is enhanced at intermediate field frequencies, which can be attributed to agglomerate forced flow.     

Gelatin—Hyaluronic Acid Hydrogels with Tuned Stiffness to Counterbalance Cellular Forces and Promote Cell Differentiation

Cells interact mechanically with their environment, exerting mechanical forces that probe the extracellular matrix (ECM). The mechanical properties of the ECM determine cell behavior and control cell differentiation both in 2D and 3D environments. Gelatin (Gel) is a soft hydrogel into which cells can be embedded. This study shows significant 3D Gel shrinking due to the high traction cellular forces exerted by the cells on the matrix, which prevents cell differentiation. To modulate this process, Gel with hyaluronic acid (HA) has been combined in an injectable crosslinked hydrogel with controlled Gel–HA ratio. HA increases matrix stiffness. The addition of small amounts of HA leads to a significant reduction in hydrogel shrinking after cell encapsulation (C2C12 myoblasts). We show that hydrogel stiffness counterbalanced traction forces of cells and this was decisive in promoting cell differentiation and myotube formation of C2C12 encapsulated in the hybrid hydrogels.