Demodulation of a single interferogram by use of a two-dimensional regularized phase-tracking technique

We present a two-dimensional regularized phase-tracking technique that is capable of demodulating a single fringe pattern with either open or closed fringes. The proposed regularized phase-tracking system gives the detected phase continuously so that no further unwrapping is needed over the detected phase.     

Theoretical analysis of the frictional losses in magnetohydrodynamic microflows considering slippage

In this article, we study the frictional losses in magnetohydrodynamic (MHD) microflows by analyzing the Poiseuille number defined through the Darcy–Weisbach friction factor. We consider two-dimensional fully developed flow models characteristic of MHD micropumps including the Hartmann braking effect and the existence of slippage. Unlike the purely hydrodynamic case, in MHD flows the Poiseuille number depends not only on the aspect ratio but also on the physical properties of the fluid and the externally applied magnetic field. Three different combinations of boundary conditions (slip and no-slip) are investigated. Calculations show that the Poiseuille number is considerably reduced as the dimensionless slip length is increased, while it increases as Hartmann number does. The obtained results are consistent with previous models and are helpful for the design of magnetohydrodynamic microflow devices.

     

Photopolymerizable multifunctional monomers and their evaluation as reactive Bis‐GMA eluents

Bis‐GMA {2,2‐bis[4‐(2′‐hydroxy‐3′‐methacryloyloxy‐propoxy)‐phenyl]‐propane}, TEGDMA <2‐{2‐[2‐(2‐methylprop‐2‐enoyloxy)ethoxy]ethoxy}ethyl‐2‐methylprop‐2‐enoate>, and methyl methacrylate (MMA) are some of the most commonly used monomers in the field of restorative dentistry. These compounds are characterized by having one or two terminal double bonds. Besides the effort to synthesize new monomers, several problems still affect the clinical behavior of contemporary dental materials. In this work, two monomers with three terminal double bonds, 5A13DA and 5A13DMA, were synthesized. Both monomers were used to completely replace TEGDMA as reactive diluent of photopolymerizable dental resin composites containing Bis‐GMA. The effects of 5A13DA and 5A13DMA on flexural properties, double bond conversion, water sorption, solubility, and polymerization shrinkage were evaluated. In addition, both monomers were evaluated as crosslinking agents for methylmethacrylate, resulting in copolymers with enhanced thermal stability. The results obtained suggest that newly synthesized monomers are potential substitutes for TEGDMA in the formulation of dental composites, providing 50% lower volumetric shrinkage than the composite resin used as control and adequate mechanical properties. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46240.     

Influence of shear thinning and material flow on robotic dispensing of poly(ethylene glycol) diacrylate/poloxamer 407 hydrogels

Robotic dispensing of hydrogels offers a direct way for generating complex hydrogel shapes. For this, there is a general need for hydrogel formulations with suitable rheological properties. In this contribution, hydrogel formulations containing poly(ethylene glycol) diacrylate (PEG‐DA) and Poloxamer 407 are characterized regarding their flow behavior during robotic dispensing. Formulations contain between 15% and 20% PEG‐DA and 22.5% and 25% Poloxamer 407. All formulations show shear thinning which can be described using a power law with a power law index between 0.10 and 0.11 and calculated shear rates at the wall of the dispensing needle of 379 s^?1 with a dispensing speed of 8 mm s^?1 and a dispensing needle inner diameter of 0.51 mm. Thus, facilitating the generation of smooth hydrogel strands, three‐dimensional hydrogel objects can be prepared without flow after robotic dispensing and can be cured afterward to elastic hydrogels, retaining the shape of the dispensed object. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45083.     

Synthesis and structure-activity relationship of cytotoxic marine cyclodepsipeptide IB-01212 analogues

Several recently discovered marine products have remarkable in vitro and in vivo anticancer profiles against a wide range of tumor cell lines. Some of these compounds are currently in clinical trials. These compounds show complex structures and mechanisms of action of interest. Herein, we describe the preparation of a series of totally synthetic molecules that are structurally related to the natural marine product IB-01212 and evaluated them as antitumor agents. For this, total solid-phase syntheses of the products were performed in parallel by two distinct routes: linear synthesis and convergent synthesis. Structural modifications were introduced in several residue positions to afford 21 IB-01212 analogues for structure-relationship studies. An increase in the number of methyl groups in the macrocycle enhanced cytotoxic activity. Also, the replacement of an ester bond by an amide bond favored antitumor activity against several human cell lines. In addition, the L configuration analogues were more active against all the tumor cell lines than those containing the D configuration. A significant increase in the size and asymmetry of the macrocycle diminished biological activity with respect to that of IB-01212. These results are of great value for the discovery of new and more effective anticancer agents.     

Recombination and trapping in multicrystalline silicon

Minority carrier recombination and trapping frequently coexist in multicrystalline silicon (mc-Si), with the latter effect obscuring both transient and steady-state measurements of the photoconductance. In this paper, the injection dependence of the measured lifetime is studied to gain insight into these physical mechanisms. A theoretical model for minority carrier trapping is shown to explain the anomalous dependence of the apparent lifetime with injection level and allow the evaluation of the density of trapping centers. The main causes for volume recombination in mc-Si, impurities and crystallographic defects, are separately investigated by means of cross-contamination and gettering experiments. Metallic impurities produce a dependence of the bulk minority carrier lifetime with injection level that follows the Shockley-Read-Hall recombination theory. Modeling of this dependence gives information on the fundamental electron and hole lifetimes, with the former typically being considerably smaller than the latter, in p-type silicon, Phosphorus gettering is used to remove most of the impurities and reveal the crystallographic limits on the lifetime, which can reach 600 μs for 1.5 Ωcm mc-Si. Measurements of the lifetime at very high injection levels show evidence of the Auger recombination mechanism in mc-Si. Finally, the surface recombination velocity of the interface between mc-Si and thermally grown SiO₂ is measured and found to be as low as 70 cm/s for 1.5 Ωcm material after a forming gas anneal and 40 cm/s after an anneal. These high bulk lifetimes and excellent surface passivation prove that mc-Si can have an electronic quality similar to that of single-crystalline silicon     

Prediction of the open-circuit voltage of solar cells from the steady-state photoconductance

The steady-state photoconductance is a relevant parameter for solar cells. Minority carrier lifetimes, surface recombination velocities, diffused region recombination and open-circuit voltages can be determined from an analysis of photoconductance data. Computer simulations of archetypical cases are used here to demonstrate the usefulness of such an analysis and, in particular, the possibility of predicting device voltages from contactless photoconductance measurements. Simple theoretical models are given to provide physical insight and guide the analysis. A systematic approach is described that permits diagnosis and identification of the dominant recombination mechanisms for a given device structure.© 1997 John Wiley & Sons, Ltd.     

Revealing the Role of Anchoring Groups in the Electrical Conduction Through Single‐Molecule Junctions

A combined experimental and theoretical study is presented revealing the influence of metal–molecule coupling on electronic transport through single‐molecule junctions. Transport experiments through tolane molecules attached to gold electrodes via thiol, nitro, and cyano anchoring groups are performed. By fitting the experimental current–voltage characteristics to a single‐level tunneling model, we extract both the position of the molecular orbital closest to the Fermi energy and the strength of the metal–molecule coupling. The values found for these parameters are rationalized with the help of density‐functional‐theory‐based transport calculations. In particular, these calculations show that the anchoring groups determine the junction conductance by controlling not only the strength of the coupling to the metal but also the position of the relevant molecular energy levels.     

Hydrogen storage in hybrid nanostructured carbon/palladium materials: Influence of particle size and surface chemistry

Hydrogen adsorption on porous materials is one of the possible methods proposed for hydrogen storage for transport applications. One way for increasing adsorption at room temperature is the inclusion of metal nanoparticles to increase hydrogen–surface interactions. In this study, ordered mesoporous carbon materials were synthesized by replication of nanostructured mesoporous SBA-15 silica. The combination of different carbon precursors allowed to tailor the textural, structural and chemical properties of the materials. These carbons were used for the synthesis of hybrid nanostructured carbon/palladium materials with different sizes of metal nanoparticles. The hydrogen sorption isotherms were measured at 77 K and 298 K between 0.1 and 8 MPa. Hydrogen storage capacities strongly correlate with the textural properties of the carbon at 77 K. At room temperature, Pd nanoparticles enhance hydrogen storage capacity by reversible formation of hydride PdH_x and through the spillover mechanism. The hydrogen uptake depends on the combined influences of metal particle size and of carbon chemical properties. Carbons obtained from sucrose precursors lead to the hybrid materials with the highest storage capacities since they exhibits a large microporous volume and a high density of oxygenated surface groups.