Experimental determination of quantum dot size distributions, ligand packing densities, and bioconjugation using analytical ultracentrifugation

Analytical ultracentrifugation (AUC) was used to characterize the size distribution and surface chemistry of quantum dots (QDs). AUC was found to be highly sensitive to nanocrystal size, resolving nanocrystal sizes that differ by a single lattice plane. Sedimentation velocity data were used to calculate the ligand packing density at the crystal surface for different sized nanocrystals. Dihydrolipoic acid poly(ethylene glycol) was found to bind between 66 and 60% of the surface cadmium atoms for CdSe nanocrystals in the 1.54-2.59 nm radius size regime. The surface ligand chemistry was found to affect QD sedimentation, with larger ligands decreasing the sedimentation rate through an increase in particle volume and increase in frictional coefficient. Finally, AUC was used to detect and analyze protein association to QDs. Addition of bovine serum albumin (BSA) to the QD sample resulted in a reduced sedimentation rate, which may be attributed to an associated frictional drag. We calculated that one to two BSA molecules bind per QD with an associated frictional ratio of 1.2.     

cis-4,7,10,trans-13–22∶4 fatty acid distribution in phospholipids of pectinid species Aequipecten opercularis and Pecten maximus

The distribution of cis-4,7,10,trans-13-docosate-traenoic (c4,7,10,t13–22∶4), a peculiar FA previously isolated in the glycerophospholipids of some pectinid bivalves, was investigated in glycerophospholipid classes and subclasses of separated organs (gills, mantle, gonads, and muscle) of the queen scallop Aequipecten opercularis and the king scallop Pecten maximus. Plasmalogen (Pls) and diacyl + alkyl (Ptd) forms of serine, ethanolamine, and choline glycerophospholipids were isolated by HPLC and their FA compositions analyzed by GC-FID. Pls and Ptd forms of serine glycerophospholipids (PlsSer and PtdSer), and to a lesser extend the Pls form of ethanolamine glycerophospholipids (PlsEtn), were found to be specifically enriched with c4,7,10,t13–22∶4. This specificity was found to decrease in the tested organs in the following order: gills, mantle, gonad, and muscle. In gills, c4,7,10,t13–22∶4 was shown to be the main unsaturated FA of serine glycerophospholipids in both Pls and Ptd forms (23.8 and 19.4 mol%, respectively, for A. opercularis, and 21.0 and 26.2 mol% for P. maximus). These results represent the first comprehensive report on the FA composition of plasmalogen serine subclass isolated from pectinid bivalves. The specific association of the PlsSer with the c4,7,10,t13–22∶4 for the two pectinid species can be paralleled to the specific association of the PlsSer with the non-methylene interrupted (NMI) FA and 20∶1(n−11) observed in mussels, clams, and oysters (Kraffe, E., Soudant, P., and Marty, Y. (2004) Fatty Acids of Serine, Ethanolamine and Choline Plasmalogens in Some Marine Bivalves, Lipids 39, 59–66.) This, led us to hypothesize a similar functional significance for c4,7,10,t13–22∶4, NMI FA, and 20∶1(n−11) associated with PlsSer subclass of bivalves.     

Propane ammoxidation on bulk, diluted and supported VSb oxides

VSb oxides diluted with Mg, Al and Zr displayed substantially higher selectivity for propane ammoxidation to acrylonitrile than their bulk and supported analogues. Diluted catalysts were found to consist of oxide compounds of antimony with diluent element, such as AlSbO₄ or MgSb₂O₆, and small amounts of individual oxides of antimony and diluent element. No VSbO₄ phase was detected in their body in contrast with bulk and supported catalysts. It appears that better isolation of vanadium and antimony entities in the structure of diluted oxides was responsible for their enhanced catalytic behavior. Tungsten loaded to the surface of diluted catalysts further improved their selectivity through tuning the surface acidity.     

From pore scale to wellbore scale: Impact of geometry on wormhole growth in carbonate acidization

Acid injection in carbonate reservoir is commonly used in the oil industry to improve, or at least recover, its productivity. The aim of this stimulation technique is to create empty channels called wormholes which, if successful, would bypass the damaged area near the wellbore. During production, wormholes become pathways for the reservoir oil to reach the well. This technique increases near-wellbore permeability, and therefore improves oil production. The interaction between the transport of acid, chemical reaction, and heterogeneities encountered at different scales, controls the unstable behaviour of wormholing and, thus, the success of the treatment. Most of the experimental and numerical studies done on this subject in the past have been limited in their observations because they only considered the dissolution process at a small scale (from pore scale to core scale). The purpose of this work is to study how the geometry of the domain can constrain wormhole competition, and influence wormholing dynamics in a core submitted to acidizing.After a short review of the literature on wormholing to see how the geometry effect could have influenced previous experiments, we study specifically the question of wormhole density. We emphasize that two mechanisms are involved in wormhole competition, with one of them being effective only at small scale. Thus we conclude that wormholing is not a full-scale independent process. We describe differences in the wormhole growth dynamics between “confined” and “unconfined” domains for different dissolution regimes. We focus on optimum conditions and their transition from “confined” to “unconfined” domain to realize that the flow rate in the dominant wormhole does not depend on geometric effects. We conclude by a comparison between 2D and 3D simulations, in both linear and radial flow, and observe changes in the wormholing process. All our results serve as a discussion about definitions of optimum conditions in the literature.     

Synthesis, structure and catalytic properties of Fe-substituted barium hexaaluminates

A sol–gel method using Ba and Al isopropylates and iron nitrate has been used to synthesise barium hexaaluminate partially substituted with iron. After calcination under oxygen at 1200°C the -alumina structure was obtained. Formation of the mixed BaFe_xAl_12-xO₁₉ phase occurred for x=1–4. XRD measurements showed a good crystallinity of the structure and expansion of unit cell parameters due to the presence of larger Fe³⁺ ions substituting Al³⁺ ones in octahedral sites only. Mössbauer spectroscopy revealed that Fe³⁺ ions are present in four different octahedral sites slightly distorted. Catalytic activity in methane combustion showed that an optimum was obtained for solid containing 2 Fe ions per unit cell: the increase of the amount of introduced iron was counterbalanced by the decrease of specific surface area. Intrinsic activities have been calculated for the four solids in both the fresh and aged states. It is observed that increasing iron content increases relative activities in the same ratio as the populations of iron located in two sites as deduced from Mössbauer spectroscopy. It is then tentatively assumed that activity is attributed to octahedrally coordinated Fe³⁺ ions in some specific sites.     

New Raman spectrometer using a digital micromirror device and a photomultiplier tube detector for rapid on-line industrial analysis. Part I: description of the prototype and preliminary results

In this paper, a prototype of a new generation of Raman spectrometers, based on the use of a monochromator, a digital micromirror device as light modulator, and a photomultiplier tube as detector of the Raman light, is described. This spectrometer, containing no moving parts, is inexpensive, robust, and very precise. New in concept, this spectrometer makes it possible to record, in addition to classical Raman spectra, the intensity at several selected points of the spectrum and/or the total intensity in several selected intervals at the same time with great accuracy, thus giving new possibilities for analytical applications. Also, the work presented demonstrates the possibilities of this very simple prototype for rapid on-line industrial analysis, with an example of quantitative analysis of binary and ternary mixtures of xylene isomers. The precision obtained is satisfactory (errors of prediction approximately 3% in 5-6 seconds per sample).     

Numerical modeling of wave propagation in anisotropic viscoelastic laminated materials in transient regime: Application to modeling ultrasonic testing of composite structures

Composite laminate structures remain an important family of materials used in cutting-edge industrial areas. Building efficient numerical modeling tools for high-frequency wave propagation in order to represent ultrasonic testing experiments of these materials remains a major challenge. In particular, incorporating attenuation phenomena within anisotropic plies, and thin intermediate isotropic layers between the plies often represent significant obstacles for standard numerical approaches. In our work, we address both issues by proposing a systematic study of the fully discrete propagators associated to the Kelvin-Voigt, Maxwell, and Zener models, and by incorporating effective transmission conditions between plies using the mortar element method. We illustrate the soundness of our approach by proposing intermediate one-dimensional and two-dimensional numerical evidence, and we apply it to a more realistic configuration of a curved laminate composite structure in a three-dimensional setting.     

A macro-element strategy based upon spectral finite elements and mortar elements for transient wave propagation modeling. Application to ultrasonic testing of laminate composite materials

Proposing efficient numerical modeling tools for high-frequency wave propagation in realistic configurations, such as the one appearing in ultrasonic testing experiments, is a major challenge, especially in the perspective of inversion loops or parametric studies. We propose a numerical methodology addressing this challenge and based upon the combination of the spectral finite element method and the mortar element method. From a prior decomposition of the scene of interest into “macro-elements,” we show how one can improve the performances of the standard finite element procedures in terms of memory footprint and computational load. Additionally, using this decomposition, we are able to efficiently reconstruct important modeling features on-the-fly, such as orientations of anisotropic materials or splitting directions of perfectly matched layers formulations, altogether in a robust and efficient manner. We believe that this strategy is particularly suitable for parametric studies and sensitivity analysis. We illustrate our strategy by simulating the propagation of an ultrasonic wave into an immersed and curved anisotropic laminate 3D specimen flawed with an internal circular delamination of varying size, thus showing the efficiency and the robustness of our approach.     

Robocasting of dense yttria-stabilized zirconia structures

Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions (<38 vol%). The sintered structures were able to retain the original morphologies with >94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability.     

High sensitivity and analyte capture with desorption/ionization mass spectrometry on silylated porous silicon

Silylation chemistry on porous silicon provides for ultrahigh sensitivity and analyte specificity with desorption/ionization on silicon mass spectrometry (DIOS-MS) analysis. Here, we report that the silylation of oxidized porous silicon offers a DIOS platform that is resistant to air oxidation and acid/base hydrolysis. Furthermore, surface modification with appropriate hydrophobic silanes allows analytes to absorb to the surface via hydrophobic interactions for direct analyte extraction from complex matrixes containing salts and other nonvolatile interferences present in the sample matrix. This enables rapid cleanup by simply spotting the sample onto the modified DIOS target and removing the liquid phase containing the interferences. This approach is demonstrated in the analysis of protein digests and metabolites in biofluids, as well as for the characterizing of inhibitors from their enzyme complex. An unprecedented detection limit of 480 molecules (800 ymol) for des-Arg(9)-bradykinin is reported on a pentafluorophenyl-functionalized DIOS chip.