Numerical study of the flow in a three-dimensional thermally driven cavity

Solutions for the fully compressible Navier–Stokes equations are presented for the flow and temperature fields in a cubic cavity with large horizontal temperature differences. The ideal-gas approximation for air is assumed and viscosity is computed using Sutherland's law. The three-dimensional case forms an extension of previous studies performed on a two-dimensional square cavity. The influence of imposed boundary conditions in the third dimension is investigated as a numerical experiment. Comparison is made between convergence rates in case of periodic and free-slip boundary conditions. Results with no-slip boundary conditions are presented as well. The effect of the Rayleigh number is studied.     

Conformational analysis of 1,2-difluoroethane, an ab-initio investigation

Contrary to expectation, the gauche conformer of 1,2-difluoroethane is more stable than the trans conformer in the gas phase. In order to understand the underlying causes of the “gauche effect”, a complete geometry relaxation was performed for the gauche and trans conformers of 1,2-difluoroethane with the 4-21G, 4-31G and 4-31G** basis sets. The 4-31G** optimized geometry of the gauche conformer compares well with the experimental values obtained from a number of electron-diffraction studies. A correction for the correlation energy, calculated by means of second-order Møller—Plesset perturbation theory with the 6-31G** basis set, proves to be essential to obtain a correct estimate of the energy difference between the gauche and trans conformers 1,2-difluoroethane.     

Non-contact protein microarray fabrication using a procedure based on liquid bridge formation

Contemporary microarrayers of contact or non-contact format used in protein microarray fabrication still suffer from a number of problems, e.g. generation of satellite spots, inhomogeneous spots, misplaced or even absent spots, and sample carryover. In this paper, a new concept of non-contact sample deposition that reduces such problems is introduced. To show the potential and robustness of this pressure-assisted deposition technique, different sample solutions known to cause severe problems or to be even impossible to print with conventional microarrayers were accurately printed. The samples included 200 mg mL^–1 human serum albumin, highly concentrated sticky cell adhesion proteins, pure high-salt cell-lysis buffer, pure DMSO, and a suspension of 5-μm polystyrene beads. Additionally, a water-immiscible liquid fluorocarbon, which was shown not to affect the functionality of the capture molecules, was employed as a lid to reduce evaporation during microarray printing. The fluorocarbon liquid lid was shown to circumvent hydrolysis of water-sensitive activated surfaces during long-term deposition procedures.     

Advanced high-performance liquid chromatography method for highly polar nitroaromatic compounds in ground water samples from ammunition waste sites

An advanced HPLC-photodiode array detection method for the determination of 12 selected highly polar nitroaromatic compounds in ground water samples of ammunition waste sites has been developed and validated. After solid-phase extraction the limits of detection were in the range 0.1–0.5 μg/l. To prove the applicability of the method to other polar nitroaromatic compounds the retention time of another 32 polar compounds under the specified chromatographic conditions were determined and their UV spectra recorded. To review the method, interlaboratory comparisons were performed with a spiked and a real ground water sample.     

Photostabilizing of bisphenol A polycarbonate by using UV-absorbers and self protective block copolymers based on resorcinol polyarylate blocks

Bisphenol A polycarbonate degrades due to sunlight, humidity and oxygen. In this study two possible techniques to stabilize the polymer were compared, i.e. blending of UV-absorbers (UVAs) into the polymer or using block copolymers based on resorcinol polyarylates. Combination of different analysis techniques shows that the protection by UVAs is not as good as by the resorcinol polyarylate block copolymers. The block copolymer rearranges itself through a photo-Fries rearrangement within hours into a UV-absorbing top layer. Two different block compositions were studied, and the copolymer with the highest concentration of resorcinol polyarylate groups shows the best protection.     

Paper coatings with multi-scale roughness evaluated at different sampling sizes

Papers have a complex hierarchical structure and the end-user functionalities such as hydrophobicity are controlled by a finishing layer. The application of an organic nanoparticle coating and drying of the aqueous dispersion results in an unique surface morphology with microscale domains that are internally patterned with nanoparticles. Better understanding of the multi-scale surface roughness patterns is obtained by monitoring the topography with non-contact profilometry (NCP) and atomic force microscopy (AFM) at different sampling areas ranging from 2000 μm × 2000 μm to 0.5 μm × 0.5 μm. The statistical roughness parameters are uniquely related to each other over the different measuring techniques and sampling sizes, as they are purely statistically determined. However, they cannot be directly extrapolated over the different sampling areas as they represent transitions at the nano-, micro-to-nano and microscale level. Therefore, the spatial roughness parameters including the correlation length and the specific frequency bandwidth should be taken into account for each measurement, which both allow for direct correlation of roughness data at different sampling sizes.     

Poly(ethylene glycol)–poly(L‐lactide) star block copolymer hydrogels crosslinked by metal–ligand coordination

The aqueous solution behavior and thermoreversible gelation properties of pyridine‐end‐functionalized poly(ethylene glycol)–poly(L ‐lactide) (PEG–(PLLA)₈–py) star block copolymers in the presence of coordinating transition metal ions were studied. In aqueous solutions, the macromonomers self‐assembled into micelles and micellar aggregates at low concentrations and formed physically crosslinked, thermoreversible hydrogels above a critical gel concentration (CGC) of 8% w/v. In the presence of transition metal ions like Cu(II), Co(II), or Mn(II), the aggregate dimensions increased. Above the CGC, the gel–sol transition shifted to higher temperatures due to the formation of additional crosslinks from intermolecular coordination complexes between metal ions and pyridine ligands. Furthermore, as an example, PEG–(PLLA)₈–py hydrogels stabilized by Mn(II)–pyridine coordination complexes were more resistant against degradation/dissolution when placed in phosphate buffered saline at 37 °C when compared with hydrogels prepared in water. Importantly, the stabilizing effect of metal–ligand coordination was noticeable at very low Cu(II) concentrations, which have been reported to be noncytotoxic for fibroblasts in vitro. These novel PEG–(PLLA)₈–py metallo‐hydrogels, which are the first systems to combine metal–ligand coordination with the advantageous properties of PEG–PLLA copolymer hydrogels, are appealing materials that may find use in biomedical as well as environmental applications like the removal of heavy metal ions from waste streams. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Air-coupled ultrasonic assessment of wood veneer

Air-coupled ultrasound (ACU) provides a tool to evaluate wood samples of small or moderate thickness (<30 mm) thereby avoiding direct contact or liquid coupling. Results of through-transmission ACU measurements on wood veneer samples and related products are reported with respect to a wide variety of quality aspects. Fluctuations in the averaged received signal levels appear to be correlated to the presence of natural or machine-induced thickness and density variations, flaws and grain damage, errors produced by the manufacturing process, insufficient bonding on a substrate, etc. In addition it is seen that the variability of the signal levels enables to distinguish between quarter and crown areas.     

Another view on martingale central limit theorems

Based on the martingale version of the Skorokhod embedding Heyde and Brown (1970) established a bound on the rate of convergence in the central limit theorem (CLT) for discrete time martingales having finite moments of order 2+2δ with 0<δ1. An extension for all δ>0 was proved in Haeusler (1988). This paper presents a rather quick access based solely on truncation, optional stopping, and prolongation techniques for martingale difference arrays to obtain other upper bounds for sup

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(φbeing the standard normal d.f.) yielding weak sufficient conditions for the asymptotic normality of . It is shown that our approach also yields two types of martingale central limit theorems with random norming.