The interfacial tension of poly(ethylene oxide) and poly(propylene oxide) oligomers

Summary The interfacial tensions of a series of poly(ethylene oxides) (PEO) and poly(propylene oxides) (PPO) have been measured using a pendant drop technique. A drop of PEO was formed under the PPO, in a thermostatted cell usually at 73 °C, and it was photographed using parallel monochromatic light from a laser.The interfacial tensions were measured for a series of polymers of different molecular weights and were found to increase with increasing PPO molecular weight but to decrease slightly with increasing PEO molecular weight. The dependence on PPO molecular weight is explained as due to the adsorption of hydroxy end groups of the PPO at the PEO interface. When these end groups were "replaced by methoxy groups, the adsorption no longer took place and the interfacial tension increased.

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Zusammenfassung Die Grenzflächenspannungen einer Reihe von Polyäthylenoxyden (PEO) und Polypropylenoxyden (PPO) wurden mittels der Methode des hängenden Tropfens gemessen. Ein Tropfen aus PEO wurde erzeugt unter PPO in einer temperierten Zelle bei gewöhnlich 73 ° C und wurde in parallelem monochromatischem Licht eines Lasers photographiert.Die Grenzflächenspannungen wurden für eine Reihe von Polymeren mit unterschiedlichem Molekulargewicht gemessen und nahmen zu mit steigendem PPO-Molekulargewicht, nahmen aber leicht ab mit zunehmendem PEO Molekulargewicht. Die Abhängigkeit vom PPO Molekulargewicht wird erklärt als Effekt der Adsorption von Hydroxyl-Endgruppen des PPO an der PEO Grenzfläche. Ersetzt man diese Endgruppen durch Methoxyl-Gruppen, beobachtet man keine Adsorption und die Grenzflächenspannung nimmt zu.

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With 2 figures and 4 tables     

1H NMR, EPR, UV-Vis, and Electrochemical Studies of Imidazole Complexes of Ru(III). Crystal Structures of cis-[(Im)(2)(NH(3))(4)Ru(III)]Br(3) and [(1MeIm)(6)Ru(II)]Cl(2).2H(2)O

Comparisons of the spectroscopic properties of a number of Ru(III) complexes of imidazole ligands provide methods of distinguishing between various types of bonding that can occur in proteins and nucleic acids. In particular, EPR and (1)H NMR parameters arising from the paramagnetism of Ru(III) should aid in determining binding sites of Ru(III) drugs in macromolecules. Electrochemical studies on several imidazole complexes of ruthenium suggest that imidazole may serve as a significant pi-acceptor ligand in the presence of anionic ligands. Crystal structures are reported on two active immunosuppressant complexes. cis-[(Im)(2)(NH(3))(4)Ru(III)]Br(3) crystallizes in the triclinic space group P&onemacr; (No. 2) with the cell parameters a = 8.961(2) ?, b = 12.677(3) ?, c = 7.630(2) ?, alpha = 98.03(2) degrees, beta = 100.68(2) degrees, gamma = 81.59(2) degrees, and Z = 2 (R = 0.044). [(1MeIm)(6)Ru(II)]Cl(2).2H(2)O crystallizes in the monoclinic space group P2(1)/n (No. 14) with the cell parameters a = 7.994(2) ?, b = 13.173(4) ?, c = 14.904(2) ?, beta = 97.89(1) degrees, and Z = 2 (R = 0.052). The average Ru(II)-N bond distance is 2.106(8) ?.     

Potential of the slow component of quartz OSL for age determination of sedimentary samples

The slow component of quartz OSL exhibits a high thermal stability, and, in many of the samples studied, a high dose saturation level (several hundreds or, even thousands, of Grays). These properties suggest that the slow component has potential as a long-range dating tool. Initial attempts have been made to obtain equivalent doses for a number of sedimentary samples. Single- and multiple-aliquot techniques were modified for use with the slow component. The results indicate that there is a good potential for sediment dating, particularly for samples of significant age. Experiments concerning the optical resetting of the slow component suggest that, given its slow optical depletion rate, dating may be restricted to aeolian sediments.     

Distance Enumerators for Permutation Groups

We consider the distance enumerator Δ _G (x) of a finite permutation group G, which is the polynomial ∑ _g∈G x ^n?π(g), where n is the degree of G and π(g) the number of fixed points of g ∈ G. In particular, we introduce a bivariate polynomial which is a special case of the cycle index of G, and from which Δ _G (x) can be obtained, and then use this new polynomial to prove some identities relating the distance enumerators of groups G and H with those of their direct and wreath products. In the case of the direct product, this answers a question of Blake et al. (1979 Blake , I. F. , Cohen , G. , Deza , M. ( 1979 ). Coding with permutations . Information and Control 43 : 1 – 19 . [Google Scholar]). We also use the identity for the wreath product to find an explicit combinatorial expression for the distance enumerators of the generalised hyperoctahedral groups C _m  ? S _n .     

Resolving sets for Johnson and Kneser graphs

A set of vertices S$S$ in a graph G$G$ is a resolving set   for G$G$ if, for any two vertices u,v$u,v$, there exists x∈S$x\in S$ such that the distances d(u,x)≠d(v,x)$d(u,x)\ne d(v,x)$. In this paper, we consider the Johnson graphs J(n,k)$J(n,k)$ and Kneser graphs K(n,k)$K(n,k)$, and obtain various constructions of resolving sets for these graphs. As well as general constructions, we show that various interesting combinatorial objects can be used to obtain resolving sets in these graphs, including (for Johnson graphs) projective planes and symmetric designs, as well as (for Kneser graphs) partial geometries, Hadamard matrices, Steiner systems and toroidal grids.     

The use of resonant scattering to identify stone fracture in shock wave lithotripsy

There is currently little feedback as to whether kidney stones have fractured during shock wave lithotripsy. Resonant scattering of the lithotripter shock wave was used here to differentiate intact and fractured stone models in water. Scattering, including reflection and radiation due to reverberation from within the stone, was calculated numerically with linear elasticity theory and agreed well with measurements made with a focused receiver. Identification of fracture was possible through frequency analysis, where scatter from fractured stones was characterized by higher energy in distinct bands. High-speed photography concurrent with measurement indicated the effect was not due to cavitation.     

Role of molecular shape on bent-core liquid-crystal structures

We show how frustrations in molecular packing generated by molecular substitutions and electrostatic potentials necessitate a local C1 symmetry and lead to spontaneous polarization splay and layer bending in bent-core liquid crystals. By estimation of the entropic changes due to curvature, we calculated the elastic constants that drive the spontaneous layer bend and polarization splay and obtained length scales of these deformations. Finally, we propose a structural phase diagram which describes how the experimentally observed helical superstructures, layer undulation, polarization splay, and spontaneous fiber formation depend on the direction and magnitude of the spontaneous polarization.     

Laser trapping of 225Ra and 226Ra with repumping by room-temperature blackbody radiation

We have demonstrated Zeeman slowing and capture of neutral 225Ra and 226Ra atoms in a magneto-optical trap. The intercombination transition 1S0-->3P1 is the only quasicycling transition in radium and was used for laser-cooling and trapping. Repumping along the 3D1-->1P1 transition extended the lifetime of the trap from milliseconds to seconds. Room-temperature blackbody radiation was demonstrated to provide repumping from the metastable 3P0 level. We measured the isotope shift and hyperfine splittings on the 3D1-->1P1 transition with the laser-cooled atoms, and set a limit on the lifetime of the 3D1 level based on the measured blackbody repumping rate. Laser-cooled and trapped radium is an attractive system for studying fundamental symmetries.     

Quantification of Low Concentrations of DNA Using Single Molecule Detection and Velocity Measurement in a Microchannel

We present a novel method for quantifying low concentrations of DNA based on single molecule detection (SMD) for molecular counting and flow measurements inside a microchannel. A custom confocal fluorescence spectroscopic system is implemented to detect fluorescent bursts emitted from stained DNA molecules. Measurements are made one molecule at a time as they flow through a femtoliter-sized laser focal probe. Durations of single molecule fluorescent bursts, which are found to be strongly related to the molecular transit times through the detection region, are statistically analyzed to determine the in situ flow speed and subsequently the sample volume flowing through the focal probe. Therefore, the absolute concentration of a DNA sample can be quantified based on the single molecule fluorescent counts from the DNA molecules and the associated probe volume for a measured time course. To validate this method for quantifying low concentrations of biomolecules, we tested samples of pBR322 DNA ranging from 1 pM to 10 fM (∼3 ng/ml to 30 pg/ml). Besides molecular quantification, we also demonstrate this method to be a precise and non-invasive way for flow profiling within a microchannel.