Sonochemical reactions at 640 kHz using an efficient reactor. Oxidation of potassium iodide

Ultrasound can be used to oxidize aqueous pollutants. However, due to economic reasons higher oxidation/destruction rates and higher energy efficiency are needed. Recent studies suggest that the higher ultrasound frequencies provide better oxidation rates than the conventional 20 kHz. Another area for improvement is reactor configuration. We have tested two new reactor configurations with proper focusing and reflection of ultrasound for maximum utilization. Reactor configuration plays an important role in the overall efficiency. In the new reactors, transducers and reaction mixture are separated by a polymer acoustic window which allows efficient transfer of ultrasound energy and not the heat from the transducer to the reaction mixture. One reactor at 640 kHz provides a 100% enhancement over the best reported rate for the oxidation of potassium iodide, on a per-Watt basis. Experiments conducted at varying initial KI concentrations show interesting behavior. Increasing the KI concentration by over eight fold merely increases the iodine production rate by two fold. This suggests that in the oxidation region surrounding the bubble, the KI concentration is much different than in the bulk. It is proposed that the hydrophobic bubble region has lower and near saturation KI concentration.     

NEAR UV LIGHT AND CATARACTS*

Abstract. Sunlight and many types of artificial lighting contain near-UV light (300–400 nm). These wavelengths can enter the eye and are maximally absorbed in the lens due to its chemical composition. The lenses of certain animals develop cataracts from exposure to this light, and changes similar to those that occur in human lenses with certain types of cataracts and with aging are inducible in isolated human lenses. These changes seem to be associated with chemical alterations in the essential amino acid tryptophan either as a part of proteins or in free form. Such changes in tryptophan would result in lens cell toxicity, in increased pigmentation of the lens, and in large aggregates of proteins. The latter two changes would result in losses in the ability of the lens to transmit visible light needed for vision, and the abnormal state called cataract would result. Much more work is needed to prove that near-UV light can accelerate cataractous changes in the lenses of living humans. Studies at the basic chemical level are needed, but population studies would be most essential for the final proof. Many preventive measures could become available, including the use of special types of spectacles and dietary additives.     

Triangle-free graphs with no six-vertex induced path

The graphs with no five-vertex induced path are still not understood. But in the triangle-free case, we can do this and one better; we give an explicit construction for all triangle-free graphs with no six-vertex induced path. Here are three examples: the 16-vertex Clebsch graph, the graph obtained from an 8-cycle by making opposite vertices adjacent, and the graph obtained from a complete bipartite graph by subdividing a perfect matching. We show that every connected triangle-free graph with no six-vertex induced path is an induced subgraph of one of these three (modulo some twinning and duplication).     

Disjoint paths in tournaments

Given k   pairs of vertices (_si,_ti)$(s_i,t_i)$(1≤i≤k)$(1\le i\le k)$ of a digraph G, how can we test whether there exist k   vertex-disjoint directed paths from _si$s_i$ to _ti$t_i$ for 1≤i≤k$1\le i\le k$? This is NP-complete in general digraphs, even for k=2$k=2$ [2], but for k=2$k=2$ there is a polynomial-time algorithm when G is a tournament (or more generally, a semicomplete digraph), due to Bang-Jensen and Thomassen [1]. Here we prove that for all fixed k there is a polynomial-time algorithm to solve the problem when G is semicomplete.     

The influence of sialylation on glycan negative ion dissociation and energetics

For the analysis of native glycans using tandem mass spectrometry (MS), it is desirable to choose conditions whereby abundances of cross-ring cleavages indicative of branch positions are maximized. Recently, negative ion tandem mass spectrometry has been shown to produce significantly higher abundances of such ions in glycans compared to the positive ion mode. Much of this prior work has concerned fragmentation patterns in asialo glycans. The present work compares the abundances of critical cross-ring cleavage ions using negative mode tandem mass spectrometry for milk oligosaccharides and N-linked glycans. For comparison, product ion formation was studied for deprotonated and nitrated ions formed from asialo glycans and deprotonated ions from sialylated glycans. Breakdown profiles demonstrate clearly that more energy was required to fragment sialylated compounds to the same extent as either their asialo or nitrate adducted counterparts. The extraction of a proton from a ring hydroxyl group during the ionization process may be viewed, qualitatively, as imparting significantly more energy to the ion than would that from a molecule bearing an acidic group, so that acidic glycans are more stable in the gas phase, as the negative charge resides on the carboxyl group. These results have strong practical implications because a major portion of glycans released from mammalian proteins will be sialylated.     

Embedding (p,p−1) graphs in their complements

A graphG is embeddable in its complement ifG is isomorphic with a subgraph of . A complete characterization is given of those (p,p−1) graphs which are embeddable in their complements. In particular, letG be a (p,p−1) graph wherep≧6 ifp is even andp≧9 ifp is odd; thenG is embeddable in if and only ifG is neither the starK _1,p−1 norK _1,n ∪C ₃ withn≧4.     

Tropylium,chlorine isotopic abundances,monomeric metaphosphate anion,and conestoga wagon theory

As I look back over a career in mass spectrometry, three high points stand out especially prominently. These are associated with (1) the tropylium model for the C_uH ₇ ⁺ ion in the mass spectra of toluene and other alkylbenzenes, (2) revision of the previously accepted value for the natural abundance of the chlorine isotopes, and (3) the first direct observation of the monomeric metaphosphate anion, which had been for a quarter of a century an elusive, suspected reaction intermediate. Studies of organic ions in the rarefied atmosphere of the mass spectrometer, where only unimolecular processes are allowed, have deepened my appreciation of the role and ubiquity of bimolecular processes in more conventional chemical contexts. Consideration of the two categories of molecular behavior has prompted me to seek and find, for a selected system in the mass spectrometer, parallels both in condensed-phase chemistry and, by an anthropomorphic extension, in human behavior.     

Soft isolated photon production as a probe of the parton shower mechanism

Zeitschrift für Physik C Particles and Fields - We discuss the rate of low-energy well-isolated photons in e+e? annihilation into hadrons, which is highly sensitive to the differences in...     

Magnetic Resonance Microscopy of Heterogeneity in Polymer Electrolyte Membranes

Magnetic resonance microscopy of Nafion 117 is used to measure the spatial variation of solvent dynamics in protonated (acid form) membranes immersed in solvent. Spatial resolution allows determination of membrane material property heterogeneity via T ₂ and diffusion variations to be easily studied in the presence of strong free solvent signal. Variation of T ₂ and diffusion as a function of solvent methanol–water mole fraction is measured. Spatially averaged T ₂ and diffusion data are in general agreement with previous bulk nuclear magnetic resonance studies; however, significant disparities from sample to sample at fixed solvent concentration are present in the spatially averaged data. The variation is determined to be due to changes in solvent mobility within the membrane over scales of the order of 10 mm, indicating macroscale heterogeneity of the solvent saturated membrane morphology. Authors' address: Sarah L. Codd, Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59717-3800, USA