Enhanced VITA technique for turbulent structure identification

Enhanced Variable Interval Time Averaging (EVITA) is introduced as a method that incorporates structure information directly into the detection method. The paper tests VITA and EVITA against an ersatz turbulence signal (antisymmetric exponential time decay) inserted into a random noise distribution. It is shown that EVITA is much less dependent than VITA on the choice of both threshold level and averaging time. EVITA is then applied to particle image velocimetry turbulence data from channel flow [7] at Re = 2872, and is shown to effectively extract bursting events.This work forms part of the Ph.D. thesis of P. SullivanThe authors gratefully acknowledge Dr. R.J. Adrian for providing the channel data. The work is supported by Natural Science and Engineering Research Council of Canada, Queen's University Advisory Research Council and DANTEC, New Jersey. MD was supported through two NSERC summer undergraduate fellowships.     

Reversed-phase liquid chromatography of elastin peptides

Soluble fragments of elastin are frequently present in biological tissue in small amounts. Because of their hydrophobic character, these peptides are not well resolved by a number of conventional techniques. However, their separation should be possible by reversed-phase chromatography. A wide range of columns, gradients and solvents were evaluated. Two systems are described. One was a C18 liganded silica column eluted isocratically by gravity flow. Some degree of size fractionation was achieved with larger peptides being eluted with methanol and smaller ones with isopropanol. The second system uses a pressurized elution from another C18 ligand column. A concave gradient of trifluoroacetic acid-acetonitrile with a decreasing acetonitrile concentration was optimal. Similar resolution of peptides produced by a variety of digestion methods was obtained with the lower-molecular-mass peptides eluting in the middle of the gradient.     

Neutron activation analysis of the NIST Bovine Serum Standard Reference Material using chemical separations

Summary The US National Institute of Standards and Technology is currently in the process of certifying a Bovine Serum Standard Reference Material. In addition to elements normally considered to be of clinical interest, a number of other elements, which are analytically more difficult to determine yet are of importance from either a nutritional or toxicological viewpoint, are being determined by a variety of analytical techniques. Neutron activation analysis in combination with appropriate pre- or post-irradiation chemical separations, has been used to determine many of these difficult elements.

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Neutronenaktivierungsanalyse des Standardreferenzmaterials NIST Bovine Serum mit Hilfe chemischer Trennungen

     

Simulating the relaxation dynamics of microwave-driven zeolites

We have performed equilibrium and nonequilibrium molecular dynamics simulations to study how microwave (MW)-heated zeolite systems relax to thermal equilibrium. We have simulated the relaxation of both ionic and dipolar phases in FAU-type zeolites, finding biexponential relaxation in all cases studied. Fast-decay times were uniformly below 1 ps, while slow-decay times were found to be as long as 14 ps. Fast-decay times increase with an increase in the initial temperature difference between MW-heated ions/dipoles and the equilibrium system. Slow-decay times were found to be relatively insensitive to the details of the MW-heated nonequilibrium state. Velocity, force, and orientational correlation functions, calculated at equilibrium to explore the natural dynamics of energy transfer, decay well before 1 ps and show little evidence of biexponential decay. In contrast, kinetic energy correlation functions show strong biexponential behavior with slow-decay times as long as 14 ps. We suggest a two-step mechanism involving initial, efficient energy transfer mediated by strongly anharmonic zeolite-guest forces, followed by a slower process mediated by weakly anharmonic couplings among normal modes of the zeolite framework. In addition to elucidating relaxation from MW-heated states, we expect that these studies will shed light on energy transfer in other contexts, such as adsorption and reaction in zeolites, which often involve significant heat release.     

Lattice Boltzmann simulations of electrolysis reactions: Microfluidic voltammetry

A lattice Boltzmann model was used to simulate electrolysis reactions occurring within reactors where fluid is pumped through the device under microfluidic control. This article describes the application of two- and three-dimensional procedures for the simulation of the fluid velocities and mass transport characteristics within reactors of an arbitrary geometry. The lattice Boltzmann method is used to simulate the mass transport limited reduction of a species at a large planar electrode, embedded within one wall of a rectangular duct, under either steady-state or potential step conditions. The results of the simulations are compared to both those predicted analytically and via Finite Difference methods for this geometry and used to assess the accuracy of the approach. Good agreement is found between the lattice Boltzmann models and the well-established analytical theory, highlighting the potential of this approach for electrochemical applications within microfluidic environments. A major benefit of the lattice Boltzmann approach is the simple extension of the method to more complex cell and electrode geometries; the potential benefits of this are also noted.     

Multiple emissions from charge transfer excited states of ruthenium(II)—polypyridine complexes

The complex cis-[(bpy)₂Ru

₂]⁴⁺ (bpy is 2,2′-bipyridine) has been prepared by methylation of (bpy)₂Ru

₂]²⁺. Electrochemical studies show that introduction of the bound pyridinium group creates a chemically attached electron acceptor site (E_1/2 = ?0.76 V in 0.1 M [N(n-C₄H₉)₄]PF₆-acetonitrile versus the SSCE). Evidence for a low-lying dπ — π^*

charge transfer (CT) state has been obtained by the appearance of a low energy emission at λ_max 680 nm in ecetonitrile (τ₀ = 104 ns) and for an upper dπ — π^* (bpy) state by a higher energy emission at 580 nm in a methanol glass at 77 K (τ₀ = 7.59 μs). Both emissions appear in a water—ethylene glycol solution containing 5% by weight polyvinyl alcohol at room temperature.     

Double parton scattering inpp collisions at\sqrt s = 63 GeV

In a study ofpp collisions at \(\sqrt s = 63\) GeV with more than 29 GeV total transverse energy emitted into 1.8 units of rapidity in the central region, we have extracted a sample of 4-jet events and compared it with models of the two sources of 4-jet production: double bremsstrahlung and double parton scattering. The data cannot be described by bremsstrahlung alone, and we extract the fraction of 4-jet events attributed to double parton scattering for various definitions of the 4-jet sample. We determine the double parton scattering/2-jet yield ratio, and this leads to a determination of the proton radius. We discuss the implications of our observations for the general understanding of high-ΣE _T events.