Cyano bonded silica monolith—Development of an in situ modification method for analytical scale columns

This study investigates the synthesis and chromatographic behaviour of an analytical size cyanopropyl “cyano” bonded silica monolith. Surface modification was undertaken by treating a neat silica monolith with chloro(3-cyanopropyl)dimethyl silane in dry heptane over a two day period. The resulting monolith showed stability over the duration of the testing program that involved flushing the column with more than 2000 column volumes of mobile phase. Efficiency measurements before and after sylation verified that the integrity of the silica monolith itself was not affected by the modification process, the highest number of theoretical plates (N/m) using anisole was 81,650. A brief selectivity test was then undertaken to assess methylene selectivity and phenyl selectivity. Elemental analysis was used to determine the homogeneity of the carbon load throughout the monolithic bed, and was compared to two commercial C18 and one ‘self’ modified C18 silica monoliths. The development of the in situ modification is also discussed.     

Electrolyte-dependent multiparticle motion near electrodes in oscillating electric fields

The directed assembly of micrometer-scale particles into hexagonal lattices on electrodes was probed by subjecting them to electric fields oscillating at 100 Hz. Solutions of KOH, NaHCO(3), and KCl were used because previous investigations of particle pair behavior had shown that an electrolyte-dependent phase angle dictates whether two particles aggregate or separate at low frequencies. Here it was found that particle ensembles, aggregating or separating, adopt a 2D hexagonal lattice in both cases; the difference appears in the particle spacing. For electrolytes such as NaHCO(3) and KCl, where two isolated particles aggregate, the gap between particle edges is between 1 and 1.5 particle diameters; in KOH, where two particles tend to separate, the interparticle spacing is several diameters.     

Phase‐vanishing methods based on fluorous phase screen: A simple way for efficient execution of organic synthesis

The phase‐vanishing (PV) method is based on spontaneous reaction controlled by diffusion of reagents into fluorous media, such as perfluorohexanes (FC‐72) and polyperfluoroethers. Thus, the original PV reaction utilizes a triphasic test tube method composed of a bottom reagent phase, a middle fluorous phase, and a top substrate phase. In such a triphasic system, the fluorous phase acts as a liquid membrane to transport the bottom reagents to the top organic phase containing substrates. In the end, the bottom layer disappears and two phases remain. Since the first demonstration of the PV method by bromination of alkenes with molecular bromine, a number of applications have been developed thus far. These include halogenation of alcohols with SOBr₂ and PBr₃, demethylation of methoxyarenes with BBr₃, cyclopropanation of alkenes by CH₂I₂‐AlEt₃, and Friedel–Crafts acylation of aromatic compounds with SnCl₄. A fluorous triphasic U‐tube method is effective for chlorination of alcohols based on lighter (less dense) reagents such as SOCl₂ and PCl₃. A system using a solution containing reagents as a bottom phase is useful for oxidation with m‐CPBA, which may be defined as a new category for the “extractive PV” method. Recent advances include a “quadraphasic” PV method, in which an aqueous “scavenger” phase is added to the original triphasic PV method to remove acidic by‐products. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 351–363; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20161     

Effects of environmental noise on computer-derived voice estimates from female speakers

The purpose of this study was to examine the influence of noise on voice profile statistics from female samples. Six young adult females served as subjects. Five had normal voices; one had a pathological voice with accompanying bilateral vocal nodules. Each female subject was required to match a generated 235 Hz tone (+/- 2 Hz) while maintaining a constant output level of 70 dB SPL (+/- 5 dB). Data collected from a previous study involving a normal male subject were included for comparative purposes. Noise was generated from a personal computer fan which had a strong center frequency component at 235 Hz. Six different A-weighted signal-to-noise [S/N(A)] conditions were created, ranging in 5 dB increments from 25 to 0 dB. Results revealed that fundamental frequency was reasonably resistant to the effects of noise and to the effects of the noisy (pathological) voice signal. Jitter and shimmer estimates generally increased as noise floors elevated. The greatest amount of measurement error was found for the pathological female voice when captured in the presence of environmental noise. Findings are discussed relative to clinical issues surrounding measurement error.     

The Darwin Direct Implicit Particle-in-Cell (DADIPIC) Method for Simulation of Low Frequency Plasma Phenomena

We describe a new algorithm for simulating low frequency, kinetic phenomena in plasmas. Darwin direct implicit particle-in-cell (DADIPIC), as its name implies, is a combination of the Darwin and direct implicit methods. Through the Darwin method the hyperbolic Maxwell's equations are reformulated into a set of elliptic equations. Propagating light waves do not exist in the formulation so the Courant constraint on the time step is eliminated. The direct implicit method is applied only to the electrostatic field with the result that electrostatic plasma oscillations do not have to be resolved for stability. With the elimination of these constraints spatial and temporal discretization can be much larger than that possible with explicit, electrodynamic PIC. We discuss the algorithms for pushing the particles and solving for the fields in 2D cartesian geometry. We also detail boundary conditions for conductors and dielectrics. Finally, we present two test cases, electron cyclotron waves and collisionless heating in inductively coupled plasmas. For these test cases DADIPIC shows agreement with analytic kinetic theory and good energy conservation characteristics.     

Polyethyleneimine-mediated transfection of cultured postmitotic neurons from rat sympathetic ganglia and adult human retina

Background  

Chemical methods of transfection that have proven successful with cell lines often do not work with primary cultures of neurons. Recent data, however, suggest that linear polymers of the cation polyethyleneimine (PEI) can facilitate the uptake of nucleic acids by neurons. Consequently, we examined the ability of a commercial PEI preparation to allow the introduction of foreign genes into postmitotic mammalian neurons. Sympathetic neurons were obtained from perinatal rat pups and maintained for 5 days in vitro in the absence of nonneuronal cells. Cultures were then transfected with varying amounts of a plasmid encoding either E. coli β-galactosidase or enhanced green fluorescence protein (EGFP) using PEI.     

A unified approach to global convergence of trust region methods for nonsmooth optimization

This paper investigates the global convergence of trust region (TR) methods for solving nonsmooth minimization problems. For a class of nonsmooth objective functions called regular functions, conditions are found on the TR local models that imply three fundamental convergence properties. These conditions are shown to be satisfied by appropriate forms of Fletcher's TR method for solving constrained optimization problems, Powell and Yuan's TR method for solving nonlinear fitting problems, Zhang, Kim and Lasdon's successive linear programming method for solving constrained problems, Duff, Nocedal and Reid's TR method for solving systems of nonlinear equations, and El Hallabi and Tapia's TR method for solving systems of nonlinear equations. Thus our results can be viewed as a unified convergence theory for TR methods for nonsmooth problems.Research supported by AFOSR 89-0363, DOE DEFG05-86ER25017 and ARO 9DAAL03-90-G-0093.Corresponding author.     

A new synchroscan streak-camera read-out system for use with CW mode-locked lasers

The synchroscan streak-camera system has been further developed to obtain both picosecond temporal resolution and direct photomultiplier read-out from a single image tube. Advantages include reduction in cost, potentially improved S/N ratio, greater dynamic range and “free temporal range”, and ultimately improved time-resolution in the subpicosecond regime. An application to signal-to-noise improvement in Raman spectroscopy is described.     

On Some Finiteness Questions for Algebraic Stacks

We prove that under a certain mild hypothesis, the DG category of D-modules on a quasi-compact algebraic stack is compactly generated. We also show that under the same hypothesis, the functor of global sections on the DG category of quasi-coherent sheaves is continuous.     

The homotopy invariance of the string topology loop product and string bracket

Let Mⁿ be a closed, oriented, n-manifold, and LM its free loopspace. In [Chas and Sullivan, ‘String topology’,Ann. of Math., to appear] a commutative algebra structure inhomology, H_*(LM), and a Lie algebra structure in equivarianthomology , were defined.In this paper, we prove that these structures are homotopy invariantsin the following sense. Let f:M₁ M₂ be a homotopy equivalenceof closed, oriented n-manifolds. Then the induced equivalence,Lf:LM₁ LM₂ induces a ring isomorphism in homology, and an isomorphismof Lie algebras in equivariant homology. The analogous statementalso holds true for any generalized homology theory h_* thatsupports an orientation of the M_i. Received February 5, 2007.