Utilising μ-PIV and pressure measurements to determine the viscosity of a DNA solution in a microchannel

There is currently considerable interest in the development of micro-scale polymerase chain reaction (PCR) systems. Smaller sample volumes are required than for macro-scale systems, and faster process times are feasible. Although much attention has focused on the output of micro-PCR (μ-PCR), little attention has been devoted to the detailed fluid mechanics of such devices. There are many technical challenges associated with systems of these length scales.

In this paper the effect of PCR on biofluid viscosity is examined. A theoretical expression for viscosity in PCR is derived. Transmission electron microscopy is used to determine the geometry of a 240 base pair segment of an Escherichia coli (E. coli) DNA molecule and the results are used to predict the effect of PCR on biofluid viscosity.

Micro-particle image velocimetry (μ-PIV) and pressure transducer measurements of water, amplified and unamplified E. coli DNA solutions flowing in a polycarbonate microchannel are recorded. In a novel application of these established measurement techniques, the results are combined with curve fitting of a theoretical prediction for channel flow to estimate the viscosity of the E. coli solutions. The viscosity results are compared to the theoretical prediction for PCR viscosity and to measurements in a commercial viscometer. Viscosity measurements indicated no increase in fluid viscosity after PCR for a low molecular weight molecule.     

Edge-maximality of power graphs of finite cyclic groups

We show that among all finite groups of any given order, the cyclic group of that order has the maximum number of edges in its power graph.     

Kinetics and Mechanism of the Reduction of Sodium Chlorite by Sodium Hydrogen Ascorbate in Aqueous Solution at Near Neutral pH

The reduction of chlorite ion by the hydrogen ascorbate ion in a neutral solution safely produces chlorine dioxide. The decrease in absorbance at 268 nm with the presence of dimethyl sulfoxide (DMSO) allows measurement of the ascorbate disappearance in the reaction with excess chlorite. The measured rate constant at 25 ± 0.02°C, 3.67 × 10^?4 M DMSO, ionic strength 0.51 M (NaClO₄), and in the presence of 3.32 × 10^?9 M ethylenediaminetetraacetic acid is 13.81 ± 1.30 M^?1 s^?1. Rate constant measurements over the range 15–35°C gave an Arrhenius activation energy of 75.51 ± 4.53 kJ mol^?1. This result is the first reported determination of the kinetics of this reaction and is consistent with either electron‐ or oxygen‐transfer mechanisms. Anomalously, reduction of chlorite results in its oxidation, because intermediate hypochlorite oxidizes chlorite.     

The Local Structure of a Bipartite Distance-regular Graph

In this paper, we consider a bipartite distance-regular graph Γ = (X, E) with diameter d ≥ 3. We investigate the local structure ofΓ , focusing on those vertices with distance at most 2 from a given vertex x. To do this, we consider a subalgebra R = R(x) ofMat_{0307a0x.gif X}(C), where 0307a1x.gifX denotes the set of vertices in X at distance 2 from x. R is generated by matrices Ã, 0307a2x.gif J, and 0307a3x.gif D defined as follows. For all y, z 0307a4x.gif X, the (y,z )-entry of à is 1 if y, z are at distance 2, and 0 otherwise. The (y, z)-entry of 0307a5x.gif J equals 1, and the (y,z )-entry of 0307a6x.gif D equals the number of vertices of X adjacent to each ofx , y, and z. We show that R is commutative and semisimple, with dimension at least 2. We assume that R is one of 2, 3, or 4, and explore the combinatorial implications of this. We are motivated by the fact that if Γ has a Q-polynomial structure, then R ≤ 4.     

High‐Z′ and twinning behavior in 3,4‐dinitrobenzoic acid

The title compound, C₇H₄N₂O₆, (I), crystallizes in P with Z′ = 4, but with no approximate or pseudosymmetry. The crystals were nonmerohedrally twinned, with at least four twin components related to the major moiety by 180° rotations around the real b and c axes, and by 180° rotation around the a* axis. The excessive twinning is not caused by a phase change from an untwinned room‐temperature higher‐symmetry polymorph. The molecules are planar chiral and, owing to the tilt angle of the nitro groups and the position of protonation, there are altogether eight conformers possible. Six of these theoretically possible eight conformers are realized in the solid‐state structure of (I). Packing analysis and force‐field calculations indicate that the largest part of the packing interactions does not originate from the hydrogen‐bonding interactions, as one might initially be tempted to assume; π–π stacking and O_nitro...π interactions between neighboring molecules of (I) seem to be the dominant factor that determines the packing observed in the structure of this nitro‐substituted benzoic acid derivative.     

A modeling investigation of articulatory variability and acoustic stability during American English /r/ production

This paper investigates the functional relationship between articulatory variability and stability of acoustic cues during American English /r/ production. The analysis of articulatory movement data on seven subjects shows that the extent of intrasubject articulatory variability along any given articulatory direction is strongly and inversely related to a measure of acoustic stability (the extent of acoustic variation that displacing the articulators in this direction would produce). The presence and direction of this relationship is consistent with a speech motor control mechanism that uses a third formant frequency (F3) target; i.e., the final articulatory variability is lower for those articulatory directions most relevant to determining the F3 value. In contrast, no consistent relationship across speakers and phonetic contexts was found between hypothesized vocal-tract target variables and articulatory variability. Furthermore, simulations of two speakers' productions using the DIVA model of speech production, in conjunction with a novel speaker-specific vocal-tract model derived from magnetic resonance imaging data, mimic the observed range of articulatory gestures for each subject, while exhibiting the same articulatory/acoustic relations as those observed experimentally. Overall these results provide evidence for a common control scheme that utilizes an acoustic, rather than articulatory, target specification for American English /r/.     

Bipartite Distance-regular Graphs, Part I

Let Γ=(X,E) denote a bipartite distance-regular graph with diameter D≥4, and fix a vertex x of Γ. The Terwilliger algebra T=T(x) is the subalgebra of Mat _X(C) generated by A, E ^* ₀, E ^* ₁,…,E ^* _D, where A denotes the adjacency matrix for Γ and E ^* _i denotes the projection onto the i ^TH subconstituent of Γ with respect to x. An irreducible T-module W is said to be thin whenever dimE ^* _i W≤1 for 0≤i≤Di. The endpoint of W is min{i|E ^* _i W≠0}. We determine the structure of the (unique) irreducible T-module of endpoint 0 in terms of the intersection numbers of Γ. We show that up to isomorphism there is a unique irreducible T-module of endpoint 1 and it is thin. We determine its structure in terms of the intersection numbers of Γ. We determine the structure of each thin irreducible T-module W of endpoint 2 in terms of the intersection numbers of Γ and an additional real parameter ψ=ψ(W), which we refer to as the type of W. We now assume each irreducible T-module of endpoint 2 is thin and obtain the following two-fold result. First, we show that the intersection numbers of Γ are determined by the diameter D of Γ and the set of ordered pairs