Trapping electrophoresis and ratchets: a theoretical study for DNA-protein complexes

Recently, Griess and Serwer (1998. Biophys. J. 74:A71) showed that it was possible to use trapping electrophoresis and unbiased but asymmetrical electric field pulses to build a correlation ratchet that would allow the efficient separation of naked DNAs from identical DNAs that form a complex with a bulky object such as a protein. Here we present a theoretical investigation of this novel macromolecular separation process. We start by looking at the general features of this electrophoretic ratchet mechanism in the zero-frequency limit. We then examine the effects of finite frequencies on velocity and diffusion. Finally, we use the biased reptation model and computer simulations to understand the band-broadening processes. Our study establishes the main experimental regimes that can provide good resolution for specific applications.     

Cat scratch disease: the rare role of Afipia felis

Since its isolation in 1988, Afipia felis has been associated with cat scratch disease (CSD) in only one report and its role in CSD has been questioned. We have cultured A. felis from a lymph node of a patient with CSD. 16S rRNA gene sequencing, DNA relatedness studies, fatty acid analysis, and PCR of the A. felis ferredoxin gene showed that the isolate is identical to the previously reported A. felis isolate. To determine the role of A. felis in CSD, PCR of the 16S rRNA gene followed by hybridizations with specific probes were performed with lymph node specimens from CSD patients. All 32 specimens tested positive for Bartonella henselae and negative for A. felis. We conclude that A. felis is a rare cause of CSD. Diagnostic tests not conducive to the identification of A. felis might cause the diagnosis of CSD due to A. felis to be missed.     

Bright fluorescent dsDNA probes: novel polycationic asymmetric monomethine cyanine dyes based on thiazolopyridine‐quinolinium chromophore

Seven tri‐ and tetracationic monomeric and homodimeric monomethine cyanine dyes based on thiazolo[4,5‐b]pyridinium and quinolinium end groups were synthesised and characterised. The dyes were tested as fluorescent DNA intercalating probes to apply in DNA gel electrophoresis. The DNA samples stained with all dyes from the series demonstrated bright fluorescent signals. DNA fragments were successfully visualised under orange and green filters as well as under standard UV transillumination. Two of the studied dyes revealed higher sensitivity to DNA when compared with the commercial dimeric cyanine dye TOTO‐1. Their sensitivity reached that of the commercial dimeric cyanine dye YOYO‐1, but the emission was shifted to longer wavelengths. These qualities make the dyes suitable to apply in a wide range of medical and scientific analytical methods.     

Measuring technological diversification: identifying the effects of patent scale and patent scope

Although technological diversification is an important strategic decision for both large and small firms alike, the conventional method of measuring such diversification may well introduce significant scale bias against small- and medium-sized firms. We examine this issue in this study using a sample of 73 Taiwanese integrated-circuit (IC) design firms covering the period from 1995 to 2007 and conclude that the conventional measure of technological diversification reflects the spread or distribution amongst technology classes of a company’s current technology portfolio, and does not capture the incremental expansion in technological scope, or the ‘dynamic act of diversification’, as reflected in our alternative scope measure. Our results suggest clear constraints on the applications made under the conventional index, particularly for firms with small patent scale.     

Enhanced CO2 stability of oxyanion doped Ba2In2O5 systems co-doped with La, Zr

In the solid oxide fuel cell (SOFC) field, proton conducting perovskite electrolytes offer many potential benefits. However, an issue with these electrolytes is their stability at elevated temperatures in the presence of CO₂. Recently we have reported enhanced oxide ion/proton conductivity in oxyanion (silicate, phosphate) doped Ba₂In₂O₅, and in this paper we extend this work to examine the stability at elevated temperatures towards CO₂. The results show improved CO₂ stability compared to the undoped system, and moreover this can be further improved by co-doping on either the Ba site with La, or the In site with Zr. While this co-doping strategy does reduce the conductivity slightly, the greatly improved CO₂ stability would suggest there is technological potential for these co-doped samples.     

Potential impact of high speed networking on teaching and learning in universities

In 1992 a report was commissioned by the UK Universities and Research Councils Joint Network Team on the potential impact of the high speed SuperJANET network on the teaching and learning practices in universities. The report used structured interviews with staff at the universities of Cambridge and Kent to predict and identify any inhibitors and actions necessary to ensure effective takeup. The costs of providinginfrastructure within sites was estimated. In 1994 follow‐up interviews were carried out to identify progress and update the findings with a view to seeing how attitudes had changed. One main difference is an increased optimism. This is more pronounced where there are more demonstrators readily to hand. Another clear trend is the increased feed of active research into teaching using high speed network resources.     

Optimal protection of stabilised dry live bacteria from bile toxicity in oral dosage forms by bile acid adsorbent resins

We previously found that dried live bacteria of a vaccine strain can be temporarily sensitive to bile acids and suggested that bile adsorbing resins (BAR) can be used in oral vaccine tablets to protect dried bacteria from intestinal bile. Here, we report a quantitative analysis of the ability of BAR to exclude the dye bromophenol blue from penetrating into matrix tablets and also sections of hard capsule shells. Based on this quantitative analysis, we made a fully optimised formulation, comprising 25% w/w of cholestyramine in Vcaps? HPMC capsules. This gave effectively 100% protection of viability from 4% bile, with 4200-fold more live bacteria recovered from this formulation compared to unprotected dry bacteria. From the image analysis, we found that the filler material or compaction force used had no measurable effect on dye exclusion but did affect the rate of tablet hydration. Increasing the mass fraction of BAR gave more exclusion of dye up to 25% w/w, after which a plateau was reached and no further dye exclusion was seen. More effective dye exclusion was seen with smaller particle sizes (i.e. cholestyramine) and when the BAR was thoroughly dried and disaggregated. Similar results were found when imaging dye penetration into capsule sections or tablets. The predictions of the dye penetration study were tested using capsules filled with dried attenuated Salmonella vaccine plus different BAR types, and the expected protection from bile was found, validating the imaging study. Surprisingly, depending on the capsule shell material, some protection was given by the capsule alone without adding BAR, with Vcaps? HPMC capsules providing up to 174-fold protection against 1% bile; faster releasing Vcaps Plus? HPMC capsules and Coni Snap? gelatin capsules gave less protection.