THE INTERACTIONS OF PYRENYLMETHYL TRIBUTYLPHOSPHONIUM BROMIDE WITH SINGLE STRAND POLYNUCLEOTIDES

The binding of the water soluble derivative of pyrene, pyrenylmethyl tri-n-butylphosphonium bromide (PMTP), to single strand polynucleotides has been characterised by changes in the absorption spectra, fluorescence spectra, the fluorescence lifetime and the time-resolved fluorescence anisotropy of PMTP. For polyguanylic acid at low ionic strength, there are two modes of binding; external ionic binding and intercalation between the bases. The former results in PMTP excimer formation and the latter involves a charge-transfer complex between PMTP and guanine bases. Polyadenylic acid and polyinosinic acid show only external binding and poly[C] exhibits an interaction which is a combination of external binding and partial intercalation. Single strand DNA binds PMTP by intercalation and external binding at low ionic strength. In the presence of 0.2 M sodium chloride, only binding by intercalation between the bases occurs for poly[G]. Single strand DNA bound PMPT by partial intercalation, as well as full intercalation between the bases, but polyadenylic acid, polycytidylic acid and polyinosinic acid showed no significant binding in the presence of 0.2 M sodium chloride. The differences in the binding of PMTP are attributed to variations in the rigidity and form the structures of single strand polynucleotides adopt in solution. A full analysis of the binding isotherms has been made using methods based on Scatchard plots and the McGhee and von Hippel approach, which are critically compared.     

Numerical experiments on localization in frictional materials

Summary Two types of numerical experiment are performed in order to elucidate the nature of localization in a frictional material. In the first type, a continuum calculation is done with a strain-hardening constitutive model. Localization is shown to occur when the value of the strength parameter has a random distribution in space. In the second type of numerical experiment, the distinct element method is used to conduct a shear test on a simulated sample of 1000 disks. Localization is seen to occur: measurements are made of shear band thickness, distribution of particle spins, contact forces and stress components.

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Numerische Simulation der Lokalisierung in reibungsbehaftetem Material

übersicht Zwei Arten von numerischer Simulation zur AufklÄrung der Natur von Lokalisierungen in reibungsbehaftetem Material werden durchgespielt. Im ersten Fall wird eine kontinuumsmechanische Rechnung mit einem verfestigenden Materialverhalten vorgenommen. Es wird gezeigt, da\ Lokalisierung auftritt, wenn der Grenzreibwert rÄumlich eine Zufallsverteilung besitzt. Im zweiten Fall wird eine Methode mit diskreten Elementen benutzt und mit einer durch 1000 Scheiben simulierten Probe ein Scherversuch durchgeführt. Auch hier tritt Lokalisierung auf: Messungen der Scherzonendicke, der KontaktkrÄfte und der gemittelten Spannungen werden angegeben.

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Presented at the workshop on Limit Analysis and Bifurcation Theory, held at the University of Karlsruhe (FRG), February 22–25, 1988     

The dependence of DNA luminescence on excitation wavelength in the UV/VUV region

Luminescence emission and excitation spectra have been obtained for DNA films at 77 K under vacuum ultraviolet excitation (150–280 nm). The emission spectra, which cover the wavelength range 310 to 490 nm, consists of two components, a short-lived component around 350 nm which is attributed to fluorescence and a longer-lived component around 410 nm believed to be phosphorescence. The excitation spectra, as functions of emission wavelength, are similar in profile with a fairly broad peak around 9240–260 nm) with a shoulder around 200 nm followed by a gradual but constant decrease into the vacuum ultraviolet region of the spectrum. No evidence of autoionization was seen in the region investigated.     

ASPECTS OF CHEMICAL DAMAGE IN RADIATION AND PHOTO-BIOLOGY

Abstract— The reactions of oxidizing free radicals produced by the action of ionizing radiation on aqueous solutions with molecules of biological interest are discussed. In particular the reactions of inorganic radical anions with proteins are considered and their use as selective probes described by example.     

Resolution sensitivity of momentum‐exchange and immersed boundary methods for solid–fluid interaction in the lattice Boltzmann method

In the lattice Boltzmann method (LBM), the mechanism of fluid–solid interaction can be effectively captured by appropriately enforcing the no‐slip conditions in shear direction, and bounce‐back of the non‐equilibrium distribution portion in the normal direction at fluid–solid interfaces. Among various solid–fluid interaction schemes being proposed for LBM in recent decades, two simple fluid–solid interaction methods—the momentum exchange algorithm (MEA) and the immersed boundary scheme (IBS)—were developed based on the above concept. In this paper, MEA and IBS are implemented in a D2Q9 LBGK system and applied to measure the wall correction factors of drag force upon a stationary circular particle midway in the Poiseuille channel flow at very low Reynolds number and drag coefficients at low to moderate Reynolds numbers. MEA and IBS are also employed to compare the fluid‐induced torque over the cylinder in the Taylor–Couette flow, and the steady velocity of a particle settling under the influence of gravity inside a tube. The above experiments show that IBS seems to be more accurate and less demanding on lattice resolution. Copyright © 2010 John Wiley & Sons, Ltd.     

Lattice Boltzmann modeling of pore‐scale fluid flow through idealized porous media

In order to capture the hydro‐mechanical impacts on the solid skeleton imposed by the fluid flowing through porous media at the pore‐scale, the flow in the pore space has to be modeled at a resolution finer than the pores, and the no‐slip condition needs to be enforced at the grain–fluid interface. In this paper, the lattice Boltzmann method (LBM), a mesoscopic Navier–Stokes solver, is shown to be an appropriate pore‐scale fluid flow model. The accuracy and lattice sensitivity of LBM as a fluid dynamics solver is demonstrated in the Poiseuille channel flow problem (2‐D) and duct flow problem (3‐D). Well‐studied problems of fluid creeping through idealized 2‐D and 3‐D porous media (J. Fluid Mech. 1959; 5 (2):317–328, J. Fluid Mech. 1982; 115 :13–26, Int. J. Multiphase Flow 1982; 8 (4):343–360, Phys. Fluids A 1989; 1 (1):38–46, Int. J. Numer. Anal. Meth. Geomech. 1999; 23 :881–904, Int. J. Numer. Anal. Meth. Geomech. 2010; DOI: 10.1002/nag.898, Int. J. Multiphase Flow 1982; 8 (3):193–206) are then simulated using LBM to measure the friction coefficient for various pore throats. The simulation results agree well with the data reported in the literature. The lattice sensitivity of the frictional coefficient is also investigated. Copyright © 2010 John Wiley & Sons, Ltd.     

INFLUENCE OF FLUOROCARBON EMULSIONS ON PORPHYRIN-SENSITISED OXIDATION OF HISTIDINE

The influence of fluorocarbon emulsions on the efficiency of photosensitized oxidation of histidine in solution has been studied, using haematoporphyrin and dihaematoporphyrin derivatives as sensitisers. It is shown that the fluorocarbon emulsions at low concentrations efficiently disaggregate porphyrins, and thereby enhance photosensitised oxidation. The high solubility of oxygen in fluorocarbon emulsions maintains solution oxygen tension, optimising photooxidative damage. It is suggested that fluorocarbon emulsions might find a role in photodynamic therapy, both as carriers for sensitising dyes, and also to maintain tissue oxygenation in hypoxic regions of solid tumours.