No abstract available

No abstract available

[en] A distortion in a crystal is characterized by the existence of a macroscopic phonon wave function whose equation of motion is obtained together with that for the electron first order reduced density matrix. These form a set of coupled integro-differential equations. The Froehlich model of a one-dimensional superconductor is shown to describe a particular case of a system of electrons and phonons where the phonons are described by a macroscopic wave function associated with the existence of off-diagonal long-range order in the phonon first order reduced density matrix. The electron first order reduced density matrix for this model exhibits dynamic diagonal long range order. (Auth.)

[en] The authors have used the techniques of premature chromosome condensation (PCC) and fluorescence in situ hybridization (FISH) with a library for human chromosome 4 to analyze the rate of rejoining of chromosome breaks and development of exchange aberrations in AG1522 human fibroblasts. AG1522 cells were irradiated in plateau phase with 10 Gy and fused with mitotic HeLa cells either immediately after irradiation or at intervals up to eight days later. The slides were then hybridized with the chromosome 4 library and unrejoined breaks and exchange events (visualized as bicolor chromosomes) scored in these cells. At the earliest time point after irradiation, the number of exchange events in the irradiated cells was low, but increased with kinetics similar to that of the joining of the breaks. Furthermore, when those cells which had exchange events for their distribution were analyzed , almost all of the cells initially contained one exchange event (1 bicolor chromosome). As time progressed, the number of cells containing exchanges with two exchange events per cell increased as the number with one exchange event per cell decreased. Extrapolation of the number of exchange events to zero time (with an estimate of 20 min for the fusion and condensation times) gave a value consistent with zero exchanges at zero time after irradiation. In a separate experiment, the authors also scored AG1522 cells at the first metaphase after a dose of 6 Gy and were able to show that as many as 50% of the complete exchanges were non-reciprocal in nature, that is, the two broken ends of a single break in chromosome 4 joined to two different chromosomes. These data support the classical breakage-and-reunion model rather than the Revell Exchange Theory of exchange formation. 20 refs., 5 figs

[en] The authors combined fluorescence in situ hybridization (FISH) with specific full-length chromosome probes using the premature chromosome condensation (PCC) technique chromosome condensation (PCC) technique to simplify scoring chromosome damage and its repair. They have shown the technique works well and enables breaks and exchanges to be readily detected and scored in individual chromosomes. A chromosome 4 full-length specific library has been used in initial studies. (UK)

[en] For time-independent wave propagation in focusing media or wave guides, backscattering and coupling between propagation modes are caused by deterministic or random variations of the refractive index in the distinguished (x) direction of propagation. Various splittings of the wave field into forward and backward traveling components, which lead to coupled equations involving abstract operator coefficients, are presented. Choosing a natural explicit representation for these operators immediately yields a coupled mode form of these equations. The splitting procedure also leads naturally to abstract transmission and reflection operators for slabs of finite thickness (a≤x≤b), and abstract invariant imbedding equations satisfied by these. The coupled mode form of these equations, together with such features as reciprocity (associated with an underlying symplectic structure) are also discussed. The example of a square law medium is used to illustrate some of these concepts

[en] Time-independent wave propagation is treated in media where the index of refraction contains a random component, but its mean is invariant with respect to translation in some direction distinguishing the wave propagation. Abstract splitting operators are used to decompose the wave field into forward and backward traveling components satisfying a coupled pair of equations. Mode-coupled equations follow directly from these after implementing a specific representation for the abstract splitting operators. Here we indicate a formal solution to these equations, concentrating on the diffusion regime, where we estimate the forward- and backscattering contributions to the mode specific diffusion coefficients. We consider, in detail, random media with uniform (random atmosphere) and square law (stochastic lense) mean refractive indices

[en] Glutathione (GSH) and the rate and extent of repair of DNA strand breaks were investigated as determinants of shoulder size of the X-ray survival curve in Chinese Hamster Ovary (CHO) cells. Cell survival and DNA single strand break repair were measured at comparable radiation doses following treatment of CHO cells with dethylmaleate (DEM) at doses which reduce GSH levels from 10% to < 1% of control values. GSH depletion produced dose-modifying radiosensitization ratio (OER) from 2.6 to 1.7, with no change in the survival curve shoulder, or rate of repair of DNA strand breaks. Both mitotic and asynchronous cells had the same initial number of strand breaks for a given radiation dose, but mitotic cells had a half-life for repair of those breaks which was significantly longer. This association of reduced shoulder with reduced rate of DNA strand break did not hold when the cells were treated with 5 mM 3-aminobenzamide (ABA), a potent inhibitor of poly (ADP-ribose) polymerase and strand break repair, since little or no effect on the intitial part of the curve was observed. (U.K.)

[en] Inhibition of repair of X-ray-induced potentially lethal damage (PLD) could enhance the curability of radioresistant tumours. We have studied the effect of inhibitors of the enzyme poly (ADP-ribose) polymerase on X-ray PLD repair. Four classes of inhibitors are known: aromatic amides (e.g., 3-aminobenzamide), thymidine, nicotinamides and methyl xanthines (e.g., caffeine). Plateau-phase Chinese hamster ovary (HA-1) cultures were exposed to 10 mM concentrations of thymidine, nicotinamide, 3-aminobenzamide (3-ABA) and caffeine prior to irradiation to 12 Gy in air, and then incubated with drug at 37⁰C for varying times (0-6 h) prior to subculture. Irradiated cells without drug exhibited a 5-6 fold increase in survival over the 6 h period compared to cultures plated immediately after irradiation. Although none of the compounds proved cytotoxic to unirradiated controls over the 6.5 h exposure, all of the compounds except thymidine reduced the capacity of the cells to repair PLD. The order of the inhibitory effect was caffeine > 3-ABA > nicotinamide, and the inhibition was concentration dependent for nicotinamide and 3-ABA. We also studied the effect of 3-ABA on the radiation response of exponentially growing cells. 5 mM 3-ABA for 2h post-irradiation resulted in a dose-multiplicative sensitization reducing the D₀ from 0.88 Gy to 0.69 Gy, indicating an involvement of poly (ADP-ribose) polymerase in the radiosensitivity of exponentially growing as well as plateau-phase cells. (author)

[en] We consider the kinetics of processes where the sites of a Bethe lattice are filled irreversibly and, in general, cooperatively by monomers, dimers, or polyatomics. For nearest neighbor and sometimes more general cooperative effects (including random filling as a special case), we show that the infinite hierarchy of rate equations for probabilities of empty subconfigurations can be exacty truncated and solved using a shielding property of empty sites. We indicate, in certain cases, a connection between these Bethe lattice solutions and certain approximate truncation solutions for corresponding processes on ''physical'' 2-D and 3-D lattices with the same coordination number