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81.
Abstract— We have analyzed the kinetics of photoreactivation of ultraviolet-light-irradiated cells of two strains of the yeast Saccharomyces cerevisiae . The analysis yields plots of h(t ), the number of photorepairable lethal hits remaining in the cell as a function of the time t of exposure to a continuous source of photoreactivating light. In the case of one of the strains studied, an excision-deficient haploid strain, it is found that the time-dependence of h(t ) is given by the sum of three decreasing exponential functions of t for stationary phase cultures grown at 23 or 30°C. When the culture is grown at 37°C. the fastest component is absent and the intermediate component is reduced in importance relative to the remaining slow component. In the case of the other strain, a diploid of wild-type radiation resistance, h(t ) is found to contain just one decreasing exponential for cultures grown at 23, 30, and 37°C. The rate constant depends on the growth temperature of the cells, decreasing with increasing temperature. The results are interpreted as evidence for multiple DNA photolyases in the sensitive haploid strain. 相似文献
82.
V. T. Huang L. Haynes H. Levine L. Slade 《Journal of Thermal Analysis and Calorimetry》1996,47(5):1289-1298
Dielectric Spectroscopy (DS) and Thermomechanical Analysis (TMA) were used to identity the glass transition temperature (T g) of native wheat starch, vital wheat gluten and a commercial bread, in response to changes in moisture content. An open-ended coaxial probe technique was used to measure the permittivity or dielectric constant (?′) and the loss factor (?″) as functions of moisture, for 2.45 GHz frequency, at constant density and temperature. Plots of ?′ and ?″ as functions of moisture content showed dramatic changes in mobility-based dielectric properties, which occur upon transition from the glassy solid to the rubbery liquid state. The modified TMA method can measure the change in viscoelastic properties aroundT g. This study further confirms that synthetic polymer science principles can be applied to food systems. 相似文献
83.
P. Walden D. Ottewell E.L. Mathie T. Masterson G. Jones R.R. Johnson A. Haynes E.G. Auld 《Physics letters. [Part B]》1979,81(2):156-160
The differential cross section and analysing power of the reaction were measured at a number of proton energies between 305 and 425 MeV using a polarised proton beam extracted from the TRIUMF cyclotron, and a 50 cm Browne-Buechner magnetic spectograph for detecting the pions. The results clearly display the existence of d-wave pion production for pion momenta (cms) as low as 0.5mπc. 相似文献
84.
85.
D. P. Barber J. B. Dainton L. C. Y. Lee R. Marshall J. C. Thompson D. T. Williams T. J. Brodbeck G. Frost A. M. Osborne G. N. Patrick G. F. Pearce T. Sloan G. R. Brookes W. J. Haynes P. B. Wilkes LAMP Group 《Zeitschrift fur Physik C Particles and Fields》1979,2(1):1-6
Measurements of the photoproduction processes γρ→ρ+ n and γρ→ρ-Δ++ (1236) are reported in the energy range 2.8 to 4.8 GeV. The data show shrinkage of the differential cross section in this energy region for the process γρ→ρ-Δ++ (1236); no shrinkage is observed for the ρ+ n process. The energy dependences of the ρ+ n and ρ-Δ++ (1236) total cross sections are much steeper than current model prediction. The ρ spin density matrices for each process are also presented. 相似文献
86.
Allison S Pei H Haynes M Xin Y Law L Labrum J Augustin D 《The journal of physical chemistry. B》2008,112(18):5858-5866
There are three objectives to the present work. First, starting from a boundary element (BE) formulation of low Reynolds number hydrodynamics, model the translational diffusion of macromolecules modeled as an array of non-overlapping beads, and show how this approach is equivalent to previous formulations of "bead hydrodynamics" and under what conditions. Second, show how this approach can be improved upon by accounting for the variation in forces over the surfaces of individual beads and also extending the approach to a gel modeled as an effective medium, EM. Third, develop a "combined obstruction and hydrodynamic effect" model of the translational diffusion of irregularly shaped macromolecules in a gel. In one of the cases studied, the BE approach is shown to be equivalent to previous "bead model" formulations in which intersubunit hydrodynamic interaction is modeled using the Rotne-Prager tensor. A bead model that accounts for the variation in hydrodynamic stress forces over the individual bead surfaces is shown to be in best agreement with exact results for simple bead arrays made up of 2-4 subunits. The translational diffusion of rods, modeled as strings of from 2 to 100 touching beads in dilute gels is examined. Interpolation formulas valid over a range of gel concentrations and rod lengths are derived for the parallel and perpendicular components of the diffusion tensor as well as the orientationally averaged diffusion tensor. The EM model accounts for the long-range hydrodynamic interaction exerted by the gel support matrix on the diffusing particle of interest but does not account for the reduction in diffusion caused by the direct obstruction of the gel, or steric effect. Both effects are accounted for by writing the translational diffusion in a gel as the product of two terms representing long-range hydrodynamic interaction and steric effects. Finally, the diffusion of a 564 base pair DNA in a 2% agarose gel is examined and model results are compared to experiment (Pluen, A.; Netti, P. A.; Jain, R. K.; Berk, D. A. Biophys. J. 1999, 77, 542-552). For reasonable choices of model parameters, fair agreement between theory and experiment is achieved. 相似文献
87.
Coad BR Kizhakkedathu JN Haynes CA Brooks DE 《Langmuir : the ACS journal of surfaces and colloids》2007,23(23):11791-11803
We report the use of aqueous surface-initiated atom transfer radical polymerization (SI-ATRP) to grow polymer brushes from a "gigaporous" polymeric chromatography support for use as a novel size exclusion chromatography medium. Poly(N,N-dimethylacrylamide) (PDMA) was grown from hydrolyzable surface initiators via SI-ATRP catalyzed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA)/CuCl. Grafted polymer was characterized semiquantitatively by ATR-FTIR and also cleaved and quantitatively characterized for mass, molecular weight, and polydispersity via analytical SEC/MALLS. The synthesis provides control over graft density and allows the creation of dense brushes. Incorporation of negative surface charge was found to be crucial for improving the initiation efficiency. As polymer molecular weight and density could be controlled through reaction conditions, the resulting low-polydispersity grafted polymer brush medium is shown to be suitable for use as a customizable size exclusion chromatography medium for investigating the principals of entropic interaction chromatography. All packed media investigated showed size-dependent partitioning of solutes, even for low graft density systems. Increasing the molecular weight of the grafts allowed solutes more access to the volume fraction in the column available for partitioning. Compared to low graft density media, increased graft density caused eluted solute probes to be retained less within the column and allowed for greater size discrimination of probes whose molecular weights were less than 10(4) kDa. 相似文献
88.
We study the concept of strong equality of domination parameters. Let P1 and P2 be properties of vertex subsets of a graph, and assume that every subset of V(G) with property P2 also has property P1. Let ψ1(G) and ψ2(G), respectively, denote the minimum cardinalities of sets with properties P1 and P2, respectively. Then ψ1(G)ψ2(G). If ψ1(G)=ψ2(G) and every ψ1(G)-set is also a ψ2(G)-set, then we say ψ1(G) strongly equals ψ2(G), written ψ1(G)≡ψ2(G). We provide a constructive characterization of the trees T such that γ(T)≡i(T), where γ(T) and i(T) are the domination and independent domination numbers, respectively. A constructive characterization of the trees T for which γ(T)=γt(T), where γt(T) denotes the total domination number of T, is also presented. 相似文献
89.
90.