REDUCTION BY NEAR-ULTRAVIOLET (334 nm) LIGHT OF E. COLI CAPACITY FOR PHAGE GROWTH DEPENDS UPON THE rel GENE AND 4-THIOURIDINE

Abstract— Near-ultraviolet radiation (near UV; 300–380 nm) has long been known to produce a transient reduction of the capacity of bacteria to support phage growth. The present work shows that, at high fluenœs (40–100 kJ/m²), 85% of 334-nm-induced reduction of capacity in Escherichia coli B/r requires the rel gene; that is, it results from rel -gene activity caused by the near-UV treatment. This rel -gene activity leads to (1) a bacterial growth delay and concomitantly lowered bacterial metabolism, and (2) a parallel delay in phage development, with a considerable depression of burst size. We propose that the observed effects on phage development are a consequence primarily of the lowered bacterial metabolism, but they may also result partly from a direct inhibition of phage DNA synthesis by the rel gene product, these effects together leading to the observed reduction of capacity in a rel ⁺ strain. The remaining 15% of capacity reduction, observed in a rel strain, has an unknown mechanism, but does appear to involve a delay in phage development.
At least 95% of the total capacity reduction observed in the rel ⁺ strain in the range 40–100 kJ/m² requires the presence of 4-thiouridine, an unusual base in E. coli transfer RNA, which is presumably both the chromophore and the target for near-UV-induced capacity reduction.     

Indecomposable representations for real roots of a wild quiver

For a given quiver and dimension vector, Kac has shown that there is exactly one indecomposable representation up to isomorphism if and only if this dimension vector is a positive real root. However, it is not clear how to compute these indecomposable representations in an explicit and minimal way, and the properties of these representations are mostly unknown. In this note we study representations of a particular wild quiver. We define operations which act on representations of this quiver, and using these operations we construct indecomposable representations for positive real roots, compute their endomorphism rings and show that these representations are tree representations. The operations correspond to the fundamental reflections in the Weyl group of the quiver. Our results are independent of the characteristic of the field.     

Metallurgical behaviour of iron in brass studied using Mössbauer spectroscopy

The behaviour of small amounts of Fe in brass is investigated using Mössbauer spectroscopy. Different samples, made from the same ingot material, but run through different annealing temperatures and duration times and then quenched to room temperature, have different amount of γ-Fe. The present work shows that a suitable heat treatment can increase the amount of these precipitations and, that a heat treatment at 650°C is the optimal one for having the highest amount of this phase.     

New tokamak plasma regime with stationary temperature oscillations

During noninductively driven discharges in the Tore Supra tokamak, steady sinusoidal oscillations of the central electron temperature, lasting as long as 2 min, have been observed for the first time. Having no helical structure, they cannot be ascribed to any known MHD instability. The most plausible explanation of this new phenomenon is that the plasma current density and the electron temperature evolve as a nonlinearly coupled predator-prey system. This interpretation is supported by the numerical solution of coupled resistive current diffusion and heat transport equations.     

Remarks on a unified theory for classical and generalized interpolation and extrapolation

A unified theory for generalized interpolation, as developed by Mühlbach, and classical polynomial interpolation is discussed. A fundamental theorem for generalized linear iterative interpolation is given and used to derive generalizations of the classical formulae due to Neville, Aitken and Lagrange. Using Mühlbach's definition of generalized divided differences, Newton's generalized interpolation formula, including an expression for the error term, is derived as a pure identity.     

Theoretical study of the singlet electronically excited states of N4

Vertical excitation energies for the lowest eleven singlet states of T_d N₄ were calculated using the TD-DFT method with the B3LYP functional, and at the EOM-CCSD level of theory. The vertical excitation energies for the five lowest-lying excited states were also obtained using the state-averaged CASSCF, CASPT2, CASPT3, and MRCI + Q methods. Our results show that the five lowest-lying states are of valence character. EOM-CCSD/d-aug-cc-pVTZ calculations predict that there are two weakly allowed optical transitions of T₂ symmetry at 10.44 and 10.82 eV. The transition to the third T₂ state, which is predicted to be at 10.89 eV, has an oscillator strength about one order of magnitude higher.     

Studies of crown ether complexes aryldiazonium ion complexes

DNMR studies show that for complexation of aryldiazonium salts 21-crown-7 is the preferred host.     

Tuning the HOMO and LUMO energy levels of organic chromophores for dye sensitized solar cells

A series of organic chromophores have been synthesized in order to approach optimal energy level composition in the TiO2-dye-iodide/triiodide system in the dye-sensitized solar cells. HOMO and LUMO energy level tuning is achieved by varying the conjugation between the triphenylamine donor and the cyanoacetic acid acceptor. This is supported by spectral and electrochemical experiments and TDDFT calculations. These results show that energetic tuning of the chromophores was successful and fulfilled the thermodynamic criteria for dye-sensitized solar cells, electrical losses depending on the size and orientation of the chromophores were observed.     

Designing a new Diels-Alderase: a combinatorial, semirational approach including dynamic optimization

A computationally inexpensive design strategy involving 'semirational' screening for enzymatic catalysis is presented. The protocol is based on well-established computational methods and represents a holistic approach to the catalytic process. The model reaction studied here is the Diels-Alder, for which a successful computational design has recently been published (Siegel, J. B. et al. Science 2010, 329, 309-313). While it is a leap forward in the field of computational design, the focus on designing only a small fraction of the active site gives little control over dynamics. Our approach explicitly incorporates mutagenesis and the analysis of binding events and transition states, and a promising enzyme-substrate candidate is generated with relatively little effort. We estimate catalytic rate accelerations of up to 10?.