Maximizing edge-ratio is NP-complete

Given a graph G and a bipartition of its vertices, the edge-ratio is the minimum for both classes so defined of their number of internal edges divided by their number of cut edges. We prove that maximizing edge-ratio is NP-complete.     

Advances in microbiology EQA

External quality assessment for microbiology laboratories has seen many changes over the past ten years. EQA is much less focused on the pure analytic process of identifying single organisms submitted in an artificial medium. Samples are more realistic, and can be used to address clinical relevancy. Samples can be supplemented with a variety of non-traditional challenges to extend testing to include a wider range of the pre- and post-analytic aspects of the laboratory cycle. A look to the future sees a broad range of newer targets, with increasing interest in virology and point-of-care testing. Received: 13 April 2002 Accepted: 24 June 2002     

Improved analytical prediction of facilitation factors in facilitated transport

An improved analytical solution for the facilitation factor in facilitated transport that covers a wide range from diffusion-limited to reaction-limited mass transport has been developed. This solution is attained after assuming a small non-zero solute concentration at the membrane exit. Based on previous analysis a graph that provides a reasonable downstream solute concentration was extracted. The exit solute concentration was found to be dependent on both the mobility ratio, , and the inverse Damkohler number, ε. The quick and reasonable results in this work can be used for design and scale-up purposes.     

Kinetics of the gas-phase reaction between iodine and monogermane and the bond dissociation energy D(H3Ge?H)

The title reaction has been investigated in the temperature range of 403–446 K. Monoiodogermane and di-iodogermane together with hydrogen iodide were the main products, although at high conversions at least one other product was formed. GeH₃I is clearly the primary product. Initial rates were found to obey the rate law over a wide range of initial iodine and monogermane pressures. Secondary reactions (of GeH₃I with I₂) affect the subsequent kinetics, although at sufficiently high initial reactant ratios ([GeH₄]₀/[I₂]₀ ≥ 100) an integrated rate equation fits the data with the same rate constants as the initial rate expression. The observed kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step log k₁ (dm³/mol·s) = (11.03 ± 0.13) – (52.3 ± 1.0 kJ/mol)/RT ln 10 has been deduced. From this the bond dissociation energy D(GeH₃? H) = 346 ± 10 kJ/mol (82.5 kcal/mol) is obtained. The significance of this value, together with derived values for Ge–Ge and Ge–C bond strengths, is discussed.     

High-energy collisions of intrinsically deformed particles

The Chou-Yang model of the elastic profile function for high-energy collisions is modified to take into account the possibility that the projectile, the target, or both, are deformed from sphericity. Simple expressions for the elastic amplitudes and total cross sections are derived under the assumption that the collision times are much shorter than the rotation periods of the projectile and target (adiabatic approximation). A simplified, purely geometric interpretation of the results on total cross sections is given and justified in terms of the quantum-mechanical treatment.     

Mechahism of the base promoted fragmentatiom of chloroacetylhydrazide

Experiments are described supporting the positions that the visible transient intermediate occurring during the fragmentation of chloroacetylhydrazide is the anion of acetyldiazene, and that the concurrent reduction is not a simple recombination reaction.     

The directed polymer in a random environment

A continuous space/time approximation of the well known ‘directed polymer’ problem is considered. Connection between the ‘Helmholtz Free Energy’ and the ‘Two Walker problem’ is shown. Rigorous proof of the superdiffusive mean squared displacement exponent of 4/3 is given when there is one space dimension and one time dimension. Asymptotically diffusive behaviour of c(k)tis shown when there are one ‘time’ and two ‘space’ dimensions. For higher dimensions, the behaviour is diffusive and the mean squared displacement is asymptotically t d. These results hold for all temperature, because the phase transition in the discrete model is no longer present in the continuous model; the renormalization procedure has set the transition temperature to k _crit =0The joint distribution is also shown to be asymptotically sub-Gaussian for all dimensions and all temperatures (in the sense that the p ^thmoments as a function of pincrease more slowly than the moments of a Gaussian distribution). The ‘Helmholtz Free Energy’ is also calculated for this model and the quenched and annealed free energies are shown to be identical for all temperature     

Catalyst‐Free Deaminative Functionalizations of Primary Amines by Photoinduced Single‐Electron Transfer

The use of pyridinium‐activated primary amines as photoactive functional groups for deaminative generation of alkyl radicals under catalyst‐free conditions is described. By taking advantage of the visible light absorptivity of electron donor–acceptor complexes between Katritzky pyridinium salts and either Hantzsch ester or Et₃N, photoinduced single‐electron transfer could be initiated in the absence of a photocatalyst. This general reactivity platform has been applied to deaminative alkylation (Giese), allylation, vinylation, alkynylation, thioetherification, and hydrodeamination reactions. The mild conditions are amenable to a diverse range of primary and secondary alkyl pyridiniums and demonstrate broad functional group tolerance.