Commercialising Australia's interstate rail freight transport: Some ownership and investment issues

The paper addresses the issues of rights of way ownership and application of consistent investment appraisal techniques across modes of transport. There are linkages between ownership, rights of way, competitive strategies and market contestability which will have a significant bearing on the choice of investment criteria used by commercialised railways. Investment methodologies in competing modes of land transport must be consistent. Investment in individual elements of railway infrastructure must be integrated with the overall cost recovery strategy of the operator. Major railway projects must be submitted to both financial and economic evaluation, so that the interests of individual railway authorities and the community are considered

Axonal stress kinase activation and tau misbehavior induced by kinesin-1 transport defects

Many neurodegenerative diseases exhibit axonal pathology, transport defects, and aberrant phosphorylation and aggregation of the microtubule binding protein tau. While mutant tau protein in frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP17) causes aberrant microtubule binding and assembly of tau into filaments, the pathways leading to tau-mediated neurotoxicity in Alzheimer's disease and other neurodegenerative disorders in which tau protein is not genetically modified remain unknown. To test the hypothesis that axonal transport defects alone can cause pathological abnormalities in tau protein and neurodegeneration in the absence of mutant tau or amyloid β deposits, we induced transport defects by deletion of the kinesin light chain 1 (KLC1) subunit of the anterograde motor kinesin-1. We found that upon aging, early selective axonal transport defects in mice lacking the KLC1 protein (KLC1-/-) led to axonopathies with cytoskeletal disorganization and abnormal cargo accumulation. In addition, increased c-jun N-terminal stress kinase activation colocalized with aberrant tau in dystrophic axons. Surprisingly, swollen dystrophic axons exhibited abnormal tau hyperphosphorylation and accumulation. Thus, directly interfering with axonal transport is sufficient to activate stress kinase pathways initiating a biochemical cascade that drives normal tau protein into a pathological state found in a variety of neurodegenerative disorders including Alzheimer's disease.Fil: Falzone, Tomas Luis. Howard Hughes Medical Institute; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; ArgentinaFil: Stokin, Gorazd B.. University Psychiatric Hospital; EsloveniaFil: Lillo, Concepción. University of California at San Diego; Estados UnidosFil: Rodrigues, Elizabeth M.. Howard Hughes Medical Institute; Estados UnidosFil: Westerman, Eileen L.. Howard Hughes Medical Institute; Estados UnidosFil: Williams, David S.. University of California at San Diego; Estados UnidosFil: Goldstein, Lawrence S. B.. Howard Hughes Medical Institute; Estados Unido

Four-step and three-step systematically reduced chemistry for wide-range H₂–air combustion problems

The feasibility of developing multipurpose reduced chemistry that is able to describe, with sufficient accuracy, premixed and non-premixed flames, one-dimensional detonations, high-temperature autoignition, and also low-temperature autoignition is explored. A four-step mechanism with O and OH in steady state is thoroughly tested and is shown to give satisfactory results under all conditions. The possibility of reducing this to a three-step mechanism, to decrease computation times without compromising the range of applicability is then investigated. The originality of this work resides in introducing a single species X, representing either HO₂ for high-temperature ignition or H₂O₂ for low-temperature ignition. An algorithm is defined that covers the entire range without significant degradation of accuracy. Integrations show promising results for different laminar test cases, and applicability to turbulent flows is indicated.This work was supported by the UE Marie Curie ITN MYPLANET, by the Spanish MCINN through Project # CSD2010-00010, by the Comunidad de Madrid through Project # S2009/ENE-1597, and by the US AFOSR Grant # FA9550-12-1-0138

A generalized burke-schumann formulation for hydrogen-oxygen diffusion flames maintaining partial equilibrium of the shuffle reactions

Under a wide range of conditions of ambient pressures, temperatures, dilutions and strain rates, nonpremixed combustion in hydrogen-oxygen systems maintains partial equilibrium of the four two-body chain-carrying reactions while experiencing finite rates of the three-body radical-recombination reactions H + 03 + M -+ HOa + M and H + H + M -+ H2 + M. There then exists a three-step reduced mechanism, with H as the only intermediate species and concentrations of the radicals O, OH and H02 related to that of H through steady states. The conservation equations corresponding to this chemical description are formulated here in terms of generalized coupling functions that account for species diffusivities that differ from the thermal diffusivity, providing a set of equations that describe the flame structure for strain conditions ranging from near extinction to weakly strained flames. As a model example, the formulation is applied to the analysis of flame development in the hydrogen-air laminar mixing layer with free-stream temperatures above the crossover temperature corresponding to the second explosion limit. The formulation can be used for many other model problems as well as for computational studies of nonpremixed combustion in complex configurations involving both laminar and turbulent flows

Explicit analytic prediction for hydrogen–oxygen ignition times at temperatures below crossover

This paper addresses homogeneous ignition of hydrogen-oxygen mixtures when the initial conditions of temperature and pressure place the system below the crossover temperature associated with the second explosion limit. A three-step reduced mechanism involving H2, O2, H2O, H2O2 and HO2, derived previously from a skeletal mechanism of eight elementary steps by assuming O, OH and H to follow steady state, is seen to describe accurately the associated thermal explosion. At sufficiently low temperatures, HO2 consumption through HO2 + HO2 → H2O2 + O2 is fast enough to place this intermediate in steady state after a short build-up period, thereby reducing further the chemistry description to the two global steps 2H2 + O2 → 2H2O and 2H2O → H2O2 + H2. The strong temperature sensitivity of the corresponding overall rates enables activation-energy asymptotics to be used in describing the resulting thermal runaway, yielding an explicit expression that predicts with excellent accuracy the ignition time for different conditions of initial temperature, composition, and pressure.This work was supported by the Comunidad de Madrid through project # P2009/ENE-1597. The first two authors also acknowledge support from the EU through the Marie Curie ITN MYPLANET and from the Spanish MCINN through projects # ENE2008-06515 and CSD2010-00011.European Community's Seventh Framework ProgramPublicad

A bifurcation analysis of high-temperature ignition of H2-O2 diffusion flames

The form of the ignition branch for steady, counterflow, hydrogen-oxygen diffusion flames, with dilution permitted in both streams, is investigated for two-step reduced chemistry by methods of bifurcation theory. Attention is restricted to fuel-stream temperatures less than or equal to the oxidizer-stream temperature Tx and to T„ larger than or of the order of the crossover temperature Tc at which the rates of production and consumption of H atoms are equal. Two types of solutions are identified, a frozen solution that always exists in this kinetic approximation because all rates are proportional to the concentration of the intermedíate H atom, and an ignited solution, represented by a branch of the curve giving the máximum H concentration in terms of a Damkohler number constructed from the strain rate and the rate of the branching step H + Os - OH + O. For T„ > T„ the latter bifurcates from the frozen solution if the Damkohler number is increased to a critical valué. For T„ larger than a valué Ts > Tc, the effeets of chemical heat reléase are small, and ignition is always gradual in the sense that the limiting ignited-branch slope is positive (supercritical bifurcation) and there is no S curve. For T„ in the range Tc< T„ < T„ the heat reléase associated with the radical-consumption step causes the limiting ignition-branch slope to become negative (subcritical bifurcation), producing abrupt ignition which leads to an S curve. For valúes of Tx below crossover, the ignited branch appears as a C-shaped curve unconnected to the frozen solution. The method of analysis introduced here offers a first step toward analytical description of nonpremixed H2-02 autoignition

Chain-branching explosions in mixing layers

The chain-branching process leading to ignition in the high-temperature hydrogen-oxygen mixing layer is studied by application of a novel WKB-like method when, as is typically the case, two branching radicals cannot be assumed to maintain steady state. It is shown that the initiation reactions, responsible for the early radical buildup, cease being important when the radical mass fractions reach values of the order of the ratio of the characteristic branching time to the characteristic initiation time, a very small quantity at temperatures of practical interest. The autocatalytic character of the chain-branching reactions causes the radical concentrations to grow exponentially with downstream distance in the process that follows. It is shown that the transverse radical profiles that emerge can be described by exponential series of the WKB type in inverse powers of the streamwise coordinate. The analysis reveals that, because of the effect of radical diffusion, the rate of radical growth is uniform across the mixing layer in the first approximation, with the exponential growth in distance having the same nondimensional streamwise variation as that of a premixed branching explosion evaluated at the transverse location where the effective Damkoher number based on the flow velocity and branching rate is maximum. This functional streamwise variation, as well as the leading-order representation of the radical profiles, is obtained by imposing a condition of bounded, nonoscillatory behavior on the solution. The resulting radical profiles peak at the location of maximum local Damkohler number and decay exponentially to the sides. Analysis of the solution in the vicinity of the maximum, which is a turning point of second order in the WKB expansion, yields the second-order correction to the growth rate as an eigenvalue in a linear eigenvalue problem. The method developed can be extended to the analysis of chain-branching explosions in laminar, self-similar mixing layers with an arbitrary number of branching steps adopted for describing the chemistry