50,631 research outputs found
The interminable issue of effectiveness: substantive purposes, outcomes and research challenges in the advancement of environmental impact assessment theory
Further shock tunnel studies of scramjet phenomena
Scramjet phenomena were studied using the shock tunnel T3 at the Australian National University. Simple two dimensional models were used with a combination of wall and central injectors. Silane as an additive to hydrogen fuel was studied over a range of temperatures and pressures to evaluate its effect as an ignition aid. The film cooling effect of surface injected hydrogen was measured over a wide range of equivalence. Heat transfer measurements without injection were repeated to confirm previous indications of heating rates lower than simple flat plate predictions for laminar boundary layers in equilibrium flow. The previous results were reproduced and the discrepancies are discussed in terms of the model geometry and departures of the flow from equilibrium. In the thrust producing mode, attempts were made to increase specific impulse with wall injection. Some preliminary tests were also performed on shock induced ignition, to investigate the possibility in flight of injecting fuel upstream of the combustion chamber, where it could mix but not burn
Scramjet sidewall burning: Preliminary shock tunnel results
Experiments performed with a two dimensional model scramjet with particular emphasis on the effect of fuel injection from a wall are reported. Air low with a nominal Mach number of 3.5 and varied enthalpies was produced. It was found that neither hydrogen injection angle nor combustor divergence angle had any appreciable effect on thrust values while increased combustor length appeared to increase thrust levels. Specific impulse was observed to peak when hydrogen was injected at an equivalence ratio of about 2. Lowering the Mach number of the injected hydrogen at low equivalence ratios, less than 4, appeared to benefit specific impulse while hydrogen Mach number had little effect at higher equivalence ratios. When a 1:1 mixture by volume of nitrogen and oxygen is used instead of air as a test gas, it is found that hydrogen combustion is enhanced but only at high enthalpies
Sequential primed kinases create a damage-responsive phosphodegron on Eco1.
Sister-chromatid cohesion is established during S phase when Eco1 acetylates cohesin. In budding yeast, Eco1 activity falls after S phase due to Cdk1-dependent phosphorylation, which triggers ubiquitination by SCF(Cdc4). We show here that Eco1 degradation requires the sequential actions of Cdk1 and two additional kinases, Cdc7-Dbf4 and the GSK-3 homolog Mck1. These kinases recognize motifs primed by previous phosphorylation, resulting in an ordered sequence of three phosphorylation events on Eco1. Only the latter two phosphorylation sites are spaced correctly to bind Cdc4, resulting in strict discrimination between phosphates added by Cdk1 and by Cdc7. Inhibition of Cdc7 by the DNA damage response prevents Eco1 destruction, allowing establishment of cohesion after S phase. This elaborate regulatory system, involving three independent kinases and stringent substrate selection by a ubiquitin ligase, enables robust control of cohesion establishment during normal growth and after stress
First-principles prediction of redox potentials in transition-metal compounds with LDA+U
First-principles calculations within the Local Density Approximation (LDA) or
Generalized Gradient Approximation (GGA), though very successful, are known to
underestimate redox potentials, such as those at which lithium intercalates in
transition metal compounds. We argue that this inaccuracy is related to the
lack of cancellation of electron self-interaction errors in LDA/GGA and can be
improved by using the DFT+ method with a self-consistent evaluation of the
parameter. We show that, using this approach, the experimental lithium
intercalation voltages of a number of transition metal compounds, including the
olivine LiMPO (M=Mn, Fe Co, Ni), layered LiMO (Co,
Ni) and spinel-like LiMO (M=Mn, Co), can be reproduced
accurately.Comment: 19 pages, 6 figures, Phys. Rev. B 70, 235121 (2004
A wider audience: Turning VLBI into a survey instrument
Radio observations using the Very Long Baseline Interferometry (VLBI)
technique typically have fields of view of only a few arcseconds, due to the
computational problems inherent in imaging larger fields. Furthermore,
sensitivity limitations restrict observations to very compact and bright
objects, which are few and far between on the sky. Thus, while most branches of
observational astronomy can carry out sensitive, wide-field surveys, VLBI
observations are limited to targeted observations of carefully selected
objects. However, recent advances in technology have made it possible to carry
out the computations required to target hundreds of sources simultaneously.
Furthermore, sensitivity upgrades have dramatically increased the number of
objects accessible to VLBI observations. The combination of these two
developments have enhanced the survey capabilities of VLBI observations such
that it is now possible to observe (almost) any point in the sky with
milli-arcsecond resolution. In this talk I review the development of wide-field
VLBI, which has made significant progress over the last three years.Comment: Invited review at the General Assembly of the Astronomische
Gesellschaf
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