Effect of Deflagration-to-Detonation Transition on Pulse Detonation Engine Impulse

A detonation tube was built to study the deflagration-to-detonation transition (DDT) process and the impulse generated when combustion products exhaust into the atmosphere. The reactants used were stoichiometric ethylene and oxygen mixture with varying amounts of nitrogen present as diluent. The effects of varying the initial pressure from 30 kPa to 100 kPa were studied, as were the effects of varying the diluent concentration from 0% to 73.8% of the total mixture. Measurements were carried out with the tube free of obstacles and with three different obstacle configurations. Each obstacle configuration had a blockage ratio of 0.43. It was found that the inclusion of obstacles dramatically lowered the DDT times and distances as compared to the no obstacle configuration. The obstacles were found to be particularly effective at inducing DDT in mixtures with low pressures and with high amounts of diluent. At the lowest pressures tested (30 kPa), obstacles reduced the DDT time and distance to approximately 12.5% of the no obstacle configuration values. The obstacles also allowed DDT to occur in mixture compositions of up to 60% diluent, while DDT was not achieved with more than 30% diluent in the no obstacle configuration. A ballistic pendulum arrangement was utilized, enabling direct measurement of the impulse by measuring the tube's deflection. Additional means of impulse comparison consisted of integrating the pressure over the front wall of the tube. Impulse measurements were then compared with a theoretical model and were found to fit well cases that did not contain internal obstacles. The inclusion of obstacles allowed DDT to occur in mixtures with high amounts of diluent where DDT was not observed to occur in the cases without obstacles. Roughly 100% more impulse was produced in the obstacle configurations as compared to the no obstacle configuration under these conditions. In instances where DDT occurred in the no obstacle configuration, the use of obstacle configurations lowered the impulse produced by an average of 25%. For cases where no obstacles were used and DDT occurred, the pressure derived impulses (pressure impulse) and impulses determined from the ballistic pendulum (ballistic impulses) are similar. For cases were obstacle configurations were tested, pressure impulses were more than 100% higher on average than ballistic impulses. This difference exists because the pressure model neglects drag due to the obstacle configurations

Night-time accidents: a scoping study. Report to The AA Motoring Trust and Rees Jeffreys Road Fund

Context: Only a quarter of all travel by car drivers is undertaken between the hours of 19.00 and 08.00, but it is in this period that 40 percent of fatal and serious injuries are sustained by drivers. This indicates that car travel at night carries a greater risk of being killed or seriously injured than does travel during the day. The literature indicates that disproportionate numbers of young drivers, especially young men, are injured at night. But to be able to introduce measures targeted at this group more needs to be known about the purpose of their journeys, the types of roads they travel on, and how far they drive and at what times in the evening and at night. Older drivers tend to have fewer accidents at night, but little is currently known about how much can be accounted for by exposure related to their driving patterns. People over the age of 60 years form about 20 percent of the population, yet they make up over a quarter of traffic fatalities. These two groups of young and older drivers have been selected for study with the following aims: (a) to assess what information exists which relates to night-time exposure by activity and by group (young and older); (b) to assess what is known about exposure and risk to young and older drivers at night, in conjunction with an analysis of relevant accident data to provide a picture of the size of the potential problem areas, and gaps in current knowledge; (c) to identify people’s concerns, attitudes and beliefs with regard to the problems of night-time driving; and (d) to provide the basis for decision on what measures might be brought to bear on the problem, and what further research would be needed in order to point to focused action. This scoping study is in two parts and provides an assessment of the information available and hence the gaps in our knowledge on the nature and extent of night-time driving, and the risks involved at these times. The first part assesses the available data, and the second uses focus groups to gather the views of drivers themselves, together with their concerns, attitudes and beliefs with regard to the problems of night-time driving. The measurement of exposure, or amount of travel by car, of drivers of different age and gender is central to the assessment of the risk of being killed or injured in a road traffic accident. In this study, the measure of exposure used is distance travelled per person per year. This has been combined with casualty data to make preliminary assessments of risk to people of different ages and gender of driving at during the daytime and at night

Planar Detonation Wave Initiation in Large-Aspect-Ratio Channels

In this study, two initiator designs are presented that are able to form planar detonations with low input energy in large-aspect-ratio channels over distances corresponding to only a few channel heights. The initiators use a single spark and an array of small channels to shape the detonation wave. The first design, referred to as the static initiator, is simple to construct as it consists of straight channels which connect at right angles. However, it is only able to create planar waves using mixtures that can reliably detonate in its small-width channels. An improved design, referred to as the dynamic initiator, is capable of detonating insensitive mixtures using an oxyacetylene gas slug injected into the initiator shortly before ignition, but is more complex to construct. The two versions are presented next, including an overview of their design and operation. Design drawings of each initiator are available elsewhere [7]. Finally, photographs and pressure traces of the resulting planar waves generated by each device are shown

Analytical Model for the Impulse of Single-Cycle Pulse Detonation Tube

An analytical model for the impulse of a single-cycle pulse detonation tube has been developed and validated against experimental data. The model is based on the pressure history at the thrust surface of the detonation tube. The pressure history is modeled by a constant pressure portion, followed by a decay due to gas expansion out of the tube. The duration and amplitude of the constant pressure portion is determined by analyzing the gasdynamics of the self-similar flow behind a steadily moving detonation wave within the tube. The gas expansion process is modeled using dimensional analysis and empirical observations. The model predictions are validated against direct experimental measurements in terms of impulse per unit volume, specific impulse, and thrust. Comparisons are given with estimates of the specific impulse based on numerical simulations. Impulse per unit volume and specific impulse calculations are carried out for a wide range of fuel–oxygen–nitrogen mixtures (including aviation fuels) of varying initial pressure, equivalence ratio, and nitrogen dilution. The effect of the initial temperature is also investigated. The trends observed are explained using a simple scaling analysis showing the dependency of the impulse on initial conditions and energy release in the mixture

Entanglement cost of generalised measurements

Bipartite entanglement is one of the fundamental quantifiable resources of quantum information theory. We propose a new application of this resource to the theory of quantum measurements. According to Naimark's theorem any rank 1 generalised measurement (POVM) M may be represented as a von Neumann measurement in an extended (tensor product) space of the system plus ancilla. By considering a suitable average of the entanglements of these measurement directions and minimising over all Naimark extensions, we define a notion of entanglement cost E_min(M) of M. We give a constructive means of characterising all Naimark extensions of a given POVM. We identify various classes of POVMs with zero and non-zero cost and explicitly characterise all POVMs in 2 dimensions having zero cost. We prove a constant upper bound on the entanglement cost of any POVM in any dimension. Hence the asymptotic entanglement cost (i.e. the large n limit of the cost of n applications of M, divided by n) is zero for all POVMs. The trine measurement is defined by three rank 1 elements, with directions symmetrically placed around a great circle on the Bloch sphere. We give an analytic expression for its entanglement cost. Defining a normalised cost of any d-dimensional POVM by E_min(M)/log(d), we show (using a combination of analytic and numerical techniques) that the trine measurement is more costly than any other POVM with d>2, or with d=2 and ancilla dimension 2. This strongly suggests that the trine measurement is the most costly of all POVMs.Comment: 20 pages, plain late

A first principles study of proton transport through model helical pores

Proton transport (PT) across cell membranes is a fundamental process and a key step in many biological functions, including cell signalling and enzymatic reactions. All biochemical reactions that convert energy from one form to another are mediated by PT, which also serves as a vital route to achieve cell pH stabilisation. The coding for membrane -bound proteins constitutes 25 -30% of all genes, and they are implicated in many diseases such as diabetes and Parkinson's. Consequently, they are the subject of major drug target studies (in fact the drug targets for all neurological diseases are membrane -bound proteins). Whilst PT is known to occur via transient water molecules across the cell membrane itself, it is more often the case that the mechanism involves proteins that span the membrane surface and act as proton- specific ion channels. PT has been widely studied in protein systems such as gramicidin A, cytochrome C oxidase, the M2 channel protein in the influenza A virus and bacteriorhodopsin. Evidence for the relay of H+ by buried water molecules ('water wires') mediated by the side -chains of alpha -helices have been substantiated in these and other proteins, but finding direct experimental evidence for the reaction pathway is extremely challenging work.When experiment can provide only partial answers, it is the role of computational modelling to complete the picture. Modelling these trans -membrane proteins at the full atomistic quantum mechanical level, however, lies beyond the capabilities of current computational techniques, necessitating the use of simplified models. To this end, work undertaken in this thesis has derived and tested a simplified model that is large enough to maintain the essential tertiary structures of transmembrane proteins, but small enough to permit full ab initio MD simulations over long time periods to be performed. The model is based on a single helix scaffold placed under periodic boundary conditions to create a cavity that supports a water wire. The simulations then focus on monitoring the behaviour of a proton as it 'hops' along this wire in a manner akin to the classical Grotthuss mechanism.Mechanistic studies have taken place using poly-glycine, poly-glycine-serine and poly-glycine-aspartic models, and show that the mechanism of PT in channel environments shares some features with the simulations reported for bulk water, with, e.g., the hydrogen bond distance shortening in the time period leading up to successful proton transfer. There are, however, also some important differences, such as the observation of a heightened number of proton rattling events. The channel environment also removes the need for the loss of a water molecule from the inner coordination sphere of the receiving water molecule as the constriction in space only allows a coordination sphere of three molecules, as opposed to four for bulk water.The effect of varying the density of water molecules in the channel has also been investigated. A range of cationic states have been identified, with widely varying lifetimes and compared across all models. We also observe that the helix plays an important role in directing the behaviour of the water wire: the most active proton transport regions of the water -wire are found in areas where the helix is most tightly coiled. Finally, we report on the effects of different DFT functionals to model a water - wire using the simplest poly -glycine model, and on the importance of including dispersion corrections to stabilize the helical structure.Finally, using the poly -glycine- aspartic acid model, a study was undertaken that focused on the direction of proton transport through the channel when the side chains of the aspartic acid residues interacted directly with the water wire. In this model there were two different pathways for the excess proton to pass along: a long hydrogen - bonded network of water molecules and amino acid residues, or a short [H30]+ diffusion pathway. It was found that the proton- hopping route over multiple water molecules and amino acid residues was preferred over the diffusion route, even though this pathway was substantially longer

Resolved CO(1-0) Nuclei in IRAS 14348-1447: Evidence for Massive Bulge Progenitors to Ultraluminous Infrared Galaxies

High-resolution, CO(1-0) interferometry of the ultraluminous infrared galaxy IRAS 14348-1447 is presented. The merger system has a molecular gas mass of \~3x10^10 solar masses and a projected nuclear separation of 4.8 kpc (3.5"), making it one of the most molecular gas-rich galaxies known and an ideal candidate for studying the intermediate stages of an ultraluminous merger event. The CO morphology shows two molecular gas components associated with the stellar nuclei of the progenitors, consistent with the idea that the molecular disks are gravitationally bound by the dense bulges of the progenitor galaxies as the interaction proceeds. In contrast, less luminous infrared galaxies observed to date with projected nuclear separations of ~<5 kpc show a dominant CO component between the stellar nuclei. This discrepancy may be an indication that the progenitors of mergers with lower infrared luminosity do not possess massive bulges, and that the gas is stripped during the initial encounter of their progenitors. A comparison of the CO and radio luminosities of the NE and SW component show them to have comparable radio and CO flux ratios of f(NE)/f(SW) ~0.6, possibly indicating that the amount of star-forming molecular gas in the progenitors is correlated with the supernovae rate. The estimate of molecular gas masses of the nuclei and the extent of the radio emission are used to infer that the nuclei of IR 14348-1447 have gas densities comparable to the cores of elliptical galaxies.Comment: LaTex, 5 pages with 1 postscript and 1 jpg figure, ApJ Letters, in pres