17,915 research outputs found
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 peopleâs 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 fuelâoxygenânitrogen 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
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