3,271 research outputs found
Large-eddy simulation of kerosene spray combustion in a model scramjet chamber
No full textLarge-eddy simulation (LES) of kerosene spray combustion in a model supersonic combustor with cavity flame holder is carried out. Kerosene is injected through the ceiling of the cavity. The subgrid-scale (SGS) turbulence stress ensor is closed via the Smagorinsky’s eddyviscosity model, chemical source terms are modelled by a finite rate chemistry (FRC) model, and a four-step reduced kerosene combustion kinetic mechanism is adopted. The chamber wallpressure predicted from the LES is validated by experimental data reported in literature. The test case has a cavity length of 77mm and a depth of 8mm. After liquid kerosene is injected through the orifice, most of the droplets are loaded with recirculation fluid momentum inside the cavity. Due to lower velocity of the carrier fluid inside the cavity, sufficient atomization and evaporation take place during the process of droplet transportation, resulting in a rich fuel mixture of kerosene vapour accumulating inside the cavity. These rich fuel mixtures are mixed with fresh air by the approachmixing layer at the front of the cavity and are thus involved in burning accompanied with the approach boundary layer separation extending towards upstream. The combustion flame in the downstream impinges onto the rear wall of the cavity and is then reflected back to the front of the cavity. During the recirculation of hot flow, heat is compensated for evaporation of droplets. The circulation processes mentioned above provide an efficient flame-holdingmechanism to stabilize the flame.Comparisons with results froma shorter length of cavity (cavity length of 45mm) show that, due to insufficient atomization and evaporation of the droplets in the short distance inside the cavity, parts of the droplets are carried out of the cavity through theboundary layer fluctuation and evaporated in the hot flame layer, thus resulting in incomplete air fuel mixing and worse combustion performance. The flow structures inside the cavity play an important role in the spray istribution, thus determining the combustion performance
Metal spray Invar tooling for composites
No full textThis work was performed within IMI Spray Mould, an EPSRC joint funded programme, aimed at developing a manufacturing route for large aerospace composite forming tooling, based on metal spray technologies. Assesses the mechanical properties of Invar steel coatings, deposited using electric arc spraying, and correlates these properties to the spray parameters and processes used so as to offer coatings with characteristics appropriate to the tooling requirements. In particular, two processing methods, inert and air atomisation, and three arc spray gun configurations (air cap design) are evaluated. The mechanical properties of the coatings are found to be low compared to bulk Invar, regardless of the spray parameters and hardware used. Inert arc spraying affords more consistent coating characteristics but this comes with a compromised durability. The spray hardware is found to be more significant in determining the coating properties than the parameters employed
Thick film Tl-1223 conductors; processing, microstructure and superconducting properties
No full textTl-1223 thick films have been fabricated using 2 techniques; electro-phoretic deposition (EPD) of Tl0.78Bi0.22(Sr0.8Ba0.2)(2)Ca2Cu3Ox powder and spray pyrolysis of a precursor film followed by thallination. A partial melt process was used for EPD tapes to improve grain connectivity and increase the grain size and some c-axis alignment was achieved. For spray pyrolised tapes, Sr substitution was found to be essential to stabilize the 1223 phase and good c-axis alignment was observed
Tangle-bearing neurons survive despite disruption of membrane integrity in a mouse model of tauopathy
No full textNeurofibrillary tangles (NFTs) are associated with neuronal loss and correlate with cognitive impairment in Alzheimer disease, but how NFTs relate to neuronal death is not clear. We studied cell death in Tg4510 mice that reversibly express P301L mutant human tau and accumulate NFTs using in vivo multiphoton imaging of neurofibrillary pathology, propidium iodide (PI) incorporation into cells, caspase activation, and DNA labeling. We first observed that in live mice, a minority of neurons were labeled with the caspase probe or with PI fluorescence. These markers of cell stress were localized in the same cells and appeared specifically within NFT-bearing neurons. Contrary to expectations, the PI-stained neurons did not die during a day of observation; the presence of Hoechst-positive nuclei in them on the subsequent day indicated that the NFT-associated membrane disruption, as suggested by PI staining, and caspase activation do not lead to immediate death of neurons in this tauopathy model. This unique combination of in vivo multiphoton imaging with markers of cell death and pathological alteration is a powerful tool for investigating neuronal damage associated with neurofibrillary pathology
Lessons learned from the data analysis of the second harvest (1998-2001) of the Society of Thoracic Surgeons (STS) Congenital Heart Surgery Database.
No full textAtomisers for the Aerial Application of Pesticides in Tsetse (Glossina sp) and Armyworm (Spodoptera exempta) Control
No full textAerial application of insecticides is likely to remain an important component in
realistically-costed vector and migratory pest control operations for the foreseeable
future. The objective of this work was to identify or design improved atomisers for
use in two such operations, tsetse (Glossina sp. ) and African armyworm
(Spodoptera exempta) control, the former requiring an insecticide aerosol ýx'ith a
VMD of 20 to 30ýim at rates upto 0.5 litres/minute and the latter a fine spray with a
VMD of 80 to 120ýtm at rates around 16 litres/minute. In both cases rotary
atomisation was confirmed as the most appropriate technique.
Assessments were made of seven commerciall%, available atomisers and two existinc,
prototypes, on the basis of existing reports and new data generated under simulated
flight conditions in a wind tunnel. Droplet sizing was carried out using an optical
array probe set to give a resolution of 54m over a range of 3.6 -3) 12.54m. None of
the atomisers tested met the specification for tsetse-spraying, the limiting factors
being rotation speed and inability to distribute low volumes of liquid across their full
atomising surface. The Micronair AU4000 and AU5000 and the Micron X-I were
found to be suitable for armyworm control, the Micron X-1 having the additional
ability to produce spray with VMDs down to 40ýim.
A review of rotary atomiser literature provided design guidelines for the design of an
atomiser capable of meeting tsetse specifications. The principle effect of liquid flow
4D
within the atomiser was found to be on the uniformity of fluid distribution.
Premature ligament formation and formation of cross-flow vortices were identified
as factors which could adversely influence fluid distribution under some conditions.
Ligzan ment seperation from disks can be aided byI slender teeth, providing that these
have a spaciniz similar to the natural spacing of ligaments predicted by Taylor
instability theoInry . The effect of rotation speed and atomiser diameter on droIp let
diameter is determined by the degree of stretching of the ligament due to its
acceleration relative to the atomiser, implying that a finer spray would be achieved
using a smaller rotating diameter disc than a larger diameter disc with the same
peripheral speed.
A series of experimental studies was carried out usinrgD higZDh speed photogZ_r_a phy in
conjunction with the droplet sizinaprobe. Disturbancesh a,,i,n, g the forrn predicted for
C
cross-flow vortices were observed in liquid on a plain spinning disc. A sin(-)'Ieligament
generator was constructed. With increasing rotation speed this rt\'taled a
series of increasingly unstable ligament disintegration modes in which interaction
with the surroundin4g15 air became a controlling-- factor. Complete shattering of the
ligament occured at a Weber number of between 4 and 5, similar to reported values
for liquid jets in a cross flo%v of cyas. Droplet sizing indicated that the specified
performance for tsetse operations could be obtained from 50mm diameter atomisers
with a total of around _'30000is suing points at a rotation speed of 26000 RPNI. This
Zý
sucy(yestecdN l,i ndcr rather than disc-based atomisers.
A slit was found to be impractical as a means of distributing liquid unifom-ily at high
rotation speeds but distribution was sucýe: ssfully achieved using a porous flow
resistor. Prototype wind- and electi-ically-driven atornisers were constructed using
rotating porous cylinders fed internally by spray bars designed with the help of finite
element methods. Ligament formation was found to occur from a film of liquid on
the outer surface of the cylinder, the variation in spacing with feedrate and rotation
speed suggesting Taylor instability to be the controlling factor. The prototype
atomisers achieved a performance suitable for tsetse control operations. This was not
enhanced by the provision of discrete issuing points
Effect of Combustor Geometry on Performance of Airblast Atomizer under Sub- Atmospheric Conditions
No full textLIHNCS - Lugol's iodine in head and neck cancer surgery : a multicentre, randomised controlled trial assessing the effectiveness of Lugol’s iodine to assist excision of moderate dysplasia, severe dysplasia and carcinoma in situ at mucosal resection margins of oral and oropharyngeal squamous cell carcinoma : study protocol for a randomised controlled trial
No full textBackground:
Oral cavity and oropharynx cancer are increasing in incidence worldwide but survival outcomes have not significantly improved over the last three decades. The presence of dysplasia or carcinoma in situ at surgical margins following resection of squamous carcinoma of the mucosal surfaces of the head and neck has been shown to be associated with a higher incidence of local recurrence and reduced survival. While invasive carcinoma in mucosal surfaces can usually be distinguished from adjacent normal mucous membrane, pre-malignant disease is much less readily distinguished at operation. We describe a protocol for a randomised, controlled trial in which we will assess the effectiveness of Lugol’s iodine staining in allowing visualisation and excision of cancer margin dysplasia at time of primary surgery.
Methods/Design:
We will recruit 300 patients diagnosed with oral cavity or oropharynx squamous cell carcinoma. All participants will be planned for primary surgery with curative intent. After completion of baseline assessment participants will be randomised into either a standard surgical treatment arm or surgical treatment including Lugol’s iodine staining.
Discussion:
This paper describes the rationale and design of a unique trial in head and neck surgical oncology. If margin dysplasia visualisation with Lugol’s iodine allows complete excision of high-risk, pre-cancer mucosa at time of primary surgery, this may lead to a reduction in local recurrence and improved survival.
Trial registration: Current Controlled Trials ISRCTN03712770
On the consequences of a fragmentation due to a NEO mitigation strategy
No full textThe fragmentation of an Earth threatening asteroid as a result of a hazard mitigation mission is examined in
this paper. The minimum required energy for a successful impulsive deflection of a threatening object is
computed and compared with the energy required to break-up a small size asteroid. The fragmentation of an asteroid that underwent an impulsive deflection such as a kinetic impact or a nuclear explosion is a very plausible outcome in the light of this work. Thus a model describing the stochastic evolution of the cloud of fragments is described. The stochasticity of the fragmentation is given by a Gaussian probability distribution that
describes the initial relative velocities of each fragment of the asteroid, while the size distribution is expressed
through a power law function. The fragmentation model is applied to Apophis as illustrative example. If a barely
catastrophic disruption (i.e. the largest fragment is half the size the original asteroid) occurs 10 to 20 years prior
to the Earth encounter only a reduction from 50% to 80% of the potential damage is achieve for the Apophis test
case
The charge transfer and ion formation in liquid Li-Tl alloys
No full textThe 7Li NMR Knight shift, K, and the spin-lattice relaxation time, T1, were measured for liquid Li–Tl alloys. The K decreases rapidly with the addition of Tl up to 20 at.% Tl. In the concentration from 20 to 50 at.% Tl, the K decreases only slightly and the K of 50 at.% Tl is 60% of K for the pure liquid Li. Such a decrease of K is considered as an indication for the strong charge transfer from Li to Tl. These tendencies are similar to those from previous studies for liquid Li–Ga and Li–In alloys. However, beyond 50 at.% Tl, the K increases and reaches to an almost constant value (70% of K for the pure liquid Li). Such a back donation of charge is absent for liquid Li–Ga and Li–In alloys. It is considered that the tendency of the formation of ionic structural unit for liquid Li–Tl alloys is slightly weaker compared with the cases of liquid Li–Ga and Li–In alloys. The T1 is also discussed with the relation to the Knight shift and the electronic properties
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