529 research outputs found
Atomisers for the Aerial Application of Pesticides in Tsetse (Glossina sp) and Armyworm (Spodoptera exempta) Control
Aerial 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
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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
Matrix Ernst Potentials and Orthogonal Symmetry for Heterotic String in Three Dimensions
A new matrix representation for low-energy limit of heterotic string theory
reduced to three dimensions is considered. The pair of matrix Ernst Potentials
uniquely connected with the coset matrix is derived. The action of the symmetry
group on the Ernst potentials is established.Comment: 10 pages in LaTe
Symplectic Gravity Models in Four, Three and Two Dimensions
A class of the gravity models describing a coupled system of
Abelian vector fields and the symmetric matrix generalizations of
the dilaton and Kalb-Ramond fields is considered. It is shown that the
Pecci-Quinn axion matrix can be entered and the resulting equations of motion
possess the symmetry in four dimensions. The stationary case is
studied. It is established that the theory allows a -model
representation with a target space which is invariant under the
group of isometry transformations. The chiral matrix of the coset is constructed. A K\"ahler formalism based on the use of the Ernst
complex symmetric matrix is developed. The stationary
axisymmetric case is considered. The Belinsky-Zakharov chiral matrix depending
on the original field variables is obtained. The Kramer-Neugebauer
transformation, which algebraically maps the original variables into the target
space ones, is presented.Comment: 21 pages, RevTex, no figurie
Head-on collision of ultrarelativistic charges
We consider the head-on collision of two opposite-charged point particles
moving at the speed of light. Starting from the field of a single charge we
derive in a first step the field generated by uniformly accelerated charge in
the limit of infinite acceleration. From this we then calculate explicitly the
burst of radiation emitted from the head-on collision of two charges and
discuss its distributional structure. The motivation for our investigation
comes from the corresponding gravitational situation where the head-on
collision of two ultrarelativistic particles (black holes) has recently aroused
renewed interest.Comment: 4 figures, uses the AMSmat
Respiratory hospital admission risk near large composting facilities
AbstractBackgroundLarge-scale composting can release bioaerosols in elevated quantities, but there are few studies of health effects on nearby communities.MethodsA cross-sectional ecological small area design was used to examine risk of respiratory hospital admissions within 2500m of all 148 English large-scale composting facilities in 2008–10. Statistical analyses used a random intercept Poisson regression model at Census Output Area (COA) level (mean population 310). Models were adjusted for age, sex, deprivation and tobacco sales.ResultsAnalysing 34,963 respiratory hospital admissions in 4656 COAs within 250–2500m of a site, there were no significant trends using pre-defined distance bands of >250–750m, >750–1500m and >1500–2500m. Using a continuous measure of distance, there was a small non-statistically significant (p=0.054) association with total respiratory admissions corresponding to a 1.5% (95% CI: 0.0–2.9%) decrease in risk if moving from 251m to 501m. There were no significant associations for subgroups of respiratory infections, asthma or chronic obstructive pulmonary disease.ConclusionThis national study does not provide evidence for increased risks of respiratory hospital admissions in those living beyond 250m of an outdoor composting area perimeter. Further work using better measures of exposure and exploring associations with symptoms and disease prevalence, especially in vulnerable groups, is recommended to support regulatory approaches
Stability of Cross-Feeding Polymorphisms in Microbial Communities
This is the final version of the article. Available from Public Library of Science via the DOI in this record.Cross-feeding, a relationship wherein one organism consumes metabolites excreted by another, is a ubiquitous feature of natural and clinically-relevant microbial communities and could be a key factor promoting diversity in extreme and/or nutrient-poor environments. However, it remains unclear how readily cross-feeding interactions form, and therefore our ability to predict their emergence is limited. In this paper we developed a mathematical model parameterized using data from the biochemistry and ecology of an E. coli cross-feeding laboratory system. The model accurately captures short-term dynamics of the two competitors that have been observed empirically and we use it to systematically explore the stability of cross-feeding interactions for a range of environmental conditions. We find that our simple system can display complex dynamics including multi-stable behavior separated by a critical point. Therefore whether cross-feeding interactions form depends on the complex interplay between density and frequency of the competitors as well as on the concentration of resources in the environment. Moreover, we find that subtly different environmental conditions can lead to dramatically different results regarding the establishment of cross-feeding, which could explain the apparently unpredictable between-population differences in experimental outcomes. We argue that mathematical models are essential tools for disentangling the complexities of cross-feeding interactions.IG was supported by a Natural Environment Research Council (NERC) Advanced Fellowship NE/E013007/3 and a European Research Council (ERC) Consolidator grant MathModExp 647292, MK was funded by a National Aeronautics and Space Administration (NASA) NPP Fellowship and NASA NNX12AD87G, IG and PR were funded by a Biotechnology and Biological Sciences Research Council (BBSRC) grant BB/J010340/1, KS was supported by National Human Genome Research Institute (NHGRI) 2R01HG003328 - 07A1 and FR was supported by NASA NNX12AD87G. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
A Radiation Scalar for Numerical Relativity
This letter describes a scalar curvature invariant for general relativity
with a certain, distinctive feature. While many such invariants exist, this one
vanishes in regions of space-time which can be said unambiguously to contain no
gravitational radiation. In more general regions which incontrovertibly support
non-trivial radiation fields, it can be used to extract local,
coordinate-independent information partially characterizing that radiation.
While a clear, physical interpretation is possible only in such radiation
zones, a simple algorithm can be given to extend the definition smoothly to
generic regions of space-time.Comment: 4 pages, 1 EPS figur
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