3,737 research outputs found
Predicting the wake structure of the HART II rotor using the vorticity transport model
Brown’s Vorticity Transport Model has been used to predict the wake structure and resultant
blade loading of the rotor that was studied during the HART II experimental programme.
The descending flight condition of the experiment yields significant high-frequency content to
the blade loading due to the presence of blade-vortex interactions. PIV images of the wake
structure were compared against numerical predictions of the detailed geometry of the rotor
wake using three different computational resolutions of the flow. This was done to investigate
the origin of inaccuracies exposed in an earlier study of the system in capturing the effects of
blade vortex interactions on the loading on the rotor. The predicted positions of the vortex
cores agree with measured data to within a fraction of the blade chord, and the strength of the
vortices is preserved to well downstream of the rotor, essentially independently of the resolution
of the calculation. Nevertheless the amplitude of the loading impulses induced on the blade by
vortex interaction are strongly influenced by the resolution of the calculation through the effect
of cell density on the minimum vortex core size that can be supported. It would appear thus
that the inaccuracies in predicting the high-frequency loading on the rotor are not due to any
inherent deficiency in the representation of the wake, although viscous effects may need to be
considered in future in order to decouple the vortex core size from the cell size, but rather due
to the inherent deficiencies of the lifting line approach used to model the blade aerodynamics
Predicting blade vortex interaction, airloads and acoustics using the vorticity transport model
Interactions between the blades and vortical structures within the wake of a helicopter rotor are a significant
source of impulsive loading and noise, particularly in descending flight. Advances in the prediction and
understanding of such blade vortex interactions have been aided in recent years by the extensive experimental
dataset made available through the HART test programme. Brown’s Vorticity Transport Model was used to
predict the rotor blade loading, the resultant wake system and the acoustic noise radiation for the HART II
rotor. The vorticity conserving properties of the Vorticity Transport Model allow the detailed wake features
that are associated with blade vortex interactions to be resolved. The experimental airload data, in particular
the higher harmonic loading associated with blade vortex interactions, is matched well by the computations.
The computed vorticity distribution in the wake also shows good correlation with the experimentally measured
vortex positions. Including a representation of the fuselage within the computation yields marked improvement
in the prediction of the vortex positions compared to similar calculations with an isolated rotor. An accoustic
analysis, based on a Ffowcs-Williams Hawkings approach, is able to predict accurately the locations of the
sound pressure maxima and the upstream attenuation of the sound radiated by the rotor. The principal
discrepancies in airload, vortex position and acoustic prediction are confined almost exclusively to the rear of
the advancing side of the rotor and, if errors in measuring the blade deflection can be discounted, may be due
to minor inaccuracies in modelling the roll-up of the wake
Report on an Investigation of the Lower River Bovey
This is a Report on an Investigation of the Lower River Bovey.
It contains general information about the lower River Bovy as well as a description of the methodology, observations on the river including plants, fish and invertebrates. An extended comparison with other similar river and conclusion which contains allusions to pollution evidences, fishing deterioration, and possible causes. It includes sampling stations location map, list of collected animals, record of brown trout caught and water analysis
Characteristics of four rural horticultural markets in the south-eastern low veld of Zimbabwe
A research paper on four rural based outlets for the convenience of trading in horticultural produce in the South- Eastern Lowveld regions of Zimbabwe.Fortnightly surveys of Iruit and vegetable marketing at four rural centres representing diverse socio-economic hinterlands of communal (Ngundu), resettlement (Matandamaviri), smallholder irrigation (Rupangwana) and semi-urban (Checheche) areas were done between September 1989 and December 1990. The three most important vegetables marketed were tomato, rape and cabbage while banana, avocado and orange were the dominant fruits. Results showed differences in the type and volume of produce, source of produce, supply and seasonal availability of produce among the marketing centres. Matandamaviri had the lowest economic activity while Rupangwana recorded the most activity. For all centres, except Matandamaviri, stallholders sometimes travelled great distance of up to 300 km in search of fruits and vegetables for sale. The most commonly cited problems included transport difficulties, unreliability and poor quality of produce, and overtrading among the stallholders due to over-supply on the market
Cardiac Multidetector Computed Tomography: Basic Physics of Image Acquisition and Clinical Applications
Cardiac MDCT is here to stay. And, it is more than just imaging coronary arteries. Understanding the differences in and the benefits of one CT scanner from another will help you to optimize the capabilities of the scanner, but requires a basic understanding of the MDCT imaging physics
Emergency Mosquito Control on a Selected Area in Eastern North Carolina After Hurricane Irene
Natural disasters such as hurricanes may contribute to mosquito abundance and, consequently, arbovirus transmission risk. In 2011, flooding from Hurricane Irene in eastern North Carolina (NC) resulted in increased mosquito populations that hindered recovery efforts. Budget shortfalls in NC have reduced the functionality of long-term mosquito surveillance and control programs; hence, many counties rely on the Federal Emergency Management Agency for post-disaster mosquito control. This pilot study examines mosquito abundance pre- and post-aerial insecticide spraying at eight study sites in Washington and Tyrrell Counties in rural eastern NC after Hurricane Irene. Percent change was calculated and compared for traps in areas that received aerial pesticide application and those that did not. Traps in spray zones show decreases in mosquito abundance when compared to control traps (treatment: −52.93%; control: 3.55%), although no significant differences (P = 0.286) were found in mosquito abundance between groups. Implications of reactive rather than proactive mosquito control responses are discussed
Quark-meson coupling model with constituent quarks: Exchange and pionic effects
The binding energy of nuclear matter including exchange and pionic effects is
calculated in a quark-meson coupling model with massive constituent quarks. As
in the case with elementary nucleons in QHD, exchange effects are repulsive.
However, the coupling of the mesons directly to the quarks in the nucleons
introduces a new effect on the exchange energies that provides an extra
repulsive contribution to the binding energy. Pionic effects are not small.
Implications of such effects on observables are discussed.Comment: 12 pages, latex, 1 figure, to appear in Phys. Lett.
Community outbreaks of group A Streptococcus revealed by genome sequencing
The frequent occurrence of disease outbreaks in humans caused by group A Streptococcus (GAS) is an on-going public health threat. Conventional bacterial typing methods lack the discriminatory power to confidently confirm or refute outbreaks in hospital and community settings. Microbial whole genome sequencing (WGS) provides a potential solution to this, but, there has been limited population-based surveillance with accompanying sequence data. We performed retrospective genomic surveillance of 93 clinical GAS isolates from individuals in a defined geographic region. Detailed clinical information was obtained for closely related clusters of isolates. Genomic sequence data was contextualised through comparison with international data. We identified 18 different emm genotypes within our bacterial population, and revealed both highly diverse and closely related isolates. This high level of diversity was maintained even in the context of international sequence data. We also identified two emm1 clusters, and one emm3 cluster, of closely-related isolates that differed only by 1 to 4 single nucleotide polymorphisms. Analysis of clinical information identified no healthcare associated contact between patients, indicating cryptic community transmission. Our findings suggest that genomic surveillance of GAS would increase detection of transmission and highlight opportunities for intervention
The tragedy of the common? A comparative population genomic study of two bumblebee species
Within the theoretical framework of the small population paradigm, we investigated the population genomics and parasite load of two bumblebee species across the UK and Ireland. Bombus pratorum is widespread and common throughout its range while Bombus monticola is restricted to higher altitudes and shows a more fragmented distribution.
Bombus monticola showed stronger population structuring, isolation-by-distance, and a deficit of heterozygotes in the most isolated population in the south of its range (Dartmoor). Heterozygosity and inbreeding coefficients (FIS) were comparable between both species, but the proportion of polymorphic sites was much greater in B. pratorum. Notably, both species have suffered significant declines in Ne over the last 100 generations and estimates and declines for both species were of similar orders of magnitude. No pattern of increased parasite prevalence in populations of lower heterozygosity was observed. Instead, ecological and demographic factors (age, latitude, date, habitat suitability) were the main drivers of parasite prevalence.
Distinct patterns of selection were observed in both species in regions involved in regulation of transcription and neurotransmission and in particular pathways targeted by neonicotinoid insecticides.
Our results highlight the pressing need for monitoring to include common as well as rare species. This should not focus solely on census population counts, but include estimates of Ne. We also highlight the need for further work to establish adaptive shifts in globally important pollinator communities
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