Numerical aeroacoustic analysis of propeller designs

As propeller-driven aircraft are the best choice for short/middle-haul flights but their acoustic emissions may require improvements to comply with future noise certification standards, this work aims to numerically evaluate the acoustics of different modern propeller designs. Overall sound pressure level and noise spectra of various blade geometries and hub configurations are compared on a surface representing the exterior fuselage of a typical large turboprop aircraft. Interior cabin noise is also evaluated using the transfer function of a Fokker 50 aircraft. A blade design operating at lower RPM and with the span-wise loading moved inboard is shown to be significantly quieter without severe performance penalties. The employed Computational Fluid Dynamics (CFD) method is able to reproduce the tonal content of all blades and its dependence on hub and blade design features

Linking individual behaviour to community scale patterns in fungi

The fungi comprise a separate kingdom of life and epitomise the indeterminate growth form. Very little is known about the factors that influence the nature of fungal diversity and the link between individual behaviour and the structure and function of fungal communities is particularly poorly understood. Here, we present a theoretical framework that is capable of elucidating this link. An individual-based model for fungal community dynamics is introduced that has been developed from a physiologically based model for the fungal phenotype. The model is used to explore the role of individual interactions, the production of an external inhibitor field and the quality of the external environment on the structure and diversity of the resulting community. We show that traits relating to growth rate, autophagic behaviour and the production of inhibitors are key in influencing the success of a particular genotype in a community. The species richness increases with the amount of available resource. This is the first model of fungal community dynamics that introduces the concept of a biomass-based abundance distribution function that can be described by the log-normal form which typically corresponds to communities in equilibrium. The species abundance curve was stable to changes in the relative location of inocula, although the ranked abundance of the individuals was not. We present the first attempt to identify the traits that affect the form of that curve. Future studies should examine the role of environmental heterogeneity and spore dispersal

Propeller installation effects on turboprop acoustics

Propeller installation options for a twin-engined turboprop aircraft are evaluated at cruise conditions, aiming to identify the quieter configuration. Computational fluid dynamics is used to investigate the near-field acoustics and transfer functions are employed to estimate the interior cabin noise. Co-rotating and counter-rotating installation options are compared. The effect of propeller synchrophasing is also considered. The employed method captures the complexity of the acoustic field generated by the interactions of the propeller sound fields among each other and with the airframe, showing also the importance of simulating the whole problem to predict the actual noise on a flying aircraft. Marked differences among the various layouts are observed. The counter-rotating top-in option appears the best in terms of acoustics, the top-out propeller rotation leading to louder noise because of inflow conditions and the occurrence of constructive acoustic interferences. Synchrophasing is shown to be beneficial for co-rotating propellers, specially regarding the interior noise, because of favorable effects in the interaction between the propeller direct sound field and the noise due to the airframe. An angle closer to the maximum relative blade shift was found to be the best choice, yielding, however, higher sound levels than those provided by the counter-rotating top-in layout

Computational Aeroacoustic Analysis of Propeller Installation Effects

In line with the goal of cleaner and quieter aircraft, this paper investigates propeller acoustics aiming to improve turboprops noise emissions, as they represent the best choice for short and medium range flights in terms of fuel efficiency. CFD is used to analyse the propeller-airframe interaction physics, and assess propeller installation effects, for a full scale twinengined aircraft. The employed propellers represent advanced designs currently used in modern aircraft and the cases of co-rotating and counter-rotating top-in layout are considered. The URANS approach is used on grids of up to 195 M points aiming to directly extract from CFD the noise tonal content. Numerical results are first validated against modelscaled experimental data. A comparison between results of the full aircraft and a propeller in isolation is also carried out. Full aircraft predictions show significant differences in the external acoustics between port and starboard sides for the co-rotating case, with a louder noise generated by the inboard-up propeller. The counter-rotating layout shows a more regular distribution of overall noise, with on average slightly higher noise levels towards the front and the rear of the cabin. Acoustic predictions from an isolated propeller in axial flight significantly underestimate noise levels even on the fuselage sides where the aircraft masks the other propeller, showing the relevance of the propeller-airframe interactions in the evaluation of actual sound pressure levels in flight

Characterising the tumour morphological response to therapeutic intervention:an ex vivo model

In cancer, morphological assessment of histological tissue samples is a fundamental part of both diagnosis and prognosis. Image analysis offers opportunities to support that assessment through quantitative metrics of morphology. Generally, morphometric analysis is carried out on two dimensional tissue section data and so only represents a small fraction of any tumour. We present a novel application of three-dimensional (3D) morphometrics for 3D imaging data obtained from tumours grown in a culture model. Minkowski functionals, a set of measures that characterise geometry and topology in n-dimensional space, are used to quantify tumour topology in the absence of and in response to therapeutic intervention. These measures are used to stratify the morphological response of tumours to therapeutic intervention. Breast tumours are characterised by estrogen receptor (ER) status, human epidermal growth factor receptor (HER)2 status and tumour grade. Previously, we have shown that ER status is associated with tumour volume in response to tamoxifen treatment ex vivo. Here, HER2 status is found to predict the changes in morphology other than volume as a result of tamoxifen treatment ex vivo. Finally, we show the extent to which Minkowski functionals might be used to predict tumour grade.Minkowski functionals are generalisable to any 3D data set, including in vivo and cellular systems. This quantitative topological analysis can provide a valuable link among biomarkers, drug intervention and tumour morphology that is complementary to existing, non-morphological measures of tumour response to intervention and could ultimately inform patient treatment

A Time-Marching Aeroelastic Method Applied to Propeller Flutter

A time-marching aeroelastic method developed for the study of propeller flutter is presented and validated. Propeller flutter can take many forms with stall, whirl and classical flutter being the primary responses. These types of flutter require accurate capture of the non-linear aerodynamics associated with propeller blades. Stall flutter in particular, due to the highly detached nature of the flow, needs detailed unsteady flow modelling. With the development of modern propeller designs potentially adjusting the flutter boundary and the development of faster computing power, CFD is required to ensure accurate capture of aerodynamics. This paper focuses on the validation of the aeroelastic method using the Commander propeller blade

Insensitivity of alkenone carbon isotopes to atmospheric CO₂ at low to moderate CO₂ levels

Atmospheric pCO2 is a critical component of the global carbon system and is considered to be the major control of Earth’s past, present and future climate. Accurate and precise reconstructions of its concentration through geological time are, therefore, crucial to our understanding of the Earth system. Ice core records document pCO2 for the past 800 kyrs, but at no point during this interval were CO2 levels higher than today. Interpretation of older pCO2 has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct pCO2: the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ11B) of foraminifer shells. Here we present alkenone and δ11B-based pCO2 reconstructions generated from the same samples from the Plio-Pleistocene at ODP Site 999 across a glacial-interglacial cycle. We find a muted response to pCO2 in the alkenone record compared to contemporaneous ice core and δ11B records, suggesting caution in the interpretation of alkenone-based records at low pCO2 levels. This is possibly caused by the physiology of CO2 uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of pCO2

Management and Outcome of Prosthetic Patch Infection after Carotid Endarterectomy: A Single-centre Series and Systematic Review of the Literature

AbstractObjectivesOutcomes following prosthetic patch infection after carotid endarterectomy (CEA).MethodsRetrospective audit and systematic review.Results22 patients were treated between January 1992 and April 2012, 5 having undergone their original CEA at another institution. The commonest infecting organism was Staphylococcus. One patient was treated by antibiotic irrigation, one was stented, while 20 underwent debridement and patch excision plus; carotid ligation (n = 3), vein patching (n = 3) or vein bypass (n = 14). There was one peri-operative stroke, but no peri-operative deaths. There were no reinfections at a median follow-up of 54 months.A systematic review identified 123 patients with prosthetic patch infection in the world literature. Thirty-six (29%) presented <2 months, 78 (63%) presented >6 months after the original CEA. Seventy-nine of/87 patients (91%) with a positive culture yielded Staphylococci or Streptococci. Seventy-four patients were treated by patch excision and autologous reconstruction. Four (5%) developed reinfection <30 days, but later reinfections have been reported. Seven of nine patients (78%) undergoing prosthetic reconstruction either died or suffered reinfection. Five patients were treated with a covered stent, none developing reinfection (median followup 12 months).ConclusionPatch infection following CEA is rare. Few have undergone stenting and long term data are awaited. For now, patch excision and autologous reconstruction remains the ‘gold standard’

Cardiovascular Risk Reduction is Important for Improving Patient and Graft Survival After Ligation and Bypass Surgery for Popliteal Artery Aneurysm

OBJECTIVES: To report outcomes following ligation and bypass (LGB) surgery for popliteal artery aneurysm (PAA) and study factors influencing patient and graft survival. MATERIALS AND METHODS: A retrospective review of patients undergoing LGB surgery for PAA between September 1999 and August 2012 at a tertiary referral vascular unit was performed. Primary graft patency (PGP), primary-assisted graft patency (PAGP), and secondary graft patency (SGP) rates were calculated using survival analyses. Patient, graft aneurysm-free survival (GAFS), aneurysm reperfusion-free survival (ARFS), and amputation-free survival (AFS) rates were also calculated. Log-rank testing and Cox proportional hazards modeling were used to perform univariate and multivariate analysis of influencing factors, respectively. RESULTS: Eighty-four LGB repairs in 69 patients (mean age 71.3 years, 68 males) were available for study. The 5-year PGP, PAGP, SGP, and patient survival rates were 58.1%, 84.4%, 85.2%, and 81.1%, respectively. On multivariate analysis, the principal determinants of PGP were urgency of operation ( P = .009) and smoking status ( P = .019). The principal determinants of PAGP were hyperlipidemia status ( P = .048) and of SGP were hyperlipidemia ( P = .042) and cerebrovascular disease (CVD) status ( P = .045). The principal determinants of patient survival were previous myocardial infarction ( P = .004) and CVD ( P = .001). The 5-year GAFS, ARFS, and AFS rates were 87.9%, 91.6%, and 96.1%, respectively. CONCLUSION: This study has shown that traditional cardiovascular risk factors, such as a smoking and ischemic heart disease, are the most important predictors of early graft failure and patient death following LGB surgery for PAA

ESL learners’ online research and comprehension strategies

In order to enhance second language (L2) acquisition, English as a Second Language (ESL) students are encouraged to exploit the abundant information and opportunities for authentic language use afforded by the Internet. This study investigated the online research and comprehension strategies employed by ESL learners in a public university in Malaysia. The study was descriptive and the data was collected via the Qualtrics survey system. Data analysis demonstrated the most and least frequently used online research and comprehension strategies of 74 ESL undergraduates and uncovered an overview of the ESL undergraduates’ existing online research and comprehension strategies. The findings suggest that explicit training in the area of online research and comprehension processes is worth pursuing in the development of online study skills. This study also presents validation of a survey instrument used within the study to assess ESL learners’ online research andcomprehension strategies