bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Thermal Characterization of Precision Poly(p‐cyclohexylene alkylene)s via Acyclic Diene Metathesis Polycondensation
Authors: da Silva Lucas Caire , Wagener Kenneth B.
Published: February 2016

The synthesis and thermal characterization of poly(p‐cyclohexylene alkylene)s (PPCs) is described. Polymers containing 1,4‐cyclohexylene units on every 15th, 19th, and 21st chain carbon are prepared by the acyclic diene metathesis polycondensation of symmetric α,ω‐dienes obtained from the α‐alkylation of cyclohexane‐1,4‐dicarbonitrile. Exhaustive hydrogenation of the unsaturated polymers yields fully cycloaliphatic polymers with excellent resistance to thermal degradation. The thermal analysis of the unsaturated and saturated materials reveals a strong influence of the cis‐alkene and cis‐1,4‐cyclohexylene on the final thermal properties of each material. PPC exhibits higher melting temperature and thermal stability than similar materials, in which the aliphatic ring is replaced by aromatic rings or short chain branches. The melting behavior is discussed in terms of the higher flexibility and enhanced intermolecular packing of the symmetrical 1,4‐cyclohexylene units incorporated within the chain.

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Toxin MqsR cleaves single‐stranded mRNA with various 5' ends
Authors: Chowdhury Nityananda , Kwan Brian W. , McGibbon Louise C. , Babitzke Paul , Wood Thomas K.
Published: February 2016

Toxin/antitoxin (TA) systems are the means by which bacterial cells become persistent; that is, those cells that are tolerant to multiple environmental stresses such as antibiotics by becoming metabolically dormant. These persister cells are responsible for recalcitrant infections. Once toxins are activated by the inactivation of antitoxins (e.g., stress‐triggered Lon degradation of the antitoxin), many toxins reduce metabolism by inhibiting translation (e.g., cleaving mRNA, reducing ATP). The MqsR/MqsA TA system of Escherichia coli cleaves mRNA to help the cell withstand oxidative and bile acid stress. Here, we investigated the role of secondary structure and 5′ mRNA processing on MqsR degradation of mRNA and found that MqsR cleaves only single‐stranded RNA at 5′‐GCU sites and that MqsR is equally active against RNA with 5′‐triphosphate, 5′‐monophosphate, and 5′‐hydroxyl groups.
Generic applications of 13C‐detected NMR diffusion to formulated systems with suppression of thermal convection induced by proton decoupling
Authors: Hou Jianbo , He Yiyong , Sabatino Paolo , Yuan Ling , Redwine David
Published: February 2016

Fast and effective structural/compositional analysis on formulated systems represents one of the major challenges encountered in analytical science. 13C‐detected diffusion represents a promising tool to tackle the aforementioned challenges, particularly in industry. Toward exploring the generic applications of 13C‐detected diffusion, thermal convection induced by 1H decoupling has been identified as a key factor that resulted in significantly reduced resolution in the diffusion dimension. Optimization of experimental parameters and utilization of double‐stimulated echo‐based pulse sequence both can effectively suppress the thermal convection caused by the 1H decoupling, the success of which allows robust and generic applications of 13C‐detected diffusion to systems from mixtures of small molecules, polymer blends, and copolymers to actual complex formulated systems. The method is particularly powerful in differentiating small molecules from polymers, polymer blends from copolymers, and end‐group analysis. Copyright © 2016 John Wiley & Sons, Ltd.
Characterisation of confinement effect on jointed rock pillars using a Synthetic Rock Mass approach
Authors: Zhang Y. , Zhao X.
Published: February 2016

Confinement effect on jointed rock pillars is numerically characterised in this research using a Synthetic Rock Mass (SRM) approach. The SRM is an integrated model incorporating a discrete fracture network within a Particle Flow Code 3D particle assembly. In this paper, the confinement effect on a 3D jointed pillar SRM model is investigated in a series of simulations, including biaxial compression tests and true and conventional triaxial compression tests. The numerical results suggest that the applied confining stresses generally result in higher pillar strengths and ductile post‐peak responses. More brittle post‐peak behaviour is simulated in the biaxial and true triaxial tests when the pillar is confined by a high stress in one lateral direction and by a zero/low stress in the other lateral direction. This phenomenon is attributed to significant lateral pillar dilation in the less confined direction. Detailed pillar failure modes are monitored in the uniaxial and triaxial tests. Axial splitting fractures and long shear zones cutting through the pillar are simulated when the pillar is able to dilate in the direction of least confinement. Localised shearing along joints and failed rock blocks is the dominant failure mode when the pillar dilation is resisted by the applied confining stresses. The pillar remains relatively intact with limited cracking in the pillar core in the highly confined triaxial tests. Copyright © 2016 John Wiley & Sons, Ltd.
Higher augmentation index is associated with tension‐type headache and migraine in middle‐aged/older humans with obesity
Authors: Kalil Graziela Z. , Recober Ana , Hoang‐Tienor Ann , Bridget Zimmerman Miriam , Haynes William G. , Pierce Gary L.
Published: February 2016

Objective

Obesity is a major risk factor for chronic daily headaches, including migraine and tension‐type headache (TTH). Although migraine is associated with increased risk of cardiovascular diseases (CVD), a relation between TTH and CVD risk has not been established. It was hypothesized that higher carotid‐femoral pulse wave velocity (CFPWV) and augmentation index (AI), measures of aortic stiffness and pressure wave reflection, respectively, and biomarkers of CVD risk, would be higher among adults with obesity and migraine or TTH compared with those with no headache.

Methods

Adults with obesity (n = 93; body mass index ≥30 kg/m2) who were between 40 and 75 years old with at least one additional CVD risk factor were enrolled. Subjects had CFPWV and AI assessed and a complete neurological exam for diagnosis of headache in the past 12 months.

Results

Adults with obesity and TTH (P = 0.018), but not migraine (P = 0.29), had significantly higher AI compared with those with no headache. When both CFPWV and AI were considered in a logistic regression model with migraine or TTH, only AI was associated with TTH (P = 0.008) and migraine (P = 0.032) but could not distinguish between the two headache phenotypes.

Conclusions

Increased aortic AI but not stiffness is associated with TTH and migraine among middle‐aged/older adults with obesity and high CVD risk.
Physical Therapy Treatment of Impaired Chest Mobility in Patients with Airway Sensory Hyperreactivity
Authors: Johansson Ewa‐Lena , Ternestén‐Hasseus Ewa , Olsén Monika Fagevik , Millqvist Eva
Published: February 2016

Background and Purpose

In sensory hyperreactivity (SHR), patients have symptoms from the airways and the chest induced by environmental irritants like scenting products and cigarette smoke. They are characterized by increased cough reaction to inhaled capsaicin compared with healthy controls. Lung function tests are normal, and asthma medications have no or little effect. In a recent published article, patients with SHR were found to have impaired chest mobility and increased pain sensitivity. The purpose of this study was to evaluate if a physiotherapeutic intervention can increase chest mobility in SHR, influence these patients' symptoms and reduce capsaicin cough sensitivity.

Methods

Forty‐one SHR patients were initially randomized in to groups, one for training and one for symptom registration in this controlled training study. It consisted of a daily training programme containing simple movements to increase the flexibility of the chest, a breathing exercise and a relaxation session as well as symptom registration. Chest expansion was measured with a measuring tape and thoracic and abdominal movement with light sensors. Pain sensitivity was assessed using pressure algometry and a standardized capsaicin inhalation threshold provocation‐evaluated cough sensitivity.

Results

Twenty seven patients were left for analyses after 12 weeks and 26 patients after 24 weeks. Chest mobility and upper thoracic respiratory movements improved (p < 0.01), feeling of chest pressure and the capsaicin cough sensitivity decreased (p < 0.01). The patients also showed of significantly lowered pain pressure thresholds measured with algometry, compared with healthy controls (p < 0.001).

Conclusion

Improvement of chest mobility after physiotherapeutic intervention indicates that these patients may have acquired a dysfunctional breathing pattern. The regular use of a training programme and structural breathing instructions can be used to improve chest mobility, chest symptoms and capsaicin cough sensitivity in patients with SHR and signs of dysfunctional breathing. Copyright © 2016 John Wiley & Sons, Ltd.
Relevance of semi‐core‐valence interaction for exact exchange calculations for group IVA, IIIA–VA, and IIB–VIA semiconductors
Authors: Engel Eberhard
Published: February 2016

The importance of the semi‐core‐valence interaction for plane‐wave pseudopotential calculations with exact exchange is investigated for group IVA, IIIA–VA, and IIB–VIA semiconductors. Results for different valence spaces, either omitting or including the semi‐core d‐ and/or the semi‐core sp‐states, are compared with full‐potential LAPW all‐electron data. It is found that for group IIB, IIIA, and IVA elements only the valence space including all semi‐core states leads to accurate band structures. In fact, no real improvement over the minimum valence space is obtained for group IIIA and IVA elements, if only the semi‐core d‐states are taken into account. The particular relevance of the semi‐core sp‐states arises from the nonlocality of the exact exchange, which makes the exchange potential in the valence region sensitive to orbital structures located in the semi‐core region (such as the nodes of the valence states). In contrast, even the valence space without any semi‐core states yields very accurate results in the case of group VA elements, indicating the onset of the decoupling of the M‐shell from the valence states. To deal with valence spaces including all semi‐core states a proper construction of pseudopotentials is essential. While usually the energetically lowest state in the valence space is utilized to generate the pseudopotential for the corresponding angular momentum, it is shown here that this procedure can induce significant errors, when applied in the presence of semi‐core states. Accurate results are only obtained, if the pseudopotentials are generated from the (occupied) valence states (under the constraint that the corresponding pseudoorbitals have one node), the reason being that the norm‐conservation of the valence states is more important for the electronic structure of the bulk than that of the semi‐core states. As a byproduct, it is shown that highly accurate pseudopotential results can also be obtained for solid Ne. © 2016 Wiley Periodicals, Inc.
Electron dynamics with real‐time time‐dependent density functional theory
Authors: Provorse Makenzie R. , Isborn Christine M.
Published: February 2016

Real‐time time‐dependent functional theory (RT‐TDDFT) directly propagates the electron density in the time domain by integrating the time‐dependent Kohn–Sham equations. This is in contrast to the popular linear response TDDFT matrix formulation that computes transition frequencies from a ground state reference. RT‐TDDFT is, therefore, a potentially powerful technique for modeling atto‐ to picosecond electron dynamics, including charge transfer pathways, the response to a specific applied field, and frequency dependent linear and nonlinear properties. However, qualitatively incorrect electron dynamics and time‐dependent resonant frequencies can occur when perturbing the density away from the ground state due to the common adiabatic approximation. An overview of the RT‐TDDFT method is provided here, including examples of some cases that lead to this qualitatively incorrect behavior. © 2016 Wiley Periodicals, Inc.
Two new message authentication codes based on APN functions and stream ciphers
Authors: Wu Teng , Gong Guang
Published: February 2016

After the concept of the active wiretapper was proposed, integrity protection became more important than ever before. Therefore, message authentication code, a method that protects the message from being modified in an undetectable way, attracts more attention nowadays. In this paper, we propose two new message authentication codes based on almost perfect nonlinear functions and stream ciphers. The security of both new constructions is proved by giving upper bounds of the probability of the successful substitution forgery attacks against our new message authentication codes, and these upper bounds are negligible. We implement our algorithms and compare their time consumption with the time consumption of EIA1, the message authentication code used in the 4G LTE system. The results show that our algorithms are overwhelmingly faster than EIA1. Moreover, our new constructions are resistant to cycling and linear forgery attacks, which can be applied to EIA1. Copyright © 2016 John Wiley & Sons, Ltd.
Two‐Dimensional Visible Spectroscopy For Studying Colloidal Semiconductor Nanocrystals
Authors: Cassette Elsa , Dean Jacob C. , Scholes Gregory D.
Published: February 2016

Possibilities offered by 2D visible spectroscopy for the investigation of the properties of excitons in colloidal semiconductor nanocrystals are overviewed, with a particular focus on their ultrafast dynamics. The technique of 2D electronic spectroscopy is illustrated with several examples showing its advantages compared to 1D ultrafast spectroscopic techniques (transient absorption and time‐resolved photoluminescence).
Riboregulation of bacterial and archaeal transposition
Authors: Ellis Michael J. , Haniford David B.
Published: February 2016

The coexistence of transposons with their hosts depends largely on transposition levels being tightly regulated to limit the mutagenic burden associated with frequent transposition. For ‘DNA‐based’ (class II) bacterial transposons there is growing evidence that regulation through small noncoding RNAs and/or the RNA‐binding protein Hfq are prominent mechanisms of defense against transposition. Recent transcriptomics analyses have identified many new cases of antisense RNAs (asRNA) that potentially could regulate the expression of transposon‐encoded genes giving the impression that asRNA regulation of DNA‐based transposons is much more frequent than previously thought. Hfq is a highly conserved bacterial protein that plays a central role in posttranscriptional gene regulation and stress response pathways in many bacteria. Three different mechanisms for Hfq‐directed control of bacterial transposons have been identified to date highlighting the versatility of this protein as a regulator of bacterial transposons. There is also evidence emerging that some DNA‐based transposons encode RNAs that could regulate expression of host genes. In the case of IS200, which appears to have lost its ability to transpose, contributing a regulatory RNA to its host could account for the persistence of this mobile element in a wide range of bacterial species. It remains to be seen how prevalent these transposon‐encoded RNA regulators are, but given the relatively large amount of intragenic transcription in bacterial genomes, it would not be surprising if new examples are forthcoming. WIREs RNA 2016, 7:382–398. doi: 10.1002/wrna.1341

This article is categorized under:

RNA Interactions with Proteins and Other Molecules > Protein–RNA Interactions: Functional Implications

Translation > Translation Regulation

Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs
Overparenting and Homework: The Student's Task, But Everyone's Responsibility
Authors: Locke Judith Y. , Kavanagh David J. , Campbell Marilyn A.
Published: February 2016

A high level of parental involvement is widely considered to be essential for optimal child and adolescent development and wellbeing, including academic success. However, recent consideration has been given to the idea that extremely high levels of parental involvement (often called ‘overparenting’ or ‘helicopter parenting’) might not be beneficial. This study used a newly created overparenting measure, the Locke Parenting Scale (LPS), to investigate the association of overparenting and children's homework. Eight hundred and sixty-six parents completed online questionnaires about their parenting beliefs and intentions, and their attitudes associated with their child's homework. Parents with higher LPS scores tended to take more personal responsibility for the completion of their child's homework than did other parents, and ascribed greater responsibility for homework completion to their child's teacher. However, increased perceived responsibility by parents and teachers was not accompanied by a commensurate reduction in what they perceived was the child's responsibility. Future research should examine whether extreme parental attitudes and reported behaviours translate to validated changes in actual homework support.
Control of plume interference effects on axisymmetric afterbodies
Authors: Lee Y-K , Raghunathan S. , Benard E. , Kim H-D , Setoguchi T.
Published: February 2016

Plume interference effects on the axisymmetric flowfields around powered missiles are investigated using computational techniques. The study is mainly to understand the physics of the plume-induced shock and separation particularly at high plume to exit pressure ratios with and without shock-turbulent boundary layer control methods. Mass-averaged Navier-Stokes equations with the RNG k-ε turbulence model are solved using a fully implicit finite volume scheme and time-marching algorithm. The shock position and extent of separation was found to be dependent on the freestream Mach number and plume pressure ratio. Rounding the tail or a groove on the surface near the tail moved the shockwave downstream of the tail fin which should enhance the control of the missile.
On wake vortex response for all combinations of five classes of aircraft
Authors: Campos L. M. B. C. , Marques J. M. G.
Published: February 2016

The present paper concerns the response of a following airplane to a pair of wing tip vortices left by a leading aircraft, represented by the Hallock-Burnham model, including the effect of vorticity decay between the two aircraft. The effect of vorticity is evaluated in terms of the induced rolling moment and also the lift loss; these specify the roll acceleration and the downward acceleration, respectively. The corresponding two response equations can be put into the same dimensionless form, and integrated using exponential integrals. This specifies the roll rate and sink rate as a function of time; besides the latter, the bank angle and altitude loss, are also plotted, all also as a function of time, for all combinations of leading and following aircraft in five classes. These are the three ICAO weight categories of light, medium and heavy, plus two other cases, viz the special case of the Boeing 757, which requires larger separations distances, and the case of a future very large transport aircraft (VLTA) exceeding significantly the size of a Boeing 747.
A structure-coupled CFD method for time-marching flutter analysis
Authors: Taylor N. V. , Allen C. B. , Gaitonde A. , Jones D. P.
Published: February 2016

Aeroelastic analysis is a critical area of the aircraft design process, as a good understanding of the dynamic behaviour of the wing structure is essential to safe operation of the vehicle. The inevitable inaccuracies present in the modelling of such phenomena impose mass penalties, as large safety margins are necessitated, which in turn lead to overly stiff designs. In an effort to reduce the uncertainty in analysis methods, fully coupled CFD and structural models are under widespread development. This paper describes the results produced by such a system for a series of test cases based on the AGARD445.6 and MDO wings. Results relating to the latter are of particular interest, as significant variations were found to be produced by the different methodologies used in previous studies, the precise cause of which could not be isolated. In an effort to provide this isolation, a detailed description of the method used is given, including the interpolation scheme between the structural model and the aerodynamic surface, and particular attention is given to the issue of aerofoil shape preservation.
On self-similar behaviour of the hysteresis loops in pitching motions
Authors: Soltani M. R. , Davari A. R.
Published: February 2016

A new similarity parameter has been used for analyzing the unsteady aerodynamic behaviour of vehicles undergoing sinusoidal pitching motion. If this parameter is identical for two unsteady manoeuvres with different reduced frequencies and oscillation amplitudes, the corresponding hysteresis loops of the force and moment collapse on each other. To support and verify this, extensive unsteady wind tunnel tests have been conducted on a standard model, which is a well known fighter type configuration. The acquired data were used to train a certain type of neural network, called the Generalised Regression Neural Network (GRNN), to reduce the number of wind tunnel runs. The scheme, once proved to give the correct results for various conditions, was applied to extend the experimental data to other conditions that have not been tested in the tunnel. Both the predicted and acquired tunnel data were used to show the performance of the similarity parameter.
A question of survival – military aircraft vs the electromagnetic environment
Authors: Pywell M.
Published: February 2016

Military aircraft, by definition, need to survive the onslaught of opposing forces to successfully complete their mission. From an aircraft perspective, the electromagnetic (EM) environment can be an enabler, via the use of navigation aids, radar, radio communications etc. – in fact mission success depends on its successful use. However, this environment is also potentially a disabler, as threat weapon systems and the environment itself can harm or destroy the aircraft. This paper discusses risks and hazards thus posed to aircraft survivability, partitioned into two classes – ‘direct’ and ‘indirect’ EM threats. ‘Direct’ threats are those that occur as a result of direct coupling of EM energy to the airframe and systems within, e.g. lightning strike and directed energy weapons. ‘Indirect’ threats are those that utilise EM sensors to detect, track and target the aircraft, e.g. radar-guided surface-to-air missiles. Airframe intrinsic mechanical vulnerability is also an important part of survivability, although not addressed in this EM-related paper. It is shown that risk and hazard can be minimised by gaining a thorough understanding of operational scenarios, developing holistic system-of-systems solutions to military requirements, and using best practice design and development techniques.
Air–to–ground targeting — UAVs, data links and interoperability (project Extendor)
Authors: Edwards K. L
Published: February 2016

Time-critical targets will generally be observed or ‘sensed’ by personnel inadequately equipped to shoot at them. Since time may be a critical parameter, the passage of information from the ‘sensor’ to the ‘shooter’ must be rapid and accurate. QinetiQ has developed and integrated airborne and ground equipment to facilitate the passage of targeting data digitally over standard air and ground radios. The UK and Holland have selected an integrated rugged PC, internal modem card and purpose-designed software to equip Forward Air Controllers (FACs) to enable digital forward air control. This gives direct interoperability with UK and NATO assets equipped with Improved Data Modem (IDM) technology.

A large, and growing, number of air, land and sea assets employ Link-16. This entails entirely different frequency, data rate and, generally, protocol, from the IDM. The UK MoD’s recently-ended applied research EXTENDOR programme was a three-year operational concept demonstrator for the purpose of translating in near real-time between selected key Link-16 and IDM-based messages. The intention was to demonstrate the viability and utility of translation between disparate data links. This staged programme centred around a translation engine designed to be flown in a Predator UAV. The programme was entirely successful, demonstrating the capability to translate both own position and nine-line target data. Thus the position of a non-Link-16-equipped asset could be seen in real time in the Link-16 recognised air picture (RAP). Also, a Link-16 asset was shown to be able to task an IDM-equipped asset with a nine-line brief via the translation engine. The high equipment readiness level offers considerable potential for near-to-medium term operational exploitation.
The Fairey Rotodyne — technology before its time?
Authors: Gibbings D.
Published: February 2016

It cannot have escaped notice, that in two months time we will celebrate the centenary of the first flight of a powered aircraft carrying a man. We rightfully acclaim ‘The miracle at Kitty Hawk’ for all that it has meant to our chosen profession, albeit outside our remit as a rotorcraft section.

There is however a significant 80th anniversary, which we can add to this centenary year. On 9 January 1923, a Cierva C-4 autogyro piloted by Lt Alejandro Gomez Spencer made an officially observed circular flight of over 4km (2·5 miles) in Madrid.

This important event brought the name of Juan de la Cierva to the fore on the International scene, and was subsequently to prove to be the key to the modern helicopter, an interesting lesson in technology in that, Cierva never set out to invent the helicopter, and never produced one himself.

Of equal significance is the fact that the Rotodyne represented an innovative application of the technology that Cierva began. Many would claim that the gyroplane has never been exploited to it’s full potential; maybe the Rotodyne gave us a foretaste of what was possible.
Effect of counter-rotating vortices on the development of aircraft wakes
Authors: Panaras A. , Voutsinas S. G.
Published: February 2016

A two-dimensional vortex particle model is used for studying the development of the vortex wake generated by the wing of an aircraft in the Trefftz plane. Two-dimensional, finite-area vortex structures simulate the initial vorticity distribution at a near-field cross-section of the wing, as provided by either measurements or simulations. The code is used for studying the effect of weak or strong counter-rotating vortices on the development of an aircraft wake. Application in a three-vortex configuration, consisting of the tip and flap vortices, plus a weak negative vorticity sheet lying between them, supports the hypothesis of Graham that the merging of the tip and flap vortices is prevented, because in such an arrangement the counter-rotating vorticity sheet is wrapped around the primary vortices. The present results indicate that even in the far field the tip and flap vortices remain distinct and follow a helical trajectory with large-pitch and small-radius. The code is next applied to the two-vortex system of Savas’s triangular wing, in which the circulation of the flap vortex is comparable to that of the tip. Although a 2D analysis is inappropriate for stability analysis it is still useful for a quick qualitative investigation. Results indicate that the flap and tip vortices follow a helical trajectory with large-pitch but also very large radius. During one period, the flap vortex covers a span wise distance equal to the wing span. Such a flow has not been observed in flight or in laboratory tests. Actually, Ortegaet al, who studied experimentally the triangular wing of O. Savas, found out that before concluding one full spiral, the vortices are literally destroyed (rapid spreading of their vorticity) by an instability mechanism.
Vortex flows on UAVs: Issues and challenges
Authors: Gursul I.
Published: February 2016

Separated and vortical flows are dominant over various unmanned air vehicles (UAVs). In this article, issues and challenges of vortical flows for future UAVs are reviewed. These include shear layer instabilities, vortex breakdown and wing stall, vortex interactions, nonslender vortices, multiple vortices, and manoeuvring wing vortices. There are also issues relating to vortical flows in certain flow/structure interactions, as well as in aerodynamics/propulsion interactions. Separated and vortical flows are even more dominant at low Reynolds number flows. The main features of vortical flows, unsteady aerodynamics, and propulsion related vortical flow isssues relevant to mini- and micro air vehicles, are discussed.
Design criteria for conceptual sizing of primary flight controls
Authors: Steer A. J.
Published: February 2016

The European Supersonic Commercial Transport’s control surface configuration is based largely on Concorde’s and has been scaled to provide comparable un-augmented stability and manoeuvre performance. Hence, optimising the surface size could provide significant performance benefits in terms of reduced drag, noise, structural and actuator power requirements. Adequate control power will be required to meet current civil aviation regulations whose primary aim is to ensure the aircraft can be flown safely during both normal and emergency operation. Additional design criteria, combined with the optimum longitudinal control laws, are required to ensure desirable handling qualities with minimum pilot workload. Two critical low-speed flight conditions, normal and emergency, together with associated aircraft configurations for control surface sizing have been identified. The rudder must provide sufficient control power to achieve positive heading changes subsequent to a double asymmetric engine failure during normal operation. The fin should be sized to satisfy Dutch roll stability criteria with the un-augmented aircraft in its emergency configuration. The dual functionality of the elevons require that they are sized using both pitch and roll performance and handling quality criteria. The bank angle capture requirement provides the most critical elevon design case, the satisfaction of which also ensures adequate pitch control power. Validation using ‘pilot-in-the-loop’ simulation will be required whilst more explicit control surface size optimisation would require the definition of limiting airspeeds and operating conditions applicable to the European Supersonic Commercial Transport. Additional studies of control power requirements during transonic and supersonic cruise may also be required.
Comprehensive validation of an intermittency transport model for transitional low-pressure turbine flows
Authors: Suzen Y. B. , Huang P. G.
Published: February 2016

A transport equation for the intermittency factor is employed to predict transitional flows under the effects of pressure gradients, freestream turbulence intensities, Reynolds number variations, flow separation and reattachment, and unsteady wake-blade interactions representing diverse operating conditions encountered in low-pressure turbines. The intermittent behaviour of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, μτ with the intermittency factor, γ. Turbulent quantities are predicted by using Menter’s two-equation turbulence model (SST). The onset location of transition is obtained from correlations based on boundary-layer momentum thickness, accelaration parameter, and turbulence intensity. The intermittency factor is obtained from a transport model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction.

The intermittency transport model is tested and validated against several well documented low pressure turbine experiments ranging from flat plate cases to unsteady wake-blade interaction experiments. Overall, good agreement between the experimental data and computational results is obtained illustrating the predicting capabilities of the model and the current intermittency transport modelling approach for transitional flow simulations.
Neuro-fuzzy approach for performance optimisation of variable nozzle turbofan engine
Authors: Nada T. R. , Hashem A. A.
Published: February 2016

An algorithm employing adaptive neuro-fuzzy online identification and sequential quadratic programming optimisation techniques is developed to enhance aircraft engine performance. This algorithm is implemented and tested using digital simulation for two spool, mixed exhaust, variable geometry turbofan engine. Parametric study is conducted to select the proper measurable parameter that can represent the actual thrust during online optimisation. Subtractive clustering technique is applied to generate the minimum number of fuzzy rules that can model the engine performance at various input parameters and flight conditions. The resulting neuro-fuzzy system is then optimised through training algorithm to accurately represent the engine. This system can address engine variations by relearning the network using online measurements from the actual engine. Generating the optimum schedules and comparing them with those obtained from the complete non-linear engine model verify the algorithm. Benefits from this algorithm include fuel consumption savings, reductions in turbine inlet temperature, and preventing limit exceeding.
Equipment failures in ATC: Finding an appropriate safety target
Authors: Subotic B. , Ochieng W. , Majumdar A.
Published: February 2016

The aviation community is currently faced with various approaches for the determination of Target Levels of Safety (TLS). The targets are usually derived for a specific airspace region, for a specific type of operation or a specific phase of flight. Therefore, current practices support the determination of TLS for specific aviation components in isolation. This paper argues that the setting of a new safety target for aviation has to be driven by an integrated system approach. Relevant past research on TLS is reviewed and augmented with the results from operational reports from two countries. A possible safety target for the year 2020 is suggested and scoped down to estimate the safety budget for air traffic control (ATC) equipment. The paper concludes with a discussion of the results and recommends useful practices to achieve the proposed integrated safety approach.
Low frequency behaviour of the subsonic doublet lattice method
Authors: Zyl L. van
Published: February 2016

The results of the subsonic doublet lattice method (DLM), i.e. generalised unsteady aerodynamic forces (GAFs) at a set of reduced frequencies, are often used as input to the solution of the flutter equation. Solutions of the flutter equation are usually required at many more reduced frequencies than GAFs are calculated for by the DLM and some form of interpolation is therefore required. In the p-k formulation of Rodden, Harder and Bellinger, the imaginary part of the GAFs appear as QI/k, i.e. the imaginary part of the GAFs divided by the reduced frequency. In the case of real (i.e. non-oscillatory) roots of the flutter equation, the solution is determined entirely by the steady GAFs and the limiting value of QI/k at zero frequency. This is also true of the g-method of flutter solution as the two formulations are equivalent at k = 0. Expressions are derived for calculating the limiting values of QI/k directly from the DLM, thereby making the real roots independent of the interpolation of the GAFs. The exact way in which the low frequency DLM results are interpolated has a small effect on the interpolation quality in the case of the p-k flutter equation, whereas it has a significant qualitative effect on the results of the g-method of flutter solution of Chen.
Computational fluid dynamics study of unconventional air vehicle configurations
Authors: Ramamurti R. , Sandberg W. , Vaiana P. , Kellogg J. , Cylinder D.
Published: February 2016

Two unconventional micro air vehicles developed by the Naval Research Laboratory are described. One of the vehicles employs flapping wings which is inspired by the flight of birds or insects but does not copy it directly. The second vehicle is a stop-rotor hybrid vehicle employing a pair of single blade, rotary/fixed wing panels, attached at their roots to separate coaxial shafts. An unstructured grid based incompressible flow solver, called feflo, is used to simulate the flow past these novel configurations in order to determine the flight characteristics of these vehicles.
PIV measurements in a twin-jet STOVL fountain flow
Authors: Cabrita P. M. , Saddington A. J. , Knowles K.
Published: February 2016

Mean velocity and first order turbulence measurements were obtained from a three-dimensional upwash fountain flow generated by the impingement of two compressible axisymmetric turbulent jets onto a normal plane. The jet impingement area and fountain formation regions were examined with data obtained through the use of particle image velocimetry. Seven configurations with different nozzle pressure ratios were considered to ascertain the influence of jet compressibility on the fountain development. Results indicate that the mixing of the fountain is dependent on the nozzle pressure ratio, leading to an increase in the fountain spreading rate with increase in nozzle pressure ratio.
The behaviour of circular synthetic jets in a laminar boundary layer
Authors: Zhong S. , Millet F. , Wood N. J.
Published: February 2016

Dye flow visualisation of circular synthetic jets was carried out in laminar boundary layers developing over a flat plate at a range of actuator operating conditions and freestream velocities of 0·05 and 0·1ms–1. The purpose of this work was to study the interaction of synthetic jets with the boundary layer and the nature of vortical structures produced as a result of this interaction. The effects of Reynolds number (Re), velocity ratio (VR) and Strouhal number (St) on the behaviour of synthetic jets were studied. At low Re and VR, the vortical structures produced by synthetic jets appear as highly stretched hairpin vortices attached to the wall. At intermediate Re and VR, these structures roll up into vortex rings which experience a considerable amount of tilting and stretching as they enter the boundary layer. These vortex rings will eventually propagate outside the boundary layer hence the influence of the synthetic jets on the near wall flow will be confined in the near field of the jet exit. At high Re and VR, the vortex rings appear to experience a certain amount of tilting but no obvious stretching. They penetrate the edge of the boundary layer quickly, producing very limited impact on the near wall flow. Hence it is believed that the hairpin vortices produced at low Re and VR are likely to be the desirable structures for effective flow separation control. In this paper, a vortex model was also described to explain the mechanism of vortex tilting.
Design of composite helicopter rotor blades to meet given cross-sectional properties
Authors: Lemanski S. L. , Weaver P. M. , Hill G. F. J.
Published: February 2016

This paper examines the design of a composite helicopter rotor blade to meet given cross-sectional properties. As with many real-world problems, the choice of objective and design variables can lead to a problem with a non-linear and/or non-convex objective function, which would require the use of stochastic optimisation methods to find an optimum. Since the objective function is evaluated from the results of a finite element analysis of the cross section, the computational expense of using stochastic methods would be prohibitive. It is shown that by choosing appropriate simplified design variables, the problem becomes convex with respect to those design variables. This allows deterministic optimisation methods to be used, which is considerably more computationally efficient than stochastic methods. It is also shown that the design variables can be chosen such that the response of each individual cross-sectional property can be closely modelled by a linear approximation, even though the response of a single objective function to many design parameters is non-linear. The design problem may therefore be reformulated into a number of simultaneous linear equations that are easily solved by matrix methods, thus allowing an optimum to be located with the minimum number of computationally expensive finite element analyses.
Shock-wave induced instability in internal explosion dynamics
Authors: Bagabir A. , Drikakis D.
Published: February 2016

The paper presents an investigation of flow instabilities occurring in shock-wave propagation and interaction with the walls of an enclosure. The shock-wave propagation is studied in connection with perturbed and unperturbed cylindrical blasts, initially placed in the centre of the enclosure, as well as for three different blast intensities corresponding to Mach numbers Ms = 2, 5 and 10. The instability is manifested by a symmetry-breaking of the flow even for the case of an initially perfectly-symmetric blast. It is shown that the symmetry-breaking initiates around the centre of the enclosure as a result of the interaction of the shock waves reflected from the walls, with the low-density region in the centre of the explosion. The instability leads to fast attenuation of the shock waves, especially for smaller initial blast intensities. The computations reveal that the vortical flow structures arising from the multiple shock reflections and flow instability are Mach number dependent. The existence of perturbations of large amplitude in the initial condition strengthens the instability and has significant effects on the instantaneous wall pressure distributions. The computational investigation has been performed using high-resolution Riemann solvers for the gas dynamic equations.
A theoretical description of viscous flow along a flat plate
Authors: Hastings R. C.
Published: February 2016

Theoretical quantification of viscous effects in fluid flows is difficult, even if turbulence is absent, except when it is legitimate to simplify the Navier-Stokes equations in some way; for example by invoking the boundary-layer approximation in appropriate cases of interacting viscous and inviscid flow. The technical importance of viscous effects was thought sufficient incentive to re-examine a very simple flow configuration — namely plane, uniform and steady flow of an incompressible, viscous fluid toward a vanishingly-thin flat plate aligned with the undisturbed stream — in search of fresh insights into the general theory for viscous-inviscid interactions.

The strategy was to exploit the analogy between vorticity transport in a viscous fluid and heat conduction in a moving solid. The key to doing so was the realization that, if the perturbation of the undisturbed flow by the plate might be represented as the sum of a series of successive approximations, then the stream function of the viscous part of the flow field — not merely the vorticity which resulted from its existence — might be expressible at every stage as the solution of an analogous heat conduction problem.
Optimum design for buckling of arbitrary shaped ribs under uncertain loadings
Authors: Conrado A. C. , Faria A. R. de , Almeida S. F. M. de
Published: February 2016

Typically, aircraft wing structural panels are designed against buckling for a very large number of possible loadings that may occur during the operation of the aircraft. If the optimisation procedure accounts only for a limited number of design loads, the structure may be vulnerable to a specific type of loading that may cause the structure to fail. A novel approach for the optimisation of ribs or plates of arbitrary shapes under uncertain loads is proposed. The geometry of the rib is defined by a single closed spline or several connected splines. The loading distribution is not considered to be uniform but it is allowed to vary within an admissible set, conferring uncertainty to the applied loads. The admissible load space comprises distributed normal and shear loadings that can be represented through a collection of piecewise linear functions defined along the plate boundary. A special procedure is applied to handle the constraint that the loading must be self equilibrating. A minimax strategy is used to deal with the loading variability such that the resulting optimal design is able to withstand an entire class of linear piecewise loadings along the rib boundary. The refinement of the loading representation may be completely independent of the refinement of finite element mesh. The validity of the proposed approach is assessed by applying it to an aeronautical wing rib.
Solar-powered space flight
Authors: Kemp M. H. D.
Published: February 2016

The aim of this paper is analyse the practicality or otherwise of solar-powered propulsion (after launch using conventional chemical rocketry) for a space vehicle’s late pre-orbital trajectory phase, for orbital transfer and for post-orbital flight. We introduce a ‘concept’ vehicle that in principle permits the use of solar-powered propulsion in each of these stages. Some of the technical challenges that such a vehicle might face are analysed, including the problem of how to keep a large ultra-low mass optical concentrator arrangement sufficiently accurately positioned in different parts of such a trajectory.
A continuation design framework for nonlinear flight control problems
Authors: Richardson T. S. , Lowenberg M. H.
Published: February 2016

A methodology referred to as the continuation design framework is developed for application to nonlinear flight control problems. This forms the basis of a systematic approach to control system design for aircraft operating in highly nonlinear regions of the flight envelope. The essence of the continuation design framework is to combine bifurcation analysis with modern control methods such as eigenstructure assignment. Theoretical and practical issues of the approach are discussed with particular reference to the problems posed by agile fighter aircraft. The proposed methodology is applied to a fifth order hypothetical aircraft model and is shown to provide a visible, flexible and logical approach to nonlinear aircraft control law design.
Predicting design induced pilot error using HET (human error template) – A new formal human error identification method for flight decks
Authors: Stanton N. A. , Harris D. , Salmon P. M. , Demagalski J. M. , Marshall A. , Young M. S. , Dekker S. W. A. , Waldmann T.
Published: February 2016

Human factors certification criteria are being developed for large civil aircraft with the objective of reducing the incidence of design-induced error on the flight deck. Many formal error identification techniques currently exist which have been developed in non-aviation contexts but none have been validated for use to this end. This paper describes a new human error identification technique (HET – human error template) designed specifically as a diagnostic tool for the identification of design-induced error on the flight deck. HET is benchmarked against three existing techniques (SHERPA – systematic human error reduction and prediction approach; human error HAZOP – hazard and operability study; and HEIST – human error In systems tool). HET outperforms all three existing techniques in a validation study comparing predicted errors to actual errors reported during an approach and landing task in a modern, highly automated commercial aircraft. It is concluded that HET should provide a useful tool as a adjunct to the proposed human factors certification process.