bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.1341This 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
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

AbstractThe 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

AbstractAeroelastic 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

AbstractA 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

AbstractMilitary 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

AbstractTime-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

AbstractA 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

AbstractSeparated 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

AbstractThe 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

AbstractA 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

AbstractAn 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

AbstractThe 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

AbstractThe 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

AbstractTwo 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

AbstractMean 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

AbstractDye 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.