bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Swirl in an S-Duct of Typical Air Intake Proportions
Authors: Guo R.W. , Seddon J. 
Published: July 2016

SummaryThe paper presents the results of measurement of the static pressure, total pressure and swirl in the flow through an S-shaped duct of typical air intake proportions mounted in a wind tunnel and tested at different incidences and different through-flow ratios. In order to reduce the magnitude of swirl at high incidence, two methods have been studied - one, to change the distribution of pressures by means of a spoiler and two, to re-energize the separated flow with an inflow of free stream air through auxiliary inlets. Measurements were also made, at 0° incidence, with a perforated spoiler intended to simulate roughly the taking in of low energy flow from the fuselage boundary layer. The results show a small degree of swirl at low incidence which takes the classical pattern of two contra-rotating flows, and a large degree of swirl at high incidence, in the form of a single rotating flow. Of the anti-swirl devices, the spoiler is the more powerful and can be sized either to reverse the swirl direction or to eliminate the swirl completely. A parameter of swirl coefficient, SC60, has been suggested. Values of SC60 at 30° incidence are 0.188 for the duct as designed, 0.068 for the arrangement with auxiliary inflow and −0.039 with a solid spoiler of width 0.15 times throat width. The various arrangements tested, together with results of an earlier study, shed useful light on the general nature of swirl in an S-duct, its method of generation and its final form and magnitude. A further experiment will be made on a duct having both a horizontal and a vertical offset.
Annular Jets of Different Diameter Ratios
Authors: Ko N.W.M. , Chu F.C. 
Published: July 2016

SummaryThis paper describes part of a detailed study of annular jets of different diameter ratios. From the overall pressure and spectral measurements of conical and basic annular jets of five diameter ratios the coherent structures of the standing vortices, wake vortices, jet vortices, lower wake induced vortices and wake induced vortices can be isolated and their effects assessed. The findings are supported by the available multi-exposed schlieren photographs of both the conical and basic annular jets. The causes for the presence or absence of the additional trains of vortices in the jet flow can also be evaluated by the variation of the diameter ratio. For the standing vortices and wake vortices within the flow behind the interface good correlation is found with the available pressure behind the interface.
An Investigation of the Effects of Incidence on the Flow Around a Square Section Cylinder
Authors: Obasaju E.D. 
Published: July 2016

SummaryA study has been made of the changes that take place in the flow around a square section cylinder as the angle of incidence is increased from 0° to 45°. Measurements of the Strouhal number, S, and the vortex longitudinal spacing, a/d, are presented and used to estimate the vortex strength,, and vortex street spacing ratio, b/a.is found to vary between about 1.2 and 1.7 depending on incidence, and is given approximately by 0.52(1 - Cpb)/2πS, where Cpbis the mean base pressure coefficient. As the incidence is increased from 0°, S at first decreases slightly and then rises sharply to a maximum at 13.5° incidence, which is the incidence where reattachment of the shear layer, in some mean sense, is expected to commence. The spectra of pressure and velocity fluctuations were measured and subharmonic peaks were found in both spectra at 5° and 10° incidence. It is suggested that they may have been caused by an interaction between a vortex and a trailing edge corner. The degree of organisation of the vortex shedding process was estimated by calculating the sharpness factor, Q, of the spectral peaks at the vortex shedding frequency. In general Q fluctuated with changes in incidence. High values of Q occurred at angles of incidence where the rate of change of the mean base pressure coefficient with incidence is very small whereas low values occurred where the flow is changing to a different state.
Some Effects of Mechanical Damping on the Self-Induced Aeroelastic Oscillations of an Axial Compressor Blade
Authors: Davidson I. M. 
Published: July 2016

SummaryBy a slight modification to den Hartog’s classical theory of harmonically forced vibration off resonance it is shown that, with such distorted forcing wave forms as might be encountered in the stalling or choking flutter of an aerofoil in cascade, the influence of damping on the amplitude of motion can still be assessed with considerable accuracy by the assumption of an equivalent harmonic excitation. The result is valid for any amount of Coulomb damping at which motion is significant in the presence of any “ velocity ” damping coefficient up to that defined by a logarithmic decrement of about 1-3, the formal conclusion of the argument being stated in Section 4.
The Aiming Problem in Aerial Gunnery
Authors: Hancock M. 
Published: July 2016

SummaryThe aiming problem in aerial gunnery has formerly been analysed by approximate methods which allow results of sufficient accuracy for practical requirements to be obtained from a very simple mathematical treatment. There has therefore been no practical demand for any more elaborate analysis, although the development of a more exact treatment of the problem is not without interest from the academic point of view. In this paper a more complete analysis is developed in a form which is generally applicable to a broader class of aiming problems. The relevant parts of the standard external ballistic analysis for projectiles fired from guns are also included for the sake of completeness, and the earlier simplified analysis of the aiming problem is also presented to allow comparison of the results with those of the more complete analysis. Finally, a section on the gunner's view of the aiming problem is included, to provide an explanation of certain difficulties which frequently arise through neglect of the important differences between the points of view of an observer moving with the gun and an observer at rest in the air.
A Finite Series Solution for Grillages under Normal Loading
Authors: Holman D. F. 
Published: July 2016

SummaryA method has been given by Klitchieff for analysis of grillages of intersecting beams under lateral loading. Klitchieff's solution was in the form of infinite Fourier series and the expressions for bending moments converged approximately as Σ n–2, making numerical computation difficult. This paper shows that, for grillages in which one set of beams are evenly spaced, Klitchieff’s solution can be adapted to give finite series for deflections arid bending moments at the intersections of the beams. The number of terms in the series is not greater than the number of beams in the equally spaced set (referred to in this paper as set “ A ”). A numerical example is given and an accurate solution is obtained with appreciably less computation than other known methods would entail.
Stability and Response of Systems Satisfying a Second-Order Linear Differential Equation with Time-Dependent Coefficients
Authors: Babister A. W. 
Published: July 2016

SummaryThe differential equation considered iswhere all the a’s and b’s are real constants.The nature of the solution is investigated in the neighbourhood of the singular point and the conditions are found for logarithmic terms to be absent.The conditions for stability for large values of τ are determined; the system is stable ifare all positive for large values of τ.The form of the response is considered and its oscillatory (or non-oscillatory) nature investigated. The Sonin-Polya theorem is used to determine simple inequalities which must hold between the coefficients of the differential equation in any interval for the relative maxima of | x | to form an increasing or decreasing sequence in that interval.
On the Measurement of Supersonic Aerofoil Drag by Pressure Traverse
Authors: Meyer R. E. 
Published: July 2016

SummaryThe drag in two-dimensional flow is expressed in terms of the distributions of static and stagnation pressures along a traverse line downstream of the aerofoil. Sources of error are discussed with regard to their effect on the accuracy of drag measurement in small tunnels at medium Mach numbers.
A Reduction Method for Buckling Problems of Orthotropic Plates
Authors: Shuleshko P. 
Published: July 2016

SummarySeveral plate buckling problems are solved, using a reduction method. By this method the solution of an orthotropic plate can be reduced to the solution of an isotropic plate and the solution of a plate with bi-axial loading can be reduced to the solution of a plate with uni-axial loading and so on. Plates with simply-supported ends and various boundary conditions at the sides with uni-axial and bi-axial loading are considered and the necessary reduction equations are given.
A Solution of the Flutter Determinant on a General Purpose Electronic Digital Computer
Authors: Gillies D. B. , Hunt P. M. 
Published: July 2016

SummaryA method is given for the solution of the flutter determinant on a general purpose electronic digital computer. The method has been programmed for the N.R.D.C. 401 Computer and details of this programme are given. A quicker programme, applicable when only structural damping is present and there are two degrees of freedom, is also discussed. Appendix I discusses in detail the types of errors which occur when the method is applied and Appendix II considers the anticipated loss of accuracy which will be encountered when using the method in cases where the number of degrees of fredom is large.
The Oscillating Two-Dimensional Aerofoil Between Porous Walls
Authors: Drake D. G. 
Published: July 2016

SummaryThe compressible flow past an oscillating two-dimensional aerofoil in a wind tunnel with porous walls is considered, using linearised theory. The porous wall is assumed to have the property that the ratio of the normal velocity at the wall to the pressure drop across the wall is constant. Transform theory is used to find the supersonic longitudinal stability derivatives, and an extension of Possio's integral equation for the quasi-stationary case in subsonic flow.
An Experimental Investigation of the Secondary Flow Occurring in a Compressor Cascade
Authors: Armstrong W. D. 
Published: July 2016

SummaryWhen a non-uniform stream flows through a cascade of compressor blades a three-dimensional secondary motion is generated in the outlet stream. This motion, which consists of a spanwise re-orientation of the Bernoulli planes, together with the effects of vorticity components in the stream direction, may be predicted theoretically. In this paper experimental results obtained on a 6 in. chord cascade are reported. The experimental and computed outlet angles are compared and the discrepancies are explained qualitatively. Additional particle track and visualisation experiments were designed to investigate the local blade flows and the effects of the nose vortices.
Approximate Methods for Predicting Separation Properties of Laminar Boundary Layers
Authors: Curle N. , Skan S. W. 
Published: July 2016

SummarySome new solutions for steady incompressible laminar boundary layer flow, obtained by Gortler, have been used to test the accuracy of two methods which are commonly used to predict separation. A modification of Stratford's criterion for separation is given in this paper and is probably the most accurate and the simplest of all methods at present in use. Modified numerical functions are also given for Thwaites's method of predicting the main characteristics of the boundary layer over the whole surface, which improve the accuracy of the method.
Noise Measurements on Cold Jets using Convergent-Divergent Nozzles
Authors: Franklin R. E. 
Published: July 2016

Summary:Tests have been carried out on a series of convergent-divergent nozzles and the results compared with those from a test on a convergent nozzle. At the design pressure ratio, reductions in the noise were found, particularly at 90° to the jet direction. For lower forward pressures the noise is also less, but above the design pressure the noise rises rapidly to the same level as that with a convergent nozzle. In the experiments cold jets were used, but the results are probably applicable in certain respects to hot jets.
Flow about Cones at Very High Speeds
Authors: Zienkiewicz H. K. 
Published: July 2016

Summary:Effects of vibrational excitation and dissociation of air on inviscid high speed flow past a circular cone, at zero incidence, with an attached shock wave, are studied on the assumption of thermal equilibrium. A numerical solution of the problem is outlined and an approximate analytic solution for the flow between the surface of the cone and the shock wave is developed. Two numerical examples are given as an illustration and compared with the corresponding solutions assuming constant air properties.
Flexural Vibrations of a Thin-Walled Cylinder of Rectangular Cross Section
Authors: Mansfield E. H. 
Published: July 2016

SummaryThe natural transverse vibrations of a long cylindrical box of doubly symmetrical rectangular cross section are considered. Explicit stress-function solutions are obtained for the webs and the top and bottom surfaces so that the effects of shear lag and shear deflection are inherently included. The results are expressed simply in terms of an effective flexural rigidity, which may be determined with the aid of a number of graphs.
A Rapid Method for Calculating the “Off-Design” Performance of Compressors and Turbines
Authors: Horlock J. H. 
Published: July 2016

SummaryA model for the calculation of the “off-design” performance of turbo-machines has been suggested by Mellor, who proposed that the machine be split into an infinite number of stages, each producing a small change in stagnation enthalpy. This note suggests that the overall performance of a machine may be obtained in an integral form which permits a rapid calculation of performance maps for rotational speeds and flow rates not greatly different from design values. The method may be of use in preliminary design studies of multi-stage compressors and turbines.
Matrix Analysis of Shell Structures with Flexible Frames
Authors: Przemieniecki J. S. 
Published: July 2016

SummaryA simple matrix method is presented for the deflection and stress analysis of cylindrical shell structures of arbitrary cross section stiffened by flexible frames. The method is an extension to fuselage structures of the Matrix Force Method developed by Argyris, in which the internal load system in the structure consists of two parts:—(a) synthetic load distribution, represented by the matrix b0, satisfying the external and internal equations of equilibrium, and(b)self-equilibrating load systems, represented by the matrix b1, which are introduced to satisfy compatibility conditions. The magnitudes of these self-equilibrating load systems are determined from the generalised compatibility equations formulated using the flexibility matrix f for the un-assembled elements of the structure. The self-equilibrating systems are non-orthogonal, but are arranged in such a way that the mixing between one system and another is kept to a minimum and, consequently, the resulting compatibility equations are well-conditioned. The three basic matrices, b0, b1;and f, are compiled using only very simple formulae. The matrices b0and b1depend on the geometry of the structure, while the flexibility matrix f is a function of geometry and elastic properties. The present analysis is applied to cut-out problems in fuselage structures. It can also be used for problems involving thermal loading and diffusion of loads in curved panels stiffened by flexible frames.
Some Simple Results for Two-Dimensional Jet-Flap Aerofoils
Authors: Spence D. A. 
Published: July 2016

SummaryIt is shown from elementary considerations that the lift coefficient of a thin two-dimensional wing at zero incidence, with a narrow high-velocity jet of momentum coefficient Cj issuing from its trailing edge at a (small) downward inclination τ, is given byand the loading on the chord line (0<x<1) by(except in a certain neighbourhood of the trailing edge), for small values of Cj. These formulae agree well with known measurements. Interpolation formulae for derivatives of CL at larger values of CJ based on earlier work, are also given:
Laminar Flow in a Uniformly Porous Channel
Authors: Terrill R. M. 
Published: July 2016

SummaryThe flow in a two-dimensional channel with porous walls through which fluid is uniformly injected or extracted is considered. Following Berman, a solution is obtained giving a fourth-order non-linear differential equation which depends on a suction Reynolds number R. Numerical solutions of this equation have been obtained. Series solutions of this equation for small and large Reynolds number are given and are shown to give good agreement with the numerical solutions.
The effect of communicating the genetic risk of cardiometabolic disorders on motivation and actual engagement in preventative lifestyle modification and clinical outcome: a systematic review and meta-analysis of randomised controlled trials
Authors: Li Sherly X. , Ye Zheng , Whelan Kevin , Truby Helen 
Published: July 2016

AbstractGenetic risk prediction of chronic conditions including obesity, diabetes and CVD currently has limited predictive power but its potential to engage healthy behaviour change has been of immense research interest. We aimed to understand whether the latter is indeed true by conducting a systematic review and meta-analysis investigating whether genetic risk communication affects motivation and actual behaviour change towards preventative lifestyle modification. We included all randomised controlled trials (RCT) since 2003 investigating the impact of genetic risk communication on health behaviour to prevent cardiometabolic disease, without restrictions on age, duration of intervention or language. We conducted random-effects meta-analyses for perceived motivation for behaviour change and clinical changes (weight loss) and a narrative analysis for other outcomes. Within the thirteen studies reviewed, five were vignette studies (hypothetical RCT) and seven were clinical RCT. There was no consistent effect of genetic risk on actual motivation for weight loss, perceived motivation for dietary change (control v. genetic risk group standardised mean difference (smd) −0·15; 95 % CI −1·03, 0·73, P=0·74) or actual change in dietary behaviour. Similar results were observed for actual weight loss (control v. high genetic risk SMD 0·29 kg; 95 % CI −0·74, 1·31, P=0·58). This review found no clear or consistent evidence that genetic risk communication alone either raises motivation or translates into actual change in dietary intake or physical activity to reduce the risk of cardiometabolic disorders in adults. Of thirteen studies, eight were at high or unclear risk of bias. Additional larger-scale, high-quality clinical RCT are warranted.
SOCIOECONOMIC AND DEMOGRAPHIC VARIATION IN NUTRITIONAL STATUS OF UNDER-FIVE BANGLADESHI CHILDREN AND TREND OVER THE TWELVE-YEAR PERIOD 1996–2007
Authors: Mohsena Masuda , Goto Rie , Mascie-Taylor C. G. Nicholas 
Published: July 2016

SummaryThe nutritional status of under-five-year-old children is a sensitive indicator of a country’s health status as well as economic condition. The objectives of this study were to analyse trends in the nutritional status in Bangladeshi children over the period 1996–2007 and to examine the associations between nutritional and socioeconomic status variables. Bangladesh Demographic Health Surveys (BDHS) were the source of data, and a total of 16,278 children were examined. The Z-scores of the children were analysed as continuous as well as categorical variables (stunted, underweight and wasted). The socioeconomic status variables used were region, urban–rural residence, education and occupation of the parents, house type and household possession score. A series of General Linear Model and Sequential Linear and Binary Logistic Regression analyses were done to assess the relationship between demographic and socioeconomic variables and nutritional status. The trends of Z-scores were analysed by survey, as well as by child birth cohort. Region, house type, educational level of parents and household possession score showed significant associations with all three Z-scores of children after removing the effects of age, period of DHS and other explanatory variables in the model. No significant sex difference was observed between any of the Z-scores. There were improvements in mean WAZ and HAZ between 1996 and 2007 but deterioration in mean WHZ over this period. The obesity rate was below 2% in 2007, although the absolute numbers of obese children had nearly doubled in this 12-year period. Children from poorer households showed greater improvement than their better-off counterparts. The study reveals that over the years there has been substantial improvement in nutritional status of under-five children in Bangladesh and the main gains have been amongst the lower socioeconomic groups; it is also evident that malnutrition in Bangladesh is a multidimensional problem, like poverty itself, and warrants a proper policy mix and programme intervention.
Are Ex Ante CEO Severance Pay Contracts Consistent with Efficient Contracting?
Authors: Cadman Brian D. , Campbell John L. , Klasa Sandy 
Published: July 2016

AbstractEfficient contracting predicts that ex ante severance pay contracts are offered to chief executive officers (CEOs) as protection against downside risk and to encourage investment in risky projects with a positive net present value (NPV). Consistent with this prediction, we find that ex ante contracted severance pay is positively associated with proxies for a CEO’s risk of dismissal and costs the CEO would incur from dismissal. Additionally, we show that the contracted severance payment amount is positively associated with CEO risk taking and the extent to which a CEO invests in projects that have a positive NPV. Overall, our findings imply that ex ante severance pay contracts are consistent with efficient contracting.
3D Generalisations of Viviani's theorem
Authors: Villiers Michael De 
Published: July 2016

“The ambitious learner should carefully study a new fact; he should turn it over and over, consider it under various aspects, scrutinize it from all sides … Moreover, he should try to expand and enlarge any newly acquired knowledge by application, generalization, specialization, analogy, and in all other ways.” [1]Vincenzo Viviani, a 17th century mathematician, proved that the sum of the (perpendicular) distances from a point within an equilateral triangle to its sides is constant as shown in Figure 1. The theorem, named after him, generalises to polygons that are equilateral or equi-angled, or to 2n-gons with opposite sides parallel. Viviani's theorem is easily proved by summing the areas of triangles APB, BPC and CPA, equating to the area of the triangle ABC, and then simplifying to obtain h1 + h2 + h3 = H, where H is the altitude of ABC.
Codes, not ciphers
Authors: Baylis John 
Published: July 2016

This article is written as a companion piece to the recent account of cryptography in [1]. The aim will be similar—to explain the meaning and principles of coding, give some implementations that are feasible at school and early undergraduate level, and give a flavour of the types of mathematics involved.2. Cryptography and coding—What's the difference?Cryptography concerns the transmission of secret or sensitive information in such a way that if intercepted en route by an ‘enemy’, that enemy will be incapable of understanding it and therefore be prevented from using it for any political, financial, military or other advantage.