Showing papers by "Ministry of Supply published in 1947"

The Theory of Wedge Indentation of Ductile Materials

Abstract: The theoretical solution for the deformation produced by a rigid frictionless wedge penetrating a plastic material is presented in this paper. The solution determines the form of the lip and the deformation in the material squeezed out towards the surface. The variation with wedge angle of the force required for penetration is determined in terms of the yield stress in a tensile test. The deformation of a grid of squares on a plane normal to the axis of the wedge is shown in figure 9 for a 30° semi-angle wedge. Close agreement is obtained with experiments as shown by comparing figure 9 with the photographs in figure 10 (plate 4). Lead blocks were used with a grid of squares scribed before penetration. This investigation is a first step towards the correlation of hardness test results with the deformation properties of a material under other conditions of stress, e.g. the tensile test. The average strain due to wedge indentation is shown to correspond to an equivalent reduction of area in a tensile test which increases with increasing wedge angle.

Tables of Second Virial and Low-Pressure Joule-Thomson Coefficients for Intermolecular Potentials with Exponential Repulsion

Abstract: The potentials used are functions of r, the distance between the centres of the molecules, but not of their relative orientation. The long-range attraction between the molecules is taken to be the sum of terms proportional to r$^{-6}$ and r$^{-8}$, and the short-range repulsion is proportional to e$^{-\rho r}$. This potential has four parameters: the position and depth of the minimum of the potential, the relative importance of the r$^{-8}$ term, and the steepness of the exponential repulsion. The second virial and low-pressure Joule-Thomson coefficients are tabulated for the range of parameters likely to be found in actual molecules, and for temperatures from the critical temperature to about 20 times this value. The most important of the three quantum corrections is tabulated over the same ranges.

The spectrum of modulated pulses

Abstract: Some methods proposed for evaluating the spectra of modulated pulse trains are discussed. The basic pulse-frequency, -phase, -length and -amplitude modulation systems are defined and the spectrum of a train of rectangular pulses sinusoidally modulated in any one of these ways is derived. Modulation by more than one tone is also considered. It is shown that in none of these methods is there any harmonic distortion or audio crosstalk. Anharmonic distortion arises from sidebands of harmonics of the pulse repetition frequency, and graphs are given to illustrate its magnitude. The formulae are extended to cover non-rectangular pulses, and it is shown that the distortions to be expected are practically the same as for rectangular pulses. The reproduction of transients is briefly examined. It seems that they suffer little distortion in form but that their timing is modified by the pulse modulation, the maximum time-shift being half the pulse repetition period.

Thermal Decomposition of Organic Nitrates

Abstract: The kinetics and mechanism of the thermal decomposition of organic mono- and poly-nitrates have been studied during recent years by Bawn and Wiseman1, A. J. B. Robertson2 and more extensively by me3. Studies on the overall decomposition in liquid and vapour phases suggest strongly that fission of O—N bonds with formation of NO2 is the primary process, while I have shown3 that during the very early stages of decomposition of a wide range of organic nitrates, in which the occurrence of secondary reactions is prevented, nitrogen is eliminated from the molecule wholly as NO2. These observations and the identification of aldehydes among the decomposition products indicate that, as suggested earlier by Bawn1, the mechanism postulated by Appin et al.4 for methyl nitrate applies to organic nitrates in general, namely:

Spectral Sensitivity of Lead Sulphide Layers

Abstract: LEAD sulphide photo-conductive layers are now known as sensitive detectors in the near infra-red1, but so far their usefulness has been limited to wave-lengths less than about 3 µ.

The preparation of levulinic acid on a semi-technical scale

Abstract: A semi-technical method of preparing crystalline levulinic acid by a process commencing with the hydrolysis of starch in 100 lb. batches is described. Details are also given of large all glass apparatus for evaporating solutions of crude levulinic acid without appreciable carbonization.

Solar and Terrestrial Radio Disturbances

Abstract: In their description of the solar radio emissions from the great sunspot of February 1946, Appleton and Hey1 pointed out that a number of sudden enhancements of intensity, observed at about 5 metres wave-length, occurred simultaneously with increases in D-layer ionization as indicated by fade-outs on long-distance radio-communication circuits. This increased ionization, which is believed to be due to enhanced solar ultra-violet radiations, strongly absorbs the radio communication waves (of the order of 20 metres wave-length) but does not produce any marked absorption of the solar radio emissions at wave-lengths of 5 metres or less.

An investigation, by the method of characteristics, of the lateral expansion of the gases behind a detonating slab of explosive

Abstract: The phenomena occurring when an uncased explosive charge is detonated in a fluid medium are examined by hydrodynamical methods. Attention is focused chiefly on the pressure and velocity distributions in the gaseous products of the explosion, which expand laterally behind the detonation wave as it travels down the charge, the results being shown in graphical form. To simplify the problem, the charge, and the gas and fluid fields, were treated as two-dimensional. The hydrodynamical equations were solved numerically using the method of characteristics. This dates back to Monge, but it is only recently that it has been applied to the numerical solution of hyperbolic equations. The methods of numerical integration used in this paper are similar to those developed early in the war by the Research Section of the External Ballistics Department, Ordnance Board, for determining the velocity distributions around projectiles moving at supersonic speeds. The nature of the boundary conditions made it necessary to find explicit theoretical formulae for the gas field near the charge, and the analysis involved is given at length. For the problem in which the surrounding medium is air, the shape and position of the shock waves set up by the explosion are calculated. The shock waves are found to be straight to the nominal accuracy of the calculations (1 in 5000) for six charge widths from their intersections with the block of explosive.

The preparation of mixed benzyl pyridine isomers on a pilot plant scale

Abstract: A semi-technical method of preparing a mixture of 2 and 4-benzyl pyridines at the rate of several cwt. per week utilizing the reaction between benzyl chloride and pyridine is described Satisfactory control of the reaction on the 1 cwt. batch size was obtained by the use of circulating hot oil as the reaction vessel heating medium.

The parallel-T bridge amplifier

Abstract: The paper discusses the design and performance of low-frequency selective amplifiers using negative feedback through a parallel-T bridge network. Two basic forms of the circuit giving symmetrical selectivity are analysed, and a method of varying the selectivity while maintaining the magnitude and frequency of the peak amplification constant is indicated. The paper concludes with a brief discussion of the problems which arise in the design of bridge amplifiers having high selectivity.

Carrier-frequency-shift telegraphy

Abstract: After the history of the development of carrier-frequency-shift telegraphy has been briefly outlined, methods of frequency-shift transmission are described and discussed. Methods of detection, by band-pass filter selection, or by a discriminator, are described. Practical advantages of frequency-shift operation are discussed and some factors influencing the design of carrier-frequency-shift transmitters and receivers are considered.A theoretical analysis of the threshold value of signal and the time shift produced by random noise is given in an appendix, and formulae are derived for comparing keyed-carrier and carrier-frequency-shift systems.It is shown that the discriminator method of detection gives no theoretical advantage over normal keyed-carrier operation, but that in a typical example, post-discriminator filtration gives an improvement of 14 db and band-pass filter selection an improvement of 10 db in threshold value.

Optimum Disturbing Field for Synchrotron Beam Ejection

Abstract: SEVERAL methods have been suggested1,2,3 for using disturbing magnetic fields to eject an electron beam from a synchrotron or betatron. Important differences exist in these methods in the angular distribution of these disturbing fields. Thus the 'orbit expansion' method1,2 effectively applies a sudden decrease of field over the whole 360° of annulus, while the '+ field' method3 decreases the field over 180° of annulus, while increasing it over the other 180°. The considerations outlined in this communication lead to the suggestion of an 'optimum step field', that is, a disturbing field of angular length such that the required beam displacement is obtained with minimum reactive power in the ejector field coil.

Research and Development Applied to Bomb Disposal

Abstract: An account of some of the principal lines of research and development pursued, during the late war, to solve the complex and changing problems presented by the designers of enemy bombs, which resul...

The Development of Gas Turbine Power Plants for Traction Purposes in Germany

Abstract: The simpler and cheaper construction, and the prospect of using fuel of low quality and of considerably increasing the power-to-weight and power-to-volume ratios of the power unit, led the Germans towards the end of the war to investigate the possibility of using gas turbines for land traction units. It was expected by them that they would be able to employ this new type of power plant for a variety of ground traction purposes, but, owing to their total national mobilization, the most important immediate applications they had in mind were for war purposes. It is considered that the information obtained and given in this paper may prove a useful background when considering the possibilities of future development of gas turbine power plants.The various arrangements possible, using either one single turbine, or separate turbines to drive the compressor and provide the output of useful work, were considered by the Germans and a resume is therefore made of the characteristics of each. In addition, the salient ...

A mobile spaced-loop direction-finder

Abstract: A War Office requirement arose during the war for a direction finder suitable for taking bearings on ionosphere-reflected waves which arrive at a small angle to the vertical and which are subject to fading It was necessary that this equipment should be highly mobile, suitable for transport by air, and capable of withstanding extreme ranges of temperature and humidity Ease of erection and simplicity of operation were also to be essential features Notwithstanding all this, a high order of accuracy was to be retainedThe paper describes a rotating spaced-loop df station that was developed at the Signals Research and Development Establishment during 1944–45, to comply with these requirements In order to simplify the taking of bearings under fading conditions, a visual indicator was incorporated which was also suitable for speedily resolving the ambiguities associated with spaced-loop systems

Military radio communications

Abstract: The paper shows the importance and traces the development of radio communication for the modern, highly mobile army. It describes the principal field radio equipments used in military communications and gives an account of their essential qualities. A description is given of the war-time efforts in design and production on these types of radio equipment and the measure of improvement achieved. The paper gives the trend of design in modern military radio equipment, showing the tendency to utilize very-high-frequency and super-high-frequency transmission in substitution for high frequency for many roles. It also indicates that frequency modulation, television, facsimile and integrated line and radio systems may form part of future development projects for military communications.

A simple method of reducing the polarization error of a U-type Adcock direction-finder

Abstract: A brief description of the nature of polarization error, and the historical background of earlier work and measuring techniques, introduces the instrumental problems associated with improving the performances of U-type Adcock direction-finders, particularly on sites of poor conductivity.An Army transportable U-type Adcock direction-finder, having surface feeders and an earthing system designed for speedy installation, was tested on a site of good conductivity, and compared well with similar but more elaborate systems, indicating a standard-wave error of only a few degrees. A series of tests on ground of abnormally low conductivity, over the frequency range 2–10 Mc/s, showed that a simple counterpoise of eight radial elements could have an effectiveness comparable with that of elaborate earthing arrangements of a more permanent nature.Quantitative comparisons of the effects of various earthing arrangements (buried feeders and extended earthing plates associated with Marconi direction-finders Types DFG24/2 and DFG25) are necessarily restricted to the small frequency range 2–5 Mc/s, on account of limitations which prevent the local source from simulating plane (or natural) wave conditions and also to enable a simple workable analysis, applicable only to electrically small systems, to be used. However, this lower region of the high-frequency band is a part where reduction of polarization error is particularly required.The computed performance of a simple unscreened U-Adcock direction-finder reveals that adding a feeder screen without adequate earth return at its ends, can have a deleterious effect, but with care a fair improvement over a closed loop (reduction in standard-wave error from 35 deg to 20 deg) can be achieved on an exceptionally poor site. On a good site the performance of a U-Adcock direction-finder, even without feeder screens, is far superior to a loop. Tests on an average type of unfavourable site to be found in this country, show that the use of an eight-radial counterpoise, which, on average reduces polarization error by 4 to 1, results in a performance comparable with that for a very good site.Data available from polarization-error measurements on a directionfinder with a large circular earth mat refer only to limited measuring conditions and do not allow a strict comparison, but from general considerations a greater efficacy in reducing polarization error as compared with an 8-wire radial system can be expected. The present tests, though limited, reveal fundamental points which would suggest that a layer of crushed coke might confer similar benefits to an earth mat.The simplicity of the counterpoise of eight long radials is such, however, that its use is suggested for all but the best sites, so as to make performance less dependent on weather, and because it facilitates the approach of an external cable with a minimum of disturbance. Even with the suggested coke layer its use should still be beneficial.

Radio interference from aircraft electrical equipment

Abstract: This paper deals with the radio-frequency disturbances caused by the normal operation of electrical equipment in aircraft. A brief account is given of the events leading to the adoption of the present system of suppression, reference is made to the special problems encountered, and attention is drawn to the more common sources and means of propagation of interference.Methods of reducing interference are described, and suppression at the source is indicated as being the most satisfactory method, emphasis being laid on the feasibility of designing radio-interference suppressors and suppression systems that will be effective over a wide frequency range with predictable behaviour. It is noted that some reduction of interference is possible by measures applied to receivers and aerials, and by careful design of equipment, and that these alone are rarely adequate.The design considerations for a radio-interference suppressor are stated and expanded for the particular application of a suppressor for aircraft use, and details are given of effective components and assemblies. Reference is made to test arrangements peculiar to the work. Experience has shown that, if adequate suppression is achieved continuously over the frequency range 150 kc/s–150 Mc/s, no trouble will be experienced at higher frequencies, and that the system adopted obviates the necessity for interference tests in production.

The production of DL‐methionine on a semi‐technical and pilot scale

Abstract: Substantial quantities of DL-methionine were urgently required by the Medical Research Council in England during the latter part of the war. The Ministry of Supply undertook the development up to a pilot scale of a process thought to be suitable for quantity production of methionine of high purity. The results of the first stages of this development, i.e., laboratory research, have already been published.1 The present paper is concerned with the semi-technical and pilot scale development of the process.

A novel method of making aerosols.

Abstract: THE phenomena occurring when a closed vessel containing a simple liquid is heated to a temperature above the critical temperature of the liquid are well known. What happens when a solution, and more especially a solution of a substance having a very small vapour pressure, is treated in the same way is perhaps less familiar, although the findings of several investigators are on record1. In some binary systems a partial separation of the components takes place as the critical point is approached ; in others, no heterogeneity can be detected even when the liquid phase has vanished. In this connexion we have made some observations in small-scale experiments in which sealed capillary tubes (1 mm. bore, with thick walls) partly filled with aqueous solutions of potassium chromate were slowly heated. Even when the concentration of potassium chromate was increased to 50 gm. per 100 ml., no separation of solid occurred when the critical temperature (in this case, about 430° C.) was attained, and the whole of the system passed into the vapour state, the colour of the solute becoming uniformly distributed throughout the tube. On cooling, liquefaction took place and the original solution was spontaneously re-formed.