Showing papers by "University of Manchester published in 1969"
TL;DR: An explicit formula for the inversion of the Laplace transform is derived in this article, and the formula permits the inverse to be readily evaluated numerically, which is the case of the inverse in this paper.
Abstract: An explicit formula for the inversion of the Laplace transform is derived The formula permits the inverse to be readily evaluated numerically
320 citations
01 Nov 1969
TL;DR: The inverse Nyquist array as discussed by the authors is a set of diagrams corresponding to the elements of the inverse of the open-loop transfer function of a control system, which can be used to investigate the stability of multivariable control systems.
Abstract: The inverse Nyquist array is a set of diagrams corresponding to the elements of the inverse of the open-loop transfer function of a control system. A number of theorems are proved which show how this array can be used to investigate the stability of multivariable control systems. The application of the array to the design of such systems is illustrated.
291 citations
TL;DR: The findings indicate that, in addition to causing acute illness, inhalation of this material may lead to irreversible impairment of lung function, and that insidious lung damage could occur without episodes of overt illness.
247 citations
TL;DR: In this article, the authors consider the problem of testing a given time series for stationarity using evolutionary spectral analysis and show that the mechanics of the test are formally equivalent to a two-factor analysis of variance procedure when the residual variance is known.
Abstract: We consider the problem of testing a given time-series for stationarity. The approach is based on evolutionary spectral analysis, and the proposed method consists essentially in testing the "homogeneity" of a set of evolutionary spectra evaluated at different instants of time. Using a logarithmic transformation, we show that the mechanics of the test are formally equivalent to a two-factor analysis of variance procedure when the residual variance is known, a priori. In addition to testing stationarity, the analysis provides also a method for testing whether the observed series fits a "uniformly modulated" model, and a test for "randomness" (constancy of spectra).
243 citations
01 Mar 1969
TL;DR: In this article, a model for the case of a discharge burning on a rectangular polluted strip is introduced; solution of Laplace's equation in two dimensions enables accurate values for the series resistance of the pollution film to be calculated, and a numerical method is used to calculate a factor which accounts for the change in resistance due to heating.
Abstract: Contamination on the surface of high-voltage outdoor insulators can lead to the formation of quasistable gas discharges, which burn in series with the resistive contaminative film. Under certain conditions, these discharges may grow to cause a complete flashover. In this paper, a model for the case of a discharge burning on a rectangular polluted strip is introduced; solution of Laplace's equation in two dimensions enables accurate values for the series resistance of the pollution film to be calculated, and a numerical method is used to calculate a factor which accounts for the change in resistance due to heating. Application of the flashover criterion di/dx > 0 to this model yields results which are in good agreement with experiment. The model can also be applied to axisymmetric insulators with complex shapes by replacing the practical insulator by its `equivalent cylinder' Good agreement is obtained between the calculated flashover voltages and those measured by the VDE 0448 test method.
202 citations
TL;DR: A model is put forward to describe the non-mediated transfer of non-electrolytes in terms of diffusion in homogeneous networks.
Abstract: A model is put forward to describe the non-mediated transfer of non-electrolytes in terms of diffusion in homogeneous networks.
202 citations
TL;DR: In this paper, the ratio of the silicate components in the liquids which are in univariant equilibrium with plagioclase, alkali feldspar, quartz and gas are determined for planes at 3, 5, 7.5, and 10 weight per cent anorthite.
Abstract: Crystal-melt relations at a water vapour pressure of 1 kilobar have been determined for planes at 3, 5, 7.5, and 10 weight per cent anorthite in the system NaAlSi3O8KAlSi3O8-CaAl2Si2O8-SiO2. The ratio of the silicate components in the liquids which are in univariant equilibrium with plagioclase, alkali feldspar, quartz and gas are Ab31∶Or28∶Q38∶An3 (weight per cent) at 730°±5–10° C, Ab21∶Or34∶Q40∶An5 at 745°±5–10° C and Ab10∶Or39∶ Q43.5∶An7.5 at 780°±10° C. The univariant curve on which the above compositions lieoriginates on the H2O-saturated Or-An-Q plane at a composition containing less than 10 weight per cent An and terminates within 1.5 weight per cent An of the H2O-saturated Or-Ab-Q plane. Experimental data for the synthetic system have been used to illustrate a discussion on the partial melting of metasediments and the possible significance of such a process with respect to the genesis of granitic rocks. Data taken from the literature (Winkler and v. Platen, 1960, 1961a) have been used to illustrate that the normative salic composition of a sediment has a strong influence on the composition of any melt which form when such a rock is subjected to high temperatures and pressures.
176 citations
TL;DR: In this article, the boundary-layer flow over a semi-infinite vertical flat plate, heated to a constant temperature in a uniform free stream, is discussed in the two cases when the buoyancy forces aid and oppose the development of the boundary layer.
Abstract: The boundary-layer flow over a semi-infinite vertical flat plate, heated to a constant temperature in a uniform free stream, is discussed in the two cases when the buoyancy forces aid and oppose the development of the boundary layer. In the former case, two series solutions are obtained, one of which is valid near the leading edge and the other is valid asymptotically. An accurate numerical method is used to describe the flow in the region where the series are not valid. In the latter case, a series, valid near the leading edge is obtained and it is extended by a numerical method to the point where the boundary layer is shown to separate.
160 citations
TL;DR: In this article, the origin of the grain boundary precipitate free zone is discussed in relation to Al-Zn-Mg and Al-Cu alloys using the occurrence of homogeneously distributed precipitate as a semi-quantitative indication of the excess vacancy concentration and its variation in the quenched alloys.
153 citations
146 citations
Book•
01 Jan 1969TL;DR: In this paper, the S-theory of Spanier and Whitehead is defined as a stable homotopy theory, in which the objects are not spaces but stable objects of some sort.
Abstract: There is a number of phenomena in homotopy theory which are independent of the precise dimensions considered, provided that the dimensions are large enough. For example, nn+1(Sn) = Z2 for n > 2. Such phenomena, in general, are called stable. One can also point to more complicated theorems (e.g. about spectral sequences) such that each clause of the theorem is true for sufficiently large n, but there is no n which makes all the clauses of the theorem true at once. In proving such a theorem, if you don’t take care, you rapidly find yourself carrying a large number of explicit conditions n > N(p, q, r, ...), which are not only tedious but basically irrelevant. What we want is a standard convention that we are only considering what happens for sufficiently large n . One anproach is to work in a suitably constructed category, in which the objects are not spaces but “stable objects” of some sort. For example, the S-theory of Spanier and Whitehead is such a category.
TL;DR: In this article, a stability analysis of a rectifier-inverter induction motor drive system is performed by neglecting the harmonic content of the stator voltages and applying Nyquist stability criterion to the small displacement equations obtained by linearization about an operating point.
Abstract: A stability study of a rectifier-inverter induction motor drive system is performed by neglecting the harmonic content of the stator voltages and applying Nyquist stability criterion to the small- displacement equations obtained by linearization about an operating point. This investigation reveals that system instability can occur over a wide speed range if the system parameters are improperly selected. It appears that the method of analysis presented in this paper is sufficient to predict stability of practical rectifier-inverter induction motor drive systems. Also, with slight modifications, this method of analysis can be applied to rectifier-inverter systems which supply reluctance-synchronous machines or synchronous machines.
TL;DR: In this paper, the early stages of grain boundary precipitation in two aluminium alloys, Al-6 %Zu-3 %Mg and Al-7 % Mg, have been examined by transmission electron microscopy, and are discussed in relation to the heat treatment procedure and the properties of individual boundaries.
TL;DR: In this paper, a new method of solving the linear Debye-Huckel (D.H.) equation for the electric potential in the overlapping diffuse layers of two identical, spherical, colloidal particles at separation R is described.
01 Jun 1969
TL;DR: In this paper, the authors studied the factors contributing to stick-slip oscillations of the feed drives of machine tools with the aid of a simple model based on dynamic measurements, and the experimental work was restricted to a scraped cast iron-cup ground cast iron slideway interface.
Abstract: The phenomenon of ‘stick-slip’ oscillations of the feed drives of machine tools is an important problem in the design of certain types of machine tools. The factors contributing to this particular type of instability are studied both experimentally and analytically with the aid of a simple model based on dynamic measurements. The experimental work is restricted to a scraped cast iron-cup ground cast iron slideway interface. The principal experimental variables are lubricant viscosity and the natural frequency of the drive. The dynamic observations provide evidence and data that enable the use of a simple model rather than the more usual application of an involved analysis. The consideration of analytical and experimental results allows further understanding of the mechanism of feed drive instability to be developed.
TL;DR: In this paper, the effect of molding water content and compaction method on the structure of compacted clay is illustrated by the different compression behavior of clays compacted dry and wet of optimum.
Abstract: Compression tests under controlled effective stress paths show the stress path independence of volumetric strain and degree of saturation. Stress path dependency appears to be caused by a reversal in the direction of saturation. The swelling process does not in itself appear to introduce an important path dependency. The collapse mechanism is controlled by a potentially unstable structure, a high applied stress and a high suction pressure. The absence of one of these three factors removes the possibility of significant collapse. The effect of molding water content and compaction method on the structure of compacted clay is illustrated by the different compression behavior of clays compacted dry and wet of optimum. The compression behavior is treated best in terms of the separate components of applied stress and suction pressure, and for one-dimensional compression, the stress-strain relationship for a clay can be stated in a simple form.
01 Sep 1969
TL;DR: The paper discusses the problem of the first pole to close when a power line is being energised from a source of infinite capacity and the argument is further extended to cover simultaneous pole closure of a circuit breaker.
Abstract: In this paper, a theoretical formulation of a method of multiconductor transient analysis is developed. The method combines the use of the modified Fourier transform and the steady-state theory of natural modes. The virtues of this particular formulation are that the frequency dependence of parameters can be taken into account irrespective of the complexity of the expressions defining their steady-state values. The paper discusses the problem of the first pole to close when a power line is being energised from a source of infinite capacity. The argument is further extended to cover simultaneous pole closure of a circuit breaker. The mathematical representation of the source-side network is covered and two alternative methods of simulation of a multiconductor-source infeed are presented. Both methods are shown to retain the distributed-parameter nature of a source infeed, or a group of such infeeds, while achieving a reduction in the computation time that would otherwise be required to meet the needs of a fairly accurate form of representation. The numerical results of a series of digital-computer studies are presented. These illustrate various cases of practical important and highlight specific aspects of the behaviour of multiconductor systems.
TL;DR: It is concluded that the changes can be explained by ADH-induced modifications in water and urea permeabilities of distal nephron segments and, possibly, by changes in inner medullary blood flow; that the evidence of direct ADH stimulation of sodium transport is inconclusive; and that there was no evidence of active urea transport.
Abstract: The corticomedullary osmolal gradient, largely dissipated by sustained water-diuresis, was progressively repleted by continuous i.v. ADH infusion (lysine-vasopressin, 15 mU/min/100 g body weight) in conscious rats for up to 41/2 hr. A marked increase in sodium content was essentially complete by 1/2 hr in the papillary tip; smaller, but more progressive increases occurred in the papillary base and inner medulla. Increases in medullary urea content occurred mainly in the first 21/2 hr, especially in the papillary tip. A progressive decrease in water content of all medullary segments was preceded by a significant papillary tip increase at 1/2 hr. Papillary tip-urine osmotic equilibration was slowly achieved after about 21/2 hr. The small, but significant, tip-urinary urea concentration difference of water diuresis was more rapidly replaced by a substantial difference in the reverse direction. It is concluded that the changes can be explained, adequately, by ADH-induced modifications in water and urea permeabilities of distal nephron segments and, possibly, by changes in inner medullary blood flow; that the evidence of direct ADH stimulation of sodium transport is inconclusive; and that there was no evidence of active urea transport.
TL;DR: In this paper, an approximate solution for the elastic interaction energy between a straight dislocation and a bubble or particle at large separation distances is presented, along with an exact analysis of the interaction energy for a bubble sitting symmetrically on a screw dislocation.
TL;DR: Investigations of both let-go and fibrillating current are discussed and some of the experimental data that have been obtained are presented.
Abstract: Commercial-frequency currents of a few milliamperes flowing through the body will cause muscular contractions, resulting in the inability of the victim to release his grasp on a live conductor. Values of ``let-go'' current are very important criteria in the establishment of safe-current requirements. Since ventricular fibrillation, a condition in which circulation is arrested, is probably the most common cause of death from electric shock, studies of minimum fibrillating currents under various conditions are also significant. This article discusses investigations of both let-go and fibrillating current and presents some of the experimental data that have been obtained to date.
TL;DR: Simplified representations of a rectifier-inverter induction motor drive system are established and verified by comparing the results obtained from a computer study using these representations to those obtained using a detailed simulation of the system as discussed by the authors.
Abstract: Simplified representations of a rectifier-inverter induction motor drive system are established and verified by comparing the results obtained from a computer study using these representations to those obtained using a detailed simulation of the system. It is shown that when all harmonic components are neglected the static drive system may be conveniently represented in the synchronously rotating reference frame. The computer simulation resulting from this type of representation can be readily implemented, and in many cases it will predict the system performance with sufficient accuracy. Also, in the analysis leading to these simplified representations, the operation of the inverter is analytically expressed in the synchronously rotating reference frame with the harmonic components due to the switching in the inverter included. These equations of transformation may be used to advantage in describing the interaction between the filter and the induction motor.
TL;DR: In this article, the long term fading of pulse intensities at 408 MHz has a characteristic frequency width which varies with the dispersion measure6 (∫Ndl) of the source.
Abstract: THIS communication reports that a programme of observations at Jodrell Bank on ten pulsars has shown that the long term fading of pulse intensities at 408 MHz (ref. 1) has a characteristic frequency width which varies with the dispersion measure6 (∫Ndl) of the source. These results can be explained by a scintillation mechanism due to irregularities of electron density distributed throughout the interstellar medium. The results in this report refer to the total energy density received per pulse, referred to here as pulse energy or intensity.
01 Sep 1969
TL;DR: In this article, basic heat release data have been obtained by analysis of cylinder pressure diagrams from a variety of engines, two-stroke and four-stroke, small (3·4in) to medium size (12in) over rang...
Abstract: Basic heat release data have been obtained by analysis of cylinder pressure diagrams from a variety of engines, two-stroke and four-stroke, small (3·4-in bore) to medium size (12-in bore) over rang...
TL;DR: In this paper, a method of predicting the 6th-harmonic electromagnetic torque of an induction motor arising from a rectifier-inverter power source is presented, including both the effects of harmonic variation rotor speed and inverter voltage.
Abstract: A method of predicting the 6th-harmonic electromagnetic torque of an induction motor arising from a rectifier-inverter power source is presented. This study includes both the effects of harmonic variation rotor speed and inverter voltage. Although only the 6th harmonic is considered, it is shown that this is sufficiently accurate to predict steady-state system performance for practical speed ranges and system parameters. This investigation reveals that the 6th-harmonic electromagnetic torque pulsation may, at low frequencies, be significantly greater than that predicted by a constant speed, constant voltage analysis heretofore employed, and may materially affect the performance of the system.
TL;DR: Fusarium culmorum (W. G. Sm.) Sacc, Fusarium nivale (Fr.) Ces. Sacc and F. avenaceum (Fr., Sacc) Sacc caused lesions at the base of the shoot in living plants.
Abstract: Fusarium culmorum (W. G. Sm.) Sacc., F. avenaceum (Fr.) Sacc. and F. graminearum Schwabe ( Gibberella zeae (Schwein.) Petch) cause disease in wheat seedlings but F. nivale (Fr.) Ces. ( Griphosphaeria nivalis (Schaff.) Mull. & Arx) and F. poae (Peck) Wollenw. caused no disease under the experimental conditions employed. Both F. culmorum and F. graminearum caused pre-emergence and post-emergence death of seedlings as well as distinct lesions at the base of the shoot in living plants. Although causing lesions at the base of plants, F. avenaceum brought about little pre-emergence or post-emergence death of seedlings. From the symptoms it was not possible to determine which of the three species caused lesions at the base of surviving plants. In greenhouse experiments F. culmorum and F. graminearum caused most pre-emergence death of seedlings in dry soil where an increase in the number of those killed occurred with increasing temperature. Severe post-emergence death of seedlings was also associated with dry soils. With both species the smallest number of dead plants or of surviving plants with lesions occurred in wet soil, particularly when the temperature was low. F. culmorum brought about a marked reduction in the height of infected seedlings. F. avenaceum caused lesions on fewer surviving plants in cold wet soils than in drier soils. Examination of fairly mature cereal crops during growth in Lancashire and Cheshire in 1961 showed that symptoms associated with the presence of Fusarium spp. occurred in practically all wheat crops. F. nivale was isolated very frequently from diseased plants but F. culmorum was less prevalent. F. avenaceum and F. graminearum were isolated from a few plants in occasional crops.
TL;DR: In this paper, the authors used plan and scanning electron microscopy to study the alloy-oxide interface after oxidation of Fe Cr Si and Fe Cr Y alloys in 1atm oxygen at 1000-1300°C.