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The United States creates or acquires increasingly more complex intelligence, surveillance, and reconnaissance (ISR) systems to maintain a strong, leading presence within the world. As a result, ISR systems have become more costly and difficult to manage. The research team focused on continuing previous year efforts of another team to utilize commercial off-the-shelf (COTS) technologies in the development of more flexible and cost-effective ISR systems. The primary goal was to design and implement an autonomous quadcopter that integrated an Android smartphone, an Arduino microcontroller, and several ultrasonic sensors to independently explore and map an unknown area. The project was broken down into three main tasks: construction of the quadcopter and integration of ultrasonic sensors, Android phone, and Arduino microcontroller, development of an Android application that generates navigation commands and avoids collisions, and development of an Android application that uses sensor data for Simultaneous Localization and Mapping (SLAM). This project, a proof-of-concept of a quadcopter system for autonomous navigation and mapping of an unknown environment, demonstrates the feasibility of developing inexpensive ISR systems with commercially available products. The team also found that the Arduino-Android interface was quite complex and caused issues with basic flight stability. The team also found that ultrasonic sensors were capable of partial SLAM by producing rudimentary maps under controlled conditions and simulated stable flight. However, the inexpensive sensors are unlikely to yield the detailed maps necessary for autonomous flight or actionable navigation information.

Simple one-dimensional theory of detonation indicates that the propagation characteristics of a detonation wave may be modified in a controlled manner by the addition of an energy source to supplement the chemical energy release within the wavefront. Provided that a sufficient level of electrical conductivity is obtained in the front then one possible means of providing such an additional energy source is that of ohmic heating. Results are first presented on the conductivity levels found in gaseous detonation, and the means by which they may be increased are discussed. These are followed by experimental studies that attempt electrical enhancement of gaseous detonation. Experimental studies are then described in which transient electric fields are applied transversely to the propagating wave. Under these experimental conditions theoretical estimates show that only 4% of the stored energy was deposited in the reaction zone. Not surprisingly, therefore, no observable enhancement of the wave occurs. The bulk of the energy is deposited further downstream, where it cannot influence the detonation characteristics. Attempts at increasing the field strength (and thus current) merely resulted in arcing in the reaction products.

The paper reports the results of experimental measurements of the reflection pressures close to spherical charges of TNT. These measurements were made using a pressure bar technique. Charge weights of up to 3.6 kg were used, with the reflecting plane in the range 25 to 300 mm from the charge surface.

Methods designed to quench a detonation wave in a pipe usually rely on some passive device which often presents an unacceptable impedance to the normal pipe flow. One method which overcomes this problem is a triggered water spray barrier, the principles of which are examined in the present study. Experimental data on detonation quenching were obtained in a vertical tube, 76 mm diameter, fitted with various spray generators. The empirical relations of Ranger and Nicholls were then used to calculate the rate at which water is stripped from a droplet in the shock flow field to form a micromist, thus enabling the energy loss from the wavefront in heating and vapourising the micromist to be found. Application of the Shchelkin criterion to the quenching mechanism shows that a 20% energy loss is required from the wavefront. This requirement is met at distances ranging from 0.2 to 1.0 cell lengths which is in reasonable agreement with the expected position of the CJ plane.

The Bacillus subtilis protein DivIVA controls both the positioning of the vegetative cell division site and the polar attachment of the chromosome during sporulation. In vegetative growth DivIVA attracts the bipartite cell division inhibitor MinCD away from the cell centre and towards the cell pole. This process ensures the inactivation of old polar division sites and leaves the cell centre free for the assembly of a new cell division complex. During sporulation MinCD and DivIVA levels fall, but DivIVA remains at the cell poles and becomes involved in the migration of the chromosomes to the pole. In order to investigate polar targeting of DivIVA, we undertook a mutational analysis of the 164-amino-acid protein. These studies identified one mutant (divIVA(R18C)) that could not localize to the cell pole but which retained the ability to support both vegetative growth and 50% sporulation efficiency. Further analysis revealed that, in the absence of polar targeting, DivIVA(R18C) localized to the nucleoid during vegetative growth in a Spo0J/Soj-dependent manner and required Spo0J/Soj and MinD to orientate the chromosomes correctly during sporulation. We demonstrate that polar targeting of DivIVA(R18C) is not essential during vegetative growth because the mutant can recognize the cell division site and influences the localization of MinD. Similarly we show that DivIVA(R18C) can function during sporulation because it can support the Spo0J/Soj orientation of the chromosome. In addition, we establish that both residues 18 and 19 constitute a DivIVA polar targeting determinant.

By using non-linear techniques to analyse irregular histamine-induced pressure oscillations in an isolated rabbit ear resistance artery, we have shown that the pressure oscillations are generated by deterministic rather than stochastic mechanisms. The average fractal dimension of the oscillations was between 2 and 3, thus implying that three (or more) independent control variables were necessary to account for the complexity of the dynamics. EDRF suppressed the pressure oscillations, but their fractal dimension was not altered by graded stimulation of EDRF activity by acetylcholine, or by inhibition of EDRF activity with NG-nitro-L-arginine methyl ester (L-NAME) or haemoglobin. This implies that EDRF is not one of the primary control variables involved in the genesis of their dynamics. The oscillations exhibited distinct 'fast' and 'slow' components, with periods of 5-20 s and 1-5 min respectively. The fast subsystem involved ion movements at the cell membrane level, and was inhibited by low [Ca2+]o, by verapamil (which inhibits voltage-dependent Ca2+ influx) and by tetraethylammonium (TEA) and apamin (which block Ca(2+)-activated outward K+ channels). In contrast, the slow subsystem was selectively inhibited by ryanodine, and therefore involved intracellular Ca(2+)-induced Ca2+ release. Each of these interventions decreased the fractal dimension to2 and thus removed one degree of freedom from the dynamics. We conclude that the interaction of a fast membrane oscillator and a slow intracellular oscillator generates chaotic pressure oscillations which are modulated by EDRF.

A deletion in the structural gene for the soluble lytic transglycosylase, the predominant murein hydrolase in the soluble fraction of Escherichia coli, has been constructed. The mutant grows normally but exhibits increased sensitivity toward mecillinam, a beta-lactam specific for penicillin-binding protein 2. In the presence of furazlocillin or other beta-lactams with a specificity for penicillin-binding protein 3 which normally cause filamentation, bulges were formed prior to rapid bacteriolysis. Similar morphological alterations are known to develop in wild type E. coli cells when furazlocillin is combined with bulgecin, an antibiotic of unusual glucosaminyl structure. It turned out that bulgecin specifically inhibits the Sl-transglycosylase in a noncompetitive manner. Since bulgecin shows some structural analogy to the murein subunits we postulate that the soluble lytic transglycosylase, in addition to its active site, has a recognition site for specific murein structures. The possibility of an allosteric modulation of the activity of the enzyme by changes in the structure of the murein sacculus is discussed.

We have used x-ray microangiography to investigate the influence of EDRF and endothelin-1 on arterial diameters (70-800 microns) at bifurcations in the isolated rabbit ear and the "optimality" of its branching geometry. The median value of the junction exponent x (which is given by d0x = d1x + d2x, where d0, d1 and d2 are parent and daughter artery diameters respectively) was close to 3 at different flow rates in unconstricted preparations. When x = 3, branching geometry is optimal in that i) power losses and intravascular volume are both minimised, and ii) fractal considerations suggest that the total surface area for metabolic exchange is maximised. Under conditions of vasoconstriction (by 5HT/histamine) the junction exponent deviated from its control value but was restored towards 3, both by basal and by acetylcholine-stimulated EDRF activity. In contrast, endothelin-1 caused a dose-dependent reduction in the junction exponent from its optimal value 3. This suggests that the endothelium helps to optimise microvascular function through EDRF but not endothelin-1 release.

The endothelial lining of arteries is anatomically well sited to convey physiological information about local blood flow to underlying smooth muscle cells, and by releasing endothelium-derived relaxing factor (EDRF) in response to shear stress (Pohl et al., 1986; Rubanyi et al., 1986) mediates flow-dependent dilatation of both conduit (Holtz et al., 1983; Melkumyants et al., 1989) and resistance arteries (Griffith et al., 1987; Griffith and Edwards, 1990). Flow-dependent dilatation provides a way of coordinating responses in different parts of the arterial tree: a metabolically-induced reduction in distal resistance, for example, can produce a secondary fall in the resistance of more proximal “feed vessels” simply as a consequence of the accompanying increase in flow (Holtz et al., 1983).

A shock wave is found to occur behind a driven planar detonation in a shock tube where the piston motion is provided by the contact surface between the detonated and expanding driver gas. Pressure and luminosity records taken in an oxyacetylene mixture, at an initial pressure of 30-50 Torr, show that the secondary shock has similar properties to those predicted by Lee's theory (1965); it is concluded, therefore, that the shock arises because of flow divergence behind the detonation front. Divergent flow in detonations confined in tubes is known to originate through the influence of the wall boundary layer, which effectively causes a negative or outward displacement of the flow boundary. By using this nozzle flow model, which is the basis of velocity deficit theory, measured secondary shock strengths and positions are found to be in agreement with the theoretical predictions over the range of values which are experimentally accessible.

A method of temperature measurement behind reflected shock waves in argon is investigated, which utilizes the integrated emission over a large number of rotational lines in the 2Σ->2II band system of OH. In the majority of experiments the OH emission is generated by the addition of 05% (H2+O2) to the argon, and the intensity, from two spectral regions, is monitored by two monochromators. From the ratio of the observed intensities the gas temperature can be calculated from the known spectroscopic data for OH. Theoretically derived intensity ratios for several bands, compared with that of the (0,0) band, are given as a function of temperature. Values of spectroscopic temperatures, over the range 3000-6000 K, agree with the gas dynamic values, derived from incident shock wave velocities with Mach numbers varying from 35 to 52, to within the predicted experimental error. The method is shown to be inapplicable at initial pressures greater than about 80 Torr because of self-absorption and at pressures lower than 20 Torr radiative disequilibrium may equally limit its use. Moreover, the pre-association reaction of oxygen and hydrogen atoms is found to enhance the intensity of most bands except the (0,0) and (1,1); only the latter bands may therefore be used to obtain the time variation of temperature behind the shock front.

A study has been made of how initially planar shocks in air propagate around 90° bends in channels of nearly rectangular cross-section. In shallow bends for which the radius of curvature R is much greater than the radius r of the channel, the shock recovers from a highly curved profile at the start of the bend to regain planarity towards the end of the bend. This occurs on account of the acceleration of the triple point across the channel following its interaction with the expansion waves generated at the convex wall. In sharp bends the shock profiles retain their pronounced curvature for some distance downstream of the bend.At the start of a shallow bend (R/r ≈ 6) the shock at the concave wall, initial Mach number M0, accelerates to Mw = 1.15M0 and remains at this value until towards the end of the bend it begins to attenuate. At the convex wall, shocks of M0 > 1.7 attenuate to Mw = 0.7M0 and propagate at this value for some distance around the bend. In the early stages of a sharper bend (R/r ≈ 3) the shock at the concave wall strengthens to Mw = 1.3M0, remaining at this value for some distance downstream of the bend. At the convex wall the shock decelerates to 0.6M0.Whitham's (1974) ray theory is shown to predict with reasonable accuracy the Mach numbers of the wall shocks at both surfaces for both bends tested and the range of incident shock velocities used, 1.2 < M0 < 3. The agreement between the theory and experimental results is particularly close for stronger shocks propagating along the inner bend. Predictions from 3-shock theory (Courant & Friedrichs 1948) of the Mach number at the outer wall are consistently higher than those from Whitham's analysis. In turn, the latter tends to slightly overestimate the strength of the wall shock.A model is developed, based on an extension of Whitham's analysis, and is shown to predict the length of the Mach stem produced by shocks of M0 > 2 over the initial stages of the bend.

Four cases are presented of men who sustained burns after contact with premixed concrete. The pathogenesis of the condition is discussed.

Under certain narrow limits of initial pressure conditions, self-sustaining detonation waves in gaseous mixtures exhibit large periodic variations of velocity with distance, although the mean value is close to the calculated Chapman-Jouguet value; these waves are known as `galloping' waves. A microwave interferometer, employing the fundamental TE01 mode at a frequency of 9000 MHz, is used to study the propagation of these waves in a rectangular tube of 23×10 mm2 section and 30 m in length. A continuous monitor is obtained of the combustion zone velocity trajectory, with a spatial resolution of about 2 cm, over the whole length of the tube. The technique also enables changes to be detected in the frontal configuration of the wave through the accentuated reflection of microwave energy from the transverse shocks; in this way, modal changes preceding the deceleration phase are clearly depicted. During the low-velocity regime, in which the causal shock and combustion fronts are dissociated, new and more detailed information is obtained on the unsteady behaviour of the latter.

Previous experimental work on the diffraction of a detonation wave at a large and abrupt area change in a tube, has shown that every system is characterized by a critical tube diameter at which quenching of the detonation occurs. Zeldovich, Kogarko & Simonov (1956) established that the critical tube diameter, for the oxy-acetylene system with varying dilution of nitrogen, lies between 500 and 700 times the one-dimensional induction zone length. Later, Mitrovanov & Soloukhin (1964) discovered that, for the same system, the critical diameter is 10 or 13 times the transverse wave spacing for a flat channel and cylindrical tube respectively. The two results are shown to be equivalent and are confirmed by further experiments in a 75 × 6 mm channel in which the flow is two-dimensional.Smoked foil and schlieren records show that, for supercritical waves, re-ignition occurs at sites along the wedge formed by the head of the expansion from the diffracting aperture and criticality is attained when the site is located at the apex of the wedge. A universal feature of re-initiation, which is also observed in liquid and solid explosives, is the sudden appearance of a transverse detonation which sweeps through the compressed, but unreacted, gas of the dissociated shock-reaction zone regime; this is signalled by the appearance of fine triple-point writing on smoked-foil records.A criterion for re-initiation is formulated by equating the critical velocity gradient which characterizes the decay of the wavefront in a cell, to that obtaining in the diffracted shock front at the head of the expansion fan; an expression for the latter is derived from Whitham's (1957) theory for non-reactive shocks. The prediction of the criterion is in good agreement with observation.

Cylindrical reactive blast waves were generated in a rectangular shock tube by the incidence of a detonation wave on a two-dimensional converging-diverging nozzle, with a narrow throat, placed in the tube. The observed trajectories of the shock front and reaction zone in the diverging section show that the blast wave behaves in a similar manner to that of the lead shock in a detonation cell. One particular similarity is the abrupt rate of decay that occurs in both types of waves following the decoupling of the exothermic reaction zone from the frontal shock. From the post-shock density field, obtained by a Mach-Zehnder interferometer, and the velocity profile, it is shown how the locus of the reaction zone may be calculated. A comparison is made of the predicted and observed reaction zone trajectories for oxyacetylene at an initial pressure of 15 Torr; these agree well for an assumed value of the activation energy of 71 kJ mol-1 for this system. It is suggested that the nozzle technique could be used for induction-delay measurements in detonation waves.

Interferograms of detonation fronts, with a single Mach stem interaction in each principal plane orthogonal to the front, have been used to determine the variation of strength of the transverse shock along its length. As the transverse shock interacts with the reactive flow field behind the incident shock, both its strength and inclination vary with distance downstream. From the observed density profile and the reaction kinetics of the system, values of the density ratio across the transverse shock are computed. The predicted particle velocity profile behind the front confirms that a one-dimensional approximation is valid in the region of interest close to the front, and also that the calculated values are compatible with the Chapman-Jouguet (CJ) theory at a distance further downstream. The theoretically derived transverse wave velocity is taken to be the measured quasi-steady value of 1.2 aCJ, where aCJ is the equilibrium CJ sound speed.

Experimental work is described on the initiation of spherical detonation waves, in oxyacetylene with various diluents, using an exploding wire and a lead azide pellet as sources. The transition of the spherical blast wave to a detonation, when the source energy is either above or at the critical value, is studied by three methods. Changes in wave structure are inferred from the cellular patterns obtained on smoked foils orientated radially to the flow: the wavefront velocity is derived from the Doppler frequencies and the pilot pressure variation is measured. For supercritical source energies the results obtained provide a detailed pressure history of the transition process. At critical source energy it is shown that the transverse wave structure, which is present in the initially overdriven wave, disappears when the low-velocity regime is established. The duration of the quasi-steady regime is approximately 10 mu s (or distance approximately 1 cm) before the establishment of a normal CJ wave.

Summary In a randomized, controlled clinical study, dextran-70, warfarin, or low-dose heparin were administered to patients undergoing total hip replacement on one surgical unit in an attempt to prevent deep venous thrombosis and pulmonary embolism. Calf vein thrombosis was detected by the 125I-fibrinogen uptake test. None of the methods prevented calf vein thrombosis (dextran-70, 51%; warfarin, 58-6%; heparin, 52-6%). Pulmonary embolism was completely prevented in patients treated with warfarin but occurred in 4% of patients treated with dextran-70 and 15-5% of those treated with low-dose heparin. The incidence of complications of therapy was small and comparable in each group. It is suggested that calf vein thrombosis is a frequent and in itself a non-serious complication of total hip replacement surgery and that emphasis might be placed more usefully on prevention of pulmonary embolism.

An improved method of generating a cylindrical blast wave is described which overcomes the disadvantages inherent in the converging-diverging nozzle technique previously used by the authors (1981). A diverging detonation vessel was constructed from two sheets of glass and two Tufnol blocks which form a variable-angle sector. An exploding wire, placed at the apex of the sector, was used to generate blast waves of variable strength. The trajectory of the shock wave and the density field behind the front was recorded by a streak-Schlieren interferometer. It is shown that the observed velocity profile simulates the behaviour of that found in freely propagating detonations satisfactorily. Moreover it is confirmed that the post-shock density decay parameter has a constant value of 4 which is in accord with previous studies; it is suggested that this is a universal value in detonation cells.

Temperature profiles behind detonation waves have been measured by the emission-absorption method using the integrated radiation over a large number of rotational lines of the fundamental vibrational band of OH at 306.4 nm. The lower temperature limit of the method is determined by the gas radiance and for oxyhydrogen detonations, at subatmospheric initial pressure; this is around 2600K, whereas the upper limit at which the method was tested is 4000K in oxyacetylene waves. The estimated error of the measurements is +or-2.6%. In the two systems studied good agreement is found between the observed values and those computed by the one-dimensional Chapman-Jouguet theory. Measurements are also described of the temperatures behind the shock wave formed by the normal reflection of a detonation wave at the closed end of the tube and also of the secondary shock wave which is found to occur, under certain conditions, in an overdriven detonation wave.

A new method of generating a tension pulse in a liquid column is described. The test liquid (deionised water) is contained in the lower part of a sealed vertical tube, the upper part of which contains a combustible gaseous mixture. When a detonation wave is initiated in the gas it is propagated down the liquid column as a compressional wave. At the base of the column, which is supported by a thin Mylar diaphragm, this pulse is reflected as an upward-going tension pulse. The pressure changes in the liquid are monitored by pressure transducers mounted in the wall of the tube and the cavitation bubbles are studied using schlieren photography techniques. The measured value of the breaking tension agrees well with those of other dynamic methods.

In 1968 a study was made of the spinal changes in 32 children with multiple congenital abnormalities due to thalidomide. Twenty-eight of these children have been traced and their spinal changes reviewed. Only four patients had normal spines on radiography. In eight children, scoliosis was present and had progressed though it was still of mild degree. Disc and end-plate abnormalities were seen in 14 children, and in some appeared to be progressive, leading to intervertebral fusion.

Measurements are described of the pressure amplitude of the transverse wave oscillations occurring in detonation waves in oxyhydrogen and oxyacetylene mixtures contained in a circular-section tube. The dependence of the amplitude on initial gas pressure and acoustic model number of the oscillation is established, and this is found to be different from the invariant character observed for the initial portion of the transverse shock which is supported by chemical reaction. An estimate is made of the average density of the acoustic energy of the oscillations in terms of the chemical energy density; close to the front this is found to vary from about 10 to as much as 60%. However, the oscillations are observed to attenuate in a distance of two to four 'cell' lengths downstream of the front.

The structure and mode of propagation of spinning detonation waves in stoichiometric oxyhydrogen, at initial pressures of 20–30 mm, have been investigated. The waves were generated in a square-section tube and observations have been made by the smoked-film technique, spark schlieren photography and pressure gauges. At the front of the self-sustaining detonation waves obtained at these pressures, two Mach interactions exist, the trajectories of which are derived from the imprints made on the smoked foil. As the triple point traverses the tube section, its direction of motion is found to vary between 50° and 70° with the tube diameter. An analysis of a Mach triple point for these conditions predicts the absence of chemical reaction behind the Mach stem in the immediate neighbourhood of the triple point. Experimentally determined pressures and triple shock angles confirm, to within experimental error, the postulated theoretical configuration.

An account is given of photographic and pressure observations made on the oblique shock waves occurring in the wake of self-sustaining detonation waves in hydrogen-oxygen mixtures initially at atmospheric pressure. Four explosion tubes were employed, of which three are of circular cross-section with internal diameters of 10, 5 and 1·6 cm and the fourth is a square-section tube of side 1·5 in.On the assumption that the oblique shocks are sufficiently weak to be regarded as Mach waves, the flow Mach number relative to the detonation front is determined; these are found to be substantially higher than the values predicted by deal one-dimensional theory. The measured flow Mach numbers in the rarefaction are then used to calculate the pressure distribution in this region on the basis of the supersonic nozzle model due to Fay (1959, 1962). The predictions of this model are found to disagree with with the observed static pressure profiles. Moreover, the pressure following the initial peak persists at a higher value than the theoretical for distances of the order of 5–10 cm behind the front. This phenomenon implies that the wall boundary-layer pressure remains higher than the C-J value and it is suggested that the pressure difference across the boundary layer can account for the formation of the oblique waves.The supersonic features of the flow can be accounted for by the turbulent-structure hypothesis of White (1961). Some validation of this hypothesis is provided here by the observation of the absence of the oblique shocks in overdriven detonation waves caused by the diminished effects of turbulence. This observation is consistent with the view that the oblique shocks are generated by the pressure difference across the boundary layer near the front as this difference would also be diminished in an over-driven wave.

A photographic investigation is described, using a Schlieren system and rotating-drum camera, of detonation waves in hydrogen-oxygen mixtures propagating in a 1.6 cm diameter tube of circular section. It is found that mixtures near the limits of detonability exhibit the phenomenon of spin in which the motion is of long wavelength and the frequency is in agreement with values predicted by existing theories. In stronger detonating mixtures a high-frequency spin of short wavelength is present which shows the same characteristics on a streak photograph as a normal long wavelength spin; measured values of frequency and wavelength agree reasonably well with those calculated. In a range of mixtures of intermediate composition both types of vibration are present. Longitudinal pressure waves, the recurrence frequency of which is twice that of the fundamental mode transverse vibration, are also observed behind the detonation front in all mixtures; the existence of these waves is confirmed by pressure recordings and a possible explanation of their origin is discussed.

The paper describes an experimental investigation of the pressures developed at the seat of collapse of cavities in water. Single transient cavities, generated by a spark discharge, are allowed to collapse on the end of a piezoelectric pressure-bar gauge which measures the variation of thrust with time. It is shown that both the peak force and duration of the cavity collapse pulse are functions of the cavity lifetime. From an estimate of the minimum radius attained by the cavity and the peak force, the peak pressure on collapse is found to be at least 10,000 atm. Streak schlieren photographs of the collapse process show that a shock wave is radiated into the water at the moment of collapse and that the cavity rebounds. At the collapse of the rebound cavities the pressures developed are comparable with those developed by the collapse of the initial cavity, and these probably contribute materially to cavitational surface damage.

A prerequisite to a study of a detonation wave structure is the establishment of an equilibrium frontal configuration, which is repeatable at equi-spaced distances along the detonation tube, together with a constant average wave velocity. A microwave interferometer is described which is capable of giving a continuous monitor of the velocity of a marginal planar detonation wave propagating in a narrow rectangular channel of transverse dimensions 3×¼ inch and 6 metres long. One important conclusion of this work is that some marginally propagating waves may appear to acquire a sensibly constant velocity, near the C-J value, over a distance of 1-2 m before a rapid decay in velocity occurs. This observation emphasizes the need for continuous velocity measurement in all waves near the limit.

A pressure bar gauge is described in which the average stress over the cross-section of the bar is measured by means of an X-cut quartz disk. Bars of duralumin and lead are employed since the acoustic impedances of these materials closely match the value appropriate to longitudinal thickness vibrations in the quartz. The design of a gauge housing, suitable for mounting in the wall of an explosion or shock tube is discussed.

The fundamental physical, chemical and mechanical processes which occur when a detonation wave passes through an explosive were imperfectly understood at the beginning of the recent war. As part of the scientific war effort in the British Common-wealth and in the United States of America, many theoretical and experimental studies were made of detonation processes. Much of the work has recently been declassified and some has been published. Several centres of research in this country and elsewhere are vigorously continuing with these studies. As later papers will show, the quality and general scientific interest of much of this work was considered sufficient to form the basis of a Discussion of the Royal Society. If one neglects the finite width of the zone in the detonation front where chemical reactions occur, a freely running steady plane detonation front can only advance through an explosive with the Chapman-Jouguet velocity defined by D = u + c . Once the explosive products are formed, their subsequent chemical reactions and motion in the detonation front may be considered as adiabatic. Although Chapman (1899) and Jouguet (1901) correctly stated their equation, neither attempted to discuss the reaction zone itself. It was therefore thought necessary that the recent views on the reaction zone should be described in a manner which throws new light on the Chapman-Jouguet equation. Professor J. von Neumann, Dr⋅ S. F. Boys and Dr A. F. Devonshire were the principal contributors on the theoretical side and von Neumann’s theory (1942) will be outlined later.

After a brief description of a new sand-tank laboratory and equipment for studying problems of the flow of fluids in porous materials, the remainder of the paper is devoted to an account of the application of a part of this equipment to a study of the flow of water between a pair of wells, such as is required for the determination of the permeability of the sand by the method described in part I. The potential distribution about the wells is found to conform sufficiently well with theory to justify the application of the analysis of part I, the interference due to the confining walls being satisfactorily negligible. The perturbation of the water table inseparable from the imposition of a potential difference between the wells is found not to invalidate the results based on an assumption of two-dimensional flow, while the corrections on account of the presence of a capillary fringe and a surface of seepage are satisfactorily made by adding to the measured depth of water in the well an increment equal to about half the thickness of the capillary fringe. The end correction for non-penetrating wells is also sufficiently well made by an addition to the measured depth of water; the magnitude of the correction is given for isotropic media for a well system of the dimensions used here, and the method of applying it to anisotropic media is indicated. The two-well method is used to estimate the permeability of the sand, which is then discussed in relation to the pore-size distribution. The elucidation of the permeability profile in a succession of strata is then discussed. Finally, techniques suited to work in the field are described, and a few preliminary fields results are quoted.

The use of microwave cavity techniques in the study of ionization in detonation waves and shock waves in reactive gas mixtures is discussed. Absorption measurements were conducted using a cavity oscillating in the TM010 mode at S band frequency and the shift in resonant frequency of a TE011 mode cavity, operating at X band frequency, was obtained by repetitively sweeping the frequency through the cavity resonance and displaying the response by means of a raster scan generator. The results are compared with microwave free-propagation experiments obtained at X and Q band frequencies in which both the microwave power absorbed by the ionized medium and the power transmitted through and reflected from the medium are monitored. Some results obtained by dc probes are also included for comparison. Equilibrium conductivities measured for the oxyhydrogen and oxyacetylene detonation waves are in reasonable accord with theoretical values. For the reactive shocks, however, the results obtained from the microwave reflection techniques yield far higher values of electron density than those obtained by the absorption methods; this is attributed to the inhomogeneous nature of the ionized medium.

Following the first interaction between the reflected shock from the end wall and the advancing contact surface in a shock tube, cold gas has been observed at the end plate at a time much earlier than that predicted on the basis of simple shock tube theory. Investigation of the nature of this cold gas has been made by an infra-red absorption technique. The driver gas hydrogen is "tagged" with a small quantity of infrared active gas, and shocks are driven with this gas mixture into an infrared inactive test gas. The time of arrival of driver gas at the end plate is measured from the absorption records and calculations based on a modification of the shock bifurcation model agree substantially with these experimental results. Use is also made of an infrared absorption/emission technique to determine the temperature of the infrared source.

Numerous investigations have shown that the wave velocity of a self-sustaining detonation is less than the ideal Chapman-Jouguet (C-J) value and that the deficit increases with decreasing tube diameter. Moreover, in small diameter tubes, the pressure gradient in the expansion behind the wavefront is steeper than that predicted by isentropic relations. Estimates of these deviations from ideality by the nozzle model of Fay, based on a viscous boundary-layer displacement, only partly account for the observed values. Numerical integration by Skinner of the non-steady equations of motion of the burned gases, assuming the Reynolds' analogy to hold between friction and heat transfer, shows that a growing region behind the front becomes time-steady as the wave recedes from its plane of origin. This prediction is confirmed in the present work by gas velocity measurements. An approximate solution of the non-steady equation is derived that is valid near the front and which allows a simple criterion to be stated for the attainment of a steady profile. Wall heat transfer measurements are described using platinum resistance gauges coated with silicon monoxide to suppress the effect of ionization. Transfer rate measurements near the wavefront of oxy-hydrogen waves agree well with the calculations of Sichel and David for the situation obtaining near the C-J plane. The value of the friction coefficient derived from the heat transfer data is used to compute the pressure and gas velocity profiles; these profiles are found to be in satisfactory accord with the observational values.

Measurements are described of the reflexion and transmission of 3 cm wavelength microwaves b y detonation waves in stoichiometric oxyhydrogen seeded with nitrogen, and oxyacetylene mixtures. Conductivity measurementsare also obtained by means of two types of d.c. probe, termed ‘axial’ and ‘gap ’ probe respectively. The observed reflexion coefficient in the oxyhydrogen waves is approximately tenfold greater than the calculated value assuming a step profile and equilibrium ionization at the detonation front. The character of the gap probe records indicates that regions of higher ionization occur along the detonation tube axis at locations which correspond to the intersection points o f the oblique shock waves generated b y the wavefront and the w all boundary layer. It is shown that the enhanced power reflexion can be explained in terms of these regions. Microwave absorption and d.c. axial probe measurements give values of conductivity in reasonable agreement with theory, assuming the absence of OH ions. The measured values o f reflected pow er and conductivity in oxyacetylene waves show no anomaly for initial gas pressures in the range 760 to roughly 300 m m H g. A t lower pressures the reflexion coefficient is w ell in excess o f the calculated value and both m icrow ave and d.c. probes exhibit a frontal ionization peak. This is in accord with the observation, by other investigators, o f chemiluminescence in the reaction zone of waves in organic fuel mixtures and chemi-ionization process in the reaction zone of flames. A value for the ionelectron recombination rate constant is derived which is in agreement with that observed in flames.

The transverse shocks associated with the Mach configurations comprising a spinning detonation front are shown to give rise to transverse oscillations whose pressure amplitudes are consistent with the assumed structural model for the wavefront. In the limit of weak interactions, when the transverse shocks degenerate into Mach waves, agreement is found with the acoustic theory of spinning waves.

Using an isolated perfused coronary-artery preparation, we have demonstrated the ability of endothelium inhibit markedly to vasomotion in rabbit coronary arteries. Using a bioassay system, we have shown this effect to be mediated via the release of an unstable humoral agent (t 1/2 approximately equal to 6 sec) from endothelial cells, and we have partially characterized its chemical nature.

Most studies on the ignition and propagation of detonation waves are carried out with systems of uniform composition. However, fuel/air clouds, whether they are produced accidentally or deliberately, will exhibit varying degrees of inhomogeneity. The manner in which both flames and detonation waves propagate in such clouds has received scant attention in the past largely because of the difficulties, both experimental and theoretical, which such problems present. Because of the lack of information on the influence of gradients on wave behaviour it is often tacitly assumed in hazard analyses that the presence of concentration gradients will hamper rather than enhance the propagation of a detonation wave; but this assumption is by no means proven. The present study therefore aims at elucidating the fundamental mechanisms which control the behaviour of detonations in the presence of compositional variations. (Author)

Experimental studies of endothelium-dependent relaxation have to date largely focused on the properties of pharmacologically and physiologically vasoactive agents in conduit vessels. The phenomenon has been demonstrated in vitro (Furchgott, 1983) and in vivo (Angus et al., 1983), although it has become apparent that species and vessel differences exist (Furchgott, 1983; Kalsner, 1985; Katusic et al., 1984). There is evidence that injury to the arterial wall, as occurs in experimental models of atheroma (Habib et al., 1984) or hypertension (Konishi and Su, 1983), may functionally impair endothelium-dependent responses. These observations may have clinical relevance. Relatively little is known, however, about endothelium-dependent relaxation in the microvasculature, where it may have an important physiological role, since small vessels regulate peripheral resistance and hence govern the distribution of blood flow in the intact circulation.

Laser angioplasty with the pulsed dye laser and integral ball-tipped optical fibres was used for primary treatment of occlusive femoropopliteal vascular disease in 26 limbs of 24 patients, all of whom warranted operative intervention. 19 had "critical ischaemia", 8 had pedal ulceration, and 4 had distal gangrene. The delivery device consisted of the laser fibre loaded retrogradely into a standard 6 mm balloon angioplasty catheter, and was introduced through a common femoral artery cutdown in an attempt to recanalise femoropopliteal occlusions of a mean length of 21 cm (range 3-49). Angiographic recanalisation was achieved with a mean energy of 250 J (range 38-727 J) in 23 of the 26 limbs; in each case the channel created by the laser fibre was augmented by balloon angioplasty. Technical failure occurred in 3 patients, due to wall dissection, persistent side-branch entry, and incomplete lesion penetration, respectively. Acute occlusion within 48 h occurred in 2 diabetic patients with very poor run-off and distal gangrene, and early failure occurred in another patient due to inadequate balloon dilatation. 1 patient with segmental tibial disease below a technically successful recanalisation did not show clinical improvement. Several patients had coexisting coronary artery disease, 3 of whom died of myocardial infarction—all with patent femoropopliteal vessels. In the 21 survivors, 14 vessels remained patent at a median of 7 months' follow-up.

One hundred and ten female patients, over the age of 60, with intertrochanteric or transcervical femoral fractures were included in a controlled, randomized, clinical trial investigating the value of low dosage heparin in the prophylaxis of deep vein thrombosis. There were 50 completed pairs. Eight (16 per cent) deep vein thromboses occurred in the heparinized group compared with 23 (46 per cent) deep vein thromboses in the control group. The incidence of pulmonary embolism was also reduced. The diagnosis of deep vein thrombosis was made on clinical grounds, supplemented by phlebography and autopsy. There was no difference in the wound haematoma or infection rate. The heparin was commenced on admission to hospital and it is suggested that in this group of. patients low dosage heparin prophylaxis should start on admission and not wait until surgery.