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Calculations are presented for the determination of radiation dose delivered by internally administered radioisotopes to specific tumour sites and to critical areas in the body. Some of the variables included in these calculations are: the metabolizing function of the isotope in the various sites, the half life, the beta and gamma ray energies of the isotope, and the tumour size. From this, an expression has been obtained for the ratio of dose in the critical volume and the tumour, and the effect of the various parameters on this ratio. The derived expressions are used to calculate the relative advantage of various iodine isotopes from data on nine patients who received therapeutic doses of 131I. The calculatiosn indicate that for most patients the iodine isotopes having a higher beta to gamma ray energy ratio are more advantageous to use, as long as their half life is of the order of one day or more. It appears that 131I is probably not always the most desirable of the iodine isotopes for maximal tumour and minimal critical volume irradiation.

An extensive critical evaluation of available correlations for predicting critical properties of binary defined hydrocarbon as well as some multicomponent hydrocarbon and hydrocarbon-nonhydrocarbon mixtures is presented using all available literature data. The Li method is recommended for critical temperature prediction based upon its accuracy and simplicity, although the Chueh-Prausnitz method is equivalent in accuracy. The Kreglewski method is most accurate for critical pressure prediction. All methods evaluated yielded high errors for the critical properties of methane-containing mixtures. Current correlations on critical volume are discussed, and correlational work on prediction using an excess volume approach is described.

(a) Theoretical derivation of the Rao's relation R V = a ( T c / M ) 1/6 v c has been performed on the basis of the Lennard-Jones and Devonshire's liquid model and using Wentorf, Buehler, Hirschfelder and Curtiss' equation of state. Here R V means the molecular sound velocity defined by R V =( M /ρ) V 1/3 , with M the molecular weight, ρ the density and V the sound velocity; T c and v c mean the critical temperature and the critical volume respectively, and a is an empirical constant with average value 2.68, according to Rao. The theoretical value of a obtained in this paper is 4.64. (b) Re-examination of Rao's relation has been performed on organic liquids and on some liquified gases employing existing ultrasonic velocity data and the following average values have been obtained: a exp =2.86 (on five liquified gases), a exp =2.69 (on 21 organic liquids except alcohols, acids and acetonitrile). The a exp for alcohols and acids are somewhat lower, the lowest example being a exp =1.825 for acetic acid. These...

Volumetric data of nonpolar gaseous mixtures are analyzed in terms of the theory of corresponding states. Special attention is given to an analysis of the second virial coefficient and to the calculation of pseudocritical constants. Second virial coefficients are calculated from experimental data for ten binary systems. These coefficients, with those previously published, are correlated by means of a generalized equation involving three parameters for each component: the critical volume, the reduced temperature, and the acentric factor. Equations are derived for the pseudocritical temperature and pressure of mixtures. These equations are considerably more accurate than those given by Kay's rule. Because of the complexity of the proposed equations for the pseudocritical parameters, a simplified pseudocritical method is presented which is sufficiently accurate for most chemical engineering purposes, especially at reduced temperatures exceeding 1.3.

Optimum conditions were found for the grading of chromatographic supports and packings. The standard deviation of the graded fraction with a diameter of 25 μm was ± 2.5 μm at the pressure regulation attained. An optimum period of time was suggested for the grading of one fraction as well as for the distribution of a sample into a greater number of narrower fractions. A critical volume of sample was determined so as to enable the device to provide the maximum output.

SummaryThe respective roles that the act of swallowing and the presence of an esophageal bolus exert on the genesis of esophageal peristalsis were studied in dogs. In the absence of a bolus, peristalsis in the esophagus did not follow the act of swallowing, while in the absence of swallowing peristalsis did occur if the bolus was of adequate size. The size of the bolus required to induce esophageal peristalsis was significantly less when swallowing occurred than when it was absent. Thus, the threshold stimulus required to initiate peristalsis was related to the volume of bolus and the magnitude was reduced by the act of swallowing. When the size of the bolus was below a critical volume, peristalsis was not initiated even though this intraesophageal stimulus was reinforced by swallowing.

In einem sehr kleinen Kugelfallviskosimeter wurden die Viskositaten vom Polyathylenphthalat-Polyester und seiner Losungen in Anisol und Nitrobenzol im Grundmolverhaltnis 1/10, 1/8, 1/4, 1/3, 1/2, 1/1, 1/0,5 und 1/0,2 uber den gesamten Temperaturbereich gemessen. Die Beschreibung der Meswerte nach der sog. Vogel-Gleichung ergab die Moglichkeit zur Definition zweier flussiger Zustande: des behindert- und freiflussigen Zustandes Fur den letzteren gilt T0 = 0 und freies Volumen vf(T0) = 0, fur den ersteren T0 · 0 und vf(T0) · 0. Beim reinen Losungsmittel Anisol konnten zwei behindertflussige Zustande, bei den Losungen infolge der Mesbereichsbeschrankung nur einer festgestellt werden. Die Ubergangstemperaturen lassen sich aus der Annahme einer Additivitat der freien Volumina berechnen. Die Werte des effektiven kritischen Platzwechselvolumens sind im Bereich der freien Flussigkeit groser als in dem der behinderten. The viscosities of polyethylenephthalate and its solutions in anisole and nitrobenzene in a molar ratio of 1/10, 1/8, 1/4, 1/3, 1/2, 1/1, 1/0.5, and 1/0.2 have been measured over the entire temperature range. The Vogel equation was used for the description of the experimental values. It permitted the definition of two fluid phases: the free and hindered liquid. The free liquid is characterized by the condition T0 = 0 and the free volume vf (T0) = 0, the hindered fluid follows the condition T0 · 0 and vf (T0) · 0. Pure anisole showed two hindered fluid phases, the polyestersolutions only one due to the temperature limitation of the measurements. The position of the transitiontemperature can be explained under the assumption of an additivity of the free volumes. The effective critical volume for the viscous flow is larger in the free than in the hindered liquid state.

Vapour pressure measurements on sulphur were performed up to a temperature of 1273 K (144.5 atm) with the aid of a special all-silica Bourdon gauge. Densities of the coexisting vapour and liquid were measured to 1273 K (vapour) and 1193 K (liquid). From the results the critical quantities of S were estimated to be: critical temperature, To = 1313 K; critical pressure, pc = 179.7 atm; critical volume, Vc = 158 cm3 mol−1; critical density, pc = 0.563 g cm−3; mean number of atoms per molecule at the critical point, vo = 2.78. The vapour pressure of sulphur between 590 K and the critical point is given by the formula: log ⁡ 10 ( p s a t / atm ) = 6 0 . 9 1 0 6 - 2 4 9 7 1 ( K / T ) + 1 . 0 8 1 7 × 1 0 7 ( K / T ) 2 − 2.2060 × 10 9 ( K / T ) 3 − 14.4102 log ⁡ 10 ( T / K ) .

By virtue of two properties, lysis on reaching a critical volume, and a discoidal shape, the hemerythrin-containing corpuscles of the coelomic fluid of Phascolosoma gouldi have proven to be excellent material for the quantitative estimation of permeability constants. The constants evaluated by the method of Jacobs from times of lysis show a general similarity between these cells and unfertilized Arbacia eggs in respect to permeability to water and a series of non-electrolytes. The Phascolosoma cells also resemble Arbacia eggs in their low permeability to both cations and anions.

(1892). LVII. On the determination of the critical volume. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 34, No. 211, pp. 503-507.

A linear relationship between particle volume and instrument response is confirmed for particles between 0.75 and 2.5 μ3, but this relationship may not hold for smaller particles. The implicit assumption of negligible surface conductance in derivations of this relationship is found acceptable for polystyrene spheres about 1 μ in diameter. A potential source of error in calibration is identified and allowed for. A relationship is developed between observed count and true count which allows coincident passage correction to be based on all available experimental points. The critical volume is found experimentally to be a function of particle volume.

A cell method for the evaluation of the configurational free energy is presented in which each cell can contain 0, 1 or 2 particles. This method which is a generalisation of the method used by L e n n a r d-J o n e s and D e v o n s h i r e 3 ), gives a correct evaluation of the so called “communal” entropy of the system. Numerical computations based on simple laws of force indicate that the value of the critical volume so calculated is in much better agreement with the experimental value than the value given by the L e n n a r d-J o n e s and D e v o n s h i r e method.

Copolymerisate aus Styrol und Methylmethacrylat wurden radikalisch in Losung bzw. in Emulsion synthetisiert und durch Fallungspunkttitration untersucht. Bei den Titrationssystemen Benzol/n-Hexan und Methylisopropylketon/n-Hexan wurde die normale, lineare Abhangigkeit der kritischen Volumbruche des Fallungsmittels (extrapoliert auf 100% Polymeres) von der Bruttozusammensetzung der Losungscopolymeren gefunden. Bei den Titrationssystemen Benzol/Isopropanol bzw. Methylisopropylketon/Isopropanol wurden dagegen relativ zu hohe kritische Volumbiuche beobachtet, wobei die Abweichungen vom normalen Verhalten bei Bruttozusammensetzungen des Copolymeren Maxima bei 60 hzw. 80% Methylmethacrylat-Grundbausteinen im Copolymeren aufwiesen. Die Anomalien konnten auf Verknupfungen von Methylmethacrylateinheiten durch Isopropanolmolekule zuruckgefuhrt werden. Ein Einflus der Sequenz war nicht nachweisbar, wie auch zusatzliche Versuche an einem Blockcopolymeren aus Styrol und Isopren und den entsprechenden Unipolymeren ergaben. Die kritischen Volumbruche der Emulsionscopolymerisate lagen bei gegebener Bruttozusammensetzung der Copolymeren bei allen untersuchten Systemen stets tiefer als die der Losungscopolymerisate, was nach fruheren Versuchen durch kleine Beimengungen von Unipolymeren bedingt ist. Copolymers from styrene and methyl methacrylate were synthesized by radical initiators in solution and in emulsion and the resulting products investigated by cloud point titration. Normal, linear relationships were found between the critical volume fractions of the non-solvents (extrapolated to 100% polymer) and the overall compositions of the polymers for the titration system benzene/n-hexane and methyl isopropylketone/n-hexane. Using the systems benzene/isopropanol and methyl isopropylketone/isopropanol anomalous behaviours were observed. With these systems, maxima of the critical volume fractions appeared at definite overall compositions of the copolymers with respect to the ideal curve. These anomalies are due to a linkage of different methyl methacrylate units by isopropanol molecules. No influence of the sequence was detectable, as could be shown by additional experiments with block copolymers of styrene and isoprene and the corresponding homopolymer. The critical volume fractions of the emulsion copolymers were always lower than those of the corresponding solution copolymers which may be explained by the presence of small amounts of the homopolymers.

It has been found that spermatozoa of bull, rabbit and man swell in hypotonic media and in media of penetrating non-electrolytes. 1. 1. When the volume of the spermatozoon increases, due to osmotic uptake of water, the cell membrane takes on a more and more spherical shape, apparently without a significant enlargement of its area. 2. 2. The flexible “motor apparatus” of the tail is hereby forced by the cell membrane to bend and coil. 3. 3. When the cell has attained a critical volume the cell membrane ruptures and the coiled “motor apparatus” is abruptly straightened out. 4. 4. Calculations indicate that bull spermatozoa with maximally swollen tails might have increased their volumes 3.5–4 times. 5. 5. The plane of bending and coiling of the “motor apparatus” of the bull spermatozoon is determined by the plane sectioning fibre 1 and passing between the central fibres and fibres 5 and 6. 6. 6. Swollen spermatozoa loose water, straighten out (“uncoil”) and regain normal flagellation when the salt concentration of the medium is raised to isotonicity. 7. 7. Swelling manifests itself in a lowering of the specific gravity of epididymal bull spermatozoa. 8. 8. The close association of the cell membrane with Jensen's ring, which normally may prevent the cytoplasmic droplet from a migration down the principal piece, does not influence the alteration in shape of the cell when its volume is increased. 9. 9. Coiled spermatozoa in ejaculates apparently are the result of osmotic swelling.

Protection of erythrocytes by chlorpromazine against osmotic haemolysis has been described before in the literature. This phenomenon has been investigated in some detail, in order to determine its physical chemical background. Experimental evidence is presented, indicating that the decrease of osmotic fragility is based on a drug induced increase of the critical volume of the erythrocytes.

Lennard-Jones force constants calculared from viscosity values at normal pressures for nearly forty nonpolar organic and inorganic substances have been used to develop relationships for the estimation of these constants from the critical temperature and volume of the substance. The product of the critical temperature and volume TcVc was found to correlate linearly with the force constant modulus . When the collision diameter ρ was plotted against the cube root of the critical volume on log-log coordinates, a straight line of slope 5/4 resulted. The corresponding relationship was found to predict ρ values with an average deviation of 3.1% when compared with values calculated from viscosity measurements. The temperature force constant ϵ/κ was found to vary as the 5/6 power of the critical temperature, and the resulting relationship produced an average deviation of 10%.

The van der Waals' constanta a andb evaluated from structural considerations of the unsaturated aliphatic hydrocarbons are used to calculate the critical constants for these types of compounds. For these unsaturated hydrocarbons, both van der Waals' constants are calculated through the additive contribution of unsaturated bonds to the van der Waals' constants of the corresponding saturated aliphatic hydrocarbons calculated according to a method previously proposed (6). With both van der Waals' constants available, the critical temperatures, pressures, and volumes for these types of compounds can be obtained. By use of this approach, the critical temperatures, pressures, and volumes of several olefins, diolefins, and acetylenes have been calculated. These calculated values have been compared whenever possible with values reported in the literature to produce an average percentage deviation of 1.3 for the critical temperature, 3.0 for the critical pressure, and 1.5 for the critical volume. In this comparison questionable literature values have been included, and consequently the reported deviations present the worst possible expectation.

An estimation method for critical properties that is easily available for both organic and inorganic compounds with considerable accuracy is proposed. In this method critical temperature, critical pressure and critical volume can be estimated solely from data of the normal boiling point and the liquid density of pure substance by means of succesive approximations that are repeated until calculated critical pressure (Pc) converges. The average errors of Tc, Pc and Vc for about 24O substances studied were 1.39, 2.61 and 2.OA percent, respectively, but the errors for nitrogen compounds, bromide compounds, metallic elements, and compounds associated in the vapor phase were sometimes larger.

A brief review of the theoretical and experimental work on the yield of material under contact load is given, and it is concluded that the experimental evidence is consistent with the well-known effect of size or stress gradient on the yield of mild steel. Experimental work has been carried out on a 0·19 per cent carbon steel, given various heat treatments to vary the grain size, and on Vibrac V30 or EN25 steel. The results on Vibrac show very little influence of ball size except for 1 2 in. dia. balls and smaller. Appreciable size effect was noted with the 0·19 per cent carbon steel, which was increased as the grain size was increased. Reasonable correlation is obtained if it is assumed that yield can only occur when the “true” yield stress is exceeded in a critical volume of material.

Simultaneous measurement of hemolysis, the volume of the intact cells, and the K lost from the intact cells of systems containing resorcinol, sodium taurocholate, and saponin shows that the volume increases may be conspicuously small while the K losses are large, and that the volume increases are un-equal for equal K losses produced by different lysins. In higher concentrations of the same lysins, the critical volume for hemolysis is a function of the nature of the lysin and of its concentration. It is impossible to say whether these observations are compatible with the current "dual mechanism" and "colloid osmotic" hypotheses of hemolysis, in which the swelling of the cell is supposed to result from the lysin having made it cation-permeable. The difficulty to be overcome is that the theory cannot be developed to describe volume changes in finite time unless we know what assumptions to make about the mobilities of K and Na, the forces driving them into and out of the cell, etc. The experimental results do not suggest, however, that any simple set of assumptions would be satisfactory. The conditions which regulate the upper limit of the swelling, i.e. the point at which a swelling phenomenon becomes a hemolytic phenomenon, are functions of the nature of the lysin and sometimes of its concentration. They require to be specified by an independent statement, over and above any statement which may be made about the rate at which swelling occurs in the system. The simplest view of the situation is that the conditions which regulate the critical volume and those which regulate the rate of swelling are both functions, as yet undefined, of the reaction which takes place between the lysin and the structural components of the red cell.

From an adjustment of the parameters of the Lennard-Jones potential to fit the effective ion-ion interaction in the alkali metals, their critical volume and temperature are calculated.

A PRESENTATION AND ANALYSIS OF AN EXPERIMENTAL STUDY ON CREEP AND STRENGTH ASPECTS OF POLYCRYSTALLINE ICE AND SAND- ICE MIXTURE ARE DISCUSSED. REFERENCE IS MADE TO A GIVEN FIGURE WHERE THE PEAK STRENGTH DETERMINED FROM STRESS-STRAIN TESTS IS PLOTTED AGAINST PERCENTAGE OF SAND BY VOLUME IN SAND-ICE SAMPLES. THE RESULTING BILINEAR RELATIONSHIP DETERMINED BY THE POINT OF INTERSECTION AND REFERRED TO AS THE CRITICAL VOLUME OF SAND CONCENTRATION, POINTS OUT VERY CLEARLY TWO TYPES OF SAND-ICE BEHAVIOR. BELOW THE CRITICAL SAND VOLUME, THE ADDED STRENGTH AND CREEP BEHAVIOR OF THE DISPERSED SAND IN ICE MAY BE SIMILAR TO THE BEHAVIOR OF DISPERSION-STRENGTHENED ALLOYS UNDER APPLIED STRESS. THE INCREASE IN STRENGTH WITH INCREASED VOLUME CONCENTRATION OF SAND IN THE DISPERSED CONFIGURATION APPEARS TO BE A FUNCTION OF INTERPARTICLE SPACING. THE WRITER HAS OBSERVED SIMILAR BEHAVIOR ON CREEP OF A FROZEN CLAY SOIL. THE RESULTS OF IDENTIFICATION AND MINEROLOGICAL TESTS ON THE CLAY SOIL ARE SUMMARIZED IN A TABLE. CREEP SAMPLES WERE SUBJECTED TO A PRESCRIBED STRESS-STRAIN HISTORY IN THE SECONDARY REGION OF CREEP. TWO FIGURES PRESENT RESULTS OF THE EFFECT OF STRESS- STRAIN HISTORY OF CREEP OF FROZEN SAULT ST. MARIE CLAY. THE RELOADING PORTIONS OF THE STRESS-CREEP RATE CURVES SEEM TO PARALLEL THE UNLOADING PARTS EXCEPT FOR SOME SHIFT TO THE LEFT INDICATING SLOWER CREEP RATES. THIS DECREASE IN CREEP RATE WITH INCREASED STRAIN SUGGESTS THAT THE NET EFFECT OF HARDENING AND SOFTENING PROCESSES THAT OPERATE SIMULTANEOUSLY DURING CREEP OF THIS FROZEN CLAY SOIL TEND TO INCREASE SAMPLE RESISTANCE TO DEFORMATION. REFERENCES: MECHANICAL PROPERTIES OF A SAND-ICE SYSTEM, ROY R. GOUGHNOUR, O. B. ANDERSLAND, ASCE PROC. PAPER 6030, JULY, 1968.

The hypothesis that general anesthesia or pressure-induced convulsions occur when a hydrophobic region is expanded or compressed, respectively, by critical amounts is consistent with recent data obtained with mice. Calculations show that anesthesia occurs at an expansion of 1.1 percent and convulsions at a compression of 0.85 percent, the latter site of action being more compressible.

There is direct and indirect evidence that the kidneys are involved in the onset of hypertension in spontaneously hypertensive animals. In the Dahl strain, rather convincing evidence exists for a primary, inherent renal defect that is worsened by high dietary salt. In the Okamoto and New Zealand strains, an intrinsic defect may be provoked by increased sympathetic nerve activity. Similarities between all of these strains and Goldblatt hypertension suggest a fluid volume abnormality, but the gradual onset of elevated pressure and continuing growth during development of hypertension may obscure critical volume changes. Theoretically, arterial pressure, somewhat independent of intermediate steps, will reach the level which is dictated by renal function as being necessary for the maintenance of salt and water homeostasis. While widespread use of different spontaneously hypertensive strains may currently be complicating our understanding of the intermediate steps, studies of dissimilar strains should, in time, enhance our understanding of the many different facets of long-term blood pressure control.

Dimethylsulfoxide protects human red blood cells against haemolysis. This protection is caused by a drug-induced increase of the critical volume of the cells. Protection is abolished, when the cells are preincubated with dimethylsulfoxide in isotonic NaCl. Dimethylsulfoxide-induced K + loss from red blood cells appeared to depend on the red cell volume. Presumably this phenomenon is related to volume dependent conformation changes at the cell surface, as described in recent literature. Further, dimethylsulfoxide causes a strong decrease of the red blood cell deformability, reflecting its profound influence on the physico-chemical properties of biomembranes. This effect also depends on the red cell volume. The results indicate that dimethylsulfoxide has similar effects on biomembranes as a wide variety of anesthetics. The effects of these anesthetics on biomembranes are usually attributed to a hydrophobic interaction with the membrane. It is shown, however, that a different interpretation of the results is also possible.

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The vapor pressures and orthobaric liquid densities of isobutane (propane−2‐methyl) were measured from 30° to 125°C. The equation log10p (normal atmos.)=4.31269–1126.71/T (T=t∘C (Int.)+273.13) gives a fair representation of the vapor pressures.The critical constants of isobutane are determined by the compressibility method. They are: tc=134.98±0.05°C (Int.), pc=36.00±0.05 normal atmos., vc=0.263 liters per mole (4.53 ml per g), dc=3.80 moles per liter (0.221 g per ml). The uncertainty in the critical volume and density is 2 percent.

It is known that if a fluid at its critical density is cooled toward its critical temperature, then its compressibility becomes infinite proportionally to (T—Tc)—f, where T and Tc are the temperature and critical temperature, and where the exponent f depends only on the dimensionality of the system. It is also known that along the coexistence curve in the temperature—volume plane, Tc—T becomes proportional to | V—Vc |d near the critical point, where V and Vc are the volume and the critical volume, and where the exponent d, like f, depends only on the dimensionality of the system. If it is conjectured that two features of classical (i.e., infinite‐dimensional) systems are in fact independent of dimensionality, it then follows that f=2(1–1/d). The pair f=1, d=2 and the pair f=7/4, d=8 are well known for classical and for two‐dimensional systems, respectively. For three‐dimensional systems it has often been conjectured that f=5/4, from which it would follow that d=8/3, while it has also often been conjecture...

The vapor pressure of neopentane has been measured from 50° to the critical point. The equation, log10p(atmos)=3.901633−1136.462T+4.99118×10−4T (T=t∘C+273.16), gives a fair representation of the observations.A study of the compressibility of neopentane in the critical region gives for the critical temperature, pressure, volume, and density the values: tc = 160.60°±0.05°C (Int.), pc = 31.57±0.03 normal atmospheres, Vc = 0.303 liter per mole (4.20 ml per g), dc = 3.30 mole/liter (0.238 g per ml). The uncertainty in the critical volume and density is 1 percent.

THE thermal theory of ignition of gases explains certain phenomena in the ignition of explosive mixtures by electric sparks involving capacitive and break or make discharges. However, a number of important questions for theory as well as practice remain to be answered. In this connexion the author has made some introductory investigations on the ignition of explosive gas mixtures having in mind the simplified assumption that the ignition process is essentially thermal in character, so that some critical temperature is involved in the initiation of the ignition. This temperature may be attained by a single process, such as the heating of a wire, or by more than one process, for example, the heating of a wire plus an electric discharge. In the case of an 8.3 per cent methane–air mixture the initiation of ignition involves a certain critical volume of gas attaining a minimum temperature.

The critical constants of propane (C3H8) are: tc = 96.81±0.01°C, pc = 42.01±0.02 normal atmospheres, vc = 0.195 liter per mole (4.43 cc per gram), dc = 5.13 moles per liter (0.226 gram per cc). The uncertainty in the critical volume and density is 1 percent.

For a real gas, the distribution function of Carnahan and Starling has been used to represent the hard-sphere contribution, and the resulting critical volume and temperature have been calculated. The result does not differ appreciably from that obtained using the ordinary virial expansion.

A means to determine the fatigue notch factor is devised by identifying the zone of metal at the notch root which is thought to govern the fatigue process. Corrections are then developed for the effects of the stress gradient and critical volume in this zone. The resulting equation for the fatigue notch factor embodies these corrections and the theoretical elastic stress concentration factor. experimental verification is obtained by testing notched plate specimens and by utilizing data from the literature. Predictions of the fatigue notch factor over fatigue lives of from 10 to the second power to 10 to the sixth power cycles are within 4 percent of experimental values when calculated in terms of stress and within 9 percent in terms of strain.

THE explosion in an 'atom bomb' occurs when two masses of uranium-235, each too small to retain sufficient neutrons to start a chain reaction, are brought into juxtaposition within a certain critical volume. A similar state of affairs will account for the phenomena of pulsating stars, but with this difference, that whereas in terrestrial experiments the reacting material is dissipated by the force of the explosion, in the interior of a star those heavy nuclei which have escaped fission during the course of one explosion are reconcentrated by gravitational attraction and are available as a neutron source, or for fission, a few days later.