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[RALPH ADAIR Ore Dressing Consultant Bull Mtn. Rd., Asheville, N. C. Phone 4-1893 JAMES A. BARR Consulting Engineer Mt. Pleasant, Tennessee Washington, D.C. BEHRE DOLBEAR & COMPANY Consulting Mining Engineers and Geologists 11 Broadway New York 4, N. Y. I. R. BERENT Engineering Consultants and Contractors Mineral Exploration, Mine Evaluation, Mine Designs and Mine Management ` 188, Ataturk Bulvari-Ankara, Turkey BLANDFORD C. BURGESS Registered Professional Engineer Mining Consultant Monticello, Georgia GLENVILLE A. COLLINS Mining Engineer Uranium examinations Cable "Coins" 8 Haward-Canfleld Bldg. Santa Barbara, Calif.]

Jan 1, 1952

By M. J. Mullikin, J. B. Conway

for use in describing combined first- and second-stage creep data. In the above ?o represents the instantaneous strain on loading, ?t the limit of transient creep, ?S the steady-state creep rate, t the time, and ? a constant leading to the exhaustion rate of transient creep. It was noted that this equation was similar in form to that proposed originally2 by McVetty. This type of equation was also suggested by Andrade and Aboav3 in studies of the shear strain of cadmium. Calculation of the constants ?o, ?t, ?, and ?s, in Eq. [ l] is somewhat involved due to the slight complexity of this relationship. In the paper by Garofalo a computer approach based on a least-squares analysis was recommended. Such an approach involves a trial and error solution but when a computer facility is available the difficulties in this calculation are of little consequence. It does mean however that the evaluation of this type of equation would become quite tedious if computer facilities were not available. Some recent studies have identified a fairly straightforward method for calculating the constants in the Garofalo equation. While not leading to a least-squares evaluation the approach is accurate and is recom-

Jan 1, 1967

By M. Sagheer

This paper gives a report of the laboratory work investigating the fundamental flotation characteristics of chromite and its commonly associated mineral, serpentine. Floatability curves, showing floatability of chromite at different concentrations of sodium oleate and pH, were obtained by pick-up method. One of the difficulties encountered in flotation of chromite in presence of serpentine has been attributed to dissolved metal ions. The influence of metal ions, dissolved in pulp filtrate, on floatability of pure chromite and serpentine has been studied and it has been shown that Mg, Ca and Fe ions depress chromite. A considerable amount of work applying bubble pick-up method was carried out to counteract the depressing action of metal ions. Various methods and reagents were applied in this connection. Validity of each method and reagent has been discussed. Probably due to the abundance of high-grade chrome ores, very little has been published concerning the flotation of chromite. As improvements in mineral beneficiation are realized, more attention is being directed to low-grade ores previously considered unusable. Currently, gravity concentration is the principal process applied to upgrade chrome ores, but this cannot be used for finely disseminated ore because of the substantial losses in the fines,1,2,3 To avoid these losses, flotation can be applied to material which is too fine for satisfactory gravity concent ration, and it is probable that a combination

Jan 1, 1967

By C. E. Birchenall, R. H. Condit

THREE surface activity procedures are in com--L mon use for the determination of diffusion coefficients in solids. In the oldest of these' the activity observed at the original surface is compared before and after diffusion, where all the activity is in a thin, plated layer on the surface before diffusion. Partial absorption of the radiations from active atoms which have diffused below the surface reduces the effective activity after diffusion. The formula employed to calculate the diffusion coefficient is where F, is the ratio of final to initial activity at the surface, measured with identical counting geometry; Z=u3Dt, where D is the diffusion coefficient; t is the diffusion time; and u is the absorption coefficient for the radiation in the solid as defined by Lambert's law. This absorption law implies that all the rays are parallel to each other and normal to the specimen surface. This assumption of a collimated beam used by Steigman, Shockley, and Nix has been adopted by all other investigators and, although it gives results which are approximately correct under restricted physical conditions, it does not represent many actual circumstances. It is the purpose of this paper to show the importance of the divergent rays and to indicate a procedure for taking them into account. In the residual activity method the activity is determined on a series of surfaces ground on the specimen at progressively greater depths in the diffusion layer parallel to the initial surface. Gruzin2 has de- rived a formula for this procedure, which may be put in the form where I is the ratio of the activity measured at a newly ground surface at distance k below the initial surface to the activity at the initial surface measured after diffusion, and K= k/2p Dt. A third procedure involves the autoradio-graphic determination of activity on a plane ground at a small angle to the initial interface through the penetration zone. Aut oradiography can be particularly sensitive to the oblique rays. Unlike most counters which detect essentially all ß particles or X-rays which enter the active volume as a single event, the photographic emulsion may be thin enough so that oblique rays with longer path length in the emulsion produce more darkening than rays which move normal to the film plane. Consider a plane containing a source of radiation uniformly spread over a circle and a point counter located on the perpendicular through the center of the circle. As the counter moves along this line, the total angle 6, at the counter subtended by the specimen will vary. For a fixed counter distance, let 6 be angle between the counter axis and the line connecting the counter to a point P on the active plane. If an absorber of thickness X is interposed parallel to the source between counter and source, the ray from point P to the counter will pass through an absorber thickness X secant 6. Exponential absorption is assumed to hold for all rays. If r, is the ratio of intensity at the counter with absorber to the intensity without absorber and a = pX, 1 00 The behavior of this integral, evaluated numerically,

Jan 1, 1957

By Simon T. Johnson

Potential applications for boom tunnelling machines requires reliable assessment of in-situ performance. The majority of existing classification schemes concentrate on the prediction of excavation rate, neglecting the important influence of tool consumption rates. A statistical approach is taken to the analysis of the performance data, which was obtained first-hand through in-situ monitoring, and laboratory testing of representative rock samples. A statistical discrimination technique is used to produce a scheme for the prediction of performance groups, each of which covers a limited range of cutting rate and/or tool consumption rate.

Jan 1, 1984

By R. L. Schmidt, J. D. Verhoeven

The diffusion coefficients and electrotralzsport mobilities of aluminum, gallium, and arsenic have been determined in molten germanium with the capillary reservoir technique. The diffusion coefficients are slightly higher than those determined by the solidification technique of Brirton et a1.1 It was found that aluminium and gallium migrate to the cathode in molten germanium) whereas arsenic migrates to the anode under an electric field. A possible technique for producing p-n junctions by means of electric field freezing is discussed in view of the experimental data. In the past decade or so the literature has abounded with articles concerning the solid-state properties of the semiconducting elements germanium and silicon. It is surprising by comparison how little has been published concerning the liquid-state properties of these materials. In the production of doped germanium or silicon the diffusion coefficient of the dopant in liquid germanium or silicon is an important quantity. Yet, to the best of our knowledge, no one has ever made a direct measurement of the diffusion coefficient of solutes in either molten germanium or silicon. A number of authors'-4 have determined some diffusion coefficients by the indirect technique developed by Burton et al.1 This technique appears to give numbers of the correct order of magnitude but it does depend upon a number of assumptions in the analysis and also requires prior knowledge of the viscosity of the melt. In the present work a more direct measure of the diffusion coefficients of arsenic, gallium: and aluminum in molten germanium has been made. It has been shown independently by two groups of authors5, 6 that, when an electric current is passed through the interface of a solidifying metal containing an impurity, the resulting electrotransport in the liquid boundary layer at the interface offers a mechanism for control over the redistribution of the impurity accompanying the solidification. These authors show that the degree of control is proportional to the mobility, U of the impurity atoms in the liquid boundary layer, where the mobility is defined as the drift velocity relative to the solvent per unit electric field. In principle the results apply to the solidification of a doped semiconductor and offer an interesting technique for control of the doping of a semiconductor. In the present work the mobilities of aluminum, gallium, and arsenic were determined in molten germanium in order to evaluate the potential usefulness of electro-transport as a technique for solute control when applied to the solidification of doped germanium. EXPERIMENTAL PROCEDURE Both the diffusion coefficients and the mobilities were measured using high-purity alumina capillaries and a resistivity technique for analysis. A schematic diagram of the electrotransport apparatus is shown in Fig. 1 and the details of the cell design are shown in Fig. 2. For the mobility experiments electrical contact with the bottom of the capillary was made with graphite, as shown in Fig. 2. In order to prevent electrical contact with the melt the graphite was coated with a thin layer of alumina using a plasma spray torch. The cell assembly, a graphite electrode, and another assembly containing two blank capillaries were fastened to the lavite disk shown in Fig. 1. To make a run the system was evacuated and the doped germanium was outgassed at the operating temperature of 1030°C. The cell and blank capillaries were then submerged beneath the melt and a slightly positive pressure of helium was introduced to fill them. After passing current through the cell for a given time the cell and blank capillaries were raised from the melt and the furnace was shut off. The temperature of the cells dropped below the freezing point of germanium within 1 to 2 min after the furnace was shut off.

Jan 1, 1968

By R. H. Thorpe

Longwall working in Britain developed to overcome problems arising from depth of seams causing roof and ventilation difficulties. This system became very widespread particularly in the thicker seams, where faces of up to one mile in length were not uncommon. In the thinner sections, in order to remain competitive, the longwall undercutting machine was developed. Following the development of the coal cutter, every other aspect of the face operation was examined and mechanized as it became a bottleneck to output and efficiency. The face system itself was modified and workings concentrated with the same objectives.

Jan 1, 1977

By Sam F. Harrison

Most hydraulic system malfunctions make their presence known by sending out warnings that are loud and clear to the initiated mechanic, according to Aeroquip Corp. service engineers. To detect problems in many systems, they suggest that the use of four senses-sight, smell, hearing and touch-and a knowledge of how to interpret the information gathered are all that's needed to identify hydraulic malfunctions.

Jan 3, 1978

By John A. Gann

The following investigation constitutes a brief réumé of the more important binary magnesium alloys from the standpoint of metallo-graphic technique, and the effect of heat treatment on structure and properties. The comparative newness of the subject justifies this procedure as a preface to a more detailed study of each individual series of alloys. The work was started with the idea of practical application in the industry rather than as a theoretical investigation. The alloy compositions studied were selected as those most likely to show whether heat treatment would produce beneficial results. Furthermore, it was considered satisfactory to use commercial 99.9 per cent. magnesium, the best commercial grade of alloying ingredients, and to limit the time of heat treatment at the expense of incomplete equilibrium. These facts must be kept in mind when examining the results obtained, and the conclusions drawn. Preparation of Alloys All melts were made in an oil-fired cast-steel pot, approximately 12 in. dia, by 12 in. deep. Approximately 15 lb. of flux and 50 lb. of magnesium were melted and the calculated amount of alloying metal was added. After thorough alloying and puddling, the metal was chill cast in a graphite mold with four 1/2 by 1/2 by 4 in. bars fed from a common sprue and runner. The next higher composition alloy in a given series was made by adding the calculated amount of metal to the heel from the preceding cast. The pot was thoroughly cleaned after each series and new flux then introduced, thus avoiding possible contamination from earlier melts. The percentage compositions given in Table 1 are the calculated values. While not all alloys were analyzed, enough were checked to indicate that the reported compositions are correct to a few tenths of one per cent. A more detailed description of the foundry methods employed has been given in a previous paper. 1

Jan 1, 1929

By R. L. Fleischer

IN 1925 a criterion for localized deformation in a single crystal was derived by Taylor and Elam.' They noted that for a single active slip plane the slip plane area is constant, but the direction of the stress with respect to the slip direction changes during deformation so that, when the increase in stress due to this rotation is large enough relative to the work hardening, instability occurs. (By instability is meant continued slip on the active slip plane.) The instability criterion may be written t>dt/d?/m tan2? [1] where t and ? are resolved shear stress and strain, m the Schmid factor for resolving shear stress, and ? is the angle between the slip direction and the axis of tension. The formula points out that regardless of the atomic mechanism involved, for large flow stresses and low work hardening rates, slip on a single plane—once started—should continue. The case of alloying provides a direct possibility of adjusting the parameters in Eq. [I]: As an alloying element is added to a pure metal, the flow stress is raised and the work hardening in easy glide may be either decreased2 or unaltered.3 Since flow stresses in easy glide may rise to the kg/mm2 range for alloy crystals while easy glide slopes may be less than % kg/mm2, 2 it is possible for the inequality to be satisfied. Indeed Garstone and Honeycombe3 report that slip becomes coarser with increasing stress in the easy glide range, where the flow stress would be increasing and the slope would be essentially constant. Another case where high flow stresses and low hardening rates accompany coarse slip is that of quench hardening.4 Maddin and Cottrell report that quenched aluminum crystals display slip markings resembling those of a brass. A similar effect has been observed after irradiation.'

Jan 1, 1960

By J. H. Clemes

The process of leaching silver ores with sodium hyposulphite is comparatively new, and published accounts of the details and losses of the process are as yet very few. The following account of a careful series of experiments to determine the actual loss in this process may therefore be acceptable to members of the Institute. The ore treated was highly calcareous, and the principal sulphide present was iron pyrites. Following is an analysis by Professor Price, of San Francisco, of the ore treated : Per cent. Silica,..........15.13 Sulphur,.........13.31 Arsenic,.......... 9.82 Iron............ 17.33 Alumina,..........1.35 Zinc,...........4.92 Lead,..........1.78 Carbonate of lime,..33.78 Magnesia,.......... 2.58 100.00 Ten tons were crushed dry with a 30 X 30 screen = 900 holes per square inch. In order to feel our way with this ore, two experimental or "pilot" charges were roasted. Pilot Charge No. 1. Treated 1000 pounds in a four-hearth reverberatory. 8.30 p.m.—Entered fourth hearth, remaining there one and onehalf hours; sulphur began to burn. 10 p.m.—Changed to third hearth; ore became red-hot half an hour after entering; the fireplace was kept almost destitute of fuel. 2.30 A.M.—Changed to second hearth. Charge continued, giving off a large quantity of sulphurous fume; the fireplace was kept dark.

Jan 1, 1884

By R. K. Dunham, A. N. Styler

The results of two studies into the effects of undermining offshore room and pillar workings by longwall faces are presented. The first study indicated no potential instability from undermining one level of room and pillar workings. On the basis of this it was decided to undermine two levels of room and pillar workings, again monitoring pillar stability. The results showed no signs of increased instability.

Jan 1, 1982

Restrictions on the use of zinc will be a thing off the past in a few months. Government allocations on the metal are also expected to go by the board. Concurrently, action is also expected in reference to lead allocations. Government stockpile goals for zinc have been reached. The International Union of Mine, Mill and Smelter Workers lent support to United Steel Worker demands and at the same time put in their own bid for a 25-cent an hour increase at a meeting held in Denver. While backing the USW, the IUMMSW charged the Steel Workers with membership raiding. Iron and steel companies producing about 92 pct of steel ingots in the United States, showed nearly a 13 pct decline in net profit during 1951, compared with the previous year, despite a 22 pct increase in their combined revenue. Federal income tax rose 61 pct, to more than 012 million. New iron ore reserves are being sought in Canada by Jones & Laughlin Steel Core, The company has acquired exploration options near Petersborough on the north shore of Lake Ontario in Durham, Northumberland and Frontenac Counties. *'A fourth property is southwest of Ottawa, in the Kingston, Ontario area..

Jan 1, 1952

Jan 1, 1946

By Carl Keuffel

THE manufacture of optical glass is a new industry in this country. In 1914, after the war started, the supply of optical glass from Europe was cut off, but as there was a fairly large stock of glass on hand, it was not until the end of 1915 that the optical instrument makers made serious efforts to produce their own glass. These early attempts were generally made by practical glass men and, due primarily to the fact that very little scientific help was used, the first attempts were unsuccessful. It was not until the whole problem was attacked by technically trained men who used advanced methods of research that good results were obtained. These researches proved that the accurate control of the temperature was a most important factor in the manufacture of optical glass. The early glass maker judged temperatures with his eyes; later, Seger cones were introduced into the furnace at various stages of the melt. Then radiation, indicating and recording pyrometers with rare-metal thermocouples were introduced. Now, in addition to these, an optical pyrometer every hour or so is sighted right into the pot and on the molten glass. Figs. 1 and 2 show how pyrometers are used to control the melt. InFig. 2, Y is the clay pot in which the batch is melted to glass within the furnace X. The rare-metal thermocouple S, protected by a clay tube, extends through the wall and about 4 in. into the furnace. This couple is connected to an indicator T and a recorder U so that a complete record of the furnace temperatures is obtained. The section of the curve ABCD, Fig. 1, shows how gradually and carefully the clay pot must be heated to get rid of moisture AB and during the calcining at CD. The stem of an expansion pyrometer R is extended through a hole in the door Z of the furnace and into the pot in order to more closely follow the temperatures of the clay pot itself during the burning process, that is from A to D. After the pot is calcined, the temperature can be rapidly raised to E (about 1430° C.); from E to F this temperature is much higher

Jan 9, 1919

By John F. Elliott, David L. Schroeder

SURFACE depletion can be a significant source of error in the use of the effusion method for determining the thermodynamic properties of alloys, particularly in the case of solid alloys.' However, as yet this problem has not been treated quantitatively by experimentalists in the field.1-3 The method necessitates diffusive transport of material out of the source alloy to obtain a relevant measurement. The general character of the system is shown in Fig. 1. The diffusive flux (nD) at the alloy surface is equal to the effusive flux (nE): where D is the diffusion coefficient of the diffusing substance, C is its concentration, X is the distance from the surface into the source alloy, p is the density of the alloy, and AS is the actual available surface of the alloy. The concentration of the diffusing substance at the surface is CS, and Here fE is the Clausing factor, AE is the area (sq cm) of the orifice, y is the activity coefficient of the substance in the alloy, PO is the vapor pressure (Torr) of the pure substance, M is the molecular weight of the effusing species, and T is the absolute temperature. The differential equation for diffusive transport in the source alloy is Fick's second law. Its solution is dependent on the geometry of the source alloy. Two boundary conditions must be established to obtain the proper solution, the first being Eq. [1], or its equivalent. The solutions for several important forms of the source alloy are considered below.

Jan 1, 1967

By Daniel T. Brian, O&apos

Exploration targets and results in the mining industry are commonly summarized in terms of tonnage and grade. Business appraisals require, as additional information, the expected profit or loss implied by the physical summay. The early incorporation of knowledge gained through financial analysis computations can provide a means for economically resolving many common exploration and development problems. Examples of such applications from the activities of exploration planning, reconnaissance, land acquisition, and development planning are presented. While prospecting for mineral deposits, geologists are frequently asked what they hope to find or have found. The response is usually descriptive, such as "50 million tons of 1% copper," and the economic implications are deferred until a capital investment decision is required. At that time, a financial analysis integrating the four analysis components is completed. These components are: 1) Tonnage and Average grade above cutoff grade 2) Capital and operating costs 3) Product value 4) Appropriate profit or loss accounting Close examination of these components reveals that there is no intrinsic reason for avoiding financial analyses at earlier stages in exploration, as long as the uncertainty of the estimate is realized. Tonnage and average grades are commonly estimated at early stages in exploration. For this component, the appropriate cutoff is the major uncertainty. Capital and operating costs are difficult to estimate before detailed quantitative information is available, but estimates useful for the types of applications pertinent to earlier exploration stages are possible. Product value estimates may or may not be difficult, depending on the pricing structure of the particular commodity. A simplified accounting procedure usually may be adopted without introducing any significant loss of validity. This paper describe some of the financial analysis applications which are pertinent during mineral exploration and deposit development. These applications lend additional insight during exploration planning, land acquisition, physical exploration, and development. The examples are oriented toward a hypothetical management investment policy which is based on a single criterion, a minimum 15% discounted cash flow rate of return. In reality, managements use multiple criteria. This simplification is convenient for purposes of presentation and does not invalidate the examples. Computers are useful, but not a requirement, for the applications described. The use of computers provides the results on a more timely basis at costs lower than equivalent manual computations. UNDERLYING PRINCIPLES AND ANALYSIS METHODS Data estimates are subject to uncertainty. The analyst may choose to assess this uncertainty by using one of two principles. Each principle has some advantages. The principle most commonly employed is "assumed certainty." Each financial analysis is based on one set of selected data, which may represent the average estimates, minimum expected conditions, etc. The critical data is identified by making successive calculations, varying the values used. Such studies, called sensitivity analyses, isolate the economic effect of various uncertainties, and guide the allocation of future efforts toward improving the overall accuracy of the analysis. A second principle, "assumed risk," examines the interactive effect of the current uncertainties by qualitatively assigning probability distributions to each data element. These probability distributions indicate the currently appraised chance that a given numerical value will prove to be true. The corresponding procedure, risk analysis, consists of processing many individual financial analyses, each analysis being based on randomly selected numerical values from the probabilistic distributions. The result is a numerical presentation of the uncertainty, but care must be exercised in the interpretation of results. The advantage of this procedure is the direct measurement of economic uncertainty caused by the interaction of uncertain estimates. Kennecott Copper Corp. has developed computer systems for accomplishing sensitivity and risk analyses.

Jan 1, 1970

Jan 1, 1934

By Harmon D. Nine

DISCONTINUITIES in the strain vs cycles to failure (S-N) fatigue curves have been reported for polycrystalline materials by Porter and Levy for copper,&apos; by Benham and Ford for mild steel,&apos; and by Williams and Stevens for 18/5 stainless steel.3 However, the considerable scatter of the points for polycrystalline materials have made a statistical analysis of the data necessary to confirm the discontinuities. By using oriented single crystals of high-purity material and low grown-in dislocation content, the reproducibility has been improved to a degree which makes statistical analysis unnecessary and clearly shows discontinuities in the S-N curves. A recent publication4 reports an abrupt change of slope in the S-N curve for ( 100) axially oriented copper single crystals fatigued in torsion. The reported discontinuities in the S-N curve, along with a different mode of failure in the two branches of the curve, have been interpreted as being due to two different amplitude-dependent mechanisms. Further work on copper single crystals of (111) axial orientation has now been completed which supports the existence of an amplitude-dependent change in the mechanism of fatigue. In the present study torsional-fatigue experiments were performed at room temperature in air on (111) axially oriented single crystals. The crystals were grown and prepared as reported in Ref. 4. Two different methods of growing the crystals also discussed in Ref. 4 produced crystals of two different perfections: Type I with dislocation density of >l06 per sq cm and Type I1 with dislocation density of <l05 per sq cm. In accordance with the accepted hypothesis that crystal flaws are primarily responsible for the scatter of fatigue lifetimes, particularly at low amplitudes, the values for the three lowest amplitudes for Type I crystal are believed to be uncertain. They are marked in braces in Fig. 1. On the other hand, at amplitudes above a surface shear strain (SSS) of *0.003, the data for both types of crystals are in agreement. Most remarkably the S-N curve for torsional fatigue of (111)-oriented single crystals is composed of three segments separated by rather large discontinuities, Fig. 1. Metallographic and X-ray measurements indicate that the lower branch corresponds to the low-amplitude (F) region of the (100) copper single-crystal results as discussed in Ref. 4, and the two upper branches correspond to the high-amplitude (H) region. The lower discontinuity in the (111) S-N curve and metallographic evidence give further support to the hypothesis that different mechanisms of failure operate for high and low strain amplitudes. Reference to the resolved shear stress diagram, Fig. 2, shows that the highest stressed systems in

Jan 1, 1965

By A. J. Miller, G. R. Brophy

The Grossmann principle1 for the calculation of hardenability of steel from composition is attractive because of its simplicity. It postulates that the hardenability of a steel for any particular grain size may be expressed in terms of an ideal critical diameter, which is the product of an ideal critical diameter for a "pure" iron-carbon base multiplied by a succession of factors for each element of composition contained, including the incidentals. It infers that the multiplying factor for a given quantity of an element is constant for all combinations of composition. Gross-mann has stated that in the great majority of cases the experimental values of hardenability are found to be well within 10 per cent of the calculated values. The validity of the scheme has been confirmed in principle by Crafts and Lamont2,3 and by Kramer et al.4 Their results differ from the original in the magnitude of the effect of some elements but, since they accepted the product concept and followed its direction, it is to be ex~ected that similar results would be obtained. Crafts and Lamont, in their second Paper, recognized that the factor relations for manganese and nickel were not continuously linear, but beyond certain critical amounts increase sharply. Austin, Van Note and Prater6 demonstrated nonlinear relations between hardenability and alloy contents. Their curves for chromium, silicon, manganese and nickel were all convex upward to show decreasing incremental effects. They concluded that Grossmann&apos;s factors under-evaluate the hardening effect of low percentage additions of these elements, and overevaluate the larger additions. More recently W. Stevens has found that the factor method fails when applied to complex steels containing two or three principal alloying elements other than carbon. Multiplying factors derived from his results bear a complex relation to composition and are not constant for a given amount of an element as the base composition varies. C. A. Liedholm7 found that, using either the Grossmann or the Crafts-Lamont multiplying factor values, not only were the relative hardenabilities of two heats of S.A.E. 6130 chromium-vanadium steel

Jan 1, 1947