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By Kent E. McElhattan

The selection of efficiency machinery for an underground mining system is a highly skilled art. Modern techniques of mining, based on sound engineering principles, increase the probability of success. These techniques alone, however, will not guarantee maximum productivity. Human judgement, based on experience with mineral seams and geological conditions, remains the single most important input of the decision-making techniques in selecting high production equipment. The myth of a "Scientific Selection Factor" is absurd. The belief that such a factor exists can waste the time and resources of mining management. Until now, mineral extraction from the original desposit has defied all attempts to systematize the knowledge. Computerized programs are excellent for solving underground transportation and ventilation problems. The variables can be defined by mathe¬matical techniques in this type of problem. By the same, token, "Trial and Error" is not an acceptable method in today's technology-minded world. The candid truth of the matter is that practically nothing is known of the phenomenon of extracting a mineral from the solid. Likewise, local conditions make it nearly impossible to predict accurately the reaction of surrounding strata after the mineral has been removed. The unpredictability of the environment resulting from extracting minerals underground will remain a challenge to mining engineers for many years. In fact, we are barely beyond the trial and error stage at this point in time.

Jan 1, 1969

By R. V. Colligan

[CONTENTS PACE Educating and Training Economic Geologists of the Future. By C. H. BEHRE, JR. (TP 2278, Min. Tech., Nov. 1948. Discussions by R. V. COLLIGAN and EVAN JUST) ....... I Mercury Industry in Italy. By EDWIN B. ECKEL. (TP 2292, Min. Tech., Jan. 1948. Discussion .............................. by C. N. SCHUETTE) 3 Chert in the Kingsport Formation at Mascot, Tennessee. By ARTHUR T. ALLEN. (TP 2299, ............... Min. Tech., Jan. 1948. Discussion by M. M. BUTLER) 5 Wall Rock Alteration at Butte, Montana. By RENO H. SALES and CHARLES MEYER. (TP 2400, Min. Tech., May 1948. Djscussions by C. D. HULIN, W. D. JOHNSTON, JR., and L. C. ................................... GRATON) 5] Educating and Training Economic Geologists of the Future R. V. COLLIGAN*-I can best illustrate my opinions by drafting another five year plan (Table 2). This plan is set up following the same stipulations outlined by Dr. Behre, namely: (I) the student is preparing himself for commercial work as a mining geologist; (2) he is attending an institution with a sufficiently broad curriculum (that is, engineering school and mining school as well as liberal arts college) to furnish the courses listed; and (3) he is not planning to continue his studies through to a doctor's degree before going into commercial work. A comparison of my study plan (Table 2) and that submitted by Dr. Behre (Table I) will at once point up the basic similarity, due to the obvious fact that there are so many essential courses which must be included in any outline of study. However, a more detailed analysis will show up certain differences, which, in fact, are only certain refinements on Dr. Behre's program. These I plan to discuss in order of their importance. The first and most important change is the addition of 12 hr of optional subjects, making a total of 24 hr of optional subjects as against a total of 12 hr under Dr. Behre's schedule. This of course entails the elimination of certain courses, which I shall discuss later. However, I wish to make it clear that I suggest eliminating these courses not because I feel that they are unnecessary, but rather because I feel the optional courses are more necessary to the complete education of the individual. I appreciate that Dr. Behre recognizes the importance of the cultural side of education, but I take issue with his thesis that the student will get it without credit and in his spare time. I do not think that the average college student, and certainly not the college freshman, is mature enough to know what he needs and where to get it in his spare time. I think it must be "spoon-fed"; he must be oriented through specific courses. University life (or should I say "college life") is too full of athletics, fraternity activities, dances, "bull sessions," and countless other enjoyable distractions, all of which contribute to the "full man." I fail to see how the average young American male can possibly sandwich in a necessary complement of "cultural activities" in his spare time. Since these latter activities do not fall within the pattern set by the "group," and show less promise of immediate return in enjoyment, or increased social status on the campus, they are bound to suffer in competition with the more popular, "group" activities. No doubt much of the criticism levelled against arts colleges, namely, that the cultural courses are useless, is well taken, for the culture

Jan 1, 1947

By A. Bauer, P. Calder, N. H. Carr, G. R. Harris

Smallwood mine is part of the Iron Ore Company of Canada's Carol Lake operation and is situated in Labrador, 240 miles north of Sept-Iles, Quebec. Last year, 15 million tons of crude ore were crushed to yield 6.3 million tons of concentrate and pellets. This year the figures will be 17 million of crude and 7 ¼ million tons of concentrate and pellets, which is the full plant capacity. Carol Lake ores consist primarily of specularite and magnetite mixed with quartz. Since both rotary and jet piercing drills are used, it is often desirable in planning to know in which regions of the orebody, or new orebodies, a particular drill will be most economic. This makes it necessary to establish a correlation between drillability and pierceability and some physical rock property. For the rotary drills a good correlation was found with penetration rate and grinding factor index. The jet piercers were found to have a reciprocal relationship in the sense that the best rotary ground was the worst jet ground and vice versa. It is also indicated how an economic comparison could be made using these penetration rate versus grinding factor index curves, the hole size distribution curves for single pass and chambered holes, and the mine distribution curve for grinding factor index.

Jan 9, 1965

By James P. Connell

The Berkeley Pit of The Anaconda Company is located on the southeast slope of the Butte Hill, the legendary "Richest Hill on Earth," and is one of the largest pit operations in the world completely dependent on truck haulage. Through October 31, 1968, the Berkeley stripping and mining operations have moved more than 442,589,000 tons of material. Present scheduled production is at the rate of 260,000 tons per day, with a record quantity of 306,900 tons having been hauled on September 23, 1968. Although the Berkeley Pit has been in production only a little more than ten years, it has been the proving ground for many of the presently used large trucks. Beginning with the original R. G. LeTourneau 75-ton electric truck in 1960, Unit Rig 85- and 100-ton electric drives, Haulpak 65- and 105-ton electric drives, and Caterpillar 100-ton electric drives have all been tested under production conditions. In addition, engine development has kept pace with both 1000-hp diesel and 1100-hp gas turbine engines now under test. As the size of the Berkeley operation has grown, the truck fleet has changed in size and appearance in order to maintain economic mining costs. The original fleet consisted of forty-three 36-ton trucks with conventional mechanical drives. The present fleet is made up of eighty-nine trucks: nineteen 85-ton Unit Rig electrics with 700-hp diesel engines; sixty-nine 100-ton Unit Rig electrics with either 700- or 1000-hp diesel engines; and one 100-ton Unit Rig electric with an 1100-hp gas turbine engine.

Jan 1, 1969

In a future world of 8.5 billion people in 2035, the Energy Information Administration's (EIA) projected 50% increase in energy consumption will require true "all of the above" energy resource use from oil, gas, renewables, nuclear, and coal. In particular, coal will continue to be the world's energy cornerstone, providing more incremental energy over that same time period than any other single fuel. Coal has long been a centerpiece of a low-cost, high-reliability electricity grid. Today there are 1.3 billion people across the globe without access to electricity and 2.7 billion people who do not have clean cooking facilities. The problem is spread across the developing world, but it is particularly severe in sub-Saharan Africa and developing Asia, which together account for 95% of people in energy poverty. Without a commitment to achieve universal energy access it has been estimated that by 2030, there will be an additional 1.5 million premature deaths per year caused by household pollution from burning wood and dung and through a lack of access to clean water, basic sanitation and healthcare. Modern energy sources are essential to meeting these challenges.

Jan 1, 2012

By Hamid-Reza Manouchehri

"The triboelectric charge attributes of feldspar, quartz and wollastonite minerals, after contacting different triboecharging medium made of different materials, were considered. Their charge acquisitions by different size fractions of minerals were monitored and accordingly their energetic work function values were estimated. Moreover the separation behaviours of these minerals through the electric field of a laboratory free falling separator were determined and the effects of some chemical reagents on separation their separation characteristics were studied.Finally an attempt was made to translate the findings from single mineral systems to a complex silicate ore, containing quartz, feldspars, wollastonite and some other silicates. The results show favourable prospect to apply the triboelectric separation technique for beneficiation such a complex raw material."

Jan 1, 2003

By J. M. Skeaff

"The main solution, ore and residue pulp streams in the Rio Algom Quirke I uranium mill at Elliot Lake have been sampled and analyzed for radium-226. Analysis of the ore and leached residues indicates that Ra-226 dissolves and precipitates within the first pachuca tank. A maximum of approximately 0.2% of the Ra-226 in the ore remains in solution during leaching.IntroductionConcern over the acid drainage and radionuclide dissolution problems associated with uranium tailings disposal sites in Canada has prompted investigation into methods for improving current uranium processing practice.Present commercial practice usually involves leaching of the uranium ore with sulphuric acid, ion-exchange separation of the uranyl sulphate complex from the leach liquor and"" precipitation of the uranium as yellowcake. Daughter products of U-238, such as Th-230, Pb-21O and Ra-226 remain with the tailings and undergo long-term dissolution.Table I summarizes the probable behaviour of the radionuclides during milling. The concern here is with Ra-226, because it will deposit in the bones if ingested and is ""thus considered a serious health hazard(1), Similarly, Po-218 and Bi-214, which are daughter products of Rn-222, can be retained in the lungs and are considered to be the principal sources of radiation dosage(2) arising from the inhalation of Rn-222. Previous investigations(3-9l indicate or imply that Ra-226 undergoes redistribution during milling. However, detailed published information on the behaviour of Ra-226 in the uranium milling process appears to be lacking. A knowledge of the behaviour of Ra-226 in uranium mills, particularly during leaching, could lead to improved methods for its control.This paper reports the occurrence of Ra-226 in the Rio Algom mill. The main objectives of the study were to determine (1) the distribution of Ra-226 within the solids, (2) at what point, and how rapidly, redistribution occurs and (3) whether there are high concentrations of Ra-226 in solution."

Jan 1, 1981

By G. Richards

Mines are facing fresh challenges over how they deal with the huge quantities of water consumed. industry analyst Frost and Sullivan, demand for treatment equipment and services alone is expected to be worth US$3.6bn by 2016, while a report by consultancy Bluefield Research estimates that the total mine water market - which includes water infrastructure such as reservoirs, pipelines and dewatering systems as well as the equipment and services - will be worth US$17bn by the end of 2019. Methods of water decontamination are described.

May 1, 2015

By Timothy Batchler

"Standing roof supports help to provide a stable working environment in coal mine gateroads. NIOSH participates in the development of these support systems by conducting full-scale tests in their Mine Roof Simulator. These tests have established the performance characteristics of every coal mine support system currently in use in the United States. Through these tests, mine operators and regulatory officials have acquired a fundamental understanding of the various types of support performance that guides the assessment and use of these support systems. However, some little known factors that influence support behavior can lead to misconceptions and, perhaps, a poor assessment of support behavior at times. This paper highlights several of these factors and discusses their significance. The paper also examines a current longwall tailgate support and discusses the inefficiency with this approach. Finally, the NIOSH Mine Roof Simulator (MRS) is the world’s most powerful load frame built specifically to test full-scale roof supports, including longwall shields. are addressed in this paper to provide a more in-depth assessment of the limitations of the MRS and what the MRS testing protocol is designed to do. INTRODUCTION Over the years, considerable research has been conducted to develop standing support technologies and to evaluate their performance characteristics. The load and displacement characteristics of the standing supports have been determined from full-scale testing conducted using the National Institute for Occupational Safety and Health (NIOSH) Mine Roof Simulator (MRS) (Barczak and Tadolini, 2008) located in Bruceton, PA. Performance traits, installation patterns, and ground responses are observed in various geological and mining conditions and are evaluated to determine the support performance in the field (Dolinar, 2010; Campoli, 2015; Zhang et al., 2012). Despite widespread use of standing supports, not every aspect of their performance and resulting ground support capability are always well understood. This paper discusses 10 factors, several of which are surprising, that impact standing support performance."

Jan 1, 2017

By R. Kobialka

In the article results of experiments over jaws? linings in jaw crushers with different shaping of working surface were presented. Following sets of jaws were under investigation: immobile plain jaw and moving jaw with grooving surface. Grooving jaws have groves with circular, triangular and trapezoid cross section. In order to evaluate efficiency of comminution both the grain composition of product and the content of irregular grains were determined, as well as the size of crushing forces and process efficiency were measured. For the combination: plain jaw with grooved one, a good results were obtained as regards the grain composition of product and the content of irregular grains. Crushing forces were higher at crushing with mixed types of jaws (the one plain, the second grooved), in comparison to crushing with using both grooved jaws. Efficiency of the process was definitely higher for mixed jaws.

Jan 1, 2014

By C Agreda

The Cushion Blasting Technique applied to solve the high risk case history represented by a 10,704 TM rock locate at 120 M from the hydroelectrical plants of 350 KV each, is described, analyzed and discussed. The generation and distribution of 700 KV produced by two hydroelectrical plants must not be interrupted by any reason, because the 26 district of the province of cajatambo, of the Lima department; would not have electrical power. The search of the best alternative and methodology, the drilling and blasting pattern calculations, charge design and loading, connections and initiations of the 50 blasts are described, analyzed and discussed. Finally, the excellent results from a technical, economical, enviromental and safety point of view of the 50 primary blasts are discussed and emphasized.

Jan 1, 2005

C. H. GIBBS,* Salt Lake City, Utah (written discussion?).-The development of the coke industry in Utah had a somewhat checkered career for the first 50 years of its existence. About 1851 the iron-ore deposits of the Iron Springs and Iron Mountain mining districts, Iron County, Utah, were discovered. Obtaining of iron for any purpose at the time involved its shipment from the Mississippi River to Utah, by ox-team. The result was that the pioneers endeavored to establish an iron-ore smelting plant at what was known as Iron City, near Iron Mountain, in Iron County. Bishop Taylor, who headed this enterprise, endeavored to obtain coal suitable for coking from the Cretaceous coal measures immediately east of Cedar City. A few small bee-hive coke ovens were built and lump coal was coked in these ovens; or, more properly speaking, the volatile matter of the lump coal was driven off, leaving a carbonized material that retained the lump shape, although it was extremely, friable. This coke was promptly found to be unsuitable for iron smelting, not only clue to its extreme weakness under smelting load, but also because of the fact that it carried about 5 per cent. sulfur. Bishop Taylor made a very thorough and exhaustive effort, covering a considerable period of years, to locate suitable coking coal in Southwestern Utah. His efforts failed, and in 1902 the iron-ore property acquired by him and associates was sold to the Colorado Fuel and Iron Co. It is of interest to note in this connection that the iron-ore deposits of Iron County at present are the largest known undeveloped iron-ore fields on the North American continent. It is safe to say that there is at least one hundred million tons of 55-per cent. ore actually in sight. In 1878, coal-mining operations were begun at Connellsville, in Huntington Canyon, Emery County. Ten 8-ft. bee-hive ovens-were constructed, and lump coal was carbonized for use in the Salt Lake valley smelters. The product was somewhat better than that obtained in Iron County, but was still of very inferior quality. It had to be hauled a distance of 140 miles by wagon to the two small smelters then operating in Salt Lake valley. These ovens operated only a very short time. The next move toward obtaining a coking coal was in 1889 when the Pleasant Valley Coal Co. began operations in the Castle Gate district. In 1890, eighty 8-ft. bee-hive ovens were constructed, and the product. was used until 1900 in all the smelters in Utah. During this period, 124 additional. ovens were constructed, making a total of 204 bee-hive ovens operating at Castle Gate.

Jan 11, 1918

By Rebecca Hardy

The escalating demand for coal, in addition to the steady depletion of reserves, has produced increasingly difficult mining conditions for coal mining companies within the United States, resulting in mining above or below previously mined areas. The safe and productive extraction of coal in a multiple seam environment requires specific design technology for effective mine planning. Presently, one of the most useful design approaches for multiple-seam feasibility analysis is using numerical modeling techniques. Therefore, numerical modeling programs LaModel 2.1 and Lam2D were used to determine the feasibility of mining the Herrin (No. 6) coal seam over an existing room-and-pillar mine in the Springfield (No. 5) coal seam in the Illinois Basin.

Jan 1, 2006

By C. J. B. Dreyer

In terms of resources of amphibole asbestos only South Africa can be considered. There are only two asbestos producing fields, one in the Northern Cape Province producing only crocidolite and one in the Eastern Transvaal producing only amosite. The banded ironstone sequence in which amphibole asbestos occurs is discussed, and the genesis of the fibre is briefly reviewed. The properties and characteristics of amphibole asbestos are discussed and compared to those of chrysotile. Approximately 300,000 tonnes of amosite and crocidolite are produced annually. Crocidolite has a potential for a fivefold increase of production, which could be sustained beyond the year 2000. An estimate of the resources of the various producing fields in South Africa is made. Mining methods are reviewed and evaluation techniques discussed.

Jan 1, 1978

By Robin M. Forbes. Jones, Suhas V. Patankar, Ramesh S. Minisandram, Jr. Carter, Kanchan M. Kelkar

"The nucleated casting process currently under development has the potential for production of Ni-base superalloy preforms that possess superior microstructure to product made by conventional casting processes, primarily for gas turbine applications. In this process, electroslag remelted (ESR) clean (i.e., free of ceramic inclusions) molten metal is conveyed via a watercooled copper Cold-walled Induction Guide (CIG) to a gas atomizer. The spray of clean metal droplets is then directly cast into a water-cooled crucible for ingot production. The microstructure of the resulting ingot preform evolves within the length scale of the individual droplets and is a function of the thermal state of the incoming metal droplets. This, in turn, depends on particle size, flight time and heat exchange with the gas phase.In the present study, computational models is developed for the analysis of the flow and heat transfer in the gas-metal spray system under axisymmetric and steady-state conditions. The gasphase flow is analyzed using an Eulerian framework and turbulent mixing within the gas phase is modeled using the two-equation k-e model. The dynamics of the metal particles is analyzed using a Lagrangian framework that involves calculation of the trajectories of the metal droplets. A two-way coupling is considered whereby the transport and heat transfer in the gas and the metal phases influence each other.The analysis is developed at two levels. The spray model performs a detailed calculation of the spray dynamics in the vicinity of the spray and is intended for predicting the temperature and mass flux distributions of the metal spray depositing into the mold. The chamber model enables prediction of gas flow and motion of metal particles in the entire spray chamber."

Jan 1, 2004

By Chas. F. Jackson

The mining literature is replete with descriptions of methods and costs of operation at producing mines. To day the mine manager can find published information bearing upon almost any problem with which he may be faced. From this literature he can familiarize himself with methods employed by otter operators for coping with problems similar to his own, under more or less parallel conditions. Transaction of mining societies, publications of the U. S. Bureau of Mines, technical journals, and handbooks all afford valuable information dealing with operating methods and costs, Very little has been published, however, regarding methods and costs of equipping and developing new properties and bringing them to tae productive stage. There may be some question in the minds of many as to the value of papers on this subject, due to the great variety of conditions encountered. No two prospects are alike. Obviously, it is impossible to forecast what expenditure will be required to develop a mine from a raw prospect or even to predict whether the prospect can be developed into a productive mine.

Jan 1, 1933

By H. J. Rose

Graphic methods have long been used to advantage in dealing with diverse phases of fuel technology and research. Not only are graphs convenient for presenting data and making calculations, but they are invaluable for deriving generalizations from a mass of data. This is particularly true when relationships are obscure and numerical correlation is poor. This paper describes a new form of graph, the Multibasic Coal Chart, which has been developed to facilitate the study and comparison of coals of all ranks from peat to anthracite on any moisture and purity basis. This type of chart is of unique value for coal classification purposes, since it permits a direct visual comparison of the results obtained when coals are classified by the various systems which have been proposed. Coals are highly variable in character as a result of wide differenees in original vegetal ingredients, degree of metamorphism, and nature and amount of associated impurities. For nearly 100 years, attempts have been made to devise a satisfactory method of classification, and many tables, formulas, ratios and graphs have been suggested. Many of the suggested systems possess considerable merit and have found a limited use, thus promoting a better understanding of coal. However, objections have been raised against each system, and none has received general adoption. When the various systems of classification are compared, it is found that there is an apparently almost hopeless confusion due to: 1. Serious lack of agreement as to the proper moisture and purity basis on which to classify coal. More than ten different bases have been proposed, each of which requires complete recalculat.ion of the analysis data used. 2. Lack of agreement as to what chemical and physical properties are most important and best to use for classification purposes. There is too little knowledge of the degree to which these properties can be correlated.

Jan 1, 1930

By Hugh R. Wilson

Echo Bay's Waste Management Program for its Lupin Mine was developed in response to the terms and conditions of the water license issued to the mine in 1981 by the Northwest Territories Water Board. The gold mine, located about 80 km (50 miles) south of the Arctic Circle, commenced production in 1982. The Waste Management Program was based originally on the total containment concept, contingent on future treatability testwork results indicating the best treatment method to ensure pond discharges would be in compliance with stated Northwest Territories Water Board discharge criteria. To assess the various treatment technologies, an investigative program was established to determine the most effective means for treating the tailings pond water. In the course of milling, about 850,000 m3 (11 million cu yd) of tailings are produced annually that require appropriate management to protect the environment. This annual tailings stream consists of about 175,000 m3 (229,000 cu yd) of solids and 675,000 m3 (883,500 cu yd) of water. Following the completion of the required waste management studies, a two-ponds-in-series concept of tailings impoundment was developed. To attain this concept, the tailings impoundment area would require modification and construction to enable the use of such a system.

Jan 1, 1991

By M. E. Ramos Rada

Mexicana de Cobre, which is part of Grupo Mexico, carried out studies for the construction of a copper refinery in the La Caridad Metallurgical Complex located in Nacozari, in the state of Sonora, Mexico. After the studies were concluded, the decision was made to construct a 180,000 t/y refinery using the state of the art permanent cathode Kidd Process. The basic engineering was developed by Fluor Daniel and the detail engineering and the construction were carried out in record time by the Mexican company Bufete Industrial. During the construction phase, Grupo Mexico decided to expand the refinery, and actions were taken to increase its capacity by an additional 120,000 t/y; the final result was a refinery capable of producing 300,000 tonnes of grade A cathode per year. Construction began in January 1996, and the operation of the first stage began on July 1, 1997. The operation of the second stage commenced on January 7, 1998. The capacity of the first stage was reached in November, 1997 and the total capacity of the refinery was achieved in May, 1998. This presentation describes the process and equipment installed in the refinery, the steps leading to the start-up, the operation and the results obtained during the first two years, the handling of anodes with high impurity contents, and the problems confronted and the way they have been solved. It also includes personnel productivity, the control parameters and the most relevant data on the operation of the process.

Jan 1, 1999

Australia has a long history of underground mining. Even withadvances in open cut mining equipment, techniques andeconomics, many orebodies are still best mined by undergroundmeans. In addition, modern exploration tools are æuncoveringÆorebodies that are at increasing depths. South African mines arecurrently producing from below 3 km, and developing down to5 km depths û it is likely that Australian mines will also becomemuch deeper over the next 20 years. One of the most significanttechnical challenges in deep mines is the problem of heat.Community expectations and legislated standards continue todrive operations towards improving the working conditions inmines. The hazards and costs associated with chronic hotworking conditions (heat illness, poor safety, poor productivity,higher operating costs and poor morale) are also becomingincreasingly recognised (Brake, Donoghue and Bates, 1998). Theexposure of miners to many other occupational hazards has beenreduced over the past 50 years. However, despite air-conditionedcabins greatly reducing the heat stress on mobile plant operators,there are still many Australian mine workers subject to levels ofthermal stress that existed a century ago. There are severalreasons for this, including a frequently-poor understanding of thephysiology of working in heat by mine management, no agreedmining code of practice for working in heat, the lack of a robust,practical-sized instrument to measure heat stress, the costpressures on the industry and, to some extent, deep-seatedtraditional management and worker practices. Howeversignificant progress has been made in many of these areas (Brakeand Bates, in press), with the net result that there is likely to be a trend towards installation of refrigeration of some form in manyAustralian mines in the future. This will add directly to the costof operation, but will also have direct and indirect benefits,including cost benefits. It should also be noted that Australia isnot at the forefront of adopting practices to manage temperaturesin the workplace: South African metal mines usually haverefrigerated cooling, and Canadian mines spend large sums onheating, with heating costs (averaged over a full year) of up to$A1 per tonne mined (Bandopadhyay et al, 1997). The history of mine refrigeration dates back to 1919 when thefirst plant was installed at Morro Velho, Brazil. By 1965, the totalinstalled capacity (worldwide) reached about 100 MW(R)i. Since 1965 the growth in mine refrigeration capacity has beenexponential, with a doubling every six or seven years (Howes andNixon, 1997). South Africa is by far the largest user of minerefrigeration, with over 300 refrigeration machines installed. This paper discusses the key design issues associated with theapplication of refrigeration in underground metal or coal mines.Whilst the emphasis is on large, surface plants, small, surface orunderground refrigeration plants can also be very effective in thecorrect application and many of the principles of design andoperation are the same.

Jan 1, 2001