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"A 3-dimensional finite element model for stress/stability analysis of rock excavations in underground mines is presented. Developed for use on personal computer under OS/2 operating system, the model employs the 8-node isoparametric brick element and accounts for such loading conditions as in situ stresses and gravity loading of the rock mass. In addition, modelling of backfill in mine stopes as in situ stress-free material is incorporated. Material failure is assessed by Mohr-Coulomb or Hoek-Brown failure criterion. A mine design example is presented to illustrate the potential use of the model as a tool for stope design.IntroductionNumerical modelling of mine structures has become a vital tool for mine design in recent years. The need to maximize ore extraction ratio and to reach deeper mineral deposits underground has led the mining industry to employ numerical methods of analysis to undertake complex ground control studies in order to better understand the ground response to mining excavations and to evaluate the ground support requirements. Thanks to the rapid developments in computer technology, it is now possible to perform very comprehensive analyses including, but not limited to, 3-dimensional, elasto-plastic, or large deformation or time dependent nonlinear analyses on personal computer.During the past ten years or so, many researchers undertook 3-D finite element analyses of rock mechanics problems in mining engineering. The following is only a sample review. For example, Chan'!' used three-dimensional finite elements to study the mechanical response of jointed granite during shaft sinking at the Canadian Underground Research Laboratory. Wang et al.(2) performed 2-D and 3-D finite element analyses of room-and-pillar mining system with flat and rolling coal seams. Thatejatu used three-dimensional finite element method to examine the problem of branching tunnels. Dolezalovaw used three-dimensional finite elements for the analysis of tunnel-face advance with partial excavation as well as full-face excavation in combination with rein for cement of the face by long anchors. Peili (5) used three-dimensional finite elements for the simulation of rock-liner interaction near the tunnel face."

Jan 1, 1992

By N. E. Yasitli

There is a considerable amount of lignite reserve in the form of thick seams in Turkey. It is rather complicated to predict the characteristics of strata response to mining operation in thick seams. However, a comprehensive evaluation of ground behaviour is a prerequisite for maintaining an efficient production, especially when top coal winning by means of caving behind the face is applied. A comprehensive modelling of deformations and induced stresses is vital for the selection of optimum production strategy. In this study, numerical modelling and analysis of a longwall panel at Omerler underground coalmine have been carried out by using the software called FLAC3D developed based on the finite difference technique. Firstly, a 3-D numerical model of the M3 panel has been prepared. Secondly, induced stresses formed around the longwall face have been determined as a function of face advance where the face was located at the bottom of thick coal-seam. Results obtained from modelling studies have revealed that the front abutment vertical stress was maximum at 7 metres in front of the face and magnitude of front abutment stress was found to increase up to a distance of 200 metres away from the face start line. As the face was further advanced after 200 m from the face start line, there was not any significant change in the characteristics of front abutment stresses. Results of numerical analysis of the panel were in good agreement with in situ observations.

Jan 1, 2005

By Ian Martin

A precious metals refinery’s switch to personal computer-based, three-dimensional piping design saved many hours in the design of a South African precious metals refinery. Bateman Minerals and Industrial provided engineering, procurement and construction management services for Impala Platinum Limited-Refineries’ new $60 million refinery in Springs, South Africa. This project is one of the largest platinum refineries in the world. Bateman evaluated a new design method during this project that involved developing a three-dimensional model for the project. The new method saved time by reducing the man-hours required to generate complete project documentation, including plans, sections, isometrics and material takeoffs. The new method also saved design and construction time by allowing designers to detect clashes before construction began.

Jan 1, 2000

By Y. H. Wang, S. Kou

"Three-dimensional weld pool convection was computer simulated using dimensionless variables. The electromagnetic force, the buoyancy force and the surface tension gradient on the pool surface were treated through the use of the dimensionless electromagnetic force, the Grashof number and the Marangoni number. Other typical dimensionless numbers such as the Prandtl number and the Peclet number were also used. The calculated and experimentally observed fusion boundaries were compared. The convection patterns were shown and the effect of the Marangoni number was demonstrated. IntroductionSeveral weld pool convection models have been developed by Oreper et al. (1,2), Chan et al. (3) and Kou et al. (4). These models describe two dimensional convection in stationary weld pools in a semi-infinite workpiece. Since the vast majority of arc welding practices involve a moving heat source and weld pool, and the workpieces are finite in thickness rather than semi -infinite, a 3-D convection model for a moving heat source and a workpiece of finite thickness is expected to be much more useful.Weld pool convection can strongly affect the structure and properties of the resultant welds. Variations in weld characteristics which are likely to occur from changes in weld pool convection are: weld penetration, macrosegregation, gas porosity, solidification structure, undercutting and surface smoothness. Apparently, the quantitative understanding of convection and heat flow in weld pools is of considerable practical interest. Mathematical models describing convection and heat flow in weld pools are essential, not only because of the quantitative understanding they provide, but also because of the difficulties associated with the experimental measurements of weld pool convection. These difficulties are mainly due to the fact that only surface flow, rather than the overall convection pattern in the weld pool, can be observed. In fact, due to arc glow even the observation of surface flow can be rather inconvenient."

Jan 1, 1986

By Mahmoud Sepehrmanesh, Verya Nasri, Maziar Partovi

"This paper presents an assessment of the impact of tunneling and its associated risks on pile foundations located in the influence zone of tunneling operation. Tunneling in proximity of pile foundations introduces deformations in piles and in turn induces additional axial and bending forces. In modern mechanized tunneling, ground convergence is controlled through balancing the earth pressure at the tunnel face as well as applying pressurized bentonite through the shield. Reducing ground deformation can consequently lower the additional deformations and forces developed in the pile foundation and lessen the associated construction risk. In this paper, comprehensive detailed finite element modeling was performed to quantify the effect of the different parameters on induced forces in piles. Finite element models took into account the nonlinear behavior of soil and pile-soil interface. The modeling results are of practical importance in risk evaluation of tunneling in vicinity of pile foundations. INTRODUCTION Tunneling operation in congested urban areas becomes more frequent as demand for further utilizing underground spaces grows. In urban settings, it is not uncommon for tunnel designers to plan a tunnel route in close proximity to other structures to satisfy other competing objectives like raising the alignment to reduce excavation volume. Setting the alignment close to existing structures increases the risk involved in the project. It is the responsibility of the designer to thoroughly identify, assess, and mitigate all design risks involved. In this paper, we focus on the aspects involved in tunnel construction in proximity to existing pile foundations. Tunnel operations introduce deformation in the soil mass. Consequently, a pile located within deformation zone experiences extra forces as a result of the imposed deformation. The developed forces and bending moments can be in orders comparable with the pile capacity depending on the relative horizontal proximity of the tunnel and the relative depth of tunnel with respect to the pile length."

Jan 1, 2016

There are many inherent risks in creating a mine plan for a new ore zone in an underground mine; one of such risks is the redistribution of stresses that could be a cause of instability. Using numerical modelling tools, it is possible to model the planned stope extraction sequence and evaluate the influence of mining induced stresses on the stability of remnant pillars, and use this information to remedy potential setbacks. This paper demonstrates this approach through a case study of the short-term mine plan of the Lapa mine of Agnico Eagle Mines Ltd., an underground gold mining operation near Val d?Or. Three-dimensional boundary element modelling is used to compute the stresses induced by the stope extraction sequence as planned with a longitudinal retreat mining method. The proposed methodology can be generalized to other mines that require an understanding of the stress concentrations at the pre-feasibility stage of mine design.

May 1, 2009

By Gilmore R. Tostengard

The advent of inexpensive computers has opened vast opportunities for improved planning and control of capital projects. The mining and mineral processing industries have welcomed the opportunity, and new and improved quantitative management techniques have abounded. This chapter will discuss commonly used computer applications for economic justification of the project, preparation of the cost estimate, planning the work schedule, monitoring work progress, and control of costs and productivity. Finally, there is a review of the degree to which the industry uses these applications. Our experience suggests that while we in the industry have been quick to adopt the new techniques, the quality of our input data has not always kept pace. During the next decade, our push should be toward improving the quality of the basic data and assumptions so that we can fully benefit from the sophisticated techniques. The GIGO (garbage in, garbage out) principle is a wellworn cliche, but it is especially valid here. One of the keys to getting good input is commitment. Unless the managers who are to use or benefit from the system are committed to it, the effort will fail. They must be com- mitted to the underlying principles of planning and control sufficiently to expend their time and resources on them; planning should be especially given emphasis. They can't be too busy to plan.

Jan 1, 1979

By D. P. Plute

The mechanization of the materials management function must contribute to the overall goal of optimization of profits. A computerized system contributes to the profitability of the company by saving more than it costs to operate. Design and implementation of the sys- tem must respond to the needs of users, the operating environment of the property, and must support the objectives of materials management. Three basic functions interact within the scope of materials management. They are inventory control, purchasing, and warehousing which have the following objectives: 1) Inventory control-to request materials in a timely manner and in quantities that provide the best level of support to users at the lowest cost. 2) Purchasing-to purchase requested materials and services at the required time and at the lowest cost. 3) Warehousing-to efficiently receive, store, and issue materials and to prepare accurate transaction documents for the activities. The development of the mechanized materials management system will require a plan and objective analysis by management and system users of system requirements. A typical plan would include: 1) System Design Objectives-the development of objectives that support mechanization of the materials management function. 2) System Characteristics and Concepts- the development of key system concepts and characteristics, which identify the needs of materials management. 3) System Inventory Item Classification- development and assignment of inventory category codes to inventory items. 4) System Order Decision Rules-the development of decision rules and forecasting techniques to minimize the inventory investment and to provide acceptable support levels. 5) System Report Structure-the development of a report structure to support the goals and objectives of materials management. 6) System Report Design-the development and design of reports for effective utilization of the mechanized system.

Jan 1, 1979

By Victor F. Hollister

Skam deposits considered as porphyry copper deposits have been classified into three basic prospecting models: (I) the skam deposit associated with a mineralized intrusive (Pima-Mission), (2) the deposit associated with a barren igneous stock (Ertsberg), and (3) mineralized rock that seems to have no clear association with apluton (Phoenix). Pima-Mission, Christmas, and many other copper-bearing skarns developed in carbonate sequences near mineralized intrusives form an important part of the deposit. Historically, copper derived from the mineralized intrusion accounts for less than half of the metal produced by most porphyry mines, as most mineralization occurs in the intruded rocks. Skam mineralization is an important part of wall-rock metal deposition, because carbonate sequences are preferentially replaced by sulfide and skarn minerals. Exploration for skam mineralization is an important phase of porphyry copper exploration. Impure carbonate beds can become better host rocks for skam deposits than pure carbonates, and these in particular should be included in porphyry-exploration programs if the impure strata are cut by the stock. Skam deposits can also form near stocks that are barren of sulfide. In this model, the two best ore guides are strata favorable for mineralization (usually impure carbonate beds) and the intrusive contact. Faults can also act as important ore controls. Some skarn deposits form that have no clear genetic connection with a stock, although intrusive rocks are known in the district. In such cases, the best ore guides are strata and district-wide faulting. Dikes and sills are also common and mineralization can locally prefer their contacts even though the igneous rocks are barren. Skam minerals are influenced by the chemical composition of the carbonate. Forsterite, brucite, tremolite, and talc are common in skams developed in dolomitic beds. Skams derived from calcic beds often contain wollastonite, calcite, stilbite, or idocrase. Diopside, however, is a common accompaniment of copper sulfide in skam regardless of the original composition of the carbonates. Tremolite and possibly other amphiboles and chlorite can occur significantly in the zinc-lead portion of skams. Gamets occur in magnetite, copper, and zinc-lead zones of skams, but are not as diagnostic as diopside for the copper zone or tremolite for the zinc-lead zone. A general desciption of skam-deposit mineralogy can be used to construct prospecting models of porphyry copper skams. An abstract of such a description follows.

Jan 1, 1991

By David E. Sims

Asarco has been using computer-aided open-pit mine design since 1966. The in-house developed program package includes drill-hole analysis programs, interpolation routines, and three-dimensional open-pit design programs. The financial analysis step after pit design required that a reasonably accurate schedule be produced so that a good cash flow model could assess the feasibility of a project. The manual method of scheduling was too time-consuming for feasibility work, so a computerized scheduler was required. Since no computerized mine scheduling programs existed, we requested proposals from consulting firms to develop such a program. The selection of a consulting firm, the formulation of the contract and design specifications required about three years to accomplish. The consulting firm, Systems Control Inc. (SCI), of Palo Alto, spent over one year doing the programming and testing alone. The details of the program development were reported in "Computerized Year-by-Year Open-Pit Mine Scheduling," SME-AIME Transactions, December 1974. In June of 1973 the program, which SCI dubbed Optimum Resource Extraction or ORE, was installed. Version 1 of ORE was utilized successfully on three separate properties over a period of two years. During this time it became obvious that some of the original design specifications were restrictive, and certain modifications were required. The ORE program was submitted for modification, and after one year version 2 was operational in May of 1976. The program now consists of approximately 20,000 lines of FORTRAN source statements grouped into 190 subprograms, and runs in a 450K region of Asarco's 370/148 in Cranford, NJ. The Tucson com¬puter (370/115) is tied to the Cranford computer via a 9600 baud leased T.P. line, for running mine scheduling and other large mine planning programs.

Jan 1, 1979

By L. H. E. Weyher

A mine is essentially a vast materials-handling system. All other systems found in the mine exist to one degree or another to support the materials-handling functions, from the cutting at the face to the hoisting in the shaft. In this chapter computerized planning of underground materials-handling systems will be examined by dividing this function into: (1) the planning of the production section, and (2) the planning of underground rail or belt haulage from the production section to the shaft, slope, or surface. While alternative divisions might focus on the different materials- handling functions, i.e., production, supply, and manpower transportation, historical computer analysis has focused on the various systems rather than functions. The emphasis in this chapter is directed toward coal mine applications; however, most of the programs and methods are equally applicable to other underground mines. Markedly different methods are encountered in each system, and moreover, marked differences exist in the nature and the degree to which the materials-handling subsystems in each interact with the environmental or support systems. The most intimate interaction exists at the faces where geologic, human, and machine performance factors are closely related and constantly varying. In view of this, the planning of the materials-handling systems for the face will usually stress flexibility, while the outby materials-handling systems will generally place decreasing emphasis on flexibility and more on system reliability, capacity, and cost effectiveness. Thus, hoisting and main haulage systems are generally designed and constructed as permanent installations and cannot be readily changed, whereas secondary haulage systems and face operations are relatively mobile. These differences may have considerable significance for the mine planner in making technical and financial comparisons of alternatives to provide the scheduled mine production.

Jan 1, 1979

By A. L. Mular

Optimization has been defined as the procedure of locating the best of something or the best way of doing something (Mular, 1971). Several texts (Himmelblau, 1972; Ray and Szekeley, 1973; Box and Draper, 1969; and Lee, Adams, and Gaines, 1968) on the subject are available. Such techniques have been placed in two categories, namely, off-line optimization and on-line optimization. For the former, an optimization model is employed; for the latter, a black box approach is involved. The essence of an optimization problem becomes obvious, when a response surface is considered. Suppose that a response (in this case, a criterion of improvement such as profit per day; grade of concentrate per day) denoted by Y, depends only on two variables, X1 and X2, which can be manipulated and controlled. The relationship between Y, X1 and X2 may be represented graphically as shown in Fig. 1. The diagram is called a response surface and its height, Y, is determined by X1 and X2. Points associated with equal responses constitute response contours. The shape is that of a hill, and optimization is the procedure of ascending the hill to reach the top (maximum). In practice, a response surface is subject to disturbances which distort its shape and shift its location from time to time, so that the exact location of a maximum is imprecise. Generally, constraints (restrictions of some sort) on responses and manipulable variables serve to define a region of permissible operation.

Jan 1, 1979

By Edward L. Beutner, Robert M. Crump

Benson Mines low-grade iron ore reserve is a replacement deposit within the Grenville gneisses of the Adirondacks. The average grade of the crude ore is about 23 per cent iron. The iron minerals are principally magnetite and hematite disseminated throughout the gneisses as discrete grains about 1 mm in size. Both the ores that are beneficiated by magnetic means and the non-magnetic ores that are treated by a gravity method of concentration are found in stratigraphically different positions but are mined from one open pit, which is about 2.5 miles long and 800 feet wide and are treated separately. The gneisses are described and named according to the distinctive mineralogy of each. Recognition of the gneissic types permits the interpretation of the structure as a northward-plunging syncline overturned to the west. A large subsidiary anticline-syncline complex occurs on the east limb of the major syncline. Iron minerals in sufficient quantity to be considered ore are confined to areas where the footwall rock has been overturned to become the hanging wall.

Jan 1, 1968

By L. H. E. Weyher

The Bethlehem Mines Corp. is a captive mining subsidiary of Bethlehem Steel Corp. Its coal production is tied to the demands for and production of steel, a situation that has to balance between the following two extreme strategies: (1) either the mines are designed and operated for some optimum production level and the demand fluctuations within the steel corporation are met by supplementary corporate coal sales and purchases, or (2) the mines absorb all the demand fluctuations, regardless of the effects on mine costs. A rational definition of the best strategy between these extremes is, of course, needed but is very difficult to formulate in view of the complexity of the many factors that would have to be included in the analysis. Consequently, rather than setting profit targets for each given mining division and/or individual mine, the practice evolved to set production targets for producing specified tonnages of coking coal for shipments to the ovens located at the corporation's iron and steelmaking plants. This in turn leaves the mines with the dilemma of having to explain demand-related cost-per-ton fluctuations while essentially depriving them of the ability to control profit through tonnage optimization. In the early 1970's, the coal prices rose significantly, while other factors led to sagging productivity in underground coal mining. Thus, the role of Bethlehem's coal operations in the corporate profit picture gained in relative importance. This, in turn, sparked a closer attention to the coal mining cost structure and factors controlling productivity. At the same time, the drastic increase in the capital needed to open a new mine also increased the amount of planning required to minimize risks. All of this called for more well-defined, quantitative operating data. Bethlehem therefore launched, in the early 1970's, a number of innovative steps that, as the future may show, represented pioneering contributions to the growing sophistication of North American underground coal mine planning and management control practices. This case study describes the changes that led to the current implementation of a novel production reporting system at Bethlehem's coal mines. These changes took place in two distinctly different phases. The current system that resulted from the Phase II developments utilizes, of course, experience gained earlier and is expected to be amplified to incorporate more advanced concepts and technology as future experience dictates.

Jan 1, 1979

By Robert M. Dreyer

AGGREGATE With an annual domestic production of over 1.6 billion tons at a value of over $2 billion (see Table 15.1.1), the production of aggregate (crushed rock, sand, and gravel) is a basic industry of utmost economic importance. Because of the role of aggregate materials as essential ingredients of concrete, asphalt surfacing, and plaster, their delivered prices are major factors in determining the cost of construction. The annual domestic production comes from nearly 10,000 plants. About 15% of these plants account for over one-half the production. In a rapidly inflating economy, the average mine sales price of aggregate has remained relatively stable. The actual mine sales prices, however, vary greatly depending on quarrying costs in various parts of the country. Of much more importance in construction costs, however, is the delivered price of aggregate. This varies for each job, depending on the distance from the quarry and resulting transportation costs, as well as the initial cost at the mine. Because of a proliferation of regulations limiting new quarries in the vicinity of the encroaching urban sprawl, the average distance which aggregate must be transported has been increasing rapidly. Although it is impossible to derive an average delivered cost for aggregate, it should be noted that even an increase of only $1 per ton in average delivered cost over the last decade (probably a minimal assumption) would mean an annual cost $1.5 billion higher than ten years ago. In recent years, structural engineering considerations, as well as an increasing use of lightweight concrete blocks, have resulted in a rapidly increasing demand for lightweight concrete and plaster, the essential ingredient of which is lightweight aggregate. Principal lightweight aggregates are: pumice, slag, perlite (thermally expanded hydrous volcanic glass), vermiculite, and expanded shale, formed by the thermal expansion of shale and slate. The United States now has the capacity to expand, annually, over 13 million tons of shale and slate and to expand over 600,000 tons of perlite. In locating a site for aggregate production. the following factors must be considered: (1) tonnage available; (2) quality of aggregate (including local variations); (3) distance from major use areas; (4) transportation costs, including those resulting from present and possible future haulage restrictions; (5) zoning regulations; (6) operating costs, including the cost effects of compliance with local regulations governing blasting, air pollution, water pollution and drainage, noise levels, and operating periods. At one time, locating a suitable site for the production of crushed rock, sand, or gravel, in most areas, was regarded as an extremely simple task. In the past few years, however, finding a site for profitable production of aggregate has assumed ever-increasing com-

Jan 1, 1976

By Robert M. Dreyer

During the past two decades, synthetic abrasives have taken over successively greater percentages of the high-grade abrasive market, so that now, with the exception of natural diamonds (discussed in section 3.15.4C of this chapter), the importance of natural high-grade abrasives is negligible. The predominance of synthetic abrasives is indicated in Table 15.4A.1. This shows that the 1968 value of domestically produced synthetic abrasives (excluding synthetic diamonds) was over $80 million, whereas the value of garnet, the largest domestically produced, natural high-grade abrasive, was less -than $2 million. The major synthetic abrasives (other than synthetic diamonds) are: alumina, silicon carbide, boron carbide, tungsten carbide, and metallic oxides, including various iron oxides. A major advantage of synthetic abrasives is that the size and shape of grain can be closely controlled during manufacture. Although Table 15.4A.1 gives the average price of synthetic abrasives, such averages are of somewhat limited value. This is because the actual price varies within wide limits, depending on composition, hardness, size, and shape of grain. In 1968 the approximate total consumption of abrasives in the United States was valued at about $200 million, of which about two-fifths was in the form of synthetic abrasives (other than diamonds), one-third in synthetic diamonds, and the remainder in natural diamonds. Natural abrasive products, such as silica sand, tripoli, and pumice, are important in the low-cost abrasive field. Of the low-cost abrasives, silica sand continues to be the most important, with domestic production of about 300,000 tons at a value of $1.8 million (see Table 15.4A.1). In general, the lower the sales price of the abrasive product, the more limited is the market which can be served from a given production center. Each abrasive has applications for which it is especially useful, but there is a continual struggle among abrasive suppliers to induce substitution of one product for another. Such substitution can be stimulated by changes in method of preparation affecting hardness, shape, and size of grain.

Jan 1, 1976

By Peter W. Lotz

Contents of: ?Sampling for Cyanide in Metallurgical Processes? ?Sampling at process level of operation ?Sampling at environmental level ?Sample stability and integrity issues ?each citing possible objectives, practical example and reasons for surprises Overall recommendations on sampling plans and procedures to maintain sample integrity

Jan 1, 2005

By R Kerrich

Early-Archaean (3.26 Ga) volcanogenic massive sulphide (VMS) deposits located within the low strain and sub-prehnite-pumpellyite metamorphic-grade Strelley greenstone belt, East Pilbara, Western Australia, contain exceptionally well preserved sulphide textures which are directly analogous to those of sulphide chimneys formed by black smokers at present day submarine hydrothermal vents. The VMS deposits are associated with seafloor alteration zones in and below silica-carbonate laminites, at the top of tholeiitic to calc-alkaline intermediate and felsic rocks. VMS mineralisation comprises stratabound Zn-rich sulphide lenses with significant Cu and barite, and variable Pb and Ag, above Cu-rich stringer zones, all of which are similar to Phanerozoic polymetallic or Kuroko VMS deposits. Sulphide-sulphate mineralisation implicates hydrothermal discharge into sulphate-bearing ocean waters, ruling out a globally anoxic Archaean hydrosphere. The volcanic rocks and co-magmatic sub-volcanic intrusion hosting the VMS deposits are characterised by the conjunction of LILE>LREE>HREE, and Phanerozoic La/Yb with negative normalised anomalies of Nb, P and Ti, consistent with derivation via subduction zone hydrous metasomatism fusing the mantle lithosphere.

Jan 1, 1995

By Y. C. Kim

One aspect of long-range mine planning in an open-pit mine is first to define the ultimate pit limit, i.e., the projected size and shape of the pit at the end of its life. This chapter is concerned with various techniques that are currently in use today in determining the ultimate pit limits using the computer. Prior to the early 1960's, open-pit limits analyses were entirely performed manually. This manual technique has been well explained by Soderberg and Rausch in Surface Mining (1968). Soderberg and Rausch also explain clearly the need for establishing the ultimate pit limits in long-range mine planning, i.e., location of surface facilities, dumps, etc. Consequently, the need for ultimate pit limit design will not be reiterated here. Nor will the definitions of the most commonly accepted terminologies such as break-even stripping ratio, economic cutoff grade, ultimate and working slope angles, preproduction stripping, etc. be repeated here. Briefly, the objective of the ultimate pit limit design (which is also frequently referred to as pit design in short) is to determine the projected final pit limits of an ore body and its associated projected grade and tonnage, which will maximize some prespecified economic criteria while satisfying practical operational requirements.

Jan 1, 1979

By Mark Dangerfield

[Power-Point Presentation]

Jan 1, 2005