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By S. G. Hardcastle, C. K. Kocsis

Ventilation is an expensive prerequisite for underground mining. Current mining trends, including increasing depth and mechanization and more stringent health regulations would generally dictate that more air volume is required in order to provide good working conditions underground. However, any increase in the mine’s intake airflow can produce a disproportionate increase in power consumption and hence operating costs due to the cubic relationship between the sup-plied air power and the airflow (Power a Flow3). Furthermore, forecasts of significant increase in energy prices and new commitments with regard to reductions of greenhouse gas(GHG) emissions, determined the mining industry to look into developing new concepts, design tools and incorporate the latest mining technologies in order to lower capital and operating costs while meeting commitments regarding GHG emissions. The advances in computing power and modelling software now make it possible to design, model and schedule a mine from opening to closure. A developing trend is to design and plan the mine by means of orebody modelling software, followed by using discrete-event simulation techniques to predict production rates and evaluate various operating scenarios throughout the life of the mine. The authors are currently evaluating how such process simulators could be adapted in order to forecast the need for materials or a specific resource, and one of these would be the mine’s “life-cycle” airflow demand as a function of scheduled production rates and mine operating characteristics. Further to this, based upon the mine’s life-cycle airflow demand schedule, the ventilation system could then be designed using a mine ventilation simulator. This new design approach would integrate in parallel the development of the ventilation system with the current mining conditions, therefore, heading towards “develop-as-you-go” as opposed to developing the system for final requirements with high upfront costs. This new ventilation system design criteria would also incorporate the use of the “ventilation-on-demand” technology, which will further lower development and production costs and implicitly, the mines’ GHG emissions.

Jan 1, 2004

By Jeremy Cawley, Jeff Murphy, Horry Parker, Brock Gaspar, Jake Keegan

The Lower Olentangy Tunnel project includes 47,000 cubic yards of planned ground improvement for earth pressure balance machine (EPBM) tunneling (5.2 km) and microtunneling (335 m) in glacial soils. Jet grouting started in late 2021 and will continue through 2023 to complete operations at 5 shafts, 14 safe havens, 5 watermain ground improvement zones, and a river crossing. Typical jet grout columns are installed at depths between 15–24 meters. Discrete soil-cement blocks range from 267–8,900 cubic yards in volume. This paper discusses the methodology, testing, and technical considerations associated with jet grouting operations in glacial overburden across an urban environment.

Jun 13, 2023

By Grant R. Brown

The purpose of this opening paper is to provide an overview of incentives strategies. This overview includes a discussion of the different types of incentives, their advantages and disadvantages and their potential application to the mining setting. Objective The primary objectives of incentive plans are to increase worker (including management) effectiveness and reduce unit labor costs. These plans can be grouped into two major categories: 1) non-financial plans 2) financial plans

Jan 1, 1983

By J. J. Scott

Friction Rock Stabilizers, trade name Split Set*, is a new support system invented by the author and under development by Ingersoll-Rand and Lee-Norse Company. Split Sets are a substitute for standard bolts or fully grouted resin bolts and have certain advantages which are: 1. Improved safety for the miner 2. A rational design is possible based on rock mechanics principles 3. Supports can be made either to be yieldable or rigid 4. Supports can be used to build a roof beam or to suspend roof material 5. It is cheaper than the resin system and costs about the same as standard bolts.

Jan 1, 1974

By Earl M. Frizzell

Investigation of mined land characteristics, evaluation of irrigation systems and evaluations by the mining industry determined that irrigation is a feasible method for aiding the revegetation of coal mined lands in the western arid and semi-arid regions (Sherman, et al. 1980). The various regions studied displayed a commonality of characteristics which enables, independent of the site or region, the recommendation of solid-set irrigation. Irrigation should be supplemental by complimenting natural precipitation and should be implemented on a temporary basis. For germination, the vegetation requires application of small amounts of water in a gentle, frequent, and timely manner. For the establishment phase of growth, moisture should be applied and stored in the soil either through pre-irrigation or deep irrigation.

Jan 1, 1985

By L. Hales

Process control systems have evolved from single loop control to distributed control with computer based expert control strategies. The next step is to add adaptive control to the expert control strategies. An object-oriented adaptive optimization approach is defined and simulated results are presented for a plant.

Jan 1, 1996

By J. D. Patsey

A computer program has been developed for use by the mining engineer for analyzing drum-type hoists prior to the modification of an existing system or the designing of a new one. Its use permits the preliminary evaluation of a system before seeking the technical assistance of mine hoist designers and manufacturers. Compatible with an IBM-PC, the user-friendly program accepts a variety of data and can analyze hoisting systems for any balance state. The extensive program can be used to: (1) calculate skip capacity to yield a desired production rate; (2) solve for required drum face width; (3) select a permissible wire rope from a menu of 50 available rope types: (4) estimate total horsepower of the hoist plant; and (5) estimate power cost. An example of the model's use in evaluating a hoisting system will conclude the paper.

Jan 1, 1986

"On-site research and development as well as in-situ testing are key factors to the successful implementation of new mining equipment and technology. Unfortunately the demands and necessities of research and development often conflict with the reality of mine production in operational mines, especially during early stages of research and development and the initial testing of new equipment. Several experimental mines under university supervision attend to this problem and provide a close-to- reality testing environment for the mining industry and mining equipment manufacturers. This paper gives an overview of the design and organization of such an underground testing area as well as of the wide range of possible operations it can facilitate at the example of the FLB Experimental and Teaching Mine (Forschungs- und Lehrbergwerk) at Technische Universität Bergakademie Freiberg, the central European underground research mine. INTRODUCTION As well as the Mining Engineering education follows the same pattern worldwide, the tasks and duties to be fulfilled by engineers in the productive mines are comparable around the globe. This also holds true for the technologies and equipment needed, both in surface and underground mines. Almost all mining equipment brands are being distributed worldwide. The tasks and challenges of guaranteeing an ever- increasing productivity at the mines, while simultaneously maintaining, respectively improving, safety standards, also in the developing countries and emerging economies, requests a constant development, improvement and adaption both of the engineering education and of R&D in technology and equipment. The increasing safety requirements at the mines, in combination with also increasing safety and liability policies, do often not allow a proper practical education of mining engineering students. At the same time, new technologies and equipment to be deployed / brought to the mines have to be fully functional in a production operation from the very first moment. Time losses like break-down time or even repair and maintenance breaks are often costly and, even when expected up to a certain degree with newly developed machines, have a wider negative impact on the neighboring operations and operations within that mine, thus often being unacceptable within the ongoing production process and extremely costly."

Jan 1, 2015

By W. Lin, M. J. McPherson

When a large area of open gob collapses suddenly, a windblast is produced that can cause considerable damage throughout the infrastructure of a mine. In a few cases, the windblast has been accompanied by ignitions of methane and/or coal dust. This paper describes the conduct and results of laboratory tests involving the compression of mixtures of air, methane and coal dust under a falling weight and while allowing controlled escape of the mixture. The transient responses on pressure and temperature sensors were recorded. In addition to an analysis of those records, the paper highlights those conditions in which ignitions occurred.

Feb 24, 1997

By D. X. Tang, G. Wilson, S. S. Peng

Design and implementation of a roof bolting plan requires reliable geotechnical information of strata, such as rock strength, and locations of interfaces and voids/fractures. The drilling parameters obtained during normal roof bolt installation cycle provide a fast and economic way to gather information on the geological structure within the bolted horizon. The purpose of this research project is to develop a method for identifying the geological features in the mine roof strata based on drilling parameters of roof bolter. The criterion for void/fracture prediction has been developed and proven valid. This paper focuses on the estimation of the strength of roof strata by using drilling parameters. Based on the results of a series of underground and laboratory tests, feed pressure is found to be the most sensitive parameter when the strength of roof strata changes. Moreover, it was also found that both penetration rate and rotation rate have obvious impact on the magnitude of feed pressure. Based on these findings, the criterion for the estimation of roof strata strength has been developed using the relationship among feed pressure, penetration rate and rotation rate and implemented in MRGIS.

Jan 1, 2006

By Nick Katsikaros, A H. Gray

Gold concentrates are produced at many mines by a variety of centrifugal and gravity machines, such as Knelson and Falcon concentrators, however the subsequent recovery of gold is relatively inefficient and subject to security problems. The InLine Leach Reactor (ILR) offers a new method to recover over 95% of gold in concentrates using a simple, secure leaching process. The InLine Leach Reactor is of particular benefit in treating slow or difficult leaching sulphide concentrates and its performance can be reliably predicted from simple laboratory tests. The InLine Leach Reactor is now successfully operating in two gold mines providing benefits of high gold recovery, low operating costs, high security and ease of operation.

Jan 1, 1999

By Carl Eschman

Productivity from large walking draglines is primarily dependent on operator skills. This machine may be in operation three shifts a day, 364 days a year, and its output is directly related to coal uncovered and mine profitability. Dragline operators must have highly developed manual skills and be knowledgeable in mine planning and working strategies. When using equipment costing more than $25 million, some formal training is usually required before an operator is allowed to assume complete con¬trol; however, dragline operators rarely receive any structured training before operating these giant excavators. A form of apprenticeship is usually followed where an operator candidate progresses from a groundsman to an oiler position. As an oiler, he is permitted to operate the dragline for short periods under supervision. After apprenticeship, the operator is considered sufficiently prepared to operate the largest, most powerful machine at the mine. The apprenticeship training method has obviously provided the surface mining industry with skilled dragline operators; however, conditions are arising that require a realistic and effective training tool that can be accessed by mining companies. New mines -either planned, under construction, or recently opened in the West-do not have access to a pool of experienced operators and oilers as do Midwest mines. As coal mining activities increase in both the West and Midwest, demand for trained dragline operators could be required in a short amount of time. Also, the more productive techniques along with sound basics of strip mining are sometimes lost in the informal "OJT" training method. Modern draglines are the pacemakers of the strip mine, and are simply too expensive to be used as a training device where lost productivity and susceptibility to damage can directly affect mine output. The Dragline Training System is a logical first step in formally educating or retraining operators. The program, started by the US Bureau of Mines and continued by McDonnell Douglas Electronics Co. under contract with the US Department of Energy, was installed and evaluated at DOE's Carbondale Mining Technology Center in Carterville, IL, last year. It is now being operated by Southern Illinois University at Carbondale. System Description The Dragline Training System addresses specific environments and work practices encountered during an actual mining operation at a midwestern US surface mine. This area was chosen because of its high number of strip mines using large walking draglines. Most draglines in the region are Bucyrus-Erie 1370, 1450, and 2570 models, so the dragline trainer was patterned after the company's 1370 machine. Operating and emergency controls are sufficiently standardized for most large walking draglines, and peculiar dynamics and responses from any specific dragline can be programmed into the computer system. The computer simply prompts the user to select the manufacturer and any peculiar response or rate changes needed. A 46-m3 (60-cu yd) bucket is simulated, but for closer simulation, various bucket configurations can be provided. Dragline Trainer The dragline trainer uses the TV-model simulation technique. A scaled model of the dragline is positioned in a model mine. A television camera is positioned at the operator's theoretical eyepoint, and the view captured is projected into a large screen in full scale. The screen is positioned in front of the operator seated in a full-size cab at Bucyrus-Erie controls. By manipulating the controls, the trainee can operate the model dragline and observe its reaction in the television display. In addition to housing dragline controls and consoles, the wooden, oversized cab contains the digital computer, terminal, video recorder and monitor, power switch box, air conditioner, and has enough room for the instructor and five student observers. The 50:1 scaled dragline model contains servo-controlled functions for hoist, drag, swing, delta swing, and longitudinal and lateral position. The delta swing provides bucket lag during swing and a realistic pendulum action when the swing is terminated. The over-responsive second order servo system is designed to provide hoist, drag, and swing rates exceeding present draglines. In all cases, position servos are used for better control and sta¬bility. The normal rate operation of an actual dragline is computed for the specific machine and presented to the servo amplifiers as iterative position commands increasing or decreasing

Jan 6, 1982

By Brian F. Taylor

The Mexican fluorspar industry is faced with and will face serious problems, some of their own making and others beyond their control. However, they still offer the most secure source of fluorspar for North American' consumers. Since 1975, even in light of declining markets, they have, increased then production capabilities' as shown in Table #1. In analyzing Table #1, we note that Compania Miners Rio Colorado has closed down due to their ore reserves being exhausted. Fluorita de Rio Verde expanded their acid grade fluorspar capacity in anticipation of additional North American business. Campania Miners Las Cuevas presumably increased capacity to meet their North American contractual commitments and to supply their own hydrofluoric acid plant (Fluorex) at Juarez, Mexico. Historically, the Mexican fluorspar industry has relied on the United States as the mainstay for their sales. As shown in Tables #2 and #3, the Mexican share of the United States market has moderately decreased. However, as noted in Table #4 the volume loss is substantial as explained below.

Jan 1, 1985

By Don Muraoka

Soda ash, anhydrous sodium carbonate, is produced from underground trona deposits occurring in the Green River Sasin of Southwestern Wyoming. Stauffer Chemical Company of Wyoming, a jointly owned subsidiary of Stauffer Chemical Company and Rocky Mountain Energy Company mines the trona and processes it into high-purity soda ash. Stauffer Wyoming has been in operation since 1962 with a current production capacity of approximately 2.2 million tonnes (2 million short tons) per year of soda ash. The Refinery has five parallel operating trains utilizing the monohydrate process which is a series of chemical processing unit operations described below. Screening and Crushing the Trona The mined trona is brought to the surface in two counterbalancing ore skips. The ore is initially screened with Refinery feed, less than peagravel size material, entering the process while the oversize is conveyed to an outdoor stockpile.

Jan 1, 1984

By Liaqat Ali Shah, Muhammad Farooq, Zait Ullah Shah, Francisco Rolando Valenzuela-Díaz

Bentonite collected from Nowshera (Pakistan) was treated with NaCl, and the < 2-μm clay fractions were separated by sedimentation process. The textural changes in NaCl treated purified bentonite were compared with raw and physically purified sample. It was detected that the NaCl-treated purified bentonite and the sample purified by simple sedimentation, respectively, consist of sodium-montmorillonite and calcium-montmorillonite as a major clay mineral. The honeycombed-type morphology was observed for both the purified samples; however, the particles of NaCl treated purified bentonite were relatively in a compact form. The particle sizes of both the purified samples were found considerably smaller. The high volume percent of the fine particles was noticed in the NaCl-treated purified bentonite. This attributed that the sodium exchange has a valuable impact on the bentonite dispersion in aqueous media during particle size measurement. The relatively high mesopore area/volume and micropore area/volume and specific surface area (SSA) were detected in purified samples. The NaCl-treated purified sample showed relatively high mesopores area/volume than the sample obtained by simple sedimentation. These changes seem to be originated from either high montmorillonite contents and/or the smaller particle size, which might be produced after the layer rearrangement during the interlayer cation replacement by Na+ ions. The large SSA and high porosity of purified samples particularly the NaCl-treated bentonite suggest their potential use as adsorbents, catalysts, pharmaceuticals, and cosmetics.

Jan 7, 2021

By Tim O’Neil

Until about three years ago, Asarco&apos;s copper business consisted predomi¬nantly of custom smelting of ores and concentrates produced by other mining companies. Since then, the company has been transforming itself into a fully integrated producer in copper mining, smelting, and refining. In doing this, Asarco has lowered its costs and restructured its operations and finances. Now, Asarco hopes to complete this process by spending $260 million over the next three years, to expand and modernize its copper facilities and boost production by some 40%. The capital spending program includes: • $130 million at the Ray mine about 113 km (70 miles) north of Tucson, AZ, to expand mining capacity and install an in-pit ore crusher, mill, and concentrator; • $100 million, to expand the mining capacity at the Mission Complex located south of Tucson, AZ, and refurbish the adjacent, idle Pima mill and concentrator. (Asarco had earlier exercised an option to purchase the Pima mill for about $6 million); and • $30 million, to modernize the copper smelter in El Paso, TX, with a new flash smelting process. The new program is in addition to a recently completed first-phase expansion of the Mission mine, mill, and concentrator. This $13 million debottlenecking of existing operations in¬creased production capacity by 46% or 24.5 kt/a (27,000 stpy), to 79 kt/a (87,000 stpy) of copper in concentrates. In addition, a previously an¬nounced $12 million expansion program at the Ray mine is scheduled for completion in early 1990. It will expand mill capacity, to offset the anticipated effects of increasing ore hardness as the pit deepens. Ray produces 68 kt/a (75,000 stpy) of copper in concen¬trates and an additional 36 kt/a (40,000 stpy) of electrowon copper. By 1992, when Asarco&apos;s expanded and modernized copper facilities are operating at capacity, the company&apos;s mine output will have increased by 67 kt/a (74,000 stpy), to 263 kt/a (290,000 stpy) of contained copper. That will be enough to provide all of the feed required for Asarco&apos;s two copper smelters - by then, both of them modern, state-of-the-art facilities. Asarco&apos;s expansion and modernization program will further reduce costs and provide added assurance that the company&apos;s copper business will be profitable at the bottom of the cycle, according to Chairman Richard de J. Osborne The Ray mine portion of the new program will include construction at the mine of a new mill and concentrator, with a capacity of 18 kt/d (20,000 stpd) of ore. These new semiautogenous grinding mills and large capacity flotation cells will augment the present 27.2 kt/d (30,000 stpd) concentrator located 29 km (18 miles) away, in Hayden, AZ. A 29 km (18 mile) pipeline will be built to carry tailings in slurry form from the new Ray mill to the present tailings pond. Concentrates from the new facility will be shipped by rail to Asarco&apos;s Hayden copper smelter. Ray&apos;s present 27.2 kt/d (30,000 stpd) crusher, adjacent to the open-pit, will be replaced by a 54.4 kt/d (60,000 stpd), portable in-pit crusher and conveying system. This will reduce the more expensive ore haulage by truck. The Ray project is scheduled for completion by 1992. It will increase the mine&apos;s annual output of copper in concentrates by an additional 33.5 kt/a (37,000 st), to 102 kt (112,000 st). And the project could mean an additional 400 jobs at the 730 employee Ray operation. Work at the Mission Complex involves reactivation of the Pima mill and concentrator and expansion of mine output sufficient to provide ore to both the Pima mill and the present Mission mill. In 1985, Asarco purchased the Pima mine, which occupies one end of the Mission pit. The work at Mission will increase its annual capacity by 33.5 kt (37,000 st), to 112 kt/a (124,000 st) of contained

Jan 1, 1989

By Brad Grothen, Lok Home

The choice of TBM type is never easy, but it becomes especially challenging when faced with a hard rock tunnel with expected high water flows and pressure. Slurry Shield tunneling has a long history of being used in these conditions to minimize the risk, though this method has brought with it other risks along with cost considerations. At recent projects around the world, another method has been proven to effectively manage these project risks without utilizing Slurry Shield tunneling: Shielded, NonContinuous Pressurized (NCP)-TBM tunneling in rock with a comprehensive grouting program. In this paper, the authors will analyze the use of Shielded NCP TBMs at projects around the world as compared with slurry shield tunneling in rock under water pressure. Recommendations will be given in order to establish a clear picture of the optimal tunneling method.

Jun 13, 2021

By Thomas V. Falkie, Howard L. Hartman, Bruce R. Palmer, Donald W. Gentry, John E. Frost, Peter T. Luckie, Michael K. McCarter, Lee W. Saperstein

Education in the mineral engineering professions is in the same flux and turmoil as is the entire minerals industry. Overcapacity in some areas, undercapacity in others, and the constant fear of substitution plague education as well as industry. The exercise in long-range planning that The Society of Mining Engineers has undertaken gives an excellent opportunity to examine the problems and the opportunities in minerals engineering education. Charge to the Committee The Educational Activities Committee was asked by the Long-Range Planning Commission (LRPC) to examine SME&apos;s future role with respect to "education policy, role and organization, education department, education board, continuing education, short courses, and extension courses." This examination is timely. It follows a reorganization of SME&apos;s Education Board designed to make the Board more efficient in its operation, more responsive to the needs of education, and more active in the setting of Society policy on education. In addition, the roller-coaster cycle of boom and bust experienced by the mineral industry in the last decade has been shared by the minerals schools and has created enrollment problems that need to be addressed promptly. Within SME there is much experience on educational issues to draw from and many problems to solve. Major Premise The committee is emphatic in espousing the philosophy that SME should support, in word and in deed, the highest possible standards that can be maintained by the minerals schools. As guardians of the various mineral engineering and scientific professions (geological engineering, geophysical engineering, mineral engineering, mineral processing engineering, and mining engineering), it is appropriate for the Society to be a watchdog for academic standards. One member of the committee put it succinctly, "We need to educate engineers and technologists, not muckers." A vital and profitable minerals industry needs professionals educated by good teachers, equipped with the most modern available methods, techniques, and knowledge, and challenged by their education to be innovative contributors to their chosen profession. Such education occurs only if it takes place in an institution that is vital and challenging. SME can enhance the quality of its membership if it works to maintain the standards of the schools that graduate new members. Education does not end with the award of a degree. It is appropriate for SME to strive for continued technical quality of its membership. To this goal, SME should maintain its attention to the process of licensing professional engineers, and it must continue and expand its efforts in continuing education for the membership. Recommendations for Action The following recommendations were submitted by the committee and then amended slightly by the full commission. The recommendations have support from the SME Board. • SME Education Coordinator and Staff Department of Education - Staff support for education should be provided by someone with experience in engineering education who would be appointed as SME Education Coordinator for all educational activities: accreditation, continuing education, student affairs, and liaison with mineral schools. The Board has approved an Education Coordinator and the position has been filled. • Advisory Committee on Education - SME should recognize, by amending its committee structure, that functions important to education are filled by SME-appointed representatives to the Accreditation Board for Engineering and Technology (ABET), its Engineering Accreditation Commission (EAC), and Technology Accreditation Commission (TAC). It is suggested that these persons, plus the chairman of the Education Council, plus two other persons appointed by the SME Board, form an advisory committee on education. The Board has approved this. • Education Council - The recently organized Education Board, having full agendas for its committee meetings and having

Jan 6, 1984

By J. B. Goddard

Abstract. Leaching of, uranium in situ from sandstone deposits with ammonium carbonate solution containing: dissolved oxygen occurs rapidly compared with the leaching of the bulk of the sulfur present as FeS2. However because of their high reducing, capacity and their relative abundance, the FeS2 minerals consume; the bulk of the oxidants A pressure leach apparatus was-construtted which permitted the measurement of oxygen consumtion by FeS2. Oxygen consumption by FeS2 is best described by a first-order reaction. The experimental rate constants for various cores are roughly proportional to their FeS2 contents.

Jan 1, 1980

By G. Le Bel

Discussion by G. Le Bel The paper proposes three methods to determine optimum lifetime of a mining project 1. The conclusion is that the three methods arrive at the same optimum production rate (by coincidence). It is also stated that: "The stochastic and option pricing models, in addition to providing a more realistic optimum mine life than the traditional NPV (net present value) calculation, showed that the example project has the potential for substantially higher return. By explicitly considering a project&apos;s potential risks, the stochastic or option pricing techniques can more accurately describe its probable investment performance." This discussion is intended to demonstrate that: •It is no coincidence that the three methods arrive at the same optimum production rate. • The stochastic and option pricing models do not provide a more realistic optimum mine life than the traditional NPV calculation. •The potential for a substantially higher return is misrepresented. First, a review of investment decision theory in mining is needed. Net present value is the preferred performance measure because of the flexibility offered when comparing various alternatives. However, it presents the following disadvantages: • The discount rate selection is not straightforward. • The NPV obtained represents a deterministic characterization of the variables included in the cash flow calculations, i.e. a single-point estimate. Discount rate selection The opportunity cost of capital represents the rate of return that would be obtained if the capital was instead invested in other opportunities considered to exist. Such opportunities must be bypassed if the available capital is invested in the project studied 2. If these other opportunities carry risk similar to the project under analysis (for example, if they are other mining projects), there is no need to add incremental [ ] risk factors. On the other hand, if these opportunities are represented by the acquisition of government bonds yielding 7%, a risk premium factor must be included. The types of risks associated with a mining venture are shown in Table 1. Together they represent the "business risk" of being a mining company. The individual project risk is important to investors if it differs substantially from the business risk of the company and that of the other investments in mining ventures that we must pass up to invest in this particular project. A risk premium or discount would then be required. This can be illustrated by the following example. Consider that a company has two investment alternatives: one is the Cavender hypothetical project located in Nevada, and the other is the same project located in a civil war zone of central Europe. The second project requires a risk premium factor on the discount rate. Conversely, a project showing highly uncertain returns that are negatively correlated with the returns of the firm&apos;s other assets may decrease the company&apos;s corporate risk. Deterministic character of NPV calculation The cash flows used in NPV calculations are obtained from a set of variables. These variables are estimated using one parameter obtained from the engineering studies. Each parameter is thus a single value that is often termed a "realistic" or "best estimate" as opposed to "optimistic" or "pessimistic." However, considering that each variable can assume a range of values between the

Jan 1, 1994