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LOS TEXTOS CIENTIFICOS (II)
CURSO DE LECTURA COMPRENSIVA DE TEXTOS CIENTIFICOS ESCRITOS EN INGLÉS
Escuela de Posgrado
El Artículo Científico de Divulgación.
UNIVERSIDAD NACIONAL DE SANTIAGO DEL ESTERO - FACULTAD DE CIENCIAS FORESTALES
ESTUDIO #11
Un buen artículo científico es como cualquier otro de los medios de comunicación técnica: atiende un problema o tema importante para la audiencia a la que está dirigido y presenta los argumentos en una forma clara y coherente. Sin embargo, se diferencia un poco de ellos en el sentido de que es escrito para una audiencia muy diferente. Como dijimos, existen ciertos textos científicos que deben incluir información dirigida a una variedad de lectores con distintos intereses, especialidades (técnicas y no técnicas) y disponibilidad de tiempo; incluso quizá pertenecientes a campos que van desde la misma área del conocimiento hasta unas tan diferentes como las de la economía y finanzas, como es el caso de un pedido de subsidio. Por el contrario, el artículo periodístico o de divulgación científica es escrito teniendo en mente una audiencia mucho más reducida: los especialistas en el campo, con quienes el autor comparte supuestos, conocimientos, antecedentes, y que tienen la necesidad y el interés suficiente en el área como para leer cuidadosamente el artículo. Por eso es que este tipo de texto puede eliminar algunas de las partes presentes en los otros tipos de textos técnicos como el informe, los memos y los pedidos de subsidios que lo llevan a no incluir, por ejemplo, la presentación y el resumen; sin embargo debe mantener las características que proporcionan claridad y facilidad para la lectura por parte de expertos como es el caso del movimiento de lo general a lo particular y la referencia o apoyo en los datos. Algunas veces, como resultado de la excesiva confianza del autor en la disponibilidad e interés del lector en la lectura del artículo o del conocimiento compartido con él, este movimiento se hace más corto de lo necesario. Los artículos científicos en los distintos campos de las ciencias y revistas varían un poco en el estilo en virtud de los distintos requerimientos que imponen los editores. Así es posible encontrar revistas y “journals” que presentan los artículos con distintos formatos para las notas al pie, los títulos y subtítulos, los gráficos y tablas, longitud de los párrafos y otras características. Sin embargo, a pesar de variar en el estilo, la gran mayoría de los artículos comparten irremediablemente una estructura y un propósito. El propósito de un artículo es el de proponer a la comunidad científica un hecho o una opinión: (1) un hecho que los resultados sustentan como válido, o que confirma (o no) teorías anteriores; o (2) una opinión en cuanto a que ciertos resultados anteriores deben ser desechados, reinterpretados o corregidos, o que una teoría debe ser abandonada, ampliada o reformulada. Estas argumentaciones se hacen dentro de una estructura que ya se dijo es bastante rígida, y consistentemente sostenida y usada en muchos campos del conocimiento que incluye las siguientes secciones: 1. Introducción, en la que se define el problema y se establece su importancia. Es una parte muy particular puesto que, en poco espacio debido al conocimiento que comparten, se presenta mucha información y se dan pistas respecto a la naturaleza y alcance del problema investigado. Aquí se ubicar al lector dentro del problema a través de la revisión de los conocimientos existentes sobre el tema por lo que normalmente se incluyen detalles técnicos específicos y se construye el contexto contra el cual el autor va a contrastar una observación o un inconveniente con alguna teoría. 2. (Materiales) y Método, en la que se describe cómo la investigación llegó a los resultados. Esta es una parte crítica del informe puesto que establece la validez de los resultados y les da seriedad. Aquí el autor intenta demostrar que se ha aplicado escrupulosamente un método aceptado, y que hecho todo lo necesario en forma correcta, cuidadosa, y que no se han cometido errores. Esta sección también proporciona los mecanismos por los cuales la comunidad científica puede repetir y verificar el trabajo que se presenta, requisitos estos incluidos en el método científico. Aquí se dan los detalles necesarios y suficientes para que cualquier investigador pueda reproducir los resultados exactamente; esto significa que en esta sección se pueden encontrar los datos usados para:
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Identificar exactamente los materiales usados en el desarrollo de la investigación (reactivos, enzimas, organismos, sujetos (humanos, animales, vegetales), Identificar las condiciones particulares en las que se realizó la experiencia (temperatura, irradiación, etc). Identificar cualquier criterio especial usado en la selección del material, sujetos, aparatos, métodos de ensayo). Identificar el método específico usado en la investigación; si es uno estándar es mencionado sin mayores detalles, en cambio si es un método original o no ortodoxo debe ser descrito detalladamente. Justificar, en el caso necesario, cualquiera de las elecciones de criterios, materiales, métodos o condiciones realizadas
3. Resultados, en donde se describe lo que se descubrió. En esta sección se presentan: (1) las principales generalizaciones que el autor extrae a partir de los datos, y (2) los datos que apoyan esas generalizaciones. Las generalizaciones son explicados detalladamente de tal forma que el lector pueda evaluar su fuerza. 4. Discusión, en la que se analiza la importancia de los resultados y su(s) implicancia(s). Aquí se busca adecuar los datos al contexto del campo de estudio relacionándolos con los de otros trabajos tanto teóricos como experimentales. Junto con la Introducción aquí se explican la importancia del trabajo y cómo contribuye al avance del conocimiento. Esta sección está orientada a responder preguntas como: ¿fueron los resultados los esperados? Si no, ¿por qué?; que generalización puede hacer a partir de los resultaos obtenidos? ¿cómo las interpreta? ¿los resultados obtenidos, concuerdan o se contraponen, confirman, amplían otros de otras experiencias? ¿abren nuevos campos de investigación? ¿las conclusiones tienen alguna aplicación práctica?
A manera de práctica en el reconocimiento de la estructura de un artículo de divulgación científico se transcribe uno a continuación. Léalo e identifique sus partes y complete lo siguiente:
TITULO
ABSTRACT
OBJETIVO MATERIALES EMPLEADOS
RESULTADOS
PRINCIPALES CONCLUSIONES
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A B S T R A C T
A. L. Hammet and Robert L. Youngs An innovation in design and processing of forest products is essential to meeting the challenges of 21st century of forestry. Forests and attitudes toward their use are changing while demand for wood in its various forms increases with the population. Engineered wood products offer new opportunities to meet consumer needs from a diverse resource. In addition, processes such as nondestructive evaluation, recycling of wood and paper, and advances in pulping and papermaking offer new possibilities for managing the forest for its many uses.
Keywords: composites; engineered lumber products; recycled wood he forest of the 21st century is a forest under great pressure to meet many needs –environmental and social as well as for wood and nonwood products. The goals of forest sustainability and productivity have required a steadily increasingly amount of innovation as those needs are balanced and joined under a wide variety of conditions. Fortunately, innovation in the forest products industry is nothing new. The history of forestry and forest products is full of examples of innovative approaches to forest management, forest product extraction and utilization, and expansion of forest products
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and services to meet new challenges (Young, 1999). The forest resource itself has been changing for thousands of years, influenced by climatic and human forces. Change has become particularly rapid as we move into st the 21 century. While here in the United States total forest area is increasing, its composition and structure are changing, and public attitudes toward forest use are becoming more acute. Dramatic changes in wood processing technology are needed to meet new demands for products. Improvements in processing efficiencies have made possible economical use of a wider range of forest-based resources, as well as residues and recycled material
formerly burned or dumped. Markets for wood and competing nonwood products have evolved as consumer options and opinions have changed and as technology bas brought forth new ways to meet more stringer expectations of product performance. Competition from and combination with materials such as metal, plastics, and ceramics have changed both the ways wood products are made and the ways they are marketed. Growth in total wood consumption closely follows population growth (Bowyer, 1995). World population has more than doubled since 1950, leading to greater demand for wood products as well as less available land on which to grow the forests supplying such products. Even though annual per capita consumption of wood has declined slightly worldwide (from about 0.67 cubic meters in 1999), demand for wood is now 65 percent greater than it was in 1961 (FAO, 2001). Interestingly, during that same period, worldwide demand for industrial roundwood, the source of pulp and wood products, has increased 75 percent, while the demand for wood fuel has increased about 80 percent (fig. 1). This is partly attributable to the fact that the most rapid increases in
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population have been in parts of the world where people are more likely to depend on fuelwood for heat and other energy needs in their daily lives. Production of roundwood in the United States has remained at about 15 percent of the world total. The portion of this world total produced in the United States is greater for industrial roundwood, about 25 percent, and less for fuelwood about 5 percent (FAO, 2001). Timber production has increased as a result of improved silviculture and fire control, as well as advances in genetics and tree improvement. Meeting Increased Demand Several factors together help meet this increased demand for wood. New technologies are increasing the output of wood products per unit of raw material input. Between 1961 and 2000, US output increased by more than 50 percent (fig. 2). These two new technologies are making possible a wider variety of product options from a wider variety of wood sources than was the case a halfcentury ago. Advances in technology for using mixtures of species, diverse species, and groups of species are improving options for adding such material to the resource base. Assurance of supply and effective marketing schemes are keys to exploiting the many forms of the wood resource effectively. Many residues from processing operations are now raw materials for composite products engineered for specific applications. Field chipping of residual stems and precommercial harvest of smaller stems also help meet wood fiber and fuel needs. Particular attention has been given to the effective use of smalldiameter timber removed in various thinning approaches and harvesting operations, as well as to effective and economical means of grading lumber and fastening components in timber structures (Stern, 2001). Forest management plans and marketing schemes now encourage the use of “secondary” or underutilized species, a practice that may provide material for newly emerging products and improve management of this oftenoverlooked forest resource (Youngs and Hammett, 2001). Perhaps most significant are approaches to resource utilization
that gather cost, availability, technology, and environmental considerations into integrated plans and strategies. This article reviews several approaches that have the potential for far-reaching impacts on how our forests will be managed and how we will use wood and competing raw materials. Wood Composites The current Forest Rangeland Renewable Resources Planning Act (RPA) Timber Assessment, with projections to 2050, predicts a steady increase in consumption of both structural and nonstructural composites (Adams, 2002). Major advances are being made in this area: except for plywood, woodbased composites as we know them today are less than 50 years old. Composites include panel
products, molded products, inorganic bonded products, and lumber and timber products (Maloney, 1995). The “nonperiodic table of wood elements” presented by Marra (1969) illustrates some of this potential by considering the elements of wood that can be combined in various ways with each other or with other wood or nonwood elements to meet specific size, appearance, and performance requirements. Marra’s vision of more than 30 years ago has become a commercial reality. For many engineered products, both the raw material and the processing conditions are designed and controlled to yield specified performance characteristics. For example, high-performance lignocellulosic composites with uniform density, durability under 4
GUÍA adverse exposure, and high strength can be produced using fiber modification to overcome the natural deficiencies of wood fibers. New opportunities are being explored to combine lignocellulosic with glass, metals, plastics, inorganics, and synthetic fibers to tailor products to specific end-use requirements. Engineered products, particularly structural composite lumber, are moving into the expanding global forest products trade with international assurances provided by ISO 9000 standards for product design, components for special production and services, and final inspection and testing (Winistorfer and Streudel, 1997). Composite technologies are generally more adaptable to available type and quality of woodbased raw material than are solid wood products or plywood, which use lumber or veneer from largediameter trees. A common composite, oriented strand board (OSB), has been rapidly accepted in the market and is commonly used as sheeting, subflooring, and roof decking; it currently dominates the market for structural composites. OSB combines strands of wood –at least three times as long as wide- which are oriented and glued under pressure to produce a panel with good mechanical properties. OSB is substituted for softwood structural plywood because it is increasingly difficult to obtain veneer-grade logs of adequate size and because it can be made from a diverse set of species and log sizes. OSB now supplies more than 55 percent of the structural panel market, and the demand continues to grow (Structural Board Association 2001, pers. comm.) Laminated veneer lumber (LVL) is a form of structural composite lumber that requires veneer from logs of moderate to large size. Veneers for LVL are evaluated nondestructively for strength and stiffness using stress-wave technology. The resulting product justifies the careful preparation by serving in many high-strength products that can be produced
continuously in long lengths and large sizes. Additional forms of structural composite lumber are parallel strand lumber (PSL) and oriented strand lumber (OSL). PSL
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made under higher pressure and with orientation of the strands. The particleboard industry grew out of the need to make use of sawdust, planer shavings, and other relatively homogeneous mill residues in addition to roundwood. Mechanically reducing the raw material into small particles, applying adhesive to the particles, and consolidating a loose mat of particles with heat and
a
composite of wood strand elements with relatively long strands (about 2 feet long and ¾-inch wide) of veneer oriented along the length of the member. Both LVL and OSL are made in continuous presses to any length that can be handled by equipment at the plant and by truck or rail for transport to the point of use. Other variations of this concept, including laminated strand lumber (LSL) and OSL, are an extension of the OSB technology. These products use strands of a size between those of OSB and those of PSL and are commonly
pressure into a panel product produces particleboard. It is typically made in three layers, with fine particles on the outer faces and coarse particle in the core. Varying the shape, size, and location of the particles, and varying the adhesive and the processing conditions makes it possible to produce a wide variety of boards. Another common composite product, fiberboard, includes products such as hardboard (highdensity), medium-density fiberboard (MDF), and insulation board. Fiberboard is made from comminuted material that is broken
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GUÍA down to the fiber level. Because wood is basically fibrous, fiberboard exploits the inherent strength of the wood more effectively than does particleboard. Fiberboard is usually classified by density and can be made by either dry or wet processes. Dry processes are used for hardboard and MDF. Such boards are made in a manner somewhat similar to particleboard, with resin-coated fibers being pressed by techniques that differ somewhat between hardboard and MDF. One firm makes MDF from recycled materials and mill residues and locates its manufacturing plants near large urban areas to access materials that normally would be sent to landfills. Production of wood panel products has increased more than six-fold since 1960, due largely to the introduction of many types of wood-based composites and their adaptability both to the raw material resource and to the market. A major contribution also comes form plywood production in South Asia. Even though US plywood production has quadrupled, the US portion of world production had declined from 40 percent to 25 percent (fig. 3). This trend reflects the increased ability to produce such products and their increasing market acceptance in many other parts of the world. Wood panel products have increased dramatically in world trade, from scarcely any in 1960 to about half the volume of major roundwood exports in 1999 (FAO, 2001). Composites Using Other Materials Combining wood with other materials such as plastics, gypsum, and concrete has led to a variety of composite products with unique properties to meet special needs. These products are designed to reduce material costs, use recycled materials to make recyclable products, and develop specific properties superior to those of the raw material from they are derived. Fiber-plastic composites can be used in a variety of products form door panels to decking to moldings. One producer of wood-plastic thermoplastic lumber used sawdust and wood waste mixed with recycled plastic bags to make a plastic lumber suitable for substitution for lumber treated with chromated copper arsenate (CCA). Most of the polymers used traditionally and to bond lignocellulosic composites are
thermosetting –they react to become permanently fixed in shape and size. A new product concept uses thermoplastic polymers as a binder or matrix for a variety of mats producing high-density composites. Wood fiber composites are a fast growing segment of the plastics industry. These plastics use fibers or wood flour as reinforcement and can be processed by extrusion, injection, or possibly blow-molding. Sheets made by extruding wood fiber and polypropylene are used in the automobile industry, extruded molding and decking are used as building materials, and other products are finding application in glulam beams and truck flooring. Inorganic bonded wood composites of molded products or panels combine 10 to 70 percent wood particles or fibers with 30 to 90 percent inorganic binder. The inorganic binders are primarily gypsum, magnesia cement, or Portland cement. These products have the unique advantage of being produced with a variety of lignocellulosic materials on a small scale using unskilled labor. Inorganic bonded wood and fiber composites are developing as a family of products for the construction and industrial markets, which combine the properties of organic and inorganic components. These products provide opportunities to engineer products to meet a wide range of requirements. Nondestructive Evaluation Nondestructive evaluation is becoming widely used in the wood products industry to save resources and energy and enable more economical use of the resource. Several systems are being used in sawmills for scanning and automatic grading of logs. These systems use either optical scanners or gamma ray scanners. The
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optical scanners measure log diameter at 10-milimeter intervals along the length in two or three directions to measure taper, butt swell, and irregularities. The gamma ray scanner uses green density variables together with outer shape variables to predict internal log quality. Scanning data for each log or board is relayed by microprocessors to program saw settings for appropriate cutting of that material. Mechanical grading of structural lumber is now common. Based on the relationship between stiffness and strength, it produces estimates of stress capacity that are much more reliable and consistent than is visual grading, which has been used for decades. Other nondestructive approaches make use of vibration or stress waves to determine stiffness. As hardwoods receive increasing attention for structural applications, commercially viable approaches to their evaluation are evolving. Lumber is evaluated by means of an X-ray scanner, through which density is measured at regular intervals along its length, and the location and approximate sizes of knots are determined (Schajer, 2001). Other systems use a color scan camera and laser scanner to determine optimum cuttings and use of individual boards. Recycled Wood Products In the United States, more than 160 million tons of waste wood were generated in 1998 and converted into a wide variety of useful products (McKeever, 1999). Wood waste from pallets, other wood products, and construction and demolition sites is increasingly valuable as a raw material for many products –structural, nonstructural, and decorative- and is suitable for the manufacture of composites than can incorporate performanceenhancing treatments and be 6
GUÍA molded or shaped as needed. Pallet pieces can be recycled to make new pallets or flooring, wainscoting, and furniture. Modern composite technologies combine waste paper or materials derived from wood waste with other fibers or materials, such as various recycled consumer plastics. Wood that cannot be converted to other products economically can be made into mulch and compost. Pulp and Paper Changes in papermaking have enabled mores species and smaller-diameter trees to be used, and the paper industry is especially effective in using recycled material in its furnish. While giving attention to both economy and paper characteristics, the level of recycling has grown substantially. For example, paper and paperboard in 1970 was made up of more than 80 percent wood pulp. By 1977 this percentage had dropped to 56 percent, and by 2010 it is expected to drop below 50 percent; 1999 data show wood pulp providing 55 percent of the fiber supply and recovered paper providing 39 percent (Abramowitz and Mattoon, 1999). This trend is due to successful recycling efforts and increased demand for more printing and writing paper, which have a lower fiber content than many other types of paper (AF&PA, 2001). Alternatives to kraft pulping, the world’s major pulping process, are becoming more and more a part of the diversified approach to papermaking. These alternative approaches take advantage of new ways to break down the lignin matrix in wood, the target of chemical pulping (Youngquist and Hamilton, 1999). Biological pulping, involving white lignin, both as a step in chemical pulping, and as a way of reducing energy consumption in mechanical pulping (Behrendt et al, 2000). Compression of chips before refining reduces energy consumption in mechanical pulping (Law et al, 2000). Production of pulp and paper products on the world scene has followed somewhat the same trend as wood panel products. World production has increased more than four-fold since 1960, and the US portion of that has decreased from 40 percent to less than 30 percent (fig. 4). Increased production of paper products has accompanied economic
development in most part of the world. The change in use of the raw material resource is shown in the 270 percent increase in use of wood pulp but an almost 800 percent increase in use of recovered paper (fig. 5). Exports of recovered paper have increased 750 percent during the same 40year period, indicating wide interest and broad market acceptance. Conclusion Technological changes in wood processing are keeping pace with market, environmental, and resource trends and concerns. The forest products industry has
develop ways to use more of the tree, processing it into a variety of new valued-added products. What would have been waste (e.g., sawdust and slab) now is manufactured into new and improved products, thus saving valuable landfill space and extending our forest resources. The increased production of reconstituted panels such as OSB and MDF and developments in engineered wood products will continue to improve efficiency in using a diversified wood resource. Engineered wood products increase opportunities for using small-diameter logs as well as lower-quality or lesser used species. As we look at the challenges to maintaining the wood supply in the face of rapidly growing population, increasingly severe environmental concerns, recognition of the need for resource sustainability, and the changing nature of the forest itself, we must recognize the urgent need for new process and product options. Many that we mentioned here are just now finding common
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consideration and will become increasingly valuable as the technology and economics are blended with new market opportunities and emerging forest management approaches. Composites seem especially promising, as they provide many valuable options that can be st realized and adapted to 21 century forestry. As the forest resource and its management evolve, the scientific, engineering, and technical innovations that have influenced forest products during the past 50 years must continue to keep pace with raw material and market needs.
Literature Cited ABBRAMOWITZ, J.N., AND A.T. MATTOON, 1999. Paper cuts: Recovering the Paper Landscape. Worldwatch Paper N°49. Washington, DC; Worldwatch Institute. ADAMS, D.B. 2002. Solid wood products: Rising consumption and imports, modest price growth. Journal of Forestry 100(2):14-19. AMERICAN FOREST & PAPER ASSOCIATION (AF&PA). 2001. Paper recovery progress report. Available online at www.afandpa.org; accessed by authors May 2001. BEHRENDT, C.J., R.A. BLANCHETTE, AND M. AKHTAR. 2000. Biomechanical pulping with Phlebiopsis gigantea reduced energy consumption and increased paper strength. Tappi Journal 83(9):65 BOWYER, J. 1995. Wood and other raw materials for the 21st century. Forest Products Journal 45(2):17-24 FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS (FAO). 2001. Available online at http://apps.fao.org/page/collections?s ubset=forestry; accessed by authors May 2001.
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GUÍA A.L. Hammet (
[email protected]) is associated professor and Robert L. Youngs is professor
emeritus, Department of Wood Science and Forest Products, Virginia Polytechnic Institute
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and State University, Blacksburg, VA 24061)
Extraiga las estructuras que más hayan dificultado su interpretación del texto.
En base a lo leído, elabore un cuestionario para que sus pares respondan.
Interprete la sección correspondiente a la Conclusión.
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