【正文】 nd interactions with their nuclei. On an atomic level, structure enpasses the organization of atoms or molecules relative to one another. The next large structural realm, which contains large groups of atoms that are normally agglomerated together, is termed microscopic meaning that which is subject to direct observation using some type of microscope. Finally, structural elements that may be viewed with the naked eye are termed macroscopic. The notion of property deserves elaboration. While in service use, all materials are exposed to external stimuli that evoke some type of response. For example, a specimen subject to forces will experience deformation。 mechanical, electrical, thermal, magnetic, optical, and deteriorative. For each there is s characteristic type of stimulus capable of provoking different responses. Mechanical properties relate deformation to an applied load or force: examples include elastic modulus and strength. For electrical properties, such as electrical conductivity and dielectric constant, the stimulus is an electric filed. The thermal behavior of solids can be represented in terms of heat capacity and thermal conductivity. Magnetic properties demonstrate the response of a material to the application of a magnetic field. For optical properties, the stimulus is electromagnetic or light radiation: index of refraction and reflectivity are representative optical properties. Finally, deteriorative characteristics indicate the chemical reactivity of materials. In addition to structure and properties, two other important ponents are involved in the science and engineering of materials, namely processing and performance. With regard to the relationships of these four ponents, the structure of a material will depend on how it is processed. Furthermore, a material39。 normally, a material having a high strength will have only a limited ductility. In such cases a reasonable promise between two or more properties may be necessary. A second selection consideration is any deterioration of material properties that may occur during service operation. For example, significant reductions in mechanical strength may result from exposure to elevated temperatures or corrosive environments. Finally, probably the overriding consideration is economics. What will the finished product cost? A material may be found that has the ideal set of properties, but is prohibitively expensive. Here again, some promise is inevitable. The cost of a finished piece also includes any expense incurred during fabrication. The more familiar an engineer or scientist is with the various characteristics and structureproperty relationships, as well as processing techniques of materials, the more proficient and confident he or she will be to make judicious materials choices based on these criteria.(Selected from Materials Science and Engineering: An Introduction, by William D Callister,2002) New Words and Expressions pottery n. 陶瓷 by virtue of 依靠 （……力量），憑借，由于，因?yàn)? empower ，準(zhǔn)許，使能夠 empower do sth. 授權(quán)某人做某事 forerunner n. 先驅(qū)（者），傳令官，預(yù)兆 stepwise a. 逐步地，分階段地 interdisciplinary a. 交叉學(xué)科的 metallurgy n. 冶金學(xué) nebulous a. 星云的，云霧狀的，模糊的，朦朧的 agglomerate n. 大團(tuán)，大塊；，凝聚的 elaboration n. 詳盡的細(xì)節(jié)，解釋?zhuān)U述 electrical conductivity 電導(dǎo)性，電導(dǎo)率 dielectric constant 介電常數(shù) thermal conductivity 熱導(dǎo)性，熱導(dǎo)率 heat capacity 熱容 refraction n. 衍射 reflectivity n. 反射 ductility n. 延展性 corrosive a. 腐蝕的，蝕壞的，腐蝕性的；n. 腐蝕物，腐蝕劑 overriding a. 最重要的；高于一切的 prohibitive a. 禁止的，抵制的 judicious a. 明智的 criterion n. 標(biāo)準(zhǔn)，準(zhǔn)則，尺度Notes1. It was not until relatively recent times that scientists came to understand the relationships between the structural elements of materials and their ，強(qiáng)調(diào)時(shí)間。參考譯文：直到最近，科學(xué)家才終于了解材料的結(jié)構(gòu)要素與其特性之間的關(guān)系。參考譯文：“property一詞的概念值得詳細(xì)闡述。be exposed to,暴露，面臨，處于……境地。 only rare occasion does a material possess the maximum or ideal bination of ，其原句為：A material possesses the maximum or ideal bination of properties on only rare “具有”的意思。 biomaterials are implanted into the human body. A brief explanation of the material types and representative characteristics is offered next. Metals: Metallic materials are normally binations of metallic elements, they have large numbers of nonlocalized electrons。 a polished metal surface has a lustrous appearance. Furthermore, metals are quite strong, yet deformable, which accounts for their extensive use in structural applications. Ceramics: Ceramics are pounds between metallic and nonmetallic elements: they are most frequently oxides, nitrides, and carbides. The wide range of materials that falls within this classification includes ceramics that are posed of clay minerals, cement, and glass. These materials are typically insulative to the passage of electricity and heat, and are more resistant to high temperatures and harsh environments than metals and polymers. With regard to mechanical behavior, ceramics are hard but very brittle. Polymers: Polymers include the familiar plastic and rubber materials. Many of them are organic pounds that are chemically based on carbon, hydrogen, and other nonmetallic elements。 examples include electronic equipment (VCRs, CD players, etc.), puters, fiber optic systems, spacecraft, aircraft, and military rocketry. These advanced materials are typically either traditional materials whose properties have been enhanced or newly developed, highperformance materials. Furthermore, they may be of all material types (. metals, ceramics, polymers),and are normally relatively expensive. Modern Materials NeedsIn spite of the tremendous progress that has been made in the discipline of materials science and engineering within the past few years, there still remain technological challenges, including the development of even more sophisticated and specia