Aesthetical

Of the five possible shapes, the cube/parallelepiped and the truncated octahedron have been most widely used, with some simulations in the hexagonal prism. The formulae used to translate a particle back into the central simulation box for these three shapes are given in Appendix 6.4. It may be preferable to use one of the more common periodic cells even if there are aesthetic reasons for using an alternative. This is because the expressions for calculating the images may be difficult and inefficient to implement, even though the simulation would use fewer atoms. 

In general, textile fibers should be optically opaque so that their refractive indexes need to be significantly different from those of their most common environments, namely, air and water. Luster and color are two optical properties that relate to a fiber s aesthetic quatity and consumer acceptance. 

The predominant cellulose ester fiber is cellulose acetate, a partially acetylated cellulose, also called acetate or secondary acetate. It is widely used in textiles because of its attractive economics, bright color, styling versatiUty, and other favorable aesthetic properties. However, its largest commercial appHcation is as the fibrous material in cigarette filters, where its smoke removal properties and contribution to taste make it the standard for the cigarette industry. Cellulose triacetate fiber, also known as primary cellulose acetate, is an almost completely acetylated cellulose. Although it has fiber properties that are different, and in many ways better than cellulose acetate, it is of lower commercial significance primarily because of environmental considerations in fiber preparation. 

Triacetate offers better ease-of-care properties than secondary acetate ia many apparel appHcations. Of particular importance are surface-finished fabrics, eg, fleece, velour, and suede for robes and dresses. These fabrics offer superb aesthetic quaHties at reasonable cost. Triacetate is also deskable for print fabrics, where it produces bright, sharp colors. The recent discontinuance of triacetate fiber Hi the United States has led to the use of acetate with fibers such as polyester (47—50). 

Physically or chemically modifying the surface of PET fiber is another route to diversified products. Hydrophilicity, moisture absorption, moisture transport, soil release, color depth, tactile aesthetics, and comfort all can be affected by surface modification. Examples iaclude coatiag the surface with multiple hydroxyl groups (40), creatiag surface pores and cavities by adding a gas or gas-forming additive to the polymer melt (41), roughening the surface... 

The air jet textured yam process is based on overfeeding a yam into a turbulent air jet so that the excess length forms into loops that are trapped in the yam stmcture. The air flow is unheated, turbulent, and asymmetrically impinges the yam. The process includes a heat stabilization zone. Key process variables include texturing speed, air pressure, percentage overfeed, filament linear density, air flow, spin finish, and fiber modulus (100). The loops create visual and tactile aesthetics similar to false twist textured and staple spun yams. 

Coextrusion. An increasingly popular technique to produce tailored film or sheet products is to coextmde one or more polymer types in two or more layers of melt (6). In this fashion the benefits of specific polymer types or formulations may be combined. Thus high cost barrier resins may be combined with a low cost thicker layer of standard resin to achieve an optimum barrier film at lower cost. Thin sUp-control layers may be used on the surface of a bulk layer of opticaUy clear resin to obtain an aesthetic film with good handleabUity. Lower melting outer layers may be used to provide heat sealing for polymers that seal with difficulty by themselves. 

Deteriora.tlon. Apart from physical damage that can result from carelessness, abuse, and vandaUsm, the main problem with metal objects Hes in thek vulnerabihty to corrosion (see Corrosion and corrosion control) (127,128). The degree of corrosion depends on the nature and age of the object. Corrosion can range from a light tarnish, which may be aesthetically disfiguring on a poHshed silver or brass artifact, to total mineralization, a condition not uncommon for archaeological material. 

Conserva.tlon, Because the most common conservation problem with metal objects occurs when corrosion processes form a threat to the safety of the object or disfigure its appearance to an unacceptable degree (130,131), many conservation treatments are intended to stabilize the corrosion processes and to remove aesthetically displeasing corrosion cmsts. The latter requkes a great deal of thought and discussion as to when a corrosion layer ceases to be a deskable patina and becomes unacceptable. 

Packaging. Because of the extremely broad demands on the mechanical properties of packaging materials, the entire range of ceUular polymers from rigid to flexible is used in this appHcation. The most important considerations are mechanical properties, cost, ease of appHcation or fabrication, moisture susceptibUity, thermal conductivity, and aesthetic appeal. 

Other Additives. To provide and maintain the clarity of clear shampoos, the use of either ethyl or isopropyl alcohol maybe employed. Perfumes are added to make shampoos more pleasing in terms of odor, while dyes are incorporated to give visual aesthetics to the products. Salts of ethylenediaminetetraacetic acid are found to sequester and prevent formation of insoluble alkaline-earth metal salts. 

In certain brilliantine compositions, vegetable and animal oils are used as substitutes for mineral oil. In these systems, because of their potential for rancidity, antioxidants must be included. Other alternatives to mineral oils that have found utiHty in brilliantines are the polyethylene glycols which come in a variety of solubiHties and spreading properties. Use of these materials offers the advantage of chemical stabiHty to rancidity. Other additives found in brilliantines to improve their aesthetics include colorants, fragrance, medicated additives, lanolin, and fatty acid esters. 

Aesthetic properties are of greatest concern in decorative laminates. These include gloss, appearance, cleanabiUty, wear resistance, stain resistance, and other surface properties. Physical properties are of most importance for industrial laminates. These include strength, electrical and thermal properties, expansion coefficient, and punchabiUty. The definitions of the laminate grades in these standards foUow. 

Miscellaneous Types. Various decorative effects have been developed which meet specific aesthetic requirements. These laminates may have special visual appeal, such as gloss finish, deeply embossed textures, and metallic surfaces. They are designed for specific installations and may not be suitable for all apphcations. For this reason, they are not included in these standards. Information concerning thein proper appHcation, properties, and care should be requested from the manufacturer. 

As engineered stmctures, nonwovens can be designed to have appearances, textures, and other aesthetic properties comparable to traditional wovens and knits, and performance and functional properties superior to traditional wovens and knits. Nonwovens are, indeed, a distinct class of fiber-based materials with the characteristics of fabric and many of its useful properties. 

The fabric may also be given one or more of a number of other finishing treatments, either ia tandem with web formation and bonding or off-line as a separate operation, as a means of enhancing fabric performance or aesthetic properties. Performance properties iaclude functional characteristics such as moisture transport, absorbency, or repeUency flame retardancy electrical conductivity or static propensity abrasion resistance and frictional behavior. Aesthetic properties iaclude appearance, surface texture, and smell. 

Early marketing efforts for spunbonded fabrics centered on their substitution for existing, ie, woven, textile fabrics. Generally, success was achieved ia areas where only fiinctionahty was important. Extremely slow progress has occurred ia areas where textile-like aesthetics are required. Nevertheless, spunbonded fabrics are recognized as a unique class of materials within the general category of nonwoven fabrics (see Nonwoven fabrics, staple fibers). 

Diverse appHcations for the fabric sometimes demand specialized tests such as for moisture vapor, Hquid transport barrier to fluids, coefficient of friction, seam strength, resistance to sunlight, oxidation and burning, and/or comparative aesthetic properties. Most properties can be deterrnined using standardized test procedures which have been pubHshed as nonwoven standards by INDA (9). A comparison of typical physical properties for selected spunbonded products is shown in Table 2. 

Naturally Derived Materials. The following are descriptions of some of the most important naturally derived materials in use. Importance in this context is defined in terms of the total value of the materials, which range from expensive, low volume materials that have great aesthetic value to relatively inexpensive and widely used products. Eor some of the naturals, it is indicated whether they can be distilled to provide individual chemicals for use as such or as intermediates. Materials produced in this way from a given natural source are usually not interchangeable with those from other naturals or synthetics. In some cases this may be due to optical isomerism, which can have a significant effect on odor, but usually it is due to trace impurities. 

Jasmine. Jasmine is one of the most precious florals used ia perfumery. The concrete of jasmine is produced by hydrocarbon extraction of flowers from Jasminum officinale (var. GrandijJorum). The concrete is then converted to absolute by alcohoHc extraction. It is produced ia many countries, the most important of which is India, followed by Egypt. Jasmine products are rather expensive and are produced ia relatively small amounts compared with other materials. However, jasmine is particularly important ia perfume creation for its great power and aesthetic quaUties. Eour of the principal odor contributors to jasmine are OT-jasmone [488-10-8] (14), methyl jasmonate [91905-974-] (15), benzyl acetate [140-11 ], and iudole [120-72-9] (16). 

QuaHtative arguments deal primarily with the sense of ownership and security which result from individually owned generation systems. Additional complexity will arise from the aesthetic criteria specific to both individual homes and the surrounding community. Of course, the autonomy inherent in distributed rooftop arrays probably constitutes an institutional barrier to their acceptance by some utiHty companies, unless they are involved in the financing and/or marketing chain. 

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