Machine knots

The use of construction plastics allows one to create principally new technology of creation the details, machine knots and devices what provides for the high economical efficiency. The construction polymers are well used by means of modem methods casting and extmsion to the articles operating in conditions of sign-altering loads at temperatures 100-200 °C. 

This process uses coUated signatures that ate sewn on special machines which pass thread through the folds of each signature and ate knotted at the back Glue is appHed to the spine and hard covets ate attached. Finished books ate then dried in special hydraulic presses. 

After numerous answers were brought to the synthetic challenge itself, there arose ever more insistently the quest for functions and properties of such special compounds. Already, even if still far from real applications, one can imagine, based on interlocked, threaded or knotted multi-component molecules, new organic materials, specific polymers, molecular devices or machines able to process and transfer energy, electrons or information. 

Jean-Pierre Sauvage is a CNRS director of research and is located at the Universite Louis Pasteur in Strasbourg, France. His current research interests include the development of models of the photosynthetic reaction centre using transition metals and porphyrins [5], topology (synthetic catenanes and knots) [6], and molecular machines [7]. 

The mechanical bond and technology have gone hand-in-hand since the advent of machinery. Indeed, many of the world s simplest and oldest machines, a wheel on an axle or a pulley (Fig. 7i), for example, are based on the mechanical bond. It has been especially important in transportation imagine trying to sail without knots and pulleys or drive without wheels It also appeared as early as 2,700 b.c. in the world s first calculator the abacus (Fig. If). And, just as we find it near the beginning of human history, most of us meet the mechanical bond near the beginning of our lives it is still among the most common features in children s toys, such as the timeless rattle or the bead maze in Fig. 7g. 

The prepared cotton waste on arrival at the factory contains a notable percentage of hygroscopic moisture, also wood, pieces of iron, metal, string, rubber, etc . The mechanical impurities are removed as far as possible by hand-picking, and the cotton is then passed through a teasing machine (Fig. 30), which separates the cotton fibres and opens out knots and lumps. It is then again picked over as it leaves the machine. 

The attraetion of machine grading lies in the fact that individual pieces are tested so that the defleetion in bending (the usual method for alloeating a pieee to a grade) reflects both the natural defects (knots etc) and the intrinsie features (density, MFA etc.) of that piece. 

Before going on to discuss molecular electronic machines, it will be useful to describe their structural foundation at a molecular level, namely those based on interlocked molecules. Interlocked molecules can take on a variety of forms, the most common being catenanes, rotaxanes, knots [16], and carceplexes [17]. For the purpose of this review, only catenanes, rotaxanes and their geometrically related complexes - pseudorotaxanes [18] - will be discussed. When conferred with the ability to undergo some mechanical motion as a result of an applied stimulus - be it chemical, electrochemical, or photochemical - these interlocked molecular and interpenetrated supramo-lecular systems often take on the characteristics of molecular machines [19]. 

With precise design criteria established, supramolecular interactions have been exploited to design and synthesise new and functional mechanically interlocked molecules in high yields [9]. Over a relatively short period of time, mastery of controlled synthesis of mechanically interlocked molecules has led to an extraordinary array of functional materials and molecular machines [10]. Examples of these include logic gates, sensors for explosives, anions and cations, in addition to exquisite molecules with complex topologies (such as molecular knots) that have yet to be thoroughly exploited. 

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