Repeat pattern

In 1869, fhe Russian chemisf Mendeleev nofed fhaf fhe repeating patterns of... 

In Chapter 5 we said that many important engineering materials (e.g. metals) were normally made up of crystals, and explained that a perfect crystal was an assembly of atoms packed together in a regularly repeating pattern. 

Stereoregular polymer (Section 7.15) Polymer containing chirality centers according to a regular repeating pattern. Syndiotactic and isotactic polymers are stereoregular. 

Polymers, large molecules made up of smaller molecules in a repeating pattern, are used for many electrochromic materials. Conjugating polymers, which have alternating single and double bonds, are particularly suitable. Figure B shows the electrochemical oxidation of the conjugated polymer, polythiophene. Oxidation (in which electrons are removed) produces a semiconductive polymer. The neutral (unoxidized) polythiophene is red in color, whereas the semiconductive polythiophene (oxidized) is blue. In their neutral... 

Protein chains (Figure 23.8) can align themselves so that certain patterns are repeated. These repeating patterns establish what we call the secondary structure of the protein. The nature of the pattern is determined in large part by hydrogen bonding. Oxygen atoms on C=0... 

One problem with Mendeleev s table was that some elements seemed to be out of place. For example, when argon was isolated, it did not seem to have the correct mass for its location. Its relative atomic mass of 40 is the same as that of calcium, but argon is an inert gas and calcium a reactive metal. Such anomalies led scientists to question the use of relative atomic mass as the basis for organizing the elements. When Henry Moseley examined x-ray spectra of the elements in the early twentieth century, he realized that he could infer the atomic number itself. It was soon discovered that elements fall into the uniformly repeating pattern of the periodic table if they are organized according to atomic number, rather than atomic mass. 

A drawing by M. C. Escher that contains a repeating pattern. One two-dimensional unit cell is highlighted. 

Polyethylene has a repeating pattern of [— CH2 — CH2 —] units, each one derived from an ethylene... 

Figure 8 shows the trace of the application of Axiom- , Axiom-2, Rule-l, Rule-2, Rule-3, and Rule-4 in our specific scheduling problem. The trace consists of a repeated pattern of rule applications Rule-4 followed by either Rule-2 or Rule-3. At each step the intrasituational rule converts an end-time to a start-time, and then the start-time is matched to the... 

The TCNQ molecule in [TR(bzim)]2-TCNQ is sandwiched between two units of [ J,-N, C -bzimAu]3 in a face-to-face manner so that it is best represented by the formula (7t-[ J,-N, C -bzimAu]3)( j,-TCNQ)(7t-[p-N, C -bzimAu]3). The cyanide groups clearly are not coordinated to the gold atoms. The distance between the centroid of TCNQ to the centroid of the AU3 unit is 3.964 A. The packing of [TR(bzim)]2-TCNQ shows a stacked linear-chain structure with a repeat pattern of-(Au3)(Au3)(p-TCNQ) (Au3)(Au3)(p-TCNQ)- an ABBABB repeat The complex [TR(bzim)]2-TCNQ contains two very short intermolecular Au Au distances of 3.152 A (identical for the two aurophilic bonds). The intermolecular Au Au distance is even shorter than the intramolecular distances in the starting compound, which are 3.475, 3.471, and 3.534 A. The adjacent AU3 units in [TR(bzim)]2-TCNQ form a chair-type structure rather than the face-to-face (nearly eclipsed) pattern reported in Balch s studies of the nitro-9-fluorenones adducts with the trinuclear Au(I) alkyl-substituted carbeniate complexes. 

M. Eigen suggested that the primeval forms of tRNA consisted of iterative PurXPyr, thus, for example, GXC triplets. This assumption is present in the title of the publication Transfer-RNA, ein friihes Gen (Transfer RNA, an early gene ) (Eigen and Winkler-Oswatitsch, 1981). As shown above, a nucleotide chain with a repeating pattern naturally leads to the generation of a complementary antiparallel nucleotide sequence ... 

Because there are numerous silicates whose structures are made up of repeating patterns based on the Si04 tetrahedron, a type of shorthand notation has been developed for drawing the structures. For example, the Si04 unit can be shown as follows. 

But HREM enables us to "read off" directly the nature of the repeat patterns (see Figure 8), rather like reading off the constituents of a polypeptide chain (25, 26). 

The atomic structure of the nuclei of metal deposits, which have the simplest form since they involve only one atomic species, appear to be quite different from those of the bulk metals. The structures of metals fall mainly into three classes. In the face-centred cubic and the hexagonal structures each atom has 12 co-ordination with six neighbours in the plane. The repeat patterns obtained by laying one plane over another in the closest fit have two alternative arrangements. In the hexagonal structure the repeat pattern is A-B-A-B etc., whereas in the face-centred cubic structure the repeat pattern is A-B-C-A-B-C. In the body-centred cubic structure in which each atom is eight co-ordinated, the repeat pattern is A-B-A-B. (See Figure 1.4.)... 

TERMINATING DECIMAL a decimal that terminates. Eventually, when performing long division, the divisor divides evenly into one of the sub-dividends. Example 4.5, 23.6003. REPEATING DECIMAL a decimal whose fractional part follows a repeating pattern. The divisor never divides evenly into one of the sub-dividends, but a pattern emerges. Examples 8.99999. . ., 0.1 21 21 2. . . ., 4.567777... . ... 

This laboratory investigation will help you conceptualize the size of an atom. You will experiment with a latex balloon containing a vanilla bean extract. Latex is a polymer, meaning that it is a large molecule (a group of atoms that act as a unit) that is made up of a repeating pattern of smaller molecules. The scent of the vanilla extract will allow you to trace the movement of its molecules through the walls of the solid latex balloon. 

Symmetry elements (which should not be confused with the elements in a set) are the operators that generate the repeated pattern of symmetry. 

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