THE BIG CHAPTER


The application of molecular dynamics to liquids or solvent-solute systems allows the computation of properties such as diffusion coefficients or radial distribution functions for use in statistical mechanical treatments. A liquid is simulated by having a number of molecules (perhaps 1000) within a specific volume. This volume might be cube, a parallelepiped, or a hexagonal cylinder. Even with 1000 molecules, a significant fraction would be against the wall of the box. In order to avoid such severe edge effects, periodic boundary conditions are used to make it appear as though the fluid is infinite. Actually, the molecules at the edge of the next box are a copy of the molecules at the opposite edge of the box. These simulations are discussed in more detail in Chapter 39.  [c.64]

As described in the box Di ene Polymers in Chapter 10 most synthetic rubber is a copolymer of styrene and 1 3 butadiene  [c.449]

The selection process of power cables is almost the same as that of a bus system discussed in Section 28.3. For simplicity we consider only the basic data for selection which would suffice the majority of applications. For accurate calculations a similar approach will be essential as for the bus systems (Chapter 28). For site conditions and laying arrangements which may influence the basic rating of a cable, corresponding derating factors have also been provided. The information covered here will be useful to users to meet their cable requirements, although the data may vary marginally for different manufacturers. For more data on cables, not covered here, reference may be made to the cable manufacturers.  [c.531]

This Structure is far from ideai. The first probiem is one of segregation as the iong coiumnar grains grow they push impurities ahead of them." If, as is usuaiiy the case, we are casting alloys, this segregation can give big differences in composition - and therefore in properties - between the outside and the inside of the casting. The second probiem is one of grain size. As we mentioned in Chapter 8, fine-grained materiais are harder than coarse-grained ones. Indeed, the yield strength of steel can be doubled by a ten-times decrease in grain size. Obviously, the big columnar grains in a typical casting are a source of weakness. But how do we get rid of them  [c.93]

As described in the box "Diene Polymers" in Chapter 10, most synthetic rubber is a copolymer of styrene and 1,3-butadiene.  [c.449]

The determined eddy-eurrent parameter is the inductance of the eomplex impedance measured by impedance analyzer at j=100 kHz. Therefore the impulse response function from chapter 4.2.1. is used for calculation. The depth of the cracks is big in comparison to coil size. For presentation the measured and pre-calculated data are related to their maxima (in air). The path X is related to the winding diameter dy of the coil.  [c.372]

Chapter 13 Spectroscopy has been supple mented by an expanded discussion of H and C chemical shifts and a new section on 2D NMR A new box Spectra by the Thousands points the way to websites that feature libraries of spectra and spectroscopic problems of every range of difficulty  [c.1331]

As its name implies, this important analytical technique combines two separate procedures gas chromatography (GC) and mass spectrometry (MS). Both individual techniques are quite old. GC developed as a means of separating volatile mixtures into their component substances and provided a big step forward in the analysis of mixtures. The method is described fully in Chapter 35, but it can be summarized as follows (Figure 36.1) by passing a mixture in a gas stream (the gas phase) through a long capillary column, the inside walls of which are thinly coated with a liquid (the liquid phase), the components of the mixture become separated and emerge (elute) one after another from the end of the column. In a simple GC instrument, the emerging components are either burnt in a flame for detection (the popular flame ionization detector) or passed to atmosphere after traversing some other kind of detector. The detected components are recorded as peaks on a chart (the gas chromatogram). The area of a peak correlates with the amount of a component, and the time taken to pass through the column (the retention time, i.e., the time to the peak maximum) gives some information on the possible identity of the component. However, the identification is seldom absolutely certain and is often either vague or impossible to determine.  [c.253]

As its name implies, this important analytical technique combines two separate procedures liquid chromatography (LC) and mass spectrometry (MS). Both individual techniques are quite old. LC developed as a means of separating nonvolatile mixtures into their component substances and provided a big step forward in revealing their complexities and analyzing them. The method is described fully in Chapter 35, but it can be summarized as follows (Figure 37.1) by passing a mixture in a liquid stream (the mobile or liquid phase) through a long column packed with a stationary phase (particles of a special solid), the components of the mixture become separated and emerge (elute) one after another from the end of the column. In a simple LC instrument, the emerging components dissolved in the liquid mobile phase are measured by passing the liquid stream through either an ultraviolet (UV) or a refractive-index detector. The detected components are recorded as peaks on a chart (the liquid chromatogram). The area of a peak correlates with the amount of a component, and the time taken to pass through the column (the retention time, i.e., the time to the peak maximum) gives some information on the possible identity of the component. However, the identification is seldom absolutely certain and is often either vague or impossible to determine.  [c.261]

We discuss in detail in Chapter 28, the procedure to design a bus system, including its mounting and supporting structure and hardware for a required fault level.  [c.368]

The design criteria and construction details of this system are totally different from those of a non-isolaled phase bus system. This type of enclosure is therefore dealt separately in Chapter 31.  [c.861]

We will discuss this aspect in two parts, one for the nonisolated bus systems and the other for the phase-isolated bus systems as in Chapter 31.  [c.886]

Healing of enclosures for bus systems in such large ratings is detrimental to their design. In smaller ratings (say, up to 3200 A) it has been easier to do this by increasing the size of enclosure, choosing larger bus sections, changing their configuration or using a non-magnelic enclosure or by adopting more than one of these measures, as discussed in Chapter 28. But this is not the case in large ratings, where heal generated, particularly in the enclosure, is enormous due to carrying almost the same amount of indueed currents as the rating of the main conductors. Therefore, dissipating the heal of the conductor and the enclosure is a major task in an IPB system. When designing such a system it is imperative to first check the adequacy of the enclosure to dissipate all the heal generated within permissible limits.  [c.938]

To arrive at the most appropriate and economical design of the enclosure is a complex subject and requires detailed study. For brevity, in our present attempt, we have derived inferences from the established work in this field by engineers and authors (see the further reading) and have underlined briefly the basic approach to design such a system. For smaller ratings, up to 3200 A, the discussions in Chapter 28 will generally suffice to design a good bus system. There we have assumed the content of proximity on the conductors and exercised care while selecting the size and material of the enclosure, spacings between the enclosure and the busbars and between the busbars of two adjacent phases etc. In an IPB system, however, when the space occupied by the electric field is large may cause excessive parasitic currents within the enclosure and in the metallic structures in close proximity outside the enclosure and excessive heating in both. The assumptions made earlier may not suffice for its effect on the enclosure, supports and the structures in the vicinity.  [c.940]

Aluminium-based metals are the obvious choice" (Table 1.4) - they are light, corrosion resistant and non-toxic. But it took several years to develop the process for forming the can and the alloy to go with it. The end product is a big advance from the days when drinks only came in glass bottles, and has created a new market for aluminium (now threatened, as we shall see in Chapter 21, by polymers). Because aluminium is  [c.8]

The interaction area between the underside of the TBP saddle and the minor groove of DNA is formed by two large, complementary surfaces with no water molecules between them. A surprisingly large amount of this area is hydrophobic, in contrast to protein-DNA interactions that involve the major groove, which are mainly hydrophilic and sometimes mediated by water molecules (see Chapter 8). In TBP, side chains from the eight central p strands interact with both the phosphate sugar backbone and the minor groove of the eight nucleotides of the TATA box. Fifteen side chains projecting from the P strands make hydrophobic contacts with the sugars and bases of DNA. The phosphate groups are hydrogen bonded to arginine and lysine side chains at the edges of the interaction area.  [c.157]

The only DNA sequence-specific aspect of these hydrophobic contacts is that they exclude G-C base pairs that are, of course, absent from the TATA box. The amino group of guanine (see Chapter 7) would, if present, sterical-ly disrupt or modify the interface. Surprisingly, 12 of the 16 hydrogen bond acceptors of the minor groove (N3 of adenine and 02 of thymine) are buried in this interaction area without forming hydrogen bonds either to protein side chains or to water molecules. Studies of site-directed mutations have shown that burying polar side chains in a hydrophobic environment without satisfying their hydrogen-bonding requirements is energetically unfavorable. Clearly, the large number of energetically favorable hydrophobic interactions between TBP and TATA-box DNA must compensate for these unfavorable interactions in order to achieve binding constants in the nanomolar range.  [c.157]

Like Thr 124 and Thr 215, the Asn 69 and Asn 159 residues occupy equivalent positions in the two homologous motifs of TBP. By analogy with the symmetric binding of a dimeric repressor molecule to a palindromic sequence described in Chapter 8, the two motifs of TBP form symmetric sequence-specific hydrogen bonds to the quasi-palindromic DNA sequence at the center of the TATA box. The consensus TATA-box sequence has an A-T base pair at position 4, but either a T-A or an A-T base pair at the symmetry-related position 5, and the sequence is, therefore, not strictly palindromic. However, the hydrogen bonds in the minor groove can be formed equally well to an A-T base pair or to a T-A base pair, because 02 of thymine and N3 of adenine occupy nearly stereochemically equivalent positions, and it is sufficient, therefore, for the consensus sequence of the TATA box to be quasi-palindromic.  [c.158]

The untwisting and strand separation of DNA are distortions necessary for transcription. These distortions occur at specific DNA sequences that contain a T-A step in the double helix, either in isolation, as described in Chapter 8 for CAP promoter regions in bacteria, or as the tandem repeat T-A-T-A in the TATA box of eucaryotic DNA. The B-DNA structure of such sequences is less stable than those containing G-C base pairs because the stacking interactions between A-T and T-A base pairs are relatively weak. TBP exploits this property of the TATA box to distort and bend the DNA and initiate transcription. The TATA box thus carries information for transcriptional initiation primarily at a physical level its DNA is easily deformed. Chemical information, in the form of sequence-specific interactions between nucleotides and the protein, plays only a minor role, in contrast to the binding of specific transcription factors to the major groove of DNA. This is also reflected in the sequences of different TATA boxes, where the actual combinations of T-A and A-T base pairs are quite diverse. The minor groove recognition and the bend-ability of DNA works equally well for different combinations provided there are no G-C or C-G base pairs involved.  [c.158]

Since the advent of Bakelite some 90 years ago phenol-formaldehyde moulding compositions have been used for a great variety of purposes. Perhaps the most well-known applieations are in domestic plugs and switches. It should, however, be pointed out that since World War II, in Britain at least, urea-formaldehyde plastics have largely replaeed phenol-formaldehyde for these purposes beeause of their better anti-traeking properties and wider colour range. There are, nevertheless, many applications where the phenolies have proved quite adequate and continue to be used as insulators. In general it may be said that the phenolies have better heat and moisture resistance than the urea-formaldehyde mouldings (see Chapter 24). Phenol-formaldehyde mouldings have also found many other applications in the electrical industry, in some instances where high eleetrieal insulation properties are not so important. These include Instrument cases, knobs, handles and telephones. In some of these applications they have now been replaced by urea-formaldehydes, melamine-formaldehydes, alkyds or the newer thermoplastics because of the need for bright colours or in some cases in an attempt to produce tougher produets. In the car industry phenol-formaldehyde mouldings are used in fuse-box covers, distributor heads and in other applications where good electrical insulation together with good heat resistance are required.  [c.652]

Chapter 13, Spectroscopy, has been supplemented by an expanded discussion of H and C chemical shifts and a new section on 2D NMR. A new box. Spectra by the Thousands, points the way to websites that feature libraries of spectra and spectroscopic problems of every range of difficulty.  [c.1331]

In addition to its role in preventing scurvy (see Human Biochemistry box Ascorbic Acid and Scurvy and also Chapter 6), ascorbic acid also plays important roles in the brain and nervous system. It also mobilizes iron in the body, prevents anemia, ameliorates allergic responses, and stimulates the immune system.  [c.599]

In Chapter 2, I mentioned that there was great interest in water as a solvent, and explained about the pioneering calculations of Rahman and Stillinger (1972). Many molecular mechanics (MM), Monte Carlo (MC) and molecular dynamics (MD) studies have been made based on their box of 216 water molecules. A good starting point is the work of Jorgensen and coworkers.  [c.254]

The alcohol intermediate happens to be the exact kind of intermediate that was produced by the Grignard reagent reaction with propanal to produce isosafrole back-a-ways in the big chapter. So what the chemist does is apply the 1g of KHSO4 to that crude alcohol intermediate and process it just as was done before to give isosafrole, or propenylbenzene or 3,4-methylenedioxyphenyl -1-butene or phenylbutene (yield=91% ). This is a great little procedure.  [c.246]

The Stem and double-layer systems play an important role in stabilizing colloidal suspensions, and conversely, the study of suspensions has provided much information about the electrical nature of the interface. In particular, lyopho-bic sols are often stabilized by the presence of a surface charge. Two particles approaching closely will flocculate because of the dispersion interaction discussed in Chapter VI. The electrostatic repulsion discussed in Section V-6 deters this approach hence, variations in ionic strength and or f will have a marked effect on the stability of such sols. Some classic data [89] shown in Table V-4, illustrate the generd relation between stability and f potential for a gold sol in a solution containing added Al. A review of these stability issues in ceramic materials is given by Pugh [90].  [c.189]

The reason for this difference in behavior was elucidated by Pollard and Present [8]. These authors were not able to solve the complete problem of pressure-driven flow in a capillary throughout the intermediate pressure range indeed, as mentioned in Chapter 3, this remains unsolved today. Instead they considered the simpler case of isobaric self-diffusion, in which the tube contains molecules of a single species, some of which are considered to be "tagged". It is then possible to extend the well known theory of Kiiudsen streaming [9] Co calculate the diffusion rate of the tagged molecules under the influence of a gradient in their concentration, and this can be done throughout the range of pressures over which the mean free path and the tube diameter are comparable. As p" 0 the flux approaches the well known limit given by equations (2.5) and (2.8), but as p increases from zero Che flux decreases as a result of the added resistance to motion posed by inter-molecular collisions. In Pollard and Present s calculation this decrease is monotonic--there is no mininjum--buC their system differs from that investigated experimentally by Knudsen, since pressure gradients can generate viscous streaming in the latter case when the pressure is sufficiently high. As the mean pressure increases, the increase in flow as a consequence of viscous streaming in the experimental situation exceeds the decrease resulting from intermolecular collisions, as estimated by Pollard and Present. Thus the ratio of flow to pressure drop passes through a minimum..and begins to rise again.  [c.55]

O. L. Davies and co-workers. The Design andAna/ysis of Industria/Experiments, 2nd ed., Hafner, New York, 1956 reprinted by Longman, New York, 1987. This book, which is a sequel to the authors basic text Statistica/Methods in Eesearch and Production, is directed at industrial situations and chemical appHcations. Three chapters are devoted to factorial experiments and one chapter to fractional factorial plans. A lengthy chapter (84 pp.) discusses the deterrnination of optimum conditions and response surface designs, which are associated with the name of G. Box, one of the seven co-authors. Theoretical material is presented in chapter appendices.  [c.524]

Many carbamates have been used as protective groups. They are arranged in this chapter in order of increasing complexity of stmcture. The most useful compounds do not necessarily have the simplest stmctures, but are /-butyl (BOC), readily cleaved by acidic hydrolysis benzyl (Cbz or Z), cleaved by catalytic hy-drogenolysis 2,4-dichlorobenzyl, stable to the acid-catalyzed hydrolysis of benzyl and /-butyl carbamates 2-(biphenylyl)isopropyl, cleaved more easily than /-butyl carbamate by dilute acetic acid 9-fluorenylmethyl, cleaved by /3-elimination with base isonicotinyl, cleaved by reduction with zinc in acetic acid 1-adamantyl, readily cleaved by trifluoroacetic acid and ally], readily cleaved by Pd-catalyzed isomerisation.  [c.316]

A study of seismic effects on a structure, equipment or device will reveal its worthiness to withstand an earthquake without appreciable damage and perform satisfactorily during and after sudden shocks and vibrations. It is possible to study their performance through prescribed seismic withstand tests. Where a test is not possible, due to the size and/or weight of the object, performance can be assessed through mathematical analysis. Seismic testing is a complex subject. To provide the full details here is neither possible nor the purpose of this text. We have covered this subject only broadly to provide an introduction to the applicability of earthquake engineering to more constructive use structures, particularly to uike safety measures in the initial stages when commencing a new project. For those in this field and who are seeking more details/clarifications on the subject, references have been provided at the end of this chapter. Whatever minimum information is considered necessary to familiarize an engineer with this subject are provided below. National and international specifications on rotating machines, switchgears and switchgear and eontrolgear assemblies and bus systems as diseussed in Chapters 11,14 and 32, respectively, do not normally require such tests. They become vital when such equipment is installed in a nuclear power plant and where, by virtue of its failure or malfunetioning during or after sueh a disturbanee, they may cause a process destabilization. Such a destabilization may jeopardize the safety and integrity of the main plant, and result in an accident or radioactive radiation beyond critical limits. The radiation may cause a catastrophe to  [c.444]

To limit the fault level, if it is likely to exceed the designed limits, or the breaking capacity of the interrupting device, or the associated equipment and to limit the induced circulating currents in the enclosure during normal operation, to contain enclosure losses in very large ratings of bus systems, say, 25 000 A and above (above 500 MW), then unsaturable type series reactors (for details refer to Chapter 27) may be provided in the enclosure circuit, as illustrated in Figure 31.8 to limit such high currents especially during a fault. The reactors should not saturate under fault conditions, as they are provided to supplement the enclosure circuit impedance to limit the high currents through the enclosure, especially during faults, and reduce the forces between the main conductors. For a better flow of circulating currents, it is also grounded only at one point. Accordingly, it is supported on non-conducting supports to keep the ground path continuous and completely isolated. The enclosure must also be insulated electrically from the rest of the plant by rubber bellows.  [c.934]

The grain boundary energy tied up in a polycrystalline metal works in the same sort of way to give us a driving force for grain coarsening. As we shall see in Chapter 13, grain coarsening can cause us big problems when we try to weld high-strength steels together. A typical y b(0.5 J m ) and grain size (100 jUm) give us a Wj of about 2 x 10 J mohk  [c.55]

Nucleation - of one sort or another - crops up almost everywhere. During winter plants die and people get frostbitten because ice nucleates heterogeneously inside cells. But many plants have adapted themselves to prevent heterogeneous nucleation they can survive down to the homogeneous nucleation temperature of -40°C. The "vapour" trails left by jet aircraft consist of tiny droplets of water that have nucleated and grown from the water vapour produced by combustion. Sub-atomic particles can be tracked during high-energy physics experiments by firing them through superheated liquid in a "bubble chamber" the particles trigger the nucleation of gas bubbles which show where the particles have been. And the food industry is plagued by nucleation problems. Sucrose (sugar) has a big molecule and it is difficult to get it to crystallise from aqueous solutions. That is fine if you want to make caramel -this clear, brown, tooth-breaking substance is just amorphous sucrose. But the sugar refiners have big problems making granulated sugar, and will go to great lengths to get adequate nucleation in their sugar solutions. We give examples of how nucleation applies specifically to materials in a set of case studies on phase transformations in Chapter 9.  [c.74]

Emphysema is often associated with a specific mutation of the serpin antitrypsin. The mutant serpin molecules form aggregates in the liver, causing a deficiency of antitrypsin in the blood plasma and consequently increased proteolytic degradation of elastin fibers in the lung by the enzyme elastase. It has been shown that the formation of aggregates in vivo is due to an extremely slow folding process of the mutant antitrypsin leading to accumulation of a folding intermediate that aggregates. This is one example of aggregation of incompletely folded or misfolded molecules that can lead to pathologic consequences or even severe disease. Other examples involve the formation of large aggregates, plaques, of proteins in amyloid structures associated with Alzheimer s disease and spongiform encephalopathies such as scrapie, BSE "mad cow disease" and Creutzfeld-Jacob disease (see Chapter 14). A better understanding of the folding and misfolding processes might, therefore, open up new approaches to drugs for these diseases.  [c.113]

TFIIB is arranged in two domains, both of which have the cyclin fold described in Chapter 6. Both domains bind to the TBP-TATA box complex at the C-terminal stirrup and helix of TBP. The phosphate and sugar moities of DNA form extensive non-sequence-specific contacts with TFIIB both upstream and downstream of the middle of the TATA box.  [c.159]

Some 50 years later, in the 1990s Bayer produced their BAK polyesteramides by co-reacting either hexamethylene diamine or e-caprolactam with adipic acid and butane glycol. These materials do have sufficient regularity to be crystallisable and are of interest as biodegradable plastics and are discussed further in Chapter 31.  [c.529]

For reviews of the synthesis and properties of bridgehead alkenes, see G. L. Buchanan, Chem. Soc. Rev. 3 41 (1974) K. I Shea, Tetrahedron 36 1683 (1980) R. Keese, Angew Chem. Int. Ed Engl. 14 528 (1975) G. Szeimies, in Reactive Intermediates. Vol. 3, R. A. Abramovitch, ed., Plenum Press, New bik, 1983, Chapter 5 G. Szeimies, Adv. Strain Org. Chem. 2 1 (1992).  [c.166]

Although it is not inherent in the LESF method of event tree construction, it is customary to treat support system dependencies by defining degraded states that are evaluated using separate event trees to show the degradation. That is, the nodal probabilities have one set of values for. say, full electric power and another set for a degraded state in which one bus is out. Some PSAs carry this one step further by defining "binary conditionals" (.see BETA in Chapter 12). A generic set of probabilities are specified for a given tree in a given degraded state, but the probability of system failing is not the same throughout the tree and may take on different values depending on the preceding sequence of events  [c.117]

Class I The Class I BSC provides personnel and environmental protection, but no product protection. It is similar in air movement to a chemical fume cupboard, but has a HEPA filter (see Chapter 9) in the exhaust system to protect the environment (Fig. 10.94). In the Class 1 BSC, unfiltered room air is drawn across the work surface. Personnel protection is provided by this inward air velocity as long as a minimum velocity of 0.37 m s" is maintained through the front opening (see the discussion on fume cupboards in Section 10.2.3.3). In many cases Class I BSCs are used specifically to enclose equipment.  [c.984]

Many carbamates have been used as protective groups. They are arranged in this chapter in order of increasing complexity of structure. The most useful compounds (not necessarily the simplest structures) are /-butyl (BOC), readily cleaved by acidic hydrolysis benzyl (Cbz or Z), cleaved by catalytic hydrogenol-ysis 2,4-dichlorobenzyl, stable to the acid-catalyzed hydrolysis of benzyl and /-butyl carbamates 2-(biphenylyl)isopropyl, cleaved more easily than /-butyl carbamate by dilute acetic acid 9-fluorenylmethyl, cleaved by /3-elimination with base isonicotinyl, cleaved by reduction with zinc in acetic acid 1-adamantyl, readily cleaved by trifluoroacetic acid and allyl, readily cleaved by Pd-catalyzed isomerization.  [c.503]


See pages that mention the term THE BIG CHAPTER : [c.231]    [c.313]    [c.66]    [c.135]    [c.136]    [c.557]    [c.879]    [c.156]    [c.156]    [c.157]    [c.364]   
See chapters in:

Total synthesis II  -> THE BIG CHAPTER