Large structures

The choice of bctiling lirnc depends on ibc purpose of llic molecular dynarn ics simulation. If the sim u lalioti is for con form aliori al search es. lb e b catin g step is not critical for a successfti I calculation, The healing step may be rapid lo induce large structural changes that provide access to more of tbc conformational space. 

Jack A and M Levitt 1978. Refinement of Large Structures by Simultaneous Minimization of Energy and R-factor. Acta Crystallographica A34 931-929. 

Today, cement and concrete replace stone in most large structures. But cement, too, is a ceramic a complicated but fascinating one. The understanding of its structure, and how it forms, is better now than it used to be, and has led to the development of special high-strength cement pastes which can compete with polymers and metals in certain applications. 

Although the dynamic nature of biological molecules has been well accepted for over 20 years, the extent of that flexibility, as manifested in the large structural changes that... 

The specific protein-DNA interactions described in this book are all with DNA in its regular B-form, or, in some cases with distorted B-DNA. In biological systems DNA appears not to adopt the A conformation, although double-stranded RNA does preferentially adopt this conformation in vivo. Whether or not Z-DNA occurs in nature is a matter of controversy. However, the formation of A-DNA and Z-DNA in vitro does illustrate the large structural changes that DNA can be forced to undergo. 

TBP binds in the minor groove and induces large structural changes in DNA... 

TBP-TATA box complexes are known A p sheet in TBP forms the DNA-binding site TBP binds in the minor groove and induces large structural changes in DNA The interaction area between TBP and the TATA box is mainly hydrophobic Functional implications of the distortion of DNA by TBP... 

Since cross-linking occurs via an addition mechanism across the double bonds in the polyesters and the reactive diluent there are no volatiles given off during cure (c.f. phenolic and amino-resins) and it is thus possible to cure without pressure (see Figure 25.1). Since room temperature cures are also possible the resins are most useful in the manufacture of large structures such as boats and car bodies. 

The major process today is the hand lay-up technique in which resin is stippled and rolled into the glass mat (or cloth) by hand. Moulds are easy to fabricate and large structures my be made at little cost. 

Difficulties in moulding large structural parts with no control on fibre orientation. 

Because of this continued emphasis on adhesive bonding technology development over the years, the airframes of modem front-line aircraft such as the B-2 bomber and the F-117 and F-22 fighters are largely structurally bonded advanced composites. They tend to be comprised of materials that are more advanced (expensive) than commercial aircraft such as carbon and boron fiber reinforcements with cyanate esters, bismaleimides, polyimides or other high-temperature resin matrices and adhesives. 

On the other hand, for aircraft and spacecraft structures, real laminate behavior is pretty typically linear. Laminate behavior is reasonably linear even with some 45° layers which you would expect to contribute their nonlinear shear deformation characteristic to the overall laminate and degrade its relative performance. If you go beyond the behavior of a laminate and look at a large structure, typically the load-response characteristics are linear. Even around a cutout, linear behavior exists. Beyond that apparent linear performance of many laminates, you might not like to operate in some kind of a nonlinear response regime. Certainly not when in a fatigue environment and probably not in a creep environment either would you like to operate in a nonlinear behavior range. 

A recent adaptation of the procedure employing perchlorate and fluoro-borate salts has been reported by Leonard and Paukstelis (J5). This report includes proof of structure by direct comparison to iminium salts prepared by protonation of enamines. The general reaction reported was that of a ketone or aldehyde with a secondary amine perchlorate to give iminium salts. A large structural variety of carbonyl compounds and several amine... 

Parallel /3-sheets tend to be more regular than antiparallel /3-sheets. The range of (f) and i/t angles for the peptide bonds in parallel sheets is much smaller than that for antiparallel sheets. Parallel sheets are typically large structures those composed of less than five strands are rare. Antiparallel sheets, however, may consist of as few as two strands. Parallel sheets characteristically distribute... 

This is a very general and mild method for the preparation of amides, applicable to large structural variations in both the acid and the amine. A variety of chloro-formates can be employed, but isobutyl chloroformate is used most often. The solvent is not critical, but generally, THE is used. 

It is significant that most of the data from which a remarkable uniformity of attack is deduced are derived from small isolated panels. This is the most convenient form of specimen for measurements of corrosion rates by loss of weight but it eliminates the important effect of galvanic currents passing between remote parts of a large structure. It is believed that the experience of civil engineers and other users would not support the conclusion suggested by panel tests that corrosion is no faster in tropical than in temperate waters. 

Most steels fall into this category, ranging from large structural sections to thin sheet, and minor variations in composition do not markedly affect their corrosion resistance. This is not generally important since such steels are usually protected by some form of coating which is specific for the condition of service. 

Thermally treat the structures to effect a re-solution of the chromium carbide this is often impractical in large structures unless local heat treatment is employed, but is not always satisfactory since a sensitised zone could be produced just outside the local thermally treated region. 

Large structures, even in near-neutral pH environments, require a considerable current for cathodic protection. As a result structure coatings are... 

It has been noted that the total current required to protect large structures can be substantial even in mildly corrosive environments. In seawater, for example, an initial current in the region of 200mA/m for bare steel might well be required in the North Sea. This is because the relatively high oxygen concentration and the tide and wave action all contribute to a facile cathodic reaction. Fortunately this current diminishes with time. The reason for this is the protective scale on the steel surface which forms during cathodic protection by decomposition of the seawater. 

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