Structural concerns

Sometimes there are problems with self-induced bin vibrations. If these vibrations are high in frequency but low in amplitude, an interesting phenomenon called silo music (humming) or sik) honking may be experienced. This can be a nuisance to personnel or neighbours nearby but is usually not a structmal concern. If, on the other hand, the bin vibrations are low in frequency but high in amplitude, the result is what are called silo quakes. These apply massive dynamic loads that most vessels are not designed to withstand. Structural failures have occurred due to this mechanism. 

Construction errors include poor quality workmanship (incorrect bolts, incorrect placement of reinforcing steel, incorrect material type or thickness) and unauthorised design changes made during construction. 

Whatever the structural problem, it is essential that, at the first sign of trouble, there be an appropriate response. Continuing to empty a vessel that is already starting to fail may well result in complete collapse of the structure. Engineers trained in structural issues as well as solids flow should be consulted to ensure that property damage is kept to a minimum and personnel are kept out of harm s way. 

Silos and bins should be inspected on a routine basis to anticipate potential flow and structural problems before these become major. 

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The results of these experiments have been considered by the Joint Committee for the Co-ordination of the Cathodic Protection of Buried Structures and, in view of the various types of buried structures concerned and the circumstances in which field tests are conducted, the Committee decided not to amend its provisional recommendation that when cathodic protection is applied to a buried structure the maximum permissible potential change in the positive direction on a nearby pipe or cable should be 20 mV. If there is a history of corrosion on the unprotected installation no detectable positive change in structure/soil potential should be permitted. These criteria of interaction have been adopted in the British Standard Code of Practice for Cathodic Protection . 

Tertiary structure concerns the relationships between secondary structural domains. Quaternary structure of proteins with two or more polypeptides (oligomeric proteins) is a feature based on the spatial relationships between various types of polypeptides. 

Information, particularly structural, concerning vanadium-dependent nitrogenases, is relatively limited. The consensus is that they resemble the molybdenum nitrogenase in most aspects except for the presence of a FeV cofactor, and they will not be discussed further. 

Fig. 23 Plot of C-OX bond length versus pKUO for 1-phenylethyl and l-(4-nitrophenyl)ethyl compounds [108], The error bars represent two standard deviations in the bond-length measurements, and the numbers accompanying each point are mean values of the torsional angle 8 [110] for the structure concerned. Reprinted with permission from Edwards et al. (1986a). Copyright 1986 American Chemical...

A simpler question related to structure concerns the folding. We know that our proteins display a biological function only when they assume a specific conformation. Let us assume to be able to make a large library of NBPs what would be the frequency of folding - namely which percentage of them would assume a stable tertiary conformation ... 

Heteropolyanions and isopolyanions are polymeric oxoanions (polyoxometalates) (2, 3, 5, 6). The structure of a heteropolyanion or polyoxoanion molecule itself is called a primary structure (5, 6, 77). There are various kinds of polyoxoanion structure (Section II.A. 1). In solution, heteropoly anions are present in the unit of the primary structure, being coordinated with solvent molecules and/ or protonated. Most heteropolyanions tend to hydrolyze readily at high pH (Section 1I.C). Protonation and hydrolysis of the primary structure may be major structural concerns in solution catalysis. Heteropoly compounds in the solid state are ionic crystals (sometimes amorphous) consisting of large polyanions, cations, water of crystallization, and other molecules. This three-dimensional arrangement is called the secondary structure. For understanding catalysis by solid heteropoly compounds, it is important to distinguish between the primary structure and the secondary structure (5, 6, 17). Recently, it has been realized that, in addition... 

In Figure 5 we show an example decomposition of the security trust objective. We can notice some similarities between the structures presented in figures 4 and 5. This similarity suggests that the two domains (i.e. safety and security) have developed similar conceptual frameworks which possibly could be harmonized into a common one. To illustrate this, compare the notions of hazard and vulnerability or mishap and incident from figures 4 and 5 respectively. In particular, it suggests that the trust cases aiming at safety or security can have similar structures concerning their decomposition into more specific trust objectives. This in particular can lead to the concept of trust case patterns which will not be further discussed in this paper. 

An interesting aspect of the bridging hydride structure concerns the direction of the Jahn-Teller axis on nickel. With the hydride, there are five ligands around nickel and one of these are therefore forced to... 

The first question posed by this structure concerns the formal charge distribution between the two Gd, B6 and B2 units. If we naively apply the Zintl-Klemm concept we arrive at [Gd3+]2[B6, B2]6. The [B6]2 cluster with six external bonds obeys the cluster electron-counting rules. Consequently, the B2 fragment must have a charge of —4. This corresponds to saturated eight-electron B centers, and requires non-planar (tetrahedral) B centers. This does not agree with the observed planar B centers. But we know the metal does not need to be fully oxidized. Consider sp2-hybridized B atoms which satisfy the octet rule. This would lead to [Gd2+]2[B62 ][B22 ] and suggests a B=B double bond. OK, but planar B is... 

The main feature of the structure concerns the neighbourhood of atom Pi the presence of the loop pulls Pt away from N2 along the two-fold axis, the endocyclic... 

The simplest process which may initially occur is the removal of a single electron from the intact molecule to give the positively charged molecular ion . The abundance of this molecular ion varies according to the structure concerned. For example, lysergide (mol. wt 323) contains a stable ring structure and the molecular ion is the most intense ion (Fig. 3) whereas it is totally absent in the spectrum of amphetamine (mol. wt 135) in which a... 

The only example presently available of photochemically controllable ring motion through an electron transfer reaction in a catenane structure concerns a Cu+-based [2]catenate, which is discussed in Volume 111, Part 2, Chapter 8 [64], Examples of catenanes containing cis-trans photoisomerizable units and where ring motions can be photochemically controlled are also known [65]. 

In the case of semi-crystalline PET, comparing the TEM photographs and the measured spherulite sizes, it can be assumed that the individual reactive particles should be distributed in within the spherulitic structure. Concerning the non-reactive one it is highly probable, knowing the small size of the semi-crystalline microstructure, that the modifier clusters remain outside the spherulites. 

Another controversial aspect of the bishydrazone structure concerns the hydrazone residues. The bishydrazone was proposed to have the structure 46, which mutarotates in solution to 47 (47). More recently, on the basis of a comparative study of the spectroscopic properties of the bis(phenylhydrazone) with some related compounds, the bishydrazone was assigned the structure 2,3-dideoxy-3-phenylazo-2-phenylhydrazino-L-threo-hex-2-enone-l,4-lactone (48) (48). However, this latter structure was inconsistent with its NMR spectra (49). 

The control of reaction rates by a bulk difiusion process is not usually demonstrable by microscopic observations, but support may be obtained from measurements of diffusion coefficients of appropriate species within the structure concerned. This approach has been invaluable in formulating the mechanisms of oxidation of metals, where rates of reaction have been correlated with rates of transportation of ions across barrier layers of product. Sometimes the paths by which such movements occur correspond to regions of high difi isivity, involving imperfect zones within the barrier layer, compared with normal rates of intracrystalline diffusion across more perfect regions of material [63]. Difiusion measurements have been made for ions in nickel sulfide and it was concluded that the decomposition of NiS is diffiision controlled [50]. 

Ultraviolet and infrared spectra have been considered in some detail in the section dealing with structure. Concerning the ultraviolet spectra it can be stated that, while there is considerable absorption by pryazolinones and some pyrazolidinones, these absorptions are so complex, owing to tautomerism, that little can be deduced from them. 

The ESR spectrum of a simple free radical, 2,5-dimethylquinone, is shown in Figure 17. This spectrum has a total of 21 lines (seven triplets), and since each line is characterized by two parameters (position and width) there are a total of 42 bits of data from which to deduce information about this one relatively small molecule. In contrast, the ESR spectra of humic substances are characterized, in general, by only a single line, and one is then left with only two pieces of data from which to deduce information, functional or structural, concerning the nature of the complicated, multicomponent mixtures in humic substances. This, again, puts into perspective, the limitations imposed on various investigational methods when applied to humic substances. 

History. Many different structures concerning the complexes have been tested over the years. The most famous theory was the chain theory [3] scientists postulated that the ligands are attached at the metal particle like in a chain (see Fig. 9.4). Alfred Werner was the acclaimed chemist who solved the problem in 1893 [4] he placed the metal ion in the center of the new compound and assumed that the dichlorotetraammincobalt complex has two octahedral structures. He... 

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