CASS scheme

Turning to the field of safety-related control systems, a significant initiative in the UK is the development of a scheme known as the conformity assessment of safety-related systems (CASS), already mentioned in Chapter 13. The initiative, which is supported by the DTI under its sector challenge programme and which will be championed and implemented by a UKAS-accredited company known as CASS Scheme Ltd, is concerned with conformity assessment for systems based on the aforementioned standard lEC 61508. The scheme has a broad scope and covers all those involved in the design, development, manufacture, implementation, support and application of complete safety-related systems and their components. 

The ISA Working Group (WG) was set up in order to develop and promote the role of the ISA as a safety professional. It is affiliated to the lET and BCS and is subject to the direction of the Inter-Institutional Group on Health and Safety. Membership includes ISAs woiking in a wide range of industries, academics and representatives from the Health and Safety Exeeutive (HSE), MoD, the Safety Assessment Federation (SAFed), CASS Scheme Ltd, lET and BCS. 

Anticipating the requirement for FSA services the established certifying organizations already offer FSA services. In the UK a new company has been formed to specialize in providing training for conformity assessment and has taken the name The CASS Scheme Ltd . The implications of this scheme are that competency guidelines and training schemes are in place for persons to be trained as Functional Safety Assessors. 

Surprisingly, when the same disiladigermetene 73 was reduced with alkaline earth metals (Mg, Ca) instead of alkali metals, strikingly different prodncts were obtained Mg or Ca derivatives of l,3-disila-2,4-digermabicyclo[1.1.0]butane-2,4-dianions 76 and 76 Ca (Scheme 2.69). ... 

Studies of the Polonovski reaction in conformationally rigid polycyclic systems reveal the stereochemical requirements for the elimination step. For example, the 6p,7p-dideutero derivative (22) of nu-pharidine is converted on reaction with acetic anhydride into A -dehydrodeoxynupharidine (24) containing a single deuterium atom at Ca (Scheme 4). ... 

The selection of the active space in CASSCF and CASPT2 calculations is by no means trivial. In the present case we assumed that (i) the selected active space should at least represent the valence bonding and antibonding tr orbitals in BMe, (ii) the corresponding CAS scheme must lead to correct dissociation products (B 2P, Me 2S) and should be well balanced along the potential curve up to the dissociation limit, (iii) the CAS scheme should account for as much dynamical correlation as possible, and (iv) the same active space can be employed for all molecules in the series, i.e., BCu, BAg, and BAu. 

A number of simple zinc(II) complexes have been designed in order to gain basic knowledge of Zn ion chemistry in the zinc(II) hydrolases.Most of them feature tridentate or tetra-dentate ligands with vacant sites. In 1975, Wooley reported the first well-defined zinc(II) complex (33) with a macrocyclic tetramine as a model for CA (Scheme 27). " It was demonstrated that the Zn -bound HO species is a reactant that attacks CO2 to afford HCOs , with a second-order rate constant for hydration, of 2x lO M s at 25 ""C. On the basis of the... 

The coordinating ligands to Zn in /3-lactamases (Scheme 9) are essentially similar to those of CA (Scheme 11). In addition to acting as a CA model, Zm -cyclen (34) was found to catalyze the hydrolysis of A-benzylpenicillin (Scheme 36). Interestingly, (34) also catalyzed epimerization of the hydrolyzed product, (57 )-benzylpenicilloate, to (5 S)-benzylpenicilloate, unlike the enzymatic reaction. 

The cellular automata (CA) scheme, applied for the streamer and microdischarge interaction modeling, consists of a lattice of cells that can have any dimension and size coupled with... 

The diiodo derivative of dibenzo[a,e]cyclooctene (entry e, Table 24.25) undergoes cross-coupling with 2 equiv of 6-ferf-butyldiemthylsilyl-8-trimeth-ylsilyl-3-methyl-3-(Z)-octen-l,7-diyn-5-ol (ca. Scheme 24.30) to afford the silylalcohols as a 1 1 mixture of two diastereomers in 64% isolated yield. The subsequent KH treatment gives the corresponding Z,Z,Z,Z-tetraentetrayne (Scheme 24.34) [10]. 

Poly(butylene adipate) (PBA) is a typical biodegradable synthetic plastic prepared by the polycondensation of 1,4-butanediol and adipic acid. PBA is readily transformed into the repolymerizable cyclic oligomers mainly consisting of BA dimer by lipase CA (Scheme 27). Commercially available PBA with an Mw of 22 000 was degraded into a cyclic BA oligomer with an of 600 by... 

The two possible initiations for the free-radical reaction are step lb or the combination of steps la and 2a from Table 1. The role of the initiation step lb in the reaction scheme is an important consideration in minimising the concentration of atomic fluorine (27). As indicated in Table 1, this process is spontaneous at room temperature [AG25 = —24.4 kJ/mol (—5.84 kcal/mol) ] although the enthalpy is slightly positive. The validity of this step has not yet been conclusively estabUshed by spectroscopic methods which makes it an unsolved problem of prime importance. Furthermore, the fact that fluorine reacts at a significant rate with some hydrocarbons in the dark at temperatures below —78° C indicates that step lb is important and may have Httie or no activation energy at RT. At extremely low temperatures (ca 10 K) there is no reaction between gaseous fluorine and CH or 2 6... 

Synthetic phenol capacity in the United States was reported to be ca 1.6 x 10 t/yr in 1989 (206), almost completely based on the cumene process (see Cumene Phenol). Some synthetic phenol [108-95-2] is made from toluene by a process developed by The Dow Chemical Company (2,299—301). Toluene [108-88-3] is oxidized to benzoic acid in a conventional LPO process. Liquid-phase oxidative decarboxylation with a copper-containing catalyst gives phenol in high yield (2,299—304). The phenoHc hydroxyl group is located ortho to the position previously occupied by the carboxyl group of benzoic acid (2,299,301,305). This provides a means to produce meta-substituted phenols otherwise difficult to make (2,306). VPOs for the oxidative decarboxylation of benzoic acid have also been reported (2,307—309). Although the mechanism appears to be similar to the LPO scheme (309), the VPO reaction is reported not to work for toluic acids (310). 

The overall objective of research under way as of ca 1997 is to develop a system of sale by description for fine and medium wools whereby the buyer is presented only with measured data on the principal characteristics of the raw wool, as well as an assessment of the less important characteristics by an independent skilled appraiser (8). A scheme for assessing the risk of the presence of colored fiber content in greasy wool has been proposed which depends on production parameters and on the age and sex of the sheep (5). Instmmentation and computer algorithms for the measurement of style and handle... 

The low basicity of pyrrole is a consequence of the loss of aromaticity which accompanies protonation on the ring nitrogen or on carbon 2 or carbon 3 of the ring. The thermodynamically most stable cation is the 2H-pyrrolium ion, and the p/sTa for protonation at C-2 has been recorded as -3.8 the corresponding pK values for protonation at C-3 and at nitrogen are -5.9 and ca. -10 (Scheme 7). 

Mercury(II) acetate tends to mercurate all the free nuclear positions in pyrrole, furan and thiophene to give derivatives of type (74). The acetoxymercuration of thiophene has been estimated to proceed ca. 10 times faster than that of benzene. Mercuration of rings with deactivating substituents such as ethoxycarbonyl and nitro is still possible with this reagent, as shown by the formation of compounds (75) and (76). Mercury(II) chloride is a milder mercurating agent, as illustrated by the chloromercuration of thiophene to give either the 2- or 2,5-disubstituted product (Scheme 25). 

Anchimeric assistance by oxirane oxygen may accelerate the solvolysis of (44 Scheme 33) (by a factor of ca. 10 -l6 ) compared to the exo isomer (45 Scheme 34) (81JOC3512). 

In this work a novel five-step leaching scheme for HM has been developed addressing exchangeable, acid soluble (carbonate), easily reducible (bound to Mn oxides), easily oxidizable (bound to humic and fulvic acids), and moderately reducible (bound to amorphous Ee oxides) fractions extractable by 0.05 M Ca(N03), 0.43 M CH3COOH, 0.1 M NH,OH-HCl (non-acidified), 0.1 M K/,03 (pH 11), and 0.1 M (NH4),C,04 (pH 3), respectively. The sequence of extractants was chosen according to recent studies on the selectivity of leachants toward dissolved phases of soils. 

A short review of the CA process is given before proceeding with the applications of the technique to several industrial case studies. The three key stages of CA are shown in Figure 2.24 within the simplified process of assessing a design scheme. 

The case studies that follow have mainly come from live product development projects in industry. Whilst not all case studies require the methodology to predict an absolute capability, a common way of applying CA is by evaluating and comparing a number of design schemes and selecting the one with the most acceptable performance measure, either estimated Cp, assembly risk or failure cost. In some cases, commercial confidence precludes the inclusion of detailed drawings of the components used in the analyses. CA has been used in industry in a number of different ways. Some of these are discussed below ... 

The reaction is generally carried out in an alcoholic solvent, resulting in formation of the acetal the general scheme is called the Mattox rearrangement, and the yields are usually high. If a nonalcoholic solvent and acid are used, the aldehyde is obtained directly, but in lower yield. However, the use of zinc acetate as catalyst instead of an acid permits isolation of the aldehyde in ca. 50 % yield. Tire use of refluxing acetic acid alone... 

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