Abstraction type

Our models center on either the behavior expected of individual objects (large and small) or the designs for how groups of objects collaborate. Each of the primary abstractions— type and collaboration—has two main forms of refinement. Collaboration refinements affect multiple participants in the collaboration type refinement should not affect a client in any way. Most design steps are a combination of these basic four varieties. 

Usage imports, in contrast, can be circular. It is permitted, but not good practice, for usage imports of designs and implementations to be circular, if they are, it means that no one can use one in the circle without bringing all the others. Often the key to breaking circles is that an implementor should refer to someone else s specifications and abstract type definitions rather than implementations or classes. For example, A s reference to B s implementation is suspect It would be better to depend only on the requirements spec that B has implemented. (See Section 7.4.1.)... 

This model framework uses abstract types such as Job, Requirement, and Resource and abstract relationships such as meets, provides, and so on. These types will map in very different ways to a car rental application (Resource=Vehicle, Job=Rental, meets=model category matches) than to assigning instructors to seminars (Resource=lnstructoi Job=Session, meets=instructor qualified for session topic). 

Declare every variable and parameter with an abstract type written for that purpose.4... 

Concrete classes are outlined in bold, abstract types with light rules.) Each type represents a role that the instances play in relation to the source of the link. Now it is easy to imagine BookHolders other than Members and to imagine LibraryUsers other than Members. 

For molecules in which intramolecular hydrogen-abstraction (Type II reaction) is structurally prevented, intermolecular abstraction from a hydrogen-donating solvent may take place (see Scheme 6). This type of reaction usually results in reduction of the carbonyl group (see Table VII). 

To the present time about 100 reactions of CHa radicals with stable molecules have been reported. These are almost all of the atom abstraction type and in particular, they involve the abstraction of an H atom from a molecule we can label RH. Table I lists the Arrhenius parameters for a representative number of these reactions and it appears to... 

It would be very interesting to speculate on the behavior of the iso-electronic species NH and O atoms. From limited kinetic studies these appear to undergo addition to double bonds as well as abstraction type of reactions.21 22 However no definitive studies have been made on the existence of the insertion type of reaction which would be very much expected for both species, particularly for the O atom, in view of its fairly large electron affinity.8... 

Figure 8.16 Schematic structures of the complexes leading to homolytic dissociation (type I) and intramolecular hydrogen atom abstraction (type II)...

Aromatic ketones, which undergo intersystem crossing with great efficiency, give Type II (and Type I) reactions solely from the triplet state. Like the products of intermolecular hydrogen abstraction, Type II products are largely suppressed if the lowest triplet is 77,77. 91... 

It is seen with such correlation diagrams that the n-iu excited state in reactions such as hydrogen abstraction, Type II fission, etc. proceeds directly to the ground state of product (note the heavy line in Fig. 12). This paraphrases the Zimmerman 1961-63 n-it theory in slightly different language but arrives at this same conclusion. 

Schcinatically. these reactions are of the direct type [2]. They involve potential surfaces which have no deep well. The reaction inechanisni is of the abstraction type. The A atom approaches atom B and forms a new chemical bond while the old BC bond is broken gradually. The product angular distributions arc backward peaked while rotational and vibrational distributions arc very specific. 

Class I E. coli ribonucleotide reductase (RNR) exploits all the PCET variances of Fig. 17.3 in order to catalyze the reduction of nucleoside diphosphates to deoxynu-cleoside diphosphates. This reaction demands radical transport across two subunits and over a remarkable 35 A distance [187,188, 219]. The crystal structures of both R1 and R2 subunits have been solved independently [220-222] and a docking model has been proposed [220]. R2 harbors the diferric tyrosyl radical ( Y122) cofactor that initiates nucleotide reduction by generating a transient thiyl radical ( C439) in the enzyme active site located >35 A away in R1 [223]. Substrate conversion is initiated by a hydrogen atom abstraction (Type A PCET) at the 3 position of the substrate by C439 [192]. 

SCHEME 13.11 Homogeneous synthesis of graft copolymers by hydrogen abstraction type photoinitiation. 

Phenyl alkyl ketones that possess a y-hydrogen, undergo mainly an intramolecular H-abstraction (type II process) in homogeneous solution. The 1,4 biradical, formed as the primary intermediate, undergoes cyclization... 

The abstraction type photoinitiator acts by abstraction of a l drogen atom from a donor compound, the most common of which are aliphatic amines such as triethylamine, methyl diethanol amine (MDEA), or dimetl l ethanol amine. The radical produced (R) is the initiator of the free radical polymerization process. The semi-pinacol radical is unreactive and simply couples to give the pinacol. The abstraction process is, however, highly dependent on the amine co-initiator. Examples of abstraction type photoinitiators are given below ... 

It should finally be emphasized that the use of DPB is not restricted to acrylic compounds since it proved to be also a very efficient photoinitiator for the polymerization of vinyl monomers, like N-vinylpyrrolidone (NVP). In addition, DPB appeared to be particularly well-suited to photo-cure systems that need hydrogen abstraction type photoinitiators, like the thiol-polyenes resins (2), since it is then to be compared to the poor-performing benzophenone. 

Photoinitiators are classified according to the type of photopolymerization system they initiate (i.e., radical or ionic). The basic photochemical routes that produce radicals are photocleavage (type I), intermolecular hydrogen abstraction (type II), and electron transfer followed by proton transfer. Schematics of these photochemical routes are given in Scheme 5. The efficiency of these routes directly determines the monomer conversion, molecular weight of the polymer, and degree of polymerization, and hence the structural, physical, and mechanical properties of the final product. The general relationships of Pp, Pi, and DP were provided in the previous section. 

DDD provides a collection of transformations to replace an abstract data type occurance with a more concrete representation. Incorporating a representation requires defining a correspondence between terms in the abstract ADT and combinators in the concrete ADT. DDD assumes that a given representation has been verified, that is, that an implementation relationship has been established between the two ADTs. We usually work with a simple notion of implementation, involving a partial equivalence relation on the (term algebra of) the concrete type which supports the equational theory of the abstract type. 

Radical polymerization is induced by photoinitiators, cleaverage type, and hydrogen abstraction type. The merits of radical polymerization are its higher cure rate and availability of a variety of materials. Most acrylate and methacrylate monomers are applied for radical polymerization. Figure 4.7 shows typical polymerization of a monomer. Mono-, bi-, and multifunctional vinyl monomers are used for polymerization. Figure 4.8 shows typical initiators for photopolymerization. Benzophenone is a hydrogen abstract type initiator. 2,2-Diethoxy-l,2-diphenylethane-l-one is a cleavage type initiator. 

A combination of benzophenone and 1,3-dioxane is a convenient hydrogen abstraction-type photoinitiator system for the free radical photopolymerization of methyl methacrylate, styrene and other monomers. As an advantage, this system does not require an additional hydrogen donor as other conventional initiators. In a similar way, mixtures of thioxanthone derivatives and fluorenes can be used as visible light absorbing oil- and water-soluble photoinitiators for free radical polymerization of methyl methacrylate, ethyl 2-(2-phosphonoethoxymethyl)acrylate and trimethylolpropane triacrylate. Photopolymerization and laser flash photolysis studies reveal that initiation occurs by intra- and intermolecular hydrogen abstraction by the thioxanthone-like triplet excited state. 

ABSTRACT Type of collapsibility of site is an important content in evaluation of loess collapsibility, the results calculated according to indoor test is often contradict with field test results. In order to solve the contradiction, the paper analyzes the factors that brings about difference in indoor and field test results based on the in-situ immersion test results in loess site completed in recent years, makes a study of the influence of discontinuous distribution of collapsible loess on collapse settlement, and presents the improved empirical formula for collapse settlement calculation under overburden pressure. The results show that indoor collapsibility test succeeds but impairs the correlation between factors such as loess property, stratum configuration, stress history, buried depth and settlement by immersion, during collapse settlement calculation, the correction of these influential factors shall be taken into consideration the standard used for judgment of loess as to whether it is collapsible may be properly heightened, in case of discontinuous distribution of collapsible loess, stress redistribution effect shall be taken into account. 

In the model context component, we introduce the abstract type STATES and its partitioning into disjoint subsets IN-MISSION, COMPLETED, UNSAFE, and DEGRADED. Moreover, we define the relation Trans modelling possible transitions between states. The allowed transitions depicted in Fig.l are formulated as a number of axioms constraining Trans, as shown below ... 

Those that undergo intermolecular H-abstraction from an H-donor, known as H-abstraction type or Type II photoinitiators (non-fragmentation type). Tertiary amines with abstractable a-H atoms have been shown to be particularly effective as synergists (H-donors). Type II photoinitiators include benzophenone, Michler s ketone. 

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