Attacker model

The RADACK (contraction of RADiation-induced attACK) model, that we have developed [9,10], accounts for the experimentally determined probabilities of radiolytic damages caused by the OH radical attack in all forms of DNA (B [11], Z [12], triplex [13], quadruplex [14]), in DNA-protein complexes [15] and has the potential to predict radiolytic attack probabilities in other molecules or assemblies. Direct ionisation effects are not taken into account. The determination of relative probabilities of reaction ofthe target with the OH radicals takes into account two factors 1) the accessibility of the reactive sites of the target since it uses the exact tridimensional structure of the macromolecule or assembly as determined by NMR, crystallography or as built up by molecular modelling, and 2) the chemical reactivity of the residues (nucleotides or amino-acids). 

This was already anticipated in Section 5.2.1, Why Interest Groups . Recall that an interest group is formally a set of identities, and that the entities belonging to it are those that are directly connected to the access points with these identities. This may be called the standard attacker model of cryptology. Combined with suitably small interest groups, it may also be called the standard trust model. 

The reactions of ailylboranes, -silanes and -stannanes with carbonyl compounds and imines always take place with double-bond migration, and the structural stability of the reagent is a common problem that is encountered ( 2.7). The reactions of ailylboranes and -boronates occur without catalysis, while those of allylsilanes and -stannanes usually require the presence of a Lewis add [253], The mechanism of the reactions of allylboron derivatives is concerted, and the addition occurs via a six-membered cyclic transition state. A slightly distorted chair transition state model in which the oxygen of the carbonyl group is coordinated to the boron atom is usually invoked (Figure 6.42). Various steric and polar interactions dictate whether the Si or Re face of the prochiral aldehyde is attacked (models C j... 

Theoretical Elaborations of the Rearside Attack Model Baldwin s and Liotta-Burgess Trajectory Analyses... 

Among the first to explore implications of the rearside attack model was Baldwin [30]. In 1976, he proposed a qualitative method, based on the use of resonance struc-... 

Another formal treatment of the rearside attack model was proposed by Liotta, Burgess and Eberhardt [31]. These authors extended frontier orbital analysis of the interactions between a nucleophile and a n-electrophile by including the stabilizing two-electron interactions of the nucleophile HOMO with all the unoccupied n and a MO s on the rt-electrophile, as well as the net destabilizing four-electron interactions of the nucleophile HOMO with all the occupied n and a MO s. The analysis... 

The rearside attack model became equally important in the discussion of stereoselectivity in the aldol condensation. In 1981, Seebach and Golinski proposed a topological rule for aldol-like reactions which says that the H atom, the smaller substituent on the donor component, adopts an anti position with respect to the acceptor double bond C=A in the preferred transition state, cf. A and B in Scheme 6.28 [35]. This preference of A over B comes about as a result of the increases in steric hindrance when the donor substituent R2 is jammed against Rj and H of the acceptor in the non-perpendicular approach B. 

In the spirit of Baldwin s rules, the rearside attack model is often invoked to rationalize the stereochemical course of intramolecular carbonyl additions or to discriminate between various mechanistic options in such processes [183]. However, in contrast to the case of Sj,j2 displacements, unambiguous experimental support for such conjectures is lacking. 

Fig. 4.30) with various substitution pattern at Cl and C2 were investigated. Experiments with alkyl substituents at C2, in place of the sulfur heteroatoms, eliminate the viability of a chelation-controlled selectivity and reveal the significance of geminal substitution [geminal substitution influenced the selectivity in other oxocarbenium ion systems [108]]. Perturbation of the Cl substituent of the oxocarbenium ion intermediate has little effect on reaction stereoselectivity, and analysis of this observation lends additional support for stereoelectronically preferred inside attack of the nucleophile. The results demonstrate that selective formation of the 1,4-c/s product 84 does not require a chelated transition stracture, reinforcing the utility of the inside attack model to analyze the reactivity of complex five-membered ring oxocarbenium ion intermediates. 

Back-side attack imposes an important stereochemical consequence complete inversion of configuration. Remember that the conversion of 7 to 8 proceeds with complete inversion of configuration. This inversion of configuration via back-side attack is the model used to explain experiments by Paul Walden (Latvia 1863-1957) and it is called Walden inversion in his honor. Is inversion of configuration intuitively obvious No Inversion of stereochemistry is determined by the observation that the sign of the specific rotation in the product changed relative to a chiral starting material, and this key experiential observation led to the back-side-attack model now used for aliphatic substitution reactions. 

The paper is structured as follows. In Section 2, the system, data, fault, and attack models as well as the requirements on SCADA protection are introduced. Section 3 presents om solution. The simulation environment and evaluation results are described in Section 4. The related work is presented in Section 5 and the conclusion as well as futme work are provided in Section 6. 

We now present om system model which describes a large-scale SCADA system along with the data model and a fault/attack model. The system model gives an overview of the node tjq)es in the system and how they interact with each other. The data model specifies the different data flows and control loops within the SCADA system. Pmthermore, the attack and fault model describes faults and attacks that are addressed by our solution to enhance the overall SCADA system resilience. Finally, requirements for SCADA systems are presented to provide mitigation for the considered faults and attack classes. 

In this section, we analyze the security of our approach against the attack model presented in Section 3. We proceed by analyzing a number of significant security... 

Fig. 4 defines the interface of the Attack model it is constituted by the init input place (that means the phase may start), the start output transition (the action has started) and the end output transition (the action has ended). Fig. 5 proposes a simple GSPN pattern for a single-phase attack. 

To build all the scenario models, we considered a two-phase pattern for the Attack model. Each sensor is modelled by a simple sensing pattern. AND-based models are proposed to implement the Assessment model (scenarios SI, S3, S4) while a 2-out-of-3 GSPN pattern is used with reference to scenario S2. As Intervention model, we choose a single phased pattern. For the sake of the space, only the first scenario is shown Fig. 17 represents high level model as an instantiation of the formalism independent schema in Fig. 2 Fig. 18 shows the GSPN resulting from the substitution of the specified patterns. 

Several models have been proposed to account for the non-random distribution of oligosaccharides formed when polysaccharides are hydrolysed by a-amylase. The preferred-attack model assumes that the probability of bond-cleavage depends on the position of the bond in the chain the repetitive (or multiple-attack) model assumes that a-amylase can form a cage-like complex with the substrate and attack it several times during a single encounter the multiple-enzyme (or dual-site) model assumes that the substrate is hydrolysed by the combined actions of exo- and en /o-enzymes. The effects of pH, inhibitors, and the chain length of the substrates have been studied in an attempt to decide which of the three models best fits the action of a-amylase. The effects of these variables on either the distribution of products or the action pattern of the enzyme were incorporated into the models, which were then used to interpret experimental data obtained with porcine pancreatic a-amylase. 

Moore, A.P., Ellison, R.J., Linger, R.C. Attack modeling for information security and survivability. Technical report, DTIC Document (2001)... 

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